Influence of operating variables on the removal of heavy metal ions from aqueous solutions by nanofiltration

The focus of this paper is to test the ability of a commercially available nanofiltration membrane (AFC 80) to remove polluting and toxic Pb(II) ions from aqueous solutions in order to meet the USEPA guidelines regarding the toxicity threshold limits. The investigation has been conducted for aqueous solutions containing lead in a wide concentration range and also with similar composition with real wastewaters, both in batch circulation and in concentration mode. The influence of the operating variables on the membrane performance was investigated. Experimental results show that the rejection of lead ions slightly increases when increasing the cross-flow velocity and operating pressure, and slightly decreases when increasing the metal concentration in feed. The metal rejection and the permeate flux were found to slightly decrease and strongly increase, respectively, when increasing the feed pH. Generally, the rejection of lead ions is greater than 98% even for very concentrated feed solutions. Additionally, the membrane is able to concentrate lead containing aqueous solutions with pH 5.8 at a medium operating pressure of 25 bar, and concomitantly obtains non-toxic permeates. The metal concentration in permeate and the metal rejection during the concentration process were successfully predicted with high accuracy by a simple model. © 2013 Elsevier B.V. All rights reserved.

CF (-) Fig. 7. Performance of the AFC 80 membrane in the removal of Pb(II) and Cd(II) from the model solution simulating a mining effluent (a). Lead and cadmium concentrations detected in permeate and the heavy metal rejection rates during the concentration of a feed solution with the initial concentration of 150 mg Pb/L and 40 mg Cd/L (operating pressure 25 bar, pH 5.8, cross-flow velocity 1.25 m/s) (b).