层状双金属氢氧化物的制备、表征及硫酸根和氟离子吸附性能研究

发布时间：2018-06-05 20:25

本文选题：层状双金属氢氧化物 + 硫酸根　；参考：《太原理工大学》2015年博士论文

【摘要】：我国高硫酸根、高氟离子地下水分布范围较广，，未经处理直接饮用会引起健康问题。《生活饮用水卫生标准》（GB5749-2006）要求硫酸根浓度不超过250mg/L，氟含量应小于1.0mg/L。常规处理方法存在去除效率低、工艺流程长、运行和维护成本高等缺陷。吸附法因具有处理工艺简单、适应范围广而受人重视，其中吸附材料是吸附污染控制技术的关键部分和核心基础。层状金属氢氧化物作为典型的阴离子吸附剂在处理阴离子方面具有独特优势。因此本课题采用焙烧的Mg/Fe层状金属氢氧化物处理硫酸根离子，淀粉稳定化的Mg/Al层状金属氢氧化物处理氟离子，焙烧的Mg/Fe层状金属氢氧化物同时处理硫酸根离子和氟离子。主要研究内容和结论如下：（1）采用共沉淀法制备了晶相单一的Mg/Fe层状金属氢氧化物（Mg/FeLDHs），400℃焙烧后得到产物Mg/Fe CLDH。Mg/Fe LDHs和Mg/Fe CLDH用ICP、元素分析、XRD、FT-IR、TG-DSC、BET和SEM进行表征。结果表明：Mg/Fe LDHs具有典型的层状结构，Mg/Fe CLDH为金属氧化物结构。Mg/Fe CLDH比表面积和孔容都比Mg/Fe LDH有所增加，SEM显示有微小团聚。吸附实验表明Mg、Fe摩尔比为3:1，焙烧温度为400℃的Mg/Fe CLDH表现出高效的吸附硫酸根离子能力。等温吸附研究表明Mg/Fe CLDH去除水体中硫酸根满足Langmuir等温吸附模型，说明吸附过程为单层吸附。KL值大于0，表明吸附为优先吸附。热力学分析表明不同温度下吉布斯自由能△G0分别为-20.67KJ/mol、-22.02KJ/mol、-23.02KJ/mol，说明吸附过程是自发的；标准焓变△H0为15.01KJ/mol，说明反应是吸热的；标准熵变△S0为14.18J/(mol·K)，说明吸附时固液界面是随机的。动力学吸附表明Mg/FeCLDH去除水体中硫酸根满足拟二级动力学模型，反应速率常数较小，说明反应很快。对应吸附阶段的活化能为74.25kJ/mol，说明主要为化学反应控制。粒内扩散模型表明吸附包括从溶液相扩散到吸附剂外表面的过程、缓慢的吸附过程和平衡过程三个阶段，说明Mg/Fe CLDH吸附模拟水中硫酸根是一复杂过程。吸附后的XRD和FT-IR表征表明Mg/Fe CLDH有效地吸附了硫酸根。在pH为3~11的变化过程中，CLDH对模拟水中硫酸根的吸附量随pH的增大而不断减小，但幅度不大，吸附结束后pH变为11，表明发生了“记忆效应”。（2）首次将淀粉作为稳定剂，采用共沉淀法稳定化处理Mg/Al LDHs（S-LDH）。Mg/Al LDHs和S-LDH采用XRD、FT-IR、TG-DSC、SEM和粒度分析等表征。粒径分析表明S-LDH粒径较Mg/Al LDHs合成粒度尺度更小，粒径分布范围更窄。吸附试验表明淀粉含量为10mg时S-LDH吸附氟离子的能力高于没有稳定化的Mg/Al LDHs吸附氟离子的能力。等温吸附研究表明，S-LDH去除模拟水中氟离子满足Langmuir等温吸附模型，去除天然水中氟离子满足Freundlich等温吸附模型，表明模拟水中氟离子和天然水中氟离子具有不同的吸附过程，这与天然水中存在的共存离子干扰有关。S-LDH去除模拟水中氟离子热力学分析表明吸附过程是自发的，反应是吸热的，吸附时固液界面是随机的。吸附动力学满足拟二级动力学。S-LDH吸附氟离子的过程是一复杂过程，包括离子交换和表面吸附。（3）Mg/Fe CLDH同时去除模拟水中硫酸根和氟离子的性能表明，pH值对模拟水中硫酸根去除的影响小于对氟离子的影响。等温吸附研究表明CLDH去除模拟水中硫酸根和氟离子均满足Langmuir等温吸附模型。动力学吸附表明CLDH去除模拟水中硫酸根和氟离子均满足拟二级动力学模型。去除硫酸根和氟离子的机理包括表面吸附、离子交换和结构重建等。
[Abstract]:The distribution of high sulphuric acid and high fluoride ions in our country is wide, and the health problem is caused by untreated direct drinking. The hygienic standard for drinking water (GB5749-2006) requires that the concentration of sulfate is not more than 250mg/L, and the content of fluorine should be less than that of the conventional treatment method of 1.0mg/L., which has low removal efficiency, long process flow and high cost of operation and maintenance. The absorption method is the key part and core base of the adsorption pollution control technology because of its simple processing technology and wide range of adaptation. The layered metal hydroxide is a typical anion adsorbent for the treatment of anions. Because of this problem, the Mg/Fe layered metal hydrogen roasted is used in this project. The oxide treatment of sulfate radical ions, the stabilized Mg/Al layered metal hydroxide for the treatment of fluorine ions, the Mg/Fe layered metal hydroxide calcined at the same time treated the sulfate ion and fluorine ions. The main contents and conclusions are as follows:
(1) a single crystalline Mg/Fe layered metal hydroxide (Mg/FeLDHs) was prepared by coprecipitation method. After calcination at 400 C, the products Mg/Fe CLDH.Mg/Fe LDHs and Mg/Fe CLDH were obtained with ICP, elemental analysis, XRD, FT-IR, TG-DSC, BET, and CLDH.Mg/Fe. The specific surface area and pore volume of CLDH are higher than that of Mg/Fe LDH, and SEM shows a small agglomeration. The adsorption experiment shows that the molar ratio of Mg to Fe is 3:1 and the Mg/Fe CLDH at the calcination temperature of 400 C shows the ability to adsorb the sulfate ion efficiently. The isothermal adsorption study shows that Mg/Fe CLDH removes sulphate