A comparison of ceramic and carbon-based reductants for vitrification of low-activity waste

Sucrose is the current baseline additive at the Hanford Waste Treatment and Immobilization Plant in Washington to control foaming during waste feed to glass transitions and the redox state of the glass melt. Alternative reductants are being investigated to alleviate strain on effluent treatment from toxic acetonitrile production from incomplete combustion of sucrose. This study evaluates ceramic additive options including B₄C, B₆Si, SiC, and VB₂ in simulated low-activity waste feed, as well as coke dust, probing the feed volume expansion during melting as well as the gas evolution. All alternative reductant options examined significantly reduced acetonitrile production; however, there was variability in their effectiveness as foam-reducing agents. VB₂ and coke matched the performance of sucrose in controlling foam volume and glass redox state, but with notably less acetonitrile production. B₄C, B₆Si, and SiC demonstrated improved foam control and very little acetonitrile production; however, the final glasses were over-reduced, that is, Fe²⁺/Fe_T ≥ 0.5. These alternative reductant studies provide operational flexibility to the operation of the vitrification plant, as well as options for alternative raw materials in industrial glass melting.