Gold Refining

[GAHD]

I was looking into gold refining and came across a lot of information on Aqua Regina. While I found quite a feww step-by-step articles, I have yet to find anything that explaines exactly why mixing these acids can dissove gold.

 

Anyone care to lent this old phogy some help in the matter? (pardon the pun)

[gpdone]

It's been awhile but this may serve as a starting point;

Fisrt of all I've never heard of Aqua Regina out side of classical Lit. It sounds like a brand name for something. If it is uric acid in solution that would make sense heap leaching gold wise as uric acid acts to corrode (oxidise) iron in which much native lode gold is found in association. In addition uric acid or urea the chrystal when heated during electrolysis produces cyanide (the primary agent for leaching processes for precious metals)which further creates micron gold for deposition on the plates. This is from years ago research into mining methods and hopfully will be clarified or corrected by a for real Chemist!

Good luck,

 

Lee

 

PS DONT try this at home. Cyanide is DEADLY even in small amounts so no heating you urin on the stove just to see what happens!;-)

[Tim_Lou]

yeah, cyanide performs a complexation reaction with gold.

well, i dont know much, here is some info found on the internet:

http://doccopper.tripod.com/gold/AltLixiv.html

 

"Au + 2CN - = Au(CN)2 - + e -"

the gist of the whole article. : )

*notice Au(CN)2- is (CN)2, not 2- charged.

[Tim_Lou]

btw, cyanide is really poisonous, pure hydrocyanic acid (HCN, a gas actually) can kill a person in minutes.

 

"Cyanide gas is highly flammable and reacts violently in some situations (e.g., a largeamount of cyanide gas mixed with air may suddenly explode). There is an extremelyhigh risk of explosion if cyanides are exposed to heat or flames. Most of the safetyprocedures are aimed at preventing the substance from entering the human body andavoiding situations where cyanide solids or liquids might react to produce the highlypoisonous and flammable cyanide gas."

 

all credit from:

http://www.safetyline.wa.gov.au/pagebin/hazshazd0005.pdf

[GAHD]

My bad, Aqua Regia (Royal Water), not Aqua Regina.

 

From what I've gathered it's made with 1 part nitric acid to every 4 parts muriatic acid.

 

Gold will not dissolve in either of these acids alone but will dissolve when they are mixed into Aqua Regia.

 

Aqua Regia is also used for etching of other metals, but is relatively useless for dissolving Silver.

[GAHD]

*bump*

[UncleAl]

Aqua regia "royal water" is 3:1 HCl/HNO3 vol/vol that after mixing rapidly evolves nitrosyl chloride, (NOCl) and chlorine. Nasty and hazardous.

 

Dissolution of gold requires oxidation and complexation. Brine and air or hydrogen peroxide will do it (tetrachloroaurate(III) as end product), so will cyanide and air (tetracyanoaurate(III)). Aqua regia is a buzz saw for metallic gold, giving tetrachloroaurate(III) as end product. Metallic gold is typically recovered by oxalate reduction. Platinum is unaffected.

 

Presence of ammonia during gold recovery will lead to "explosive gold" with roughly the sensitivty and power of lead azide.

[GAHD]

'Buzz saw"? You mean just that it reacts quickly?

 

also,do you think I could recover pure gold from the end product with electrolysis?

[Turtle]

It is possible to recover gold from findings left from sluicing by simple smelting. :)

[thaupt]

I have been thinking of refining my own platinum and gold... I have found an interesting and not to expensive "Home refining" kit. The link is... well i was going to post a link... but the system will not let me. What I did was a google search for...

 

home gold refining

 

and found this.

 

shorinternational dot com slash RefineStart dot htm

 

It seems simple enough and no harsh chemicals always a plus.

[Mercedes Benzene]

Here's an interesting bit about aqua regia (one of my favorite chemical solutions!).

 

"It has been said that James Franck, the Nobel Prizewinner, dissolved his gold metal in aqua regia in 1943 to prevent it falling into the hands of the Nazis when he fled Denmark, and left it unobtrusively in his laboratory. When he returned in 1945 the bottle of acid was still there, so he reclaimed the gold and a new medal was struck."

[Scrib]

In regards to the post about Shor products. The chemicals they sell can be had for pennies on the dollar from ebay, hardware stores and home brew stores. The information they provide sounds really good when your in the gold fever phase but be careful, they are selling a myth. I know this from experience.

 

As far as Aqua Regia (AR) goes. I've dabbled with it with limited results. It's not for the faint of heart. The chemicals and fumes are VERY DANGEROUS. For the hobbyist, like myself, I recommend using acid-peroxide. It's safer, in comparison, to AR and much easier if your working with limited equipment and access to materials. Good luck!

