CR(III) AL(III)/FE(III) ION-BINDING ON MIXED BED ION-EXCHANGERS - SYNERGISTIC EFFECTS OF THE RESINS BEHAVIOR/

Ion exchange, as a conservative technology, allows for removal and rec ycling of metals from liquid effluents. Chelating exchangers may be us ed to the purpose due to their specificity toward metal species. The s pecificity, related to the metal-functional group affinity and thus th e high stability of the complexes formed, is paid in terms of regenera tion levels necessary to reverse the exchange reaction by mass action. Moreover, the liquid-phase speciation of the metals with organic and inorganic ligands, commonly present in industrial effluents, determine s the active metal concentrations at the binding sites and thus the re moval efficiency of the chelating resins which is, in general, more af fected by stereochemical factors during the interaction of the active species at the functional groups. In this context, we investigated the behaviour of a mixed bed weak electrolyte anion (amino) and cation (c arboxylate) conventional ion-exchangers as an alternative to chelating resins. The synergistic effects of the two functional groups to selec tively remove, separate and recover Cr(III), Al(III), Fe(III) from seg regated industrial effluents are discussed. The exhaustion behaviour o f the carboxylate resin toward chromic and aluminum species is synergi zed by the cooperative presence of the anion resin, this latter being able to selectively retain ferric species. Difficult regeneration beha viour of the metal-form carboxylate resin is also favored by the prese nce of the weak base amino functional groups in the free base form.