Abstract
Owing to the depletion of bauxite and increasing demand for alumina, calcination methods for extracting alumina from coal fly ash (CFA) were developed. However, these methods have disadvantages such as the need for high temperatures and the emission of toxic gases. Hence, in this study, Al2O3 was extracted from CFA via low-temperature potassium bisulfate calcination technology. Effects of the potassium bisulfate amount, calcination temperature, and calcination time on the alumina extraction efficiency were investigated using X-ray diffraction, thermal gravimetry, scanning electron microscopy, differential scanning calorimetry, and energy-dispersive spectroscopy. It was found that this technique could recover alumina efficiently, and potassium bisulfate significantly contributed to the degradation of mullite and corundum phases. Al2O3 in CFA was converted into soluble K3Al(SO4)3. With a KHSO4/Al2O3 molar ratio of 7:1, calcining temperature of 230 °C, and calcining time of 3 h, the alumina extraction efficiency reached a maximum of 92.8%. The Avrami–Erofeev equation showed the best fit with the kinetic data for the low-temperature calcination of CFA with KHSO4. The activation energy was 28.36 kJ/mol.
Highlights
The discharged amount of coal fly ash (CFA) from high-temperature coal-burning power plants is expected to be 560 to 610 Mt/year based on the China Electric Power Federation forecast from 2016 to 2019 [1]; it will exceed three billion tons by 2020 in China and is behind only the tailings found in industrial solid waste [2]
The chemical compositions of the CFA, calcined products, and residue were measured via X-ray fluorescence analysis (XRF, Axios, PANalytical, Almelo, The Netherlands)
4 addition activated CFA and the underlying mechanism, we investigated the crystallographic structures of the CFA, calcined products, and via X-ray diffraction (XRD). we investigated
Summary
The discharged amount of coal fly ash (CFA) from high-temperature coal-burning power plants is expected to be 560 to 610 Mt/year based on the China Electric Power Federation forecast from 2016 to 2019 [1]; it will exceed three billion tons by 2020 in China and is behind only the tailings found in industrial solid waste [2]. The use of calcination is limited by the formation of more toxic gases and the reduced activation effectiveness at high temperatures. Alumina extraction from CFA through sintering is costly, and the residual red mud generated because of the high reaction temperature and lime addition is a new pollutant. High-purity alumina was produced through sintering, leaching, NH4 Al(SO4 ) precipitation, and calcination of fly ash and ammonium sulfate. With this method, the Al extraction rate under optimized conditions was. Thermal activation improves alumina extraction, problems such as the need for high calcination temperatures and release of toxic gases like NH3 still exist. The mechanisms of CFA activation and alumina extraction were explored
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