The effects of magnafloc and zinc on electrowinning of cadmium in sulfate solutions

The effect of an organic additive magnafloc and/or zinc on the electrowinning of cadmium from acidic sulfate solutions are studied. It is observed that addition of magnafloc increases the current efficiency and decreases the energy consumption both in the absence and presence of zinc in the solution. The addition of magnafloc increases the cathodic current efficiency of cadmium from 84.3% at 5 mg dm - 3 to ~ 97% at 40 mg dm - 3 and decreases the energy consumption by 133 kWht - 1. Magnafloc when present in the solution polarizes the cathode causing the electroreduction of cadmium at more negative potentials. The presence of either magnafloc or zinc or both affects the degree of crystallinity of the electrodeposits, however, with magnafloc the degree of crystallinity is higher indicating that the deposits are also more ductile. Scanning electron micrographs of cadmium deposits obtained in the presence of magnafloc show that compact deposits are formed with an instantaneous nucleation and growth mechanism. It is evident that the presence of magnafloc decreases the number of grains and increases the sizes of the crystallites. However, the presence of zinc in the solution has opposite effect on the morphology as compared to that of magnafloc