Uranium extraction from its solutions using novel urea embedded fatty acids as an ecofriendly solvent – a comparative mechanistic and thermodynamic study

A bio-derived Bis-Linolenoyl Urea extractant (MFA) was synthesized from waste frying oil and evaluated as a green alternative to di-2-ethylhexyl phosphoric acid (D2EHPA) for uranium (VI) recovery from aqueous sulfate media. Structural characterization by FTIR, UV–Vis, and TGA/DTG confirmed successful formation of the urea-embedded fatty acid framework and its thermal stability up to ~200°C. Batch extraction experiments showed that MFA operates optimally at pH 5 in kerosene, achieving ~90–92% U(VI) extraction at an O/A ratio of 1:3 and 45 minutes contact time, with a saturation loading of 263 mg U per mL of working organic phase (10 vol% MFA/kerosene), determined by successive contact analysis across 17 extraction stages, with the high-affinity primary bidentate chelation regime accounting for 126 mg U/mL of this total capacity, compared with ~200 mg U mL−1 for D2EHPA. Kinetic analysis confirmed that both MFA and D2EHPA obey pseudo-second-order kinetics (MFA: R2 = 0.9945, k2 = 0.00396 g mg−1 min−1,qe,cal = 9.43 mg/g; D2EHPA: R2 = 0.9988), consistent with chemisorptive bidentate coordination as the rate-determining step for both extractants, as confirmed by the complete statistical error function analysis including SSE, RMSE, ARE, and χ2. Kinetic analysis confirmed that both MFA and D2EHPA obey pseudo-second-order kinetics (MFA: R2 = 0.9945, k2 = 0.00396 g mg−1 min−1, qe,cal = 9.43 mg/g; D2EHPA: R2 = 0.9988, k2 = 0.00659 g mg−1 min−1), consistent with chemisorptive bidentate coordination as the rate-determining step for both extractants, as confirmed by the multi-parameter statistical error function analysis including SSE, RMSE, ARE, and χ2. Response surface methodology (central composite design) yielded statistically significant quadratic models for both systems and revealed a broader, more tolerant optimum region for MFA, implying greater robustness to pH and concentration fluctuations. Van’t Hoff analysis confirmed exothermic, spontaneous extraction in both cases, with slightly more favorable thermodynamic parameters for MFA. Selectivity tests demonstrated that MFA tolerates markedly higher concentrations of common competing ions (e.g. Fe, Ca, Na) before uranium extraction falls below 90%, and stripping with mildly acidic saline solutions recovered ≥95% of loaded uranium from MFA under ambient conditions, versus substantially lower values for D2EHPA. Overall, the results show that urea-functionalized fatty acid derived from waste oil can match or outperform a benchmark phosphoric extractant in capacity, selectivity, and regenerability, while offering clear advantages in sustainability and process safety.