The effects of additives on the electrowinning of zinc from sulphate solutions with high fluoride concentration

Effects of additives on zinc electrowinning from zinc sulphate aqueous solution with a higher concentration fluoride (300 mg L− 1) have been investigated based on the measurements of polarization curves (PC), cyclic voltammetry (the working electrode was made from pure aluminum, a graphite rod was used as counter and a saturated calomel electrode (SCE) as the reference electrode) and zinc electrodeposition experiments, in which gelatin, boric acid, citric acid and aluminum sulfate served as additives and were added into the electrolytes alone or in combination with different dosages. Zinc deposit morphology on aluminum cathode surface after zinc electrowinning was observed using SEM (scanning electron microscopy). The results indicated that all additives within a certain concentration scope increased nucleation overpotential, stimulated cathodic polarization and promoted electrodepositing with fine-grained zinc. The nucleation overpotential increased from 124 mV to 183 mV in addition of 5 mg L− 1. Finer-grained zinc deposits, lower specific power consumption (maximum reduction from 3129 kWh t− 1 to 2192 kWh t− 1) and higher current efficiency (86.2% to 96.2%) were available by these additives combination.