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topic 38870

Refining Electronic Scrap---- Can't get nitric acid any more



A discussion started in 2006 but continuing through 2020

2006

Q. I've been working electronic scrap for over 20 years now as a hobby. I used nitric and distilled water to get rid of most base metals and then refined with aqua regia as normal. One of my nitric acid suppliers went out of business and the other one retired and sold his business to a larger one. This outfit has a minimum of $600.00 per order; I can't do it. So, I started using ammonium nitrate fertilizer for my nitric needs (it works well with sulfuric acid to break down the base metals). Now the government stopped the sale of this fertilizer. I'm so small that chemical companies don't want to mess with me.

I'm looking for a way to dissolve the base metals but not the gold without using nitric acid. I've read old & new books, but can't seem to find the answer.

I've been using commonly available chemicals such as H2SO4 and HCl.

P.S. I use hydrazine sulfate to drop the gold out of diluted aqua regia.

Franklin T. Zahn
hobby - Denver, Colorado


2006
Nitric Acid from Duda Diesel

A. Franklin

If you do not require large volumes, you might try Rocky Mountain Reagents in Denver. Otherwise, there is Interstate Chemicals in Pueblo.

Willie Alexander
- Colorado Springs, Colorado


2006

A. Hi Franklin,
Unfortunately I don't know a way of dissolving the base metals without the use of nitric acid. Have you considered using a non-cyanide gold strip (normally sold in powder form), then dropping the gold out of solution? You will need a few tanks, heater, mixer, but in the long run it may be cheaper for you. I'm not supposed to mention suppliers on this website, but there are a few good companies headquartered in Rhode Island which have much lower cost minimums, and the ability to help with any questions you may have regarding product. You could use Thomasregister.net under precious metals for electroplating or plating chemicals. If you don't want to go that route have you tried local laboratory supply houses to buy in smaller amounts? Just some thoughts ... Good Luck!

Mark Baker
process engineer - Malone, New York


2006

A. They pulled ammonium nitrate off the shelves because of its key roll in meth amphetamine production, but sodium nitrate or nitrate of soda found at most garden suppliers works just as well. I dissolve it in cold water until no more dissolves then add Liquid Fire [affil link to Amazon -- never mix with draino/lye/caustic type!] or Roto ACID drain cleaner [linked by editor to product info at Amazon -- never mix with draino/lye/caustic type!] 98% sulfuric until it turns orange and fumes red this generates a lot of heat and boils use it right away. Much more effective then battery acid and ammonium nitrate due to the heat generated.

Arthur Sommer
granite works - Bayshore, New York


2006

A. These procedures sound so dangerous, Arthur, that they should be labeled "Professional driver. Closed course. Do not attempt". The internet is a giant one-room schoolhouse, folks, and not every lesson you overhear may be appropriate for your experience and training level :-)

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


March 10, 2010

A. Franklin you can get ammonium nitrate in instant ice packs, the kind that comes in first aid kits and medical suppliers.

doug russell
- lincolnton North Carolina


August 2, 2018

grainger.com sells nitric in small quantities.

Michael Whitlock
- CORPUS CHRISTI


2006

Q. Hi

I'm looking for a way to recover gold, palladium etc from electronic scrap using commercially available chemicals. I've read about non-cyanide gold strippers and gold precipitators so I'm curious: can you make this from base chemicals, and if so where to find a description of the process?

Jesper Knutsson
Researcher - Gothenburg, VG, Sweden


2007

A. I cut up clean gold plated scrap, put 1 lb potassium nitrate stump remover (or other nitrate fertilizers) in gallon pickle jar, this is in pot of sand on a hot plate outside, made a Teflon lid with hole in it which poly hose runs to another bottle small-neck with little water in bottom of it, boil new battery acid to concentrate, cool as not to shock thermally glass, pour into gallon jar of scrap and KNO3 put lid on, tape Teflon then electrical then cloth.

