Removal of arsenic (III) form water with a new solid supported thiol

Document Type

Dissertation

Publication Title

PhD Thesis, Department of Chemistry, University of Kentucky

Abstract

Arsenic is a highly toxic, easily transportable and widespread contaminant in groundwater throughout the world. Arsenic causes acute toxicity by disrupting biological functions. In groundwater arsenic concentrations can reach up to a few milligrams per liter. Current regulations on arsenic content in drinking water are becoming more stringent and require the standard to be reduced to a few parts per billion. Arsenic exists as oxyanions in aqueous solution in either trivalent or pentavalent oxidation states depending on the oxidation-reduction potential and pH of the medium. Several treatment methods are available for removing arsenic from water. However, cost, operational complexity of the technology, skill required to operate the technology and disposal of arsenic bearing residual are factors that should be considered before the selection of any treatment method. Most of these techniques are also effective only in removing As(V) and not As(III). N,N’-bis(2-mercaptoethyl)isophthalamide), abbreviated BDTH2, is known to effectively precipitate soft heavy metals from water. A solid-supported reagent with the metal capture ability of BDTH2 would be ideal to use as a filtration column packing material for removal of aqueous As(III). In order to attain this objective, a new dithiol compound, 2,2'-(isophthaloylbis(azanediyl))bis(3-mercaptopropanoic acid) (abbreviated ABDTH2) has been synthesized and immobilized on silica beads. Silica-supported reagent ABDTH2 (SiABDTH2) thus prepared, completely removed As(III) from water by forming As-S bonds. In batch study, SiABDTH2 reduced the concentration of As(III) in aqueous solutions from 200 ppb to below 5 ppb at pH 5, 7 and 9. XAFS study of ABDT-As(III) and SiABDT-As(III) indicated that arsenic was present in +3 oxidation state as well as As(III) was only bonded to sulfur atom of ABDT unit. When SiABDTH2 was used as filtration column material, only 3% of ABDTH2 was leached out from the column. However, 100% As(III) was removed from 20 L of 200 ppb As(III) aqueous solution at a flow rate of 20 mL/min.

Publication Date

2012

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