Direct Comparison of Tributyl Phosphate Against Monoamide Extractants in Uranium and Nitric Acid Systems for Solvent Extraction

Interest in improved disposal pathways and proliferation-resistant systems for used nuclear fuel recycling has driven research on monoamide extractants. Existing comparisons against the industry standard, tributyl phosphate (TBP), emphasize a fundamental approach and span a wide range of test conditions. This work narrows that range and addresses process-scale considerations by presenting hydrodynamic performance results alongside extraction capacity at optimized conditions. The monoamide solvents, 1.0 M DEHiBA (N,N-di(2-ethylhexyl)isobutanamide), 1.5 M DEHBA (N,N-di(2-ethylhexyl)butanamide), and 1.5 M DEHDMPA (N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide), are compared to 1.1 M TBP in bench-scale extraction tests with nitric acid (2–6 M) and uranium (∼0.8 M). Performance is assessed with distribution ratios and dispersion number ratings and supported by specific gravity and viscosity measurements. DEHBA and DEHDMPA exhibited inadequate coalescence behavior with failed or poor dispersion ratings despite uranium distribution ratios of 2.06 ± 0.03 and 0.86 ± 0.01 at O/A = 1.9, limiting suitability for process application. TBP and DEHiBA maintained adequate dispersion ratings across all conditions tested, with maximum distribution ratios of 4.37 ± 0.08 at O/A = 2.6 and 0.67 ± 0.01 at O/A = 2.9, respectively. Higher viscosity values for DEHBA (5.21 cP ± 0.3%) and DEHDMPA (6.53 cP ± 0.4%) relative to TBP (2.04 cP ± 0.4%) and DEHiBA (3.18 cP ± 0.4%) correlate with observed coalescence deficiencies. The methods presented in this work demonstrate the significance of evaluation beyond extraction capacity.