Rare earth production is more involved than the production of well-known base and precious metals. This is due to the complexity of the mineralogy and the fact that one rare earth mineral may contain up to 16 different elements. These elements exist in different distributions specific to each deposit. Generally speaking, the various rare earth elements must be separated from one another in order to be economically saleable. The generalized phases of rare earth production are described below and represented graphically in Figure 2, using magnet alloy production as an example. These phases may also be considered as a value chain, as the margins on products increase through the phases.
Globally, there are over 250 firms involved in exploration for rare earth deposits. Rare earth deposits are found in various geologic environments across the globe, and each deposit may host one or more rare earth bearing mineral. Some common rare earth minerals are bastnaesite, monazite, and ion-adsorption clays. Ion-adsorption clays are only found in China. Other rare earth minerals include xenotime, trachyte, fergusonite, apatite, loparite, parasite, and synchysite.
Mining involves removing mineralized rock from ground through open-pit or underground methods. The vast majority of rare earth mining occurs in China, mainly as a bastnaesite byproduct from the Bayan-Obo iron ore mine in Inner Mongolia, and various ion-adsorption clay deposits in southern China. Currently, there is little significant rare earth oxide (REO) production outside of China. This rest-of-world production includes REO produced in California (3,000 tpa), Russia (4000 tpa), and India (3000 tpa) representing approximately 7% of global production in 2010.
Processing the minerals contained in ore consists of two components, namely beneficiation and leaching. Beneficiation produces a mineral concentrate and consists of crushing, milling, and concentration technology such as gravity, magnetic, and floatation techniques. Leaching takes the mineral concentrate and produces a liquid sulfate, nitrate, or chloride (RECl3) of mixed rare earths. This mixed product contains the various REEs in the same general proportions found in the deposit. For transportation or further removal of impurities, the chloride is usually turned into a solid carbonate. The ROW market for mixed rare earth chloride or carbonate is very small, as most end users require separated oxides of individual elements. Rare earth chloride or carbonate is generally not considered a saleable product outside of China.
The separation stage takes as input the mixed rare earth chloride. The mixed chloride is then separated into rare earth oxides of individual elements (e.g. Nd2O3) using a process called solvent extraction. Separated oxides are the first economically saleable rare earth products in the value chain. Presently there is very little operational separation capacity outside of China.
Rare earth oxides are converted into high purity metals (e.g. Nd metal) or alloys of rare earths (e.g. mischmetal or ferro-alloys). Two may be used methods are used: electrolysis or metallothermic reduction. Metals may be sold or used for the production of end-use alloys.
End-Use Alloy Making
Companies such as LCM or GWTI use high purity metals to create end-use alloys that incorporate rare earths as well as other metals. These end-use alloys may be “super alloys” of aluminum for use in the aerospace industry or permanent magnet alloys such as neodymium-iron-boron (NdFeB) or samarium-cobalt (SmCo). End-use alloys are sold to a range of customers such as magnet manufacturers that use the alloys to produce permanent magnets.
Figure 2: Generalized Phases of Rare Earth Processing for Magnet Alloy Production