# Recovering precious metals from polishing sweeps



## Ageo308 (Dec 1, 2007)

Hi guys, I'm after the simplest method of trying to extract the precious metals from polishing sweeps. So all you masters out there let me have it 

P.S I'm not after refining and separating the metals from each other, just separating all the gunk from the precious metals then form it into a bar.

cheers


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## Harold_V (Dec 1, 2007)

I recommend Hoke's book as well----regardless of the direction you may take.

Incineration is mandatory.

Unless you investigate chemical refining, your best chance is incineration and then furnace reduction. You'd need a good flux, and perhaps even a collector to recover the finely divided particles. It's not exactly something you can do with success without some serious equipment. 

I'm of the opinion that you won't enjoy much success by any other means. 

Harold

NOTE; this is the condensed version of this thread, it was originally posted when the GRF was relatively new. Notice Hoke was not available as a download on the forum back then.


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## Ageo308 (Dec 1, 2007)

Hi guys. I'll definately be getting the book so thanks.

Would the correct term to be used here is smelting?


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## Harold_V (Dec 1, 2007)

Not in my opinion, but I can see where it might be a gray area. 

Smelting, as I understand it, is the reduction of metals from chemical compounds (ores). What you'd be working with isn't remotely the same in that it won't contain sulfides or other troublesome elements. Could be I'm tripping over semantics, however. 

I never referenced my melting operation as smelting when I processed my wastes, although in many ways the process was identical. I reserve the term smelting to working with ores------anything else is melting---with or without flux. 

Incidentally, if you choose to do this with a furnace, one of the constituents of your flux should be fluorspar. It, better than anything else I ever tried, thins the flux exceedingly well, which is a factor in not losing traces of values to prills. The negative aspect is its aggressiveness towards crucibles and furnace lining. The flux will pour water thin, but it takes along with it a generous portion of the components you hope to retain (read that as the crucible and furnace lining). It's the price you'll pay for good extraction, and, in my case, was a negligible loss, although not cheap. 

Harold


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## Ageo308 (Dec 10, 2007)

Hi guys, while I'm waiting for the book to be sent out I came across these instructions to prepare polishing sweeps ready to refine.

Let me know what you think


> Standard methods of sweeps burnout are ineffective and produce a product similar in appearance to lava rock, and which is more, rather than less, difficult to refine. The following method requires about the same amount of work as ineffective methods but reduces to sweeps to a material that can be melted to obtain a bar of metal
> 
> Polishing sweeps are composed of grease (the binder in polishing compound), sandy grit (the active ingredient in polishing compound), lint (from the buffs) and very tiny balls of karat gold (from the gold that was polished). Sometimes it will also include paper and buffs.
> 
> ...


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## Harold_V (Dec 10, 2007)

I'm not sure you want to hear what I think. :wink: 

I don't agree with anything posted. Total nonsense-----not to say that it doesn't work. It probably does. 

I processed polishing wastes for over 20 years and never experienced hardening. To suggest that a product akin to lave rock is formed is absurd. That is a sure sign of a process that isn't proper for the purpose. 

If you incinerate as suggested, and do it indoors, you'll quickly come to understand how stupid it is. The described process is a coking operation, totally unsuited for the desired result. By roasting the material, you can expect the production of smoke that would fill a huge room, cover everything with a waxy deposit, and you'd likely never get rid of the smell, which would rival that of cooking your dog. Incineration should involve burning, not roasting. You'll understand that the first time you attempt to process polishing wastes. 

Sorting paper products, as suggested, makes absolutely no sense. They should be burned, along with the other materials. That's what the process is for. 

You can effect a perfectly good incineration by simply burning these materials in a shallow container, one that permits oxygen to access the material for complete combustion. It must be heated to the point where carbon burns, or about 1,100° F. The ash that results is fine and easily screened. 

There is no need for the use of lye, which is far more dangerous than the use of acids. A drop of lye in your eye is pretty much a guarantee of blindness. A wash with HCl before digesting the values will suffice. An alternate would be a digest with nitric acid, assuming one expected a silver recovery. You must tailor the process to the source, in other words. Wastes from the silver bench would be handled differently from wastes from the gold bench. 

All too many times we are told that there's more than one way to do most things. While it's true, there is generally one way that is best suited----and that's the one you, or anyone, should seek. The choice is yours. 

The most efficient way to process these wastes is to incinerate, then melt in a furnace, using litharge as an oxidizer and collector. That involves cupellation to eliminate the lead, and is likely beyond the ability of the average home refiner. Your other option is to incinerate and then chemically refine the residues. 

Follow Hoke's advice and you'll be well served, although you should avoid using gasoline for incineration. 

Harold


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## Ageo308 (Dec 10, 2007)

Thanks Harold, although I must admit when my jeweller friend tried this process, he did burn in the kiln as stated then melted straight away and the piece actually turned into a real hard piece of glass. So he's trying this method today to actually see if any of this rings true.

I'm assuming the cheapest method is the chemical way yes? Once I get Hoke's book I will study it to death  thanks for the advice Harold.


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## Harold_V (Dec 10, 2007)

Ageo308 said:


> Thanks Harold, although I must admit when my jeweller friend tried this process, he did burn in the kiln as stated then melted straight away and the piece actually turned into a real hard piece of glass.


Of course it did. For all practical purposes, he melted with the idea that the values would magically appear as a solid piece. It doesn't work like that. Melting that material without a collector, and a thinning agent for the silica, which should be left behind but dissolved with soda ash, is a mistake. Much of the material won't dissolve, so there must be a thin flux to absorb the non-metallics and allow the metallics to collect and settle. Your friend is now stuck with something that will require either processing by ball mill, or it must be broken very fine, properly fluxed, and run with a collector. Had he stayed away from the furnace, that would not be the case. 

Mind you, I have no quarrel with anyone that chooses to process polishing wastes by furnace----I'm simply stating that the process presented isn't a good one. It works, but the losses are likely to exceed what should be considered acceptable. That, of course, depends on what was used as a flux, but the indication is this person didn't have a clue. 



> So he's trying this method today to actually see if any of this rings true.


This method? Not sure of your meaning, but if you're implying the one I recommended, it never failed me. I processed polishing wastes on an ongoing basis, for more than 20 years. 



> Im assuming the cheapest method is the chemical way yes?


I'd prefer to have you think of it as a functional way for those that don't have at their disposal a great reducing furnace to process such wastes, yet a need to achieve a decent recovery. The problem with melting, even after the removal of considerable sand, is that it's very hard to collect the miniscule bits of values. Unless the flux is very fluid, and a collector of sorts is used to agglomerate the often colloidal sized particles, much of it is lost in the slag, some identifiable as prills, with the rest so fine it isn't recognizable. Have your friend pay for a fire assay of his piece of glass so he'll understand how poor was the advice he followed. 

I do not recommend the home refiner attempt to melt such material, and if the decision to do so is made, the last thing that should be done is to remove the silica as recommended. If you'll study a good fluxing recipe, you'll come to understand that silica is a very important component. The one I used included the *addition* of silica, so I see no reason to eliminate what is a necessity. 

By the way, my flux was assayed after the recovery of values and was so low in content that it was not acceptable at a refinery that specialized in recovering values from low grade wastes. The formula I developed worked very well, but it was very aggressive in that it would dissolve crucibles and furnace lining in short order. That was the chief reason I got such good extraction. In my case, the damage created was more than offset by a virtually complete recovery. I relied on silver chloride to act as my collector-----which turned out to work exceedingly well, at least from all indications. 

Harold


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## Ageo308 (Dec 11, 2007)

I thought I would update you guys, my friend didnt take any photos but he said the result was better than expected. This time when he melted it (doing the process, that's listed above) it didn't turn to glass but just stayed more liquidy and the gold is much more visible and it's coming together. He said the only thing that's left is to remove the tripoli (polishing compound) and rouge, so I was wondering since we have come this far what's the best way to remove these 2 things. Is there any acids that will dissolve them?

cheers


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## Harold_V (Dec 11, 2007)

All of it?

Harold


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## Ageo308 (Dec 11, 2007)

Did he melt all of it? Is that what you're asking Harold?


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## Harold_V (Dec 11, 2007)

No------I'm asking if he recovered all of the gold. You have to understand that there is no reason for minute particles to gather. The density of the flux makes it difficult for them to move about, especially by gravity. Polishing waste, unlike filings and larger pieces, is made up of mostly invisible particles. So fine that the dust, once well incinerated, is purple in color (colloidal). It shifts to a yellow/green/beige color instantly when AR is introduced, a sure sign that you are dissolving the miniscule particles that I speak of. Those are unlikely to be recovered well by melting unless the flux is very thin, you have a collector of sorts, and the heat is sustained for a period of time. 

Best thing for you to do is pursue this as you are, then have your flux assayed. If I'm wrong (and I certainly can be), your flux will assay low, fractions of an ounce/ton. If it assays high, you're on your way to understanding what I've been trying to have you understand. 

Harold


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## Ageo308 (Dec 16, 2007)

Ok Harold, we hit a road block (as I expected). We are still stuck with the rouge and tripoli left on the metals. If we apply AR will that dissolve the gunk (rouge/tripoli)? If not what chemical will do the job?

cheers


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## Harold_V (Dec 16, 2007)

You are likely stuck with a good amount of your values in the flux as well. 

If you're hell bent on running this material as you suggest, you may discover that a boil in HCl & water prior to melting will serve to reduce the amount of rouge & tripoli, which is, if memory serves, just iron in a given state of oxidation. 

I'm still at a loss to understand why you don't use the chemical process. It does an adequate job, at least as good as melting, assuming you don't use a collector. 

If you get involved in chemical extraction, do not discard the material when you're finished. It will still contain substantial value, and can be sold to the proper refinery (assuming you have enough). Heat it to dryness and store it for the future. 

Harold


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## Ageo308 (Dec 16, 2007)

Well Harold I'm just waiting for the Hoke's book to arrive so I can perform the chemical extraction. 

In the mean time (while I wait) if you don't mind could you break down the process from start to finish (including the chemicals used) I'm after extraction of just gold at this present time.
Your information is tops and I thank you for your patience


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## Harold_V (Dec 16, 2007)

My approach was very simple. 

1} Incinerate in a shallow pan, heating from below. Ignite the material to eliminate the majority of smoke and stink. It will readily burn once hot enough. Incinerate until all carbonaceous material has been eliminated. There should be no glowing embers. Allow them to burn completely. Insure the pan is hot enough by heating with a torch from the bottom. Don't burn through the pan. An old stainless fry pan works very well for this operation. Find them at Goodwill or other second hand stores. DO NOT USE ALUMINUM.

2} Screen after cooling, to remove any sizeable pieces that would be difficult to dissolve without inquartation. 

3} Run a magnet through the material to remove free iron particles. They should be placed in the stock pot, not discarded. They generally will transfer miniscule traces of values. 

4} Place screened wastes in a beaker, or a container that will tolerate being heated. 

5} With an approximate mixture of 50/50 tap water and HCl, cover the contents with solution, then place on hot plate. Heat slowly until contents are brought to a boil. Stir regularly to prevent the container from overheating and breaking from thermal shock. 

6} After a reasonable boil period, (contents will change color), remove from heat and fill container with tap water. Stir well. 

7} After solids have settled well, decant solution. Test for values, then discard if barren. It is rare to find values in the solution unless you have allowed nitrates to be included. 

8} Repeat the above operation until the rinse water is clear, or nearly so. 

9} Apply AR @ 5 ounces per troy ounce of values expected to be recovered. Use only what is necessary, to minimize the amount of nitric that must be evaporated later. Heat to boiling, and stir regularly. Do not allow the material to dry on the bottom of your container, which will lead to thermal shock and cracking, as above. Make your AR @ 4 HCl/1 nitric, not less. If in doubt, move up to 5 HCl/1 nitric. Too much HCl does no harm, unlike too much nitric. 

10} When values are in solution (note color change of solids, and the yellow color of the solution), and you see no fumes coming from the container, remove from heat and add a few ounces of water. Stir, then allow contents to settle. 

11} Decant, then add more water to solids and stir well. Repeat this operation until you have removed the bulk of values. Note the color of the solution, which will slowly shift towards clear as it is washed. 

After the final decantation, place the solids in a filter (Sharkskin works very well for this operation) and extract all solution possible. 

Combine all solutions from the AR process and evaporate to eliminate water and nitric. Add a few drops of sulfuric to the evaporation process early on, which will precipitate any traces of lead that may be included in the process. Be very careful about adding sulfuric to hot solutions. It is best added while they are cold. Stir as it is added to prevent local generation of steam.

After evaporation, take up with water, filter, precipitate, and wash appropriately. 

I suggest you do none of the extraction processes until you've read Hoke's book---so you have a general understanding of what you're doing, and why. None of this is difficult----it becomes routine after you've done it a few times. Do not allow the outline to discourage you. 

Dry the waste solids by heating, then save them. Do not store them wet----they will give off fumes endlessly and destroy anything of value in the immediate vicinity by corrosion. Please take my word on this part (the solid waste material, after acid processing) ---it is a wonderful savings plan. The values remaining are not substantial, but they add up. Remember------you will have left silver behind in this operation, not just traces of gold. 

