Electrochemical In Situ Cyanide Monitoring in Gold Mine EffluentsUnited Science
Li Chen, Ph. D.
Introduction: We developed potentiometric cyanide (CN–) sensors based on receptor-doped polymeric membranes, as described below. This sensor can be applied to erform on-line CN– monitoring in mining industry for controlling of cyanide leaching and detoxification processes.
Background: The high toxicity of cyanide and environmental concerns from its widely and continuously industrial use arouse interests in selective and sensitive methods for cyanide detection in various matrices, such as drinking water, surface water and biological fluids. To date, cyanide leaching is used as a key extraction process in the mining industry for the efficient recovery of gold from complex ores. Thus, on-line cyanide analyzers that could be used to monitor cyanides are very important for controlling of cyanide leaching and detoxification processes.
Methods: Potentiometric cyanide sensors, composed by cationic site, tridodecylmethylammonium chloride (TDDMACl), receptor, Zn(II) metallotetraphenylporphyrin, and o-NPOE plasticized polyvinylchloride (PVC), were prepared. The sensors exhibit a linear response range of 10-1 to 10-5 M and a lower detection limit of 10–5.5 M (i.e., 3 ?M), which is below the maximum contaminant level for cyanide in drinking water (200 ?g/L) permissible in the USA. The Zn(II) tetraphenylporphyrin-based ISEs have a high selectivity over interfering ions relevant to applications in the mining industry, i.e., chloride, sulfate, thiosulfate. The logarithmic selectivity coefficients for CN– over chloride, sulfate and thiosulfate are -3.71, -5.08 and -6.57, respectively. Importantly, this electrode exhibits a higher selectivity for CN– over OH– (logarithmic selectivity coefficient for CN– over OH–is -3.42), which enables accurate monitoring of CN– in cyanide-leaching processes in the mining industry, where sample matrices are maintained above pH 10.5 and include anions such as Cl–, S2O32– and SO42–. While the suitability of this electrode will depend on the local ore composition at specific mining sites, preliminary results show that cyanide can be detected in the relevant concentration range in samples that also contain SCN–, Cu(CN)43-, Zn(CN)43-, Ni(CN)43-, and Fe(CN)64-, as representative of gold mine tailings.
Reference: Chen, L. D., Zou, X. U., Buhlmann, P. “A Cyanide-Selective Electrode Based on Zn (II) Tetraphenylporphyrin as Ionophore” Analytical Chemistry, 2012, published on-line.2012, 84, 9192–9198.