Iron phosphate glass for immobilization of Hanford LAW

Three iron phosphate glasses containing up to 35 wt% of a high sulfur Hanford LAW simulant were successfully melted in electric furnaces at 1150-1250degreesC for 2-3 hours. No sulfate salt segregation was found in the glass when examined by SEM. The glass retained up to 73% of the sulfur originally present in the waste, which was equivalent to 2.4 wt% SO3 on a target glass oxide basis. This suggests that the waste loading in the iron phosphate glasses will not be limited by the SO3 content of the LAW as it typically is by the baseline technology for Hanford LAW treatment. The chemical durability of the iron phosphate glasses was determined by the product consistency test (PCT) and the vapor hydration test (VHT). The mass release of sodium from both annealed and canister centerline cooled (CCC), partially crystallized iron phosphate wasteforms after the PCT at 90degreesC for 7 days was below the current DOE specification for LAW. The VHT alteration rates (200degreesC for 7 days) of the iron phosphate glasses for both annealed and CCC treated samples were also significantly lower than the current DOE limit and those of standard borosilicate glasses. All of the iron phosphate wasteforms met all of the existing requirements for aqueous chemical durability and the crystallization that occurred during CCC treatment did not reduce the chemical durability. Iron phosphate glasses were successfully melted in a hot-wall induction furnace and in a microwave oven. These melting processes avoid any corrosion problems associated with metal electrodes needed for joule heated melting.