The Activity Behavior of the NdNO₃—HNO₃—H₂O—HDEHP—AMSCO System

Abstract

The thermodynamic behavior of the two-phase NdNO 3 -HNO 3 -H 2 O-HDEHP(Di-2-ethylhexyl phosphoric acid)-AMSCO Odorless Mineral Spirits system has been studied to provide experimental data for use with a model to predict the distribution coefficients of neodymium. The presence of high hydrogen ion concentration was taken into account in determining the nitrate ion activities in the aqueous phase using the nitrate ion selective electrode. The nitrate ion concentration in the organic phase was back-extracted with sulfuric acid before analysis with the nitrate and sulfate concentrations. The activity coefficients of the HDEHP dimer were estimated from the data of Baes who made isopiestic comparisons with triphenylmethane in n-octane as the reference solution assuming that the activity coefficient of triphenylmethane is unity. Τ iquid-liquid extraction of the lanthanides from an aqueous salt solution to a chelate in an organic phase has been somewhat difficult to analyze thermodynamically for a number of reasons. First, very httle data exists on the activity behavior of a single-component lanthanide salt in the aqueous solution. These data, generally more common for 1:1 electrolytes such as NaCl, KN0 3 , etc., are in the form of the mean activity coefficient of the salts. Second, this value of the mean activity coefficient for a particular salt is a measure of the combined effect of both 1 Present address: Photo Products Department, Du Pont, Towanda, PA 18848. 0-8412-0428-4/79/33-177-323$05.25/l