Removing silver and lead

[maynman1751]

First of all, I'm new here and I can't say enough about how helpful and informative this site and its members have been. I have started refining e-scrap. With reading Hoke several times plus the other fine resources here I have managed to be reasonably successful. I started with small lots just to get the basics down and yes, I made my mistakes along the way but I was usually able to find out what I did wrong with the help of this wonderful forum. But now I need some advice. I have precipitated some gold using SMB. I DID NOT eliminate silver or lead. Should I put the gold powder back in solution and still drop these contaminates or is it even necessary? Also, if I use sulfuric acid to do this, what strength do I require?

 

[maynman1751]

Sorry! This is probably in the wrong forum. When I started this I was only going to ask about sulfuric acid.

 

[butcher]

I have precipitated some gold using SMB. I DID NOT eliminate silver or lead. Should I put the gold powder back in solution and still drop these contaminates?

Yes.

Lead and silver do not dissolve too much of an extent in solution with gold, basically insoluble in chloride solution (some can be in solution though),
(I know this statement is confusing but I do not know how to explain but I will try)
AgCl silver chloride is insoluble, but in strong oxidizers and acid a small portion of the silver will form AgCl2 which is slightly soluble in these strong acids, diluting or chilling helps to change AgCl2 back into AgCl an insoluble white powder).

Reprocessing your impure gold will improve its quality. (The more times we re-crystallize a metal salt the more pure that salt) this is the same with our gold the more times we refine the more pure, many times refined gold needs re-refining.

Following the washing procedures also help (if you did not have much lead or silver salts involved this may clean your gold up considerably)

I am somewhat unsure about your question or statement about sulfuric acid.

Using a few drops of sulfuric acid if you do have lead in solution (such as aqua regia with gold, will precipitate the lead as an insoluble sulfate).


Studying Harold posts will get you pure gold (and do not forget Hoke's instructions).

 

[maynman1751]

I am somewhat unsure about your question or statement about sulfuric acid.

I read that you can use sulfuric to drop the lead (and the silver???) together???? Yes, no, maybe??? If so, what strength acid?

 

[butcher]

In aqua regia the small amount of lead will precipitate if you add a few drops of sulfuric acid, I do not think the concentration would not make too much difference, as long as it was not too dilute (I would use 30% minimum to 90% H2SO4), how many drops you added would also depend on how much lead was in solution.

I feel you would not want to use sulfuric acid to try and make silver sulfate (I feel it would take too much H2SO4), the methods we use to remove silver is either dilution with water, or some chill their solution with Ice. silver will not stay in solution when diluted.

Harold’s washing procedure will clean up the little bit of drag down of metals, read the “getting your gold pure” posts.
Many times refined gold needs refined a second time for purity.

Some time’s we say this is black or that is white (in reality some time’s it has a little gray area) keep that in mind.
Like we may say the silver will precipitate out of solution by diluting your aqua regia (this is black and that is white) (there will still be very small traces that may be still in solution, and be dragged down with gold when you precipitate it, that you can clean up in washing procedure, and even then you may need to re-refine your gold to get it pure and wash again to remove traces of silver (gray area).

Hoke's book also states the few drops of sulfuric acid (when removing the lead) also helps in the evaporation process, she say's that you are less likely to form crystals if you accidentally evaporate the aqua regia too far past the syrup stage.

 

[maynman1751]

Thank You Butcher for your response!!!!

 

[Lino1406]

Silver (more than) and lead salt can also be removed by washing
with ammoniac. Final lead salt washing with hot water

 

[butcher]

Lino1406 is giving some good tips.

Lead chloride is fairly soluble in almost boiling hot water, where silver chloride is fairly insoluble in hot or cold water; this can be used to separate these two salts.

The hot water washes of your gold powders will also help to dissolve the lead chloride powders from your gold, as well as some other salts like sodium chloride, and even some base metal chlorides.

Silver chloride which is pretty much insoluble in hot or cold water, also insoluble in HCl and aqua regia, acidic solutions, silver chloride will form a complex with ammonia or ammonium hydroxide (household ammonia) and become soluble in solution as silver diAmine, we can use this when washing our refined gold powders or other processes, but take note of following precaution:

Any time you dissolve silver salts (AgCl) in ammonia, the Ag(NH3)2 a silver diAmine formed, which can be very dangerous if allowed to dry, you should always add acid (I use HCl) to precipitate the silver out of this solution, making it safe, never leave some setting in your lab, you may forget what was in that jar.

Read getting your gold pure posts for more great details.