The IMRE Journal Volume 7 (2) 2013 2013. TU Bergakademie Freiberg http://tu-freiberg.de/fakultaet6/imre/

ProduProductionction Process and Recycling of RRareare Earth EElementslements

Jan C. Bongaerts Abstract TU Bergakademie Freiberg

Correspondance: Technological innovations resulted in manifold applications using rare Prof. Dr. Jan C. Bongaerts earths which lead to a dramatic increase in their demand. Rare earths are a TU Bergakademie Freberg relatively abundant group of 17 rare earth elements (REEs) including the Lessingstrasse 45. 15 elements, scandium and yttrium. 09599 Freiberg Germany Given their relative abundance in the earth’s crust, however, they seldom e-mail : occur in concentrated forms in economically exploitable ore deposits. The [email protected] production can be technically challenging and require s substantial and dedicated mineralogical, ch emical and processing expertise. Furthermore, Jiangxue Liu the chemical extraction processes have generated severe environmental problems. TU Bergakademie Freiberg The paper deals with the production process and the recycling of REEs. Correspondance: First, an introduction to rare earths, mineralogy and depo sits is presented. Jiangxue Liu Then, a description of the production process from mining to separation TU Bergakademie Freberg and the environmental risks during the process are given. Next, the Lessingstrasse 45. 09599 Freiberg recycling of REEs is covered. Germany e-mail : [email protected] Keywords : Rare earths mining, processing, separation, recycling.

Introduction

Rare earth elements (REEs) include 15 lanthanide elements (Z = 57 through 71). Scandium (Z = 21) and yttrium (Z = 39) are considered REEs as they have similar chemical and physical properties. The are commonly divided into the light rare earth elements (LREE) – lanthanum through to europium, and heavy rare earth elements

(HREE) – gadolinium through to lutetium (Table 1).

Revised: 27.06.2013 Online Publication Date: 01.08.2013

Page 2 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements

Table 1: REEs, atomic numbers and abundances & Krishnamurthy, 2005). Ion adsorption clays or Lateritic are known from Southern . With up to Element Symbol Atomic Atomic Density Melting Relative 60% of REO content in these clays, ion-adsorbed clays number weight (gcm -3) Point abundan (°C) ce (ppm) are a very important source of HREE. Scandium Sc 21 44,95 2,989 1541 -- Yttrium Y 39 88,90 4,469 1522 22/29 Rare earths are considered indispensable in modern Lanthanum La 57 138,90 6,146 918 30/29 industry because of their unique physicochemical Cerium Ce 58 140,11 8,160 798 64/70 properties. They are extensively used in new materials, Pr 59 140,90 6,773 931 7,1/9 energy conservation, environmental protection and IT Neodymium Nd 60 144,24 7,008 1021 26/37 devices as well as in military weapon systems. They Promethium Pm 61 145,00 7,264 1042 Na have also significantly contributed to the Samarium Sm 62 150,36 7,520 1074 4,5 miniaturization of electronic components, as used for Europium Eu 63 151,96 5,244 822 0,88 cell phones and laptop computers. Rare earths are Gadolinium Gd 64 157,25 7,901 1313 3,8/8 essential for green technologies such as wind powered Terbium Tb 65 158,92 8,230 1356 0,64 turbines. They are widely applied in the automotive Dysprosium Dy 66 162,50 8,551 1412 3,5/5 industry for catalysts, hybrid vehicle batteries, motors Holmium Ho 67 164,93 8,795 1474 0,8 and generators, etc. (Hurst, 2010). Figure 1 illustrates Erbium Er 68 167,26 9,066 1529 2,3/3,3 the major REE applications: Thulium Tm 69 168,93 9,321 1545 0,33 Ytterbium Yb 70 173,04 6,966 819 2,2 Lutetium Lu 71 174,97 9,841 1663 0,32 Source: Taylor and McClennan 1985 Na = not available

