The Year of Elements, and a Crisis

This is the International Year of the Periodic Table, and since it is almost over, one can debate how useful it was. I wonder how many readers were aware of this, and how many really understand what the periodic table means. Basically, it is a means of ordering elements with respect to their atomic number in a way that allows you to make predictions of properties. Atomic number counts how many protons and electrons a neutral atom has. The number of electrons and the way they are arranged determines the atom’s chemical properties, and thanks to quantum mechanics, these properties repeat according to a given pattern. So, if it were that obvious, why did it take so long to discover it?

There are two basic reasons. The first is it took a long time to discover what were elements. John Dalton, who put the concept of atoms on a sound footing, made a list that contained twenty-one, and some of those, like potash, were not elements, although they did contain atoms that were different from the others, and he inferred there was a new element present. The problem is, some elements are difficult to isolate from the molecules they are in so Dalton, unable to break them down, but seeing from their effect on flames knew they were different, labelled them as elements. The second problem is although the electron configurations appear to have common features, and there are repeats in behaviour, they are not exact repeats and sometimes some quite small differences in electron behaviour makes very significant differences to chemical properties. The most obvious example is the very common elements carbon and silicon. Both form dioxides of formula XO2. Carbon dioxide is a gas; you see silicon dioxide as quartz. (Extreme high-pressure forces CO2 to form a quartz structure, though, so the similarity does emerge when forced.) Both are extremely stable, and silicon does not readily form a monoxide, while carbon monoxide has an anomalous electronic structure. At the other end of the “family”, lead does not behave particularly like carbon or silicon, and while it forms a dioxide, this is not at all colourless like the others. The main oxide of lead is the monoxide, and this instability is used to make the anode work in lead acid batteries.

The reason I have gone on like this is to explain that while elements have periodic properties, these are only indicative of the potential, and in detail each element is unique in many ways. If you number them on the way down the column, there may be significant changes depending on whether the number is odd or even that are superimposed on a general change. As an example: copper, silver, gold. Thus copper and gold are coloured; silver is not. The properties of silicon are wildly different from those of carbon; there is an equally dramatic change in properties from germanium to tin. What this means is that it is very difficult to find a substitute material for an element that is used for a very specific property. Further, the amounts of given elements on the planet depend partly on how the planet accreted, thus we do not have much helium or neon, despite these being extremely common elements in the Universe as a whole, and partly on the fact that nucleosynthesis gives variable yields for different elements. The heavier elements in a periodic column are generally formed in lower amounts, while elements with a greater number of stable isotopes, or particularly stable isotopes, tend to be made in greater amounts. On the other hand, their general availability tends to depend on what routes there are for their isolation during geochemical processing. Some elements such as lead form a very insoluble sulphide and that separates from the rock during geothermal processing, but others are much more resistant and remain distributed throughout the rock in highly dilute forms, so even though they are there, they are not available in concentrated forms. The problem arises when we need some of these more difficult to obtain elements, yet they have specific uses. Thus a typical mobile phone contains more than thirty different elements

The Royal Society of Chemistry has found that at least six elements used in mobile phones are going out be mined out in at least 100 years. These have other uses as well. Gallium is used in microchips, but also in LEDs and solar panels. Arsenic is also used in microchips, but also used in wood preservation and, believe it or not, poultry feed. Silver is used in microelectrical components, but also in photochromic lenses, antibacterial clothing, mirrors, and other uses. Indium is used on touchscreens and microchips, but also in solar panels and specialist ball bearings. Yttrium is used for screen colours and backlighting, but also used for white LED lights, camera lenses, and anticancer drugs, e.g. against liver cancer. Finally, there is tantalum, used for surgical implants, turbine blades, hearing aids, pacemakers, and nosescaps for supersonic aircraft. Thus mobile phones will put a lot of stress on other manufacturing. To add to the problems, cell phones tend to have a life averaging two years. (There is the odd dinosaur like me who keeps using them until technology makes it difficult to keep doing it. I am on my third mobile phone.)A couple of other facts. 23% of UK households have an unused mobile phone. While in the UK, 52% of 16 – 24 year olds have TEN or more electronic devices in their home. The RSC estimates that in the UK there are as many as 40 million old and unused such devices in people’s homes. I have no doubt that many other countries, including the US, have the same problem. So, is the obvious answer we should promote recycling? There are recycling schemes around the world, but it is not clear what is being done with what is collected. Recovering the above elements from such a mixture is anything but easy. I suspect that the recyclers go for the gold and one or two other materials, and then discard the rest. I hope I am wrong, but from the chemical point of view, getting such small mounts of so many different elements from such a mix is anything but easy. Different elements tend to be in different parts of the phone, so the phones can be dismantled and the parts chemically processed separately but this is labour intensive. They can be melted down and separated chemically, but that is a very complicated process. No matter how you do it, the recovered elements will be very expensive. My guess is most are still not recovered. All we can hope is they are discarded somewhere where they will lie inertly until they can be used economically.

