Recovery from gold polish buff

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S

shahravij

Member
Joined
Dec 28, 2011
Messages
5
First of all, let me thank all of the people here for some excellent discussions.
Now to my question. We have our own jewellery making workshop, where we also so polishing of the gold jewellery. My uncle keeps precise data of how much gold (also of which carat) was lost for the entire month. In this way, he is able to calculate total fine gold that was lost in the polish buff.

We have been trying to use Aqua-regia method for gold recovery from this polish buff. Some of my uncles friend told us that it is possible to recover around 90 % of the gold which was lost. But when we try the process ourself, we barely recover 75-77 % of the total gold lost.

Does any one have any idea of how much percentage of gold is recovered by Aqua regia process ? or there is other process which is more efficient than Aqua regia for recovery of gold from buff polish ?

Thanks in advance,
Ravi
 
If done right there should basically no loss of gold in aqua regia.

Are you saving filters and stockpots for solutions?

How are you pre-treating polishing sweeps?

How are you incinerating, you could have some loss there, do you filter exhaust?

In your calculations are you figuring the base metals and silver?

Are you collecting all of the gold sweeps, carpets, hand washing sinks, the fine gold may not be just at the bench.


Harold, and his posts on the subject, and Hokes book are your best source of information in this area; there are a few other members that may help also.
 
I process bench sweeps/buffings via these general steps:

  • Incineration
  • Screen out trash
  • Magnetic Separation
  • 35% Nitric Acid Leach - Ag + some PGMs in liquid
  • Filter out Solids
  • AR Leach on Solids - Au in liquid
  • Filter out Solids

Typically you will have some values trapped in the solids that remain after AR treatment.

The remaining solids should be fluxed in a furnace to recover the trapped values.

Steve
 
When I was refining commercially I found exactly the same you get 90% of the gold from floor sweeps and polishing dusts on the first extraction, if done correctly with plenty of acids and using a good boiling action with a watch glass on the beaker, this agitates the solution and allows the acid to penetrate further. The decision to make is whether it's worthwhile to refine the material a second time, as the material is yours I'd say it is so long as the time is available and acids aren't too expensive.
Your uncles calculations will not be spot on, when polishing the dust flies everywhere, use a vacuum cleaner regularly and save the dust with other low grade materials to recover and refine when the volume makes it worthwhile.
The other factor to remember is not to burn your sweeps or polishing in an open container or at too hot a temperature to start as the gold can be lost as it is so light it can literally go up in smoke!

Edited for clarity.
 
butcher said:
If done right there should basically no loss of gold in aqua regia.

Are you saving filters and stockpots for solutions?

How are you pre-treating polishing sweeps?

How are you incinerating, you could have some loss there, do you filter exhaust?

In your calculations are you figuring the base metals and silver?

Are you collecting all of the gold sweeps, carpets, hand washing sinks, the fine gold may not be just at the bench.


Harold, and his posts on the subject, and Hokes book are your best source of information in this area; there are a few other members that may help also.
Click to expand...


Thank you for the help. I am new to this forum and to jewellery business too. I had to ask quite a few things to my uncle for it. Firstly, while burning the polish buff, my uncle does not collect the filter exhaust, and he also adds a bit of gasoline to the polish buff in order to burn it properly (which I have now learned is not a good practice, can someone give me the right way to do it ?) The burning leaves him with the metal waste which he thinks has around 5-6 grams of gold per 100 g of residue. To this he uses auqa regia in the ratio of 1:3 for nitric acid:hydrocloric acid (i have some confusion here too, as Hookes book mentioned the ratio of 1:4). After the dissoving of the gold (for which he leaves the solution overnight, without heating or mixing), he adds a solution of urea to counteract the acids. After this, he adds ferrous and leaves it overnight again. This leaves him with gold powder at the bottom (mixed with some other stuff, i think, as it needs to be washed repetedly before getting fine gold).

So this is how my uncle does his refining of polish buff. He gets 75 % recovery. In his calculations, he has accounted for base metals and silver. He also collects waste from water sinks and carpets, still the loss is in tune of 20%, which I think loss of i think is still quite high. What do you guys think ? any suggestions to improve the recovery ?

Also, I did a small experiment. My uncle has some old jewelly which he wanted to get rid off. I used the aqua-regia method, along with normalization by urea and treatment with ferrous to get a recovery of around 97 %. Now my uncle feels he should get around 90 % from polish buff too!
 
nickvc said:
When I was refining commercially I found exactly the same you get 90% of the gold from floor sweeps and polishing dusts on the first extraction, if done correctly with plenty of acids and using a good boiling action with a watch glass on the beaker, this agitates the solution and allows the acid to penetrate further. The decision to make is whether it's worthwhile to refine the material a second time, as the material is yours I'd say it is so long as the time is available and acids aren't too expensive.
Your uncles calculations will not be spot on, when polishing the dust flies everywhere, use a vacuum cleaner regularly and save the dust with other low grade materials to recover and refine when the volume makes it worthwhile.
The other factor to remember is not to burn your sweeps or polishing in an open container or at too hot a temperature to start as the gold can be lost as it is so light it can literally go up in smoke!

Edited for clarity.
Click to expand...