Rare earths are moderately abundant in the earth’s crust, some even more than copper, lead, gold, and platinum (Harben 2002; USGS 2002). The relative abundance of individual REEs varies widely, from cerium being the most abundant at 64 ppm, to lutetium with a concentration of 0.3 ppm (Taylor and McLennan, 1985). REEs do not occur naturally as metallic elements, but mostly as rare earth oxides (REO) or other combinations due to their strong affinity for oxygen. An Figure 1 – Major Rare Earth Applications (Öko Institut e.V., 2010) exception is promethium, which does not have a stable isotope and occurs only in very few quantities in natural materials. Because of their reactivity, it is difficult to 111 REEs deposits and reserves refine the rare earths to a pure form (Jackson and Rare earth deposits can be broadly divided into two Christiansen, USGS, 1994 P.4). categories: primary deposits and secondary deposits. REEs occur in more than 200 minerals but the most Primary deposits are associated with igneous and economically significant minerals known to contain hydrothermal processes (hard rock deposits), they are essential or significant REEs are bastnäsite, monazite, relatively rich in LREE, while secondary deposits are xenotime and ion adsorption clays. Bastnäsite and concentrated by sedimentary processes and weathering, monazite contain mostly LREE, only small amounts of they contain more HREE. HREE. Due to the content of thorium, monazite is According to the United States Geological Survey radioactive. Xenotime is an yttrium phosphate, it Circular (Orris & Grauch, 2002), there are 799 rare contains about 67% REO, mostly of the HREE, but it earth deposits in the world and they are located in 76 occurs less commonly than monazite in deposits (Gupta countries. Most of the deposits are located in the United The IMRE Journal Page 3 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements States and China, followed by Australia, Brazil, depends on ore grades, nature of the overburden, and Canada, Russia and India. With respect to the REO the stripping ratio (EPA, 2012). content, more than 90% REO is contained in hard rock Mining methods for Placer deposits depend on the deposits. criterion whether the ore is covered by water or In January 2013 the USGS estimated global rare earth mineable from the dry surface. If placer deposits are reserves at 110 million metric tonnes (Mt) REO. covered by water, their extraction typically uses Reserves are defined as the part of identified resources dredges, which apply a series of buckets or suction which can be economically extracted or produced at the dredges. If placer deposits are not covered by water, time of determination. China, with 55 Mt REO, is the they are mined by variations of open pit excavation country with the largest REO reserve. The United States methods, which use scrapers, bulldozers, loaders has 13 Mt REO. India with 3.1 Mt REO and Australia shovels and draglines to collect the ore for further with 1.6 Mt are ranking in fourth and fifth place processing. Drilling and blasting are not required except respectively. for deposits in which the sand is cemented by ferruginous or calcareous precipitates (Gupa and Krishnamurthy, 2005). 222 Production ppprocessprocess of REEs

The production process of REEs consists generally of mining, processing, separation & refining. Unlike the Processing common metals like copper and iron, which usually have higher concentrations in their deposits, REEs are Beneficiation widely distributed in low concentrations. The diversity After mining, the ores are processed to produce a of each deposit’s chemical composition requires concentrate with high REE contents. REEs processing specific mining and processing methods. Moreover, the is a very complex and specific process due to the separation of the individual REEs and refining them to complexity of REEs bearing minerals. Many factors pure metals are difficult challenges, because of their affect the selection of treatment processes, such as chemical similarity. deposit type, REE grades, type of gangue minerals, and composition of the individual REO minerals.

