Magnetic Pecan Nutshell Biochar for Arsenic and Fluoride Removal: Effects of Particle Size and Pyrolysis Temperature

Magnetic biochar derived from various residual agricultural wastes have been widely studied due to their abundance, low cost, and minimal environmental impact. Pecan nutshell ( Carya illinoinensis ) residuals were incorporated with γ-Fe 2 O 3 , transforming them into magnetic adsorbents. The effect of particle size (granular: 0.38-0.7 mm; powder: 0.15-0.38 mm) and pyrolysis temperature (500 °C and 650 °C) were investigated for their influence on adsorption capacity of arsenic and fluoride in aqueous solutions. Our findings showed that finely powdered magnetic biochar produced at 650 °C (PMPH-650) exhibited the highest removal efficiency (99.09%) and adsorption capacity (4.925 mg/g) for arsenic compared to other materials. The arsenic adsorption isotherm followed both Langmuir and Freundlich models well. The kinetics of fluoride adsorption fit the Elovich equation, suggesting chemisorption and chemical bond formation. XRD and FTIR analyses confirmed the presence of the γ-Fe 2 O 3 phase. SEM/EDX and FTIR analyses confirmed the presence of arsenic on the biochar surface after the adsorption. This research paves the way for using magnetic biochar derived from pecan nutshell as a cost-effective and eco-friendly approach for arsenic and fluoride remediation in water.