An investigation on the effects of orthophenylene diamine and sodium lignin sulfonate on zinc electrowinning from industrial electrolyte

In this work, we investigated the effects of orthophenylene diamine (OPD) and sodium lignin sulfonate (at a range of 3-10 ppm) in industrial zinc sulfate electrolyte on the current efficiency, the energy consumption of zinc electrowinning, and the physical characteristics of zinc deposits. The electrowinning experiments were conducted using a laboratory-scale apparatus, at a plating time of 80 min, a current density of 500 A m(-2), and a temperature of 38degreesC. Industrial zinc sulfate electrolyte having zinc and H2SO4 concentrations of 62 and 170 g L-1, respectively, was employed. Scanning electron microscopy (SEM) was used to characterize the zinc deposits with respect to surface morphology. The results clearly showed that OPD had a very negative (catastrophic) effect on the current efficiency and, consequently, the power consumption of zinc electrowinning. Current efficiency dropped from about 90% at no addition to less than 60% at only 3 ppm addition level. On the other hand, the addition of up to 10 ppm sodium lignin sulfonate had no negative impact on the zinc electrowinning process, nor on the quality of the zinc deposits. (C) 2003 Elsevier Science B.V. All rights reserved.