Continuous flow system for arsenate uptake by horticultural peat impregnated with Fe

Osama M. Rageh, Cynthia A. Coles

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Laboratory and Field Testing

ABSTRACT: us flow system for arsenate uptake by horticultural peat impregnated with Fe Osama M. Rageh Japan Canada Oil Sands, Calgary, Alberta, Canada Cynthia A. Coles Department of Civil Engineering Memorial University of Newfoundland, Canada ABSTRACT The objective of this research was to employ horticultural peat impregnated with Fe in column experiments to remove arsenic from water to a level of 10 µg/L or less. The point of zero charge and the cation exchange capacity of the peat and important elements and metals contained in the peat were determined. Batch tests revealed that the optimum Fe impregnated peat for the column studies was the peat impregnated with 0.54 M Fe. It was possible to reduce the arsenic concentration exiting the column to < 10 µg/L and to a minimum of 0.61 µg/L. During the column tests the pH increased and the leaching of Mn, Ca, Mg, Cu, Pb, and Br from the peat decreased. RÉSUMÉ égal ou inférieur à 10 µg/L. On a déterminé le point de la tourbe. Des essais par lots ont révélé que la valeur optimale de la tourbe imprégnée au Fe était celle qui était olonnes, le pH a augmenté et le lessivage du Mn, Ca, Mg, Cu, Pb et Br contenus dans la tourbe a diminué. 1 INTRODUCTION In Canada and the United States, sources of drinking water from groundwater that contain arsenic above the 10 L limit must be treated. This may be expensive for small rural communities and so more economical arsenic removal is needed. There is also an interest in better understanding the conditions that contribute to arsenic release into waters used for human consumption. Aqueous phase arsenic exists as arsenate, As (V) and arsenite, As(III) (Lorenzen et al., 1995). Soluble arsenite can be oxidized to arsenate which can be adsorbed to soils and then become mineralized (Environment Canada, 1995). Arsenate exists in water as H3AsO4 (at < pH 2.2), H2AsO4- (from pH 2.2 6.7) and HAsO42- (from pH 6.7 11.6) (Chuang et al; 2005). Arsenic is effectively removed from water by adsorption onto activated alumina, granular activated carbon (AC) and engineered oxides of Fe, Al and Ti, and by ion exchange, Fe oxide precipitation, lime softening, coagulation/filtration, membrane filtration, reverse osmosis, and reverse electro-dialysis (Berg et al., 2006; García et al., 2004; Partey et al., 2008; Poots and McKay, 1979) though methods employing Fe oxides are most common (García et al., 2004). Employing energy intensive processes (such as AC adsorption or reverse osmosis) may not be sustainable (Høibye et al., 2008; Jones et al., 2007) or generally affordable (Bert et al., 2006). Adsorption has often been preferred for arsenic removal (Pokonova, 1998) but inexpensive and appropriate sorbents are needed. Peat is abundant and economical, and as with AC has a high organic content, but there are limited studies of arsenic adsorption with peat. Under oxidizing conditions arsenic is taken up predominantly with Fe forming scorodite, FeAsO4·2H2O and under reducing conditions (in aquifer walls) arsenic is incorporated into sulfide minerals such as orpiment, As2S3 and realgar, AsS. Arsenic commonly forms inner sphere complexes with Fe oxy-hydroxides and oxide surfaces and is attracted to the positively charged surfaces of AC below pH 7 7.5, and Fe impregnated AC below pH 8.2 8.7 (Budinova et al., 2006; Deutsch, 1997; Evans, 1989; Reed et al., 2000). Adsorption of arsenate by oxide surfaces is maximized near pH 4 and competes with antimony, silica and phosphorus for adsorption sites (Dixit and Hering, 2003; Ngo et al., 2002). When the peat is impregnated with Fe, it is oxidized to form Fe oxy-hydroxide or FeOOH and ligand exchange (and uptake) of arsenic with the OH- (carboxyl and hydroxyl) functional groups is promoted (Gu et al., 2005; Lorenzen et al., 1995; Manju et al., 1998; Subramanian et al., 1997; Viraraghavan and Kapoor, 1995). The Fe concentration in solution influences impregnation. Initially the Fe may be bonded organically with the peat but as organic sites become saturated and if oxidizing conditions are encouraged, Fe oxide precipitation may occur (Henrot and Wieder, 1990). In

RÉSUMÉ: tinuous flow system for arsenate uptake by horticultural peat impregnated with Fe Osama M. Rageh Japan Canada Oil Sands, Calgary, Alberta, Canada Cynthia A. Coles Department of Civil Engineering

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Cite this article:
Osama M. Rageh; Cynthia A. Coles (2014) Continuous flow system for arsenate uptake by horticultural peat impregnated with Fe in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper266,author = Osama M. Rageh; Cynthia A. Coles,title = Continuous flow system for arsenate uptake by horticultural peat impregnated with Fe,year = 2014}