Effects of Methanol on the Seeded Precipitation of Al(OH)3 from Potassium Aluminate Solution

Abstract The effects of methanol on the seeded precipitation of Al(OH) 3 from potassium aluminate solution are investigated. The solubility of Al(OH) 3 decreases in the presence of methanol, leading to a faster crystallization and a higher precipitation ratio than the normal seeded precipitation process. Under the optional precipitation conditions of temperature 323.15 K, K 2 O concentration 170 g L −1 , and addition of an equal volume of methanol to potassium aluminate solution, the precipitation ratio can exceed 85% within 7 h. Characterization of the Al(OH) 3 products using X‐ray diffraction, scanning electron microscopy, and particle size distribution shows a typical gibbsite crystal phase composed of sheet‐like agglomerates with an average particle size of 74 µm. An interaction model between methanol molecules and Al(OH) 3 crystal face is established and calculated by using the molecular dynamics method, which indicates the morphology transition mechanism of the Al(OH) 3 crystal. The result indicates that methanol molecules would hinder the growth of the (002) crystal face, so that the (002) crystal face is eventually retained and becomes the main crystal face for the Al(OH) 3 product. Infrared radiation and Raman spectra analyses suggest that the added methanol captures water molecules from the aluminate ion hydration sphere and thus catalyzes the crystallization process.