Synergistic extraction of gadolinium from nitrate media by mixtures of bis (2,4,4-trimethylpentyl) dithiophosphinic acid and di-(2-ethylhexyl) phosphoric acid

The extraction of gadolinium (III) from aqueous nitrate solution with bis (2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301), di-(2-ethylhexyl) phosphoric acid (D2EHPA) and the mixtures of extractants was investigated. Various parameters affecting the extraction process including the pH of aqueous phase, nitrate ion, extractant concentration, temperature, and stripping agents were studied. The stoichiometric coefficients of reactive extraction, thermodynamic and equilibrium parameters were obtained for two extractants and their mixtures. The results showed that the extraction ability of Cyanex301 was lower than that of D2EHPA extractant. As a result, the extraction of Gd3+ at low concentration of Cyanex301 was investigated by the addition of D2EHPA to the extraction system. The reactive extraction in the mixture system was spontaneous in nature as referred to the negative sign of Delta G while it was not favorable in case of single Cyanex301 system as indicated by the positive sign of Delta G. The experimental results showed that the mixture of extractants provided better extraction efficiency and effective stripping performance in comparison with single D2EHPA or Cyanex301 system. (C) 2013 Elsevier Ltd. All rights reserved.