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letter 34532

Solution for precipitating gold from HAuCl4 solution

A discussion started in 2005 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.


Q. Respected Sir,

My technical problem is how to precipitate gold from HAuCl4 solution. We recover gold from Filings, Setting, Waste water, Consumables used in production, Emery papers, and sweeps from the production floors.

We dissolve the above mention media into aqua Regia solution & on filtration precipitate it with a solution which is called as AURO8032, locally available, which has a pH Factor of 8-9, & gives out white fumes when the can is opened. The solution also smells strongly of ammonia.

When we pour the precipitate in the HAuCl4 solution,the solution becomes black giving out yellow fizz in the solution. After few seconds you can practically see big brown spongy ball like gold getting precipitated & once all the gold in the solution has precipitated the solution at the top has lot of white foam, which indicates the end of precipitation.

We let the solution stand overnight to settle down & recover gold from it by washing it with water.

Though I know Sodium Metabisulfite, Ferrous Sulphate, S02,Copper, can precipitate gold. But with these above chemicals it takes whole day & with AURO 8032 its takes only few minutes & the precipitation is over. What could be this solution? its extremely effective & has no gold residues left in the solution. The left over solution becomes Dark bluish & Greenish in color & I am always getting 999.99 purity gold with this solution on precipitation.

Refining Precious Metal Wastes

I would also appreciate if you give me guide lines & Step By Step instructions on how to refine Platinum.

I am also on the lookout for books by C M Hoke & other good authors. I would like to buy these books if they are available in the market.

Awaiting an early response from you;

Best regards,

Prakash V Pai
Jobshop Employee cum Hobbyist - Maharashtra, INDIA

Ed. note: One source of the Hoke book is Amazon =>


A. You use hydrazine hydrate for gold precipitation. Don't add urea in gold chloride solution.

Bhupesh Mulik
jewellery - India


A. Dear Sir: Your product most likely contains hydrazine hydrate 64 or 85% (liquid) or hydrazine 2HCl (solid). It works well with acid gold plating baths, but does not work well with alkaline CN based baths. Please be careful: despite smelling like ammonia, it is carcinogenic and toxic to fish and people. It will also reduce platinum salts to Pt metal in highly alkaline media (pH>10).

Richard Michael Grazul
- Juiz de Fora, MG Brazil


thumbs up signKind attn: Richard Michael Grazul & Bhupesh Mulik,
Thanks a ton. It was great to get a reply from you. I will try the mentioned solution for precipitation this week.

Q. I would further like to know how to precipitate Platinum From the Aqua regia solution!.
Secondly why should I not add urea to the solution as this helps remove the Nitric Fumes from the solution to Neutralize before Precipitation with the help of Hydrazine hydrate? (64% or 85%?)

Can we mix HCl & Hydrazine Hydrate directly?
Or is there a process for the same?

Thanking you once again for your kind gesture.....

PRAKASH V PAI [returning]
- Maharashtra, India

May 22, 2010

A. Hi I'm bhupesh mulik
I dilute hydrazine hydrate with five parts of water, that is 1:5. Then you add it in your gold chloride solution. You can get exact value by checking your pH level of gold chloride.

bhupesh mulik
jewellery - mumbai


Q. Precipitate gold from aqua regia. I'm investing about gold precipitating from aqua regia. I know sodium metabisulfite, ferrous sulfate. But I want to learn more about hydrazine hydrate, SO2, formaldehyde, hydroquinone and Oxalic Acid [linked by editor to product info at Rockler]. My company will begin to use aqua regia process for refining gold; can you give me an answer about when I must use which precipitant for the best purifying?

Catalyst for gold analysis? A few days ago, I began to use ICP-MS for gold analysis. I want to learn if some interference the gold and affect my result. If I must use a catalyst for analysis. I use aqua-regia solution for analysis.

þenay þen
chemical engineer - Istanbul, TURKEY



Jimi Lim
- Singapore

February 12, 2008

Q. Dear sir, I want to know the process of refining of gold from aqua regia by step by step.

Mohammad Shakir
jeweler - Saharanpur U.P. India

sidebar February 13, 2008

A. Hi, cousin Mohammad. Prakash named a good book, "Refining Precious Metal Wastes: Gold, silver, platinum metals" by C. M. Hoke, if you wish to know the whole of this broad subject. Another good one is "Recovery and Refining of Precious Metal" by C. W. Ammen. =>

After getting your hands on such a book, if you can please come back with specific questions that can be answered in a few paragraphs, readers of this forum may be able to help you with it. But condensing a subject that fills whole shelves in libraries down to a paragraph can't work :-)

Good luck, and Thanks!

Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

February 22, 2008



March 19, 2008

Q. I have done a small research about precipitating gold out of Aqua Regia solution.
I use 3 HCL+1 Nitric Acid to make Aqua Regia.
Let it work 1 night or simply heat it up for a while to shortened the process.
Filter the solution and neutralize it with Urea or just heat it up until all of the nitric vaporized. Watch out not to lose any precious metal during the heating. Test the pH.
Precipitate gold using sodium metabisulfite/ zinc.

You can use above method for any kind of source which contains gold.
I need a favour about precipitating platinum out of the solution. Should I use salmiac?


Ivan Christianto
- Salatiga, Central Java, Indonesia

Sal Ammoniac

Ed. note: "Salmiac"? Sorry, that word doesn't sound familiar. Is that perhaps the same as "sal ammoniac"?

June 27, 2008

Q. I buy scrap gold from market , granulate it and digest it to aqua regia digestion. The excess nitric of the gold solution is driven with urea addition till the point where the urea dose not react any more. Then I use pure S02 to precipitate the gold. but I do not get the full recovery . I get only 75%. rest I have to get thru metabisulphite treatment. my question;

Why I am not getting the full recovery with S02 at first ?

d. bhatta
jewellery making - Calcutta, India

July 7, 2008

A. In response to d. bhatta
To drop a larger % you must slowly heat solution to simmering, just below 200 °F (do not boil). Wait at least 1 hour before filtering, re-filter. Also consider your ct/in (?) compared to ct/out (24K).
If Pt is in solution you want to drop that first, same way with NH4Cl. Hope this helps.

