腐殖酸对纳米零价铁修复污染物的抑制及抗抑制机理研究

摘要

进入21世纪，随着人口的增加和国民经济的快速发展，我国面临着水资源和水质危机，尤其是水质危机日趋严重。无论是地表水还是地下水，我国的水质污染非常严重。其中六价铬广泛应用于制革、纺织品生产、印染、颜料以及镀铬等行业中，是普遍存在的污染物。有机氯化合物在制造业、清洗业、有机溶剂、农药、除草剂、化工生产等行业大量使用，导致含氯有机物大量排放，使很多地表水和地下水都受到含氯有机物的污染。因此，对水中含氯有机物及重金属的治理具有十分重要的意义。自从有人提出金属铁屑可以用于地下水的原位修复以来，用Fe0还原修复地下水中的污染物就成为一个非常活跃的研究领域。零价铁(Fe0)具有廉价、高还原势和反应速度快的特点，已成为地下水原位修复中最有效的反应介质材料之一。目前零价铁已被广泛应用于含氯有机物、含氮有机物、重金属等污染物的净化和修复。但地下水中存在的各种物质，例如腐殖酸和硬度离子等将会对零价铁除铬和脱氯的应用产生影响，故本研究采用纳米级Fe0及纳米级Ni-Fe和Pd-Fe双金属为主要工具修复受污染水体中的六价铬和2，4-二氯苯酚(2，4-DCP)，并着重考察腐殖酸(HA)的存在对零价铁(ZVI)还原修复技术的抑制作用，初步探讨了腐殖酸(HA)对ZVI还原修复技术抑制作用的机理。通过实验室实验，探索了克服腐殖酸(HA)对ZVI还原修复技术抑制作用的方法及其抗抑制的机理。结果表明：
　　 ⑴腐殖酸对纳米级Pd-Fe和纳米级Ni-Fe双金属催化还原脱氯具有明显的抑制作用，并且这种抑制作用在HA的浓度较低(5 mg L-1)时就明显的表现出来。HA对纳米级Pd-Fe和纳米级Ni-Fe双金属催化还原2，4-DCP脱氯的抑制作用随着HA投加量的增大而变得越来越明显。腐殖酸之所以会抑制纳米级金属颗粒催化还原脱氯的主要原因是腐殖酸会吸附在纳米级双金属的表面，占据双金属表面的活性反应场所，从而阻碍反应的进一步进行。HA存在时，影响纳米级Ni-Fe双金属对2，4-DCP催化还原脱氯效果的因素有：HA的投加量、pH值、镍化率、纳米级Ni-Fe投加量和反应温度。实验结果表明较大的镍化率、较低的pH值、较高的纳米级Ni-Fe投加量和较高的反应温度有利于脱氯反应；脱氯效率与2，4-DCP的初始浓度关系不大。HA存在时，纳米级Pd-Fe和纳米级Ni-Fe双金属颗粒催化还原脱氯的动力学模型均可以用准一级反应动力学描述。在计算纳米级Pd-Fe催化还原2，4-DCP脱氯的实验中发现，HA投加量的增加与反应速率常数的增大成线性关系，随着HA投加量的增加，反应速率常数线性减小。
