Ammoniacal thiosulphate leaching of gold in the presence of pyrite

The effect of pyrite on gold dissolution was investigated in the ammoniacal thiosulphate leaching system using pure gold foils. Special emphasis was placed on gold leaching in association with pyrite dissolution, thiosulphate decomposition and gold leaching passivation. The presence of pyrite retarded gold dissolution and this detrimental effect became more pronounced at higher pyrite contents. Pyrite catalysed the decomposition of thiosulphate to trithionate. The addition of sulphate enhanced gold leaching by retarding the dissolution of pyrite in ammoniacal thiosulphate solutions. XPS analysis indicated the presence of iron hydroxide species at the gold surfaces in the presence of pyrite, which was likely responsible for the reduced gold dissolution. SEM analysis indicated a lesser extent of gold dissolution occurring in the presence of pyrite.