China Nonferrous Metallurgy

Coal fly ash is the main solid waste produced by coal-fired power plants. Besides rich in aluminum, fly ash also contains valuable elements such as gallium and lithium, which is a potential extraction resource of valuable metals such as aluminum, gallium and lithium. The traditional alkaline process, alkaline solution process and acid process can not meet the requirements of low energy consumption, low reagent consumption, low emission and high recovery. Other new processes, such as hydrochemistry, vacuum thermal reduction and carbothermic chlorination, have the advantages of less slag production and environmental protection, but are still in the stage of small laboratory trials. The content of gallium and lithium in fly ash is relatively low, the recovery process generally includes precipitation, solvent extraction and resin adsorption. Resin adsorption has the advantages of good selectivity and small environmental pollution, but it is mainly used in alkaline system. The cooperative recovery of aluminum, gallium and lithium is an important way to realize the resource utilization of fly ash. The “one-step acid dissolution” process is the most promising technology in the utilization of fly ash resources, with the extraction of alumina as the main line and the extraction of gallium and lithium and the preparation of silical-aluminum based materials as the secondary lines. In the future, the recovery of valuable metals in fly ash needs to be strengthened in the following aspects: developing new sintering technology and comprehensive utilization of silicon calcium slag, to completely solve the problem of high energy consumption and large amount of waste slag in alkali process; increasing the research and development of inorganic non-metallic material modification, to solve the problem of equipment corrosion in acid process; developing inexpensive extractants and adsorbent resins, or developing more efficient impurity removal processes, to reduce the investment cost of acid processes.