LIQUID-LIQUID-EXTRACTION OF SOME LANTHANIDE METAL-IONS BY POLYOXYALKYLENE SYSTEMS

Polyoxyalkylene systems, namely, polypropylene glycol (PPG-1025), poly ethylene glycol (PEG-600) and polybutadieneoxide (PBDO-700) dissolved in either nitrobenzene or 1,2-dichloroethane have been tested as prosp ective extractants for some lanthanide metal ions (Eu3+, Pr3+ and Er3) from their aqueous solutions in the presence of picrate anions. The metal ions were quantified before and after extraction using the induc tively coupled plasma emission spectrophotometry technique. The percen t extraction and the distribution coefficients have indicated that pH of the aqueous phase, picrate concentration and the organic solvent ar e the major parameters that affect the extraction efficiency of the me tal ions. The optimum pH range was found to be 3.5-5.5 and the picrate concentration should be as high as possible; however, a picrate conce ntration of about 0.05 M proved to be adequate for a near quantitative extraction. In all cases, nitrobenzene enhanced a higher percent extr action compared to 1,2-dichloroethane. The efficiency of the polyoxyal kylene systems to extract certain lanthanide metal ions was in the ord er PBDO-700 > PPG-1025 > PEG-600 when nitrobenzene was the organic sol vent and in the order PPG-1025 > PBDO-700 approximate to PEG-600 when 1,2-dichloroethane used as the solvent in the organic phase. The extra ctability of PPG-1025 towards the lanthanide metal ions was in the ord er Pr3+ > Eu3+ > Er3+ irrespective of the organic solvent used. The st oichiometry of the extracted polyoxyalkylene ion-pairs with the lantha nide metal ions has been estimated. Each mole of metal ions is associa ted with three moles of picrate anions and 13 to 14 moles of propylene oxide units in the case of PPG-1025, and about 9 to 10 moles of ethyle neoxide units in the case of PEG-600 and 10 moles of butadieneoxide un its in the case of PBDO-700. (C) 1997 Elsevier Science B.V.