【作者】 杨华；

【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， 2013， 博士

【摘要】 海水苦卤中含有丰富的镁盐,大量镁盐得不到有效的开发利用,造成了资源浪费和环境污染。所以苦卤镁资源的开发利用不仅是苦卤化学资源综合利用中急需解决的问题,还能为镁盐大规模的开发利用提供新领域。本论文以氯化镁、硫酸镁、九水硅酸钠和水玻璃为原料,采用溶胶-凝胶法和水热法制备了一系列不同镁硅摩尔比的硅镁胶多孔吸附材料；通过比表面及孔径分析仪、X-射线衍射仪、扫描电镜／能谱仪、傅立叶红外光谱仪等现代分析仪器和多种化学分析手段,研究了硅镁胶的比表面积、孔径分布、表面活性基团、结构形貌、表面酸碱性和稳定性等；考察了硅镁胶对水溶液中染料、重金属离子和磷酸根离子的吸附性能,并研究了吸附过程的热力学和动力学原理,初步探讨了硅镁胶的吸附机理。主要研究内容及结果如下：1.采用溶胶-凝胶法和水热法制备了一系列不同镁硅摩尔比的硅镁胶多孔吸附材料,以亚甲基蓝作为评价硅镁胶吸附能力的目标对象,系统地研究了反应物浓度、时间、水热温度等因素对硅镁胶制备的影响。结果表明,物料添加顺序、反应物浓度、硅酸钠溶液pH值、Mg/Si摩尔比、镁源和硅源、水热温度等都会影响硅镁胶的吸附性能。硅镁胶的最佳合成条件是：反应物浓度为1mol·L-1、Mg/Si摩尔比为1：1、pH值在10-12之间、水热温度为120℃。2.采用现代分析仪器和多种化学分析手段对硅镁胶多孔吸附材料的结构形貌进行了表征。结果表明,氮气吸附脱附曲线都属于经典的IV型,具有明显的滞后环,溶胶-凝胶法制备的硅镁胶的比表面积介于202.49-494.19m2·g-1之间,平均孔径介于2-5nm;水热法制备的硅镁胶的比表面积可达576.38m2·g1,焙烧对样品的比表面积和孔结构影响很大；FT-IR分析表明硅镁胶表面含有丰富的硅羟基(Si-OH)和镁氧基(MgO)；硅镁胶衍射图谱中出现三个非晶衍射峰,表明具有非晶态的晶相结构；SEM分析表明,硅镁胶都是无定型结构,颗粒分散性好,颗粒间易聚集；硅镁胶表面酸碱性和化学稳定性实验表明,硅镁胶具有很好的缓冲作用和化学稳定性。3.亚甲基蓝评价硅镁胶的吸附性能表明不同镁硅摩尔比的硅镁胶的吸附性能不同,R-MS-Cl-1的吸附性能最好；水热条件下制备的硅镁胶的吸附性能均较好,水热温度对不同镁硅摩尔比的硅镁胶的吸附影响较大。根据硅镁胶对不同性质的污染物的吸附性能不同,考察了污染物的浓度、硅镁胶的用量、溶液pH值、吸附时间和温度等对硅镁胶吸附性能的影响。4.分别选用亚甲基蓝、弱酸性红2R、碱性棕和直接冻黄G为染料吸附对象,研究了不同种类的硅镁胶的吸附性能。结果表明,四种染料在硅镁胶上的脱除率随着投加量增加而增大,溶液pH值对脱色率影响不大。吸附热力学研究表明,Langmuir吸附模型能够很好地描述硅镁胶对各种染料的吸附,且吸附为优惠吸附；吸附自由能变△G<0,表明吸附过程是自发进行的不可逆过程；吸附焓变△H>0表明吸附过程为吸热反应,△H值较小,说明吸附过程为物理吸附,升高温度有利于吸附进行。吸附动力学研究表明,伪二级动力学方程能够很好描述硅镁胶对各种染料的吸附,吸附平衡在很短时间内完成；颗粒内扩散不是唯一的控速步,整个吸附过程由快速吸附阶段、逐渐吸附阶段和吸附平衡阶段三个吸附阶段完成。5. H-MS-C1-2对磷酸根吸附的最佳条件是吸附剂用量为2g·L-1,磷酸根浓度为50mg·L-1,溶液pH值对磷酸根的吸附影响不大,平衡吸附量为41mg·g-1; Freundlich吸附等温模型和伪二级动力学模型都能很好地描述H-MS-Cl-2对磷酸根的吸附行为,吸附速率常数k2随着吸附温度的升高而降低；吸附过程的ΔG<0, ΔH>0, ΔS>0,表明吸附是自发进行的吸热的物理吸附过程,磷酸根和硅镁胶的作用力较弱。6. R-MS-Cl-1对Ni2+和CO2+表现出良好的吸附性能,吸附平衡时间在1.5-2h,溶液pH为5时R-MS-Cl-1对两种离子都有很好的脱除效果；伪二级动力学模型能够描述R-MS-Cl-1对两种离子的吸附行为,真实地反映出硅镁胶对两种离子的吸附机理；不同温度下的吸附是自发进行的不可逆过程,△H值介于4.67-35.1kJ·mol-1范围,说明吸附过程为物理吸附。本论文立足于自然界中具有高吸附性能的富镁硅酸盐矿物和卤水中丰富的镁资源,通过溶胶-凝胶和水热两种方法制备了一系列不同镁硅摩尔比的硅镁胶多孔吸附材料,并应用于水溶液中染料(亚甲基蓝、弱酸性红2R、碱性棕和直接冻黄G)、重金属离子(Ni2+和Co2+)和磷酸根离子的吸附脱除研究。本研究既得到了一类在环境治理中具有一定的实用价值和明显的环境效益的新型吸附材料,又为卤水中镁盐的大规模利用提供了新领域。因此,该研究不仅具有重要的理论创新意义,还具有潜在的实用价值和明显的环境效益。更多还原

【Abstract】 Magnesium chloride is very rich in the ocean. Magnesium salt has not been applied effectively, which wastes magnesium resources and pollutes the environment. Therefore, the development and utilization of the marine magnesium resources would resolve the question of the comprehensive utilization of chemical resource and develop the new field of magnesium usage. This thesis involved the preparation of magnesium silicate gels by the ways of sol-gel and hydrothermal methods based on the reaction of magnesium chloride, magnesium sulfate and sodium silicate. The physicochemistry properties (special surface area, pore-size distribution, surface activated group, structure morphology, surface acid-base property and stability) of the obtained samples were characterized through N2adsorption/desorption isotherms analysis, X-ray diffractometer, FT-IR spectrometers, Scanning electron microscope and other chemical analysis methods. Moreover, the adsorption properties of the