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With the recent emergence of oxyanions chromate (HCrOsub4/subsup-/sup/CrOsub4/subsup2-/sup), arsenate(Hsub2/subAsOsub4/subsup-/sup/HAsOsub4/subsup2-/sup), and perchlorate (ClOsub4/subsup-/sup); and their contamination and naturaloccurrence as an important drinking water quality issue, a careful assessment ofmembrane technology for trace inorganic contaminants removal has been performed. Abench-scale cross-flow flat-sheet filtration unit has been used to evaluate the transport(rejection) of mono-valent and/or divalent oxyanions (HCrOsub4/subsup-/sup/CrOsub4/subsup2-/sup, Hsub2/subAsOsub4/subsup-/sup/HAsOsub4/subsup2-/sup,and ClOsub4/subsup-/sup) through negatively charged reverse osmosis (RO), nanofiltration (NF), andtight ultrafiltration (UF) membranes, and a diffusion cell testing unit has been used toinvestigate oxyanion transport (by hindered diffusion) through membrane pores undervarious water chemistry conditions.In this study, RO, NF and tight UF membranes have been tested to evaluate theeffects of pH and conductivity (ionic strength) on the transport/rejection these three toxicoxyanions. The study investigated the transport (rejection) mechanisms of chromate,arsenate, and perchlorate including solution diffusion, steric (size) exclusion, and/orelectrostatic exclusion for RO, NF and tight UF membranes.The target anions were characterized according to molecular mass, hydratedionic radius (size), and diffusion coefficient in water (Dw). A diffusion cell containingactual RO, NF, and tight UF membrane specimens has been used to estimate hindered diffusion (Dp) embodying various solute-membrane interaction, with measured hindereddiffusion coefficients several orders of magnitude less than corresponding diffusioncoefficients in water, thus demonstrating the importance of electrostatic and sterichindrance in trace anion rejection. Includes 11 references, table, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 12File Size: 1 file , 420 KB