Interactions of Natural Aminated Polymers with Different Species of Arsenic at Low Concentrations: Application in Water
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Interactions of Natural Aminated Polymers with Different Species of Arsenic at Low Concentrations: Application in Water Treatment CLAIRE GERENTE∗ Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, BP 20722, 44307 Nantes Cedex 3, France [email protected]
GORDON MCKAY Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong YVES ANDRES AND PIERRE LE CLOIREC Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, BP 20722, 44307 Nantes Cedex 3, France
Abstract. In the present work, the interactions between the amine functionnal groups present in chitosan, a natural polysaccharide and different species of inorganic arsenic are studied. Depending of the N -deacetylation rate, chitosan provides amine functions that could be protonated and shows interesting affinities to adsorb oxyanions of arsenic in solution. Two species, arsenate (AsV) and arsenite (AsIII), have been tested at pH 5, and commercial chitosan and chitin were used. Kinetics have been carried out at two initial concentrations (50 and 500 µg/L) and different temperatures fixed between 4 to 40◦ C. The results have shown the reaction is very fast, and consequently, the equilibrium times are short (30 min in the best case). Experimental data are well fitted with a first order kinetic model. In a second part, isotherms have been performed with an As concentration range of 10 to 500 µg/L and 0.5 g/L of biosorbent. Maximum adsorption capacities, deduced from the Langmuir model, range between 260 µg/g at 40◦ C and 730 µg/g at 4◦ C. Finally the fixation mechanism could be described by an ion exchange reaction between the protonated amine moities of the chitosan and the arsenate anion in solution. Keywords: arsenate, chitosan, sorption, traces, water treatment 1.
Introduction
Arsenic contamination in natural waters is a world wide problem and is always a challenge for scientists since the admissible levels, especially in drinking waters, decrease continuously. Arsenic is introduced in water through natural and anthropogenic sources: release from mineral ores, probably due to long term geochemical changes (Sengupta, 2002), from various industrial effluents like metallurgical industries, ceramic industries, dye and pesticides manufactoring industries, wood preservatives and many others. . . Due to its es∗ To
whom correspondence should be addressed.
tablished toxicity and its presence in overcrowded areas (Viraraghavan et al., 1999; Jain and Ali, 2000), the guideline value recommended by WHO has been 10 µg/L since 1993. The EC maximum admissible concentration for As in drinking water has been reduced recently to 10 µg/L and also to this level for the Japanese and US-EPA limits. Whilst many national authorities are seeking to reduce theirs limits, many other countries still operate at present to the 50 µg/L standard, in part because of lack of adequate removal technologies for low concentrations, and because of the increasing treatment costs (SenGupta, 2002). The two predominant species found in natural waters a
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