Aluminum recycling

from Wikipedia, the free encyclopedia
A symbol of aluminum recycling
The labeling of recyclable aluminum by the European Committee for Standardization

Among aluminum recycling the recycling of scrap aluminum (scrap) as will be understood aluminum waste in any form, where " aluminum " is a generic term not only pure aluminum, but also for the majority resulting alloys.

If aluminum alloys are sorted and recycled, the corresponding alloys can be recycled from the resulting remelted aluminum without any loss of quality. Since various alloying elements (e.g. magnesium) cannot be removed during remelting, so-called downcycling occurs if they are not collected according to type . The great economic and ecological advantage of “recycled aluminum” is that the recycling process, compared to primary production, requires far less than a tenth of the energy required for the same amount of aluminum.

Procedure

Aluminum scrap ready for transport

The aluminum scrap that accumulates in many places for recycling and is collected in many types and forms contains both rolled and cast, as well as production waste, in which chips dominate as fine - grained material, but also metal-rich dross .

The scrap, which is usually mixed during the remelting operation, is melted in large-volume furnaces ( drum furnace ) with the addition of approx. 50% of a chloride salt mixture with an addition of fluorspar ( calcium fluoride ) at 650-700 ° C with constant movement of the furnace contents. In the process, contamination of the insert, primarily of an oxidic type, is absorbed in the slag flow of the molten salt and further oxidation is also limited by the furnace atmosphere. The finished melts are less often cast directly into raw ingots; They are mostly transferred to a so-called “mixer”, which enables further treatment steps that serve to clean, influence the structure and also qualify as a specific remelting alloy (see melt treatment ). The recycled aluminum goes in ingot form or as process heat-retaining liquid metal transport for further processing, usually to foundries.

While the actual recycling process is the task of medium-sized remelting companies or one of the remelters connected to the primary smelter, the processing of the quantities of salt slag that occurs during recycling is a special branch of waste management.

amounts

  • Around 723,000 tons of recycled aluminum were produced in Germany in 2016.
  • Approximately 30% of the aluminum made in the US comes from the recycling route.
  • In Europe, 52% of the aluminum produced comes from the recycling route, worldwide it is approx. 30% (as of 2017).
  • Worldwide recycling rates of around 40% are given for aluminum .

Economy and ecology

The recycling efficiency of aluminum is very good because it is much more energy-intensive to obtain primary aluminum by breaking down bauxite (aluminum ore) and converting it to aluminum oxide with subsequent fused-salt electrolysis than to melt scrap aluminum (melting point> 660 ° C). With aluminum recycling, only 5% of the amount of energy used in primary production is required. In addition, the amount of residues per ton of aluminum produced is reduced from two tons in primary aluminum production (especially red mud to be disposed of ) to 100 kg in aluminum recycling (especially recyclable salt slag ). A significant amount of electrical energy is required to extract aluminum from bauxite; when recycling, primary energy sources, e.g. B. natural gas can be used. Since various alloying elements (e.g. magnesium) cannot be removed during remelting, if the material is not collected correctly, there is no full recycling, but what is known as downcycling .

swell

literature

  • Maximum sorting efficiency, increased quality. In: Recycling Magazin , No. 5/2020, pp. 46–47

Individual evidence

  1. minerals.usgs.gov (PDF; 85 kB)
  2. UNEP-PNUE report "Recycling Rates of Metals", 2011 [1] (PDF; 2.3 MB)
  3. http://www.economist.com/node/9249262