[aogneun]

Hi,

 

Aqua Regia, a combination of nitric acid and hydrocloric acid, mixes quitly.either acid may be poured into the other.It's a very aggressive liquid. As soon as mixed, the aqua regia start to form and slowly emits chlorine gas for a day or two. Aqua Regia containers must NOT be closed. Thje chlorine pressure in a closed container can produce enough pressure to break the bottle. It should be stored in a suitable fume hood.

 

The dissolution of metals by aqua regia produces an oxide of nitrogen that is a colorless gas. However, as soon as this oxide of nitrogen reaches air, it combines with oxygen of the air and forms a reddish brown fume. This is choking , coorosive and toxic gas.

 

Gold can be refined in a number of ways. There are special rteasons for use these different methods. Some proccesses are very very old. a few where devised in the late 1800's. Some methods are fairly new but these tend te be applies to specialized needs.

 

The disadvabtage of Aqua Regia method is that it requires strong acids, produces rather vile fumles and the leftovers barren solution is a pollution problem.

 

Gold chloride is formed when aqua regia digezst gold scrap.

The reaction of the aqua regia with the metals in the scrap produces nitrogen oxides. When the alloy contains about 8 to 10% of silver an adherent layer of silver chloride forms and "protects" the metal from dissolution. Melting and dilution with copper is the only reasonable way of dissolving high silver material.

 

When the gold content of the scrap is below 30% any copper and silver present can be dissolved with nitric acid.

 

FILTERING:

 

The aqua regia now contains various metal chlorides in solution and insoluble silver chloride as well as a lot of unwanted material in the sludge, and the mixture muqt be cooled and filtered; reason for cooling is that the silver chloride; quite insoluble in water, is slightly soluble in stron,g acids and this solubility is lower in cold acids.

It is gopod practice to add a little sulfuric acid to the dissolution vessel before filtering. When there is lead in the scrap it forms a very hard to filter gelatinous material ( also true for tin). The the aqua regia solution has to be filtered with a bucher filtering funnel. After filtering the filter paper contains the unwanted material (also silver chloride). The filtered liquid is usually a rather handsome clear green color, due to nickel and copper. If only gold chloride were present, it would be yellowish.

 

The excess aqua regia that was added to insure complete solution of the gold is still in the solution at this stage and must be eliminated at this stage to allow the gold to be precipitated.

 

The classic procedure for nitric acid elimination is repeated boiling to near dryness with trhe addition of hydrochloric acid with some sulfuric acid near the end. There are a number of other chemical methods to eliminate the nitric acid... see use of Urea (carbamide)...

 

PRECIPITATING THE GOLD:

 

The classic method of reducing gold chloride in solution to solid gold is to add "copperas" to the solution. (=ferrous sulphate)also can use hydroquinone (experimantal use). Also other procedures excists. Copperas is prefered also because it leaves platinum in a chemical state easily changed to an insoluble condition. Also other procedures excist with for example sodium bisulfite, sodium sulfite, sulfur dioxide gas can be used as reducers.

 

Thge end point is easily determined by a test for the presence of dissolved gold (stannous chloride test) ... i can tell you receipt if needed.

 

Filtration:

 

When the solution has been cleared of gold it should be allowed to stand preferably overnight. Althought gold is heavy and most of it settles quicly, some particles are very small and require time to go to the bottom.

Before doing any filtering the solution is tested with the stannous chloride test)

 

Washing The gold and Melting the gold.... etc....

 

GOLD CHEMISTRY:

Aqua regia is a mixture of hydrochloride and nitric acids.

 

Au + HNO³ + 4HC1 = H²O + NO + HAuC1(4) as for all chemical formulas i will have to send them by mail .. if your interested you mail me at [email protected]. i will send you a copy of some pages in proffessional literature about gold refining.

 

Hope i helped a bit in your search..

 

all the best...

 

Frederic Carpentier Buddy's Gold Belgium Brugge.

 

Specialized in Antique jewellry , watches , precious gemstones, etc...

You always welcome with any questions regarding jewelry. Actually refining is not my speciality. I'm more into antique jewelry and watches.

:hihi: next year our website will be online CRE Loaded 6 - AllTimesjewels online store

[aogneun]

Hi,

 

Aqua Regia, a combination of nitric acid and hydrocloric acid, mixes quitly.either acid may be poured into the other.It's a very aggressive liquid. As soon as mixed, the aqua regia start to form and slowly emits chlorine gas for a day or two. Aqua Regia containers must NOT be closed. Thje chlorine pressure in a closed container can produce enough pressure to break the bottle. It should be stored in a suitable fume hood.

 

The dissolution of metals by aqua regia produces an oxide of nitrogen that is a colorless gas. However, as soon as this oxide of nitrogen reaches air, it combines with oxygen of the air and forms a reddish brown fume. This is choking , coorosive and toxic gas.

