Characterization of cadmium removal from aqueous solution by biochar produced from a giant Miscanthus at different pyrolytic temperatures

The objective of this study was to investigate the feasibility of biochar for removing Cd from aqueous solution. Biochars were produced from a Miscanthus sacchariflorus via slow pyrolysis at 300, 400, 500 and 600 °C. Higher pyrolytic temperature resulted in biochar with a higher aromatic structure and fewer polar functional groups. In particular, pH and surface area of biochar increased greatly at pyrolytic temperatures ⩾500 °C, which increased Cd sorption capacity up to 13.24 mg g−1. The diffuse-controlled Cd removal was likely due to a surface sorption or a precipitation reaction depending on pH. A simulation with the visual MINTEQ program indicated that the precipitate was Cd(OH)2. In addition, biochar treatment significantly removed the acute toxicity of Cd toward Daphnia magna, resulting in increase of EC50 (50% effective concentration) value from 0.16 to 0.76 mg L−1.