Experimental study of the dissolution rates of a simulated borosilicate waste glass as a function of pH and temperature

To quantify the rate of glass dissolution, a series of experiments have been conducted using the single-pass flow-through (SPFT) apparatus. The SPFT apparatus allow for the transfer of fresh input solution from a reservoir bottle into a Teflon reactor and finally into a sample collection vial. These experiments were conducted under varying conditions such as: temperature, from 23 to 90 C, and solution pH, from 7 to 12. Results from these experiments show that as the temperature and solution pH increases the glass dissolution rate also increases. For example, the dissolution rate at 90 C was approximately 56 times higher at pH (23 C) 12.0, 5.66± 1.08 g m-2 d-1, compared to pH (23 C) 7.0, 0.016 ±0.003 g m-2 d-1. Performing a linear regression as a function of pH at each temperature resulted in a slope [power law coefficient (plc)] of 0.50 ±0.05 indicating that plc does not depend on temperature within experimental error. Temperature also affects the dissolution rate, evident by as much as a 14x increase in the rate with a 30 degree increase in temperature. Applying an Arrhenius expression to the data obtained at each pH suggested that the dominant mechanism of dissolution was a surface-controlled process, evident by an overall activation energy (Ea) of 60 ±6 kJ mol-1. Although translation and interpretation of these SPFT results to long-term glass dissolution under repository conditions requires further analysis, these results provide the rate-law parameters needed to conduct source-term release calculations using reactive transport models