Recovering precious metals from polishing sweeps

[Harold_V]

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

 

[Ageo308]

Aha I feel like an ***** 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.

 

[Ageo308]

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.

 

[Harold_V]

Aha I feel like an ***** 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)?

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

 

[Harold_V]

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

 

[Ageo308]

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:

 

[Harold_V]

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

 

[Ageo308]

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.

 

[Harold_V]

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

 

[Ageo308]

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

 

[Harold_V]

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

 

[Harold_V]

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

 

[Ageo308]

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

 

[Ageo308]

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

 

[Harold_V]

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

 

[Ageo308]

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.

 

[Harold_V]

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

 

[Ageo308]

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.

 

[Harold_V]

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

 

[Ageo308]

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.