Sustainable exploitation of siderite ore using fluidization roasting technology without reductant

• Reductant-free fluidized roasting converts low-grade siderite to magnetite under N2. • Optimal roasting (700 °C, 30 min, 200 mL/min N2) yields 60.60 % TFe and 89.54 % recovery. • Thermal decomposition and in-situ gas–solid reactions enhance magnetism and separation. The development of efficient and environmentally friendly technologies for processing low-grade iron ores is essential to address the depletion of high-grade resources. In this study, a phase transformation process was proposed for the direct conversion of siderite into magnetite under an inert nitrogen atmosphere, without the use of any external reductant. The optimal fluidized roasting condition was identified as 700 °C for 30 min under a nitrogen flow rate of 200 mL/min. The final magnetic concentrate exhibited a total iron content of 60.60 %, with a corresponding iron recovery rate of 89.54 %. The phase transformation mechanism was investigated using XRD, SEM-EDS, and VSM techniques. The results reveal that siderite decomposes at elevated temperatures to form FeO and CO 2 , while the generation of surface cracks enhances gas–solid interaction. Subsequently, FeO reacts with CO 2 to form magnetite, and the in-situ generated CO further reduces hematite present in the raw ore, also contributing to magnetite formation. These coupled reactions result in a substantial increase in saturation magnetization from 1.94 Am 2 /kg to 29.61Am 2 /kg, confirming the successful transformation into strongly magnetic phases. This additive-free process enables efficient phase transformation and separation, providing a clean and scalable pathway for the sustainable utilization of low-grade siderite resources.