Study of Pb²⁺, Cd²⁺ and Ni²⁺ adsorption onto activated carbons prepared from glycyrrhiza residue by KOH or H₃PO₄activation.

The activated carbons (ACs) were prepared from glycyrrhiza residue by KOH or H₃PO₄activation and were used for removing Pb²⁺, Cd²⁺ and Ni²⁺ from simulated wastewater. The changes of the physical structure and chemical properties of the glycyrrhiza residue before and after activation were characterized by using a variety of analytical instruments and methods. Kinetics and equilibrium isotherms were obtained and the effects of solution pH value and adsorbent dosage were studied in batch experiments. The results indicated that after activation, the surface structure of glycyrrhiza residue changes and surface area, micropore volume also increase accordingly. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The Freundlich model fitted the equilibrium data better than the Langmuir isotherm. According to the Langmuir equation, the maximum adsorption capacities of ACs prepared from glycyrrhiza residue by KOH and H₃PO₄activation for Pb²⁺, Cd²⁺ and Ni²⁺ are 2.170 mmol/g, 2.617 mmol/g, 3.741 mmol/g and 2.654 mmol/g, 3.095 mmol/g, 3.076 mmol/g, respectively, which are much higher than ACs prepared from other raw materials.