Synthesis of Mg-, Al- and Mg/Al-date palm fronds modified biochars: characterization and investigations on phosphorus adsorption characteristics

Phosphorus (P) recovery by engineered biochars for a further subsequent use in agriculture promotes circular economy and sustainability concepts. In this study, three biochars were synthesized at 500 °C from pre-impregnated date palm fronds (DPFs) with 1 M solutions containing either MgCl 2 (DPF-Mg-B), AlCl 3 (DPF-Al-B) or a combination of MgCl 2 /AlCl 3 (DPF-Mg/Al-B). Subsequently, the structural, textural, and surface chemistry properties of these biochars were assessed. Then, the P recovery of these biochars from aqueous solutions was evaluated under various experimental conditions. Characterization results revealed that the synthesized biochars exhibited high loads deposition of Mg- and/or Al-based nanoparticles. The DPF-Mg/Al-B showed the most interesting physicochemical properties. Notably, the corresponding Mg and Al contents; BET surface area and total pore volume were evaluated to 99.6 and 136.0 mg·g –1 ; 180.0 m 2 ·g –1 and 0.09 cm 3 ·g –1 , respectively. Batch P recovery assays showed that P recovery efficiency by the three studied biochars was influenced by the contact time, the initial aqueous pH, P concentration and also the presence of foreign anions, especially nitrates and chlorides. Moreover, owing to its attractive properties, the DPF-Mg/Al-B exhibited the highest P recovery capacity (14.1 mg·g –1 ) which is 1.3 and 1.7 higher than that of DPF-Mg-B and DPF-Al-B, respectively. The kinetic and isotherm experimental data modelling suggest that P recovery process was governed by both physical and chemical mechanisms. These P-loaded biochars have the potential to serve as promising fertilizers, offering a sustainable alternative to synthetic counterparts.