Note that this process will not be suited to processing wastes high in silver. It will remain in the solids. If you process waste from the silver bench, it becomes somewhat more complicated. I can talk about that if and when it is an issue. It is a waste of time to pursue traces of silver with each batch. 

Harold


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## Ageo308 (Jan 21, 2008)

Hi Harold, last night we started your technique and got till the end of the rinsing process and ready for the AR process. Everything is looking good so far. My partner and I read Hoke's book a few times to understand the evaporation process especially as you mentioned but 1 thing we can't find is when making AR, does it matter if you mix HCl to Nitric or Nitric to HCl? Tomorrow night will be the final stage and I will update you on the progress.

thanks again


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## Harold_V (Jan 21, 2008)

Ageo308 said:


> when making AR, does it matter if you mix HCl to Nitric or Nitric to HCl? Tomorrow night will be the final stage and I will update you on the progress.
> 
> thanks again



I don't recall ever having any problems with mixing those two acids, regardless of the sequence of combining them. If any heat is generated, it is miniscule, so it's not a problem. 

I did my mixing in a graduate, pouring from stoppered bottles, in random sequence. I usually poured my nitric first, then the HCl. It was then poured into the container where it was to be used. The only caution, aside from common ones, is to not mix any that you don't intend to use immediately. It tends to gas a little, so it's not a combination that you should make and store. 

I suggest you use an excess of HCl. It does no harm, and guarantees you use all of the nitric. I favored a 4:1 ratio, and often went as high as 5:1. 

Harold


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## Ageo308 (Jan 22, 2008)

Harold we are basically using a large syringe to transport the acid from the container to the beaker. It has the exact measurements so we can do it nice and slow (for the experimenting stages).

It's much more cleaner and we didn't spill any.

Basically we are going for the 4:1 in the AR mix but if in doubt for whatever reason as you mentioned will move up to 5:1.

Fingers crossed everything will go as planned.


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## Ageo308 (Jan 23, 2008)

Ok Harold we did the final process, as we are letting it dry and before we melt which flux will suffice? We tried melting whilst still wet using borax and it seemed like it did the job fine. I think we didn't do the last bit correctly thow as it still has a brown mud on the bottom along with the gold and other metals.

If you don't mind could you go into a bit more detail from the AR process onwards? We are going to try some more tomorrow night.

Also for the filter we used the coffee filters which seemed like it did a very good job (have you ever used that before)??

anywayz I look forward to your valuable input.

thanks


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## Harold_V (Jan 23, 2008)

Ageo308 said:


> Ok Harold we did the final process, as we are letting it dry and before we melt which flux will suffice?


I trust you went through the proper wash procedure? While gold that comes from this process tends to be of quite high quality, I don't recommend you melt any gold that has been precipitated without first washing properly. I've discussed the washing process at length in previous posts. Be certain you follow that, or a comparable, procedure. The wash should include at least one application of ammonium hydroxide, even if you don't feel it is necessary. It performs a valuable operation in dissolving substances that may not, otherwise, get washed from the precipitated gold. 

Regards the flux you use. Use nothing but borax for melting pure gold. The use of other chemicals has the potential to reduce oxides, recombining them with the pure gold, defeating your purpose in processing the gold. If your gold is clean, you need only a film of borax covering the dish, which will serve to "lubricate" the molten gold and allow it to flow well. If your flux discolors when you melt your gold, the gold is not clean. The flux should remain clear of color, shifting towards purple. If any other color develops, the gold is contaminated. Once melted, the surface of your gold should remain shiny, with on oxide skin forming, and will cool with a large crystalline pattern. It should also pull a very deep hole in the center, as it solidifies. If it frosts up and refuses to form the hole (pipe), the gold is not pure. 



> We tried melting whilst still wet using borax and it seemed like it did the job fine. I think we didn't do the last bit correctly thow as it still has a brown mud on the bottom along with the gold and other metals.


This is a little confusing. For starters, while melting the mud while it's wet will work, you risk breaking your melting dish, depending on how long the wet material is in intimate contact with the melting dish, and how well it is coated with flux. 

There should be nothing on the bottom of your container aside from gold. If other metals have precipitated with the gold, something has gone woefully wrong. Can you tell me what you think is there with the gold? 

If you've read my washing procedure, you know that the gold that is ready for melting has been well washed and dried. It never leaves the beaker in which you precipitate the gold------not until it has been through all of the process. By following this procedure, the gold gets washed and dried, and acts as its own collector for the very fine particles of gold that can be troublesome. The only time it doesn't collect all the dusty particles is when the gold is very dirty, from dirty solutions. In that case, it is usually accompanied by a dark color, but not always.



> If you don't mind could you go into a bit more detail from the AR process onwards? We are going to try some more tomorrow night.


I'm going to assume you have done a good hot wash with HCl and water, and have rinsed the mud enough times (tap water) that the rinse water is coming off the mud in an almost clear color. The mud at this point should be a maroon to purple color, depending on the volume of gold it contains, and what medium was used for polishing. If the benchman did a lot of platinum work, it's possible the mud could even be green in color. I've seen them vary widely, so color alone is not a good indicator of contents. 

It's hard to guess the amount of value in the mud, for various reasons. The entire objective is to dissolve all the values, which can then be rinsed from the mud via a few tap water washes. Start with AR (mixed @ 4 parts minimum HCl and 1 part nitric). If you have a hunch on content, assume that amount to dissolve 1 troy ounce. Do not use too much AR----if you add unneeded nitric to the mix, it must be eliminated before recovering the gold. The negative side is that if you don't use enough, you won't get total extraction. The best policy is to estimate your recovery and use slightly less acid than is required. Let it work, heated, until it has done all the work it can, then add a little HCl to insure that you did not run out of it in the process, leaving some nitric unconsumed. If you get no further reaction (fumes) by adding the HCl, add a small amount (half ounce or so) of nitric and observe fuming, if any. Repeat this process until further additions of acid yield no reaction. At this point you're wise to allow the mud to stew for a while, to insure that you have dissolved larger bits of gold. Polishing waste usually contains bits of gold from the use of abrasives at the wheel, and they take a little longer to dissolve. The mud should have changed color completely, and reflect a cream color. Solution, if you've done your washing properly before dissolving the gold, will now be a nice deep yellow orange color, a sign of dissolved values and few, if any, base metals. If the solution is green, or darker, the preliminary wash was not carried out well, and an abundance of base metal was left in the mud. 

I never used urea, so I can't discuss its proper application. My method was to evaporate the solution, which eliminates unused nitric acid, plus was an indicator that I had used enough AR to dissolve all of the contents of the mud. Had I not, there would be no unused nitric present. I proved the unused nitric by adding a weighed button of gold to the solution, which gradually dissolved as the solution was evaporated. By weighing before and after, you can determine how much gold you added to the process, which should be subtracted from the gross yield to determine the net yield. By using the button, evaporation need not be carried to a totally thick solution, so it saves time in evaporation. Note that a few drops of sulfuric acid should be included in the evaporation process, which will serve to precipitate any traces of lead as lead sulfate. This is an important part of the process. Do not leave it out. Lead is death on gold's ductility. When the solution has been evaporated until it is well concentrated, and has shifted color towards a dark red, some HCl is added. If there is no reaction at the gold button (considerable bubbling and some brown fumes), you can consider that there is no more nitric present, and the solution can be diluted with tap water and filtered. Once filtered, it can be precipitated with the precipitant of your choosing. I favored SO2 from a bottle, but you can use any of a wide variety of precipitants. One that is easy to use and is readily available at a garden shop is ferrous sulfate. Hoke's book discusses the application in fine detail. The ferrous sulfate, if that be your choice, should be a nice green color. If the color has shifted to brown (exposure to excessive moisture), it will not precipitate gold. 



> Also for the filter we used the coffee filters which seemed like it did a very good job (have you ever used that before)??


No, I did not use coffee filters, although I did use something that is very similar (Shark Skin, made by S&S) for filtering the solution from the mud. Once my solutions were evaporated, I preferred a Whatman #2 paper, which I purchased in the 32 cm size if memory serves correctly. They fit, when properly folded, the filter funnels that are readily available from chemical supply houses. I found it to be the best filter on the market for filtering solutions prior to precipitation. 

The exception to this is that when I filtered gold that was re-refined, I then switched to a Whatman #5, same size. That is a very tight and slow filter paper, and will remove the smallest of contaminants. Unless you're working with very clean solutions at the outset, they perform very poorly. They're quick to stop flowing, but very good at removing miniscule particles from otherwise clean solutions. That describes the gold that I re-refined perfectly, so it was a perfect match for the process. 

There's nothing wrong with using coffee filters aside from the fact that they tend to allow very fine particles to pass. As long as your solution is crystal clear (of flocculence, not color), it doesn't matter if you use a coffee filter or don't filter at all, for that matter. The important thing is to separate all the particulate matter from the solution before gold is precipitated, otherwise you recombine unwanted materials with your processed gold. Gravity alone can be used to separate solutions from insoluble materials, it just takes more time, and it makes retrieving the last little bit more difficult. I was way too busy to take the time, so fast and good filtration was important to my operation. I learned to turn out solutions that would filter readily. How well a solution filters revolves around doing the proper washes before you ever dissolve the gold. By doing so, compounds that are formed by acids and difficult to filter are eliminated in the preliminary washes and rinses. These are things you'll learn as you progress. 

Harold


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## Ageo308 (Jan 23, 2008)

Aha I feel like an idiot but we did miss a couple of things.

1: the ammonium hydroxide which we didn't add but will do next time.

2: the precipitation process, I feel like a dummy as I skipped this bit (I will go and buy some ferrous sulfate. 

If you don't mind could you go into some detail with both these things, i.e how much ammonium needs to be used and do i just add it to the rinse? (with tap water)?

Also with the precipitation you mention take up water, filter, precipitate, and wash appropriately so once I filter it and have the brown mud sitting on the bottom is that when I add the sulfate? and if so how much? these 2 are the only areas i haven't done and will do tonight.

Thanks again


P.S as for the wash procedure, we basically filled the beaker with tap water, stirred it then let it settle, decanted it and made sure no value were in the liquid then emptied it and repeated the process until the rinse water was clear. Sound right? We did the same rinse process with the HCI/water and the AR mix.


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## Ageo308 (Jan 24, 2008)

Thanks af I'll go through that to get a better understanding. Also Harold you said any garden center has ferrous sulfate but I couldn't find any, the closest I came to is sulfate of iron (which I'm assuming is the same stuff) or a sulfate ammonia both are which a lawn fertilizer, so let me know which 1 will suffice.

As for the ammonium hydroxide I'm assuming the chemical factory that I picked up the nitric and HCl should have some so I will contact them.

I'll await for your replies before proceeding.

cheers

Edit: I found this product http://www.yates.com.au/Products/Fertilising/Specialised/SulphateofIron.asp

Iron Sulphate (Australian) so I'll be getting some of that.


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## Harold_V (Jan 24, 2008)

Ageo308 said:


> Aha I feel like an idiot but we did miss a couple of things.
> 
> 1: the ammonium hydroxide which we didn't add but will do next time.
> 
> ...


Regards the ammonium hydroxide, be certain you understand when this process is used. It should *NEVER* be combined with *gold chloride solution*. The ammonium hydroxide operation, for me, came after the first HCl wash and rinse of the precipitated gold powder. Cover the gold powder with ammonium hydroxide and then some tap water, and heat it. You'll see a change in the color of the solution, indicating it is dissolving unwanted compounds. Usually a light blue color. If you get no color change, great! That's a pretty good indicator that the gold is quite clean. Boil for a few minutes, then decant and rinse with more tap water, bringing it to a boil once again. Decant, and add enough HCl to cover the gold. Add a little water and boil for a while. If the color of the solution doesn't change, the gold is as clean as you're going to get it by washing. That isn't necessarily an indicator that the gold is pure; it may not be. Only a second processing will put more of the contaminants in solution, where they can be left behind by a second precipitation and wash cycle. That improves gold tremendously and is worth the effort if you're striving for 4 9's quality. You should get close, if not there, by this method. 



> Also with the precipitation you mention take up water, filter, precipitate, and wash appropriately so once I filter it and have the brown mud sitting on the bottom is that when I add the sulfate? and if so how much? these 2 are the only areas I haven't done and will do tonight.


I mentioned ferrous sulfate only as an example. As I may have mentioned, there are many things that will act as a precipitant. If you are precipitating by any other means, that's fine, so if you have brown mud sitting on the bottom of your beaker, you've already accomplished that operation.



> as for the wash procedure, we basically filled the beaker with tap water, stirred it then let it settle, decanted it and made sure no value were in the liquid then emptied it and repeated the process until the rinse water was clear. Sound right? We did the same rinse process with the HCl/water and the AR mix.



I maybe should have been more specific. I have posted on this procedure and covered anything of importance in fine detail. Aflac has provided a link in the post, above. Please follow that link and read the various posts. There is a lot of information there that will benefit you far beyond the time it takes to read the comments.

