Changing of mechanisms of self-diffusion of water molecules under nanofiltration of electrolyte solution

• Published in: Desalination Vol. 184; no. 1; pp. 337 - 345
• Main Authors: Karmazina, T.V., Kavitskaya, A.A., Slisenko, V.I., Petrachkov, A.A., Vasilkevich, A.A.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2005; Elsevier
• Subjects: Applied sciences; Chemical engineering; Electrolyte; Exact sciences and technology; Filtration; Liquid-liquid and fluid-solid mechanical separations; Membrane separation; Membrane separation (reverse osmosis, dialysis...); Nanofiltration; Neutronoscopy; Pollution; Self-diffusion mechanism; Water; Membrane separation; Water; Neutronoscopy; Nanofiltration; Electrolyte; Self-diffusion mechanism; Persistence; Self diffusion; Lifetime; Filtration; Electrolyte solution; Particle motion
• ISSN: 0011-9164; 1873-4464
• DOI: 10.1016/j.desal.2005.03.053

It is known, that volume flux of membranes depends on their chemical nature and structural-porous characteristics. There are data on change of a condition and mobility of water molecules on membrane surface. Hence, it is possible to assume, that as a result of the complex processes occuring on a surface of membranes and in volume of a solution during treatment, the state and mechanisms of self-diffusion of water molecules changes in comparison with the same solution, but not taking place through a membrane. To test this assumption, characteristics of mechanisms of self-diffusion of water molecules in a water solution of calcium chloride before and after membrane treatment have been quantitatively obtained. These characteristics have been calculated by the spectra of quasi-elastic slow neutron scattering (QENS) measured experimentally. As characteristics are valued: total coefficient of self-diffusion ( D), the contribution to it from collective ( D l ) and single-particle motions ( D f ), and also molecule lifetime at vibrational state ( τ 0). For usual water according to QENS data: D = 2.23·10 −9 m 2s −1; D l = 0.46 × 10 −9 m 2s −1; D f = 1.77 × 10 −9 m 2s −1; τ 0 = 2.8 × 10 −12 s. A nanofiltration membrane OPMN–KM3 has been used for study. Initial concentration of calcium chloride in a solution was 1.311 mmol/l. Concentration of this substance in a filtrate was 0.836 mmol/l. As a result of the complicated processes occuring during filtration of the solution through the membrane it has been established that mechanisms of water molecules self-diffusion changed in comparison with a solution of the same concentration which was not under the membrane treatment.