Extraction of tungsten (VI), molybdenum (VI) and rhenium (VII) by diisododecylamine

The aggregation of amine-type extractants was studied in sulphuric acid media and applied to systems containing molybdenum, tungsten and rhenium. This article is mainly concerned with the micellization of diisododecylamine (DIDA) and compares the micellization of DIDA with that of two other extractants - trioctylamine (TOA) and dioctylamine (DOA). The degree of water solubility in the organic phase correlated with the degree of amine aggregation. The factors influencing the micellization of amine compounds-surfactant geometry, dipole moments, and amine concentration are described. The influence of diluent (kerosene and toluene) and long-chain alcohol on the micellization of amine compound are also discussed. The addition of octanol in the system TOA/toluene and DIDA/toluene (kerosene) results in increased micellar curvature. This increased micellar curvature causes a decrease in water solubility in the reversed micelles. Molecules of toluene penetrate deeper into the surfactant monolayers than does the nonpolar kerosene and decreases the polarity of the amine monolayers, providing stronger interactions between surfactant chains. Increasing acid concentration (0.2-2.0 M H2SO4) leads to displacement of water molecules by acid molecules, thereby decreasing both water solubility and the distribution coefficient of metal between the organic and aqueous phases. Distribution coefficients of molybdenum, tungsten and rhenium was found to correlate with the water content in the organic phase. (C) 2000 Published by Elsevier Science B.V. All rights reserved.