# Does gold always become gold chloride when dissolved with HCl and an oxidizer and can it always be precipitated with sodium metabisulfate?

I tried to extract gold from computer parts by STRIPPING the gold using $\ce{HCl}$ and $\ce{H2O2}$ by dissolving the copper & nickel underneath but i added FAR too much $\ce{H2O2}$ by a stupid mistake and I ended up dissolving the gold... I didn't know that could happen? I am correct in understanding the $\ce{HCl}$ dissolves the gold, but it needs both energy and oxygen to do so? Nitric acid (commonly added to $\ce{HCl}$ to form aqua regia which dissolves gold) is $\ce{HNO3}$ which has lots of oxygen and Hydrogen Peroxide is $\ce{H2O2}$ which has oxygen also, albeit less than Nitric Acid.....

My mixture is VERY dark red... It's fuming very lightly, and makes you choke if you get near it. It's not see-through but rather very dark and a bit murky, but could be transparent if you added 200% of water.

I am afraid to try anything because if I screw it up I will lose $200 of gold but am I correct in understanding that adding sodium metabisulfate will drop the gold? What if it is too acidic? Will I have to add Urea or Sodium Bicarbonate to neutralise the pH??? HELP!! ## 1 Answer You may find to your dismay that getting dissolved gold separate from dissolved copper and nickel is dicey (to give you some idea, I still have a dissolved solution of gold and copper sitting in my garage ca. 2 years ago because I hesitate to mess with it; also it looks kind of cool). You should use urea to neutralize first, just going on experience. I've done the same procedure you describe here to try to recover gold from RAM cards etc. Add urea slowly and check pH regularly. I wouldn't try sodium bicarbonate only because I've never done that and it seems you ought to go with the most well-used method if you're risking a big loss. Sodium metabisulfate is indeed a common reagent for precipitating the gold. It smells pretty terrible before and after adding it (because of sulfur content). I think$\ce{SO2}$gas is released when you react with gold so you should have a well-ventilated area for this. You should get a brownish precipitate. I would keep adding it to the neutralized solution until no more precipitate is formed, then let it settle. This point is probably your best hope for separation of the gold. Recover the precipitate by filtering and leave off as much of the fluid as possible (wash with DI$\ce{H2O}$, and melt the brown salt to remove metabisulfate and get the pure metal. In the future I would not use any oxidizer when stripping the gold from$\ce{Cu}$/$\ce{Ni}$. I found that a much better method is to stir/air-bubble the material in$\ce{CuCl2}$which can be made from pure copper,$\ce{HCl}$, and careful additions of$\ce{H2O2}$. It will take longer but it is much safer. You'll recover solid bits of gold instead of dissolving it undesirably. i.e.$\ce{CuCl2}$>$\ce{HCl} + \ce{H2O2}$> aqua regia A lot of this procedure is difficult to improve because (even academic) literature is nebulous on the topic. I once bought a ~$250 book on the topic. "The Properties of Electrodeposited Metals and Alloys: A Handbook" by Safranek. It's hard to get a hold of.

P.S. it does not form gold chloride when dissolved in aqua regia ($\ce{HCl}$ alone won't effectively dissolve it). It forms a complex with $\ce{Cl-}$, chloroauric acid $\ce{HAuCl4}$.