Hydrated aluminium sulfate precipitation by enzyme-catalysed urea decomposition

Hydrated basic aluminium hydroxide precipitates were obtained from aluminium sulphate solution at room temperature and at 92°C by using urea. Enzyme urease was used to decompose urea at room temperature. It was observed that precipitates obtained at room temperature were much finer than those obtained at 92°C but they had similar chemistry. On calcination at 1200°C, each precipitate obtained at room temperature converted to a discrete α-Al2O3 crystal whereas that obtained at 92°C converted to a rather densely packed agglomerate of α-Al2O3 crystals. As a result of this, α-Al2O3 powder obtained from 25°C precipitates showed much better sintering behaviour.