【作者】 陈男；

【导师】 冯传平；

【作者基本信息】 中国地质大学(北京) ， 地下水科学与工程， 2012， 博士

【摘要】 近年来，地下水氟污染已经逐渐成为世界性问题而引起关注。世界上多个国家和地区饮用水中氟化物的含量都超过世界卫生组织规定的标准，严重威胁到动植物以及人类的健康。对于国内外来说，吸附法由于其操作简便性和环境友好性已经成为应用最广泛的去除地下水及饮用水中氟化物的方法。目前，常用的除氟吸附剂主要有天然、合成和生物类材料，这些材料虽然具有一定的吸附除氟能力但是也存在一定的缺陷。其中，一些材料对环境pH值的适应性较差，一些材料成本高昂，且大多为粉末状，容易堵塞水道，因此在实际的水处理除氟工艺中受到了限制。本文主要以氟污染地下水为主要研究对象，探讨天然粘土材料和人工合成多孔性矿物材料对地下水氟化物的吸附特性，着力于为吸附除氟材料的开发及地下水氟化物去除提供理论依据和技术支持，为实现地下水中氟污染物的去除提供理论依据。论文工作从整体上分为三大部分：第一部分采用静态和动态试验方法，研究了天然鹿沼土对水溶液中氟离子的吸附性能，获得了吸附热力学和动力学曲线；建立了吸附平衡热力学、动力学模型；求取了模型参数，计算了天然鹿沼土吸附氟化物的有关热力学状态函数；探讨了鹿沼土的吸附除氟机理，并采用实际地下水样配制含氟废水对鹿沼土吸附除氟能力进行了研究。结果发现，鹿沼土对氟化物的吸附反应初始速率很快且在2h左右达到吸附平衡；溶液初始pH值介于4.0-10.0之间时除氟效率达到最大；吸附等温线可以用Dubnine-Radushkevich（D-R）方程和Freundlich方程描述，吸附过程符合二级动力学方程；吸附过程为吸热反应，根据其焓变H = 11.782 kJ/mol可以推断鹿沼土与氟离子的吸附作用力主要为氢键力和偶极间作用力；氯离子和硝酸根离子对天然鹿沼土的吸附除氟过程基本没有影响，硫酸根离子和碳酸氢根离子对吸附过程略有消极影响，碳酸根和磷酸根对吸附过程有明显抑制作用；在动态柱吸附试验中，随着进水流速的增大，柱子高度的降低以及入水氟离子浓度的增大，鹿沼土柱的穿透时间逐渐缩短，从而使鹿沼土对氟离子的吸附达到饱和状态变快。动态土柱实验中鹿沼土对氟离子的吸附过程符合Thomas动力学公式和BDST模型。第二部分主要采用静态吸附试验方法，研究了分别以FeSO₄·7H₂O和Fe₂O₃为铁质的合成多孔性粘土材料对水溶液中氟化物的吸附性能，获得了吸附热力学和动力学曲线；建立了平衡吸附热力学、动力学模型；求取了模型参数，计算了两种铁质合成材料对吸附氟化物的有关热力学状态函数。探讨了合成材料对氟化物的吸附机理，并采用实际地下水样对以FeSO₄·7H₂O为铁质合成材料的吸附除氟能力进行了研究。结果发现，以FeSO₄·7H₂O和Fe₂O₃为铁质的合成多孔性粘土材料对氟化物的吸附过程都符合二级动力学和内扩散方程，氟离子在以FeSO₄·7H₂O和Fe₂O₃为铁质的两种合成多孔性粘土材料上的静态吸附平衡时间都为48 h左右；以FeSO₄·7H₂O和Fe₂O₃为铁质的合成多孔性粘土材料分别在溶液初始pH值为7.0和4.0左右时对氟化物的去除率达到最大值，氟化物去除率分别为94.23%和60.48%；以FeSO₄·7H₂O和Fe₂O₃为铁质的合成多孔性粘土材料对溶液中氟化物的吸附过程都符合Langmuir和Freundlich吸附等温方程，其Langmuir最大吸附容量分别为2.16和1.70 mg/g；以FeSO₄·7H₂O和Fe₂O₃为铁质的合成多孔性粘土材料对氟化物的吸附过程均为吸热反应；溶液中共存的氯离子和硝酸根离子基本不影响以FeSO₄·7H₂O为铁质的合成多孔性粘土材料对氟化物的去除效果，而硫酸根离子对除氟效果有一定的消极影响，碳酸根和磷酸根离子对以FeSO₄·7H₂O为铁质的合成多孔性粘土材料的除氟效率影响最大；以FeSO₄·7H₂O为铁质的合成多孔性粘土材料的吸附除氟过程主要以化学吸附作用为主。第三部分采用静态吸附试验方法，分别研究了以木节粘土和金刚土为骨架的Fe/Al改性多孔性粘土材料对水溶液中氟化物的吸附性能，获得了吸附热力学和动力学曲线；建立了平衡吸附动力学模型和等温模型；求取了模型参数，探讨了两种改性合成材料对氟化物的吸附机理，并采用实际地下水样对以两种材料的吸附除氟能力进行了研究。结果发现，以木节粘土和金刚土为基本骨架的改性多孔性粘土材料对溶液中的氟化物均具有较好的吸附能力；两种材料均在溶液初始pH = 6.0条件时达到最大吸附容量，溶液初始pH值低于4.0或高于10.0均不利于两种材料对氟化物的吸附；两种材料的吸附除氟过程均符合二级动力学方程；两种材料的Langmuir最大吸附容量分别为1.79 mg/g和3.38 mg/g；Freundlich吸附等温方程中的1/n值均小于1，表明两种改性材料的吸附除氟过程均为有利吸附；以金刚土为基本骨架的改性材料对氟离子的亲和能力要强于以木节粘土为基本骨架的吸附材料，前者的氟吸附容量约为后者的2倍；以金刚土为基本骨架的改性吸附材料在多种离子共存条件下仍能保持较好的吸附除氟性能。当初始氟浓度为10 mg/L，吸附剂量为20 g/L条件时，氟化物去除率保持在80%以上，而以木节粘土为基本骨架的吸附材料除氟效果则明显降低。总之，天然鹿沼土、含铁质多孔性合成材料及Fe/Al改性的粘土材料均对溶液中的氟化物具有良好的吸附性能，本论文的研究成果为地下水除氟技术的实际应用和优化运行提供了理论依据和技术指导。更多还原

【Abstract】 Fluoride contamination in groundwater is a worldwide problem and manyregions have fluoride concentration higher than prescribed by WHO, which is aserious threat to flora and fauna including humans. Adsorption method is an attractivealternative to other treatment because of its environmental respectability and ease ofoperation.In recent years, considerable attention has been focused on the study of fluorideremoval using natural, synthetic and biomass materials. They have