典型原生高砷地区砷暴露及其吸附去除机理研究
文献类型：学位论文
| 作者 | 崔金立 |
| 学位类别 | 博士 |
| 答辩日期 | 2014-11 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 景传勇 |
| 关键词 | 高砷地下水，健康风险，砷吸附，同步辐射，微界面，TiO2， geogenic groundwater arsenic, health risk, arsenic removel, synchrotron, micro-interface, TiO2 |
| 其他题名 | Arsenic Exposure in Typical Geogenic Areas and its Adsorptive Removal Mechanism |
| 学位专业 | 环境科学 |
| 中文摘要 | 砷是毒性极强的类金属元素，含砷地下水（> 10 μg/L）是世界范围内亟待解决的环境问题。长期饮用高砷水会引发癌症等疾病，因此如何高效去除地下水中砷已成为环境领域的研究热点与难点，也是本研究拟解决的关键科学问题。本研究目的在于通过调查分析典型原生高砷地区环境及人体样品中砷含量，评估砷暴露对当地人群构成的健康风险，进而研发新型高效除砷材料，并从分子水平阐明砷的微界面去除机理。本研究建立的高效砷去除方法为原生高砷地区饮用水安全提供了新的解决思路，具有重要的环境意义和社会意义。 首先，本文对比研究了环境中砷浓度与人体砷浓度的关系，分析结果表明原生高砷地区 77%的地下水（n=131）、92%的蔬菜（n=120）及 32%的粮食（n=32）样品砷浓度超出国家标准；70%的尿液（n=99）、76%的指甲（n=176）和 62%的头发（n=61）样品砷浓度超出背景值。当地居民日均砷摄入量与尿液、指甲及头发砷浓度呈现出显著的正相关性(p均小于 0.01)，表明砷摄入会造成人体内砷累积。基于同步辐射的微区 X射线荧光分析（μ-XRF）结果表明指甲横断面中砷主要分布在内外两侧。微区 X射线近边吸收结构（μ-XANES）光谱表明指甲和头发中砷主要与硫结合，证明砷易富集于含巯基的角质层。基于日均砷摄入量的健康风险评估表明地下水砷暴露已对当地人群构成较高的致癌风险，高砷地下水亟待治理。 其次，本研究比较了铁盐与聚合铁盐絮凝法去除地下水中砷，并评估了铁盐絮凝的可行性及安全性。试验在山西山阴县现场，集成了次氯酸氧化、铁盐絮凝、直接过滤及活性炭深度处理相结合的工艺。结果表明此工艺在 5个循环中能持续提供~75倍床体积（~500 L）的安全饮用水。XANES结果表明铁盐和聚合铁盐的絮凝产物中主要成分均为水铁矿。扩展 X射线吸附精细结构（EXAFS）结果证明砷主要以双齿双核结构吸附于原位生成的水铁矿上，而不是与三价铁离子形成 FeAsO4沉淀。毒性滤出实验表明两种絮凝残渣滤液中砷浓度（0.9 μg/L-0.487mg/L）远低于危险固体废物的限定值（5 mg/L）。聚合铁盐因其除砷效果较好且残渣量较少，在地下水砷去除中优于铁盐。然而砷去除过程中产生的残渣在长期物理化学及生物作用下会缓慢释放砷，这仍将造成潜在的环境威胁。 再次，为了克服传统絮凝法存在的缺陷，本研究合成了 TiO2颗粒除砷材料。该TiO2颗粒可再生循环使用，在地下水除砷过程中不产生残渣等二次污染。实验表明地下水中共存钙/镁离子促进了 As(V)在TiO2颗粒上的吸附，吸附量分别提高了 37%和 42%；但对 As(III)的吸附影响不大。硅酸根的存在使 As(V)和As(III)的吸附量分别降低了 57%和 50%。共存碳酸氢根使 As(V)的吸附量降低了52%，但对 As(III)影响不大，只降低了 8%。将 TiO2颗粒用于高砷地区快速小柱实验，结果表明当地下水中砷浓度为 700 μg/L，空床接触时间为 1.08 min时，进水968倍柱体积后出水砷浓度达到 10 μg/L，此时砷吸附量为 0.96 mg/g。应用地球化学模拟软件 HREEQC，结合砷及共存离子在固液微界面上的吸附结构，较好地模拟了地下水中砷在小柱中的穿透曲线，实现了电荷分配多位络合模型（CD-MUSIC）及一维反应迁移模块的有效结合。同时设计了装载 TiO2颗粒的小型家用滤水壶，可为当地居民持续提供安全饮用水。 最后，本研究针对某些高砷地区地下水中砷氟复合污染的问题，本以活性炭为载体，负载 TiO2与镧化合物制备得到复合吸附材料（TLAC），实现了砷氟共同去除的目的。吸附等温线、吸附动力学和 pH边等实验结果均表明TLAC对砷氟有较高的吸附容量，效果明显优于传统铁和铝基吸附剂。同步辐射μ-XRF表明钛和镧均匀分布于活性炭表面。EXAFS结果表明砷选择性地吸附于TiO2上，砷钛原子间距为 3.34 Å，证明砷在 TiO2表面形成稳定的双齿双核络合结构，该结构不受共存氟离子的影响。吸附实验和红外光谱分析证明氟选择性地吸附于镧氧化物上。由于砷与氟在 TLAC表面的吸附位点不同，该材料可实现砷氟共同去除。CD-MUSIC模型综合微界面分析出的吸附结构，较好地模拟了砷氟的吸附曲线，实现了宏观实验和微界面吸附构型的有效结合。综上表明，TLAC吸附材料可同时去除地下水中砷和氟，在砷氟复合污染地区有广泛的应用前景。 |
| 英文摘要 | As a much toxic metallic element, elevated geogenic arsenic (As) in groundwater(>10 μg/L) has becoming an urgent environmental problem in the world. Chronic exposure to As can lead to many diseases including cancer, thus groundwater As treatment has attracted worldwide interest. Our key objective is to: 1) estimate the health risk from As exposure in typical geogenic areas by analyzing the relevance between As contaminated environmental samples and As content in human body; 2)develop novel materials to remove groundwater As efficiently, and illustrate its micro-interfacial removal mechanism on molecular level. This study provided a practical method to supply As-safe drinking water, which is of great environmental and social significance. Firstly, we compared As levels in environmental samples and human biomarkers.The results indicated 77% of groundwater (n=131), 92% of vegetables (n=120), and 32% of cereals (n=25) samples contained higher As levels than the national standards. Furthermore, 70% of urine (n=99), 76% of nails (n=176), and 62% of hair (n=61) samples exhibited higher As concentrations than the acceptable levels. The average As daily dose is positively correlated with As concentrations in urine, nails, and hair,suggesting As exposure induced its accumulation in human body. The synchrotron based μ-XRF indicated a three-layer distribution of As in nail section. μ-XANES analysis suggested that As was mainly associated with sulfur in nails and hair,confirming As is easier to be accumulated in keratin rich