Gradual cyanide treatment using AYR and ozone/UV systems with various catalysts in silver mill effluents

摘要

Wastewater of a silver processing plant at the Eti Gumus plant located at Kutahya, Turkey was treated with an acidification, volatilisation and reneutralisation (A VR) process for cyanide recovery as a preliminary treatment, and with ozone and ozone/UV light plus catalysts as a secondary treatment. Average NaCN concentrations of slurry with AYR were reduced from 900 + - 50 ppm to 50 + - 10 ppm. Then, oxidation of cyanide in the presence of titanium dioxide, zinc sulphate and copper sulphate as catalysts was investigated and variations in CN~- and CNO~- ion concentrations were measured with a cyanide electrode and ion chromatography, respectively. The reaction time reduced to 12 min with the addition of catalysts when ozone consumption was 0-100 min~(-1) after 25 min with ozone alone and 0-071 g min~(-1) after 20 min for the ozone/UV system. As a result, the most effective method to achieve appropriate discharge values for cyanide with respect to environmental protection laws was the ozone/UV/TiO_2 system with AYR recovery for the effluents of silver ore leaching.