渔塘坝黑色富硒岩石中硒的赋存状态及其对局域环境的效应研究

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	渔塘坝黑色富硒岩石中硒的赋存状态及其对局域环境的效应研究
	朱建明
	2001
学位授予单位	中国科学院地球化学研究所
学位授予地点	中国科学院地球化学研究所
学位名称	博士
学位专业	地球化学
关键词	黑色富硒岩石自然硒硒化物硒的结合态赋存状态微束分析连续化学浸提实验淋滤实验硒的环境效应恩施渔塘坝湖北省
摘要	选取世界上迄今唯一发生过人群硒中毒爆发性流行的地区一中国湖北省恩施市双河乡渔塘坝为研究对象，利用扫描电子显微镜、透射电子显微镜与电子探针等微束分析技术和连续化学浸提技术，系统地研究了渔塘坝北部出露的黑色富硒岩石中硒的赋存状态和各结合态中硒的分布：使用柱式和混合流式淋滤装置，在不同淋滤原液pH值的条件下，初步研究了黑色富硒岩石中硒的淋滤行为和淋滤过程中的pH变化；在全面了解渔塘坝岩石、土壤、水系和植物硒分布的基础上，对渔塘坝硒的局域环境效应进行了初步的研究。通过上述研究，得出了以下几点发现和认识：1．在渔塘坝废弃的“石煤堆”和富硒的碳质硅质岩段，首次发现了多形态、多成因的自然硒。按照自然硒的成因分类，主要是“石煤”自燃型、风化型和构造热活动型。按照自然硒的赋存条件和产出环境，可分为五种类型：①产于废弃“石煤堆”近地表的自然硒矿物晶体;②与石英或碳质共生的微发状、针状硒晶体；③产于高碳质泥岩中的微针状硒晶体；④由富硒岩石、含硒矿物的风化或硒晶体再风化形成的硒晶体；⑤碳质硅质岩中的元素硒微粒和微生物形态的自然硒或硒化物。岩石中元素态硒的提取也表明富硒岩石中有元素硒的存在。元素硒在富硒岩石中除直接赋存于硅质介质外(如碳质硅质岩中的元素硒微粒)，另一种是以纳米级超微矿物包体的形式存在，如千酪根中的元素硒微粒。2．在渔塘坝碳质硅质岩段，已发现硒铜蓝、方硒铜矿、硒银矿、含硒黄铁矿和罕见的水硒铁石等硒的独立矿物和含硒矿物。从已有的硒矿物组合和地球化学热力学资料分析，推测渔塘坝黑色富硒岩层中应当有诸如硒铅矿等其它硒矿物和亚硒酸盐的存在。岩石中与生物有关的硒或硒化物还有待进一步的研究。3．渔塘坝黑色富硒岩石中的硒主要以有机结合态(F2：20％)和残渣态(F5：59％)的形式存在，其次是硫化物与硒化物结合态硒(F4：13%)、元素态硒(F3：4％)和可利用态硒(F1：4％)。硒的F1、F2、F3和F4结合态间彼此都存在显著的正相关关系。以线性方程中斜率值_(F1-F3)=0.363>S_(F1-F4)=0.180>_(F1-F2)=0.120来代表各结合态间硒的转化关系，可以得知元素态硒易于向可利用态硒转化，其次是硫化物或硒化物的结合态硒，而有机结合态硒的转化则相对比较困难。相关系数R_(F2-F3)=0.6999>R_(F3-F4)=0.5877表明元素硒倾向与有机质结合，而不易形成硒化物。4.岩石中四种结合态F1、．F2、F3和F4中的硒含量；及其总和与岩石总硒间存在显著的正相关关系(=0.969，p<0.0001，n=19)，这说明岩石总硒对硒在各结合态中的分布起着控制作用。但新鲜岩石中可利用态硒的极低和风化岩石中可利用态硒的特高分布，表明风化岩石中的硒是影响局域生态环境的主要因素。岩石的风化程度和硒的赋存状态或结合方式对浸提剂的提取效率有一定的影响，浸提剂提取效率的高低在一定程度上可以作为鉴别硅质岩石新鲜与风化程度的判据。5．柱式和混合流式淋滤实验研究的结果表明，随着液固比的增大和淋滤时间的延长，淋出液中硒含量变化的总体趋势是降低的。不同岩石类型淋出液中的硒含量存在差别。岩石硒含量并不是影响淋出液中硒含量的唯一因素，硒的赋存状态、环境的pH、Eh条件、岩石类别、性质及其矿物组成对淋出液中的硒含量也存在影响。就岩石类别来讲，硒的淋出量是碳质硅质岩大于高碳质硅质岩，含碳硅岩最差。6．淋滤原液的pH值对硒的淋出量有显著影响，硒淋出量的排列顺序是pH=2.0>pH=6.5>pH=4.0。淋出液pH值的变化主要取决于岩石中碳酸盐和黄铁矿的含量之比。柱式和混合流式的简单模拟实验研究表明，对于近中性的淋滤原液(pH=6.1～6.5)，在无氧和有氧的淋滤条件下，碳酸盐呈现滞后于酸化反应的中和特性。对处于碳酸盐岩地区的渔塘坝而言，碳酸盐的中和作用在某种程度上比黄铁矿的酸化作用对pH的影响更加稳定、明显。7．对渔塘坝硒的局域环境效应的研究表明，渔塘坝北部的富硒岩石不仅为渔塘坝中的土壤和植物提供了硒的物质来源，而且是渔塘坝高硒区形成的直接因素。渔塘坝水硒(59.36±17.31μg／l)和居民饮用水硒含量(48μg/l)已达到风险水平，渔塘坝玉米硒含量(8.07±5.02m/kg)也已达到潜在毒性水平。就硒的环境效应来讲，渔塘坝依然是硒中毒可能发生的高风险区。当地居民的耕作和生活方式是导致硒在食物链中富集的主要因素。目前，渔塘坝硒中毒的高风险主要受玉米硒(主食硒)的控制。总之，本项研究中渔塘坝自然硒及其系列硒化物的发现有重要意义。它不仅为硒的矿物学、矿床地球化学提供了新的认识和研究空间，而且为硒的环境地球化学及其对人体健康与生态效应的研究方面提供了良好的研究场所。渔塘坝中元素硒的普遍存在，不仅说明元素硒的形成过程是渔塘坝富硒岩石风化和各结合态硒间转化的关键环节，而且也是影响表生环境中岩石硒的释放、转化和地球化学迁移的重要因素。渔塘坝风化岩石中可利用态硒的特高分布，表明风化岩石中的硒是影响渔塘坝局域生态环境的主要因素。渔塘坝富硒岩石的风化过程可能是一种硒次生富集的地球化学过程，同时也是废弃“石煤”堆和岩层特定地段中发现特高硒样品的主要原因。硒在渔塘坝局部环境中高度富集的现象在理论上有重要价值，在环境与健康关系上值得重视，但以其作为资源开发的依据，则应持。慎重态度。因此，对当地政府部门来讲，妥善管理和保护恩施州内的高硒岩段和采挖“石煤”过程中产生的废弃堆积物是极其重要的。
其他摘要	Yutangba the only site in the world where a sudden incidence of Se (selenium) poisoning took place in 1963, is located in the northern part of Shuanghe Town of Enshi City in the SW of Hubei Province, China. It is one of the most typical high-Se areas in Enshi Prefecture, and thus it is selected as our study area. Using SEM-EDX, TEM-EDX, EPM (electron probe microanalyser) and sequential extraction technique, we systematically studied the modes of occurrence of Se and Se fractionation in black Se-rich rocks of Yutangba. By doing the leaching experiment using column and mixed flow reactor, under the condition of three different initial solutions (pH=2.0, 4.0, 6.5), we preliminary studied the leaching behavior of Se in black Se-rich rocks and the change of pH in leachate. 