研究生知识库

铊（Thallium, Tl）是国际上13种优先重视的金属污染物之一，在自然界中存在一价和三价两种价态，其化合物具有剧毒性。铊在地壳中含量低，常与其他矿物伴生存在，在众多含铊矿石中，铅锌矿是铊的主要来源，伴随其采矿、选矿和冶炼等工业活动过程，铊未能回收利用而直接进入采选冶固体废物、废水和废气中，在表生环境迁移、扩散与富集，产生铊环境污染及健康危害。而国内外对此问题的基础性研究还很不足，主要体现在：（1）铊价态测试方法不成熟，对水体铊价态转化和迁移机制的研究欠缺；（2）铅锌矿采选冶生产环节和环境介质（土壤、水体及冶选废弃物等）中铊的迁移转化规律的认识不明晰；（3）对铅锌冶选废物中铊的环境地球化学和生物地球化学行为的研究也较为缺乏。基于此，本论文选取了集采、选、冶为一体的云南兰坪金顶铅锌矿为研究区，系统采集了金顶矿区各生产环节主要排污节点样品，以及水、沉积物、悬浮物和土壤样品。通过元素分析、赋存形态分析、价态分析、风险评价分析和微生物群落分析等手段，研究了铊在铅锌矿采、选、冶过程中的迁移转化规律，查明了铅锌矿生产过程的主要排污节点和主要污染物的性质；通过研究铊在矿区水体中的污染特征和赋存形态，探讨了铊在水环境中的迁移转化规律和生态风险；同时，通过研究铊在土壤中的空间分布规律和时间累积效应，探讨了土壤中铊的污染来源和生态风险；我们还研究了冶选废物中铊的环境地球化学和微生物地球化学行为，并探讨含铊固体废弃物胁迫下的微生物响应效应和作用机制。获得以下研究认识：（1）开发了一种新的铊的分离测试方法。该方法基于固相萃取技术，利用DTPA与Tl3+形成稳定的阴离子络合物，防止Tl3+的还原，并利用AG1-X8阴离子树脂作为吸附剂，选择性吸附Tl3+而达到Tl3+和Tl+分离的目的。通过对不同 Tl+和Tl3+浓度比、不同pH和复杂溶液基质的结果对比验证，显示该方法标准溶液回收率误差均小于±10%，方法切实可行。（2）金顶铅锌矿区矿石中铊含量较高（0.96 ~ 729 mg/kg），矿石中的铊主要赋存在黄铁矿和白铁矿（55 ~ 3850 mg/kg）等原生矿物及风化作用形成的铅铁矾（647 ~ 16300 mg/kg）、黑锌锰矿（13 ~ 962 mg/kg）和褐铁矿（26 ~ 1200 mg/kg）等次生矿物中。铊在铅锌矿的采矿过程中，含铊矿石的淋滤作用造成了采矿废水的铊污染（12 ~ 14 μg/L），其中南大沟水体铊污染（1.97 ~ 2.4 μg/L）主要来自采矿废石的淋滤；另外硫化矿的堆放还会造成堆场附近土壤的铊污染（11 mg/kg）。在选矿过程中，铊主要转移至洗矿废水和废泥，以及尾矿渗滤水和尾矿中。元素相关性分析和单矿物分析显示，尾矿中的铊主要赋存在黄铁矿中。在冶炼过程中，铊不断的进行着转移和赋存形态的转化，大量原本存在于硫化物中的铊经冶炼过程转移至弱酸可交换态和可还原态，并最终转移至冶炼渣库和废水中。选矿和冶炼各生产节点产物中铊含量高，存在环境隐患，应对重要的排污节点进行防护。（3）研究区主要河流为沘江，河水呈弱碱性。研究发现上游水中铊含量（0.01 ~ 0.06 μg/L）与区域背景值接近，在矿区段明显升高（0.3 ~ 20 μg/L），下游受到自然沉降和清水稀释作用逐渐衰减（0.16 ~ 0.59 μg/L。沘江沉积物（0.37 ~ 18 mg/kg）和悬浮物（0.95 ~ 27 mg/kg）中铊含量较高，变化趋势与溶解态铊相似。矿区沉积物中的铊主要赋存在残渣态（占比30% ~ 79%），受矿山开采活动影响强烈的地方，沉积物中可氧化态和可还原态比例明显升高，可还原态的铊主要来自铁锰氧化物和氢氧化物对水溶液中铊的吸附，可氧化态的铊主要是受到含铊硫化物污染。沘江水体和支流水体的水化学特征变化趋势的研究表明，沘江水体中的铊主要来自高铊含量水体的汇入。水中溶解态铊的价态测试结果显示，矿区各类水体中溶解态的铊主要以Tl+的形式存在，Tl3+占比多在1%以下，是因为Tl3+在水溶液中很难稳定存在，Tl3+极易水解为Tl(OH)3而存在于水体的悬浮物和沉积物中。沉积物和悬浮物的DTPA水溶液提取液中铊的价态分析显示，大多数沉积物和悬浮物中的铊以Tl+为主，仅在南大沟（Tl3+占比23 ~ 34%）和选矿废水池样品（Tl3+占比52 ~ 59%）中有较高的Tl3+含量占比。沉积物的富集指数显示铊在沉积物中较为富集，地累积指数显示沉积物中铊污染较为严重，潜在生态危害指数显示沉积物中铊的生态危害较高，建议在河道清淤时应妥善处置沉积物，避免造成二次污染。沘江矿区段水样中的铊饮水摄入风险值超过建议值，会产生健康风险，应禁止作为人畜饮水。所有水样中铊通过皮肤摄入的风险值在可接受范围。（4）研究区土壤中铊的含量较高（0.2 ~ 7.9 mg/kg），铊的污染程度主要由污染源的性质和污染源影响程度等因素决定。通过主成分分析和相关性分析发现研究区土壤中铊含量与金顶铅锌矿体中的成矿元素关系密切。矿区表层土中铊呈现出沘江东岸明显高于西岸的特征。土壤剖面的研究发现，沘江西岸土壤剖面中铊含量从表层至底部逐渐降低（从0.61mg/kg降至0.35 mg/kg），而在东岸土壤剖面中铊含量呈现出在表层土中含量较高（3.1 mg/kg），中部逐渐降低（从2.3 mg/kg到1.6 mg/kg），剖面底部显著升高（从2.6 mg/kg到5.6 mg/kg）的特征。研究区地质图上也显示，沘江东岸有着西岸没有的铅锌矿体和碳酸盐岩，因此，沘江西侧表层土中的铊主要来自表层人类活动，而东岸土壤除了受到表层人类活动影响外，还受到矿化基岩风化的污染。土壤中铊主要赋存在残渣态中，高铊含量的土壤中可还原态和可氧化态的铊所占比例明显升高。土壤中的铊通过皮肤和经口摄入风险均在可接受范围。（5）尾矿和冶炼废渣中铊含量较高（0.39 mg/kg ~79 mg/kg），呈现出新尾矿＞冶炼废渣＞老尾矿的特征。铊在样品中的赋存形态从高到低依次为：残渣态＞可还原态＞可氧化态＞可交换态。通过对尾矿样品的微生物群落组成研究显示，在门的水平上，样品中前十种微生物按平均丰度排名依次为：Proteobacteria、Cyanobacteria、Acidobacteria、Actinobacteria、Bacteroidetes、Deinococcus-Thermus、Chloroflexi、Tenericutes、Verrucomicrobia和 Firmicutes。样品的微生物群落α多样性分析指标Shannon、Simpson、Chao1和ACE均与电导率（EC）显著负相关（p≤0.05），说明样品中的微生物群落丰度和微生物群落多样性主要受样品中可溶性离子浓度决定。PCoA 和UPGMA分析发现，样品中微生物组成主要受到样品性质的影响，不同样品的微生物组成差异显著，而性质相似的样品其微生物组成相似。物种丰度聚类热图表明，冶炼废渣与Ralstonia、Shewanella、Vibrio、Acinetobacter和Balneola等具有重金属抗性的微生物密切相关。 CCA分析发现，TOC对微生物群落分布的影响较小，是因为样品中大量的细菌为化能无机自养型。铊的存在不利于微生物的生长，但我们通过相关性分析发现：Flavobacterium、Ralstonia、Acinetobacter、Shewanella、Balneola、Vibrio、Thiovirga、Chryseobacterium等细菌与铊显著正相关，其中Vibrio、Ralstonia和Shewanella等细菌被证实具有一定的铊的抗性；Flavobacterium、Acinetobacter、Chryseobacterium被证实具有对其他重金属的抗性；而Thiovirga为硫氧化菌，与含铊的硫化物关系密切，因此，这些与铊正相关的微生物种类是潜在的铊抗性微生物。

