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- Copper Smelter - Generalized
- Copper Smelting Process:
- Historically, the most abundant copper bearing ore was called
chalcopyrite, CuFeS2. This ore is first enriched by
a process called flotation. Powdered ore is mixed water as a
slurry and then further mixed with oil and a chemical called
amyl xanthate. Compressed air is then blown through the mixture.
The flotation process is dependent on pine oil droplets, but
it's really xanthate-coated chalcopyrite grains sticking to air
bubbles on their way up and over the tank. Pine oil simply makes
the bubbles. Almost any frother would do, but pine oil is cheap
and readily degrades in the environment. The less dense oil covered
copper sulfide particles are carried to the top in the foam and
are then skimmed off.
The next step carried out in an oxygen flash furnace is heated
using natural gas to a high temperature. Next is added limestone,
sand, and fresh copper ore concentrate (chalcopyrite) is blown
into the furnace with oxygen. It is heated to 1100 C. The combustion
with oxygen is endothermic, and chalcopyrite is actually the
fuel that keeps the furnace hot at that point. The oxygen in
the air selectively reacts with the iron to form the iron oxide,
FeO, and leaves copper in the form of the sulfide, CuS. Sulfur
dioxide is a by product and pollutant unless captured and converted
to sulfuric acid.
The silicon dioxide in the sand reacts with the limestone and
the iron oxide to form slag, FeSiO3 and CaSiO3.
At the same time the excess sulfur in the ore reduces copper(II)
sulfide, CuS, to copper (I) sulfide, Cu2S, which melts
and flows out of the bottom of the furnace. The slag is less
dense and floats on the top.
The molten copper(I) sulfide, called copper matte, is run into
a converter furnace, where air containing oxygen is blown through
the copper matte to oxidize the sulfide ions to sulfur dioxide.
At the same time some of the sulfide ions reduce the copper (I)
ions to impure blister copper metal. A final heating in an anode
furnace is used to burn off the remaining oxygen.
An interesting aside is that for every ton of copper produced,
1.5 tons of slag and 2 tons of sulfur dioxide are also produced
as waste products.
- The final step is the conversion of the impure copper to
pure copper. This is done by electrolysis where the impure copper
is made into the anode electrode and the pure copper is formed
at the cathode electrode. The copper electrodes are immersed
in a solution of sulfuric acid and copper(II) sulfate. Oxidation
occurs at the anode, therefore copper metal is converted to copper
(II) ions with the release of two electrons. At the cathode the
opposite reaction occurs: copper (II) ions are joined with two
electrons to form copper metal. During the transformation of
copper metal into copper ions and back to copper metal, the impurities
drop to the bottom of the electrolysis cell. Some of the impurities
are gold, silver, nickel, platinum which are themselves recovered
to be used.