Microwave digestion and alkali fusion assisted hydrothermal synthesis of zeolite from coal fly ash for enhanced adsorption of Cd(Ⅱ) in aqueous solution

粉煤灰微波碱熔辅助水热合成沸石及其对水溶液中Cd(Ⅱ)的强化吸附作用（英文）

A novel microwave digestion and alkali fusion assisted hydrothermal method was proposed to synthesize zeolite from coal fly ash and the zeolite product was studied for removal of Cd(II)from aqueous solution through batch experiments.The adsorbent was characterized by X-ray diffraction,scanning electron microscopy,Fourier transform infrared spectroscopy,surface area analyzer and zeta potential measurement.The results show that the synthetic zeolite was identified as faujasite.The optimum conditions for removal of Cd(II)are found to be:adsorbent dose of0.5g/L,pH6,contact time of90min and initial concentration of20mg/L,the removal rate of Cd(II)is98.55%.The experimental kinetic data agree well with the pseudo second-order equation;the Langmuir isotherm model is found to be more suitable to explicate the experimental equilibrium isotherm results than Freundlich,Dubinin-Radushkevich and Temkin models,and the maximum adsorption capacity of Cd(II)is found to be86.96mg/g.The thermodynamic parameters such asΔGΘ,ΔHΘandΔSΘwere evaluated and the results show that the adsorption of Cd(II)onto the as-synthesized zeolite is spontaneous,endothermic and feasible under studied conditions.

针对传统水热法合成沸石存在碱熔温度高、反应时间长的问题,提出了一种新的粉煤灰微波碱熔辅助水热合成沸石的方法,并将沸石产品用于吸附水溶液中的Cd(Ⅱ)。其合成工艺是将粉煤灰与氢氧化钠混合物置于微波箱式高温反应器中以450°C反应15 min,碱熔产物加水在常温下磁力搅拌4 h,再在90°C下静置12 h,过滤、洗涤、干燥得到沸石产品。采用X射线衍射分析、扫描电镜分析、红外光谱分析、比表面积分析和zeta电位分析表征吸附剂。结果表明:合成的沸石为八面沸石,含量约为93%,比表面积为75.72 m^2/g,pH_(zpc)为3.80。从水溶液中去除Cd(Ⅱ),优化的吸附剂用量为0.5 g/L,p H 6,吸附时间为90 min,初始浓度为20 mg/L。在此条件下,Cd(Ⅱ)的去除率达98.55%。Cd(Ⅱ)在沸石表面的吸附符合伪二级动力学模型,Langmuir等温吸附模型比Freundlich模型、Dubinin-Radushkevich模型和Temkin模型更适合于描述等温吸附过程,最大的Cd(Ⅱ)吸附量为86.96mg/g。热力学计算表明:Cd(Ⅱ)在合成沸石表面的吸附为自发、吸热过程。