In the present study, the thermodynamics and mechanisms of vanadium extraction by a mixture of bis-2-ethylhexyl phosphoric acid (D2EHPA) and tri-n butyl phosphate (TBP) from sulfate medium were investigated. It was found that the maximum extraction percent of vanadium occurs at pH 1.8 under ambient conditions; this phenomenon was ascribed to the predominant presence of cationic species of vanadium (VO2+) at this pH. Based on the Fourier Transform Infrared (FT-IR) spectrums, the P-O-H bond of D2EHPA was found responsible for the extraction of VO2+ species through a cationic exchange mechanism. Employing the slope analysis method showed that the stoichiometric reaction between VO2+ and D2EHPA was CO2+ + RH <-> (VO2R) over bar + H+ regardless of the D2EHPA concentration. It was also shown that the TBP has no synergistic effect on the VO2+ extraction except in the experiments conducted at 60 degrees C. This was further elucidated by applying a modifying factor for TBP in the slope analysis method. Results showed that vanadium extraction was an endothermic reaction with an apparent molar enthalpy of 22.76 kJ/mol. (C) 2015 Elsevier B.V. All rights reserved.