Production of rare earth oxides

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UCL dissertation focusing on the environmental impacts of rare earth oxide production in two Chinese mines.

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Production of rare earth oxides

  1. 1. Production of rare earth oxidesAssessment of the environmental impacts in two Chinese minesDissertation for the Master of Science inEnvironmental Systems EngineeringAländji BOUORAKIMASupervisor: Julia STEGEMANNUniversity College LondonDepartment of Civil, Environmental & Geomatic EngineeringLondon, United Kingdom, September 2011
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  3. 3. Abstract The recent interest in environmental friendly technologies has created a significantincrease in the demand of rare earths. Rare earths are indeed used in many applications(e.g. car electric batteries, rechargeable batteries, energy saving light bulbs) because oftheir specific properties. As such, it was interesting to shed a light on the environmentalcost of producing these rare earths. Thus, this study aims at determining the different environmental impacts fromproducing rare earth. It appraises the impacts from the mining of virgin ore until theproduction of rare earth oxides (which is the most commonly used and produced form ofrare earth). This study focuses on two Chinese deposits (Bayan Obo and Maoniuping) thataccount for 70% of the world production of rare earths. After two literature reviews describing firstly the rare earth market and then theprocesses used in the two deposits, the emphasis is laid on the life cycle assessmentmethodology. Based on both data collected in the literature reviews and personalestimations, the life cycle assessment is carried out using a standardised methodology. As a result, the environmental impacts of producing rare earth oxide are assessedregarding the following categories: global warming, acidification, eutrophication,radioactive waste generation, land use and toxicity in wastewaters. To conclude, on the one hand this study provides an extensive analysis of rareearths in general, then it describes in detail the two biggest mines presently in operations.On the other hand, the life cycle assessment methodology provides results concerning sixdifferent impact categories. These results are potentially generalizable since it appraisesgeneric processes to this industry. This study can be useful to whoever is trying tomeasure the environmental impacts of a product that contains rare earth oxides. Keywords: rare earths, rare earth oxide, life cycle assessment, Chinese rare earths,Bayan Obo, Baotou, Maoniuping, environmental impacts. 3
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  5. 5. Acknowledgement I would like to thank Julia Stegemann whose help was invaluable to me. She gaveme the proper advices at the proper times and helped me to design this study from thebeginning to the end. Thanks to her, I have enjoyed carrying out this study. I also would like to express my thanks to Marie for her support. 5
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  7. 7. Table of contents 1.   Introduction ....................................................................................................... 15   1.1.   Background information............................................................................. 15   1.2.   Aim of the study ......................................................................................... 16   1.3.   Objectives ................................................................................................... 16   1.4.   Approach .................................................................................................... 16   2.   Information on rare earth elements.................................................................... 17   2.1.   How rare are rare earths? ............................................................................ 17   2.2.   Description of the main rare earth minerals ............................................... 18   2.3.   Description of the rare earth reserves ......................................................... 22   2.4.   Historical production of rare earth oxide.................................................... 22   2.5.   Description of the main applications of the rare earth elements ................ 24   3.   Production of rare earth elements ...................................................................... 27   3.1.   World production of rare earth elements .................................................... 27   3.2.   Chinese production of rare earths ............................................................... 27   3.3.   Prospective other productions .................................................................... 30   4.   Scope refining.................................................................................................... 32   5.   Bayan Obo deposit ............................................................................................ 32   5.1.   Description of the deposit........................................................................... 32   5.2.   Composition of the original ore.................................................................. 32   5.3.   Description of the beneficiation process .................................................... 32   5.4.   Composition of the mixed rare earth concentrate....................................... 34   5.5.   Processing of the mixed rare earth concentrate .......................................... 34   5.6.   Obtaining of rare earth oxides .................................................................... 34   6.   Maoniuping deposit ........................................................................................... 37   6.1.   Description of the deposit........................................................................... 37   6.2.   Composition of the original ore.................................................................. 38   6.3.   Description of the beneficiation process .................................................... 38   6.4.   Processing of the mixed rare earth concentrate .......................................... 40   6.5.   Obtaining of rare earth oxides .................................................................... 40   7.   Life cycle assessment methodology .................................................................. 42   8.   Goal definition and scope .................................................................................. 42   8.1.   Goal of the life cycle assessment................................................................ 42   8.2.   Level of specificity ..................................................................................... 43   7
