By Claire Asher
- Green energy technology growth (especially wind, solar and hydropower, along with electric vehicles) is crucial if the world is to meet Paris climate agreement goals. But these green solutions rely on technology-critical elements (TCEs), whose production and disposal can be environmentally harmful.
- Mining and processing of TCEs requires huge amounts of energy. Mines use gigantic quantities of fresh water; can drive large-scale land-use change; and pollute air, soil and water — threatening biodiversity. TCEs may also become pollutants themselves when they are disposed of as waste.
- We know relatively little about what happens to TCEs after manufacture and disposal, but trace levels of many critical elements have been detected in urban air pollution, waterways and ice cores. Also of concern: Rare-earth elements have been detected in the urine of mine workers in China.
- Green mining technologies and new recycling methods may reduce the impacts of TCE production. Plant- and microbe-based remediation can extract TCEs from waste and contaminated soil. But experts say a circular economy and changes at the product design stage could be key solutions.
The rapid development of renewable energy technologies — including wind, solar and hydropower, and the commercial success of hybrid and fully electric vehicles — are helping put the world on track to achieve a net-zero carbon economy and meet Paris climate agreement targets.
Yet these positive advances rely on a small number of “technology-critical elements,” or TCEs, rare materials whose mining, production and disposal are linked to myriad environmental problems, ranging from large-scale energy and water consumption, to serious soil, water and air pollution.
These 30 to 35 TCEs are essential to computers, consumer electronics, solar cells, wind turbines, electric cars, plus military and medical applications.
They include the platinum family of precious metals, rare-earth elements such as neodymium and scandium, and other metals such as cobalt, lithium and tungsten. What this diverse grouping has in common isn’t some shared chemistry, but rather its technological necessity and geopolitical scarcity. They especially share indispensable characteristics — the ability to store energy or form permanent magnets, for example — that make them essential for technologies that could help meet the Paris goal of limiting global warming to 2° Celsius (3.6° Fahrenheit) above pre-industrial levels.
But the reliance on TCEs to make high-tech green products puts these elements at risk of contributing to the breach of the nine planetary boundaries that demarcate habitable conditions on Earth.
Mineral extraction consumes gigantic quantities of fresh water and can pollute soil, water and air, while vast open-pit mines drive large-scale land-use change, cause deforestation and threaten biodiversity. Mining, processing and transporting minerals also uses enormous amounts of energy, generating greenhouse gas emissions. In the end, the TCEs themselves may become pollutants when released back into the environment as emissions or waste.
In the urgent rush to curb climate change, the risks posed by TCEs are being little addressed at present. But making their production truly green, and recycling them via a circular economy, is vital to Earth’s sustainable future.
Defining the TCE problem
Although most aren’t rare, TCEs are seldom found in large deposits, so they’re largely inaccessible to most living organisms. By extracting, using and discarding them widely, we are introducing them into new environments, with unknown consequences. That’s one reason TCEs are of emerging concern to scientists as novel chemical entities and potentially harmful pollutants.
Global production and release of all novel chemical entities — each posing different potential environmental threats — already exceeds the global capacity for safe assessment and monitoring, putting us outside the safe Earth operating zone for this poorly understood planetary boundary.
But even so, to meet the Paris targets, green technology implementation needs to ramp up substantially. By 2050, the global electric vehicle fleet must expand from around 1.2 million cars today to more than 950 million. Solar energy generating capacity needs to increase from 220 gigawatts (GW) to more than 7,000 GW. Total rechargeable battery capacity — needed for solar installations and electric cars — must increase from 0.5 gigawatt-hours (GWh) to more than 12,000 GWh.
Consequentially, demand for TCEs like cobalt, lithium, neodymium and dysprosium will soar; currently the market for these substances is growing by 5% annually. By 2050, demand for lithium and cobalt could increase as much as 500%, requiring 3 billion tons of minerals extracted. Rare-earth elements needed for wind turbines could see demand increase by a factor of 26.
Mining activities must surge to keep up with this need, with major impacts on the natural world. Extracting TCEs often involves clearing forest, removing mass quantities of soil and rock, and using water-polluting acids to isolate valuable elements. Devastating effects are multiplied when ores are located in highly biodiverse tropical regions, as is happening in the Venezuelan Amazon, or the Democratic Republic of the Congo, where coltan mining by armed militias has put the critically endangered Grauer’s gorilla (Gorilla beringei graueri) at high risk.
