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.