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Silver sulfide (Ag2S) is an insoluble black compound of silver and sulfur. Commonly found as the black tarnish on silver objects. Naturally found as the mineral achantite.
Solubility in water is 12 mg/l.
Nitric acid turns silver sulfide into silver nitrate and silver sulfate.
Sources of silver sulfide
Silver sulfide is not that common. It is sold as a photosensitizer for photographic work.
For the refiner silver sulfide is mostly encountered as a step in recovering silver from photographic fixer.
Silver sulfide can be formed from most silver solutions by adding sodium sulfide.
Reduction back to silver
There exists several ways of converting silver sulfide back into metallic silver.
- Using nitric acid to convert it into silver sulfate or silver nitrate. Warning, could release toxic H2S! Continue process as for silver nitrate.
- Using aqua regia to convert it into silver chloride. Continue process as for silver chloride.
- Using sodium or potassium nitrate and borax in a two step process in a crucible. (See reference below on Juan Manuel Arcos Franks method)
- GRF : Juan Manuel Arcos Frank sharing his method of converting silver sulfide into silver
- Wikipedia : Silver sulfide
- Saltlake Metals : MSDS for silver sulfide