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topic 34532p2

Solution for precipitating gold from HAuCl4 solution

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A discussion started in 2005 & continuing through 2017

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"

September 7, 2017

Q. The gold plating on electronics usually ranges from about .001 to .01 grams of gold per square inch of gold plated surface area. In rare cases, you might find gold that runs .02 grams per square inch. In any case, there's not much there unless you have a lot of gold plated scrap. The higher number (.01 g) is found on parts that will experience wear, such as circuit board fingers or connector pins. The lower figure (.001 g) is mainly for corrosion resistance or solderability on non-wear surfaces, such as the boards, themselves, in cell phones.

So, specifically, what type of scrap did you run? How much weight of that scrap did you run? How much muriatic and peroxide did you use? What strength peroxide did you use? Did you test the solution after precipitation with stannous chloride solution, to see if all the gold was precipitated?

The process you used has been discussed 100's of times on the forum at That is the largest and most complete forum of that type on the internet.

Chris Owen
- Benton, Arkansas, USA

Problem precipitating gold

October 12, 2017

Q. Hi, I have an HAuCl4 solution (no nitric acid) of about 0.12 g of gold per liter.
I tried To precipitate with sodium metabisulfite but no gold had precipitate.
Thank you for your help..
Note: i made the solution using HCl and hydrogen peroxide and the solution turned yellow.

Pierre julien
- St-Adolphe d'Howard, Quebec, Canada

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