en Research Paper Research Paper 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 HNO₃media 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 H₂SO₄were 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 SmH₃A₆and SmH₃B₆, respectively. Thermodynamic parameters of extraction reactions were calculated to be K_eequal 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. Samarium,Speciation diagram,Solvent Extraction,D2EHPA,PC88A 1 10 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-13-12&slc_lang=en&sid=1 Hamed Tavakoli hamedtavakoli@gmail.com 1800319475328460014720 1800319475328460014720 No Iran University of Science and Technology Mohammad Reza Aboutalebi mrezab@iust.ac.ir 1800319475328460014721 1800319475328460014721 Yes Iran University of Science and Technology Hossein Seyedein seyedein@iust.ac.ir 1800319475328460014722 1800319475328460014722 No Iran University of Science and Technology Seyed Nezameddin Ashrafizadeh ashrafi@iust.ac.ir 1800319475328460014723 1800319475328460014723 No Iran University of Science and Technology