果胶对可变电荷土壤吸附铜镉的影响及机制

发布时间：2018-06-05 01:34

本文选题：果胶 + 可变电荷土壤　；参考：《南京林业大学》2017年博士论文

【摘要】：我国南方热带和亚热带地区分布着大面积的可变电荷土壤。可变电荷土壤的游离铁铝氧化物含量较高,pH值和阳离子交换量较低。因此这类土壤中重金属的活性和生物有效性较北方恒电荷土壤要高,也更容易受重金属的污染。果胶是植物根尖粘液中的一种成分,果胶参与土壤中许多重要的反应。植物通过根系吸收土壤溶液中的有效金属,这使得土壤溶液中重金属的浓度对生态系统尤为重要。植物分泌的粘液可以进去根际土壤,粘液可以被可变电荷土壤吸附,正如有机酸能增加重金属吸附作用那样,从而降低重金属在根际土壤中的活性。基于以上研究背景,论文应用果胶添加到可变电荷土壤中,模拟根际土壤中的真实情况。旨在探明植物根尖粘液中的果胶对可变电荷土壤吸附重金属的影响,揭示植物根尖分泌物对重金属在根-土-水界面中的化学行为的影响。研究果胶的添加量、重金属离子的初始浓度、体系的pH对可变电荷土壤吸附铜(Cu)、镉(Cd)的影响。研究果胶对无定形铁铝氢氧化物吸附重金属的影响,阐明果胶增强可变电荷土壤吸附重金属的直接机理。研究果胶参与的铝水解物的表面性质及其吸附重金属的影响,阐明果胶增强可变电荷土壤吸附重金属的间接机理。综合运用多种分析技术(红外光谱、Zeta电位、表面电荷测定、电子显微镜、X射线衍射)探究果胶影响可变电荷吸附重金属吸附的机理。主要结果如下:(1)果胶促进了两种可变电荷土壤(砖红壤和红壤)对铜的吸附。增加量与果胶的添加量成线性关系,砖红壤的增加量比红壤的增加更大。Langmuir和Freundlich方程拟合可变电荷土壤对铜的吸附等温线。两个方程的拟合参数表明,果胶不仅增加了土壤对铜吸附量,也增加了吸附强度。在体系pH 3.0-6.0条件下,随着pH的升高,虽然静电吸附有所增加,但是果胶增加静电吸附的作用减小。傅里叶变换红外光谱分析和Zeta电位测定表明:土壤胶体吸附果胶后,使得其表面负电荷更大,导致可变电荷土壤对铜的静电吸附增加。总之,果胶能增强可变电荷土壤对铜的吸附,特别是在低pH值的条件下。果胶可以降低铜在酸性可变电荷土壤中的活性性和可移动性。(2)果胶促进了两种可变电荷土壤(砖红壤和红壤)对镉的吸附。当果胶用量小于30 g/kg时,随着添加量的增加,其对可变电荷土壤吸附镉的促进作用大于其添加量大于30g/kg时。虽然Langmuir和Freundlich方程都能拟合镉的等温吸附和静电吸附的等温线,朗格缪尔方程具有较好的拟合效果。由于果胶的存在,两种可变电荷土壤对镉的最大吸附量的增加几乎相等,而砖红壤对镉的最大静电吸附的增加远大于红壤。因为砖红壤比红壤含有更大量的游离铁、铝氧化物,导致砖红壤表面的负电荷增加更多。因此,果胶主要通过静电机制增加可变电荷土壤对镉的吸附。果胶增加可变电荷土壤对镉的吸附,从而降低镉在可变电荷土壤中的活性和可移动性。(3)研究了果胶对无定形铁铝氢氧化物吸附铜镉的影响,揭示果胶对可变电荷土壤吸附重金属直接影响的证据。运用电子显微镜和X衍射仪对矿物表面进行观察;运用红外光谱仪对矿物的表面官能团进行分析。在pH 3.5-6.5之间,无定形铝氢氧化物对果胶的吸附量远远大于无定形铁的吸附量,因为无定形铝氢氧化物具有更高的正电荷密度,因此与果胶之间具有更大的静电作用。果胶的加入降低了无定形铁铝氢氧化物表面的正电荷。果胶增加了无定形铁铝氢氧化物对铜的吸附。无定形铁氢氧化物对铜的吸附增量,在低pH条件下高于高pH条件下;而无定形铝氢氧化物具有相反的趋势。当pH3.9,4.3,4.9时,无定型铁氢氧化物对铜的吸附量分别从24.4,76.6,177.0 mmol/kg升高到61.6,98.8,192.0mmol/kg,增加了37.2,22.2,15.0 mmol/kg。当pH为4.3和4.9时,无定型铝氢氧化物对铜的吸附量分别从3.7和27.0 mmol/kg升高到17.3和69.4 mmol/kg,增加了13.6和42.4mmol/kg。相对与无定形铁氢氧化物,无定形铝氢氧化物吸附更多的果胶,主要导致在高pH条件下对铜的吸附增加。无定形铁铝氢氧化物吸附果胶,降低了其表面正电荷,增加了铁铝氢氧化物对铜的吸附。果胶对无定形铁铝吸附镉的影响与铜的影响相类似。(4)研究了果胶对铝水解产物的表面性质的影响,揭示了果胶促进可变电荷土壤吸附重金属的间接影响的机制。通过X衍射、表面形貌和红外光谱对果胶存在下铝的水解产物的表面结构进行表征,证实了果胶使得铝水解产物的结晶度下降,形成了结构中的缺陷。果胶降低了铝水解产物的等电点和表面正电荷。随着果胶添加量增加,效果越明显。果胶增加了铝水解产物对铜的吸附。综上所述,本文选取砖红壤和红壤两种可变电荷土壤为研究对象,通过模拟实验的方法,研究发现果胶可以促进可变电荷土壤对铜镉的吸附。通过对无定形铁铝氧化物的研究,果胶的吸附,降低了氧化物表面的正电荷,揭示了果胶促进可变电土壤吸附重金属的直接影响的机制。其次,在我国南方地区,果胶也可以通过影响铝水解产物,降低其表面正电荷,对果胶促进可变电荷土壤吸附重金属具有间接影响的作用。因此,果胶可以促进可变电荷土壤中的重金属的吸附,从而降低毒重金属在可变电荷土壤中的活性。
[Abstract]:A large area of variable charge soil is distributed in the tropical and subtropical regions of the south of China. The free iron and aluminum oxide content of the variable charge soil is higher, the pH value and the cation exchange rate are lower. Therefore, the activity and bioavailability of heavy metals in this kind of soil are higher than that in the northern constant charge soil, and are more susceptible to heavy metal pollution. Pectin is planted. A component in the mucus of the root apex. Pectin participates in many important reactions in the soil. Plants absorb the effective metals in the soil solution by the root system. This makes the concentration of heavy metals in the soil solution important to the ecosystem. The mucus secreted by plants can go into the rhizosphere soil, and the mucus can be adsorbed by the variable charge soil, just as there is one. Organic acid can increase the adsorption of heavy metals to reduce the activity of heavy metals in the rhizosphere soil. Based on the above research background, the paper uses pectin into the variable charge soil to simulate the true situation in the rhizosphere soil. The purpose is to explore the effect of