【作者】 朱培怡；

【导师】 王海增；

【作者基本信息】 中国海洋大学 ， 海洋化学工程与技术， 2009， 博士

【摘要】 我国镁资源丰富,大量镁资源得不到利用,浪费了资源,污染了环境,迫切需要开发大规模利用镁盐的新领域。本研究以镁盐(MgCl2·6H2O)和商品硅胶、硅溶胶为原料,分别采用浸渍法、溶胶-凝胶法、水热法等多种方法,制备出镁化合物改性硅胶和多孔硅酸镁两个系列的新型含镁多孔材料。采用比表面积及孔径分析、傅立叶变换红外光谱分析、X射线衍射分析和热分析等现代分析手段对产物进行了分析表征。评价了这些多孔材料对水体污染物(染料、金属离子、氟离子)、空气中水蒸气和二氧化硫的吸附脱除性能。浸渍法制备氯化镁改性硅胶,对水蒸气的吸附量可以与目前广泛应用的氯化钙改性硅胶干燥剂吸水性相当。经过两级脱水后得到的低水合氯化镁改性硅胶,其比表面积为232.35 m2·g-1、孔径为10.95 nm。氯化镁改性硅胶不是氯化镁与硅胶的简单物理混合,而是氯化镁填充到硅胶的孔隙中,既充分利用了硅胶大的比表面积和孔结构,又充分发挥低水合氯化镁的强吸湿性,根据改性硅胶中镁含量不同,复合干燥剂的吸湿能力可以增加为硅胶的10 ~ 30倍,克服了单一硅胶干燥剂吸湿量小的缺点,同时避免了氯化镁的液解现象。根据不同的吸湿要求,可以通过两级脱水制备出氯化镁含量从0.1 %到30 %的一系列改性硅胶干燥剂,满足不同条件下的空气除湿要求。采用过量浸渍、等体积浸渍和浸渍沉淀三种方法,制备出氧化镁改性硅胶,对三种制备方法得到的改性硅胶进行吸附性能综合评价,发现:等体积浸渍法制备改性硅胶具有方法简单、产物比表面积大、吸附性能好的优点。控制制备过程中氯化镁浓度,采用多次浸渍的方法,将硅胶加入氯化镁浸渍液中,在25℃恒温振荡浸渍24 h后,于500℃焙烧4 h,可以得到氧化镁含量高、吸附性能好的氧化镁改性硅胶。采用氯化镁和硅溶胶为原料,溶胶凝胶法制备多孔硅酸镁。不断搅拌下,向氯化镁中逐滴加入硅溶胶,调节混合物体系的pH值为10,待原料完全混匀后,加入聚丙烯酰胺絮凝剂,陈化24 h后,在750℃焙烧1 h。根据混合物中镁含量不同,可以制备出一系列针对不同性质污染物的复合吸附剂。根据多孔硅酸镁中镁和硅的不同配比,吸附剂的比表面积从14.18 m2·g-1到177.37 m2·g-1变化。通过对水中污染物包括金属离子、染料和氟离子的吸附,研究不同种类含镁多孔材料的性能。考察了吸附时间与温度、污染物初始浓度、溶液初始pH值及环境盐度对吸附性能的影响,发现:在实验温度范围内,几种含镁多孔材料对污染物的吸附均遵循伪二级动力学模型,吸附过程可用Langmuir吸附等温式、Freundlich吸附等温式和D-R吸附等温式描述。相同试验条件下,氧化镁改性硅胶和多孔硅酸镁对染料、金属离子和氟离子的吸附量分别为硅胶的5 ~ 30倍。氧化镁改性硅胶对二氧化硫的吸附能力随吸附剂用量的增大而增强,随气体流速的增加而降低,水蒸气的存在有利于吸附过程的进行。改性硅胶的脱硫能力明显高于商品硅胶,在相同的实验条件下,改性硅胶对二氧化硫的吸附量约为商品硅胶的5 ~ 7倍。吸附机理研究表明:有水蒸气存在的情况下,二氧化硫可以进入硅胶发达的孔隙中,也可以与复合物中硅胶上负载的氧化镁反应生成MgSO3,提高吸附效率。上述研究结果表明,利用镁盐(主要是MgCl2·6H2O)和硅胶、硅溶胶制备的一系列含镁多孔材料具有较好的吸附性能和广阔的应用前景。本研究中首次将氯化镁和硅胶、硅溶胶作为研究对象制备新型含镁多孔材料,并应用于空气除湿和污染物脱除领域。为卤水中镁盐的大规模使用提供了新思路,同时制备出一种可用于治理污染物的新型吸附材料,达到了双向治理的目的。更多还原

