Comparison of characterization and adsorption of biochars produced from hydrothermal carbonization and pyrolysis

Two types of rice-husk biochars, hydrothermally produced hydrochar and slow-pyrolysis pyrochar, were produced at different temperatures and were characterized and used as adsorbent material for the removal of methylene blue, iodine, and copper ions from aqueous solution. The characterization results showed that the hydrochars contained higher heating value, volatile matter content, carbon content and oxygen functional groups, and retained lower oxygen content and ash content than the pyrochars. Although the hydrochar retained relatively lower surface area, its adsorption capacity for methylene blue, iodine, and copper ions was much higher than pyrochar due to its ion-exchange and complexation. The adsorption isotherms of copper ions by two types of biochars were well described by the Langmuir and Freundlich models.