Abstract
Separation of U(VI) from Th(IV) and rare earth elements (REEs) present in monazite leach solution (nitric acid medium) has been studied using tris(2-ethylhexyl) phosphate (TEHP) and tri-n-butyl phosphate (TBP) dissolved in n-paraffin as solvents under varying experimental conditions such as nitric acid, extractant and metal ion concentrations etc. There is an increase in distribution ratio of U(VI) (D U ) with increase in aqueous phase acidity up to 5 M HNO3 beyond which a decrease is observed. Typically for 1 × 10−3 M U(VI), the DU values increase from 8 (0.5 M HNO3) to 80 (5 M HNO3) for 1.1 M TEHP, and from 2 (0.5 M HNO3) to 43 (5 M HNO3) for 1.1 M TBP in n-paraffin. The separation factors of U(VI) (β: DU/DM) over metal ions (M) such as Th(IV) and Y(III) (chosen as a representative of heavy REEs) are better for TEHP than TBP at all nitric acid concentrations. Batch solvent extraction data have been used to construct the McCabe-Thiele diagrams for the recovery of U(VI) employing TEHP as the extractant. A process flow sheet has been proposed with 0.2 M TEHP in n-paraffin as solvent for the recovery of U(VI) from simulated monazite leach solution in HNO3 medium.
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