 

Gold can be refined in a number of ways. There are special rteasons for use these different methods. Some proccesses are very very old. a few where devised in the late 1800's. Some methods are fairly new but these tend te be applies to specialized needs.

 

The disadvabtage of Aqua Regia method is that it requires strong acids, produces rather vile fumles and the leftovers barren solution is a pollution problem.

 

Gold chloride is formed when aqua regia digezst gold scrap.

The reaction of the aqua regia with the metals in the scrap produces nitrogen oxides. When the alloy contains about 8 to 10% of silver an adherent layer of silver chloride forms and "protects" the metal from dissolution. Melting and dilution with copper is the only reasonable way of dissolving high silver material.

 

When the gold content of the scrap is below 30% any copper and silver present can be dissolved with nitric acid.

 

FILTERING:

 

The aqua regia now contains various metal chlorides in solution and insoluble silver chloride as well as a lot of unwanted material in the sludge, and the mixture muqt be cooled and filtered; reason for cooling is that the silver chloride; quite insoluble in water, is slightly soluble in stron,g acids and this solubility is lower in cold acids.

It is gopod practice to add a little sulfuric acid to the dissolution vessel before filtering. When there is lead in the scrap it forms a very hard to filter gelatinous material ( also true for tin). The the aqua regia solution has to be filtered with a bucher filtering funnel. After filtering the filter paper contains the unwanted material (also silver chloride). The filtered liquid is usually a rather handsome clear green color, due to nickel and copper. If only gold chloride were present, it would be yellowish.

 

The excess aqua regia that was added to insure complete solution of the gold is still in the solution at this stage and must be eliminated at this stage to allow the gold to be precipitated.

 

The classic procedure for nitric acid elimination is repeated boiling to near dryness with trhe addition of hydrochloric acid with some sulfuric acid near the end. There are a number of other chemical methods to eliminate the nitric acid... see use of Urea (carbamide)...

 

PRECIPITATING THE GOLD:

 

The classic method of reducing gold chloride in solution to solid gold is to add "copperas" to the solution. (=ferrous sulphate)also can use hydroquinone (experimantal use). Also other procedures excists. Copperas is prefered also because it leaves platinum in a chemical state easily changed to an insoluble condition. Also other procedures excist with for example sodium bisulfite, sodium sulfite, sulfur dioxide gas can be used as reducers.

 

Thge end point is easily determined by a test for the presence of dissolved gold (stannous chloride test) ... i can tell you receipt if needed.

 

Filtration:

 

When the solution has been cleared of gold it should be allowed to stand preferably overnight. Althought gold is heavy and most of it settles quicly, some particles are very small and require time to go to the bottom.

Before doing any filtering the solution is tested with the stannous chloride test)

 

Washing The gold and Melting the gold.... etc....

 

GOLD CHEMISTRY:

Aqua regia is a mixture of hydrochloride and nitric acids.

 

Au + HNO³ + 4HC1 = H²O + NO + HAuC1(4) as for all chemical formulas i will have to send them by mail .. if your interested you mail me at [email protected]. i will send you a copy of some pages in proffessional literature about gold refining.

 

Hope i helped a bit in your search..

 

all the best...

 

Frederic Carpentier Buddy's Gold Belgium Brugge.

 

Specialized in Antique jewellry , watches , precious gemstones, etc...

You always welcome with any questions regarding jewelry. Actually refining is not my speciality. I'm more into antique jewelry and watches.

:hihi: next year our website will be online CRE Loaded 6 - AllTimesjewels online store

[Kayra]

A friend of mine once claimed he bought scrap supercomputers (back when they were mostly hand made), disassembled them, and left parts in a bath of mercury.

 

Afterward he would take the gold dissolved in the mercury and filter it through a true leather shammy to recover the gold.

 

In the end, he said he would take 20-40 used shammies and smelt them.

 

He also mentioned that at some point the mercury solidified. I did not know it could do that.

 

While sometimes prone to stories of the tall sort, this gentleman was also an knowledgeable, accomplished, and meticulous inventor, so I am left with not knowing how valid his method was.

[mista_miker]

GAHD....

a couple of things to clarify

aqua regia is a useful solvent for noble metal removal

now

AR can be "made" in many ways

the easiest, and least hazzzzzzardous is taking HCl (muriatric acid) and reacting a salt such Na NO3(sodium nitrate) with surplus HCl...........the product is NaCl (non iodized table salt, or "canning salt") in solution+ water+ HNO3(nitric acid) and HCl..........

 

so you need a bit of math.......the concentration of the HCl is a biggie.....and beware.........is that HCl 75% by weight or volume?

 

things to watch out for is the brown gas.........very bad, add urea or add your piss to stabilize to clear the brown gas............but do not pee into or on the AR

[UncleAl]

Once noble metals are dissolved you can bring them down with controlled potential electrolysis or by chemical reduction (e.g., oxalic acid).