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topic 34676 p.4

Best and Easiest way to refine gold dust to get 99.9% purity

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A discussion started in 2005 but continuing through 2020

January 2, 2018

Q. Hey guys, I need a chemical name a 3rd grader can read. Not all these chemical codes to demonstrate your complexity and knowledge. This may be my last time but every response here is extremely frustrating or YOU'RE DOING IT ON PURPOSE!

I'm a med graduate and a financial advisor. I can break it down simple or completed. All I'm asking for is simplicity!

1) give me the name or sales or chemical one. Is it a powder or liquid? What color is the product? Where can I buy it on a local level. Pool store. Home Depot. Where?

2) How long does it take the gold to melt? Do I place them in a certain order?
3) Does glass matter? Can I use an iron pan! ?
4) What color will it change.

Also I very familiar with all the safety precautions. I just need to know can someone help me.

Mark Thomas
New hobby - Riverside California

January 2018

thumbs up sign Hi Mark, I sympathize! As a med school graduate maybe you can tell me what shape & color is the appendix so I can recognize it, and what store sells those scapular blade thingies I'll need?

Seriously, while I hope a reader can help you, dissolving gold may not be simple, and do-able with hardware store chemicals and supplies just because we wish it was. It would probably be best if you explain what it is you're trying to do and why. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

January 3, 2018

A. Mark,
Dissolving gold isn't a trivial thing. Here's some light reading for you =>
Note that this isn't really stuff you want to be messing around with in your garage. A properly outfitted chemistry lab is recommended.

As Ted asked, what exactly is your end goal here?

You even keep saying "melt", which is a totally different thing. If you want to MELT gold, you just need to heat it to 1948 °F inside of a container that itself will not melt at that temperature.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

January 4, 2018

A. Gold can be dissolved in muriatic acid (hardware store) and hydrogen peroxide or, a combination of muriatic acid and laundry bleach (sodium hypochlorite). Muriatic acid is about 30.5% hydrochloric acid. Both solutions produce toxic fumes that will surely rust any steel present in the immediate area. Must use these solutions upwind outside, away from neighbors and cars, or in a fume hood inside that exhausts to the outside. These are probably the least hazardous chemicals that are commonly used to dissolve gold.

The other choices are the very dangerous aqua regia, usually used hot, or the extremely poisonous sodium (or potassium) cyanide plus an oxidizer like hydrogen peroxide. Also, the expensive combination of potassium iodide plus iodine or potassium bromide plus bromine will dissolve gold.

The only thing I've mentioned that will effectively dissolve bulky pieces of gold is the aqua regia (hot) that Ray just provided the link for. Everything else I mentioned would only be practical for very thin gold, like 30 millionths of an inch thick gold plating or gold powder. For bulk gold, these other chemicals might take weeks or they may not completely dissolve the gold in your lifetime.

And, like Ray said, you MELT with heat and DISSOLVE with chemicals.

Chris Owen
- Benton, Arkansas, USA

March 20, 2018

Q. Most of the processes described are for gold bound to plastic using another metal/ alloy.

I have gold coated on plastic sheets by a physical process call sputtering. Is it possible to physically strip the gold layer using some chemicals?

Arthur James
- Redwood, California

March 2018

thumbs up sign  Hi Arthur. All things are possible, but when it comes to recycling/recovery the question is usually what is economically feasible & practical (because chemicals and waste disposal can cost more that the value of the recovered gold) ... so the first thing we must almost always ask is: "How thick is this gold?". Also, what are these "sheets" if you know?

silly :-) It's unfortunate that you're from Redwood California, as it is one of the world's least likely places to be friendly towards you conducting such a chemical operation, whereas Mumbai, for example, might be a different situation.


pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

March 23, 2018

Dear Ted,
You got Mumbai since I am currently here for work and posted the message.

The plastic sheet is polyethylene, and gold is deposited using the process of sputtering - a fine layer.

I am looking for a process of recovery, that is all.
I know it will not be commercially or economically viable, but I am only looking for some way that I haven't read elsewhere. This is not a mining operation, you see!

-Arthur. :)

Arthur James
- Redwood, California.

March 2018

A. Hi Arthur.

The point about Bombay vs. Redwood is that every major environmental organization rails against amateur recovery of gold from waste, usually showing street waifs in India in their videos; whereas Californians fancy themselves as environmentally sensitive as can be, and will do their best to impede you at every step ...

