The reserves of some rare earth minerals used in electronics, medical equipment and renewable energy could run out in less than 100 years.
Rare earth minerals are naturally occurring resources, which cannot be recreated or replaced. Some are present in only very small quantities in the Earth’s crust. They were created when the extreme heat and pressure conditions produced by a star’s evolution pushed atoms together to create elements. When a star’s core collapses, it explodes as a supernova.
They accumulated over time as stars exploded and the elements fell to Earth. “Planets such as the Earth are made from the remnants of old, dead stars, and the products of star explosions like supernovae, all gravitating together; the Earth and everything on it, including ourselves, are made of stardust,” says Elisabeth Ratcliffe at the Royal Society of Chemistry.
There are five very rare earth minerals used in technology we take for granted today. They are tantalum, silver, lithium, gallium and indium.
Some minerals are only present in very tiny quantities. Many are used in today’s electronics devices, such as smartphones, and, increasingly, in renewable energy products such as solar panels and the batteries for electric vehicles (EVs). “They are created geologically and there is nothing that we can do, at the moment, in the lab to recreate them. The current reserves for a lot of these elements at the moment are quite limited,” Ratcliffe explains.
Tantalum (Ta) is found in tantalite ores, principally columbite-tantalite. It was discovered in the 18th century, but industrial mining only began in the 1920s. The heavy metal is extremely tough. It has a high melting point of 3,017°C and a high corrosion resistance that is the same as that of glass. It can withstand chemical attack at up to 150°C, is stable at room temperature and is also extremely ductile: it can be drawn into a thin, tough and pliable wire. It can also be rolled into a very thin plate in its cold state without the need for annealing, a heat treatment that can alter a material’s chemical properties to make it workable.
Today, its energy-storing capability is used in electronic capacitors in computers and mobile phones. It has a low failure rate, so it is used in automotive and aerospace electronics, atomic energy and wind turbines. It does not react with fluids in the body so it can be used in medical implants, including bone implants and pacemakers.
Silver (Ag) is also used in small electronic components. “It is naturally anti-bacterial, so it has been proposed for use in wound dressing,” says Ratcliffe.
Lithium (Li) is a soft, lightweight metal. It has a low melting point and a high boiling point. It is ubiquitous in batteries for electronic devices, from laptop computers to phones, yet is estimated to take up just 0.0007 per cent of the Earth’s crust.
Its energy-storage capabilities and light weight have made it the dominant choice for battery technology in EVs. Forbes reports that between 2019 and 2025, demand for lithium will increase five-fold to reach 1.3 million tonnes of lithium carbonate equivalent.
Lithium has also been found to target the central nervous system, strengthening nerve connections to boost the release of mood-balancing chemicals in the treatment of bipolar disorders and depression.
Medical research uses lithium and gallium (Ga) in some cancer treatments where metal atoms in drug molecules may be used as a catalyst in the synthesis of a drug to measure the reaction.
In liquid form, gallium is also used for displays, screens and solar panels. The metal has a low melting point but has a high boiling point (2,204°C). It is used in gallium arsenide (GaAs) and gallium nitride (GaN) compounds in semiconductors, for its heat-transfer and cooling properties.
Indium (In) is transparent, conducts electricity and adheres well to glass. It is used in flat-panel displays, high-brightness LEDs and photovoltaic technologies, including solar panels.
Gallium and indium are extracted from bauxite, zinc, tin and silver ores. The environmental impacts of mining and the cost of production may limit the availability of these resources and the potential to extract them, says David Merriman of Roskill, an industry research consultancy. In addition to water and energy used in mining the deposits, the chemical processes to extract pure metals from metal ore are carbon-intensive.
While no one is extracting rare elements on a large scale, some minerals are being extracted through recycling. Electrical cables, for example, can be split into copper chips and plastic chips for recycling. Gold and metals like aluminium can be recycled effectively and reused but the rarest elements are not being recycled. The Royal Society of Chemistry is advocating ‘reduce, reuse, recycle’.
Although recycling incurs a cost in terms of energy use and greenhouse emissions, it is still less than for initial mining. “We can start by using less, then extend the lifetime of products and recycling is actually the last resort,” says Ratcliffe. “Everything has an energy cost, so we will need to do two things: decrease consumption and decrease our dependence on some of these elements by using others – but it’s important to remember the special properties they have, which is the reason we are using these elements in the first place.”
The scarcity and cost of extracting these rare earth elements is driving a tranche of research into alternatives.
One of the principal areas for research is in graphene. This carbon is a single layer of atoms arranged in a hexagonal lattice. The strong, lightweight, thin substance conducts electricity, is a thermal conductor and is transparent.
For touchscreens, for example, it has many of the same conducting properties as indium, although currently it cannot be produced in sheets sufficient for use on large areas.
A team of researchers from University College London and the Chinese Academy of Sciences used graphene laminate films to design a supercapacitor that will charge EVs quickly and with greater power densities than conventional fast-charging technologies.
The project used graphene laminate films and boosted energy density by altering the membranes’ pore sizes to match the size of electrolyte ions. The result was an increase in volumetric energy density from 5-8 watt-hours per litre (Wh/L) to 88.1Wh/L. The supercapacitor also exceeded a conventional battery by retaining 97.0 per cent of the energy capacity after 5,000 cycles.
It is proposed that such a supercapacitor could be paired with lithium batteries in EVs to store a large amount of energy in a compact system for a quick charge and controlled output. The adoption relies on sufficient quantities of commercially priced graphene, which is not currently feasible.
An alternative to lithium-ion batteries is lithium-sulfur batteries. They can hold up to five times more energy – reducing battery weight – and would be cheaper to produce as sulfur is more readily available.
The problem for developers is that the batteries degrade quickly with each charge cycle. An international team led by researchers at Monash University in Australia have altered the balance of carbon and binder to allow the sulfur more space to accommodate changes in structure during charging, which relieves stress and allows it to maintain its integrity. A patent for the manufacturing process has been approved and Dr Mahdokht Shaibani at the Department of Mechanical and Aerospace Engineering, Monash University expects commercial availability within four years. Prototypes are being tested in electric aircraft by Abingdon-based Oxis Energy and in cars and solar grids in Australia.