| Chromium widely exists in the nature with variable oxidation number. Cr(Ⅲ) and Cr (Ⅵ) are the mainly two forms which present in the environment. Cr(Ⅵ) has high toxicity and high mobility, which poses a seriously threat to human health and the environment. Due to the special physical and chemical properties, chromium and its compounds are the basic raw material used in the industries of metallurgy, metal processing, plating, leather, pigments and organic synthesis. Solid waste, gas, waste water containning chromium generated in the production process of these industries can not be effectively controlled or unreasonable discharged, this makes many parts of our country with serious chromium pollution problems. Dynamic adsorption method was widely concerned due to closer to natural conditions and with high efficiency, harmless and no secondary pollution. This paper investigated the effects of the different factors including flow rate, pH and interfering ions on the dynamic adsorption of Cr (Ⅵ) by sehwertmannit and the adsorption mechanism.The thesis includes two parts:In Part Ⅰ:Sehwertmannite was synthesized through oxidation of FeSO4by Acidithtobacillus ferrooxidans strains (i. e. A. ferrooxidans LX5), and the synthesis products was identified as pure sehwertmannlte by X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy.In Part Ⅱ:At room temperature, we investigated the effects of different pH and interfering ions on the dynamic adsorption of Cr (Ⅵ) by sehwertmannit and the adsorption mechanism through the bulk dynamic experimental. The results showed that different pH values affect dynamic adsorption of Cr (Ⅵ) by sehwertmannit by changing the surface charge of the sehwertmannit and the forms of Cr (Ⅵ). At the same pH conditions, different cations has little effect on the dynamic adsorption of Cr(Ⅵ) by sehwertmannit. H2PO4-with higher power of specific adsorption has obvious influence on the process of adsorption. However SO42-, NO3-has no obvious influence on this process. pH6.0as the optimum pH value was finally determined, and we conjecture that Cr(Ⅵ) is adsorbed into the Helmoltz layer, that is to say, Cr(Ⅵ) is attached to the mineral internal structure of sehwertmannit by ion-exchanged. In addition, at room temperature, and pH6.0, we carried out the bulk dynamic trials to study the impact of different flow rates and different amount of mineral on the adsorption of Cr (Ⅵ) by sehwertmannit and its influence mechanism. The results show that the mineral amount has obvious influence on the dynamic adsorption of Cr(Ⅵ) by sehwertmannit. The theoretical adsorption capacity increases with increasing mineral amount, and adsorption rate first increases and then decreases with the mineral amount increasing. The flow rate is an important factor in the process of dynamic adsorption, the capacity and the rate of adsorption first increase with the increase of the flow rate, and then decrease. The optimum flow rate and mineral dosage were determined to be1.0mL/min and0.1g, respectively. The experimental data of effluent curves can be fitted by Yoon-Nelson model very well. At last, the infared spectrum of sehwertmannit was compared before and after the adsorption of Cr(Ⅵ). We found that the absorption peak of SO42-was greatly reduced, and the absorption peak of Cr(Ⅵ) presented to the infared spectrum of sehwertmannit after the adsorption of Cr(Ⅵ). |
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