Geochemical and environmental baseline of major and trace elements in Zarand coals, southeastern Iran

Abstract

In order to establish a geochemical baseline for environmental impacts of coal measures in Rhaeto-Jurassic Zarand coalfields, multielement geochemistry of 22 host rocks, 26 coal seams and 9 coal ashes was determined by ICP-MS, ICP-AES, XRF, PGM-ICP24 and CV-ASS methods at ALS Chemex, Canada. The discrimination diagrams of major trace elements show a continental margin granitoid arc provenance for coal-bearing sandstones and shales. Compared to the crustal abundance, world coals and American coals, the geochemical baseline for most of the elements is within the limits of safeguard background values. However, higher contents of Li (49.31-185 mg/kg), Rb (71.12-131.73 mg/kg), Cs (7.13-16.12 mg/kg), V (72.19-213.1 mg/kg), Th (7.63-11.8 mg/kg), As (10.1-31.31 mg/ kg), Nb (5.4-15.07 mg/kg),Ta (0.4-1 mg/kg), Hf (1.89 mg/ kg), Ga (12.63-32.16 mg/kg), Ce (37.31-64.28 mg/kg), Pb (40.23-55.76 mg/kg), Cr (48.23-133 mg/kg), Zr (60.39 mg/ kg), and Hg (0.24 mg/kg), are of some environmental as well as economic concerns. The low values of B (0.12-12 mg/kg), S (7,839-10,567 mg/kg) and Zn (63.25-157.6 mg/kg) in Zarand coals may indicate a fluvial freshwater environment of coal deposition. Au, Pt and Pd contents are slightly higher than the crustal abundance and further studies are required for their possible environmental and economic evaluation. As the mean Hg value in ash (0.0075 mg/kg) is almost 32 times lower than the mercury content of the coal seams (0.24 mg/ kg), it is noteworthy that much of Hg is released by coal combustion to the atmosphere, which has certainly a detrimental environmental impact. The Ce, Cs, Ga, La, Li, Rb and V values are much higher than the average world and American coals and merit further investigations for being the economic by-products.