Two other things,
1) Na2SO4 is better for dropping the gold (free electrons
greater reactivity)
2) Rest solution 24 hours after dropping last of Pt
It falls out on its own, filter and save up.
It will help pay for your chems.
If you are selling your Pt bring the It with you
some buyers will try to tell you your Pt is 10% It
This way you can say this is Pt and this is It and get
full value for your Pt.

Tim Evans
ores - LaGrange Texas

July 9, 2008

Q. Dear Sir:
I am a hobbyist in gold refining, after using the different steps in getting the gold mud, I am left with liquid that is a brilliant blue or sometimes a vibrant green. Can you tell me what these are? Are they unreclaimed silver, platinum, palladium or rhodium?
What do the different colors mean? And if so, how do I reclaim those? Thank you

Ronda White
hobbyist - Chloride, Arizona

July 12, 2008

A. I'll give the green blue question a try.
Vivid almost neon green is the norm color of a used up (or near empty) solution. I test with with aqua ammonia test liquid to see if I missed anything, but do that, to the side in a test dish. If gold is still present it winnings. with ammonia turning your solution blue.
Pt group metals normally just make the solution look muddy till dropped.
Anybody else have any other ideas?

BTW Aqua Regia should be filtered before adjusting the pH and just after.
If silver and/or a couple other nasty insoluble alloys get in the further process you run the risk of creating silver fulminate (bad stuff, highly unstable sim. to nitro when dry or dry heated)
2 simple filterings may save a lot of grief.

Tim Evans
- LaGrange Texas

October 20, 2008

Q. I recently started gold recovery on a small scale, I dissolved circuit boards in a aqua regia solution, but now I'm lost. I would like to recover the gold in the solution but it seems way too dangerous for an amateur like me. So is there a SAFE EASY WAY TO DO THIS or do I need a chemistry lesson, and can I dispose of the solution safely? Any help would be greatly appreciated.

wes covert
newby - defuniak springs, Florida

December 5, 2008

A. Just some quick info. I know the owner/ops really dislike "gold recycling" :) I see their point it's finishing, not financing.

I will say that you are using a form of Hydrazine or more likely Hydroxyl Amine- HCl. The HCl is usually neutralized with KOH or NaOH to a pH of 7. Hydrazine is rocket fuel. 3 factory explosions have been attributed to it spontaneously. It is not a contaminant.
Hydrazine is N2H4 with a sulfate or HCl
Hydroxyl Amine - is NH2OH-HCl.

For my application there is no comparison. I have tried, every cementing and reducing agent. NH2OH wins hands down. It rains sand. There is a bit of chem needed to use it. I strip gold based on ammonium iodine/Iodine. Don't try it unless you have a degree. screw up just a little and you made a touch sensitive explosive! I will say it strips all precious metals including rhodium. 3 minutes to strip MilSpec gold plate. The solution is regenerated and reused with H202. 1 Gallon -(3.7 L) strips about 4 ounces troy vs cyanide which is 0.7 oz Troy it is done in the presence of a buffer. pH is neutral to slightly basic. Doesn't burn, isn't toxic, and does not "REQUIRE" a fume hood.
The best part is that the attack of base metals is virtually none. Until using this I hated all that was nickel and copper. :)

Just remember be safe,
Find the right forum to join,
and to all those of you get rich quick-start a lab in the garage types -got 50 beakers of witches brew and are stuck...It's not your fault. The GOOD lack of information is absurd. The first thing a person does is googles gold. Aqua regia comes up, they run to the lab supply and are knee deep in it.

While it is not your desire to provide info on the topic, I do feel it is your responsibility to give better redirection. I have Hoke's book. and cottons, and every other one. They all read fine, if you have done it before... The point is that no one is going to buy the book. They want to use the internet. They want to interact with others. why, what, how? Hoke is most likely dead and rendering him unavailable to email.
Please find a responsible refining forum to represent as a service to yourself and others.
Sorry if I stepped on toes.

Don V [last name deleted for privacy by Editor]
- Lake Geneva, Wisconsin

thumbs up signHi, Don. Yes, the main focus of this site is metal finishing, but we have dozens of threads about precious metal refining, and many helpful & knowledgable responders.

We've posted many hundreds of helpful responses on this page and those other pages about refining, and we certainly appreciate yours -- but I don't understand your "not financing" complaint. Also, please don't include ad hominem bitching; that is unwelcome on any site.

The inquirer specifically asked where he could buy Hoke's book, but you insist that "no one is going to buy the book. They want to use the internet", so I shouldn't have answered him :-)

People must have books and reputable materials! Can you imagine being on the witness stand after someone was maimed or killed in an accident (been there several times), and trying to justify that you don't believe in books, so you proceeded on internet forum advice from strangers who were possibly even posting with fictitious names?


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

January 29, 2009

A. Wes Covert: Since you are a newbie to gold refining, you might try Very knowledgeable. Great people and many answers. B

Ben Peters
- E. Flat Rock, North Carolina

August 6, 2009

A. A source of information for which you are looking is

That site has topics about gold and other precious metals, from eScrap, ore, and old jewelry.

It had detailed information on refining, of course.

On this site, safety is a big topic.

There is a lot to read on the site, and it is usually better to read and follow links there before asking questions (especially long complicated questions which would be answered if you just read your corresponding topics first). Single item questions about anything which is not totally clear to you are best received, and will certainly be answered.

I'm new to recovery and refining, and the Gold Refining Forum is the best site I've found for learning this stuff safely. Also they are big on helping to determine which chemicals would be most economical for your particular applications.

Have fun.

Eethr Don
- Oakland, California

August 15, 2009

thumbs up signHi, Eethr. Your recommendation of certainly isn't a problem; it was already suggested right above your posting, as well as many times on this site. We offer what help we can, without claiming that our coverage of a topic is better or not as good as another site.

But please try to contribute at least a little technical content with your postings. First, links go bad, and we don't like to offer nothing but the distraction & frustration of broken links if that happens. Second, not everyone likes every forum -- you can see that some people like this one and other people don't :-)

Thanks again!


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

What is AURO 8032 Gold Precipitant?

August 25, 2008

Q. Dear sir,
I am working in a branded jewellery manufacturing group. Can I know the supplier for AURO 8032 chemical which is used to precipitate the gold solution. Please reply to me.

