Migration regularities of impurities C, O, Fe, Co and Ni and effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport

Abstract

Migration regularities of impurities C, O, Fe, Co and Ni and the effect of crystal transition on C, O and Fe in purification of metal La by solid-state electrotransport (SSE) were studied. The impurity migration direction, removal extent and difficulty were intuitively judged by impurity residual rate distribution curve. It is indicated that major impurities Fe, Co, Ni, C and O in metal La are found to significantly migrate to anode and migration effects are much better with the increase in temperature and prolongation of time in purification of La by SSE. Impurities Fe, Co and Ni in La may be fast diffusion elements, which are very extreme to be removed, and removal difficulty is in the order of Fe < Co < Ni < O < C. When La was migrated for 100 h at 800 °C by SSE, the residual rates of impurity Fe, Co, Ni, O and C are 0.25%, 10.10%, 40.04%, 64.00% and 70.04%, respectively. The crystal transition of La, transformed from fcc crystal to bcc crystal, has significant effect on migration of interstitial impurities, and removal effect of interstitial impurities C and O can be significantly improved when purification was performed above crystal transition temperature of 865 °C of La. However, there is little effect on Fe. When La was migrated at 880 °C for 100 h, residual rates of impurities C and O are, respectively, 19.90% and 32.67% lower than those at 820 °C for 100 h, while that of Fe is lower than 0.25% in both situations. Therefore, more pure metal La can be obtained through further increasing temperature, especially above crystal transition temperature of 865 °C of La.