In this study the distinctive benefits of thiourea as an electrolyte additive are investigated and its limitations in the electrorefining process are evaluated in depth. A laboratory-scale electrorefining circuit consisting of five anodes and four cathodes was used for the experiment process with the addition of glue, Avitone, sodium chloride and thiourea as additives in the industrial electrolyte. Thiourea concentrations were varied in the experiments and the deposited copper cathodes analysed through different methods and weighed for calculation of current efficiency. Spark analysis for traces (SAFT) machine was used for chemical composition analysis while a scanning electron microscopy with electron dispersive spectroscopy (SEM/EDS) was used for analysis of cathode morphology. X-ray diffraction spectroscopy (XRD) was used for detection of phases on the cathode surface after electrodeposition. Contamination of cathode by sulphur was found to be directly proportional to the thiourea concentration in the electrolyte. Sulphur from thiourea contaminates the cathode by complexing with copper and other elements of the cathode impurities such as nickel and iron to form chalcopyrite and Pentladite on the cathode surface. Despite the sulphur-contamination of cathode by thiourea, increasing the concentration of thiourea in the electrolyte was found to increase copper grain sizes and produce deposits that are evenly deposited and free of dendrites and nodules. On the other hand, addition of thiourea in the electrolyte reduced the current efficiency by up to 5.3% when compared to deposition in the absence of thiourea.
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