Setting the REE Industry-Specific Criteria and their Significant Role in the Viability of Rare Earth Underground Mining Projects

To evaluate the feasibility of a future underground mining operation is a complex problem in itself, with several different parameters to be accounted for and evaluated to secure investment decisions over the viability of any potential underground mining project. This procedure gets even more complicated when it comes to exploiting rare earth deposits. Various concerns are expressed regarding the environmental impacts that an underground mining operation may cause due to the radioactivity of the rare earth elements during mining and in waste treatment. Furthermore, the fragile market and the diversified supply and demand of the different rare earth elements can significantly affect the viability of such a venture, among other factors. This paper deals with the definition and classification of the specific criteria that govern the REE mining industry. Moreover, a thorough investigation is made of how these criteria can determine not only the selection of the underground mining method to be applied, but also of the impact that they may have to the overall feasibility of any given potential project.

This paper was presented by George Barakos at the conference of the Society of Mining Professors (SOMP) on 24th June 2015 at the TU Bergakademie Freiberg, Germany.

Introduction

The continuously growing demand for rare earth elements (REEs), in combination with the market crisis of 2009 and the price spike of 2011, have initiated a treasure hunt for new rare earth deposits all over the world in recent years. This has led to the discovery of numerous rare earth deposits that could consequently evolve into potential surface or underground mining projects.

The history of REE mining can be classified into three periods:

1. Monazite-placers,
2. Mountain Pass and
3. Chinese era.

China has been leading the market over the last 30 years due to the geological advantage of holding more than half of the world’s known REE reserves that are economically advantageous as well, in terms of mine development. China has also developed the intellectual capital needed for the development of the REE industry which the rest of the world is still lacking and it will take years until the Chinese skills level can be reached, let alone that in underground mining operations the level of expertise demanded will be even higher. Yet, a fourth, new era may begin and new rare earth projects may be developed.

Nevertheless, there are some special issues that govern rare earths, unlike other common ores, such as the environmental consequences that may result from their mining and processing. China represents the most typical example of this, as lax environmental laws and standards have led to extended pollution of the areas that rare earth mines develop (1,2).

Furthermore, the balance between the demand and the natural abundance of the individual rare earth elements in the ores is a significant issue for the industry, known as the balance problem and it can be considered more important than the availability of rare earth resources itself (3). The fragile REE-market, in combination with the social arguments and insufficient legislation are equally important factors for the REE industry.

All these criteria combined do not only affect the feasibility of mining operations in terms of selecting a proper mining method, but can also determine the overall viability of potential rare earth underground mining projects.

Traditional Evaluation Methods and Standardized Criteria in the Global Mining Industry

Selecting the appropriate mining method requires the consideration of many single factors. Such a procedure is even more sophisticated when it is applied to underground mining operations. Several approaches, both linguistic and numerical, have been presented in the past regarding the selection process of mining methods for common ores. Most of the schemes focus on determining the proper underground mining method, since there are so many possible choices and the process is far more complicated (4).

Boshkov and Wright (5) introduced one of the first mining method selection tools, developed specifically for underground mining operations. This tool was based on a qualitative classification system using general descriptions of the thickness, dip and strength of the ore. Morrison (6) took another approach by dividing the underground mining methods into three basic groups: (a) rigid pillar support, (b) controlled subsidence, and (c) caving. By considering ore width, support type and strain energy accumulation, this tool is based on choosing one method over another to the final selection.

Laubscher (7) presented a selection procedure based on a rock mass classification system of his own for an appropriate mass underground mining method. He primarily focused on cavability, comparing block caving to stoping. Nicholas (8) came up with a quantitative analysis via a numerical ranking of the suitability of mining methods to given characteristics. By adding up the values of each method, engineers choose two or three mining methods that have the highest overall positive ranking in a given case and then analyze them economically to come to a final decision. Hartman (9) brought out a qualitative method, similar to that proposed by Boshkov and Wright. He put forward a selection chart based on the geometry of the deposit and the ground conditions of the ore zone.

