The effects of melting reactions on laboratory-scale waste vitrification

Abstract

At the U.S. Department of Energy's Hanford Site, processes are being developed to vitrify waste generated during nuclear materials processing. One of the wastes slated for vitrification is known as neutralized current acid waste (NCAW). The batch chemistry of simulated NCAW was varied with oxidants and reductants. Untreated, formated, nitrated, or sugar-added samples were combined with frit to produce melter feed. Offgas measurements of the formated melter feed showed that formates decomposed at temperatures too low for participation in melt redox reactions. Sugar pyrolyzed and produced CO and H₂ at temperatures exceeding 665 °C. For the sugar-added samples, the glass quenched from 1200 °C produced an Fe²⁺ /ΣFe of 0.79. The measured iron redox ratios from the glasses made from untreated, formated, and nitrated wastes were essentially indistinguishable (0.0024 at 1000 °C and 0.032 at 1200 °C). However, the batch chemistry affected volume expansion and the reaction paths.