Study on the correlation between trace elements in coal and coal-forming plants: a case study

Abstract

ABSTRACT For this study, coal samples were sourced from the Yan’an Formation (J2y), a middle Jurassic coal formation in the Northern Shaanxi province in China. We investigated the correlations between trace elements in coal and occurrence of coal-forming plants (CFPs) in an effort to determine the relationship between the abundance of CFPs and trace elements in the coal formation. Twenty-one trace elements (Be, B, P, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Sr, Mo, Ag, Cd, Ba, Hg, Tl, and Pb) in coal were determined using inductively coupled plasma-atomic emission spectrometry (ICP-AES). The enrichment characteristics of trace elements in coal were performed by using concentration coefficient value. CFPs were identified and measured by analyzing spore-pollen in the coal samples. Correlation analyses between trace elements in coal and CFPs were conducted using the SPSS 21 software package. Our results indicated that the coal formation contains an enriched concentration of Cd, slightly enriched concentrations of Zn and Ag, low concentrations of V and Mo, normal concentrations of the other 16 trace elements. CFPs identified in the samples included 17 families (Cupressaceae, Cyatheaceae, Cycadaceae, Dicksoniaceae, Dipteridaceae, Ephedraceae, Equisetaceae, Ginkgoaceae, Gleicheniaceae, Lycopodiaceae, Lygodiaceae, Osmundaceae, Pinaceae, Pteridaceae, Podocarpaceae, Polypodiaceae, and Taxodiaceae). Polypodiaceae is the richest in Pteridophyta. Ginkgoaceae, Cycadaceae, and Podocarpaceae were richer in Spemaiophyla. Those with a correlation coefficient more than 0.5 were found between the following: (i) Be, Sr, and Equisetaceae; (ii) V, Ni, and Cu, and Polypodiaceae; (iii) P and Ginkgoaceae; and (iv) Ba, Pb, and Cupressaceae. Significant negative correlations were found between the following: (i) Ni, Cu, Ba, Pb, and Osmundaceae; (ii) Sr and Polypodiaceae; and (iii) Sr and Ginkgoaceae.