Study on the separation of rare earth La/Sm by roasting modification of lanthanum samarium slag and electrochemical method of molten salt

The regeneration and utilization of La in its thermal reduction slag of rare earth metal are of great significance for the high-value utilization of rare earth secondary resources. In this paper, the roasting modification of lanthanum samarium slag (LaSlag) and the electrochemical reduction separation mechanisms of La/Sm in (LiF-LaF₃)_eut fluoride molten salt carrier were studied. The effect of cathode current density and temperature on the (LiF-LaF₃)_eut.-LaSlag electroreduction parameters (cell voltage, back electromotive force and overpotential) was explored to provide a basis for optimizing external reduction conditions. The results showed that all the lanthanum-samarium slag could be dehydrogenated to stable rare-earth lanthanum-samarium oxides by roasting modification at no less than 823 K. Within the temperature range of 1 223~1 323 K, during the electroreduction process of the（LiF-LaF₃)eut.-LaSlag system, as the cathode current density increased within the range of less than 4.0 A/cm², the cell voltage and overpotential of the system also gradually increased, while the anode effect period progressively shortened. When the current density was higher than 4.0 A/cm², its three electroreduction parameters tended to be stable. As the cathode current density remained constant, the effect of cathode overpotential and anode effect period was relatively small. Below 1 273 K, the cell voltage and back electromotive force decreased slightly with the increase in temperature, while they tended to be stable at temperatures above 1 273 K.