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    高砷地下水的反向地球化学模拟:以中国吉林砷中毒病区为例

    Inverse geochemical modeling of high arsenic groundwater: a case study of the arsenic endemic area in western Jilin Province

    • 摘要: 提要:饮水型砷中毒分布在中国台湾、新疆、内蒙、山西、吉林等地。笔者采用GIS的空间数据叠加技术、化验测试与环境模拟技术,进行了地下水砷的反向地球化学模拟研究。研究表明,受构造运动控制,低洼地带堆积了巨厚的粉砂淤泥质沉积物和富含有机质的湖积物,为砷的赋存提供了空间。地下水砷的富集受水中Fe、Mn、pH、Cl-、PO3-4、HCO-3、SO2-4、Se的影响,其中,重碳酸钙型水中砷含量最低,氯化物重碳酸钠型水砷含量最高。臭葱石(FeAsO4:2H2O)等含铁、含锰矿物在进入地下水的溶解过程中,形成铁(锰)氧化物和砷化合物(砷酸盐或亚砷酸盐)。随着Eh降低,氧化物被还原形成更为活泼的离子组分,吸附在氧化物表面的砷化合物随之解吸,还原环境有利于砷从沉积物中向水中溶解、迁移。研究结果为实施安全供水提供了重要依据。

       

      Abstract: Abstract:A study area in Jilin was selected from lots of arsenic endemic regions, which are mainly distributed in Taiwan, Xinjiang, Inner Mongolia, Shanxi and Jilin. The area is physiogeographically located along the western flank of Songnen plain, and hydrogeochemically regarded as a basin with groundwater generally flowing eastward. A total of 196 groundwater samples were collected, which not only covered the whole study area but also extended to different depths/aquifers that included Quaternary phreatic groundwater, Quaternary Baitushan Formation confined groundwater and Neogene confined groundwater. Cluster analysis was also performed to identify the degree of relationship between each chemical constituent and arsenic by the SPSS statistical package. The result reveals that the distribution of arsenic at the present time has a close relationship with the spatial variation of Fe, Mn as well as Cl-, PO3-4, HCO-3, SO2-4 and Se. An inverse geochemical model was established to demonstrate the above relationship by using the PHREEQC software. The simulation results have confirmed that the arsenic presence and its distribution in the groundwater of this area result largely from the leaching-migration-accumulation from the edge to the central area of the basin. The dissolution of the redox sensitive ferric oxide compounds and hydrous ferric oxides as well as the arsenic compounds (arsenate or arsenide) is probably the major mechanism for the control of the spatial variation of arsenic in the study area. As groundwater flows stagnantly in the low-lying central area, the afore-mentioned minerals become less stable due to lower Eh and move into the groundwater with relatively high solubility under the lower Eh condition. At the same time, the arsenic complexes adsorbed by these minerals are released and migrate with the movement of the groundwater. It is concluded that the presence of arsenic in the regional groundwater flow regime exhibits the highest concentration in chloride-sodium bicarbonate groundwater in the central area, which is consistent with the above findings and many previous studies in this special field of the international community.

       

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