Studies on the equilibrium and mechanism of Th(IV) extraction by CYANEX 272 in kerosene from nitrate medium

The extraction behavior of Th(IV) from aqueous nitrate medium by the commercial bis(2,4,4-trimethylpentyl) phosphinic acid extractant, (CYANEX 272) in kerosene has been studied. Batch extraction investigation was firstly carried out to elucidate the stoichiometry of the extracted Th(IV) species and deduce the suitable conditions to be applied in the kinetic studies using Lewis cell technique. The extracted species was found to be [Th(OH)3A(HA)3] on the basis of slope analysis method. The different parameters affecting the extraction rate of Th(IV) as well as temperature were separately investigated, and a rate equation was deduced. The experimental results indicate that the rate of Th(IV) extraction is first order dependent on CYANEX 272 concentration, first order dependent on hydrogen ion concentration and inversely first order dependent on thorium concentration. The proposed mechanism for the extraction process is controlled by chemical reaction in the bulk phase rather than at the interface. (orig.)