Mining and processing Hard rock deposits The general beneficiation process of hard rock ores Mining involves crushing/grinding and separation of REO from There are three mining methods to extract the REEs- other minerals by flotation. There is a series of reagents bearing deposits: surface mining (open pit mining), which are used in the flotation to optimize the flotation underground mining and In-Situ Leaching (ISL), which process. Principally, flotation reagents can be classified is also called solution mining. into: collectors, frothers, regulators, and depressants. The most important reagent is collector. Two collectors, Hard rock REE ores are usually mined by conventional fatty acids and hydroxamates, are most widely applied open pit methods, which typically involve removing the in the rare earth flotation process. overburden, blasting, excavation, and milling. Two of The largest deposit is the Bayan Obo iron-niobium- the world’s largest rare earth mines, Bayan Obo mine in REEs deposit. The main product is iron ore, while China and Mountain Pass mine in the United States, are LREE are by products. The main rare earth minerals of open pits. This method is also used at Mount Weld the ore are bastnäsite, monazite, mixed minerals of mine in Australia. Hard rock REEs ores are also mined bastnäsite and monazite. The ore contains also barite, underground. fluorite, calcite, silicates and iron minerals. It is very Loparite from the Lovozero complex in Russia are difficult to separate rare earth minerals from other mined by both underground and open pit methods. associations. A process which combines gravity Open pit mining, if applicable to the deposit, is often separation, magnetic separation and froth flotation is cheaper and safer compared to underground mining. used. The ores are crushed and milled into 0,074mm The applicability of open-pit or underground methods particles. The iron concentrate is then separated through low-intensity magnetic to high-intensity separation. The IMRE Journal Page 4 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements After froth flotation the rare earth concentrate with 60% However the acidic method has many disadvantages. REO grade is produced. At present, the collector H205 The radioactive element Thorium is converted to (2-hydroxyl-3-naphthyl hydroximic acid) and the Thorium Phosphate (ThP 2O7), which can be not depressant sodium silicate are mostly used as main recovered. Moreover, the equipment used during reagents in rare earth flotation process (Zhu, J. G., roasting is easily corroded. The process generated a Zhou, Q., 2009). large volume of waste gas. In order to improve the environmental standards, a new acidic method with low Placer deposits roasting temperature (150~330°C) is now applied. The Placer deposits are accumulations/concentrations of solution after water leaching is leached with primary heavy minerals transported and deposited by rivers or amine N1923, form which 95% Thorium can be coastal process. Placer deposits can be classified into recovered (Huang, X., 2011). Figure 2.1 illustrates one marine placers, alluvial placers and paleoplacers. The of the clean metallurgical processes developed by most important REE-bearing mineral in placer deposits Changchun Institute of Applied Chemistry at the is monazite, with minor quantities of xenotime and Chinese Academy of Sciences. other minerals (Möller, 1986). Type and complexity of beneficiation methods for placer deposits depends on the mineralogy and chemical composition of the placer deposits. Generally, gravity, magnetic, electrostatic techniques and flotation are used for separating rare earth minerals from associated minerals.

Decomposition processes Following beneficiation the REEs concentrates are further processed to increase the REO grade from 60% up to 90%. Hydrometallurgy, which is involving leaching, washing, filtering and drying, is the most common chemical extraction method.

Hard rock deposits At the Bayan Obo deposit, two methods are used: the acidic and the alkaline method. The bastnäsite and monazite concentrates are roasted at 400~500°C in concentrated sulphuric acid. The REEs and other minerals are precipitated as sulphates. Then the sulphates are leached in water and filtered to remove the impurities. REEs are then leached with hydrochloric Figure 2.1 - Clean metallurgical processes (Bi, Y.F., 2012) acid and solvent extraction agent Di-(2-ethylhexyl) phosphoric acid (P204). Through this method, REE At the Mountain Pass deposit the bastnäsite concentrate chlorides (RECl 3) as well as few individual RE oxides (with 60% REO) was roasted at 620°C to remove are produced. The acidic method is used for 90% of the carbon dioxide and then leached with hydrochloric acid REEs products in due to its advantages (Huang, for purification. X. et. al., 2005):  The recovery rate of REEs is relatively high Placer deposits  The REEs are separated directly by solvent REEs from monazite and xenotime can be extracted extraction from sulphate solution without using the acid method and caustic soda method. The saponification, so that the production costs as well as sulphuric acid method has been used in the past but it is waste water containing ammonium are low. no longer in use as it does not yield a pure product  The process is simple and easy to be controlled (Gupta and Krishnamurthy, 2005). The caustic soda  Content of impurities is low method is used in India by Indian Rare Earths Ltd. The IMRE Journal Page 5 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements Monazite is insoluble in a concentrated solution of HREEs are separated by using P507 and naphthenic sodium hydroxide at 140~150°C. The REEs and acid diluted with kerosene. Figure 2.2 presents the thorium are converted to hydroxides. REEs are then typical optimized flowchart: separated from thorium by leaching with hydrochloric acid (Gupta and Krishnamurthy, 2005).

