Sodium thiosulfate is one component of an alternative lixiviant to cyanide for extraction of gold. Sodium thiosulfate also works as an antidote to cyanide poisoning. However, 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. Some problems with this alternative process include the high consumption of thiosulfate, and the lack of a suitable recovery technique, since [Au(S2O3)2]3- does not adsorb to activated carbon, which is the standard technique used in gold cyanidation to separate the gold complex from the ore slurry. Sodium thiosulfate is also used: •As a component in hand warmers and other chemical heating pads that produce heat by exothermic crystallization of a supercooled solution. •In bleach •To dechlorinate tap water for aquariums or treat effluent from waste water treatments prior to release into rivers. The reduction reaction is analogous to the iodine reduction reaction. Treatment of tap water requires between 0.1 grams and 0.3 grams of pentahydrated (crystalline) sodium thiosulfate per 10 liters of water. •To lower chlorine levels in swimming pools and spas following super chlorination. •To remove iodine stains, e.g. after the explosion of nitrogen triiodide. •Similarly, sodium thiosulfate reacts with bromine to render harmless products. •In bacteriological water assessment. •In the tanning of leather. •To demonstrate the concept of reaction rate in chemistry classes. •To demonstrate the concept of supercooling in physics classes. •As part of patina recipes for copper alloys. •It can also be used as a very interesting solute in supersaturation experiments.
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