Recovery of gold from polishing dust, sweeps floor or dirt material

A. Precious metal refining can be an exceptionally complex operation, Joseph, not something easily dispatched with an internet posting of a couple of paragraphs. I was recently involved in assessing some fire damage to a good size precious metal refinery and the cost of the repairs to about one quarter of the refinery was, as I recall, about 30 million dollars. Admittedly, that was a large refinery with redundant tanks and furnaces, but refining correctly, for complete recovery rather than partial, is incredibly capital intensive.

I would strongly urge you to sell those floor sweepings, used mops, etc. to a refinery rather than trying to build a small refinery yourself. But if you insist on doing it yourself, then I think you could start with "Recovery and Refining of Precious Metals" by C.W. Ammen =>

Good luck.

A. Joseph,

There is a simplistic approach to capturing the solids and 'floating' off the rest...

This involves two tanks. The first one is fairly tall but min. 30 gallons. The 2nd one could be rectangular.
Both made of Polyethylene.

This 'approach' is used by Assayers on claiming any 'valuable' dust that comes from the fume hoods.

In your case, mix up that dust with some water.

Then into the first tank (which has, of course, a big bottom drain) you use a vertical pipe say l/3 the depth of the tank. This is the feed pipe. Then at HIGH LEVEL you weld on a 6" or so pipe which protrudes into the tank horizontally by, say, 6" or so. Where it extends outside, you baffle it and weld on at the very bottom a l"Ø drain outlet pipe.

Now, that 6" pipe extending into the tank should have a real loose moulded cap. Then you cut out the inside of that cap and get some very ordinary coarse cloth and place it over the end of that pipe, push on that cap ... but use a 'screw' to just hold it in place.

On filling up, that easily replaceable/cleanable cloth will prevent any macro sized gold solids from escaping but the main solids will settle to the bottom of the tank.

Sorry we don't sell such books, Joseph, we're just telling you which book our readers suggest for this issue, and we note that this one gets excellent reviews. Sorry, but we would not know what book stores accept checks or ship to Zhuhai City, etc. Apologies.

Sorry, Joseph, I run the website and my specialty is electroplating; I do not have personal knowledge of those refining processes or analytical procedures.

A. Dear Joseph,
Hey! It's simple you know. Just collect all the sweepings, manually remove what is obviously not gold like pieces of paper, plastics etc, dissolve the high grade sweepings in aqua regia, precipitate the gold with Sodium Metabisulfite, filter - tapos!

I just came across your letter today.

Regards,

A. First you put all the dust in a lot of water, e.g., if you have 1/4 of a 4 gallon container of dust you need to fill the whole container with water. You add some laundry detergent and stir it well. The gold and other heavy metal will sink to the bottom. You then pour the water out very slowly (about 1/2 of the water). You repeat several times until all the floating material floats out. The water will become clean with the gold and other metal and sand at the bottom. You then filter it, leaving only the solid material on the filter paper. Take a magnet to take all the steel and iron out. Then you put it in nitric acid to remove most of the other metal remaining. Leave for at least 24 hours. You then wash again to float all the acid out. You then melt it. Add some Borax [linked by editor to product info at Amazon] when melting. After melting you could file it to dust again. Put acid again to improve quality. Then melt it again.

A. To Joseph Caranto,

As far as my experience is concerned, first burn all the sweepings to remove all organic impurities and unwanted pieces of paper etc......you have two options to the burned dust...melt the burn dust with flux (borax) you will get an ingot then proceed to the aqua regia gold refining process,or without melting proceed directly to the aqua regia process.

Note: Screen first the burn dust prior to the gold refining process.

A. Hello to all. My name is tanaji mane from India; I work in gold and silver testing melting and purifying shop.

Mr. Joseph: burn all dust on fire in an iron pot, then all waste material will burn (like paper , plastic). Then you have to wash that. Other dust will flow away , some dust with gold will remain in iron pot , gold & silver are heavy metal not flow with water , Be careful in washing, then collect iron from that dust with a magnet.

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Ed. note: Hello, Murtaza. We've noticed that if a reader ignores the previous postings and just takes it from from the top again, the other readers tend to follow his example and ignore his posting as well :-)   Please do your best to frame your question in terms of the answers that have already been offered, and I think you will get some helpful replies. Good luck.

A. To Mark Vincent....

Just follow the procedure of gold refining ( aqua regia process) and you will recover 99% of gold. What precipitant you are using? the process is very simple and surely you will end excellent gold recovery......

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Ed. note: Cousins Vanraj, Hasitha, Sanjava --
Sorry, but we editors don't know gold recovery and can't help you except to repeat that when you ignore the answers already on the page and start over it accomplishes nothing except killing the thread. Please cast your questions as requests for clarification on what has already been said. Thanks!

A. The purchase and/or processing of polishing wastes, floor sweeps, filings, carpets, traps, etc., is quite complex, but it can be very profitable if done right.

The value of polishing wastes, often called buffing dust, can range all over the map from about $20/pound to $800/pound, depending mainly on the metal(s) being polished (silver, gold of various karats, platinum, etc.) It and the other materials listed above are extremely non-homogeneous and it is impossible to sample and assay them in their untreated condition. In order to determine their value, they must first be "prepared", i.e., putting them into a homogeneous state. For example, to prepare buffing dust, this entails, in order, incineration, ball milling, screening, magnetic separation, and blending (or sample splitting). At that point, it can be sampled and fire assayed.

A common method for processing prepared sweeps and dust was to melt them along with special fluxes containing lead. All the precious metals (PMs) were collected in the lead, which was then then removed by cupellation (like a huge fire assay). The residue was almost purely all of the PMs, in alloy form. There are also acid methods for treating the prepared dust.

There are 2 excellent books that generally cover these methods - Hoke's "Refining Precious Metal Wastes" [link is to info about book at Amazon] and Loewen's "Small Scale Refining of Jewellers' Waste" [link is to product info at Amazon]

Dealing with these materials is not for those that are unknowledgeable.

Q. Chris Owen, Thank you for your helpful response. Due to the complexity of the refining process I was planning on just focusing my self on procurement of sweeps, filings, and polishing dust. I have a 3rd party refinery I will be using.

Is there are more advice in regards to procurement of such items for a profit?

Is my $50,000 goal attainable?

I was just planning on going from bench jeweler to bench jeweler see if they will sell.

A. After treatment (incineration, ball milling, screening, magnetic separation) and before using aqua regia to dissolve the values, a separate hot HCl leach is advisable. I see no advantage in using HCl on untreated polishing dust.