Preparation of pseudo-boehmite via carbonation of sodium aluminate lixivium extracted from coal fly ash

Abstract

The hydrothermal process was employed to extract alumina from coal fly ash, resulting in the production of sodium aluminate lixivium. The lixivium exhibited a low concentration of Na2O and Al2O3, which was subjected to carbonation to synthesize pseudo-boehmite in this study. During carbonation, the pH of the lixivium was decreased as CO2 aeration, resulting in the formation of amorphous aluminum hydroxide, which subsequently transformed into pseudo-boehmite as the solution pH reached 10.0–10.5. Further decrease in solution pH below 9.5 caused the conversion of pseudo-boehmite into dawsonite. Monophase pseudo-boehmite was prepared from the lixivium after carbonation at 80–100 °C for 30–120 min with the final solution pH of 10.0–10.5. The resulting pseudo-boehmite exhibited a fibrous morphology and formed porous aggregations, which displayed a BET specific surface area of 445.48 m2/g, a cumulative pore volume of 0.76 cm3/g, with the majority of pores falling within the mesopore range of 2–50 nm. The pseudo-boehmite would dehydrate and transform into γ-Al2O3 while maintaining its original morphology after calcination at 450–700 °C, making the product promisingly use as a precursor for preparing mesopore γ-Al2O3 of widespread applications in industrial catalysis.