Detoxification of Cyanide in a Gold Processing Plant Tailings Water Using Calcium and Sodium Hypochlorite

In laboratory experiments, cyanide in waste water from the Muteh gold mine in Iran was oxidized by sodium and calcium hypochlorite to cyanate (CNO − ), which is 1,000 times less environmentally hazardous than cyanide. Experiments were conducted using waste water containing 270 mg/L cyanide over a pH range of 6–13 and temperatures between 25 and 50°C. Cyanide was removed completely at a pH of 12.3 at the higher temperatures. The experimental results were simulated in Visual MINTEQ 2003 EPA software using all of the components in the waste water. The model readily predicted most of the chemical reactions in the experiments and explained the mechanism of complexation of cyanide with metals, free cyanide, and cyanide acid formation.