Thermodynamics of Extraction of Nitric Acid by Tri-n-Butyl Phosphate–Hydrocarbon Diluent Solutions: I. Distribution Studies with TBP in Amsco 125-82 at Intermediate and Low Acidities

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Abstract
The distribution of 0–8 M HNO3 between aqueous and 5–100 vol % solutions of TBP in Amsco 125–82 has been measured and used to obtain a quantitative description of this extraction process. Up to ~5 M aqueous HNO3, a limit arbitrarily chosen because of uncertainties in HNO3 activity coefficients, the data of this report at any particular concentration of TBP in Amsco are accurately described by the equation log [(HNO3)org/{[HNO3]aq(3.75493-(HNO3)org)}] = A + B (HNO3)org, where parentheses refer to concentrations, square brackets to activities, and subscripts org and aq to organic and aqueous phases.The antilogarithms of the constants A for the six TBP-diluent solutions studied can be described as a linear function of (Y0H2O + Y0TBP), the sum of the mole fractions, Y0H2O and Y0TBP, of water and TBP in the acid-free water-saturated organic phase. These antilogarithms were interpreted as the product K1mγT, where K1m is the thermodynamic equilibrium constant for the extraction reaction and γT is the mean activi...