Thermodynamics of Separating Molybdenum(VI) Over Iron(III) from High Acid Leach Solutions with Mixtures of P507 and N235

In view of the difficulty of separating molybdenum over iron from high acid leach solutions, the thermodynamics of separating molybdenum(VI) over iron(III) with mixtures of 2-ethylhexyl phosphonic mono-2-ethylhexyl ester (P507) and long chain tertiary amine (N235) were investigated to enhance the separation efficiency. Different parameters affecting the extraction of the investigated metal ions, such as aqueous acidity, extractants concentrations, and temperature, were carried out. The extraction reaction was determined by slope analysis. The results show that the extracted complex of Mo(VI) was determined as Mo(OH)_4(H_2O)_2·(OH)_2·R_3N· 2H_2A_2 in a P507+N235 system. The P507 or N235 single system failed to completely separate Mo(VI) over Fe(III) from high-acid leach solutions, whereas the N235+P507 system exhibited excellent separation efficiency. The thermodynamic parameters (enthalpy change ΔH, Gibbs energy ΔG, and entropy change ΔS) have been calculated, indicating that the extraction reaction of Mo(VI) in the P507+N235 system is an exothermic process, and the formation of a more stable and intense coordination bond between Mo(VI) and P507 at low temperatures.