Modeling the ion-exchange adsorption of heavy metal ions on the surface of metal oxides.

TAMURA Hiroki, KATAYAMA Noriaki, FURUICHI Ryusaburo

doi:10.2116/bunsekikagaku.42.11_719

The ion-exchange adsorption of heavy metal ions (Cu²⁺, Mn²⁺, Co²⁺, Zn²⁺, and Ni²⁺) on metal oxides (MnO₂, Fe₃O₄, and Al₂O₃) was modeled so as to enable a description and prediction of the amount of adsorption as a function of the ion concentration, exchange-site density, and solution pH. The model assumes that heavy metal ions are adsorbed through (1 : 1) and (1 : 2) ion-exchange reactions with the protons of the acid-type surface hydroxyl groups on metal oxides (-OH(a)), and that each exchange reaction is steadily suppressed along with the progress in ion exchange due to electrostatic lateral interactions between the species in the solid/solution interphase. The equilibrium conditions of the (1 : 1) and (1 : 2) exchange reactions are given by : K₁°=K₁exp(B₁ θ₁) and β₂°=β₂exp(B₂θ₂), where K₁° and β₂° are the equilibrium constants, K₁ and β₂ the concentration ratios, B₁ and B₂ the suppression constants, and θ₁ and θ₂ the coverages of the exchange sites. The values of K₁°, β₂°, B₁, and B₂ were determined by fitting the model equations to the experimental adsorption isotherms. With the established constants the fractions of adsorbed ions were calculated as a function of the pH for given concentrations of added metal ions and metal oxides. From the calculations, the adsorption affinity order of ions for MnO₂ is Cu²⁺ >Mn²⁺ >Co²⁺ >Zn²⁺ >Ni²⁺, and the Co²⁺ adsorption ability order of oxides is MnO₂>Fe₃O₄>Al₂O₃.

Modeling the ion-exchange adsorption of heavy metal ions on the surface of metal oxides.

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