Abstract:Because of the highly toxic cyanide in the gold cyanide residues, cyanide must be removed for environmental protection. The process mineralogy of residues was studied firstly, and then cyanide removal was carried out by three chemical methods. The results showed that the residue mainly contained Si, S and Fe. Pyrite was the main metallic mineral, and the iron-complex cyanides make cyanide removal difficult. The minerals in residues were in ultrafine particle size with high monomer dissociation degrees. In H₂O₂ oxidation process, the self-decomposition and side reactions resulted in high consumption of H₂O₂. In Na₂S₂O₅-air oxidation process, the time for complete process was long because of the reactions between Na₂S₂O₅ and O₂. Na₂SO₃ oxidation method was found to be a new method for cyanide removal without air inflation device. The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na₂SO₃ dose of 2.0 g/L.

Key words: gold cyanide residues; process mineralogy; cyanide removal; H₂O₂ oxidation; Na₂SO₃ oxidation