Enhanced phosphate adsorption and desorption characteristics of MgO-modified biochars prepared via direct co-pyrolysis of MgO and raw materials

Abstract

Biochar modified by metal ions—particularly Mg—is typically used for the effective recovery of phosphorous. In this study, MgO-modified biochars were synthesized via the direct co-pyrolysis of MgO and raw materials such as rice straw, corn straw, Camellia oleifera shells, and branches from garden waste, which were labeled as MRS, MCS, MOT, and MGW, respectively. The resulting phosphate (PO) adsorption capacities and potential adsorption mechanisms were analyzed. The PO adsorption capacities of the biochars were significantly improved after the modification with MgO: MRS (24.71 ± 0.32 mg/g) > MGW (23.55 ± 0.46 mg/g) > MOT (15.23 ± 0.19 mg/g) > MCS (14.12 ± 0.21 mg/g). PO adsorption on the modified biochars was controlled by physical adsorption, precipitation, and surface inner-sphere complexation processes, although no electrostatic attraction was observed. Furthermore, PO adsorbed on modified biochars could be released under acidic, alkaline, and neutral conditions. The desorption efficiency of MRS was modest, indicating its suitability as a slow-release fertilizer. Graphical Abstract

Advancements in Biochar Modification for Enhanced Phosphorus Utilization in Agriculture

“…The mechanism is driven by reactions where Ca or Mg ions in the biochar react with phosphate to form precipitates such as Ca 5 (PO 4 )3OH and Mg 3 (PO 4 ) 2 , mitigating phosphate mobility. In a recent study by Tu et al [79], the research focused on the effectiveness of biochar modified with MgO for P recovery. This study involved the co-pyrolysis of MgO with various raw materials, resulting in different modified biochars: MgO-rice straw, MgO-corn straw, MgO-Camellia oleifera shells, and MgO-garden waste.…”