　　 ⑵HA对纳米级零价铁去除Cr(Ⅵ)的反应也有明显的抑制作用，并且这种趋势随着HA的浓度增大而增大，担当腐殖酸浓度增大到一定程度时，这种趋势变得不再明显。HA对纳米级零价铁去除Cr(Ⅵ)的作用机理是双重的，一方面，腐殖酸要吸附在纳米级零价铁的表面，占据纳米级零价铁表面的活性反应场所，抑制反应的进行；另一方面，溶液中的腐殖酸又可以作为电子穿梭体(电子转移媒介)促进反应的进行。
　　 ⑶在制备纳米级Fe0过程中投加稳定剂CMC可以阻碍纳米级颗粒的团聚，使其保持高度分散状态，从而维持其高反应性。CMC稳定化纳米级Fe0在一定程度上可以促进修复反应的进行，消除HA带来的抑制作用。40mg/L的HA存在时，投加0.5g/L的CMC，纳米级Fe0对水中Cr(Ⅵ)的去除效率由不加CMC时的49.1％上升到78.6％，这个值非常接近不加HA的82.65％，表明在制备纳米级Fe0的过程中投加稳定剂CMC在一定程度上可以消除HA带来的抑制作用。CMC对HA抑制的抗抑制机理在于，由于CMC的存在，有效的克服了磁力的影响。在静电斥力和位阻效应的作用下，纳米级Fe0颗粒不易发生团聚，呈现高度分散的状态，能维持巨大的表面积。除了减弱物理间相互作用外，CMC包裹在纳米级Fe0颗粒表面，阻止了ZVI表面高活性位点与周围的介质(溶解氧和水)反应。虽然表面钝化作用可能会阻止其与目标污染物反应，但由于颗粒的粒径很小，比表面积巨大，因此，处理效果比未稳定的ZVI颗粒好数倍。
　　 ⑷在制备纳米级Fe0过程中投加磁铁矿可以使纳米级零价铁附着在磁铁矿表面，从而阻碍铁颗粒的团聚，使其保持高度分散状态，维持其高反应性。结果表明，在本实验条件下，最适宜的Fe3O4：Fe0=10:1。Fe3O4稳定化纳米级Fe0在一定程度上也可以促进反应的进行，部分消除了HA带来的抑制作用。但Fe3O4稳定化纳米级Fe0抗抑制的机理与CMC稳定化纳米级Fe0是不同的。Fe3O4对HA抑制的抗抑制机理在于，一方面，纳米级Fe0附着在磁铁矿表面，从而使得纳米级Fe0颗粒不易发生团聚，呈现高度分散的状态，能维持巨大的表面积。另一方面，Fe3O4的加入解决了纳米级Fe0由于表面钝化而导致电子传递困难的问题，促进了Fe0表面的电子传递，从而使得Fe0的还原能力得到大幅度提高。

