Pb和Cd在娄土不同剖面土壤中的吸附特性和形态转化特征

发布时间：2018-02-28 20:19

本文关键词： 土壤 Pb Cd 竞争吸附形态水分　出处：《西安建筑科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着现代化和工业化的不断发展,土壤重金属污染问题逐渐成为我们关注的焦点。污染土壤中往往不止含有某一种特定重金属离子而是多离子共同污染,离子之间相互影响,从而影响其生物有效性和迁移特征。本文以娄土为对象,采用吸附等温实验及室内培养实验研究了单一Pb、Cd元素及其共存时的吸附特征、存赋形态及其含水量变化的影响,得到了下面的主要结论:1.单一的Pb在娄土耕层、黏化层和钙积层的分配系数为8.00、8.11和6.05,Langmuir方程最大吸附量为6.07、5.75和6.01mmol/kg;而Cd的分配系数为4.19、7.05和4.72,最大吸附量为5.54、4.77和2.95mmol/kg;均表现出Pb在三种土壤上比Cd具有强的吸附性能。当Pb、Cd共存时,两种离子具有竞争吸附作用,致使土壤对Pb、Cd的吸附量均降低,Pb、Cd互为竞争性吸附离子的亲和力效应在0.8-0.9之间,修正得到双离子的竞争性Langmuir吸附方程可用于描述Pb、Cd的竞争吸附。2.耕层、黏化层和钙积层土壤中Pb、Cd的形态分布具有相似性,Pb、Cd总量中以残渣态为主,交换态的含量都小于10%。当外源Pb、Cd加入土壤后,交换态含量随时间进程逐渐降低,碳酸盐结合态在起始阶段呈现短暂上升,而在培养后期含量逐渐下降,Pb、Cd的铁锰氧化物结合态与有机化合态的含量随时间进程逐渐增加,而在较短的培养时间内,重金属离子较难进入土壤矿物的晶格中,残渣态含量基本保持不变。3.水分条件对于重金属在土壤中的形态及其重新分配具有重要的影响,Pb、Cd在三个不同层次土壤中在干湿交替条件下交换态向其他形态转变的速率最快,其次是75%田间持水量,干旱条件下转变的速率最慢,即干湿交替75%田间持水量50%田间持水量干旱条件。4.存在竞争离子条件下,Pb和Cd的形态转化方向与单一离子存在下有显著不同,其中交换态与碳酸盐态的相对含量增加,残渣态的含量相对降低,铁锰氧化物结合态与有机结合态的含量变化不大,Pb和Cd更倾向于向交换态和易受外界环境影响的碳酸盐结合态转化。重金属在土壤中的共存和竞争,可显著影响其生物有效性和迁移性,研究重金属复合污染的特征是治理的基础,本文仅仅在这些方面做了初步的工作,有待于进一步深入的研究。
[Abstract]:With the development of modernization and industrialization, the problem of soil heavy metal pollution has gradually become the focus of our attention. In this paper, adsorption isotherm experiment and indoor culture experiment were used to study the adsorption characteristics of single Pb ~ (2 +) CD element and its coexistence, and the effects of storage forms and water content on the bioavailability and migration characteristics. The following main conclusions are obtained: 1. A single Pb in the plow layer of Lou soil, The partition coefficients of the viscous layer and the calcium layer are 8.11 and 6.05% Langmuir equation respectively. The maximum adsorption capacity of Pb is 6.07 ~ 5.75 and 6.01 mmol 路kg ~ (-1), while that of CD is 4.19 ~ 7.05 and 4.72, and the maximum adsorption capacity is 5.54 ~ 4.77 and 2.95 mmol 路kg ~ (-1) respectively. The results show that Pb has a stronger adsorption performance than CD on the three soils, and when Pb ~ (+) CD coexists with CD, the distribution coefficients of CD are 4.19 ~ 7.05 and 4.72, and the maximum adsorption capacity is 5.54 ~ 4.77 and 2.95 mmol 路kg ~ (-1) 路kg ~ (-1), respectively. The adsorption capacity of Pb ~ (2 +) and CD ~ (2 +) in soil was decreased by competitive adsorption, and the affinity effect of PbN ~ (2 +) was between 0.8-0.9, and the adsorption capacity of Pb ~ (2 +) ~ (2 +) was 0.8-0.9 (P < 0.05). The modified competitive Langmuir adsorption equation can be used to describe the competitive adsorption of Pb ~ (2 +) CD. 2. The speciation distribution of Pb ~ (2 +) CD in topsoil, clay layer and calcium accumulation layer is similar. The contents of exchangeable state were all less than 10. When exogenous PBO / CD was added into soil, the content of exchangeable state decreased gradually with time, and the carbonate bound state increased briefly in the initial stage. However, the content of ferromanganese oxide bound and organic compounds of PbPbPbCd decreased gradually during the later period of culture, and the heavy metal ions were difficult to enter the lattice of soil minerals during the short incubation period, and the content of Fe / mn oxides and organic compounds increased with the time course of culture. The residual state content remained basically unchanged .3.Water condition had the most important influence on the speciation and redistribution of heavy metals in soil. In three different layers of soils, the rate of transformation of exchange state to other forms of heavy metals was the fastest in three different layers of soils under the alternate conditions of dry and wet. The second was 75% field water holding capacity, and the rate of transformation was the slowest under drought, That is, dry and wet alternate 75% field water holding capacity 50% field water holding capacity drought condition. 4. The direction of speciation transformation of Pb and CD in the presence of competitive ions is significantly different from that in the presence of a single ion, and the relative content of exchange state and carbonate state increases. The content of residuals is relatively low, and the contents of Fe and mn oxides bound to organic compounds are not changed much, Pb and CD tend to convert to exchangeable and carbonate-bound forms which are easy to be affected by external environment, and the coexistence and competition of heavy metals in soil. The study of the characteristics of heavy metal compound pollution is the basis of treatment. This paper has only done some preliminary work in these aspects, which needs to be further studied.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53

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