Regards what you did with your wash operation, it leaves a great deal to be desired. It doesn't come close to washing the gold in the way it needs to be washed. You may not understand that until you've actually seen what comes from the gold, and how it is changed by the procedure I've mentioned. There's no doubt in my mind, you'll rarely, if ever, produce gold that rivals gold that is washed properly after precipitation. Only when it comes from a very clean solution do you have a remote chance, for drag-down (of contaminants) is the enemy. Prolonged boiling in acid and ammonium hydroxide insure that traces are removed as much as is possible. I advise that you do not short cut the process by avoiding the wash cycle. 

Please read the provided link, and tell me what you feel you've learned. It might help in fine tuning what you're trying to learn. 

For the record-----gold that comes from this process (polishing wastes that are well washed before the gold is dissolved) tends to be of very high quality because you start with material that lends itself to easy dissolution of the metals. Your quality may be quite good now----but washing is good insurance. You'll see that when you process dirty material, such as filings. 

Harold


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## Harold_V (Jan 24, 2008)

Ageo308 said:


> Thanks af I'll go through that to get a better understanding. Also Harold you said any garden center has ferrous sulfate but I couldn't find any, the closest I came to is sulfate of iron (which I'm assuming is the same stuff) or a sulfate ammonia both are which a lawn fertilizer, so let me know which 1 will suffice.


Sulfate of iron appears to be the one you'd buy. If you have the opportunity, look at the contents. They should be a very nice light green color. If you find brown, it's not good for use. I have used some that is mixed, brown and green, by adding a few drops of HCl to the solution after dissolving and filtering. The brown material, as I understand it, has already lost the needed electron that precipitates gold---so it stands to reason that if you use some that is mixed, it will do less work. No matter---you simply use a little more. Again, you may not need this material if you have chosen a different method to precipitate your gold. Don't duplicate processes----that makes no sense. Buy this material only if you are not happy with what you used already. 



> As for the ammonium hydroxide I'm assuming the chemical factory that I picked up the nitric and HCl should have some so I will contact them.


I used to buy it from a chemical supply house in a box of six (1) gallon plastic containers. If, by chance, you have difficulty buying-----use any unscented (and uncolored) ammonia from the grocery store. 



> I'll await for your replies before proceeding.


Also, please read Hoke on processing polishing wastes----and see if I've left out anything important. It's been years since I last ran a batch. I'm quite rusty! :wink: 

Harold


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## Ageo308 (Jan 24, 2008)

wow I have a sore head  Harold is this something your referring to for a clean wash



> First wash should be in boiling HCl and tap water. Boil for a prolonged period of time. Take up the solution with tap water, decant after the gold has settled, then rinse with tap water, which should again be brought to a boil. After it has boiled for a period of time, add more tap water to cool the lot, then decant as before. Rinse again, and do it until the wash water comes off clear. :arrow: Next, wash the gold with ammonium hydroxide and tap water. Heat it until it boils. You'll notice that the solution gets discolored. How much is determined by how dirty your gold was when you started. The ammonia evaporates fairly quickly, so you can't boil very long. Add tap water to cool, decant, and follow up with a tap water rinse, again, boiling the water. Add tap water to cool, then decant. You now repeat the HCl and tap water wash. You'll be amazed that suddenly more contaminants will come off. Boil well, add water to cool, decant, repeat the water rinse, decant, then, and this is important-------start the refining process all over again by dissolving the well washed gold powder in aqua regia. I'll talk about that in a minute, but these are indicators you should have observed along the way, aside from the fact that you could see contaminants being washed from your gold powder.


If that's exactly how I should do it then I have 2 more questions, 
1: since I have boiled in AR already and the gold has somewhat dissolved will it be dangerous to repeat the above wash since ammonium and gold chloride don't mix well?

2: Believe it or not but I didn't use anything to precipitate, I simple boiled the AR then added water and rinsed but the way I stated before (without re-boiling). So do you recommend me adding some sulfate to the AR mix whilst I rinse it a few times?

Tonight I'm going to get stuck into Hoke's book again to refresh my memory.

cheers :wink:


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## Harold_V (Jan 24, 2008)

That is the washing procedure *for precipitated gold*---the familiar brown powder that comes from precipitation. Sounds involved, but it isn't, and it improves the quality of gold tremendously. Understand that you can stop the process after using ammonia, followed by the last wash with HCl, and a water rinse once again. If the gold came from a very clean solution and you do not intend to re-refine it, it would then be dried and melted. If the final wash with HCl comes off clean, that would certainly be the case. I always refined a second time, but you may or may not wish to do so. 

As far as your concern about ammonia-----If you have washed gold powder with ammonium hydroxide, then rinsed with water, followed with another wash with HCl, there is no ammonium hydroxide present. It will have been completely replaced with the HCl wash and rinse. You have nothing to fear. Fact is, when you force dry the gold, even after a good rinse in water, you'll notice a distinct smell of HCl coming off the gold as it dries. Dry it until the smell is gone. Follow the instructions for drying the gold in a beaker. Use low heat until loose water is gone, otherwise you experience steam bumps that can throw gold out of the beaker, and usually does. I've had beakers bump so hard they came off the hot plate and broke. Be careful when drying your gold. 



> 2: Believe it or not but I didn't use anything to precipitate, I simple boiled the AR then added water and rinsed but the way I stated before (without re-boiling). So do you recommend me adding some sulfate to the AR mix whilst I rinse it a few times?


If you didn't precipitate, how did you recover the gold? How did you eliminate all the garbage that typically accompanies gold in process? None of this makes any sense. 



> Tonight I'm going to get stuck into Hoke's book again to refresh my memory.
> 
> cheers :wink:


Right now you have me in a complete state of confusion. I have serious doubts that you have followed the instructions as they have been presented. Please------do not try processing material until you understand the process. You stand to lose a great deal of value if you do, or you can create problems that can be difficult to undo. 

There are two distinct HCl washes that accompany the processing of polishing waste. One of them is to dissolve unwanted crud in the *dirt *you have incinerated. Only after you have processed the dirt and washed (with HCl) and rinsed it until the rinse water comes off clean do you dissolve the gold. When the gold has been dissolved, it (the gold solution) should have been separated from the dirt, with the dirt rinsed with tap water until the rinse shows little or no values. At that time the solution would be evaporated as I've instructed, filtered after it has been well evaporated, and then the gold precipitated as the familiar brown mud. _The last washes with HCl occur only on the precipitated gold_, and that is the ONLY time your gold should see any ammonia. If you've done anything different from the above, please detail it EXACTLY as you've done it. Include all details, even if you think they don't matter. 

Harold


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## Ageo308 (Jan 24, 2008)

Ok let me explain what we have done so far, We incinerated the sweeps, then sifted it (removed the larger pieces and stored them), then ran a magnet through it to remove any iron particles.

* Once that was done we boiled it in 50/50 HCl/water until it changed colour (cream brown then green), basically from there we added some water to cool then decanted the solution, then added some more water but didn't bring it to boil (wasn't sure) after a quick stir and let it settle we rinsed it again (5 times roughly). 

* From there we put the mud into AR and did the same process as the HCl which is wrong I know but I'm just explaining what we did. Tonight we basically put the dried dirt into a 50/50 HCl/water mix and boiled for about 20 min then added water, decanted (the solution was yellow), and rinsed again with new tap water and again brought to boil. This time we repeated that process about 8 times and had to stop but the rinse water is becoming much clearer and the mud is now becoming a nice smooth fine dust (lightly brown) with no sludgyness. I can see gold particles in there so I'm guessing that's a good thing. 

* Tomorrow night we are going to finish off the rinsing process then start with the ammonia rinse and do that until its clear and then finally back to HCl/water with a final rinse to make sure there is nothing left to clean.


So tell me where I went wrong and if we are going in completely the wrong direction. From what I can see thow the powder is looking much nice then it did before.


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## Harold_V (Jan 25, 2008)

Ageo308 said:


> Ok let me explain what we have done so far, We incinerated the sweeps, then sifted it (removed the larger pieces and stored them), then ran a magnet through it to remove any iron particles.
> 
> * Once that was done we boiled it in 50/50 HCL/water until it changed colour (cream brown then green), basically from there we added some water to cool then decanted the solution, then added some more water but didn't bring it to boil (wasn't sure) after a quick stir and let it settle we rinsed it again (5 times roughly).


At this point you've done quite well. The whole idea is to dissolve anything that will dissolve, but not the precious metals. If your solution tested barren, it can be discarded. The five rinses would indicate that you had removed the vast majority of unwanted materials, so when you dissolved the gold and other values, the solution would then be quite clean. Well done to this point.



> * From there we put the mud into AR and did the same process as the HCl which is wrong I know but I'm just explaining what we did.


No, it's not wrong--it's exactly what you were supposed to do. What you did with the solution is what I think you did wrong. If you discarded it, you tossed your gold. AR dissolves gold, which is EXACTLY why you introduced it to the mud. It is intended to dissolve the gold and other values, so they can be separated from the dirt, which has no value. You get a much better extraction by dissolving than you do by melting, unless you use litharge in melting, but that involves cupellation, which is beyond the average guy's ability, and is also very hazardous because you're burning lead and producing large volumes of lead fumes. 



> Tonight we basically put the dried dirt into a 50/50 HCl/water mix and boiled for about 20 min then added water, decanted (the solution was yellow), and rinsed again with new tap water and again brought to boil. This time we repeated that process about 8 times and had to stop but the rinse water is becoming much clearer and the mud is now becoming a nice smooth fine dust (lightly brown) with no sludgyness. I can see gold particles in there so I'm guessing that's a good thing.


If you combined all these wash waters with the first (yellow) solution and have started evaporating them, you're on the right track. If you discarded the wash water, as I said before, you tossed the values. If you can still see gold in the mud, it's because you didn't use enough acid to dissolve all of it. Fact is, the mud is what you should have been trying to eliminate, not keep. By washing it until you had rinsed out all of the yellow color, you would have removed all of the gold, assuming you had dissolved all of it in the first place. For some reason you seem to think that the dirt is the target-----*it is not*. 



> * Tomorrow night we are going to finish off the rinsing process then start with the ammonia rinse and do that until it's clear and then finally back to HCl/water with a final rinse to make sure there is nothing left to clean.



Don't do that. You should have evaporated the golden solution to expel the unused nitric, diluted the evaporated solution with water, filtered, then precipitated the gold FROM the solution. You're spinning your wheels working on worthless dirt, assuming you dissolved all of the gold in the first place. Your only hope is if you had enough sense to keep all of those solutions aside from the very first one, where you used HCl and water the first time, plus the rinses. If you did not, you have lost your gold. 



> So tell me where I went wrong and if we are going in completely the wrong direction. From what I can see thow the powder is looking much nice then it did before.


It may look "nicer", but what does that mean? You've possibly tossed the baby with the bath water. I hope you haven't.

Can you see why I suggested you not do anything until you understand the process? Do you see why I suggested you hold off until you had Hoke's book? 

Had you kept the instructions near you while you were working, and checked each step to verify what you were doing, you wouldn't be where you are right now. 

Let me know if you saved your gold colored solutions. If so, you must turn your attention to them. 

If you think you're seeing gold in the mud, you may not have dissolved all of the values. Heating with a little more AR will disclose if you did, or did not. If there's values remaining, you'll see the solution turn yellow to orange, depending on the degree of concentration. 

I haven't heard you mention stannous chloride much in your report. Did you ever bother to check solutions? 

*NEVER DISCARD A SOLUTION WITHOUT TESTING WITH STANNOUS CHLORIDE THAT IS KNOWN TO BE ACTIVE. * That means you should have on hand a standard gold solution, which is used to test the stannous chloride. It's all in Hoke. 

Harold


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## Ageo308 (Jan 25, 2008)

Ok Harold, we haven't discarded any solution and all of them have been filtered.

I just re-read Hoke's book and revised some of the important areas. A quick question on what she says.

Basically she mentions that you should Incinerate, sift, magnet then if there is shellac/grease etc.. to boil in caustic soda/lye (to remove it). Then she mentions to wash in nitric/water acid unlike your procedure which is HCl/water, it says in her book you can use HCl but it doesn't dissolve copper or nickel (which will be present in these sweeps), the only draw down with using nitric/water is that it will dissolve silver but you can store that and recover it at another time.

* so I'm interested to know why you choose HCl over the nitric?

* And why not boil in caustic as she mentioned to remove the shellac/grease etc?


And I can't see anywhere that stannous chloride is mentioned in Hoke's book, is this to determine what metals are present in the solutions???

cheers

P.S the sweeps we are using is my partner's and he has plenty to spare and experiment with.

P.SS I think I'm getting you now Harold




> If you combined all these wash waters with the first (yellow) solution and have started evaporating them, you're on the right track. If you discarded the wash water, as I said before, you tossed the values. If you can still see gold in the mud, it's because you didn't use enough acid to dissolve all of it. Fact is, the mud is what you should have been trying to eliminate, not keep. By washing it until you had rinsed out all of the yellow color, you would have removed all of the gold, assuming you had dissolved all of it in the first place. For some reason you seem to think that the dirt is the target-----it is not.


