Removal of zinc and nickel ions from aqueous solutions by means of the hybrid complexation-ultrafiltration process

This paper presents the possibility of removing metal ions by applying the hybrid complexation-ultrafiltration process. The research was conducted on model solutions containing Zn(II) and Ni(II) ions. The complexing agent applied in the research was sodium polyacrylate, To separate the formed polymer-metal complexes, porous membranes made from polysulfone were used. Ultrafiltration of the model wastewater containing metal ions aimed at finding an optimum ratio between the concentrations of the complexing agent and metal, and determining the most favourable pH value. The ratio between polymer and metal concentrations was changed in the range 10:1-100:1. In the case of both examined metals, the complexation-ultrafiltration process was most effective at a 10-fold excess of the polymer with respect to the metal. The pH value was adjusted over the range 2-10 using HNO3 and NaOH solutions. An increase in alkalinity brought about an improvement in the effectiveness of the separation process. To remove metal ions from water solutions, the concentration process was carried out according to the previously determined polymer:metal ratios, and at optimum pH. The permeate obtained comprised 90% of the initial volume of the feed. The process was characterized by good effectiveness and enabled a 97-99% retention of the metal present in the feed solution. The retentate separated during the concentration process was subjected to decomplexation-ultrafiltration. High concentrations of the metals obtained in the permeates after decomplexation indicate the possibility of an effective separation of metal ions from the complexing polymer. (C) 1999 Elsevier Science B.V. All rights reserved.