Auric chloride solutions, how to procede?

[oldtimmer]

I removed gold plating from several large boards with large plated ares. I used the AP and bubbling air. I ended up with just under 3 grams of foil. After 2 x wash with hot HCl followed by water wash x 2. As the foils appeared to have a brownish color along with the gold foil, I did a 3rd hot HCL and water wash.

I then dissolved the foil in HCL + Cl. The foil was slow to dissolve even though I had added a little extra Cl. I did not get a lot of fizzing as expected. So I heated the HCl + Cl and the gold began to dissolve better. When I added a little more Cl, I got a nice rapid fizzing, but the color was almost red. After all of the foil is dissolved, I have a brownish solution. I had expected the usual yellow color that I have seen in the past. I then did a stanus chloride test and get an immediate strong brown coloration on the filter paper. When it dries, it is a very dark brown with some purple. I also have a second flask that I had dissolved 3.7grams of gold leads from diodes that is close to 24K.

Below is both flasks with the filter paper stanus chloride test attached. The question is what has caused the brownish coloration and how best to drop the gold and what else is in solution. Also as the concentration of dissolved gold in the brownish solution is less then that of the yellow, why is the brown indicator so dark as compared to the yellow solution?

Thanks,

 

[DNIndustry]

were the boards coated/sealed?

You could have disolved the base metals to get the foil yet have the coating on the gold... the AP may not have been able disolve it but the heat & hcl+cl probably would. my guess is that you have some organix mixed in. Not knowing what they are i wouldnot use any thing radical (hydroxyl amine/hydrazine) to precipitate.
: )
Get some Amberlite XAD-7 resin media, a column, a peristaltic pump, ORP meter, and run it over it when its at -990mV vs AgCLvs.KCL...( A personal joke..a rather complex suggestion for me to lightly mention)

 

[lazersteve]

Oldtimer,

Can you confirm your stannous test with a known solution of gold as a control? Dissolve a couple loose gold foils from a finger ( no copper) in HCl-Cl and test the resulting solution. If the test color is the same (brown not purple), I would suspect you have something in the stannous chloride that is causing the brown color.

The brown solution obviously has something in it besides gold, possibly a base metal. The yellow solution looks to possibly be a dilute solution of gold.

Where did you get the stannous chloride test solution?

Could your stannous have become contaminated?

Steve