Some features of group separation process of transplutonium and rare earth elements by extraction with HDEHP from solutions containing DTPA

The effect of concentration of separable elements in case of transplutonium and rare earth elements extraction with di-2-ethylhexylphosphoric acid (D2EHPA) from solutions containing diethylenetriaminepentaacetic acid (DTPA) on their distribution coefficients and separation at a relatively low concentration of the extracting agent (0.2-0.5 mol/l) and complexon (0.01-0.1 mol/l) is studied. It is shown that the changes in metal distribution at the change of its concentration to a great extent is determined by the distribution coefficient (DC) of the element microamounts. In case of small DC values the increase of metal concentration decreases the equilibrium complexon concentration. This causes the increase of DC metal. At high DC values dominates the effect of the decrease of extracting agent equilibrium concentration which results in the DC decrease. Another peculiarity of the studied system is slow attainment of transplutonium and rare earth elements extraction equilibrium. The process rate depends on the intensity of mixing solutions reagent concentration and admixtures. With the increase of DTPA concentration and pH-value of solution the process rate constantly decreases. Introduction of citric or other carbonic acids in the system permits to accelerate the mass exchange. With increase of atomic number of the distributable element in the RE and TPE series the process rate constantly decreacses. Approximate relations reflecting the effect of the studied factors have been found, the program of coefficients of computerized distribution is developed