RI 6957 Electrowinning High-Purity Neodymium, Praseodymium, And Didymium Metals From Their Oxides

High-purity neodymium, praseodymium, and didymium (a cerium-free mixture of light rare-earth elements) were prepared by electrolysis of the oxides in a medium consisting of the respective rare-earth fluorides and lithium fluoride. The metals were electrodeposited in the liquid state and collected as nodules on a skull of frozen electrolyte. Cells were operated from 1,000° to 1,100° C. The requisite temperature was maintained by passing alternating and direct currents through the bath. Graphite was used for the anodes and tungsten for the cathode. The metal products contained <0.02 percent each carbon and oxygen and <0.025 percent tungsten as major impurities. Analysis of typical didymium metal nodules showed an approximately twofold enrichment in neodymium and praseodymium over their respective concentrations in the cell feed. The lanthanum content of the metal was about one-half its content in the oxide.