Abundance and distribution pattern of rare earth elements and yttrium in vitrain band of high-rank coal from the Qinshui basin, northern China

Abstract Vitrain bands are clean and contain less ash than the bulk coal. A comprehensive study on rare earth elements and yttrium (REY) in vitrain may provide insights into the REY affinity. In this study, abundance and distribution pattern of REY in bulk coal, vitrain band and HCl-HF demineralized vitrain band was investigated. The coal studied in the present work was low-ash (ash yields ranging from 4.13 to12.86%, with 8.59% as the average), high-rank (anthracite to semi-anthracite, with volatile matter yields of 7.52–13.42%, 9.58% on average) coal of Permian Shanxi Formation, collected from the Sihe and Zhaozhuang mines, southern Qinshui Basin. The major minerals identified by powder XRD are illite and kaolinite, with small amount of ankerite, chlorite, calcite, siderite and pyrite. In comparison to the bulk coal, vitrain band displays a lower REY content and smaller compositional range. The bulk coal has N-, H- and L-type REY patterns based on Seredin-Dai’s classification, while the REY distribution for the vitrain band is commonly characterized by an H-type pattern. Moreover, the La N /Lu N ratio in the vitrain band is usually lower than that in the bulk coal. This probably suggests that the organic component has a higher HREY association than LREY compared to the inorganic part. The limited impact of HCl-HF demineralization on content and distribution pattern of REY in vitrain band probably reflects the weak acid solubility of REY in the vitrain band. The sequential chemical extraction procedure reveals that the clays and the residual organics, which have a stronger association with LREY and HREY respectively, are the dominant carriers of total REY in the studied bulk coals.