Clay-based nanocomposite membranes for removal of heavy metals from rainwater

Montmorillonite/halloysite or metakaolin were used as nanofillers for the preparation of ultrafiltration clay-based nanocomposite membranes (CN-membranes). The addition of montmorillonite and metakaolin increased membrane porosity, while halloysite decreased it. Elements of Al, Si in EDS spectra confirmed that clays were effectively embedded in membrane structure. CN-membranes were used for the removal of Pb²⁺ and Ni²⁺ from real rainwater in ultrafiltration at 2.5 bar and 5 bar. Higher removal of lead (85–100 %) compared to nickel (56–90 %) can be explained by higher adsorption of lead on membrane structure than nickel during ultrafiltration. Adsorption was a main retention mechanism of both metals. 100 % retention of lead was obtained for all CN-membranes, while PES + MK and PES + Hal were the most effective (90 %) in removal of nickel. Higher TMP resulted in a decrease in the removal of nickel. In case of lead, the effect of TMP was negligible. Flux decline showed that nanocomposite membranes exhibited the lowest fouling than pristine PES. From nanocomposite membranes, PES + MM had the lowest fouling affinity. Moreover, surface properties such as zeta potential, isoelectric point and contact angle of nanocomposite membranes remain almost identical for clean and fouled membranes. PES + MK membrane was prone to regeneration with 2 % HCl. After fifth cycle of UF-regeneration, removal of lead and nickel was 76.3 % and 45.6 %, respectively.