【作者】 刘学；

【导师】 梁成华；

【作者基本信息】 沈阳农业大学 ， 农业生态与环境， 2009， 博士

【摘要】 由于工业化进程的加速,加之含砷农药、化肥、杀虫剂等的大量使用,使得越来越多的砷进入土壤环境,土壤砷污染现象日益突出。与其它重金属污染相比,砷的相关研究较为薄弱,有关棕壤对砷吸附特性方面的系统研究目前鲜有报道。本文以辽宁地区代表性土壤—棕壤作为试验材料,采用室内模拟分析法、平衡吸附法、动力学批实验法以及X射线衍射(XRD)对砷(V)的吸附-解吸行为及其影响因素进行了研究。同时采用连续提取法对不同污染水平土壤中砷的各个形态含量进行了测定。旨在明确砷在棕壤中的环境行为、影响因素及其作用机制。主要研究结果如下:1.利用一次平衡法研究了东北地区四种主要类型棕壤(棕壤、潮棕壤、棕壤性土、白浆化棕壤)及其剖面对砷的吸附-解吸特性。结果表明:砷(V)在棕壤中的等温吸附可用Langrnuir、Freundlich方程进行拟合,相关系数均达到显著或极显著水平。四种类型棕壤中以潮棕壤对砷(V)的吸附容量最大。淀积层及母质层土壤对砷(V)吸附量远远超过淋溶层土壤。解吸实验表明,吸附态砷(V)不易解吸,且解吸量随吸附量的增加而增加,两者之间关系符合二次幂方程。2.运用多元线性逐步回归分析了砷(V)的最大吸附量与棕壤各项理化指标之间的关系.回归结果显示砷(V)在棕壤中的吸附能力与土壤有机质含量、铁锰含量、pH值和全磷含量等有关。3.pH2-10范围内,砷(V)吸附量随pH值变化的大致趋势是:随pH值的升高,吸附量逐渐降低;pH10-12范围内,砷吸附量随pH值的升高而急剧上升。强酸条件下,吸附量增加的主要原因是静电吸附机制,强碱条件下吸附量的增加是由于砷(V)与土壤中的离子生成了难溶性的砷酸盐沉淀。4.进行有机质去除处理后,两种肥力水平棕壤对砷的最大吸附量分别为原土的3.2和2.3倍,同时其可变负电荷数量分别降低了27.9%和20.3%,说明有机质中存在大量的负电荷可能是抑制砷吸附的重要原因。5.磷添加顺序及浓度影响砷在棕壤中的吸附及解吸。土壤中磷浓度越高,砷(V)的吸附量越小,吸附态砷(V)的解吸率越高。三种磷处理方式中(处理Ⅰ:砷先于磷24h添加;处理Ⅱ:砷与磷同时添加;处理Ⅲ:砷后于磷24h添加),以磷先加入土壤(处理Ⅲ)对砷吸附的抑制作用最明显。但是土壤中存在着专门针对砷的具有优先性的吸附位点,随着磷浓度的进一步加大,砷(V)的吸附量和解吸率变化不大,趋于平缓。6.砷在铁锰结核中的最大吸附量是土壤的10倍左右,说明铁锰结核是砷(V)在棕壤中吸附的主要载体之一.砷在铁锰结核中吸附量随pH值的增加而降低。吸附过程受离子强度的影响较小,吸附态砷(V)不易被解吸下来,说明砷(V)在铁锰结核上的吸附以专性吸附为主。动力学研究表明砷(V)在铁锰结核上的反应分为两部分,起初的快反应是表面反应,而后的慢反应受扩散作用的影响,以快反应为主。7.土壤外源添加不同浓度砷(V)后,制备不同浓度梯度的含砷土壤,研究砷(V)在棕壤中的吸附量和解吸量与砷污染负荷的关系。结果表明:污染负荷越重,吸附量越小,解吸量越大。动力学研究表明,反应速度不受污染负荷的影响,吸附与解吸动力学方程可由Elovice与双常数方程来描述,表明砷在棕壤中的吸附是由表面吸附和内部扩散所控制。8.砷(V)污染水平不同的棕壤中,各形态砷(V)随老化时间的变化经研究表明:时间及引入到土壤系统中的砷含量是形态分配的重要影响因素。外源砷在老化开始的30d内迅速被土壤固定.随土壤中砷浓度的增加,砷从不稳定形态向稳定形态转化的时间增加,各形态达成相对稳定的可能性减小,砷的活性增强,其对生态环境的威胁增大。更多还原

