Study on recovering the scattered metals from coal gangue by low-temperature activation and two-stage selective leaching

As metal deposits are developed on a large scale and at high intensity, the strategic metals under "protective measures" will inevitably face resource depletion. It becomes particularly important to sustainably and stably maintain the supply of strategic metals. A method is proposed to selectively extract Li and Ga from coal gangue through a process of ammonium sulfate roasting followed by stepwise leaching. Li and Ga in coal gangue are converted into metal sulfates or ammonium sulfates through low-temperature roasting, and then selectively extracted through a water-acid combined stepwise leaching process. Under the conditions of 450 degrees C and 2 h, with a coal gangue to ammonium sulfate ratio of 1:2.5, the leaching rates of lithium and gallium reach 88.35 % and 90.28 %, respectively. During the roasting process, ammonium sulfate decomposes into ammonium hydrogen sulfate, which enters the core through the pores of gangue and reacts with kaolinite to enhance activation. Li is converted into lithium sulfate ammonium and extracted through aqueous solution leaching, while metal gallium is first converted into gallium sulfate ammonium and then, with increasing temperature, into ammonium sulfate and extracted through dilute acid leaching.