Cadmium recrystallization in the process of zone refining

The effect is studied of ion magration and crystallization rate on the extent of the purification of cadmium in the process of its zonal refining. The cadmium purification degree has been evaluated from the effective distribution coefficient, Ksub(eff), by comparing it to the Pfannian distribution curves. It has been established that as the crystallization rate decreases the degree of the purification of cadmium from impurities increases, improving the values of Ksub(eff) for Pb, Tl, Cu and Ni. To keep the degree of purification stable, to reduce the thickness of the diffusion layer at the crystallization front and to increase the yield of refined metal, it is necessary for the zonal recrystallization to be accomplished at a monotonically diminishing rate, while reducing the length of the molten zone of one passage. The migration of impurity ions in molten cadmium in static state has indicated that most impurities, viz. Ag, Cu, Fe and Al, concentrate on the cathode, Ni and Pb migrating-to the anode; the distribution of Tl has not been established