The metals critical list

Materials World magazine
4 Jul 2016

Which metals could be in dangerously short supply in five or 10 years’ time? A new method of predicting is billed as an improvement on previous approaches – but will miners take notice? Guy Richards reports

Mining companies know all too well that they are utterly at the mercy of the cyclic rises and falls in commodity prices, and that what could be dug profitably out of the ground a few years ago may now be little more than a static pile of rock. In the face of underwhelming prices for copper and iron ore, for example, the drastic restructuring over the past several months by Glencore, Anglo American and other majors bear witness to this.

Supply and demand is the driving force, of course. Although no-one can confidently predict which metals will be in demand in, say, five years' time — and to the extent that supply cannot meet that demand — organisations such as the British Geological Survey and the European Commission regularly publish lists that identify impending critical shortages. They don't all agree on which metals should be put on this 'critical' list but now a study by researchers at Yale University, USA, has produced what it calls a transparent and flexible tool to provide a more reliable method of gauging shortfalls in supplies.

How it works

The tool is essentially a methodology that places individual metals — 62 in the study — in a 3D 'criticality space', the axes being supply risk (SR), environmental implications (EI) and vulnerability to supply restrictions (VSR). Evaluations of each axis involve a number of criticality-related indicators, the sources of information for which draw upon, for example, material flow studies, lifecycle assessment studies, geological and mineral commodity data and estimates derived from information from industry experts.

All the indicators are weighted equally, although users can apply different weighting if they wish. Uncertainties are estimated for each parameter, and are subsequently used in a Monte Carlo calculation to generate 'uncertainty clouds' for each resulting evaluation.

The researchers say an important aspect of the methodology is that while SR and EI are element-dependent, and thus universal, VSR is not. Rather, it is user-dependent in the sense that an industry that makes little use of a specific element is not vulnerable to its absence, whereas one that relies on the element can be quite vulnerable to supply limitations. As a consequence, no single determination of criticality is appropriate across the board, so they have generated slightly different VSR methodologies for industries, nations and the world.

Like many academic studies, the study is punctuated with caveats and qualifications. For example, the researchers concede that determining the criticality of a metal is very challenging, pointing out that it depends not only on geological abundance, but on factors such as the potential for substitution, the degree to which ore deposits are geopolitically concentrated, the state of mining technology, the amount of regulatory oversight, geopolitical initiatives, governmental instability and economic policy.

They also point out that, although the methodology is appropriate for timescales of five-to-ten years and beyond, the results of their analysis are a snapshot in time, largely because of the inherent delays in obtaining the necessary data, which at the moment is for 2008. However, they add that they are updating this with data for 2012, the most recent year for which satisfactory data is available, and that any revisions to the results are likely to be modest.

What it means

The results show that the limitations for many metals important in emerging electronics technologies (gallium and selenium, for example) are largely those related to SR. Those of the platinum group metals and mercury to EI, and steel-alloying elements (including chromium and niobium) as well as elements used in high-temperature alloys (tungsten and molybdenum, for example) to VSR.

The metals of most concern tend to be those available largely or entirely as by-products — indium, arsenic, thallium and antimony, for example — that are used in small quantities for highly specialised applications and have no effective substitutes.

Explaining the value of the study and its importance to the mining industry, lead author Thomas Graedel, Professor Emeritus of Industrial Ecology at Yale, says, 'Our approach is transparent because all the values used in the analysis are published along with the results, which some other assessments have not done. It is also flexible because users can weight the variables as they deem appropriate.

'For miners, the more critical a metal, the better the opportunity for them. This might also encourage them to do a better job of recovering trace metals of high criticality from their ores.'

Dr Gawen Jenkin, Senior Lecturer of Applied Geology at the University of Leicester, UK, has studied the research, and says, 'It's a good study — rigorous and potentially gets around some of the issues of the other lists — and incorporates environmental factors. But it almost gives the reader too much choice, as they have to decide on the balance between different variables. I suspect many mining companies would just give up and ignore it. Getting the big mining companies to take notice is an issue

'In an ideal world, where everyone works for the environmental benefit of the planet and its population, miners would look at the list and target metals with high criticality for exploration and production, reducing supply risks. In reality, it doesn't work like that — the bottom line for a mining company is to make a profit, something that is particularly challenging at the moment.'

As Jenkin points out, the big mining companies make their profits from major commodities such as gold, diamonds, iron and copper, and in general don't care about most critical metals because global production is small and prices are low, and can fluctuate wildly. He cites the example of tellurium, which is seen as an unremarkable element but is essential for solar panels. It is about as rare in the Earth's crust as gold, yet gold sells for about $1,200/oz, whereas tellurium fetches only about $3/oz. Their respective annual global production come to around 3,000t and 100-500t.

'Tellurium is produced predominantly as a by-product from refining copper ores — there is no mine where it is the primary product, simply because it is not economically viable,' he explains. 'The refiner will eke out a small profit but this is often not passed on to the miner, and in some cases the refiner will even charge a smelter penalty to the miner for the presence of 'deleterious' elements, including tellurium, in ore concentrates. Thus at present there is little financial incentive for the major mining companies to explore for a tellurium deposit, or to bother about increasing the recovery of tellurium from ores they are already mining.'

But, he says, given that a huge amount of effort and energy has already gone into finding, developing and operating an ore deposit for a major commodity, it would make sense to expend a little more to see if any other metals can be extracted from ore that has already been crushed and milled. At the moment, significant amounts of critical metals, including tellurium, are simply discarded to mine tailings.

At the back of all this, he says, is the question — how do we provide sustainable resources of critical elements for the future?

One approach, advocated by the EU, is to develop the by-product recovery route and make it more efficient. As part of this it recently called for proposals under the Horizon 2020 programme for developing new technologies for the enhanced recovery of by-products, including critical raw materials.

To the end, Dr Jenkin and colleagues from the university, as well as researchers elsewhere, are working to develop a technology based on the use of environmentally benign ionic liquids to target specific by-product bearing minerals in an ore concentrate for leaching and recovery. He says that for small to medium mining operations the technology could be implemented at the mine site so that recovered critical metals can be sold direct by the miner, who will therefore gain the full value of the contained by-products and hence have an incentive to recover them.

Ultimately, as the Yale team points out, 'Modern technology is completely dependent on the routine availability of the full spectrum of metals. Tomorrow's technology cannot be predicted with much confidence, especially in the longer term, but it would be quite short-sighed were one or more metals to be depleted to the extent that their use in new technologies could not be confidently assumed.'

All figures reproduced with permission from the Proceedings of the National Academy of Sciences USA.