Dissolution of Na₂O · CaO · nSiO₂ glasses in Na₂CO₃ solution for long-term and short-term experiments

Dissolution of the glasses with compositions of Na₂O · CaO · nSiO₂ (n = 2.5-6) in 0.5 M Na₂CO₃ solution was studied experimentally. The experiments were carried out with autoclaves under the conditions of the autogeneous pressure, 150 °C, and durations from 16 hours to 60 days. Experimental results show that the dissolution rate is increased with the increase of silica-content of the glass, especially in long-term ones. By comparison, the dissolution rate is significantly slower in long-term experiments than in short-term ones. During dissolution, the surface reaction generally plays the main role in short-term experiments, whereas in long-term ones, the solid diffusion and the surface reaction may both act significantly. In this kind of alkaline solution, percentage of Ca would be rich on the glass surface, and Na/Si depletion occurred. As the solution was renewed in short-term systems, the dissolution rate of Na was faster than Si on the glass surface. While the precipitation occurred, Si were consumed by the precipitated phases continuously and therefore the depletion of Si became more obviously. In addition, the high-Si glasses own higher dissolution rates than low-Si ones in long-term experiments, because the minerals growing on the low-Si glasses are closed and they prevent the reaction solution and glass.