Mathematical modeling of solvent extraction of uranium from sulphate media employing 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) and its mixture with trioctylphosphine oxide (TOPO) as extractants

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, H2A2 in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO2(HA2)2. This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (%E) and the acidity (Hi). A mathematical model correlating the experimental distribution ratio values of U(VI) (DU) with initial acidity (Hi) and initial uranium concentrations (Ci) was developed: DU 12.98(±0.90)/(Ci-0.75±0.05) x [Hi]2). This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any Ci and Hi. The extraction data were used to calculate the conditional extraction constant (Kex) values at different acidities (2-7 M H+), uranium (0.02 - 0.1 M) and PC88A (0.2 - 0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium. (author)