  8. 8. 8.3.   Display of results ........................................................................................ 43   8.4.   Scope of the life cycle assessment.............................................................. 43   8.5.   Guideline to life cycle assessment methodology........................................ 43   9.   Process Modelling: ............................................................................................ 43   9.1.   Bayan Obo deposit ..................................................................................... 43   9.2.   Maoniuping deposit .................................................................................... 51   10.   Life Cycle inventory ........................................................................................ 57   10.1.   Input of chemicals, energy and explosives ............................................... 57   10.2.   Air emissions ............................................................................................ 57   10.3.   Output of wastes and chemicals ............................................................... 57   11.   Life Cycle Impact Assessment ........................................................................ 62   11.1.   Global Warming ....................................................................................... 62   11.2.   Acidification ............................................................................................. 63   11.3.   Eutrophication .......................................................................................... 64   11.4.   Radioactive waste generation ................................................................... 64   11.5.   Land use ................................................................................................... 65   11.6.   Toxic chemical discharge in wastewater .................................................. 65   12.   Life Cycle Interpretation ................................................................................. 67   12.1.   Identification of the significant issues ...................................................... 67   12.2.   Completeness, sensitivity and consistency of data ................................... 68   12.3.   Conclusions of the life cycle assessment.................................................. 70   13.   Conclusion ....................................................................................................... 74  8
  9. 9. List of figuresFigure 1: Relative abundance of chemical elements in the Earths crust (Haxel 2002).....17  Figure 2: Concentrations of rare earth elements in the Earth’s crust (Tyler 2004) ...........18  Figure 3: Contents of the main rare earth elements in bastnaesite for two mines (Kingsnorth 2010) .............................................................................................19  Figure 4: Contents of the main rare earth elements in monazite for three deposits (Kingsnorth 2010) .............................................................................................20  Figure 5: Contents of the main rare earth elements in xenotime (Kingsnorth 2010) ........20  Figure 6: Contents of the main rare earth elements in Chinese ionic clays (Kingsnorth 2010) ..................................................................................................................21  Figure 7: Breakdown of the economically viable rare earth resource (USGS 2011) ........22  Figure 8: Global production of rare earth oxide (USGS 2010) .........................................23  Figure 9: World production of rare earth oxides from 1950 to 2000 (Haxel 2002) ..........23  Figure 10: Global rare earth consumption in 2006 (Roskill 2007) ....................................24  Figure 11: Global production of rare earth oxides in 2010 (USGS 2011) .........................27  Figure 12: Breakdown of rare earth oxide-content at Bayan Obo (Crédit Suisse 2011) ...28  Figure 13: Bastnaesite content of rare earth elements at Maoniuping (Spooner 2005) .....29  Figure 14: Ionic clay content of rare earth elements at Longnan (Crédit Suisse 2011).....29  Figure 15: Distribution of the Chinese production of rare earths in 2010 .........................30  Figure 16: Composition by weight of the mixed bastnaesite-monazite concentrate (Wang et al. 2002) .............................................................................................34  Figure 17: Composition of a tonne of rare earth oxides produced from Bayan Obo ore (Spooner 2005) ..................................................................................................37  Figure 18: Composition of the ore in Maoniuping’s mineral (Zhu et al. 2000) ................38  Figure 19: Composition of a tonne of rare earth oxides produced from Maoniuping ore (Spooner 2005) ..................................................................................................40  Figure 20: Beneficiation process in Bayan Obo for one tonne of original rock ................47  Figure 21: Beneficiation process in Maoniuping for one tonne of original rock...............51  Figure 22: Separation factor of rare earths in the Ln(III)-HCl-EHEHPA system (Sato 1989) ..................................................................................................................83  Figure 23: Separation flowsheet for bastnasite (Yan et al. 2006) ......................................83  Figure 24: Relative proportion of light rare earth elements in Bayan Obo concentrate (Spooner 2005) ..................................................................................................85  Figure 25: Relative proportion of light rare earth elements in Maoniuping concentrate...87   9
