Rare earth elements geochemistry in surface floodplain sediments from the Xiangjiang River, middle reach of Changjiang River, China

The Xiangjiang River is one of the most important tributaries of the Changjiang River in southern China. In this study, floodplain sediments from the Xiangjiang River have been analyzed for sediment grain size, and trace and rare earth elements (REEs). The results have been used to characterize the sediments REE composition and distribution and to identify the sediment sources and the effects of industrial pollution. The total REE (ΣREE) concentrations of the river sediments show wide variations, ranging from 37.5 to 237.4 μg g −1 , with an average of 145.6 μg g −1 . The chondrite-normalized REE patterns can be differentiated into two groups, whereas the average upper continental crust (UCC)-normalized REE pattern can be classified four groups. ΣREE shows strong positive correlations with clay (%) ( r = 0.91), and r = 0.89) and strong negative correlations with sand (%) ( r = 0.91), implying that the grain size is an important factor in controlling the REE abundance because REEs are preferentially enriched in clay minerals in fine sediments and diluted by quartz and carbonate minerals in coarse sediments. ΣREE yields strong positive correlations with Mn ( r = 0.78) and Fe ( r = 0.97), suggesting that the REE composition of Xiangjiang river sediments is controlled by clay mineral compositions. The reason is that Fe- and Mn- oxyhydroxides accumulate in fine-grained sediments and control the REE abundance. Two stations (XJ08 and XJ14) show different UCC- and chondrite-normalized REE distribution patterns with relative light rare earth element (LREE) depletion and heavy rare earth element (HREE) enrichment compared with other stations, suggesting they have been polluted by industrial effluents. Therefore, REEs can be effectively used to trace sediment provenance and pollution sources.