Solubility effects on the corrosion of nuclear defense waste glasses

Abstract

One of the factors found early to be of importance in glass corrosion was the development of a protective or nonprotective surface film on the material. Once such films were identified, the next challenge was to determine what controlled their composition and growth. Recent research suggests that the answer to the question is the solubility limits of the metal ion complexes involved. The concentration of a metal ion in solution, through dissolution, becomes large enough that the solubility limit of the dominant metal ion complex is exceeded and the complex precipitates onto the surface of the cell, the glass sample, and the surface of any colloids present in the corrosion solution. To show that precipitation was occuring, Grambow plotted the ratio of the normalized mass loss for five elements (Ca, Fe, Zn, Ce, and Nd) to that for silicon for a specific nuclear waste glass (PNL 76-68). The resulting graphs showed that the ratio was unity at low pH values (the result expected for congruent dissolution) and fell below 1 at a pH value determined by the solubility limit of a particular metal ion complex. Grambow also showed that if the concentration of an ion was lowered through the usemore » of a chelating agent, the ratio returned to unity. Expanding on these results, the purpose of this research was to determine if results similar to Grambow's could be obtained with other types of nuclear waste glasses.« less