Migration regularities of impurity aluminum and copper in purification of metal lanthanum by solid-state electrotransport

In view of the previous studies on the migrations of impurity aluminum (Al) and copper (Cu) in purification of rare earth metal by solid-state electrotransport (SSE), there are still some questions about that which direction they migrate to and whether there are significant migrations or not. The metal lanthanum (La) was used as research object, and the effects of migration temperature and time on the distributions and migration regularities of impurity Al and Cu were investigated in the present study by increasing concentration of impurity Al and Cu in raw metal La. The impurity migration direction and removal difficulty were intuitively judged by the residual rate distribution curve of impurity. It is indicated that metal impurity Al and Cu in metal La at 800 °C with direct current are found to significantly migrate to anode and their residual rates near cathode decrease with the increase in migration temperature and prolongation of migration time. The relatively large vapor pressure of Al and Cu makes their residual rate distribution curves being low in middle and high in ends. When metal La was continuously purified for 100 h at 800 °C by SSE, the residual rates of impurity Al and Cu at 20 mm from cathode are 68.43% and 57.43%, respectively, showing that Cu is much easier to be removed than Al.