Thursday, October 19, 2017

Bardi's Universal Mining Machine


A number of years ago, Dr Ugo Bardi published a very thought-provoking essay about the possibility of a universal mining machine (which I’ll refer to as “Bardi’s machine” from now on). Such a machine can take common dirt, melt it down, atomize it, and separate it into its elements, each in its own little pile. This would allow us to extract valuable elements from common dirt. It would also prevent us from ever running out any any elements, as I'll explain below.

Common dirt contains small amounts of all naturally occurring elements. You could dig up a cubic meter of dirt from behind your house, and it would contain trace amounts of every element which occurs naturally. If we atomized common dirt, using Bardi's machine, we would obtain all elements from any piece of earth fed into it. As a result, we would never absolutely "run out" of any element until we had exhausted all dirt on this planet.

Furthermore, the amount of rare elements available to us would be massive and practically inexhaustible. More than 99.9% of the rare elements (such as copper) exist as very low concentration deposits. The overwhelming majority of rare elements are found as an atom here, an atom there, spread out thinly throughout the earth's crust. If we could mine the low-concentration deposits, then we would increase the total supply of rare elements by more than a factor of 1,000x.

What's more, we would no longer be "running out" of rare elements at any rate. Once we began mining common dirt, the amount of all elements available to us would be constant, and would not diminish over any time period. When we throw away old smart phones, or we build structures that rust away, they would just return to being common dirt (eventually) and could easily be re-mined. As a result, the amount of materials available to us would not diminish over time.

Presumably, we will eventually be forced to use Bardi's machine at some point. If we continue mining and dispersing the concentrated deposits of rare elements, as we are doing, we will eventually exhaust all of them. At some point, far in the distant future, we will have exhausted all concentrated copper deposits, all the concentrated rare earth deposits, and so on. At that point, only common dirt will remain. If we wish to continue mining the rare elements at that point, we'd need to use something like Bardi's machine.

The problem with mining common dirt is that it takes so much energy to do so. Lower concentrations of elements require higher amounts of energy to mine them. The lower the concentration, the higher the energy requirement. For example, it takes 10 times as much energy to mine an ore which is only 1/10th the concentration. The problem is, the concentration of rare elements is extremely low within common dirt. As a result, it would be energetically extremely expensive to obtain any particular rare element from common dirt. From Bardi’s article:

"Consider copper, again, as an example. Copper is present at concentrations of about 25 ppm in the upper crust (Wikipedia 2007). To extract copper from the undifferentiated crust, we would need to break down rock at the atomic level providing an amount of energy comparable to the energy of formation of the rock. On the average, we can take it as something of the order of 10 MJ/kg. From these data, we can estimate about 400 GJ/kg for the energy of extraction. Now, if we wanted to keep producing 15 million tons of copper per year, as we do nowadays, by extracting it from common rock, this calculation says that we would have to spend 20 times the current worldwide production of primary energy."
That is a valid point. It seems to rule out the possibility of mining undifferentiated crust.

However, one of the commenters for that article pointed out that mining undifferentiated crust would allow us to obtain all the elements at once, not just copper, for the same expenditure of energy. In other words, that expenditure of 400 GJ would yield not just 1 kg of copper, but many kilograms of many other elements also.

Bardi wisely made a concession to that point. In his subsequent book, he calculates the energy expenditure of mining undifferentiated crust while obtaining many uncommon elements thereby.

However, I wish to continue with the commenter’s line of thinking. I wish to explore the possibility of mining undifferentiated crust (dirt) and using all the elements obtained thereby, including the common elements such as iron, aluminum, silicon, oxygen, and so on. That is the purpose of this article: to explore the energetic effects of mining undifferentiated crust and using all the material obtained thereby, or at least using as much of that material as possible.

Can we mine undifferentiated crust?

If we started mining undifferentiated crust, using Bardi’s machine, then the elements emitted from it would not correspond to our needs for them. For example, almost 80% of the material emissions from Bardi’s machine would consist of silicon, oxygen, sodium, potassium, and magnesium, which only could be used for making glass, at least in those quantities. Another 18% or so of the material emissions would be common metals such as aluminum, iron (for steel), titanium, and so on. Less than 1% would be the “uncommon elements” such as copper, nickel, rare earths, and so on. We must use the elements in precisely those proportions if we wish to avoid throwing away any elements emitted from Bardi’s machine.

