【作者】 郑刘春；

【导师】 党志；

【作者基本信息】 华南理工大学 ， 环境工程， 2011， 博士

【摘要】 近年来,包括含镉废水在内的许多工业废水给周边的环境以及人类的健康造成了严重危害,从而引起广泛的关注和成为研究的热点。许多的水体重金属离子去除技术应运而生,然而这些治理技术面临的最大缺陷就是运行成本较高。吸附法能通过选择来源广泛、价格低廉、以及吸附性能良好的吸附剂,有效地去除水体中的重金属离子。因此,吸附法成为一种较为流行的废水处理方法。玉米秸秆是世界上生物量巨大的农业废弃物。它富含纤维素成分,可以在许多领域发挥重要的作用。但是现有的利用状况造成了相当一部分的玉米秸秆被低值使用和直接废弃,其后果是既浪费了资源,又污染了环境。现有的农业废弃物吸附剂改性方法和制备技术,为玉米秸秆作为重金属离子吸附剂提供了理论基础和研究方向。如果能把成本低廉的玉米秸秆,通过适当的化学改性,研制成性能良好的吸附剂,不但可以解决水体重金属污染的问题,而且为玉米秸秆的综合利用开辟了一条新途径。本研究通过使用改性剂丙烯腈,选择两种原理不同的改性方法——醚化和接枝化改性方法,将玉米秸秆（RCS-A和RCS-B）制备出两种不同的吸附剂AMCS和AGCS。同时,对玉米秸秆纤维素实现提纯和接枝化改性,可得到纤维素吸附剂AGCS-Cell。然后分别地对它们的性质表征和吸附性能进行研究,详细地阐述了它们的改性和吸附机理,并具体地拟合了吸附过程的各种模型,以及对吸附后的AMCS和AGCS进行了解吸研究。主要的研究结果如下:1、从表征分析的结果来看,AMCS和AGCS结构的内部表面积比RCS （-A \ -B）分别大2.74和3.43倍;经过醚化或接枝化改性后,AMCS和AGCS结构内成功地被引入了新的官能基团—氰基（-CN）,而且氰基的进入造成结构中N元素含量的增加;XRD图谱分析出X-射线结晶指数关系AGCS < AMCS < RCS （-A \ -B）,意味着AGCS和AMCS中的-OH大部分从氢键的束缚中被“解放”出来,可以更加容易地被新引入的-CN基团所替代,并且更有利于接触并吸附水体Cd²⁺离子。¹³C核磁共振图谱解释了AGCS和AMCS的结晶度降低和氰基引入位置的原因。此外,TGA及DSC曲线证实了AGCS良好的热稳定性。2、从吸附效果、吸附过程动力学和热力学的研究结果,可以得知它们的吸附能力主要受到溶液初始pH值和吸附剂投加量的影响。当pH值较高和投加量在较少时,它们的吸附效果最好,而且AGCS的吸附能力要好于AMCS和RCS （-A \ -B）。这四种吸附剂对水体镉离子的吸附符合Langmuir吸附等温式,AMCS和AGCS的理论最大吸附量分别为12.73和22.17 mg g^-1。AMCS和AGCS还符合准二级动力学方程学,说明了它们的吸附速率由膜扩散和颗粒内扩散的速率共同决定的,是与驱动力的平方成正比关系。3、AMCS和AGCS吸附水体Cd²⁺主要机理包括:因化学改性而获得的较大比表面积和孔隙层状结构的物理吸附;它们结构中的新功能基团——氰基（-CN）对Cd²⁺具有配位络合作用以及它们带负电荷的表面电位,可与Cd²⁺金属阳离子之间产生静电吸附作用。唯一不同的是AGCS对水体镉离子还具有空间网捕作用。4、对比分析AGCS和AGCS-Cell结构和吸附,表明AGCS-Cell接枝化改性程度更高。并推导出玉米秸秆纤维素二元接枝共聚反应的动力学速率方程,指出反应速率是与引发剂和单体浓度有密切的正比关系。验证结果也表明二元纤维素接枝共聚反应的动力学模型一定的条件下是合理的。5、解吸效果研究表明:纯水、硝酸、氢氧化钠、柠檬酸、氯化钠和EDTA这六种解吸剂的解吸效果会受到解吸温度和浓度的影响,性能有所差异。EDTA的解吸效果较为明显。更多还原

