Not a coal mine but...
April 23, 2010 9:25 AM   Subscribe

I am looking to compare the cost (monetary AND environmental) of mining/producing 1 pound each of steel, aluminum and titanium. Any resources tracking this type of thing?

In a discussion with a bike lover, he was extolling the virtues of steel for bikes because of its features and its low impact on the earth compared to the evil titanium. Aluminum was in the middle and okay.

I am looking to read more about this as I am not sure mining iron ore to produce steel is all that much better than aluminum or titanium. Am curious what resources are available to compare an equal amount of each.
posted by fluffycreature to Science & Nature (14 answers total) 1 user marked this as a favorite
Without fully answering your question, steel can be recycled/reused to make more components many times over. For many machined parts, aluminum has to be "virgin".
posted by Burhanistan at 9:40 AM on April 23, 2010

I don't have a resource for calculating the cost you're after, but I wanted to mention that if your scenario is set in the US, you have to include the cost of labor and most (if not all) of the major steels are unionized. There was an article in American Metal Market in 1999 stating that for the first time the most expensive component in US-made cars wasn't steel, but health care benefits. The majority of iron ore used in steel purchased by the US comes from China. I haven't been in the steel business for years, but iron ore used to be priced by "agreement" between miners and steelmakers. The miners would propose a sale price and steelmakers would consult and decided how large of a markup the market would bear.
posted by Oriole Adams at 9:43 AM on April 23, 2010

For many machined parts, aluminum has to be "virgin".

I'd like to see a citation for that. I can't find anything to support it and a fair bit to counter it. For example: "Aluminium can be recycled indefinitely, as reprocessing does not damage its structure." Source.
posted by jedicus at 10:17 AM on April 23, 2010

Steel has carbon "baked" into it, usually from coal or related high-carbon mined rocks. So, I'm not sure that it's especially better than Titanium in terms of eco-impact.

Also, the majority of sturdy metal things that you buy are carefully made alloys that include a lot of different metals and other materials. So, the titanium frame is more likely to be a form of steel as well, just with a good percentage of titanium in it. It might also include Vanadium, Nickel, Chromium, etc. They're probably not as different in terms of impact as your friend thinks.
posted by Citrus at 10:23 AM on April 23, 2010

I'd like to see a citation for that. I can't find anything to support it and a fair bit to counter it. For example: "Aluminium can be recycled indefinitely, as reprocessing does not damage its structure." Source.

Sorry that I don't have an actual source offhand, but it is my understanding that the FAA certification standards for airframe aluminum are so strict that it is difficult to use recycled materials for. Cans and other simple alloys can be reused indefinitely, but larger, more complex components require a fair amount of stripping, retreating, separation, etc before they can be recycled for other aluminum goods. So, I should have been more specific.
posted by Burhanistan at 10:30 AM on April 23, 2010

Mining and refining metals is a very energy intensive process. As a result, I suspect that the relative costs of the bulk metals is probably a good estimate of the relative energy requirements of producing each metal. Further, I think the energy requirements are probably a good proxy for the relative overall environmental impact of producing each material (for example, strip mining takes a lot of energy).

Costs are likely going to be expressed per unit of mass, so you'd need to adjust for the mass of each material required for a given application.

One place this breaks down is that energy sources aren't completely fungible, and so you can't treat the environmental impacts uniformly. Aluminum refining is generally driven by cheap hydropower, which doesn't exactly polute, but it screws up rivers. Virgin steel uses a lot of coal. Scrap steel uses a lot of electricity to recycle. Titanium refining seems to require a lot of magnesium, which looks like it requires a lot of electricity to produce.
posted by Good Brain at 10:47 AM on April 23, 2010

I can't add much, apart from that refining aluminum requires an ungodly amount of electricity.

