Surface complexation modeling of soluble molybdenum adsorption by Mn3O4

BACKGROUND: Mo is a harmful element that should strictly be limited in electrolytic manganese dioxide but can readily be removed by Mn3O4. However, as its adsorption mechanism is not yet clear the aims of this work are to clarify the absorption phenomena and specific reaction processes of Mo onto Mn3O4. RESULTS: Some theoretical parameters have been obtained: the total surface site density and protonation constants (NT = 6.84 × 10−3 mol g−1, Kₐ₁ⁱⁿᵗ = 2.0 × 10⁻⁵ , Kₐ₂ⁱⁿᵗ = 1.49 × 10⁻¹⁰ ) were obtained by non‐linear data fitting of acid‐base titrations. Distribution of soluble Mo species derived from thermodynamic calculations showed that the concentration of poly‐molybdenum acid ion was extraordinarily low and could be ignored when the concentration of soluble Mo was 1 mg L−1. The adsorption isotherm followed the Freundlich adsorption equation. Under the conditions V = 0.15 L, W = 2 g L−1, [Mo]T = 1.12 mg L−1, T = 80 °C, P = 1.013 × 105 Pa, 1.0 mol L−1 MnSO4 and pH range 1–6.5, the non‐electrostatic model (NEM) was used to quantify Mo adsorption. CONCLUSION: The surface adsorption complexation modeling of Mo onto Mn3O4 can be successfully applied to predict adsorption rates of Mo onto Mn3O4 at different pH values, with an absolute error less than 6%.