【作者】 李雅；

【导师】 张增强；

【作者基本信息】 西北农林科技大学 ， 环境科学， 2011， 博士

【摘要】 地下水污染修复技术是现今环境领域的研究热点之一。可渗透反应墙（Permeble Reactive Barrier）是一种新兴的原位修复技术,它具有运行稳定、成本低、长效等优点。近年来,PRB技术迅速发展,在反应机理、结构安装、活性材料的改进等方面取得了突破。目前,PRB技术正逐步取代运行成本高昂的抽出处理技术,成为地下水修复技术的发展方向。其中零价铁可渗透反应墙（Fe⁰-PRB）应用最为广泛,它具有持续原位处理、处理组分多和价格便宜等优势,已在许多国家地下水污染处理的众多方面得到了研究和发展。Fe⁰-PRB已被证明是一项能够修复受卤代烃、卤代芳烃、有机氯农药以及重金属（如铬、硒、铀、砷和锝）等污染地下水的有效技术。本研究通过批实验和柱实验,研究了Fe⁰-PRB技术修复铬铅复合污染地下水的效果和主要影响因素,探讨了以Fe⁰为填料的PRB修复铬铅复合污染地下水的可行性和有效性,为了解决单独以铁粉为介质的PRB去除效率易下降的问题,首次使用堆肥-Fe⁰混合PRB修复铬铅复合污染地下水,并对其作用机理进行了研究,得到了以下结论:⑴零价铁能够有效、快速地去除水体中的铬污染,机理为氧化还原和共沉淀,产物为Fe（OH）₃、Cr（OH）₃和(Cr_xFe_1-x)（OH）₃;对铁粉进行酸洗和镀镍等预处理能有效提高六价铬去除率;去除过程受铁粉投加量、污染物初始浓度及初始pH的影响;零价铁去除六价铬的过程伴随着pH值上升和Eh值下降;本实验条件下,铁粉最佳投加量为铁粉与铬的质量比为1000:1;当反应液为酸性时,Fe²⁺浓度可以作为Cr（Ⅵ）是否完全去除的指示剂。⑵零价铁能够有效去除水体中的铅污染,机理为氧化还原和混凝吸附,产物为Pb（0）、Pb（OH）₂和PbO·XH₂O等;零价铁去除铅的过程伴随着pH值上升和Eh值下降;铅去除率随铁粉投加量的增大而增大,随反应液初始pH值的上升而下降。⑶零价铁能够快速有效地去除水体中的铬铅复合污染,去除率随铁粉投加量的增加或初始pH的下降而升高;相同反应条件下,零价铁对六价铬的去除率高于铅;复合污染时零价铁对六价铬的去除率略小于单独污染时,但铅的去除率明显低于单独污染时的去除率;⑷分别研究了单独污染和复合污染时零价铁去污的动力学模型,结果表明:无论是单独污染还是复合污染,六价铬及铅的去除都符合准一级动力学方程,随着铁粉用量增加或反应液初始pH下降,反应速率常数增大。⑸比较了不同阴离子及同一种离子以不同浓度存在对零价铁去除铬、铅污染的影响,其中四种无机离子存在时,Cr（Ⅵ）的去除率顺序:Cl^->SO₄^2->HCO₃^->PO₄^3-。离子浓度为1 mmol/L时,Cl^-及SO₄^2-加快六价铬去除,HCO₃^-和PO₄^3-减慢六价铬去除;当无机阴离子浓度为3 mmol/L时,HCO₃^-变成了促进六价铬去除,此时只有磷酸根起抑制作用;由于Cl^-、SO₄^2-和高浓度的HCO₃^-（3 mmol/L）可以与铁反应生成绿锈从而促进了六价铬去除,低浓度的HCO₃^-（1 mmol/L）和PO₄^3-抑制六价铬去除是因为它们可以与铁粉或铁腐蚀产物发生专性吸附;高浓度或低浓度有机离子存在时,Cr（Ⅵ）的去除率顺序结果如下:C₆H₅O₇^3-> C₂O₄^2-> CH₃COO^-,其中前两者表现为促进作用,而CH₃COO^-则显著抑制六价铬去除;由于柠檬酸根(C₆H₅O₇^3-)的吸附和螯合作用,草酸根(C₂O₄^2-)与金属的强配位能力和刻蚀作用,所以它们的存在使六价铬去除率上升;CH₃COO^-与铁和铁的腐蚀产物,在铁粉表面发生络合或吸附,从而阻碍的零价铁去除六价铬;对于铅来说,测试的阴离子均使其去除率上升,其中四种无机阴离子存在时Pb的去除率结果如下:PO₄^3->Cl^->HCO₃>SO₄^2-;三种有机离子存在时Pb的去除率结果为:C₂O₄^2- > C₆H₅O₇^3-> CH₃COO^-;阴离子存在时,铅的去除率增加不仅与阴离子改进了铁粉的活性有关,还与Pb²⁺容易和阴离子生成较小溶度积常数的化合物有关。⑹考察了不同浓度阳离子存在对铬、铅污染去除的影响,结果如下:不同浓度的阳离子存在时,Cr（Ⅵ）的去除率如下:Fe²⁺ > Fe³⁺ > Ca²⁺ > Mg²⁺,其中Fe²⁺和Fe³⁺起促进作用,Ca²⁺和Mg²⁺起抑制作用,且Mg²⁺的抑制作用更大;Ca²⁺、Mg²⁺阻碍零价铁去除铅;因为Fe²⁺能直接还原污染物,而Fe³⁺可以与铁反应生成Fe²⁺,所以二者可以促进反应;由于Ca²⁺、Mg²⁺易与水中OH-生成沉淀附着在铁粉表面,降低了铁粉的活性,造成污染物去除率下降。⑺无论是促进作用还是阻碍作用,都随着离子浓度的增大而增大;总体上,不同离子存在时零价铁修复铬、铅污染的过程,伴随着溶液pH升高,Eh降低,但不同离子作用下二者变化的程度过程不相同;不同离子存在时六价铬及铅的去除符合准一级动力学模型,速率常数的大小与离子种类及浓度有关。⑻分别用堆肥、零价铁、堆肥+零价铁为反应介质,对PRB处理铬铅复合污染地下水的可行性和有效性进行了研究。实验结果表明:用以堆肥、零价铁、堆肥-零价铁为反应介质的PRB处理铬铅复合污染地下水是可行的,其中以堆肥+零价铁作为介质的反应柱去除效果优于单独以堆肥或铁粉为介质的反应柱,且去除效果更长久。⑼当反应介质为堆肥+零价铁的混合物时,污染物的去除率随堆肥或铁粉用量的改变而改变;堆肥时间对去除效果影响不大;吸附作用是堆肥去除污染物的主要作用,微生物作用为次要作用;添加活性炭有助于污染物的去除。⑽对单独使用零价铁的反应柱、使用堆肥+零价铁的混合物为介质的反应柱以及添加活性炭的反应柱出水中可溶性总铁的含量进行了检测,其中添加活性炭的反应柱出水可溶性总铁含量最低,以堆肥+零价铁混合物作为介质的反应柱出水可溶性总铁含量次之,单独使用零价铁的反应柱出水总铁含量最高,但三者出水可溶性总铁含量都小于0.3 mg/L,符合《生活饮用水卫生标准》要求。这说明使用Fe⁰-PRB修复铬铅污染地下水是安全可靠的。更多还原

