Responsible sourcing of critical metals

Most critical raw materials, such as the rare-earth elements (REEs), are starting products in long manufacturing supply chains. Unlike most consumers, geoscientists can become involved in responsible sourcing, including best environmental and social practices, because geology is related to environmental impact factors such as energy requirements, resource efficiency, radioactivity and the amount of rock mined. The energy and material inputs and the emissions and waste from mining and processing can be quantified, and studies for REEs show little difference between ‘hard rocks’, such as carbonatites, and easily leachable ion-adsorption clays. The reason is the similarity in the embodied energy in the chemicals used for leaching, dissolution and separation.


References
Laterites are a major resource for Ni. Understanding how these deposits form and how Ni can be extracted from these deposits requires that we understand the mineral phase association and crystal chemistry of Ni. Extended X-ray absorption fine structure (EXAFS) analysis of Ni laterites provides insight on the exact association between nickel (Ni) and the host minerals as well as the metallurgical techniques for optimum extraction of Ni. Here, we characterise discrete mineral grains of oxide Ni laterites from Kalgoorlie and Cerro Matoso with different Ni contents using microfocus scanning EXAFS. We find that in these oxic laterites, Ni is associated with goethite and has no association with Mn-oxides and hydrous Mgsilicates. However, we find variations in the mechanism of phase association with goethite. Cerro Matoso and Kalgoorlie Ni laterites containing 0.88 wt-% Ni and 1.02 wt-% Ni, respectively, suggest structural incorporation as the association between Ni and goethite. Fitting these data indicate progressive transformation from surface complexation to polynuclear surface complexes. However, for Cerro Matoso Ni laterite with 4.6 wt-% Ni, 70 ± 10% Ni is associated with goethite via surface precipitation or extended polynuclear Ni complexes, whereas the remaining 30 ± 10% of the Ni is structural incorporated in the goethite.

Funding
This paper is part of a PhD thesis by Ifeoma M. Ugwu and was sponsored by the Tertiary Education Trust Fund (TETFund) of Nigeria.
mines are sufficient to satisfy world demand. Annual rare earth production, for example, is two orders of magnitude lower than that of copper. Critical metals are defined as eco-nomically important but produced from just a few mines or countries such that they are particularly vulnerable to supply disruption (European Union 2014; British Geological Survey 2015). These critical metals are essential for new 'green' and 'digital' technologies such as renewable energy, state-of-the-art medical technologies, computers and smartphones. Considerable effort has been made in the last few years to increase recycling, diversify supply or find alternatives to these critical metals. Less attention has been paid to responsible sourcing. Yet, it seems common sense that raw materials needed for environmentally-friendly technologies should come from environmentally-friendlyand 'people friendly'sources. How easy is this to achieve for the critical metals? Is it a case of 'beggars can't be choosers' or is responsible sourcing an important factor in determining critical metal supply chains?
The answer is that responsible sourcing of specialist metals has only really been widely considered in the case of conflict minerals. The USA has legislation that requires the source of Ta ('coltan') and of W, Sn and Au from the Great Lakes area of Africa to be certified as conflict-free, and Europe is following suit. The ITRI Tin Supply Chain Initiative assures a chain of custody to prevent conflict minerals entering the supply chain. However, the conflict mineral rules are a 'single issue' measure. Although the Ta capacitors in smartphones are now more likely to be conflict-free, there is no assurance about factors such as environmental protection, workforce well-being, community relations, or mine closure planning.
The main drivers for responsible mining are not yet responsible sourcing initiatives from consumers but the need for mining companies to (1) satisfy investment banks in order to raise capital, (2) gain their social licence to operate from their host communities, and (3) comply with legislation. These drivers and controls apply to critical metals mines (outside China) just as well as to the mainstream commodities. However, there are so many different management and reporting systems that it is still difficult to identify any clear 'responsible mined' mark that could penetrate and influence supply chains.
So is there a role for geology in responsible sourcing? There may well be an opportunity here alongside development of new sources of critical metals. For example, there are a wide range of potential rare earth deposits under development and each has different characteristics. Some are hard rock, high grade; some low grade but with higher proportions of the more sought after, and rarer, heavy REE; others can be easily leached without any need for the usual minerals processing. Life cycle analysis-type approaches can compare environmental characteristics right from the first stages of exploration. Several studies have now been done but results vary widely depending on how far along the supply chain the analysis is taken, how co-products are valued and how the data are collected.