  10. 10. List of tables Table 1: Categorisation of rare earth elements (Hedrick 2010) ........................................... 15   Table 2: Beneficiation process in Bayan Obo...................................................................... 33   Table 3: Processing of mixed rare earth concentrate in Bayan Obo .................................... 35   Table 4: Separation and refining processes in Bayan Obo .................................................. 36   Table 5: Beneficiation process in Maoniuping .................................................................... 39   Table 6: Processing of rare earth concentrate in Maoniuping ............................................. 41   Table 7: Summary of the mining and comminution processes modelling........................... 46   Table 8: Summary of the beneficiation modelling .............................................................. 46   Table 9: Summary of the stoichiometric coefficients in Bayan Obo ................................... 50   Table 10: Summary of the beneficiation modelling in Maoniuping .................................... 53   Table 11: Summary of the mining and comminution processes modelling in Maoniuping 53   Table 12: Summary of the stoichiometric coefficients in Maoniuping ............................... 56   Table 13: Required inputs for the different stages ............................................................... 58   Table 14: Emission to the air during processes in Bayan Obo ............................................ 59   Table 15: Outputs discharged .............................................................................................. 59   Table 16: Impact indicator for global warming ................................................................... 62   Table 17: Impact indicator for acidification ........................................................................ 63   Table 18: Impact indicator for eutrophication ..................................................................... 64   Table 19: Impact indicator for radioactive waste generation............................................... 64   Table 20: Impact indicator for land use ............................................................................... 65   Table 21: Impact indicator for toxicity in wastewater ......................................................... 66   Table 22: Assumptions analysis........................................................................................... 69   Table 23: Calculation of the chemical inputs for Bayan Obo .............................................. 88   Table 24: Calculation of the chemical outputs for Bayan Obo ............................................ 89   Table 25: Calculation of the chemical inputs for Maoniuping ............................................ 91   Table 26: Calculation of the chemical outputs for Maoniuping .......................................... 92   Table 27: CO2 emissions for mining operations ................................................................. 94   Table 28: CO2 emissions from electricity use ..................................................................... 94   Table 29: Calculation of the SO2 emissions ........................................................................ 95   Table 30: Acidification potential characterisation factors (Azapagic 2011) ....................... 95   Table 31: Acidification potential of different chemicals ..................................................... 95   Table 32: Eutrophication potential characterisation factors (Azapagic 2011)..................... 96   Table 33: Eutrophication potential of different chemicals .................................................. 96  10
  11. 11. Table 34: Activity in waste slag........................................................................................... 97  Table 35: Activity in wastewater ......................................................................................... 97   11
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  13. 13. List of abbreviations GWh gigawatt-hour (109 Wh) kWh kilowatt-hour (103 Wh) MWh megawatt-hour (106 Wh) Mt megatonne (106 t) LCA life cycle assessment LCI life cycle inventory LCIA life cycle impact assessment REE(s) rare earth element(s) REO(s) rare earth oxide(s) t tonne tpd tonne per day 13
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  15. 15. 1. Introduction 1.1. Background information Rare earth elements (abbreviated as REE, also called rare earth metals) are a groupof 17 chemical elements. They are all part of the third column of the periodic table andpossess therefore similar chemical and physical features (Hedrick 2000). They are divided into two groups: light REEs and heavy REEs. Table 1 gives information on REEs and the group to which they belong. Table 1: Categorisation of rare earth elements (Hedrick 2010)Chemical  element   Abbreviation   Atomic  Number   Category   Scandium   Sc 21 None 1 Lanthanum   La 57 Cerium   Ce 58 Praseodymium   Pr 59 Neodymium   Nd 60 Light REEs Promethium   Pm 61 Samarium   Sm 62 Europium   Eu 63 Gadolinium   Gd 64 Yttrium   Y 39 Terbium   Tb 65 Dysprosium   Dy 66 Holmium   Ho 67 Heavy REEs Erbium   Er 68 Thulium   Tm 69 Ytterbium   Yb 70 Lutetium   Lu 71 1 Scandium has physical properties that make it impossible to classify as either light 15