Plating Shop Employee - Hosur,Tamil Nadu,India

March 17, 2009

Q. What is the AURO 8032 solution and from where I could find this solution? And what would be the approx. price of this solution

Anshul Mundra
- India

April 22, 2010

Q. Bhupesh Mulik, Many thanks for your advice regarding the use of Hydrazine Hydrate for precipitating gold. Kindly shed more light as to exact measurements or quantities to be used for a given gold chloride. Any particular ratios? Or depending on particular reaction taking place?

Godfrey Banda
Hobbyist - Lusaka Zambia

June 13, 2010

A. Hi godfrey, I'm bhupesh mulik working in jewellery company.
I hope this reaction information will solve your problem.

bhupesh mulik
jewellery - mumbai,india

August 12, 2010 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am working in Gold Refining industry since 1994. I have read questions and answer in your It is interesting. After read this, idea come - alternate for Sodium bi-sulphate while doing Gold Precipitation. The alternate chemical name is AURO 8032. Can you tell me the address for buying the above mentioned chemical. It will be very useful for alternate precipitate gold process. I am eagerly waiting for your reply.

Ravi Kumar
product designer - Tamilnadu, India

October 23, 2010

A. You may get AURO 8032 from Aurotech bureau, JVPD MUMBAI INDIA

amit mehta
- mumbai,india

Storm gold precipitant

March 20, 2009

Q. I'm wondering as to how you can use copper as a precipitant. I've never heard of this method and wanted to know if you could elaborate on this. Currently I use a precipitant called Storm =>
and, whilst it works well, it's rather expensive.

Also if anyone knows a good distributor of sodium bisulfate in the US I would appreciate it greatly.

William P. Momani
- Yardley, Pennsylvania

June 11, 2012


- New Delhi, India

January 15, 2013

A. Dear sir, you use sodium metabisulphite for ppt of gold. You can obtain 99.99 gold reaction with smbs Na2S205. Redox value will be 300 mv.

Shadab [last name deleted for privacy by Editor]
- Gurgaon, India

March 15, 2009

Q. Hey, dear folks.
Please, I want to ask you if can I precipitate gold from aqua regia with (pb) or not.

abdo alarbi
small shop - Tripoli, Libya

Ed. note: What does "(pb)" mean in this context? Lead maybe?

April 3, 2009

! Dear Readers,
I have previously visited this web site which is a great place to acquire and give advice from others interested in gold and precious metal recovery from many sources in general.

The book by Hoke is one of the best available references of information. I either have a copy of the book or photocopy for educational purposes.

I usually work with materials left at old mine sites. I have worked with boards. I mesh and grind the mine site materials,then table these on a Wilfley to acquire a concentrate for either furnacing or leaching. After furnacing I granulate the metals to increase the surface area then do a dissolution in Aqua Regia. Using Nitric first on your granulated metal enables you to recover your silver by precipitation with either salt water or Hydrochloric Acid. You will also dissolve your Palladium in this process which can be recovered later. However Dimethylgloxime is expensive and possibly just using the aluminium method that follows will enable you to recover a metal for assay and sale.

If no silver is present I go to Aqua Regia (weak or strong),boil it down,add urea to remove any remaining Nitric and then adjust my pH to 7. I then add Sodium Metabilsulphite to drop the metals,filter and dry. I then clean the powder with weak ammonia to remove any possible co- precipitated silver. Again filter and dry and clean with hydrochloric or just boil in water to lump it together.

You should be able to furnace this directly using just Borax [linked by editor to product info at Amazon]. Also add a small pinch of saltpeter to the charge before pouring into a suitable mould. Clay crucibles are good to use with this method. The gold should be 99.99% or four nines as they say.

If you had Platinum in your solution and after gold recovery using Sodium Metabilsulphite (used for sterilizing bottles etc) you can use Ammonium Chloride or simply add aluminium foil(within the periodic table and reactive series) and let it do an exchange. This will drop all metals as either a brown or fine black powder which could also include any gold you have missed. Also if anything goes wrong during the initial precipitation process and you think you have lost metals simply dilute your solution with 50% hot water water and add a small amount of hydrochloric acid and add aluminium. Ensure there is enough hydrochloric to maintain a pH for the aluminium to work.

Undertake your dissolution again with your Aqua Regia on your dry powders and follow the precipitation process/recovery process. Never throw or discard solutions until these are finally tested with aluminium.

A further method to recover all metals from solution is to add Soda Ash slowly to a boiling solution. It will slowly neutralize. This will drop all of your metals as a black powder.

I would like to see more information on the precipitate Hydrazine Hydrate as I have never used it before. What is its industrial use? Can someone advise? I am presently developing a leaching process suited for the materials I am interested in locally.

If you are using aqua regia to dissolve boards etc, aluminium will recover your gold which you will see coming to the top as yellow gold powder or flake. Tin solder should be cleaned from pins and points using something like hydrochloric before Aqua Regia. This can cause problems later as it will also bring down your metals.

To be sure simply filter the powders and dry. Then boil in Sodium Hydroxide at a pH of 12 for about two hours to covert the metals to an oxide. Again filter and dry. Then place in an oven at 400 °C for about two hours to convert this from an oxide to metal.

I hope the above helps or that it can at least can rectify or get you out of trouble if something goes wrong.

Don Buckley
- Braidwood NSW Australia

May 25, 2009

Q. Hi,
I have just started with gold refining. I have dissolved my gold findings and gold plated pins in Aqua Regia; the solution turned a deep, almost black green color. I neutralized the nitric acid with Urea and added Ferrous Sulphate but nothing happened; no gold precipitated out of the solution.
Can you please give me advice?

Thanks in advance!

Johan Geyser
Hobbyist - Lephalale, Limpopo, South Africa

June 14, 2009

Q. Dear friends. I am a medical practitioner, age 61. I have been in practice for approx. 35 years. My serious interest in gold refining is triggered by the fact that the pension that I was promised will not materialize. I am stockpiling computer pins, CPU's, and gold fingers from the edges of boards. It is my aim to have 100-150 kilograms of pins, etc. before turning this into cash (income tax reasons.)I need all the basic help that I can get so as not to waste this opportunity. Sourcing material, i.e. computer boards etc, is not too difficult. I need a basic users guide book or something like it so as not to do myself in or injure anyone. I know the danger of reactive chemicals. Please help me with a workable solution to achieve maximum results. I must admit that I am enjoying the whole discovery to the envy of some friends and family!
I hope to hear from you soon. Many thanks. Mark.

