Ion dehydration using magnetic fields and impacts on permeability across RO membranes

Abstract

Magnetic fields have been used as a mitigation process for controlling mineral scaling in diverse applications, including membrane systems. Changes in scale formation have been attributed, in part, to changes in ion hydration. The objective of this study was to evaluate how passage through a multi-directional magnetic field affected the permeability of relevant cations and anions through a seawater reverse osmosis membrane (SW30HR). Changes in ion permeability were evaluated as a function of flow velocity through the magnetic system and described in terms of changes in the ion hydration and in turn changes in the energy penalty that a given ion must incur to permeate across the RO membrane. Ion permeability across the SW30HR membrane increased after having passed through the magnetic system. Increases in ion permeability became most pronounced once a flow velocity through the magnetic system was ≥35 cm/s and were a function of the ion charge density for ions of the same valence. Increases in ion permeability were attributed to dehydration of the ions by the magnetic system resulting in a reduction in the energy penalty required for the relevant ions to transport across the membrane barrier.