Abstract:Kinetics of SiO₂ leaching from Al₂O₃ extracted slag of fly ash with sodium hydroxide solution was studied. The effect of leaching temperature, mass ratio of NaOH to SiO₂ and stirring speed on SiO₂ leaching rate was investigated. The results show that increasing leaching temperature, mass ratio of NaOH to SiO₂ and stirring speed increases SiO₂ leaching rate. The SiO₂ leaching rate is 95.66% under the optimized conditions. There are two stages for the SiO₂ leaching process, and the leaching reaction is very rapid in the first stage but quite slow in the second stage. The whole leaching process follows the shrinking core model, and the outer diffusion of no product layer is the rate-controlling step. The activation energies of the first and second stages are calculated to be 8.492 kJ/mol and 8.668 kJ/mol, respectively. The kinetic equations of the first and the second stages were obtained, respectively.

Key words: fly ash; leaching; kinetics; SiO₂