Just re-read Hoke's washing:
Correct me if I'm wrong but when you say combining the wash waters (yellow) solution is the colour yellow because it's suppose to be gold? We haven't discarded this solution and if I'm understanding right we are suppose to evaporate that yellow solution to expel the excess nitric then once that is all done make a separate iron sulfate solution with water and add some HCl to make it a clear green (as the book says) and then slowly add it to the main gold contents to precipitate the gold. Once the dark cloud fumes stop then it should be done. So I filter the gold then rinse it with water a few times and finally a few times with HCl/water mix until the gold powder is clean. Then filter again and let it dry in the funnel. After this it's ready to be melted.....

This sound about right???

If it is I will add more AR to the mud to dissolve any more undissolved gold then wash with the HCl and add to the yellow solution.

I'm looking forward to your reply


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## Harold_V (Jan 25, 2008)

Ageo308 said:


> Ok Harold, we haven't discarded any solution and all of them have been filtered.


I'm pleased to hear that. I feared you took a wrong turn and had discarded your gold, as you may have noticed. 



> I just re-read Hoke's book and revised some of the important areas. A quick question on what she says.
> 
> Basically she mentions that you should Incinerate, sift, magnet then if there is shellac/grease etc.. to boil in caustic soda/lye (to remove it). Then she mentions to wash in nitric/water acid unlike your procedure which is HCl/water, it says in her book you can use HCl but it doesn't dissolve copper or nickel (which will be present in these sweeps), the only draw down with using nitric/water is that it will dissolve silver but you can store that and recover it at another time.
> 
> * so I'm interested to know why you choose HCl over the nitric?


It was my reasoning that there is far more iron in the waste (from polishing compounds) than copper or nickel, each of which will be dissolved to some degree because they are oxidized by incineration. HCl is an excellent solvent for iron, unlike nitric, although it, too, will dissolve iron. The solutions are very different, however, with the nitric solution eager to precipitate the iron as rust, which would occur when you rinsed the material. That can complicate your processing, and leaves behind unwanted iron. 

My experience in running my wastes by this manner tended to support that logic in that the solution, after precipitation of gold, was relatively clean. If you test your initial wash solution for copper and nickel, I'm quite sure you'll find that a good deal of it does, indeed, get dissolved with the HCl operation. A drop of ammonium hydroxide in a drop of the solution will turn dark blue if there is copper present. Likewise, a drop of the solution, along with a drop of ammonium hydroxide and a drop of DMG (see Hoke) will disclose nickel with a pink display. It left the silver behind either as a chloride, or in the elemental state, although I imagine it was converted to chloride by the gold chloride solution if that was the case. You would be unlikely to be able to recover any silver by this process, but it is not lost, it's still in the dirt. More on this, below. 

Note that I did NOT process filings by this method. Only floor sweeps and polishing wastes. Filings are processed with nitric acid, then AR. 

You see considerable evidence of my claim in the color of the original HCl wash. Beyond that, what you'll come to discover is that solutions that come from dirty substances and a nitric wash tend to be difficult to filter. Without the HCl wash, your gold chloride solution has a tendency to plug filters. I've had a liter of solution take as long as three days to filter. From that, I learned to incinerate suspect materials and then do an HCl wash, even if the material had already undergone a nitric wash. In that case, the material must be incinerated a second time, to kill any nitric that is present. I found nothing to equal HCl's ability to clean material of substances that were difficult to filter. That is particularly true of refining gold filled objects in volume. There is often a little lead and tin included in gold filled objects. They respond to the treatment I mention in a very positive way. 

What you have been instructed by me is a process that evolved through trial and error and was used for many years. To be quite frank, I don't recall what Hoke recommended, so it's been interesting to hear that her version varies from mine. I assure you, if you follow my instructions, you'll achieve a level of quality and extraction that is very good, although if you have doubts, don't hesitate to follow her instructions. I've commented time and again, I learned refining from her book, and know that aside from her recommendation to use gasoline freely when incinerating, her information is trustworthy. 



> * And why not boil in caustic as she mentioned to remove the shellac/grease etc?


It's redundant. A boil in lye will remove a good deal of the unwanted material, but it won't eliminate everything that will be troublesome. In the end you still must incinerate, so I see no good reason to duplicate operations unless there is some gain. Incineration performs every possible useful function, and eliminates the hazard of using lye. Should you splash lye in your eye, blindness is guaranteed, yet a drop of nitric in the eye, while painful, is not serious. I've been through that and came out fine. Learned from that to wear eye protection. 



> And I cant see anywhere that stannous chloride is mentioned in Hoke's book, is this to determine what metals are present in the solutions???


 That's correct. Read the chapter that involves testing of precious metals, and follow her instructions in buying and building the necessary solutions. In her book, I recall that she refers to stannous chloride as testing solution A, but I could be wrong. I haven't looked at a copy in well over 12 years. 

If you do not have stannous chloride, immediately work in the direction of obtaining it. Do a search on the board if you must, for there's a lot of information available. Many of the guys here are making it with 95/5 solder. Personally, I preferred to use pure tin and stannous chloride crystals, which was my routine. Without it's use, you run blindly, not knowing the status of any of your solutions. Also, do yourself a favor and discard solutions by proper means the moment you conclude they have no value. It takes very little time to find yourself inundated with a huge variety of unknown and unwanted solutions, so you not only trip over them, but you spend a good amount of time screwing with them unnecessarily when you finally decide on disposal. 



> P.S the sweeps we are using is my partner's and he has plenty to spare and experiment with.
> 
> P.SS I think I'm getting you now Harold


I hope so. I'd like to see you succeed. This method is quite good. I have serious doubts that you could come up with one any better. 



> Correct me if I'm wrong but when you say combining the wash waters (yellow) solution is the colour yellow because it's suppose to be gold?


That's correct. Gold chloride that isn't contaminated with copper or nickel is yellow, deepening to a dark red/orange, depending on concentration. The wash water is nothing more than dilute gold chloride, which is why you combine it with the darker yellow solution. If you had stannous chloride, you'd see by testing that the solution would react with a purple stain. That's what gold looks like when combined with stannous chloride. As the concentration deepens, so too does the color. Very slight presence of gold will yield a faint purple reaction. 



> We haven't discarded this solution and if I'm understanding right we are suppose to evaporate that yellow solution to basically have clean gold??? Is this correct???


No----evaporation does NOTHING to improve gold quality. That's determined by the washes you do prior to dissolving the gold, by the precipitant you choose to use, and by the washing you do after the gold has been precipitated. Evaporation serves two purposes. One is to concentrate voluminous solutions so you aren't working with gallons when a liter is adequate, but most importantly, it, when carried out properly, eliminates unused nitric acid. That is a requirement to recovering your gold. If you leave it behind, it will react with not only the precipitant, slowing or stopping the operation, but assuming you are successful in precipitating your gold, when you wash it, the residual nitric will re-dissolve some of your gold, until it has been consumed. That's not desirable, as you might understand. Please read Hoke on evaporation of solutions, and learn to do so. Also, if you have a button of gold at your disposal, it really helps to add one, as I've already mentioned. Weigh it before introducing to the solution you're evaporating, and weigh it afterwards if you want to know how much of the button was dissolved in the process of eliminating any free nitric. The use of a button will avoid evaporating the gold solution down to a heavy syrup, so it saves a lot of time. If you choose to use a button, you must still add some free HCl as the solution thickens. That way it will form AR and consume the free nitric by dissolving the gold button. Very slick way to process, if I must say so myself. 



> If it is I will add more AR to the mud to dissolve any more undissolved gold then wash with the HCl.


I'm not convinced you understand the wash purpose in using HCl. It is NOT used to wash the material once you have introduced AR. In this case, if you subject the material to more AR, simply boil the material in the AR and water mix, then add a small amount of HCl to insure that you haven't depleted what you introduced with AR. If, when you add the HCl, you see brown fumes coming off the beaker, that's a sign that you did just that. If you see no reaction, the next thing to do is add a few drops of nitric. If there is any undissolved gold present, you should see brown fumes coming from the beaker. If you do not, you can safely assume that the dirt is now barren of undissolved gold, and needs no further processing. At this point, add a little water, stir well, and allow the solution to settle. Decant the solution, then add a generous amount of water and stir, again allowing the contents to settle well. Your objective here is to rinse the mud clear of all dissolved gold-----which requires NO HCl. Just plain old tap water will suffice. Wash the mud until you're satisfied that you are not getting a return worth the trouble, then get the dirt in a coffee filter and extract the last of the liquid, which should be combined with the balance of the yellow solutions we've been dealing with. 

The dirt, at this point, is relatively valueless, although it will contain traces of values that you haven't recovered. Included in that there can possibly be platinum, which dissolves very slowly, and silver in the way of silver chloride. I suggest you dry this material by heating, just as if you would to incinerate. You'll see nitric fumes coming off at the very end of drying. Heat until you no longer see the fumes, then cool the material and store in a covered drum. If you collect enough of the polishing waste in this fashion, it has market value, or, down the road, when you have enough, you can run it in cyanide and extract the silver, along with traces of gold, all of which are never fully recovered, try as you might. 

DO NOT STORE WET WASTE MATERIALS. THEY WILL RUST EVERYTHING IN YOUR WORK AREA THAT WILL RUST. 

Hope some of this helps. 

Keep us all informed on your progress.

Harold


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## Harold_V (Jan 25, 2008)

Ageo308 said:


> Just re-read Hoke's washing:
> Correct me if I'm wrong but when you say combining the wash waters (yellow) solution is the colour yellow because it's suppose to be gold? We haven't discarded this solution and if I'm understanding right we are suppose to evaporate that yellow solution to expel the excess nitric then once that is all done


When evaporation is concluded, you dilute the gold chloride solution and filter the solution until it is clear of flocculance. Do not precipitate any solution that is cloudy---all you do is recombine the gold with unwanted junk. 



> make a separate iron sulfate solution with water and add some HCl to make it a clear green (as the book says) and then slowly add it to the main gold contents to precipitate the gold. Once the dark cloud fumes stop then it should be done.


Do NOT assume it's done. Check with stannous chloride. This is important for a solution that has iron dissolved within will still be yellow in color. You'd have no way of knowing if the color was gold or iron without testing. You may also detect the presence of the platinum group when gold has been precipitated. If you get a yellow to brown display, that's a sign of platinum in solution. 



> So I filter the gold then rinse it with water a few times and finally a few times with HCl/water mix until the gold powder is clean. Then filter again and let it dry in the funnel. After this it's ready to be melted.....
> 
> This sound about right???


That is one place where I depart from anything you may read, and I encourage you to listen to me. Do NOT filter the gold powder. There is nothing to be gained by doing so, and you lose some in the process, although you would recover it in future processing. 

What I would like to see you do is, after you have precipitated your gold, and tested the solution and know that it is barren, to allow the gold to settle by gravity alone. This may take a day, but you can see the progress by the stratification that comes from the finest of particles, which are slow to settle. When the solution has settled totally, decant with a hose, then place the beaker on a burner and add some HCl and water. You will do the three wash and rinse phases without ever removing the gold from the beaker. You will also dry the gold in the same beaker. If you do your work properly, when the gold is dry, it will be a light brownish gold color, and will cling in clumps, making handling very easy. Again, I strongly encourage you to follow my advice in this regard. It is the fastest and easiest way to deal with your gold. 

Harold


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## Ageo308 (Jan 25, 2008)

Ok so next step before I do anything is to purchase some stannous chloride crystals & pure tin and read Hoke's book on testing precious metals.

Once I read the crap out of it we will continue the process

I will keep you updated

thanks for the info and I wasn't judging your experience before just clarifying the difference between Hoke's methods and yours and you cleared that up for me rightly so.

cheers


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## Ageo308 (Jan 25, 2008)

> At this point, add a little water, stir well, and allow the solution to settle.. Decant the solution, then add a generous amount of water and stir, again allowing the contents to settle well. Your objective here is to rinse the mud clear of all dissolved gold-----which requires NO HCl. Just plain old tap water will suffice. Wash the mud until you're satisfied that you are not getting a return worth the trouble, then get the dirt in a coffee filter and extract the last of the liquid, which should be combined with the balance of the yellow solutions we've been dealing with.



Quick question Harold, when you add the generous amount of tap water do you bring it to boil again? or just stir and let it settle? If you don't bring it to boil then I did this wash process successfully before as stated in my earlier posts. And will do the same next time round


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## Harold_V (Jan 26, 2008)

While boiling would likely do no harm, I don't think it would be a necessity. At this point, anything that will dissolve has done so, so all you're doing is rinsing the values from the solution. Assuming the material isn't overly porous, I'm of the opinion that a simple stirring and settling will serve the purpose well enough. I sure as hell hope so, that's all I ever did!  



> If you don't bring it to boil then I did this wash process successfully before as stated in my earlier posts. And will do the same next time round


Good show! We've talked about so much in the past couple days that I'm a bit lost as to what, exactly, we have discussed. At any rate, I feel you're getting the picture. 

