【作者】 刘学贵；

【导师】 王恩德； 邵红；

【作者基本信息】 东北大学 ， 矿业工程， 2010， 博士

【摘要】 膨润土是当今应用范围较广和经济价值较高的粘土矿物之一。改性膨润土材料是以膨润土作为原料,利用膨润土矿物的层间结构特点及其吸水膨胀、低渗透性能,通过改性剂改善膨润土微观结构和颗粒表面性能,提高了改性膨润土作为功能材料的实际使用效能。目前,改性膨润土在环境污染净化、修复与控制等方面显示出广阔的应用前景和实用价值。本文以吉林省刘房子天然钠基膨润土为原料,选用聚丙烯酰胺作为改性剂,采用水溶液聚合法,对膨润土进行插层改性,合成了聚丙烯酰胺改性膨润土材料。即首先利用单体丙烯酰胺插层聚合改性膨润土,制备了聚丙烯酰胺改性膨润土材料,通过简单、正交实验优化了改性膨润土材料的制备条件,对其吸水膨胀、耐热、抗盐性能进行了测试,运用分析仪器表征手段对其形成机理和结构进行了探讨和分析。然后在此研究基础上,针对填埋场防渗材料的研究现状,首次利用改性聚丙烯酰胺直接插层聚合改性膨润土,制备了一种新型聚丙烯酰胺改性膨润土防渗材料,重点是合成了改性聚丙烯酰胺,对聚丙烯酰胺改性过程中的工艺条件进行了讨论,并考察了改性聚丙烯酰胺加入量对改性膨润土防渗材料结构的影响。最后,采用新型聚丙烯酰胺改性膨润土作为防渗材料,以沈阳大辛生活垃圾填埋场渗滤液为处理对象,在静态吸附条件下,探讨了改性膨润土防渗材料对渗滤液中COD的吸附机理；通过动态实验,研究了改性膨润土防渗材料去除垃圾渗滤液中主要污染物的有效性和控制垃圾渗滤液渗透的可行性。主要研究内容及结果如下：1、以天然膨润土为原料,采用水溶液聚合法,通过单体丙烯酰胺对膨润土进行插层聚合改性,制备了聚丙烯酰胺改性膨润土材料。(1)简单实验结果表明,交联剂用量、引发剂用量、溶解水用量、膨润土用量等都会影响改性土材料的吸水膨胀效果。由正交实验结果得出改性土样品最优制备条件为：交联剂用量(mC/mM确)为2.16×10,引发体系用量(mI/mM)为0.08,溶解水量(mW/mM)为2.3,膨润土用量(mB/mM)为1.2,各因素对改性膨润土吸水膨胀的影响依次是引发剂量>膨润土用量>溶解水用量>交联剂用量。(2)在实验条件下,改性膨润土材料样品的吸水倍率(g/g)可达到35.98,比膨润土原土增加近1个数量级;改性膨润土材料样品在一定浓度的NaCl、CaCl2、FeCl3水溶液中吸水倍率(g/g)为7.491～12.22,比原土吸水倍率(g/g)3.595还大,并且不同类型、浓度的盐溶液中的吸液倍率差别不大；改性膨润土材料在20-80℃,1 h内进行吸水膨胀性能测试,吸水倍率数值的变化不大；说明聚丙烯酰胺改性膨润土具有较好的吸水膨胀、耐盐和热稳定性能。(3)聚丙烯酰胺改性膨润土形成机理探讨。聚丙烯酰胺的聚合机理为自由基反应。当交联剂N,N’-亚甲基双丙烯酰胺存在时,会发生交联反应,使聚合物具有适度的交联密度,同时与膨润土相互作用,形成聚丙烯酰胺改性膨润土材料。(4)聚丙烯酰胺改性膨润土结构分析。X射线衍射(XRD)表征结果说明,由于有反应性单体插入到膨润土的层间聚合后,使得层间距变大的较为明显。但是改性膨润土材料除了001晶面层间距较钠基膨润土有所增大外,其他衍射峰的位置几乎不变,这表明膨润土的基本结构不变；红外(FT-IR)表征结果显示,聚丙烯酰胺改性膨润土同时具有聚丙烯酰胺和膨润土的特征峰,说明聚丙烯酰胺存在于膨润土层间。扫描电镜(SEM)及电子显微表征结果说明,改性膨润土材料中膨润土与聚丙烯酰胺相容性较好,改性膨润土材料存在三维交联的网状结构。初步分析改性膨润土结构如下：一部分丙烯酰胺(AM)嵌入到膨润土层间,通过范德华力和氢键结合到膨润土层间,在发生交联聚合后,膨润土主要担负改性膨润土材料的骨架支撑作用；一部分的丙烯酰胺(AM)则通过与膨润土表面交换阳离子形成氢键结合；最后部分丙烯酰胺在膨润土粒子间生成“自由”聚合物网络,通过聚合物链将膨润土连接、粘结在一起。2.在单体丙烯酰胺插层聚合改性膨润土的研究基础之上,以天然膨润土为原料,采用水溶液聚合法,在室温条件下,首次通过改性聚丙烯酰胺对膨润土进行直接插层改性,制备了一种新型聚丙烯酰胺改性膨润土防渗材料。重点对改性聚丙烯酰胺的合成方法、条件进行了研究,结合表征结果讨论了不同改性聚丙烯酰胺加入量对改性膨润土材料结构的影响,并对改性膨润土材料的基本性能进行了测试,主要研究结果如下：(1)改性聚丙烯酰胺的合成分两步实现,即首先以丙烯酰胺为单体,以过硫酸铵为引发剂,甲酸钠为链转移剂合成(相对)低分子量的聚丙烯酰胺；然后用甲醛在碱性条件下对低分子量的聚丙烯酰胺羟甲基化,使羟甲基化聚丙烯酰胺和丙烯酰胺在碱性条件下进行缩合反应得到改性聚丙烯酰胺。①通过改变合成体系引发剂、链转移剂的浓度和反应时间,考察其对聚丙烯酰胺分子量的影响程度。实验结果说明,引发剂浓度的变化对聚丙烯酰胺分子量影响效果较为直接,而链转移剂、反应时间的改变对其影响不是十分明显。合成低分子量聚丙烯酰胺的适宜条件为：引发剂浓度为2.5×10-2 mol/L,转移剂浓度为8.0×10-2 mol/L,反应时间3h,所合成低分子量聚丙烯酰胺溶液粘度适中,有利于后续低分子量聚丙烯酰胺的改性操作。②低分子量聚丙烯酰胺与甲醛的羟甲基化反应的适宜条件是n(PAM):n(F) =1:1～1:0.5,反应时间为2 h,反应温度为45℃,pH=9-10。羟甲基化聚丙烯酰胺与单体丙烯酰胺的脱水缩合反应的适宜条件是：反应温度为55℃,n(AM):n(F)=1:1,反应时间为3 h,pH=10.当n(PAM):n(F):n(AM)=1:0.6:0.6时,羟甲基化率为99%。丙烯酰胺的转化率为95%。③在室温下,以N,N’-亚甲基双丙烯酰胺为交联剂,通过氧化还原引发体系引发改性聚丙烯酰胺迅速交联,与膨润土作用制备新型聚丙烯酰胺改性膨润土防渗材料。交联发生在改性聚丙烯酰胺的侧链,主链结构相对稳定,由于酰胺基团的转化发生在侧链,由伯酰胺转化为仲酰胺,活性降低,抗水解能力得到增强。当n(PAM):n(F):n(AM)=1:0.6:0.6时,室温交联聚丙烯酰胺的交联度为67%,可满足改性膨润土材料的实际使用要求,保证改性聚丙烯酰胺交联后可以对膨润土进行有效地粘结；改性聚丙烯酰胺室温交联产物、改性膨润土防渗材料的吸水倍率分别为3.584、3.621g/g,与实验所使用的膨润土吸水倍率3.595 g/g较为接近,保证了新型改性土防渗材料吸水膨胀后整体的稳定性能,避免了开裂现象的产生。(2)通过仪器分析手段对改性膨润土材料的结构进行了表征。比表面积、粒度分布表征结果说明,2#(即聚丙烯酰胺加入量为30%)改性膨润土比表面积较原土增大,粒径分布较好；XRD表征结果说明,聚丙烯酰胺插层使膨润土的层间距变化不大,对膨润土的其它部分的结构及形貌等未产生影响,d001峰的比较尖锐,说明聚丙烯酰胺在膨润土中分散性较好；SEM表征显示改性膨润土表面的不规整程度明显增加；IR、TG分析结果说明膨润土层间存在聚丙烯酰胺,聚丙烯酰胺插层使膨润土层间的结构水消失。(3)由改性膨润土浸泡实验结果可知：半限制状态下,改性膨润土在自来水中浸泡1d后,其体积膨胀率就达到182%,然后曲线总体呈上升趋势。但随后体积膨胀率的增长速度变缓,最高为190%；改性膨润土防渗材料经过22 d浸泡,仍保持整体膨胀无离析、无碎块的出现,具有一定的耐久性、稳定性。3.采用新型聚丙烯酰胺改性膨润土作为防渗材料,选用沈阳大辛填埋场的垃圾渗透液为处理对象,利用静态吸附实验对新型聚丙烯酰胺改性膨润土防渗材料吸附渗滤液的吸附机理进行了探讨。结果表明,改性膨润土对有机污染物的吸附性能效果明显好于膨润土原土,对含高浓度有机物的垃圾渗滤液的COD最大去除率可达30.73%；由等温吸附曲线可知,改性膨润土吸附过程可用Freundlich模型进行适宜地描述,等温吸附曲线方程为y=O.4211x-1.3787, R2=0.9921;改性膨润土在静态吸附条件下,对COD的吸附去除作用以物理吸附为主。在动态实验下,抗渗性能测试结果表明,改性膨润土防渗性能较好,渗透系数可以达到1.04×10-7 cm/s满足固体废物填埋场的防渗材料国家标准1.0×10-7 cm/s的使用要求。在动态实验过程中,改性膨润土对COD、氨氮、重金属离子去除效果较好,吸附作用较强,COD、氨氮最大去除率分别达到81%、91%, TFe、Zn2+和TCr的最大去除率分别达到71%,58%,73%。实验结果验证了新型聚丙烯酰胺改性膨润土防渗材料具有优良的抗渗、截污性能。更多还原

