title: Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum:iron hydroxides.
abstract: Although arsenic adsorption/desorption behavior on aluminum and iron (oxyhydr)oxides has been extensively studied, little is known about arsenic adsorption/desorption behavior by bimetal Al:Fe hydroxides. In this study, influence of the Al:Fe molar ratio, pH, and counterion (Ca2+ versus Na+) on arsenic adsorption/desorption by preformed coprecipitated Al:Fe hydroxides was investigated. Adsorbents were formed by initial hydrolysis of mixed Al3+/ Fe3+ salts to form coprecipitated Al:Fe hydroxide products. At Al:Fe molar ratios < or = 1:4, Al3+ was largely incorporated into the iron hydroxide structure to form a poorly crystalline bimetal hydroxide; however, at higher Al:Fe molar ratios, crystalline aluminum hydroxides (bayerite and gibbsite) were formed. Although approximately equal As(V) adsorption maxima were observed for 0:1 and 1:4 Al:Fe hydroxides, the As(III) adsorption maximum was greater with the 0:1 Al: Fe hydroxide. As(V) and As(III) adsorption decreased with further increases in Al:Fe molar ratio. As(V) exhibited strong affinity to 0:1 and 1:4 Al:Fe hydroxides at pH 3-6. Adsorption decreased at pH > 6.5; however, the presence of Ca2+ compared to Na+ as the counterion enhanced As( retention by both hydroxides. There was more As(V) and especially As(III) desorption by phosphate with an increase in Al:Fe molar ratio.
authors.affiliation: Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843-2474, USA. ymasue@stanford.edu
authors.forename: Yoko
authors.initials: Y
authors.lastname: Masue
authors.forename: Richard H
authors.initials: RH
authors.lastname: Loeppert
authors.forename: Tim A
authors.initials: TA
authors.lastname: Kramer
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry*; D001149:Arsenates / Q000737:chemistry / Q000302:isolation & purification; D018053:Arsenites / Q000737:chemistry / Q000302:isolation & purification; D002118:Calcium / Q000494:pharmacology; D011232:Chemical Precipitation; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010710:Phosphates / Q000737:chemistry; D012964:Sodium / Q000494:pharmacology; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*
chemical_list: D001149:Arsenates; D018053:Arsenites; D005290:Ferric Compounds; D010710:Phosphates; D014874:Water Pollutants, Chemical; C021024:ferric hydroxide; D000536:Aluminum Hydroxide; D012964:Sodium; C015001:arsenite; C025657:arsenic acid; D002118:Calcium