Polyethylene is very acid resistant and it would not surprise me if it could withstand aqua regia or aqua regia substitutes, allowing direct dissolution of the gold with no need for any fancy approach which you haven't already read about.

But burning the poly is perhaps one possible route to recovery, although people will be unhappy with that. There have been developments with bacteria that will consume polyethylene, and there has reportedly been some development work towards converting polyethylene back into oil.

Again, though, the first question which simply must be answered is "How thick is the gold?". 'A fine layer' is not quantitative enough, not only because you can't know the viability, but also because you can't properly run the process, knowing how much chemical to add and how much gold or intermediate product to expect at each step until you answer that question. There is gold everywhere, even in seawater, but you have to know how much; if you can't track the gold you can't process it. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

March 24, 2018

A. I think the question is basically about the best and easiest way of taking out thin films of gold from the surface of plastic sheets. Economics, pollution, etc. are of course important which cannot be avoided in a practical situation.
I wonder if one can use some kind of a solvent - alcohol, acetone, TCE, etc. to delaminate the gold layer from the plastic substrate which dissolves in the solvent.
India is a vast country where different levels of economies and technologies coexist. I know of a company in Bangalore by name E-Parisara which treats e-waste in a scientific and environmentally safe manner. It is run by a qualified electrochemist who also runs electroplating and PVD coating systems. He mines all the gold required for decorative PVD from electronic waste. But gold is not the only precious metal he recovers.

H.R. Prabhakara - Consultant
bangaloreplasmatek.com - Bangalore Karnataka India

March 2018

thumbs up sign Thanks, Prabhakara. I have never had the pleasure of visiting your fascinating country, but from running this website for 23 years I have learned of its incredible diversity. On the one hand we get inquiries every month from remote villagers who believe old lightning rods have the ability to release stored lightning power on command if magic words are spoken, and on the other hand we receive insightful answers from people with far deeper technical knowledge than I'll ever achieve :-)


pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

Karat refining with copper inquartation

July 2, 2018

Q. My situation: what if I use copper with 9 & 10 karat gold scrap for inquartation and then further with AR process to get pure out.

Please let me know the complete process; I use hydrazine hydrate to precipitate.
What purity will I achieve? Will I have any copper traces?

Arman Joshi
- mumbai, INDIA

July 16, 2018

Q. I would like to have enlightenment about this process with the target of getting high purity of gold while buying it from a artisanal gold trader:
Suppose you buy a piece of already melted gold and you want to be sure you don't have scrap or a lower grade of gold and you decide to treat it again; could someone melt it again using a borax flux to remove the impurities and other metals mixed with the gold?
Can someone melt again with the borax flux and pour the melted gold into a bowl with nitric acid to cleanse it and reduce other metals such as silver or copper if melted before with the gold and wash it later with distilled water?

L. Bob
- Nigeria

July 22, 2018

A. Pouring molten gold into nitric acid would be EXTREMELY DANGEROUS and unlikely to achieve anything useful.
For someone with little or no knowledge of chemistry, by far the best process is fire assay. It requires little equipment, produces high purity gold and has been practiced for hundreds of years.
Here is a good guide:

geoff smith
Geoff Smith
Hampshire, England

July 24, 2018

A. None of your ideas will work, at all. There's no simple way to purify gold in a melt. Borax will do nothing but act as a flux. You could remove some of the copper using Borax and an oxidizing agent, such as sodium or potassium nitrate, but that reaction will quickly destroy crucibles and it won't remove the silver.

Like Geoff said, the quenching of molten gold in nitric acid is a terrible idea. Besides being extremely dangerous, it wouldn't work.

As Geoff said, fire assay is the very best and most reliable way.

You might be able to develop some sort of accuracy with a touchstone, if you could come up with standard alloys to compare with.

Specific gravity measurements could possibly be used, but, of you don't do it right, you can introduce error. This would be my last choice.

You could melt it together, drill several holes, and refine maybe a 10g sample of the drillings with aqua regia, but you would need some experience for that.

Chris Owen
- Benton, Arkansas, USA

Gold testing and refining

July 24, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My situation: So I am new at this gold refining and recovery but can pick it up fast. So I have been buying gold nuggets and flakes for fun and melting them down into a bar. I bought a test kit so I could test everything I buy to know if it is real. So far I have a bar that is about 24 grams. So when I do the acid test with it on the testing stone the 10k, 14k, and the 18k don't dissolve it but the 22k acid does. And I tested the bar itself and the spot I put the acid in turned dark. It didn't bubble or fizzle or act funny it just slowly turned dark but it only did that with the 22k acid. The other acids didn't do anything to the bar. Why is that. And my next question is the more I melt my bar down does it make it more pure?

