Research on the adsorption mechanism of Cu and Zn by biochar under freeze-thaw conditions.

To investigate the adsorption mechanism of heavy metals by biochar under freeze-thaw conditions, based on indoor simulation experiments, the changes in pH value, surface area (SA), pore structure and functional groups of biochar under natural and freeze-thaw conditions were analysed. Using isothermal adsorption method, Langmuir and Freundlich adsorption equations of heavy metals, the adsorption characteristics of biochar for heavy metals Cu and Zn were analysed. The results showed that after 10 periods (30 cycles), the pH value of the biochar decreased from 8.80 to 7.99, the SA increased from 6.28 m2/g to 20.26 m2/g, the pore volume (PV) decreased from 0.009 mL/g to 0.003 mL/g, and the pore diameter (PD) decreased from 1.692 to 1.423 nm. In period 10, compared to the control group (CK), the adsorption capacity of Cu and Zn increased by 72.00% and 44.55%, respectively, and the number of oxygen-containing functional groups -OH, -COOH and -C=O greatly increased. This study provides scientific and reasonable theoretical guidance for future studies on the biochar adsorption and biochar remediation of soil.