By Liam Hardy
Rare earth elements (REEs) are big business these days, a big and somewhat complex business. Along with lithium and other ‘critical metals’ they’re hitting headlines, liquifying their own markets and striking fear into governments. But why? Here we offer a glancing guide to the mysterious systems that control their geological distribution and the politics surrounding their criticality.
WHAT ON EARTH?
You’ve probably read about the importance of REEs and skimmed articles in the Mining News while dribbling our 9am coffee, but it’s worth knowing what they are and why we’re so excited about them. REE is the group term used to describe the lanthanide group elements and normally yttrium & scandium (as they share similar chemical properties). Figure 1 shows a periodic table with the REEs highlighted.
WHY ON EARTH?
From yttrium based monitors in car fuel tanks, Promethium compound ‘glow-in-the-dark’ emergency signs, and samarium-cobalt magnets used in computer processors and mobile phones, we are currently intertwined with REEs throughout our daily lives, probably without even noticing, a few examples are shown in figure 2.
Your phone might look like a neat shiny box on the outside, but inside, thousands of components whizz and engage with each other to bring you every cute video of a cat playing the piano.
Around 60 different metals are used in a modern mobile phone, not just your common conductive copper and gold for wires, but also a host of more obscure elements from neodymium in the miniature phone speaker magnets, to the lanthanum in your crystal clear and scratch resistant screen.
While we might prize and value our phones, they’d be no use without a decent source of clean energy to charge them up and rare earths play a big part in the capture and supply of wind and solar energy too.
RARE ON EARTH?
So, what’s the fuss about? Just dig some more up?
A brief look at REE abundance worldwide shows there’s more of them combined in the earth’s crust than copper  and, we’re not panicking about copper? (Or are we?).
Well, the term ‘rare’ might not be suitable for their overall abundance of around 40ppm, but it certainly does apply to their distribution. Mineable sources for REEs are few and far between and their chemistry in geological systems is still not well understood so, this makes finding and accessing these resources difficult. On top of this, the amounts needed are so small (<0.1g/device) and the costs of extracting REEs from their host rocks so high, that mining companies are struggling to get REE projects off the ground outside of China.
No problem, we’ll just use Chinese REEs…
In 2012 an estimated 95% of the world’s supply of REE originated in China, this is not only a geological phenomenon, but also an economic and political one. Although massive resources exist worldwide, notably in the Canada, Turkey, America and Australia , China has used its global economic power to fix the market supply and prices, thus undercutting other exploration and extraction projects, making them impossible to finance and operate. While several countries have retained stockpiles (notably the USA) , these have been reserved specifically (and controversially) for military use in times of emergency .
Several researchers and international institutions (including the United Nations) have suggested that gross environmental and human rights issues are attached to the mass production of REE in China. Beijing University, suggests that a 17.1% increase in average water table pH can be seen around ‘in-situ-leaching’ mines and some 32000 deaths can be attributed to controversial mining methods in the south of China . A 2012 UN report argues further to suggest REE mining is the greatest cause of freshwater biodiversity loss and risk to human life facing modern China .
HOW ON EARTH?
We all want a phone, but we don’t like child labour and environmental destruction… Let’s see what we can do about this dilemna. We’ve now started to put our heads together in Europe to normalise our industrial supply (see EU-RARE and SOS RARE), with some €1 billion being put aside as part of Horizon 2020 in the EU, to investigate critical resources here at home (including REEs, lithium and many industrial minerals).
This is great news, where shall we start? It’s not all going to be complicated science jargon is it? Unfortunately for us, yes, the money is being used to fund advanced economics projects, geochemical research, field investigations and hi-tech, hi-definition analysis of known REE deposits to help us to find and target more REE resources in Europe. That doesn’t mean that it can’t be shared though, let’s look at what we’ve learned so far and where we’ve already found REEs…
The cartoon in Figure 4 shows all the common geological environments that EU-Rare and SOS-Rare have been investigating. REEs are known to show an affinity for alkaline igneous intrusions and their associated fluids and weathering products so, exploring these is a great way to kick off.
Magmatic deposits of REEs are normally found within deep crustal peralkaline intrusions that have been either contaminated when melted, or subject to some chemical evolution during cooling. This can cause concentrations of higher field strength elements like Zr, REE, Nb, and Ta in layers or regions of the intrusion
Europe’s biggest alkaline intrusions are found in Greenland (Ilimaussaq), Sweden (Norra Kärr), Portugal (Serra de Monchique) and Romania (Ditrau). These igneous intrusions commonly host pockets of minerals such as eudialyte and monazite which contain REEs, but also radioactive Th, which makes their separation and use as an ore difficult and potentially environmentally risky.
So, with many magmatic ores off the table for their radioactive contents, the most promising new projects for REEs in Europe actually come from supergene (secondary surface formed) deposits associated with the weathering of these intrusions. Deposits such as those in Serra de Monchique in Portugal, where thousands of years of autochthonous weathering have produced deep soil profiles (Figure 7) which preserve the REEs in organic acids and on the surface of clay minerals, but allow Th to be leeched away.
