Extraction of lanthanoids(III) as thiocyanates with trioctylphosphine oxide into aliphatic and aromatic solvents

The extraction constants of Pr-III, Eu-III, and Yb-III were determined when the lanthanoids(III), Ln(III), were extracted from a 1 M sodium thiocyanat e aqueous solution with trioctylphosphine oxide (TOPO) into decane, and int o commercially available mixed solvents, aliphatic or aromatic consisting o f carbon numbers C9 to C13. The extracted species, LnX(3), are associated w ith 3 molecules of TOPO for Yb-III and 4 molecules for Eu-III and Pr-III. T he extraction constants obtained for decane and the aliphatic mixed solvent s are very similar to hexane, regardless of the lanthanoids. The separation factor, represented by the ratio of the distribution ratio between two met als at a given TOPO concentration, is larger for aromatic than for aliphati c solvents. The use of C-9 - C-12 hydrocarbons, either singly or as mixed s olvents, is recommended instead of hazardous solvents such as hexane and be nzene.