A novel biomass-derived magnetic nanocomposite, named as BMN, was fabricated by one-step pyrolysis process. BMN showed excellent As(III) removal performances such as high adsorption capacity (16.23 mg/g), collectability of magnetism, reusability and low cost. Importantly, when BMN was loaded in sponges with a microporous structure, the collectability of BMN in soil was improved. The system of BMN and sponges could efficiently remove As(III) from soil and the resulting BMN/sponge/As(III) could easily separate from soil using a magnet. In addition, when BMN was loaded on filter paper, the system of BMN and filter papers could be conveniently used as an excellent filter layer to control the migration of As(III) in soil. Pot incubations indicated that BMN could increase the pH value of soil and decreased the concentration of available arsenic in soil. Wherein, the As(III) ions removal by BMN contained three pathways: (1) adsorption of As(III) anions through electrostatic attraction; (2) oxidation of As(III) to As(V) by reactive oxygen; and (3) immobilization of As(III) and As(V) by iron nanoparticles. Therefore, this work provides an executable approach to remove As(III) from soil with low cost, which also promoted the recovery and utilization of palm wastes.