Use of ozone in the treatment of cyanide containing effluents

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Courtesy of Absolute Systems Inc.

The treatment of effluents of the gold and silver cyanidation process is one of the main problems that the precious metals industry faces. These effluents contain variable quantities of free cyanide, weak complexed cyanide, strong complexed cyanide and thiocyanate. Different methods are used for the removal of cyanide but most of the times the consumption of reagents raises the operation cost to unaffordable levels, and there exists as well the possible formation of residual by-products that are also toxic. Ozone is an alternative gas for oxidation of cyanide compounds that presents several advantages; however the lack of information on the reactions of these compounds with ozone has delayed its industrial application in the treatment of cyanidation effluents.

This paper summarizes the research work developed at CINVESTAV between 1996 and 2001 to study the use of ozone to treat cyanidation effluents. Results are presented on the stoichiometry of free cyanide oxidation and copper cyanide complexes. The effects of pH, of temperature and of ozone addition rate on the cyanide oxidation rate are also presented. 2003 SDU. All rights reserved.

Keywords: Cyanidation; Cyanide oxidation; Thiocyanate; Ozone

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