Growth process of boehmite with large particles in ammonia system

Abstract

The development of a novel technology for extracting aluminum resources from coal fly ash through direct leaching with an ammonium hydrogen sulfate solution represents a significant advancement. A pivotal stage within this process is the reaction crystallization between NH4Al(SO4)2·12H2O solid and NH3·H2O. Despite its many benefits, the fine particle size of the resultant product has impeded its widespread adoption. To tackle this challenge, this study concentrated on examining the growth mechanism of boehmite with larger particles in the presence of ammonia. Analysis revealed a distinct morphological evolution process for large-particle boehmite, progressing from a flaky morphology to a flower-like nanostructure with flaky features, and then further transitioning into particles displaying flower-like nanostructures and culminating in the formation of large particles with smooth surfaces. Initially, the early stages of crystallization were governed by kinetic factors, followed by a self-assembly phase, ultimately resulting in the final morphology of large particles, dictated by thermodynamic considerations. Density functional theory calculations underscored the significant role of H2O molecule adsorption in boehmite's growth trajectory, leading to the formation of pseudo-boehmite and inducing shifts in the X-ray diffraction peaks. The growth units remained integral throughout the entirety of the crystal growth process.