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Towards cleaner transport with aluminiumThe green movement is a response to the recognition of global warming and the resultant climate change as the single greatest environmental threat facing our planet today.
Global warming is largely caused by greenhouse gas emissions. Carbon dioxide is the biggest contributor.
While over 50% of the world’s greenhouse gas emissions relate to the embodied energy in the construction, refurbishment, operation and demolition of buildings, the transport sector in South Africa is a significant contributor to energy use.
Embodied energy reflects the full costs to the earth resources, the extent to which the earth’s overall resources are depleted.
The local energy use (DME 2002) is derived from electricity (mainly from coal) 26%, coal as coal 30%, liquid fuels and gas 35%, and biomass (wood) 9%.
The energy consumption in South Africa is shared between industry (45%), transport (20%), residential (10%), agricultural (3%), commerce (3%) and other (2%). The 17% balance of non-energy use of energy resources refers to energy sources used for other purposes such as chemicals and paper.
What is clear is the huge dependency on fossil fuels (including biomass). Note that from an embedded energy point of view, electricity is a very poor convertor of the energy of coal (Eskom achieves a 17% conversion efficiency from existing plant).
Sustainable development comprises three basic elements: profit (economic), people (social) and planet (environmental) considerations. A local, regional and global balance is required between the three to enable the present generation to meet its obligations toward future generations.
What has this to do with aluminium?
The fabrication and operation of transport fleets are consumed from the resources of the earth. Aluminium as a material of fabrication offers payload advantage, freedom from maintenance, a high residual value and clean operation.
Green friendly practices include efficient use of energy and materials, reducing waste, pollution and environmental degradation and improving productivity.
On the vehicle, aluminium offers the advantages listed above. Typically a payload gain of 15% to 20% can be achieved from a body of mass half (or less) that of a steel equivalent. In effect, for the same load, about every sixth complete transport unit is not required. This is a green contribution in itself.
In addition, when the vehicle is empty on its return run, it is lighter. This in turn saves energy, saves tyre wear, reduces both the CO2e load on the planet and the drain on finite resources.
Aluminium, as the third most common element on earth, will not run out. But the extraction of aluminium from its oxide is expensive in terms of embedded energy.
From a superficial point of view, reducing aluminium oxide to aluminium uses around twice the energy per ton as steels. However, this view ignores two realities.
The first is the reality of the effects of strength /density, the second the reality of run round scrap.
All industries and materials develop run round scrap.
This is new scrap (off cuts) related to production processes prior to the development of a final good.
This is tracked in the aluminium industry because the material has a very high scrap value.
Unlike most materials, the remelting of aluminium is highly cost effective. This is why aluminium has actively been recycled since the 1880s.
While, theoretically, remelting aluminium from recovered metal only requires 2% of the energy used to extract aluminium from its oxide, 5% is more commonly cited, this accommodating various inefficiencies.
This compares favourably against the remelting energy used for most materials which is by and large similar to the initial energy cost of extraction. This, for instance for steels, relates to relatively fragile oxide bond between iron and oxygen in nature. This makes initial extraction easy.
On the other hand, the tight bond between aluminium and oxygen is both key to many properties and why it is difficult to extract in the first place.
Figure 1 above shows the global aluminium flow; 75.5 million tons of ingots are produced from 37.8 million tons of primary aluminium plus 37.8 tons of remelted aluminium of which recycled old scrap represents 8.3 million tons.
The remaining 29.5 million tons comes from the waste minimisation policies adopted; 80% of the primary production volume. This is why the aluminium market equals the current primary production, plus the recovered old scrap (less remelt loss) 44.4 cf 44.5 million tons.
If we assume that the percentage of in-process loss is similar or the same for steel, then we can compare energy uses of a specific use ignoring used scrap recovery effects.
Because aluminium is corrosion resistant (as a result of its tightly bound oxide surface), it does not require corrosion protection – unlike the friable oxide surface formed on steel (the energy cost of the corrosion protection has been ignored).
The high reactivity of aluminium with oxygen leads to a tight bond formed which is difficult to break. This is why so much energy is required to break down the oxide, and why aluminium has a high corrosion resistance in the pH range 4-8.5.
Scratched, the hard, inert, rapidly forming oxide skin will rapidly rebuild if exposed to oxygen or an oxidising environment. The rapidity of oxide formation can be seen with the naked eye on molten aluminium within less than 10 seconds. In the case of welding, removal of the oxide within four hours of welding is required.
The fact that over 75% of the volume of aluminium ever produced (since 1886) can be traced and found to be still in service, is testimony to the longevity of aluminium.
It is clear that if one included recovered old scrap and allowed for corrosion protection, the numbers would favour aluminium.
In conclusion, there is no material that comes at zero cost to the earth’s resources. However, aluminium does not use more energy to produce the shaped and flat products used for fabrication than competing materials, this thanks largely to the reality of run round scrap and a low recycling cost.
However, aluminium also lasts considerably longer than competing materials and offers the advantage of higher economic use efficiency and high residual value.
Once claimed from the earth’s crust, aluminium is forever, cradle to cradle. This makes it a viable candidate for claiming a green mantle.
Article supplied by the Aluminium Federation of South Africa (AFSA)
