强化动态纳米零价铁复合流动体系修复土壤六价铬污染研究

发布时间：2017-12-27 19:06

本文关键词：强化动态纳米零价铁复合流动体系修复土壤六价铬污染研究　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：土壤作是人类赖以生存发展的自然环境和物质基础,随着当前工业和农业的发展以及土壤污染具有潜伏性和累积性等特点,当下土壤污染状况更加严重并引起人们的广泛关注。而具有强致癌致畸毒性Cr(VI)对土壤的污染更是不容忽视,所以对Cr(VI)污染土壤的有效修复方法更是目前研究的热点。目前对Cr(VI)污染土壤的修复方法主要有微生物修复法、淋洗法、电修复法、固化稳定法及还原法。化学还原法具有成本低,可大规模应用,可进行原位修复的特点,故本试验选择了化学还原法为土壤修复的方法。本试验选择的还原修复材料为具有优良还原性质的纳米材料纳米零价铁(n ZVI),尽管n ZVI具有还原方面的优势,但其易团聚、氧化等缺点会制约其特性的发挥,本文选择无毒无害的环境友好型材料羧甲基纤维素钠(CMC)作为稳定剂,采用液相还原法制备出CMC-n ZVI作为Cr(VI)污染土壤的还原修复剂。CMC的来源丰富,无毒易降解而且目前很多学者对其原料来源进行改进从而进一步降低其成本,可以使土壤修复剂的成本降低,更加有利于其推广应用。为了证明CMC对n ZVI具有稳定性的作用,本试验分别对CMC-n ZVI和bare-n ZVI进行分散稳定性试验并绘制吸收光谱,并对其分别进行TEM和SEM表征。本试验分为静态试验及动态土柱试验,其中静态试验流程为将污染土壤和CMC-n ZVI修复剂以1g:5ml的比例混合于离心管中,震荡反应一定时间后离心、过滤并测吸光度;动态试验在三种模式下进行,这三种模式分别为“模式一”(简单连续流)、“模式二”(间歇流)与“模式三”(循环流)。本文以自制的模拟Cr(VI)污染土壤为试验土壤样品,浓度为102mg Cr(VI)/kg土,通过对试验土壤样品进行XRD表征表明:负载在砂土和粘土上的铬主要以Cr2O3形式存在。以自制的一定浓度的CMC-n ZVI作为Cr(VI)污染土壤的修复剂分别进行静态试验和动态土柱试验,研究不同试验条件对土壤修复效果的影响,并通过反应动力学研究分析其反应机理,得到以下结论:(1)以CMC为稳定剂以化学还原法制备的CMC-n ZVI胶体悬浊液作为Cr(Ⅵ)污染土壤的修复剂,通过分散稳定稳定性试验及对CMC-n ZVI进行TEM、SEM表征证明CMC确实能够起到稳定纳米铁颗粒防止其氧化团聚的作用,并且只有添加CMC的n ZVI颗粒的大小在100nm以下,起到纳米材料的作用。通过对CMC-n ZVI和bare-n ZVI绘制吸收光谱可知CMC-n ZVI的吸光度值比bare-n ZVI的要大13倍左右,可知CMC能够起到稳定n ZVI的作用。(2)静态试验研究结果表明:土壤组分中粘土比例越高,对于土壤中Cr(Ⅵ)的去除更不利。同时CMC的投加量、CMC-n ZVI投加量与p H值会对Cr(Ⅵ)去除效果产生影响。适当增大CMC投加量可以增大Cr(Ⅵ)去除率,在适宜的CMC-n ZVI的投加量范围内,随着CMC-n ZVI投加量的增大,Cr(Ⅵ)去除率增大,但过度投加会破坏土壤结构;偏酸性环境更有利于Cr(Ⅵ)的去除。得出最佳的反应条件为:CMC与Fe0的摩尔比为0.0186、CMC-n ZVI投加量为1g/L、p H值为6。在这种条件下,污染土壤Cr(Ⅵ)浓度为102 mg Cr(Ⅵ)/kg土,CMC-n ZVI对砂土和粘土污染土壤Cr(Ⅵ)除率分别为91.34%和85.91%。(3)“模式一”复合流动体系的动态土柱试验结果表明:CMC-n ZVI投加量、葡萄糖添加量、凹凸棒土填料使用情况、CMC-n ZVI泵入流速会对Cr(Ⅵ)去除效果产生影响,在一定范围内增加CMC-n ZVI浓度能较为明显的增大Cr(Ⅵ)去除率,土壤中添加葡萄糖不利于纳米零价铁对土壤中Cr(Ⅵ)修复作用;Cr(Ⅵ)去除率随着流速的增加先增大后减小,凹凸棒土填料的添加可以增大Cr(Ⅵ)去除率。其最适的试验条件为:CMC-n ZVI投加量为1g/L,葡萄糖添加量为0g/kg土,CMC-n ZVI泵入流速为5ml/min,条件凹凸棒土填料。在此条件下,污染砂土浓度为102mg Cr(Ⅵ)/kg土,Cr(Ⅵ)去除率可达98.75%。(4)在动态试验最佳的试验条件下,进行“模式二”动态土柱试验,结果证明随着间歇停留时间的增加,Cr(Ⅵ)去除效果出现波动。(5)在动态试验最佳的试验条件下,进行“模式三”动态土柱试验,结果证明循环时间为4h时Cr(Ⅵ)去除率的初始值及增加趋势最快,初始去除率为42.68%,最终去除率为98.89%,在2h、1h、6h和8h时去除率由大到小变化,且在不同循环时间条件下,最终的去除率效果都较好。对“模式三”与“模式一”动态试验结果进行对比结果可知,在0min~12min内Cr(Ⅵ)“模式三”的去除率更大,其初始去除率为42.68%,且去除率大小增加的的更快。在12min~60min内Cr(Ⅵ)去除率几乎保持一致,且都具有较大的Cr(Ⅵ)去除率,在98%左右。(6)CMC-n ZVI对土壤Cr(Ⅵ)污染的修复可以和伪一级反应动力学模型的拟合,kobs随反应条件的变化趋势为:(a)kobs值与CMC-n ZVI添加量之间有较好的线性关系,且kobs值与CMC-n ZVI投加量成正比;(b)kobs与葡萄糖添加量之间有较好的线性关系,且kobs值与葡萄糖添加量成反比(R2=0.9211);(c)kobs与流速之间有较好的线性关系,且kobs值与流速成正比(R2=0.9447);(d)使用凹凸棒土填料的kobs值要大于普通砾石试验中的值。
[Abstract]:Soil is the natural environment and material basis for human survival and development. With the development of industry and agriculture and the latent and Accumulative Characteristics of soil pollution, the soil pollution is becoming more and more serious. The pollution of Cr (VI) with strong carcinogenesis and teratogenicity is not neglecting. Therefore, the effective remediation method of Cr (VI) contaminated soil is the focus of current research. The main methods for the remediation of Cr (VI) contaminated soil are microbial