Competitive Equilibria in the System: Water, Nitric Acid, Tri-n-Butyl Phosphate, and Amsco 125-82

Alternative mass action models were assumed to study competitive equilibria for nitric acid and water extraction in the range of 0-8.4 M nitric acid. Those models yielding the best data fits suggest that tri-n-butyl phosphate (TBP) and hydrocarbon phases contain several complexes. Four complexes appear to result from the association of nitric acid and water with the TBP dimer: [TBP]2[H20]O] 4 [TBP] 2 HN03H2O, [TBP] 2[HNO3] 2[H2O] 2, and [TBP] 2 HNO3 [H2O] 3. One complex, TBP HNO3, apparently predominates from the association of nitric acid with the TBP monomer. The TBP monomer primarily coordinates with nitric acid. The TBP dimer appears to coextract nitric acid and water together. This model gives an excellent fit to nitric acid extraction data in this concentration range and does well at predicting water extraction.