Hamed Tavakoli, Mohammad Reza Aboutalebi, Seyed Hosein Seyedein, Seyed Nezameddin Ashrafizadeh,
Volume 18, Issue 1 (3-2021)
Abstract
Separation of samarium and lutetium was investigated through solvent extraction from their mixed aqueous species using commercial extractants of D2EHPA and PC88A. The Response Surface Method (RSM) was utilized to design the solvent extraction experiments. In which, a Central Composite Design (CCD) was applied to set the optimum conditions for highest separation factors between Sm and Lu. Design of Experiments (DOE) was conducted by making use of four operating variables, namely initial pH of the aqueous solutions (A: 0.2–2.6), extractant concentration (B: 0.01-0.09 molar), mole fraction of D2EHPA in the extractant mixture (C: 0 - 0.8) and a type of acidic solution (D: sulfuric and nitric acid) at three levels. The results indicated that the initial pH was the most paramount variable in solvent extraction of samarium and lutetium, while in the case of lutetium, the molar fraction of D2EHPA in the mixed extractants was non-influential. The statistical model predictions were confirmed by experiments for both samarium and lutetium extraction with high validity parameter of 97 and 98%, respectively. The optimum conditions for samarium and lutetium separation were identified as: A=0.8, B= 0.05, C= 0.2 and D= sulfuric acid. According to the findings of the model, the desirability value at the optimum conditions was evaluated as about 0.93, in which 71% of lutetium was extracted while the amount of extracted samarium was only less than 1%.
Hamed Tavakoli, Mohammad Reza Aboutalebi, Hossein Seyedein, Seyed Nezameddin Ashrafizadeh,
Volume 18, Issue 3 (9-2021)
Abstract
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.
