Enhancing efficient reclaim of phosphorus from simulated urine by magnesium-functionalized biochar: Adsorption behaviors, molecular-level mechanistic explanations and its potential application

Magnesium-functionalized Magnolia grandiflora Linn leaf-derived biochar (MBC) capable of efficiently reclaiming phosphorus from urine was synthesized by slow co-pyrolysis. Four adsorption kinetic and seven adsorption isotherm models were fitted to the batch adsorption and desorption experimental data, and it was found that pseudo-first-order kinetic model and multilayer model with saturation best described the phosphate-phosphorus (PO43--P) adsorption process by MBC. MBC and phosphorus-saturated MBC (P-MBC) were found to offer outstanding phosphorus adsorption and slow release properties, respectively. Based on material characterization, statistical physics, adsorption energy distribution and statistical thermodynamics, a multi-ionic, inclined orientation, entropy-driven spontaneous endothermic process of MBC on PO43--P was proposed, involving physicochemical interactions (porous filling, electrostatic attraction, ligand exchange and surface precipitation). Further, seed germination and early seedling growth experiments proved that P-MBC can be used as a slow-release fertilizer. Overall, MBC offers prospective applications as an efficient phosphorus adsorbent and then as a slow-release fertilizer.

Automated summary

Magnesium-functionalized Magnolia grandiflora Linn leaf-derived biochar (MBC) was synthesized by slow co-pyrolysis and showed efficient phosphorus reclamation from urine. The adsorption process of phosphate-phosphorus (PO43--P) by MBC was best described by the pseudo-first-order kinetic model and multilayer model with saturation. MBC and phosphorus-saturated MBC (P-MBC) exhibited outstanding phosphorus adsorption and slow release properties respectively, and P-MBC was confirmed to be a suitable slow-release fertilizer through seed germination and early seedling growth experiments.