Effect of high ionic strength on the extraction of uranium(VI) ions

Preparation and characterization of didodecylphosphoric acid (HDDPA) as an extractant in toluene was carried. Mass spectroscopy showed that the monomer peak at 457.4 amu [M–Na^+] is double that of the dimer at 891.9 amu [M–M–Na^+] and the monomer molecules concentration dominate the dimer molecules in toluene. HDDPA was used as an extractant for the extraction of U(VI) ion from perchlorate and nitrate media that have ionic strength (1.00, 3.00, 5.00, 7.00 M). The effect of HDDPA concentration, pcH, ionic strength of supporting electrolytes, and temperature in the range 15–45 °C on the extraction process have been studied. The stoichiometry of the extraction of U(VI) ion, the free energy change (∆G), the enthalpy change (∆H), the entropy change (∆S), and Kex at different ionic strength have been calculated. The formula of the complexes, which were formed has been established to be UO2(X)(R2)(HR2) at pcH equal 2.00 and UO2(X)(R2)(HR2) and UO2(X)(R2) at pcH =1.00, where (X) is ClO4^- 4 or NO3^-3 and (HR2) is didodecylphosphoric acid monomer, (R2) is the deprotonated didodecylphosphoric acid, where R is the dodecyl group.