【作者】 王俊丽；

【导师】 刘文霞；

【作者基本信息】 河南农业大学 ， 生态学， 2015， 硕士

【摘要】 重金属废水的治理问题已被各国科学家普遍关注,其对人类健康造成严重威胁也被人们逐渐认识到。重金属废水的传统方法有化学还原法、离子交换法、吸附法、膜分离法,这些方法主要适用于重金属离子浓度较高的情况,当重金属离子浓度较低时,用传统方法处理存在运行成本高、操作繁琐、处理效率低、容易造成二次污染等问题。目前,我国农林废弃物利用率很低,一般的处理方法是露天堆置和焚烧,不仅造成能源巨大浪费而且还造成环境污染。然而,农林废弃物也有一些自身的优越性,比如来源广泛、价格低廉、再生周期短、可降解等,其主要成分纤维素、半纤维素、木质素等含有丰富的-OH、-COOH、-NH2等活性基团且比表面积较大。研究表明,农林废弃物经过化学改性,能够很好地去除废水中的重金属离子。农林废弃物的改性方法很多,大量实验发现,碱处理能够使农林废弃物暴露更多的吸附位点,从而能达到更好的吸附效果。泡桐在我国分布广泛,种植数量大,每年冬季产生大量落叶废弃物,弃置于自然环境或露天焚烧,既造成了环境污染,又造成了资源的极大浪费。我们研究发现,经Na OH-乙醇改性后的泡桐树叶粉末对废水中Pb²⁺的去除率接近100%,可见碱改性泡桐树叶粉末对Pb²⁺具有良好的去除效果。但Na OH生产成本高,加工过程易污染环境,不符合节约、环保的要求。而Ca（OH）2作为Na OH生产的天然原材料,既具备其强碱性质又廉价易得。因此,利用Ca（OH）2改性泡桐树叶粉末,制备重金属离子的高效生物吸附剂,具有重要的科研价值和现实意义。本论文选取泡桐落叶为研究对象,用Ca（OH）2对泡桐树叶粉末进行改性,吸附溶液中低浓度的Pb²⁺,并探讨了吸附时间、吸附剂浓度、溶液p H、重金属初始浓度这四个因素对吸附效果的影响;并通过扫描电镜（SEM）、能谱分析（XPS）、X-荧光光谱半定量分析三种方式对对未改性、改性后和吸附后的粉末进行了表征。结果表明,吸附时间、吸附剂用量、溶液p H、金属离子的初始浓度都会对吸附效果产生影响。当吸附剂浓度为0.8g·L-1,溶液p H为5,60 min即可达到吸附平衡,此时吸附量为60.43 mg·g-1,去除率为95.61%;当Pb²⁺初始浓度在15—100 mg·L-1范围内时,碱改性泡桐树叶粉末吸附剂对Pb²⁺的去除率都在93.0%以上,且随着重金属初始浓度的增加,吸附量明显增加。碱改性泡桐树叶粉末吸附剂吸附对Pb²⁺的吸附过程可用准二级吸附动力学模型和等温吸附模型描述。通过扫描电镜（SEM）发现未改性粉末表面光滑,各官能团相对分散呈颗粒状;而改性后的粉末变化很大,原有结构形态已经被破坏,表面变得松散粗糙,呈薄片状和絮状;吸附Pb²⁺之后,粉末表面重新由松散状态变成聚集状态,具有众多颗粒物和粉状物,且颗粒间衔接紧凑。能谱分析（XPS）和X-荧光光谱半定量分析发现,吸附过程中Pb²⁺被吸附到泡桐树叶粉末吸附剂表面,与吸附剂中的Ca²⁺、Mg²⁺、Si²⁺、Al²⁺和Fe²⁺等离子发生了阳离子交换。用Ca（OH）2替代Na OH制备改性泡桐树叶粉末吸附剂,不仅节能、环保、低成本,而且达到几乎同样的去除效果。因此,Ca（OH）2改性泡桐树叶粉末做吸附剂去除重金属离子是一种值得深入研究和推广的重金属治理方法。更多还原