【Abstract】 Magnesium chloride is abundant in salt lakes in China. In some extent, it is bad for life and production. In order to make use of magnesium chloride, magnesium contained porous materials were prepared by mixture of magnesium chloride, silica and silica solution. The optimum preparation conditions were assured by uniform designs. The magnesium contained porous materials prepared under the optimum conditions were characterized by N2 adsorption/desorption isotherms, X-ray diffractometer, FT-IR spectrometers and thermogravimetry. The adsorption capacities of magnesium contained porous materials were evaluated by adsorbing dyes, metal ions and fluoride from aqueous solution, SO2 from gas and water vapor from air.The preparation of magnesium chloride modified silica need two steps of dehydration. The optimum preparation conditions were: first dehydration temperature of 60℃, second dehydration at 140℃for one and a half day. The BET surface areas of the sample prepared is 232.35 m2·g-1, which is intervenient of silicon dioxide (303.61 m2·g-1)and magnesium chloride(24.05 m2·g-1). The average pore radius is 10.95 nm, while the pore radius for silicon dioxide and magnesium chloride are 11.41 nm and 7.37 nm, respectively. These data indicate that the combined desiccant is not mechanical mix, but magnesium chloride penetrate into the pore of silica. The combined method can conquer the disadvantage of low uptake capacity of silicon dioxide and the deliquescence of magnesium chloride. And the water vapor uptake capacity of magnesium chloride modified silica is about 5 to 30 times larger than silica gel.Magnesia modified silica was prepared by three ways, namely superfluous solution soakage, equal solution soakage and equal solution soakage- precipitation methods. Compare the three methods, it can be find that the equal solution soakage way is easy to operate, economic and the best property for adsorption. By changing the concentration of magnesium chloride and repetitious soakage, the content of magnesia can be much more. The optimum preparation conditions were: Dipping at 25℃for 24 h, and then calcining at 500℃for 4 h. Sol-gel is the way for preparation of porous magnesium silicate use magnesium chloride and silicon solution. In uninterrupted mix round, the magnesium chloride and silica solution are mixed. The optimum pH value is about 10. Then, 0.2 % polyacry lamide act as flocculant was added in mixture. After aging for 24 h, the mixture were calcined at 7500℃for 1 h. The content of magnesia in porous magnesium silicate was controlled by the concentration of magnesium chloride solution. The BET surface area changed from14.18 m2·g-1 to 177.37 m2·g-1.The magnesium contained materials prepared were examined for the adsorption of dyes (Methylene blue and Weak acid red), metal ions ( Cu2+ and Ni2+) and fluoride from aqueous solutions by varying the parameters of adsorption time, temperature, initial pH, initial concentration and salinity of solution. Studies showed the adsorption of all the pollutants are followed the pseudo-second order model and could be described by Langmuir isotherm, Freundlich isotherm and D-R isotherm. Also, the adsorption mechanisms are not the same.The study of adsorption SO2 onto magnesia modified silica prepared showed that the adsorption capacities increase with the increasing of sorbent amount and decrease with the flow velocity and SO2 inlet concentration. Water vapor is beneficial for desulfurization. The adsorption amount of SO2 is much better than commercial silicon dioxide when water vapor presented. The adsorption mechanism of SO2 study showed that the mechanism of SO2 adsorption in SO2-H2O system is of physical adsorption and it could be changed to chemical adsorption when water vapor presented. The chemical adsorption played a more important role than physical adsorption.The study of preparation and adsorption behavior of magnesium contained porous materials show that all the materials have good characteristics. This is the first study of preparation of magnesium contained materials by magnesium salts from brine and salt lakes, the study can serve two purposes. First, it can provide a new way for magnesium salts from brine utilization; second, a useful, cheap and value-added sorbent for pollution treatment can be made. So this study is such an exploring research that has the certain prospect, innovation and important applied foreground.更多还原