大同盆地高砷地下水稀土元素特征及其指示意义

对大同盆地典型高砷地下水开展了稀土元素地球化学研究.研究表明: 高砷地下水具有低∑REE含量及富集重稀土(HREEs)特征.地下水中低含量∑REE与含水层沉积物中Fe-Mn氧化物/氢氧化物对REEs的吸附有关.地下水中重稀土元素相对于轻稀土元素的富集可能是吸附作用和碳酸根离子同REEs发生络合作用的共同结果.采用平均大陆上地壳标准化的地下水稀土元素分布表现出显著的Ce及Eu正异常.地下水Ce/Ce*值及Eu含量与Fe+Mn具有显著相关性, 表明铁锰氧化物还原性溶解是控制Ce/Ce*值及Eu含量特征的主要因素.Ce/Ce*值及Eu含量与As浓度的关系表明, Ce异常及Eu含量特征能对地下水中As的富集进行有效指示. 

Characteristics and Implications of Rare Earth Elements in High Arsenic Groundwater from the Datong Basin

In order to better understand the occurrence of high arsenic groundwater, rare earth elements (REEs) analyses were conducted for groundwater from the Datong basin. The results indicate that high arsenic groundwater usually has low ∑REE concentration and enriches in HREEs relative to LREEs. The low concentration of ∑REE in groundwater samples could be due to the scavenging of REEs onto the surface of solid phase Fe-Mn oxides/hydroxides within aquifer sediment. The enrichment of HREEs can be attributed to the combined result of complexation, and desorption and readsorption. The average up crust normalized REEs patterns clearly exhibit significant positive Ce and Eu anomalies in high arsenic groundwater. The observed good correlation between Ce/Ce* values and Eu and Fe+Mn could be related to the reductive dissolution of Fe and Mn oxides/hydroxides. The relationship between As and Ce/Ce* value and Eu suggests that Ce/Ce* value and Eu concentration are useful indicators of arsenic mobilization in groundwater system.