Also tape other jar with hose into bottom so NO2 gas will bubble through H2O,
KNO3+H2SO4+Au+Cu = HCuSO4+Au+NO2+H2O
This dissolves base metals except gold, platinum, etc. The NO2 bubbled through H2O gives NO2+H2O = HNO3 68%. I save this for cleanup testing. etc., boiled until no more NO2 gas seen in jar and solution color changes green to blue, and gold flakes float easy. Cool, pour solution off gold flakes to another jar; add water to prevent copper sulfate salts crystallizing, let settle to recover a little Au that settles. I save this blue copper sulfate for electroplating, etching copper, electrowinning, root removal in sewer lines, fungicide, soil amendment, algaecide for ponds, or to make other copper salts, etc. Or add aluminum and Baking Soda to make safe for disposal. Done properly this is safe and environmentally and economically acceptable. We capture the gases that normally go into atmosphere or lungs and reuse them safely.

Richard Butcher
engineer - Selma, Oregon


April 22, 2008

A. Acid peroxide (HCl + H2O2) will dissolve base metals. It's not as nasty as nitric and it's readily available. I use it to strip gold from cutoff fingers and CPUs.

Steve S [last name deleted for privacy by Editor]
- Rhinelander, Wisconsin


October 28, 2009

Q. A Message for Steve S

Dear Steve,

May I know the exact quantities of the acids to be mixed in acid per oxide mixture (HCl+H2O2)?

Can this acid peroxide mixture be gainfully employed to remove base metals like Ba, Ca, Na, Mg etc from gold ores other than pyrite and sulfide ores?

Thank You

Johnson Lall
hobby gold refiner - Punjab India


December 6, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,

I want to start gold refining from electronic scrap as hobby. Currently I can buy nitric acid 68% HNO3. I can try to get a small furnace also if needed.

So here is the question

1- When I use nitric acid process on the gold plated item, should it be done as reverse plating to remove the gold plate?

2- Remove gold plate: what is the quality of raw removed gold, as in what gold percentage?

3- I try not to use aqua regia ( because it might be hard to buy it and it's a very dangerous chemical) , can I use a furnace to refine the gold, quality aside then melting it to one piece from the flake ?

TH Lee
- Georgetown, Penang, Malaysia


December 12, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi All
Please, What is the simple steps to recover gold from aqua regia solution , when dissolving electronic scrap, can I use hydrazine ?
Best Regards

Aeed Enad
plating shop employee - IRAQ


April 17, 2012

Q. I have been using aqua regia to dissolve gold plated materials. After gold is dissolved it's a nice emerald green and transparent. Then I simmer the solution down to small amount of liquid, add more hydrochloric acid then when it has cooled to 120 degrees I add urea. First problem is that everything I've read says its supposed to fizz and add until no more fizz ... well, it's not fizzing! I assumed it was because nitric had already been neutralized in boiling down. What's happening there and what temp should I simmer? Second, I add half oz of sodium metabisulfite (half oz is what I expect weight of gold I'll recover) to 4 oz hot distilled water. 32 hours later nothing has dropped. What am I doing wrong?

Matthew Christopher
- Hurst, Texas



Will nitric acid safely dissolve all metals that may be mixed with gold?

October 30, 2014

Q. I'm about to dip a metal bar from computer parts into some nitric acid. Will it dissolve everything but the gold? Of course I'm going for the gold so to speak. Will urea still neutralize the acid or should use something else? I heard vinegar is a good neutralizer but I never took chemistry so I don't know. I know, I know, leave it to the pros -- but I'm greedy. LOL I don't know any pros.Thanks

Brett Parker
- Denver, Colorado USA


39970Treasuremadre
October 2014

A. Hi Brett. Yes, nitric acid will dissolve most metals you encounter, like copper (probably not aluminum and some other metals).

But "safely" for people who don't need no stinkin' badges from having taken chemistry, and who know they should leave it to the pros, but are instead driven by gold fever? Are you kidding?  :-)

Luck & Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


October 31, 2014

thumbs up sign Mainly I was worried about the copper and brass I think are most of the mix. I cut a piece off of one of the bars I got and melted it with some chapmans flux but still see a huge mix of other metals. I just wanted to be sure that I wasn't going to destroy anything. Thanks, Brett

Brett Parker [returning]
- Denver, Colorado USA


October 31, 2014

A. Nitric acid will dissolve most base metals if the gold content is about 25% or less. If higher, the undissolved gold will coat the bar and block penetration of the acid. Hot dilute nitric (cut at least 50% with water, by volume) will work better than concentrated nitric. It takes about 1/2 gallon of concentrated 70% nitric diluted to one gallon with water to dissolve a pound of base metals.

