title: Modeling the effect of charge density in the active layers of reverse osmosis and nanofiltration membranes on the rejection of arsenic(III) and potassium iodide.
abstract: We used an extended solution-diffusion model that incorporates Donnan electrostatic exclusion of ions and unhindered advection due to imperfections, and measurements of charge density in the polyamide active layers of reverse osmosis (RO) and nanofiltration (NF) membranes, to predict the rejection of a strong electrolyte (i.e., potassium iodide) and a weak acid (i.e., arsenious acid) as a function of the pH of the feed aqueous solution. Predictions of solute rejection were in agreement with experimental data indicating that (i) the extended solution-diffusion model taking into account Donnan exclusion and unhindered advection due to imperfections satisfactorily describes the effect of pH on solute rejection by RO/NF membranes and (ii) measurement of charge density in active layers provides a valuable characterization of RO/NF membranes. Our results and analysis also indicate that independent ions, and not ion pairs, dominate the permeation of salts.
authors.affiliation: Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States. coronell@unc.edu
authors.forename: Orlando
authors.initials: O
authors.lastname: Coronell
authors.forename: Baoxia
authors.initials: B
authors.lastname: Mi
authors.forename: Benito J
authors.initials: BJ
authors.lastname: Mariñas
authors.forename: David G
authors.initials: DG
authors.lastname: Cahill
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D004058:Diffusion; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D008962:Models, Theoretical; D036103:Nanotechnology; D009757:Nylons / Q000737:chemistry; D009995:Osmosis; D011193:Potassium Iodide / Q000737:chemistry*; D055672:Static Electricity; D014462:Ultrafiltration / Q000295:instrumentation / Q000379:methods; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000295:instrumentation / Q000379:methods
chemical_list: D008567:Membranes, Artificial; D009757:Nylons; D014874:Water Pollutants, Chemical; D011193:Potassium Iodide; D001151:Arsenic