The dissolution of Mg-Al hydrotalcites in aqueous solution and its mechanism were investigated

with the dissolution kinetics and thermodynamics at different temperatures and pH. The kinetic model with the outer diffusion and chemical reaction control can be used to describe the dissolution process appropriately

with different controlling steps in various pH ranges. In the pH range from 1.0 to 3.8

the hydrotalcites dissolve completely and the dissolution rate decreases as pH increases

with the dissolution controlled by desorption. In the pH range from 4.2 to 9.4

the hydrotalcites partly dissolve

independent of pH

with the dissolution controlled by surface exchange reaction. On the other hand

the Gibbs free energy change of the dissolution reaction from the Mg-Al hydrotalcite is estimated as 29.516 kJ·mol-1 at 298 K. The result is consistent with the experimental evidence.