4 Mitutes on diamonds removal

[Harold_V]

Something else I hadn't thought of. When Harold leaches the gold powder with hot HCl, he is very possibly dissolving the AgCl. Of course, the HCl couldn't be diluted or some of the AgCl would re-precipitate. Maybe best to add HCl, heat, leach, pour off, and repeat twice more. That way, the final HCl leach would have very little AgCl in it and rinsing would cause no AgCl to precipitate.

That's certainly possible. Because I precipitated from heavily concentrated solutions, I knew I had traces of silver chloride in my gold, as the solution would develop a hint of cloudiness when ice was added. I knew it wasn't much, but there's no question it was there. I relied on the ammonium hydroxide wash to ensure it was removed, but it may well have been pretty much eliminated at the outset, with the first HCl wash. All of my washes were done at a boil (covered with a watch glass, to retard loss of vapors, and to ensure no garbage fell in the vessel) so I fully expect that at least traces of silver chloride were eliminated. Bottom line is----my gold was quite good.

Harold

 

[Oz]

I would expect the ammonia hydroxide washes were far more effective at removing silver chloride than HCl would ever be. Not that the solubility of the silver chloride in HCl should be discounted of course.

 

[HAuCl4]

One option is to use ammonium hydroxide to convert the silver chloride to silver nitrate and the other option is to use sodium thiosulfate to do the same. Each route has pro's and con's which we can discuss further if you would like.

typo?. :shock: :?:

 

[4metals]

You are correct.

Actually not silver nitrate, ammonia acts as a ligand forming an ammine complex like this;

AgCl + NH4OH = Ag [ NH3 ]2 + Cl + H2O.

 

[HAuCl4]

fwiw, silver chloride will also dissolve in hot concentrated sulfuric acid, in a cast iron pan. Not the friendliest of substances, but very cheap. Diamonds will not be affected.

 

[4metals]

I've noticed you have a thing for cast iron! :lol:

 

[Noxx]

I've noticed in the past that AgCl will dissolve easily in hot concentrated HCl, while doing Ag purification. I do not have exact numbers, but the solubility is important.

 

[Harold_V]

I've noticed in the past that AgCl will dissolve easily in hot concentrated HCl, while doing Ag purification. I do not have exact numbers, but the solubility is important.

I saw evidence of the dissolution of silver chloride when I'd evaporate. When I had the solution concentrated, I'd add some water, to dilute the solution so it wasn't too aggressive towards filter papers. That there was silver in solution was not a doubt, as the moment water was added, silver chloride precipitated immediately, even with a hot solution. The scant amount of silver chloride that was evident after icing the solution (after filtration) was not great, so indications are even some dilution will eliminate the vast majority of the silver. Bottom line, however, is that the separation of gold from silver is not easy when it gets down to ultra pure gold. I believe it was 4metals that stated, some time ago, that silver can be expected to be the contaminant in relatively pure gold.

Harold

 

[HAuCl4]

I've noticed you have a thing for cast iron! :lol:

Gotta find a use for all those Christmas gifts... :lol:
Seriously though, it ìs hard to fight technology that has been proven for thousands of years.

Now if I could find a cheap and easy way to teflon coat cast iron...and avoid glass altogether (even fiber-glass)... :idea: :shock: :lol:

Off topic: Now, for the people that don't mind a little experimentation, and if you really want to get rid of silver in your gold chloride (trust me, I have tried...). If you SLOWLY rise the pH towards 7-8 by adding diluted NaOH dropwise, mixing and agitating all the time, your diluted AgCl will convert to AgOH and then Ag2O, and so will all the other base metal impurities convert to hydroxides, even palladium and others, that can be decanted and filtered out. Only platinum, if any, will stay in solution with the gold. Then you precipitate the silver-less gold from your silver-less gold chloride solution. 8)

Try it in a small sample, before you object!. :lol:

 

[4metals]

Using diluted caustic on a concentrated acid to raise the pH to the point of dropping the contaminants as hydroxides will increase the volume of the solution exponentially. More waste equals more costs.

 

[HAuCl4]

I once had this fantastic girlfriend, nice body, upper and lower, beautiful face, fantastic personality, great mind, funny and charming... I just couldn't get over that one freckle in the back of her left ear lobe... :lol:

 

[jimdoc]

I once had this fantastic girlfriend, nice body, upper and lower, beautiful face, fantastic personality, great mind, funny and charming... I just couldn't get over that one freckle in the back of her left ear lobe... :lol:

That is what earrings are for.

Jim

 

[Lobby]

What did you fine folks decide on the final process?

I can't get past two issues:

- the AR in the original post is contaminated with base metals

- the AgCl from the initial AR boil is contaminated with gold

Looks like lots of additional processing will be required for those two phases.

 

[samuel-a]

What did you fine folks decide on the final process?

I can't get past two issues:

- the AR in the original post is contaminated with base metals

- the AgCl from the initial AR boil is contaminated with gold

Looks like lots of additional processing will be required for those two phases.

Both are a non issue actually, as both the gold and silver go through a second refining in any case.

 

[Lobby]

That was the essence of my question. I couldn't see the 2nd refining processes for both those scenarios.