Montmorillonite‑sodium alginate/chitosan beads: A green potential solution for phosphorus removal from wastewater and slow-release phosphorus fertilizer application.

Effective recovery of phosphorus from wastewater and its subsequent reutilization are crucial for controlling water eutrophication and promoting resourceful utilization of pollutants. In this study, an eco-friendly and highly efficient montmorillonite‑sodium alginate/chitosan beads (CS/SA-FeMT) was synthesized via the semi-interpenetrating network method for phosphorus adsorption, and its potential application as a fertilizer after phosphorus adsorption was also preliminarily investigated. The results revealed that the surface of CS/SA-FeMT was coated with granular montmorillonite, exhibiting a rougher layered stacking structure. Consequently, the phosphorus adsorption capacity of CS/SA-FeMT was significantly enhanced compared to montmorillonite or sodium alginate/chitosan beads alone, reaching a maximum adsorption capacity of 88.3 mg P/g. Furthermore, the adsorption interference experiment indicated that the CS/SA-FeMT composite demonstrated exceptional resistance to interference from common ions (Cl-, SO42- and NO3-) and organic acids (humic acid and fulvic acid) typically found in wastewater. Additionally, the CS/SA-FeMT exhibited low leaching of Fe and Ca, and maintained 81.65 % phosphorus adsorption efficiency after five adsorption/desorption cycles. The adsorption mechanism of CS/SA-FeMT was primarily attributed to electrostatic attraction, surface precipitation, ligand exchange, and ion exchange. In addition, the phosphorus release characteristics showcased the CS/SA-FeMT hydrogel beads' exceptional slow-release capabilities, with complete phosphorus release (>99 %) achieved within 19, 19, and 20 days in deionized water at pH levels of 5, 7, and 9, respectively. Overall, CS/SA-FeMT demonstrated excellent potential for removal phosphorus from water and further use as a phosphorus fertilizer.