Recovery of iron from iron tailings by co-pyrolysis with coal gangue: process optimization and economic evaluation
摘要
Iron tailings and coal gangue are voluminous solid waste byproducts. However, traditional disposal methods and conventional reduction roasting often are hindered by high costs and a reliance on external fossil fuels as reductants. To overcome these challenges, this study introduces a novel co-pyrolysis process utilizing coal gangue as the sole reductant source for recovering iron from tailings. Key process parameters, including co-pyrolysis temperature (600 – 900 °C), co-pyrolysis time (20 – 60 min), coal gangue ratio (10 – 50 wt%), and magnetic separation intensity (60 – 140 mT), were optimized. In optimal conditions (800 °C, 30 min, 20% wt%, 100 mT), an iron concentrate with 59.10% total Fe (TFe) and 75.4% recovery rate was obtained. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) revealed that the pyrolysis of coal gangue generated reducing gases (CO, H2, CH4) and fixed carbon. These reductants were capable of converting the weakly magnetic hematite (Fe2O3) to the strongly magnetic magnetite (Fe3O4), facilitating efficient low-intensity magnetic separation. An economic evaluation of a production scale of 250,000 t/y showed a net cost of 86.79 USD/t after accounting for byproduct revenue. Importantly, aiming for a zero-waste process, the residual waste was successfully transformed into high-strength non-fired bricks, providing a technically viable and economically superior closed-loop solution compared to existing single-stream utilization methods.