# sulfuric acid will it digest silver? & more



## Anonymous (Dec 22, 2007)

Hi all,
Got my old books out from chemistry class, circa 1982 wow that was long ago. Any who, my question is will sulfuric acid digest silver, now, I know I could just go out to the shed and drop some of my material in there and see what happens. But it is kinda cold outside, and I do not have heat in the shed, so I am really just gathering materials until I get heat or spring arrives. 

My other question is if I add KNO3 to my Sulfuric will it digest the base metals the same or nearly/similar to actual nitric. I would like to not make nitric or buy it since I have learned from this forum the hcl/cl and hcl/ap methods and they make sense to me. Thank you all very much. 

3rdly, if the solution of KNO3 & sulfuric does digest the base metals including copper and silver and leaves my gold that would be great, I could filter clean and reprocess etc. Now I was thinking, if I precip the silver with copper until all of the nitrate is used then evaporate the water, either the KSO4 or the CuNO3 is going to precip out of solution first then I could filter and recover the CuNO3 and heat to 170 C causing it to degrade to Cu and HNO3 and have a complete cycle from that point on
seriously reducing the need to buy sulfuric, nitric or KNO3.

Jim


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## lazersteve (Dec 22, 2007)

Jim,

The basic principles of what you proposed are correct, but there are a few drawbacks to your proposed method.

Cold sulfuric acid won't dissolve silver very quickly, but it will work. Hot concentrated sulfuric acid will dissolve silver very well. As the acid cools and/or becomes diluted a good portion of the silver sulfate will precipitate.

Mixing the sulfuric acid and salt peter will form dilute nitric acid mixed with a salt (potassium sulfate) which will precipitate partially from the solution depending on the temperature and concentrations of the solution. If you do not completely separate the salt at this stage it will be mixed in your gold powder/foils once the nitric acid dissolves the base metals in your reactions. 

If you don't control the amount of water in the reaction your nitric will be very weak and won't work very well. 

If you don't lower the temperature of the sulfuric acid /salt peter solution below zero degrees C for a short period before you pour off the nitric acid from the potassium sulfate salt, you will still have a good bit of salt peter dissolved in the solution. This potassium salt won't allow the solution to absorb the optimum amount of base metals and the sulfate could also precipitate certain base metal compounds.

Obtaining nitric acid via copper nitrate thermal decomposition is a fairly simple procedure which is very viable, leaving you with copper oxide powder to dispose of. I would advise that you use a good lab glass rig when performing this reaction as NOx gases can be lethal if inhaled. Of course all the proper safety equipment is a mandatory requirement.

The cold method of nitric acid is not a complex experiment and requires minimal equipment and no distillation. You can find this reaction in the Guide to the Forum link under the Guided Tour link below my signature.

It is best practice with any chemical reaction to follow the rule GIGO (Garbage In = Garbage Out) especially when trying to refine a precious metal like gold.

There are many conditions under which a certain mix of chemicals will accomplish a desired goal, but there are only a few of these combinations that will produce the desired results with minimal contamination. By controlling what you add to the reaction at each step you greatly increase the purity of your output product.

Even when using AP and HCl-Cl you need to practice proper safety. These methods are, by their very nature, slower than aqua regia. 

Steve


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## Anonymous (Dec 22, 2007)

Thank you. My main concern is using the sulfuric to get the silver. The stuff I am going to process will be 90 percent + silver and I do have the ability to to apply heat to the flask while processing, (just not my shed).
I believe that even if some silver sulfate did drop out I could wash it out with water when I filter the left overs which should be any gold or pt which may be contained - small chance, but possible - then use the hcl/cl to get the gold dissolved and leave an pt to worry about way down they road when I eventually have enough to worry about. Make any sense?
If this would work I would then dissolve any silver sulfate and cement with copper then decompose the copper sulfate to get my sulfuric back then use the nitric process once I have enough gold to be worth my time just like the pt.

Guess, I'm just being hard headed on not wanting to use the nitric or to reduce it to the very minimal possible. I have to say, I have been reading
through the forum since I joined and you guys are great. This place is like the flint knappers forum everyone is helpful and friendly, I can not believe people would steal your information when you give it so freely and openly and they could just use it to honestly make a buck.
Thanks again and hopefully someday, I will be able to actually contribute 
to the forum.

Jim

jim


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## eagle2 (Dec 25, 2007)

Hello James:

I would like to add that Silver Sulfate is slowly soluble in 125 parts water, 71 parts boiling water (My Merck index).

This means 1 part of your precip to 71 parts of hot water will dissolve.

Also if this helps Silver Sulfate is soluble in Ammonia. Gold and Pt would be untouched. But be sure to eliminate all Ammonia before going on to the next step.

Al


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## goldsilverpro (Dec 25, 2007)

An old method that is still used for dissolving silver from hi-silver, lo-gold dore' bars was to use boiling concentrated sulfuric acid, with nothing else added. I think they used fine-grained white cast iron vessels. The process is very, very dangerous. It is detailed in T.K. Rose's, "Metallurgy of Gold".


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## Anonymous (Dec 25, 2007)

Yes, 
I have have been doing some more research and have found that 
using sulfuric at high concentrations for inquartation was practiced but is not recommended because the sulfuric acts as an oxidizer. I am not sure but I believe from what I was reading the process would not yeild
CuSO4 & AgSO4 but CuS & AgS compounds. This would not fit into my plans of reusing my acid by decomposing the CuSO4. So, I will take
the information and advice from you well experience guys here and make the nitric and use it. 

Your sage advise has saved me from having wasted some time finding out the hard way with a sample that I would have not gotten my desired result.

Thanks.

Jim


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