It is well known that following variables are most important in flotation:
• slurry properties (density, solids
content)
• slurry flow rate (retention time)
• electrochemical parameters/potentials
(pH, Eh, conductivity)
• chemical reagents and their addition
rate (frothers, collectors, depressants, activators)
• pulp levels in cells
• air flowrates into cells
• froth properties (speed, bubble size
distribution, froth stability)
• particle properties (size distribution, shape, degree of mineral liberation)
• mineralogical composition of the ore
• mineral concentrations in the feed,
concentrate and tailings (recovery, grade)
• froth wash water rate (especially in
flotation columns)
(Laurila et al., 2002)
Laurila, H., Karesvuori, J., Tiili, O., 2002. Strategies for instrumentation and control of flotation circuits. Mineral Processing Plant Design, Practise and Control, Volume 1, pp. 2174–2195. ISBN-10: 0873352238.
As seen from the Table particle shape is one of the affecting variable in Flotation systems (Harris, 1975):
Harris, C C, 1975. Flotation Machines, in Flotation (ed M.C. Fuerstenau), pp 753-815 AIME: New York
Manipulating/measuring each of these variables
simultaneously may well be unnecessary to achieve a good process control
result. However, each of these variables and their effects on the flotation process
should be considered.
Interaction of gas bubbles with solid
surfaces plays an important role in many areas of technology. Most significant
is the role in particle separation of the flotation process. The essence of the
separation is bubble attachment to the surface of hydrophobic particles, which
leads to flotation due to the buoyancy of the particle/bubble aggregate. In
this way, separation is achieved from other particle types that are maintained
in a hydrophilic state. By no means is the interaction of bubbles with solid surfaces
or particles a simple process. On the contrary, it is a complicated process,
which can be divided into several steps governed by different forces (see Fig below:
These steps will describe the behavior of
the bubble at various distances from the solid surface during the approach and
ultimate displacement of the liquid phase. The bubble–solid interaction starts
at a certain distance where bubble and particle approach each other in a gravitational
field or another applied force field. During this approach, hydrodynamic forces
between the bubble and solid surface are of great importance. On closer approach,
interfacial forces become most important, governing further stability of the
liquid film between the gas–liquid and solid–liquid interfaces. Depending on
the type of solid surface and the solution chemistry of the liquid phase, these
forces can be repulsive, thus stabilizing the liquid film between interfaces,
or they can be attractive, resulting in destabilization of the liquid film. In
the latter case, the liquid film becomes unstable and ruptures, leading to the
formation of a three-phase contact (TPC) line and attachment of the bubble.
After rupture, the TPC line moves across the solid surface at a certain rate.
This relaxation process initiated during rupture of the film leads to a stable or
metastable state, governed by the thermodynamic properties of the gas–solid,
liquid–solid, and gas–liquid interfaces as well as the quality of the solid surface.
The bubble–solid approach can take place
with different trajectories due to their respective directions of motion. If a
particle approaches a bubble in a direction normal to the bubble surface, the
momentum of the approach is high, causing strong deformation of the local gas–liquid
interface (Fig. 2). This bubble–particle interaction is called the
collision contact. Another extreme case is the sliding contact when a bubble
and a particle meet each other without any significant deformation of the local
bubble surface. In this case, the particle usually slides on the bubble surface
after initial encounter. The hydrodynamic interactions during bubble–particle
approach have been modeled based on these extreme cases [Nguyen
et al., 2007]
Anh V. Nguyen, Jaroslaw Drelich, Miroslav Colic, Jakub
Nalaskowski, Jan D. Miller, 2007, Bubbles:
Interaction with Solid Surfaces, Encyclopedia of Surface and Colloid
Science DOI:10.1081/E-ESCS-120022194, Taylor & Francis.
Bubble–particle interaction is called the
collision contact [Nguyen et al., 2007, Bubbles:
Interaction with Solid Surfaces, Encyclopedia of Surface and Colloid Science DOI:10.1081/E-ESCS-120022194,
Taylor & Francis]
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