In-Situ Leaching Another extraction method is In-Situ Leaching (ISL) , which is currently used in exploration of ion adsorption deposits in southern China. Instead of excavation, blasting and milling, a chemical solution with dissolving chemical components is injected into the ore body in situ , and the rare earth minerals are leached out selectively. Processing of ion adsorption clays is relatively simple compared to the processing of hard rock ores. Initially, the rare earth minerals are leached with ammonium sulphate (NH 4)HCO 3. Subsequently, they are precipitated with ammonium bicarbonate (NH 4)HCO 3. This method can recover 92% REEs Figure 2.2 – Flowsheet for ionic adsorptive RE deposit (Yan, concentrate (Li, Y.X, el., 2012). C.H. et al., 2006) The separation for HREEs with naphathenic or Separation of individual REEs carboxylic acid needs a very long cascade and it is therefore not efficient. In the separation process, other The value of individual RREs depends on their purities separation methods, for instance ion exchange, after separating from REEs concentrates (>99,999%). extraction chromatography, are used (Huang, 2010). However, the separation process is very hard task due to the similar chemical properties of REEs. Ion exchange and solvent extraction are two advanced methods used Environmental impact of REEs mining for separating. REEs processing is most advanced in There are many environmental issues associated with China. Already in 1970s, Prof. Guangxian REEs production process. In the mining stage, the established the Counter-current extraction process, by overburden material as well as the waste rock must be which high REEs purities of 99.99% even 99.999% can removed. During the extraction, separation and refining be economically achieved (Yan, C.H. et al., 2006). processes, a large number of chemical materials are In the counter-current extraction process, organic used, leading to waste discharges to air and water if phosphoric acids, P204 or P507 (C 16 H35 O3P) are widely there is a lack in environmental control. The main used as extractant. The extraction process can be environmental concern is the association of most REEs divided into four steps: saponification, RE-loading, Ion- deposits with significant concentrations of radioactive exchange and stripping. The rare earth ions are elements: uranium and thorium. normally extracted by saponificated extractant P507 and At Bayan-Obo mine, after 50 years operation, the rare transferred respectively into the organic phase. Then, earth resources are excessively depleted. The recovery the loaded rare earth ions are stripped from the organic rate of REEs as by-products is very low. Thorium is not phase into the aqueous phase by the acid. In order to recovered at all. After flotation and further processing, reduce the chemical consumption as well as waste 80.63% thorium remains in the tailings and 1.83% in pollution, a “hyperlink process” was developed, with the REEs concentrate (Gao, Z., 2011). The tailings, which the chemical consumption can be reduced by containing radioactive substances, fluorides, sulphides, nearly 30% (Yan, C.H. et al., 2006). Then the solvent is acids and heavy metals are stockpiled in a large precipitated by ammonium bicarbonate (NH 4)HCO 3 or impoundment and its size grows annually. Until 2010, oxalic acid C 2H2O4. the impoundment covers eleven square kilometres. There is no water barrier at the bottom of the tailings The IMRE Journal Page 6 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements impoundment and drainage water can easily penetrate into to groundwater and flow to the . An ecological disaster could occur if the highly toxic water and sludge flood the surroundings.