It’s necessary to avoid throwing away materials, because that’s what would determine how much energy would be required for Bardi’s machine, per kilogram of materials mined. If we used everything emitted from Bardi’s machine, in the proportions in which they were emitted, then the amount of energy used for mining undifferentiated crust would be 10 MJ/kg, as per Bardi’s quotation above, which is a modest amount of energy and is similar to what we use for mining today. If, on the other hand, we mine only copper from undifferentiated crust, and throw everything else away, then the energy expenditure is 400 GJ/kg, which is 40,000 times higher.

Since we wish to avoid throwing away material, we must align our mining of undifferentiated crust with our usage of materials. Presumably, only a fraction of all mining could be done using Bardi’s machines. Some of the common elements (like aluminum and iron) would still be mined using traditional methods, so only a fraction of our mining would use Bardi’s machines. That fraction must be low enough that no materials are emitted from Bardi’s machine in greater quantities than are used by that civilization. In that manner, Bardi’s machines would displace the energy which otherwise would have been used to obtain materials for glass, steel, and so on, using traditional mining methods. We would get the common elements “for free” from Bardi’s machines, as a side effect of trying to obtain the rare ones, which would reduce the energy expenditure for mining elsewhere in the economy. As a result, the net effect of using Bardi’s machines would not increase the energy requirements for mining as a whole, at least not by very much. The advantage of using Bardi’s machine is that it would also emit small quantities of all the uncommon elements, so we would never run out of them over any time scale.

Let’s suppose that civilization has exhausted all ores and all concentrated deposits, of all rare elements, everywhere. All that remains is undifferentiated crust for uncommon elements. Also assume that civilization wishes to use Bardi’s machines as much as possible to obtain uncommon elements from that point forward. We’ll assume the civilization uses the same proportions of common elements (such as silicon, iron, and so on) as we use today.

In which case, Bardi’s machines could be used to mine all the materials for all glass produced by that civilization. Glass would be the material which was relatively most over-supplied from Bardi’s machines (almost 80% of the material emitted could only be used for making glass). As a result, if there was enough demand for all that glass from Bardi’s machines, then there would also be enough demand for all the iron, aluminum, calcium (for cement), and so on. Little material would be thrown away. All other glassmaking operations in civilization could cease, thereby saving the energy that had been expended on it. Also, some of the mining for bauxite, iron, and so on, would also be displaced by Bardi’s machines. The amount of energy used by Bardi’s machines would be on the order of 10 MJ/kg, which is not higher than civilization was already expending upon glass, aluminum, and so on.

It would be possible to make glass directly from the output of Bardi’s machines, by mixing together the necessary elements while they were still molten, and cooling the result quickly enough that glass is formed. This would displace the amount of energy used for glassmaking elsewhere in the economy, which is on the order of 15 MJ/kg of glass. Of course, we would also make some steel and some aluminum from the output of Bardi’s machines.

This strategy would reduce the amount of energy required for mining undifferentiated crust. The amount of energy for mining altogether would not be much higher than today. Furthermore, we would get all of the elements which occur in the Earth’s crust, as long as mining continued.

Elemental Scarcity

As a result, we could use Bardi’s machines to a limited degree, and could obtain all elements indefinitely, without ever increasing the energy we use for mining. We would just have to limit the use of Bardi's machines so that they don't produce much more of any elements than were otherwise mined.

The problem is, the amounts of uncommon elements would be emitted in fairly limited quantities. We’d never run out of uncommon elements, but the amounts produced per year of copper, nickel, and so on, would be fairly limited, assuming we don’t wish to “throw away” anything, and thereby increase the amount of energy devoted to mining intolerably.

At present, global civilization produces about 70 million tonnes of glass per year. If all that glass were produced from materials from Bardi’s machines, then the following amounts of rare elements would also be obtained:

Copper (70 megatonnes * 70ppm) = 4,900 tonnes/year
Nickel (70 megatonnes * 90ppm) = 6,300 tonnes/year
Lithium = ~1,800 tonnes/year
"Rare Earth" elements = ~20,000 tonnes/year

As a result, we would mine 0.7 grams of copper per person per year, and also 0.9 grams of nickel, worldwide, and similar or smaller amounts of all the other uncommon elements per person each year. Doing so would never require more energy than is expended on mining now. We could mine those rare elements, in those amounts, from undifferentiated crust until the sun explodes. We would never run out of them, and would never expend any more energy on mining than we do now.


As a result, our civilization could always have enough of the uncommon elements for things like smart phones, flat screen televisions, computer chips, and so on. Many of those devices use less than one gram of uncommon elements, per device. We could always mine enough materials for those purposes, even after billions of years.

