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

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 HN031 a l imit arbitrarily chosen because of un-certainties i n HNO3 act ivi ty coefficients, the data of this report a t any particular con-centration of TBP i n ~ m s c o are accurately described by the equation log (HNOCJ)~~S/ ([HNO~],q(3.75493-(~~03)0rg)) = A + B (HN03)org,, where ~arentheses refer to concentrat~ons, square brackets to activities, and subscr~pts 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 (Yo + Y;B,)l the sum of the mole fractions, Yo H 2 0 and YTBp of water and TBP i n the aHc?%free water-saturated organic phase. These antilogarithms were interpreted as the product K 1 Y p where K 1 i s the thermodynamic equilibrium constant for the extraction reaction and i s the mean act ivi ty coefficient T of TBP and TBP.H20 i n the acid-free, water-saturated organic phase. As the concentra-tion of TBP in Amsco 125-82 increases from 0 to 100%, KIYTl i n molal units, varies from 0.2 to 1.5. The quantities B of the above equation are proportional to (YfBp+ %20.)1/