| Hexavalent chromium (Cr (VI)) has been widely found in both natural water supplies and industrial waste water streams and can cause serious health problems to living beings and thus has been designated as one of the top-priority toxic pollutants by the U.S. EPA. Among the numerous processes that have been investigated for Cr (Ⅵ) removal, adsorption has been one of the most widely investigated areas owing to its simplicity and economic viability. The development of the absorbents with good adsorption performance is the significant factors for the adsorption method. Most recently, various porous metal oxides, activated carbon and natural ore have shown potential for Cr (Ⅵ) removal.In particular, alumina with large surface area and a large number of surface hydroxyl groups has been regarded as an attractive adsorbent material for water treatment. Additionally, the strong resistance to thermal degradation of alumina and large-scale production make this non-hazardous material an excellent candidate for water decontamination. In the third chapter, we have successfully synthesized alumina material using aluminum nitrate as precursor and urea as precipitator by a simple hydrothermal process followed by a calcination step through a set of optimized reaction conditions. The final alumina products showed rod-like morphology with extremely large surface area (773m2g-1) and an abundance of hydroxyl groups. When tested as adsorbents for Cr (Ⅵ) removal, the rod-like aluminas exhibited good adsorption properties for Cr (Ⅵ). The maximum adsorption capacity for Cr (Ⅵ) was40mg g-1, which is superior to most previously reported alumina adsorbents. Such excellent adsorption performance originated from the ion exchange between the hydroxyl groups on the alumina surface and chromium anions. Together with an outstanding adsorption-regeneration performance, the as-synthesized alumina is a promising absorbent in environmental remediation.Activated carbon material has been considered to be an effective adsorbent for Cr (Ⅵ) adsorption due to its high specific surface area, large number of active sites, high thermal and chemical stability, and superb Cr (Ⅵ) adsorption capacity. In the forth chapter, based on the properties of the waste delivered in the furfural production, we proposed to produce activated carbon by waste residue through activation in a steam of water and studied the adsorption capacity for Cr (Ⅵ) removal, which provided theoretical bases and practice experiences for energy saving and emission reduction and non-pollution manufacture in furfural industry. The porous activated carbon products showed high large surface area (>700m2g-1). Adsorption tests demonstrated that these materials exhibited an excellent Cr (VI) removal performance. The adsorption efficiency of the activated carbon was highly pH-dependent and the maximum Cr (Ⅵ) adsorption capacity of the as-obtained activated carbon was215mg g-1at pH3, which was much higher than those of other carbon-based adsorbents reported recently. Furthermore, Cr (Ⅵ) species on the carbon adsorbent could be reduced into Cr2O3through pyrolysis, which was widely applied in fields as catalysts, advanced colorants, and wear resistance materials. Thus, the prepared materials may serve as an ideal candidate for chromium removal in water treatment.For the practical application, the selectivity ability of the obtained materials in aqueous with other anions and continuous fixed-bed column studies were evaluated in the fifth chapter. The separation measurement illustrated that Cr (Ⅵ) was easily separated from other anions at25℃. Continuous fixed-bed column studies showed that the adsorption saturation capacity of Cr (Ⅵ) could reach140mg g-1... |
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