pectin on the adsorption of heavy metals on variable charge soil in the root tip mucus. The effect of plant root exudates on the chemical behavior of heavy metals in the root soil water interface. The effect of the amount of pectin, the initial concentration of heavy metal ions, the effect of pH on the adsorption of copper (Cu) and cadmium (Cd) on the variable charge soil. The effect of pectin on the adsorption of heavy metals on the amorphous iron and aluminum hydrogen oxidizing substances was studied, and the enhanced variable charge of pectin was clarified. The direct mechanism of soil adsorption on heavy metals. The study of the surface properties of the aluminum hydrolysates involved in pectin and the influence of heavy metals on the adsorption of heavy metals, and to elucidate the indirect mechanism of the adsorption of heavy metals by pectin reinforced variable charge soils. The comprehensive application of various analytical techniques (infrared spectroscopy, Zeta potential, surface charge determination, electron microscope, X ray diffraction) to explore pectin The main results are as follows: (1) pectin promotes the adsorption of two variable charge soils (brick red soil and red soil) to copper. The increase is linear with the addition of pectin, and the increase of red soil is greater than that of red soil by.Langmuir and Freundlich equation fitting variable charge soil to copper The adsorption isotherm. The fitting parameters of the two equations show that pectin not only increases the adsorption capacity of soil to copper, but also increases the adsorption strength. Under the condition of system pH 3.0-6.0, the electrostatic adsorption increases with the increase of pH, but the effect of pectin on the increase of electrostatic adsorption is reduced. The Fourier transform infrared spectrum analysis and the Zeta potential meter The soil colloid adsorbed pectin on the pectin, which makes the surface charge more negative, which leads to the increase of electrostatic adsorption of copper in variable charge soil. In conclusion, pectin can enhance the adsorption of copper by the variable charge soil, especially under the low pH value. Pectin can reduce the activity and mobility of copper in the acid variable charged soil. (2) pectin promotion Two kinds of variable charge soils (brick red soil and red soil) adsorb cadmium. When the amount of pectin is less than 30 g/kg, with the increase of adding amount, the promotion effect on the adsorbed cadmium in variable charge soil is greater than that of 30g/kg. Although both Langmuir and Freundlich equation can fit the isothermal adsorption isotherm of cadmium and the electrostatic adsorption isotherm, Lange The Muir equation has a good fitting effect. Due to the existence of pectin, the increase of the maximum adsorption of cadmium in two kinds of variable charge soils is almost equal, while the maximum electrostatic adsorption of cadmium in red soil is much greater than that in red soil. Adding more. Therefore, pectin mainly increases the adsorption of cadmium in variable charge soil by electrostatic mechanism. Pectin increases the adsorption of cadmium in variable charge soil, thus reducing the activity and mobility of cadmium in variable charge soil. (3) the effect of pectin on the adsorption of copper and cadmium on amorphous iron aluminum hydroxide is studied, and the effect of pectin to variable charge