Comparative Evaluation of Tri-n-butyl Phosphate (TBP) and Tris(2-ethylhexyl) Phosphate (TEHP) for the Recovery of Uranium from Monazite Leach Solution

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.