Characteristics and retention properties of a mesoporous γ-Al2O3 membrane for nanofiltration

A mesoporous gamma-Al2O3 membrane was produced by the sol gel dipping technique, followed by a thermal treatment (calcination and sintering), Different sintering temperatures were applied, which led to membranes with an average pore diameter ranging from 8.7 to 3.4 nm, the latter one corresponding to a MWCO of 900 Da. Salt retention was very much dependent on the pH of the solution as such membranes have an amphoteric character. Minimal salt retention was found at the isoelectric point (pH 7.5). Experiments were carried out with NaCl, MgCl2 and LaCl3 at different concentrations and in both single salt solutions and mixtures. The results are interpreted in terms of Donnan exclusion and in terms of the formation of an electrical double layer in the pores. Dynamic corrosion tests showed that some corrosion occurs at a pH of 2 or lower. (C) 1999 Elsevier Science B.V. All rights reserved.