Determination of heavy metals concentrations in coal and coal gangue obtained from a mine, in Zambia

During mining, processing and utilization of coal, the environment is exposed to piles of coal, coal gangue and coal ash, which have human health concerns. Coal and coal gangue samples were obtained from a coal mining company located in Southern Province, Sinazongwe District, Zambia. The main objective of this research was to determine the level of heavy metals in coal gangue and coal from Sinazongwe District. Six metals (Ni, Pb, Cu, Cd, Fe and Zn) were determined using an atomic absorption spectrophotometer. The mean concentration of heavy metals in four grades of coal was as follows: Zn (23.83–71.67), Cu (20.82–44.59), Fe (7148.85–22,905.44), Ni (0.89–16.24), Cd (0.38–1.11) and Pb (13.96–46.02) mg/kg. The mean concentration of heavy metals in two types of coal gangues was as follows: Zn (36.62–63.56), Cu (1.51–44.28), Fe (11,619.86–12,193.46), Ni (6.48–7.89), Cd (0.97–1.17) and Pb (58.67–70.18) mg/kg. Generally, the concentrations of heavy metals detected were within the safe environmental disposal limits except Pb which was elevated in coal gangue. Digestion of samples was done in a mixture of hydrofluoric, nitric and perchloric acids. ANOVA was used to analyse the data, with means separated using Duncan’s multiple range test at 95% significance level. Generally, significant differences (p < 0.05) were noticed for the mean concentration of heavy metals with all four grades of coal. The mean concentrations of Zn, Cu, Ni and Pb showed significant differences with all grades of coal (p < 0.05). There was a significant difference (p < 0.05) in mean concentration of Zn with mudstone, sandstone and control sample.