Co-production of high-quality syngas and valuable elements: combination of chemical looping gasification and acid leaching to cleanly dispose red mud solid waste

A novel method combining chemical looping gasification and hydrometallurgical processing is proposed for clean disposal of red mud solid waste, which enables co-production of syngas (CO, H₂) and valuable elements. Initially, chemical looping gasification experiments utilized calcined red mud as the oxygen carrier for coal char gasification. Subsequently, acid digestion was used to concentrate Fe and Al elements from the gasification residues. The results showed that calcined red mud exhibited excellent performance in chemical looping gasification, achieving H₂ and CO yields of 79.34 mmol/g and 39.72 mmol/g, respectively. Meanwhile, the CO₂ emission was reduced. Acid leaching efficiency significantly increased with the aid of chemical looping gasification. Fe leaching ratios of gasification residue rose sharply to 35.29 % (HCl) and 93.82 % (H₂SO₄), compared with only 1.58 % (HCl) and 9.57 % (H₂SO₄) of calcined red mud. Al leaching followed a similar trend. Key factors influencing leaching process, including liquid-to-solid ratio, time, temperature, acid concentration, were optimized with optimal conditions at 8.0 mL/g, 80 °C, 4.0 mol/L H₂SO₄, and 80 min. Mechanism analysis revealed the chemical looping gasification process disrupted and changed the complex mineral phases in red mud, enhancing dissolution efficiency of Fe and Al. The leaching kinetics for Fe and Al in the gasification residue showed high correlation (R² > 0.97) with the boundary layer diffusion model. To conclude, the approach proposed effectively produces syngas while facilitating Fe and Al recovery from red mud, which may promote the efficient treatment of this solid waste.