Thermal stability of biochar and its effects on cadmium sorption capacity

In this study, the thermal stability of a wood shaving biochar (WS, 650 °C), a chicken litter biochar (CL, 550 °C) and an activated carbon (AC, 1100 °C) were evaluated by combustion at 375 °C for 24 h to remove the labile non-carbonized organic matter. Results showed that WS and CL biochars were not thermally stable and can lose most of the organic C during combustion. The combusted WS and CL biochars retained considerable amounts of negative charge and displayed higher sorption for Cd (from 5.46 to 68.9 mg/g for WS and from 48.5 to 60.9 mg/g for CL). The AC retained 76.5% of its original C and became more negatively chargely after combustion, but its sorption for Cd slightly decreased (from 18.5 to 14.9 mg/g). This study indicated that after potential burning in wildfires (200–500 °C), biochars could have higher sorption capacity for metals by remaining minerals.