Preparation of high purity spherical γ-alumina using a reduction-magnetic separation process

A purified alumina hydrosol has been prepared by removing metal impurities using a new reduction-magnetic separation process. The amount of iron in the alumina hydrosol was reduced by over 78% from 0.0094% to 0.0020%. As a result of co-crystallization, the copper content was simultaneously reduced from 0.0003% to 0.0001%. Spherical γ-alumina granules were prepared by the oil-drop method using the purified alumina hydrosol as starting material. The γ-alumina granules had a bulk density of about 0.50 g cm−3, crush strength of around 90N per granule, specific surface area of about 200 m2 g−1 and pore volume of about 0.75 cm3 g−1. The purification process employed during the preparation of the alumina hydrosol had no effect on the physical properties, pore structure and crystal structure of the final spherical alumina granules.