Recovering precious metals from polishing sweeps

[Harold_V]

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. Its not enough to tell you the purity (9999 terms) but its enough to tell us if it falls in a certain karatage (which is all we need for quick testing).

I fully expect it's 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 im 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 to wards 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 the 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

 

[Anonymous]

Does any one know what i must do to refine silver.I have lots and i mean lots of scrap silver that would sell better if put in molds.jewerly scrap from one who made it.i have a small kiln from him also.can i use that to melt it ?Is there a book on this?help needed[/list][/b]

 

[goldsilverpro]

What does LOTS mean? What form is it in?

 

[Ageo308]

Ok Harold, ive havent updated you as im moving area to work on and building fume hoods and bench's and other things. Im 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 cotents 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 im 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 unitl negative test results.
Let settle completely.
Pour or Siphon off the barren solution into the stock pot.
Wash the powder with 3-5 rinses of hot water. (Add water to beaker with gold and heat until near boiling for 3-5 minutes)
Pour or siphon off water.
Wash the powder with 3-5 rinses of hot HCl.
(Add HCl to beaker with gold and heat until near boiling for 3-5 minutes)
Pour or siphon off HCl.
Wash the powder with 3-5 rinses of hot water. (Add water to beaker with gold and heat until near boiling for 3-5 minutes)
Pour or siphon off water
Wash the powder with 1-2 rinses of hot Ammonium Hydroxide if silver was present in source material.
(Add ammonium hydroxide to beaker with gold and heat until near boiling for 3-5 minutes)
Pour or siphon off ammonium hydroxide. (DO NOT add the ammonium hydroxide rinses to the acid rinses!)
Wash the powder with 3-5 rinses of hot water. (Add water to beaker with gold and heat until near boiling for 3-5 minutes)
Pour or siphon off water
With only the now clean gold powder (and very little water) in the same beaker which it was dropped, begin heating over low heat.
Swirl the gold powder around the low heat until the gold clumps up and forms nice globs that stick together.
Continue heating until any acid vapors are gone.
Dump clean dry gold into prepared melting dish, glass jar for storage, or a few filters to transfer to dish or jar later.

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 HCI/water where is he does water on its own, then HCI on its own then Ammonia on its own etc... as you can see. Your method is diluted 50/50 with water so im curious whats more effective?

thanks

 

[Ageo308]

Just bumping the above post Harold just incase you missed it.

thanks

 

[Harold_V]

Ok Harold, ive havent updated you as im 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 HCI/water where is he does water on its own, then HCI on its own then Ammonia on its own etc... as you can see. Your method is diluted 50/50 with water so im curious whats 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

 

[Ageo308]

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

 

[Ageo308]

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 its similar to what i have been doing but i just want clarification.

cheers

P.S Happy Easter

 

[Harold_V]

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 its similar to what i have been doing but i just want clarification.

cheers

P.S Happy Easter

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

 

[Ageo308]

Hi Harold, sorry i should have been more specific. Its not filings that im 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 100grams 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 its 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?

 

[Harold_V]

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

 

[Ageo308]

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 dont 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 precipitate 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.

 

[Lou]

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.

 

[Harold_V]

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

 

[Ageo308]

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.

 

[Harold_V]

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 consumerwith less than honesty.

Things are looking up for you!

Harold

 

[Irons]

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.

 

[Ageo308]

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 im evaporating for too long and its starting to cake?
(i thought that only happens when the liquid becomes low)? ill take some pics tomorrow and see if anyone knows what the story is. Im 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.

 

[Harold_V]

Did you dilute your solution after evaporation? If not, that may be the problem. If so, it's common for a lot of flocculance 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

 

[Ageo308]

Harold i havent 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 didnt precipitate but im assuming the crust could have been caused by that. Anywayz i will post a pic today showing you what i mean.

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