Kinetic Size Effect During Dissolution of a Synthetic γ-Alumina

The dissolution process of a technical, nanodispersed γ-alumina in water was studied at 25 °C in the pH range 3.0 ≤ pH ≤ 11.5. Thereby, especial attention was paid to the influence of supersaturation on the dissolution behaviour observed. In conclusion, we were able to verify a size effect during the dissolution process, in the whole pH range investigated. In addition, we observed that changing supersaturation under identical conditions, leads to a shift of the maximum in the concentration profiles both, in absolute value and in time, when the maximum occurs. X-ray powder diffraction analysis and nitrogen adsorption measurements were used to identify the solid material collected during selected dissolution experiments. As a result, the formation of the aluminium phase -bayerite/gibbsite- could be excluded as a possible reason for the observed dissolution behaviour. The rate constants of the dissolution process were evaluated using the model of Gibbs free energy of cluster formation, which considers size effect among other factors. As a result, we were able to prove that the observed maxima in the concentration profiles were due to a kinetic size effect, caused by the size of the primary particles of the starting material, surface tension, and supersaturation in the system.