Semi-industrial-scale detoxification of cyanide tailings by suspension oxidation roasting and feasibility evaluation for underground backfilling

• First semi-industrial roasting detoxifies tailings to 220 mm, UCS 2.8-4.5 MPa (5-10% cement). • Meets HJ943-2018, GB/T14848 ideal backfill material. Cyanide tailings, a hazardous waste from gold cyanidation, contain highly toxic complex cyanides that pose serious environmental and health risks. This study presents the first semi-industrial demonstration of deep detoxification of cyanide tailings using a suspended oxidation roasting system. Based on laboratory-scale optimization, a 48-hour continuous stable operation was conducted at 600°C with a treatment capacity of 52.5 kg h⁻ 1 (≈11 min residence time) in air. Under these conditions, total cyanide in the roasted solids was reduced from 775.18 mg kg⁻ 1 to an average of 0.03 ± 0.005 mg kg⁻ 1 (well below the 0.04 mg kg⁻ 1 regulatory limit), achieving > 99.99% removal. The dominant ferrocyanide complex K 4 Fe(CN) 6 decomposed via a two-stage mechanism involving a KCNO intermediate, as confirmed by thermogravimetric analysis coupled with differential scanning calorimetry and mass spectrometry (TG-DSC-MS) and X-ray diffraction (XRD). Sulfur fixation averaged 61.81 ± 2.3%, and flue-gas emissions (particulate matter, SO 2 , N x , HCN) complied with GB 16297–1996 and regional standards after baghouse and desulfurization treatment. The roasted product exhibited excellent fluidity and pozzolanic activity, meeting both Chinese (HJ943-2018, GB/T14848) and key international benchmarks (ICMC WAD cyanide, EU Mining Waste Directive) for use as underground backfill aggregate or partial cement raw material substitute. These results demonstrate the technical feasibility and resource-recovery potential of suspension oxidation roasting for large-scale, reagent-free detoxification of cyanide tailings.