Removal of zinc and nickel ions by complexation membrane filtration process from industrial wastewater

Many industrial wastewater streams contain toxic metal cations, for example, Ni2+, Zn2+, etc. or their oxyanions in up to few hundred mg/dm3, which must be removed before water recycling or discharging directly into surface waters. The conventional processes to treat this kind of wastewater are, e.g. chemical precipitation, ion exchange, membrane separations (such as electrodialysis, nanofiltration, reverse osmosis and ultrafiltration), adsorption or biosorption. In this work a membrane technique, ultrafiltration, completed with complexation was investigated. During the experiments, impact of conditions of membrane, pH and polymer/metal ratio have been investigated. The study series were carried out both of zinc and nickel. According to our studies, the most effective composition both tested metals is the following: PES-10 membrane, PAA complexation agent and pH /8. The volume ratio of the polymer bounding agent and metal ion because of environmental and economical aspects should be about unit.

In this paper, polymer enhanced ultrafiltration of Zn2+ and Ni2+ was studied. During the experiments, the effect of conditions of membrane, pH and polymer/metal ratio on the metal ions removal have been investigated. In all cases, results of experiments showed that the metal removal was affected by the conditions of membrane, e.g. using original or already used (not original) wet membrane. Cases when investigated both original and previously used membranes, the used membrane was more effective in the most cases. It might be explained e by membrane fouling [19], but it was not supported in all cases by the flux. According to Ref. [12] the complexation can be significantly influenced by the ratio of the complexation agent and metal ion and by the initial concentration of metal or polymer complexation agent. According to the results of Ref. [6], the polymer/metal ratio did not affect the effectiveness of metal bounding. According to results presented obtained the polymer/metal ratio has higher effect than that of the initial metal ion concentrations in the feed solution. Another important factor is the membrane properties [7]. It can be said that the effect of pH is not so important like written in papers [4,5], but it depends on the complexation agent. It has to be some further experiments to clarify the effect of the ratio of the polymer and metal. According to the presented studies, the most effective composition, for both tested metals, is the following: polyether-sulphone (PES) membrane with 10 kDa cut-off, poly(acrylic-acid) (PAA) as complexation agent as well as pH value above 8. As further tasks of this work, experiments are planned to carry out in order to improve the separation efficiency, to get better complexation agents and integration of an elctrodialyzer to the system.