Study on the Mineralogical and Geochemical Characteristics of Arsenic in Permian Coals: Focusing on the Coalfields of Shanxi Formation in Northern China

Abstract

The Huainan Coalfield is a typical multi-coal seam coalfield. In order to systematically investigate the distribution, occurrence, and integration of arsenic (As) in Shanxi coal, 26 coal samples and three rock samples were collected in the No. 1 coal seam of Huainan coalfield. The minerals, major element oxides, and As were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), polarized light microscopy, X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma-mass spectrometry (ICP-MS). The results indicated that the coals of Shanxi Formation were characterized by very low ash yields and low total sulfur contents. The identified minerals by XRD in the studied coals are dominated by kaolinite, quartz, calcite, and a lesser amount of pyrite. The As content ranges from 10.33 mg/kg to 95.03 mg/kg, with an average of 44.74 mg/kg. Compared with world coals, the studied coals have higher contents of As, which are characterized by enrichment. Based on statistical analyses, As shows an affinity to ash yield and possible association with silicate minerals. The contents of As in all occurrence fractions were ranked from high to low as follows: residual > Fe-Mn oxides > organic > exchangeable > carbonate. Using B, w(Sr)/w(Ba) and w(B)/w(Ga) geochemical parameter results to invert the depositional environment of the Huainan Shanxi Formation, a suitable coal-forming environment can cause relatively enriched As in coal.