as-prepared magnesium silicates gel were determined through the remove the dyes, heavy metal ions and PO43-from aqueous solution, and the principle of thermodynamic and kinetics in the adsorption process was also studied, then the adsorption mechanism was discussed. The main research contents and results are as follows:1. The different Mg/Si molar ratio magnesium silicate gels were prepared through sol-gel and hydrothermal methods. The adsorption capacity of magnesium silicate gels was evaluated through MB as target object. The effect of reactant concentration, time and hydrothermal temperature on the synthesis of magnesium silicate gels was investigated. The results showed the material adding order, reactant concentration, sodium silicate solution pH value, Mg/Si molar ratio, magnesium source and silicate source and hydrothermal temperature would influence the synthesis of magnesium silicate gels. The optimal synthesis condition could be obtained with reactant concentration as1mol·L-1, Mg/Si molar ratio as1:1, pH value as10-12and hydrothermal temperature as120℃。2. The structure morphology of magnesium silicate gels was determined by modern analytical instruments and chemical analysis methods. The results presented the N2 adsorption/desorption isotherms were belonged to the classical type IV with the obvious hysteresis loop. The special surface area of magnesium silicate gels obtained from sol-gel varies from202.49-494.19m2·g-1with the average pore size as2-5nm, and the high special surface area as576.4m2·g-1was obtained through hydrothermal method. The calcinations influenced the special surface area and pore structure seriously. FT-IR showed the abundant silicon hydroxyl group and magnesil group on the magnesium silicate gels surface. XRD diffraction patterns have three amorphous diffraction peaks, which proved magnesium silicate gels were non-critical phase structures. SEM analysis demonstrated that magnesium silicate gels were amorphous structure and the particals showed preferably dispersibility and inter-particles aggregation. The studies of surface acid-based properties and chemical stability showed magnesium silicate gels had good buffer function and chemical stability.3. MB chosen as adsorption target object indicated the difference in the adsorption properties of the different Mg/Si molar ratio magnesium silicate gels and R-MS-Cl-1showed the best adsorption efficiency. The samples obtained with hydrothermal method displayed better adsorption properties and the hydrothermal temperature greatly affected the adsorption of the different Mg/Si molar ratio magnesium silicate gels. Based on the difference in the adsorption of the different contaminants onto magnesium silicate gels, the effect of the pollutant concentration, adsorbent dose, solution pH value, contact time and temperature on the adsorption properties was investigated.4. MB, WAR2R, basic brow and chrysophenine were chosen as adsorption objects to study the adsorption properties of magnesium silicate gels. The results proved