Lignin-based nanoparticles for recovery and separation of phosphate and reused as renewable magnetic fertilizers.

In this work, magnetic lignin-based nanoparticles (M/ALFe) were developed and used to adsorb phosphorus to obtain phosphorus-saturated nanoparticles (M/ALFeP). The nanoparticles were then used as renewable slow-release compound fertilizers. First, aminated lignin was synthesized via Mannich reaction, and then Fe3O4 nanoparticles were loaded and Fe3+ was chelated on the aminated lignin to prepare M/ALFe. Finally, M/ALFeP were obtained after adsorption of phosphorus. The effects of nanoparticle dosage, solution pH and adsorption time on adsorption efficiency were determined. Adsorption isotherm and adsorption kinetics results suggested that the adsorption was coincided with the pseudo-second-order and Temkin model, respectively. The cumulative release of Fe and phosphorus from M/ALFeP increased gradually and reached to 67.2% and 69.1% in soil after 30 days, respectively. After the release of nutrients, M/ALFeP can be separated by a magnet with a high recovery ratio from water or soil and regenerated for phosphate recovery again. Therefore, the magnetic lignin-based nanoparticles have a promising application potential as an efficiently separated and renewable nanomaterial for removal of low concentration phosphate in wastewater treatment and as a slow-release fertilizer in sustainable agriculture.