SOLVENT-EXTRACTION OF LANTHANUM(III) AND CERIUM(III) WITH DIALKYLDITHIOPHOSPHORIC ACIDS - SEPARATION FROM THORIUM(IV)

The extraction of lanthanum(III) and cerium(III) with dialkyldithiophosphoric acids, Hdtp, into different polar and nonpolar solvents (cyclohexane, benzene, carbon tetrachloride, chloroform, diethyl ether, dibutyl ether, n-butanol and cyclohexanone) from aqueous solutions containing perchlorate, nitrate and chloride anions has been investigated. The effect of various factors, such as nature of the solvent, pH, metal concentration and foreign anions present in the aqueous phase was investigated in order to establish the mechanism of extraction process. The data obtained suggest an ion-exchange mechanism. The anions present in the aqueous phase do not participate in the extraction process and do not influence significantly the magnitude of the extraction ratios either. The extracted species in the organic phase is a 1:2 complex of lanthanide with Hdtp. The extraction efficiency (E%) is calculated and the possibility of Th-rare earths separation is discussed.