I am trying to dissolve base metals off of gold plated electronic scrap, and I am using HCl to dissolve some of the base metals.
I pored in the HCl into a flask containing the scrap ( the contents of the flask where later moved into the 2 liter jar as seen in the photo ) Once I dissolved the base metals I tried to neutralize the acid with baking soda. However this neutralization was taking too long and about 400 ml of baking soda later I decided to try to react the rest with sodium sulfate to bring the ph down.
I figured this would produce sodium chloride witch wouldn’t be a big deal. This did help by reacting the rest of the HCl and it brought the ph down to about 5, but there was also baking soda along with the sodium sulfate so I don’t know witch brought the ph down. The sodium sulfate was reacting though because before I had a odorless gas ( CO2) and now I was getting chlorine gas.
However the day after the gold off the scrap had disappeared. The piece of scrap in the photo was a piece I observed during the reaction. At the beginning it had about 2mm ( my measurements are not off it was very heavily plated ) of gold plated onto the surface. And at the end the gold had dissolved away and the copper base metal was coated in a black durable substance. This deposit was not on the gold it was on the copper the gold was once plated on. I even cut it in half to be sure that it wasn’t just deposited onto the gold. The only other chemical that was possibly in it was about 25-50 ml of acetone wich I used to dissolve the plastics with. At first the solution was a brownish yellow then the brown particles settled out and the solution was yellow.
My question is where did the gold go and what gold compound produced.
And for those who say the gold didn’t dissolve it did. I had over a quarter of a pound of gold plated scrap disappear and the solution turned yellow. The gold doesn’t just evaporate. 
!
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2$\begingroup$ I do not see reason for adding sodium sulphate. It is pH indifferent salt. Baking soda solution is not the best choice, as its solubility is limited and produces a lot of gas. HCl wil leave a lot of metal not dissolved, like copper..HNO3 would dissolve copper and silver too. When Metals are dissolved, why not to get rid of extra HCl first, and neutralize it separately ? $\endgroup$– PoutnikFeb 5, 2020 at 6:42
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1$\begingroup$ I agree with Poutnik. Sodium sulfate is not going to help. $\endgroup$– William R. EbenezerFeb 5, 2020 at 11:39
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1$\begingroup$ Adding baking soda will never bring the pH down. And sodium sulfate does not react with gold, copper or any other metal. And finally you do not tell us what you have really done. You say that you have smelted the odor of chlorine. It is impossible to obtain chlorine gas Cl2 with the metals and chemicals you have used. $\endgroup$– MauriceFeb 5, 2020 at 16:04
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1$\begingroup$ Chemical reactions are not used to participate in element transmutations, otherwise alchemists would already use it. How can $\ce{HCl}$ and $ce{Na2SO4}$ produce carbonic acid, if neither of them contains carbon ? In fact, they do not react, if they are what you say they are. If mixed, they form a solution of 4 respective ions. What sulphate may do in concentrated solution is to restrict solubility of hydrogenchloride. $\endgroup$– PoutnikFeb 6, 2020 at 7:57
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2$\begingroup$ I suggest you to break your questions into paragraphs. It looks like a block of text. $\endgroup$– Nilay GhoshFeb 6, 2020 at 9:23
2 Answers
Per a 2017 article from the Journal of Molecular Liquids some interesting comments.
Yes, you can use HCl albeit in conjunction with a chlorate (or bromate or iodate..) and added chloride, to quote:
It has been found that mixtures between sodium chlorate and HCl (NaClO3 + HCl ⇆ HClO3 + NaCl) in 20 mL are effective media for the dissolution of pure gold-wire...In HClO3 solution containing abundant halide ions (X- = Cl-, Br-), the Au metal should be oxidized mainly by X2 to be AuX4-, where X2 is produced by the oxidizing power from HClO3, just as dilute HNO3 (< 2 mol dm-3) containing abundant NaCl.
Also interestingly, hypochlorous acid with added NaCl may also work, to quote from the same source:
The gold dissolution in hypochlorous acid (HClO) containing halide ions has been also examined...
The last comment may imply that treating a concentrated solution of calcium hypochlorite with CO2 (creating, in situ, HOCl and a precipitate of CaCO3, see as a reference, and also here ), then removing the calcium carbonate, and further adding more CaCl2, may actually dissolve gold!
Seven mistakes in seven lines!! Caleb is of course allowed to write down any sorts of equations. It is not forbidden by law. The trouble is that it is no use creating equations for reactions that simply do not happen in the reality. For example,
1) $\ce{Pb}$ does not react with $\ce{HCl}$, as he imagines. It does not react at all.
2) A mixture of $\ce{HCl}$ and $\ce{Na2SO4}$ will not produce sulfuric acid, as he says. In solution it simply produces a mixture of $\ce{Na^+, H3O^+. Cl^-}$, and $\ce{SO4^{2-}}$ ions.
3) Sulfuric acid does not react with metallic gold $\ce{Au}$, despite his assertion.
4) Sulfuric may react with some metals to produce sulfates, but will never produce perchlorates, despite his view.
5) Chlorine cannot be produced by a mixture of $\ce{HCl}$ and sulfuric acid, with or without some other compound like $\ce{PbSO4}$ or $\ce{PbCl2}$.
This being said, Caleb should absolutely learn that :
1) Sulfuric acid is not $\ce{HSO4}$. No! It is $\ce{H2SO4}$, with 2 $\ce{H}$ atoms
2) Lead chloride is not $\ce{PbCl}$ but $\ce{PbCl2}$. $\ce{PbCl}$ does not exist!
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1$\begingroup$ "A mixture of HCl and Na2SO4 will not produce sulfuric acid, as he says." It could produce bisulfate, though. Bisulfate dominates over sulfate if pH<2, as that number is the pKa for bisulfate. $\endgroup$ Feb 5, 2020 at 21:30
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3$\begingroup$ I don't get it! Why such a high rep user don't use
\ce{^}at all.. $\endgroup$ May 27, 2020 at 1:04