【摘要】 选取江汉平原典型地下水砷中毒区仙桃市沙湖原种场为研究区,对3个长50m的钻孔沉积物砷含量与赋存形态及其他化学组成进行了分析。结果表明区内沉积物砷质量分数为1.35~107.5mg/kg(平均值为12.8mg/kg)。黏土或亚黏土层中砷含量较高,这与细粒沉积物中铁锰氧化物、黏土矿物对砷的吸附有关。地下20m左右深度内含水层沉积物中砷含量最高,相应地下水中砷质量浓度高达到1 000μg/L。草酸-草酸铵选择性提取结果指示沉积物中10%~77%(平均38%)的As与无定形铁氢氧化物结合,表明无定形铁氢氧化物还原性溶解可能是控制砷释放与还原的主要地球化学过程,并且有机质生物氧化机制极大地促进了该过程。然而,沉积物中仅1.2%~23%的铁被草酸-草酸铵提取,含水层中砷浓度主要受铁的氢氧化物还原性溶解影响,但其他形式的铁、有机物的吸附作用亦控制着砷的含量。更多还原

【Abstract】 To identify the mechanism of arsenic mobilization from sediments to groundwater in the Jianghan Plain,sediment samples of three 50 mdeep boreholes from the endemic arsenicosis area located in Shahu village were chosen for study.The results indicated that the arsenic concentrations of sediments in the region have a range of 1.35-107.5mg/kg,with a median of 12.8mg/kg.The arsenic content in the silt and clay samples were higher because arsenic could be bounded with iron,manganese oxides and clay minerals in fine grained sediments.Chemical composition of the sediments was affected by their lithology and particle size.The maximum content of arsenic was found at a depth of 20 mthe content in the groundwater was up to 1 000μg/L.Reductive dissolution of amorphous iron oxides may be the main geochemical mechanism controlling arsenic mobilization from sediments to groundwater.Between 10%-77%(a median value of 38%)of arsenic in the sediments could be extracted by ammonium oxalate,only 1.2%-23% of iron could be extracted.Arsenic concentrations in the aquifer are mainly influenced by reductive dissolution of the Fe oxyhydroxides.In addition,adsorption of other forms of iron,organic matter also controls the content of arsenic.更多还原