0n the basis of the distribution of Se in the rocks, soils, water and vegetables in Yutangba, we preliminary assessed the Se impact on the local environment. Based on the above studies, major conclusions are drawn as follows: 1. Native Se, which varies morphologically due to different mechanisms, has been discovered within the abandoned stone coal spoils and Se-rich carbonaceous siliceous rock. According to its origin, native Se is mainly divided into three types, which are derived from natural burning of stone-coal, weathering and tectonic activity. But. based on its occurring environments and conditions, native Se can be divided into five kinds. The first is produced near the surface of abandoned stone coal spoils with well developed crystal morphology and the largest grain size up to 28mm. The second is closely associated with quartz and carbonaceous matter with good crystal morphology but very small grain size as micro-needles. The third oecurs as micro-acicular crystals, found in the highly carbonaceous mudstone. The fourth is formed from weathering of Se-rich rocks, Se-bearing minerals (such as pyrite) and surface redox of the larger Se crystals. The fifth is elemental Se (Se~0) or selenides with microorganism morphology, only found in the carbonaceous siliceous rock. Elemental Se extracted from all rock samples indicates that there is elemental Se in the black Se-rich rocks, and there are two types. One could be found in the carbonaceous siliceous rock as Se micro-grains, and the other is enveloped as Se nano-grains by organic matter such as kerogen. 2. At present, a series of selenides has been tbund within the Se-rieh carbonaceous siliceous rock, which are krutaite(CuSe_2), klockmannite(CuSe), naumanite (Ag_2Se), mandarinaoite(Fe_2(SeO_3)_3) and Se-bearing pyrite. Based on the known assemblage of Se minerals and their thermodynamical phase relations, it is possible to find other Se minerals such as clausthalite, chalcomenite and so on. As to native selenium or selenides with microorganism morphology in Se-rich rocks, a further study is necessary. 3. The Se fractionation in black Se-rich rocks of Yutangba has been studied by sequential extraction experiment. Results show that Refractory-Se (F5:59%) and Organic- Se (F2:20%) are predominant, the others are sulfide and selenide-Se (F4:1 3%), elemental Se (F3:4%) and available Se (F1:4%), respectively. Significant correlations among F1, F2, F3 and F4 are found. This is suggestive of a probable conversion or combination among these four fractions. If the slope (S) in linear regression equations is used as an index on behalf of the transformed magnitude among F1, F2, F3 and F4 fractions, based on _(F1-F3)=0.363>S_(F1-F4)=0.180>S_(F1-F2)=0.120, it could be predicted that the elemental Se is easier to be transformed to available Se than the sulfide and selenide-Se, while organic-Se is more difficult to be transformed. Correlative coeffhicient R_(F2-F3)=0.6999>R_(F3-F4)=0.58 77 indicates that elemental Se prefers to combine with organic matter instead of forming selenides. 4. The significant correlations among the total Se, the Se in four fractions (F 1, F2, F3, F4) and the sum of these four fractions in black Se-rich rocks, show that the distribution of Se among different fractions is controlled by the total Se. However, the fact that available Se is higher in weathering rocks than it in fresh rocks, ,indicates that Se in Se-rich rocks exposed in the air is a major factor affecting the local environment. To some extent, the weathering magnitude of rock and modes of occurrence of Se in rocks affect the extraction efficiency, and hence the higher or lower extraction efficiency may be served as an index to distinguish fresh rocks from weathered rocks. 5. The results from the leaching experiment using column and mixed flow reactor show that Se contents in leachates are gradually decreased along with the increase of the ratio of leachate volume to sampling weight and prolonging time. Se content is different in leachate frorn the different types of rocks. Se content in leachate is not controlled by the total Se in rocks but the modes of occurrence of Se, pH, Eh, rocks type, rock features and its mineral conposition. Se content in leaehate is the highest in carbonaceous siliceous rock, with carbonaceous siliceous rock coming next, followed by carbonaceous silicalite. 