remediation, leaching, electrical repair, stabilization and reduction. Chemical reduction method has the characteristics of low cost, large scale application and in situ remediation. Therefore, chemical reduction method is selected as a method for soil remediation. The reduction of repair materials selected in this experiment for nano nano materials with excellent redox properties of zero valent iron (n ZVI), while n ZVI has the advantage of reducing, but its easy agglomeration and oxidation and other shortcomings will restrict its characteristics of play, this paper choose non-toxic environmentally friendly materials of sodium carboxymethyl cellulose (CMC) as a stabilizer, ZVI as Cr CMC-n was prepared by liquid phase reduction (VI) reduction of polluted soil restoration agent. The sources of CMC are abundant, non-toxic and easy to degrade. Many scholars improve their raw material sources, which further reduce their cost, reduce the cost of soil remediation agents, and are more conducive to its popularization and application. In order to prove the effect of CMC on the stability of n ZVI, the dispersion stability tests of CMC-n ZVI and bare-n ZVI were carried out in this experiment, and the absorption spectra were plotted, and TEM and SEM were characterized respectively. This experiment is divided into static and dynamic soil column test, the static test process will pollute the soil and CMC-n ZVI repair agent mixed with the ratio of 1g:5ml in the centrifuge tube, the shock response after a certain time of centrifugation, filtration and absorbance; dynamic test was carried out in three modes, the three modes respectively "mode" (a simple continuum), model two (intermittent flow) and "mode three" (circulation). In this paper, the self simulated Cr (VI) contaminated soil was used as the test soil sample, and the concentration was 102mg Cr (VI) /kg soil. XRD characterization of the tested soil samples showed that the chromium loaded on the sand and clay mainly existed in the form of Cr2O3. In a certain concentration of homemade CMC-n ZVI as Cr (VI) contaminated soil repair agent respectively the static test and dynamic soil column test, to study the effect of different experimental conditions on soil remediation, and through the study of reaction kinetics analysis of the reaction mechanism, we get the following conclusions: (1) by chemical reduction of CMC-n stabilizer ZVI colloidal suspension prepared using Cr as CMC (VI) repair contaminated soil, the CMC-n ZVI TEM, SEM characterization proved that CMC can indeed play a stable iron nanoparticles to prevent the oxidation of agglomeration by dispersing stability and stability test, and only add n ZVI the size of the CMC particles in the 100nm below to the effect of nano materials. The absorption spectra of CMC-n ZVI and bare-n ZVI show that the absorbance value of CMC-n ZVI is about 13 times larger than that of bare-n ZVI, indicating that CMC can play a role in stabilizing n ZVI. (2) the results of static