Mark McDonogh
New experimenter - Pietermaritzburg. South Africa

July 22, 2009

Q. I have been working with this for about 6 months, but have spent a lot of time and money and work trying to drop and recover the gold out of computer boards and phone boards.
Use urea have followed directions I use aqua regia, I urea, I use sodium metabisulfite , I then start cleaning , Wash , then add back HCL, boil, then clean water, then ammonia, then water, then refilter.
Then I am getting my precipitant is almost a silver, nickel platinum color. I see specks of red. I use a torch gas MAPP with Air.
I then tried oxalic acid to drop with, then same cleaning process.
I can take criticism just please be kind. I tried last week after my precipitant dropped good color nice yellow powder. I used lye to boil trying to clean out anything left. I am still getting the same drop when heated. And the same platinum, nickel, silver color result when torched. Suggestions please.

John Gamel
retired ,income - helena Alabama

T-6 Leaching for Gold Recovery

November 17, 2009

Q. I recently started gold recovery and have used aqua regia but I heard using a method called T-6 leaching an easier method. Does anyone know the T-6 method?

Lynn Tucker
hobbyist - Elgin, Texas

November 11, 2010

Q. I am responding to Lynn Tucker of Elgin Texas who asked about T-6. I know it was a year ago. I just now found this site and would like to find anyone familiar with T-6.

Steve Rogers
- Denton, North Carolina USA

January 16, 2010

Q. I need an alternative for sodium metabisulfite/ferrous sulphate/ sulphur dioxide gas. apart from these what else can be used as a reagent in gold refining get 99.99%purity.

anil chavan
job work - sangli,mh,India

February 4, 2011

A. Dear Anilji,
Please use Hydrazine Hydrate to precipitate gold from Aqua regia after neutralising the solution with 25% urea solution.
This will give you the necessary result in recovering pure gold.

prakash v pai
- India

February 9, 2010

! For those who are a bit farther along in the chemistry side; I stumbled onto a patent using 1:5-ish ratio of Hydroquinone to Oxalic acid for a reducing agent. It works really, really well!
The purification steps after reduction cut down to virtually nothing. This is for clean solutions though, the oxalic acid brings down the house. The powder is a blend of particles 3 micron to 15 micron I believe.... thought I would share.

Donovan Vanderbloomen
- Lake Geneva, Wisconsin

May 19, 2010

Q. Hello,
First I want to admit I am not a chemist, I did take chemistry but I was doing my own experiments with the THC. So I'm chemistry limited and I hope you guys don't tear me up too bad for asking questions which to you are dumb. I am not a chemist but I am a metallurgist and I am puzzled when I read about all the work you guys go thru to isolate these metals with costly and environmentally dangerous chemicals? Do you do this for fun or to experiment? I ask because a good furnace can separate with very impressive results.

Harold Bawlcz
metals enthusiast - Chicago, Illinois

February 4, 2011

Q. Your kind attn: Mr.Harold Bawlcz,
metals enthusiast - Chicago, Illinois
I am quite curious with the separation technique you have put forward in this site. I would like to know more & am interested in trying out the same for better results.
Could you be more specific about separation of metals as mentioned by you?

Awaiting for your response.

prakash v pai
- India

September 23, 2010

! Hello,

I read with interest the observations regarding the recovery of gold.
It seems appropriate to use basic microchemical test to identify elements present in solution.
"liquid that is a brilliant blue or sometimes a vibrant green" may indicate copper is present : on dilution the solution is blue and adding hydrochloric acid, the color turns green.
I work on gold produced via transmutation of silver. The dissolution of silver with nitric acid then adding HCl , heating and filtering silver chloride gives a solution that contains copper (also part of the initial silver alloy ) and eventually gold.
Chromatography of the solution with n-butanol/HCl and the test with p-dimethylaminobenzilidenerhodanine, gives a reddish spot at the front of the eluent that indicates gold, sensitivity is 0.2 µg.

To recover gold from the solution (hundreds of micrograms) , I proceed, first, to a concentration of gold with ethyl acetate, then I treat again the organic phase : evaporation, dissolution by aqua regia, ... and precipitation with hydroquinone as recommended by Beamish, because this precipitant gives a workable precipitate free of copper and other elements.

To follow the precipitation of gold, I use chromatography of one drop of the solution with n-butanol/HCl and the test with p-dimethylaminobenzilidenerhodanine.

Albert Cau
- Toulon - Var - France

October 9, 2010

Q. 1. Can I use Sodium Sulfite (Na2SO3) to precipitate gold from aqua regia? What is the different if I use Sodium Metabisulfite (Na2S2O5), Sodium Sulfate (Na2SO4), and Sodium Sulfite (Na2SO3)? What is the best precipitant from all of that?
2. If I want to neutralize the water (there is no contain gold anymore), can I use Sodium bicarbonate (NaHCO2)? Are the rest of the metal will precipitate with the sodium bicarbonate, or only with Sodium Carbonate/Soda Ash the metal will precipitate?

Thank you, sorry if I ask too much.

Handy Tan
- Indonesia

September 25, 2011

A. Hi, mr. handy tan
you are using smb for Au precipitation, but according to my opinion it will be better to use ferrous sulphate. Second, for neutralisation you add urea and add zinc dust to reduce all metals, another thing is for recovering colloidal particles you add very few polyelectrolyte in your waste solution.

bhupesh mulik
lignin research centre - mumbai,india

September 11, 2012

A. I did my final paper on the gold precipitate from aqua regia solution using hydroquinone. It was so simple and attaining 99.99% purity after firing was an incredible delight.

Refining the silver chloride left over from the solution was a little more of a chore but I got to within 80%.

Just wish I could remember the book it was all published in.

Graham [last name deleted for privacy by Editor]
- ottawa ontario canada

May 19, 2012

Q. Hello. Can somebody help me how can I precipitate silver from aqua regia? Thanks.

Bujar Bakiu
- Skopje, Macedonia

May 21, 2012

? Hi Bujar.

