Highly selective and sustainable clean-up of phosphate from aqueous phase by eco-friendly lanthanum cross-linked polyvinyl alcohol/alginate/palygorskite composite hydrogel beads

Abstract The development of feasible adsorbent for phosphate removal is of great urgency to remediate water eutrophication and maintain sustainable development of water resources. In the present work, eco-friendly lanthanum cross-linked polyvinyl alcohol/alginate/palygorskite (LPAP) composite hydrogel beads were synthetized for phosphate removal from aqueous solution. The encapsulation of palygorskite (PAL) into polymers enhanced the mechanical strength of LPAP hydrogel and selectivity towards phosphate as well. The characterization of synthesized hydrogel was conducted by SEM-EDS, BET, XRD, FT-IR and XPS, etc. Batch experiments indicated that phosphate uptake by LPAP was pH dependent with the optimal pH range of 3-6, and efficient phosphate removal (nearly 100%) was maintained in the co-existence of anions (Cl-, NO3- and SO42-). The adsorptive behavior of LPAP beads could be satisfactorily described by Freundlich isotherm model and pseudo-second-order kinetic model, with the experimental maximum phosphate uptake of ∼33.2 mg/g obtained at pH 4. Thermodynamics analysis suggested the spontaneous and endothermic character of adsorption process. More crucially, the superior reusability of LPAP beads confirmed through sorption-desorption cyclic experiments provided access for waste elimination at the minimum cost. The main phosphate removal routes were identified as electrostatic interaction, ligand exchange and Lewis acid-base interaction, and crystalline LaPO4·xH2O was formed on the surface of LPAP beads. Overall results demonstrated the applicable potential of LPAP beads as an environmental-sustainable, low-cost, anti-interfering and easily-recovered biosorbent for environmental remediation.