HYDRATION KINETICS OF RECARBONIZED LIME

The hydration rate of partially recarbonized lime pellets has been stu died by employing a single pellet into a stream of air/vapor water mix tures using a computer aided thermo-gravimetric technique. The hydrati on reaction takes place on a sharp, well defined interface between the product layer and the unreacted core. It has been found that the hydr ation mechanism consists in two steps. The first observes very slow hy dration rates and the second higher ones. During the first step the wa ter molecules diffuse through a close porous carbonate structure and t he second one begins when these molecules reach the calcium oxide-calc ium carbonate interface to continue through the lime core. A theoretic al model was derived to explain the results of this study. The experim ental results were acceptably well predicted with calculations perform ed using this model. On the other hand, it was found also that the hig her is the lime calcination temperature the thinner is the recarbonize d layer formed even under high CO2 partial pressures. However, these t hin layers are more effective to increase the hydration resistance of lime pellets than thicker ones. Th is is an important experimental fin ding since it indicates that low recarbonization extents are good enou gh to increase the hydration resistance of steelmaking lime without im pairing its quality.