The ion adsorption clay deposits in Southern China are free from radioactive elements. They are, however, mined by ISL. A significant environmental issue with ISL is associated with high residuals of strong chemical reagents such as ammonium nitrogen, as well as acids in mine tailings, which can lead to the destruction of vegetation and ground water pollution. An improper injection of liquid can lead to mountain body sliding Figure 2.3: REEs production from 1990 – 2011 (USGS, 2012) (Chi, R.A., 2008). The REEs separation and refining process requires the After the Chinese government placed restrictions on use of toxic acids. It was estimated that, in 2005 the rare earth production and exports, many industrialized process generated 20,000 to 25,000 thousand t of waste countries such as the US, Japan and EU member states water, with total ammonia nitrogen concentrations (Öko identified REEs, particularly HREEs, as critical Institut, 2010). materials according to their importance for their Additionally, illegal mining and smuggling is economies and supply shortage. They started to seek for widespread in China, which exacerbates the alternative REEs supply outside China. In 2010 and environmental problem. Especially in Southern China, 2011 381 REEs exploration projects started (Hatch, due to the relative simple extraction process of HREE, 2011). The most advanced mining projects are the there are poorly constructed illegal mines which have restarted Mountain Pass mine by Molycorp Minerals severely depleted local resources and contaminated soil and the Mt Weld mine in Australia by Lynas and water. Corporation Ltd. (processing in Malaysia, LAMP). In A mining and production management policy was 2012, Molycorp produced 7000 t of REEs. Lynas has launched in 2007. However, due to the lack of received a temporary operating license for a refinery supervision by governments, especially local plant (LAMP), despite of protests of local citizens. governments, China’s rare earth industry was out of When the two mine projects are operated at full control. In order to protect the rare earth resources, capacity, an oversupply of LREE on the global rare Chinese government implemented a comprehensive earths market is anticipated. In contrast, for HREE, series of regulations and standards from 2009, including such as europium, terbium, dysprosium and yttrium, levying higher resource tax, enforcing stricter shortage is expected for the next several years. HREE environmental standards; setting rare earth production are essential for downstream applications, but the quotes as well as export quotas; consolidation and production of HREE is still concentrated in Southern restructuring of the rare earth industry and developing China. Many other potential rare earth mining projects clean rare earth production technologies and processes. are currently in different development stages. However, the production of REEs is subject to high risks because of the technological challenges, environmental World production problems, funding of capital and the approval From the 1960s until the 1980s, the United States was procedures. the world leader in REO production. In the 1970s, While the world’s rare earth supply patterns are China started to produce REEs and rapidly became the undergoing profound changes, the REEs market is world’s dominant producer. In 2002, the Mountain Pass relatively volatile. In 2010, China announced its REEs mine was closed, whereas only the separation of REEs export quota. As a result, prices went up dramatically from stockpiles was continued until 2007. China now and, in 2011, they were nearly 11 times higher than in dominates global production of REEs and is currently 2009. After September 2011, however, prices dropped responsible for 95% of supply. Figure 2.3 illustrates the sharply. Figure 2.4 illustrates this development for REEs production from 1990 to 2011. neodymium oxide, praseodymium oxide, lanthanum The IMRE Journal Page 7 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements oxide and cerium oxide. The trends of the prices of The largest rare earth recycling potential is related to other REEs are similar. end products containing high levels of REEs and an established collection or recycling infrastructure, for instance, fluorescent lamps, magnets, car batteries and catalytic converters (EPA, 2011). According to the study report of UNEP (UNEP, 2011), only a small amount of magnetic scrap containing neodymium, praseodymium and dysprosium and yttrium from laser and garnet are being recycled. However, it should be noted that many countries and companies are in the process of developing recycling technologies. Table 3.1 provides examples of the main reported recycling activities:

