by Kidela Capital Group
“There is a reason why the Rare Earths are called rare. They’re not called rare because they’re truly rare. They’re called rare because it’s very difficult to isolate these elements individually and it takes a lot of skill to do that.”
Constantine Karayannopoulos, chief executive of Neo Material Technologies1
Rare Earth Elements have become an indispensable part of modern life, found in everyday items like computers, camera lenses and high efficiency light bulbs to complex, emerging technologies in the optics, medical and defence spheres. But before these elements end up in your smartphone, they need to be transformed into highly processed, high-purity compounds, oxides and metals. This is an expensive, time-consuming, and arduous process. One of the consequences of having one country – China – holding a near monopoly on Rare Earth production over the past two decades is that around the world there is a general lack of processing expertise or knowledge on how to do this.
Here is a brief overview on what is involved in converting the raw material that comes out of the ground, into usable Rare Earth (RE) products.
Step 1: Mining the Ore
The first step is to mine the ore. These ores contain RE bearing minerals like bastneasite and monazite, but generally contain very low concentrations of the Rare Earth Elements (REEs) themselves.
Even a relatively high grade ore only contains about two percent Rare Earth Oxides (REOs),2 which at this stage are undifferentiated groupings of REs combined with oxygen. Depending on the grade, it can take anywhere from 6 to 86 tons of ore to produce a single ton of RE mineral product.3
Step 2: Producing RE Concentrates
The next step is to mill the ore, a process otherwise known as beneficiation or mineral dressing. Here, the ore is ground up to form fine particles (usually less than 1 mm or even less than 0.1 mm) using crushers and rotating grinding mills.4 The valuable minerals are then concentrated using such separation techniques as froth flotation, magnetic separation, and gravity or electrostatic concentration.5
The milling process produces a concentrate of RE minerals, which usually contains five or more times the original RE concentration in the mined ore. The milling equipment – the crushers, grinding mills, flotation devices, and magnetic, gravity, and electrostatic separators – all have to be configured in a way that suits the type of RE ore being mined. No two ores respond the same way, which means every RE milling plant is different.6 And because transporting large volumes of RE concentrate is so expensive, the mineral dressing plant is almost always located very close to the mine where the ore is mined.7
Step 3: Producing RE Compounds
At this stage, the RE concentrate contains Rare Earths at a higher grade than the raw ore (up to five times as much), but it is still in the form if the original natural minerals.8 These minerals have to undergo chemical treatment to allow further separation and upgrading of the REEs. This process – called cracking – includes techniques like roasting, salt or caustic fusion, high temperature sulphation, and acid leaching which allow the REEs within a concentrate to be dissolved.9
Because REEs are so similar to one other, what’s often produced initially is an undifferentiated REO product with large amounts of Light Rare Earths like cerium and lanthanum, and smaller amounts of the others according to their proportions in the ore mineral.
Processing techniques such as selective precipitation, ion exchange, and solvent extraction technologies are now required to remove most of the impurities and produce the desired combinations of RE compounds.
Once produced, these mixed RE compounds can be used on their own, for applications where any one of the REEs has the desired effect – for example, in the production of steel alloys, in catalysts, or as an abrasive for glass polishing.10 Alternately, they continue on to the next stage in the RE processing chain, as a higher grade, intermediate chemical compound that is now ready for additional refining. The nature of the final product of the chemical upgrading process depends on the exact composition of the mineral concentrate, market demands, and the size of the operation.11
The equipment used here – sophisticated analytical devices, furnaces, filters, and the vast array of collection, evaporation and clarification tanks required in ion exchange and multi-stage solvent extraction technology – are usually configured in a way that best suits a particular RE concentrate.12 Because each concentrate has a different combination of minerals, each RE workflow –– and a result each chemical upgrading plant – is typically unique.13
The chemical upgrading process generally eliminates most impurities and produces one or more kinds of mixed RE concentrate. If it contains a generally high amount of REOs (say, 50%), this product can transported fairly long distances without adding a great deal of cost to the commodity.14
Step 4: Producing RE Oxides
The major value-add relative to RE processing lies in the production of high purity RE oxides and metals. But creating the 99.9% purity (or even higher) REs15 required to make phosphors, lamps, magnets, batteries, and other products that need REs to function efficiently, is not simple – far from it. Separating the REEs into their individual oxides may take 50 chemical tanks to separate Light Rare Earth Elements (LREEs), and up to 1,000 tanks of sequential solvent extraction to properly separate Heavy Rare Earth Elements (HREEs).16
The typical RE refinery uses ion exchange and/or multi-stage solvent extraction technology to separate and purify the REEs. These processes break the mixed RE compounds down through the exploitation of the subtle differences between the REEs. It`s done by atomic weight – cerium, the first of lanthanides on the periodic table and the most abundant of the Rare Earths, is separated first. To get the more valuable HREEs like dysprosium, terbium and yttrium other REEs on the periodic table must be separated out beforehand.17
The refinery plant can be combined with the chemical upgrading plant described earlier, or it can be a stand-alone facility. As in the case of the other plants, the RE refineries are sized and configured to suit the unique composition of the feed material.18 For this reason, a plant designed to purify LREE compounds would normally have difficulty handling an increased proportion of HREEs.19
High purity Rare Earth Oxides are one product
of the refining process. The composition of these REOs can vary greatly, since they are generally designed to meet the specifications laid out by end product manufacturers.20 A REO that suits one customers needs may not suit another.
Step 5: Producing RE Metals
The rapid advance of science and technology has led to some RE applications that require very high purities of individual REEs – as much as 99.99999 percent.21 For these applications, multi-stage solvent extraction is generally used to refine the REOs into their essential metal form. These Rare Earth Metals (REMs) can used on their own in end products, or combined with other elements to form alloys for advanced technology applications. Techniques such as optical or mass spectrometry are commonly used to help assess the purity of RE products.22
Upgrading Rare Earth ores to high-purity metals adds orders of magnitude to their value. For this reason, prices for mixed RE concentrates are generally much less expensive than for high purity Rare Earth metals.23
RE metals, or earlier stage products like an REO concentrate or mixed element compound, are now ready for use in the end product, be it a hybrid car, a BlackBerry, or the permanent magnet of Magnetic Resonance Imaging machine. It’s important to remember that it’s by no means a simple path from Rare Earth ore to any of the growing number of Rare Earth applications that we’ve come to depend on in this green, information age.
1, 3, 17 From mine to wind turbine: the rare earth cycle
2, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 19, 21 Extracting & Refining Rare Earths… Can some processes be centralized
10, 18, 22 Rare earths from supernova to superconductor
16 Critical Times for Critical Metals
20 From mine to wind turbine: the rare earth cycle
23 Rare Earth Processing in Malaysia: Case Study of ARE and MAREC Plants