Effect of Crystallization, Redox, and Waste Loading on the Properties of Several Glassy Waste Forms

Abstract

A laboratory study performed on three waste streams with high metal content (between 20 and 60 wt%) showed that waste form durability was strongly influenced by processing conditions and waste form compositions. The study involved varying the waste loading, melting conditions, and heat treatment of a total of 15 waste forms. The normalized sodium release obtained from the product consistency test (PCT) was the main criterion used for durability comparisons between each waste form. It was found that a reducing melt condition had no effect on the durability of some waste forms, yet it decreased the durability of others up to 700% when compared to the oxidized melts. One waste form composition tested showed a 140% increase in durability when devitrified (crystallized) relative to its glassy form. Some compositions showed no change in durability after devitrification, while others showed a 200% decrease. Increased waste loading was also found to have varying effects dependent on the composition of the waste form and the processing atmosphere. These responses to processing and composition variations were dictated by fundamental glass chemistry and can be adjusted to achieve maximum waste loading, acceptable durability, and desirable processing characteristics with optimized formulations.