Interaction mechanism of cyanide with pyrite during the cyanidation of pyrite and the decyanation of pyrite cyanide residues by chemical oxidation

The toxic cyanides in cyanide residues produced from cyanidation process for gold extraction are harmful to the environment. Pyrite is one of the main minerals existing in cyanide residues. In this work, the interaction of cyanide with pyrite and the decyanation of pyrite cyanide residue were analyzed. Results revealed that high pH value, high cyanide concentration, and high pyrite dosage promoted the interaction of cyanide with pyrite. The cyanidation of pyrite was pseudo-second-order with respect to cyanide. The decyanation of pyrite cyanide residue by Na₂SO₃/air oxidation was performed. The cyanide removal efficiency was 83.9% after 1 h of reaction time under the optimal conditions of pH value of 11.2, \mathrmS\mathrmO_3^2- dosage of 22 mg·g⁻¹, and air flow rate of 1.46 L·min⁻¹. X-ray photoelectron spectroscopy analysis of the pyrite samples showed the formation of Fe(III) and FeSO₄ during the cyanidation process. The cyanide that adsorbed on the pyrite surface after cyanidation mainly existed in the forms of free cyanide (CN⁻) and ferrocyanide ( \mathrmF\mathrme\left(\mathrmC\mathrmN\right)_6^4- ), which were effectively removed by Na₂SO₃/air oxidation. During the decyanation process, air intake promoted pyrite oxidation and weakened cyanide adsorption on the pyrite surface. This study has practical significance for gold enterprises aiming to mitigate the environmental impact related to cyanide residues.