BUSINESS
In copper mining, about 80% of the produced quicklime is used in flotation processes.
The limestone used for
metallurgical purposes
must be of superior
grade, have a silica and
alumina content of less
than 2%, and it should
have a low sulphur and
phosphorus content.
(silver) minerals, while it also prevents
the generation of hydrocyanic acid in the
cyanide hydrolysis and is used as alkalising
agent in cyanidation. During alkaline
flotation, it is used as pH regulator, pyrite
depressant, calcium salts precipitant,
and linkage of the active silica contained
in clays, among others. It is also used in
leaching gravels to neutralise the residual
acidity and it stabilises the clays contained
in the ore.
As part of non-metallic mining activities,
lime products are used as pH regulator in salt
and nitrate products and as linking agent in
boric acid production. It is used as the binder
in obtaining granulated ulexite (fertiliser)
and potassium nitrate and as a linking agent
and depressant of the magnesium present in
the brines containing lithium.
The major copper-producing countries, such as Zambia and Chile, have domestic supply of
lime and can produce limited amounts of quicklime.
34 _ QUARRY SA | JULY/AUGUST 2018
Quicklime production
Quicklime is produced by the conversion
of limestone through calcining in rotary or
vertical kilns. During the lime process, for
every tonne of saleable quicklime produced,
about two tonnes of ‘pure’ limestone or six
tonnes of impure limestone is consumed.
The limestone consumption is dependent
on the type of product, limestone purity,
degree of calcing, water temperature, and
the quantity of waste products. For every
part of lime produced, two parts carbon
dioxide (CO 2 ) are generated. A distinction
is made between ‘brown lime’ and ‘white
lime’, having available lime contents of 68%
and 72%, respectively.
Soft-burned lime is the most reactive
and is difficult to produce because of the
delicate operating balance that must be
achieved, sufficient heat to drive off the
CO 2 without overheating closing the pore
structures. Depending on the kiln age and
design, between 200kg (new kilns) and
350kg (old kilns) of coal is required to
produce one tonne of quicklime.
Application in copper production
The limestone used for metallurgical
purposes must be of superior grade, have
a silica and alumina content of less than
2%, and it should have a low sulphur and
phosphorus content. For fluxing, the iron
content may be high, but the material must
be lumpy and finely crystallised to avoid
decreptitation. In a powdered form, the
milled carbonates can be mixed with ore
and pressed as self-fluxing pellets.
Quicklime as a flux removes impurities
such as phosphorus, silica, and sulphur. In
the beneficiation of non-ferrous metals,
lime is used to control pH in the flotation
process, to neutralise iron sulphides, and
to extract and recover metals through
precipitation or leaching processes.
Quicklime and hydrated lime are widely
used in the flotation or recovery of many
non-ferrous ores, in particular copper ore
flotation in which lime acts as depressant and
maintains proper alkalinity in the flotation
circuit. Lime is also used in the flotation of
zinc, nickel, and lead-bearing ores. In the
smelting and refining of copper, zinc, lead,
and other non-ferrous ores, noxious gas
fumes of SO 2 can be ne