Synergic extraction of uranium from phosphate solutions with di-(2 ethylhexyl) phosphoric acid and tri-n-octylphosphine oxide

The synergic extraction of uranium from concentrated aqueous phosphate solutions with di-(2 ethylhexyl) phosphoric acid and tri-n-octylphosphine oxide in kerosene has led to an investigation of the complex species formed by the U(VI) in the organic phase. The role of the phosphoric acid concentration in forming complex species in the aqueous phase which interfere seriously with the extraction process has been explored. It was found that U(VI) was extracted in the organic phase as UO2X2(HX)2mTOPO where m <= 1 depending on the TOPO concentration. Increasing temperature also diminishes the extraction coefficient. An investigation of the latter effect led to values of the enthalpy changes for the process. Ferrous iron reduces U(VI) in acid phosphate media and in the case of U(IV) there is no synergic effect, in agreement with the fact that the U(IV) complexes are coordinately saturated. Moreover this synergic system gives fairly good extraction coefficients even in concentrated solutions of phosphoric acid. (author)