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Electrochemical oxidation of cyanide and simultaneous removal of heavy metals from gold cyanidation wastewater
Delius Cordova, Inge
Delius Cordova, Inge
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2023
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Abstract
Cyanide is widely used in the gold mining industry to extract gold from different gold-bearing ores and as a result gold cyanidation process wastewater can contain high amounts of cyanide as well as other heavy metals that can pose risks if released to the environment. Electrochemical methods such as electrooxidation have been shown to effectively treat cyanide contaminated wastewater. However, past studies have largely focused on cyanide oxidation and metal recovery using synthetic solutions which may not accurately represent conditions of mining process waters. In the present study, the electrochemical destruction of cyanide and simultaneous removal of heavy metals using a graphite anode and copper cathode under alkaline conditions was investigated. Batch experiments were conducted on synthetic and real gold process wastewaters. First, the kinetics of cyanide electrooxidation were studied by examining the effects of applied voltage, electrolyte composition, and copper concentration. The effects of electrolyte composition were of particular interest as several gold cyanidation facilities have shifted towards using partially desalinized and even raw seawater for their processes. Results indicated that cyanide follows a first order reaction with respect to CN- ions for most wastewater samples examined. In addition, increased voltage and NaCl concentrations lead to an increase in the rate of cyanide oxidation.
The effect of applied voltage, NaCl concentration and initial cyanide concentration on heavy metal removal was then evaluated for synthetic wastewater samples. Results showed that lower applied voltages and lower NaCl concentrations led to an increased removal of copper. For real process wastewater samples, only the effects of applied voltage and conductivity on metal removal were studied. Results indicated that a higher applied voltage and higher conductivity lead to increased removal of copper and zinc. The variation in results between real and synthetic wastewaters can be attributed to the higher amount and stability of metal-cyanide complexes measured in real process wastewaters. Although optimal conditions for an electrochemical system can vary depending on the water’s composition, results indicate that an applied voltage of 5V and addition of NaCl can help increase the rate of cyanide oxidation as well as metal removal. Overall, this study shows that electrochemical treatment of gold cyanidation process water can be an effective method for cyanide oxidation and simultaneous metal recovery.
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