Extraction of valuable components from coal gangue through thermal activation and HNO3 leaching

• A technology for the high-value utilization of coal gangue was proposed. • Activation behavior and phase transformation during thermal activation were revealed. • Fe was removed synchronously during extracting Al, Ga, and Li with HNO 3 . • Leach residue owning high available Si content was a promising Si fertilizer source. Coal gangue has the dual attributes of hazard and resource. With the increasing awareness of resources conservation and ecological sustainability, the high-value utilization of coal gangue has attracted active attention. In this research, thermal activation followed by HNO 3 leaching were performed to extract valuable components from coal gangue. Firstly, the activation behavior and phase transformation mechanism during thermal activation were revealed through the Gibbs free energy calculation and experimental research. After activation, inert kaolinite was converted to active metakaolinite. Subsequently, the potential-pH diagrams analyses confirmed that the strategy of extracting Al, Ga, and Li into the leach liquor while precipitating Fe into the leach residue was feasible. Meanwhile, systematic leaching experiments showed that 95.2% of Al, 56.4% of Ga, and 80.5% of Li were extracted, while only 2.1% of Fe was dissolved at the optimal conditions. The leaching behavior of each component agreed well with the thermodynamic analysis. Finally, the raw ore, activated product, and leach residue were analyzed via a suite of characterization techniques. In contrast to the raw ore and activated product, the leach residue had large BET surface area and high available Si content, and was a promising Si fertilizer source. This study provides a useful reference for the high-value utilization of coal gangue.