Some of our most cherished devices – smartphones, computers and medical equipment, for instance – rely on a rich list of elemental ingredients. Mobile phones alone contain a whopping 60 to 64 elements. “Many of these metals are present in only minute amounts, a milligramme or less,” says Armin Reller, a chemist and the chair of resource strategy at Augsburg University in Germany. “But they are very important for the function of the device.”
For starters, some resources such as indium – found in computer and smartphone display screens – are byproducts of other mining operations. Almost all of the world’s indium comes from zinc mines; there are no dedicated indium mines, because it occurs in such small amounts mining for it is impractical. So if demand for zinc declines – say, because car manufacturers switch from steel to aluminum bodies, as they have been doing recently – then this would have an impact on indium. “Nature puts deposits where it feels like, without worrying about whether we have the energy or water handy to deal with it,” says Graedel.
China – which produces around 90% of the world’s rare earth metals – claims that its mines might run dry in just 15-20 years. Likewise, if demand continues for indium, some say it will be gone in about 10 years; platinum in 15 years; and silver in 20 years. Looking farther into the future, other sources claim that things like aluminum might run dry in about 80 years.
The thin, transparent material used in current modern mobile phones is called indium tin oxide, and according to some research, the world is running out of it. Industry experts are saying that the world could be out of indium, the metal that is mined to make ITO, within the next decade. It is transparent like glass, but also conducts—not as much as most metals, to be sure, but enough. That makes it ubiquitous in modern electronic devices that manipulate light. In flatscreen televisions, each display pixel is switched on and off by a pair of transparent ITO electrodes. In thin-film solar cells, the light-absorbing layer needs an electrode front and back to form a circuit and so convert sunlight to electricity.
But how much longer can we count on the material behind that wonder? No one is quite sure how much or little indium there is left, says Thomas Graedel of Yale University, who heads the United Nations Environment Programme’s working group on global metal flows. In part, that is because it is only a mining by-product and not all mines go to the trouble of recovering it. The US Geological Survey estimates that known reserves of indium worldwide amount to some 16,000 tonnes, overwhelmingly in China. Dividing that by the rate at which we are currently using the stuff suggests those reserves will be exhausted by 2020.
The EU has identified 20 critical raw materials, including indium, with economic importance and a high supply risk. Indium is mainly used for the production of LCD screens and is predominantly sourced from Chinese mines. This study, funded by the European Commission1, details the development of a process to recycle indium from waste LCD panels, where indium is found as indium tin oxide (ITO). The study is one of the first to describe how to recover indium from a leaching solution of waste LCD panels. Developing methods to recover materials from waste equipment is an important way of saving resources and reducing primary production of materials.
The researchers recovered indium from waste LCD panels through cementation: the process by which a solid is created from a solution. The panels were first shredded into small pieces and sieved to remove glass and plastic fragments, then indium was dissolved in a strong acid solution. Zinc metal powder was used in the solution to collect the indium, which becomes solid by reacting with zinc during the cementation process.
This indicated that, in general, indium recovery through recycling has environmental benefits when compared to landfill or incineration options. Incineration had the highest costs in terms of global-warming impacts. Indium recovery also had a net environmental benefit in relation to natural resource depletion. The study demonstrates a method to recycle indium from end-of-life touchscreens rather than mining from natural reserves, which will be valuable for industries and researchers working in critical raw materials recovery. The study also supports the development of effective strategies for the recovery of secondary indium in Europe (relevant to the EU Directive on waste electrical and electronic equipment), with resulting benefits of decreasing dependency on imports from other countries.
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