Figure 6.

Biochar sorption mechanisms for Cd²⁺, Pb²⁺ or Zn²⁺. A) Cation–π interaction, B) Carboxylic group acting as a chelating ligand, C) Carboxylic groups forming a complex with a divalent cation. Surface complexation mediated by cation exchange of D) monovalent cations K⁺ or Na⁺ and E) divalent cations Ca²⁺ or Mg²⁺.