Hydrated aluminium sulfate precipitation by enzyme-catalysed urea decomposition

Hydrated basic aluminium hydroxide precipitates were obtained from aluminiu m sulphate solution at room temperature and at 92 degrees C by using urea. Enzyme urease was used to decompose urea at room temperature. It was observ ed that precipitates obtained at room temperature were much finer than thos e obtained at 92 degrees C but they had similar chemistry. On calcination a t 1200 degrees C, each precipitate obtained at room temperature converted t o a discrete alpha-Al2O3 crystal whereas that obtained at 92 degrees C conv erted to a rather densely packed agglomerate of alpha-Al2O3 crystals. As a result of this, alpha-Al2O3 powder obtained from 25 degrees C precipitates showed much better sintering behaviour. (C) 2000 Elsevier Science Ltd. All rights reserved.