| Montmorillonite(MMT) is considered to be an effective adsorbent in removing heavy metal ions as a result of its cheapness and abundance, layered structure, exchangeable interlayer cations, and high surface area, etc. However, due to the presence of some impure components, such as metal oxides, the natural MMT generally shows a low adsorption capacity to heavy metal cations. Based on the available reports and our previous studies, in this thesis, the modification of MMT by the acid activation and the introduction of chitosan(CTS) via a simple mixing method was quantitatively investigated to improve its adsorption capacity to metal cations. The samples were characterized by SEM, N2adsorption at low temperature, XRD, and FT-IR techniques. By using Co2+as a model ion of heavy metal cations, effect of modification parameters, e.g., acid concentration, activation temperature, the molecular weight of CTS, and the weight ratio of CTS to MMT, on its adsorption properties was investigated at various adsorption temperature, and the corresponding thermodynamics parameters and kinetics equations were obtained. Finally, the adsorption behaviors of Cu2+, Ni2+, Fe3+, and Zn2+on MMT modified under optimal conditions were studied. The experimental and main results are summarized as follows.(1)The natural Na-MMT acid activated by using the concentration of0.5-20%hydrochloric acid at30-90℃, preparation of a series of acid activated MMT。 Taking Co2+as a model of heavy metal ions, the acid activated MMT of adsorption process at different temperatures were investigated. The results showed that the acid activated MMT by1%hydrochloric acid at50℃was the best. When the adsorption temperature was at30℃, Co2+equilibrium adsorption amounts reached1.6969mmol/g. The Temkin model can be described more better than others for adsorption Co2+by acid activated MMT. According to the equilibrium adsorbance under different adsorption temperatures, ΔGθ, ΔHθ, ΔSθ and Ea of Co2+were calculated. The results of kinetic showed that the adsorption process of Co2+by acid activated MMT was found to be followed the pseudo-second-order kinetic model and some corresponding dynamic parameters were obtained. Based on the above work, a comparative study on the adsorption behavior of Fe3+, Ni2+, Cu+, and Zn2+by the best acid activated MMT and the equilibrium adsobrance were3.6080,2.2786,1.7229and0.9662mmol/g respectivly. At the same time, the Temkin model can be described the adsorption characteristics of Fe3+very well, and Ni2+, Cu2+, Zn2+were fitted for Freundlich model. In addition, the adsorption process of four kinds of heavy metal ions can be described by pseudo-second-order kinetic model. The experimental results of mixed heavy metal ions showed that the equilibrium adsorbance decrement according to the order of Cu+Ni2+>Co2+>Fe3+>Zn2+.(2) MMT was modified with CTS which having different mass ratio. Co2+was selected as a model cation of heavy metals, and the effect of molecular weight of CTS, CTS/MMT mass ratio for adsorption of Co2+was investigated. The molecular weight for50000of CTS with MMT composite having to mass ratio of0.25:1is a best adsorbent, and the maximum adsorption capacity can reached2.5384mmol/g. The adsorption isotherms of Co2+were best fitted to the Temkin equation, and have nothing to do with the molecular of CTS. Kinetics study revealed that the adsorption of Co2+on CTS-MMT followed the pseudo-second-order equation, The adsorbance for Fe3+, Cu2+and Zn2+over the best adsorbent are the same and the adsorbance was2.5354,2.5384, and2.5314mmol/g, respectively. |
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