Cleaner extraction of alumina from coal fly ash: Baking-electrolysis method

•Baking-electrolysis method was designed to recover alumina from coal fly ash.•Product hydrogen can be treated as a clean energy to realize efficient process.•Product sulfuric acid, sulfur trioxide can be returned to the baking-electrolysis process to promote zero pollution discharge. Clean and efficient extraction of aluminum hydroxide from coal fly ash has environmental and economic benefits. The current study mainly aimed to develop an efficient and nonhazardous baking-electrolysis process to extract aluminum hydroxide from coal fly ash. During acid baking, the important parameters that affect aluminum, iron, and calcium leaching efficiency were studied. The maximum leaching efficiency of aluminum reached 86.8% (iron leaching efficiency was 61.0% and calcium leaching efficiency was 83.0%) under the optimal conditions of T = 200 °C, t (acid baking) = 90 min, and t (ball milling) = 5 min. X-ray diffraction, scanning electron microscopy and laser granulometry were used to investigate the mineralogy phases, microstructures, particle size distributions, and the mechanism of the acid baking process. X-ray diffractometry and scanning electron microscopy results revealed that aluminum hydroxide with porous plate-like structures was the main electrolytic product. The electrolysis mechanism was analyzed by cyclic voltammetry. This method offers the advantages of reusing the effluent after electrolysis, and the hydrogen product is a clean form of energy. Thus, the proposed baking-electrolysis process provides a promising technique as an efficient and potential zero-waste integrated process for sustainable valorization of coal fly ash.