Tailoring phase modifiers for selective uranium extraction: conventional and phosphate ores

Selective uranium extraction from sulfate and phosphate-based leachates remains challenging due to co-extraction of impurities such as Mo, Zr, and Fe, which limits process efficiency and economic viability. This study investigates how the nature and concentration of phase modifiers influence uranium selectivity across three mining systems: two conventional uranium ores and one phosphate-associated ore. U, Mo and Zr were quantified by ICP-OES, while Fe was analyzed by gamma-ray spectrometry. Results show that phase modifier effects on selectivity are highly system dependent. In AMEX-based sulfate systems, increasing EXXAL 10 enhances selectivity through systematic improvements in extraction performance: in Mine A, U/Zr increases from 50 to 221 at 50 vol% (vs. 5 vol% industrial conditions), while in Mine B, U/Mo increases from 377 to 1459 at 22 vol%, with optimal U/Zr selectivity between 10-50 vol%. In contrast, the phosphate-based Mine C exhibits a weakly structured organic phase, with dimer-dominated extractant species and limited sensitivity to phase modifier addition; optimal selectivity is achieved at low modifier content, where 2 vol% EXXAL 13 increases the U/Fe ratio from 61 to 214. These results highlight the importance of system-specific phase modifier optimization for maximizing uranium selectivity. SAXS analysis further reveals that extractant molecules self-assemble into reverse aggregates whose structure and inter-aggregate interactions are strongly influenced by phase modifier concentration. Crucially, these structural modifications directly correlate with selectivity variations, demonstrating that phase modifier effects are fundamentally mediated through changes in extractant aggregation in the organic phase.