A small fan in my solar electric system died. It kept a major part of the system from
overheating and is necessary for continuous operation. To manufacture that small fan a massive
industrial infrastructure is necessary to provide the components.
The fan motor is wound with copper wire that comes from
newly mined copper because of the need for purity. “Wire supply is produced predominantly from newly refined
copper . . .”
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Joseph, Günter, 1999, “Copper: Its Trade, Manufacture, Use, and Environmental
Status”, edited by Kundig, Konrad J.A., ASM International Vol. 2.03, Electrical
Conductors
Copper mining is done in huge pits using massive
machines. The refining of the ore
is a series of processes, chemicals and along with the mining, intensive energy
use. You can see a DVD of this
process on “Modern Marvels: Copper”.
You can also see a diagram and pictures of the equipment and process at:
A fascinating recent documentary on PBS – “Raw to Ready” -
showed the development of the massive Komatsu 930-E:
“to extract precious metals found beneath the earth requires
a massive 232-ton, two-story-tall dump truck with a load capacity of 320 tons —
a giant earth-mover like the Komatsu 930E. This amazing engineering achievement
is made possible by five essential raw ingredients: coal, chromium, mineral
oil, latex rubber and sulphuric acid, an electron superhighway that generates
massive power.”
The manufacture of my solar electric system, in its use of
copper, is tied into an international infrastructure of machines, equipment and
energy. Aluminum, rare metals, coal, plastics, glass, rubber, multiple
chemicals and many other material components are also a necessary additional
part of this global material complex.
Furthermore, it is dependent on this far ranging system for
replacement parts.
Where are the motors in your world? – water pump, air
conditioner, windshield wiper, and on and on and on.
Being aware of where things come from and what is involved
in obtaining them is a major step in being responsible.
There are many who will in private admit we are trashing the
earth.
Mindlessly!
Copper Mining Info
The above flowsheet shows a basic copper mine process, from
mine to metal. There are two distinct types of copper ore, the sulfide ore and
the oxide ore. The sulfide ores are beneficiated in flotation cells, while the
oxide ores are generally leached. First the copper ore from a open pit mine is
blasted, loaded and transported to the primary crushers. Then the ore is
crushed and screened, with the fine sulfide ore (~-0.5 mm) going to froth
flotation cells for recovery of copper. The coarser ore goes to the heap leach,
where the copper is subjected to a dilute sulfuric acid solution to dissolve
the copper. Then the leach solution containing the dissolved copper is
subjected to a process called solvent extraction (SX). The SX process
concentrates and purifies the copper leach solution so the copper can be
recovered at a high electrical current efficiency by the electrowinning cells.
It does this by adding a chemical reagent to the SX tanks which selectively
binds with and extracts the copper, is easily separated from the copper
(stripped), recovering as much of the reagent as possible for re-use. The
concentrated copper solution is dissolved in sulfuric acid and sent to the
electrolytic cells for recovery as copper plates (cathodes). From the copper
cathodes, it is manufactured into wire, appliances, etc. that are used in every
day life. Below are some photos of the process:
The primary crusher at a copper mine. The truck dumps ore
into the crusher which crushes the ore. Screens size and distribute the
classified ore to a series of conveyors, like those above, for transportation
to the mill for further processing.
Conveyors and trucks deposit coarse ore on a heap leach pad,
which has a series of pipes and hoses dispensing a diluted sulfuric acid
solution to the ore. Copper is dissolved and flows to a pond at the bottom of
the pad. This process can take several months. The leached solution is pumped
to the SX (Solvent Extraction) circuit, which looks like a series of agitation
tanks or cells. The fine sulfide ore is sent to froth flotation cells like
those below for recovery.
The concentrates from the flotation cells are sent to the
smelter for processing to a copper plate. The copper plate is then dissolved in
sulfuric acid and sent to the electrowinning cells for plating onto cathodes,
along with the concentrated copper from the SX circuits. The copper leach
solution typically consists of 40 gm of copper and 200 gm sulfuric acid per liter.
Current densities on the electrowinning cells can be 300 amperes per square
foot, or more.
Banks of electrowinning cells with cathodes. Copper on the
annodes ranges from 99.0 to 99.5 percent pure. Power consumed in electroplating
copper ranges from 0.08 to 0.20 KWH per pound of copper. Any gold or silver in
the copper does not plate out and drops to the bottom of the cell with the
sludge to be recovered later.
Machine transporting and handling the copper cathodes that
were removed from the electrowinning cells. That's it, the rest is
manufacturing products from the pure copper!
