The Petrography, Mineralogy and Geochemistry of Some Cu- and Pb-Enriched Coals from Jungar Coalfield, Northwestern China

Dongna Liu,Fenghua Zhao,Yu Zou,Anchao Zhou,Fangui Zeng

doi:10.3390/min8010005

Abstract

The petrological, geochemical, and mineralogical composition of the Carboniferous-Permian coal deposit in the Jungar coalfield of inner Mongolia, Northwestern China, were investigated using optical microscopy and field emission scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer (SEM-EDX), as well as X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The Jungar coal is of high volatile C/B bituminous quality with 0.58% vitrinite reflectance and has a low sulfur content of 0.70% on average. Inertinite (mineral-free basis) generally dominates in coal from the lower part of the Shanxi formation, and vitrinite is the major maceral assemblage in the coal from the Taiyuan formation, which exhibits forms suggesting variation in the sedimentary environment. The Jungar coal is characterized by higher concentrations of copper (Cu) in No. 6 coal, at 55 μg/g, and lead (Pb) in No. 4 coal at 42 μg/g. Relative to the upper continental crust, the rare earth elements (REE) in the coal are characterized by light and medium–heavy REE enrichment. The minerals in the Jungar coal are mainly kaolinite, dickite, pyrite, calcite, siderite, quartz, and, to a lesser extent, gypsum and K-feldspar. The enrichment and occurrence of the trace elements, and of the minerals in the coal, are attributed to the fragmental parent rock during diagenesis and coalification. The main elements with high enrichment factors, Cu and Pb, overall exhibit a notably inorganic sulfide affinity and a weak organic affinity. Primary and epigenetic sedimentary environment and the lithology of the terrigenous parent rock are the key factors that influence the occurrence and formation of Cu and Pb in coal. The depositional environment is more influential in the formation of Cu than Pb in coal. Lead is more easily affected by the terrigenous factors than Cu when they are under a similar depositional environment.

Highlights

Coal is a major source of nitrous oxide (NOX ) and sulfuric oxide (SOX ) pollutants, but is a geological repository for many inorganic elements
Coal geochemists have focused on the distribution, occurrence, and enrichment mechanisms of some harmful trace elements and beneficial metal elements in coal, such as As, Pb, Se, and Cr, rare metals, and rare-scattered elements
According to the classification of toxic trace elements in coal determined by Swaine [17], Cu belongs to the group of IIB harmful elements, Pb is one of the most harmful trace elements, and has received much attention by the environmental protection administration [18]

Summary

Introduction

Coal is a major source of nitrous oxide (NOX ) and sulfuric oxide (SOX ) pollutants, but is a geological repository for many inorganic elements. Coal geochemists have focused on the distribution, occurrence, and enrichment mechanisms of some harmful trace elements and beneficial metal elements in coal, such as As, Pb, Se, and Cr, rare metals, and rare-scattered elements. As harmful elements in coal, Cu and Pb have not received as much attention as As regarding their. Minerals 2018, 8, 5 occurrence and formation mechanism in coal [12,13,14,15,16,17,18,19]. According to the classification of toxic trace elements in coal determined by Swaine [17], Cu belongs to the group of IIB harmful elements, Pb is one of the most harmful trace elements, and has received much attention by the environmental protection administration [18]. The content of Cu and Pb has been thought to be relatively low in coal; some published literature has shown that the Cu and Pb content in coal is too high in parts of China [20,21,22,23], which in turn may be a potential threat to human health and plant growth

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