Arsenic Removal with a Dithiol Ligand Supported on Magnetic Nanoparticles

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Theses and Dissertations--Chemistry


Exposure to arsenic (As) in water, the ubiquitous toxin that poses adverse health risks to tens of millions, is the result of both anthropogenic and geochemical mobilization. Despite recent publicity and an increased public awareness, the dangers associated with arsenic exposure rank among the top priorities of public health agencies globally. Existing sequestration applications mainly include reductions and adsorption with zero-valent metals and their oxides. The performance of adsorption media is known to preferentially favor aqueous As(V) over As(III) due to the charge of the dissolved oxyanion. Magnetic nanoparticles (MNP) have been the focus of multidisciplinary research efforts for the removal of aqueous toxic metals and metalloids since they can be magnetically separated from the treated water. This improves isolation and allows for regeneration of the MNP, reducing cost and resource consumption. This research is focused on As(III & V) sequestration through the use of synthetic ligands N,N’bis(2-mercaptoethyl)isophthalamide (abbreviated BDTH2) and 2,2’- (isophthaloybis(azanaediyl))bis-3-mercaptopropanoic acid (abbreviated ABDTH2). Additionally, As(III) sequestration with ABDTH2 functionalized on silica core-shell MNP (ABDTH2 MNP), magnetite MNP (ABDTH2@MNP), and commercial silica beads (ABDTH2 Si60) is demonstrated. Both BDTH2 and ABDTH2are effective precipitation agents for the removal of As(III) through the formation of S-As covalent bonds. ABDTH2MNP reduced a 200 ppb As(III) batch solution to below 10 ppb at pH 5,7, and 9. Additionally, complete removal was achieved in the presence of anions at concentrations of 200, 500, and 1000 ppb. This system was evaluated for the removal of total arsenic from industrial solutions accumulated during the production of renewable biogas in landfills. Direct precipitation with BDTH2 and ABDTH2 was inhibited by the complex matrix. However, batch removal with ABDTH2@MNP was effective in removing 82% of the inorganic arsenic. Sequestration of arsenic and speciation from these industrial solutions remains a challenge.


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