冻融对砷在土壤中吸附解吸特性及赋存形态影响的研究

发布时间：2018-05-27 21:47

本文选题：冻融 + 砷　；参考：《沈阳农业大学》2016年硕士论文

【摘要】：冻融是北方地区常见的自然现象,是作用于土壤的非生物应力,其会对土壤中的矿物、电荷和有机物质的数量、电荷的种类以及有机物质的形态产生影响。前人对于砷在土壤中的吸附解吸行为及赋存形态等问题开展了较为细致的研究,关于冻融条件对土壤理化性质及重金属Cd形态转化影响的报道也并不少见,但是冻融条件对砷在土壤中的吸附解吸行为及赋存形态影响的研究还未见报道。本研究以棕壤为试验材料,采用室内模拟培养试验的方法分析不同冻融条件下土壤对砷的吸附-解吸特性及其影响因素,研究外源砷在土壤中的赋存形态及其对冻融作用的响应,探讨外源砷在冻融条件下的释放特征,可为冻融区砷污染土壤的修复及其生态环境风险评价提供数据参考和理论依据,具有重要的理论和现实意义。得到的主要结果和结论如下：1.应用不同等温吸附模型对所得数据进行拟合,以Langmuir模型为最优；在同一含水量条件下,冻融土壤对As的吸附量低于未冻融土壤,解吸率都高于未冻融土壤,并且随着冻融周期的增加,土壤对As的吸附量降低,解吸率增大,即冻融能够抑制砷的吸附能力但增强砷的解吸能力。不同水分处理土壤As的最大缓冲容量(MBC)随冻融周期增加分别由40.2、35.5、31.5下降到22.1、19.8、19.6。冻融能减弱吸附一解吸过程中的滞后效应。各处理土壤MBC值与有机质(OM)、阳离子交换量(CEC)和可变电荷(CECv)均呈显著正相关关系,说明冻融条件下土壤有机质(OM)、阳离子交换量(CEC)和可变电荷(CECv)的变化是改变土壤吸附解吸砷特性的最主要原因。2.应用Elovich方程和双常数方程均可以较好的拟合土壤对As的动态吸附和解吸行为。吸附和解吸过程均表现为先快、后慢两个阶段,120分钟后吸附或解吸达到平衡；各处理Elovich方程中的初始速率常数A随冻融周期的增加而减小,双常数方程中的速率常数B值均在0-1之间,且随冻融周期的增加而增大,均表明土壤吸附砷速率由于接触时间的增长而变慢,土壤对砷的吸附速率随冻融作用增强而降低。3.冻融周期变化对土壤中各形态砷的含量均有不同程度的影响。活性砷、铁型砷含量随冻融周期的增加而减少,铝型砷、钙型砷和闭蓄态砷随冻融周期的增加而增大,且主要以难溶态砷和闭蓄态砷为主。当含水量为40%时,经过冻融处理后的土壤中各形态砷含量大小顺序是：Ca-AsAl-AsFe-AsO-AsH2O-AsA-As;当含水量为70%和100%时, 经过冻融处理后的土壤中各形态砷含量大小顺序是：Al-AsO-AsCa-AsFe-AsH2O-AsA-As。4.当污染土壤中砷的含量在10-30mg·kg-1时,经过冻融处理的土壤中砷的释放量均比未冻融土壤高,且砷的释放量与冻融周期之间呈极显著直线正相关关系(P0.01)。冻融作用可以促进土壤中As的释放；在砷浓度较高时,砷释放量随冻融周期增加的速度更快。
[Abstract]:Freezing and thawing is a common natural phenomenon in northern China. It is an abiotic stress acting on soil, which will affect the amount of minerals, electric charge and organic matter, the type of electric charge and the form of organic matter in soil. Previous studies on the adsorption and desorption behavior of arsenic in soil and its occurrence forms have been carried out in detail, and reports on the effects of freeze-thaw conditions on soil physical and chemical properties and transformation of CD forms are not uncommon. However, the effects of freeze-thaw conditions on the adsorption and desorption behavior of arsenic in soil have not been reported. In this study, the adsorption and desorption characteristics of arsenic in brown soil under different freezing and thawing conditions and its influencing factors were analyzed by means of simulated culture experiment in laboratory. To study the form of exogenous arsenic in soil and its response to freezing and thawing, and to explore the characteristics of arsenic release under freezing and thawing conditions, can provide a data reference and theoretical basis for the remediation of arsenic contaminated soil and the assessment of ecological environment risk in frozen and thawed areas. It has important theoretical and practical significance. The main results and conclusions are as follows: 1. Different isothermal adsorption models were used to fit the data and the Langmuir model was used as the optimum. Under the same water content, the adsorption amount of as in freeze-thawed soil was lower than that in non-frozen and thawed soil, and the desorption rate was higher than that in unfrozen and thawed soil. With the increase of freezing and thawing cycle, the amount of as adsorbed in soil decreased and the desorption rate increased, that is, freezing and thawing could inhibit the adsorption ability of arsenic but enhance the desorption ability of arsenic. The maximum buffer capacity of as in different water treatments decreased from 40.2 to 19.819.6 with the increase of freezing and thawing cycle, respectively. Freezing and thawing energy weakens the hysteresis effect in the process of adsorption-desorption. Soil MBC values of each treatment were positively correlated with organic matter, cation exchange capacity (CEC) and variable charge (CECV), respectively. The results showed that the changes of soil organic matter (OMN), cation exchange capacity (CEC) and variable charge (CECv) were the main reasons for changing the characteristics of arsenic adsorption and desorption under freezing and thawing conditions. The dynamic adsorption and desorption behavior of as can be well fitted by Elovich equation and double constant equation. The process of adsorption and desorption was fast first, then reached equilibrium after 120 minutes in two stages, and the initial rate constant A in each Elovich equation decreased with the increase of freezing and thawing period, and the adsorption and desorption reached equilibrium after 120 minutes of adsorption and desorption, and the initial rate constant A decreased with the increase of freeze-thaw period. The rate constant B values in the double constant equation were between 0 and 1, and increased with the increase of freezing and thawing period, which indicated that the adsorption rate of arsenic on soil slowed down with the increase of contact time, and the adsorption rate of arsenic on soil decreased with the increase of freezing and thawing. The changes of freezing and thawing cycle have different effects on the content of arsenic in different forms of soil. The content of active arsenic and iron type arsenic decreased with the increase of freezing and thawing cycle, while the content of aluminum type arsenic, calcium type arsenic and closed storage arsenic increased with the increase of freezing and thawing cycle, and the insoluble arsenic and closed storage arsenic were the main ones. When the water content was 40%, the order of arsenic content in the frozen and thawed soil was: 1: Ca-AsAl-AsFe-AsO-AsH-As-AsA-As-As@@ When the content of arsenic in polluted soil was at 10-30mg kg-1, the release of arsenic in freeze-thaw treated soil was higher than that in non-freeze-thawed soil, and there was a significant linear positive correlation between arsenic release and freeze-thaw period. Freezing and thawing can promote the release of as from soil, and the release rate of arsenic increases more rapidly with the freeze-thaw cycle when the concentration of arsenic is higher.
【学位授予单位】：沈阳农业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X53

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