Wednesday, October 23, 2013

A Small Fan

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 .  .  .”
k Joseph, G√ľnter, 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. 


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!

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