Characterization of Aluminum Trihydroxide Crystals Precipitated from Caustic Solutions

Gibbsite is one of the polymorphs of aluminium trihydroxide and is produced commercially by the Bayer Process through its crystallization from sodium aluminate solutions. This work demonstrates that there is a complex interplay of factors which affect the polymorphism and morphology of aluminium trihydroxide crystals precipitated from concentrated aluminate solutions. The formation of gibbsite is favoured at higher temperatures, while bayerite is formed predominantly at room temperature. The nature of the alkali metal ion present in the aluminate solution has a substantial influence on the morphology of the single crystals of gibbsite formed, with hexagonal plates resulting from sodium aluminate solutions and elongated hexagonal prisms from potassium aluminate solutions.