Original and Fe-activated clay minerals to remove arsenic in groundwater: surface characterization by Laser techniques

MARÍA J. GONZÁLEZ, GUILLERMO BERTOLINI, DELIA GAZZOLI, IRMA L. BOTTO, CARMEN I. CABELLO, RICARDO ARIZAGA AND MARCELO TRIVI

Cardiff City Hall

Conferencia; ECASIA'11 European Conference on applications of surface and interfaces Analysis; 2011

Adsorption technology is a common technique adopted for arsenic removal. The presence of iron (as iron hydroxides or oxides) in lamellar type aluminium hydrosilicates opens up the possibility of these natural species to be used as adsorbent of the toxic species, including arsenic in groundwater. Arsenic occurrence in natural water is a worldwide problem and a 10 ppb (0.01 mg/L) level should be the standard for drinking water, according to the World Healt Organization (WHO) [1]. Laser Raman Microprobe (LRM) and Dynamic Laser Speckle techniques (DLS) complemented with more conventional tools such as XRD, chemical analysis (ICP ES), BET and ESEM-EDS have been applied to analyze original and chemically modified clay minerals for the removal of oxoarsenate (V) species. The mineralogy of the used raw materials is dominated by the presence of illite, pirophyllite and kaolinite, containing iron oxides of different crystallinity. The activation of natural samples has been done by chemical modification with iron nanosize phases to improve the capacity of As-sorption. This effect was reached by treatment of soluble Fe(III) salts by a slight pH modification and thermal treatments. Mineral samples showed an initial surface area of 12 m2 /g and a typical lamellar morphology. The modified phases containing iron (as Fe2O3) from 2 to 6 % showed an increase of surface areas. The exhausted solid adsorbent after the treatment with As-rich waters did not reveal appreciable changes of morphological and textural parameters. LRM technique identified bands at about 222, 289 and 410 cm-1 due to the ferrihydrite phase in the Fe-modified clays and an additional low intensity band at about 850 cm-1 in the arsenic-exposed materials. This band can be attributed to As-O stretching vibrations of arsenate species resulting from the interaction with the iron modified surface [2]. According to DLS technique [3], the different hydro-adsorption ability of the various samples can be related to the modification of surface properties in terms of distribution and type of aggregation of Fe nanometer particles; to alteration of the surface charge; to chemical composition (Fe/Si,Al ratio), factors that are expected to affect the arsenate bonding.