The effect of lead and some operating parameters on cathode contamination during zinc electrowinning

The influence of various operating parameters such as lead concentrations as impurity, current density, acid concentration and temperature was investigated in acid zinc sulfate electrolyte. Nucleation overpotential (NOP) for various experimental conditions was determined using cyclic voltammetry technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Inductively coupled plasma (ICP) were employed to study the physical and chemical characteristics of zinc deposits. By adding lead to the electrolyte, the current efficiency (CE) was changed from 94.04% for the electrolyte without lead to 95.37% for the solution containing 0.2 mg L− 1 Pb (1.33% increase). However, in the presence of higher lead concentrations (0.2-0.8 mg L− 1), a gradual improvement of CE (0.94%) was found. The results revealed an increase of NOP up to 25 mV with the increase of lead concentration up to 0.8 mg L− 1 in the electrolyte while the rise of acid concentration and temperature lowered the NOP for zinc deposition for 14 and 9 mV, respectively. The increase of current density from 45 to 60 mA improved CE from 94.59% to 95.41% while that of temperature from 35 to 45 °C, enhanced the CE from 94.63% to 95.64%. However, the increase of acidity (158 to 170 g) lowered the CE from 96.58% to 95.60%. The stirring rate up to 412 rpm did not significantly influence the nucleation overpotential values. However, increasing the scanning rate resulted in an increase of NOP values, indicating nucleation improvement and crystal rearrangement.