Potentially hazardous air polluting elements such as Cr, Ni, As, Se, Cd, Sb, Hg and Pb, and potentially corrosive elements such as Zn and Pb are present in coal in concentrations lower than 1% (trace elements). These give rise to various environmental and technological problems during coal utilisation for energy production. In order to be able to address these problems and to develop methods of retention, behaviour of these elements during coal combustion & gasification processes were studied. Although trace element behaviour in conventional coal combustion systems is reasonably well known, there is a lack of similar knowledge in coal gasification, especially in the case of coal waste gasification. In this paper, thermodynamic equilibrium calculations using MALT for windows code were performed to predict the behaviour of the potentially toxic and corrosive trace elements during burning processes. The influence of temperature, pressure, chlorine and sulphur on equilibrium composition was studied. The results obtained from this study provide a strong data for model development in order to predict and mitigate the release of these elements into the environment.