The kinetics for the decomposition of tetrathionate in alkaline solutions

Tetrathionate is one of the principal products of thiosulfate degradation during gold leaching with ammoniacal thiosulfate solution. Its presence in the leach solution may interfere with the recovery of gold using ion exchange. It is therefore desirable to examine the kinetics of tetrathionate decomposition. The kinetics of tetrathionate decomposition in strong alkaline solutions deaerated with nitrogen has been investigated by means of ion chromatography. The effect of pH and temperature on the reaction rate was studied. It was found that the reaction was first order with respect to both tetrathionate and hydroxide. With constant hydroxide concentration, the pseudo-first order rate constants have been determined at various pH and temperatures. The activation energy of the reaction in the temperature range 22–40 °C was found to be 98.5 kJ mol−1. The reaction pathways and stoichiometry of the reaction have also been discussed.