The influence of the concentration of nitric, hydrochloric and phosphoric acids, petroleum sulfoxides (PSO), salting-out agent,
kind of diluent and temperature on the distribution ratio of U(VI) and Th(IV) has been systematically studied. It is found
that the extraction regularity of PSO is similar to that of TBP. The distribution ratio in phosphoric acid is lower, but it
increases with the increase of hydrochloric acid concentration and reaches a high value. The U(VI) exhibits the maximum distribution
ratio at 3–4 mol/l HNO3. The distribution ratio of U(VI) and Th(IV) increases rapidly in the presence of a salting out agent. The extracted compounds
are determined to be UO2(NO3)22PSO and Th(NO3)42PSO. The extraction enthalpies of U(VI) and Th(IV) with PSO were also calculated.