Photoelectrocatalytic Degradation of Cyanide Using TiO₂ on Conducting Glass and Polarographic Analysis of the Products

Abstract

Cyanide used in gold mines is collected in tailing dams and has a high risk of contaminating the surrounding environment. Cyanide contaminations in the atmosphere, as well as in water and soil are insufficiently studied so far. The lack of interest, the complexity of the reaction mechanisms and the challenging analysis of the products are major reasons for this deficiency. The circumstance that a prominent part of cyanide is volatilsed during and after the gold extraction is often neglected; volatalised HCN is said to be sufficiently destroyed by the sunlight and the oxygen of the atmosphere which can easily be disproved by analysis of the cyanide content in the contaminated atmosphere. The investigation of the products of cyanide decomposition is an essential part in the evaluation of the toxicity originating from effluents of gold processing. In this work, spray pyrolysed TiO2 on conducting glass is used for the photoelectrocatalytic treatment of cyanide. In UV-A irradiating the catalyst and applying an external bias for the separation of the charge carriers, the cyanide is oxidised in solutions of different pH. The cyanide content after the process as well as the quantity of the products is analysed via polarography. Besides the oxidation, hydrolysis was detected as well, correlating to the pH of the solutions. The proposed method allows the evaluation of the level of environmental contamination of gold processing as well as the analysis of products that result from decontamination processes in gold mines. Furthermore the photocatalytic capability of TiO2 for the decontamination of cyanide wastewaters is determined.