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

The influence of temperature and oxygen partial pressure on the oxidation o f pure CaS particles (empty set = 18.6 mu m) in the regime of low SO2 relea se (T < 890 degrees C for p(O2,O) = 0.21 atm, or T < 840 degrees C at any o xygen partial pressure) has been studied by means of thermogravimetric anal ysis. The kinetics of the process was analysed with the unreacted core mode l. After a short period of chemical control, the process is governed by sol id-state diffusion through the product layer. The effective diffusivity of oxygen in the CaSO4 lattice decreases with conversion and is a function of temperature and oxygen partial pressure. This dependence can be explained b y a grain boundary diffusion mechanism. This is thought to proceed via migr ation of Ca2+ and S2- ions from the CaS/CaSO4 interface to the particle sur face, where the ions are oxidised to CaSO4 by gaseous oxygen. (C) 1998 Else vier Science Ltd. All rights reserved.