Geology Reference
In-Depth Information
8.4 Copper
8.4.1 Process
Although copper ores can occur in many different oxide forms, the most common one
used in metal production is chalcopyrite CuFeS
2
whose current mine concentration
is in the order 0.5-1%, whereby an ore concentration is first needed before it can be
processed further. After grinding, the ore is enriched by a floatation process in water
which uses pine oils and compressed air to separate it into fractions. A foam filled
with air bubbles traps the ore while the remaining substances sink. The foam is then
filtered producing a 15-45% Cu rich concentrate, water, and various minor quantities
of elements such as As;Sb;Bi;Cd;Pb;Se;Mg;Al;Co;Sn;Ni;Te;Ag;Au;Pd and
Pt (BCS, 2002a).
Primary copper production, of which 10% comes from the hydrometallurgical
route with the rest produced through the pyrometallurgical one described next,
entails not only roasting but also smelting, converting, refining and electro-refining
5
.
The roasting process, separated or integrated within the smelting process, heats
the concentrate and partially oxides the chalcopyrite into simpler sulphides and
reduces the previously listed impurities. The most common smelting process is
completed in the oxygen flash furnace (Mullinger and Jenkins, 2008). This furnace,
which operates with natural gas and air at 1000-1100
o
C, combines roasting with
smelting and converts the chalcopyrite into copper sulphide and ferrous oxide. The
raw materials are concentrated chalcopyrite and two fluxes: limestone and sand.
The excess oxygen in air reacts selectively with the iron to produce iron oxide whilst
also liberating copper (II) sulphide. Later the excess sulphur reduces Cu (II) to
Cu (I) sulphide which melts. The silicon dioxide in sand reacts with the limestone
and the iron oxide to produce a slag which is predominately constituted by calcium
and ferrous silicates. This slag floats in the molten copper sulphide, referred to as
copper matte and both can be tapped off separately at the bottom of the furnace.
If the air is oxygen enriched, the process used is flash smelting, otherwise it is bath
smelting. The former is almost an autothermal process producing a higher SO
2
concentration in the off-gases, something that facilitates their recovery for sulphuric
acid production.
Copper oxide can also be recovered in the process - from the slag leaving the
flash furnace via a slag cleaning furnace capable of exploiting the simple conver-
sion of copper oxide into copper sulphide. Once this happens, the copper matte
can be treated in a continuous converter furnace with oxygen-rich air which is
blown through a granulated matte blended with the flux. The copper sulphide and
the remaining iron sulphide are then oxidised into copper, iron oxide and SO
2
in
a very exothermic reaction. The slag and the 98-99% pure “blister copper”, are
then tapped. The blister copper and subsequently the volatile metallic impurities
5
A detailed description of all these processes can be seen in IPPC (2009) which follows the report
“Plant information of copper industry” from H. Traulsen for Eurometaux (1998).
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