江汉平原浅层含砷地下水稀土元素特征及其指示意义

江汉平原被确认为我国南方新的饮水型砷中毒病区，目前对于江汉平原高砷地下水的成因机理研究还有待完善.综合运用水文地球化学分析与PHREEQC地球化学模拟计算，分析了地下水和沉积物中REE分异特征及其沿地下水流向形态变化规律.江汉平原地下水REE含量为0.032~0.843 μg/L，富集LREE，具显著Eu正异常，且地下水中Eu异常与As含量呈正相关关系.地下水中REE形态主要以LnCO₃+及Ln(CO₃)₂-为主，沿地下水流向LnCO₃+降低、Ln(CO₃)₂2-升高.地下水REE浓度分布受到HCO₃-的络合作用及Fe氧化物矿物的还原性解吸附过程控制，径流途径中继承沉积物矿物的REE配分模式及Fe氧化物矿物对LREE的优先解吸附可能是地下水富集LREE的原因，并且沿流向上REE形态分布受到pH控制.研究区中Eu含量及Eu正异常对地下水As富集程度具有一定的指示意义. 

Geochemistry and Implications of Rare Earth Elements in Arsenic-Affected Shallow Aquifer from Jianghan Plain,Central China

Jianghan plain has been determined as a new endemic arsenic-poisoning area in the southern China. In order to understand the role of rare earth elements (REE)on arsenic mobilization in groundwater from the Jianghan plain, REE concentrations were measured in 114 groundwater samples and 9 sediment samples from the shallow arsenic-affected aquifer system and the REE speciations along the groundwater flow path were caculated by the hydrogeochemical PHREEQC simulation. The results indicate that the REE concentrations range from 0.032 to 0.843 μg/L. The groundwater exhibite the enrichment of LREE and dramatically positive Eu anomalies, and the Eu anomalies are positively correlated with As concentration. The REE speciation mainly existes as LnCO₃+ and Ln(CO₃)₂-, meanwhile the LnCO₃+ concentrations decrease and Ln(CO₃)₂2- concentrations increased along the regional groundwater flow path. The distribution of REE concentrations was mainly affected by the complexation with HCO₃- and the reductive dissolution of iron oxide minerals. The enrichment of LREE in the groundwater was affected by the REE distribution patterns of minerals in the aquifer and the preferential desorption with LREE of iron oxide minerals, and the REE speciation was controlled by the pH along the groundwater flow path. The Eu concentrations and positive Eu anomalies could indicate the enrichment of arsenic in the groundwater.