Miller-Tait et al. (10) presented a modified scheme of Nicholas’ system and developed the UBC mining method selection tool that represents typical Canadian mining design practices. Many researchers in the recent years (11, 12, 13) have also introduced numerical methods and methodologies considering multi-decision making tools and analytical hierarchical processes. Finally, Hartman and Mutmansky (14) proposed a total of 36 criteria classified in six main groups to analyze the Underground Mining Method Selection (UMMS) problem in details.
However, none of these approaches has taken into consideration the special boundary conditions that govern mining operations on rare earth element deposits. Thus a need is created to develop a new overall assessment tool for rare earth mining projects in order to add the REE-Industry specific criteria and evaluate them together with the standardized specifications that determine the viability of such investments.

REE-Mining Industry Specific Criteria

A first description has been made of the special factors that govern rare earth mining in general. In deeper analysis, the REE-Mining Industry specific criteria could be divided into four major subcategories:

1. Economic,
2. environmental,
3. sociopolitical and
4. technical.

All of the above characteristics, either individually or combined, can predetermine the mining method to be applied as well as the viability of any future rare earth underground mining project and the according investment decisions to be made.

Economic Criteria

Besides the usual economical evaluations that are made for all underground mining case studies, rare earths implement some special boundary conditions as well. The small and opaque market of REEs deters big mining companies from getting involved, so China currently holds more than 90 % of the global production. The rest of the world is dependent on the Chinese government’s export policies and despite the calls to create a centralized Rare Earth Element Exchange, the situation remains unclear.

Notwithstanding the fact that the prices are stable for the time being, the crisis of 2009, the price spike of 2011and the rapid decline in prices again indicate the fragility of the REE market. It is difficult to estimate future REE prices and therefore, future cash flows for the economic evaluation of REE projects.

Parallel to the exploration burst, fruitful efforts have been made to bring new non-Chinese resources into production; Mountain Pass mine in the USA and the Mount Weld mine in Australia have already launched operations. Nevertheless, these projects are not enough to balance the supply needs for rare earths and more mining projects have to get on track. But the main issue regards the viability of such investments, since there are no reliable estimates on the costs of mining and processing operations for rare earths, let alone the fact that rare earth underground mining procedures can be more costly. It should be mentioned that there are no current active rare earth underground mining projects to provide knowledge and experience, whilst just a few potential underground mines are about to being launched. But even if this knowledge existed, the challenge of Chinese low-cost labor and manipulation of the global market and prices would still exist, thus posing barriers difficult to cross.

Illegal mining and smuggling of rare earths is also an issue of major importance, especially in China, as it keeps prices low and depletes resources more quickly, thus causing supply problems for the Chinese industry. China’s tolerance of illegal mining is quickly diminishing and the government is taking actions to deal with this issue by clamping down on illegal mining and reducing export quotas.

The global annual production of rare earth elements for the year 2014 was estimated at 110,000 t according to the United States Geological Survey (15), although these numbers are not accurate. In any case, these figures do not give any indication of the supply of individual rare earth elements. Admittedly, REEs are not present in equal amounts in the REE ores. Following the rule of the increasing atomic number Z, they are generally divided into the Light Rare Earth Elements (LREEs) and the Heavy Rare Earth Elements (HREEs) with the HREEs being much less abundant. Another classification of rare earth elements divides them into critical and non-critical REEs, taking into consideration the perspective of their individual supply and demand, as well as the cruciality of their applications and end uses (Figure 1).

A perfect match between demand and supply of REEs would be ideal, yet the existing balance problem is significant enough to terminate any prospects of mining even before getting started.

The presence of several – if not all – of the REEs together in REE-bearing geological formations is in random concentrations which raises issues as far as their mining and extraction are concerned. If the REEs in higher demand have a lower abundance within these geological formations, the minimum quantity that needs to be mined, processed and separated must be at least the amount required for these critical applications. As a consequence, elements of higher abundance and lower criticality will be produced in larger than required quantities and due to the surpluses they will have to be stockpiled, thus increasing the costs of mining, processing and storing.