  16. 16. REEs have become topical because they are found in many technological applications of daily life and notably many green technologies such as wind turbines, recyclable batteries, electric vehicles or compact fluorescent lamps (see 2.5). Since these elements are common in modern life, this report considers the impacts of extracting and producing REEs. REEs exist in several forms (rare earth chlorides, metals, carbonates, oxides, etc.). However, only rare earth oxides (and rare earth metal to a lesser extent) are of interest for industrial applications (Kingsnorth 2010). 1.2. Aim of the study The aim of this study is to assess some of the environmental impacts related to the production of rare earth oxides (REOs). 1.3. Objectives The objectives of this study are as follows: - describe precisely the rare earth market (e.g. production, applications) - select the most representative mines - refine the scope of the study - develop a model representing the processes taking place in these mines - determine a suitable method for measuring the impacts - assess both quantitatively and qualitatively the environmental impacts 1.4. Approach In order to complete the objectives, the study was decomposed into several parts. Firstly, an extensive literature review was carried out with the aim of collecting information on REEs, their minerals, the REE market and their applications. Based on this literature review, it was possible to define the scope of the study and single out two mines for the next step. Secondly a further literature review was conducted to describe and understand the processes to produce REO. This second literature review was used to help build models representing these processes. Thirdly, life cycle assessment was applied to the models developed in the previous section using data extracted from the literature. Finally, the results were discussed.16
  17. 17. 2. Information on rare earth elements 2.1. How rare are rare earths? Although they are called rare earths, some of these elements are quite abundant inthe Earth’s crust (Ce is the 25th most abundant elements in the Earth’s crust) and thescarcest of them (Tm and Lu) are even 200 times more abundant than gold (Hedrick 2000;Haxel 2002). One REE, promethium, is a radioactive element with a half-life of 17.7 years for itsmain isotope. As a result, it does not exist naturally. Figure 1 and Figure 2 illustrate the abundance of REEs both relatively to otherelements and quantitatively. Figure 1: Relative abundance of chemical elements in the Earths crust (Haxel 2002) 17
  18. 18. 70   Concentration  in  the  Earths  crust    (ppm)   60   50   40   30   20   10   0   Figure 2: Concentrations of rare earth elements in the Earth’s crust (Tyler 2004) 2.2. Description of the main rare earth minerals According to Kanazawa and Kamitani, around 200 different types of rare earth minerals have been reported (Kanazawa and Kamitani 2006). However, in practice, the extraction of REEs relies primarily on four different minerals: • Bastnaesite • Monazite • Xenotime • Ion adsorption clays This is notably due to their high contents of REO. These four minerals account for 90% of economic production of REEs (Roskill 2007). 2.2.1. Bastnaesite Bastnaesite is a fluorocarbonate with the following formula: ReFCO32. The grade of REES in bastnaesite is up to 75%3. Bastnaesite is the primary source of light REO (primarily lanthanum, cerium, praseodymium and neodymium oxides) and accounts for more than 80% of the overall amount of REO in the world (Kanazawa and Kamitani 2006; Roskill 2007; Naumov 2008). Figure 3 illustrates the abundance of the main REEs in bastnaesite. 2 From this point on, the symbol Re represents a rare earth atom. 3 The grade of a mineral is defined as the mass fraction of the REEs in the ore.18
  19. 19. %  among  rare  earth  elementss  in   60   USA,  Moutain  Pass   China,  Baiyun  Obo   50   40   bastnaesite     30   20   10   0   Lanthanum   Cerium   Praseodymium   Neodymium   Figure 3: Contents of the main rare earth elements in bastnaesite for two mines (Kingsnorth 2010) 2.2.2. Monazite Monazite is a rare earth phosphate that contains up to 70% REEs (formula: RePO4).With bastnaesite, it represents the most important source of light REEs. Until 1965,monazite was the main source of REEs. It was historically produced as a by-product of sand exploitation. However,nowadays, the production of REEs from monazite has been considerably reduced becauseof radioactivity caused by thorium and radium impurities (ThO2 has a concentration of6-7% in monazite produced from mineral sand operations) (Roskill 2007; Naumov 2008;Kingsnorth 2010). Figure 4 illustrates the abundance of the main REEs in monazite. 19
  20. 20. 50   %  among  rare  earth  elements  in  monazite     45   Mt  Weld,  Australia   India   40   Guandong,  China   35   30   25   20   15   10   5   0   Lanthanum   Cerium   Praseodymium   Neodymium   Samarium   Figure 4: Contents of the main rare earth elements in monazite for three deposits (Kingsnorth 2010) 2.2.3. Xenotime Xenotime is a phosphate which is composed primarily of yttrium (YPO4). This mineral contains generally around 55% of REO. Moreover, it contains a particularly high rate of heavy REEs which makes it valuable. This mineral occurs usually in rocks that also contain uranium and thorium. Historically, it was produced as a by-product of tin mining in Malaysia, Indonesia and Thailand (Alex et al. 1998; Roskill 2007) Figure 5 illustrates the abundance of the main REEs in xenotime. 70   %  among  rare  earths  in  xenotime   Lahat  Perak,  Malaysia   60   Guangdong,  China   50   40   30   20   10   0   Figure 5: Contents of the main rare earth elements in xenotime (Kingsnorth 2010)20
  21. 21. 2.2.4. Ion Adsorption Clays These minerals are peculiar to the Jiangxi province of southern China. They are theresult of the weathering of two minerals: xenotime and apatite. Although they have a very small content of REEs (0.05% to 0.2%) (Kanazawa andKamitani 2006), these clays are particularly interesting because they contain relativelyhigh contents of heavy REEs compared to other rare earth minerals. (Roskill 2007;Kingsnorth 2010). Another advantage of these minerals is that they can be easily mined andprocessed4. Besides, they contain very few radioactive elements (Kanazawa and Kamitani2006). However, as illustrated in the following figure, even though they come from thesame geographical area, their contents of REEs vary significantly. Figure 6 illustrates the abundance of the main REEs in ionic clays. 70   Xunwu,  Jiangxi,  China   %  among  rare  earths  in  ionic  clays   60   Lognan,  Jiangxi,  China   50   40   30   20   10   0   Figure 6: Contents of the main rare earth elements in Chinese ionic clays (Kingsnorth 2010) 4 The processing of ion adsorption clays does not require any milling and REOs areproduced by a simple method (Kanazawa and Kamitani 2006). 21
