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 lanthanide 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 lanthanides 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 China. 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, Praseodymium 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.