Thanks nickvc, for the comment. It turns out my uncle has been burning the polish buff in a room without filter exhaust using gasoline :(. Could this lead to high loss ? How do you suggest he burn his polish buff ?
When you say you got 90% of gold, you mean 90% of the total gold that was lost in polishing ? or 90% of gold from aqua regia ? Also, is there any way to test how much gold is there in the polish buff ?
 
lazersteve said:
I process bench sweeps/buffings via these general steps:

  • Incineration
  • Screen out trash
  • Magnetic Separation
  • 35% Nitric Acid Leach - Ag + some PGMs in liquid
  • Filter out Solids
  • AR Leach on Solids - Au in liquid
  • Filter out Solids

Typically you will have some values trapped in the solids that remain after AR treatment.

The remaining solids should be fluxed in a furnace to recover the trapped values.

Steve
Click to expand...

Thanks Steve for the help. What do you mean should be fluxed in a furnace ?
 
5 to 6 grams per 100 grams of buffing residue after burning is in the right range it all depends on what karat you are polishing.

Back when I was involved burning sweeps the finished powder ranged from half an ounce per pound (15 grams gold per 454 grams of sweep) all the way up to in excess of one ounce per pound (31 grams gold per 454 grams of sweep)

Coming from India, where the jewelry is often 22 karat, you can expect to be on the higher end of the range.

Harold once posted a detailed chemical method for recovery of sweeps from the early days of the forum, possibly one of our members will be able to dig out that link and post it here for our friend Shahravij
 
I agree with 4metals. Find Harold's process and use that. I think it's the best and most complete one that has been written up on the forum. These will get you started.

http://www.goldrefiningforum.com/phpBB3/search.php?keywords=polishing+dust&terms=all&author=harold_v&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search

http://www.goldrefiningforum.com/phpBB3/search.php?keywords=polishing+wastes&terms=all&author=harold_v&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search
 
Well I would try to give the polishing sweeps a cover, a garden rubbish burner, a metal trash can with a spout on the top and with holes around the sides will work and don't get the material too hot too fast.
When you heat the AR it extracts more values even boiling won't hurt too much as the action exposes more of the values to the acids but even after a good initial dissolution you probably will only recover 90% of the values in the material, a second treatment should recover most of the rest.
Without boiling the AR I'm not sure you will recover much more than 50% of the values as much of the material will remain untouched by the acids.
As GSP and 4metals have stated Harold posted a good detailed method for this type of material which works very well but to recover most of the values two treatments at least will be needed and a Goidelic filter pump and good rinsing of the material to remove the pregnant AR.
 
If you have access to a large enough furnace, the proper fluxes can result in a successful melting of the sweep. This is how it is processed on a large scale but it is also beneficial on a smaller scale as the silver is recoverable.

If there is interest we can discuss this technique in detail.
 
If I remember correctly, 22k gold does not have any silver in it. It is a gold copper alloy. No need to worry about silver recovery.

I too would suggest smelting the material first if possible rather than go to aqua regia directly.

If aqua regia is the only option, make sure you are not boiling the solutions as you will incur gold loses. Still, I think 30% loss is excessive. If you smelt and get a bar you can assay a sample to determine if the gold loss has come before or after smelting.
 
I am not aware of other countries, but the 22kt gold in India has some percentage of silver as well.

Based on the requirement of the color of gold, the percentage of silver and copper varies.
 
Hi saharajiv,
Read the thread i posted about Polishing waste. Everyone helped out in the process. I actually ended up doing smelting the polishing waste ( including buffs) i had a hard time doing ar before.
 
4metals said:
If you have access to a large enough furnace, the proper fluxes can result in a successful melting of the sweep. This is how it is processed on a large scale but it is also beneficial on a smaller scale as the silver is recoverable.

If there is interest we can discuss this technique in detail.
Click to expand...

Can you give me more details. On Asia they burned dust with baking soda lead powder flux and salt.
Can you give me shot to see how is going and how is results. Thanks
 
Hi everybody!!
First of all, I want to thank all of the people here for the precious advice and idea

I tried to refining some gold polishing waste but something went wrong!!At first i burned all the waste and i took a fine dust, then I dissolved it in aqua regia  (1HNO3 and 4HCl) and every thing was good, but in the moment that i filterated the solution was very difficult to filtrate it even with vacuum pump. I got a considerable amount of white sludge that is not only AgCl (as i usually get when i refine old jewelry).Even when i precipitated the elementary gold later the filtration process was very difficult.
Can anyone tell me what else could be that white sludge except the AgCl?

What went wrong with the process?

I'll be glad if anyone give me some advice concerning the refining of gold polishing dust

Thank you
 
Once incinerated Harold used to advise boiling in HCl to make filtering afterwards easier but you then will still end up with silver chloride. Another tip is to use the largest filter you can find and not to overload it and not to pull too much vacuum through it or it will compact the residue.
Polishings are never easy to process so do not worry if you have had problems.
 
Thank you for your reply Nickvc
If i will boil in HCl the dust (burned) i'll get AgCl and my actual problem is that when i refine burned polishing dust the AgCl is more 'viscous' that when i refine scrap gold (old jewelry) and this complicate the filtration later. 

I would like to know why i get more white sludge when i refine burned dust compare when i refine gold scrap?
Is it possible that the white sludge is not only AgCl but maybe has abrasive material too?

How could i eliminate those elements that make AgCl so 'viscous'?
 
The AgCl isn't causing the viscosity, the base metals are.

Boil the burnt polishings in HCl first. No oxidizer. Then allow to settle. Decant. Add water, allow to settle, decant.

Finally, use nitric to effect. Allow to settle first, but, it will now filter fine.

If you go back and look at Harold's method, it's the first wash in HCl that makes it filterable. It gets rid of all the base metals.
 

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