Equilibrium and mechanism of samarium extraction from chloride medium using sodium salt of CYANEX 272

Kinetics and extraction of samarium(III) from aqueous chloride medium at constant ionic strength were studied using a sodium salt of bis(2,4,4-trimethylpentyl) phosphinic acid (CYANEX 272®) in kerosene. The different parameters affecting the extraction of Sm(III) under equilibrium conditions were separately investigated to elucidate the stoichiometry of the extracted Sm(III) species. The extraction percent of the metal ion was found to increase with the increase in pH. On the basis of slope analysis method, the extracted species appears to be Sm(OH)A2·2HA, where HA refers to CYANEX 272. The loaded organic phase was stripped with 1 M HCl in one stage at 1:1 (organic: aqueous) phase ratio. Kinetic studies on the extraction process were also carried out using a stirred Lewis cell. The results were interpreted by a reaction mechanism where the extraction process is controlled by a chemical reaction in the bulk phase rather than at the interface.

The plot of different concentrations of CYANEX 272 and the values of reciprocal of hydrogen ion against their corresponding values of the samarium extraction rate constant yields straight lines passing through the origin which verifies the suggested rate equation:Figure optionsDownload as PowerPoint slideResearch highlights▶ Extraction of samarium from chloride medium by sodium salt of CYANEX 272 was studied. ▶ The extraction showed a dependence on the pH values of the aqueous phase and extractant concentration. ▶ Controlling extraction reaction kinetically takes place in the aqueous phase rather than at the interface. ▶ The rate of extraction is first-order dependent on CYANEX concentration and inverse first-order with respect to samarium and hydrogen ions.