Thallium (Tl) is a toxic trace metal and one of the USEPA’s priority metal pollutants, and all of its compounds are considered toxic. In nature, Tl mainly exists in two oxidation states, Tl+ and Tl3+. Although Tl is a rare element with low abundance in the Earth’s crust, it is widely distributed in nature in the form of associated elements in other minerals. Among them, Pb-Zn ores are the most important source for hosting Tl, discharging Tl into wastes during mining, mineral processing and smelting processes without recycle for Tl, causing environmental pollution of Tl. However, little knowledge was still known about the geochemical behaviors of Tl pollution during the mining, processing and smelting of Tl-bearing Pb-Zn ores. For example, the already analytical methods for determination of Tl are hardly replicated resulting in a lack of sufficient Tl species data which hinder the studies about the migration and transformation mechanism of Tl in water. In addition, the processes and mechanisms of Tl from ores to production, and finally into environmental medium (e.g, Soil, water and solid waste) are still unclear.The Jingding Pb-Zn Mine area which contains mining, mineral processing and smelting activities was selected as the study area. Wastes from industrial processes, soils, waters and sediments were collected and analyzed following various geochemical approaches, to study the migration and transformation pathway of Tl during the whole industrial process. The aims are to know the properties of the intermediate pollutants; To study how Tl transform to environmental medium (e.g, Soil and water), and to know the occurrence of Tl in them as well as evaluating their ecological risk; To study the microbial geochemical behavior of Tl in solid waste, to understand the response of microbial communities to Tl-rich wastes. Some conclusions were obtained as following.(1) In order to speciation of thallium, a novel method based on solid phase extraction (SPE) technology was developed. The diethylene triamine pentacetate acid (DTPA) was used to prevent the reduction of Tl3+ by forming a stable complex of Tl(III)-DTPA, then Tl3+ and Tl+ can be separated by selective adsortion of Tl(III)-DTPA on the anion resin of AG1-X8. The validity of this method was confirmed by standard solutions of different Tl+ and Tl3+ concentration ratios, different pHs and high concentration of other interference electrolytes, the recoveries are between 90 and 110%, which prove that the method is feasible.