【Abstract】 Bentonite is a kind of clay mineral. It has high economic value and has been applied widely today. With bentonite as the main raw material, using its multi-layered structure, water swellability and low permeability, and by improving its microstructure and particle surface properties with modifiers, its practical application efficiency as a functional material can be enhanced. Therefore, it has high application value and a wide prospect in purification, remediation and control of environmental pollution.In this paper, with the Na-base bentonite from JiLin Liufangzi as raw material and with polyacrylamide as modifier, the polyacrylamide modified bentontites are synthesized by aqueous solution intercalation polymerization. Firstly, bentontite is modified by the intercalation polymerization with acrylamide as monomer to prepare polyacrylamide modified bentonite material. The preparation conditions are optimized by simple and orthogonal experiments; its water swelling, thermal stability and salt resistance are measured, and the structural characteristics and formation mechanism of the modified bentonite are researched with analytical instruments. Based on this research and according to the present research situation of sanitary landfill impermeable materials, a new type of polyacrylamide modified bentonite impermeable material is synthesized by direct intercalation polymerization of modified polyacrylamide. The focal point of study is synthesis of modified polyacrylamide, the processing conditions of modified polyacrylamide are discussed and the effect of quantity of the modified polyacrylamide on structure of the modified bentonite impermeable material is investigated. Finally, with leachate of Shenyang Daxin landfill as the treatment object and with new type polyacrylamide modified bentonite as impermeable material, the adsorption mechanism of the modified bentonite impermeable material for COD of leachate is investigated at the static adsorption conditions, and the effectiveness of removing pollutants and feasibility of controlling penetration of the modified bentonite impermeable materials for the leachate are investigated. Main contents and the results are as follows:1 With Na-base bentonite as raw material, by solution intercalation polymerization of acrylamide monomer, a type of polyacrylamid modified bentonite was prepared.(1) Simple experimental results show that the amounts of crosslinker, initiator, dissolved water and bentonite all affect the swelling effect of polyacrylamide modified bentonite. Optimal preparation conditions obtained by the orthogonal experiment are:the amount of crosslinker (mC/mM) is 2.16×10-4, the amount of initiator (mI/mM) is 0.04, the amount of dissolved water (mW/mM) is 2.3, the amount of sodium bentonite (mB/mM) is 1.2, and the various factors affecting the swelling of modified bentonite in turn are:initiator> bentonite> dissolved water> crosslinker.