soil is revealed. Evidence of the direct influence of soil adsorption on heavy metals. The surface of minerals is observed by electron microscope and X diffraction instrument; the surface functional groups of minerals are analyzed by infrared spectrometer. Between pH 3.5-6.5, the adsorption amount of amorphous aluminum hydroxide on pectin is much greater than that of amorphous iron because of amorphous aluminum hydroxide. There is a higher positive charge density, so there is greater electrostatic interaction with pectin. The addition of pectin reduces the positive charge on the amorphous iron aluminum hydroxide surface. Pectin increases the adsorption of amorphous iron aluminum hydroxide to copper. The adsorption increment of amorphous iron hydroxide on copper is higher under the low pH condition than the high pH condition; Aluminum hydroxide has the opposite trend. When pH3.9,4.3,4.9, the adsorption capacity of amorphous iron hydroxide on copper increases from 24.4,76.6177.0 mmol/kg to 61.6,98.8192.0mmol/kg, respectively, increasing 37.2,22.2,15.0 mmol/kg. when pH is 4.3 and 4.9, and the adsorption of amorphous aluminum hydroxide on copper increases from 3.7 and 27 mmol/kg to 17, respectively. .3 and 69.4 mmol/kg increased 13.6 and 42.4mmol/kg. relative to amorphous iron hydroxide, and amorphous aluminum hydroxide adsorbed more pectin, which mainly resulted in increased adsorption of copper under high pH conditions. The effect of amorphous iron and aluminum on cadmium adsorption is similar to that of copper. (4) the effect of pectin on the surface properties of aluminum hydrolysates was studied, and the mechanism of the indirect effect of pectin on the adsorption of heavy metals on variable charge soil was revealed. Surface structure of the hydrolysate of aluminum in the presence of fruit gum was observed by X diffraction, surface morphology and infrared spectroscopy. It is confirmed that pectin makes the crystallinity of the hydrolysate of aluminum decrease and forms a defect in the structure. Pectin reduces the isoelectric point and surface positive charge of the hydrolysate of aluminum. As the amount of pectin is increased, the effect is more obvious. The pectin increases the adsorption of aluminum hydrolysate to copper. In this paper, two kinds of variable charges in red soil and red soil are selected. The soil is the research object. Through the simulation experiment, it is found that pectin can promote the adsorption of copper and cadmium by the variable charge soil. Through the study of the amorphous iron and aluminum oxide, the adsorption of pectin, the positive charge of the oxide surface is reduced, and the mechanism of the effect of pectin to promote the adsorption of heavy metals on the variable electric soil is revealed. Secondly, the mechanism of the effect of the pectin on the adsorption of heavy metals on the variable electric soil is revealed. In southern China, pectin can also reduce the surface positive charge by influencing the hydrolysate of aluminum, which has an indirect effect on the adsorption of heavy metals by pectin on variable charge soil. Therefore, pectin can promote the adsorption of heavy metals in variable charge soil, thus reducing the activity of toxic heavy metals in variable charge soils.
【学位授予单位】：南京林业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X53;S153

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