KINETICS OF ALKALI RELEASE FROM CAO-AL2O3-SIO2 SLAGS

The kinetics of alkali oxide (K2O or Na2O) release from a wide range o f CaO-Al2O3-SiO2 slags has been studied by heating in graphite crucibl es. The kinetics of the alkali release reactions has been determined b y chemical analysis of solidified slag samples. The effects of tempera ture, gas flowrate, gas composition, slag composition, and stirring of the slag have been evaluated. A theoretical analysis of the results o btained has established rate controlling mechanisms for alkali release under the experimental conditions studied. Reaction kinetics is prima rily controlled by diffusion of alkali oxide in the slag. In the latte r stages the onset of wetting of the graphite crucible by the slag may occur, leading to an increase of reaction kinetics. The onset of wett ing is associated with the formation of SiC and is enhanced by high te mperature, low slag basicity, and the presence of K2O rather than Na2O .