Sodium thiosulfate (Na2S2O3), also spelled sodium thiosulphate, is a colorless crystalline compound.
Sodium thiosulfate is one component of an alternative lixiviant to cyanide for extraction of gold. It forms a strong complex with gold(I) ions, [Au(S2O3)2]3-. The advantage of this approach is that thiosulfate is essentially non-toxic and that ore types that are refractory to gold cyanidation (e.g. carbonaceous or Carlin type ores) can be leached by thiosulfate.