XAFS studies of the arsenate adsorption onto substituted goethites

ANA E. TUFO; LIDIA HEIN; ELSA H. RUEDA; ELSA E. SILEO

LNLS, ACTIVITY REPORT 2009

LABORATORIO NACIONAL DE LUZ SINCROTRON

Lugar: SAO PAULO, BRASIL; Año: 2010 p. 1 - 2

1518-0204

Elevated levels of arsenic are often present in the environment due to both natural and anthropogenic sources, including weathering of rocks, industrial products and wastes, agricultural use of arsenical herbicides, wood preservatives, and mine drainage. The mobility of As in natural environments is strongly governed by its interaction with the surfaces of major mineral phases, such as metal hydroxides and oxides of iron, aluminium and manganese. Particularly important are the hydrated oxides of iron, which occur very widely as colloidal materials in natural waters, soils, and sediments or as coatings on the surfaces of mineral detritus. Arsenate is the most stable species under aerobic conditions and adsorbs strongly to iron oxide surfaces in acidic and near-neutral-pH water [1], the ion also interacts with aluminium oxides and clays. The strong sorption of As onto these minerals is considered to be an important mechanism of natural attenuation of arsenic pollution in soils, ground waters, mine drainage, and even marine systems [2],[3],[4]. Most studies or arsenic adsorption in natural environments indicated ferric oxides as the main adsorbents [5],[6]. Very little attention has been given to the possibility of modifying the structure of the iron oxides to improve its adsorptive capacity for arsenic in solution. It is well known that many cations can be incorporate into the goethite structure changing the bulk structure and the surface properties. Schwertmann and Cornell [7] have investigated the coprecipitation of both Al (III) and Mn (III) with Fe(III) to form an alumina ferrihydrite and a manganese ferrihydrite. Both materials have shown considerably better capacity for arsenic adsorption. In this project our first interest is to analize and compare the adsorption properties of Mn-, Al-, Al+Mn substituted goethites over As(V), and also analyze the surface complexes formed by As with the the Fe(III), Mn(III) and Al(III) ions present in the samples. The adsorption process has been done at pH 4, at 25 degrees, and using solutions containing arsenate ion (As(V))concentrations of about 10-5 M.