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Acid activation for pre-desilicated high-alumina fly ash

Zhang, Jian-Bo, Li, Shao-Peng, Li, Hui-Quan, He, Ming-Ming
Fuel processing technology 2016 v.151 pp. 64-71
X-radiation, X-ray diffraction, aluminum, aluminum oxide, energy-dispersive X-ray analysis, fluorescence, fly ash, iron, leaching, silica, silicon, solid wastes, surface area, temperature, zeolites
High-alumina fly ash (HAFA) is a special solid waste because it consists of more than 40wt.% alumina and 40wt.% silica, which can be applied in the alumina extraction and preparation of Al–Si composite if the Al/Si weight ratio can be elevated to a high level (>2.55). However, traditional desilication cannot satisfy this demand because of its low desilication ratio and the presence of abundant impurities. Therefore, this study systematically analyzed acid activation of desilicated HAFA (DHAFA) to extensively remove amorphous silica and impurities. The efficient desilicated ratio (EDR) is first applied to characterize DHAFA. Moreover, the effects of different factors on the mineralogical structure, pore structure, specific surface area and extraction of Al and Fe were investigated. The results of energy-dispersive X-ray spectroscopy and X-ray diffraction indicate that zeolites on the external and internal portion of DHAFA can be decomposed. Results also indicated that increased acid concentration, reaction temperature, and reaction time elevated the EDR values from 11.1% to 29.51% and evidently increased the Al³⁺/Fe³⁺ leaching ratios. The removal of zeolites and reactive Al³⁺/Fe³⁺ result in an increase of specific surface area from 23.86m²/g to 70m²/g and formation of more mesopores (3–4nm). X-ray fluorescence results revealed that the Al/Si weight ratio can be elevated from 1.2 to approximately 2.85.