shown a certaindegree of fluoride adsorption capacities but some of them can only be used in anarrow pH range (5.0-6.0) and some of them are too expensive to be considered forfull-scale water treatment. Furthermore, most of them are fine particles or powderswhich would be suspended in water, making separation difficult and blocking flumes.Therefore, an effective and low-cost adsorbent with coarse particles is desired as anefficient treatment technology for fluoride in large-scale water samples. This researchfocused on the fluoride removal from contaminated groundwater and discussed thefluoride adsorption characteristics by using natural clay materials and artificialsynthesis porous mineral materials. This study focused on solving the key technicalproblems for the fluoride removal methods, which will provide the theory andscientific basis for fluoride removal from groundwater.The first section investigated the fluoride adsorption ability using one kind ofnatural mud in a batch and column study. The influences of contact time, solution pH,adsorbent dosage, initial fluoride concentration and co-existing ions were investigatedby batch equilibration studies. Batch experiments indicate that the time to attainequilibrium was 2 h and adsorption was followed the pseudo-second-order kineticmodel. Maximum adsorption for fluoride removal was achieved at pH range of5.0-7.0. The adsorption of fluoride on Kanuma mud in batch systems can be describedby the Dubnine-Radushkevich (D-R) and Freundlich isotherm models. The adsorptionprocess was an endothermic process. According to the enthalpy change of H = 11.782 kJ/mol, it can be inferred that the adsorption force was hydrogen bondingforce and the coupling reaction force. Chloride ion and nitrate ion had no effect onfluoride adsorption by natural Kanuma mud; sulfate ion and bicarbonate ion had aslightly negative influence on fluoride adsorption process; while carbonate ion andphosphate ion had a significant inhibitory effect on fluoride adsorption. The fixed-bedcolumn breakthrough curves were analyzed at different flow rates, bed depth andinitial fluoride concentration. Thomas and BDST model can be used for predicting ofbreakthrough curves for fluoride removal by a fixed bed of Kanuma mud for differentflow rates and bed depths.The second section has successfully combined Kanuma mud, with starch, zeoliteand FeSO4·7H2O salts to calcine clay materials (particle size: 3-5 mm) andinvestigated the fluoride adsorption capability of these adsorbents. Both GC(FeSO4 7H2O) and GC (Fe2O3) adsorbents can be used for fluoride removal fromaqueous solution, while GC (FeSO4 7H2O) is more effective for fluoride removal thanGC (Fe2O3). Maximum adsorption of fluoride on GC (FeSO4 7H2O) and GC (Fe2O3)at pH 7.0 and 4.0 were 94.23% and 