Abstract
The precipitation of spherical boehmite was studied by surface energy calculations, measurements of precipitation ratios, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The surface energy calculation results show that the (001) and (112) planes of gibbsite surfaces are remarkably stable because of their low surface energies. In addition, the (010) plane of boehmite grows preferentially during precipitation because of its low surface energy. Thus, we propose a method to precipitate spherical boehmite from a supersaturated sodium aluminate solution by adding gibbsite as seed in a heterogeneous system. In this method, gibbsite acts as the preliminary seed and saturation modifier. The results show that the fine boehmite first nucleates on the (001) and (112) planes of gibbsite and then grows vertically on the (001) and (112) basal planes of gibbsite via self-assembly, thereby forming spherical boehmite. Simultaneously, gibbsite is dissolved into the aluminate solution to maintain the saturation for the precipitation of boehmite. The precipitation ratio fluctuates (forming an M-shaped curve) because of gibbsite dissolution and boehmite precipitation. The mechanism of boehmite precipitation was further discussed on the basis of the differences in surface energy and solubility between gibbsite and boehmite. This study provides an environmentally friendly and economical method to prepare specific boehmite in a heterogeneous system.
Highlights
Boehmite (γ-AlOOH) is a significant intermediate hydrated alumina that can maintain its shape during transformation to transition alumina (γ, δ, and θ-Al2O3) or α-Al2O3
The boehmite was precipitated from a 100-mL sodium aluminate solution with a caustic molar ratio of 1.41 at 180°C in an autoclave (150 mL) by adding gibbsite (226 g·L− 1) as a seed material
These results all suggest that boehmite is readily precipitated from sodium aluminate solution by the addition of gibbsite as seed
Summary
Boehmite (γ-AlOOH) is a significant intermediate hydrated alumina that can maintain its shape during transformation to transition alumina (γ-, δ-, and θ-Al2O3) or α-Al2O3. G.H. Li et al, Precipitation of spherical boehmite from concentrated sodium aluminate solution by adding gibbsite as seed highly hazardous waste water increase AlOOH production costs and limit the industrial application of this two-stage method. We present a simple, economical, and environmentally friendly route to precipitate boehmite with a specific morphology in a heterogeneous system. In this method, soluble gibbsite is added as a preliminary seed material and saturation modifier in solution. Nearly spherical boehmite was precipitated from a concentrated sodium aluminate solution by the addition of gibbsite as a seed material. Scanning electron microscopy (SEM) and Transmission electron microscope (TEM) were used to analyze the change in morphology
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