【作者】 姜立萍；

【导师】 刘鹏；

【作者基本信息】 兰州大学 ， 高分子化学与物理， 2014， 博士

【摘要】 重金属污染的主要来源是工业活动。重金属矿在开采、存放和运输过程中所产生的废气、废渣、废水对周边的土壤、水和大气造成严重的污染。不同于有机物,重金属污染物在生物体内不易分解,因此可以通过食物链在生物圈内迁移。譬如,植物吸收了水或土壤中的重金属,然后传递给食草类动物,人类在食用受污染的蔬菜、水果或肉食后,重金属污染物会最终进入人体,并在人体内富集,当超过人体的容忍限量时,会对人体产生不可逆的器质性损害。随着工业的发展,重金属废水日益增多,对环境安全及人体健康造成了极大的危害。由于水具有流动性和渗透性,导致水体中的重金属更容易迁移和扩散,因此水体中的重金属污染更难控制和治理。因此,对重金属废水的治理近年来引起了广泛的关注。目前,重金属废水必须经过有效处理后才能排放进入自然环境,主要的处理方法包括化学沉淀法、物理吸附法、化学吸附法、离子交换法、萃取法和生物法等。其中,化学沉淀法和物理吸附法适用于处理高浓度重金属废水；离子交换法和萃取法存在二次污染问题；生物法因不具备“广谱性”而应用大大受限。因此,化学吸附法以其操作简便、处理周期短、去除率高、选择性好等优点而被广泛研究和应用。某些天然高分子,如木屑、废弃蛋壳、蓝藻等,常被用作化学吸附剂去除水体中的重金属,这些天然高分子不仅对重金属有一定的吸附能力,而且可自然降解、对环境友好、成本低；但是其降解性也会同时导致吸附剂的重复使用性差,且降解产生的小分子吸附的少量重金属会随小分子残留在处理后的水体中,从而影响处理效果。膨润土、凹凸棒土、沸石等天然矿也常用来去除水体中的重金属,虽然成本低,但其对重金属的选择吸附性能不佳,且某些粘土不易从水体中分离从而影响了其重复使用性、对水体的pH敏感从而影响了其处理范围。合成高分子吸附剂和合成高分子／无机纳米复合吸附剂具有优异的稳定性,且对重金属有较高的吸附容量及较好的吸附选择性,因而近年来成为研发热点。在本研究中,使用廉价的多功能基纳米凹凸棒土和(或)工业废料粉煤灰为交联剂、无需添加任何有机交联剂,以端羟基有机硅单体为桥梁,以丙烯酸及丙烯酰胺为接枝共聚单体,通过反相悬浮聚合工艺,制备聚合物基体与凹凸棒晶(和/或粉煤灰粒子)以共价键键合的新型珠状聚合物/无机复合微凝胶吸附剂,具有成本低、吸附效率高、重复使用性好、易固液分离的特点。1.采用反相悬浮聚合工艺,以来源丰富的多功能基纳米凹凸棒土为唯交联剂,“一锅法”制备具有三维交联网络结构的新型聚丙烯酸/凹凸棒黏土纳米复合微凝胶吸附剂。其中,凹凸棒晶的改性是在液体石蜡中进行,成本低、安全、无毒；改性后的中间体无需分离,可以直接进行下一步聚合反应,工艺简单,并可解决改性凹凸棒土纳米棒晶在中间处理环节再团聚的问题。丙烯酸单体成功地接枝聚合在凹凸棒晶的表面形成具有三维网络交联结构的纳米复合微凝胶,由凹凸棒晶构建的无机网络骨架大幅提高了微凝胶的机械稳定性；微凝胶内部含有大量的吸附功能基,吸水溶胀后重金属离子可以扩散进入微凝胶内部。微凝胶对Pb2+具有选择吸附性,吸附容量为42mg/g,吸附的Pb2+在一定条件下可以完全解吸；优化的聚丙烯酸/凹凸棒黏土纳米复合微凝胶还具有优异的可再生性,10个循环的吸附确吸过程中,对Pb2+的吸附容量和解吸率基本保持不变。因此,该吸附剂在处理重金属废水领域具有很好的应用前景。2.以丙烯酸和丙烯酰胺为共聚单体、多功能凹凸棒土为单一交联剂,采用反相悬浮聚合工艺制备新型丙烯酸-丙烯酰胺共聚物/凹凸棒黏土纳米复合微凝胶微珠。系统优化了加料工艺、丙烯酸的中和度、共聚单体和多功能凹凸棒土的用量比等合成条件。TGA结果显示,在一定工艺条件下,共聚单体和多功能凹凸棒土的用量比为5：1(质量比)时,近100%的共聚单体成功接枝聚合在凹凸棒晶的表面。得到的纳米复合微凝胶具有离子交换与螯合吸附双重功能,对重金属离子的吸附去除表现出良好的选择性,尤其对Pb2+和Cu2+的去除效果更佳,吸附的Pb2+和Cu2+可以完全解吸。3.粉煤灰是一种工业废料,并会对周围环境造成污染。选择改性粉煤灰作单一交联剂、采用反相悬浮聚合工艺合成新型磁性聚合物/粉煤灰复合微凝胶微珠并用于重金属废水的处理,可以达到“以废治废”的目的。丙烯酸单体或丙烯酸/丙烯酰胺共聚单体成功地接枝共聚到粉煤灰粒子表面,得到的聚丙烯酸/粉煤灰复合微凝胶微珠以及丙烯酸-丙烯酰胺共聚物/粉煤灰复合微凝胶微珠都对Pb2+表现出较好的选择吸附性。粉煤灰的引入不仅增强了复合微凝胶的机械稳定性,而且使微凝胶微珠具有磁感应性,从而可以利用磁性分离。另外,吸附的Pb2+在0.2mol/L盐酸溶液中可以完全快速地解吸,表明磁性微珠的重复利用性好。4.以来源丰富的功能凹凸棒土和工业废料粉煤灰为复合交联剂、采用反相悬浮聚合工艺合成了新型磁性粉煤灰/聚合物/凹凸棒土纳米复合微凝胶微珠。FT-IR和TGA结果表明,丙烯酸单体(或丙烯酸/丙烯酰胺共聚单体)成功地接枝聚合在长径比非常大的纳米凹凸棒晶及磁性粉煤灰微粒所构筑的无机刚性三维网络骨架上,从而获得机械稳定性和应力释放能力均佳的粉煤灰/聚丙烯酸/凹凸棒纳米复合磁性微凝胶以及粉煤灰/丙烯酸-丙烯酰胺共聚物/凹凸棒纳米复合磁性微凝胶。两种微凝胶不仅机械强度高、具有磁性、易从水中分离,而且成本低、对Pb2+有很好的选择吸附性、并很容易解吸,5个连续再生循环过程中,吸附容量和解吸率保持稳定。因此,作为重金属离子吸附处理剂具有工业化意义。更多还原

【Abstract】 Heavy metal pollutions are serious issues in the areas of mining and deserted mine sites. Mining activities often cause water, atmosphere and subsequently soil pollution. Different from organic compounds, heavy metal pollutions are non-biodegradable and could accumulate in living organisms. Consequently, all living organisms within a given ecosystem could be affected through the food chain. As such, plants adsorb heavy metals in polluted soils and gain a certain accumulation in their tissues; animals feeding on the plants or polluted waters would also have these metals accumulated in their tissues; humans are in turn exposed to heavy metals by consuming contaminated plants and animals. Research has verified that some of heavy metals may cause a range of ailments and seriously threaten ecosystem and public health. Water is susceptible to heavy metal pollution through industrial wastewater disposals. The fluidity and permeability of water often spread the pollutants easily, which results in much severer and more uncontrollable damages to environment and all living organisms. Therefore, the water contamination from heavy metals has been great concerns in many environmental considerations in recent years.At present, heavy metal-contained