I should like to conclude my review of the spring meeting of the Yale Criticality Consortium (the Consortium), organized by the Center for Industrial Ecology at the university’s School of Forestry & Environmental Studies, with a look at just one further presentation and, in particular, the research paper with which it is associated.
As a reminder, together with the National Science Foundation, the Consortium has helped fund the Criticality of Metals project at the school’s Center for Industrial Ecology. The research group there has recently completed the assessment of the contemporary criticality for 62 elements. These comprise the metals of the periodic table, together with metalloids and some other elements. The methodology created to quantify the degree of criticality comprises three dimensions – supply risk, environmental implications and vulnerability to supply restriction. This provides a structural, and robust, approach that “reflects the multifaceted factors influencing the availability of metals in the 21st century.”
National Level Methodology
The presentation, “Platinum-group metal cycles, companionality, and substitutability”, was given and the research paper, “By-product metals are technologically essential but have problematic supply ” was “lead authored” by Nedal Nassar, then one of the stalwarts of the Center’s criticality research group. (Dr Nassar has since been appointed Physical Scientist at the U.S. Geological Survey down in Reston, Virginia where, I am sure, he will continue to exercise his exceptional intellect in solving a stream of knotty problems in the field of the material flows of critical metals!) Dr Nassar’s presentation provided us with excellent illustrations of some of the fascinating findings described in his research paper. I shall, in turn, try to describe some of these.
Companionality
All of us involved with minor metals are, often, too well aware, that many are by-products, or “companion” metals, recovered during the processing of other “major” or “host” metals, for example, copper, iron, lead or tin. Having already assessed the contemporary criticality for 62 metals and metalloids, Dr Nassar and his colleagues then turned their attention to assessing the “companionality” of these same elements, with companionality being described as “the degree to which a metal is obtained largely or entirely as a by-product of one or more host metals from geologic ores.”
While the results of this research may not necessarily come as a surprise to us, to anybody outside the business, they should, if nothing else, both reinforce the importance of the market in which we are involved and illustrate very effectively its complexity. Of the 62 different metals, 61% (38 of 62) have companionality greater than 50%. Essentially, what this means is that nearly two thirds of all these metals have the majority of their global production obtained as a companion metal. (I should note, however, that, while the results are based on 2008 production data, and, as Dr Nassar describes it, represent a “snapshot in time”, even having reviewed more recent data, he and his colleagues saw only “modest revisions”.)
The periodic table of companionality on a global basis for 2008
Metals that are mainly produced as hosts appear in blue, and those that are mainly produced as companions are in red. As Dr Nassar further points out, included in the companion metals groupings in the periodic table are a number of metals increasingly being used in:
- Electronic and solar energy applications (Ga, Ge, In, Se and Te)
- Alloys in high-temperature applications (Co, Hf and Re)
- Wind energy, lighting and medical imaging (Dy, Lu, Nd, Pr and Tb)
This leads him to note as the “central point” that “many of the metals so important to modern technology are available mostly or completely as companions.” And that “[i]n many cases, their most likely substitutes are elements with similar physical and chemical properties, elements that are companions as well.”
And, as Dr Nassar pointed out to me subsequently, interestingly, the best substitutes are often elements that are co-produced with the elements of interest (e.g., Ni can substitute for Pd in multi-layer ceramic capacitors; Se and Te in pigments, rubber, and free-machining alloys; and the rare earth elements for each other in a number of applications). This, he said, is not surprising given that elements that are found in the same mineral deposits often have similar chemical and physical properties and are, thus, likely to substitute for one another in commercial applications.
As if to compound further these companion metals’ dependence on their host metals – with all that implies regarding the speed and ease of meeting demand with supply, and pricing (in)elasticity – the results also show that “although there are a few companion metals associated with multiple hosts, many more are primarily (that is, most of their primary production) associated with only one or two hosts. Similarly, although host metals may be hosts to multiple companions, they are often the principal host (that is, supply the majority of a companion’s primary production) for only a few companions.
The wheel of companionality
The principal host metals form the inner circle. Companion elements appear in the outer circle at distances proportional to the percentage of their primary production (from 100 to 0%) that originates with the host metal indicated. The companion elements in the white region of the outer circle are elements for which the percentage of their production that originates with the host metal indicated has not been determined.
Another Way to Measure Companionality
Whilst companionality can be measured using a model that addresses quantities produced, as Dr Nassar explained to us in his presentation, it can also, and may more precisely, be defined using an economic evaluation model. In such a model, companionality describes the degree to which the revenue contribution of a specific metal covers the cost of sales. Thus a metal that covers the entire cost of sales is “economically independent of the other metals,” while a metal that covers only a small portion of the cost of sales is (proportionally) economically dependent on the other metals for profitable recovery.
This approach he illustrated very clearly and succinctly for us with an analysis of the economics of five different PGM-producing mines in five different countries that quantified the host-companion relationship.
Revenue contribution by metal (in descending order) for five mines producing platinum group elements.
In the above illustration, the red line marks the point at which revenues cover the cost of sales, thus defining dependency of the metals. For the Canadian and U.S. mines, costs of sales exceed revenues, as indicated by the red number at the right.
With the host being the metal with the largest economic contribution and the companions those with smaller economic contributions, it can be seen that, in 2008, for the South African and Zimbabwean mines platinum was the largest revenue contributor and, hence, the host in both. In Norilsk’s Russian mine, nickel was the host. And both the U.S. and Canadian mines ran a deficit that year!
I believe, however, that it is particularly important to note, as pointed out by Dr Nassar subsequently, that when the economic companionality analysis was done for the platinum group metals, the data was obtained for the vast majority of operations, covering nearly all global production. However, such data are often absent for most minor metals. Indeed, data such as potential recovery rates and price elasticity of supply for most minor metals are often not known (at least to outsiders) and so the responsiveness of their supply to changes in demand is difficult to anticipate.
There were a number of other fascinating results discussed in the research paper, and which Dr Nassar also addressed in his presentation. Two such results which cannot be addressed here were: 1) the importance of understanding the dynamic nature of companionality – “changes in production in different countries or in ore deposits within countries may change over time ” and, indeed, do; and 2) since 18 of these 38 elements having companionality greater than 50% (“including such technologically essential elements such as germanium, terbium, and dysprosium”) can be “further characterized as having geopolitically concentrated production and extremely low rates of end-of-life recycling”, the issue of supply constraints from these particular metals should not be overlooked.
I can only exhort you to Dr Nassar’s paper (dated April 3, 2015) in Science Advances at http://advances.sciencemag.org/content/1/3/ e1400180. It is excellent.
© 2015 Tom Butcher, MMTA Sustainability Working Group
