Preparation, characteristics and mechanisms of Cd(II) adsorption from aqueous solution by mango kernel-derived biochar

The removal potential of cadmium (Cd(II)) from aqueous solution by waste mango kernel biochar (MKB) was investigated for the first time. MKB was prepared by pyrolyzing mango kernel waste at 300–700 °C for 2 h. The effects of pyrolysis temperature on physicochemical characteristics of MKB were described by Brunauer–Emmett–Teller (BET), scanning electron micrographs with energy dispersive system (SEM–EDS), Fourier transform infrared (FTIR), and X-ray diffractometer (XRD). Batch adsorption experiments were also performed to study adsorption properties for Cd(II) of MKB. The results indicated that the pH, C content, specific surface area, and pore volume increased obviously with the pyrolysis temperature increased, while the element ratio and surface functional groups decreased. The variation of Cd(II) adsorption capacity with time and initial concentration were better fitted by pseudo-second-order and Langmuir isotherm models, respectively, indicating that the MKB adsorption process was a monolayer adsorption dominated by chemical adsorption. Increasing the pyrolysis temperature increased the maximum adsorption capacity and MKB700 had the highest Langmuir sorption capacity for Cd(II) (27.81 mg g−1) at pH 6.0. Multiple consecutive adsorption–desorption cycles revealed the good reusability of MKB. Further analysis showed that the Cd(II) adsorption mechanism on MKB700 was primarily attributed to complexation reaction with functional groups, ion exchange, and precipitation reaction. This study demonstrated that MKB could be a low-cost and recyclable adsorbent, which could be a promising method of mango kernel waste resourceful treatment.