Heavy Metals Concentrations In Coal, Coal Ash, Soils And Grass Samples From Maamba Coal Mine, Zambia.

Abstract

Maamba Collieries Limited (MCL), is a large coal mining concession in Zambia and manages the only coal-fired Thermal Plant in Zambia. Coal mining activities are generally associated with human and environmental health concerns. Therefore, the purpose of this study was to assess the concentration of heavy metals in coal, coal waste, soil and grass in Maamba coal mining area in Zambia. The concentration of Nickel (Ni), Lead (Pb), Copper (Cu), Cadmium (Cd), Iron (Fe) and Zinc (Zn) were determined in Coal, Coal ash (fly and bottom ash), Sandstone and Mudstone. Most of the samples were digested by wet method using a mixture of nitric, hydrofluoric and perchloric acid as recommended in the literature. The grass forages were digested using a combination of nitric, sulphuric and perchloric acid. The standards for the various metals studied were prepared and Atomic Absorption Spectrophotometer (AA − 6300) was used to analyse the resultant solutions. The levels of heavy metals in coal in their decreasing order were: Fe ˃ Zn ˃ Cu ˃ Pb ˃ Ni ˃ Cd. The levels of heavy metals in coal ash in their decreasing order were: Fe ˃ Pb ˃ Zn ˃ Cu ˃ Ni ˃ Cd. The concentrations of heavy metals in coal ash were higher than the parent coal. The order of selected heavy metals concentration in sandstone and mudstone in their decreasing order were: Fe > Pb > Zn >Cu > Ni > Cd. The mean levels of selected heavy metals in mudstone were higher compared to sandstone. The physiochemical properties such pH and conductivity of the surface soils collected were determined. The results revealed that the pH ranged from 3.2 – 7.4 and conductivity ranged from 0.2 – 589.0 ms/cm. The overall, mean concentrations ranges of heavy metals investigated in soils from Maamba Collieries Limited (MCL) such as Pb, Zn, Cu, Cd and Ni were below the World Health Organization and Food and Agricultural Organization (WHO/FAO) permissible limits. Contamination factor values (CF) were used to assess the level of pollution in soils. The heavy metal contamination from East and West transects were ranked as follows: Pb > Cu > Fe > Ni > Cd > Zn and Pb > Ni > Cu > Zn > Cd > Fe respectively. The CF values of heavy metals from North and South were ranked as follows: Ni > Cu > Cd > Fe > Pb > Zn and Fe > Ni > Cd > Cu > Zn > Pb respectively. Whereas the samples of grass forages analysed were found to be uncontaminated by Ni, however, there were slight contamination of the following metals Fe, Cu, Cd and Pb as their concentrations were above the concentration of the control sample and the permissible limits set by WHO/FAO for plant materials.