There is nothing else dissolved in the aqua regia, just pure silver?


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

June 1, 2012

Q. Dear Friends,
Until now I see that, for the precipitation of gold from aqua regia, I can use "hydrazine hydrate, zinc, sodium metabisulphite and hydroquinone."
I study physics, so, no relation with chemistry. But all my energy is concentrated in this operation. Please help me sir.

Ingrit Xhomaqi
- Tirana, Albania

June 2, 2012

Q. Hello, I'm questioning myself, how can I separate the gold from aqua regia if I dissolve the e-waste. In the waste I don't get only gold, but a variety of dissolved metals.

Ingrit Xhomaqi
- Tirana, Albania

August 21, 2012

Q. Could anyone help me with recovering gold from sodium cyanide solution which we use to etch gold? We have recovered 97% but are unable to recover the rest.

ritesh dhakan
jeweller - mumbai india

February 16, 2013

Q. I want to use the aqua regia method to recover gold from my computer scrap. I thought I would start with some gold plated pins and foils off of fingers and RAM chips so I wouldn't have to worry about any ferrous metal contamination but I want to be sure about my process just in case. I am using hydrochloric acid and sodium nitrate instead of nitric due to the cost of nitric. I have the proper ratio to use after consulting the correct chart for molecular weigh etc. but the aqua regia mix is not my concern.

I am using sodium metabisulphite to precipitate the gold once dissolved but I don't want ferrous metal dropping too to ruin my gold. I am to understand that before adding the SMB that I need to kill off the nitric and lower the ph so no metal drops also. I also read you can add a little zinc. First I heard of the zinc but I thought the urea would keep anything but the gold from dropping. Starting with a small amount of non metallic plated pins and gold from board fingers separately in small amounts, I didn't think metal contamination would be a problem anyway but I want to be sure. After all metal is dissolved in aqua reqia and I add urea until reaction stops will this protect anything but the gold from dropping?

Please give advice because even though I will use small quantities for first test, I want to do it right. Then with more experience I will process my CPU's. Please tell me proper procedure so I can learn right. I will use peroxide/muriatic or clorox method to remove gold from fingers so I don't expect problems there but I am concerned about processing the pins. I know about washing the gold properly before melting and using borax but post is too long to give all details. Please give advice if this process will work without dropping any unwanted metals or if I need to add a process or do something different? Thanks in advance for any help!!

Joseph Smith
computer repair-self employed - Stanley, North Carolina, united States

June 27, 2013

Q. Hello everyone. I know that I can use sodium metabisulphite and sodium bisulphite to precipitate gold. But my problem is that those two products are very hard to find where I live. I got some sodium sulphite and I wonder if I could use that instead or can I mix it with something to get smb? Thank you in advance for any help or suggestions. Oh and I've seen all the other stuff one can use for gold precipitation but its all hard to get hold of. Thanks

Hannes van Loggerenberg
- Richardsbay, Kzn, South Africa

August 11, 2013

Q. Let me say first that your advice is excellent and very well phrased. Thank you.
I have tried to precipitate platinum and gold from a solution of aqua regia. Broken ceramic computer chips were covered with aqua regia and left to work over night. This was done in accordance with the C.M. Hoke book. The next step was to add water to the solution and filter out the broken computer chip pieces. Then the solution was boiled down to almost nothing and hydrochloric acid added and this was done a second time. Then I added 4 volumes of water. Not knowing if any platinum was present I added ammonium chloride to the solution and waited for the Platinum to precipitate. Nothing came down. I just had a blue green clear solution. I then added ferrous sulfate to bring down the gold. Nothing happened. I still had a clear blue green solution. I then boiled down the solution to one quarter of its volume. The solution became dark green with a yellow tint. It stayed this color permanently. I don't know what I did wrong and I don't know what to do next. Any help would be very much appreciated.

Gerry Braxton
- Romney, West Virginia, USA

Ferrous sulphate didn't precipitate the gold as it should, nor fizzle

October 23, 2013

Q. I use aqua regia to process some scrap gold from computers, everything went well up until the point where the ferrous sulphate didn't fizzle or show progress in dropping the gold mud. Can you tell me a solution to fix this problem? Or I have no choice but to dump the batch and use metabisulphate next time, as this is the first time I'm working with ferrous sulphate.

Keith Morrison
- Miramichi, New Brunswick, Canada

Is the recovered gold in the solution or in the black precipitate?

September 10, 2014

Q. This is a question for clarification on use of Sodium Carbonate for neutralizing CPU pins dissolved in Aqua Regia.
This resulted in formation of Blackish precipitate, which settled at the bottom on standing. Decanted Clear solution did not give any brownish Gold precipitate.
Now my question is where did I go wrong? Now where to find the Gold - in the Black ppt or Clear Solution? Please help.

Ashok Rao K
- Austin, Texas, USA

October 5, 2014

A. For neutralisation you please add more water and urea.
After addition of urea add slowly FeSO4 to precipitate gold.

bhupesh mulik
- mumbai,maharashtra,india

October 18, 2014

Q. Hi.

I am from UAE. Under our washbasin in our gold smith, there is mud where all the liquid from washbasin goes. Acid has been going down the drain since few years. We have collected around 100 kg mud (UAE sand) from below and got 1kg sample tested to find 2-3 gms gold.

We want to do the gold recovery from the rest of the mud available. I have got aqua regia chemicals, SMB, urea and all the apparatus required.

Here are my questions regarding it:

1) What treatment do I have to do on the sand before aqua regia?
2) how much quantity of each chemical I have to use for 1 kg of sand at a time?
3) What will be the best chemical to use for precipitating gold after aqua regia? SMB, Hydrogen Hydride or Ferrous sulphate?
4) Do I have to use UREA?

Please let me know.

Kind Regards,

Sati Mehul
GoldSmith - Sharjah, UAE

October 28, 2014

A. Dear sir,
You have a mud from washbasin.
You first dry that mud.
You got the 2-3 grams gold in wet mud or from dried mud? Which is more important for chemical use. Let me know whether if your work is related to gold or silver because method of drying mud using chemicals is more effective role in dissolution of silver from wet mud.
Kindly give me brief details.

bhupesh mulik
cac admixtures - mumbai, maharashtra, india

October 29, 2014

Q. Hi Bhupesh,

The mud that I removed was then burnt into ashes by me. So now it is just black burnt powder form.