(2) Under experimental conditions, water absorbency of modified bentonite material is up to 35.98(g/g), rising by nearly one order of magnitude than that of the original bentonite; in a certain concentration solution of NaCl, CaCl2, FeCl3, water absorbency (g/g) of modified bentonite material is 7.491～12.22, which is larger than water absorbency (g/g) 3.595 of original bentonite, and the difference of their water absorbency rate in different kinds of salt solution with various concentration degrees is small; the water absorbency test of modified bentonite material at 20～80℃for 1h show that water absorbency changes little, it show that polyacrylamide modified bentonite has good water swellability, salt tolerance and thermal stability.(3) Formation mechanism of polyacrylamide modified bentonite. Polymerization mechanism of polyacrylamide is a kind of free radical reaction. When the crosslinking agent N, N-methylene bisacrylamide is present, crosslinking reaction occurs, so that polymer has a moderate crosslinking degree, and together with bentonite forms polyacrylamide modified bentonite. (4) Structural analysis of polyacrylamide modified bentonite. X-ray diffraction (XRD) characterization results indicate that the insertion of reactive monomers among the layers of bentonite leads to the significantly increased spacing of layers after polymerization. However, except that the spacing of crystal faced layer 001 in modified bentonite slightly increases than that of Na-base bentonite, the positions of other diffraction peaks hardly change, which indicate that basic structure of bentonite does not change; FT-IR characterization results show that polyacrylamide modified bentonite also has the characteristic IR peaks of polyacrylamide and bentonite, which indicate that there is polyacrylamide among layers of bentonite. Scanning electron microscopy (SEM) and electron microscopy characterization results show that there is a good compatibility between bentonite and polyacrylamide in modified bentonite, and the modified bentonite has a three-dimensional cross-linked network structure. All characterization results indicate that the structure of the modified bentonite is as follows:a part of acrylamide (AM)are embedded into the layers of bentonite and bonded by van der Waals force and hydrogen bond at the layers of bentonite. After cross-linking polymerization, bentonite was mainly responsible for the framework support of modified bentonite while another part of acrylamide (AM) forms hydrogen bonds by exchanging cations with bentonite surface and the last part of acrylamide generates "free" polymer network among bentonite particles and bonded with bentonite by polymer chains.2. Based on study on modified bentonite by intercalation polymerization with acrylamide monomer, it is the first time a new type of modified bentonite impermeable material is prepared by direct intercalation polymerization of modified polyacrylamide at room temperature with original