This study investigated the adsorption capacity and adsorption mechanism of phosphate by calcined aluminum oxide (GB) at temperatures of 200 to 1150• C. The results showed that GB and GB calcined at a temperature of 200• C exhibited almost no adsorption capacity, and GB calcined at temperatures of 300 or 400• C exhibited the highest adsorption capacity. After that, adsorption capacity tended to decrease with increasing calcination temperature. The specific surface area and the concentration of surface hydroxyl groups exhibited the highest values in GB calcined at temperatures of 300 and 400• C. From the above facts, it is conjectured that the specific surface area and concentration of surface hydroxyl groups contribute to the adsorption of phosphate in calcined GB.The results of X-ray diffraction showed that the structure of GB changed drastically at temperatures of 200 to 300• C and 900 to 1000 • C. Also, it was evident that phosphate was adsorbed selectively even in complex solution systems containing chloride, nitrate, sulfate, hydrogen carbonate and phosphate ions, and that calcined GB is suitable for adsorption of phosphate. For the adsorption of phosphate, it was found that the optimum pH is around 4. When calcined GB is suspended in purified water, it is thought that hydroxyl groups form through dissociative adsorption with water molecules, and that these hydroxyl groups conduct ion exchange with phosphate.

This study investigated the ability of cerium hydroxide (CE) to adsorb phosphate, and compared it to the aluminum compounds boehmite (BE) and gibbsite (GB), which possess high phosphate adsorption ability. Specific surface area, number of hydroxyl groups, and amount of phosphate adsorbed were measured. Results indicated that specific surface area increased in the order GB < CE < BE, number of hydroxyl groups increased GB < BE < CE, and amount of phosphate adsorbed increased GB < BE < CE. These results showed that the adsorption mechanism of phosphate using CE was more closely related to chemical factors involved in the exchange of phosphate with hydroxyl groups onto CE than to physical factors such as specific surface area.