Fast nitrate and fluoride adsorption and magnetic separation from water on α-Fe₂O₃ and Fe₃O₄ dispersed on Douglas fir biochar

α-Fe₂O₃ and Fe₃O₄ dispersed on high surface area (663 m²/g) Douglas fir biochar (BC) was prepared for fast nitrate and fluoride ion removal from water using magnetic separations. This biochar, made originally at 900 °C, was impregnated with FeCl₃ and converted by pyrolysis at 600 °C to magnetic (494 m²/g) biochar (MBC). MBC and its precursor BC were characterized using SEM, SEM-EDX, STEM, S_BET, PZC measurements, XRD analysis, and XPS. Dispersed α-Fe₂O₃ and Fe₃O₄ particles caused magnetization and generated most adsorption sites, causing more nitrate and fluoride uptake than BC. Both nitrate and fluoride adsorption on MBC remained high over a pH range from 2 to 10. Sorption was evaluated from 298 to 318 K using the Langmuir and Freundlich isotherm models. Langmuir adsorption capacities were 15 mg/g for nitrate and 9 mg/g for fluoride, higher capacities than those reported for other biochar and iron oxide adsorbents.