The Effect of Solution Ph and Ion Concentrations on Leaching of Silicate Glass

For complex glasses such as simulated nuclear wastes, glass dissolution is a complex process, involving selective leaching of cations, reprecipitation reactions, and protective film formation. In order to begin to understand this complex behavior, each of the above phenomena is being studied, one reaction at a time, on simple alkali silicate glasses under controlled environmental conditions. To date, two types of reactions have been investigated. The first reaction type is the selective leaching of cations from the glass, resulting in the formation of a hydrated “gel” layer on the glass surface. The second reaction type is the reaction of ionic or colloidal species in solution with this gel layer. Reactions in the second category include ion exchange reactions and sorption reactions which can result in protective film formation. Studies of these simple reactions have led to the development of new leaching models and to observations which begin to explain the behavior of complex glasses, and predict how glass dissolution should change as a function of the chemical environment.