Some thoughts on Mining

Too many people do not know where the materials that make up the products they use come from. Worse still, too many people do not even wonder about it.

I confess to being one of those people at one point. I only really learned about the larger story as an undergraduate. I really should have known considering that I was studying materials science (a modern offshoot of Metallurgical and Mining Engineering).One of my professors asked our class about this and, receiving no response, said, frankly, that most materials come from giant holes in the ground. He was of course referring too mines. Clearly other materials, like some textiles, food, wood, etc. come from biomass. However, metals, ceramics, and polymers (except bio-polymers) were exhumed from the earth at some point in some other form.

Materials like metals and ceramics usually aren't found buried in usable forms. They are dug up in a raw form called ore and must be refined. Polymer feedstock is usually petroleum which must be drilled for and refined. Reaching these raw feedstocks requires displacing massive amounts of rocks and soil (including all the plants living in it). The term "material rucksack" refers to the mass of material that must be moved, displaced, transformed or otherwise upset in order to get a final engineering material... sheet metal, for example. This term, "material rucksack," generally does not consider the mass of material that finds its way into landfills from disposal of products after consumer use. "Material rucksack" refers to all the material displaced during the fabrication of the product, before it even gets into the consumer's hands.

For some materials the mass of earth moved compared to the mass of the final useful material can be staggering. Consider platinum, an important ingredient in fuel cells and catalytic converters. Obtaining 1 gram of platinum requires a mining operation to displace 350,000 grams of earth. On the other hand, drilling for petroleum is surprisingly benign judging from this particular environmental metric. See other "material rucksack" ratios in the figure below from an IEA coal research and DOE study:

Material Rucksack ratio of various engineering materials. From IEA/DOE: 1983.

The "material rucksack" is an important environmental metric but is rarely considered among manufacturers and virtually unheard of among consumers. But every time one hears of a disaster like the Kingston coal fly ash spill in Tennessee in 2008 or the recent aluminum tailings spill in Hungary, it is an example of the negative consequences of letting the "material rucksack" get out of control. There are usually some nasty leftovers in the displaced material from mining processes. For example, Coal mining leaves behind displaced earth from mining and fly ash from processing and burning. Aluminum mining leaves behind a rich cocktail of ingredients collectively called tailings. Leftovers have various names like slag, sludge, tailings, leach residue and others. The mining leftovers often have high concentrations of dangerous heavy metals (arsenic, mercury etc.) and the slurry can be highly acidic or highly caustic and can severely injure living tissue.

In order to create a truly sustainable industrial ecology, the "material rucksacks" of all extractive processes must become smaller and under better control. There are some attempts at solving this problem but it is not an easy nut to crack. Consuming less is always an option, however unattractive. Re-manufacturing can be very effective. This approach implies that products would be re-obtained by the manufacturer to be fixed or upgraded when they break or become obsolete. Then they can be resold at a discount.

A fairly new idea is using bacteria, so called biomining. This uses various extremophiles or other specially adapted bacteria to break down various ores for recoverable resources. There are two promising possibilities here for sustainability. One, these bacteria can make very dilute mines economical again by recovering ores that would not be recoverable by mechanical or chemical processes. This reduces the number of new mines that would need to be opened. Two, these bacteria can even be set on the tailings and sludge heaps to recover various minerals that would otherwise head for a landfill or a permanent sludge reservoir. This could potentially reduce the volume of toxic sludge while recovering useful materials from it simultaneously! This creates some exciting prospects, but I don't believe it is a widely used technique because it isn't a mature technology quite yet. But there's promise here.

Recycling also helps reduce the amount of virgin raw material that needs to be mined but it isn't a perfect solution. Ideally materials could be recycled through infinitely cycling loops such that no new material would ever need to be mined. This is nearly feasible for some materials, like aluminum and perhaps iron/steel, but some imperfections and losses will dictate that new virgin aluminum/iron be periodically added to the respective loop to refresh it now and then. For other materials this indefinite recycling loop is not even theoretically feasible (at least given current recycling practices). One such material is plastic. Recycling plastic degrades its mechanical properties a small amount each cycle through, thereby preventing it from becoming the same product it started as. This is called downcycling and plastic must be downcycled. Eventually it becomes of such poor quality that nothing more can be done with it other than putting it in a landfill or incinerating it.

A uniquely promising solution is approaching this problem from a design perspective. By carefully choosing materials used in product design for their affinity for indefinite recycling one can decrease "material rucksacks." Product designers committed to this approach would compile a "palette" of materials and remove any from it that cannot be indefinitely recycled. All of these options must be explored to find a production regime that optimizes sustainability. It won't be easy and it will take lots of people thinking a lot about it. It'd be great if more people would begin to wonder more about where the material in their possessions comes from and maybe even go the extra step of wondering how that whole process could be redesigned for sustainability.