Perhaps the best-studied example of TCE mining impacts is in the Bayan’obo district of Inner Mongolia, an autonomous region of China that supplies half the world’s rare-earth elements. For decades, the Bayan’obo open-pit iron mine has also extracted niobium, lanthanum and neodymium for smartphones, electric cars and wind turbines, with local communities and ecosystems paying a heavy price.
Each metric ton of rare-earth element mined there necessitates clearing 300 square meters (3,230 square feet) of vegetation and topsoil, and releases 1,000 metric tons of contaminated wastewater and 2,000 metric tons of solid or liquid waste tailings.
Today, elevated levels of rare-earth elements are being detected in wastewater, rivers and groundwater near mining and processing plants. Alarmingly, they’ve also been detected in urine samples of people living in Bayan’obo.
Many TCEs have well-documented toxic effects at high concentrations, putting the workers mining, processing and recycling these minerals at risk. These risks are compounded because many TCE mines are in less-industrialized nations with weak environmental and health regulations. Globally, hundreds of thousands of laborers are exposed to rare-earth elements, with occupational exposure associated with numerous possible health impacts.
In fact, the huge environmental and human health cost of mining TCEs is one factor making them geopolitically scarce. “The developed world has basically outsourced its raw materials to the developing world. It’s cheaper to produce them there and that is fundamentally because regulations are generally more lax,” explained Murray Hitzman, director of the Irish Centre for Research in Applied Geosciences (iCRAG) and an expert on mineral extraction.
A prime example of TCE-related human rights issues: cobalt mining in the Democratic Republic of Congo. Cobalt is economically important for the DRC: 10 million to 12 million people depend directly or indirectly on its mining for their livelihoods. But cobalt miners there are exposed to dangerous and noxious conditions in mines and build up elevated levels of toxic metals in their bodies. A 2016 Amnesty International report found that 15% of cobalt in the DRC comes from hand-dug, artisanal mines, where conditions are often even more hazardous and child labor common.
How dangerous are TCEs? ‘More questions than answers’
While we know some things about TCEs and their production risks, we know little about what happens to them after manufacture and disposal. This is partly because their meteoric rise to global importance has left scientists and policymakers playing catch-up, and partly because of the “ultra-trace” concentrations in which they’re used, making tracking challenging.
One exception: the platinum-group elements (PGEs), widely used since the 1970s to reduce vehicle exhaust emissions. PGEs are essential to catalytic converters, which have been required for new motor vehicles in the U.S., Canada, the EU and Australia for decades. These PGEs, which include palladium, platinum and rhodium, react with and remove toxic gases like carbon monoxide and nitrogen oxide from exhausts. But modern gasoline-powered cars now emit PGEs as a byproduct. These fine particulates disperse and can travel large distances in the atmosphere before settling to earth, where they can be washed away by rainwater, entering rivers, estuaries and oceans.
Platinum-group particles are now found at elevated levels in urban air, road dust, roadside soil and vegetation, and even in remote sites far from human activity. One study detected a rise in PGE levels on the Greenland ice sheet after 1990, and estimated that PGEs were being deposited there at 600 times the background rate.
Most other TCEs have not yet become as ubiquitous as the platinum family, with their environmental pathways likely quite different. Take consumer electronics, for example, which contain tiny quantities of cobalt, lithium, neodymium, indium, niobium and other TCEs, embedded with other materials like silicon and plastic. These TCEs may be released as aerosol particulates when waste is crushed or burned, or leach from landfills into soil and groundwater; but we simply don’t know for sure as the research hasn’t been done.
Research led by Brian Berkowitz and Ishai Dror at Israel’s Weizmann Institute of Science suggests rare-earth elements trapped inside e-waste are relatively immobile, and if they make their way into soil, they’re likely to stay put. In lab experiments on soil, rare-earth elements “are not very mobile — you have to work really hard to get them to move,” Berkowitz said, adding, “the good news is that they really don’t pollute the groundwater, the bad news is they’re in the soil forever.”
Some industries will be bigger sources of rare-earth element pollution than others. Along Germany’s heavily industrialized Rhine River, for example, potentially toxic levels of gadolinium, lanthanum and samarium were detected downstream of an industrial effluent pipe, although the exact source remains unclear. A 2019 study found elevated levels of rare-earth elements, including praseodymium, neodymium, dysprosium and holmium in the Pearl River Estuary in China — partly attributable to upstream e-waste recycling facilities.
