Steel

Steel is one of the most recycled materials in the world, and, as of 2007, more than 78% of steel was recycled in the United States. In the United States it is the most widely recycled material; in 2000, more than 60 million metric tons were recycled.

The most commonly recycled items are containers, automobiles, appliances, and construction materials. For example, in 2007, more than 97% of structural steel and 110% of automobiles were recycled, comparing the current steel consumption for each industry with the amount of recycled steel being produced. A typical appliance is about 75% steel by weight and automobiles are about 65% steel and iron.

The steel industry has been actively recycling for more than 150 years, in large part because it is economically advantageous to do so. It is cheaper to recycle steel than to mine iron ore and manipulate it through the production process to form new steel. Steel does not lose any of its inherent physical properties during the recycling process, and has drastically reduced energy and material requirements compared with refinement from iron ore. The energy saved by recycling reduces the annual energy consumption of the industry by about 75%, which is enough to power eighteen million homes for one year.

The BOS steelmaking uses between 25 and 35% recycled steel to make new steel. BOS steel usually has less residual elements in it, such as copper, nickel and molybdenum and is therefore more malleable than EAF steel so it is often used to make automotive fenders, soup cans, industrial drums or any product with a large degree of cold working. EAF steelmaking uses almost 100% recycled steel. This steel contains more residual elements that cannot be removed through the application of oxygen and lime so it is used to make structural beams, plates, reinforcing bar and other products that require little cold working. Recycling one ton of steel saves 1,100 kilograms of iron ore, 630 kilograms of coal, and 55 kilograms of limestone.

Because steel beams are manufactured to standardized dimensions, there is often very little waste produced during construction, and any waste that is produced may be recycled. For a typical 2,000-square-foot (200 m2) two-story house, a steel frame is equivalent to about six recycled cars, while a comparable wooden frame house may require as many as 40–50 trees.

Copper

Copper is 100% recyclable without any loss of quality whether in a raw state or contained in a manufactured product. Copper is the third most recycled metal after iron and aluminium. It is estimated that 80% of the copper ever mined is still in use today. Common grades of copper for recycling are:

  • Bare bright – very clean and pure copper wire usually 12 AWG or larger that has insulation and any tarnish removed

  • #1 copper – pipe with a new appearance and free of any foreign material

  • #2 copper – pipe with corrosion or foreign material and small gauge wire with no insulation

Insulated wire is also commonly recycled once the insulation is stripped off.

High purity copper scrap is directly melted in a furnace and the molten copper is deoxidized and cast into billets, or ingots. Lower purity scrap is usually refined to attain the desired purity level by an electroplating process in which the copper scrap is dissolved into a bath of sulfuric acid and then electroplated out of the solution.

Aluminum

Aluminium is 100% recyclable without any loss of its natural qualities. Recovery of the metal via recycling has become an important facet of the aluminium industry.

Recycling involves melting the scrap, a process that requires only five percent of the energy used to produce aluminium from ore. However, a significant part (up to 15% of the input material) is lost as dross (ash-like oxide). The dross can undergo a further process to extract aluminum.

Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public awareness.

In Europe aluminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.

Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium is produced in a wide range of formats and is employed in 80% of the alloy injections. Another important use is for extrusion.

White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium which can be extracted industrially. The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manage. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia) which spontaneously ignites on contact with air; contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, however, the waste has found use as a filler in asphalt and concrete.

Aluminum Cans

Aluminium beverage cans are usually recycled in the following basic way:

  1. Cans are first divided from municipal waste, in utilisation of an ECS.

  2. Cans are cut into little, equal pieces to lessen the volume and make it easier for the machines which separate them.

  3. Pieces are cleaned chemically/mechanically.

  4. Pieces are blocked to minimise oxidation losses when melted. (The surface of aluminium readily oxidizes back into aluminium oxide when exposed to oxygen.)

  5. Blocks are loaded into the furnace and heated to 750 °C ± 100 °C to produce molten aluminium.

  6. Dross is removed and the dissolved hydrogen is degassed. (Molten aluminium readily disassociates hydrogen from water vapor and hydrocarbon contaminants.) This is typically done with chlorine and nitrogen gas. Hexachloroethane tablets are normally used as the source for chlorine. Ammonium perchlorate can also be used, as it decomposes mainly into chlorine, nitrogen, and oxygen when heated.

  7. Samples are taken for spectroscopic analysis. Depending on the final product desired, high purity aluminium, copper, zinc, manganese, silicon, and/or magnesium is added to alter the molten composition to the proper alloy specification. The top 5 aluminium alloys produced are 6061, 7075, 1100, 6063, and 2024.

  8. The furnace is tapped, the molten aluminium poured out, and the process is repeated again for the next batch. Depending on the end product it may be cast into ingots, billets, or rods, formed into large slabs for rolling, atomized into powder, sent to an extruder, or transported in its molten state to manufacturing facilities for further processing.