Aluminium encyclopaedia

In the field of technology, recycling is the reuse of scrap and used finished products as secondary raw materials for the manufacture of new products. The recycling of industrially used metals has been practiced from the very beginning. Particularly in the case of aluminium it pays to recycle because of the high inherent material value. Aluminium recycling has developed into an independent branch within the aluminium industry. Worldwide, the so-called "secondary production" accounts for about a third of the total production. Aluminium recycling is an important integral part of a country"s economy.

• Recycling of aluminium conserves natural raw materials such as bauxite. Moreover, it makes an important contribution to energy-saving production because the energy needed for remelting is up to 95 per cent less than that required for the extraction of primary aluminium.

• Although the recycling of aluminium products is of prime concern, recycling of operating materials and in-house fabrication scrap in aluminium industry plants is also important.

Recycling of aluminium products

Recycling involves two stages:

• The metal scrap trade undertakes collection and supply. Up to 100 per cent of the aluminium used in electrical engineering, building construction, mechanical engineering, and rail and road vehicles is recycled as is a large part of that used in household equipment and a growing amount of that used in packaging. Worldwide, the relationship between the production of primary aluminium and recycled aluminium ("secondary aluminium") is about 70:30. One should note that although the amount of recycled aluminium is increasing, the relationship is remaining about the same because the overall demand for aluminium is also increasing. As there are no differences in quality between recycled aluminium and primary aluminium, and because the physical properties remain unchanged or depend on the alloying content, which is optimised in line with market requirements, it is not possible after the subsequent production steps to determine which aluminium billets contain recycled material or from which types of scrap the aluminium billets have been produced.

• Remelting is carried out in special remelting furnaces using different processes. One process, for example, is to cover the molten metal with fluxes (mixtures of sodium and potassium chlorides) to reduce burn-off (melting loss) and to purify the melt (melt purification). The waste gases produced are cleaned. To summarise, one can say that aluminium can be used as part of a material loop and is thus not consumed.

Recycling of operating materials

When recycling operating materials within the aluminium industry it is possible in principle to combine environmental protection with economic efficiency, as the following two examples show:

• It is possible to recover the fluxes used as cover fluxes during remelting and to use them again.

• Aluminium oxide is used in the dry scrubbing of the waste gases from the fused-salt electrolysis process and combines with fluorides and dust. When this aluminium oxide is then used as a raw material in the fused-salt electrolysis, it saves a considerable portion of the fluorides required there.

The fraction of aluminium products that can be subjected to energy-saving recycling depends on the field of application. In electrical engineering, building construction or mechanical engineering it can be up to 100 per cent (for example, in the refurbishment of buildings all used aluminium window frames and doors are recycled via the metal scrap trade), in transportation the figure is up to 95 per cent and in packaging it is up to 76 per cent.

In the most important fields of application, recycling rates are between 85 and 95 per cent and for fabrication scrap they are almost 100 per cent. Thus, most aluminium is not "consumed" but "used" and subsequently repeatedly made into something useful. There is no limit to the quantities of aluminium products that can be recycled. They can be completely returned to the material loop. This is an important reason why the quantity of recycled aluminium in circulation is growing.