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Coals can be potent sources of heavy metal pollution upon their mining and utilisation. While Tanzania has many coal deposits, the coals have not been evaluated to determine their heavy metal contents and their potential to cause environmental pollution. Therefore, a study was undertaken to determine the heavy metal contents of the coal and its by-products from the Songwe-Kiwira mine, Tukuyu district, southern Tanzania. This is the area in the country where, currently, coal is being mined. The contents of lead (Pb), copper (Cu), chromium (Cr), cadmium (Cd), zinc (Zn), selenium (Se), and manganese (Mn) in different coal grades, in coal combustion by-products, and in various coal-derived sediments were determined by atomic absorption spectrophotometry (AAS) following aqua-regia digestion. The results showed the presence of heavy metals in the Kiwira coal. The highest levels of metals recorded in the different grades of coal were 6.8, 4.7, 7.9, 35.1, 72.4, 58.9, 59.5 and 801.1 mg/kg for Cr, Ni, Cd, Pb, Zn, Cu, Se and Mn, respectively. Long-term disposal of these coals will result in pollution of the surrounding environment. Some metal (Zn, Cr, Mn, Pb, Cd) levels in the coal indicated significant (p = 0.05) differences with coal sampling periods, an indication that the metal contents of the Kiwira coal were not uniform along the coal seams or layers. The highest levels in the solid ash were 6.4, 5.2, 9.4, 33.3 and 60.4 mg/kg for Cr, Ni, Cd, Pb and Se, respectively. The highest levels for the fly ash were 7.1, 4.5, 10.8, 90.9 and 45.4 mg/kg, for Cr, Ni, Cd, Pb and Se, respectively. Long term accumulation of these metals will cause environmental pollution. Results showed variations in metal contents between the coal grades, its combustion by-products as well as between the sampling periods. |
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