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Biochar was modified by an acylation reaction using EDTA. Then, a novel biochar-based porous composite was successfully prepared using modified biochar as a base to remove Cu(II) in wastewater. In addition, functional groups, morphologies and the specific surface areas of EDTA-BIOC hydrogel were characterized by FT-IR, SEM, and BET, respectively. Various factors affecting the adsorption of Cu(II) on EDTA-BIOC hydrogel were investigated, such as pH, temperature, contact time, salinity, and initial concentration of Cu(II). Addition of EDTA greatly improved the adsorption capacity for Cu(II), and the maximum adsorption capacity of EDTA-BIOC hydrogel for Cu(II) was 93.9 mg g−1 at 318 K, which was higher than for biochar, gel-0 and EDTA-BIOC/SiO2 hydrogel. Cu(II) adsorption on EDTA-BIOC hydrogel was shown to fit well with the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption mechanisms of Cu(II) by the hydrogel are systematically discussed, including physical adsorption, electrostatic attraction, cation exchange and complexation. Furthermore, EDTA-BIOC hydrogel could maintain a high adsorption capacity after five adsorption–desorption processes, which provided the possibility for recycling the EDTA-BIOC hydrogel multiple times. Finally, the adsorption capacity of EDTA-BIOC hydrogel for Cu(II) was studied in various water samples. The experimental results showed that EDTA-BIOC hydrogel exhibited great potential for treating different wastewaters containing Cu(II). [ABSTRACT FROM AUTHOR]