wastewater cannot be disposed to the nature without adequate treatment. Among many methods for separating and removing heavy metal ions from water, which include chemical precipitation, physical adsorption, chemical adsorption, ion exchange, extraction and biological treatment, chemical precipitation and physical adsorption are not very effective for treating wastewater containing heavy metal at low concentration; ion exchange and extraction have the problem of secondary contamination; and biological treatment is not widely applicable; on the other hand, chemical adsorption has exhibited many advantages, such as reaching adsorption condition easily, broad range adaptability, easy to deploy, and excellent adsorption effectiveness. As a result, the chemical adsorption process is currently one of the major techniques for the removal of heavy metal ions form wastewater.Some natural high molecular materials, such as sawdust, waste eggshell, blue green algae (cyanobacteria), are often used as chemical adsorbents to remove heavy metals. They not only show some degree of adsorption to heavy metals, but also have the advantages of environmentally friendly biodegradability and low cost since they are either abundant in nature, or by-product or waste material from industry. However, with biodegradation, these materials produce micromolecules which are soluble in water, thus cause the secondary water pollution. Also due to the bio-degradation, the reusability of these materials are poor as well. There also have been reports on clays used to remove heavy metals, such as bentonite, attapulgite, zeolite. True value of these materials is their low cost, while the problems for using these materials include poor reusability due to the difficulties of separating them from water and excessive pH-susceptibility. In recent years, polymer adsorbents and polymer/inorganic nanocomposite adsorbents have become hot research topics due to their excellent stability, good adsorption capacity and good adsorption selectivity to heavy metal ion.In this study, we attempted to address the above-mentioned problems by using inexpensive, functionalized clay or waste material from industry instead of cross-linking agents to prepare novel organic-inorganic hybrid composite adsorbents.1. A facile strategy was developed to synthesize the novel attapulgite/poly(acrylic acid)(ATP/PAA) nanocomposite microgels via the "one-pot" inverse suspension polymerization with the multifunctionalized attapulgite (ATP) as the unique cross-linker. The multifunctionalized ATP was in situ produced directly in the form of water-in-oil emulsion and then used as prepared for the inverse suspension polymerization without being separated; so the proposed strategy was much simpler compared with the traditional methods. Almost all AA monomers had been successfully grafted onto ATP to form the3-dimensional cross-linking network of the nanocomposite hydrogels, in which the multifunctionalized ATP nanorods, as cross-linker and structural strengthening agent, drastically improved the mechanical stability of the resulting ATP/PAA hydrogels. The nanocomposite hydrogels exhibited selective adsorption toward the Pb2+ion with a maximum adsorption capacity of42mg/g, and the adsorbed Pb2+ion could be eluted completely. The optimized nanocomposite hydrogel adsorbent also exhibited an excellent reusability. The adsorption capacity and desorption rate remained unchanged for at least10cycles of adsorption-desorption. These strong points make it a potential adsorbent for heavy metal-contaminated water.2. Novel