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

• Analysis of separation process of lead ions from synthetic wastewaters by NF using the AFC 80 membrane
• Effective removal of heavy metals concomitantly with obtaining non-toxic permeates
• Concentration by NF of aqueous solutions simulating the real wastewaters
• Modeling of the concentration process of synthetic wastewaters containing heavy metals

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.