Kinetics of oxidation of CaS particles in the regime of high SO2 release

Oxidation experiments of pure CaS particles (18.6 mu m size) in the regime of high SO2 release (890 degrees C < T < 1175 degrees C at P-O2,P-O = 0.21 atm) were carried out in a thermogravimetric analyser. Additionally, the ev olution of SO2 liberation during oxidation was followed by experiments carr ied out in a quartz microreactor. SEM-EDX analyses of oxidised CaS pellets allowed the structural changes during oxidation to be disclosed. Air oxidat ion of the CaS particles used in this work, consisting of agglomerates of C aS crystallites, takes place via oxidation of the CaS surfaces to CaSO4. Th e product so formed rapidly reacts with the contiguous CaS via a solid-soli d reaction to form small CaO grains of a rounded shape. These grains are su lphated by the SO2 released in the solid-solid reaction, thus growing in si ze and eventually plugging the pore structure of the particle. The growing of the CaO grains involves crystallisation towards a cubic-like shaped CaSO 4 phase. A fraction of the SO2 formed via the solid-solid reaction is relea sed to the bulk gas phase during the first stage of reaction, before closur e of the pore network of the particles takes place. Afterwards, the gases d iffuse inside the particles via a solid-state mechanism. A kinetic model fo r CaS oxidation, which takes into account the above consideration, was deve loped. (C) 1999 Elsevier Science Ltd. All rights reserved.