Diffusion dialysis processes of inorganic acids and their salts: The permeability of different acidic anions

The diffusion dialysis (DD) processes of different inorganic acids in the presence of their corresponding sodium salts have been investigated with a two-compartment cell in the following systems: HCl + NaCl, H2SO4 + Na2SO4 and H3PO4 + Na3PO4. The permeability coefficients (P) of anions (Cl−, SO42−, or PO43−) from a novel organic–inorganic hybrid anion exchange membrane are determined by a simple method. Namely, the concentration of the ions at water side is determined and then fitted based on the mass transfer and ionic equilibrium equations, combined with an optimized procedure. The fitted P   values for the three anions follow the order in the investigated concentration range: PSO42−total   (2.5×10−6   m/s)>PCl−total   (1.6×10−6   m/s)>PPO43−total(1.0×10−7   m/s). This changing trend is then correlated with the physic-chemical characterizations, adsorptive and transporting properties of HCl, H2SO4 and H3PO4 in membrane: with the anion's size and charge increasing, its adsorption amount increases, while its diffusivity decreases due to the decreased water molecules and the enhanced electrostatic interaction between the anions and the fixed groups. The balance of adsorption and diffusivity determines the DD effect, as reflected well by the P values. Our work here investigates and compares the permeability of different inorganic acids through the application of a simple and easy method. Therefore, the results and findings can give clues for further development and applications of DD.

Research highlights▶ Inorganic acids with different valences of anion radicals have been investigated through diffusion dialysis (DD) method. ▶ Simple mathematic model have been used to calculate the permeability coefficients (P) of different acidic anions. ▶ The P values were correlated with the physic-chemical characterizations, adsorptive and transporting properties of the corresponding acids. ▶ Better understanding was achieved for DD processes of different acidic anions.