60.48%, respectively. The equilibrium data ofsamples fitted well to both Langmuir and Freundlich isotherms. The adsorptioncapacity of GC (FeSO4 7H2O) and GC (Fe2O3) was 2.16 mg/g and 1.70 mg/g. Both ofthese two granular adsorbents followed second-order kinetics and were governed byintra-particle diffusion model. Chloride ion and nitrate ion had no effect on fluorideadsorption by GC (FeSO4 7H2O); sulfate ion had a slightly negative influence onfluoride adsorption process; while carbonate ion and phosphate ion had a significantinhibitory effect on fluoride adsorption by GC (FeSO4 7H2O). The calculatedthermodynamic parameters showed that both of the adsorption processes werethermodynamically favorable, spontaneous and endothermic in nature. For theadsorbent of GC (FeSO4 7H2O), the fluoride adsorption process was mainly chemicalreaction.The third section has developed another kind of adsorbent, which was preparedby mixing Knar clay/King Kong clay, zeolite and starch with mass ratio 1:1:1. Porousgranular clay adsorbents that contain dispersed aluminum and iron oxides have been synthesized by impregnating with salt solutions followed by precipitation at process.This adsorbent was sphere in shape, 2-3 mm in particle size, highly porous andshowed particularly high specific surface area. Both of the materials can achieve themaximum adsorption capacity when the initial pH was 6.0, and the fluoride removalefficiency will decrease when the initial pH less than 4.0 or higher than 10.0. Theexperimental data revealed that both the Langmuir and Freundlich isotherm modelsfitted well with the fluoride sorption process. The monolayer adsorption capacity was1.79 mg/g and 3.38 mg/g, respectively. The adsorption process was well explainedwith pseudo-second order kinetic model. The 1/n value of Freundlich isotherm wasless than 1, which showed that the adsorption process was favorable or preferential forboth kinds of materials. Besides, the fluoride adsorption capacity of King Kong claymaterial was two times than the Knar clay material. The King Kong clay material hadgood adsorpotion ability under various ions coexistence conditions. The adsorptionefficiency can achieve 80% under the initial fluoride concentration of 10 mg/L,adsorbent dosage of 20 g/L conditions by the King Kong clay material. Results fromthis study demonstrated potential utility of Fe/Al coated porous granular clay materialthat could be developed into a viable technology for fluoride removal from aqueoussolution and groundwater.In short, Kanuma mud, iron-impregnated porous synthstic materials and Fe/Almodified porous clay materials have good fluoride adsorption performance. Theseresults may provide the theory basis and the technical guidance for groundwaterfluoride removal in the practical application.更多还原