test showed that the higher the clay proportion in the soil composition, the removal of Cr (VI) in the soil was more unfavorable. At the same time, the dosage of CMC, the dosage of CMC-n ZVI and the value of P H will affect the removal efficiency of Cr (VI). The increase of CMC dosage can increase the removal rate of Cr (VI). In the range of suitable CMC-n ZVI dosage, the removal rate of Cr (VI) increases with the increase of CMC-n ZVI dosage, but excessive addition will destroy the soil structure. The acidic environment is more conducive to the removal of Cr (VI). The optimum reaction conditions are as follows: the molar ratio of CMC to Fe0 is 0.0186, the dosage of CMC-n ZVI is 1g/L, and the P H value is 6. Under this condition, the concentration of Cr (VI) in contaminated soil is 102 mg Cr (VI) /kg soil, and the Cr (VI) removal rate of CMC-n ZVI to soil and clay contaminated soil is 91.34% and 85.91%, respectively. (3) the dynamic soil column test results of a composite model "of the flow system showed that the CMC-n dosage of ZVI, glucose addition, attapulgite filler, CMC-n ZVI of Cr pumping velocity (VI) removal effect, increases in a certain range of CMC-n concentration of ZVI can obviously increase the removal rate of Cr (VI), in favor of nano zero valent iron in soil without adding Cr glucose in soil (VI) repair; Cr (VI) removal rate with the increase of flow rate increased first and then decreased, attapulgite added filler bump can increase the Cr removal rate (VI). The optimum test conditions are as follows: the dosage of CMC-n ZVI is 1g/L, the dosage of glucose is 0g/kg soil, the flow velocity of CMC-n ZVI pump is 5ml/min, and the condition palygorskite is filled. Under this condition, the concentration of contaminated sand is 102mg Cr (VI) /kg soil, and the removal rate of Cr (VI) can reach 98.75%. (4) under the best test condition of dynamic test, the "mode two" dynamic soil column test was carried out. The results showed that the removal efficiency of Cr (VI) fluctuated with the increase of intermittent residence time. (5) in the best experimental conditions in dynamic tests, "three" model of dynamic soil column test, results show that cycle time is 4H the removal rate of Cr (VI) initial value and increased the fastest, the initial removal rate is 42.68%, the removal rate was 98.89%, in 2H, 1H, 6h and 8h when the removal rate varies from large to small, and in the condition of different cycle time, the final removal rate are better. The comparison between "mode three" and "mode 1" dynamic test results shows that in 0min~12min, the removal rate of Cr (VI) "mode three" is greater, the initial removal rate is 42.68%, and the removal rate increases faster. In 12min~60min, the removal rate of Cr (VI) is almost consistent, and the removal rate of Cr (VI) is larger than 98%. (6) the restoration of soil Cr (VI) pollution by CMC-n ZVI and the pseudo first order kinetic model
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：X53

【参考文献】