Hydrogen peroxide modification enhances the ability of biochar (hydrochar) produced from hydrothermal carbonization of peanut hull to remove aqueous heavy metals: Batch and column tests

Biochar converted from agricultural residues can be used as an alternative adsorbent for removal of aqueous heavy metals. In this work, experimental and modeling investigations were conducted to examine the effect of H₂O₂ treatment on hydrothermally produced biochar (hydrochar) from peanut hull to remove aqueous heavy metals. Characterization measurements showed that H₂O₂ modification increased the oxygen-containing functional groups, particularly carboxyl groups, on the hydrochar surfaces. As a result, the modified hydrochar showed enhanced lead sorption ability with a sorption capacity of 22.82mgg^-1, which was comparable to that of commercial activated carbon and was more than 20 times of that of untreated hydrochar (0.88mgg^-1). When used as filter media in a packed column, the modified hydrochar was also much more effective in filtering lead than the unmodified one. The lead removal capacity of the modified hydrochar packed column was about 20 times of that containing untreated hydrochar. In a multi-metal system, the modified hydrochar column still effectively removed lead, as well as other heavy metals (i.e., Cu²⁺,Ni²⁺, and Cd²⁺) from water flow. Model results indicated that the heavy metal removal ability of the modified hydrochar follows the order of Pb²⁺>Cu²⁺>Cd²⁺>Ni²⁺. Findings from this work suggest that H₂O₂-modified hydrochar may be an effective, less costly, and environmentally sustainable adsorbent for many environmental applications, particularly with respect to metal immobilization.