 4 ( <unk> denotes a mixture of all the lanthanides except <unk> ) , and the third is a <unk> <unk> . <unk> also contains thorium and yttrium , which <unk> handling because thorium and its decay products are radioactive . For the extraction from the ore and the isolation of individual lanthanides , several methods have been developed . The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate . <unk> the ore and subsequent acidic and basic <unk> is used mostly to produce a concentrate of lanthanides . If cerium is the dominant lanthanide , then it is converted from cerium ( III ) to cerium ( IV ) and then precipitated . Further separation by solvent <unk> or ion exchange chromatography yields a fraction which is enriched in europium . This fraction is reduced with zinc , zinc / <unk> , electrolysis or other methods converting the europium ( III ) to europium ( II ) . Europium ( II ) reacts in a way similar to that of alkaline earth metals and therefore it can be precipitated as carbonate or is co @-@ precipitated with barium sulfate . Europium metal is available through the electrolysis of a mixture of molten <unk> and <unk> ( or <unk> ) in a graphite cell , which serves as <unk> , using graphite as <unk> . The other product is chlorine gas . 
