Cathodic Behavior of Samarium(III) and Sm-Al alloys Preparation in Fluorides Melts

Abstract

The electrochemical behavior of samarium ions in LiF-CaF2 melts at tungsten electrodes is investigated by cyclic voltammetry and square wave voltammetry. The electrochemical reduction of Sm(III) into Sm(II) according to Eq. (1) is reversible within 900mV/s.Sm3++e−→Sm2+(1)The reduction process for Sm(II) to Sm cannot be observed due to a more negative potential than that of Li(I) ions. Cyclic voltammograms results have proved that Sm and Al ions can be co-reduced from LiF-CaF2-AlF3-SmF3 melts. The cathodic product from LiF-CaF2-Sm2O3 (0.15mol/L)-AlF3 (8.89mol/L) melts at −731.4mA/cm2 is a thin layer metallic plate mainly composing Al, Al2Sm and Al3Sm. EDS mapping manifests that Sm-Al alloy exists in the cross-section of the deposit with the molar ratio of Sm/Al of 0.020, smaller than the original value of 0.034. By galvanostatic electrolysis in LiF-CaF2-Sm2O3 (0.225mol/L)-AlF3 (0.296mol/L) with Al (6mol/L) at –800mA/cm2 for 3h, only small metal particles dispersed in the molten salts are found, giving a lower Sm/Al molar ratio from 0.1 to 0.2 less than the original value of 1.52 in the melts. The results indicate that it is feasible to extract small amounts of Sm with larger amount of Al by codeposition from fluoride melts.