中国不同区域高砷地下水化学特征及形成过程

Chemical Characteristics and Geochemical Processes of High Arsenic Groundwater in Different Regions of China

在中国广泛分布2类高砷地下水区(干旱内陆盆地和湿润河流三角洲),严重危害居民的身体健康。选择以河套盆地、呼和浩特盆地、大同盆地和银川盆地为代表的干旱内陆盆地和以江汉平原和珠江三角洲为代表的湿润河流三角洲为研究对象,分析中国不同区域高砷地下水化学特征和水文地球化学过程。结果表明:江汉平原高砷地下水以HCO3-Ca型为主,大同盆地、河套盆地和银川盆地高砷地下水主要为HCO3-Na型,而珠江三角洲高砷地下水为Cl-Na型;高砷地下水的氧化还原电位低,处于还原环境;SO2-4和NO-3质量浓度总体较低,其中江汉平原SO2-4最低,而河套盆地NO-3最低;铁与砷质量浓度之间的相关性并不显著,珠江三角洲高砷地下水中铁、锰质量浓度最高,砷质量浓度相对较低,而大同盆地高砷地下水中铁、锰质量浓度最低,砷质量浓度相对较高;风化作用、阳离子交换吸附作用和还原作用等不同程度地发生于高砷地下水系统中,在河套盆地和呼和浩特盆地,除铁/锰氧化物矿物的还原性溶解外,黄铁矿沉淀可能是控制地下水中铁、砷质量浓度的一个重要过程,而在江汉平原,铁/锰氧化物矿物的还原性溶解和Fe(Ⅱ)的再吸附是地下水中的主要水文地球化学过程;在地下水pH值较高的干旱内陆盆地,吸附态砷的解吸附也是一个重要的富砷过程。

High arsenic groundwater has been widely found in two kinds of regions （including arid inland basin and humid river delta） in China, which seriously affects resident health. Hetao Basin, Huhhot Basin, Yinchuan Basin and Datong Basin were selected as the arid inland basins, and Pearl River Delta and Jianghan Plain as the humid river deltas. Chemical characteristics and hydrogeochemical processes of high arsenic groundwater in different regions of China were analyzed. The type of high arsenic groundwater is HCO3-Ca in Jianghan Plain, HCO3-Na in Datong Basin, Hetao Basin and Yinchuan Basin, and Cl-Na in Pearl River Delta. Oxidation- reduction potential in high arsenic groundwater is low, indicating reduction environment. In theseenvironments, mass concentrations of SO4^2- and NO3 are generally low. Mass concentration of SO4^2- in Jianghan Plain is the lowest among all the six regions, while that of NO3 in Hetao Basin is the lowest. There is no significant correlation between mass concentrations of As and Fe. Mass concentrations of Fe and Mn are the highest, but As is relatively lower in Pearl River Delta, and mass concentrations of Fe and Mn are the lowest, but As is relatively higher in Datong Basin. Weathering, cation-exchange adsorption and reduction occur in high arsenic groundwater system. Pyrite precipitation may be an important process for controlling mass concentrations of Fe and As in addition to reductive dissolution of Fe/Mn oxides in Hetao Basin and Huhhot Basin. However, reductive dissolution of Fe/Mn oxides and Fe（ II ） re adsorption are the major hydrogeochemical processes in Jianghan Plain. Desorption of adsorbed arsenic also contributes to arsenic enrichment in groundwater of arid inland basins with weak alkaline environment.