Effect of a siliceous additive on aqueous alteration of waste glass with engineered barrier materials

A simulated waste glass was leached in the presence of bentonite, iron and magnetite (as a corrosion product), with and without amorphous silica at 60°C for 364 days. These experiments were carried out to assess the effect of silica on the aqueous alteration of waste glass in contact with engineered barrier materials. The weight losses of samples without amorphous silica increased with time, while the weights of samples with amorphous silica were almost unchanged. This shows that the concentration of silicic acid in the porewaters reached the solubility of amorphous silica quickly, so that the detrimental effects of the engineered barrier materials were efficiently reduced. We also conducted MCC-1 type experiments with the same glass using silica saturated solutions at 60°C, 75°C and 90°C to understand the alteration mechanisms of glass under these conditions. The results show that the glass alteration under these conditions is dominated by glass hydration, and the release of soluble elements from the waste glass closely follows a relationship dependent on the square root of time.