Phosphate adsorption improvement using a novel adsorbent by CaFe/LDH supported onto CO₂ activated biochar

It is imperative to remove phosphate from the aquatic system. This nutrient in excess can cause environmental problems such as eutrophication. Therefore, aiming to enhance phosphate removal, this work presents a novel adsorbent developed from the construction of Ca²⁺/Fe³⁺ layer double hydroxides (CaFe/LDH) supported onto biochar physically activated with CO₂ [CaFe/biochar (CO₂)]. Pristine biochar was produced from the pyrolysis of Eucalyptus saligna sawdust, activated with CO₂, and then impregnated with CaFe/LDH. The CaFe/biochar (CO₂) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET). The characterization confirmed a proper synthesis of the new adsorbent. Experiments were conducted in the form of batch adsorption. Results indicated that the optimum pH and adsorbent dosage were 2.15 and 0.92 g L^-1, respectively. Adsorption kinetics, isotherms, and thermodynamics were also evaluated. Adsorption kinetics and isotherms were better fitted by the pseudo n order and Freundlich models, respectively. Results also indicated a better adsorption capacity (99.55 mg·g^-1) at 55 °C. The thermodynamic indicators depicted that the adsorption process was favorable, spontaneous, and endothermic. Overall, CaFe/biochar (CO₂) could be potentially applied for the adsorptive removal of phosphate from an aqueous solution.