Thermodynamic investigation into extraction of cerium(III) by tributyl phosphate from phosphoric acid solutions

A mechanism of extraction of cerium by tributyl phosphate (TBP) from phosphate solutions using model and production solutions containing, %: 26–28 P2O5, 1.2–2.8 SO3, 0.3–0.8 CaO, 0.1–0.4 Al2O3, 0.3–0.4 Fe2O3, and 0.09–0.1 REE(NO3)3 is investigated. The model solution of phosphoric acid corresponds to the industrial solution of extraction phosphoric acid (EPA) by the content of P2O5 and Ce(NO3)3 and value of pH (0.6). Dependences of extraction parameters on the TBP concentration in o-xylene and concentration of nitrate ions introduced by magnesium and calcium nitrates, which are used as a salting-out agent, are found. The composition of the extracted organic complex of cerium Ce(H2PO4)(NO3)2TBPorg is determined. A constant of extraction equilibrium and the Gibbs energy of extraction are calculated. It is concluded by the results of the experiment that it is unreasonable to use TBP to extract Ce from phosphoric acid systems without introducing a considerable amount of the salting-out agent.