We would also have enough uncommon elements for "massive" uses of them, such as electric cars, as long as we enforce high rates of recycling. For example, we would have enough lithium for electric cars indefinitely, provided that the batteries are sealed from the environment and the recycling rate is 99% or higher. If we assume that an electric vehicle has 30 kg of lithium in its batteries, the batteries are sealed from the environment, the car lasts 20 years, and 99.9% of the lithium in electric cars is recycled, then an average electric vehicle would require a net of 1.5 grams of lithium per year to be mined. That amount is on the order of what would be emitted from Bardi's machines, with no additional expenditure of energy. As a result, we would have enough lithium (and other uncommon elements) for "bulk" uses, indefinitely, as long as we enforce high rates of recycling.

We would not, however, have enough rare elements for “bulk” usages that are just thrown away. Some day, we will not have enough uncommon elements to allow people to throw away larger than single-digit gram quantities of rare elements per year. At some point, careful recycling will be required for devices (such as electric cars) which use large quantities of uncommon elements.

A few caveats are necessary here. It's possible that we won't have enough lithium in the future to build additional new electric vehicles. We would have enough lithium to sustain the peak number of electric cars indefinitely, but not enough to build additional new electric cars. Also, it is quite possible that we will simply substitute other elements when rare ones become scarcer, in which case, we would not pursue the diffuse deposits for those elements.

However, we will never "run out" of any element over any time period. The conclusion is that we can mine undifferentiated crust, in limited amounts. It is energetically feasible to do so. As a result, we will never run out of any element over any time period. We may have much lower extraction of some elements, far in the future, but extraction will never be zero for any important element. All uncommon elements will always be available, at tolerable energy expense.

NOTE: I made two changes to this article the day after it was published, as explained in the comments below. I also added the "caveats" paragraph shortly after this article was first published.


  1. I think that here is mixing two different things.

    One is about consider to extract multiple elements at once.
    It's ok. Sometimes could be a useful strategy. sometimes not.

    The other is about use "common dirt" as a reference of "unexahustible raw source"
    I understand that it's useful as a "worst case scenario", but very unrealistic.

    Some arguments about that.

    First, the method of extraction change a lot about the energy of recovering. Even if it's about milligrams into a kilogram, if
    it's a substance that it could be disolved where most of the mass will not, you can recover that milligrams if minimal costs.
    There is always a fixed cost of moving/operate a certain mass of some substance, so a minimal energy cost, but very different from
    "turn into raw components". See, for example, extract elements from sea water. You don't need to turn water into hydrogen and
    oxygen to recover that trace elements.
    Simply boling work better, and membranes works even better.

    Second... the Earth is not uniform, so while, as I said, "common dirt" seems useful for an abstract idea to talk about the
    problem, in practice, we will mine different places with different compositions.

    Third... if we talk about "completely mass recovering" that it's a theorical BUMM (Bardi's ...), one of the best places of
    raw recovering is waste.

    We are seen the problem from a extraction/consume perspective. Instead, we should see the problem from
    "concentrate"/"use"/"recycle+avoid any loose" perspective.

    Materials without nuclear process, don't destroy. So our problem is not to extract matter, but turn matter from a easy
    extraction place (concentrate mine) into a bad extraction place (bad waste managed + wear-disolved release to environment)

    The idea is...
    1- Make products to last much as possible, but recover materials (specially most valuate ones) easily.
    2- Non easily recovering materials (ej. dopping, diffuse), should be use a BUMM like machine to recover even more.
    3- Avoid expensive looses through weathering making shieldings based on abundant elements.
    4- Completely the circular economy with sustainable extraction. Sustainable extraction is what you can mine from disperse
    sources, so they can replenish or the reserve is so long-lived as a billion years... (until we abandon/die in the planet)
    If you reduce the consumption to so low values as you conclude in your text, you can reach that premise.
    Remember that weathering don't destroy the mass. Only displace into another place, like sea water, so if you mine sea water, you
    are closing a circle, not exahusting the sea.

    Of course... there is limitations anyway. Just is not as hard as replicate the same proportions of "common dirt" in our usage.
    We could raise some orders of magnitude over the low concentration values.

    The real goal here is closing the circle. Zero net waste so recovering every "loss". We could reach better quality life reaching
    new source materials (like space mining) and adding into the circle so remaing into our usage forever.

    Of course do that extreme mining before reach cicle economy is silly. A lot of energy spending for a very short surplus of
    raw materials. It is to steal quality life to future generations.
    But in a circle economy, you are adding material to a accesible form (in products that you can recicle easily).

