Abstract A kinetic model has been obtained for the selective dissolution of the glassy matrix with dilute sulphuric acid at 70–100°C to liberate the zinc-rich phase obtained by reheating Imperial Smelting Process slags at above 900°C. Data were analyzed according to the “shrinking core models” Kt = 1 − (1 − a) 1 3 for chemical control, Kt = 1 − (2 3) a −, (1 − a) 2 3 for diffusion through a solid matrix. The kinetic mechanism can be divided into two stages. The first is chemically controlled, the second diffusion controlled. Experimental data showed a good fit with the proposed equations.