Efficient removal of hexavalent chromium from wastewater using a novel magnetic biochar composite adsorbent

Hexavalent chromium (Cr(VI)) in wastewater poses serious environmental and ecological risks. A novel Fe3O4-loaded magnetic biochar (MBC) using Acacia falcata leaf powder was synthesized via one-step hydrothermal carbonization for efficient Cr(VI) removal. FESEM images revealed porous, irregular structures, and EDS analysis confirmed Fe, O, C, and Cr presence, validating chromium adsorption. XRD indicated a lattice parameter of 0.8407 nm, characteristic of magnetite nanoparticles, with an average crystallite size of 11.29 nm. MBC exhibited superparamagnetic behavior facilitating easy separation. The deconvolution of XPS spectra for chromium revealed distinct peaks at 575.6 and 585.7 eV, corresponding to Cr(III), and 577.3 and 587.8 eV, corresponding to Cr(VI), thereby confirming the dual roles of reduction and adsorption. Batch adsorption followed pseudo-second-order and Hill models, highlighting physisorption and reduction mechanisms. At pH 2, 303 K, and 0.4 g/L, MBC achieved a saturation capacity of 36.15 mg/g. Thermodynamic analysis confirmed endothermic, spontaneous Cr(VI) removal. Desorption studies revealed reversible behavior via ion exchange. 0.1 M NaOH showed better regeneration ability compared to 0.5 M NaOH solution. Phosphate ions reduced Cr(VI) adsorption compared to other competing ions. MBC showed significant potential for environmental remediation by effectively removing Cr(VI) from various water sources, achieving results comparable to distilled water. Sustainable synthesis of Fe3O4-loaded MBC from A. falcata leaf powder offers a promising solution for Cr(VI) removal, addressing critical environmental challenges.