title: Quantification of the effects of organic and carbonate buffers on arsenate and phosphate adsorption on a goethite-based granular porous adsorbent.
abstract: Interest in the development of oxide-based materials for arsenate removal has led to a variety of experimental methods and conditions for determining arsenate adsorption isotherms, which hinders comparative evaluation of their adsorptive capacities. Here, we systematically investigate the effects of buffer (HEPES or carbonate), adsorbent dose, and solution pH on arsenate and phosphate adsorption isotherms for a previously well characterized goethite-based adsorbent (Bayoxide E33 (E33)). All adsorption isotherms obtained at different adsorbate/adsorbent concentrations were identical when 1 mM of HEPES (96 mg C/L) was used as a buffer. At low aqueous arsenate and phosphate concentration (∼1.3 μM), however, adsorption isotherms obtained using 10 mM of NaHCO(3) buffer, which is a reasonable carbonate concentration in groundwater, are significantly different from those obtained without buffer or with HEPES. The carbonate competitive effects were analyzed using the extended triple layer model (ETLM) with the adsorption equilibrium constant of carbonate calibrated using independent published carbonate adsorption data for pure goethite taking into consideration the different surface properties. The successful ETLM calculations of arsenate adsorption isotherms for E33 under various conditions allowed quantitative comparison of the arsenate adsorption capacity between E33 and other major adsorbents initially tested under varied experimental conditions in the literature.
authors.affiliation: Department of Civil and Environmental Engineering, University of California-Davis, Davis, California 95616, United States of America. mkanematsu@ucdavis.edu
authors.forename: Masakazu
authors.initials: M
authors.lastname: Kanematsu
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Young
authors.forename: Keisuke
authors.initials: K
authors.lastname: Fukushi
authors.forename: Dimitri A
authors.initials: DA
authors.lastname: Sverjensky
authors.forename: Peter G
authors.initials: PG
authors.lastname: Green
authors.forename: Jeannie L
authors.initials: JL
authors.lastname: Darby
mesh_terms: D000327:Adsorption; D001149:Arsenates / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods; D006531:HEPES / Q000737:chemistry; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008903:Minerals / Q000737:chemistry*; D008956:Models, Chemical; D009994:Osmolar Concentration; D010710:Phosphates / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D001149:Arsenates; D002254:Carbonates; D058085:Iron Compounds; D008903:Minerals; D010710:Phosphates; D014874:Water Pollutants, Chemical; C094886:goethite; C025657:arsenic acid; D006531:HEPES