【Abstract】 Issues concerning treatment of heavy metal wastewater have been widely given attention by scientists from all over the world, and serious threats caused to human health have also been gradually recognized. Traditional methods（such as chemical reduction method, ion exchange method, adsorption method and membrane separation method） for treatment of heavy metal wastewater are mainly applied to condition that concentration of heavy metal ion is high, when concentration of heavy metal ion is low, problems such as high operating cost, complex operation, low treatment efficiency and secondary pollution easily caused exist in case of treatment by traditional methods. While as to forestry and agricultural residues, because of low utilization rate, general treatment methods including open-air stacking and burning, may not only lead to tremendous energy waste, but also cause environmental pollution. However, forestry and agricultural residues possess some advantages such as short regenerative cycle, abundant production, biodegradation, extensive sources and low cost etc., besides, major components such as cellulose, hemicellulose and lignin contain abundant –OH,-COOH,-NH2 and other active groups with great specific surface area. It is indicated through study that forestry and agricultural residues can better remove heavy metal ions in wastewater after chemical modification. There are many methods for modification of forestry and agricultural residues, and it is found through lots of experiments that more adsorption sites of forestry and agricultural residues may be exposed through alkali treatment, thus reaching better adsorption effects. Paulownia is widely covered in the country, and there is a large planting amount, and it may produce lots of fallen leaf wastes in winter each year, not only possibly leading to environmental pollution, but also leading to huge resource water in case of being discarded under natural environment or open-air burning. Additionally, it is found through our research that removal rate of Pb²⁺ in waste water by paulownia leaf powder modified by Na OH- alcohol approaches to 100%, thus showing that paulownia leaf powder modified by alkali may generate good removal effect to Pb²⁺. However, production cost of Na OH is high, and processing may easily cause environmental pollution, not conforming to saving and environmental protection requirement. In contrast, as the natural material for production of Na OH, Ca（OH）2 possesses strong basicity and is low-cost and easily obtained. Therefore, paulownia leaf powder modified by Ca（OH）2 to produce efficient bio-adsorbent of heavy metal ions is of great scientific value and practical significance.In the paper, paulownia leaves were selected as object of study, and paulownia leaf powder was modified by Ca（OH）2 to adsorb low-concentration Pb²⁺ in the solution, additionally, influences of reaction time, adsorbent concentration, p H and initial concentration of heavy metal these four factors on absorption effect were discussed. Moreover, unmodified powder, modified powder and adsorbed powder are characterized through scanning electron microscope（SEM）, energy spectrum analysis（XPS） and X-fluorescence spectrum semi-quantitative analysis. Results indicated that adsorbing time, adsorbent amount, solution p H and initial concentration of metal ions may influence adsorbing effect. Adsorption equilibrium may be reached in case of adsorbent concentration of 0.8g/L, solution p H of 5 and reaction time of 60 min, and at that time adsorbing capacity reached 60.43 mg/g, removal rate reached 95.61%. In case that initial concentration of Pb²⁺ was within 15-100 mg· L-1, removal rate of Pb²⁺ through utilization of alkali-modified paulownia leaf powder adsorbent reached over 93.0%, and with increase of initial concentration of heavy metal, adsorbing capacity obviously increased. Adsorption process of Pb²⁺ may be described with pseudo-second-order adsorption kinetic model and isothermal adsorption model. It is found through scanning electron microscope（SEM） that the surface of unmodified powder is smooth, and each functional group is relatively dispersed which is appearing granular; while modified powder changes greatly, and the original structural form has been destroyed, and the surface becomes loose and rough, appearing laminar and flocculent; after adsorption of Pb²⁺, powder surface becomes aggregate again, and there are lots of particulate matters and meals which are closely linking among particles. It is found through energy spectrum analysis（XPS） and X-fluorescence spectrum semi-quantitative analysis that Pb²⁺ is adsorbed onto the surface of paulownia leaf powder adsorbent during adsorption process and cation exchange occurs with Ca²⁺, Mg²⁺, Si²⁺, Al²⁺, Fe²⁺ and other ions in the adsorbent.Preparation of modified paulownia leaf powder adsorbent by Ca（OH）2 instead of Na OH is not only energy-saving, environmental and low-cost, but it may also reach similar removal effect. Therefore, paulownia leaf powder modified by Ca（OH）2 acting as adsorbent to remove heavy metal ion is a method for heavy metal treatment which is worthy of intensive study and popularization.更多还原