【作者】 王春燕；

【导师】 周集体；

【作者基本信息】 大连理工大学 ， 环境工程， 2012， 博士

【摘要】 近年来国内经常发生的镉污染事件,严重威胁着人们健康。因此,探索和开发制备成本低、价格低廉、去除镉离子能力强的环保处理材料和处理技术刻不容缓。沸石分子筛由于具有很好的热稳定性和水热稳定性、良好的离子交换性能和独特的阳离子选择吸附性能,在重金属废水处理中有广泛应用前景。但目前,沸石分子筛的制造成本和价格较高,严重影响了其在环境保护等领域的大规模使用。因此,选取价格低廉的原料来合成低成本沸石分子筛成为当务之急。本文以廉价的低品位铝矾土为原料,经碱熔融活化后,成功地合成了沸石分子筛,并系统地研究了合成沸石分子筛的各种影响因素。利用X射线衍射、扫描电镜、红外、物理吸附分析等测试技术对产物晶相、形貌、热稳定性、钙离子吸附能力及比表面积进行了系统表征测试,将分子筛的结构及性质等与其吸附性能进行了关联。进一步研究了沸石分子筛吸附金属离子的吸附等温线、热力学和动力学特征。所有研究为有效利用低品位铝矾土矿产资源、开发廉价环境保护材料奠定实验基础。主要研究结果如下：1、以低品位铝矾土为原料、偏铝酸钠为补充铝源、碳酸钠为活化剂,采用碱熔融-水热法合成了单一晶相、高结晶度的A型沸石分子筛。原料经碱熔融活化后全部用于合成沸石分子筛,未再有其他后处理,合成工艺简单,使其有重要的工业应用价值。探讨了晶化反应条件对合成A型沸石分子筛的影响。最佳合成工艺条件是：反应物配比为1.5Na2O:0.5A12O3:1SiO2:128H2O,晶化温度：90℃,晶化时间：12h。合成的A型沸石分子筛形貌为斜切边的立方体形状,平均晶粒直径1-2μm,在700℃以下能够保持稳定的结构,钙离子交换能力为369mg CaCO3/g沸石分子筛,具有较高的吸附性能。2、首次以铝矾土类天然矿物为原料,通过氢氧化钠碱熔融活化、补充硅源后,水热合成了单一晶相、高结晶度的X型沸石分子筛；补充硅源并添加导向剂,合成出结晶度较高Y型沸石分子筛。详细研究了SiO2/Al2O3(?)匕、碱度、晶化时间、晶化温度、导向剂组成、用量及陈化时间对合成的影响,得到由低品位铝矾土制备X型、Y型沸石分子筛的结晶规律。合成的沸石分子筛X和Y形貌均为八面体结构,平均晶粒直径2-3μm,具有良好的热稳定性。X型沸石分子筛具有较大的比表面积(SBET56Om2/g)、孔容(0.441cm3/g)和较高的钙离子交换能力(317mgCaCO3/g沸石分子筛),具有良好的工业应用价值。3、分别以A型和X型沸石分子筛作为吸附剂,研究了水溶液中Cd2+离子在沸石分子筛上的吸附行为。研究表明Cd2+离子在沸石分子筛上的吸附过程均符合准二级动力学速率方程,其中,液膜扩散是Cd2+离子在沸石分子筛上吸附的主要控制步骤。A型沸石分子筛吸附等温线可以用Langmuir和Freundlich模型来描述,X型沸石分子筛吸附更符合Langmuir等温吸附模型。两种分子筛最大吸附容量分别为161.3mg/g和178.6mg/g。随着Cd2+离子溶液初始pH、沸石用量和吸附温度的增大,Cd2+离子去除率增大。热力学研究表明沸石分子筛吸附Cd2+离子是吸热、熵增和自发过程。沸石分子筛的解吸与再生实验表明,A型沸石分子筛可以多次再生循环使用,在处理含镉重金属废水方面表现出良好的应用前景。对竞争体系中Cd2+、Zn2+和Ni2+离子在A型沸石分子筛上的吸附规律研究发现在单组分中沸石分子筛对3种离子的吸附能力都比较强,等温吸附均可用Langmuir模型较好地描述。在所有组分体系中,吸附能力从强至弱均为：Cd2+>Zn2+>Ni2+,这与三种离子的水合焓和离子半径大小的顺序一致。更多还原

