Trace and major metal abundances in the shale and coal of various seams at Okaba coal mine, Kogi State, Nigeria

Abstract

The distribution of a number of trace and major elements in the shale and coal of differing seams in Okaba, Kogi State, Nigeria, was studied using energy dispersive x-ray fluorescence spectrometer. The study was necessary to compare the quality of Okaba coal to world standards of coal quality. Major elements of Al, K, Ca and Fe showed concentration ranges of 5.93±2.49 – 8.42±0.003 mg/g, 0.18±0.46 – 2.16±0.0 mg/g, 0.53±0.41 – 2.23±0.35 mg/g and 6.05±0.004 – 18.28±1.2 mg/g respectively. The mean concentrations are 7.24mg/g (Al), 1.25 mg/g (K), 0.91 mg/g (Ca) and 11.86 mg/g (Fe). These values are clearly above the recommended concentrations in coal quality standards and for air emission standards by the World health organization. Trace metals of Ti, Cr, Mn, V, Ni and Cu showed concentration range of 0.84±0.007 – 2.98±0.007 mg/g , 0.03±0.0 – 0.12±0.025 mg/g, 0.02±0.11 – 0.30±0.02 mg/g, 0.02±0.44 – 0.2±0.05 mg/g, 0.01±0.075 – 0.12±0.001 mg/g and 0.03±0.02 – 0.62±0.001 mg/g respectively. These results indicate that Okaba coal and shale is enriched in the major elements analysed in comparison to worldwide averages of coal while the trace elements with exception of Ti are below the coal quality standards. Correlations between the various metals were also established. The S content correlated inversely well with the K content of both the shale and coal. Expectedly, the percentage Si content was high in the shale1  (26.70%) and shale2 (26.38%), while the lowest concentration was  recorded at Okaba coal seam 5 (6.58%). The absence of Cl, Br, Na, and Mg in the samples clearly indicates the extent of surface leaching on the study area. This is evident by the various mountainous depressions in the study area.

Keywords: Trace metals, EDXRF, coal, shale, major metals, seam.