MCM-41 “LUS”: alumina tubular membranes for metal separation in aqueous solution

Heavy metals are discharged to the environment through industrial effluents in which certain amounts of valuable metal ions such as gold and silver are present. Current technologies remove metal ions nonspecifically, which constitutes a serious difficulty for metal recovery and reuse. The present article describes the synthesis of MCM-41 (LUS-type) membranes and their further surface functionalization with aminopropyl and sulfonate groups to separate valuable and/or toxic metal ions species in aqueous medium. A feasibility test for metal-ion separation is demonstrated using two model systems: (1) toxic metal removal by separating anionic chromate from cationic copper ions and (2) precious metal recovery by separating gold from copper ions. The results reveal that aminopropyl functionalized LUS membranes might show high selectivity to Cu(II) for the Cu(II)/Au(III) system, approaching virtually infinite selectivity depending on the pH values of both the feed and stripping solutions and the concentration of chloride counteranions. We provide a critical discussion about the relative role of cation diffusion and migration to gain insight into the metal-ion separation mechanisms