Implication of Thermodynamic Functions and Speciation Diagrams in Analysis of Solvent Extraction Behavior of Samarium from Acidic Solutions

Solvent extraction of samarium from aqueous solutions by two different types of extractants, namely D2EHPA and PC88A, in kerosene was investigated. Through identification of speciation diagrams, the chemically stable complexes of samarium in different acidic solutions (H2SO4, HCl and HNO3) were first investigated. Regarding the various types of samarium species in sulfate medium in comparison with other acidic environments, H2SO4 and HNO3 media were chosen to examine the extraction behavior of samarium complexes. Thermodynamic parameters of samarium extraction reactions by D2EHPA and PC88A from aqueous solutions of HNO3 and H2SO4 were calculated as ∆G∘ (D2EHPA-HNO3),  , ∆G∘ (D2EHPA-H2SO4) , ∆G∘ (PC88A-HNO3), ∆G∘ (PC88A-H2SO4)  equal to -5.58, 3.40, 6.70 and 14.26, and respective ΔHº values equal to -9.38, -2.75, 4.01 and 16.95 kJ/mol, respectively. According to the results, D2EHPA seemed to be a more efficient extractant than PC88A and nitric aqueous solution was a better media than the sulfuric one. The synergistic effect of binary extractants revealed that synergistic factors were 2.94 and 5.74 in sulfuric and nitric solutions, respectively, for a D2EHPA:PC88A ratio of 2:3. The compositions of extracted complexes by D2EHPA and PC88A in sulfuric and nitric solutions were SmH3A6 and SmH3B6, respectively. Thermodynamic parameters of extraction reactions were calculated to be Ke equal to 9.513, 0.254, 0.067, and 0.003 and ∆S∘ (D2EHPA-HNO3),  , ∆S∘ (D2EHPA-H2SO4) , ∆S∘ (PC88A-HNO3), ∆S∘ (PC88A-H2SO4) equal to -12.75, -20.64, -9.03, and 9.03 (J mol-1), respectively.