Studies of the kinetic and sorption characteristics of OFAM-K and OPMN-P membranes in the process of electron-nanofiltration separation of an aqueous solution of potassium sulfate

The paper presents an analysis of existing methods of membrane separation of solutions on semipermeable and ion-exchange membranes, where their advantages and disadvantages are noted. The objects of study were OFAM-K and OPMN-P nanofiltration membranes and aqueous solutions of potassium sulfate used in the production of mineral fertilizers. The change in the retention coefficient on the near-anode OFAM-K membrane for sulfate ions and on the near-cathode membrane OPMN-P for potassium ions was studied at current densities of 12,82 and 15,38 A/m2 with varying transmembrane pressure. An analysis of the retention coefficient of the OPMN-P cathode membrane for potassium ions with increasing pressure shows its increase by 20-30%, which is probably caused by an increase in the water permeability rate, which causes permeate dilution. In the case of analysis of the retention coefficient for sulfate ions on the anode OFAM-K membrane in the region of low current densities, the retention capacity first decreases with an increase in the transmembrane pressure, and then reaches a constant value with a slight increase at a pressure of 1,5 MPa. At higher current densities, the retention coefficient for sulfate ions on the anode OFAM-K membrane with an increase in transmembrane pressure, as well as on the OPMN-P cathode membrane, for potassium ions increases. The time dependences of the specific output flux are given at transmembrane pressures of 0,75, 1, and 1,5 MPa and current densities of 12,82 and 15,38 A/m2. It is noted that the specific output flux increases on the near-anode OFAM-K membrane, while on the near-cathode membrane OPMN-P it decreases with time, which is due to the transformation of the physical properties of the membranes and boundary layers formed on their working surface. On the near-anode OFAM-K membrane, water permeability increases with time, and on the near-cathode membrane OPMN-P it decreases. The presented data on the desorption of potassium ions and sulfate ions on the near-anode membrane OFAM-K and near-cathode membrane OPMN-P indicate that the desorption of ions decreases with time, and the desorption index of potassium ions on the near-anode OFAM-K membrane is higher, although in the process Electronanofiltration ions are transferred in equivalent ratios.