Randy Mcaroy
Hobbyist - Bethany, Oklahoma, Usa

July 26, 2018

A. The touchstone test is a comparative test. You can buy a set of gold "keys" that are tipped with various karat golds. You use these to make side by side streaks with a streak of the gold you are testing. Then, you apply one of the acids and watch what happens. The object is to find a streak of known gold content that has the same rate of attack and color change as the unknown sample you're testing.

The acids, themselves, tell you nothing. Whether or not a drop of a certain karat acid dissolves your gold is meaningless. The higher the karat number of the acid, the stronger the acid. If you put a 22K acid on a streak of 10K gold, it would dissolve so fast, you wouldn't be able to see the progressive dissolving that would take place with a weaker acid. You, therefore, can best see the changes that take place, on 10K gold, by using the weaker 10K acid. Same thing with the other karat golds. The 14K acids work at the best speed with 14K gold, etc.

Most jewelers that use a touchstone are experienced enough in testing the same, fairly consistent, karat alloys, day after day, that they can sort various karats by using only the various acids and watching how fast the streaks are attacked and by observing the resulting color.

The touchstone methods is designed for karat golds. Yellow karat gold contain silver, copper, and a little zinc, of fairly consistent amounts, depending on the karat and the color. If any other metals are present in the alloy, or, if the silver content is higher than about 10%, it can alter the rate of the attack of the acids and give false answers.

Although placer gold always contains silver and copper, it also contains other metals and some placer has a lot of silver in it. These can alter the rate of acid attack considerably. Therefore, any results on placer nuggets using a touchstone are iffy, at best.

If you really want to know what the gold content really is, send about a 1/2 gram sample of drillings to a lab that does fire assaying. It will cost about $50-$100. Also, many jewelers, especially those that buy a lot of scrap gold, now have XRF (x-ray) guns that can tell you the various percentages of all the metals, in about a minute. These XRF guns are somewhat operator dependent, though, and some readings can be faulty, especially if the operator is inexperienced. Most would probably test your gold for free and, if possible, you should back that reading up with an XRF reading from a second jeweler, or gold buyer. Get a second opinion.

Re. your second question: No, you can't purify gold in a melt. The copper and some of the other impurities can be reduced by adding certain chemicals, but these are corrosive to the crucible and you'll never remove any of the always present silver that's in placer gold. By repeated melts, the copper can decrease by a very small amount, just by the reaction of the copper on the surface with the oxygen in the air. The resulting copper oxide is transferred to the slag. But, for repeated melts as a purification process, the answer is an emphatic NO.

Hope this helps.

Chris Owen
- Benton, Arkansas, USA

July 31, 2018

A. Hi randy,
Your 10,14 or 18 carat gold contains alloy; it has silver in an alloy. If the ratio of composition of silver from alloy to pure gold mismatch, thEn masking of greyish blackish silver chloride coating occurs on metal surface in AR treatment. That is called 'masking'. It dissolves in ammonium hydroxide but returns when metal comes in contact with AR.

Bhupesh Mulik
CAC admixtures - Mumbai,india

September 18, 2018

Q. How to kill iridium in gold with 99.99% silver and HNO3 (NITRIC ACID)?

vasu rastogi
hobbyist - india

Ed. note: Reminder from the question submittal form --

February 7, 2019

Q. Hi everyone,

Thank you all for your wonderful responses. Recently I got to know about gold extraction from computer scrap, and I purchased a little stuff to have some fun and add a little knowledge. I took around 90 pentium 4 cpu's and dipped in solution of HCl and Nitric acid. I found no reaction occurs so I added a little sulphuric acid to it. Fumes started and after some time gold pins and gold plating left in that solution. Now I'm worried to know what should be my next best step to get complete process. If anyone wants to add in it, I would be very thankful to it.

