Separation of selenium (IV) and tellurium (IV) from nitric acid medium by solvent extraction using CYANEX 301

Throughout the process of our study, a solvent extraction method has been developed to separate tetravalent selenium, Se(IV), and tetravalent tellurium, Te(IV), from the nitric acid medium using CYANEX 301/kerosene organic solution. The effects and influences of main parameters having an impact on the extraction process, such as acid and extractant concentration, the acidity of the stripping agent, and temperature, were studied in detail, and the nature of the extracted metal ions species was elucidated. The Se(IV) and Te(IV) extraction decrease with increasing temperature, indicating that the metal ion extraction reaction is exothermic. Under the optimum conditions, the extraction of Se(IV) was over 98%, and a separation factor equal to 201.7 was obtained. According to the obtained results, the optimum acid concentration for the separation of Se(IV) and Te(IV) is 2.0 M HNO3 and 0.06 M CYANEX 301 makes possible the effective and selective extraction and separation of Se(IV) and Te(IV). Among the investigated stripping agents, a mixture of 2.0 M HNO3, 0.06 M KSCN, provides adequate stripping efficiency, so that the stripping percentage of Se(IV) from the loaded organic phase in one stage reached 74%. Almost complete recovery of Se(IV) was achieved by three times contacting this stripping solution. The extracted species, established by the conventional slope analysis method, are H2SeO3(HA)4 (at < 2 M HNO3) and Se2OA2 (at > 2 M HNO3); and H3TeO3A(HA) (at < 3 M HNO3) and H2TeO3.(HA) (at > 3 M HNO3), respectively.