  22. 22. 2.3. Description of the rare earth reserves In 2011, it was estimated that the total recoverable resource amounts approximately 140 Mt (USGS 2011). The economically viable reserves of REEs are summarised in Figure 7. Australia   Brazil   1.6  Mt   48,000  t   1%   0%   United  States   Other  countries   13  Mt   22  Mt   12%   19%   Malaysia   30,000  t   China   0%   55  Mt   48%   India   3.1  Mt   3%   Commonwealth  of   Independent   States   19  Mt   17%   Figure 7: Breakdown of the economically viable rare earth resource (USGS 2011) 2.4. Historical production of rare earth oxide REOs were first produced in the 1880s with the mining of monazite in Sweden and Norway. Their first industrial application was in the Welsbach incandescent lamp mantle in 1884. The production of REOs in the USA began in 1903 with the mining of monazite in South Carolina. Over the first half of the last century, the production remained quite low. It then increased due to the discovery of new applications such as catalysts to crack crude oil into petroleum. Until the 1960s, the production of REEs from placer monazite took mainly place in the southeast of the USA. It was then abandoned due to its high content of thorium (Hedrick 2000). Then, the production moved to a major deposit located at Mountain Pass, California. This mine was in operation from 1965 until the mid 1990s and over this period only bastnaesite was processed in Mountain Pass. At Mountain Pass, the reserves of REEs are still over 20 million tonnes with an average grade of rare earth minerals of 8.9% (Castor and Hedrick 2006). Through the 1990s, China’s exports grew importantly causing American production to be undercut. Most of the Chinese production comes from Bayan Obo deposit (Inner Mongolia, China) which represents the largest known REE resource in the world. In this22
  23. 23. mine, both bastnaesite and monazite are processed (Castor and Hedrick 2006; Hurst2010). Figure 8 illustrates the growth in the production of REOs over the 20th century. 160,000   140,000   120,000   Production  (tonne)   100,000   80,000   60,000   40,000   20,000   0   1900   1910   1920   1930   1940   1950   1960   1970   1980   1990   2000   Figure 8: Global production of rare earth oxide (USGS 2010) Figure 9 illustrates the great periods of REE exploitation from 1950. Figure 9: World production of rare earth oxides from 1950 to 2000 (Haxel 2002) 23
  24. 24. 2.5. Description of the main applications of the rare earth elements This section is entirely based on the two following works: - Roskill 2007 - Schüler et al. 2011 Figure 10 describes the world demand of REEs in 2006. Other   8%   Phosphors   9%   Catalyst   21%   Magnets   20%   Glass,  Polishing,   Ceramics   25%   Metal  Alloys   17%   Figure 10: Global rare earth consumption in 2006 (Roskill 2007) 2.5.1. Magnets There are two main kinds of rare earth magnets: neodymium-iron-boron magnets and samarium-cobalt magnets. Neodymium-iron-boron (Nd2Fe14B) magnets are the strongest available magnets. In addition to neodymium, they comprise other REEs: praseodymium (30% the amount of neodymium) and dysprosium (3% the amount of neodymium). This market is growing very quickly since its average annual growth was 25% between 1986 and 2006. This growth is driven by three main applications: electric motors for hybrid and electric vehicles, generators in wind turbines and computer hard disks. Moreover, several other applications requires neodymium magnets such as: - loudspeakers, earphones and microphones - MRIs scanners - electric bicycles24
  25. 25. 2.5.2. Catalyst REEs are used as catalysts in the automobile industry, petroleum refinery andchemical processing. REEs are use for the following applications: - automotive catalysts and diesel additives (cerium) - fluid cracking catalyst for the petroleum industry (cerium, lanthanum) In the automobile industry, cerium is used to: - reduce nitrogen oxide into nitrogen and water - oxide CO to CO2 2.5.3. Glass, polishing, ceramics 2.5.3.1. Glass polishing Thanks to its specific properties of physical and chemical abrasion cerium ismassively used to produce high-quality glass for the following markets: - mirrors - televisions and monitors - panel displays - glass platters in hard disks This sector represents 13% of the global REE consumption. Its growth rate followsthat of plasma displays, LCDs and computer monitors. 2.5.3.2. Glass additives REEs are used as glass additives for the following applications: - colouring of glass (cerium for yellow and brown, neodymium for red, erbium for pink) - decolouring of glass (cerium) - UV-resistant glass (e.g. for glass bottles, sunglasses, solar cells) (cerium) - optical lenses, filters or coating (lanthanum, gadolinium, praseodymium) This sector represents 12% of the global REE consumption. The growth of thismarket is mainly driven by the growth in optical applications (e.g. digital cameras,security cameras, mobile phones). 2.5.3.3. Ceramics REEs are used in ceramics for the following applications: - ceramic capacitors and semiconductors (lanthanum, cerium, praseodymium, neodymium) - superconductors (yttrium) - dental ceramics (cerium) - refractory materials (cerium, yttrium) - laser (yttrium) This sector represents 5% of the global REE consumption. The growth of electronics results in an increase of the demand of REEs for ceramicuses. 25
  26. 26. 2.5.4. Metal alloys REEs are used in metal alloys for different applications. They bring new properties to the metal they are mixed with. They can be used in: - pyrophoric alloys (cerium, lanthanum) - high-performance alloys to improve their performances (lanthanum, cerium, yttrium) - solid state storage of hydrogen in metallic matrixes - scandium-aluminium alloys used in military aviation - lanthanum-nickel alloys in Ni-MH batteries 2.5.5. Phosphors and luminescence REEs are inserted into crystals of various natures in order to give them luminescence properties. Depending on the wavelength expected, it is possible to choose between cerium, samarium, europium, gadolinium, terbium, dysprosium, erbium, thulium or lutetium. As a result, these REEs are used in mainly two fields: energy saving lighting and display technologies. They are found in the following applications - compact fluorescent lamps (energy saving lamps) - fluorescent tubes - LEDs and OLEDs - electroluminescent foils - plasma displays - LCDs The growth in this sector is driven by: - the general growth in the lighting demand (7% per year from 2004 to 2011) - the replacement of incandescent bulbs in many countries by among other compact fluorescent lamps and halogen lamps - the growth of the LED market - the replacement of cathode-ray tubes by plasma displays and LCDs 2.5.6. Other Many other applications require REEs: - agricultural use of REEs in phosphate fertiliser (cerium, lanthanum) - Ni-MH batteries (lanthanum, cerium, neodymium, praseodymium) - solid oxide fuel cell electrolytes (yttrium) - neutron absorbers in nuclear reactors (europium, gadolinium) - waste water treatment (cerium)26
