Thermodynamics adsorption of heavy metal ions Pb2+, Cd2+ and Cu2+ on hydrothermal δ-MnO2

δ-MnO₂ was prepared with hydrothermal treatment, and its crystalline structure was verified with X-ray diffraction spectroscopy. FTIR showed there were copious hydroxyl groups on the surface of δ-MnO₂ for the adsorption. The adsorption capacity of three kinds of heavy metal ions Pb²⁺, Cd²⁺ and Cu²⁺ on the δ-MnO₂ was all increased with the increase of ion concentration and the increase of pH. The adsorption isotherms of Pb²⁺ exhibited good correlation with Freundlich equations, Langmuir equations and Temkin equations, whereas equilibrium data of Cu²⁺ was best fitted to Freundlich isotherm, and Langmuir isotherm was best for Cd²⁺. Adsorption thermodynamics indicates that as the temperature in the range of 298.15 ~ 323.15K, all the adsorptions were endothermic, spontaneous reaction. Therefore, increasing temperature was good for the adsorption, and the higher the temperature, the higher the spontaneity.