【Abstract】 Nowadays, the remediation technology of groundwater pollution is a hot topic in the field of environment. Permeable reactive barrier （PRB） technology is a new in situ remediation technology. It has the characteristics of less cost, stable operation and long-term efficiency. Moreover big progress has been made recently in remediation mechanism, design and construction of the system and the reactive materials in practical projects. Currently, PRB technology is gradually replacing the Pump-Treat technology which has high running costs. In a word, PRB is the developing direction of groundwater treatment technologies. The Fe0 permeable reactive barrier which is widely used was proved that the approach is characteristic with in situ remediation, good long-term performance, many remediable contaminants and low costs. It has been using in many countries and has been dealing with many aspects of research and development in groundwater pollution. It is an effective technology for the remediation of groundwater contaminated by chlorinated hydrocarbons, chlorinated aromatic hydrocarbons, chlorinated pesticides and toxic metals such as chromium, selenium, uranium, arsenic and technetium.Batch and column experiments were conducted to investigate the effect and major effect factors for Fe⁰-PRB removal Cr-Pb contaminated groundwater and confirm the feasibility and effectiveness of Fe⁰-PRB used in the Cr-Pb polluted groundwater. The results were as follow.⑴Hexavalent chromium was removed quickly and effectively by zero valent iron, removal mechanism was redox and coprecipitation, products are Fe（OH）₃, Cr（OH）₃ and (Cr_xFe_1-x)（OH）₃; the removal ratio was effected by the pretreatment with acid and nickelaqe; the amount of iron, the initial concentration of hexavalent chromium and initial pH; the removal of hexavalent chromium was accompanied by a sharp increase in pH, and a sharp decrease in Eh; Fe²⁺ could be used as an indicator for complete reduction of hexavalent chromium in the acidic condition. q⑵Pb was removed effectively by zero valent iron, removal mechanism was redox and flocculating settling, products were Pb（0）, Pb（OH）₂ and PbO·xH₂O; the removal ratio was effected by the amount of iron and initial pH; the removal of Pb was accompanied by a sharp increase in pH, and a sharp decrease in E_h.⑶Cr-Pb polluted groundwater was removed quickly and effectively by zero valent iron, the removal ratio was effected by the amount of iron and initial pH. The removal ratio of Pb was decreased obviously, and hexavalent chromium removal ratio was almost uninfluenced when the two metals existed simultaneously.⑷The removal kinetics model of Cr（Ⅵ） and Pb by iron were studied as single pollutant or co-exsiting system.The results showed that the removal of Cr（Ⅵ） and Pb could be fit to pseudo-first-order reaction kinetics model in single pollutant or co-exsiting system. More iron,biger rate constant; lower initial pH, biger rate constant.⑸The zero-valent iron for Cr（Ⅵ） removal ratio as follows: Cl^-> SO₄^2-> HCO₃^-> PO₄^3-, in the presence of four inorganic anions. Because the effect of anion on iron and the effect of green rust, the results demonstrated that Cl^- and SO₄^2- enhanced remediation , however HCO₃^- and PO43- inhibited remediation observably when the 1.0 mmol/L inorganic anion existed. All anions except PO₄（3-） enhanced reaction when the 3.0 mmol/L inorganic anion existed. Because of adsorption , Cr（Ⅵ） removal