Hope this helps. Please let me know what I should do next.



Mehul Sati [returning]
- Sharjah, U.A.E

November 23, 2014

A. Hi, sorry for delay of answering.
After burning mud, Sieve this material by sieve of 300 micron mesh size. Remove iron particles by magnet from retained dust from sieve.
Passing dust taken in beaker, add aqua regia in it. Stay in it for 24 hours. Slightly boil to get rid of nitric acid by adding HCl slowly & carefully. Filter this solution. Neutralise by adding water & Urea. Then add ferrous sulphate to recover gold.

bhupesh mulik
cac admixtures - mumbai,india

June 3, 2015

Q. I washed off my steel wool cathode by aqua regia with excess content of HCl, and now gold is not precipitated by hydrazine.
What can I do? Please help.

Mohsen forp
tarbiat modares - tehran, iran

June 3, 2015

A. Offhand, I can think of 3 possibilities.

(1) There was no gold in the aqua regia solution to begin with. This can be tested with a drop of the solution combined with a drop of stannous chloride solution preferably made fresh - I use 1 g stannous chloride crystals dissolved in a mixture of 20 ml HCl plus 10 ml water. A white plastic spoon works well for this test. If it turns purple or black, gold is present. If it doesn't, try it again with a fresh drop of sample, dilute with 2-3 drops of water, and then add a drop of stannous solution. If still no purple or black, this would indicate that there is no gold in the solution.

(2) If all of the steel wool wasn't dissolved by the aqua regia, the gold could have cemented (reduced) back onto the iron in the form of a fine dark brown to black powder. With aqua regia, the iron wants to dissolve before the gold. If some gold does dissolve, it will immediately be reduced back to a powder on any remaining steel wool.

(3) There is still a lot of free nitric acid in the aqua regia solution. Until most all of this is eliminated, the gold may not drop. The standard way of eliminating free nitric is to evaporate the solution to a syrup, add a little HCl, evaporate, and repeat 2 more times.

Dissolved sulfamic acid can be used instead of evaporation to eliminate the nitric but it takes a lot of sulfamic acid and it is quite reactive when it is added. It converts the nitric to sulfuric acid and the nitrate ion is converted to nitrous oxide - laughing gas, N2O. The sulfuric causes no gold precipitation problems.

If too much nitric is the problem, this can be avoided next time by adding only enough nitric to dissolve whatever you're dissolving - no more, no less. This is done by covering the material with HCl, heating it slightly (to about 60 °C), add the nitric in small increments, each time letting the reaction die down before adding more. Continue until either the material is dissolved or a small nitric addition produces no reaction.

Chris Owen
- Nevada, Missouri

June 4, 2015

Q. Thanks for your kind reply.
Can you tell me about all methods that are used to destroy nitric acid in aqua regia?
Best regards

Mohsen forp [returning]
tarbiat modares - tehran, iran

June 10, 2015

! About the only one I haven't mentioned is urea. This doesn't really destroy the nitric but, if there isn't a great amount, it can suppress its effects enough so the gold can be precipitated. I haven't had much luck with urea so I never use it. Some people swear by it.

The very best way is to not add too much nitric to start with. It's quite easy to do this once you adapt to it. Beginners tend to add too much because it makes the aqua regia work a little faster. Patience is needed.

Something I always do before filtering the gold-bearing aqua regia is to dilute it first with 3 equal volumes of water. The purpose is that it will precipitate any silver present, as silver chloride, which is then removed by filtration before precipitating the gold. The reason is that silver chloride is much more soluble in strong aqua regia than in weak aqua regia. Also add about 5ml of sulfuric acid after diluting but before filtering. If any lead (often present in jewelry solder) is in there it will precipitate as lead sulfate. If you do these things, you will get much purer gold.

A bonus of the dilution is that the gold will drop much easier, even if you were a bit heavy-handed with the nitric. There are limits to this, however.

Chris Owen
- Nevada, Missouri

June 4, 2015

Q. Now, I surely know my problem was excess nitric acid; and can you tell me all of destroying method? Can I use urea for this purpose?
Thanks for your kindness

Mohsen forp [returning]
tarbiat modares - tehran, iran

June 28, 2015

A. Hi mohsen,
If you have to remove excess nitric you add hydrochloric acid which reacts with your excess nitric to form again aqua regia.

bhupesh mulik
cac admixture - mumbai,maharashtra-india

June 27, 2015

! Dear All, Hi to you all.
I am back, recently I found out that, many people add FERROUS SULPHATE to Gold Chlorate solution to precipitate gold. Actually it does precipitate gold but being a IRON salt it precipitates Iron in the solution and when the precipitated sponge is washed & dried & melted, and later when used for casting jewelry it gives HARD SPOTS. These hard spots are basically GRAIN REFINERS, like TUNGSTEN, RHUTHENIUM, SILVER, BORON, ETC... This creates a lot of problems in the production and a lot of material gets rejected due to this. Hence I tried precipitating with HYDRAZINE HYDRATE, which I have diluted to 1:5 to distilled water and after that I have added 100 ml of HCl to this solution. This when used for precipitating gold gave me 100% pure metal and there were no HARD SPOT inclusions on the cast jewelry. This was a revelation to me and all my productions are on time.

PRAKASH V PAI [returning]
Jobshop & hobbyist - navi mumbai, maharashtra, india

simultaneous June 28, 2015

A. Prakash,

I used hydrazine sulfate for years to drop gold from aqua regia solutions and the gold almost always had to be re-purified to meet the minimum 999.5 Fine purity required by much of industry. The gold drops made with the hydrazine were never as pure as those made with a sulfite or ferrous sulfate.

Hydrazine hydrate should work about the same as the sulfate as far as final purity.

There is no such thing as 100% pure gold. No matter what the purity is, if the only impurities are small amounts of copper, silver, and zinc, it would work fine, after alloying, for the casting of jewelry. However, being able to cast jewelry from it doesn't mean it is high purity.

