Hydrochar preparation from black liquor by CO₂ assisted hydrothermal treatment: Optimization of its performance for Pb²⁺ removal

Hydrochar was produced from hydrothermal treatment of corn straw black liquor. Response surface methodology (RSM) and the central composite design (CCD) were employed for determination of optimal char with maximum Pb²⁺ removal capacity. The operational parameters such as hydrothermal temperature (°C), duration (min) and solid liquid ratio (LSR) were chosen as independent variables in CCD. The statistical analysis indicates that the effects of hydrothermal temperature, duration, LSR and combined effect of hydrothermal temperature and duration are all significant for the Pb²⁺ removal capacity. The optimal condition for achieving the maximum Pb²⁺ adsorption capacity is obtained as the following: hydrothermal temperature (205 °C), duration (28min), LSR (12) with Pb²⁺ removal capacity reaching 47mg/g. The BET specific surface area of char prepared at optimal conditions could reach 85m²/g.