Journal of Hazardous Materials 171 (2009) 980–986 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat X-ray absorption spectroscopy as a tool investigating arsenic(III) and arsenic(V) sorption by an aluminum-based drinking-water treatment residual Konstantinos C. Makris a,∗ , Dibyendu Sarkar b , Jason G. Parsons c , Rupali Datta d , Jorge L. Gardea-Torresdey c a Cyprus International Institute for the Environment and Public Health in Association with The Harvard School of Public Health, 5 Iroon Street, Nicosia 1105, Cyprus b Department of Earth and Environmental Studies, Montclair State University, Montclair, NJ, USA c Department of Chemistry, University of Texas at El-Paso, TX 79968, USA d Department of Biology, Michigan Technological University, Houghton, MI, USA article info Article history: Received 6 May 2009 Received in revised form 19 June 2009 Accepted 19 June 2009 Available online 26 June 2009 Keywords: Residuals Drinking-water Arsenic (As) XANES EXAFS abstract Historic applications of arsenical pesticides to agricultural land have resulted in accumulation of residual arsenic (As) in such soils. In situ immobilization represents a cost-effective and least ecological disrupting treatment technology for soil As. Earlier work in our laboratory showed that drinking-water treatment residuals (WTRs), a low-cost, waste by-product of the drinking-water treatment process exhibit a high affinity for As. Wet chemical experiments (sorption kinetics and desorption) were coupled with X-ray absorption spectroscopy measurements to elucidate the bonding strength and type of As(V) and As(III) sorption by an aluminum-based WTR. A fast (1h), followed by a slower sorption stage resulted in As(V) and As(III) sorption capacities of 96% and 77%, respectively. Arsenic desorption with a 5mM oxalate from the WTR was minimal, being always <4%. X-ray absorption spectroscopy data showed inner-sphere complexation between As and surface hydroxyls. Reaction time (up to 48h) had no effect on the initial As oxidation state for sorbed As(V) and As(III). A combination of inner-sphere bonding types occurred between As and Al on the WTR surface because mixed surface geometries and interatomic distances were observed. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Arsenic (As) toxicity and carcinogenicity have promulgated extensive research on various treatments and remediation tech- nologies to decrease soil and water As concentrations below threshold values that undermine human health [1,2]. The risk of human contact with soil As has greatly increased in the last two decades as residential areas continue to expand into former agri- cultural land. Elevated As concentrations have been detected in soils used for residential development located on former orchards that had received repeated annual arsenical pesticide applications [3,4]. Playgrounds constructed with chromated copper arsenate (CCA)- treated wood present another source of As exposure to children, due to rainfall-induced As leaching from treated timber to the surround- ing soil [5]. Geophagia, a Greek term (geo-soil and phagia-eating) may occur from incidental hand-to-mouth activities by children playing in As-contaminated soils, being the #1 exposure route for As in soils [6]. ∗ Corresponding author. Tel.: +357 224 49292; fax: +357 224 49293. E-mail address: kmakris@cyprusinstitute.org (K.C. Makris). Immediate remedial action is deemed necessary to minimize the risk of exposure to soil As by children playing in As-contaminated soils. In situ treatment technologies have gained popularity over the conventional ex situ treatment of contaminated soils due to their environmental friendly (minimal ecological disruption) and cost-effective characteristics [1]. Examples of in situ treat- ment technologies include soil cementing/solidification, flushing, electro kinetics, bioremediation, vacuum or air stripping, and immobilization onto selective media/sorbents. In situ As treatment technologies largely depend upon adsorption and absorption reac- tions with media that exhibit high affinity for arsenical compounds. Various As sorbents have been tested to immobilize soil As with relative success and cost, such as, granular ferric hydroxide, anion exchange polyfunctional resins, activated alumina, reverse osmosis [7], fungal biomass [8], titanium dioxide [9], Fe-oxyhydroxides [10], and other inorganic and/or organic (poly)electrolytes [11]. However, soil As treatment technologies utilizing the above sorbents may be cost-prohibitive for small communities and developing countries. For example, the granular ferric hydroxide method yields a cost of $350 per ton [7]. Coagulation and filtration methods require an infrastructure at a cost of $32,000 m -2 of treated soils [11]. Models show a wide range of costs for the different technologies, which can hinder their implementation to As-contaminated soils [11]. 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.06.102