二酸化マンガン粒子表面における銅 (II) イオン吸着挙動のキャラクタリゼーション

抄録

The adsorption of Cu²⁺ ions on MnO₂ was examined as a function of pH and concentrations of Cu²⁺ and MnO₂. The adsorption isotherm shows that the surface concentration of adsorbed Cu²⁺ increases with pH and concentration of Cu²⁺ in solution, and that, at higher coverages, the surface concentration is lower than predicted by the Langmuir isotherm The behavior was characterized by considering the stoichiometry and equilibrium and concentration conditions of the adsorption. The surface acid hydroxyl groups, ≡MnOH(a), react with Cu²⁺ ions to form the following two surface complexes.≡MnOH(a)+Cu²⁺+NO^-₃_??_≡MnOCu⁺·NO^-₃+H⁺, 2≡MnOH(a)+Cu²⁺_??_(≡MnO)₂Cu+2H⁺. The equilibrium conditlons of these surface complexations are given by. K₁^int=Q₁^eq exp (B₁[≡MnOCu⁺·NO^-₃]), β₂^int=Q₂^eq exp(B₂[(≡MnO)₂Cu]), where K₁^int and β₂^int are“intrinsic”stability constants of[1:1]and[1:2] surface complexes, Q₁^eq and Q₂^eq are concentration quotients at equilibrium, and B₁ and B₂ are constants expressing the extent of suppression of surface complexation by the respective complexes. The equations of equilibrium conditions and of concentration conditions for both solution and surface species were fitted to the adsorption isotherm, and the values of the constants were determined by the nonlinear leastsquares method. The values are: K₁^int=8.15×10^-3m³mol^-1, β₂^int=2.41×10³m^-1, B₁=3.81×10⁶m²mol^-1, and B₂=1.62×10⁶m²mol^-1 at an ionic strength of 0.1 (NaNO₃) and 25°C. These values well describe the observed adsorption behavior.