Iron-modified orange peel biochar for highly efficient arsenic(III) removal: Adsorption performance and process optimization via box-Behnken design

Herein, waste orange peel (OP) biomass residues were upcycled with iron oxide (Fe2O3) and calcination, and assessed for their adsorption efficiency for arsenite (As(III)) using a series of batch adsorption experiments that took into account different operational parameters, including contact time, starting concentration of arsenite, starting pH, and the impact of other ions in the solution. In addition, optimization of As(III) removal by OPFC was achieved by the use of RSM and BBD analysis. The OPFC exhibited an As(III) adsorption capacity of 23.6 mg/g at neutral pH, superior to many reported adsorbents, attributed to its high surface area (81.47 m2/g), pore volume (0.18 cm3/g), pore radius (21.14 nm), and abundant surface-active sites. Adsorption equilibrium data conformed to the Freundlich model, while the kinetic data were best described by the pseudo-second-order model. The OPFC also demonstrated strong resistance to coexisting ions, excellent regeneration-ability, and high efficacy in treating simulated As(III)-contaminated water. In addition, response surface methodology (RSM) with Box Behnken Design (BBD) optimization demonstrated that at pH 5.25, with 500 μg/L of initial As(III) concentration, OPFC could reach to a maximum adsorption capacity of 472.38 μg/g in 720 min. These results indicate OPFC's strong potential as a sustainable mesoporous adsorbent for practical As(III) remediation.