Elemental characterization of Nigerian coals and their ashes using particle induced X-ray emission (PIXE) spectrometry for environmental pollution assessment

Nigerian coals and their ashes were investigated using PIXE spectrometry to ascertain their elemental composition, characterize and correlate them, and to determine their environmental risk assessment when combusted. Eleven and 18 elements detected in the raw coals and the ashes, respectively, were subjected to appropriate statistical analyses. Mean elemental summation (%) of the coals and ashes were 8.4 and 39.0, respectively, while average % ash content was 29.6, indicating that they were rich in potential toxic elements which could be emitted into the environment during coal combustion. This was corroborated by t-test results. It is found that pollution index (PI) values for V, Co, Mn, Ni, Cu, and Zn in the coal ash are greater than 1.0. This implies that combustion coal/coal ash may serve as a source of toxic element pollution in environmental media which could produce ill-health. Cross-plot analysis results showed moderate positive correlations, suggesting inter-element correlations among the samples, establishing relationships among the coals. This was validated by the clustering analysis results which indicated three major groups which were also fairly correlated with one another, signifying similar genetic origin. Elemental clustering indicated closest inter-element association among transition metals. This was also confirmed by their Pearson correlation matrices results, indicating chemical affinity and/or similar genetic origin.