Hydrothermal treatment of Hanford waste constituents

The destruction of nitrates, organics, and ferrocyanides wastes contained in underground storage tanks at the Department of Energy site in Hanford, WA would significantly reduce the volume, the hazards, and the toxicity of the waste, while meeting pretreatment requirements for vitrification and grouting. The purpose of this study was to investigate the applicability of hydrothermal methods for the destruction of nitrates, organics, and ferrocyanides. Laboratory studies examined the redox reactions of nitrate with a simple organic compound (methanol), with ammonium, and with ferrocyanide. When reacted with methanol above 500 degree C, greater than 99% of the nitrate was destroyed at the shortest residence times (< 6 seconds) while greater than 80% of the methanol was converted to bicarbonate and carbon dioxide. The reaction of nitrate and nitrite with ammonium proceeds to completion in short residence times (< 30 seconds) at temperatures above the critical point of water (374.2 degree C). Ferrocyanide also reacted rapidly with nitrate above the critical point, producing carbon dioxide, ammonium, and an iron precipitate.