GENERAL-MODEL FOR AGGREGATION OF METAL-EXTRACTANT COMPLEXES IN ACIDIC ORGANOPHOSPHORUS SOLVENT-EXTRACTION SYSTEMS

The physicochemical nature of the metal-extractant aggregates formed in the organic phase of acidic organophosphorus solvent extraction systems was investigated to further understand hydrometallurgical extraction. The experimental techniques of fluorescence, FT-IR, and NMR spectroscopy, static and dynamic light-scattering, tensiometry, as well as classical physicochemical methods and extraction measurements, were employed to clarify the nature of the molecular aggregates associated with the extraction of Ca2+, Co2+, Ni2+, and Zn2+ by di(2-ethylhexyl)phosphoric acid (HDEHP) in n-alkane diluents. Significantly, there appears to be three regimes of aggregation behavior in solvent extraction systems consistent with the mechanism suggested earlier by Neuman and co-workers [Colloids Surfaces, 46, 45 (1990)]. A simplified model is proposed herein for the aggregation of metal-