  27. 27. 3. Production of rare earth elements 3.1. World production of rare earth elements Since the end of the 1990s, China has been the main producer of REEs in the world.In 2010, its official production amounted to 130,000 tonnes of REOs while the secondand third largest producers (respectively India and Brazil) produced, respectively, 2,700tonnes and 550 tonnes of REOs (USGS 2011). As a result, the main REE mines and processing plants are to be found in China. Figure 11 summarises the global production of REEs: Brazil   550  t   1%   Malaysia   350  t   China   India   0%   130,000  t   2,700  t   97%   2%   Figure 11: Global production of rare earth oxides in 2010 (USGS 2011) 3.2. Chinese production of rare earths The Chinese production of REEs takes place in three different areas: InnerMongolia, Sichuan province, and seven southern provinces. 3.2.1. Inner Mongolia Inner Mongolia houses the largest deposit of REEs in the world, namely Bayan Obodeposit. It accounts for 80% of the Chinese reserve of REEs (Crédit Suisse 2011; Schüleret al. 2011). However, it appears that the precise amount of the REO resources contained in thisdeposit varies according to the measurement method: the reserve ranges from 28 milliontonnes of REO (USGS classification) to 44 million tonnes (Chinese classification) (CréditSuisse 2011). The definitions of the different classifications are given in Appendix 1. In Bayan Obo, REOs are produced as a by-product of iron ore whose reserveamounts to 1.46 billion tonnes (Spooner 2005; Roskill 2007). The REOs mined in Bayan Obo are composed primarily of light REEs thatrepresent 97% of the whole rare earth minerals. The rare earth minerals are concentratedin two different minerals: bastnaesite and monazite (there is about 2.5 as much bastnaesiteas monazite) (Huang et al. 2005; Crédit Suisse 2011). 27
  28. 28. Figure 12 illustrates the composition of rare earth mineral in Bayan Obo’s ore. Figure 12: Breakdown of rare earth oxide-content at Bayan Obo (Crédit Suisse 2011) This deposit is owned by one state-owned company called Baotou Steel Rare Earth Group Hi-Tech Co, Ltd (Baotou Rare Earth). It is a fully integrated company (from mining operations to the production of REOs). Besides, the Chinese Ministry of Land and Resources has decided to restructure the industry of REE production in Inner Mongolia. As a result, Baotou Rare Earth will soon become the only company extracting and producing REEs from the Bayan Obo deposit (Crédit Suisse 2011; Global Times 2011). In 2010, Baotou Rare Earth produced 62,400 t of REO (Crédit Suisse 2011). 3.2.2. Sichuan province The second largest deposit of bastnaesite mineral in China is located in the county of Mianning (Sichuan Province). This deposit is called Maoniuping after the name of a surrounding city. It is estimated to contain 3% of Chinese reserves of REO. This represents 1.56 Mt of REOs according to the Chinese classification (Crédit Suisse 2011; Schüler et al. 2011). In this deposit, rare earth minerals are contained almost exclusively in bastnaesite (Tse 2011). Since Bayan Obo’s ore is composed of approximately 70% bastnaesite, the content of REEs in the Maoniuping’s ore is quite similar to Bayan Obo’s.28
  29. 29. Figure 13 illustrates the composition in REEs of the bastnaesite in Maoniuping: Figure 13: Bastnaesite content of rare earth elements at Maoniuping (Spooner 2005) The REO production in Maoniuping accounts for 24% of China’s total production,i.e., approximately 31,200 tonnes, in 2010 (Crédit Suisse 2011; Tse 2011; Wong and Li2011). As in Bayan Obo, the mining operations are controlled by a single company namedJiangxi Copper (JXC Group) (Crédit Suisse 2011). 3.2.3. Southern Provinces The seven southern provinces that contribute to the production of Chinese REEsare: Jiangxi, Guangdong, Fujian, Guangxi, Hunan, Yunnan and Zhejiang. They representthe majority of China’s production of heavy REEs (Crédit Suisse 2011). In these provinces, REEs are found in ionic clays which are composed at 90% ofheavy REEs. Figure 14 illustrates the content of ionic clay. Figure 14: Ionic clay content of rare earth elements at Longnan (Crédit Suisse 2011) 29
  30. 30. The production of REEs from Chinese ionic clays was approximately 36,000 tonnes in 2010 representing 28% of the China’s REE production (Crédit Suisse 2011; Tse 2011). 3.2.4. Summary of Chinese rare earth production Figure 15 was drawn to summarise the information in the previous sections. It shows the distribution of the REE production between the different Chinese regions. Maoniuping   24%   Bayan  Obo   48%   Southern   Provinces   28%   Figure 15: Distribution of the Chinese production of rare earths in 2010 Light REEs account for 72% of Chinese REE production. Since Chinese production amounted to 97% of the global production, light REEs represented at least 70% of the REEs produced globally in 2010. As a result, since the production of light REEs from bastnaesite takes place only in Bayan Obo and in Sichuan province, these two regions will be subsequently analysed. 3.3. Prospective other productions In response to the introduction of quotas by the Chinese government and the increase in REE prices, western companies have launched important projects that aim at supplementing the Chinese production. Among these projects, two are particularly significant because: • they are both very large (production > 20,000 tonnes of REOs per year) • they are in the final stages of development and, are planned to open in the next two years 3.3.1. Mount Weld, Australia Mount Weld is located in southwestern Australia. This deposit is own by Lynas Corporation Ltd which is an Australian REE mining company. Mount Weld is estimated to include 1.4 Mt of REO contained mainly in monazite (i.e. composed primarily of light REEs) (Crédit Suisse 2011).30
