Cyanide detoxification of gold cyanidation tails and process streams

Cyanide detoxification by chemical means (sulphite, hydrogen peroxide or Caro's acid) has typically been adopted by the gold industry to meet the International Cyanide Management Institute (ICMI) code and/or regulatory compliance for discharge into tailings storage facilities (TSFs), treatment of TSF return water or the discharge of excess water from the mining operation. This paper presents and discusses results from a number of different evaluations that have been conducted to reduce the cyanide concentration in cyanidation tails and process streams by chemical means. Preoxidation before cyanidation and the ore mineralogy were both found to potentially have a significant impact on reagent requirements in the treatment of cyanidation tails. The solution speciation provided important insights into the reagent consumption, which becomes very high in targeting residual weak acid dissociable (WAD) cyanide concentrations below 1 mg L-1. Preliminary evaluations of polishing and alternative processes for reducing the WAD cyanide showed potential to achieve these low concentrations and reduce the treatment costs.