湘中HJC铀矿区黑色页岩土壤重金属污染地球化学分析

Geochemical Study of Heavy Metal Contamination of Soils Derived from Black Shales at the HJC Uranium Mine in Central Hunan,China

本文以湘中HJC铀矿区黑色页岩土壤为研究对象，对黑色页岩土壤重金属污染进行了地球化学分析。通过测制A、B、C、D等土壤剖面并系统取样，借助ICP-MS等分析技术，对土壤、成土母岩、玉米等进行了系统的主量元素、重金属和其他微量元素（稀土元素）分析。结果表明，矿区黑色页岩土壤具富Al2O3、Fe2O3，而贫CaO、Na2O的化学组成特征，其化学风化指数CIA值在79～84之间。土壤因继承成土母岩的元素富集特征而富集V、Cr、Co、Ni、Cu、Zn、Mo、Cd、Sn、Sb、T1、Pb、Th、U等多种重金属，其中Mo、Cd、Sb、U的富集最强。土壤重金属综合富集指数（EI值）在3～9之间，各剖面EI值大小顺序是：D〉A〉B〉C，以D剖面土壤重金属综合富集最强。土壤重金属污染富集因子（F）评价结果显示：矿区土壤普遍存在Cd、Mo、Sn、Sb、U等重金属污染，其中Mo、Cd、Sb等的污染最强，达显著（3级，2〈F〈20）污染程度以上。重金属污染效应既表现为Sc、Cd、Sn、Sb、U、Tl、Pb等生物毒性重金属在玉米中的富集，又表现为Mo、Co、Ni、Cu、Zn等生物有用金属在玉米中的明显亏损。黑色页岩即为土壤重金属污染的污染源。土壤重金属污染与重金属在成土母岩和土壤中的富集程度（Ks、EI、F）、重金属的活动性（Change%）等多种因素有关。重金属污染主影响因子的Pearson相关系数分析显示：Cd对土壤构成持久性污染，Mo、Sn、Sb、U等的污染程度可随土壤风化的进行因淋失而趋于降低，而Zn、Mn、Ba、Co、Ni、Th等目前未达到污染水平的重金属则可因次生富集而在未来引发污染。

This study carried out a geochemical approach on heavy-metal contamination of soils derived from black shale （balck-shale soils） from the HJC uranium mine in central Hunan, China. Four soil profiles numbered as A, B, C and D were surveyed and sampled. The concentrations of major elements, heavy metals, and other trace elements as well as rare earth elements of the soils from the four profiles, the bedrocks （the black shale） and the maize were analyzed using the ICP-MS machine. The results show that the black-shale soils of the mine are enriched in Al2O3 and Fe2O3 ,and depleted by CaO, Na2O, with CIA ranging from 79 to 84. The black-shale soils are distinctly enriched in heavy metals including V, Cr, Co, Ni, Cu, Zn, Mo, Cd, Sn, Sb, Tl, Pb, Th and U, among which Mo, Cd, Sb and U are in highest degrees, with enrichment factors （Ks） ranging from 5.1 to 112, 4.2 to 8.5, 3.0 to 12, and 2.1 to 12, respectively. The synthetic enrichment index （EI） values of the four soil profiles range from 3 to 9 with an order of D〉A〉B〉C, showing that the soils from the profile D are enriched with heavy metals in highest degree. The heavy-metal contamination assessment using the method of enrichment factor （F） shows that the soils of the mine area are mostly contaminated by heavy metals Cd, Mo, Sn, Sb and U, among which the metals Mo, Cd and Sb are in highest degrees of contamination, with F values ranging from 5 to 20. The impact of the heavy-metal contamination of the soils was testified by some maize growing from the soils, for which the biological toxic metals including Sc, Cd, Sn, Sb, U, Tl are enriched in the maize and depleted in biological essential trace metals including Mo, Co, Ni, Cu and Zn. The sources for the heavy- metal contamination of the soils are directly related to the bedrock, the carbonaceous black shale. The heavy-metal contamination of the soils was controlled by many factors such as the enrichment of heavy metals both in bedrock and the soils derived from it, the mobility of heavy metals during the processes of soil formation, and others. Therefore, understanding the relationship between the heavy-metal contamination and the influencing factors can help to predict the future developing tendency of the heavy- metal contamination of the soils. The results show that the metal Cd might be a long-time lasting heavy- metal contamination for the soils, and the contamination extents of metals Mo, Sn, Sb and U might be reduced by releasing of the metals during weathering of the soils. However, the metals Zn, Mn, Ba, Co, Ni and Th that have not achieved the contamination degree at present might cause the heavy-metal contamination to the soils in the mine area in future due to the secondary enrichment during weathering.