6. Se content in leach-rte differs signifificantly under the different pH conditions and tends to decrease in the following order pH=2.0>pH=6.5>pH=4.0. The change of pH in leachate is mainly dependent on the ratio of carbonate to pyrite in the rocks. The results from mixed flow reactor show that, under anoxic (nitrogen) and oxlc (oxygen) conditions, carbonate presents the characters of lagging neutralization, and this feature is sometimes more obvious, persistent to affect pH than acidification produced by pyrite oxidation in Yutangba environment. 7. The results from studying Se impact on the local environment of Yutangba demonstrate that the Se-rich carbonaceous siliceous rock and carbonaceous shale of the Pennian (Maokou and Wujiaping) are the original source of Se for soils and plants in Yutangba, and these Se-rich rocks are also a predominant factor for Yutangba developed into a high-Se area. In Yutangba, Se content in brook water (59.36±17.31μg/1) and drinking water(48μg/l) has reached the hazardous level, and Se content in corn(8.07±5.02mg/kg)has also reached the potential toxic level for the local human inhabitants. So, Yutangba is still an area with high risk of Se poisoning, and Se poisoning is possible to take place. The manners of cultivating activities and life of local inhabitants are the main factors that cause Se to accumulate in food chain, and high risk of Se poisoning is mainly controlled by Se content in com (main food). To some extent, a sudden incidence of Se poisoning took place in Yutangba in the past is probably caused by human factors under favorable natural conditions such as exposed Se-rich rocks, heavy rain for a long time and so on. in conclusion, the discovery of native Se and selenides in Yutangba is of important significance. It not only would be helpful to further study on mineralogy and ore geochemistry, but also provides a good study area for us to carry out a detailed study on the environmental geochemistry of Se and its effect to human health and ecology. Native Se is widely distributed in Yutangba, and this demonstrates that its forming process is not only tho. key phase for Se transforming armong the different Se fractionations in Sc-rich rocks, and also for Se releasing, mobilizing and transporting during Se-rich rocks weathering. Higher content of available Se in weathering rocks indicates that the Se in Se-rich rocks exposed in the air is a main factor affecting the local environment. In Yutangba, Se is perhaps undergoing such a geochemical process that Se released from weathered Se-rich rocks is re-deposited. This may be the main reason why we can find the sanples with extremely higher Se content within abandoned stone coal spoils and caroonaceous siliceous rock. The extremely accumulated Se at special sites is important to study the geochemistry of Se in the environment and assess the relationships between human health and Se effects. But this phenomenon is regarded as the bass for mining, we should hold prudent attitude to carefully deal with these problems. So, to the local government, it is important to protect black Se-rich rock in Enshi prefecture from mining again; and thoroughly manage the abandoned stone coal spoils produced from the mining of black Se-rich rocks.
页数	118
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3570
专题	研究生_研究生_学位论文环境地球化学国家重点实验室
推荐引用方式 GB/T 7714	朱建明. 渔塘坝黑色富硒岩石中硒的赋存状态及其对局域环境的效应研究[D]. 中国科学院地球化学研究所. 中国科学院地球化学研究所,2001.

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