The Anatomy of a Mine - Mining and the Environment: From Ore to Metal - page 206

FIGURE 4.17
Ball Mill Illustrated

The reduction of ores to small parti-
cles is generally the most expensive
phase of mineral benefi ciation.

TABLE 4.5
Classifi cation of Basic Size-reduction Steps - Comminution is a general term for size reduction that may be applied
without regard to the actual breakage mechanism involved

Size reduction step Upper size Lower size

Explosive shattering Unlimited 1 m

Primary crushing 1 m 100 mm

Secondary crushing 100 mm 10 mm

Coarse grinding 10 mm 1 mm

Fine grinding 1 mm 100 µ m

Very fi ne grinding

100 µ m 10 µ m

Superfi ne grinding 10 µ m 1 µ m

Source:
Weiss 1985

using gravity, l otation, or other physical processes. Chemicals may be used for mineral
separation or ore concentration. A variety of gravity concentration techniques are used
to separate targeted minerals of high specii c gravity from the less dense gangue miner-
als. Partly physical and partly chemical in its action, l otation is the reverse of gravity con-
centration. With its use, heavy minerals can l oat while light, undesired minerals sink.
Flotation involves the use of various chemical l otation agents and pH regulators such as
lime. Physical processes include magnetic separation for magnetic ores.
The method of concentrating depends on the ore type. For example ground copper
suli de ore is commonly enriched (concentrated) by Froth Flotation, in which the powdered
ore is mixed with special parafi n oil which makes the copper mineral particles water repel-
lent. It is then fed into a bath of water containing a foaming agent which produces a kind
of bubble bath. When jets of air are forced up through the bath, the water repellent copper

Flotation is the reverse of gravity
concentration.