Sequential separation of selenium(IV) from tellurium(IV) by solvent extraction with N-n-octylaniline: Analysis of real samples

Liquid-liquid extraction of selenium (IV) ions from hydrochloric acid solution using Aliquat 336 dissolved in kerosene

Solvent extraction of selenium(IV) ions from highly concentrated hydrochloric acid using 0.4 mol/L Aliquat 336 dissolved in kerosene was investigated. As a modifying agent, 1-octanol (10% v/v) was added to the organic phase to avoid the third phase formation. The effect of different parameters affecting the liquid-liquid extraction of selenium(IV) such as the acid concentration, shaking time, metal ion concentration in the aqueous phase, loading capacity, diluents, and temperature, was studied. The results indicate that selenium(IV) is extracted efficiently by 0.4 mol/L Aliquat 336 dissolved in kerosene. It was noticed that the extraction increased with the increase in the acid and Aliquat 336 concentrations, reaching an extraction percentage of about 92% at 8 mol/L HCl and 97.1% at 1 mol/L extractant. The extracted organic species is postulated to be [H2SeO2Cl2.2R4NCl]org by using the slope analysis method, and the value of Kex for selenium(IV) extraction was found to be 26.17 ± 2 M- 2. The structure of the extracted organic species was confirmed by FT-IR. The effect of diluents using various aliphatic and aromatic diluents indicated that kerosene is the most preferred diluent. This is owing to safety ground purpose, economic consideration, the lower cost, availability, and lower toxicity. Thermodynamic parameters indicate the endothermic nature for the solvent extraction of selenium(IV) for the investigated system according to the positive value obtained of the enthalpy change (ΔH). Depending on the obtained results, the method was used to recover selenium(IV) from a simulated solution synthesized in hydrochloric acid medium, which is expected in anode slime leach liquor solution.

Extraction of Se(iv) and Se(vi) from aqueous HCl solution by using a diamide-containing tertiary amine

Here, we investigated the mechanism underlying the extraction of Se(iv) and Se(vi) from aqueous HCl solutions by N-2-ethylhexyl-bis(N-di-2-ethylhexyl-ethylamide)amine (EHBAA). In addition to examining extraction behavior, we also elucidated structural properties of the dominant Se species in solution. Two types of aqueous HCl solutions were prepared by dissolving a Se^IV oxide or a Se^VI salt. X-ray absorption near edge structure analyses revealed that Se(vi) was reduced to Se(iv) in 8 M HCl. Using 0.5 M EHBAA, ∼50% of Se(vi) was extracted from 0.5 M HCl. In contrast, Se(iv) was hardly extracted from 0.5 to 5 M HCl; however, at molar concentrations above 5 M, the extraction efficiency of Se(iv) increased drastically, reaching ∼85%. Slope analyses for the distribution ratios of Se(iv) in 8 M HCl and Se(vi) in 0.5 M HCl showed that apparent stoichiometries of Se(iv) or Se(vi) to EHBAA were 1 : 1 and 1 : 2, respectively. Extended X-ray absorption fine structure measurements revealed that the inner-sphere of the Se(iv) and Se(vi) complexes extracted with EHBAA was [SeOCl₂] and [SeO₄]^2-, respectively. Together, these results indicate that Se(iv) is extracted from 8 M HCl with EHBAA via a solvation-type reaction, whereas Se(vi) is extracted from 0.5 M HCl via an anion-exchange-type reaction.