The rare earth supply challenge
Dr Gareth Hatch, President of Innovation Metals Corp in Canada, discusses supply issues.
See a pop-up map showing the location of current sources of rare earth oxide production, as well as the location and status of more than three-dozen development projects currently underway with defined mineral-resource estimates
Rare earth elements (REE) are increasingly important to the technologies that underpin modern-day life. With roles in clean technologies and sustainable technology initiatives such as wind turbines, and the use of REE-based permanent magnets in electric vehicles, demand is only set to increase. Recent global demand projections for rare earth oxides (REO) in various end-use applications are described in this table:
The REEs are a group of 17 elements that exhibit a range of unique electronic, optical and magnetic properties. The group consists primarily of the lanthanoid series of elements, plus scandium (Sc) and yttrium (Y).
In practice, while Y frequently occurs with the lanthanoids, Sc is seldom found with these elements. In addition, promethium (Pm) is a radioactive element and is not usually found in nature. This leaves the 15 elements shown in the table below as those most frequently referred to as the rare earths.
Rare earth elements can be further divided into the so-called light (LREEs), medium (MREEs) and heavy REEs (HREEs), where the LREEs are La-Ce-Pr-Nd, the MREEs are Sm-Eu-Gd, and the remainder are the HREEs. These groupings reflect the elemental contents of the various mixed concentrates that result from the initial processing of rare earth ores.
These elements are frequently separated and sold in their oxide form, and thus it is customary to render mineral-deposit data in terms of REO equivalents.
Heavy REEs are generally much scarcer than the other rare earths and, as such, more valuable. They frequently occur in minerals that are significantly more challenging to process than the more common L/MREE-rich minerals, which have a well-established history of processing.
Current and future supply
Technology Metals Research in the USA estimates that approximately 113kt of REOs was produced worldwide in 2011, with 95% coming from China. Projections from Industrial Minerals Company of Australia Pty Ltd for 2016 indicate a total global supply of 180–210kt of REOs, with approximately a third of this supply coming from new sources outside China.
Despite the significant number of projects, in terms of new production, while some individual REOs such as CeO2 are likely to be in surplus in 2016, others such as Eu2O3, Tb4O7, Dy2O3 and Y2O3 will almost certainly still be in deficit. This is one reason why new deposits of HREE-rich minerals are a key focus for exploration and development.
Processing of rare earths
Found together in a variety of minerals, REEs are notoriously difficult to separate. Bastnaesite, monazite, loparite and xenotime are the most commonly exploited REE-bearing minerals, and the HREE-rich ion-adsorption clays of southern China are also commercially processed. Other minerals of increasing interest, in particular for their relative enrichment in HREEs, include eudialyte, gittinsite and fergusonite.
There are literally hundreds of different REE-bearing minerals, and each rare earth deposit has a unique signature in terms of specific mineral content and the relative distribution of REEs within the minerals present. Consequently, numerous process flow sheets have been developed.
Hard-rock REE ores are initially subject to crushing and grinding, while ores found in mineral sands or other finely divided states generally do not require this step. The materials are then concentrated using flotation or other physical separation processes, such as magnetic, electrostatic or gravity separation.
The resulting mineral concentrate is then subject to a range of chemical processes, tuned to the particular mineral(s) present in the concentrate. This typically involves an initial leaching process using acids or alkalis, combined with roasting of the mineral concentrate in a rotary kiln. The resulting slurry is separated and the mixed REEs precipitated and calcined to form a mixed REE concentrate.
The final processing step is aimed at separating the individual REEs, typically resulting in REOs. This is usually accomplished via the solvent-extraction (SX) process, which uses special organic reagents to separate the individual REEs on the basis of their relative solubilities. This is an intensive, painstaking process requiring hundreds of individual mixer-settler cells in order to obtain the purity levels required for commercial use. The production of individual HREOs can require weeks or even months to complete the process.
The processing of multiple feedstocks
Innovation Metals Corporation is in the process of developing the first independent, centralised rare earth separation facilities, with the goal of helping to solve a potential processing bottleneck for the industry via low-cost tolling. Mixed REE concentrates from multiple sources will be blended together before using SX to separate the materials into individual REOs.
A recent technical study focused on the ability of existing processes to achieve high recovery rates of REEs when applied to multiple REE-concentrate feedstocks, originally produced from different mineral concentrates. Four minerals were chosen for the study – bastnaesite, monazite, xenotime and ionic clay.
The bastnaesite, monazite and xenotime concentrates were blended together and successfully processed to produce a mixed REE chloride, via both acid leach (hydrochloric acid) and alkali leach (caustic soda) processes. The ionic clay was initially processed separately, using ammonium sulphate followed by oxalic acid to produce a mixed REE oxide, which was then converted to a chloride with the application of hydrochloric acid. In both cases, high recovery rates (>90%) were achieved.
The resulting mixed REE chlorides were then blended together and processed via a pilot-scale solvent-extraction process using standard techniques, resulting in separated rare earths. The tests successfully demonstrated the principle of blending mixed REE concentrates as a precursor to separation by SX. The next step is to conduct similar tests on larger volumes of material.
Rare-earth export quotas
With China producing 95% of the world’s REEs, in recent years the country has imposed quotas on the export of rare earth-based products. An unexpected 40% drop in export quotas in 2010 led to dramatic price increases of all the rare earths, peaking in 2011 and leading to demand destruction for some rare earths and industries (most notably for La- and Ce-based compounds in the petrochemical fluid-cracking catalyst and glass-polishing sectors respectively). Prices have decreased since those peaks, but the volatility has increased concern for the security of supply of rare earths.
Recent export-quota numbers have remained fairly level. In the announcement of the first round of quota allocations for 2012, the Chinese Ministry of Commerce made some departures from its usual approach to export quotas –
- The Ministry issued separate quota allocations for light and medium/heavy rare-earth products, not just for the rare earths as a whole. Although this was anticipated, 2012 marks the first time these separate allocations have been made.
- Also for the first time, the Ministry clearly telegraphed the intended total export quota for the entire year, prior to making the usual follow-up allocation announcement in the summer of 2012. The Ministry stated that the fi rst round of quota allocations (totaling 24,904t) will represent 80% of the quota allocations for 2012, indicating a total of 31,130t for the coming year.
- The Ministry separated individual companies into two groups. The first received confirmed quota allocations, while the second received only provisional allocations. Companies were placed into one of these groups based on their progress towards implementing new pollution-control regulations, with the latter group only getting their allocated quotas if they meet the requirements by July 2012 – failure to do so will result in quota re-allocation.
In March 2012 the United States, the European Union and Japan filed simultaneous and near-identical complaints with the World Trade Organization (WTO), in which they requested consultations with China on the measures that it has in place related to the export of rare earths, tungsten and molybdenum. The complaint focused on the imposition of export duties, quotas and other quantitative restrictions that are alleged to discriminate against foreign entities doing business with Chinese companies, as well as the maintenance of unofficial minimum export prices.
The Chinese response is likely to focus on certain exceptions that may be allowed under WTO rules, relating to measures put in place to protect the environment and conserve exhaustible natural resources. Having recently lost a similar case concerning bauxite, coke and other materials, it is unclear as to whether China will be able to win this time should the dispute go forward. A narrower set of restrictions might be allowed on heavy rare earth exports only, but this remains to be seen.
Dr Gareth Hatch, firstname.lastname@example.org