Synergistic extraction of rare earths with bis(2,4,4-trimethylpentyl) dithiophosphinic acid and trialkyl phosphine oxide

Synergistic extraction of trivalent rare earths from nitrate solutions usin g mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301 = HX) and trialkyl phosphine oxide (Cyanex 923 = TRPO) in xylene has been in vestigated. The results demonstrate that these trivalent metal ions are ext racted into xylene as MX3.3HX with Cyanex 301 alone. In the presence of Cya nex 923, La(III) and Nd(III) are found to be extracted as MX2.NO3.TRPO. On the other hand, Eu(III), Y(III) and heavier rare earths are found to be ext racted as MX3.HX.2TRPO. The addition of a trialkylphosphine oxide to the me tal extraction system not only enhances the extraction efficiency of these metal ions but also improves the selectivities significantly, especially be tween yttrium and heavier lanthanides. The separation factors between these metal ions were calculated and compared with that of commercially importan t extraction systems like di-2- ethylhexyl phosphoric acid. (C) 1999 Elsevi er Science B.V. All rights reserved.