The word trace is key here: Away from mines and recycling facilities, rare-earth elements are released at extremely low concentrations — so low that scientists are still figuring out how to accurately measure them and determine impacts. Most are not currently environmentally monitored or included in regulations, and Dror says he has yet to find “a smoking gun of huge contaminants from the [domestic] use of TCEs.” At these low levels, TCEs aren’t likely to cause acute effects on plants and animals, but long-term exposure could bring chronic effects.
Those impacts may not be known any time soon: “There is a lack of incentive at the moment and a lack of funding,” to study the chronic effects of TCE pollution, said Sebastien Rauch, professor of urban environments and systems at Chalmers University of Technology in Sweden. Important research into long-term toxicity simply isn’t being done.
That doesn’t mean there isn’t risk. For example, in their natural forms, platinum elements are inert, and so their use in catalytic converters had long been assumed not to be hazardous. However, tiny particles of PGEs found in road dust can be transformed into their active, toxic forms if dissolved in rainwater. “We know, for instance, that platinum binds to DNA [but] is that important, if it’s at a low concentration? We don’t know,” said Rauch.
At very low concentrations, some rare-earth elements can even be beneficial to plant growth. In China, this discovery prompted the additions of rare-earth mixtures to fertilizers. But evidence also shows that platinum-group and rare-earth elements can bioaccumulate in the tissues of living organisms, and so could reach potentially toxic levels with long exposure. They may also build up in the food chain, where bioaccumulation could pose a risk to humans or top predators.
Perhaps most crucially, we know nothing yet about how TCEs interact with each other, or with other pollutants, to produce synergistic effects. “I think there are more questions than answers, at the moment,” Rauch said.
Making green tech supply chains sustainable
Finding new sources of TCEs is a national security priority for the U.S. and EU as they seek to protect their global supply chains against natural, socioeconomic and political disruptions. But that search is also an opportunity to improve environmental outcomes. Finding TCE sources in less-industrialized nations could, for example, be a first step toward bringing more stringent regulation to green tech industries and addressing environmental justice issues, while also reducing the global transport footprint.
“DRC is without a doubt the best endowed place for cobalt on the planet that we know of; I’ve been looking for 24 years for another place and haven’t found it yet,” said Hitzman. “But is there cobalt elsewhere? Yes, absolutely. And are there amounts that could be minable? Absolutely!”
The U.S. Geological Survey, in collaboration with Geoscience Australia and the Geological Survey of Canada, recently launched a mapping initiative to locate new deposits of TCEs, including cobalt. A recent British Geological Survey study identified more than 500 cobalt-bearing sites in Europe.
The ocean could also provide a potential source of critical elements. The International Seabed Authority is currently drawing up regulations to govern oceanic mineral extraction, but scientists are fiercely divided on whether breaching this new frontier will bring about a new mining panacea, or spell environmental disaster. The Clarion-Clipperton Zone of the Pacific Ocean is covered in polymetallic nodules rich in cobalt and other valuable metals, but is also home to extraordinarily rare deep-sea creatures and ecosystems we’ve barely begun to understand.
Replace, reuse, recycle
One potential TCE solution: For some high-tech applications, TCEs could be replaced with more readily available materials, mined in a more environmentally friendly way. For instance, a promising replacement for lithium-ion batteries —found today in everything from smartphones to electric vehicles — could be sodium-ion batteries; sodium is an abundant mineral extractable from rock salt.
For TCEs that can’t be switched out with abundant eco-friendly alternatives, there are two main avenues to improved sustainability: Diminish mining impacts, while also reducing the demand for mining by recovering TCEs from waste. Remarkably, the richest potential source for TCEs may be mine waste itself, and techniques for extracting these elements from tailings are under development.
“Greater vigilance of waste management from mining sites, particularly tailings produced by mineral processing,” is needed for a smooth transition to a low-carbon circular economy, said Saleem Ali, professor of energy and the environment at the University of Delaware in the United States.
When it comes to recycling, platinum-group elements lead the way: One-quarter of the world’s supply of PGEs now comes from recycled catalytic converters — but that’s quite low-hanging fruit. Catalytic converters contain relatively large amounts of platinum, palladium and rhodium, and are found on all modern gasoline-powered autos, making dedicated recycling operations financially viable.
