Study on the interaction of cyanide with pyrite and the decyanation of pyrite cyanide residue

The toxic cyanides in cyanide residues produced by cyanidation process for gold extraction are harmful to environment. Pyrite (Py) is one of the main minerals in cyanide residues. The interaction of cyanide with pyrite and the decyanation of pyrite cyanide residue were investigated in this study. The results showed that high pH, high cyanide concentration and high pyrite dosage promoted the interaction of cyanide with pyrite. The cyanidation of pyrite was of pseudo-second-order with respect to cyanide. The decyanation of pyrite cyanide residue by Na₂SO₃/Air oxidation was conducted. The cyanide removal efficiency was 83.9% after 1 h reaction time under optimal conditions: pH 11.2, SO₃²⁻ dosage of 22 mg∙g⁻¹ Py and air flow of 1.46 L∙min⁻¹. X-ray Photoelectron Spectroscopy (XPS) analysis of pyrite samples demonstrated the formation of Fe(Ⅲ) and FeSO₄ during the cyanidation process. The cyanide adsorbed on the pyrite surface mainly existed in the forms of free cyanide (CN⁻) and ferrocyanide (Fe(CN)₆⁴⁻) after cyanidation, which were effectively removed by Na₂SO₃/Air oxidation. During the decyanation process, the air intake promoted the oxidation of pyrite and weakened the adsorption of cyanide on the pyrite surface. This study has practical significance for the gold enterprises aiming to mitigate the environmental impact associated with cyanide residues.