目录

文摘

英文文摘

RESUM

1 Literature review

1.I Research background and significance

1.1.1 Overview of groundwater pollution

1.1.2 Sources and harmfulness of heavy metals and chlorinated organic compounds in water

1.2 The treatment technology of Cr(Ⅵ)and chlorine-containing organic compounds in water

1.2.1 The treatment technology of Cr(Ⅵ)6

1.2.2 Treatment of chlorinated organic compounds

1.3 Development and limitations of the metallic reducing-remediation technology

1.3.1 The existence and nature of humic acid

1.3.2 Impact of Humic Acid on the dechlorination by zero-valent iron

1.3.3 Impacts of HA on Cr(Ⅵ)removal by zero-valent iron

1.4 Improvement of metallic reducing-remediation technology

1.4.3 The Progress of the CMC Applications

1.4.4 The application of CMC in the Preparation of nanoscale Fe0

1.4.5 Existence of Magnetite，Characteristics and applications

1.5 Choice of the present Topic

1.6 Conclusion of this chapter

2 Experimental part

2.1 Principles of the Experiments

2.1.1 The mechanism of the removal of Cr(Ⅵ)by zero-valent iron in wastewater water

2.1.2 Analysis of the mechanism of the catalytic reduction of 2，4-DCP by the bi-metallic

2.2 Main reagents and equipments of the experiment

2.2.1 Main experimental equipments

2.2.2 Main Experimental reagents

2.3 Experimental methods and devices

2.3.1 Preparation methods

2.3.2 The preparation of HA reserve Solution

2.3.3 Equipments of the batch reaction

2.4 Methods of Analysis

2.5 Characterization of iron filings and nanoscale Fe0 particles

2.6 Conclusion of this chapter

3 Impacts ofhumic acid on the removal of 2，4-DCP by nanoscale Pd/Fe and Ni/Fe

3.1 Impacts of Humic acid on the removal of 2，4-DCP by nanoscale Ni/Fe in water

3.1.1 The inhibition of HA to reductive dechlorination of nanoscale Ni-Fe

3.1.2 Impacts of HA dosage on the catalytic reductive-dechlorination by nanoscale Ni-Fe

3.2 Impacts of HA on the removal of 2，4-DCP by nanoscale Pd-Fe

3.2.1 Inhibition of nanoscale Pd-Fe catalytic reductive-dechlorination by HA

3.2.2 Impacts of HA dosage on the catalytic reductive-dechlorination by nanoscale Pd-Fe

3.2.3 Effects of Pd content on 2，4-DCP dechlorination in the presence of humic acid

3.2.4 Effects of NO3-on 2，4-DCP dechlorination in the presence of humic acid

3.3 Conclusion of this Chapter

4 Impacts of HA on the removal of the Cr(Ⅵ)by nanoscale Fe0

4.1 Impacts of HA on the removal of Cr(Ⅵ)by nanoscale Fe0

4.2 Effect of the initial Fe0 concentrations removal of Cr(Ⅵ)

4.3 Effect of the initial pH values on the removal of Cr(Ⅵ)

4.4 Effects of Cr(Ⅵ)concentrations removal of Cr(Ⅵ)

4.5 Effect of the reaction temperatures on the removal of Cr(Ⅵ)

4.6 Comparison of Fe0 type

4.7 Reduction mechanism of Cr(Ⅵ)

4.8 Impacts of p-benzoquinone on the reduction of Cr(Ⅵ)by nanoscale Fe0

4.9 Conclusion

5 Study of the coating mechanism on the agglomeration of nanoscale particles and HA on the surface area of nanoseale Fe0

5.1 The agglomeration of nanoseale particles

5.1.1 Behavior of the agglomeration of nanoscale Fe0 particles at micro-level

5.1.2 Behavior of the agglomeration of nanoNi-Fe at micro-level

5.2 Coating mechanism of HA on the surface area of nanoscale Fe0

5.3 Conclusion

6 Studies on the preparation，anti-inhibition effects of CMC and pollutants removal

6.1 Study on the preparation of CMC-Fe and pollutants removal

6.1.1 The preparation of stable nanoseale Fe0 by CMC

6.1.2 Impacts of CMC dosage on the removal efficiency by nanoscale Fe0

6.2 Study on the anti-inhibitory effects of CMC on the inhibition by HA

6.2.1 Effects of different concentrations of CMC on the elimination of the inhibition by HA

6.2.2 Effects of CMC on the elimination of HA inhibition

6.2.3 The analysis of the mechanism of the HA anti-inhibition by CMC

6.3 Conclusion

7 Studies on the preparation，anti-inhibition effects of Fe3O4-nanoscale Fe0 and pollutants removal

7.1 Study of the preparation of Fe3O4-nanoscale Fe0 and the pollutants removal

7.1.1 The preparation of Fe3O4-nanoscale Fe0

7.1.2 Comparison of chromium removal results Fe0 different systems

7.1.3 Impacts of magnetite dosage on the nano-Fe0 reactivity

7.1.4 Impacts of the initial pH value

7.1.5 Impacts of the temperature

7.2 Study on the anti-inhibitory effects of Fe3O4 on the inhibition by HA

7.2.1 Effects of different dosages of Fe3O4 on the elimination of HA inhibition

7.2.2 Fe3O4 versus the elimination of the HA inhibition

7.2.3 The analysis of the mechanism of the HA anti-inhibition by Fe3O4

7.3 Conclusion

8 Conclusion and prospects

8.1 Conclusion

8.2 Innovation points

8.3 Prospects

References

Presentation of the Candidate

Acknowledgments