Solvothermal synthesis and adsorption performance of layered boehmite using aluminum chloride and high-alumina fly ash

High alumina fly ash (FAHAl) is a kind of bulk solid waste unique to China, whose availability of high-value aluminum and the threat to the environment make its high-value utilization urgent. In this work, the alumina containing leaching solution obtained from Na2CO3 roasting and HCl leaching of FAHAl was used as the mother liquor to prepare layered boehmite in situ. The preparation process with AlCl3 as the raw material was also compared. The formation process and mechanism of boehmite, the choice of solvent, along with the adsorption capability of Congo red were analyzed by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller method and adsorption experiments. Results showed that during the preparation of layered boehmite, the precursor Al(OH)3 from the reaction of Al3+ and OH– is transformed into boehmite γ-AlOOH. The existence of ethanol is beneficial to regulate and promote the growth of boehmite crystal effectively. When water and ethanol is mixed with a volume ratio of 2:1 and used as the solvent, the maximum specific surface area of the boehmite is obtained of 135.7 m2·g–1, and 99.16% of Congo red can be absorbed after 10 min when AlCl3 is used as raw material. As purified leaching solution is used as the mother liquid, the crystallinity of boehmite decreases slightly when the pH value decreases from 12.5 to 11. When pH is 11, the removal efficiency of Congo red reaches a maximum of 72.25%. This process not only achieves the extraction of aluminum and high-value utilization of FAHAl, but also provided a thought to prepare layered boehmite with adsorption properties.