Once you've been through a batch of this stuff, and see what happens, and why, it will start answering some of your questions. In a sense, it's all perfectly logical. You incinerate the material to eliminate oils and other contaminants, screen it to separate solids from dirt, dissolve unwanted substances with HCl and water, then dissolve the gold and recover it from the dirt. If you look at it that way, jumping through each necessary hoop, it's real easy to know what to do, and when to do it. 

Be certain to keep us all advised. I'm in hopes that others have been following your experience, and learning as you go, so it would be good for all involved to know how it ends. 

Harold


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## Ageo308 (Jan 26, 2008)

Harold I purchased the Iron Sulphate from a garden store and when I opened it the granules were white. They could have a green tinge to it but you would need a loupe scope to pick it up. Would this be useless? It says on the contents 20% iron sulphate (that's it). Does it have to be stronger?

Or would a few drops of HCl along with water be enough? I'm going to try it and see if a green solution appears so I will update you.


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## Harold_V (Jan 26, 2008)

I bought a reagent grade once, and found the crystals to be a very light green color (similar to the color of the inside of a lime), with traces of white. I'm of the opinion that what you have will work. It's real easy to make a test. Take a drop of the yellow AR solution and place it in a spot plate cavity. If you have no spot plate, use a shot glass or some such, something that will keep the drop in a small area. Place one of the crystals of ferrous sulfate on the drop and observe if you see gold forming. It will be dark, or may even form a thin sheet, much like gold leaf. If you get any kind of precipitation, it's exactly what you wanted. When you dissolve it to introduce it to your gold solution, if it's not perfectly clean, filter the solution. Be certain to add a few drops of HCl to the dissolved material. Watch it closely and you'll see it flash a slightly different color, and get clearer. You may or may not see that, depending on how clean the material is. Make sure when you introduce the solution to the gold solution that each of them have been filtered to the point of absolute clarity---meaning no flocculance. They will each have their distinctive colors, but they should be absolutely clear.

If you don't have stannous chloride yet, you can use the same test to determine if you have precipitated all the gold. When you introduce a crystal to a drop of solution, it won't show any precipitate. It's not as sensitive as stannous chloride, and it won't replace it for testing for the platinum group, but it's a reliable test for gold. 

Edit for more comments:

It's possible your material has a filler, something that limits the speed of dissolution, or buffers the material so it won't burn plants as easily. If that be the case, when you filter it, it should be fine. As far as the percentage of iron goes, I don't know if what you have is typical, or not. 

Typically, an ounce of ferrous sulfate will precipitate an ounce of gold, but a little excess does no harm. 

Hope this helps. Let us know!

Harold


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## Ageo308 (Feb 12, 2008)

Hi Harold, question:

when we started our boil in AR I was wondering when do you know exactly all the gold has been dissolved?? I mean testing with stannous only tells you if there is gold present but it doesn't tell me if "all" the gold has been dissolved. Is it when I add a fresh batch of AR (when the last batch has been killed off, small amounts at a time) and the brown fumes change to clear does this mean there is no more reaction? I mean the brown fumes simply mean the reaction with the base metals from the nitric and the dissolving of gold yes?

We boiled for well over an hour (we only had 20 grams of dust/mud to test) adding small amounts of AR at a time until each amount died off and each time it died off we poured the solution into a beaker (gold solution that is). I think where we went wrong is over boiling and we evaporated some gold (is that possible?) Anywayz I will post a photo of a 2 gram gold button we got (I'm happy we got this far) I just know along the lines we had more wastage and lost some gold. P.S As we were melting we noticed that the borax become real thick and sludgy and we couldn't retrieve all the gold, I'm assuming that we didn't clean the gold properly and that will need some more attention on our next test run.

I'll see if I can post the photo tomorrow sometime.

cheers

P.S the stannous does become real handy in testing solutions to see if they are worth keeping or discarding.


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## Harold_V (Feb 12, 2008)

Ageo308 said:


> Hi Harold, question:
> 
> when we started our boil in AR I was wondering when do you know exactly all the gold has been dissolved?? I mean testing with stannous only tells you if there is gold present but it doesn't tell me if "all" the gold has been dissolved. Is it when I add a fresh batch of AR (when the last batch has been killed off, small amounts at a time) and the brown fumes change to clear does this mean there is no more reaction?


That's a good indicator, with one exception. Once action has ceased with AR, it's a good idea to introduce a little more HCl. That way, if you've depleted the original amount, but have not depleted the nitric, it will start dissolving more gold, assuming it isn't all in solution. The addition of more HCl costs very little, and does not complicate the recovery of your gold, unlike excessive nitric. 



> I mean the brown fumes simply mean the reaction with the base metals from the nitric and the dissolving of gold yes?


That's correct. If there is anything present that can be dissolved, fumes will be produced. 



> I think where we went wrong is over boiling and we evaporated some gold (is that possible?)


Yes------very possible----and you likely did unless you had a watch glass covering the beaker. If you had it covered, you'd notice that gold chloride solution forms on the inside of the watch glass and drips back in the beaker. Anything that is not condensed on the watch glass is lost. That's why I worked in a fume hood that had a condensing chamber, along with a filter. While the amount of gold lost is a small percentage, when you handle large amounts of gold, it adds up. 

Regards the boil time, in the case of screened polishing wastes, the largest particle of gold will still be quite small, and will dissolve readily. The amount of time that you boil the material should be relatively short. An hour is far more than is necessary. I would suggest that a few minutes would be adequate. The moment fumes cease to evolve, you have either consumed all of the acid, or all of the material that will go into solution. Prolonged boiling won't change anything, and puts you at risk of losing values via rapid evaporation. Hoke cautions against evaporating too fast for that reason. You should keep the material covered while dissolving, for the effervescence carries minute bits of value out of the beaker. A watch glass returns to the beaker that which would be lost. 



> P.S As we were melting we noticed that the borax become real thick and sludgy and we couldn't retrieve all the gold, I'm assuming that we didn't clean the gold properly and that will need some more attention on our next test run.


Unless you heated the melting dish for a prolonged period of time, overheating the flux and dissolving some of the dish, the flux should have done nothing aside from assume a little purple cast, the result of colloidal particles of gold being picked up by the flux. If it changed color beyond the purple I mentioned, your gold is not very clean. Don't skimp on the wash process. I've noted some that have reported on its use have put time constraints on how long it is boiled in HCl and water rinses. That makes no sense. It should be boiled as long as there is a change in results. Stopping too soon leaves contaminants behind that would have been removed. If your objective is high quality gold, it should be washed until it is clean-----until the last application of HCl yields no change in color (of the solution. The gold powder will also become lighter in color as it is cleansed). The alternative is to stop after a good first wash and rinse, then to re-dissolve the gold and precipitate a second time. That is the procedure I followed, and got exceptional results. I never short changed the first wash, however, so the gold was already of decent quality. 



> P.S the stannous does become real handy in testing solutions to see if they are worth keeping or discarding.


I hope all readers see the wisdom in its use! 

Harold


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## Ageo308 (Feb 13, 2008)

Hi Harold, thanks for the advice.

I was wondering thow let's say we do a 10 min boil in AR and extract all the gold solution. Correct me if I'm wrong but when we evaporate (with the lid off, to get rid of excess nitric) would the gold evaporate as well? since its still a chloride (liquid) and the evaporation process takes at least an hour if not more depending on quantity?

Besides the washing process (which we will improve next time) I'm sure we evaporated some gold (if it's a liquid and it's evaporating long enough surely you would lose some amount)?

We are doing the next test on Sunday so I will keep you posted.


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## Harold_V (Feb 13, 2008)

Ageo308 said:


> Hi Harold, thanks for the advice.
> 
> I was wondering thow let's say we do a 10 min boil in AR and extract all the gold solution. Correct me if I'm wrong but when we evaporate (with the lid off, to get rid of excess nitric) would the gold evaporate as well?


No, not if you do it properly. (Don't hesitate to read what Hoke says about evaporating). You will have separated the solution from the mud, and will be evaporating only solution. It is done at a reduced temperature, never allowed to boil. It must remain tranquil, and have little or no effervescence. If a button of gold is introduced to consume the free nitric, it will react relatively slowly, assuming you don't have a huge amount of nitric present. I strongly advise the use of a gold button, which minimizes the amount of evaporating that must be accomplished. Frankly, I think that's one of the reasons I enjoyed considerable success, and never ever used urea. 

When evaporating, you must observe the vapors that leave the dish. If you see any signs of color in them, you're going too fast (too hot), so heat must be cut back. It's not a hard thing to do, it's just a little strange at first. It becomes routine once you've done it a few times, and you know exactly what to look for, and how to react to your observations. 



> Besides the washing process (which we will improve next time) I'm sure we evaporated some gold (if it's a liquid and it's evaporating long enough surely you would lose some amount)?


Actually, how long you evaporate makes no difference. If you evaporate at or below the correct temperature, the solution will slowly condense, changing color as it thickens. If you continue the evaporating process, the solution will finally bake out as a dark brownish black substance, precipitating some of the gold in the process. Try to never take it that far. When it gets to the point of being a dark red color, that's a great time to introduce a little HCl. A half ounce or so. If, when you add the HCl it does not result in brown fumes coming off, that's a pretty good sign you have eliminated the nitric. You'll notice that as the solution thickens and darkens, that it takes a higher and higher temperature to make it boil. Armed with that knowledge, you should see slight boiling when you add the HCl. If the solution boils but you don't see any fumes, the job is done. Take it up with water, then it's time to filter, which will eliminate traces of silver chloride and lead. Remember, during the evaporation process, you should have introduced a few drops of sulfuric acid, which will have precipitated any traces of lead that may have been put in solution. Lead is death of gold quality, so don't skip that part. 



> We are doing the next test on Sunday so I will keep you posted.


Sounds like a plan! Looking forward to your next post. 

Harold


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## Ageo308 (Feb 19, 2008)

Hi Harold, good news. We did our 2nd test batch with going through the proper washes and it come out as 24ct (not sure on the exact purity thow). This time it melted with ease and took about 2 min to melt and pour (only very small amount).

Basically after we let the gold precipitate and dropped the gold completely we washed in HCl/water until the liquid discoloured then rinsed off (it became clear after 1 rinse). We were left with a fine brown powder which was then melted with ease and poured. I didn't rewash with ammonia and then again with HCI as I wanted to see the results without doing those and even thow we might not achieve the highest of purity it's not a matter for us as the gold will be sold off, basic 24ct is good enough for us for now.

That stannous is excellent as we test all solutions before discarding them. The silver chloride which is caught in the filters is dried and stored in a jar for processing later down the track. Once we have mastered this a few times and get the ball rolling we will concentrate on extracting palladium and other precious metals which are also in the sweeps. A big thank you from us over here again and anyone that 2nd guesses you will have to be crazy, your information is 2nd to none.

Thanks heaps again Harold :lol:


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## Harold_V (Feb 20, 2008)

Ageo308 said:


> I didn't rewash with ammonia and then again with HCl as I wanted to see the results without doing those and even thow we might not achieve the highest of purity it's not a matter for us as the gold will be sold off, basic 24ct is good enough for us for now.


The additional washes serve to insure quality. The one thing that may have been of service would be the ammonium hydroxide wash, which is intended to remove traces of silver (as chloride) which often hitches a ride with the gold. The theory is well documented by Rose, whereby small amounts of silver behave as gold, and will follow the solution in spite of having been introduced to chlorine. 

GSP suggested that diluting the solution at least three volumes will cause the silver to precipitate, at which time it can be easily removed from the batch by proper filtration. You often see evidence that he's right in that a solution that is clear of flocculence will often cloud up when water is introduced. The ammonium hydroxide wash is intended to remove the traces that make it through filtration. No harm done even then, assuming the gold is to be used for yellow, green or rose gold. Each have silver added, anyway. Not so good for white gold, which contains no silver. No matter-----you've done a great job and are to be commended. 



> Once we have mastered this a few times and get the ball rolling we will concentrate on extracting palladium and other precious metals which are also in the sweeps.


Do check your solutions for values after you've precipitated the gold. If they show anything in the way of a green/brown or orange reaction, that's a sign of platinum group metals. If you prefer to not pursue them directly, pour the solution on some scrap steel that you have in a plastic bucket. Here in the states they sell ice cream in 5 quart buckets. That makes a reasonable size container for the purpose. The scrap steel will precipitate the values, which you will eventually run in a furnace with the saved silver chloride. It will be reduced to elemental silver and act as a collector for the values. It's a wonderful savings plan---one that allowed me to retire at a relatively young age. 



> A big thank you from us over here again and anyone that 2nd guesses you will have to be crazy, your information is 2nd to none.
> 
> Thanks heaps again Harold :lol:


Chuckle! 

Thanks for the kind words. I know you'd have done the same for me were conditions reversed. Your success is my pleasure, believe me. 

Well done!

Harold


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## Ageo308 (Feb 21, 2008)

> The additional washes serve to insure quality. The one thing that may have been of service would be the ammonium hydroxide wash, which is intended to remove traces of silver (as chloride) which often hitches a ride with the gold. The theory is well documented by Rose, whereby small amounts of silver behave as gold, and will follow the solution in spite of having been introduced to chlorine.


