Pilot Study Of Nickel On The Zinc Electrowinning Process And Removal Of Ni In The Leaching Solution Purification

Zinc is one of the most nonferrous metals in Modernization Construction, Chinese reserves and yields of zinc are the biggest in the world and China is the main producing and exporting country. At present, zinc is mainly produced by hydrometallurgy of roasting-leaching-electrodeposition-purifying process. For the mostly process of the hydrometallurgy, electrodeposition of zinc's development requirement is mechanization and automation,the long period zinc-elelctrowinning(the period is not less than 48h) is the premise of mechanization and automation. The existing of impurity ions is directly related to the electrowinning and process index of zinc. So the behavior and impact of the impurity to the zinc electrowinning have been studied a lot by some of metallurgist, the nickel ions is one of the impurities that have the most influence.In this paper analyzed the present status of thermodynamics and kinetics of zinc electrowinning process and the influence of the mainly impurities, summarized the methods of nickel removal from zinc electrolyte. Base on this foundation, we studied the electrochemical behaviour of the nickel ions in the zinc electrolyte, the influence of nickel ions to the zinc electrowinning and the removal of nickel from zinc electrolyte.Studied the electrochemical behaviour of nickel ions in the zinc electrolyte, through the studying of the conductivity, with the slowly increasing of nickel ions, the conductivity of the electrolyte have a slowly increasing trend too, but this trend can be neglected in the whole range of the electrolyte. Cathodic polarization curves with different concentrations of nickel showed that the existing of nickel ions can decrease the polarization of cathodic and the overpotential of hydrogen, so it can increase the releasing of hydrogen. Through the Tafel fitting of the Cathodic polarization curves, we can find that the exchange current density and the mass transfer coefficient will be increased with the concentration of nickel ions. Therefore, it changed the mechanism of zinc electrowinning because of the existing of the nickel ions in the zinc electrolyte, increased the reversibility and the rate of the electrode reaction. In addition, chronoamperometry curves also prove that hydrogen evolution is stimulated by nickel.Through the Electron Probe (EPMA) and scanning electron microscope(SEM),we studied the quality of electrolytic zinc.The study shows that the simple substance nickel would be released in the electrowinning process, in the same time, it could be increase the releasing of hydrogen, consequently, the surface of cathode zinc could be found some holes with different size and depth.Through the experiment of the routine-period (26h) zinc electrowinning and the long-period(48h) zinc electrowinning, it studied the influence of the nickel ions to the current efficiency, the electrical power consumption, the cell voltage and the quality of electrolytic zinc.The study shows that it can be have a serious effect when the nickel ion content is 0.5mg·L-1 in the routine-period zinc electrowinning process but 0.15mg·L-1 in the long-period.By studying the experiments of the purification of nickel from the zinc electrolyte which contains the unique impurity of nickel by zinc dust precipitations and the really industrial purification experiment, we could include that time, temperature and additive are the three mostly factors to the removal of nickel from zinc electrolyte.In this paper, we can obtain the main effects of nickel ions in the zinc electrowinning process though the behavior of nickel ions and long-period zinc electrowinning experiments. This research can provide some of guidance for the further study of deep purification of zinc electrolyte and the influence of other impurities in long-period zinc electrowinning.