The emphasis of the present study is to investigate the potential of magnetic iron oxide nanoparticles synthesized using bagasse from sugarcane (M‐NIOB). M‐NIOB was infused onto the modified batch reactor (M‐BR) stirrers using mesh structures for the adsorption of Cr6+ contained in effluent from the leather industry. M‐NIOB exhibited supermagnetic properties under an external magnetic field with a saturation magnetization value of 9.192 emu/g at room temperature. M‐NIOB nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, vibrating sample magnetometer, and Brunauer–Emmett–Teller analysis. The size of the M‐NIOB particles ranged from 50 to 200 nm. The most favorable time, pH, and temperature for the application of M‐NIOB to Cr6+ removal from tannery effluent was found to be 180 min, 5, and 318 K, respectively. M‐NIOB adsorbent performed its best at an adsorbent dosage of 800 mg/150 mL with a particle size of 150 nm. Kinetic and thermodynamic studies have been conducted. The applicability of various adsorption models for the Cr6+ adsorption data was tested. Moreover, the desorption studies carried out at 60 °C proved the capability of M‐NIOB for regeneration and reuse. Hence, M‐NIOB could be potentially applied for the treatment of effluent that has Cr6+ as a major constituent. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46683.