The Removal of Lead and Cadmium from Solution by K₂CO₃ Activated Biochar Derived from Corn Straw/Spent Mushroom Substrate/Hardwood Sawdust

The biochar (BC) pyrolyzed from corn straw (CS), spent mushroom substrate (SMS) and hardwood sawdust (HS), which are activated by K₂CO₃, were utilized for lead (Pb) and cadmium (Cd) sorption in solution. The effects of different pyrolysis factors on the Pb and Cd sorption capacities of three types of K₂CO₃-activated biochar (ABC) were analyzed. A series of characterization analyses were applied to compare the differences between various ABCs and to explore the Pb and Cd removal mechanisms. The results showed that the pyrolysis temperature, residence time and K₂CO₃ concentration obviously affect the sorption capacity of all ABCs. According to characterization, SMS had a loosely porous structure, which might be more favorable for K₂CO₃ activation. Furthermore, SMS possessed a rich elemental composition. Therefore, the pyrolysis product derived from SMS exhibited a larger specific surface area and higher polar functional group content, which might be the reason why ABCs synthesized from SMS exhibited better Pb and Cd sorption capacities than did ABCs synthesized from CS or HS. Moreover, the contributions of different Pb or Cd sorption mechanisms by different ABCs decreased as follows: mineral precipitation > cation exchange > complexation of oxygen-containing functional groups > π-bonding or physical sorption. Overall, the ABC synthesized from SMS was more suitable for Pb or Cd removal in solution, which also provided a new approach for the comprehensive utilization of SMS.