Transport of arsenate through anion-exchange membranes in Donnan dialysis

The transport of arsenate across the main known types of polymeric anion-exchange membranes: heterogeneous, homogenous and monovalent-anion-permselective ones, was systematically studied under batch and continuous Donnan dialysis operating conditions. The experiments were carried at a low arsenate level of 0.1 mmol L-1 (equivalent to about 7.5 mg L-1 of As) in the feed solutions in order to allow for elucidating the transport rate and removal efficiencies of As within the concentration range relevant for contaminated drinking water supplies. The results are discussed in the light of the existing knowledge on the properties of the investigated anion-exchange membranes, complemented, when missing, with experimental data obtained in the present study. It has been found that the Donnan dialysis process performance depends strongly on the anion-exchange membrane used under batch operating conditions, but the differences vanish for a continuous operation mode, for which similar degrees of As removal have been obtained. Implications of the experimental findings as applied to removal of arsenate from dilute aqueous solutions are considered. The most appropriate anion-exchange membranes appear to be those possessing a relatively open structure and low tortuosity of the polymeric matrix. On the other hand, the use of membranes with monovalent-anion-permselective properties is not recommendable because of a slow transport rate of arsenate and its significant retention in the membrane phase. (C) 2012 Elsevier B.V. All rights reserved.