Relationship between Anion Adsorption and Physicochemical Properties of Aluminum Oxide

Abstract

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.

Phosphate Adsorption Ability of Granular Gibbsite and Cerium Hydroxide

“…Previous reports have shown that the highest amount of phosphate adsorbed was obtained using calcined GB at 450 P-GB and virgin CE P-CE 18 . The phosphate adsorption isotherms of GB and CE are shown in Fig.…”

Granulation of Boehmite without a Binder and its Capacity for Phosphate Adsorption in Aqueous Solution

“…We have previously reported the amount of phosphate adsorbed based on specific surface area and surface hydroxyl groups. The amount of phosphate adsorbed onto GA was greater than that onto virgin BE, as the specific surface area of GA is larger (The adsorption capacity and specific surface area of GA or virgin BE is 74.2 mg/g and 283.1 m 2 /g or 56.9 mg/g and 253.9 m 2 /g, respectively) (Kabayama et al, 2005;Kawasaki et al, 2008). The experimental data were fitted to the Langmuir and Freundlich isotherm equations.…”

“…The maximum adsorption of phosphate occurs at a pH of about 3. Kawasaki et al (2008) reported that the adsorption mechanism for phosphate ions onto aluminum compounds was by ion exchange with surface hydroxyl groups on the aluminum compounds. In this study, we used GA as the adsorbent for the removal of phosphate.…”

Adsorption of Orthophosphoric, Pyrophosphoric, and Tripolyphosphoric Acids from Aqueous Solutions by Calcined Gibbsite

“…A previous study reported similar trends. 21) We also evaluated the amount of phosphorus on the GB400 surface (Fig. 3).…”

“…Kawasaki et al reported that the optimal pH for adsorption of orthophosphoric acid on aluminum oxide at different temperatures was acidic (pH around 4.0). 21) Many researchers have reported that the adsorption of condensed phosphates improved with decreasing pH. 24) The increase in the amount of condensed phosphates adsorbed on aluminum hydroxide at low pH could be attributed to electrostatic attraction and acid catalysis, as illustrated by the follow- Effect of Contact Time on Phosphoric Acid Adsorption on GB400 Figure 5 shows the adsorption rates of phosphoric acids on GB400; equilibrium was reached within 24 h. The amount adsorbed increased in the order orthophosphoric acid>pyrophosphoric acid>tripolyphosphoric acid.…”