Reducing the Environmental Impact of the Aluminium Industry by Dr Tim Johnson
I’m one of those people who loves unusual statistics and when I saw this one I just couldn’t resist it: did you know that two-thirds of all the aluminium produced since the 1880’s is still in circulation? To put this statistic another way, the next time you reach for an aluminium drinks can just think that some of the metal in the can could have been extracted over a century ago and has been round and round the recycling loop umpteen times ever since.
Annoyingly, although this figure implies aluminium is a paragon of recycling, a little probing reveals that this number actually owes a great deal to the spectacular rise in aluminium production in the last few decades (current production levels are around four times what they were in the early 1970’s), so in fact most of the aluminium ever produced only came into circulation a relatively short time ago. On the other hand though, it would be churlish not to acknowledge that recycling rates for aluminium are pretty high or that objects made from aluminium do indeed tend to last a long time (I am sure like me, many of you will have mothers or grandmothers still using ancient aluminium saucepans). So, we can truly say this interesting factoid is at least partly a reflection of the metal’s good environmental credentials. And this is just as well, because the production of aluminium is not quite so eco-friendly.
Firstly, aluminium production requires eye-watering amounts of electricity. Now I don’t know, perhaps you might think melting aluminium requires a lot of energy [310 kWh/t to 700°C]. If so, it may come as some surprise to hear you need over 70 times this energy to extract it from its ore [22.15 MWh/t: ore production = 8.25; smelting = 13.9 MWh/t].
Secondly, the extraction of aluminium creates a number of unpleasant by-products. Aluminium ore (bauxite) has to be separated into the aluminium-containing portion (alumina) and the rest, which is a highly alkaline residue known as Red Mud and is produced at a rate of 2.2 tonnes per tonne of aluminium. This is collected in large storage lagoons that have been known to fail with deadly consequences, such as occurred in Hungary in October 2010. Aluminium smelters also emit 1.2 kg of fluorine per tonne of aluminium, which collects in vegetation and in the bones and teeth of animals that eat the contaminated plants. And then there is the lining material from the smelting pots, ‘spent potliner’, which is another especially hazardous material. It reacts in contact with water to form hydrogen, contains fluorine and cyanides and is accumulating at a rate of around 220,000 tonnes per year.
On the other hand, like many other metals and mining sectors, the aluminium industry has been working hard to improve its environmental performance year by year. Not only does this make sense from environmental and social responsibility perspectives, but increasing your recycling rates and reducing your use of expensive chemicals and energy also usually leads to lower operating costs. The fruits of their considerable efforts are reductions over the last 20 years in energy consumption and fluorine emissions per tonne of metal of 10% and 50% respectively, extensions to the longevity of potliners and an increase in the recycling rate for spent potliner when it reaches the end of its working life.
Tetronics is making its own modest contribution to these efforts through our strategic partnership with Mitsubishi Corporation’s Petcoke division. Mitsubishi already has a well-established Aluminium Carbon business value chain, which it plans on expanding to include SPL treatment processing, in order to offer an enhanced service to its client base. The strategic partnership sees Tetronics providing the technology and expertise in processing SPL waste to Mitsubishi.
Tetronics’ plasma process works by reacting the graphite in the waste with oxygen and steam in order to convert it into a gas (a process known as ‘gasification’) and then melting the remaining part of the waste. Not only does this allow us to use some of the energy released by the reaction between oxygen and graphite to reduce the electrical power required, but as an added advantage, the harmful fluorine in the waste recovered from the furnace exhaust gases in a form suitable for re-use as a raw material in more aluminium smelting, thereby further reducing the environmental impact of aluminium production.
And so as always, it is where a waste disposal problem becomes a resource recovery opportunity that our work is at its most satisfying.