Determining the Mechanism of the Formation of a Dynamic Membrane on a Ceramic Membrane Made of Clay Minerals

Abstract

Using the mathematical tools of convective filtration theory, the experimental data on the change in the specific capacity of a tubular microfiltration ceramic membrane made of clay mineral in the process of water purification from Al(III) compounds were analyzed. The mechanism and conditions of the formation of a dynamic membrane from Al(III) hydroxo compounds in the studied microfiltration process were established, and its role in improving purification efficiency and ensuring high permeate quality by the content of aluminum compounds was demonstrated. The study was carried out on a model AlCl₃ solution with an Al(ІІІ) concentration of 65 mg/dm³ and pH of 7 at a working pressure of 1.0 MPa. Based on the results of this study, the processing of kinetic data was performed. Using the Darcy and Hagen–Poiseuille equations for constant-pressure filtration, the mechanism of the formation of a dynamic membrane under the above-specified conditions was established. It has been shown that, in the process of water purification from Al(III) on the ceramic membrane, its specific capacity decreases with time due to the precipitation of insoluble hydrolyzed Al(III) forms (hydroxo compounds) onto its surface. It has been established that, in this process, the filtration mechanism is changed from the gradual clogging of pores with several particles to the deposition of a precipitate from Al(III) hydroxo compounds onto the microfilter surface with the formation of a dynamic membrane. To decrease the size of pores and improve the selective properties of the microfiltration ceramic membrane made of clay minerals, its modification via the formation of a dynamic membrane from hydroxo compounds of metals on its surface in the process of water purification from these compounds was proposed.