The continuous evolution in applications and alternation of end uses of the single REEs leads to a consequent change in their individual demand. This means practically that the market can change fast enough to make a balance very difficult, if not impossible, to achieve.

Currently, neodymium (Nd) is driving the demand for LREEs due to its application in magnets (17). HREEs are generally less abundant and are thus produced in fewer quantities. Their market is primarily driven by dysprosium (Dy) and secondarily by europium (Eu) and terbium (Tb) that are also critical for magnets among other applications. All of the above mentioned elements, including yttrium (Y), form the group of the critical REEs (Figure 1).

Environmental Criteria

The economic terms concern both surface and underground mining of rare earths with the difference lying on the fact that underground operations deterministically cost more. Almost similarly, the environmental considerations are similar up to a point but generally differ between surface and underground mining operations. Maybe the most significant environmental issue that creates concerns to the REE-industry is the generation of pollutants from the processing of rare earth elements and the use of reagents. This paper, however, focuses on the impacts caused by excavations, notably in underground mining.

One of the most controversial issues in rare earth underground mining is the presence of radioactive elements in REE-bearing minerals, primarily thorium (Th) and uranium (U), while rare earths themselves have naturally radioactive isotopes as well. The content of naturally occurring radioactive materials (NORMs) in rare earth geological formations may vary from insignificant to higher concentrations, enough to attract regulations (18) and require particular attention and close monitoring during underground mining. In some cases, uranium can be exploited as a by-product, thus increasing the economic capability of an REE mining project. However, REE-deposits have a Th-tenor rather than a U-tenor and thorium is more of a problem as it is not currently utilized for power generation, even though it has long been regarded as both, a useful nuclear fuel and a way to get rid of this kind of waste (19). Radioactivity can be a problem to surface mining as well, yet it is not of equal importance as in underground mining activities, where the remarkable dust production and the potential transfer of radioactive particles within the mine atmosphere, increase the risk of contamination. The most attention is focused on radon (Rn), as it is the only gaseous product of the primordial uranium and thorium decay chains and thus can easily migrate into the underground mine atmosphere as well as into groundwater (20). Radon is closely related to lung cancer found in mine workers, while it can also have severe impact on the surrounding eco-system of an underground mining plant.

Another factor that is interconnecting with the presence of NORMs as well as that of toxic compounds from the processing of REEs, regards the treatment and disposal of tailings. This relates to both surface and underground mining operations, as far as the surrounding geo-environmental balance is concerned. If there is no bank to protect the large amount of tailings, the risk of environmental contamination increases significantly. Moreover, waste disposal can be a problem when applying underground mining methods that implement backfilling with own tailings that are radioactive. It should be noted here that issues can also arise when the mining method implied requires the long-term residence of highly fragmented blasted ore in the stopes or when in-situ leaching methods are applied in “breaking down” ore blocks underground, thus creating possible sources for high radon and acid concentration levels.
The radioactive wastes from REE mining and milling operations are not the same as waste containing special nuclear materials that are associated with the production of enriched radioactive materials generated by nuclear fuel cycle facilities or disposed of by nuclear power plants. The principal issue at rare earth mining and milling sites is the volume of wastes containing NORMs that are produced and have to be managed. In all cases, special evaluations have to be made to confine radon emanation into the air and the spreading of radioactive pollutants and/or leaching liquids into the groundwater, thus maintaining a safe underground mining environment (20).

Sociopolitical Criteria

It is a common secret that a mining operation always raises social and political considerations due to its potential impacts on the environment and to the local societies. Additionally, in the case of REE-Mining, the extended contamination effects and health impacts of rare earth mining and processing in China have already prejudiced governments and people against any rare earth mining development and processing, despite the fact that the public engagement experience on this industry sector is relatively limited outside China (1). The danger of exposure to radiation can act as a deterrent for both the authorities and the local societies involved, even when the actual risk of contamination is low due to insignificant concentrations of NORMs in rare earth deposits, or when the actual contamination is minimized due to sufficient safety measures and precaution techniques. Such an apprehension often results to political reluctance as well, when it comes to taking important decisions for allowing mining development in the REE-Industry.

