拉林河流域地下水中稀土元素质量浓度及分异特征

Mass concentrations and patterns of rare earth elements in groundwater of Lalin River basin

为了解拉林河流域地下水中稀土元素(REE)的地球化学特征,通过稀土元素质量浓度测试和北美页岩(NASC)归一化分析研究区域地下水系统中稀土元素的质量浓度和分异特征,利用软件PHREEQC模拟计算研究稀土元素沿流向的形态分布特征。结果表明:拉林河流域地下水中稀土元素总质量浓度(ΣREE)较低,范围为0.030~2.649μg/L(均值0.328μg/L);轻稀土元素(LREE)相对亏损,而重稀土元素(HREE)相对富集,具有显著Eu正异常和轻度Ce负异常;地下水中稀土元素主要以LnCO_(3)+和Ln(CO_(3))2-形态存在;随径流距离增加,地下水中ΣREE质量浓度明显下降,Eu正异常程度增大,LnCO_(3)+和Ln(CO_(3))2-形态质量浓度分别呈下降和上升趋势,稀土元素形成二碳酸配合物是造成重稀土元素相对富集的主要原因。

To understand the geochemical characteristics of rare earth elements(REE)in groundwater of Lalin River basin,the rare earth elements in the regional groundwater system were studied through rare earth element mass concentration testing and North American Shale Composite(NASC)normalized analysis.The distribution characteristics of REE speciation along the groundwater flow path were studied using PHREEQC software modeling.The results showed that:the total amount of rare earth elements(ΣREE)in the groundwater of the Lalin River basin ranged from 0.030 to 2.649μg/L(mean value 0.328μg/L);Light Rare Earth Elements(LREE)is quite depleted,while Heavy Rare Earth Elements(HREE)are relatively enriched,with significant positive Eu anomalies and mild Ce negative anomalies;the REE in the groundwater mainly existed in the form of LnCO_(3)+and Ln(CO_(3))_(2)^(-);along the regional groundwater flow path,the groundwater in Lalin River basin demonstrated the decline ofΣREE concentration and the increase of positive Eu anomalies.Furthermore,LnCO_(3)^(+)concentrations decreased and Ln(CO_(3))_(2)^(-)increased respectively along the groundwater flow path;the formation of dicarbonate complexes of rare earth elements was the main reason for the relative enrichment of HREE.