Lithium batteries may also be suitable for dedicated recycling, though the technology doesn’t yet exist. Future demand for lithium-ion batteries is predicted to outpace global production, even as the first generation of fully electric vehicles reaches the end of their battery lifespan. Pressure is mounting, therefore, to “mine” those dead batteries rather than send them to landfills. In 2017, NGOs and private companies formed the Global Battery Alliance, aiming for a sustainable battery value chain by 2030. Major EU grants are currently focused on developing lithium-ion recycling technologies.
By contrast, recycling trace amounts of rare-earth elements found in old smartphones and computers poses a fundamentally different, and formidable, challenge. Presently, “we don’t have that technology,” said Hitzman. “The market is not demanding that we build appliances, devices [and other] things we can take apart. In fact, it’s quite the opposite: We design things that are easy to throw away.”
In future, urban mining — extracting raw materials like TCEs from mixed urban landfills — may be possible. That’s “a brilliant idea, but it’s killed by an ugly fact,” said Berkowitz: the quantities are generally too low and too dispersed to be economically viable. “We took containers of ground-up motherboards and subjected them to all kinds of acids … and you extract extremely low concentrations.”
However, two types of biological solutions could provide an answer and are attracting attention. Bioleaching uses microbes to extract valuable minerals, while phytomining relies on plants capable of accumulating metals in their tissues to extract metals from waste or contaminated land. Both methods could one day remove valuable TCEs from waste, using little energy and without corrosive chemicals. In one case, for example, growing the fern Dicranopteris linearis on mine tailings extracted 74% of the rare-earth elements. Such techniques offer a tantalizing glimpse of a hopeful future for TCE recycling.
There are many new technological advances making mining less environmentally destructive. Some mines, for example, are now fueled partly by renewable energy, reducing climate impacts, while new extraction techniques are available that use less water and fewer harmful chemicals.
Mining will “never have zero impact, because you disturb ground to mine [but] we do have much better and safer technologies. And if you spend the money you can do mining with very little impact,” explained Hitzman. The catch: green mining can be expensive and is presently only economically viable for the highest-quality mineral deposits.
Some EU countries have implemented e-waste recycling schemes to prevent electronic devices ending up in landfills. German retailers, for instance, are obliged to take back old devices when a customer buys a new one. Product lifespan policies like this, which extend the responsibility of proper disposal to the producer, can also create incentives to improve product design to allow for easier recycling.
Sunday Leonard, program management officer for the Scientific and Technical Advisory Panel to the Global Environment Facility, believes policymakers should agree on common goals for the global use and recycling of TCEs. International agreements do “play a significant role” in environmental protection, Leonard added, but “apart from the Montreal Protocol, which has moved forward in helping the ozone layer heal, the rest are yet” to achieve improvements.
In 2019, the World Bank launched its Climate-Smart Mining Initiative, which aims to help resource-rich developing countries benefit from demand for their valuable natural resources, while ensuring the mining sector is regulated to minimize its environmental footprint.
To achieve such comprehensive goals, Leonard says the international community will need to bring together TCE stakeholders across the life cycle to map environmental impacts, assess capacity development needs, and explore alternative livelihoods. For example, “We need to create social safety nets for [artisanal miners] so that they can find alternative livelihoods,” he advised.
A cradle-to-grave systems approach
TCEs are already so diversified in their uses and widespread — having many divergent environmental, economic and social impacts due to extraction, processing and waste disposal — that experts argue that a “systems-thinking” approach is the single best way to achieve workable solutions.
“If you have a good mapping of all of the impacts, then you can think of the best leverage points on how you design your product,” said Leonard. “Of course, there’s going to be trade-offs, but [the aim is] to minimize negative impacts and enhance positive impacts.”
A circular economy, cradle-to-grave, systems approach most certainly requires an end to planned obsolescence — particularly for consumer electronics.
At present, manufacturers make it extremely difficult for users to open and repair devices, with consumers prompted to replace smartphones and computers long before the end of their life spans. The answer: Product redesign to facilitate a circular economy, focused on making products more durable, easier to repair, and easier to break down into recyclable components. “Right to repair” policies, requiring manufacturers to make repairable products, are already gaining traction in the U.S. and Europe. But the application of a circular economy must go further with TCEs.
“We have not produced half of the electric cars that we need to produce in the future. We have not designed half of the wind turbines that we need, the defense systems, and so on,” said Leonard. With that in mind “we have the opportunity to come together and redesign.”
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