Abstract
The dissolution behavior of electrodeposited Zn was studied in the electrowinning solution containing an impurity such as Ag, Al, As, Cd, Co, Cu, Fe, Ge, Ni, Pb or Sb. The dissolution occurs when the operating current density becomes substantially lower than the critical current density for Zn deposition onto Zn electrode. The simulation experiments revealed that the decrease in the operating current density should be resulted from such two factors that the practical current density decreased due to the increased cathode surface area and that the critical current density increased in the presence of impurity in the solution. The impurities were classified into four groups according to their effects, previously reported by the present autnors, on tne cnticai current density. The time-dependence of Al cathode potential was measured at three levels of current densities in the solutions containing three different amounts of each impurity. The effects of each group of impurities on the electrodeposition and dissolution behaviors of Zn were discussed by considering above two factors. Further the dissolution behavior during the commercial electrowinning operation, in which the impurity concentration was usually time-dependent, was briefly referred.