  31. 31. purification of REEs) will be carried out in Malaysia by a subsidiary of Lynas (LynasMalaysia). The production will start at 11,000 t of REO p.a. and increase up to 22,000 t of REOp.a (British Geological Survey 2011; Schüler et al. 2011). 3.3.2. Mountain Pass, USA Mountain Pass is the deposit from which the REEs were historically produced forseveral years. It was undercut by the Chinese production in the 1990s and was notoperating since then. Mountain Pass contains 4.3 Mt of REO in bastnaesite minerals. It is now own by a company named Molycorp which plans to reopen the mines in2012. Like Lynas in Australia, Molycorp will produce 20,000 t p.a. when operating at fullcapacity. Thanks to the existing facilities, the mining and the processing will be carriedout on the same site (Hurst 2010; British Geological Survey 2011; Crédit Suisse 2011;Schüler et al. 2011). 31
  32. 32. 4. Scope refining To limit the scope of this project, it was decided to focus only on the production of light REEs since they account for the majority of world REE production. Since Chinese production represented 97% of 2010 global production, it was decided that concentrating on this production would give an accurate perspective of the present environmental impacts of producing light REOs. Finally, as explained in section 3.2.4, China’s light REEs come only from two deposits: Bayan Obo and Maoniuping. As a result, the scope of the study was defined to the assessment of environmental impacts of producing light REO in both Bayan Obo and Maoniuping deposits. 5. Bayan Obo deposit 5.1. Description of the deposit The Bayan Obo deposit (Inner Mongolia, China) is located 80 km south of the Mongolian border. The principal ore minerals are bastnaesite and monazite (rare earth minerals), pyrochlore (Nb), magnetite and hematite (Fe) (Campbell and Henderson 1997). In Bayan Obo, REEs were produced from more than twenty sites since the beginning of the mining in 1957. The two largest deposits are the Main and East ore bodies with a REE grade of 5.14% and 5.18% respectively5. The Bayan Obo ore is hosted in dolomite (Castor and Hedrick 2006). The mining operations are carried out using electric shovels and rail haulage at a rate of 15,000 tonnes of rock per day from the two large open pits (Castor and Hedrick 2006). 5.2. Composition of the original ore Baotou’s rock is complex and its composition varies significantly from one place to another. Therefore it is not possible to give the composition of this ore in general. However, it is possible to look at some specific elements (Drew et al. 1990; Castor and Hedrick 2006): - iron: average grade of 35% - REOs: average grade of 6% - niobium: average grade of 0.13% - fluorite (CaF2): average grade of 9% - barium oxide (BaO): average grade of 2.4% 5.3. Description of the beneficiation process The beneficiation process is described in Table 2. For each stage of this process, a description is given as well as the sources of the information. 5 These grades are surprisingly lower than the average rare earth grade (6%), this may be because in Bayan Obo, REO are produced as a by-product of iron.32
  33. 33. Table 2: Beneficiation process in Bayan Obo Stage   Purpose   Process  description   Reference   o Schüler et al. 2011 o Cheng et al. 2007 Crushing   • Crushing of 90% of the • The ore is crushed and ground in a mill o Guy et al. 2000 resulting particles to < 74 µm o Ren et al. 1997 o Drew et al. 1990 • Recovery of silicates and iron minerals (magnetite Fe3O4 and hematite Fe2O3) from the bottom of the flotation cell for ion beneficiation and niobium recovery Bulk   • Separation of rare earth minerals • pH regulation by Na2CO3 o Gupta and Krishnamurthy 2005 flotation6   and the gangue from the other valuable minerals • Depressant action by Na2SiO3 • Collection of rare earth minerals and gangue by sodium salt of oxidised petroleum (paraffin soap) • Removal of the surplus paraffin - o Hout, et al. 1991 Thickening   soap and desliming at 5 µm o Gupta and Krishnamurthy 2005 • pH regulation by Na2CO3 Selective   • Separation of rare earth minerals o Gupta and Krishnamurthy 2005 • Depressant action by Na2SiF6 and Na2SiO3 rare  earth   from calcite (CaCO3), fluorite o Ren, et al. 2003 (CaF2) and barite (BaSO4) • Collection of rare earth minerals by hydroxamic acid flotation6   (paraffin soap) o Ferron, et al. 1991 minerals o Gupta and Krishnamurthy 2005 Cleaning   • Concentration of rare earth • Thickening, filtering and drying of the resulting slurry o British Geological Survey 2010 minerals o Wang, et al. 2010 6 The flotation process is described further in Appendix 233
  34. 34. 5.4. Composition of the mixed rare earth concentrate Figure 16 illustrates the composition of the mixed rare earth concentrate obtained after the beneficiation process. MnO   0.48%   CaO   5.11%   CO2   SiO2   11.91%   1.28%   P2O5   8.22%   F   REO   6.96%   60.94%   Fe2O3   4.82%   ThO2   0.18%   Figure 16: Composition by weight of the mixed bastnaesite-monazite concentrate (Wang et al. 2002) 5.5. Processing of the mixed rare earth concentrate 5.5.1. Hydrometallurgy: acidic method An acidic method is used to process 90% of the product of Bayan Obo. It consists in the roasting and leaching of the concentrate with sulphuric acid (Schüler et al. 2011). Table 3 summarises the hydrometallurgy processes at Bayan Obo. 5.5.1. Separation and refining Table 4 describes the processes of separation and refining leading to the production of REOs. 5.6. Obtaining of rare earth oxides A tonne of REOs produced in Bayan Obo is composed as described in Figure 17.34