Chris Owen
- Nevada, Missouri, USA

June 28, 2015

A. Dear prakash,
Ferrous sulphate is far better than hydrazine hydrate because hydrazine hydrate precipitate silver and I think it will be difficult to precipitate gold in carpet jewellery dust. Also you have to wash gold with HCl to remove excess ferrous. Than wash with hot water and check purity.

bhupesh mulik
cac admixture - mumbai,maharashtra-india

June 30, 2015

thumbs up signDear Bhupesh,
Nice to hear from you. Yes I agree to Ferrous Sulphate being used to precipitate gold from the solution is the best idea. But there is a problem, you cannot practically judge the amount which is required to be added to the gold solution. You always end up adding that little more & little more with a doubt in your mind. This is where the Iron and other metals precipitate and create problems. Here in India we have people who are not exposed to chemistry or chemicals or provided proper training. Hence they always end up making mistakes.
I was using ferrous sulphate before earlier. After you suggested me to use HH my results have been excellent. I may be wrong in saying that metal is 100% pure (as dear Chris Owen has mentioned), but it serves my purpose at the end of the day. There is absolutely no contamination in the cast pieces and the polished jewelry is very glossy & glittery.The icing on the cake is HARD SPOTS have disappeared. That is what I wanted.

Jobshop & hobbyist - navi mumbai,maharashtra,india

June 30, 2015

A. Dear prakash,
If you are satisfied with your results, than use hydrazine hydrate; but when I was refining I prefered FeSO4. For your information 1 kg of pure gold requires exactly 5 kg of FeSO4. Remember your gold solution should be neutralised & diluted properly.
At last I will prefer FeSO4. I was getting trouble while precipitating gold from jewellery carpet dust. At that time I used only hydrazine hydrate. It precipitates silver (point is more important).
While adding/precipitating, please check with your eyes whether it is more reddish in colour than normal.

bhupesh mulik
cac admixture - mumbai,india

June 30, 2015 --Sorry, this was misfiled and not posted until September

thumbs up signDear Chris Owen,
Thank you for adding another chemicals to my list of Gold Precipitating chemicals. I never knew Hydrazine Sulphate acts as a precipitant.. Just for your information all the refining I did I have got a purity of around 99.80% to 99.85%.... which I agree is not totally pure.But in our manufacturing 995 purity is acceptable & actually we do not need 999.99 purity metal, as we add alloy to it for recasting & reduce the purity. We do a fire assay of all the refined gold in house for our records as we supply jewelry to our customers. What i meant by PURE METAL is pure metal of our requirement level for castings. I agree that there is no such thing as 100% Pure metal.
Thanks for pointing my error ... do keep in touch.
Best regards,

thumbs up signDear Bhupesh,
I will try one process for the carpet dust seperately, & as per your instructions. As every month end we process the dusts fro production floor to recover gold for re castings.
Will definitely keep in touch with you regards, the same. As we have a in house Assaying system & a XRF machine I can check the same...
Best regards,

- navi mumbai,maharashtra,india

July 6, 2015 --Sorry, this was misfiled and not posted until September

Q. Dear Ted
Can we use Di Butyl Glime for precipitating gold from Chlorates? I have heard someone using here in mumbai and they are getting 999.999% pure gold from using this chemical.
Firstly, If "YES" can you please let me know how to use it, as I am very much interested in using the same for my productions ... better purity ... better production of the material.

Secondly, Can you explain the process to me please? Also recently we have changed over from using commercial grade chemicals to LR (laboratory reagent) chemicals to achieve the results. But cost-wise this is getting expensive. If I use Di Butyl glime the cost will also be cut down and will get 6 purity metal.
Awaiting for your reply.

Q. Dear Bhupesh,
You have mentioned that you used to have problems while processing the carpet gold.... can you please elaborate in short as to what kind of problems you used to face?
I did the refining process of Gold by HH for polishing dust but never has any problems. As per my calculations I always used to get what was supposed to recovered from that dust after reduction in furnace....
Also before using HH I am mixing (even today) 1:5 liters of water with (500 ml of HCL (diluted) to 5 ltrs of HH.This gives me a perfect recovery....& to add to this I used to get 999.5 & over at times with this process.
I feel that after reduction & aqua regia process you are not adding UREA to the solution before precipitating gold.
This process is very very important & removes NITRIC ACID & FUMES from the Gold Chlorate solution to be precipitated. It is this process which gives perfect result ... why not try once on your Carpet dust....? One has to apply the cleanest & the purest of process in order to get 999.5%.
By the way how about using Di Butyl Glime??? If yes how to use it ?? Can you explain to me ..
Awaiting for your reply..
Best regards,

PRAKASH V PAI [returning]
Job shop hobbyist and working as Senior Technical adviser Castings & Refining - navi mumbai,maharashtra,india

September 2015

Hi Prakash. Sorry, I'm the administrator of this site which focuses on metal finishing, and I know nothing of gold refining.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

September 15, 2015

thumbs up signDear Ted,
Sorry If i have stepped in on your shoes....was just exited about the issue of refining & solving Problems on the production floor recently.
Kindly, do advice me if i am over-stepping on the issues here on the blog by giving advice and being the administrator of this. Dear Ted, I offer my apologies in any way if I have hurt you..& request you to kindly forgive me.
Always willing to learn more from you...
Best regards,

PRAKASH V PAI [returning]
- Mumbai, Maharashtra, India

September 2015

Hi Prakash. No toes have been stepped on, and no issues have been over-stepped. Bhupesh, or anyone else, is welcome to continue trying to address your questions.

Sorry that you have misunderstood what I was trying to say, which is simply that I know nothing about gold refining and therefore I cannot personally answer the questions you asked me on July 6. Others are very welcome to try :-)


pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

September 17, 2015

thumbs up signDear Ted,
Thank you...It's a pleasure to be on this page and share the knowledge with others. It's the only way to learn & update your knowledge which I strongly believe in. Also this creates a win-win situation for both the parties. Kudos to you for starting this forum.
God Bless. Regards,

- Mumbai, Maharashtra, India

July 13, 2015

Dear Bhupeshji...

Good Morning to you....

I would like to know whether there is a alternative chemical to using Sodium Cyanide used in stripping gold from cast pieces to give shine below the diamonds before filing?

