Removal of Cu²⁺ by biochars derived from green macroalgae

The by-product char of the fast pyrolysis of a green macroalga Enteromorpha compressa was used to remove copper from an aqueous solution. The surface area and the amount of cation exchange capacity (CEC) were increased by steam activation, resulting in enhanced adsorption capacity. Although chemical activation using a KOH solution increased the pore volume and surface area dramatically, it decreased the adsorption capacity because of activating in the KOH solution and washing decreased CEC. Ion exchange between the Cu ions and cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) as well as adsorption onto the functional groups on the char surface appeared to be important mechanisms for the removal of Cu. A pseudo-second-order kinetic model and Langmuir isotherm model could interpret the kinetics and equilibrium of the Cu adsorption on the E. compressa char. The maximum amount of Cu adsorption on the char was 137 mg g⁻¹.