Effect of thiourea on nodulation during copper electrorefining using scaled industrial cells

Experiments were conducted using scaled industrial and laboratory cells to evaluate the effects of ratios and concentrations of various additives on n odulation during copper electrorefining. This paper focusses on the effect of Thiourea (TU) on the binary (TU-Cl-) and on the ternary Thiourea-Gelatin -Cl- (TU-G-Cl-) systems. In the pilot plant, temperature was maintained at 65 degreesC; Cl- concentration was at 40 mg L-1 and TU ranged from 20 to 15 0 g t(-1) and G from 50 to 150 g t-1. TU influences the polarization curves , the deposit morphology (roughness and nodule formation), the crystal shap e (round or sharp) and the grain type (elongated or field oriented). TU can have a polarizing or a depolarizing effect depending on conditions tested. The polarizing effect related to a specific TU concentration leads to nodu le formation. Optical metallography and SEM micrographs show that nodules, porosities and dendrites are largely avoided in a ternary system as compare d to a binary one.