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石嘴山地区煤中微量元素特征及成煤环境对比

Characteristics of trace elements in coal and comparison of coal-forming environment in Shizuishan Area

  • 摘要: 为清晰认识石嘴山地区侏罗系煤与石炭-二叠系煤的微量元素和成煤环境特征,并对煤中微量元素特征差异提出解释。取区内汝箕沟侏罗系煤及石炭井石炭-二叠系煤为样品,借助工业分析、显微组分观察、低温灰化及中子活化等方法分析,利用浓集系数、数理统计方法分析微量元素的富集特征和共生关系,使用地球化学参数综合研究成煤环境差异,并指出其对微量元素特征的影响。结果显示:侏罗系煤和石炭-二叠系煤在微量元素特征上存在较大差异。侏罗系煤中无元素富集,多数元素亏损,石炭-二叠系煤中Se、Zr、Hf、W、Th等元素轻富集。根据共生关系,微量元素可分为与煤中水分、碱金属元素高度相关和与陆源碎屑高度相关的2组。侏罗系煤和石炭-二叠系煤整体处于氧化-氧化还原环境中,但侏罗系煤的成煤环境更加高温干燥,古盐度、碱性和沼泽封闭性更强。成煤环境向高温干燥的转变使得沼泽封闭性增强,导致在石炭-二叠系煤中为轻富集的Se、Zr、Hf、W、Th等元素在侏罗系煤中变为正常-亏损,其他陆源碎屑相关元素含量降低;氧化性加剧了两时代煤中U元素的迁移;碱性环境可能对Se元素在煤中的富集过程具有一定影响,还促进了Ba、Co、As、Ni、Cr等元素在侏罗系煤中沉积。同时成煤环境还对煤质及矿物特征具有一定影响。

     

    Abstract: In order to clearly understand the characteristics of trace elements and coal-forming environment characteristics of Jurassic coal and Carboniferous-Permian coal in Shizuishan Area, and to explain the differences in the characteristics of trace elements in coal, this paper was carried out. The Jurassic coal in Rujigou area and the Carboniferous-Permian coal in Shitanjing Area were taken as samples. The samples were analyzed by industrial analysis, maceral observation, low-temperature ashing, and instrumental neutron activation analysis. The concentration coefficient and mathematical statistics were used to analyze the enrichment characteristics and symbiotic relationship of trace elements, and the geochemical parameters were used to comprehensively study the difference of coal-forming environment characteristics, and the influence of coal-forming environment on the coal characteristics was pointed out. The results show that Jurassic coal and Carboniferous-Permian coal have great differences in trace element characteristics. There is no element enrichment in Jurassic coal, most elements are deficient, and Se, Zr, Hf, W, Th are lightly enriched in Carboniferous-Permian coal. According to the symbiotic relationship, trace elements can be divided into two groups which are highly correlated with water and alkali metal elements in coal and those highly correlated with terrigenous debris. Jurassic coal and Carboniferous-Permian coal are in oxidation-transition environment, but the coal-forming environment of Jurassic coal is more high temperature and dry, and the paleo-salinity, alkalinity, and swamp closure are stronger. The transition of the coal-forming environment to high temperature and dryness enhances the sealing of the swamp. As a result, the elements such as Se, Zr, Hf, W, and Th, which are slightly enriched in the Carboniferous-Permian coals, become normal- deficient in the Jurassic coals, and the contents of other terrigenous clasts-related elements decrease. Oxidation intensifies the migration of U element in coal in two ages. Alkali environment may have a certain influence on the enrichment process of Se, and also promote the deposition of Ba, Co, As, Ni, Cr in Jurassic coal. At the same time, the coal-forming environment also has a certain influence on coal quality and mineral characteristics.

     

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