Preparation of biochar from constructed wetland plant and its adsorption performance towards Cu²

In order to solve problems in the treatment and disposal of huge production of artificial wetland plants and heavy metal pollution, two constructed wetland plants of reed and gladiolus were selected as raw materials to prepare biochar for adsorbing heavy metals from aqueous solutions. The experimental results showed that reed biochar prepared at 600℃ and activated by KOH with an impregnation ratio of 1:3 (KRAC-3) exhibited relatively high adsorption ability towards Cu²⁺. The optimal results analyzed by Design-Expert software showed that the maximum adsorption rate of KRAC-3 towards Cu²⁺ was obtained under the optimal conditions of adsorbent dosage of 1.2 g/L, pH of 4.96, and reaction time of 137.43 min. The adsorption of Cu²⁺ followed pseudo-second-order kinetics and the Langmuir adsorption model. The theoretical maximum adsorption capacity of KRAC-3 calculated from the Langmuir isotherm model was 148.08 mg/g. Microscopic tests with the help of SEM, EDS, and XRD revealed that physical adsorption, ion exchange, electrostatic adsorption, surface complexation, and precipitation were the main adsorption mechanism of Cu²⁺ loading onto KRAC-3. This study will provide a theoretical basis for the application of biochar prepared from constructed wetland plants and the treatment of heavy metal-containing wastewater.