WINNING
PROBING THE
FINES
Effective crushing and screening are vital when it comes to minimising quarry
wastes and fines, writes Nicolaas C. Steenkamp.
A
s part of any quarrying activity,
waste and fines are produced.
As there is no market for this
product, it is mostly stockpiled
on site for the life of the operation. A
number of factors determine the amount of
waste material and fines that are produced.
The amount and type of waste depends
on the geology and rock type mined,
the degree of fragmentation achieved by
blasting, and the efficiency of the extraction
and processing operation. Increasing the
efficiency of the crushing and screening
process reduces the volume of non-saleable
fines being produced.
24 _ QUARRY SA | JULY/AUGUST 2018
Processing wastes are non-marketable,
mostly fine-grained material from
screening, crushing, and other processing
activities. The type and amount of waste
depends on the nature of the operation.
Most sand and gravel workings do not
produce much, if any, permanent waste.
On the other hand, limestone or dolomite
operations specifically target the production
of fines.
Fines are the inherent fraction of an
aggregate passing 0.063mm (63 microns).
Many quarries also refer to their sub-
economic fine aggregate, finer than 4mm, as
quarry fines or quarry dust. The term is used
for both fine aggregate and quarry fines; that
is, material <63 microns.
The aggregate produced has sizes
ranging from 20mm to 6mm and other
products. As a rule of thumb, the greater
the number of crushing stages, the
higher the amount of fines produced as a
proportion of total plant throughput.
Crushed to size
In general, impact crushers tend to produce
25–30% more fines than compressive
crushers. In turn, if the screening efficiency
of a screen in a closed circuit with a crusher
is inefficient, then undersize material will