Development of new technology for elimination of anionic species of minor toxic elements (Se, Sb, As, B) from wastewaters

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1. Fundamental study on the reactions for elimination of selenium species from wastewaters : The selenium dissolved in aqueous solutions has 4- and 6- valence oxidation states. Due to their complicated chemical behaviors of the selenium entities, the systematic consideration of the elimination technology for selenium is urgent requisite. As the fundamental systems involved in the selenium catch as insoluble solids, Se(IV)-Fe(III)-H_2O, Se(IV, VI)-Ca-H_2O and Se(IV, VI)-Ba-H_2O systems have been investigated and equilibrium phase diagrams for these systems have been constructed. Based on these information, a stream of operations for selenium elimination from wastewaters has been proposed.2. Reactions of MgO in binder materials during processing of contaminated soils : Some MgO-based binder materials for soils show more environmentally acceptable characteristics over Portland cement. When mixed with contaminated soils and water, MgO-based materials favorably adjusted pH of water phase where the heavy-metal components are leached and hydrolyzed as their hydroxides to eliminate and MgO is converted to the carbonate through HCO_3 in the aqueous phase. The anion of fluoride Can be electrostatically trapped onto the positively charged surface of the magnesium hydroxide formed on the MgO and Mg-silicate mineral constituent particles. The immobilization of the heavy-metal ions and toxic anions as well as granulation of the soils is realized using these MgO-based binder materials.3. Modification of Mg-Al double hydroxide through intercalation of organic acid ions : Inorganic double hydroxide can be modified by intercalation of organic acid anions such as EDTA, Dodecylsulfate and Naphthane sulphonate ions. The modified hybrid materials of hydroxide with functional groups of organic acids are effectively working as scavengers for heavy-metal ions and toxic organic materials like bisphenol A.