Mass transfer process and separation mechanism of sulfuric acid and aluminum sulfate mixture based on IEC technology: Modeling

Ion exclusion chromatography (IEC) is an efficient technique used for the separation of strong electrolytes from weak electrolytes and nonelectrolytes. This work focuses on the assessment of mass transfer process and separation mechanism of H₂SO₄ and Al₂(SO₄)₃ on the strong base quaternary ammonium I anion exchange resin A-853E. A dynamic model for IEC was proposed and explicitly taken into account the Donnan equilibrium. The result showed that Donnan effect played a significant role in the mass transfer process of ionic species, which was interpreted as the inability of co-ion (Al³⁺) to pass through Donnan membrane, while the counterion (SO₄^2-) can enter resin pores due to electrostatic attraction. Meanwhile, a column model, based on Donnan equilibrium and cooperative adsorption isotherm, was then developed. The model successfully predicted the concentration profiles of mixed-ion (Al³⁺ and SO₄^2-) at the outlet of the fixed-bed in the dynamic separation process. The results indicated that the Al³⁺ promoted the adsorption of SO₄^2- on the resin in view of presence of ‘concentration’ phenomenon. The separation mechanism of Al³⁺ and SO₄^2- was presented combining model prediction and experimental results. Finally, the influence of three different valence states of metal ions (Na⁺, Fe²⁺, Al³⁺) on the degree of H₂SO₄ ‘concentration’ was investigated to further verify the Donnan effect.