Reaction mechanism and kinetics of the mercury solid waste pyrolysis

Abstract

The present study focuses on the kinetic mechanism of mercury removal from contaminated solid waste generated by chlor-alkali plant using pyrolysis. The isoconversional method of kinetic analysis was used to calculate the kinetic parameters that best describe mercury thermal decomposition in the solid waste. A mechanism involving 6 heterogeneous and homogeneous reactions was proposed to represent the behaviour of mercury compounds in the solid matrix during thermal treatment. The proposed model was compared to nine models previously reported in literatures to elucidate the controlling reaction mechanism. Fitting each of these to the experimental data of thermal decomposition of the mercurial sludge sample, confirmed the hypothesis that not a single mechanism is ruling the process. The D1-diffusion mechanism could be considered the controlling step of the process at high retention times while at low thermal decomposition times (˂15 min) the diffusion mechanism (D1) as well as the third order reaction mechanism (F3) could be controlling the process. Nevertheless, as a first depth-in to the knowledge of this polydisperse and multicomponent system (mercurial sludge), the diffusion mechanism (D1) can be considered the overall controlling stage as an increase of temperature smooths the progress of the chemical reactions involved.