As stated in the previous article, the second most popular material for yacht building is aluminium. It is at the top place for yachts within the range of 30m to 50m, while for the larger ones, aluminium is the preferred option for superstructures, due to it lower weight compared to steel, combined with steel hulls.
From nature’s point of view, aluminium is the third most abundant element, surpassed only from oxygen and silicon. From practical point of view, although it can be found in its pure format in some volcanoes, it is either produced from ore or recycled. Presently the only financially viable ore extraction is from bauxite, yet there are other ores containing aluminium that could in the future add to its production.
The process of segregating aluminium and the other bauxite’s components is a two step procedure. Initially alumina, which is an aluminium oxide, is isolated from the other elements of the ore through the Bauer method. It is a chemical reaction that separates alumina from the rest that are left together as a mixture commonly referred to as “red mud’. In the second stage the oxygen has to be removed from the aluminium oxide, accomplished by the Hall-Hérault method, which is based on electrolysis and has its own by-products, inclusive of carbon blocks. I am keeping this description short, despite its complexity, but if you wish to learn more you can start with the following articles, Comhan, Council for Aluminium, AluminiumCentrum.
Still there is only pure aluminium that is actually very soft and has strength of somewhere in the range of 7-10MPa. It needs to be enriched with other metals and become an alloy with substantial mechanical properties to be used for structural purposes. In its pure format, given it excellent reflector qualities, it can be utilised for mirrors.
Having briefly explained the process of extracting and producing aluminium alloys, the following are the key points for its impact on the environment.
- In order to produce 2tons of aluminium we require 5tons of bauxite, namely we are using 40% of the overall natural resource;
- Some quantities of the “red mud” are used in colouring tiles, as filler to asphalt or water purification, which means that not all of the remaining 60% goes to waste. Yet the portions that is not alternative used, needs to be stored for 5-10 years in caustic soda to be deactivated;
- The carbon blocks of the Hall – Hérault process are also used in the steel and cement industries, therefore not a complete waste either;
- The biggest drawback is the e-power consumption, as both stages require a significant amount of electrical energy, the Bauer a 0.003GJ/ton and the Hall- Hérault 55GJ/ton. If we are to compare it with steel, it is 10 times more;
- In both process we also have emissions of Fluoride, rubbles and CO2. For the latter, it is estimated that 3.5ton of CO2 are released per ingot;
- On the more positive side, natural resources with present consumption are projected to last for another 1250 years.
Simultaneously we have recycling of aluminium that back in 2013 counted for 28% of the overall production.
- From the material used for recycling, only a 15% goes to waste, the vast majority of the old components can be re-used;
- In respect of power consumption, it requires a mere 5% compared to the processes in extraction from ore, or half the power required for steel;
Trying to have an overview for the value to the environment of the aluminium as a material, taking into account all parameters, it definitely has some advantages. Power consumption is a concern, but as long as it is generated from renewable resources, the impact is minimal. Surely waste and emissions are present, but so are the natural resources of the ores. Moreover there are brilliant chemists out there that can device new processes from the ones presently used, that can improve the negative aspects, as the presently used methods are developed in the 19th century.