The Behavior Of Germanium In Zinc Electrowinning And Additives

Zinc electrowinning is an important procedure in zinc hydrometallurdry, and zinc deposit quality is affected by metal impurities directly. A great deal of research had been done about the effects of impurities on zinc electrowinning and exploring suitable additives to inhibit influences of impurities to make electrowinning carry out smoothly. Therefore, in this paper, the behaviors of trace germanium and additives in zinc electrowinning from sulfate zinc electrolyte were studied on the basis of three main ideas:high germanium content of lead-zinc mine from Chihong Zinc & Germanium Stock Company, production practice of long period zinc electrowinning, especially, redissolution of zinc deposit in zinc electrowinning from sulfate zinc electrolyte in presence of germanium, some electrochemical techniques such as linear scanning voltammetry, Chronoamperometry, and impedance technique and analysis methods of laser Raman spectra and electron probe X-Ray microanalysis (EMPA) were used. The study may provide theoretical basis for guiding production.The behavior of trace germanium in zinc electrowinning from sulfate zinc electrolyte was studied by many electrochemical and modern analysis methods. Polarization curves of zinc deposition from base electrolyte in presence of various concentrations Ge demonstrates that germanium has an action of depolarization on the zinc deposition, and depolarization heightens with germanium concentration increases from 0.04 mg·L-1 to 0.8 mg·L-1. Moreover, Tafel fitting results of the polarization curves indicate that exchanging current density and transfer coefficient increase with germanium concentration increasing, which prove the presence of germanium in the electrolyte will change zinc electrodeposition mechanism, and increase degree of reversibility and rate of electrode reactions. Impedance diagraphs obtained at the same conditions reveals that zinc deposition is a many steps process, the presence of germanium in the electrolyte not only strongly stimulates hydrogen evolution, but also affects charge transfer step of zinc deposition. In addition, chronoamperometry curves also prove that hydrogen evolution is stimulated by germanium. Both laser Raman spectra and EPMA photographs reveal zinc deposition associating with germanium deposition, therefore, hydrogen evolution is stimulated with simultaneous zinc redissolution.A reaction kinetics model of zinc deposition in sulfate zinc electrolyte in presence of germanium was put forward. Moreover, this model was firstly verified through quantum chemistry calculation based on density functional theory. In this calculation, CASTEP software was used to carry out structure optimization and energy optimization of adsorption species on electrode surface. The results of structure optimization show that H+ adsorption makes structure of Zn(101) surface loosen, and Ge4+(Ge) adsorption actions are more serious than that of H+, which make part of Zn (101) surface loosen, and even appear defect. In addition, from energy optimization calculation, it is shown that germanium adsorption reactions on Zn, ZnHad, Znad+ and Zn* are more easily than the other reactions and hydrogen evolution on Gead is more easily than on Zn.Compound additive A was prepared using for long period zinc electrowinning, and the effects of additive A, gelatin, thiourea and cresol on zinc electrowinning were investigated. In comparison with the results, additive A is superior to other additives in aspects of increasing current efficiency, improving surface quality of zinc deposit and reducing consumption of power. Polarization curves of zinc deposition from base electrolyte in presence of various concentrations additive A demonstrates additive A has an action of polarization on the zinc deposition, and polarization heightens with additive A concentration increases from 5 mg·L-1 to 25 mg·L-1. Moreover, Tafel fitting results of the polarization curves indicate that exchanging current density and transfer coefficient faintly decrease with additive A concentration increasing. Impedance diagraphs obtained at the same conditions reveals that the presence of additive A in the electrolyte not only inhibits hydrogen evolution, but also affects charge transfer step of zinc deposition.The interaction of trace germanium and additive A in zinc electrowinning from sulfate zinc electrolyte was firstly studied by many electrochemical and modern analysis methods. Proper additive A may inhibit the effect of germanium on zinc deposition in terms of current efficiency and deposit morphology, on the other hand, from polarization curves, impedance diagraphs and chronoamperometry curves obtained from the base electrolyte in presence of 0.12 mg·L-1 Ge and various concentrations additive A, it is found that additive A may inhibit the depolarization and stimulating hydrogen evolution effects of germanium on zinc deposition, chronoamperometry curves also indicate that germanium dominate the reaction during the first second, additive A become more evident with prolonging of time.