Zinc rejection from leachate solutions of industrial solid waste - effects of pressure and concentration on nanofiltration membrane performance

The treatment by nanofiltration of real solutions of industrial solid waste leachate using the charged Nanomax-50 membrane, largely used in industrial water treatment, was investigated. The retention of zinc, present in coercive quantities, was studied according to the experimental parameters. The results show that zinc retention varied from 96 to 99%, depending on the composition of solution and operating conditions. At work pH (pH = 5.0), zinc was at 99.99% in the form of Zn2+ (Cheaqs v. L20.1, a program for calculating chemical equilibria in aquatic systems, RIVM, Bilthoven, The Netherlands,-2004); a better retention (99%) was obtained with low energy. Thus, the optimal transmembrane pressure was 5 bar in the case of a 75 ppm solution. At low concentration (3.99 ppm), the retention decreased when the pressure exceeded 8 bar. These results differ from the majority of those presented in previous works regarding metal ion nanofiltration. At P = 5 bar and when the concentration increased (from 75 to 559 ppm), the repulsion phenomenon became less important due to a higher interaction between membrane and metal ions, and consequently the latter was retained less (98%). Duly noted here is the influence of ionic strength related to the solution concentration on zinc rejection, which was found weak.