【Abstract】 Recently, many industrial wastewaters including cadmium-wastewater have become one of the most serious problems for surrounding environment and hunman health, thus cause widespread concern and research hotspot. Many heavy metal treatment technologies have been applied, but these are expensive because of higher operating costs. Adsorption, depending on various sources, low cost and excellent capacity, is a popular and effective process for the removal of heavy metals from wastewater.Corn stalk is an abundant agricultural waste in the world and usually has a high levels of cellulose, which can paly an important role in many fields. However, some corn stalks have been wasted and burnt without useful utilization. Base on the existing modification methods and treatment techniques, corn stalk can be modified into heavy metals adsorbent. These not only can solve pollution problems in aqueous, but also provide a new approach for corn stalk.In this study, acrylonitrile （AN） as chemical modification reagents, selecting two different methods to produce adsorbents. One was etherification, and another was grafting modification, then untreated corn stalks （named RCS-A and RCS-B） were modified completely in order to make the adsorbents （named AMCS and AGCS）. Meanwhile, the cellulose adsorbent （AGCS-Cell） was also produced through purification and grafting. These adrobents were analyzed by characterizated technologies, and their adsorption capacities, adsorption isotherm, kinetics, thermodynamics and models in the adsorption process were evaluated in batch experiments. The main results are as follow:1. In the characterization analysis of four adsorbents, the internal area of AMCS and AGCS were 2.74 and 3.43 times larger than RCS-A and RCS-B. After etherification and grafting modification, AMCS and AGCS structrues had been successfully introduced a new functional group, cyano （-CN）, which lead to N content increasing. The XRD patterns showed AGCS < AMCS < unmodified forms in X-ray crystallography exponential relationship, indicated that–OH groups in AGCS and AMCS were“liberated”from the hydrogen bonds and could be replaced easily by–CN groups, which were favor for Cd （II） ions adsorption. ¹³C-NMR explained the lower crystallinity and -CN location in AMCS and AGCS. In addition, TGA and DGC curves confirmed good thermal stability in AGCS.2. In the adsorption capacity experiments, adsorption kinetics and thermodynamics of four adsorbents, they were mainly affected by initial pH values and adsorbent dosage. When at high pH values and in small dosage, their adsorption capacities were better, and AGCS was best in all adsorbents. Their adsorption precesses fitted for Langmuir adsorption isotherm and the adsorption capacities of AMCS and AGCS were 12.73 and 22.17 mg g^-1, obtained from linearization of Langmuir isotherm. AMCS and AGCS met the pseudo-second-order kinetics, describing that the adsorption rate was relation with square driving force. And film diffusion and particle diffusion rate controlled mainly the adsorption rate.3. The summary in the main mechanism of removal of Cd （II） ions by AMCS and AGCS was physical adsorption depengding on their larger surface are and pore structure, chemical adsorption such as coordination-complexation reaction because of–CN groups, their surface potential was useful for Cd （II） metal cations adsorption. AGCS also had spatial netting.4. The comparative analysis between AGCS and AGCS-Cell in their structure and adsorption capacities showed that AGCS-Cell is higher grafting. The graft copolymerization binary kinetic rate equation for corn stalk cellulose was deduced and proportion relationship with initiator and monimer concentration, confirmed to be reasonable under certain conditions by the validation results.5. The desorption studies showed that the desorption capacities of six reagents such as pure water, sodium hydroxide, citric acid, sodium chloride and EDTA, were relation with temperature and concentration. EDTA was a most excellent desorption reagent obviously.更多还原