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| Recycling |
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-> Recycling of Copper
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| Recycling of Copper |
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 Scrap
Value
For thousands of years, copper and copper alloys have been recycled
again and again.
The Colossus of Rhodes, a statue spanning the entrance to Rhodes Harbour
and considered to be one of the wonders of the Old World, was said
to have been made of copper. No trace of it remains today since it
was recycled to make useful artifacts.
In the Middle Ages, church bells and other heavy items made from copper
were melted down to produce cannon during times of war. And after
the wars were over, it was common to melt bronze cannons make more
useful items.
The entire economy of the copper and copper alloy industry is dependent
on the economic recycling of any surplus products. There is a wide
range of copper based materials made for a large variety of applications.
To use the most suitable and cheapest feedstock for making components
gives the most economic cost price for the material.
Scrap Value - Copper
The usual commercial supplies of pure copper are used for the most
critical of electrical applications such as the production of fine
and superfine enamelled wires. It is essential that purity is reproducibly
maintained in order to ensure high conductivity, consistent annealability
and freedom from breaks during rod production and subsequent wire
drawing. Since the applied enamel layers are thin but have to withstand
voltage, they must have no surface flaws; consequently the basis copper
wire must have an excellent surface quality. Primary copper of the
best grade is used for producing the rod for this work. Uncontaminated
recycled process scrap and other scrap that has been electrolytically
refined back to grade 'A' quality may also be used.
The copper used for power cables is also drawn from high conductivity
rod but to a thicker size than fine wires. The quality requirements
are therefore slightly less stringent. The presence of any undesirable
impurities can cause problems such as hot shortness which gives expensive
failures during casting and hot rolling. For the same reason, scrap
containing such impurities can only be used for this purpose if well
diluted with good quality copper.
For non-electrical purposes, copper is also used to make large quantities
of plumbing tube, roofing sheet and heat exchangers. High electrical
conductivity is not mandatory and other quality requirements are not
so onerous. Secondary copper can be used for the manufacture of these
materials, though still within stipulated quality limits for impurities.
Where scrap copper is associated with other materials, for example
after having been tinned or soldered, it will frequently be more economic
to take advantage of such contamination than try to remove it by refining.
Many specifications for gunmetals and bronzes require the presence
of both tin and lead so this type of scrap is ideal feedstock. Normally
it is remelted and cast to ingot of certified analysis before use
in a foundry. Scrap of this type commands a lower price than uncontaminated
copper.
Scrap Value - Brasses
The recycling of brass scrap is a basic essential of the economics
of the industry. Brass for extrusion and hot stamping is normally
made from a basic melt of scrap of similar composition adjusted by
the addition of virgin copper or zinc as required to meet the specification
before pouring. The use of brass scrap bought at a significantly lower
price than the metal mixture price means that the cost of the fabricated
brass is considerably less than it might otherwise be.
The presence in brass of some other elements such as lead is often
required to improve machinability so such scrap is frequently acceptable.
Besides the common free-machining brasses, there are many others made
for special purposes with properties modified to give extra strength,
hardness, corrosion resistance or other attributes, so strict segregation
of scrap is essential.
Brass scrap arising from machining operations can be economically
remelted but should be substantially free from excess lubricant, especially
those including organic compounds that cause unacceptable fume during
remelting.
When brass is remelted, there is usually some evolution of the more
volatile zinc. This is made up in the melt to bring it back within
specification. The zinc is evolved as oxide that is drawn off and
trapped in a baghouse and recycled for the manufacture of other products.
Brass to be made in to sheet, strip or wire form must be significantly
free of harmful impurities in order to retain ductility when cold.
It can then be rolled, drawn, deep drawn, swaged, riveted, spun or
otherwise cold formed. It is normal therefore to make it substantially
from virgin copper and zinc, together with process scrap arising from
processing that has been kept clean, carefully segregated and identified.
Scrap Value - Other Copper Alloys
Copper alloys such as phosphor bronzes, gunmetals, leaded bronzes
and aluminium bronzes are normally made to closely controlled specifications
in order to ensure fitness for demanding service. They are normally
made from ingots of guaranteed composition together with process scrap
of the same composition that has been kept carefully segregated. Where
scrap has become mixed, or is of unknown composition, it is first
remelted by an ingot maker and analysed so that the composition can
be suitably adjusted to bring it within grade for an alloy.
Good quality high conductivity copper can be recycled by simple melting
and check analysis before casting, either to finished shape or for
subsequent fabrication. However, this normally only applies to process
scrap arising within a copper works. Where copper has been contaminated
and it is required to re-refine it, it is normally remelted and cast
to anode shape so that it can be electrolytically refined. If, however,
the level of impurities in the cast anode is significant, it is unlikely
that the cathode produced will then meet the very high standards required
of grade 'A' copper used for the production of fine wires.
Where copper and copper alloy scraps are very contaminated and unsuitable
for simple remelting, they can be recycled by other means to recover
the copper either as the metal or to give some of the many copper
compounds essential for use in industry and agriculture. This is the
usual practice for recovery of useable copper in slag, dross or mill
scale arising from production processes or from life-expired assemblies
of components containing useful quantities of copper.
Environmental Considerations
Copper is an essential trace element needed for the healthy development
of most plants, animals and human beings. In general, moderate excess
quantities of copper are not known to cause problems. Every care is
taken to avoid wasting copper and it is recycled where possible. Excess
copper is not allowed to escape into the atmosphere as fume, nor into
discharged process cooling water, all of which is generally treated
to keep within agreed limits.
Other metals associated with copper alloys are generally not in a
form that is dangerous. However, when fume is generated, for example
by melting or welding, it may be necessary to use fume extraction
equipment. Beryllium is sometimes used as an alloying element in copper
to make some of the strongest copper alloys known, being invaluable
for the production of heavy duty springs. When alloyed with copper
and in the solid state this presents no health hazard. However, if
present in the atmosphere, beryllium can cause a health hazard and
should be controlled. CDA publication 104 gives advice on health and
safety requirements for airborne fume associated with copper-beryllium.
Product Value
If the scrap is pure copper and has not been contaminated by anything
undesirable, a high quality product can be made from it. Similarly,
if scrap consists only of one alloy composition it is easier to remelt
to a good quality product, although there may have to be some adjustment
of composition on remelting.
If scrap is mixed, contaminated or includes other materials such as
solder then, when remelted, it will be more difficult to adjust the
composition within the limits of a chosen specification. Where lead
or tin have been included, but no harmful impurities, it is usually
possible to adjust composition by the addition of more lead or tin
to make leaded bronzes. For some scrap contaminated with undesirable
impurities it is sometimes possible to dilute it when melting so that
the impurity level comes within an acceptable specification. All these
techniques retain much of the value of the scrap. The way in which
alloys can be made from scrap is shown in simplified diagrammatic
form in the figure.
Where scrap has been contaminated beyond acceptable limits it is necessary
to re-refine it back to pure copper using conventional secondary metal
refining techniques that provide a useful supplement to supplies of
primary copper. |
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