Study on extraction equilibrium of U(NO3)4 and HNO3 with TBP. Pt.2. Critical concentration of uranium (IV) in organic phase

The critical concentration of uranium (IV), c(U(IV))max, in pregnant organic phase is determined for the extraction of U(IV) by 30% TBP-kerosene from U(IV)-HNO3 solution, c(U(IV))max decreases gradually with increase of concentration of HNO3 and reaches a minimum value at 4.0∼5.0 mol/L HNO3, then increases gradually. c(U(IV))max increases proportionally with the temperature. c(U(IV))max in 30% TBP-diluent is determined too, c(U(IV))max decreases with increase of carbon numbers of linear chain saturated hydrocarbon. The curve of critical concentration of U(IV) vs concentration of HNO3 is obtained. If initial concentration of HNO3 is 3.0 mol/L at of 20 degree C, critical initial concentration of U(IV) is 0.158 mol/L. However, when critical initial concentration of U(IV) is more than 0.158 mol/L in 3.0 mol/L nitric acid, the third phase will be formed for extraction of U(IV) with 30% TBP-kerosene. Distribution ratio of uranium (D(U(IV))) and nitric acid (D(H+)) are determined, and effects of concentration of uranium (IV), nitric acid and different diluents on D(U(IV)) are discussed