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Separation of ions from aqueous solutions was performed by reverse osmosis (RO) on an "-alumina-supported MFI-type zeolite membrane synthesized by in-situ crystallization. For the 0.1 M chloride single-salt solutions, the separation efficiency in terms of ion rejection was found to increase with the ion valence in the order , while the ion and water fluxes changed in the reverse order. The charge density, size, and apparent dynamic hydration number of the ion as well as the mobility of the hydrated ion were found to have critical influences on ion diffusion and water permeation through the polycrystalline zeolite membrane.

Ion separation by RO through an aluminasupported MFI membrane was investigated for a number of single-salt solutions. The ion rejection and water flux were found to depend on the charge density of the ion and the dynamic size and diffusivity of the hydrated ion. The randomly oriented MFI polycrystalline membrane contains two types of pores, i.e., the uniform 0.56-nm diameter zeolite channels and microporous intercrystal pores with a size distribution at nanometer scale. The experimental results indicate that different mechanisms control the transport of ion and water molecules through the intracrystal zeolite channels and the intercrystal pores. Ion rejection on the zeolitic channel is controlled by a size exclusion effect on the large hydrated ions. Ion separation through the intercrystal micropores is caused by the strong interaction between the This research was sponsored by the Sandia University Research Program and also partially supported under contract No. DE-FC2600BC15326, through the US DOE’s National Petroleum Technology Office in the National Energy Technology Laboratory. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US DOE’s National Nuclear Security Administration under contract DE-AC04-94AL85000. We thank Ms. Liz Bustamante for editing the manuscript.