The calcination of dolomite. Part I.—The kinetics of the thermal decomposition of calcite and of magnesite

Abstract

The kinetics of the isothermal decomposition in vacuu of calcite (two series of experiments, A and B) and of magnesite (one series of experiments, C) has been studied with the aid of an automatically recording sorption balance, over the approximate ranges 720" to 780" C for calcite and 540" to 600" C for magnesite. In all cases the course of the decomposition can be represented by the equation (w/wo)" = -kt + a, where W/WO = the fraction still undecomposed at time t ; k, a and n are constants. The value of (1n) varies slightly from one experiment to another, but its average value is 0-74 for series A, 0.72 for series B and 0.58 for series C. The decomposition probably occurs at an interface advancing from the outside of the lump, or of the whole sample, to the interior: this mechanism would require (1n) = 0-67 in the ideal case, and the deviations from this value are perhaps due jointly to self-cooling, to impedance in the escape of carbon dioxide and to a somewhat slow rate of formation of decomposition nuclei. The value of the energy of activation E of the decomposition are, for calcite (cal mole-1) : series A, 35,000 f 4,800 ; series By 41,600 d= 2,900, so that they do not differ significantly from the energy of decomposition (40,000) ; for magnesite E is 35,600 f 3,300, and so appears to be somewhat higher than the energy of decomposition (ca. 27,000). The rate of decomposition of both substances agrees reasonably with the Polanyi-Wigner expression.

Análisis microestructural por DRX de CaO obtenido a partir de carbonato cálcico molido (CCM)

“…La cinética de descomposición de CaCO 3 ha sido abordada en diversos trabajos desde el trabajo inicial de Britton y col. (2). En los trabajos de Fischer (3,4), se efectúa una caracterización física de la cal obtenida, aportándose, en el segundo trabajo, tamaños de cristalito aparente obtenidos para [100] a partir de medidas en la reflexión 200.…”

Development of Secondary-fuel Injection Technology for Energy Reduction in the Iron Ore Sintering Process

“…At first, the basic state was prescribed with differential equations based on the conservation laws of mass, enthalpy and momentum. In the mathematical model, combustion of coke breeze, [31][32][33] resolution of CaCO3, 34) evaporation-condensation of water 35) were considered as the main reactions during sintering. Moreover, the combustion rate of CH4 gas was installed into the mathematical model to calculate the temperature distribution with the gaseous fuel injection method.…”

Pioneers of Adsorption Science 2. Sidney John Gregg

“…As the calcination temperature is increased, the metastable pseudolattice always undergoes recrystallization and sintering with a reduction in surface area. With poorly ordered gels there is generally no significant thermal activation, but only an overall progressive loss of surface area (Goodman and Gregg 1960;Gregg and Hill 1953). Under carefully controlled conditions, highly active products can be prepared, but such large surface areas (approximately 300 m 2 g -1 ) are highly dependent on the chemical and physical nature of the precursor and the heat treatment (Gregg 1960(Gregg , 1961Sing 1972).…”

“…A. Behrens, J.P. Saenz and W. Diano) from the University of Montevideo. Their research contributions included aspects of powder technology (Gregg and Behrens 1951;Gregg and Saenz 1966) and of adsorption energetics (Diano and Gregg 1972). In addition, Gregg spent a busy and enjoyable six months in Montevideo as a visiting professor.…”

“…Together with George Winsor and the support of Professor H.T.S. Britton, he carried out a series of investigations on the extraction of magnesium from sea water and the thermal decomposition of calcite, magnesite and dolomite (Britton et al 1952). This work entailed the development of a more refined automatically recording adsorption balance (Gregg and Wintle 1946) and a modified standard analytical balance (Gregg and Winsor 1945).…”