bentonite as raw. The synthesis process of modified polyacrylamide is researched, and the effect of quantity of the modified polyacrylamide on structure of the modified bentonite impermeabile material is discussed through the analysis of characterization results. The basic performances of the modified bentonite are also measured. Main research results are as follows:(1) Modification of polyacrylamide is achieved in two steps, firstly with acrylamide as monomer, ammonium persulfate as the initiator, sodium formate as chain transfer agent, and then N-methylolated polyacrylamide was prepared by reacting low molecular weight polyacrylamide with formaldehyde under alkaline conditions; and finally the modificated polyacrylamide is synthesized by reacting N-methylolated polyacrylamide and acrylamide in the condensation reaction under alkaline conditions.①By changing the initiator, chain transfer agent concentration and reaction time, this research studies their effect on molecular weight polyacrylamide. The results show that effect of initiator concentration on molecular weight polyacrylamide is more direct, and effect of chain transfer agent concentration and the reaction time on molecular weight polyacrylamide is not very obvious. The optimal conditions for synthesis of low molecular weight polyacrylamide are: initiator concentration is 2.5×10-2 mol/L; chain transfer agent concentration is 8.0×10-2 mol/L; reaction time is 3h. An appropriate viscosity of low molecular weight polyacrylamide solution is favorable to the following modification operation of low molecular weight polyacrylamide.②The suitable hydroxymethylation conditions of low molecular weight polyacrylamide with formaldehyde are:n(PAM):n(F)=1:0.5～1:1, reaction time 2 h, the reaction temperature 40℃, pH=10. The appropriate dehydration condensation conditions of the hydroxymethylated polyacrylamide and acrylamide are:reaction temperature 55℃, n(AM):n(F)=1:1, reaction time 3 h, pH=10. When n(PAM):n(F):n(AM)=1:0.6:0.6, hydroxymethylation rate was 99 % and the conversion rate of acrylamide was 95%.③At room temperature and with N, N’-methylene bisacrylamide as crosslinker, the modified polyacrylamide was crosslinked rapidly by redox system, so a new type of polyacrylamide modified bentonite impermeable material was prepared by direct intercalation polymerization of modificated polyacrylamide and bentonite. The crosslinking points of the crosslinked polyacrylamide are at the side chain while the main chain structure is relatively stable. Because amide groups partly are transformed at crosslinked side chains, which means primary amides are transformed to secondary amides, the activity of the groups are decreased, so resistance to hydrolysis is increased. The crosslinking degree of crosslinked product of modified polyacrylamide (n(PAM):n(F):n(AM)=1:0.6:0.6) at room temperature is 67%, it meets the practical application demand for the modified bentonite materials, and ensures effective bonding of crosslinked modified polyacrylamide with bentonite. Water absorbency of crosslinked product of modified polyacrylamide and polyacrylamide modified bentonite impermeable material is 3.584,3.621 g/g respectively, and it is similar to the water absorbency of bentonite (3.595 g/g) used in this experiment, it ensures stability of the new type of modified bentonite impermeable material and avoids the cracking phenomenon after absorbing water expansion.