Ammonium thiosulfate
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Through Crystal, Ammonia and Solubility
Production
It is produced by treating ammonium sulfite with sulfur at temperatures between 85 and 110 °C:
- [NH4]2SO3 + S → [NH4]2S2O3
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Applications
Ammonium thiosulfate is used in photographic fixer. It is a so-called rapid fixer, acting more quickly than sodium thiosulfate fixers. Fixation involves these chemical reactions (illustrated for silver bromide):
- AgBr + 2 [NH4]2S2O3 → [NH4]3[Ag(S2O3)2] + [NH4]Br
- AgBr + 3 [NH4]2S2O3 → [NH4]5[Ag(S2O3)3] + [NH4]Br
Also exploiting the stability of thiosulfate coordination complexes, ammonium thiosulfate is also used for leaching of gold and silver. It works with presence of copper as a catalyst. This process is a nontoxic alternative gold cyanidation. The advantage to ammonium thiosulfate is that the pyrolysis of its silver complexes leaves a residue solely of silver sulfide, in contrast to complexes derived from sodium thiosulfate.
Other
Ammonium thiosulfate can be used as a fertilizer. As suggested by some research studies, it can also be used as an additive to coal-waste mixtures to reduce formation of dioxins and furans during combustion.
Safety
LD50 (oral, rat) is 2890 mg/kg.