Kinetics of fly ash leaching in strongly alkaline solutions

We have leached fly ash samples from six power stations in potassium hydroxide solutions at a water-to-solid mass ratio of 40 g/g. A wet chemical method was developed which provides for a detailed characterization of the reactivity of fly ash. The leaching process could be divided into three stages. In stage one, reaction progress measured by the relative mass of fly ash reacted (α) was controlled by the rate of glass network dissolution while very little gel formed (α 0.45). The data were modeled using a modified Jander equation and rate constants were calculated for each process. The rate constants for stage one reflect an intrinsic glass property, chemical durability, which increased linearly with increasing concentration of network formers in the glass phase of a fly ash.