These ‘ion-adsorption type’ deposits (IAD) are responsible for around 40% of the REE mining in Tropical Southern China and are being explored in Madagascar  and the rainforests of Brazil. Surprisingly, they were recently discovered, thousands of miles outside of their predicted tropical range, by a team from the University of Brighton (UK) while working in Portugal .
These IAD soils can theoretically have their REEs stripped out using weak solutions such as ammonium sulfate or even sea water to separate the REEs from the soils . They are thus highly favorable for their lower environmental impacts, but their grade is normally far lower (by around 10x) than in primary igneous sources and more soil needs to be processed for the same amount of REE. This means that, more often than not, these deposits aren’t enriched enough to be profitable.
LET’S JUST RECYCLE WHAT WE’VE GOT?
Oh, we wish we could, really! There’s an estimated 15.6 KG of electronic waste per person in Europe alone waiting to be processed. Unfortunately, every single component in a phone uses a unique and complex collection of alloys that need to be processed individually for their REE content and normally, it costs more to smash up a phone and manually pick apart the pieces than to dig more up, it’s partly an economics issue… It’s partly a global supply Vs demand issue which surrounds and complicates all recycling initiatives.
Until recently the global demand for electronic products (and thus, REEs) centered around America, Europe, Australia, Japan and other developed countries and we’d mined just about enough to maintain that demand.
As of 2015 there were more mobile phones being used in India than in the USA, Japan, Germany and the UK combined. Even if we were to achieve an impossible 100% rate of recycling of old devices, we’d still be some 300,000,000 short of supplying REEs for India’s new market alone . This is before we account for Brazil, Russia and other major developing economies, And that’s just for mobile phones! Recycling, while an important addition to our resources, is sadly never going to meet our ever-expanding requirements.
IS THERE A SIMPLE SOLUTION?
To be honest… Not yet, but we’re working on it! From projects investigating the recycling of mining waste  to ways of extracting REEs without Th , from searching for alternative technologies to tuning the recycling process, there are countless EU and international projects underway as I write. It looks promising, but needs the support of big electronics manufacturers to progress, a commitment from industry to cleaner and more environmentally friendly resources would promote the existing research and save it from stagnating while we burn into forests and pour acid into ancient soils, a bigger commitment from governments to control poorly sourced metals would go even further.
For now, all we can do is keep lobbying industry, demanding cleaner and more ethical products and buying the best we can, keep voicing our concerns for environmental protection and keep pushing the science we’ve already got for all its worth to find a cheaper, more sustainable route to the technology we crave!
|||K. H. Wedepohl, “The composition of the continental crust,” Geochimica et Cosmochimica Acta, vol. 59, no. 7, pp. 1217-1232, 1995.|
|||D. Hoatson, D. Jaireth and Y. Miezitis, “The major rare-earth-element deposits of Australia: Geological setting, exploration, and resources,” Geoscience Australia, Canberra, 2011.|
|||M. Humphries, “Rare Earth Elements: The Global Supply Chain,” Congressional Research Service (USA), 2013.|
|||EPA, “Rare earth elements: A review of production, processing, recycling and associated environmental issues; EPA600/R-12/572,” United States Environmental Protection Agency, 2012.|
|||X. Yang, “China’s ion adsorption rare earth re sources, mining consequences and preservation,” Environmental Development, pp. p.131-136., 2013.|
|||D. Petley, “Global patterns of loss of life from landslides,” Geology G33217.1 , 2012.|
|||E. Marquis, M. P. Smith, G. Estrade and K. Goodenough, “Ion adsorption-type REE deposit associated with the Ambohimirahavavy alkaline complex: potential controls on mineralisation,” Applied Earth Science, vol. 126, no. 2, 2017.|
|||L. Hardy, M. P. Smith and B. Nason, “A novel mechanism for the formation of tropically weathered REE ion adsorption deposits,” Applied Earth Science, vol. 126, no. 2, p. 63, 2017.|
|||V. G. Papangelakis and G. Moldoveanu, “Recovery of rare earth elements from clay minerals,” in ERES2014: 1st European Rare Earth Resources Conference, Milos (Greece), 2014.|
|||ITU, “ICT revolution and remaining gaps,” https://www.itu.int/en/ITU-D/Statistics/Documents/facts/ICTFactsFigures2015.pdf, 2015.|
|||E. Deady, E. Mouchos, K. Goodenough, B. Williamson and F. Wall, “Rare earth elements in karst-bauxites: A novel untapped European resource?,” in ERES2014: 1st European Rare Earth Resources Conference, Milos (Greece), 2014.|
|||A. Schreiber, J. Marx, P. Zapp, J. Hake, D. Voßenkaul and B. Friedrich, “Environmental Impacts of Rare Earth Mining and Separation Based on Eudialyte: A New European Way,” Resources, vol. 5, no. 4, 2016.|
|||K. Toeda, “JASRI,” 2017. [Online]. Available: http://www.spring8.or.jp/en/news_publications/research_highlights/no_56/. [Accessed 10 2017].|
|||Canadian Institute of Mining, “Global use of REE,” 2013. [Online]. Available: http://www.cim.org/en/RareEarth/Home/GlobalUseofREEs. [Accessed 10 2017].|
|||Reuters, “RTXU1EC,” 31 10 2010. [Online]. Available: http://pictures.reuters.com/.|