I'll keep that in mind, I mean an extra 20 min won't hurt since it's giving us more pure gold.



> Do check your solutions for values after you're precipitated the gold. If they show anything in the way of a green/brown or orange reaction, that's a sign of platinum group metals. If you prefer to not pursue them directly, pour the solution on some scrap steel that you have in a plastic bucket. Here in the states they sell ice cream in 5 quart buckets. That makes a reasonable size container for the purpose. The scrap steel will precipitate the values, which you will eventually run in a furnace with the saved silver chloride. It will be reduced to elemental silver and act as a collector for the values. It's a wonderful savings plan---one that allowed me to retire at a relatively young age.


Well I did check the solution once it was precipitated and the reaction changed to a green so I'm assuming there could be some platinum in there. We have 4 litre ice cream containers which is very similar to your 5 quarts, so you're saying have some scrap steel in there and pour the liquid in? Once precipitated dry off the dirt/mud and put it in the furnace? I'll have to try that with the next batch.

You see being in the jewellery industry we have some contacts and a few of those are polishers (people that polish jewellery all day long). These guys do about 10kgs a week on polishing sweeps and work with a variety of 9ct, 18ct and platinum also. With such large quantities it will be worth extracting these other precious metals. Anywayz I will take some pics this Sunday and show you some of our results.

Keep you posted  

P.S I'll need to ask you later about how to handle large batches (stock pots, burners, evaporating dishes etc...). But we will leave that for another time


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## Harold_V (Feb 21, 2008)

Ageo308 said:


> Well I did check the solution once it was precipitated and the reaction changed to a green so I'm assuming there could be some platinum in there.


A green reaction is likely palladium, although you may have both elements present. There is generally only a small amount of either of them unless you find the polishing waste to be a green color after incineration. That's a sign that the producer is polishing a great deal of platinum. Polishing compound for platinum is not typically rouge or Tripoli, each of which yield burned waste that is reddish brown in color. 



> We have 4 litre ice cream containers which is very similar to your 5 quarts, so you're saying have some scrap steel in there and pour the liquid in? Once precipitated dry off the dirt/mud and put it in the furnace? I'll have to try that with the next batch.


That's correct. I think you'll find that that's the best way to recover the values. The problem is that the platinum group of metals doesn't respond to precipitation the same way gold and silver do. When you find traces of them in your solutions, you can go through the proper procedures for their recovery, yet not achieve any results. In heavily concentrated solutions that isn't true, so you can achieve reasonable results, although even then you may not get full recovery. For that reason, you should place solutions that test positive on scrap steel, and allow enough time for the values to precipitate. Test the solution and decant only after it tests barren. In the process, you'll precipitate any copper that is present, but that tends to be a good thing, for if you recover the values by furnace, anything that forms a molten metal will help by acting as a collector for the values. 

You can recover these values chemically, and you can even precipitate them on copper instead of scrap steel. In that case, all you precipitate is the values, for all base metals will remain in solution. The problem with that is that you will produce very little value from most of these solutions, so the values may adhere strongly to the copper, making recovery difficult. It's the same principle as recovering silver on copper, but in that case you generally produce a lot of metal, which converts the copper to liquid in the process, shedding the silver. I highly recommend you not worry about trying to recover these values on copper, for you'll spend far more time screwing around with it than you would with steel. 

Assuming you choose to go the steel route, simply decant the solution after it is barren. Discard it by your preferred method, assuming it tests barren. Simply leave the residues in the same container (plastic bucket), and reuse it constantly. When there is a generous amount of black sludge in the container, remove the steel pieces, rinsing them to remove free sludge. Don't be concerned about getting them clean, for they will go back in the stock pot for further use. Remove all the steel, then get the sludge in a filter and allow it to dry. Once dry, incinerate well, then store the material for future processing. I'll be able to give you an excellent recipe for fluxing for furnace reduction. If you choose to chemically process the stuff, that will work, too, but you should have a generous amount of it before you do so. That will insure that you have enough value present that it will precipitate. 

Hope some of this helps. 

You mentioned posting some pics. Looking forward to your offerings. 

As you suggested, we can talk about large volumes at a later date, but in the mean time, don't discard any solutions that test positive for values. Start immediately with a stock pot, even for minute traces. You'll be pleasantly surprised at how they add up!

Harold


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## Ageo308 (Feb 26, 2008)

Ok Harold, sorry for no photos but we hit something quite weird. We followed the exact same process as we did the last test batch but added the extra ammonia wash and HCI wash in the end. Thinking the more washes the better it actually showed up less karatage then the last button we refined. I'm still trying to understand how this was possible as everything was followed as planned. Any suggestions on this?


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## Harold_V (Feb 26, 2008)

Unless you introduced something to the yield in the wash process, there's no good explanation. Washing has no ability to contaminate the material, and in the worst case scenario, you would have achieved nothing. I would suggest to you that you may well have shorted the wash process. The last wash in HCl should come out with little or no color change. If it comes out with considerable change, it's entirely possible you stopped way too soon. 

You should look to your procedures when something like this happens. How clean the material was before dissolving the values, and how clean the gold solution was when you precipitated the gold. What you used for precipitation, and if you used more than was necessary (assuming you used something like copperas), and didn't wash it until you had removed all of it. That's why you keep hearing garbage in--garbage out. The cleaner you work, the cleaner you can expect the end product to be. 

I'd suggest you review your process and see if you made any minor deviations. I'd also suggest that when you do your final filtering, you do so with an appropriate filter. If your solution does not come out clear of flocculence, anything you leave behind will report in your gold. The only question is will it become an alloy with the gold, or will it be left behind in the dish, trapped by the flux. 

Is there any way for you to determine what the contaminant is? Are you sure of your results? If you are not paying for an assay, can you tell me the method you used to determine the relative purity of each batch? If you are making visual observations, the type of contaminant can make a huge difference. Some are not really detectable visually. 

Harold


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## Ageo308 (Feb 27, 2008)

Harold the only thing I can think of is the filtering, although the filters we use are so fine that they take a while before filtering right through. The last wash is clear as water can be.

The tester we use is this one http://www.mineralab.com/M24GoldTester.htm

We have tested numerous 9ct, 18ct and other karatage jewellery items and they have all come up accurate. It's not enough to tell you the purity (9999 terms) but it's enough to tell us if it falls in a certain karatage (which is all we need for quick testing).

Quick question, when rinsing the washes as you let it settle then pour the liquid any dust that's flowing out should not be gold correct? as the gold is heavy and sets on the bottom? If I'm reading right the dust particles that flows out of the water is called flocculence. 

Anywayz I will update you on the re-purification process.


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## Harold_V (Feb 28, 2008)

I fully expect the tester is your problem, not the purity of your gold. I can't imagine you'd produce anything less than 999 fine by the method I've provided, assuming you've done all the steps without shorting them. I also can't imagine that device can discern the difference between 9995 and 995 gold. When you talk about fineness as opposed to karat, there's a huge gap that a tester simply can't fulfill-----it, I'm pretty sure, would not have the ability. There are way too many variables that can be influencing the reading, so I have serious doubts that your test is adequate, or consistent. Could be I also don't understand your meter, and I'm wrong. Bottom line---don't worry about what the meter is telling you. Use it for karat determination only, not fineness. 

One of the best tests is how your gold looks after you've melted it. Allow it to freeze in the melting dish, without applying anything to the surface (flux). It should freeze with a shiny surface, forming a coarse crystalline structure. The areas within the lines (the crystalline structure of which I speak) should remain shiny, and bright, with no discoloration. The center of the button should pull a deep pipe---very deep. If your gold does not conform to these guidelines, there's no doubt--it isn't clean, although I can't imagine it being off enough to show as a karat issue. Remember, you'd have to have 4% contamination before you'd consider your gold 23K. That's one hell of a lot of contamination. 



> Quick question, when rinsing the washes as you let it settle then pour the liquid any dust that's flowing out should not be gold correct? as the gold is heavy and sets on the bottom? If I'm reading right the dust particles that flows out of the water is called flocculence.


If your gold, after precipitation, contains anything that's visible, it's either gold, or you've done a poor job of filtration. If you have any doubts, always save the solutions you pour off and allow them to settle before decanting them for disposal. I think you'll find you are losing some of your gold. Never discard anything that comes off precipitated gold. If you have any doubts, place it in your stock pot, if nothing else. 

Here's the deal. Occasionally, gold will precipitate in a state where it won't readily adhere to other gold bits. My experience indicates that happens when you precipitate from real dirty solutions, or when you precipitate from quite dilute solutions. It often remains in very fine particles that are easily suspended and slow to settle. I've even seen gold come down so finely divided it's colloidal. Very clean gold that comes down hard and fast will usually clump up so easily that you end up with chunks instead of powder, particularly after it's been well washed and force dried. It also tends towards a very light tan color, never dark. That, of course, may be the result of the precipitant I used to use (SO2). It may not be true of gold precipitated by other means, so don't use these words as a sure guideline. 



> Anywayz I will update you on the re-purification process.


Please do so-----and maybe give me a report on what the gold looks like when you melt it. I strongly advise a new, clean dish, well seasoned (dried over a low flame) which is then heated to redness, coated with borax (glass (borax glass) or anhydrous borax works best, for they each are much heavier and dense, and don't blow around with the flame of the torch. The all work equally once melted, however, so use what you have at your disposal). Clean the torch tip well, to insure it doesn't shed copper oxides and other contaminants. That's a common source of contamination. 

You won't be able to remove a button that has been cooled in the dish, so you may have to reheat it in order for it to release from the flux coating. If you pick it up immediately upon solidification, before the flux beneath it hardens, it will come out without a fight. You can pickle the button afterwards, using a small casserole with either sulfuric acid and water, or HCl and water. Boil for a while and it should come clean from all flux. Alternately, you can tap the flux with a light metallic object and crush it. The handle of a large tweezers, for example. 

If you want to make shot, we'll have to talk again. It won't happen by pouring from a dish. 

Harold


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## Ageo308 (Mar 5, 2008)

Ok Harold, I haven't updated you as I'm moving area to work on and building fume hoods and benches and other things. I'm also ordering in whatman filter papers (grade 2 and 5 as you used).

Now for siphoning I came across a chemical pump which I think might be my best bet, It pumps out 180ml each pump. That way the contents are settled well and I only remove the solution and it will help with filtering properly also so there is no spillage.

Another thing how did you process large batches? I mean we have a 10 litre pyrex pot so I'm assuming this is suitable? for small batches 2L and 3L beakers are sufficient.

1 last thing




> Let the gold settle.
> Test the clear or slightly colored solution to see if any gold remains dissolved (use stannous chloride)
> Add more SMB if the solution test positive.
> Repeat above until negative test results.
> ...



I found this from I think lazersteves post back in September:

There is a couple of differences I found with your method compared to this, i.e the wash straight after the precipitation is with HCl/water where is he does water on its own, then HCl on its own then Ammonia on its own etc... as you can see. Your method is diluted 50/50 with water so I'm curious what's more effective? 

thanks


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## Harold_V (Mar 16, 2008)

Ageo308 said:


> Ok Harold, I haven't updated you as I'm moving area to work on and
> 
> There is a couple of differences I found with your method compared to this, i.e the wash straight after the precipitation is with HCl/water where is he does water on its own, then HCl on its own then Ammonia on its own etc... as you can see. Your method is diluted 50/50 with water so I'm curious what's more effective?
> 
> thanks



I managed to miss this one----you're right. 

For starters, I don't know that my method of washing is any better or worse than Steve's. He goes through a lot of steps that don't necessarily improve the gold-----but certainly don't do it any harm. He's come up with his own method, just as I came up with mine. It's entirely possible you'll come up with your own method as you become familiar with refining. How you get there isn't important, as long as you get there-----"there" being *fine gold. *

I routinely washed my gold in HCl and water immediately after it was decanted. Rinsing with water doesn't serve much of a purpose----but, again, it does no harm. I also didn't time my wash and rinse cycles. I ran them as long as it took to achieve the desired results. I allowed the first wash to continue until it was evident that nothing more was being dissolved or otherwise removed from the precipitated gold. I would then take up the solution with tap water, stir well, then decant (allow to settle if gold is in suspension). A hard boil with tap water following decantation, long enough for traces of the acid wash solution to be removed. Visual indicators tell you when to stop. One rinse with tap water was generally adequate, but if in doubt, a second one can be used. It makes little difference, for you insure that you shift basic by adding enough ammonium hydroxide. If there are contaminants present, you will usually see a color shift when it's added. A short boil (it evaporates quickly) followed by a water rinse, then back to HCl and tap water usually yielded a clean solution. I'd boil for a few minutes, then take up with tap water, decant, then boil for a period of time with just tap water, to remove the majority of the HCl. It doesn't all come out, but that doesn't matter------it's expelled when you force dry the gold. 

Again, I see no need for the multiple rinse and wash cycles----as long as the method I used yielded a clean solution after the third wash (HCl and water). It usually did. 

Understand that even prolonged washing will not purify gold. A certain amount of contamination will remain with the gold, and will be eliminated only by re-refining. It is for that reason that I routinely refined my gold twice. Very little is removed on the second refining----but the difference in the gold is readily noticeable. 

