Can gold be dissolved in sulfuric acid alone?

A. No winner; donate the kitty to charity :-)

Gold cannot be dissolved in sulfuric acid to my knowledge; but it can be dissolved in a number of things other than aqua regia, including cyanide, citrates, and sulfites.

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

on AbeBooks

or eBay or

Amazon

(affil links)

A. No. The only acid that dissolves gold is aqua regia. How much did you win?

Ted is of course right. Gold will dissolve in cyanide and citrates but, as far as I am aware, only with the application of an electric current.

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August 2014

Thanks for correcting me gently, Trevor. Surely I was guilty of mental sleight of hand when I tried to equate using electricity and cyanide to dissolve gold with dissolving gold by simple immersion in aqua regia.

Regards,

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

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! Trevor Crichton, Gold dissolves in cyanide solutions without application of electric current. Witness use of weak cyanide solutions for recovery of gold by heap leaching.

Fuzail Siddiqui
Independent Consulting Geoscientist - Markham, Ontario, Canada
September 16, 2014

"Can gold dissolve in sulfuric acid alone?"

A. The answer is yes, and no. According to a 1940 patent #2185858, gold or palladium are stripped from a copper based substrate by making the parts anodic in a fairly concentrated sulfuric acid solution. According to the patent, persulfuric acid is produced at the anode surface, which momentarily dissolves the gold. Once away from the anode, the dissolved gold immediately reduces to a powder. When all the gold has been stripped from the parts, the current goes to zero. All the gold powder settles to the bottom and is then collected.

I guess the keyword in the original question is "alone." The gold does dissolve, using no other chemical than sulfuric, but it does require electrolysis.

I have used this stripper many 100s of times for gold recovery from plated objects. It works for many substrates besides copper, even aluminum.

A. Sulfuric acid can dissolve gold, but it is a very dangerous process as the sulfuric acid has to be concentrated and heated to the point sulfur dioxide gas is fumed off, silver or gold will dissolve gold will form a gold persulphate soluble in the very concentrated acid, upon dilution the gold will precipitate out of solution as a powder which can be washed and refined. (Another terribly dangerous process) (never add water to concentrated sulfuric acid a steam explosion of hot acid can go everywhere)(always add acid to water slowly to dilute), concentrated boiling sulfuric acid can disable a man for life,and a little bit of gold is not worth the risk.

Another way gold is dissolved in concentrated sulfuric acid is by making the gold an anode the persulphate that forms at the anode will dissolve the gold into solution as gold persulphate, but as these gold ions migrate towards a lead cathode the gold is no longer a persulphate in the more dilute solution away from the anode, so the gold will precipitate in the cell, again gold is recovered by dilution of the acid (see warnings above), this impure gold is washed and then refined

People who would re-plate silver would use a process similar to this to remove the silver from copper or brass items (the concentrated sulfuric would not attack the copper or brass (as long it was kept concentrated), they would use electrolysis and about 5% HNO3 added to the electrolyte to strip the silver plate, silver plated article was on the anode.

To dissolve gold or platinum there are several ways to do this besides aqua regia.
Aqua regia is not the only thing strong enough to dissolve gold and form a gold chloride solution.

HCl and NaCLO 5% sodium hypochlorite (household bleach) ⇦ bleach/sodium hypochlorite in bulk on eBay or Amazon [affil links] will also dissolve gold and form gold chloride

HCl and 30% H2O2 Hydrogen peroxide will also dissolve gold to form gold chloride

There are other oxidizers that will work.

There are even salts that when fused with gold can make the gold water soluble when the fusion is dissolved into water.

Hi, Kathy. You might talk to a vet; I don't think your dog's stomach has the capacity to dissolve gold.

Regards,

Thank you for your response. Seems like a good blog, although most are probably trying to stay warm rather than typing with cold fingers!

Hello Ted,
Thought I would let you know the outcome of my dog swallowing the earring. Yesterday my dog walked out into the kitchen to exactly where I stand to dish up his food and left my gold earring on the floor for me to find ! I happened to be watching him out of the corner of my eye and he just set it down and walked away. Since I had cleaned the house from top to bottom, we are for sale down here, the only thing I did not do was check "in his bed" ! I don't know where it came from, but I would have to guess that he had taken it back there to play with. In perfect condition, both the earring and the dog ~..~ Thank you for answering my inquiry, stay warm. Best Regards.

Hi, Kathy. Thanks for sharing the happy ending.

Regards,

Interesting reading about the dog.

When you say it brought put the ear-ring on the kitchen floor, do you mean that it carried it in in its mouth, and put the ear-ring on the floor ?

or ... he did his Doggy Duty on the kitchen floor, and his special gift contained the ear-ring ?

I had food poisoning twice in 2002. I learned more than I would have liked about stomach acid.

What I was looking for was info about dissolving gold, what types of solvents & acids work.

Lots of good info here !

A. Yes, KI + I2 is a common gold stripper, especially in the electronics industry. These chemicals are quite expensive, but there schemes which precipitate the gold and rejuvenate the solution for further stripping.

Hi Yuuto. Despite your suggestion that we should live long, I'm probably not going to hold on for 30 more years -- could you please move your timetable up by a few years? Gold is very corrosion resistant but not too strong; high strength stainless steels don't dissolve in much though. Good luck.

Regards,

A. You could try adding urea. That precipitates gold from aqua regia. Or, zinc powder, or steel wool. Either would dissolve producing hydrogen and the gold would deposit out.

A. No offense, but I must disagree with Dave. Urea will not precipitate gold from an aqua regia solution. The most common gold precipitants are some form of sulfite, such as sodium sulfite, sodium bisulfite, or sodium metabisulfite. Less common but still viable gold precipitants are ferrous sulfate ⇦ this on eBay or Amazon [affil links] or oxalic acid.

If the worker uses too much nitric acid in the aqua regia, the sulfite will react with the excess nitric before any gold will precipitate with the sulfite. Urea is often used first to tie up the excess nitric so that the gold will precipitate when the sulfite is added.

It is better to use sulfamic acid to eliminate the excess nitric. Urea is a poor choice because, when there is a lot of excess nitric, crystals (urea nitrate, I think) will form in the solution. With sulfamic acid, the reaction products are sulfuric acid and nitrous oxide (laughing gas). Also, sulfamic acid decomposes the nitric, whereas urea somehow prevents the nitric from interfering with the sulfite but doesn't decompose it (as I understand it).

No matter what you use, a good fume hood is a must.

I stand corrected, then. Sorry if I confused anyone. I used to analyze the wastewater from a company that did gold refining (very highly mineralized - after the evaporation that came with the digestion, on cooling half of it would solidify) and they gave me to understand that they used urea. I guess I misunderstood.

My impulse would be to use steel wool.

? Hi Fred. You are asking how a person with no chemical knowledge, and unable to obtain either borax nor any acids, should dissolve gold, a metal prized for millennia for many reasons including being virtually non-dissolvable? But what do you mean by your "foils"? Thanks.

Regards,

Hydrofluoric Acid


"HF burns, not evident until a day after"
by Dr. Charles Eaton
(http://www.handcenter.org/resumee/resumee.html)

A. Hi Joshua. I don't know much about gold refining, so we'll have to see if some other reader helps you, or you can search the site for many other threads on the subject. But you are dealing with very dangerous stuff in HF. Many professional platers who hardly give a second thought to most acids or hexavalent chrome or cyanide are quite frightened by hydrofluoric acid. You are also possibly even dealing with complete unknowns (just because a drum you found in the woods is labeled as originally containing sulfuric acid doesn't mean that's what was in the drum when you found it).

Regards,