Electrochemical and Transport Characteristics of Membrane Systems in the Electronanofiltration Separation of Solutions Containing Ammonium Nitrate and Potassium Sulfate

Electrochemical and transport characteristics of systems equipped with OPMN-P and OFAM-K membranes during operation in electronanofiltration cell are studied experimentally. The reasons for changes in the characteristics of membrane systems under the influence of various factors in the process of electronanofiltration of solutions that simulate the ionic composition of the ammonium-nitrate- and potassium-sulfate-containing solutions from electroplating and mineral fertilizers production, as well as the process media of the Livshits АО ТАGAT electroplating plant, are revealed. The change in the local conductivity of the solution in the intermembrane channel and, as a consequence, the increase in current density at the studied solution electronanofiltration is shown to be connected with the flow restriction in the electrochemical cell and the solution heating. Analysis of the systems' electrochemical characteristics during the electronanofiltration the galvanic-production process media gave the degradation range of the OPMN-P semi-permeable membrane active layer (15–30 V) because of surplus of the operation range certified value pH > 12. Improving of the transport characteristics of membrane systems during electronanofiltration of aqueous solutions (ammonium nitrate, and potassium sulfate) is associated with the increase in the pressure differential. Increase of the voltage in the electronanofiltration cell leads to decrease in the outlet flow for the near-anodic membrane OFAM-K and increase in the outlet flow for the near-cathoduc membrane OPMN-P. This is associated with the displacement of the pH value of the near-anodic permeate toward acidic environment; of the near-cathodic permeate, toward alkaline environment. It is found that during the electronanofiltration of the electroplating process media the surface of the near-cathodic membrane OPMN-P is coated with the Fe(OH)2 and Fe(OH)3 precipitates due to supersaturation. The precipitates act as an absorber of Zn2+, [Zn(OH)4]2–, and other ions at a constant pressure differential P = 1.6 MPa, which leads to the dynamic membrane formation. Empirical equations for the calculating of the specific outlet flux and the retention coefficient are proposed basing on the analysis of experimental data obtained during the membrane separation of the studied solutions under the action of the pressure differential and voltage.