Quote by Harold
It is very easy to remove ALL of the lead from the aqua regia solution. All you do is add a little battery acid and filter well - you can't get any simpler than that. You're going to have to filter the AR solution anyway - why not get ALL of the lead out at the same time. This is 100% reliable, whereas the leaching of 100% of the lead from the foils with acetic/H2O2 is questionable, at least in my mind. If my math is right, one ml of 35% battery acid will precipitate about 1.15 grams of lead, as lead sulfate, but it doesn't hurt to add a little extra.
If you do the standard procedures correctly, the gold from refining the foils should be very pure. Can you explain in detail how you're refining the foils? If you're just melting them, that's not going to work in any case. The same with the gold that you inquart and then treat with nitric. If you don't further refine the resulting gold, the best it will be is about 99% pure.
EDIT: In thinking further about this, if you have lead on the foils, you also have tin. Therefore, it might be a good idea to leach the clean foils in hot full-strength muriatic acid, since it will dissolve both tin and lead. If any lead chloride crystals form, they can be dissolved in hot water. You could instead use a solution of 24% glacial acetic acid, by volume, 4% Hydrogen peroxide of 30% strength, by volume, (or, 40%, by volume, of 3% strength), with the remainder water, at room temperature, to dissolve both tin and lead. This will help eliminate the problem with the slimy tin compound, metastannic acid, from forming when you finally dissolve the foils in aqua regia. That may be one source of your purity problem. I would still use the battery acid in the aqua regia, however, in any case where lead was originally present.