The other thing worth mention. If the solutions coming from the washes contain no traces of values, they should be allowed to settle well, to insure that any particles of gold that may have been lost are recovered, then they should be discarded. Running them through your stock pot serves no purpose. It also does no harm---aside from consuming some of the steel or other metal used in the stock pot. 

Note that adding the wash water adds copper to the yield of the stock pot. Depending on how you process your stock pot in the future, you may not wish to add copper, which must be re-dissolved when the stock pot is processed chemically. If it's processed by furnace, copper can act as a collector, so in that case it can work to your advantage. All depends on your preferences in how you'll handle low grade wastes. 

Always test with stannous chloride (that is known to be active) before discarding any solution. If traces of values are found, the stock pot is where they should go. Polishing wastes will almost always show at least small traces of platinum. 

Harold


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## Ageo308 (Mar 18, 2008)

Thanks Harold, I should be finishing my new work area this week and when I do I'll try and post some pics (and of course the pics of the gold that I was suppose to).


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## Ageo308 (Mar 19, 2008)

Harold, while I have been setting up my work area I have many jewellers wanting to sell their scrap to me. So if you could explain the process of refining scrap gold.

I know it's similar to what I have been doing but I just want clarification.

cheers

P.S Happy Easter


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## Harold_V (Mar 20, 2008)

And a Happy Easter to you as well. 

OK-----some rambling thoughts, in no particular order. 

The very best advice I can offer you is to read Hoke. I used her recommended process, although with minor modifications. 

I processed filings by incineration, then, after screening, the fines were boiled in nitric until there was no further action from the acid, rinsed in water, then dissolved in AR. The gold that comes from this process is quite dirty, but it is very good for use as added metal when you evaporate gold chloride solutions. That way it gets dissolved and precipitated a second time, removing the vast majority of contaminants. We can talk about this concept if you think you'd like to pursue it. It is a good method to get around using urea, which I never used. 

I do not recommend melting filings ---it's too easy to lose values in the flux, a result of the often very dirty material you start with, and the quickly loaded, thick flux. If you were to do so in a furnace, with soda ash and borax, pouring to a cone mold, that's a whole different matter. Assuming you processed by that manner, you'd then have to inquart the resulting button and pour shot in order to process the material. 

I suggest you use silver for inquartation, not any of the base metals. It will serve you well, and generally needs to be dissolved anyway, assuming you are refining silver and gold. Sterling, or other alloyed silver becomes a valuable tool for inquartation. The biggest benefit is silver is digested, ounce for ounce, with far less nitric that is copper or copper alloys. 

By now you likely understand that it will be important for you to learn about inquartation----it's key to eliminating base metals easily, with the added benefit of much cleaner gold because you will have eliminated the majority of base metals from the gold alloys before you dissolve the gold. The benefit will be higher quality gold when you precipitate. 

A couple tips. Hoke talks about the ability of karat gold to be digested directly with AR instead of the inquartation process. That works with white gold, and some of the other strange colors, but not well with rose, yellow, pink or red gold. Each of those contain enough silver to make dissolution troublesome, unless you reduce the particle size to that of filings. 

Any gold that won't pass a screen with approximately 16 openings per inch I highly recommend you treat by inquartation. After incinerating filings, they should be screened, then a magnet run through them to remove bits of iron (steel). The removed material should be placed in a mortar and rubbed well to dislodge any gold that adheres, which would be returned to the lot. The remaining iron bits should be added to the stock pot, for you never achieve total separation. You'll recover those values in the future, when you process the stock pot by your chosen method. 

Filings are typically quite dirty. They should be incinerated in a small pan over an open flame (gas hot plate works well), then the pan heated by torch after they have burned off all the wax and oils that are present. Heat it to dull redness, insuring that you have eliminated all traces of carbon. 

Don't remove anything from filings until they have been incinerated, including paper and other non-metallic objects. Filings tend to be oily or greasy (from carving wax) and often carry substantial levels of values. Incineration frees them. 

Do NOT buy filings as if they are a specific karat gold. Unless a benchman is spotless with his work habits, and works only 14K, you can expect filings to run anywhere from 20% gold content to 55%. I never, in all my years of refining, ran anyone's filings that yielded 14K. There's simply too much garbage that gets included. With some experience, you will come to know how much each customer's gold will yield. Some are careful to exclude garbage, while others are not. Some include broken saw blades, while others place them in their floor sweeps. It will take you some time to establish patterns, so if you're interested in knowing, do keep records of each customer, and what is submitted. You'll slowly come to know what to expect from their material. 

Broken saw blades should be included in your stock pot, after incineration and treatment in the mortar. 

Inquartation: Weigh your material, and estimate the average gold content. After inquartation, your target should be 25% gold, the balance silver and base metals. That way you can dissolve all of the base metals without the gold preventing the nitric acid from penetrating the resulting alloy. 

I found it safe to add roughly 110% of scrap silver (sterling or coin) to gold alloy I received, which contained a majority of 14K, with some 10K and 18K. Occasionally you'll miss the mark and the gold will disintegrate when processed with nitric. Other times you'll have missed the mark and it won't dissolve well. That often happens if there's any dental gold included. It's typically quite high in gold content, so greater allowances for silver should be made. Remember-----yellow dental gold contains the pt. group metals, platinum or palladium, and often both. When you inquart with silver, they will follow the silver and be recovered on copper. You'll recover them when you part silver in an electrolytic cell. That is very much a part of processing gold alloys, so be prepared for processing silver in the very near future. It's not hard, but requires a little effort and a learning curve. We can help you with all of those issues here on the forum. 

I can talk endlessly on this subject---there are far too many variables to cover everything. Best thing you can do is read Hoke, start running a (small) batch or two, then ask specific questions. I'm happy to help, but I'll need to have specifics in order to talk about that which is important at the moment. 

Let me know---

Harold


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## Ageo308 (Mar 20, 2008)

Hi Harold, sorry I should have been more specific. It's not filings that I'm so much after to learn about but actual old pieces of jewellery that jewellers just want to on sell. Yesterday for example a customer had 100 grams of 18ct gold (old chains, pendants, rings etc..) which for some reason they would rather just get rid of it and make some quick cash.

Anyways it's not my business to question what they do, I just need to offer them a service. So we are talking about old jewellery. Would the process be the same?


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## Harold_V (Mar 20, 2008)

I touched on that when I discussed inquartation. 

Assuming you want to process the old jewelry to recover the gold, you'd melt it with the proper amount of silver to adjust the gold content to 25%, then pour the alloy in deep water in a container. Make sure it will tolerate heat (don't use plastic or glass), for the molten metal can hit bottom before chilling. That prepares the new alloy for the first step of refining, where you remove the base metals by dissolving them with nitric acid. 

Again, Hoke talks about that subject extensively. 

Do keep an eye open for filings. While most bench men save them, I found one that tossed them. His attitude was that there was little value there, so why worry? Sigh! :? 

Harold


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## Ageo308 (Mar 31, 2008)

Hi Harold, just a quick question back on Refining polishings....

What is one way to speed up dispelling excess nitric without evaporating thow? The reason I ask is Im on a tight schedule and a jeweller needs his refinings by Thursday and I don't want to be wasting a whole day on the evaporation process. The batch is quite large with lots of liquid so I was thinking urea would do the job (read it on another refining site).

I remember Hoke stating if you keep adding the precipitant eventually the nitric will stop reacting with the copperas and then it will serve its purpose.

If you have any handy hints please fire them away.

P.S this will be only for this time, all my other work will always be evaporation.


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## Lou (Mar 31, 2008)

Hydrazine hydrate or sulfate would drop out the gold regardless of nitric being present.


Otherwise the standard is urea, but I am against its use. It really does not destroy nitric, rather it destroys nitrogen oxides.


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## Harold_V (Apr 1, 2008)

If Lou's advice isn't helpful, the one thing you can do is insert a button of refined gold, which you have weighed. Weigh it again after you have finished the partial evaporation of the solution, so you can determine the amount of gold you added. Free nitric will dissolve the gold until it is consumed, assuming you have enough HCl present. It may go slowly at first if the solution is quite dilute, but once it gets concentrated somewhat you'll see the button being dissolved---witness the bubbles that come from the button. I used that process routinely, evaporating only enough to concentrate my solutions to eliminate the bulk of the water, plus some of the HCl if there was too much present. An excess of HCl tends to destroy filters, but otherwise does no harm as far as I know. It wasn't exactly uncommon to have a filter tear when the acid level was too high, which defeats the purpose of filtration, as I'm sure you'd understand. 

I can't help with urea-- I know nothing about it----I never used it, and I wouldn't if I was refining today. No specific reason aside from hearing that it complicates the recovery of pt. group metals. If that be the case, a guy that refines bench wastes should avoid its use. By now, you likely recognize that you almost always have traces of pt or pd in jewelry wastes. 

One more thought-----added after the post -----you can speed up evaporation by splitting up the solution in more containers. Use as many as you have burner space---then combine them as they get reduced. It can save a lot of time.

Sorry I'm not more help--

Harold


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## Ageo308 (Apr 1, 2008)

Well I decided that the urea option was just not for me as the volume of water I have is just too large to handle with. I had no choice but to ring the customer and let him know that it will take a little longer if he wants quality results. I will keep you posted on how it goes.


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## Harold_V (Apr 2, 2008)

Ageo308 said:


> Well I decided that the urea option was just not for me as the volume of water I have is just too large to handle with. I had no choice but to ring the customer and let him know that it will take a little longer if he wants quality results. I will keep you posted on how it goes.


I congratulate you on your decision. I made it a policy of assuring my customers that quality was my objective, and there were no shortcuts taken to quicken processes if they compromised quality. 

For the record, I promised 7 day delivery on polishing waste, assuming they didn't have hundreds of pounds. Once you get on to the processing, you don't generate huge volumes of solution. It becomes a tradeoff where you can't make a profit by being 100% accountable----so you charge a reasonable fee for your work, which includes washing the waste one time, leaving traces for later recovery by other methods. That way the customer isn't cheated---and you can get the work out in good time. If you choose to be 100% accountable, you must charge a higher fee, so the customer isn't any better off than if you charge a slightly lower one, and not account for minor traces. Once again, this becomes an excellent savings plan. 

I explained the above to my customers and had none that were unhappy with me-----especially when they realized that the return on their waste material was greater than they used to get----which was almost always the case because they had been using major refiners, many of which are known to treat the consumer with less than honesty. 

Things are looking up for you!

Harold


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## Irons (Apr 2, 2008)

You have to pick a balance between profit and the amount of business that you are able to handle.
That's what competition is all about.

You have to decide if you are running a business or a charity.


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## Ageo308 (Apr 3, 2008)

Hehe well I was back on track evaporating (been 2 days now as I have about 30 litres of solution to go through), been following everything as per normal and when I filtered it (because I did a poor job beforehand so I wanted to make sure the gold solution was clean as so once precipitated it would be cleaner) I noticed a crust of some form at the bottom of the dish I had been filtering? I also noticed it at the bottom of my buchner funnel? could it be I'm evaporating for too long and it's starting to cake? 
(I thought that only happens when the liquid becomes low)? I'll take some pics tomorrow and see if anyone knows what the story is. I'm using a grade 2 on top of the buchner and grade 5 on the bottom which is filtering the solution quite good but this flakey crust is annoying me.


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## Harold_V (Apr 3, 2008)

Did you dilute your solution after evaporation? If not, that may be the problem. If so, it's common for a lot of flocculence to come out of the evaporated solution when it's filtered, but none of it should be getting through the filter. If that's what's happening, I'm stumped. 

I suggestion for you; A Whatman #5 is an exceedingly slow filter. It catches everything, but it also clogs almost instantly. You're usually far better off to use a #2 when filtering an evaporated solution that isn't clean, reserving the #5 for the occasions when you re-refine your gold. By that time, the amount of contamination borders on zero, so the solution will filter quite well through a #5. Surprisingly, if you can get a #2 to run and not pass the fines, it will be far faster, and will eventually retain all of the contaminants. It wasn't unusual for me to re-filter a portion of my solutions once the filter settled down, and they always do. In the very end, a #2 will often yield solutions every bit as clean as the #5, and costs you a lot less money, with the added bonus of speed. 

On the outside chance that you may have some lead in your solution, did you include a little sulfuric in the evaporation process? It doesn't take much ---a few drops. Lead will self precipitate when the solution cools if you don't expel it as a sulfate. Just a thought.

If you can post a picture of the stuff you're talking about, please do. I'm not sure what it might be if it's not crystals of what ever you have in solution-----but I think there's a good explanation. All we have to do is determine what it is! :wink: 

Harold


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## Ageo308 (Apr 3, 2008)

Harold I haven't diluted the solution, I did add sulfuric to each batch I was evaporating. I must admit a mistake I made thow (due to me rushing) was when I tried expelling the nitric with urea I then added my precipitant. The next morning obviously because of the excess nitric it didn't precipitate but I'm assuming the crust could have been caused by that. Anywayz I will post a pic today showing you what I mean.

