Efficient phosphate adsorption from real industrial wastewater using a La/Mg-Fe LDH-biochar integrated guar gum-gelatin hydrogel towards sustainable resource reuse.

The recovery of phosphates from wastewater is important for mitigating eutrophication and promoting sustainable phosphorus management. In this study, a novel biopolymer-based guar gum-gelatin hydrogel composite modified with La/Mg-Fe LDH-functionalized biochar (GGLBC) was successfully synthesized for efficient phosphate adsorption and recovery from wastewater. The prepared GGLBC hydrogel exhibited a maximum adsorption capacity of 106.38 mg g-1, consistent with the Langmuir isotherm model. The adsorbent also exhibited a maximum adsorption capacity of 79.43 mg g-1 and a phosphate removal efficiency exceeding 93% in industrial wastewater, demonstrating its outstanding applicability in complex water matrices. Mechanistic studies have shown that the high phosphate sorption capacity of GGLBC is primarily attributable to the formation of La-O-P, Mg-O-P, and Fe-O-P bonds, coupled with ligand exchange, ion exchange, electrostatic interactions, and pore filling. The adsorbed phosphate can be used as a nutrient for plant growth. In phosphate release tests, phosphate-loaded GGLBC (GGLBC-P) consistently released up to about 50% of the adsorbed phosphate over 25 days, demonstrating good controlled-release properties. Soil incubation studies showed that adding GGLBC-P to soils increased available phosphate levels to 38 mg kg-1. Plant growth studies showed enhanced plant growth when GGLBC-P was added to the plants. The ANN model was successfully built to simulate phosphate release at various pH levels. This study provides a comprehensive approach to the utilization of adsorbed phosphates in agriculture.