Enhanced scavenging and recovery of low-concentration phosphate from secondary effluents using lanthanum-incorporated layered double hydroxide composites

Scavenging low-concentration phosphate in secondary effluents to ultra-low levels (e.g., <0.05 mg-P/L) is crucial for mitigating severe eutrophication issues. While adsorption shows promise for phosphate removal and recovery, challenges such as limited sorption capacity and selectivity for low-level phosphate persist, increasing operational costs. Herein, lanthanum (La)-incorporated MgFe-layered double hydroxide/biochar (La-MgFe-LDH/BC) composites were synthesized using a simple coprecipitation method for the effective sequestration and recovery of low-level phosphate. The incorporation of La promoted the formation of amorphous LDH species with markedly reduced particle sizes, enhanced porosity, and increased carbonate groups. Consequently, La-MgFe-LDH/BC exhibited an exceptional sorption capacity of 62.51 mg-P/g, rapid sorption kinetics of <60   minutes, and a broad applicable pH range (3-11), with strong anti-interference capabilities against concomitant anions and humic acids. La-MgFe-LDH/BC effectively scavenged phosphate from real secondary effluents and raw sewage, achieving extreme-low phosphate levels below 0.01 mg-P/L, making it highly applicable for effluent polishing. Furthermore, it showed excellent reusability and phosphate recovery potential with over 90% desorption efficiency, with ligand exchange mechanisms being primary pathways for phosphate capture. These findings highlight La-MgFe-LDH/BC as a promising candidate for low-level phosphate removal and advance the application of LDH-based composites.