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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 Mn 3 0 4 . 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 Mn 3 O 4 . RESULTS: Some theoretical parameters have been obtained: the total surface site density and protonation constants (N T = 6.84 × 10- 3 mol g -1 , K int a1 = 2.0 × 10 -5 , K int a2 = 1.49 x 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 = 0.75 L, W = 2 g L -1 , [Mo] τ = 1.12 mg L -1 , T=80 °C, P= 1.013 × 10 5 Pa, 1.0 mol L -1 MnSO 4 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 Mn 3 0 4 can be successfully applied to predict adsorption rates of Mo onto Mn 3 0 4 at different pH values, with an absolute error less than 6%.