Synthesis of Nano-sized Boehmites for Optimum Phosphate Sorption

Abstract

Nano-sized boehmites with different crystallinity were synthesized at the temperature range of 25 to 200°C in order to produce phosphate absorbents with high capacity. The physicochemical property of boehmites was depended on the synthesis temperature: the particle size was increased and the surface area showed the maximum for the boehmite at 50°C. The phosphate sorptions into boehmites were analyzed at room temperature in the phosphoric acid solutions as a model of wastewater at the concentration of 0.1 to 3.0 mmol l−1 and the pH of 3 to 7. The boehmite synthesized at 50°C exhibited the highest amount of phosphate sorption (1.73 mmol g−1 at pH 3.3) compared with Al-bearing materials. The reaction mechanism during phosphate sorption was described by the anion exchange reaction between phosphate ions in sodium phosphate solution and hydroxide ions on boehmite surfaces. Therefore, the variation in the amount of phosphate sorption on the different boehmite samples depends strongly on the surface area in the specimens. In addition, the sample showed high stability in near-neutral-pH solutions, and an increase in pH toward neutral was found to lead to a decrease in phosphate sorption due to a change in the phosphate species and a reduction of the surface sites.