If yes, what is the name of the solution and how that can be used to strip gold?

Can you please guide as I am having a problem of black stones and want to give luster below the diamonds, as processing by the Magnetic polisher does not give the required shine and the jewelry looks dull and lifeless. Someone suggested to use Sodium Cyanide, but I am not comfortable with the idea of using it from the point of views of Handling & safety.
Please if anyone can shed light on this issue I will grateful. I need a reply for this message ASAP...
Thanking you
Best regards,
Prakash v Pai

PRAKASH V PAI [returning]
- navi mumbai,maharashtra,india

October 18, 2015

A. Hi prakashji,
This process of extraction of gold was discovered by morris & kahn in 1968. Why you want to know about butyldiglyme: means dibutyl carbitol, E444.
When i was refining in jewellery, I burned the floor carpet in furnace, & the dust I was refining, got the salt when I added FeSO4. So I use hydrazine only for floor carpet dust.
You check that hydrazine also precipitate other metals with gold which may reduce your refined gold purity.
I'm 100% sure that hydrazine hydrate affects your refined gold purity, also check your melting loss. I had all this statistical details. You have XRF -- very good.
Did you check the concentration of gold in yr gold dissolved solution?

bhupesh mulik
cac admixtures - mumbai,india

July 13, 2015

My experiment failed. I lost my gold.

Sir, I started with some gold pins and I add 30 ml nitric acid 90 ml hydrochloric acid. I mixed into the beaker after I get light yellow color royal water. I mixed the royal water into the pins beaker. It started the reaction, it is getting dark green color. The reaction continued 2 hours. After I take the green water and poured the filter of another beaker, and I put the urea in the tape worm water to mix the dark green water. But it's not taken action. It's not fizzing. After I put the sodium metabisulphite. I put 3 spoons. It's fizzing but it's not neutralized. So I mixed the SMB with hot water and poured the green water. The sodium metabisulphite is settled under the beaker. It's a white color powder and black color powder. It's not mixed and neutralized. I am not mixed distilled water. Could you please tell me the fault of my project? I live in hill station so it's always cold, and now it's rainy season. Could you please tell me what temperature should be maintained in this process? I have a hot plate. Please explain how to do this process. Thank you so much for helping me. Note: today I used the hot plate but no use.

joseph jayan
- the nilgris, tamil nadu ,india

October 18, 2015

A. Hi joseph,
You first check whether your green coloured solution contains gold or other metals? If it contains gold, add ferrous sulphate FESO4. and check whether brown coloured power settles down or not?

bhupesh mulik
cac admixtures - mumbai,india

October 26, 2015

Q. What are the major reaction equations involved in the precipitation of:
a). Gold
b). Urea,
using Precipitation Gravimetry

Hillary Jacan
Makerere University - Kampala, Uganda

December 25, 2015


Thiourea, CSN(NH2)2 is an organic compound which dissolves easily I acid solution in a stable molecular form. Gold dissolves in acidic thiourea solution to form a stable complex,

2Au + 4CS(NH2)2 + 2Fe3+ = 2Au(CS(NH2)2)2+ + 2Fe2+

In the thiourea reaction, ferric iron is used as an oxidizing agent, whereas the cyanide process uses oxygen from the air, dissolved in the leach solution. Part of the ferric iron needed is most the time present in the ore. In the case of highly oxidized ores, enough ferric ions will be set free, and then the addition of an oxidant can be reduced. But these ores could content higher amounts of carbonates, which will increase the acid consumption. One could use hydrogen peroxide, sodium peroxide, ozone, potassium permanganate or formamidine disulphide as oxidant; however ferric ion is the most effective.

Formamidine is interesting because it can be formed in acid solution by the thiourea oxidation by the presence of an oxidant agent such as ferric iron. Successfully leaching of thiourea depends on an understanding of the role of formamidine which is a compound very active during gold leaching.
In the first step thiourea is oxidized to formamidine disulphide,

2CS(NH2)2 + 2Fe3+ = C2S2(NH)2(NH2)2 + 2Fe2+ + 2H+

Oxidation thiourea is reversible. Thus, with a specific reducing agent, formamidine can be converted back into thiourea. In the next step, gold is oxidized by formamidine and forms a cationic gold thiourea complex,

2Au + C2S2(NH)2(NH2)2 + 2CS(NH2)2 + 2H+ = 2(Au(CS(NH2)2)2)+

Formamidine acts as an oxidizer as well as a complexing agent, supplying about 50% of the ligands to the complexation. This explains the higher leaching rates observed with thiourea compared to cyanidation. The general reaction is as follow,

2Au + 4CS(NH2)2 + 2Fe3+ = 2Au(CS(NH2)2)2+ + 2Fe2+

Thiourea must be present in a stoichiometric excess. The ratio of complexing and oxidizing agents must be carefully adjusted. An uncontrolled oxidation of the thiourea solution will lead to unwanted reagent consumption.

bhupesh mulik
cac admixture - mumbai india

Sodium Borohydride for Gold Recovery

January 11, 2016

Q. I want to make recovery for gold from cyanide solution, and I was told that NaBH4 can be used in recovery as precipitator; is this possible, and what is the procedure?

Mohammed Mustafa
- Jeddah, KSA

September 20, 2016

Q. My Dear

I dissolve sand oxides & sulfides in aqua regia and there is palladium, platinum, gold, etc... my problem when I precipitated it with Sodium metabisulfite the precipitation turns to red and then to colorless and then to yellow solution and in the bottom is white powder.
Please I need a method for precipitation.

Ali Abd
- Iraq,Balad

September 5, 2017

I am having precipitation problems myself. I did the muriatic/peroxide method. Filtered and filtered again to get it all. Rinse the filters in muriatic acid, then added SMB, very little gold.

I'm sure I am missing something simple here. Any help would be appreciated!

Jacob Schwanke
- St. Cloud, Minnesota

September 2017

Hi Jacob. I don't have an answer, but I do have a question: what do you consider "very little gold"? Why do you expect to get more -- have you had the stuff assayed so you know what to expect? Your process may be 1% efficient and desperately in need of improvement, or it may be 99.99% efficient. If you are processing gold plated scrap with a few millionths of an inch of plating you would have to process an awful lot to recover non-negligible gold.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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