2. Introduction
Floatation is an extractive process where various
minerals can be selectively extracted.
Flotation is a selective process and can be used to
achieve specific separations from complex ores.
For example, in poly-metal ores such as Pb-Zn-
Cu, floatation allows separate extraction of Pb, Cu
and Zn.
3. Flotation is a physico-chemical separation process
that utilises the difference in surface properties of
the valuable minerals and the unwanted gangue
minerals.
1. Selective attachment to air bubbles (or "true
flotation").
2. Entrainment in the water which passes through the
froth.
3. Physical entrapment between particles in the froth
attached to air bubbles (often referred to as
"aggregation").
4. 1. Liberation
2. Establish hydrophobic film on minerals that are not
naturally hydrophobic.
3. Promote bubble formation.
5. o Polar
o Non-polar
All minerals are classified into polar or non-polar types
according to their surface characteristics.
Since water is a polar molecule, polar mineral
surfaces tend to be hydrophyllic
Whereas, nonpolar mineral surfaces tend to be
hydrophobic.
The goal is to make the mineral surface hydrophobic so
the minerals will attach to the bubbles in the froth.
6. Classification of polar minerals
Group 1 Group 2 Group 3(a) Group 4 Group 5
Galena
Covellite
Bornite
Chalcocite
Chalcopyrite
Stibnite
Argentite
Bismuthinite
Millerite
Cobaltite
Arsenopyrite
Pyrite
Sphalerite
Orpiment
Pentlandite
Realgar
Native Au,
Pt, Ag, Cu
Barite
Anhydrit
Gypsum
Anglesit
Cerrusite
Malachit
Azurite
Wulfenit
Group 3(b)
Fluorite
Calcite
Witherite
Magnesite
Dolomite
Apatite
Scheelite
Smithsonite
Rhodochrosite
Siderite
Monazite
Hematite
Magnetite
Gothite
Chromite
Ilmenite
Corundum
Pyrolusite
Limonite
Borax
Wolframite
Columbite
Tantalite
Rutile
Cassiterite
Zircon
Willemite
Hemimorphi
te
Beryl
Feldspar
Sillimanite
Garnet
Quartz
7. Degree of polarity of mineral types:
Sulfides < sulfates < carbonates < phosphates <
oxides < hydroxides < silicates.
The surfaces of non-polar minerals are
characterised by relatively weak molecular bonds.
The minerals are composed of covalent molecules
held together by van der Waals forces, and the non-
polar surfaces do not readily attach to the water
dipoles, and in consequence are hydrophobic.
Types of non-polar mineral include:
Coal, oil, molybdenite, diamond, talc, gold
8. Render minerals hydrophobic by attaching to the surface
of mineral particles.
A collector’s polar head will attach to a polar mineral
surface, leaving the nonpolar tails toward the
surrounding water molecules, rendering the mineral
hydrophobic,
Fig 2: interaction of collector with mineral surface
9.
10. Produces stable bubbles for hydrophobic particles to
attach.
When the mineral surfaces have been rendered
hydrophobic by the collector, the frother is meant to
produce a stable bubble. Frothers also act as
collectors, which can lead to decreased selectivity.
Some collectors are such good frothers as well that
they stabilize the froth so much as to reduce their
transportability.
Example frothers include pine oil and MIBC (methyl
isobutyl carbinol).
11. Regulators, or modifiers, are used extensively in
flotation to modify the action of the
collector, either by intensifying or by reducing its
water-repellent effect on the mineral surface.
Regulators can be classed as
activators, depressants, or pH modifiers.
12. These reagents alter the chemical nature of mineral
surfaces so that they become hydrophobic due to
the action of the collector.
Activators are generally soluble salts which ionise in
solution, the ions then reacting with the mineral
surface.
A classical example is the activation of sphalerite by
copper in solution
ZnS + Cu 2 CuS + Zn 2+
13. Depression is used to increase the selectivity of
flotation by rendering certain minerals hydrophilic
(water-avid), thus preventing their flotation.
They are key to the economic flotation of certain
ores such as platinum and nickel sulphides.
There are many types of depressants and their actions
are complex and varied, and in most cases not fully
understood, making depression more difficult to
control than the application of other types of
reagent, particularly when the froth phase is also
affected by their action.
