西江上游河水悬浮物中稀土元素的地球化学特征

采用改进的BCR逐级提取法和ICP-MS测试技术,对西江上游河流悬浮物中稀土元素进行了研究。结果表明:河流悬浮物稀土元素总量的含量变化范围在188～402mg/kg之间,并主要来源于流域内岩石的风化,反映了源区的物质特征。西江上游河水悬浮物中三种非稳定态(即酸可提取态、铁锰氧化物结合态和有机物硫化物结合态)稀土元素页岩(PAAS)标准化配分模式均显示出中稀土富集的特征。这种配分模式可能是由于流域内广布的海相沉积岩中磷酸盐矿物的风化所造成的。稳定态(即残渣态)的配分曲线较为平直,没有体现出明显的稀土分异。悬浮态稀土各赋存形态含量的顺序为:残渣态有机物硫化物结合态、铁锰氧化物结合态酸可提取态。中稀土元素Sm、Eu、Gd相对于轻、重稀土元素的稳定态所占比例偏低,而相对于三种非稳定态所占比例偏高,反映了其潜在的地球化学活性。

Rare-earth Elements (REEs) of the Suspended Particulate Matter in the Upper Reaches of the Xijiang River

The rare-earth elements (REEs) of suspended particulate matter (SPM) in the upper reaches of the Xijiang River were measured by inductively coupled plasma mass spectrometry (ICP-MS) after improving the BCR sequential extraction method. The result showed that the total REE concentrations of SPM are obviously higher than those of dissolved load, ranging from 188~402 mg/kg. The PAAS-normalized REE patterns for the three unstable fractions of REEs (AEC, bound to Fe-Mn oxides, bound to organic matter) exhibit middle REEs(MREEs) enrichment, indicating the preferential weathering of phosphatic minerals. The stable fraction of REEs (residual) presents a flat PAAS-normalized REE pattern, indicating no significant fractionation of REE in residual form. The percentage of four fractions of SPM obeys the following order: residual>bound to organic matter, bound to Fe-Mn oxides >AEC. The MREEs (Sm, Eu, Gd) have relatively lower percentages in the residual fraction and higher in other three unstable fractions.