Aluminium Manufacturing and Recycling Environmental benefits of aluminium recycling

• The recycling of aluminium saves up to 95% of the energy needed to produce

primary metal • Recycling saves also raw materials, and reduces the demand on landfill sites. • Recycling one kilogram of aluminium can save about 8 kilograms of bauxite, four

kilograms of chemical products and 14 kilowatt hours of electricity Background Aluminium is a silver-white metal obtained from bauxite, a rock composed of more than 50% aluminium hydroxides formed by weathering in tropical regions. Aluminium is the earth’s third most abundant element (after oxygen and silicon) and the most abundant metal in the earth’s crust (8% by mass). Aluminium bearing compounds have been used by man from the earliest times. Pottery was made from clays rich in hydrated silicate of aluminium and at one point in history aluminium was so valuable that rulers and the wealthy preferred cutlery made by aluminium instead of gold. Today more aluminium is produced each year than all other non-ferrous metals combined. The production of aluminium goes via two different routes: primary aluminium production from ore and recycling aluminium from process scrap and used aluminium products. Primary Aluminium Production Aluminium production is a two-stage process. In the first stage crushed bauxite is mixed with hot caustic soda, which dissolves the aluminium oxide. Impurities can be filtered out and the caustic solution is cooled to crystallise the dissolved aluminium oxide into a white sand-like powder. The second stage is the smelting process where aluminium oxide is dissolved in a molten salt bath. A powerful electric current is passed through the liquid that splits the aluminium oxide into aluminium and oxygen. The molten aluminium is drawn off and made into ingots. Four tonnes of bauxite are required to produce two tonnes of alumina, which in turn produce one tonne of aluminium at the primary smelter.

Aluminium production process

bauxite mine

primaryaluminiumplant

aluminaplant

refining remelting

scrap collection

foundry extrusion plant rolling mill

Semi-fabrication

Aluminium product

Semi-fabricated Aluminium Production Aluminium is delivered to the manufacturing industry in three main categories of shapes: § Flat rolled products, i.e. sheet and foil § Long products: extrusions, bars, rods and wires § Castings In most cases by far aluminium is alloyed with addition of other metals to make an array of aluminium alloys with different properties. The main alloying ingredients are manganese, magnesium, silicon, zinc and copper. The mechanical properties (yield strength and elongation) cover a wide range, in addition to the common fundamental properties (lightness, corrosion resistance, electrical and thermal conductivity, brightness, etc). Today, packaging and general engineering are the main end-uses for flat rolled products, building/construction for long products, and the automotive industry for castings. Aluminium scrap recycling Today recycled aluminium accounts for one-third of global aluminium consumption in Europe and aluminium recycling is a well-established industry. Recycling aluminium can require only as little as 5% of the energy needed to produce the primary aluminium from bauxite. Any aluminium product can be recycled and the metal can be melted again indefinitely. There is no difference between primary and recycled aluminium in terms of quality or properties. This explains why the value of aluminium scrap is relatively high compared to the price of aluminium ingot. There are two categories of aluminium destined for recycling: new and old scrap. New scrap is surplus material that arises during the manufacture and fabrication of aluminium alloys within the aluminium and manufacturing industry. This scrap is usually of known quality and composition and can therefore be melted down with little preparation. Examples include the trimmings from the edges of sheet aluminium, turnings and millings from aluminium fabrication and surplus extrusion discards. Nearly 100% of all new scrap is recycled. Old scrap originates from the end-of-life of final products. Such scrap could be beverage cans, car cylinder heads, window frames from demolished buildings or old electrical cabling. This scrap is recycled on average at 70-80% mainly into casting alloys and to a lesser extent into wrought alloys depending on quality and specifications. Old scrap is sorted at a recycling plant to determine composition and value. Sorting of aluminium is a key factor for optimum recycling: eddy current machines (ECM), detector-ejectors, heavy media separation have been developed to extract aluminium from mixed waste streams and work is underway on automatic sorting of aluminium alloys by main categories. The scrap is then prepared before the melting process in order to remove the major non-aluminium components (e.g. coatings of used beverage containers). Other impurities are collected in the drosses of the metal bath. These drosses are processed again, to recover the aluminium, and the secondary dross is disposed of in controlled conditions. The scrap aluminium is completely melted in a furnace and this molten metal is then cast or processed using the same techniques as primary processing. New scrap is mainly recycled by remelters, which are generally integrated into rolling mills and extrusion plants. Secondary refiners melt a mix of different scrap grades (mostly old scrap) to produce casting alloys to targeted specifications. Most of the old scrap is recycled in “open loop” (i.e. not exactly into the same alloy composition), because many scrap lots are mixed and because the demand per alloy evolves differently for each alloy.

There are two major “closed loop” (i.e. into exactly the same alloy) old scrap recycling routes: § The ‘carter’ grade (for engine blocks) § The Used Beverage Containers (UBC) recycling to produce new can stock

Energy recovery from aluminium foil in incineration Aluminium acts as an “energy bank” through its life cycle; while primary aluminium smelting requires on average 15 kWh/kg in Europe: § As scrap metal, little energy is needed to remelt it (about 5% compared to primary

smelting) § As thin gauge foil in MSW, when incinerated, it releases 31MJ/kg (equivalent to 8.9 kWh

thermal) of heat through oxidation Hence aluminium is adaptable also to incineration of MSW from which energy can be recovered from foil, while thicker-gauge products will be extracted from bottom ash as aluminium nodules for recycling. This is common practice in the Netherlands and in France, developing in Belgium, under discussion in Denmark that incinerates nearby 100% of its municipal solid waste. In total this leads to dozens of 1,000 tonnes of aluminium recovered. Collection of aluminium from the waste streams The principal non-ferrous metal to be recovered from household waste is aluminium, mostly in the form of used beverage cans and other aluminium packaging. As aluminium makes only 1% of the total packaging tonnage, it is highly diluted in multimaterial packaging recovery schemes, leading to lower yield than for other materials, whatever the technology used. Mono-material collection systems result in much higher collection rates and higher scrap quality. By contrast, building and automotive scrap are easy to collect (and are collected) either as major pieces or by eddy-current extraction from process residues. Facts and figures on recycling and recovery Aluminium enjoys globally high recycling rates in Europe, where 1/3 of 9 million tonnes of aluminium come today from recycling processes. The recycling figures per sector range from an average recycling rate of 45% for aluminium cans (within individual countries these figures vary between 20% in Spain- and 91% in Switzerland) to 85% in building and construction. The transportation sector, the biggest end-use market for aluminium where more than a quarter of

Schema Schematic Flow-chart tic Flow-chart

MeltingFurnaces

DecoaterVibrating

FinesScreen

MagneticSeparator Shredder

UBCFeed

TiltingHoldingFurnace

DegassingFiltration

Unit

Direct chillCasting unit

CanstockSlabs

Schematic Flow-chart

UBC Recycling

all aluminium is used, has a recycling rate of 95%. As regards energy recovery, the CEN standard in force considers that all aluminium foil under 50 µm thickness is fully oxidised in incineration, leading to heat production per kg similar to plastic and paper. Secondary markets for recycled aluminium Aluminium is readily recycled without any loss of quality and hence scrap aluminium has significant value, commands good market prices, and is mainly collected through market forces. Secondary refiners optimise their intake of scrap by category (new/old, grades) according to the level of global demand and to the product mix: most of their production is as casting alloys, mainly used for automotive components.

Markets for Secondary Aluminium in Europe – 2001174 Refiners: 2.5m tons Refiners Aluminium Production

6%

74%

13%7%

Building

Transport

Engineering

Others