goldsilverpro said:
I'm thinking Harold gave a way to dissolve metastannic acid with HCL.
I dealt with it when processing gold that was contaminated by incinerating, then digesting the solids in HCl. Whether it eliminates the stannous chloride or not I can't say, but it does convert the material to a substance that can be filtered. That allowed the gold chloride to be filtered without problems. I had this experience a few times when I played with escrap. I did not normally process the stuff, however, so my exposure was limited. I followed this same procedure when processing eye glass frames, however, and it paid huge dividends in yielding a solution that was easy to filter after the values had been dissolved. Incineration with a succeeding HCl wash is quite critical to easy filtering of material contaminated with tin.
I did this routinely, when I processed dental amalgam, After it was retorted, it was subjected to being heated in an open vessel (I used an old staginess fry pan) until the remains were melted. Due to the tin content, that happens at a relatively low temperature, although I am at a loss to specify what that may be. The material was stirred and kept molten for a short period of time, and then was stirred with heat removed, so it was broken up upon freezing. The resulting alloy was then digested in dilute nitric.
I
did not filter, nor is it required. The resulting material was quick to settle, so the solution, which was poured off, including the light material that was in suspension, was allowed to settle. It happened quickly. It was then siphoned, with copper introduced to cement the contained silver. All goes without a hitch. The remaining solids, which would have accumulated in the settling vessel, along with traces of solution, can then be filtered, seemingly without problems.
Anything that followed the silver when it was cemented, I'm quite comfortable, was removed by fluxing, and if not, it was separated in the silver cell. Bottom line here is that tin contaminated silver can be successfully processed, but you must do some work prior to digesting, otherwise you may be stuck with one hell of a mess.
Harold