【Abstract】 In recent years, the cadmium pollution has become a serious threat to people’s health because of the frequent cadmium pollution accidents. Therefore, exploring a cost-effective material with a high ability to remove cadmium ions from wastewater is an extremely urgent environmental protection task. Synthetic zeolites are recognized to be the most promising materials for the removal of heavy metal ions from wastewater due to their special properties such as high thermal/hydrothermal stability, large surface area, uniform three-dimensional pore structure, high cation exchange capacity, and strong affinity to transition metal cations. The important practical application in wastewater treatment and the high synthesis cost for the synthetic zeolites have incentivized the development of facile methods for synthesizing zeolites from the cost-effective earth-abundant sources.In this study, zeolites are synthesized successfully from the cost-effective low-grade bauxite without any treatment after alkali fusion activation process. The effects on the crystallization of the zeolites were discussed. Various techniques such as X-Ray diffraction, SEM, FTIR, adsorption of nitrogen have been used to characterize the crystal phase, morphology, thermal stability, and specific surface area etc. for the synthesized zeolites. The relationship between the structure properties of zeolites and the adsorption capacity was analyzed. The adsorption isotherms, kinetics, and thermodynamics of adsorption were also studied. All these studies provided some important guidance for the utilization of the low-grade bauxite and the exploiture of low-cost environmental protection material. The main results are summarized as follows:1. Using sodium carbonate as an activator and sodium metaaluminate as an extra aluminum source, phase-pure high-quality zeolite A was synthesized by alkali fusion hydrothermal reaction from the cost-effective low-grade bauxite. All the fused products were used to synthesize zeolite without any futher treatment. The process reduces the costs of synthesis greatly which shows its potential value of industrial applieations. The optimized experimental conditions are:reactant molar ratio1.5Na2O:0.5Al2O3:1SiO2:128H2O, crystallization at90℃for12h. The image of the synthesized zeolite A is a chamfered-edge shape and the mean diameter of the sample is1～2μm. The structure could be retained when the temperature is below700℃. The calcium exchange capacity value is369mg/g which shows its high adsorption capacity. 2. For the first time, Zeolite X and Y were synthesized from the raw low-grade bauxite by a two-step process method:alkali fusion activation with sodium hydroxide and hydrothermal reaction. Sodium silicate solution was added as supplementary silicon source for the synthesis of zeolite X and Y, while directing reagent was introduced into the reaction mixture for the synthesis of zeolite Y. Optimizations of the molar ratios of SiO2/AlO3, Na2O/SiO2, H2O/Na2O, the reaction time, temperature, the composition and amount of directing reagent have been investigated in details.The zeolites of X and Y are octahedral crystals with the average crystal sizes of2to3μm and high thermal stability. The data of the surface area(SBET560m2/g), pore volume(0.441cm3/g), and the calcium exchange capacity value(317mg CaCO3/g zeolite) show the zeolites have the potential value of industrial applications.3. The cadmium ion removal from aqueous solutions using the synthesized zeolite A and X powders were studied. The study of kinetics showed that the pseudo-second-order kinetic adsorption model is suitable for describing the adsorption of Cd2+ion on the zeolite A and X. Both Langmuir and Freundlich models could fit the experimental data well at pH=6for zeolite A, but the Langmuir models fitted better for zeolite X. The maximum adsorption capacitis for zeolite A and X are161.3mg/g and178.6mg/g, respectively. The cadmium ion removal from aqueous solutions increased with the increasing of Cd concentration, pH value, and adsorbent amount used. The studies on thermodynamics show that the adsorption of Cd2+ion on the zeolites is a entropy increment, endothermic, and spontaneous process. Regenerative experiments show that the zeolite could be cyclically used many times. The competitive adsorptions of Zn+, Cd2+and Ni2+ions onto zeolite A were also studied.The isotherms of the Zn+, Cd+and Ni+ions follow the Langmuir model. In single, binary and ternary systems, the adsorption capacity varied in the following order:Cd2+(aq)> Zn2+(aq)> Ni2+(aq), which is accordance with that of the hydration enthalpy and ionic radius of the cations.更多还原