MODELING OF THE ISOTHERMAL DEHYDRATION OF GYPSUM ORE TO OBTAIN BETA-HEMIHYDRATE

The kinetics and mechanism of the isothermal dehydration of gypsum ore were investigated. The gypsum ore was heated up to the dehydration te mperature of the CaSO4 . 2H(2)O --> CaSO4 . 0(5)H(2)O + 15H(2)O reacti on in a fluidized-bed reactor. Although the process was expected to be rather simple, the dehydration proved to include two reactions mechan isms, a first-order mechanism and a two dimension phase boundary mecha nism. For low temperatures, around 100 degrees C, dehydration is domin ated by the first-order reaction which seemed to consist of the extern al diffusion of water molecules evaporated from the surface of the sol id. The main mechanism probably describes the conversion of calcium su lphate from the dehydrate into the hemihydrate form in the temperature range of 110 - 140 degrees C. An Arrhenius-type kinetic equation was proposed and the parameters, a pre-exponential factor of A = 4.10(3) a nd an activation energy of E = 42 kJ/mol, were calculated.