This part of the process can be quite clean, or it can require the burning of quite a bit of coal.
posted by schmod at 11:31 AM on April 23, 2010

I'm seeing references to FAA materials requirements that necessitate virgin aluminum, but I can't find the actual guideline so far.
posted by restless_nomad at 12:20 PM on April 23, 2010

Expanding on what Citrus said, most bicycle steels have chromium and molybdenum in them, as well as carbon and iron. Most bicycle-purposed titanium is alloyed with chromium, aluminum and vanadium, though I am certain variations exist. I don't know anything about vanadium, but Cr and Mo are toxic heavy metals; molybdenum mining is responsible for some pretty substantial problems in the mountains of Colorado.

Your friend clearly needs to be riding bamboo (preferably homemade, with locally sourced pieces) if he cares enough about the environment to choose a bicycle frame material based on environmental costs.
posted by richyoung at 1:07 PM on April 23, 2010

For many machined parts, aluminum has to be "virgin".

I worked in the steel industry for a little over 20 years, and I've never seen the term "virgin" applied to any metal. If the required metal is for an exterior application and must be flaw-free, it is usually referred to as "Class 1 Exposed." Any metal supplier would automatically know from that description that the steel, Aluminum, whatever, supplied must be free of surface flaws and must confirm to the SAE or ASTM mechanical and chemical standards.
posted by Oriole Adams at 1:26 PM on April 23, 2010 [1 favorite]

Yes, there are these resources, but they cost cash-moneys. There are some really complex Life Cycle Analysis modeling software available like SimaPro that have real-world data to do all the calculations in a blink (after hours of figuring out the right way to define your subject, enter the data, etc).

A really quick down-and-dirty way to look at it would be with Embodied Energy, which is a concept that tries to account for all of those values in one energy/mass value (usually kilojoules per kilogram - screw your pounds!). You can find these numbers in journal articles, but some dude at Berkeley conveniently put all the ones you want in a presentation, see the slide "Cylindrical Pressure Vessel Example."

This doesn't get you all the way to actual environmental impact, but it goes a long way. If you really want environmental impact, you could make some hand-wavy assumptions about what is negligible, whip out of your ass that the lion's share of that energy is coming from production, and multiply by your chosen emissions/kJ from electricity generation. THIS IS WHERE IT GETS REALLY INTERESTING. Aluminum production is almost always, ALWAYS sited for hydroelectric power because it is so fucking energy intensive. So your emissions for the average kg of aluminum can in reality turn out to be much lower than your average kilogram of steel. Example, those big American plants in NW Indiana are not powered by waterfalls but rather by COAL and some oxygen-burning furnaces. Also, economics wise, this has been very interesting the last year or so: many US steel plants are at low or no production, and the whole market is topsy-turvy because of things being cancelled, unpaid, etc. Really interesting reading.

So, you have here some numbers - and I think you might like the presentation - some keywords and a method. Part of the reason I haven't given you any FINAL numbers is because LCA/embodied energy/etc. is very very dependent on your model, its boundaries, your assumptions, and what you really want to measure. (Yes, I used to do research in this field)
posted by whatzit at 1:41 PM on April 23, 2010 [2 favorites]

Nthing comments above that aluminum production is extremely energy-intensive. In fact, it makes up nearly 1% of all US energy consumption.
posted by gueneverey at 3:55 PM on April 23, 2010

In fact, aluminum requires so much effort to refine from bauxite that just 150 years ago pure aluminum was more valuable than gold, and it was a sign of royalty to have aluminum cutlery compared to ordinary silver.
posted by Rhomboid at 6:47 PM on April 23, 2010 [1 favorite]

Nthing comments above that aluminum production is extremely energy-intensive. In fact, it makes up nearly 1% of all US energy consumption.

On the other hand, aluminum is so abundant that it can be mined lots of places, but mostly near hydroelectric dams, which are a cheap and renewable source of energy with a relatively low carbon footprint, compared with burning fossil fuels. It seems like a tough question to answer, on closer inspection.
posted by Blazecock Pileon at 11:39 PM on April 23, 2010

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