Removal of Heavy Metal Ions from Aqueous Solutions by Nanofiltration

This report presents the results of investigations on the removal of toxic Pb(II) ions from aqueous wastewaters by using two commercial thin-film composite polyamide NF membranes. The influence of the operational variables, i.e. the pressure applied, feed solution pH, and feed solution concentration, on the ability of the NF membranes to remove ions was evaluated. It has been found, for example, that the rejection of lead ions increases with the higher operational pressure, increasing also with higher metal concentration in feed. The solution pH is a parameter which had influenced to a greater extent the separation by the AFC 40 membrane. The maximum rejection of Pb(II) ions achieved above 80 % for AFC 40 and 98 % for AFC 80, respectively, proving that these NF membranes have real potential for efficient removal of metal ions from highly polluted wastewaters The results obtained are discussed in correlation with both the NF membrane properties (pore size and charge) and with the chemistry of the investigated solutions. The role of the steric and electrical interactions in the rejection mechanism of the NF membranes has been finally assessed. The Spiegler-Kedem model describes with high accuracy the experimental rejection data on the concentration range investigated, offering also information about the proper separation mechanism.