I learned 1 thing from this batch, be patient and follow the procedure as per normal (no shortcuts)!


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## Ageo308 (Apr 4, 2008)

Just to update:

I think where I went wrong was not adding HCl during the evaporation. I decided to add some of the crystals in a beaker with water and some HCl to see if it will dissolve or wash the gold chloride out of it. Well it dissolved a lot of it and the remaining crystals were left white. I can't help but think the urea must of added to this. Anywayz to fix up the error I made I'm going to wash all the solution I have left with water/HCl then filter it so when it's ready to be precipitated the solution is not dirty.


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## Harold_V (Apr 4, 2008)

Adrian,

I have to confess, I'm lost. I don't recall having a situation like that, ever. I won't eliminate the addition of urea as being part of the problem, but I never used it, so I have no concept of what it does to a batch of gold. 

A couple things come to mind. You talked about evaporating and not adding HCl. My procedure was to evaporate until the solution had turned quite dark, then add HCl to expel the nitric. Assuming it had none to expel, but the solution bubbled somewhat and formed a trace of what is likely silver chloride, I assumed it to be fully evaporated. Because the evaporated solution contains no water, the boiling point is higher than one that does, so the evaporated solution is usually hotter than the boiling point of water----so you should see a slight boiling when you introduce the HCl. 

Keep in mind, I always had a button of pure gold included, which assured the consumption of any free nitric. At that point, I would take up the evaporated solution with water. I can only assume you did that, too. If not, anything that got included in solution that didn't get diluted past a level of saturation would surely grow crystals. What they are I don't have a clue---but your remedy sounds like you're on the right track. Crystals are pretty good at rejecting any impurities, so if you wash them as you suggest, you should recover almost 100% of the traces of values. 

If you have any doubts about the contents of the crystals, toss them in your stock pot and let them do what they will---which is likely to re-dissolve in good time. When you decant the solution from your stock pot, what ever it is will be discarded. which should be your objective. Any values that may have been carried over will be recovered from the wastes collected from the stock pot at some future date.

Sorry I'm not more help. Without having had a similar incident, I have no way of knowing what the score is. 

One thing to remember----the initial wash you do after you've incinerated polishing wastes should be adequate to dissolve and remove any traces of things like that. If the solution came from polishing wastes, it's entirely possible you didn't do an adequate job of eliminating things that are soluble in HCl, and they got dissolved later, and included. With proper washing and rinsing, they would have been discarded earlier. 

All of this is nothing more than me thinking out loud. I am not suggesting that I know that it's true. Just something for you to consider. 

Good luck with the next step. Let us all know how it goes. 

Harold


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## Ageo308 (Apr 9, 2008)

Hi Harold, a couple of questions I have:

* When you evaporate, what happens if you let it evaporate right down till there is minimal liquid? Would you be evaporating gold? The reason I ask is because my fans are yellow in colour and I can only think that's some from of metal chloride staining it (hopefully not gold).

* The reason I ask is because when you're dealing with litres of solution it's hard to determine what's being evaporated.

* Also how much precipitant would you allow for? And is too much no good or it does no harm? The reason I ask is because if I fall short then you need to wait another night for it to drop.


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## Harold_V (Apr 9, 2008)

Ageo308 said:


> Hi Harold, a couple of questions I have:
> 
> * When you evaporate, what happens if you let it evaporate right down till there is minimal liquid?


When you take the solution too far, elemental gold will begin to precipitate. That's a sure sign that you have eliminated the nitric. Depending on how clean the solution is, it is usually a dark red, leaning on red/brown/black when that happens, and it's very obvious. The solution, assuming you've kept if hot, will appear to have metal flakes ----much like aluminum or bronze paint. Hoke has a procedure to recover from the condition, but it has risks. I simply would add a drop of nitric, along with a few drops of HCl, and watch to see the gold dissolve. 

Using an added button of pure gold during the evaporation process pretty much eliminates the need to evaporate to that point. I evaporated until I knew the nitric was gone, then I'd evaporate a little more if I had excess HCl present, but only to guarantee no filter failure. Excess HCl does no harm otherwise. Once evaporated properly, the solution would be taken up with tap water to dilute it well. A target volume is 3 ounces of gold per liter before precipitation, although I didn't follow that rule. I also precipitated with SO2 gas, and iced my gold chloride before precipitating. 



> Would you be evaporating gold? The reason I ask is because my fans are yellow in colour and I can only think that's some from of metal chloride staining it (hopefully not gold).


That's not a good sign. Get some sunlight on the fans. If it's gold, they'll turn purple. You can also test with stannous chloride. If you don't see a color develop, you are seeing something else, but you may still be evaporating too quickly. Your solution should never boil unless it's covered with a watch glass. You must not hurry evaporation. Might pay you to read Hoke on that subject. Also----when you're dissolving your values, keep them covered with a watch glass. It's not a novelty--it's mandatory. The gasses that are evolved come off with considerable energy and carry droplets with them. A watch glass will collect the values and return them to the beaker. 



> Also how much precipitant would you allow for? And is too much no good or it does no harm? The reason I ask is because if I fall short then you need to wait another night for it to drop.


A rule of thumb is that an ounce of ferrous sulfate will precipitate an ounce of gold, but as Hoke suggests, an excess is a good idea. You might consider setting your sights on 1¼ ounces/ounce. 

There is no need to wait for gold to settle when precipitating. Test your solution immediately after introducing the precipitant. The reaction should be instantaneous. If, after you've mixed your precipitant with the gold chloride solution, you still show values when testing with stannous chloride, you can immediately introduce more precipitant. I used to mix what I expected I'd need, then hold back on a small percentage. Mix, test, then either discard the extra, or introduce it to complete the precipitation. That way you wait only once for the gold to settle. 

What you add may not be harmful----depends on the precipitant. Ferrous sulfate will wash out quite well, so I wouldn't be too concerned about using too much. Just insure that you follow the guidelines I set forth for washing. They work, and work very well. 

From this you can conclude that there are benefits to using SO2 from a cylinder. You test constantly as the gold precipitates, and stop introducing the gas when it's all down. It pays to stir the bottom when you have an abundance of gold, for gold chloride gets dragged down with the gold that comes down first if there is not a complete precipitation (assuming it settles quickly-----which is often the case).

Harold


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## Ageo308 (Apr 10, 2008)

Thanks for the tips Harold, I recovered a small batch (9 grams of gold) and I'm going to finish the next batch early next week.

I'll keep you posted


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## goldnugget77 (Sep 2, 2009)

Hi Harold
Since everyone here likes those pictures of your old factory I was wondering if you had a picture of the furnace you used for incinerating the polishing sweeps.
Thanks


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## Harold_V (Sep 3, 2009)

No furnace was used. I did all of my incinerating in a discarded stainless frying pan. You can burn a surprising amount of material in one. 

I don't recommend this process unless you have a hood that will accommodate the considerable heat, and has a filtration system to recover dusting. 

I simply heated the pan from below, using a gas hot plate. The single burner used for incineration was adjusted to provide a maximum flame. Once the material was burned, I'd raise the temperature in the pan using a large Hoke torch, to insure that I had consumed all of the carbon. Any that remained would glow brilliant yellow white when oxygen was played on the material. 

Harold


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## AuMINIMayhem (Jan 24, 2011)

> Polishing sweeps are composed of grease (the binder in polishing compound), sandy grit (the active ingredient in polishing compound), lint (from the buffs) and very tiny balls of karat gold (from the gold that was polished). Sometimes it will also include paper and buffs.



personally, the very first thing I'd probably do is take the sweeps, put them in a closed container filled with technical grade Acetone and place the container in an ultrasonic tank for a few minutes. This will help get rid of NVOCs (non volatile organic compounds) ie: waxes, greases, etc. Then I would rinse off with Isopropynol to rinse away those NVOCs (without rinsing away any "solids"). Remember that order.. Acetone _THEN_ IPA, IPA is not a good degreaser and does virtually nothing for NVOCs.. and if you just let the Acetone evaporate off without rinsing, you've just wasted it, because it will just leave the NVOCs behind.

After that point, I think incineration would be a good way to go, but I'd definitely try to clean some of that other crap out first.

There's a phrase you will see quite often on these boards GIGO ("garbage in, garbage out").. it's proven to be a VERY handy thing to keep in mind. 8)


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## Lou (Jan 25, 2011)

Mixed hexanes are a great way to degrease things, even better than acetone and much safer than leaving either acetone or isopropanol on material that concentrated acids may be added to (*always incinerate after any solvent is used!*). I prefer using hot caustic as it gets more of the silicaceous material dissolved and saponifies any grease but it's very dangerous to one's eyes.

Lou


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## Harold_V (Jan 26, 2011)

For that, and likely other reasons, I simply incinerated such wastes. Often with the plastic bag in which it came. More smoke, but less of a hazard for the refiner, and perfectly effective. I couldn't see wasting the time (and chemicals) involved, when in the end it had to be incinerated, anyway.

Harold


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## AuMINIMayhem (Jan 26, 2011)

Harold_V said:


> More smoke, but less of a hazard for the refiner, and perfectly effective.


 :?: 

ummm... I'm a heavy-smoker and even I prefer not to expose myself to the nasties that could come from incineration.

_(I only bring this up because, I suspect some people who visit these boards would do this in their garage/living room/kitchen/kid's bedroom.. without proper ventilation and not even think twice about it..)_

I'm not ball-busting you, Harold, I promise. :mrgreen: I hold your experience and opinions based on such experience in very high regard, I'm just surprised by that particular statement coming from you without some form of cautionary note to go along with it. 8)

Derek


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## silveras (Feb 21, 2011)

What is the best way to process polishing waste from silver bench?


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## 4metals (Feb 21, 2011)

Incinerate, leach with Nitric, filter, and cement out the silver. When you collect enough silver read up on setting up a small silver cell.


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## silveras (Feb 24, 2011)

I have 10 kg of incinerated powder dust from silver polishing waste. How much nitric acid do I need to leach it. How long is the process? Do I have to heat it? Can you give me more idea on the process of leaching. many Thanks.


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## Harold_V (Feb 26, 2011)

silveras said:


> I have 10 kg of incinerated powder dust from silver polishing waste. How much nitric acid do I need to leach it. How long is the process? Do I have to heat it? Can you give me more idea on the process of leaching. many Thanks.


There is no logical answer to your question, because no one can predict the amount of silver and/or base metals present without an assay. 

What I suggest you do is start with a small amount of dilute nitric and allow it to work. Keep adding in small portions until you get no further reaction. Be careful not to add too much too quickly, to avoid a boil-over. 

Unless the waste came from a bench were silver was the only value worked, you can expect the resulting material to yield gold as well, maybe even platinum and palladium. 

Read Hoke. 

Did I mention you should read Hoke?

Harold


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## silveras (Mar 24, 2011)

Hi Thanks for the info. I mixed the 10 kg pulverized, burnt polishing waste with 17 liters of water plus 3 liters of 70% nitric acid. I had it leached for 4 days. I strained the solution and rinsed the slurry with water several times. I actually have total of 80 liters of solution. How do I go about cementing the silver? Do I add more water? If so how much more? What is the ideal ph of the solution for cementing? Can I use zinc dust instead of copper to cement? Thanks.


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## Harold_V (Mar 25, 2011)

silveras said:


> How do I go about cementing the silver?


If the solution is relatively free of solids, all you need to do is put in pieces of copper. Don't use wire unless you're sure you will consume all of it. Otherwise as it gets smaller, it breaks in to small lengths, which are virtually impossible to remove because they're hard to find. That sort of defeats the purpose of cementing the silver, which will yield quite good quality, assuming you've done things right. 



> Do I add more water? If so how much more?


If you've added rinse water to the original solution, no, don't add more water. It should already be quite dilute. I used to cement from relatively concentrated solutions. It can be troublesome in that on occasion the silver will plate out as a solid surface, adhering to the copper doggedly. It's best when it cements as fine particles, which yield the general appearance of (Portland) cement, which is the source of the name we use, at least as I understand it. 



> What is the ideal ph of the solution for cementing?


Don't know that I can answer that. I was never too concerned, and on occasion dissolved some copper because there was free nitric present. It does no harm aside from consuming copper. Eventually it achieves equilibrium where no copper is lost to dissolution from acid, just from cementation. 



> Can I use zinc dust instead of copper to cement? Thanks.


Yes, you can---but that's a mistake. Zinc will cement copper, too. At first the copper may be consumed, cementing silver, but eventually you'll end up with copper and silver mixed, which defeats the purpose. You'd be far better served to recover the silver as silver chloride than to use zinc----with the sole exception being if you intend to re-use the recovered silver for inquartation, it doesn't make too much difference. The one negative (if you use the recovered material for inquartation) is the reason you use silver instead of copper, however, in that copper requires almost three times as much nitric to digest as an equal amount of silver. 

Harold


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## 4metals (Apr 13, 2015)

The moderators would like to thank all of the members that contributed to the original thread upon which this thread was based, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Recovering precious metals from polishing sweeps.

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

For those who prefer a printed copy, a pdf file of this thread is provided below.


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