Copper

Introduction

Copper is ductile, malleable, lustrous, and an excellent conductor of heat and electricity, second only to silver.   Therefore, the electrical wire industry is the biggest user of copper.   Alloys of copper, called brass (copper and zinc) and bronze (copper and tin or other metals), were used from antiquity and are still important in metal industries where superior wearability are required, such as, plumbing, kitchen utensils and roofing.   Other uses are in gun metal, an alloy of 88% copper, 10% tin, and 2% zinc, used to cast machine parts, and blue vitriol, an agricultural pesticide and algicide used in water purification.^{Lide 4-9}   Copper is also used in paint pigments, dyes mordants, and electroplating.

Copper is essential to life.   It helps the formation of red blood cells, increases iron absorption, and is a part of several respiratory enzymes.   Copper is essential for the use of vitamin C, protein metabolism, and the central nervous system.  Sources: shellfish, especially oysters, nuts, cocoa powder, beef and pork liver, kidneys, dried beans and peas, corn-oil margarine, whole wheat, prunes.   A deficiency is rare in humans, but more likely in animals where it results in anemia, retarded bone and nervous tissue growth, loss of elasticity in tendons and major arteries, poor lung growth, and abnormal structure and pigmentation of hair. ^{Brody 186, Netzer 800}

Copper is concentrated in roots of plants and plays a part in nitrogen metabolism.   It is a component of several enzymes.   Deficiencies cause the dying shoot tips, and terminal leaves develop brown spots.   Copper is bound tightly in organic matter and may be deficient in highly organic soils.   Too much copper is toxic. ^{Morgan n.p.}

Copper was known and used since ancient times in the eastern and western hemispheres.   Copper is found free and in the minerals cuprite, malachite, azurite, chalcopyrite and bornite. ^{Lide 4-9}

The extraction of copper from copper ore is performed in several stages: ^{CDA n.p.}

1. Crushing.

Mined copper sulfide or copper oxide ores are crushed into walnut-sized pieces.

2. Grinding.

Crushed ore is ball or rod-milled in large, rotating, cylindrical machines until it becomes a powder usually containing less than 1 percent copper.

3. Concentrating.

Minerals are concentrated into a slurry that is about 15% copper.   Waste slag is removed and the water is recycled.   Tailings (left-over earth) containing copper oxide are routed to leaching tanks or are returned to the mining area.

Once copper has been concentrated, it can be turned into pure copper cathode in two different ways: Leaching & electrowinning or smelting and electrolytic refining.   These methods are described below.

4a. Leaching

Oxide ore and tailings are leached by a weak acid solution, producing a weak copper sulfate solution.

5a. Electrowinning (SX/EW).

The copper-laden solution is treated and transferred to an electrolytic process tank.   When electrically charged, pure copper ions migrate directly from the solution to starter cathodes made from pure copper foil.   Precious metals, such as gold, silver, and platinum, can be extracted from the solution.

4b. Smelting.

Several stages of melting and purifying the copper content result, successively, in matte, blister and, finally, 99% pure copper.   Recycled copper is resmelted.

5b. Electrolytic Refining.

Anodes cast from the nearly pure copper are immersed in an acid bath.   Pure copper ions migrate electrolytically from the anodes to "starter sheets" made from pure copper foil where they deposit and build up into a 300-pound cathode.   Gold, silver and platinum may be recovered from the used bath.

6. Pure Copper Cathodes.

Cathodes of 99.9% purity may be shipped as melting stock to mills or foundries.   Cathodes may also be cast into wire rod, billets, cakes or ingots as pure copper or alloyed with other metals.

7. The copper cathode is converted into any of the following forms:

a. Wire Rod - Coiled rod about 1/2" in diameter is drawn by wire mills to make pure copper wire of all gages.

b. Billet - 30' logs, about 8" diameter, of pure copper are sawed into shorter lengths, which are extruded and then drawn as tube, rod and bar stock of many varied sizes and shapes.   Rod stock may be used for forging.

c. Cake - Slabs of pure copper, generally about 8" thick and up to 28' long, may be hot- and cold-rolled to produce plate, sheet, strip and foil.

d. Ingot - Bricks of pure copper may be used by mills for alloying with other metals or used by foundries for casting.

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