Metal finishing Q&As since 1989

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Search for environmentally safe alternative for aqua regia

I'm looking for an environmentally safe (comparatively) alternative to the mineral acid solutions such as aqua regia used in refining gold alloys and scrap. Any suggestions or sources for information will be appreciated.

Jim Peterson
Student/hobbyist - Minneapolis, Minnesota, US
2003

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Aqua regia is a mixture of HCl and HNO3, Jim. It's nasty stuff and dangerous to work with. But it is hard to imagine chemistry that could be more natural, common, and bio-compatible than nitrates and chlorides, and yet still be capable of dissolving a material as inert as gold. The environmental problem is probably more the metal that the solution dissolves than the chlorides and nitrates.

If you can carefully think through what you mean by "environmentally safe", and really detail what you are referring to, then you can compare aqua regia processes to cyanide processes and sulfite and citrate processes and make a real comparison of their overall environmental impact. In the end, however, I suspect that the bad news that you will uncover is that the environmental threat is small unregulated hobbyist operations per se rather than whether they use aqua regia or not :-(

Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003