Novel Y₂O₃ based calcium-alginate beads for highly selective adsorption of phosphate from aqueous solution

Recently, selective phosphorus removal from aqueous solution has been a highly desirable strategy to combat eutrophication due to the increasingly stringent phosphorous emission standards. However, conventional adsorbents pose the limitations in phosphate removal suffering from lack of selectivity and stability under complicated condition and poor separation. In this study, novel Y₂O₃ based calcium-alginate (Y₂O₃/SA) beads of feasible stability and highly selectivity towards phosphate by encapsulating Y₂O₃ nanoparticles inside calcium-alginate beads via Ca²⁺ controlled gelation process was synthesized and characterized. The phosphate adsorption performance and mechanism were investigated. In general, a high selectivity among co-existing anions was found with co-existing anion concentration up to 62.5 times of the phosphate concentration. Additionally, phosphate adsorption by Y₂O₃/SA beads exhibited stable performance over a wide pH range between 2 and 10, while reaching the maximum adsorption capacity at pH 3 (48.54 mg-P/g). The value of point of zero charge (pH_pzc) of Y₂O₃/SA beads was approximately 3.45. Pseudo-second-order and Freundlich isotherm models can well accord with kinetics and isotherms data. The FTIR and XPS characterizations analyzed that inner-sphere complexes were proposed to be the major contributor of Y₂O₃/SA beads for phosphate removal. In conclusion, Y₂O₃/SA beads as the mesoporous material exhibited excellent stability and selectivity towards phosphate removal.