Copper at Its Finest
Scrap copper can be recycled after being segregated, cleansed and compacted being achieved by incorporating it in the smelting process, at times being added to achieve a required grade of copper.
It is fed into electric induction, or reverberatory gas fired furnace, where it is melted. The molten metal is poured into ingots which after further purification processing, can be manufactured into new components or reused in smelting operations.
This is another article in my series on recycling metals and here we will examine the applications of copper, and methods used in the pretreatment and recycling scrap copper components
Some Applications of Copper in Today’s World
Copper has many applications due to its properties of ductility, which permits it to be drawn into very fine wires; malleability allowing it be formed into various shapes, and conductivity.
The electrical cabling throughout your house is likely to be copper sheathed in plastic insulation, the cables running to the cooker and immersion water heaters being particularly heavy duty. Some overhead power lines are still run in copper, especially the earth lines.
Copper is used to form components for home central heating systems such as boiler internals, copper pipes, thermostats, coils and hot-tanks. No matter where you look, you will probably find copper, from the sheathing on rooftops of old buildings, to pots and pans in the kitchen.
Because of its excellent non-corrosive, thermal and electrical conductivity, the car industry also uses a huge amount of copper. The electrical system uses it for wiring harnesses, starters, generators and motors with the hydraulic systems using it for brake and steering transmission pipes. The radiator also has a good percentage of copper.
There is also a large and varied application of copper in offshore hydrocarbons and shipping industries, where it's anti-corrosion and alloying properties are exploited in the fabrication of pipes, process coolers and pumps; especially from alloys such as nickel.
Copper is alloyed to enhance its properties. It is mixed with tin to make bronze, brass being made from mixing copper with zinc and cupronickel or cuni (an alloy used for specialized pipes in chemical,refinery and marine applications).
So now that we know what copper is and what it is used for, we can understand the need to continue to collect and recycle it. Up to 50% of the copper used in various applications throughout the world is produced from copper recycling methods using much less energy.
Pretreatment of Scrap Copper
Copper electric wire encased in insulation
The copper electric wire is of very high purity but encased in insulation which must be removed. This can be removed from the wire by striping it off in the normal manner you would use when rewiring a plug. It can also be removed by chopping up the wire and the cable into small pieces. These are fed into shakers and mesh screens where most of the insulation will come away from the wire. Various types of plastic insulation can also be segregated for recycling, both methods being highly automated and efficient at insulation removal and separation from the copper wire. Following these processes, the copper wire is then washed in a diluted acid mix to remove any lacquer or impurities.
Copper windings in electric motors, generators and starters
The removal of copper from electric motor windings is very labor intensive and time consuming, however, an innovative method is under research where the windings are subjected to very low temperatures. This makes the copper wire brittle, enabling it to be broken away from the winding frames in small pieces before it is washed in a light acid mix to remove lacquer.
Copper piping and tanks
Copper piping and tanks are immersed in a light acid bath, then washed in water. They may also be flattened after this stage.
Components made from copper alloys such as brass, bronze and nickel make up a high percentage of recycled copper. The components are immersed in light acid, washed with water and segregated into their separate categories according to their alloyed metals of tin, lead and zinc. They remain in this state for transportation to the recycling furnaces.
Recycling of copper alloys is carried out in a furnace, where the alloys are added to pure copper ingots to achieve grade of copper with certain required properties.
Where there are too many trace elements in the alloys, they are melted separately, usually in an electric furnace, where the minor trace elements are removed from the molten metal, before pouring into ingots.
Copper alloy can also be recycled by adding more pure copper, thus diluting the alloyed metals to an acceptable level.
Copper shavings from machine operations
Cuttings and swarf from machining copper will be contaminated with coolant oil, which is removed by immersion in a light acid bath after which it is washed in water.
Shredding and compacting
Once all the scrap copper has been recovered and treated, it is shredded and compacted into bales. These bales, along with the copper alloy components, are shipped to a copper smelter or remelting facility.
Methods of Copper Scrap Recycling
There are two basic copper recycling methods:
- Melting at a copper smelter along with copper ore
- Melting along with a proportion of copper ingots at a dedicated copper recycling plant
At a copper smelter, the scrap copper and alloy components are loaded into the furnace which is then fired up. The copper ore is fed into the furnace along with the required amount of limestone and sand. Oxygen and air are supplied and when the mix has become molten, it is then tapped into rectangular molds. The resultant rectangular plates are then purified to 99.9% pure copper using electrolysis processing.
At a copper recycling plant, the bales of compacted copper along with the required content of alloys are loaded into a furnace along with a proportion of pure copper ingots.
The furnace can either be of an electric induction type or a reverberatory one. The electric furnace melts all the contents and tips to pour the molten copper through a spout into molds for either further processing or they are shipped to a copper smelter.
A reverberatory furnace is a square box structure lined with firebricks and is usually gas fired, having a loading door at the front which can be lowered or raised as required. Once the copper is molten, samples are taken, and when approved, the molten copper is poured into molds and left to cool. The resultant copper ingots can be sent for further refining or dispatched to a copper smelter for further processing.
Concluding on Copper
Copper is produced by various methods of smelting and electrolysis, the end product being of very high purity.
Copper recycling methods use 85% less energy than the original smelting processes, although this does not take into consideration the pretreatment process involved.
This process involves the mechanical and chemical cleaning and segregation of various components. It is imperative that these processes eliminate the impurities, for extruding fine copper wires with any imperfections in the base metal will cause stresses leading to fractures.
The treated scrap copper is compacted, baled and dispatched to a smelter or designated copper recycling plant. Here the bales are loaded into an electric induction, or reverberatory furnace along with a quantity of shredded pure copper. Sand and limestone are added to remove unwanted by products. Once it has become molten, it is tapped or poured into molds of various shapes and left to cool.
The resultant ingots or rectangular plates are subjected to an electrolysis process where the end product is 99.9% pure copper.
Sketches of Furnaces Used in Recycling Copper
- Outotec Solutions, http://www.outotec.com/pages/Page____38082.aspx?epslanguage=EN
- Copper Motor Rotor Project, http://www.copper.org/applications/electrical/motor-rotor/index.html