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题名: 粘土矿物促使土壤中多环芳烃(PAHs)非生物转化过程及其机理研究
作者: 李莉
答辩日期: 2014-05-26
导师: 王传义
专业: 材料工程
授予单位: 中国科学院大学
授予地点: 北京
学位: 硕士
关键词: 多环芳烃 ; 粘土矿物 ; 非生物转化 ; 土壤有机质 ; 有机酸
摘要: 多环芳烃(PAHs)是一种典型的持久性有毒物质,具有致畸、致癌、致突变的“三致”效应,对生态环境和人类身体健康产生严重危害而引起人们的广泛关注。土壤是PAHs的积蓄库,汇集在土壤中的PAHs进行着生物转化和非生物转化。生物转化主要是微生物对PAHs的降解过程,非生物转化过程主要包括非光照条件下的化学氧化过程和可见光下的光催化转化过程,而土壤中粘土矿物对上述两个过程均表现出较高的催化活性,同时土壤中的有机质和有机酸对PAHs的转归也起到了重要作用。因此,本文主要研究了PAHs在粘土矿物表面不经光照的化学氧化过程和光照下的光催化氧化过程及土壤有机质和有机酸对PAHs光催化过程的影响。得到的结论如下:
1. 化学氧化反应在不经光照、相对湿度为8%的条件下进行时,PAHs的转化反应主要受粘土特性和反应条件的影响。不同类型粘土(蒙脱土、高岭土、伊利石、叶腊石)对蒽的化学氧化的速率也有很大区别,在反应时间5天内,蒙脱土能降解90%以上的蒽,而其他粘土几乎不能降解蒽,这与粘土的阳离子交换量及电荷特性有关系。而反应条件如相对湿度和pH值也会影响PAHs的转化,随着相对湿度的增大,水分子和PAHs分子竞争活性位点而使反应速率降低;而随着pH值的增大,层间三价铁离子逐渐被羟基化,蒙脱土层间以Fe3+形式存在的三价铁含量越来越少,因此降解速率变慢。
2. PAHs分子的反应活性与其本身的离域能也存在很大关系,离域能越大,反应速率越快,但是两者之间不存在线性关系。PAHs蒽在蒙脱土表面的最终降解产物是蒽醌,蒽醌相比于蒽毒性降低且更易生物降解。反应的主要机理是1)PAHs分子和层间金属离子形成cation-π键;2)电子转移形成阳离子自由基;3)化学吸附的氧气参加反应并形成最终产物。
3. 可见光下,不同离子改性的蒙脱土对菲的降解速率的关系为:Fe3+ > Cu2+ > Ca2+ > K+ > Na+,而对于Fe3+改性的不同类型粘土来说,降解速率为:蒙脱土>蛭石>高岭石,这与可交换性铁含量有关系,反应机理为类Fenton反应。
4. 土壤有机质不同组分对PAHs降解的影响不同,对于胡敏酸和富里酸来说,胡敏酸和富里酸的加入量存在临界值,分别为0.6465 mg/g和0.7035 mg/g。当加入量小于临界值时促进了菲的降解而加入量大于临界值时则会抑制降解反应的进行。对于DOM来说,它的加入对PAHs降解的影响不大。
5. 不同的有机酸对光催化效果的影响不同。草酸和苹果酸的加入促进了PAHs在粘土矿物表面的降解,而EDTA和氨三乙酸的加入强烈抑制了反应的发生。苹果酸和草酸促进反应的发生主要是由于其加入在开始步骤会吸收光子生成C2O4−•,酸根离子和三价铁的络合使得生成Fe(II)的速率加快,而Fe(II)的生成步骤是整个光Fenton反应的决速步骤。结果也显示降解速率与Fe(II)的生成量呈正相关。
英文摘要: Polycyclic aromatic hydrocarbons (PAHs), a group of typical persistent toxic substances, have attracted more and more attention due to their high degree of eareinogenieity,teratogenieity and mutagenicity. PAHs are harmful to human health and environment. Soil is considered as a major environmental reservoir for PAHs due to its high storage capacity. PAHs in soil undergo abiotic and biotic transformation. Biotic transformation mainly is conducted by the degrading strains, while abiotic transformation mainly includes chemical oxidiation and photocatalysis. Clay minerals, soil organic matter (SOM) and organic acid are all reactive soil compontens and play important role in the fate and transformation of PAHs in the soil environment. In the present study, we focus our attention on the chemical oxidiation without light ,photocatalysis under visible light and the effects of SOM fractions and organic acid on photocatalysis. The main conclusions of the thesis will be shown as following: Firstly, chemical oxidiation reaction is conducted without light under relatilvely humidity(RH). The reaction is affected mainly by the physichemical properities of clay minerals and environmental factors. The rate of anthracene transformation follows the order: Fe-smectite >> Cu-smectite > Al-smectite ≈ Ca-smectite ≈ Mg-smectite ≈ Na-smectite. Among Fe(III)-saturated clays, Fe(III)-smectite exhibits the highest catalytic activity followed by Fe(III)-illite, Fe(III)-pyrophyllite and Fe(III)-kaolinite, which is in agreement with the interlayer Fe(III) content. Moreover, effects by two common environmental factors, pH and relative humidity (RH), were evaluated. With increase in pH or RH, the rate of anthracene transformation decreases rapidly at first, and then is leveled off. Secondly, the reactivity of PAHs molecule is related to the IP. The final product of anthracene transformation is anthraquinon, a more bioavailable molecule compared to anthracene. The transformation process mainly involves cation-π bonding, electron transfer leading to cation radical, and further oxidation by chemisorbed O2. Thirdly, under visible light, for five types of cation-modified smectite clays, the photodegradation rates of phenanthrene follow the order: Fe3+ > Cu2+ >> Ca2+ > K+ > Na+, which is explained in terms of photo-Fenton-like catalysis. To further inspect the effect of clay type, additional two types of clays were paralleled. Among three types of Fe(III)-modified clays, Fe(III)-smectite shows the highest photodegradation rate followed by Fe(III)-vermiculite and Fe(III)-kaolinite. Fouthly, SOM fractions including dissolved organic matter (DOM), humic acid (HA), and fulvic acid (FA), showed different effect on the degradation of phenanthrene. A critic content is observed with FA (0.70 mg/g) and HA (0.65 mg/g). Before reaching the critic content, the removal of phenanthrene is accelerated; while after that, the photodegradation rate is suppressed. However, DOM showed negligible influence on the degradation process. Fifthly, anthracene degradation was promoted by the addition of malic acid and oxalic acid, while it was inhibited with EDTA and NTA. For Fe(III)-smectite–malic, citric, EDTA, NTA complex systems, pKa1 and redox potential have positive effect on the degradation rate. However, Fe(III)-smectite–oxalic acid complex system, though with low pKa1 and redox potential, showed high catalytic effect. This may attribute to the fact that Fe(C2O4)2- and Fe(C2O4)33- are much more efficiently photolyzed and the formation of Fe(II) and active reaction intermediates is faster in the presence of oxalaic acid.
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/3413
Appears in Collections:环境科学与技术研究室_学位论文

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作者单位: 中国科学院新疆理化技术研究所

Recommended Citation:
李莉. 粘土矿物促使土壤中多环芳烃(PAHs)非生物转化过程及其机理研究[D]. 北京. 中国科学院大学. 2014.
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