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微生物矿化修复煤矿区铀污染环境
热合曼江·吾甫尔
学位类型博士
导师潘响亮
2016
学位授予单位中国科学院大学
学位授予地点北京
学位专业生态学
关键词Clostridium Sp. Pxl2 生物源fe(Iii) 氧化物 微生物诱导fe(Iii) 氧化物共沉淀法 Halomonas Sp. Sbc20 微生物诱导碳酸钙共沉淀法(micp)
摘要近年来,铀污染问题越来越受到人们的关注。根据报道,新疆伊犁煤矿区,煤炭伴有铀含量较高,煤炭开采、运输及使用等过程造成局部土壤中天然铀总α 放射性强度明显增高(安惠民等,1982)。我们经过实地调查、采样,对煤矿区居民头发和尿液进行U(VI) 污染分析,确定了该煤矿区U(VI) 污染水平;在此基础上,以煤矿区地下水和煤灰作为修复对象,分别采用微生物诱导Fe(III) 氧化物共沉淀法和微生物诱导碳酸钙共沉淀法(MICP),在U(VI) 污染特殊环境中U(VI) 固化的可行性方面进行了研究。 首先选择Fe(II) 氧化反硝化菌(AFODN)Clostridium sp. PXL2 制备生物源Fe(III) 氧化物,研究了生物源Fe(III) 氧化物和化学合成Fe(III) 氧化物对U(VI) 的吸附特征。SEM-EDX 分析显示:生物源和化学合成的Fe(III) 氧化物均为无定型晶体形貌。SRD 分析结果确认了这两种Fe(III) 氧化物的主要成分均为水铁矿。电位滴定实验结果表明:与化学合成Fe(III) 氧化物相比,生物源Fe(III) 氧化物表面含有更多的结合点位和官能团类型,它们可能参与U(VI) 的吸附过程,并与Fe(III) 氧化物竞争吸附U(VI)。热力学实验(ITC)结果表明,两种Fe(III) 氧化物吸附U(VI) 是自发进行的放热过程。化学合成和生物源Fe(III) 氧化物吸附U(VI) 的等温吸附,经Langmuir 方程拟合计算得出最大吸附容量分别为8.788 mg/g和7.898 mg/g,经Freundlich 方程拟合计算得出吸附U(VI) 的难易度(1/n)分别为0.658和0.380;结果说明生物源Fe(III) 氧化物对U(VI) 的吸附容量略低于化学合成Fe(III) 氧化物,但是生物源Fe(III) 氧化物更容易吸附U(VI)。随着盐度和pH 值(4-7)的增加,生物源和化学合成的Fe(III) 氧化物对U(VI) 的去除率均出现增加趋势;这是由于U(VI) 与OH- 和Cl- 分别形成 (UO2)3(OH)5+ 和 UO2Cl42- 等配合物,这些配合物能够更有效的被Fe(III) 氧化物所吸附。两种Fe(III) 氧化物的等电点(pHpzc)结果显示,U(VI) 被这两种Fe(III) 氧化物的吸附属于静电吸引作用。 在以上工作的基础上,进一步将Clostridium sp. PXL2 应用到地下水中U(VI) 和NO3- 的同步修复上。地下水样品中,与酸性(pH 5.5)环境相比,在中性条件下,因细菌具有更好的生长能力和对Fe(II) 的较易氧化特点,可以得到较高的U(VI) 去除率(75.1%)和硝酸盐去除率(55.7%)。将这些地下水样品暴露于好氧条件下2 h ,结果导致Fe(II) 和U(VI) 浓度迅速下降,但未引起硝酸盐和亚硝酸盐浓度的显著改变。增加初始Fe(II) 浓度,进一步提高了U(VI) 的去除率(84.5%),但降低了硝酸盐的去除率。此外,腐殖酸钠和碳酸钠的加入在不同程度上抑制U(VI) 的去除和硝酸盐的还原。SEM-EDS分析表明,U(VI) 是由梭状芽胞杆菌PXL2 产生的非晶态Fe(III) 氧化物的吸附而得到固化的。 另外,选择具有脲酶产生功能的中度嗜盐菌 Halomonas sp. SBC20,研究了其对CaCO3 沉淀形成和U(VI) 去除的影响。QCM 实验结果表明,CaCO3 沉积量和U(VI) 去除率随EPS 浓度的增加出现下降趋势;此现象说明:EPS 中的有机质与Ca2+ 形成较强的络合物,抑制了CaCO3 沉淀的形成以及U(VI) 的去除。SEM-EDX 分析表明:与对照体系相比,在EPS 参与下形成的CaCO3 沉积物晶体结构存在缺陷;进一步说明了EPS 中的有机质与Ca2+ 形成了较强的络合物,并抑制了CaCO3 沉淀的形成。EEM 实验分析得到EPS 中的类蛋白物质峰A 和峰C 与Ca2+ 的络合常数分别为2.37 和2.13,结果显示该菌 EPS与Ca2+ 具有较强的络合能力。热力学(ITC)实验结果显示,Ca2+ 主要与EPS 当中的羧基和磷酰基形成圈内络合物,是个自发进行的放热过程。 最后,将Halomonas sp. SBC20 应用到煤灰中U(VI) 的固定实验中。经过3 个星期的培育之后,未加入菌液的对照煤灰砖样本中只有6.67% 的U(VI) 被固定;而在加入Halomonas sp. SBC20的煤灰砖样本中95.8% 的可交换态U(VI) 得到了固定。随着CaCl2 加入量的增加,抗压强度总体增强。然而,高浓度(50、80 mM)CaCl2 的加入导致煤灰砖中U(VI) 浸出浓度的提高。随着菌液浓度(OD600)的增加,抗压强度总体上出现加强趋势,这与浸出液中U(VI) 浓度的降低趋势是基本一致的。高比例(>2%)刺激因子A 加入量均不利于煤灰中U(VI) 的固定。模拟极端气候的稳定性,实验结果表明:生物修复后的煤灰砖能够承受高低温度频繁变化的极端天气。然而,高低温度频繁变化所引起的融雪等因素在一定程度上不利于煤灰砖中U(VI) 固定体系的稳定。FTIR、XRD 和SEM-EDX 等分析结果确认:MICP 是煤灰砖中CaCO3 沉淀形成和U(VI) 固定的主要过程。
其他摘要In recent years, uranium pollution has gained much attention. According to reports, high concentration of uranium was released into the soil resulted from the coal mining in Yili region, Xinjiang thus increasing the radioactivity level of the surrounding area (An Huimin et al, 1982). The aim of the present work is to investigate the on-site level of uranium in this coal mining area and U(VI) remediation by microbially induced Fe(III) oxide precipitation and microbially induced calcium carbonate precipitation (MICP). The comparative studies of U(VI) adsorption by synthetic Fe(III) oxide and biogenic Fe(III) oxide produced by Clostridium sp. PXL2 was investigated. SEM-EDX analysis showed that synthesis and biogenic Fe(III) oxides both were amorphous. SRD analysis confirmed that the main components of both Fe (III) oxides are ferrihydrite. The acid-base titration data have shown that there were more biding sites and functional groups such as carboxyl, sulfydryl, phosphoryl groups on the surface of biogenic Fe(III) oxide which might be involved in U(VI) adsorption resulting in the occupation of these binding sites by U(VI) ions.ITC data showed that U(VI) adsorption by both Fe(III) oxides is a spontaneous and exothermic process. Isotherm data of U(VI) adsorption for both synthetic and biogenic Fe(III) oxides was well fitted with both Langmuir and Freundlich equation. By calculation, the maximum U(VI) adsorption capacity was 8.788 and 7.898 mg/g, and U(VI) adsorption difficulty constant (1/n) was 0.658 and 0.380 for synthetic and biogenic