Although the contribution of REEs towards developing a “green economy” can be cited as a potential positive impact, arguments, reservations and suspicions highlight the so called NIMBY Syndrome – “Not in my Back Yard” – thus making rare earth mining unwelcome to the majority of societies.

Therefore, one of the most important social criteria is the complexity of acquiring a mining license to begin a rare earth mining operation. Establishing a rare earth element processing plant is an even more difficult procedure though, sometimes even impossible. This alone is a fact that raises issues for the mining industry of REEs as well, since many processing plants are built quite close to the mining sites in terms of sustainability of the overall projects. A rather strict legislation may prohibit the development of such projects, while on the contrary, inadequate or no legislation may create a legal vacuum where no mining and/or processing license can be acquired.

Several countries worldwide, including the European Union (EU), do not have direct legislation for rare earth mining and mining site management. The EU is using instead a variety of legislation (Figure 2) including the Mining Waste Directive – 2006/21/EC (21). This has a direct influence on mining permits since the tailings are often disposed on site, either on surface or underground.

Another criterion that could be placed in the social-political category is the lack of experience in rare earth mining outside of China in general and rare earth underground mining all around the world more specifically. When the mining activities were shut down not only the mines were lost, but in the course of the action also know-how and specialized personnel. This kind of vulnerability reinforces concerns and arguments regarding the capability of the REE-industry to avoid environmental pollution with detrimental effects on local societies. Moreover the lack of experienced staff to work in rare earth underground mines undoubtedly increases the potential risk of exposure to radiation and the possibility of both the mining site and the surrounding environment to be subjected to extended contamination.

Technical Criteria

The above described three categories of criteria follow the widely used approach of the triple-bottom-line (TBL), also referred to as the “three pillars of sustainability” (Figure 3). However, these factors can be evaluated on a common ground of technical aspects, without which it is difficult to examine and determine the overall viability of a rare earth underground mining project. The assessment of the technical criteria in rare earth underground mining can set or change the impacts of the operations in terms of minimizing them to a level that can meet the environmental, economic, social and legislative requirements.

The separation of rare earth elements remains the primary technical issue for the REE-industry worldwide and engineers are currently focusing on managing the processing and cost effective extraction of the individual REEs. Despite the fact that this technical criterion is not directly related to rare earth mining, it can influence the excavation activities as well as the production rate and consequently the selection of the proper mining method, the cash flow and thus the viability of the overall underground mining project. Furthermore, the variable composition of rare earth deposits – referred to as the “Balance problem” – makes these ores very attractive for selective mining to meet the required production targets of the individual REEs. All of the above criteria may dictate the application of specific selective mining methods, possibly different from those that the common UMMS tools would indicate.
Furthermore, the variation in commodity prices of the individual rare earth elements can determine the choice of the underground mining method, as well as the production rate and the selectivity in mining operations. A rare earth deposit essentially consisting of critical REEs in economically significant concentrations could be assessed more easily for potential exploitation.

Another important technical criterion that governs rare earth underground mining regards to the safety measures and techniques that have to be implemented in order to confine radiation in a rare earth underground mine. Engineers have to evaluate and apply special ventilation and dust-fight techniques during mining, transporting and processing of the ore (20). Sometimes it is necessary to thoroughly evaluate or even exclude from potential application specific underground mining methods that are labor intensive or require the long-term residence of the ore in-situ. Especially methods that require backfilling with own tailings should be evaluated with respect to the radioactivity that is emitted from the backfill material and specific safety measures should be taken.

Summarizing, these REE-technical boundary conditions can in turn affect other established criteria that rule underground mining operations in general.

Influence of the REE-Criteria on the Underground Mining Operations

All the factors described can affect, separately or combined, the viability of rare earth mining operations. Often two or more criteria evaluated in the same project, may counter to which has the biggest influence, thus the engineers have to decide which factor is more important. In any case, the effect of the REE-criteria can be significant, as seen in the examples described below.

