Simply synthesized sodium alginate/zirconium hydrogel as adsorbent for phosphate adsorption from aqueous solution: Performance and mechanisms

The traditional zirconium hydrogel beads were synthesized by multi-step method, which was comparatively complex. In this study, a high phosphate removal efficient sodium alginate/zirconium (SA/Zr) hydrogel was synthesized by a simple method, with the phosphate adsorption performance and mechanism be explored. The results showed that the adsorption capacity of SA/Zr hydrogel to phosphate was greatly affected by pH. With the increase of initial pH (3-11), the adsorption capacity of SA/Zr for phosphate descended. The phosphate adsorption capacity of SA/Zr hydrogel exceeded 120 mg PO43-/g at pH 2-7, while reaching the maximum adsorption capacity at pH 3 (256.79 mg PO43-/g). The process of adsorption kinetics was well fitted by intraparticle diffusion model, indicating that there was chemical adsorption during the adsorption process. The Redlich-Peterson isotherm model can well accord with isotherm data. In addition, the material showed high selectivity to phosphate. Besides, combining X-ray photoelectron spectroscopy with Zeta potential results suggested that when the pH value was less than 4.19, SA/Zr hydrogel adsorbed phosphate by electrostatic attraction and hydrogen bonding while the adsorption was made mainly through ligand exchange when pH value was higher than 4.19.