The effects of mixtures of acid mist suppression reagents on zinc electrowinning from spent electrolyte solutions

The effects of Dowfroth 250 (D) and Tennafroth 250 (T) in combination with saponin (S) on zinc deposition current efficiency and power consumption during electrowinning of zinc from industrially supplied spent electrolyte solutions were investigated. The surface morphology and crystallographic orientations of the zinc deposits were also examined by scanning electron microscopy and X-ray diffraction techniques, respectively. Acid mist suppression efficiencies were measured and investigated by frothing behavior of the additives and by surface tension measurements. Concentrations of 5, 10, and 15 ppm of each of the additives were mixed with all possible combinations into spent electrolyte to study the effects. Results showed that addition of Dowfroth 250/Tennafroth 250 as well as saponin decreased the current efficiency, increased the energy consumption while maximum acid mist suppression efficiencies of 86.1% and 87.0% were obtained at D5 + S5 and T5 + S5, respectively. The increase in saponin concentration resulted a change in preferred crystal orientation from (104) (112) (103) (102) (101) at low saponin concentrations to (101) (112) at higher saponin concentration. Bright and compact deposits were obtained at a mixture concentration level of T5 + S5 and D5 + S5.