PROPERTIES OF WETTING LIQUID FILMS IN FLOTATION PROCESSES

Wetting films are assumed the films of liquids coating the surface of bodies in condensed state. As against foam and emulsion films, liquid films are nonsymmetrical: one surface of a liquid film touches a condensed (solid or liquid) phase while the other surface adjoins gas. At interfaces of any phases, there are transition layers within which intensive properties and composition of liquids differ from bulk characteristics. A film is assumed thick when its thickness exceeds the summed thickness of the transition layers at the phase interface. The analysis is focused on polymolecular films having thickness more than a few layers of molecules have, which allows treating these wetting films as a part of bulk liquid phase in the field of the surface forces and, thus, changed under the action of this field. Assuming the polymolecular wetting films a part of the liquid phase enables the unified thermodynamic analysis of them—based on the isothermal curves of wedging pressure with regard to molecular, ion–electrostatic and structural forces. The properties of wetting films are described using the modern theory of long-range surface forces. At hydrophilic surfaces, water structure changes concurrently with the increase in the strength of intramolecular bonds and initiation of structural repulsion of the hydrophilic surfaces. Probably, the long-range hydrophobic attraction is connected with the appearance and coalescence of submicron gas bubbles on the hydrophobic surfaces. Stabilization of surface structure is the reason of its slower failure as compared to bulk structure. Free energy of the surface structure reduces slower with increasing temperature than in the bulk structure, which is the source of growth of the structural forces.

Keywords

Structural repulsion of hydrophilic surfaces, hydrophobic attraction of hydrophobic surfaces, temperature dependence.

Issue number: 6
Year: 2018
ISBN:
UDK: 622.765
DOI: 10.25018/0236-1493-2018-6-0-142-152
Authors: Evdokimov S. I., Gerasimenko T. E.

About authors: Evdokimov S.I., Candidate of Technical Sciences, Assistant Professor, e-mail: eva-ser@mail.ru, Gerasimenko T.E., Candidate of Technical Sciences, Head of the Department of Intellectual Property, North Caucasus Mining-and-Metallurgy Institute (State Technological University), 362021, Vladikavkaz, Republic of North Ossetia-Alania, Russia.

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