Occurrence characteristics of Sr in coal from Tashan Coal Mine in Datong,Shanxi Province

Datong Coalfield was intruded by igneous intrusions in both the Indosinian (Late Permian to the end of the Triassic) and the Yanshan (Late Jurassic to the Early Cretaceous) periods，which caused contact metamorphism of the coal seam. Previous studies have shown that Sr is significantly enriched in coal from the 5222 tunnel of the Tashan coal mine. The maximum concentration of Sr in thermally-altered and unaffected coal is 3067 μg/g and 2729 μg/g respectively, and the average concentration of Sr is 1165 μg/g, which is 10.6times of the world average level in hard coal. However, the modes of occurrence of Sr in the Tashan coal still remain unclear. Samples in the 5222 tunnel including coal and intrusive rock were systematically collected. Inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF) were applied to elucidate Sr concentration variations in the sample; correlation analysis, scanning electron microscope with energy spectrum (SEM-EDS), and sequential chemical extraction procedure (SCEP) were carried out to reveal the occurrence modes of Sr, as well as the characteristics of Sr-bearing minerals. The results demonstrated that Sr exhibits a strong correlation with P2O5 in coal; Sr mainly occurs in phosphate (apatite) and clay minerals that are intimately associated; apatite was distinguished as fluorapatite in the shape of hexagonal columns and hydroxyapatite in the shape of fine scattered particles embedded in the clay minerals.