Thanks & regards

Syed Hussain

April 14, 2019

Q. Aslm Alkm,
Hi there Urban miners; I'm here to have more enlightenment ...
1. which is the most proper Acid qualitative to use when extracting Gold, i.e., Concentrated or Dilute Acid?
2. is there anyone here who can help tell and explain the composition of this GOLD STRIPPER? I saw its action on Ceramic Processor; it is unlike Aqua Regia, it is so selective that it does not dissolve other metals.
I found it difficult to get it here in Nigeria, that is why I think if I can see the composition I might be able to make it myself,

Yushau Halilu
- Lafia nasarawa Nigeria

May 29, 2019

Q. I am doing aqua process to recover pure gold from 9, 10, 14 karat alloys. I am precipitating using hydrazine hydrate, getting the sponge and melting it, but in XRF and fire assay show that I'm getting fineness up to 0.995-0.996 and other parts are showing as silver. I want consistent fineness of 0.998+. Is there any silver chlorides remaining in the sponge or anything else? I want 0.998+, in my sponge I have chloride, how to remove that.

Armaan Joshi
- Mumbai,Maharashtra, India

June 19, 2019

A. Hi araman,
You precipitate gold using hydrazine hydrate, but you have not washed the gold sponge properly .

Bhupesh Chandrakant Mulik
CAC admixtures - Mumbai,india

Refined Gold has Iridium in it

June 4, 2019

Q. Actually after refining gold from dust Purity was okay and there were no more metals shown in the xrf report; but after casting pieces then filling done, then setting also done. But in polishing, Blackspots shown in the ring and those spots are Iridium. How it came inside? Can you suggest?
Or else is there any procedure to remove iridium from gold ppt? Please let me know I am facing problems due to this iridium.

Wasim Kazi
HKE pvt ltd - mumbai maharashtra India

June 2019

A. Hi Wasim. I know nothing of gold refining, but I do see it reported on thread 15854 that, because the value of iridium is far lower than gold and nitric acid does not dissolve iridium, scammers in India are diluting their gold with iridium to fool buyers about its purity. You might want to research the possibility that this report is true.


pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Aloha -- an idea worth spreading

July 1, 2019

Hi Wasim,
1) Is your alloy contains iridium then check its %
2) And if no iridium present then change your polish buffing wheel which you're taking as a dust for gold refining.
3) Check your refining process -- any contamination or any process changed.
4) After casting, when you take casting scrap in refining process.

Bhupesh Chandrakant Mulik
CAC admixtures - Mumbai,india

August 13, 2019

Q. Hey you guys, I am not as smart as you guys but I uncovered a good bit of gold dust and I'm seeing some flakes. Dropped nitrite acid on the stuff for confirmation. Checks out. Separation process I have no guidance. A lot of it is in clay it was washed into. Help.

Bryan m [last name deleted for privacy by Editor]
- Winder Georgia United states

August 18, 2019

Q. Hey guys I've recently struck gold the improbable does sometime happen. So I've been reading you guys comments -- most informative. I've discovered a large deposit of flakes, dust and fine gold thus far. I've been in need of direction. I'll include pics with this post but I am trying to keep it somewhat quiet. I bought the acid kit: positive for gold, then I gave a sample to a friend of mine who has a machine and said 22k so I went and got all I could. My family aren't really taking me seriously. I had a time at first separating it from the dirt so then I had a thought: I thought if taking the dirt away from the gold is not possible why not take the gold away from the dirt. I now have two pounds of clean gold flakes. Yes. I'm taking it to an assayer Monday. You guys would not believe. On a good guess I bet I've poured out 5 pounds on the ground just trying to clean it. But I think I've learned; now any guidance from you guys is most appreciated. bryan

Brandon m [returning]
- Atlanta Georgia

August 24, 2019

A. Hello Brandon,
Well, if your friend's "machine" proves it is 22 kt gold, let's hope the professional assayer's results are the same. Since you have clean flakes and know you have 2 lbs, there are 14.58 troy oz in a pound. If the assayer says you have 22 kt gold, then it's .9166% pure (22รท24). Get a copy of the assay analysis report with the business name and phone # in the heading of the report. You can then take it to a reputable refiner to have it melted into a bar or sell it to them outright. Get a certified check of course. Being you went to the assayer already, let us know how you made out. I'm also curious what state you found this in.

Mark Baker
Electronic Plating - Winston Salem, North Carolina USA

September 15, 2020

Q. Hello guys, I'm Wayne a metallurgist from Zimbabwe specializing in refining precious metals. Currently I am working on refining PGMs using aqua regia but having problems de-nox-ifying the solution. I used urea but it's not reacting, are there any alternatives?

Wayne Chinyama
- Harare Zimbabwe

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