湖泊沉积物中不同级分富里酸对重金属吸附行为研究

发布时间：2018-11-04 09:25

【摘要】：腐殖质作为一种复杂的天然大分子有机质,根据溶解性差异,可分为胡敏酸(Humicacid)、富里酸(Fulvicacid)和胡敏素(Humin)。富里酸含有多种酸性基团,对重金属有较强的吸附络合能力,影响着重金属的地球化学行为。不同级分富里酸在元素组成、结构特征等方面存在差异,决定了不同级分富里酸与重金属相互作用的机理机制方面存在差异。本文以连续碱提法获得乌梁素海沉积物不同级分富里酸为基础,以不同级分富里酸对重金属的吸附机制研究为主线,研究不同环境条件(pH、离子强度、离子类型、温度、光照)下不同级分FA对Cu2+、Pb2+、Cd2+的吸附特征,结合光谱学、形貌学、ligand binding模型和bi-Langmuir模型分析吸附机理,以期为湖泊生态系统中重金属污染的防控提供理论依据。主要结论如下:(1)随提取次数增加,FA有机碳含量、酸性官能团含量、芳香性、分子极性均减小;分子量、脂肪性和腐殖化程度增大。(2)动力学实验结果表明,各级分FA对Cu2+、Pb2+、Cd2+的吸附在10分钟左右达到平衡,吸附速率为Cu2+Cd2+Pb2+;随提取次数的增大,FA对重金属的吸附速率常数递减,表明后提出的FA对重金属吸附速率较慢。等温吸附实验结果表明,随提取次数的增加,FA对重金属的吸附量减少。(3)低于临界pH值时,各级分FA对Cu2+、Pb2+、Cd2+的吸附量随pH升高而升高。随离子强度的增大,各级分FA对Cu2+、Pb2+、Cd2+的吸附量逐渐降低;不同离子类型对FA的吸附影响不同,具体表现为Ca2+Mg2+K+,这是由于Ca2+水合半径小且电荷数大,对Cu2+、Pb2+、Cd2+的影响大。FA对重金属的吸附为自发的放热反应,反应后无序程度增加。光照可以降解FA,对重金属离子吸附量减少。(4)Ligand binding 模型和 bi-Langmuir 模型拟合效果良好。Ligand binding模型拟合结果表明,FA对重金属的吸附存在强弱两种点位,强点位可能为FA中含氮、含硫的官能团,对重金属吸附能力强但含量少;弱点位主要为羧基、羟基,吸附能力弱但含量多,在吸附重金属中起主导作用;bi-Langmuir模型拟合结果表明,随级分增加,理论吸附量减少,吸附量与酸性官能团呈正相关,与脂肪性、分子量呈负相关。(5)吸附前后表征结果揭示,不同级分FA吸附重金属后,其组成和结构均发生改变。紫外分析结果表明,FA的共轭度、脂肪性和分子量增加;红外分析结果表明,羟基、羧基特征峰发生明显偏移和减弱,表明这些官能团对Cu2+、Pb2+、Cd2+的吸附贡献较大;三维荧光光谱分析结果表明,peakC发生明显蓝移,peakB和peakC发生淬灭反应,peakA荧光强度有所增强,表明FA中羧基参与了对Cu2+、Pb2+和Cd2+的吸附且反应过程中伴随π-π*跃迁;扫描电镜结果表明,吸附后FA聚集成团,结构发生改变。
[Abstract]:As a complex natural macromolecular organic matter, humus can be divided into Hu Min acid (Humicacid), fulvic acid (Fulvicacid) and humin (Humin). According to their solubility differences. Fulvic acid contains many acidic groups and has a strong adsorption and complexing ability to heavy metals, which affects the geochemical behavior of heavy metals. There are differences in elemental composition and structural characteristics of different fractions of fulvic acids, which determine the mechanism of interaction between different fractions of fulvic acids and heavy metals. Based on the continuous alkali extraction of different fractions of fulvic acid in Wuliangsu Sea sediments, the adsorption mechanism of different fractions of fulvic acid on heavy metals was studied in this paper. The different environmental conditions (pH, ion strength, ion type, temperature) were studied. The adsorption characteristics of Cu2, Pb2 and Cd2 by different fractions of FA under light, combined with spectroscopic, morphologic, ligand binding and bi-Langmuir models, were analyzed in order to provide theoretical basis for the prevention and control of heavy metal pollution in lake ecosystem. The main conclusions are as follows: (1) with the increase of extraction times, the content of FA organic carbon, acidic functional group, aromaticity and molecular polarity decrease; Molecular weight, fatty property and humification degree increased. (2) Kinetic experiments showed that the adsorption of Cu2, Pb2 and Cd2 by FA reached equilibrium in about 10 minutes, and the adsorption rate was Cu2 Cd2 Pb2; With the increase of extraction times, the adsorption rate constant of heavy metals by FA decreased, which indicated that the rate of heavy metal adsorption by FA was slow. The results of isothermal adsorption experiments showed that the adsorption of heavy metals by FA decreased with the increase of extraction times. (3) when the value of FA was lower than the critical value of pH, the adsorption of Cu2, Pb2 and Cd2 increased with the increase of pH. With the increase of ionic strength, the adsorption of Cu2, Pb2 and Cd2 by FA decreased gradually. The effect of different ion types on the adsorption of FA is different, which is manifested by Ca2 Mg2 K, which is due to the small radius of Ca2 hydration and the large number of charges, and the great influence on Cu2, Pb2 and Cd2. The adsorption of heavy metals by FA is a spontaneous exothermic reaction. The degree of disorder increased after reaction. (4) the fitting results of) Ligand binding model and bi-Langmuir model showed that there were two sites for heavy metal adsorption by FA. The strong sites may be nitrogen-containing and sulfur-containing functional groups in FA, which have strong adsorption ability to heavy metals but little content. The weak spots are mainly carboxylic groups, hydroxyl groups, weak adsorption ability but high content, which play a leading role in the adsorption of heavy metals. The fitting results of bi-Langmuir model showed that the theoretical adsorption capacity decreased with the increase of fraction, and the adsorption capacity was positively correlated with acidic functional groups, negatively correlated with fatty property and molecular weight. (5) the results of characterization before and after adsorption revealed that, The composition and structure of heavy metals were changed after adsorption of heavy metals by FA with different fractions. The results of UV analysis showed that the conjugation degree, fat property and molecular weight of FA increased, and the characteristic peaks of hydroxyl and carboxyl groups shifted and weakened obviously, which indicated that these functional groups contributed significantly to the adsorption of Cu2, Pb2 and Cd2. The results of three dimensional fluorescence spectra show that peakC is blue shifted, peakB and peakC are quenched, and the fluorescence intensity of peakA is enhanced, which indicates that the carboxyl groups in FA are involved in the adsorption of Cu2, Pb2 and Cd2 and the 蟺-蟺 * transition is accompanied by the reaction process. The SEM results show that the FA aggregates and the structure changes after adsorption.
【学位授予单位】：内蒙古大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X524

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