Extraction of anions by a liquid cation-exchanger

Abstract

The distribution ratio has been measured for the extraction of tracer quantities of a number of metals from aqueous solutions of HX or LiX (X = Cl, Br) by the liquid cation-exchangers 0·1 M dinonyl naphthalene sulphonic acid and 0·1 M lithium dinonyl naphthalene sulphonate in n-heptane. In several cases at high halide concentrations the partition behaviour shows marked deviation from that to be expected from the cation exchange process. The effect arises in instances where the metal is very strongly taken up by anion exchangers and anomalous extraction is always greater from lithium halide solution than from the corresponding aqueous halogen hydracid. The dinonyl naphthalene sulphonates occur in the organic layers in micellar form and the composition of such aggregates containing invaded supporting electrolyte and water has been ascertained. Spectrophotometric and stoichiometric measurements on lithium dinonyl naphthalene sulphonate in n-heptane extracts of macro-quantities of metals M(III) or M(II) from concentrated lithium halide solutions have demonstrated the presence of anionic metal halide complexes in organic phases. Slope-analysis of partition data obtained with the metals present at trace concentration gives results in agreement with these conclusions, and the anomalous extraction behaviour can be formulated as involving equivalent exchange of a complex metal-halide anion with invaded halide associated with micelles in the organic medium.