In Situ Infrared Speciation of Adsorbed Carbonate on Aluminum and Iron Oxides

Abstract

Abstract--Surface adsorption mechanisms of dissolved inorganic carbon species on soil minerals are not well understood. Traditional infrared (IR) study of adsorbed species of inorganic carbon using air-dried samples may not reveal true species in the solid/water interface in suspension. The ptu'pose of this study was to obtain information on interracial carbonate speciation between solid and aqueous phases. The interaction of bicarbonate and carbonate ions with X-ray amorphous (am) A1 and Fe oxides, gibbsite (~/-AI(OH)3 ) and goethite (a-FeOOH) was examined by electrophoresis and in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The presence of carbonate lowered the electrophoretic mobility and decreased the point of zero charge (PZC) of all minerals, implying specific adsorption. Inner-sphere complexation of bicarbonate and carbonate was supported by a lowering in the anion symmetry due to the interaction with A1 and Fe oxide surfaces. Only complexed monodentate carbonate was identified in am-Al(OH)3/aqueous solution at pH 4.1-7.8 when the solid was reacted with either NanCO 3 or Na2CO 3 solutions. Am-AI(OH)3 was transformed to a crystalline sodium aluminum hydroxy carbonate, dawsonite [NaAl(CO3)(OH)2], and bayerite (ct-AI(OH)3) after reacting with 1.0 M Na2CO3 for 24 h. Gibbsite adsorbed much less carbonate than am-AI(OH)3 such that adsorbed carbonate on gibbsite gave weak IR absorption. It is probable that monodentate carbonate is also the complexed species on gibbsite. Evidence suggesting the presence of both surface complexed bicarbonate and carbonate species in the interfacial region of am-Fe(OH)3 in suspension and the dependence of their relative distribution on solution pH is shown. Only monodentate carbonate was found in the interracial region of goethite in 1.0 M NaHCO3. A ligand exchange reaction was proposed to describe the interaction of bicarbonate and carbonate with the surface functional groups of A1 and Fe oxides.

HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

“…Both materials have external cation ex APPEL, RHUE, MA, AND REVE SOIL SCIENCE change sites, which may exhibit constant affinities for K as exchangeable K content varies. The other major components capable of ion exchange in this soil were gibbsite, goethite, and amorphous Fe and Al oxides, which should have been positively charged at pH 4.7 and, thus, incapable of signifi cant cation exchange (ZPCs of gibbsite and goethite 5.0 to 9.0 and 7.8 to 9.0, respectively; Sparks, 1995;Su and Suarez, 1997). For the Ultisol, a quadratic equation best de scribed the relation between the integral heats of exchange and concentration of exchangeable Ca or Pb (Fig.…”

Simultaneous removal of arsenate and arsenite by a nanostructured zirconium–manganese binary hydrous oxide: Behavior and mechanism

“…is assigned to the deformation of water molecules; the two peaks at 1580 and 1380 cm À1 might be attributed to the vibration of sorbed CO 2À 3 ; three peaks at 1122, 1065, and 984 cm À1 could be ascribed to the vibration of sulfate [36]. After reaction with As(V), the peaks at 1580 and 1380 cm À1 do not obviously change, while three peaks at 1122, 1065, and 984 cm À1 disappear completely and a new peak at 832 cm À1 appears, corresponding to As-O stretching vibration.…”

Microstructural Properties of Natural Allophane/Gibbsite from a White Bauxite Deposit in Montenegro

“…The IR band at 1435 cm -1 is a ν3 fundamental vibration of adsorbed carbonate ion, while the IR band located at 1536 cm -1 can be assigned to a degenerate fraction of the ν3 vibration. [16] Su and Suarez [17] noticed IR absorption bands of adsorbed carbonates on amorphous aluminium hydroxide (Am-Al(OH)3) at 1420 and 1490 cm -1 . In the same work gibbsite adsorbed much less CO3 2-than Am-Al(OH)3 and the ν3 vibration splitting was not noticed for the experimental conditions.…”