Enrichment and distribution of trace elements in Padhrar, Thar and Kotli coals from Pakistan: Comparison to coals from China with an emphasis on the elements distribution

Abstract

This paper reports the mineralogical and geochemical compositions of the Padhrar (salt-range), Thar (Block Nos. 3 and 5) and Kotli coals. The coal investigated in this study is lignite to sub-bituminous coal, with a broad range of ash yields, volatile matter content and sulfur contents. The mineralogical characteristic, major and trace elements were determined by X-ray diffraction, inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry, respectively. The mineral assemblages, sulfur contents, ash yields, and (CaO+MgO+Fe2O3)/(SiO2+Al2O3) ratio varied significantly in the coal, which is attributed mainly to variation in the depositional environment. Pyritic sulfur is the main form of sulfur in the coals from Padhrar, Kotli and Thar coalfield. The minerals in the studied coals are dominated by quartz, pyrite, kaolinite, illite, along with calcite, feldspar, siderite, montmorillonite and gypsum. Sixteen trace elements, including Li, Be, B, Ti, Sc, V, Cr, Mn, Co, Ni, Cu, Zn, As, Rb, Sr, and Ba and five major elements P, Ca, Al, Fe, and Si, were investigated in this study. The trace element concentrations show variety within the coal seams in the Thar coals and the affinities vary among locations. The concentration of Sr, Ti, Zn, Li, Ni, Cu, Sc, As, Be, and B in the present study are within the range of average Chinese coal values, with the exception of V, Cr, Fe, P, and Rb. On the other hand, compared with world coals, the studied coals have higher contents of B, Cr, Li, Fe, V, Rb, P, and Sc. Based on statistical analyses, most of the trace elements, show an affinity to ash yield and possible association with pyrite, kaolinite, and calcite.