covalently crosslinked microbeads of the attapulgite/poly(acrylic acid-co-acrylamide)(ATP/P(AA-co-AM)) hybrid hydrogels with excellent mechanical stability were synthesized via inverse suspension copolymerization of acrylic acid (AA) and acrylamide (AM) with the multifunctional ATP nanorods as sole crosslinker. The synthesis conditions, such as feeding method, neutralization degree of AA, and feeding ratio of these comonomers to the multifunctional ATP, were optimized scientifically. The TGA result showed that near100%comonomers had been grafted onto the multifunctional ATP nanorods to form the3-dimensional network skeleton of the hybrid hydrogels, with the feeding ratio of the multifunctional ATP nanorods and the comonomers of1:5. The ATP/P(AA-co-AM) hybrid nanocomposite microgels exhibited the selective adsorption toward the toxic heavy metal ions, especially for Pb2+and Cu2+ions, and the adsorbed ions could be easily desorbed, indicating the reusability of the ATP/P(AA-co-AM) hybrid hydrogels. Their use as an adsorbent for the toxic heavy metal ions can therefore be expected to be economically and technically feasible.3. Novel magnetic fly ash/poly(acrylic acid)(FA/PAA) composite microgel and fly ash/poly(acrylic acid-co-acrylamide)(FA/P(AA-co-AM)) composite microgel were respectively designed as selective adsorbents towards Pb2+based on the " treating wastewater with wastes " strategy. The magnetic fly ash (FA) was selected as inorganic crosslinker to produce the magnetic composite microgels under an inverse suspension polymerization process, after being surface-modified with the polymerizable groups. The monomers had been successfully grafted onto the magnetic FA to form a3-dimentional crosslinked beadlike magnetic composite microgels without any foreign organic crosslinker added. Both microgels possessed high adsorption capacity and good adsorption selectivity to Pb2+owing to the carboxyl groups and the amide groups respectively form PAA and P(AA-co-AM). The introduction of the magnetic FA could not only improve the strength stability of the composit microgels, but also provide them the ability of magnetic separation. Furthermore, the adsorbed Pb2+could be easily desorbed, indicating the reusability of the beadlike magnetic composite microgels.4. The functionalized ATP (an inexpensive and locally available clay) and the FA (a by-product from coal-burning power plants) were used as cross-linkers to prepare the nanocomposite magnetic beads by the inverse suspension polymerization process. The results from FT-IR and TGA revealed that the soft and elastic PAA blocks and P(AA-co-AM) blocks were separately grafted onto the rigid3-D inorganic skeletons of ATP and FA successfully to produce fly ash/poly(acrylic acid)/attapulgite (FA/PAA/ATP) nanocomposite magnetic beads and fly ash/poly(acrylic acid-co-acrylamide)/attapulgite (FA/P(AA-co-AM)/ATP). Both nanocomposites exhibited outstanding mechanical strength due to the large aspect ratio of ATP, a certain magnetic characteristic provided by the substantial Fe3O4in FA, good adsorption capacity to heavy metal ions, especially to Pb2+, and a strong prospect for further industrialization because of the decrease in material cost. The adsorption capacity and the desorption rate remained almost unchanged within the limit of error through5cycles of regeneration, indicating that both nanocomposite microgels have excellent reusability and can be used in the continuous process of wastewater treatment in further industrialization, on the other hand, lower the production cost further.更多还原