本文關鍵詞：強化動態(tài)納米零價鐵復合流動體系修復土壤六價鉻污染研究　出處：《太原理工大學》2017年碩士論文　論文類型：學位論文

  更多相關文章： 復合流動 動態(tài)體系 納米零價鐵 六價鉻 土壤污染

【摘要】：土壤作是人類賴以生存發(fā)展的自然環(huán)境和物質(zhì)基礎,隨著當前工業(yè)和農(nóng)業(yè)的發(fā)展以及土壤污染具有潛伏性和累積性等特點,當下土壤污染狀況更加嚴重并引起人們的廣泛關注。而具有強致癌致畸毒性Cr(VI)對土壤的污染更是不容忽視,所以對Cr(VI)污染土壤的有效修復方法更是目前研究的熱點。目前對Cr(VI)污染土壤的修復方法主要有微生物修復法、淋洗法、電修復法、固化穩(wěn)定法及還原法�；瘜W還原法具有成本低,可大規(guī)模應用,可進行原位修復的特點,故本試驗選擇了化學還原法為土壤修復的方法。本試驗選擇的還原修復材料為具有優(yōu)良還原性質(zhì)的納米材料納米零價鐵(n ZVI),盡管n ZVI具有還原方面的優(yōu)勢,但其易團聚、氧化等缺點會制約其特性的發(fā)揮,本文選擇無毒無害的環(huán)境友好型材料羧甲基纖維素鈉(CMC)作為穩(wěn)定劑,采用液相還原法制備出CMC-n ZVI作為Cr(VI)污染土壤的還原修復劑。CMC的來源豐富,無毒易降解而且目前很多學者對其原料來源進行改進從而進一步降低其成本,可以使土壤修復劑的成本降低,更加有利于其推廣應用。為了證明CMC對n ZVI具有穩(wěn)定性的作用,本試驗分別對CMC-n ZVI和bare-n ZVI進行分散穩(wěn)定性試驗并繪制吸收光譜,并對其分別進行TEM和SEM表征。本試驗分為靜態(tài)試驗及動態(tài)土柱試驗,其中靜態(tài)試驗流程為將污染土壤和CMC-n ZVI修復劑以1g:5ml的比例混合于離心管中,震蕩反應一定時間后離心、過濾并測吸光度;動態(tài)試驗在三種模式下進行,這三種模式分別為“模式一”(簡單連續(xù)流)、“模式二”(間歇流)與“模式三”(循環(huán)流)。本文以自制的模擬Cr(VI)污染土壤為試驗土壤樣品,濃度為102mg Cr(VI)/kg土,通過對試驗土壤樣品進行XRD表征表明:負載在砂土和粘土上的鉻主要以Cr2O3形式存在。以自制的一定濃度的CMC-n ZVI作為Cr(VI)污染土壤的修復劑分別進行靜態(tài)試驗和動態(tài)土柱試驗,研究不同試驗條件對土壤修復效果的影響,并通過反應動力學研究分析其反應機理,得到以下結論:(1)以CMC為穩(wěn)定劑以化學還原法制備的CMC-n ZVI膠體懸濁液作為Cr(Ⅵ)污染土壤的修復劑,通過分散穩(wěn)定穩(wěn)定性試驗及對CMC-n ZVI進行TEM、SEM表征證明CMC確實能夠起到穩(wěn)定納米鐵顆粒防止其氧化團聚的作用,并且只有添加CMC的n ZVI顆粒的大小在100nm以下,起到納米材料的作用。通過對CMC-n ZVI和bare-n ZVI繪制吸收光譜可知CMC-n ZVI的吸光度值比bare-n ZVI的要大13倍左右,可知CMC能夠起到穩(wěn)定n ZVI的作用。(2)靜態(tài)試驗研究結果表明:土壤組分中粘土比例越高,對于土壤中Cr(Ⅵ)的去除更不利。同時CMC的投加量、CMC-n ZVI投加量與p H值會對Cr(Ⅵ)去除效果產(chǎn)生影響。適當增大CMC投加量可以增大Cr(Ⅵ)去除率,在適宜的CMC-n ZVI的投加量范圍內(nèi),隨著CMC-n ZVI投加量的增大,Cr(Ⅵ)去除率增大,但過度投加會破壞土壤結構;偏酸性環(huán)境更有利于Cr(Ⅵ)的去除。得出最佳的反應條件為:CMC與Fe0的摩爾比為0.0186、CMC-n ZVI投加量為1g/L、p H值為6。在這種條件下,污染土壤Cr(Ⅵ)濃度為102 mg Cr(Ⅵ)/kg土,CMC-n ZVI對砂土和粘土污染土壤Cr(Ⅵ)除率分別為91.34%和85.91%。(3)“模式一”復合流動體系的動態(tài)土柱試驗結果表明:CMC-n ZVI投加量、葡萄糖添加量、凹凸棒土填料使用情況、CMC-n ZVI泵入流速會對Cr(Ⅵ)去除效果產(chǎn)生影響,在一定范圍內(nèi)增加CMC-n ZVI濃度能較為明顯的增大Cr(Ⅵ)去除率,土壤中添加葡萄糖不利于納米零價鐵對土壤中Cr(Ⅵ)修復作用;Cr(Ⅵ)去除率隨著流速的增加先增大后減小,凹凸棒土填料的添加可以增大Cr(Ⅵ)去除率。其最適的試驗條件為:CMC-n ZVI投加量為1g/L,葡萄糖添加量為0g/kg土,CMC-n ZVI泵入流速為5ml/min,條件凹凸棒土填料。在此條件下,污染砂土濃度為102mg Cr(Ⅵ)/kg土,Cr(Ⅵ)去除率可達98.75%。(4)在動態(tài)試驗最佳的試驗條件下,進行“模式二”動態(tài)土柱試驗,結果證明隨著間歇停留時間的增加,Cr(Ⅵ)去除效果出現(xiàn)波動。(5)在動態(tài)試驗最佳的試驗條件下,進行“模式三”動態(tài)土柱試驗,結果證明循環(huán)時間為4h時Cr(Ⅵ)去除率的初始值及增加趨勢最快,初始去除率為42.68%,最終去除率為98.89%,在2h、1h、6h和8h時去除率由大到小變化,且在不同循環(huán)時間條件下,最終的去除率效果都較好。對“模式三”與“模式一”動態(tài)試驗結果進行對比結果可知,在0min~12min內(nèi)Cr(Ⅵ)“模式三”的去除率更大,其初始去除率為42.68%,且去除率大小增加的的更快。在12min~60min內(nèi)Cr(Ⅵ)去除率幾乎保持一致,且都具有較大的Cr(Ⅵ)去除率,在98%左右。(6)CMC-n ZVI對土壤Cr(Ⅵ)污染的修復可以和偽一級反應動力學模型的擬合,kobs隨反應條件的變化趨勢為:(a)kobs值與CMC-n ZVI添加量之間有較好的線性關系,且kobs值與CMC-n ZVI投加量成正比;(b)kobs與葡萄糖添加量之間有較好的線性關系,且kobs值與葡萄糖添加量成反比(R2=0.9211);(c)kobs與流速之間有較好的線性關系,且kobs值與流速成正比(R2=0.9447);(d)使用凹凸棒土填料的kobs值要大于普通礫石試驗中的值。
[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
【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：X53

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