Integrated low-hydrazine decontamination and hazardous waste treatment

Cobalt-bearing magnetite layers in pressurized heavy-water reactor (PHWR) feeder pipes generate radiation fields, while hydrazine-based decontamination produces hazardous effluent containing residual hydrazine and dissolved metals. This study developed an integrated low-hydrazine decontamination process comprising oxide dissolution, solid-liquid separation, metal recovery, and advanced oxidation. A Cu-free solution containing 29 mM sulfuric acid and 10 mM hydrazine removed Co-doped magnetite more effectively than conventional chemical decontamination process using 50 mM hydrazine and 0.5 mM Cu. The optimized formulation reduced total hydrazine consumption across the integrated process by approximately 32%, enhanced Fe and Co dissolution, and substantially decreased suspended debris. Adjusting the spent solution to pH 10 ± 0.5 with hydrazine hydrate precipitated dissolved Fe and Co as a separable Fe/O-rich solid. Subsequent H₂O₂/UV-LED oxidation reduced residual hydrazine to approximately 4.5 ± 0.5 mM and outperformed either H₂O₂ or UV-LED treatment alone; inhibition by isopropyl alcohol confirmed the important contribution of hydroxyl radicals. A screening-level techno-economic assessment estimated a 13% reduction in operating costs, while life-cycle assessment showed comparable climate-change, acidification, and eutrophication impacts but 11-21% lower toxicity-related impacts. The proposed process provides an effective strategy for reducing hazardous reagents, Cu use, contaminated solids, and hydrazine-containing radioactive waste.