Cleaner alumina production from coal fly ash: Membrane electrolysis designed for sulfuric acid leachate

The clean and efficient extraction of alumina from coal fly ash renders environmental and economic benefits. The current study mainly aimed to develop a nonhazardous approach to conduct electrolysis with two-membrane and three-chamber cell for alumina extraction from coal fly ash. The influences of the aluminum sulfate concentration, distance between electrodes, current density, temperature and electrolysis duration were systematically explored. The results revealed that Al(OH)(3) was a main electrolytic product with a yield of 64.48% and the energy consumption was 4.88 kWh/kg Al(OH)(3) after 20 h of electrolysis process. The concentrations of ions were determined by inductively coupled plasma atomic emission spectrometry, indicating that Al3+ in the middle chamber migrated to the cathodic chamber to form Al(OH)(3) precipitate under the combined action of direct current and the exchange membranes. The electrolysis mechanism was analyzed by cyclic voltammetry, which showed that H2O gained electrons and reacted with Al3+ on the cathode to form Al(OH)(3) and H-2. On the anode side, H2SO4 and O-2 were generated due to the oxidation of H2O. Al(OH)(3) is an alumina resource, H-2 is a clean energy, and H2SO4 is a common coal fly ash leaching agent and can be returned to the leaching process to promote zero pollution discharge. The solution in the middle chamber can be refreshed to attain continuous electrolysis. The proposed electrolysis process provides an efficient and environmentally friendly approach for the extraction of high-quality Al(OH)(3) from coal fly ash. (C) 2019 Elsevier Ltd. All rights reserved.