Surface and structural characteristics of gibbsite precepitated from pure, synthetic Bayer liquor

In this study, the ex situ surface and structural characteristics of gibbsite precipitated from pure, synthetic, supersaturated caustic aluminate solutions were examined by various techniques to determine the presence of an amorphous aluminium hydroxide phase which might be linked with the crystal growth process. The results showed that in unseeded, isothermal, batch precipitations from synthetic, supersaturated Bayer liquors at 65, 75 and 80°C, while gibbsite was the main product, a small amount of bayerite was also formed at the early stages. Furthermore, a poorly formed material was observed at the ex situ surfaces of some of these crystals. On further precipitation, the bayerite phase disappeared as did the poorly formed material. The entire crystal, with or without poorly-formed surfaces, was found to be crystalline throughout. No evidence was found to indicate the presence of an additional phase such as amorphous aluminium hydroxide. Hence, the poorly formed material is believed to be associated with the presence of bayerite which may precipitate as poorly formed, globular crystals. In similar precipitation experiments performed with gibbsite seeding, gibbsite possessing well-formed crystal surfaces was the only phase obtained.