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利用X射线衍射和X射线荧光分析、沉积物序列提取试验及矿物饱和度的计算,对采自江汉平原中部沙湖地区典型高砷含水层钻孔沉积物样品矿物学进行了分析,并讨论了控制含水层中砷释放和迁移的地球化学机制。对矿物在沉积物与土壤中的分布及组成的对比分析,在一定程度上指示了矿物赋存环境和/或高砷水形成的环境背景:土壤与沉积物中高岭石以低于其他3种粘土矿物的含量普遍存在,指示了含水层沉积物形成过程江汉平原存在一定的湿热古气候环境;沉积物绿泥石含量低于土壤中绿泥石,恰恰反映了土壤比沉积物略强的碱性环境;沉积物中黄铁矿的存在,显示了含水层局部的强还原性环境,指示地下水中广泛存在的Fe2+容易与二价硫发生沉淀并结合砷。砷主要以无定形铁锰氧化物结合态(平均在31%以上)形式存在,其次以碳酸盐和有机质结合态存在。无定形铁锰氧化物的还原溶解可能是控制砷迁移到地下水中主要的地球化学机制。相对高含量的绿泥石容易在含水层中发生风化,其溶解过程可以将铁释放到地下水中,从而成为影响地下水中砷活化的潜在因素。
X ray diffraction and X-ray fluorescence analysis, sediment extraction experiments and mineral saturation calculations were carried out to analyze the mineralogy of borehole sediment samples collected from a typical high arsenic aquifer in the Shahu region of central Jianghan Plain. Geochemical Mechanism to Control Arsenic Release and Migration in Aquifers. The comparative analysis of the distribution and composition of minerals in sediments and soils, to a certain extent, indicates the environmental background of mineralized environments and / or high arsenic water formation. The kaolinite in soils and sediments is lower than the other three species The content of clay minerals is ubiquitous, indicating that there is a certain hot and humid paleoclimate environment in the Jianghan Plain during the formation of aquifer sediments. The content of chlorite in sediments is lower than that of chlorite in soil, which shows that the soil is slightly stronger than the sediment The presence of pyrite in sediments shows a strong reducing environment in the aquifer, indicating that Fe2 +, which is widely present in groundwater, tends to precipitate with divalent sulfur and bind to arsenic. Arsenic mainly exists in the form of amorphous Fe-Mn oxides (average above 31%), followed by carbonate and organic matter. Reductive dissolution of amorphous Fe-Mn oxides may be the main geochemical mechanism that controls the migration of arsenic into groundwater. Relatively high levels of chlorite are prone to weathering in aquifers, and their dissolution process releases iron into the groundwater, thus potentially affecting arsenic activation in groundwater.