Stoichiometry and thermodynamics of cerium(IV) solvent extraction from sulfuric acid solutions by CYANEX 301

The paper presents a treatment of the stoichiometry of cerium (IV) extraction, in a Ce(IV)-H2SO4-CYANEX301 extraction system, which has been extended to cover determination of the conditions of feed solution pH, sulfate concentration, extractant concentration, volume ratio of aqueous to organic phase, and temperature of the extraction reaction for maximum extraction of cerium (IV). The quantitative solvent extraction of 250 mg L-1 cerium (IV) at pH 3 of aqueous phase was obtained with 0.3 M CYANEX 301 in kerosene. The stoichiometry of the extracted species was elucidated using traditional slope analysis method. A mixed ion exchange-solvation mechanism was proposed for the extraction of cerium (IV) by the sulfur donor ligand, CYANEX 301 from sulfuric acid solutions. The results of the thermodynamic investigations indicated that the extraction process was more favorable at high temperature and non-spontaneous at low temperatures (Delta S degrees < 0), and endothermic in nature in the entire investigated temperature range. The positive value of Delta G(293K)(0) suggested that the extraction reactions of cerium (IV) from sulfuric acid solutions by CYANEX 301 extractant proceed as nonspontaneous reaction at low temperature, while the negative value obtained for Delta G(>=303K)(0) showed that the cerium (IV) extraction is a feasible process at high temperature.