Solvent extraction of some lanthanides from chloride and nitrate solutions by binary extractants

The solvent extraction of some rare earth metals (REM) from chloride and nitrate solutions by binary extractants, such as salts of trioctylmethylammonium with dialkylphosphinic, dialkylmonothiophosphinic, dialkyldithiophosphinic acids in toluene, as a function of the compositions of the aqueous and organic phases has been studied. The extraction isotherms of rare earth metals in trioctylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate system were examined. The effect of binary extractant concentration in the organic phase and concentration of salt present in the aqueous phase (NaCl, NaNO3) was also investigated. The ratio of Cex:CLn(org) was found for REM chlorides close to 3, whereas that was found for REM nitrates close to 1 in the case of the loaded organic phase. Extraction efficiency of binary extractants towards lanthanum chloride as well as lanthanum nitrate decreases in the series: dialkylphosphinate > dialkylmonothiophosphinate >> dialkyldithiophosphinate of quaternary ammonium base (QAB). The separation factors of some metal pairs in the extraction of chlorides and nitrates of lanthanides were calculated using the experimental data obtained. Effective extraction systems involving binary extractants for separation of rare earth metals from chloride and nitrate solutions were found.