Investigation Of The Magnesium Ion Retention Mechanism Of γ-Al₂O₃ Mesoporous Membrane

Mesoporous membrane filtration process is similar to reverse osmosis and ultrafiltration which are both pressure driven processes, but its transport mechanism is quite different from those of the latter. The pore size of mesoporous membrane is between the reverse osmosis's and the ultrafiltration's. Beside sieving effect its separation performance is influenced by chemical potential and electrostatic potential if the surface of membrane is charged. But there is few satisfactory theory available to describe its mass transfer process.The real retention coefficient is determined by graphical method based on the experimental data, and the concentration at the membrane/feed interface comes accordingly. It is found from the experimental results that the reflection coefficientσand solute permeability co are different from those calculated by pore flow model. The main reason might be that the pore flow model assumes that separation of different permeates is achieved by size exclusion, which is only applied to non-polar solvents. When Donnan effect exists, mutual electrostatic effects between ion and membrane surface influence the separation performance, the electrostatic charge can not be neglected, and the accuracy of pore flow model becomes poor.A new model for describing the transport mechanism of mesoporous membrane is developed base on non-equilibrium thermodynamic module. For the permeate is not pure water but solution, the new model presents an idea of permeability factor A.The permeability factor is derived using dimensional analysis method. An empirical formula is established according to the experimental data under the different filtration conditions (concentration, pH, velocity). The experimental results show that there exists a power functional relationship between each factor and A; and they do not have mutual influence. So the expression of A and the new model can be obtained by multiply the expressions together. The electrostatic property under acidic condition is taken into account in the new model which is feasible in engineering. The accuracy verification of the new model was also done by comparing the calculated with the experimental data. The maximum deviation between the calculated and the observed is -13.9%, the minimum is only 0.05%. So the model is accurate under the experimental conditions.