Role of organic reagents and impurity in zinc electrowinning

The role of organic reagents (flocculant and flotation collectors) and impurity (lubricating oil) in zinc deposition and in product quality is described in this paper. In the presence of a flotation collector for zinc and a lubricating oil, characterized by polar amine and non-polar alkyl groups, respectively, by using Fourier transform infrared spectroscopy, an inhibition of the metal nucleation process was observed, which was found to be particularly significant for electrolyte contaminated with the amine-containing compound. The current efficiency (CE) dropped from 93.7% (organic-free solution) to 21.6% in the presence of 50 mg·L− 1 of collector for zinc, and a negative but smaller effect was observed in the presence of similar amounts of the lubricating oil (90.7%). The addition of a flocculant and a collector for impurities, which contain the polar amide and carboxyl groups in their molecules, respectively, caused minor increases in the nucleation overpotential for zinc deposition and only at relatively high concentrations (100 mg·L− 1). The addition of these compounds to the solution slightly increased CE. The characterization of the Zn deposits by X-ray diffraction and scanning electron microscopy revealed the formation of pores in deposits obtained from solutions containing the collector for impurities or lubricating oil, and different growth patterns were identified when the flocculant or collector for zinc was added to the solution. The observed trends have been interpreted in terms of the polar character and reactivity of the organic molecules to Zn2 + ion, and adsorption on the cathode surface.