Geology Reference
In-Depth Information
used in the various refining stages is reported to be 17 to 20 GJ per tonne of nickel.
In a comparison study of the annual sustainability reporting of Ni companies, Mudd
(2010a) suggests that the sulphide energy consumption is at about 100 GJ/t Ni,
with the unit energy costs of laterite projects meanwhile varying in the range of
252-572 GJ/t Ni. Similarly, he gives, for all sulphide projects, a GHG release of
less than 10 t CO
2
e=t, and for laterite projects specifically a range from 25 to 46
t CO
2
e=t metal. This wide variation reflects the different electricity sources that
happen to be available for a given operation and site combined with the lowering ore
grade tendency for laterites. In fact according to Norgate et al. (2007) a decrease
of 2.4% to only 0.3% Ni in ore grade almost trebles energy consumption from 130
MJ/kg to 370 MJ/kg and the carbon footprint more than four-fold from about 18
kg CO
2
e/kg Ni to 85 kg CO
2
e/kg Ni.
Norgate et al. (2007) thus obtain a life cycle gross energy requirement for the
flash furnace smelting and Sherritt-Gordon refining of 114 GJ/t, whereas for pres-
sure leaching and solvent extraction/electro-winning, 194 GJ/t for primary nickel.
They also report a GWP, for nickel smelting and hydrometallurgical nickel of 11.4
and 16.1 t CO
2
e=t Ni, respectively.
However Barkas (2009) gives an average global mix value for Ni of 271GJ/t
and 26.6 tCO2-e/t from which 244 comes from the smelting process. Barkas (2009)
also gives a range of energy consumption that is between 150 and 750 GJ/t Ni.
Therefore the energy consumption for producing nickel from sulphide origin is close
to that of aluminium and doubles or triples that for laterite Ni.
Table 8.3 shows a compilation from different sources of energy requirements and
emissions associated with the primary and secondary production of nickel.
8.8 Lead, Zinc, Cadmium and related ore metals
Galena, PbS and sphalerite, ZnS are the main lead and zinc ores and are fre-
quently found together. Galena may also contain other sulphides including copper,
silver, gold, bismuth and antimony as well as important amounts of limestone and
dolomite. Argentiferous galena, for instance, is exploited for silver extraction. Spha-
lerite, meanwhile, is frequently associated with lead, copper and silver sulphides,
whilst its black form is potentially exploitable as an iron ore. Other important
byproducts of zinc and lead are cadmium, indium and germanium.
Zinc ores are usually beneficiated at the mine via crushing, grinding and flotation
operations to get a concentrate of 50-60% zinc. Lead ores, apart from concentration,
also require rock and mineral impurities to be removed and therefore sintering is
also undertaken (BCS, 2002b).
In the next subsections, the production, environmental issues and energy con-
sumption of each metal are described.
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