Removal of metal ions by complexation-ultrafiltration using water-soluble macromolecules: Perspective of application to wastewater treatment

Complexation of metal ions with water-soluble polymeric ligands and retention of the macromolecular complex by ultrafiltration afford a method of preconcentration of metal ions in homogeneous phase. This technique has been evaluated from literature data in view of its application to the treatment of metal containing wastes. Two procedures are applicable, namely diafiltration and concentration method. Both methods yield excellent metal retention with such readily available polymers as polyacrylic acid and polyethylenimine. Synergic effects on the metal retention were reported in some cases by addition of low molecular weight ligands. Furthermore, better selectivity can be obtained using watersoluble solymers bearing specific chelating functions. However, the chelating group capacity has to be limited in order to ensure the water solubility of the resulting complex. Efficiency of the process has been discussed in terms of retention of macromolecular solutes and of membrane fouling. Both ultrafiltration procedures have been compared considering perspectives of application. Besides, coupling of complexation-ultrafiltration with electrolysis offers an elegant method of metal recovering in a pure metallic form. This promising technique is in development for waste treatment from electroplating and appears as a relevant process for treatment of wastes from nuclear plants.