The availability of alginate gels enclosing Cyanex 302 [bis(2,4,4-trimethylpentyl)thiophosphinic acid] for the uptake of cadmium and copper from highly concentrated solutions of industrial phosphoric acid wet process phosphoric acid (WPA)] was studied. For this purpose, beads of alginate gels enclosing microdrops of kerosene solutions of the industrial extractant Cyanex 302 at different concentrations were prepared. The experimental procedure gives rise to a composite bead in which alginate is the continuous phase and the organic extractant forms the discrete homogeneously distributed phase within the bead. The equilibrium in this three-phase system (phosphoric acid-extractant solution-alginate gel) was modelled in terms of the corresponding distribution factors, the main chemical reactions and their equilibrium constants. Retention isotherms of both metal ions were obtained experimentally at four concentrations (1.0, 2.5, 5.0 and 7.5 mol L −1 ) of pure phosphoric acid. High metal removal efficiency, due to liquid-liquid extraction processes, was observed even in the most acidic conditions. High values of the extraction constants were estimated, with the distribution coefficients between aqueous and alginate phase being near unity. Finally, the results obtained with industrial WPA are in close agreement with those predicted by the physicochemical model developed in synthetic media.
The extraction of Cu(II) from phosphoric acid media (0.4 -7.3 M) by the commercial reagent LIX 622 in toluene has been studied. Experimental results have been treated numerically and the formation in the organic phase of the complex CuR 2 , HR being 5-dodecylsalicylaldoxime, has been proposed. Values of the conditional extraction constants, which increase with the phosphoric acid concentration, are given. Organic extracts have been analyzed by EPR spectroscopy. The presence of a square planar complex of Cu(II) has been deduced confirming the stoichiometry CuR 2 .
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