两种碳酸系Fe-LDHs负载改性沸石对Cd(Ⅱ)吸附特性对比研究

Comparison of Adsorption Mechanisms of Modified Zeolite Coated with Two Different Fe-CO_(3)-Layered Double Hydroxides for Cd(Ⅱ)Removal

为提升以沸石为代表的天然吸附材料对重金属污染物吸附效果,并将新型功能材料层状双金属氢氧化物(layered double hydroxides,LDHs)有效应用于实际工程,采用水浴-共沉淀法制备两种Fe系碳酸型LDHs即时负载于沸石填料表面,利用场发射扫描电子显微镜(SEM)、能谱分析仪(EDS)和X射线衍射仪(XRD)对改性前后的沸石表面形态、化学成分和晶体结构进行表征;通过等温吸附及解吸附、吸附动力学、吸附热力学、竞争离子吸附和不同pH吸附试验,对比原始及改性沸石对Cd(Ⅱ)的吸附效果及其作用机理.结果表明:①改性沸石对Cd(Ⅱ)的吸附过程更符合Langmuir等温吸附模型和准二级动力学模型.②相较于原始沸石,两种改性沸石对Cd(Ⅱ)的吸附性能明显提升,且MgFe-LDHs负载改性沸石理论最大饱和吸附容量更高.③沸石改性后对Cd(Ⅱ)的吸附由放热过程变为吸热过程.④吸附时间、竞争离子及pH对沸石吸附Cd(Ⅱ)的效果产生不同程度的影响.研究显示,MgFe-LDHs负载改性沸石最大饱和吸附容量显著提升,吸附能力更强,且在不同条件下均表现出优良的吸附特性,具有作为高效除镉填料的潜力.

In order to improve the adsorption of heavy metal pollutants by natural adsorbents such as zeolite,and expand the application scope of the new functional material layered double hydroxides(LDHs),Fe-LDHs modified zeolites were prepared by hydrothermal coprecipitation method,and loaded on the surface of the zeolite immediately.Scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffractometer(XRD)were used to characterize the surface morphology,chemical composition and crystal structure of the zeolite before and after modification.The isothermal adsorption,desorption,adsorption kinetics,adsorption thermodynamic tests,adsorption tests under different pH condition and competitive ions were conducted to investigate the differences in Cd(Ⅱ)adsorption mechanisms and adsorption efficiency of modified and original zeolite.The results showed:(1)The adsorption process of Cd(Ⅱ)by Fe-LDHs modified zeolites were fitted to Langmuir and pseudo-second-order kinetic model,while original zeolite was fitted to Freundlich and pseudo-first-order kinetic model better.(2)The isothermal adsorption results showed that compared with original zeolite,the Cd(Ⅱ)adsorption ability of Fe-LDHs modified zeolites was significantly improved,and the theoretical maximum adsorption capacity of MgFe-LDHs modified zeolite was higher.(3)The results of adsorption thermodynamic experiment showed that the adsorption of Cd(Ⅱ)by zeolite before and after modification changed from exothermic process to endothermic process.(4)Adsorption time,competitive ions and pH all had effects on the adsorption.The study showed that the theoretical maximum adsorption capacity and the ability to adsorb Cd(Ⅱ)by the MgFe-LDHs modified zeolite was significantly improved.MgFe-LDHs modified zeolite can be recommended as an effective filter medium for the removal of Cd.