(2) High content of Tl (0.96 ~ 729 mg/kg) were found in Pb-Zn deposits in study area, Tl is mainly occurred in pyrite and marcasite (55 ~ 3850 mg/kg), and some secondary minerals such as plumbojarosite (647 ~ 16300 mg/kg), limonite (26 ~ 1200 mg/kg), chalcophanite (13 ~ 962 mg/kg) and so on. Soils and waters would polluted by Tl-rich ores in mining process. For example, high concentration of Tl in mining wastewater (12 ~ 14 μg/L) comes from the leaching of ores in mining process; the leaching of mining waste stones lead to high content of Tl in Nadagou river (1.97 ~ 2.4 μg/L); the soils (11 mg/kg) were polluted by ores in mining area. During the dressing process, high content of Tl were found in concentrates, tailings, water and solid wastes from mineral processing. The geochemical characteristics of tailings indicated that Tl in tailings is mainly occurred in pyrites. In the smelter, the occurrence form of Tl is transferred from oxidable fraction in ores to acid-soluble fraction or reducible fraction in intermediate products, and then Tl was eventually transferred to smelting slags and wastewaters after the smelting process. In order to prevent environmental pollution caused by mineral processing and smelting process, necessary protective measures must be taken for important sewage discharge nodes.(3) The main river in the study area is Bijiang river, the water is weak alkaline. The concentration of Tl in upstream waters (0.01 ~ 0.06 μg/L) were close to the regional background value, and it increased sharply in mining area (0.3 ~ 20 μg/L), then it gradually decreased in the downstream (0.16 ~ 0.59 μg/L) by dilution and deposition. The hydrochemical characteristics of Bijiang and its tributary show that Tl in Bijiang river is mainly derived from Tl-rich tributary. The speciation of Tl in water samples shows that the dominate species of Tl is Tl+, and the proportion of Tl3+ is usually less than 1%, which may be that Tl3+ is easily hydrolyzed as Tl(OH)3 and exists in suspended paticulate matters (SPMs) and sediments. The Tl+ is also the dominnate species of Tl in DTPA extracted solutions of sediments and SPMs, however, higher content of Tl3+ could be found in samples from Nadagou river (Tl3+: 23 ~ 34%) and mine washing pond (Tl3+: 52 ~59 %). The enrichment factor (EF) and geoaccumulation index (Igeo) of sediments show that sediments are strongly affected by anthropogenic activities; the potential ecological risk index (Eri) show that the potential ecological risk of Tl in sediments is very high, therefore sediments should be disposed properly to avoid of pollution when dredging the river. The risk values by oral intaking of Tl in water samples near the smelter exceeds the recommended value. The risk values by skin exposure of Tl in all water samples are acceptable.(4) The spatial distribution of Tl (0.2 ~ 7.9 mg/kg) is inhomogenous in soils, which was determined by geography and property of pollution source. Principal component analysis and correlation analysis show that Tl in soils comes from mineralized rocks. Because of different geological backgrounds of them, the Tl content of soils in the eastern area of Bijiang river is significantly higher than that of western area. The Tl content in the soil profile in the western side of Bijiang river is decreased from the top to the bottom (from 0.61 to 0.35 mg/kg). While in the