(2) The structure of the modified bentonite is characterized with analytical instruments. The results show that 2#(the amount of modified polyacrylamide is 30%) specific surface area of the modified bentonite is bigger than specific surface area of the original bentonite, distribution of its particle size is better. X-ray diffraction (XRD) results show that spacing of layers of polyacrylamide modified bentonite changed little and the structure and morphology of other parts are not affected, and peak of d001 is sharp, which show that dispersion of polyacrylamide in bentonite is good. SEM characterization results show that the irregularity of surface of modified bentonite significantly increased. IR and TG analysis results show that there is polyacrylamide among layers of bentonite and that the intercalated polyacrylamide made structure water among layers disappear.(3) The results from the immersion experiment of modified bentonite show that under half-limit state, if the modified bentonite is immersed in tap water for 1 d, the volume expansion rate will reach 182%, and then curve will show a general rising trend, but then the increasing of volume expansion rate becomes very slow, the maximum is 190%. After 22 d immersion, modified bentonite impermeable material is still in the state of no segregation and no fragments, and the material has good durability and stability.3. With Shenyang Daxin landfill leachate as treatment object and a static adsorption test, this research studies adsorption mechanism of the new type polyacrylamide modified bentonite for leachate. The test results show that adsorption efficiency of the modified bentonite for organic pollutants is obviously better than that of the original bentonite. The maximum COD removal rate of leachate containing high concentrations of organic compounds could reach 30.73%.The isothermal adsorption curve show that adsorption process of modified bentonite for COD can be described appropriately with Freundlich model. The equation of the adsorption curve is y=0.4211x-1.3787, R2=0.9921 and the adsorption of modified bentonite for COD at static adsorption is mainly physical adsorption. The dynamic tests show that anti-seepage capability of modified bentonite material is good, the permeability coefficient is 1.04×10-7 cm/s, which meets national standard (1.04×10-7 cm/s) of impermeable materials for landfill. During the dynamic test, the removal effect of modified bentonite for COD, ammonia nitrogen and heavy metallic ions is better, and the adsorption effect is stronger, with the maximum removal rate of COD and ammonia nitrogen being 81% and 91% respectively while the maximum removal rate of TFe, Zn2+ and TCr being 71%,58%, and 73% respectively. The test results indicate that the new type polyacrylamide modified bentonite impermeable material holds excellent impermeability and decontamination performance.更多还原