Geology Reference
In-Depth Information
contained within it, such as lead and zinc need to be captured in a connected abate-
ment plant.
The final step in the process is the production of pure copper by electro-refining.
In a solution of sulphuric acid and copper sulphate, blister copper is oxidised at
the anode into copper (II) whilst at the cathode Cu (II) is reduced to yield pure
copper. Among the impurities liberated around the anode, in the form of slime,
are Ag;Se;Te;As;Sb, and even Au;Pt and Pd. Metals like Ni and Pb become
dissolved in the electrolyte (IPPC, 2009; Moskalyk and Alfantazi, 2003; Lossin,
2000).
Contrary to the aluminium or iron ores, chalcopyrite is a sulphide and has more
chemical exergy than its corresponding copper oxide. This advantage is not fully
exploited but at least partially used for the obtaining of copper since some processes
become autothermal or do not require very large amounts of heating or electricity.
The mass balance is however significant since 1.5 tonnes of slag and 2 tonnes of
sulphur dioxide are produced for every one of copper.
Secondary copper is also produced by pyrometallurgical processes. Here the
process must take into account the constituents of the recycled copper: the accom-
panying metals or organic materials such as plastic coatings and oils. Therefore
specific pretreatments are needed as a function of the feed material whilst special
abatement equipment is needed to destroy the volatile organic compounds (VOCs),
and minimise the dioxines and furnace emissions, PCDD/F (Polychlorinated diben-
zodioxins and furans).
Secondary smelting of copper uses coke to maintain reducing conditions since
the raw material is either metallic or oxidised. The furnaces volatilise the zinc, tin
or lead of the copper alloy scrap. Such metals are collected in the filter dust and the
off-gases containing SO
2
and CO
2
are wet scrubbed for producing sulphuric acid.
The process of obtaining secondary copper runs parallel to that of the primary one.
The other route, the hydrometallurgical, although only making up 10% of pri-
mary production, is worth mentioning. It consists of heap leaching the ground ore
in sulphuric acid. The pregnant liquor is then treated and concentrated by sol-
vent extraction. Afterwards, the copper is removed by a technique similar to that
found in electrolytic refining, using inert anodes made of lead or titanium. The
latter is called electro-winning (Kawatra, 2011). Fig. 8.4 is a schematic showing the
processes involved in copper production.
8.4.2 Energy and environmental issues
The main environmental issue of primary copper production is the sulphur dioxide
emissions arising from roasting and smelting. Sulphur dioxide production is around
2 t SO
2
=t Cu. These emissions not only produce acid rain but also contain arsenic,
lead and cadmium
6
.
6
It is worth noting that modern plants achieve a 98.9% SO
2
capture rate that it is mainly
converted into sulphuric acid. The smelter gases are then washed in a sulphuric acid plant that
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