Strength modification of sodium alginate–polyvinyl alcohol gel beads and efficient aqueous phase phosphorus removal

Due to excessive phosphorus discharge in artificial ecosystems, eutrophication and the global shortage of phosphorus resources are becoming increasingly serious. Therefore, seeking for an efficient and economical phosphorus removal technology has become a pressing issue recently. In this study, sodium alginate/polyvinyl alcohol gel beads (PVA/SA) were prepared through chemical cross-linking and subsequently modified with cationic polyacrylamides (co-PAM) coating to synthesize the core–shell PVA/SA-coPAM gel beads, whose mechanical strength was improved by about 20% of PVA/SA. The influencing factors of phosphate adsorption were studied, and the reaction mechanism was explored. The scanning electron microscopy (SEM) results showed that the surface of the gel beads presented nanoscale lamellar stacking folds, and the multistage penetrating stable pore structure was formed inside. The adsorption process conformed to the pseudo-second-order kinetic equation, and the adsorption equilibrium time was 120 min. The maximum adsorption capability of PVA/SA and PVA/SA-coPAM toward phosphorus was fitted out to be 73.47 mg PO 4 3− −P/g and 69.15 mg PO 4 3− −P/g from the Langmuir isotherms model with pH 3, temperature 35 ℃, which was significantly higher than 30% of other adsorbents. In the acidic solution, the phosphate group was attracted to the material through electrostatic interaction. At the same time, Fe 3+ and Ca 2+ formed complexes with –OH and –COOH on the gel beads, and the phosphate was adsorbed to the surface of the gel beads through ligand exchange between complexes. Above all, we prepared a kind of gel beads with high strength and high phosphorus adsorption capacity for large-scale industrial applications by a simple method and economical raw materials. Also, they could be used as phosphorus fertilizer or directly used in calcination to recover phosphorus. Graphical abstract