【作者】 纳曼；

【导师】 徐新华；

【作者基本信息】 浙江大学 ， 环境工程， 2010， 博士

【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硝-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：(1)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。(2)HA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。(3)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。(4)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。更多还原

【Abstract】 At the turn of the 21 century, through an increase of the world population and rapid economic development, China is facing considerable crisis in water sources and quality. Especially critical is the increased crisis of water quality.China has serious water pollution problems in both groundwater and surface water. Cr(VI) is largely used in tanneries, printing, dyeing, production of colorants, electroplating etc. It is a common pollutant which exists in nature. Organochlorine compounds in manufacturing industries, cleaning industries; organic solvents, pesticides, herbicides producing industries and some chemical productions are used in great quantities leading to a large discharge of products containing chlorine. Many surface waters and groundwaters face the problem of organochlorine compound pollutions. Therefore, treatments of water containing organochlorine compounds and heavy metals are of great interest.Since Scholars proposed the possibility of using metallic iron filings to remediate underground water, the use of Fe0 for underground water pollutants remediation became a very active domain of research. Since zero valent iron is characterized by cheap price, a high reductive and rapid speed reaction; it became one of the most effective materials in remediating underground water sources. So far, zero valent iron is largely used in the treatments and purification of chlorine containing organic matters, nitrogenous organic compounds, heavy metals and other pollutants. But due to the existence of different materials in underground water such as humic acid, hard ions etc, the removal and elimination of chlorine would be affected. Therefore, in this research nano-scale iron and nano-scale Ni-Fe and Pd-Fe bimetallic particles were the main tools for remediation of polluted water containing hexavalent chromium and 2,4 DCP. Besides, investigations were emphatically done on the inhibition due to the existence of humic acid (HA) against the reductive removal of zero valent iron (ZVI). Initially, we dealt with the mechanism of ZVI remediation inhibition by HA. Through our experiments, we investigated methods of overcoming the ZVI remediation inhibition by HA and those opposing to the inhibition mechanism. Results showed the following:(1) The effect of humic acid on the catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics inhibition was obvious and that inhibition was shown when one reached the low concentration 5 mg L"1 of Humic acid. The inhibition of the catalytic reductive dechlorination of 2,4-DCP follows the addition of HA. As quantities of HA were increasing, the results were getting better. The reason why humic acid can inhibite catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics is that it can be adsorbed on the surface area of particles of bimetallic Pd-Fe and Ni-Fe and then reduces the reactivities of particles preventing the evolution of the reaction. When HA exists, factors influencing the results of the catalytic reductive dechlorination by nanoscale Pd-Fe and nanoscale Ni-Fe bimetallics are:doses of HA, pH, nickel ration, nanoscale Ni-Fe dosage and the reaction temperature. The experimental results showed that larger nickel ratio, a lower pH, higher nanoscale Ni-Fe dosage and higher reaction temperature are favorable to dechlorination reaction. The dechlorination efficiency has only little to do with the initial concentration of 2,4-DCP. When HA exists, the nanoscale Pd-Fe and nanoscale Ni-Fe bimetallic catalystic reductive dechlorination kinetics model can be described as a first order reaction kinetics. When computing the catalystic dechloriantion of 2,4-DCP by nanoscale Pd-Fe in our experiments, we found that HA dosages have linear relationship with reaction rates. When HA dosages increased, the reaction rates also increased, and with the HA dosages increasing, the reaction rate constants decreased linearly.(2) HA’s inhibiting effect on the nano-scale zero-valent iron to remove Cr(VI) reaction is obvious, and this trend became remarkable with the concentration of HA increasing. However when the concentration of HA reaches a certain extent, this trend is no longer obvious. The mechanism of HA on the nano-scale zero-valent iron to remove Cr(VI) is double:on one hand, humic acid would be adsorbed on the nano-scale zero-valent iron surfaces, occupying their active surfaces leading to the inhibition of the reaction. On the other hand, the humic acid in solution also can be used as electron transport bodies (Media of electrons transfer) to promote the reaction.(3) Adding stabilizer CMC in the preparation of nanoscale Fe0 could prevent from the agglomeration of nanoscale particles, and maintain them at a high degree of dispersion, and then maintain their high reactivity. CMC stabilized nanoscale Fe0 at a certain extent, can promote the remediation reaction, and eliminate the inhibitory effect brought by HA. When the HA is 40 mg L-1, add 0.5 g L-1 of CMC, the removal efficiency of Cr(VI) increased from 49.1% to 78.6%, the value is very close to 82.65% when there is no HA. This indicated that in the preparation of nanoscale Fe0, add stabilizer CMC can eliminate the inhibition due to the presence of HA to some extent. The anti-inhibition mechanism of CMC to HA’s inhibition is that the existence of CMC overcomes the effects of magnetism. Under the effect of electrostatic repulsion and steric hindrance, nanoscale Fe0 particles cannot agglomerate easily, but maintain a highly decentralized state which can maintain biggest surface areas. Besides weakening the physical interaction, CMC can wrap the surface of nanoscale Fe0 particles, and that can inhibit the reaction between high active sites of ZVI’s surface and surrounding media (dissolved oxygen and water). Although the surface passivation may prevent particles’reactions with the target pollutants, however, the particle sizes are very small and specific surface areas are huge, so the treatment efficiencies are several times better than unstabilized ZVI particles.(4) In the preparation process of nanoscale Fe0, adding some magnetite can provoke the adhesion of nano-scale zero-valent iron to the magnetite surfaces. Therefore, they would prevent iron particles from agglomerating, so it can hold them at a high degree of dispersed state in order to maintain their high reactivity. In our experimental conditions, results showed that the most appropriate efficiency of Fe3O4 and Fe0 was 10:1.Stabilized nanoscale Fe0 by Fe3O4 can also promote the reaction to some extent, and eliminate the inhibitory effect brought by HA. However, anti-inhibition mechanisms of Stabilized nanoscale Fe0 by Fe3O4 and Stabilized nanoscale Fe0 by CMC are different. The anti-inhibition mechanism of Fe3O4 to HA is, on the one hand, nanoscale Fe0 attached to magnetite surfaces make it difficult to agglomerate for Fe0 particles showing a high dispersion state. On the other hand, the addition of Fe3O4 solved problems of electron transfers due to the surface passivation of Fe0 promoting the electron transfer on the surface of Fe0, and allowing the increase of Fe0 reduction capacity.更多还原