大同盆地沉积物REE分布特征及其对碘富集的指示

大同盆地是典型的干旱-半干旱内陆盆地，盆地中部地下水碘含量异常，对当地饮用水安全造成了严重威胁.对盆地高碘地下水分布区沉积物组成及稀土元素(REE) 进行了地球化学研究，结果表明，地下水系统呈弱碱性(pH值为7.18~9.64) 的偏还原环境，沉积物多为Ce正常或轻微负异常及Eu负异常；沉积物中碘含量为0~1.78×10-6；ΣREE含量较高，ΣLREE/ΣHREE比值为2.79~4.14，即富集轻稀土元素(LREE) 而亏损重稀土元素(HREE).ΣREE与碘含量呈负相关关系，虽然铁氧化物/氢氧化物矿物的还原性溶解可导致二者的释放，但由于沉积物有机质产生的低结晶矿物对碘的强吸附性，使沉积物中碘含量较高；弱碱性环境中REE的再吸附过程会导致沉积物中富集LREE；沉积物中碘含量与氧化还原敏感组分TOC、U、V及Eu]_N的关系也表明，地下水系统的氧化还原条件及有机质含量是影响碘富集的重要因素. 

Characteristics of Rare Earth Elements in the Sediments of the Datong Basin and Its Indication to the Iodine Enrichment

Under arid and semi-arid climate, high iodine concentration in groundwater of the Datong basin, has been a serious threat to the safety of drinking water for the residents. Sediments composition and rare earth elements (REE) were studied on the 300 m core samples from iodine-affected area of the Datong basin. Results show that the groundwater system in the study area is alkalescent (pH: 7.18~9.64) partial reductive environment, and sediments show the slightly negative anomalies of Ce and Eu. The content of iodine in sediments is 0~1.78×10-6. The content of ΣREE are high and the ΣLREE/ΣHREE ratios are 2.79~4.14, which means samples are enriched in LREE and depleted in HREE. There is a negative relationship between the concentrations of ΣREE and iodine. Although the reductive dissolution of the iron oxide / hydroxide mineral can result in the release of them, strong absorption of iodine by the low crystallinity minerals produced by sedimentary organic matter makes the iodine content in sediments higher. In slightly weak alkaline environment, the process of REE re-adsorption might attributed to the enrichment of LREE in sediments. The relationship between iodine contents and redox sensitive components (TOC, U, V and Eu]_N show that the redox conditions and organic matter content in groundwater system are important factors that affect the concentration of iodine.