During the price spike of 2011 the perspectives of profitable exploitation of rare earth element deposits led to a burst in exploration. Indeed, with such high prices, even low grade deposits or potential projects with high capital and operational costs could become sustainable. The spike was followed by a quick drop of the prices though, forcing many investors to reconsider their planning and realize that the viability of a rare earth mining project is a difficult problem to deal with.

The balance problem, as it is described in this paper among other studies, can have a major impact to the viability of REE underground mining projects as well. The variation on demand and therefore the prices of the individual rare earth elements may determine to a large extent whether a deposit has the perspectives to be profitably exploited or not. A HREE enriched deposit for instance has perspectives for bigger cost ranges and thus higher capital and operational costs can be assumed. A characteristic example is the HREE carbonatite deposit in Lofdal, Namibia, where the exploration has revealed a deposit with high concentrations of yttrium and dysprosium (22). Yet, the lack of infrastructure as well as water and power supplies in the area have raised issues and difficulties due to high cost estimations. But despite these assessments, this mining project has big perspectives of being launched.

Environmental factors can also have a great influence on the viability of any REE underground mining project. Problems may arise not only in the initial evaluation stage but also in the middle of mining and processing activities. The most typical example of such a case is the closure of Mountain Pass plant in California, USA (1). In 1998 the chemical processing of rare earths stopped after a series of wastewater leaks containing radioactive waste. Thus, the mine was forced to terminate its activities in 2002 in response to both environmental restrictions and lower prices of rare earth elements.

Mining activities in Mountain Pass have been restored since 2012, however, this incident gave China the opportunity of taking the lead and dominating the REE industry over the last two decades. Nevertheless, lax legislation and lack of sufficient protection measures resulted in a big environmental disaster. The Chinese authorities are now taking action to remediate the area surrounding the rare earth mines. This, in turn, has caused a reduced production in China during the last three years, triggering reduced export quotas, and thus more problems on the already dubious global REE market (1).

Environmental concerns combined with strict regulations in Australia were the reasons that led Lynas Corporation to build the Lynas Advanced Materials Plant (LAMP) in Kuantan, Malaysia, where they ship the REE concentrates that have been mined in Mount Weld in Australia. The specific mine has clearly a lower impact than Bayan Obo (China) and Mountain Pass (USA) and far more below radiation concerns than emanation rates from high grade uranium operations (1). The company has decided to situate the site in Malaysia.

This has led to international activism and claims of environmental and social injustice. This case could easily be described with the NIMBY-syndrome from the sides of both countries involved; Australia and Malaysia. It has also created concerns and suspicions on whether the strict environmental regulations in developed countries force many mining companies, with the blessings of the authorities, to build their processing plants to developing countries where the legislation is more lax.

Conclusions

The rare earth elements are not named after their actual rareness; on the contrary they can be found almost everywhere. Yet, the particular geological conditions that promote their concentration to levels of attracting economic exploitation are rare (23). Moreover, the notable boundary conditions and requirements that are described thoroughly in this paper have to be considered when evaluating the perspectives of a rare earth underground mining operation.

Setting up an underground mining plant is a huge investment and once the mining method has been selected and applied, it is almost impossible to change it. Thus, the mining method selection process is crucial to the sustainability of any given REE project. Therefore the REE specific parameters must be evaluated on equal terms with all the other important criteria.
Common mining method selection tools based on computational processes can adopt some of the REE industry-specific criteria, yet there is no established assessment methodology that can take into account the REE market situation or the social and legislative prerequisites that will permit the development of an REE underground mining project and ensure its viability.
The underground mining industry of rare earths is in deep waters due to the fragile overall situation and the lack of intellectual capital and practical experience. Relevant practices in similar underground mining operations, e.g. in uranium deposits, can assist to better understand and evaluate some of the risks and boundary conditions. Nevertheless, dealing with rare earth elements is a far more complicated situation that requires special attention.

The REE criteria brought forward in this paper should be combined with the other parameters already well established in previous studies and in literature in order to build an overall assessment tool for future rare earth underground mining projects. This tool shall contribute to the optimization of the selection process of the proper underground mining method and also help investors to take accurate and secure decisions on if and when such investments should be made. It should also take into account the social and environmental considerations that are made due to bad practices of the past.