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How to precipitate gold from HAuCl4 solution

Q. @Don_Buckley, Hello sir how are you?

I ask these questions very late:
1, Is 98% sulfuric enough to remove any impurities from our gold powder, i.e. bringing it to 999.9 purity? Although it isn't as strong as Aqua-Regia but it can certainly get the job done right?
2, What temperature is required to boil Sodium hydroxide containing HAuCl4 powder for two hours?
3, When you say it converts from oxide to metal when heated in an oven at 400 °C (can burn filter paper), can it be brought directly to a furnace afterwards or should it be re-purified?
4, Will the above method work if I have HAuCl4/AuCl3 in moist powder form?

Anxiously awaiting to hear from you.
Best Regards.

J Naj
- Karachi, Pakistan
July 12, 2022

⇩ Related postings, oldest first ⇩

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.

"Refining Precious Metal Wastes"
by C. M. Hoke

on AbeBooks

or Amazon

(affil links)

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 ferrous sulphate [affil links], 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.

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

I am also on the lookout for books by C M Hoke ⇨
and 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

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

Q. Kind 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.

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

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
May 22, 2010

Q. Precipitate gold from aqua regia. I'm investing about gold precipitating from aqua regia. I know sodium metabisulfite, ferrous sulphate ferrous sulphate [affil links]. But I want to learn more about hydrazine hydrate, SO2, formaldehyde, hydroquinone and oxalic acid [affil links]. 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

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
February 12, 2008

"Recovery and Refining Of precious Metals"
by C.W. Ammen

on AbeBooks

or eBay or


(affil links)

A. Hi, cousin Mohammad.
It sounds like you're looking for a good book covering the whole subject? Prakash named a good one, "Refining Precious Metal Wastes: Gold, silver, platinum metals" by C. M. Hoke; another good one is "Recovery and Refining of Precious Metal" by C. W. Ammen

Readers are probably happy to answer specific questions, but probably find it difficult to explain an entire process step by step in a posting of appropriate length for a public forum :-)

Good luck, and Thanks!

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey


A. There are many options, too many to start from the beginning here. There is a free forum called the gold refining forum Everything is documented there and you will get answers from industry professionals.

But by all means start with Hokes' book, which you can download free from the refining forum as well.

Rick Hoff
- Pennsylvania USA
July 13, 2022

thumbs up sign Thanks Rick! We're happy to acknowledge the efforts of other sites; each has its strengths.

But some readers might like it here, where our strengths include aloha, education, fun, freedom from pop-up & anchor ads, no registration or passwords, and 33 years on the air :-)

Luck & Regards,

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


February 22, 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?


Sal Ammoniac

Ivan Christianto
- Salatiga, Central Java, Indonesia
March 19, 2008

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

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 does 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
June 27, 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

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 9, 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 [on eBay or Amazon (adv.)] 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

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
October 20, 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 sulphate 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 I have no idea what your "finishing not financing" complaint is supposed to mean :-)
We have dozens of threads about precious metal refining and many very helpful & knowledgable responders. There's not always a clear distinction between finishing and gold recapture because recovery is a necessary operation in every precious metals plating shop, as is stripping of gold from various substrates, etc.

Prakash said "... on the lookout for books by C M Hoke ... I would like to buy these books if they are available ... awaiting an early response", but you feel that we shouldn't have answered him because "no one is going to buy the book. They want to use the internet" :-)

People must have books and reputable support materials! Can you imagine being on the witness stand after someone was maimed or killed in an accident (I've been an expert witness on such cases several times), and trying to justify that you don't believe in books, so you proceeded on internet forum advice from strangers?


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

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
January 29, 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 6, 2009


thumbs up signHi Ben, hi Eethr. That recommendation is offered frequently on this site.

But, readers, please try to contribute at least a little technical content in postings. Links go bad and people will want something besides the distraction & frustration of broken links. Plus, some people like this site for various reasons, including that we are one of the very few which doesn't require registration or passwords, meaning there is no concern about hacking.

Thanks again!


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

What is AURO 8032 Gold Precipitant?

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
August 25, 2008

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

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
March 17, 2009

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

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
August 12, 2010

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

amit mehta
- Mumbai, India

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
April 22, 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
June 13, 2010

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 bisulphate in the US I would appreciate it greatly.

William P. Momani
- Yardley, Pennsylvania
March 20, 2009


- New Delhi, India
June 11, 2012

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
January 15, 2013

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

abdo alarbi
March 15, 2009
small shop - Tripoli, Libya

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

! 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 Metabisulphite 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 [affil links]. 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 Metabisulphite (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
April 3, 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 ferrous sulphate [affil links] 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
May 25, 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
June 14, 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
July 22, 2009

T-6 Leaching for Gold Recovery

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 17, 2009

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
November 11, 2010

Q. I need an alternative for sodium metabisulfite/ferrous sulphate ferrous sulphate [affil links]/ sulfur 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
January 16, 2010

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 4, 2011

! 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
February 9, 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
May 19, 2010

? Your kind attn: Mr.Harold Bawlcz
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
February 4, 2011

! 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
September 23, 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 sulphate (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 / washing soda [affil links] the metal will precipitate?

Thank you, sorry if I ask too much.

Handy Tan
- Indonesia
October 9, 2010

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 ferrous sulphate [affil links]. Second, for neutralisation you add urea and add zinc dust [on eBay or Amazon (adv.)] 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 25, 2011

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
September 11, 2012

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

Bujar Bakiu
- Skopje, Macedonia
May 19, 2012

A. Silver is insoluble in aqua regia as AgCl, a very small portion will dissolve in a high chloride solution as AgCl2, diluting the aqua regia with water will lower the chloride content and convert AgCl2 into insoluble AgCl.

Basically you will not have much silver dissolved in aqua regia because it forms an insoluble salt of silver.

Richard Butcher
precious metal refiner - Selma oregon
September 13, 2019

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