Removal of toxic cyanide and Cu(II) Ions from water by illuminated TiO2 catalyst

Due to its strong complex formation potential, cyanide (CN-) has been used in a variety of metal processing and metal extracting processes. As a result, the wastewaters generated from such processes always contain a mixture of cyanide and metal ions. Photocatalytic degradation using ultraviolet-irradiated TiO2 suspension has been investigated for destroying both free and complex cyanide with a concurrent removal of the metal (exemplified by copper). The process uses the photogenerated holes at the surface of TiO2 upon UV irradiation of 100W. In contrast to conventional cyanide waste treatment processes, the photocatalytic processes convert both free and complex cyanide species into carbon dioxide and nitrogen with no residual harmful chemicals remaining. Synthetic cyanide wastes (dilute solutions of sodium and copper cyanide) were used. The spent TiO2 was separated by coagulating then centrifugation. The residual CN- concentration was monitored periodically using spectrophotometric analysis. Results revealed that about 78% of free cyanide (10(-3) M) was removed after illumination for 4 h in the presence of 1 g/L (TiO2) at pH 11. Free copper (10(-2) M) was completely removed in a shorter time Q h). The co-existence of Cu(II) and CN enhanced the removal efficiency of both CN and copper; the removal (%) increased with increase of Cu:CN molar ratio reaching a complete removal for both copper and cyanide at a ratio of 10:1 at the same previous conditions of free cyanide. (C) 2004 Elsevier B.V. All rights reserved.