Novel Fe/Ca oxide co-coated biochar enables efficient phosphorus recovery

Abstract Efficient elimination and retrieval of phosphorus from water bodies are crucial for effective eutrophication management and phosphorus reuse. A novel Fe/Ca oxide co-coated modified biochar (FCBC) was synthesized for phosphate recovery using coconut shell biochar as the raw material with ferrous chloride (FeCl₂) and calcium peroxide (CaO₂) as precursors. FCBC possesses a highly intricate pore structure and an abundance of surface-active groups. Fe/Ca oxides are loaded onto the biochar in the form of Ca₂Fe₂O₅, Fe₂O₃, and CaCO₃. FCBC demonstrates a broad pH tolerance range (pH = 6 – 12) in the aquatic environment. Phosphorus absorption by FCBC was simulated using the proposed pseudo-second-order kinetic and Langmuir model. The maximal saturation adsorption capacity was found to be 53.31 mg P/g. Phosphorus elimination is influenced by the generation of Ca₃(PO₄)₂, intraparticle diffusion, and electrostatic attraction. FCBC produced demonstrated exceptional phosphorus removal effectiveness in the presence of multiple anions, except for wastewater with high concentrations of SO₄²⁻, CO₃²⁻, HCO₃⁻, and F⁻ (>500 mg/L). The phosphorus removal effectiveness of FCBC in natural water samples collected from ponds, farmlands, and ditches exceeded 94%. This paper presents a novel technique for creating iron-calcium composite-modified biochar, which offers a valuable method for efficiently recovering phosphorus from agricultural surface waters.