The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive. For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography. Pure promethium is available through the reduction of PmF 3 with calcium metal.
Excess calcium is removed from the reaction mixture under vacuum.