Studies of the complexation behaviour of transition metals applicable in membrane technologies

摘要

Many industrial processes make use of metal ions. These metal ions, however, end up in several effluent streams. Due to very strict discharge values, new technologies are constantly emerging for treating and purifying all kinds of wastewater. One of these innovative technologies is the Supported Liquid Membrane (SLM) technique. The SLM technology is a membrane-based solvent extraction method that uses a micro-porous hydrophobic membrane as supporting layer. This membrane is impregnated with an organic solvent containing the specific carrier molecules for metal ion extraction. In this study, the extractions of some metal complexes applicable in Supported Liquid Membranes were investigated in depth. The studies were mainly focused on the metal ions copper(II), nickel(II), cobalt(II), iron(III, II) and magnesium(II). As extractants, organophosphorous acids (D2EHPA, CYANEX 301, CYANEX 302 and CYANEX 272) and hydroxyoximes (LIX 860-I, LIX 84-I) were investigated either separately or in combination with a second extractant molecule in order to determine synergistic effects. Hexane and 1-decanol were applied as diluents in order to determine the effect of the polarity of the diluent on the extraction efficiency of the metal ions and to investigate if changes occur in the configuration of the metal complexes. Furthermore, the influence of the presence of acetate ions in the aqueous phase was investigated. Secondly, Job’s method was applied to determine the stoichiometry of the metal-organic complexes. This spectrophotometric method was compared with a water-free procedure. By following up the release of hydrogen chloride during complexation, a correlation is obtained with the number of extractant molecules participating in the complexes. Furthermore, a practical application of the Supported Liquid Membrane technology was evaluated, viz. recovery of nickel(II). The results on real effluent streams have shown hat nickel(II) can be recovered out of industrial effluents below the PARCOM value of 0.5 mg.L-1 with a mixture of LIX 860-I and CYANEX 302. Finally, an introduction has been given of the potential abilities of Polymer Inclusion Membranes (PIM) and Immobilized Liquid Membranes (ILM) as alternative wastewater treatment techniques. The results indicated however that it seems very doubtful that fluxes in the same order of magnitude will be reached as for Supported Liquid Membranes.