soil profile of the eastern side, the content of Tl is high in the surface soils (3.1 mg/kg), and decreased in the middle (from 2.3 to 1.6 mg/kg), then increased in the bottom (from 2.6 to 5.6 mg/kg). The spatial distribution of Tl in soils indicated that, Tl is mainly derived from surface human activities (such as precipitation of smelting soot, transportation dust, or from agricultural activities) in the western soils, while the eastern area is not only polluted by surface human activities, but also polluted by the weathering of mineralized bedrocks. Tl is mainly occurred in the residual fraction in most soils, however, the proportions of reducible fraction and oxidable fraction are increased obviously in some soils with a higher content of Tl. The risk values by skin exposure or oral intake of Tl is less than the recommended value according to the government guideline.(5) The content of Tl in tailings and smelting slags is high (Tl: 0.39 mg/kg ~79 mg/kg), from high to low are: new tailings > smelting slags > old tailings. The occurrence forms of Tl in most of samples from high to low are: residual > reducible > oxidable > weak acid exchangeable. The 10 most abundant phyla were Proteobacteria, Cyanobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Deinococcus-Thermus, Chloroflexi, Tenericutes, Verrucomicrobia, and Firmicutes. The indexs of Shannon, Simpson, Chao1 and ACE were significantly negatively correlated with conductivity (EC) (p ≤ 0.05), indicating that the total species richness and community diversity were mainly determined by the concentration of soluble ions of the samples. According to PCoA and UPGMA analysis, the microbial communities are determined by the properties of the samples, similar characteristic will lead to similar microbial communities. According to species abundance clustering heat map and CCA analysis, smelting slags are significant positive correlation with bacteria which could resist to heavy metal, such as Ralstonia, Shewanella, Vibrio, Acinetobacter and Balneola, this maybe due to the presence of soluble heavy metals in smelting slags could be detrimental to microbial growth, especially which cannot resistant to heavy metals. The CCA analysis also showed that the function of TOC is less in influence microbial communities, because a large number of bacteria in the samples were chemolithoautotrophy, and they can used inorganic materials as energy. Although the presence of Tl is not conducive to microbial growth, correlation analysis still shows that many bacterial genera are significant positive correlation with Tl, such as Flavobacterium, Ralstonia, Acinetobacter, Shewanella, Balneola, Vibrio, Thiovirga and Chryseobacterium. Among them, Vibrio, Ralstonia and Shewanella have been proved could resist to Tl, and Flavobacterium, Acinetobacter, Chryseobacterium could resist to other metals; Thiovirga is reported as a sulfur oxide bacterium, tend to live with sulfides. Therefore, these bacteria are most likely to have thallium resistance and can be applied in Tl-rich environment.