【Abstract】 As a result of the accelerated process of industrialization, and the popular use of agricultural chemicals, fertilizers and pesticides, more and more arsenic enter to the soils, arsenic pollution has become increasingly prominent. Compared with other heavy-metal, research of arsenic contamination was relatively weak, especially the characteristics of arsenic adsorption on brown soil was still remained elusive. This paper chooses the arsenic(V) for typical representative pollutant, used brown soil which was a typical soil in Liaoning province, to study As adsorption behavior and its influencing factors. With the help of methods such as balanced adsorption, indoor culture and mathematical analysis, batch system dynamics as well as X-ray diffraction (XRD). Simultaneously, we determined the As form of different As burden soils with the methods of continuous extraction. The purpose of the study was to understand the behavior of As adsorption in the soils, and the impact factors and its mechanisms. The main results of this study were presented:1.Characteristic of As(V) sorption-desorption was studied on farm and natural forest soils and its soil profile with the method of one way balancing towards the brown soil、fluvo-aquic brown soil、brown earth soil and bajing brown soil. The result indicated: Isothermal adsorption of As(V) can be fitted by Langmuir and Freundlich equation, the correlation coefficient achieves remarkable or the extremely remarkable level. The maximum adsorption from the Langmuir equation indicated that the fluvo-aquic brown soil has the biggest amount of As sorption; Capacity of As(V) sorption on illuvial horizon and parent material horizon were far beyond eluvial horizon; As(V) adsorption capacity of high fertility level should be less than the level of low fertility. Desorption experiments show that desorption of adsorbed As(V) was not easy, and the amount of desorption increases with the adsorption, the amount of sorbed and desorbed As(V) could be described by twice power function equation.2. Relationship between maximum As(V) sorption and physical and chemical properties was conducted by establish model with the help of multiple linear stepwise regression. Regression equation was derived. Regression results showed that capacity of arsenic (V) adsorption in the brown soil was related to organic matter content, Fe and Mn content, pH value, phosphorus content ect.3. On the pH range 2-10, As(V) sorption mostly increase with pH fluctuate, as the further increase of pH (pH=11.59), As(V) sorption increase suddenly. The reason was that under the low pH values, electrostatic adsorption play a major role on adsorption; but under the high pH value, the increase in adsorption due to generated insoluble precipitation of arsenate.4. After remove of organic matter, amount of As(V) adsorption on high fertility and low fertility levels were 3.23 and 2.3 times than origin soil, variable charge decrease 27.9% and 20.3%, its may conclude that organic matter compete adsorption sites with arsenic to inhibit As(V) Adsorption in the brown soil.5. Adsorption and desorption process was affected by the order and the concentration of phosphorus. Adsorption of As(V) decline with the increased of P, while desorption rate of As(V) was step up .About the order of P added (Ⅰ:As>P;Ⅱ:As = P;Ⅲ:As<P), the most obviously inhibitation of As was treatmentⅢ. But phosphorus was not inhibit the adsorption or replace it completely, with the further increase of phosphorus concentration, As(V) adsorption and desorption rate changed little, become more gentle. It shows that the existence of preference As(V) adsorption sites in the soil.6. Isotherm adsorption experiments showed that capacity of iron-manganese nodules on As(V) adsorption was strong, its 10 times to the corresponding soil, indicating that the existence of iron-manganese nodules may be the main vector of As(V) adsorption in the brown soil . The amount of As(V) adsorption decline with the increase of pH value. Adsorption was less affected by ionic strength, adsorbed arsenic (V) can not easily be replaced, conclude that the mechanism of As(V) adsorption on iron-manganese mainly to specific adsorption. Kinetic study shows that reaction of As on iron-manganese nodules could be divided into two parts, the initial fast reaction was surface reaction, and the slow reaction response to the impact of diffusion.7. Different concentrations of As(V) was added to Soil, with the methods of indoor cultivation, preparation of different levels of polluted soils, to study the relationship between capacity of adsorption and desorption with different As pollution load. The results showed that: the more serious the pollution load was, the smaller the adsorption capacity, the greater the desorption volume. The reaction rate was not impact by pollution load. Kinetics of adsorption process can be divided into two parts; kinetic equation could be described by Elovice and two-constant equation, indicated that the sorption involved surface sorption and inner diffusion.8. In different metal burden soils, forms of As were changed with aging time, showed that: Time and As pollution load were the factor which influnced the distribution form. When aging time was 30d, added As can be quickly fitted by soil. With the increase of As content, transformation time from unstable to stable form increased, the possibility of every form to achieve the relative stabilization deduced. As activity and its threatment to environment inhanced.更多还原