Synthesis of polysulfone beads impregnated with Ca-sepiolite for phosphate removal

Abstract

Former studies revealed that sepiolite thermally treated at high temperature have high adsorption capacity for phosphate. However, its micron size (75 µm) limits its application to water treatment. In this study, we synthesized sepiolite impregnated polysulfone (PSf) beads to separate it easily from an aqueous solution. PSf beads with different sepiolite ratios were synthesized and their efficiencies were compared. The PSf beads with 30% impregnated sepiolite (30SPL-PSf bead) possessed the optimum sepiolite ratio for phosphate removal. Kinetic, equilibrium, and thermodynamic adsorption experiments were performed using the 30SPL-PSf bead. Equilibrium adsorption was achieved in 24 h, and the pseudo-first-order model was suitable for describing the phosphate adsorption at different reaction times. The Langmuir model was appropriate for describing the phosphate adsorption onto the 30SPL-PSf bead, and the maximum adsorption capacity of the 30SPL-PSf bead obtained from the model was 24.48 mg-PO4/g. Enthalpy and entropy increased during the phosphate adsorption onto the 30SPL-PSf bead, and Gibb's free energy at 35 °C was negative. An increase in the solution pH from 3 to 11 induced a decrease in the phosphate adsorption amount from 27.30 mg-PO4/g to 21.54 mg-PO4/g. The competitive anion influenced the phosphate adsorption onto the 30SPL-PSf bead was in the order of NO3- > SO42- > HCO3-. The phosphate breakthrough from the column packed with the 30SPL-PSf bead began after ~2000 min, reaching the influent concentration after ~8000 min. The adsorption amounts per unit mass of 30SPL-PSf and removal efficiency were 0.775 mg-PO4/g and 61.6%, respectively. This study demonstrates the adequate performance of 30SPL-PSf beads as a filter for phosphate removal from aqueous solutions.