from the water body to satisfy the Langmuir isothermal adsorption model, indicating the absorption of the adsorption model. The adsorption.KL value is greater than 0, indicating that adsorption is preferential adsorption. Thermodynamic analysis shows that the Gibbs free energy is -20.67KJ/mol, -22.02KJ/mol, -23.02KJ/mol respectively at different temperatures, indicating that the adsorption process is spontaneous; the standard enthalpy Delta H0 is 15.01KJ/mol, indicating that the reaction is endothermic; the standard entropy change Delta S0 is 14.18J/ (mol. K). It shows that the solid-liquid interface is random when adsorption. Kinetic adsorption shows that Mg/FeCLDH can meet the quasi two order kinetic model in the water removal. The reaction rate constant is small and the reaction is very fast. The activation energy of the corresponding adsorption stage is 74.25kJ/mol, which is mainly chemical reaction control. The intragranular diffusion model shows that the adsorption includes from solution phase. The process of diffusion to the external surface of the adsorbent, the slow adsorption process and the three phases of the equilibrium process, indicate that Mg/Fe CLDH is a complex process for the adsorption of sulfate roots in water. The adsorption of XRD and FT-IR shows that Mg/Fe CLDH adsorbed sulfate radical effectively. In the process of pH 3~11, the adsorption amount of CLDH to the simulated water is with pH. The pH decreased to 11 after the adsorption, indicating a "memory effect".
(2) starch was used as a stabilizer for the first time. Mg/Al LDHs (S-LDH).Mg/Al LDHs and S-LDH were stabilized by co precipitation method. XRD, FT-IR, TG-DSC, SEM and particle size analysis were used to characterize the starch. The particle size analysis showed that the size of S-LDH particle size was smaller than that of Mg/Al, and the size distribution was narrower. The ability of fluorine ion is higher than that of Mg/Al LDHs without stabilization. The isothermal adsorption study shows that S-LDH removal of fluorine ions in simulated water satisfies the Langmuir isothermal adsorption model, and the removal of fluorine ions in natural water satisfies the Freundlich isothermal adsorption model, which shows that fluorine ions in the simulated water and the natural water fluorine ions have different absorption. The thermodynamic analysis of.S-LDH removal of fluorine ions in the simulated water shows that the adsorption process is spontaneous, the reaction is endothermic and the adsorption of the solid-liquid interface is random. The adsorption kinetics satisfies the pseudo two kinetics.S-LDH adsorption process as a complex process, including ion exchange. And surface adsorption.
(3) the performance of Mg/Fe CLDH at the same time removal of sulphate and fluorine in simulated water shows that the effect of pH on the removal of sulfate radical in simulated water is less than that of the fluoride ion. The isothermal adsorption study shows that the removal of sulphate and fluorine ions in simulated water satisfies the Langmuir isothermal adsorption model. Kinetic adsorption shows that CLDH can remove sulfuric acid in simulated water. Both the root and the fluorine ions satisfy the pseudo two stage kinetic model. The mechanisms of removing sulfate and fluoride include surface adsorption, ion exchange and structural reconstruction.
【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ424.2;TU991.2

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