STUDIES ON PARTICLE BREAKAGE DURING HYDRATION OF CALCINED MAGNESITE

The paper deals with the process of continuous particle breakage observed during the hydration of calcined magnesite and is studied as a case of substantial comminution of particles under a chemical process. The material studied was magnesite from Chalk Hills of Salem, India, calcined at 700°C and observed under hydration at different temperatures from 30° to 80°C. Starting from a narrow range of particle size (-75 + 63 microns), a rapid degradation of particle size by breakage was observed throughout the progress of hydration. The behaviour of the sample was studied by way of size analysis at various time intervals, the degree of hydration and the determination of variation of number of particles, surface area, etc. during the process. It was not possible to correlate the observed results on the basis of simpler matrix models or common first order equations of the kinetic models. Earlier studies have suggested a mechanism of advancing interface for the reaction with the usual equation obeying 2 3 index law. The present work however indicates that the reaction may not progress inwards by way of an interface, but takes place on a fresh surface made available by breakage. The reaction causes further breakage and a repetitive cycle of breakage, formation of fresh surface and a rapid reaction leading to further breakage appears to be taking place, without appreciable ageing of the hydrated product in the presence of water. © 1990.