Adsorption of copper and zinc by biochars produced from pyrolysis of hardwood and corn straw in aqueous solution

► Different biochars were investigated as adsorbents to remove Cu and Zn in solution. ► The characteristics of biochars depend on feedstocks and pyrolysis conditions. ► Adsorption was quite rapid and could be well described by Langmuir isotherm. ► Adsorption was a physically endothermic process and did not occur spontaneously. ► Cu can compete with Zn for binding sites at higher heavy metal concentrations.