    1. Hi Oatleg,

      I agree with what you are saying.

      I was using "common dirt" as a WORST POSSIBLE theoretical case. Assume that nobody ever recycles anything, we've mined all concentrated deposits of everything over millions of years, and we threw away everything at random until all rare elements are evenly distributed everywhere. That is the worst possible theoretical case, and even then, we still can mine all elements (even rare ones) at tolerable energy expense.

      There are many options which could be used before that. There are lower-concentration deposits of (say) copper which are still much better than common dirt, but which require new chemical methods to extract. There are many possibilities that could be used before we revert to Bardi's machines.

      I just wanted to skip right to the end, and find out what is implied by the worst possible case. Even then, we have not run out of anything.

      I agree with your point about recycling. It would be much easier just to close the loop as much as possible. I added a paragraph to the conclusion about recycling.

      -Tom S

  2. NOTE: I made two changes to the article, as follows. First, I re-worded the opening paragraphs which were clumsily written. Second, I added a paragraph in the conclusion for the possibility of recycling uncommon elements for devices which use large quantities of them (such as electric vehicles).

    -Tom S

  3. This seems an odd way of arguing "the unwanted side-products from conventional mining are not unwanted at all, hence the obvious decrease in mining efficiency doesn't exist" -- in other words, it has the sound of an accountant's trick, rather than being something _actual_.

    A moment's reflection bears this out -- Earth's crust is about 1/3 silicon, and 1/2 oxygen. Ignoring how reactive pure oxygen is (and hence energetically expensive to separate from other elements), why would we mine it?!?

    Further, another moment's reflection on the colossal upscaling of mining infrastructure (a factor of 10000? 100000? 1000000? from our already-bloated mining infrastructure) begs the question -- from what materials will all this infrastructure be built? It seems to me that we'd convert the Earth's crust in large part to mining infrastructure with a little bit of the material left over for other uses (this assumes, of course, infinite energy -- however, consuming energy at the scale required to perform this sort of industrial activity might boil the oceans -- I'm talking the waste heat only, not global warming).

    Tom, I think you have written some interesting articles on EROI and your article on energy storage was also interesting. This article is, in my opinion, ridiculous.

    Best wishes, Angus

    1. Hi Angus,

      "Earth's crust is about 1/3 silicon, and 1/2 oxygen. Ignoring how reactive pure oxygen is (and hence energetically expensive to separate from other elements), why would we mine it?!?"

      But we already mine silicon and oxygen. That is what glass is made from. That's why glass would be the relatively most over-supplied material. Approximately 80% of the material emissions from Bardi's machines could be only be used for glass.

      "Further, another moment's reflection on the colossal upscaling of mining infrastructure (a factor of 10000? 100000? 1000000? from our already-bloated mining infrastructure) begs the question -- from what materials will all this infrastructure be built?"

      But it wouldn't require any more dirt to be mined than now, or any upscaling of earth-moving machines. The amount of dirt extracted and fed into Bardi's machines would the same as what is used now for glass-making.

      Granted, there would be additional energy and material requirements. There would be an additional energy expenditure in order to atomize the earth and break all chemical bonds (10 MJ/kg, according to Dr Bardi), rather than just melt the material for glass. There would also be an additional energy expenditure for separating the elements. Also there would be additional energy, and materials, required for constructing Bardi's machines.

      However, I think those things would be fairly modest. It's possible that Bardi's figure of 10 MJ/kg is a theoretical minimum, but it represents only a fairly small fraction of the energy used for mining today. I don't know how much energy and materials would be required to construct Bardi's machines, but I can't imagine it would be enormous.

      -Tom S

  4. In many ways, your reply emphasises the problem with your thinking. Why mine silicon from "undifferentiated crust" when it can be mined as sand (and require much less refining)?

    Imagine that you mine 1 kg of crust. More than 750g of it are elements that can be more easily got elsewhere with relatively low-tech equipment (ie. a spade*), but with this machine we will spend 7.5 MJ to extract them.

    *I'm a bit tongue-in-cheek here, and realise that some purification is needed, but I think the point stands.

    1. "In many ways, your reply emphasises the problem with your thinking. Why mine silicon from 'undifferentiated crust' when it can be mined as sand (and require much less refining)?"

      Because we would get _all_ the elements thereby, as a side-effect of making glass.

    2. The entire premise of your article is "mining undifferentiated crust would allow us to obtain all the elements at once, not just copper, for the same expenditure of energy"

      You are now saying: "look, it will be colossally expensive to obtain rare elements by mining dirt, but as a bonus you get all this crud that you could more easily get elsewhere" -- doesn't sound like a good deal to me.