Fe(III) oxides, respectively, implying that biogenic Fe(III) oxide has slightly lower U(VI) capacity than synthetic Fe(III) oxide, but more easily adsorbs U(VI) than synthetic Fe(III) oxide. With the increase in the salinity and pH (4-7), rate of U(VI) removal by both types of Fe(III) oxides increased due to the formation of (UO2)3(OH)5+ and UO2Cl42-, which can be more effectively adsorbed by both Fe(III) oxides. The point of zero charge of these two types of Fe(III) oxides suggested that the U(VI) adsorption process by these Fe(III) oxides belongs to electrostatic attraction. Further, Clostridium sp. PLX2 was applied to remediate both U(VI) and NO3- in groundwater simultaneously. U(VI) immobilization and nitrate reduction rates in groundwater samples inoculated with this bacterium reached up to 75.1% and 55.7% respectively, under neutral condition. Increasing the initial Fe(II) concentration resulted in the further increase of U(VI) immobilization (84.5%), however reduced nitrate reduction. Addition of sodium humate and sodium carbonate suppressed U(VI) immobilization and nitrate reduction to varying degrees. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) showed that U(VI) immobilization was mainly due to sorption to amorphous ferric oxides. In addition, urease-producing bacteria Halomonas sp. SBC20 was chosen to study its effect on CaCO3 formation and U(VI) removal. QCM results showed that CaCO3 precipitation and U(VI) removal decreased as the concentration of EPS increased explaining that the organic substances in EPS formed strong complexes with Ca2+ ions inhibiting CaCO3 precipitation and U(VI) removal. SEM-EDX analysis showed that CaCO3 sediments formed with EPS participation had crystal structure defects compared to the control CaCO3 sediments without EPS further explaining that the involvement of EPS Inhibited the CaCO3 precipitation process. EEM test results showed that complexation constants for peak A and peak C (protein substances in EPS) with Ca2+ ions were 2.37 and 2.13 respectively, meaning that bacterial EPS has strong complexation ability with Ca2+. ITC results indicated that Ca2+ ions mainly interact with carboxyl and phosphoryl groups as inner-sphere complexes on EPS molecules. The complexation is a spontaneous and exothermic process. Last, Halomonas sp. SBC20 bacterium was applied to immobilize U(VI) in coal ash. After 3 weeks of incubation, 95.8 % of exchangeable U(VI) in bacterially treated coal ash bricks was immobilized while only 6.67 % was immobilized in the control bricks. With the increase in the initial concentration of CaCl2, the compressive strength intensified as a whole. However, higher concentrations up to 50 and 80 mM CaCl2 led to the increase in the leaching of U(VI) concentration. With the increase of cell concentration (OD600), the compressive strength generally intensified which was in consistent with the decrease in U(VI) concentrations released from the bricks. Addition of high percentage stimulating factor A (>2%) was not good for the U(VI) immobilization in coal ash bricks. Emulation test of extreme weather conditions showed that the bioimmobilized coal ash bricks were able to withstand extreme weather conditions during high and low temperatures. However, other factors such as snowmelt caused by frequent changes in high and low temperatures led to the decrease of compressive strength and increase of U(VI) mobility in coal ash bricks. FTIR, XRD and SEM-EDX analysis confirmed the role of MICP on CaCO3 precipitation and U(VI) immobilization. Key Words: Clostridium sp. PXL2, biogenic Fe(III) oxide, microbially-induced Fe(III) oxide precipitation, Halomonas sp. SBC20, microbially-induced calcium carbonate precipitation (MICP)
学科领域生态学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14745
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
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热合曼江·吾甫尔. 微生物矿化修复煤矿区铀污染环境[D]. 北京. 中国科学院大学,2016.
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