鄱阳湖流域赣江北支水体和沉积物中稀土元素的含量和分异特征

稀土的开发和广泛应用使得人们倍加关注其在环境中的分布及其环境地球化学行为。赣江作为鄱阳湖流域五大入湖河之一,发源于稀土资源富集的赣南地区,而其下游水体及周边地下水中稀土元素的含量和分异特征目前尚不完全清楚。以赣江北支水体及沉积物为研究对象,开展了稀土元素地球化学研究。结果表明,赣江北支水体中稀土元素总量在地表水中为230~1 146 ng/L(均值458.85 ng/L),地下水中为284~1 498 ng/L(均值634.94 ng/L),沉积物中稀土元素总量为177.9~270.7 mg/kg(均值226.99 mg/kg)。PHREEQC模拟计算表明,水体中的稀土元素主要以碳酸根络合物(REEC0₃⁺)的形式存在。地表水和地下水总体上均表现为重稀土元素相较于轻、中稀土元素富集,沉积物未表现出明显的富集特性;水体具有Ce、Eu负异常特点,而沉积物表现为Ce正异常和Eu负异常,指示氧化还原环境和水岩相互作用对稀土元素在水-沉积物系统中迁移转化的影响。地下水中稀土元素的含量沿流向具有上升趋势,而水体中重稀土元素的富集程度不断减弱,同时碳酸根络合物(REEC0₃⁺)的占比不断降低,反映水体中稀土元素的含量受到pH、胶体吸附、络合作用以及地下水-地表水相互作用的影响。水体中重稀土元素的富集受到碳酸根络合反应的影响,Ce、Eu负异常与Ce氧化沉淀和母岩特性相关。Gd异常值表明,研究区中下游水体中的Gd元素受到人为输入的影响。

REE Concentration and Fractionation in Waters and Sediments from the Northern Branch of Ganjiang River,Poyang Lake Catchment

The enhanced exploitation and widespread use of rare earth elements (REE) have led to increasing interest in REE distributions in environments and their geochemical behaviors. The Ganjiang River is one of the five major rivers in the Poyang Lake catchment, and is originated from the rare earth district in southern Ganzhou. However, the REE concentration and distribution in the downstream water bodies and surrounding groundwater are poorly understood. We investigated the REE geochemistry in waters and sediments of the northern branch of Ganjiang River. Results show that the total REE concentrations are of 230-1,146 ng/L (average 458.85 ng/L, surface water), 284-1,498 ng/L (average 634.94 ng/L, groundwater), and 177.9- 270.7 mg/kg (average 226.99 mg/kg, sediment). The PHREEQC simulation indicates that REEs are mainly in the form of carbonate complex (REEC0₃⁺) in the water samples. Both surface water and groundwater generally show enrichments of heavy REE (HREE) over light REE (LREE) and middle REE (MREE), while the sediments do not show significant enrichment features. The water samples are characterized by negative Ce and Eu anomalies, while the sediments show positive Ce but negative Eu anomalies, indicating that redox and water-rock reactions have influenced REE transformation in the water-sediment system. Along the flow path, REE concentrations tend to increase in groundwater, while both the degree of HREE enrichment and the REEC0₃⁺ proportion decreases. These behaviors reflect that REE concentrations are controlled by pH, colloidal sorption, complexation and surface water-groundwater interactions. The water HREE enrichment is likely attributed to carbonate complexation, and the negative Ce and Eu anomalies are related to the oxidative Ce precipitation and the parent rock REE inheritance. The positive Gd anomalies in the water samples from the middle and lower reaches of the river suggest anthropogenic REE input.