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Space Mining

Most readers will have heard that there are a number of proposals to go mine asteroids, or maybe Mars. The implication is that Earth will become short of resources, so we can mine things in space. However, if we mine there for the benefit here, how would we get such resources here, and in what form. If the resources are refined elsewhere, then there is the “simple” cost of getting them here. If we bring them down in a shuttle, we have to get the shuttle back up there, and the cost is huge. If on the other hand, we drop them (and gravity is cheap) we have to stop whatever we send from burning up in the atmosphere, so to control the system we have to build some sort of spacecraft out there to bring them down. Overall, this is unlikely to be profitable. On the other hand if we build structures in space, such as space stations, or on Mars for settlers, then obviously it is very much cheaper to use local resources, if we can refine them there.

So, what are the local resources? The answer is it depends on the history. All the solid elements are expelled in novae (light elements only) or supernovae (all). The very light elements lithium, beryllium and boron are rather rare because they tend to be destroyed in the star before the explosion. The elements vary in relative amounts made, and basically the heavier the element the less is made, and elements with an even number of protons are more common than elements with odd numbers. Iron, and to some extent nickel, are more common than those around them because the nuclei are particularly stable. The most common elements are magnesium, silicon and with iron about 10% less. Sulphur is about half as common, calcium and aluminium are about 6 – 8% as common as silicon, while the metals such as copper and zinc are about 100,000 times less common than aluminium. The message from all that is that unless there is some process that has sorted the various elements, an object in space is likely to have the composition of dust, which are mainly silicates, i.e. rock. There may well be metal sulphides as well, as there is a lot of sulphur there.

So what sorting could there be? The most obvious is that if the body formed close enough to the star during primary accretion, the heat in the accretion disk could be sufficient to melt the element, if it were there as an element. It appears that iron was, because we get iron meteorites and iron-cored meteorites. The accretion disk, of course, was primarily hydrogen, and at the melting point of iron, hydrogen will reduce iron oxides to iron, also making water. So we could expect asteroids to have iron cores? Well, we are sure most members of the asteroid belt do not, and the reason why not is presumably it did not get hot enough to melt iron where they formed. However, since the regolith (fine “soil”) on the Moon has iron dust in it, perhaps there was iron dust where the asteroids formed. However, the problem is what caused them to solidify. If they melted, steam would be created, and that would oxidise iron dust, so the iron then would be as an oxide, or a silicate.

The ores we have on Earth are there due to geochemical processing. For example, in the mantle, water forms a supercritical fluid that dissolves all sorts of things, including silica and gold. When this comes to the surface, it cools and deposits its solids, which is why gold is found in some quartz veins. The big iron oxide deposits we have were formed through carbon dioxide weathering iron-containing silicates (such as olivine and pyroxene) to make ferrous and magnesium solutions in the oceans. When oxygen came along, the ferrous precipitated to form goethite and haematite, which we now mine. All the ore deposits on Earth are there because of geochemical processing.

There will be limited such processing on Mars, and on the Moon. Thus on the Moon, as it cooled some materials crystallised out before others. The last to crystallise on the Moon was what we call KREEP, which stands for potassium, rare earths and phosphate, which is what it largely comprises. There is also anorthite, a calcium aluminosilicate on the Moon. As for Mars, it seems to be mainly basaltic, which means it is mainly iron magnesium silicate. The other elements will be there, of course, mixed up, but how do you get them out? Then there is the problem of chemical compatibility. Suppose you want rare earths? The rare earths are not that rare, actually, and are about as common as copper. But copper occurs in nice separate ores, at least on Earth, but rare earths have chemical properties somewhat similar to aluminium. For every rare earth atom, there are 100,000 aluminium atoms, all behaving similarly, although not exactly the same. So it is far from easy to separate them from the aluminium, then there is the problem of separating them from each other.

There is what I consider a lot of nonsense spoken about asteroids. Thus one was reported to be “mainly diamond”. On close questioning, it had an infrared signature typical of carbon. That would be typically amorphous graphitic carbon, and no, they did not know specifically it was diamond. Another proposal was to mine asteroids for iron. There may well be some with an iron core, and Vesta probably does have such a core, but most do not. I have heard some say there will be lots of platinum there. Define lots, because unless there has been some form of sorting, it will be there proportionately to its dust concentration, and while there is more than in most bits of basalt, there will still be very little. In my opinion, beware of investment opportunities to get rich quickly through space mining.