Table 3.1 – Main reported recycling activities

REEs Major Company/ Recycling activities Figure 2.4 - – Price development of Rare earth elements, example application used REEs researcher Nd oxide, Pr Oxide, La Oxide and Ce Oxide, 2 001 - 2012 (Metal Magnets Nd, Dy Hitachi, Magnet from air Pages Ltd) Japan’s condition, hard disks and compressors (Hitachi, 2010) The main reason for this steep decrease is caused a Zhang et. Rare earth from Nd reduction of demand. Reacting to the price peak of al. magnet scraps 2011, many companies reduced the usage or REEs or (Zhang et. al., 2010) switched to alternative materials. Batteries Nd, Honda, Batteries from As a reaction to the export quota, some companies Toyota Hybrid car moved their manufacturing to China. It should be noted, (Honda, 2012) however, that, despite the restriction of production and Umicore Nickel Metal the export quota, smuggling takes place on wide scale und Rhodia Hydride (NiMH) Batteries and it remains a persistent problem for export (Rhodia, 2011) regulation. According to the export statistics of China’s TU Rare earth metal customs, China exported 18.600 tons of rare earths in Bergakade from the slag of the 2011. At the same time, more than 21.000 tons were mie pyro-metallurgical smuggled (State Council, 2012). Freiberg treatment of used Ni-MH batteries (Heegn, 2009) 333 Recycling Lighting Ce, La, Y, OSRAM Yttrium and Gd, Tb, EU europium from Considering the shortage in the supply of the rare earth discharge lamps minerals, especially HREE, and the environmental risks (OSRAM, 2009) related to the production of REEs, it is essential to Resende Yttrium and and Morais europium from TV establish a recycling process for REEs. The potential of tubes and computer rare earth recycling is affected by the three main factors monitors (UNEP, 2011): (Resende and 1) Technical feasibility Morais, 2010) 2) Cost of recycling must be less than the value of Others Kosaka Neodymium and elements to be recycled, Smelting Dysprosium from used electronics 3) Availability of the logistic system for collecting (Tabuchi, 2010) end-of-life products containing rare earth Source: self completed elements.

The IMRE Journal Page 8 Production process and recycling of Jan Bongaerts, Jiangxue Liu Rare earth Elements Rare Earth Oxides, U.S. Geological Survey Circular 930-N 444 Conclusion Gao, Z.Q., Zhou, Q.X. (2011): Contamination from rare Rare earth mining and processing is an ore-specific, earth ore strip mining and its impacts on resources complex process and has huge impacts on the and eco-environment, Chinese Journal of environment unless it is controlled and managed Ecology, Vol. 30 (In Chinese) appropriately. To make REEs economically exploitable, Hatch, G.P. (2011): Critical Rare Earth: Global Supply the production process is not only determined by their & Demand Projections and the Leading relative abundance in the earths crust. Many other Contenders for New Sources of Supply, factors, such as 1) the metal concentration in ore Technology Metals Research, LLC. deposits, 2) the feasibility of exploration and mining, 3) Heegn, H. (2009): Recycling moderner Batterien, Teil the complexity of processing and refining of the ore 1: Aufbereitung von Nickel-Metallhydrid- play a role. The wastes and radionuclide pose hazards to Batterien. Aufbereitungstechnik 50, Nr. 6, 48-61. human health and the environment. To protect the Hitachi (2010): Hitachi Develops Recycling environment and ensure the sustainable use of REEs Technologies for Rare Earth Metals, download resources, it is crucial to develop new production from technologies and recycling processes. Currently, http://www.hitachi.com/New/cnews/101206.html commercial recycling of REEs is very limited. Honda (2012): Honda to Resuse Rare Earth Metals However, many recycling research activities are taking Contained in Used Parts, download from place. The secondary sources could reduce the pressure http://world.honda.com/news/2012/c120417Reuse on primary production. -Rare-Earth-Metals/ Huang, X.W., Long, Z.Q. Li, H.W., Ying, W.J., Zhang, G.C., Xue, X.X. 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