Geology Reference
In-Depth Information
As for energy requirements, Norgate et al. (2007) obtain a life cycle gross energy
requirement for smelting/converting and electro-refining of 33 GJ/t, whereas for
heap leaching and solvent extraction/electro-winning 64 GJ/t of primary copper.
These authors also obtain a global warming potential for copper smelting and hy-
drometallurgical copper of 3.3 and 6.2 tCO
2
/t Cu respectively. This constitutes an
intermediate case between aluminium and iron primary production.
Chapman and Roberts (1983), meanwhile, reported that 66.7 GJ/t was needed
for the concentration of chalcopyrite from the ground through a flotation process
while the energy consumption in the electrolytic refining process to obtain pure
copper was 47 GJ/t. Kennecott Utah Copper (2004) reports an energy breakdown
of copper production as follows: 18% for mining, 42% for concentrating, 27% for
smelting, 7% for refining and 3% for tailings impoundment.
According to the Bureau of Internanational Recycling (Grimes et al., 2008) the
energy consumption for the production of one tonne of copper is 16.9 GJ and 25.5
GJ for pyrometallurgical primary production (from ore concentrate to cathode cop-
per metal) and hydrometallurgical primary production (from oxide ores to cathode
copper metal) respectively. The value for secondary production from scrap stands
at only 6.3 GJ. Carbon footprints for primary production are 1.25 t CO
2
(pyromet-
allurgical) and 1.57 t CO
2
(hydrometallurgical) respectively, whereas secondary
production CO
2
emissions are much lower at only 0.44 t. The Ecoinvent database,
meanwhile reports a total primary energy consumption of 12.3 GJ/t plus around
21.4 GJ/t assuming a 33% rate of e
ciency in the production of electricity from
primary energy sources (Classen et al., 2007) .
In Table 8.3, additional sources for energy requirements and environmental emis-
sions are listed.
8.5 Copper related metals: Selenium and Tellurium
Selenium is a byproduct of copper smelting. Specifically, it is found concentrated
in the anode slimes of copper electrolytic refining. These slimes may contain about
10% Se and 5% Te. They are also likely to contain precious metals which are the
first to be recovered. With regards to selenium and tellurium they are recovered by
roasting slime pellets with soda ash at 550-650
o
C. This process oxidises the metals
to their hexavalent state. The resulting product is then leached in water. Sodium
selenate dissolves but sodium tellurate (which is insoluble in alkaline solution) can
be filtered out. The dissolved sodium selenate is then reduced with charcoal to
form sodium selenide, which is then leached further with water and oxidised with
an air flow blown to produce selenium slurry. The resultant precipitate is melted
and passed through a sieve, allowing selenium metal particles to drop into water
(Ally et al., 2011).
The reason for obtaining tellurium metal or its oxide is, as in the case of sele-
nium, to produce a sodium telluride solution. Tellurium can be recovered from the
Search WWH ::
Custom Search