inhibited by HCO₃^- and PO₄（3-）. The zero-valent iron for Cr （Ⅵ） removal ratio as follows: C₆H₅O₇^3-> C₂O₄^2-> CH₃COO^-, when three organic anions existed. The results demonstrated that C₆H₅O₇^3- and C₂O₄^2- enhanced remediation, however CH₃COO^- inhibited remediation observably. Because of chelation of C₂O₄^2- and complexation of C₆H₅O₇^3-, they enhanced remediation. In the presence of four inorganic anions exist, the zero-valent iron for Pb（Ⅱ） removal ratio as follows: PO₄^3->Cl^->HCO₃>SO₄^2-. When three organic anions existed, the zero-valent iron for Pb（Ⅱ） removal ratio as follows: C₂O₄^2- > C₆H₅O₇^3-> CH₃COO^-, and all anions enhanced reaction. This was not only because of increasing activity of iron, but also because Pb（Ⅱ） could react wih anions and prduce low Ksp compound.⑹The zero-valent iron for Cr （Ⅵ） removal ratio as follows: Fe²⁺ > Fe³⁺ > Ca²⁺ > Mg²⁺, when different cations existed. The results demonstrated that Fe²⁺ and Fe³⁺ enhanced remediation. This was because that Fe²⁺ could deoxidize Cr （Ⅵ）. Ca²⁺ and Mg²⁺ could react wih OH^- by formation precipitation, so they inhibited remediation. Moreover inhibition of Mg²⁺ was greater than Ca²⁺. The results also demonstrated that Ca²⁺ and Mg²⁺ played inhibition role in Pb（Ⅱ） removal.⑺The higher ions concentration was, the stronger enhance role or inhibition, when different ions existed. The removal process was accompanied by a sharp increase in pH, and a sharp decrease in E_h. The removal of Cr（Ⅵ） and Pb could be fit to pseudo-first-order reaction kinetics model when different ions existed. The rate constant was effected by ions kinds and concentration.⑻With the compost, ZVI, and ZVI-compost as reaction media respectively, the feasibility and effectiveness of the Cr-Pb polluted groundwater remediation by PRB were studied. The results showed that the using of compost, ZVI, and ZVI-compost as reaction media to remediatiton Cr-Pb polluted groundwater was feasibility. The reactor packed with ZVI-compost had a better performance than the reactor packed with compost or ZVI alone.⑼With the ZVI-compost as reaction media, increasing the amount of compost and ZVI could increase the removal effects; moreover the removal effects were little influenced by the time of composting; adsorption was the primary role of compost removal pollutants, microorganisms as a secondary role; and the removal effects could be increased by adding active carbon.⑽With the ZVI, ZVI-compost and ZVI-compost-active carbon as reaction media respectively, the dissoluble iron concentration in effluent were detected. The results showed that the dissoluble iron concentration in effluent of the column（ZVI-compost-active carbon） was lowest, the dissoluble iron concentration in effluent of the column（ZVI-compost） was lower than the column（ZVI）; however total iron in effluent of all column could meet the requirement of standards for drinking water quality. So it indicated that the using of Fe⁰-PRB is the safe method for Cr-Pb removal from groundwater.更多还原