| A large amount of heavy metal wastewater has been produced with the rapid development of industry.The heavy metal has caused serious damage to the ecological environment and human health, and how to effectively remove the heavy metals has become one of the important environmental problems. Many heavy metal ion removal technologies have emerged, however, the biggest drawback of these technologies is the high operating costs. Compared with other treatment methods of heavy metal, the advantages of selecting adsorbent which has a wide range of sources,low price and good adsorption capacity to remove the heavy metal ions in the water is more obvious.Montmorillonite and vermiculite often used as adsorbent for the management of environmental pollution because of their advantages of abundant reserves,low prices and environment friendly. However,the adsorption ability of heavy metals and organic matter in natural clay is poor. If we can develop the low cost of montmorillonite and vermiculite into the good performance of adsorbent through appropriate chemical modification, this work not only can solve the problem of heavy metal pollution in water bodies, but also open up a new way for the comprehensive utilization of clay minerals. In addition the review of the properties, modification methods and the applications of montmorillonite and vermiculite in the environmental pollution control, the paper mainly included the following contents:1.Cysteamine modified vermiculite(MEA-VER) was synthesized with vermiculite(VER)by organic modification method. The structure and surface properties of MEA-VER were analyzed by XRD, FTIR, BET, SEM, TG-DSC and Zeta potential analysis. The results show that:(1)The specific surface area and micropore volume of vermiculite increased after modified by cysteamine. This provides more adsorption sites for the adsorption process and improve the adsorption capacity of MEA-VER;(2)The maximum uptake of Ag+of VER and MEA-VER were 104.6 and 120.6 mg·g-1, respectively;(3)The rate of Ag+ adsorption by VER and MEA-VER were relatively fast with an equilibrium time of 200 min;(4)The adsorption process was in keeping with Langmuir adsorption isotherm and the Pseudo-second-ordermodel;(5)The coexistence of Ca2+was more inhibit the Ag+adsorption than Na+;(6)MEA-VER can better selective adsorption of Ag+ when Ag+ coexist with Pb2+, Ni2+ and Zn2+;(7)Citric acid can used as desorption agent that is effectively to the desorption and regeneration of MEA-VER, the adsorption capacity is essentially the same after the repeated use of 4 times;(8)The adsorption mechanisms of Ag+ on VER and MEA-VER mainly involved ion-exchange and the coordination, respectively.2. Three mercapto propyl trimethoxy silane modified vermiculite(MPTMS-VER) was synthesized with vermiculite by organic modification method. The structure and surface properties of MPTMS-VER, MEA-VER and VER was analyzed contrastively by XRD, FTIR,BET, SEM, TG-DSC and Zeta potential analysis.The ppb level concentration of Hg2+adsorption performance of this three materials were investigated by adsorption experiments.The results of characterization showed that the basic crystal structure of vermiculite has not been destroyed by the modification of MPTMS and MEA. The interlayer distance of MPTMS-VER was not change compared to VER,but for MEA-VER, is smaller. The surface area and micropore volume of MEA-VER increased, while MPTMS-VER decreased,which is because of the blocked of pore structure. Besides,MPTMS-VER and MEA-VER possessed more negative charge than VER,which indicates that the modification improved the surface properties and adsorption performance of vermiculite. Adsorption experimental results suggested that:(1) MPTMS-VER,MEA-VER and VER could remove Hg2+fastly and the adsorption equilibrium time was 120 min;(2)While the adsorbent dosage was 2 g·L-1, the temperature was 303 K and the pH was 5, the maximum adsorption capacity of VER,MEA-VER and MPTMS-VER were 99.95,176.33 and 286.29 μg·g-1, respectively. The adsorption capacity of MPTMS-VER was greatly improved relative to MEA-VER;(3)The Hg2+ adsorption process could get better description by the Pseudo-second-order model and Langmuir adsorption isotherm. Besides, the adsorption was spontaneous exothermic reaction;(4)Coexisting cations in the solution could obviously inhibit the Hg2+ adsorption of VER and MEA-VER, but no effect for MPTMS-VER;(5)XPS analysis showed that the coordination adsorption of thiol functional groups consist in MPTMS-VER and MEA-VER with Hg2+werepredominant in the adsorption process.3.Dimercaprol modified montmorillonite(BAL-Mt) and vermiculite(BAL-VER) was prepared with natural montmorillonite and vermiculite. The physicochemical properties of BAL-VER, VER, BAL-Mt and Mt were analyzed by XRD,FTIR, BET, SEM, TG-DSC,BAL-VER and Zeta potential. The adsorption properties of these four materials were studied by the adsorption experiments of ppm concentration of Hg2+. The results show that:(1) the interlayer distance of VER and Mt was not change after the modification of BAL, but the specific surface area was decreased and more negative charge was catched in surface;(2)The maximum uptake of Hg2+of vermiculite increased from 1.75 to 9.63 mg g-1after modification.For montmorillonite, was increased from 1.68 to 3.21 mg g-1;(3)The Pseudo-second-order model and Langmuir adsorption isotherm could interpret well the Hg2+adsorption on four kinds of materials;(4)The equilibrium time was 300 min, and the adsorption rate of BAL-VER and BAL-Mt were greater than that of VER and Mt;(5)The rise of solution temperature had small effect on adsorption and the adsorption process was geared to spontaneous exothermic reaction;(6)The adsorption capacity of BAL-VER was better than that of BAL-Mt because of the more thiol groups on BAL-VER through comparative analysis;(7)Adsorption experiment data and characterization results displayed that the removal mechanisms of Hg2+ on BAL-VER and BAL-Mt contain coordination adsorption,ion-exchange,electrostatic attraction and channel interception. |
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