with sulfhydryl groups.Health risk assessment based on As ingestion demonstrated As exposure has resulted in a high cancer risk. Thus, groundwater As contamination earns urgent remediation. Secondly, since coagulation is widely used in As remediation, we employed mono- and poly-ferric salts to remove As, and evaluated its feasibility and security.The results confirmed that coagulation with ferric salts in two-bucket filtration system can supply ~500 L As safe drinking water in 5 cycles. Fe k-edge XANES analysis indicated ferrihydrite dominated in the coagulated solid residue from the two ferric salts. As k-edge EXAFS analysis indicated As formed a bidentate binuclear complexon the in situ formed ferrihydrite, with no observation of FeAsO4 precipitate.Leachate As (0.9 μg/L- 0.487 mg/L) was observed from the residue using three leaching tests, which is much lower than the EPA regulatory limit (5 mg/L).Poly-ferric salt is superior to ferric salt because of its lower dose, much lower solid residue, and lower cost for As-safe drinking water. However, the residue is a potential threat because of As leaching during long disposal time. Thirdly, to overcome the disadvantages of coagulation method, we synthesized granular TiO2 (GTiO2) to remediate groundwater As in geogenic areas. The spent GTiO2 media can be regenerated and reused with no secondary pollution in groundwater As remediation. A coexisting ion effect study showed that Ca2+ and Mg2+ enhanced As(V) adsorption on GTiO2 by 37% and 42%, respectively, whereas no significant impact was observed on As(III). Silicate substantially decreased As(V) adsorption by 57% and As(III) by 50%. HCO3- remarkably inhibited As(V) adsorption by 52%, whereas it slightly reduced As(III) adsorption by 8%. Field column results demonstrated that ~700 μg/L As was removed at an empty bed contact time (EBCT)of 1.08 min for 968 bed volumes before effluent As concentration exceeded 10 μg/L,corresponding to 0.96 mg As/g GTiO2. The column tests with systematic variation of EBCTs were successfully simulated using PHREEQC incorporating a charge distribution multi-site complexation (CD-MUSIC) model and one-dimensional reactive transport block, integrating the micro-interficial adsorption structures. The household filters loaded with GTiO2 can continually supply As safe drinking water. Finaly, according to our survey, coexisting As and fluoride (F) in groundwater prevail in some areas. Thus, we fabricated a novel material to simultaneously remove As and F. The bifunctional material is composed of titanium and lanthanum oxides impregnated on granular activated carbon (TLAC). Adsorption isotherms, kinetis, and pH edge results indicated TLAC exhibits higher adsorption capacity than the commercially available iron- and aluminum based adsorbents. μ-XRF analysis demonstrated that La and Ti were homogeneously distributed on TLAC. EXAFS spectroscopic results suggested that As(V) formed bidentate binuclear surface complex as evidenced by an averaged Ti-As bond distance of 3.34 Å in the presence of F. Adsorption tests and Fourier transform infrared spectroscopy analysis indicated that F was selectively adsorbed on lanthanum oxides. The surface configurations constrained with the spectroscopic results were formulated in the CD-MUSIC model to well describe the adsorption behaviors of As(V) and F. The results indicated that TLAC can be used as an effective adsorbent for simultaneous removal of As(V) and F in the complex pollution areas. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34120]  |
| 专题 | 生态环境研究中心_环境化学与生态毒理学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 崔金立. 典型原生高砷地区砷暴露及其吸附去除机理研究[D]. 北京. 中国科学院研究生院. 2014. |
入库方式： OAI收割
来源：生态环境研究中心
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