the rate of removal increased with increasing dyes concentration, and it was not affected by solution pH value. The studies of the adsorption thermodynamics showed Langmuir adsorption model could describe the adsorption process of four dyes and the adsorption was preferential adsorption. Adsorption free energy ΔG<0showed the adsorption process were spontaneous, irreversible process. Enthalpy change ΔH>0presented the adsorption action was endothermic, and the little AH value explained the adsorption was physical adsorption in nature, and high temperature was favorable for the adsorption. The studies of kinetics proved Pseudo second-dynamics equation could describe the adsorption behavior and the adsorption equilibriums could be attained in a short time. Intra-particles diffusion was not the unique control step and the whole adsorption process contained three stages:rapid adsorption process, adsorption equilibrium process gradually and adsorption equilibrium process.5. The optimal adsorption condition of PO43-onto H-MS-Cl-2was the adsorbent dose as2g·L-1and PO43-initial concentration as50mg·L-1. The solution pH values did not influence the adsorption efficiency and the equilibrium adsorption capacity was41mg·g-1. Freundlich adsorption model and Pseudo second-dynamics equation could describe the adsorption behavior, and the rate constant k2decreased with increasing the adsorption temperature. The thermodynamics parameters with ΔG<0,ΔH>0,ΔS>0presented the adsorption was spontaneous, endothermic and physical adsorption process. The value of adsorption enthalpy change AH showed the weak force between H-MS-Cl-2and PO43-.6. The adsorption of nickel and cobalt ions onto R-MS-Cl-1showed good adsorption efficiency and the adsorption equilibrium time was reached in1.5-2h. The maximum removal was attained with solution pH equal to5, Pseudo-second order adsorption kinetics could describe the adsorption behavior very well and reflect the adsorption mechanism of ions adsorbed onto magnesium silicate gel. Adsorption was spontaneous, rapid and physically endothermic process at the different temperature, and the high temperature was favorable for the adsorption of two metal ions.The study focused on the natural rich magnesium silicate minerals with the high adsorption properties and the rich magnesium resources in the brine. A series of the different Mg/Si molar ratio magnesium silicate gels were synthesized by sol-gel and hydrothermal methods, and successfully applied in the removal of dyes (MB, WAR2R, Basic brown and Chrysophenine), heavy metal ions (nickel and cobalt ions) and PO43-from aqueous solution. The aims of the research involve in preparing a kinds of new adsorbent materials which could have a certain practical value and high-efficiency environmental benefits in environmental governance and providing the new fields for the utilization of magnesium salt. Therefore, the research would have important theory innovation significance, potential practical value and obvious environmental benefits.更多还原