Display omitted •The MBCI was prepared through coupling reaction and functional modification.•The mass ratio of biochar: Fe3O4 nano-particle was well determinated.•The MBCI after adsorption equilibrium can be effectively separated by a magnet.•The maximum Qe calculated from the Langmuir model was 197.96 mg/g at 323 K.•The MBCI showed high removal rate, separation and reusability for Cd (II). A novel iminodiacetic acid magnetic biochar (MBCI) was prepared, characterized and evaluated its adsorption performance for the removal of Cd(II) from aqueous solution. The biochar (BC) derived from palm fiber was served as a novel matrix, first oxidized by hydrogen peroxide (BCO) and loaded of Fe3O4 nano-particles (MBCO), followed by a coupling reaction and functional modification (MBCI). The characterization results showed that the Fe3O4 nano-particles were successfully loaded on the surface of biochar and the carboxyl groups of MBCI were obviously more than that of the pristine BC. The mass ratio for magnetization was well determined to be 1.8:1–2.3:1, which could guarantee high removal and recovery efficiency. The adsorption kinetics could be well fitted by the pseudo-second-order model and adsorption isotherm was well described by the Langmuir model. The surface complexation model was established to illustrate the adsorption process and adsorption of Cd (II) on MBCI was controlled by the surface complexation mechanism between functional groups in MBCI and Cd (II). MBCI possessed high adsorption capacity (197.96 mg/g at 323 K), reusability (retained 82.18% after five successive cycles) and sharing magnetic property (16.88 emu/g), which guaranteed it readily and efficient separation from the aqueous solution.