    3. "The entire premise of your article is that mining undifferentiated crust would allow us to obtain all the elements at once, not just copper, for the same expenditure of energy"

      Yes, that's correct. That was the premise of the article, and it is correct, insofar as I know.

      "You are now saying: look, it will be colossally expensive to obtain rare elements by mining dirt, but as a bonus you get all this crud that you could more easily get elsewhere"

      No, because you would get the "crud" for FREE, or for very little energy, as a side-effect of mining the rare elements. You would get glass, aluminum, steel, and so on, for almost NO additional expenditure of energy.

      If you're going to mine undifferentiated crust, then you may as well get as much from it as you can.

      Look at it this way. Suppose I wish to drive Alice and Bob to New York. Alice lives three blocks away from Bob, in Miami, Florida, and they both need to get to New York. Wouldn't it be easier to drive them both in the same car? Bear in mind that you could drive Alice separately, and it would be "easier" to do that, and skip driving the additional 3 blocks to pick up Bob. However, if you are calculating the fuel cost of driving BOTH of them, then it is easier drive both of them at the same time.

      If it's _necessary_ for us to mine undifferentiated crust (because there are no concentrated deposits left anywhere, which is not imminent) then this is the optimal way of doing so, with the minimal expenditure of additional energy. If we are going to calculate the expenditure of energy for something, then we should calculate the expenditure for an optimal solution.

      The point is not that we should start mining undifferentiated crust now. The point is that it can be done while imposing only a modest additional energy cost for the global mining system as a whole. As a result, it IS possible to mine undifferentiated crust for small amounts of rare elements, should that ever become necessary. Frankly, I don't know if it will ever be done, but it is quite possible.

    4. Your calculations about the cost of mining undifferentiated crust *only* hold if we can make use of everything we get out of it, in the exact proportions we find it. If that's not the case, then we need to pay to extract/isolate silicon when we're actually after molybdenum (and don't need any more silicon).

      To use your analogy of Alice and Bob, it's like saying to Alice: "I'm driving Bob to NY, wanna lift (and halve transport costs)?" and she says "No, I have to return my mum's car anyway". Just because you can do a thing, does not mean that it is useful.

    5. Sure, I definitely grant that point. That's why I picked glass as a bottleneck material. Glass is the relatively most over-supplied material. If we use that much glass, we will also use that much iron, aluminum, and so on.

      Still, there would be some over-supplied materials which are thrown away. Sulfur would be oversupplied. Scandium would be oversupplied. Magnesium might be oversupplied, because it's a flammable metal, and therefore not suitable as a building material. As a result, the calculations are off by perhaps a few percent.

      Still, the calculations are off by only a few percent. It's like Alice living 10 miles away from Bob in Florida, and Bob has to drive out of his way to pick her up before heading to New York. As a result, the increase in efficiency is not quite as much as if they had both departed from exactly the same location.

      I can't perform a more precise calculation because I don't know if that extra magnesium could be used. Magnesium metal is used for some purposes already (such as some auto parts), but presumably the entire car couldn't be made out of magnesium because of the fire hazard. I'd guess that magnesium could replace aluminum in beverage containers, but I'm not sure.

      If all the magnesium metal were used, and it displaced aluminum usage, then the materials thrown away from Bardi's machine would be less than 1% of the total. All the uncommon elements combined (rarer than titanium) make up less than 1% of the mass of the Earth's crust. Much of that material (such as copper, nickel, zinc, chromium, and phosphorus) would be needed.

      A 1% error in calculation is equivalent to Bob having to drive 12 miles out of his way to pick up Alice before they both head to New York.

      -Tom S

  5. Good data collecting, calculations and insights, Tom. I've been wondering about this myself for awhile.

    If we wanted to mine more of the non-silicon elements, perhaps (after processing to remove other elements) we could turn the silicon back into sand to use for concrete, and thus be able to mine a lot more of it and thus also the elements that associate with it.

  6. Thanks hitssquad.

    I see your point.

    I wonder if it would be possible to use glass-cemented aggregate or something like that, rather than concrete. The reason I suggest it is that we must expend the energy to melt down the undifferentiated crust anyway, so we may as well make glass out of it and get as much as we can for that expenditure of energy. If we just used the molten glass and mixed in aggregate rock during cooling, perhaps we could get glass/rock bricks, or glass cemented aggregate.

    My background is in math, not chemistry, so I don't know offhand if the glass would bind properly to the aggregate as cement does.

    -Tom S