There is likely some tin, from solder, in the bar. If so, the nitric will form metastannic acid with the tin. This is a slimy gunky material that will make filtering quite difficult.

All in all, this is probably a very non-profitable way to get the gold. It shouldn't have been melted all together in the first place. If you're lucky, you might get about $20 worth of gold from a one pound bar.

If you do this, be safe. The fumes are quite toxic and must be exhausted. Use a good fume hood.

Chris Owen
- Nevada, Missouri, USA


October 31, 2014

thumbs up signThank you Chris. I'd hate to think that's all the gold I will get. I've already started dissolving the metals so we'll see what happens. I do have protection though. I have about 1000 grams of this metal mixture so hopefully I can get back what I have in it. Thanks all!

Brett Parker [returning]
- Denver, Colorado USA


November 1, 2014

A. I guess I should have first asked you what type of parts were melted. If they were small to medium sized connector pins that were completely gold plated, they might run as high as $80/pound. If the pins were only partially plated (common) or, if the pins were of a large diameter and were comparatively heavy in weight per pin, they could run much less per pound.

I may be wrong, but this sounds like the bars made from melted pins that are now being widely offered on online auctions. In most cases that I have seen, these are made from lo-grade pins. If the seller were to list these pins as is, unmelted, the photos would show them to be lo-grade. By melting them, their visual identity is erased. Buying these is always a pig-in-a-poke, no matter what the seller claims.

Connector pins and circuit board fingers are plated, on average, with about 30 microinches (.000030") of gold. They might be plugged and unplugged into female connectors many times during their life-span and, therefore, the gold must be thick enough to exhibit good wear characteristics. About 30 microinches of hard gold plating has long been the average standard for this. Except for some CPU's and some military components, this is about the thickest gold plating you'll find on a modern electronic part. On other types of gold plated components that are not plugged into connectors, the gold can be as thin as 5 microinches. One square inch of 30 microinch gold plating has a value of about 36 cents, at the present gold spot of $1172/tr.oz. If thicker or thinner, the value is proportional to this.

Chris Owen [returning]
- Nevada, Missouri, USA


February 6, 2015

thumbs up signWell you were right, Chris, about the amount of gold. So I used nitric and it pretty much ate up everything. From what I hear the bars like I got are 97% brass with about 3% gold. So I've moved on to different things. I have some military grade stuff that I was gonna try next but not without some gold stripper. I may just use the ole muriatic acid and hydrogen peroxide as it seems to work pretty good. I also have nitric for after to clean the gold once the other acid has done what it can. Seems to be working.

Oh ya for those who just want to make a hobby out of it ... DON'T. It's far more expensive than you think and you just have a bunch of acids that you have to discard. It's really not worth it. Sell what you have on an auction site or something. You'll make money instead of lose it. And it's safer :)

Brett Parker [returning]
- Denver, Colorado USA


February 8, 2015

3% gold would be over $500 per pound. It's more like 0.05%-0.40% for gold plated pins.

Chris Owen
- Nevada, Missouri, USA


October 4, 2016

! I hope anyone using hydrazine knows that it is a carcinogen.

bill murray
- wilmington, Delaware


August 7, 2017

A. 2 parts muriatic acid, 1 part hydrogen peroxide. Cut gold fingers off computer boards, use tempered glass container or plastic. Put gold parts in container, cover with acid & peroxide. Do this outdoors. All safety gear. Chemicals will release the gold. Might take 3 days. Make sure there is no solder on the parts. Remove boards, filter liquid through coffee filter. You can do this twice. Liquid will turn green. look up scrapping on YouTube.

Douglas Deckner
retired - Sun City, Arizona, U.S.A.



October 22, 2020

Q. I used muriatic acid and peroxide to dissolve base metals but then I melted it all down. I got my samples mixed up and melted gold, silver and platinum group metals together. It looks like gold but will not test positive for even 14k gold because of the other precious metals. My question is how do I separate the gold, silver and platinum without using nitric acid. My sample is about 130 grams.

joe street
- Baker city, Oregon

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