Determination of hazardous trace elements in select Hwange, Zimbabwe coal samples with a comparison to select South African coal samples.
Date
2015-04-28
Authors
Mguni, Nonhlanhla Gugu
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Abstract
In southern Africa, coal is a relatively abundant and cheap fossil fuel which is a major source of energy and a huge income generator. Although coal has found a lot of use, it is an anthropogenic source of trace element emissions and although these trace elements (TEs) may occur in parts per million, mass consumption of coal during utilisation results in the release of large quantities of potentially harmful TEs to the environment. With reported diseases like arsenism, minamata disease and selenosis (Zheng et al., 1999) from coal combustion emissions, it is important to regulate TE emissions. Due to global perception, the following TEs were chosen for consideration: As, B, Be, Co, Cd, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se and V (which were analysed by ICP-MS) and Hg (which was analysed using an automatic Hydride Generation-Flow Injection Mercury System).
There is limited data on TEs in African coals and whilst no TE control legislation exists, Pb in petrol is currently being regulated in South Africa. Important factors such as the mode of occurrence of TEs and their associations with other minerals in coal influence, or affect, the fate of TEs release during coal utilisation.
Three run-of-mine (ROM) belt cut coal samples were supplied by Hwange Colliery and two South African samples were used for comparison. The coal samples were subjected to density fractionation and sequential leaching. Mineral matter was determined using XRD and coal petrography was used to consider the organic components. Comparisons of the ROM coals with average global and mean South African values were carried out. Generally, TEs like Cd, Sb and Se in ROM samples of both coalfields appear consistent with published SA data and global average values, whilst values of Hg and Mn in all the coal samples are above the global and SA average values.
Density fractionation data show most TEs are concentrated in higher density fractions, hence showing an association with minerals over organic matter. Most TEs in Zimbabwean coals seem to show a strong correlation with mineral matter which should be able to be removed prior to coal utilisation during efficient beneficiation practises.