arthurcorbit wrote:I have a question along these lines and I was wondering if you would answer it. When you dissolve the plated gold you can't do it without dissolving at least a little junk metal. Does the SMB just drop the gold or all thew metals? If it drops all the metals then you still have to purify the gold some other way, correct? If that's correct then what method do you use.? I haven't come across anything on the fourm that explains that yet. Thanks
Once again, Hoke is your friend.
When you precipitate gold, regardless of the precipitant you choose, there is mechanical drag-down of other elements. They aren't normally precipitated unless you use poor judgment and choose something like copper as your precipitant.
It is for that reason that it's so important to eliminate base metals in the preliminary operation(s). Then it becomes important to wash the gold well, using HCl, even if you feel your gold chloride solution was free of contaminants. It almost never is.
I do NOT recommend the use of nitric for the washing procedure. Not because it doesn't work, but because the gold comes from a chloride solution. Unless you can eliminate it totally after precipitation, some of it (the gold) will be re-dissolved when you introduce the nitric for the wash. Considering the contaminants you are trying to remove are normally not solids, but metals in solution, a wash with HCl is more than adequate. I regularly produced gold of greater quality than 9995 by a second refining and my preferred washing procedure.
Below, you'll see a picture that, by now, has likely worn out its welcome on the group. I've posted it several times.
Take note that the gold you see required NO pickle to achieve its brightness. It came from the melting dish with no oxidation.
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