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以湘中发育于下寒武统黑色页岩之上的土壤为研究对象,选择安化东坪、烟溪,桃江,宁乡等地的典型土壤及相应成土母岩,利用等离子质谱(ICP-MS)、X射线荧光光谱(XRF)等分析技术,对土壤、成土母岩(黑色页岩)的主量元素和微量元素(包括重金属元素、稀土元素等)进行了较系统的分析测定。结果表明,湘中下寒武统黑色页岩土壤风化作用强烈,风化指数CIA均在73以上。强烈的风化使得土壤具有明显贫CaO、Na2O,而富Al2O3、Fe2O3的化学组成特征。土壤因继承成土母岩(黑色页岩)的特征而富集Mo、Cd、Sn、Sb、U、V、Cr、Co、Ni、Cu、Zn、Tl、Pb、Th等多种重金属元素,其综合富集指数(EI值)平均在3以上,最高达17。地质累计指数(Igeo)评价结果显示,土壤重金属的富集已达到污染程度,土壤存在Cd、Mo、Sb、U、Sn、V、Cu、Tl、Ba等重金属的污染,并以Cd、Mo、Sb等重金属污染最强,达中度至极强污染程度。重金属与主量元素的相关性分析显示,土壤中的重金属主要赋存于黏土矿物和铁氧化物(针铁矿)等矿物相中,其中Ba、Sn、Th、Cu、Sc等主要赋存黏土矿物中;Zn、Ni、Mn、Co、Cd、Tl、Pb等则主要赋存于铁氧化物矿物(针铁矿)中;而Cr、V、Mo、Sb、U等则不受黏土矿物和铁氧化物矿物的控制。此外,不同地区土壤的Zr/Hf、Ta/Nb、Nd/Sm等元素比值相对稳定,依次为36.20、0.085、5.30(n=73),并与相应的成土母岩(黑色页岩)相应值基本一致。土壤与成土母岩具有相同的稀土配分型式,且成土过程中稀土元素不发生明显的分异。微量元素比值和稀土元素特征指示土壤中的重金属来自成土母岩(黑色页岩)本身,为自然污染源。
Taking the soil developed in the Lower Cambrian black shale in Hunan Province as the research object, the typical soils and corresponding parent rocks from Dongping, Yanxi, Taojiang and Ningxiang of Anhua were selected and characterized by ICP -MS) and X-ray fluorescence spectrometry (XRF) were used to systematically analyze and determine the major and trace elements (including heavy metal elements and rare earth elements) in soils and rock-forming rocks (black shale) . The results show that the Lower Cambrian black shale in the middle part of Hunan Province had a strong weathering effect and the weathering index (CIA) was above 73. Strong weathering makes the soil has significantly poor chemical composition of CaO, Na2O, and rich Al2O3, Fe2O3. The soil is enriched with many heavy metal elements such as Mo, Cd, Sn, Sb, U, V, Cr, Co, Ni, Cu, Zn, Tl, Pb and Th due to the inheritance of the parent rock (black shale) Its comprehensive enrichment index (EI value) on average more than 3, up to 17. The results of geointeger index (Igeo) evaluation showed that the enrichment of heavy metals in soil had reached the level of pollution. The soil was contaminated by heavy metals such as Cd, Mo, Sb, U, Sn, V, Cu, Tl and Ba. Sb and other heavy metal pollution strongest, reaching moderate to extremely high levels of pollution. The correlation analysis between heavy metals and major elements showed that the heavy metals in the soil mainly existed in the mineral phases such as clay minerals and iron oxides (goethite), among which Ba, Sn, Th, Cu, Sc, In minerals, Zn, Ni, Mn, Co, Cd, Tl and Pb are mainly present in iron oxide minerals (goethite); while Cr, V, Mo, Sb and U are not affected by clay minerals and Iron oxide mineral control. In addition, the ratios of elements such as Zr / Hf, Ta / Nb and Nd / Sm in different areas were relatively stable, followed by 36.20,0.085,5.30 (n = 73) and corresponding to the corresponding parent rocks (black shale) The value is basically the same. The soil and parent rocks have the same REE pattern, and there is no obvious difference of rare earth elements in the process of soil formation. The ratio of trace elements and the characteristics of rare earth elements indicate that heavy metals in soils originate from soil-forming host rocks (black shales) themselves, which are natural sources of pollution.