A Peculiar Morphology of Gibbsite and Nordstrandite Co-Crystallized in the Presence of Tartrate in a Strongly Alkaline Environment

The nature and morphology of Al(OH)3 polymorphs obtained by precipitating Al and tartrate at pH 12.0 and at a tartrate/Al molar ratio (R) of 0.1 were studied by X-ray diffraction, transmission electron microscopy and electron diffraction. Co-crystallization of unusually long (up to 18 µm) ‘stick-shaped’ gibbsite with platy particles of both nordstrandite, mainly, and bayerite was observed. Face-to-face associations of plates nucleated perpendicularly on the gibbsite surfaces parallel to the c axis produced peculiar elongated ‘brush’ -shaped particles. In a strongly alkaline environment the inhibiting effect of tartrate on Al(OH)3 polymorph formation is reduced and production of co-crystallized phases with structural crystallographic similarities can be observed.