  35. 35. Table 3: Processing of mixed rare earth concentrate in Bayan Obo Stage   Purpose   Process  description   Reference   • Mixing of rare earth concentrate and 98% sulphuric acid (H2SO4) in a rotary kiln at 500°C for 4 hours. o Schüler, et al. 2011 • Removal of CO2, • Reactions for bastnaesite: o Huang, et al. 2005 Sulphatising   phosphate and fluoride ReFCO3  ReFO + CO2 • Conversion of rare o Gupta and Krishnamurthy 2005 roasting   2 ReFO + 3 H2SO4Re2(SO4)3 +2 HF +2 H2O earth minerals into rare o Nguyen, et al. 2002 earth sulphates • Reactions for monazite: o Wang, et al. 2010 2 RePO4 + 3 H2SO4  Re2(SO4)3 + 2 H3PO4 o Todorovsky, et al. 1993 • Decantation of the mixture to remove the solid o Roskill 2007 Removal  of   • Filtration and leaching with water o Schüler, et al. 2011 impurities   • Removal of impurities • Obtaining of a pure rare earth sulphate solution o Kul, et al. 2008 o Nguyen, et al. 2002 o Gupta and Krishnamurthy 2005 • Rinsing of rare earth sulphates with bicarbonates o Nguyen, et al. 2002 • Selective precipitation Carbonate   and recovery of the rare NH4HCO3 in an acid solution: o Schüler, et al. 2011 precipitation   earth sulphates into Re2(SO4)3+ 6 NH4HCO3  Re2(CO3)3 + 3 (NH4)2SO4 o Kul, et al. 2008 + 3 CO2 + 3 H2O o Abreu and Morais 2010 carbonate precipitate • Transformation of rare • Rinsing with hydrochloric acid (HCl) Acid   earth carbonate • Transformation to rare earth chlorides: o Schüler, et al. 2011 leaching   precipitate into rare earth Re2(CO3)3 + 6 HCl  2 ReCl3 + 3 H2CO3 o Huang, et al. 2005 chlorides35
  36. 36. Table 4: Separation and refining processes in Bayan Obo Step   Purpose   Process  description   Reference   • The liquid-liquid extraction is carried out using 2- ethylhexylphosphonic acid mono-2-ethylhexyl ester (also named HEH(EHP), EHEHPA or P 507) in a HCl medium. o Schüler, et al. 2011 Solvent   • Separation of REEs • Complexation reaction: o Fontana and Pietrelli 2009 Extraction7   from each other Re3+ + 3 (HX)2  ReX6H3 + 3 H+ o Sato 1989 HX referring to P507 • The separated rare earth solution is precipitated by • Separation of rare ammonium bicarbonate (NH4)HCO3 or oxalic acid C2H2O4 o Qiu, et al. 2010Precipitation   earth complexes from • Chemical reactions: o Schüler, et al. 2011 the solvent 2 ReCl3 + 3 C2H2O4  Re2(C2O4)3 + 6 HCl • The precipitates are heated in order to oxidise them intoProduction  of   • Oxidation of the REO • Oxidation reaction: o Schüler, et al. 2011 REO   precipitate Re2(C2O4)3 + 3/2 O2  Re2O3 + 6 CO2 8 7 The solvent extraction process is described further in Appendix 3 8 The oxidation reactions depend on the rare earth concerned: - for La, Nd and Sm: Re2(C2O4)3 + 3/2 O2  Re2O3 + 6 CO2 - for Ce: Ce2(C2O4)3 + 2 O2  2 CeO2 + 6 CO2 - for Pr: 3 Pr2C2O4 + 11/2 O2  Pr6O11 + 6 CO236
  37. 37. La2O3   235.4  kg   Pr6O11   51.2  kg   Nd2O3   CeO2   184.2  kg   512.8  kg   Sm2O3   16.4  kg   Figure 17: Composition of a tonne of rare earth oxides produced from Bayan Obo ore (Spooner 2005)6. Maoniuping deposit 6.1. Description of the deposit Maoniuping deposit is located at 22 km southwest of the Mianning county town(Sichuan Province, China). The soil is composed mainly of granite (K-feldspar graniteand alkali feldspar granite). Among rare earth minerals, bastnaesite is the most important in this deposit(Wu et al. 1997). The average grade of REEs in this deposit is about 4%. This depositcontains also manganese (Mn) (2-10%), lead (Pb) and aluminium (Al) among otherminerals (Zhu et al. 2000). Maoniuping is the second largest deposit of light REEs in China after Bayan Obo(Xu et al. 2003). 37
  38. 38. 6.2. Composition of the original ore Figure 18 illustrates the composition of the ore in Maoniuping deposit. TiO2   SO3   0.28   3.9   BaO   Al2O3   1.89   16.3   CaO   1.3   CO2   SiO2   3.77   36   F   Fe2O3   1.29   11   Rare  earths   H2O   4.34   6.22   Pb   K2O   1.97   MnO   3.89   3.78   P2O5   Na2O   MgO   0.64   0.4   3.03   Figure 18: Composition of the ore in Maoniuping’s mineral (Zhu et al. 2000) 6.3. Description of the beneficiation process The process of beneficiation in Maoniuping is described in Table 5.38
  39. 39. Table 5: Beneficiation process in Maoniuping Step   Purpose   Process  description   Reference   • Reduction of the size of the particles so • The ore is crushed and ground in a mill o Schüler, et al. 2011 Crushing   as to increase the o Zhu, et al. 2000 surface of reaction Gravity   • Separation and o Schüler, et al. 2011 - separation   recovery of certain o Yang and Woolley 2006 valuable minerals Selective  rare   • Separation of rare - o Schüler, et al. 2011 earth  flotation   earth minerals from the gangue • The resulting slurry is thickened, filtered and dried o Gupta and Krishnamurthy 2005 • Recovery of rare • The overall recovery of REEs lies between 80 and o British Geological Survey 2010 Cleaning   earth concentrate 85% and the concentrate contains up to 70% REEs o Wang, et al. 2010 o Li and Zeng 200339
  40. 40. 6.4. Processing of the mixed rare earth concentrate 6.4.1. Hydrometallurgy: acidic method Table 6 summarises the hydrometallurgy processes at Maoniuping. 6.4.2. Separation and refining operations The separation and refining operations in Maoniuping are the same as those in Bayan Obo (see 5.5.1) (Schüler et al. 2011). 6.5. Obtaining of rare earth oxides A tonne of REOs produced in Maoniuping is composed as described in Figure 19. La2O3   296.1  kg   Pr6O11   CeO2   46.7  kg   510.1  kg   Nd2O3   131.8  kg   Sm2O3   15.2  kg   Figure 19: Composition of a tonne of rare earth oxides produced from Maoniuping ore (Spooner 2005)40
  41. 41. Table 6: Processing of rare earth concentrate in Maoniuping Step   Purpose   Process  description   Reference   • The concentrate is mixed with 98% sulphuric acid o Schüler, et al. 2011 • Removal of CO2 (H2SO4) in a rotary kiln at 500°C for 4 hours o Huang, et al. 2005 Sulphatising   and fluoride • Reactions: o Nguyen, et al. 2002 roasting   • Conversion of rare ReFCO3  ReFO + CO2 o Wang, et al. 2010 earth minerals into ReFO + H2SO4Re2(SO4)3 +2 HF +2 H2O o Gupta and Krishnamurthy 2005 rare earth sulphates • The mixture is decanted to remove the solid o Todorovsky, et al. 1993 • The solution is filtered and leached with water o Roskill 2007 Removal  of   • Removal of • A pure rare earth sulphate solution is obtained (this o Schüler, et al. 2011 impurities   impurities solution contains around 40g/L of rare earth o Kul, et al. 2008 sulphates) o Nguyen, et al. 2002 o Gupta and Krishnamurthy 2005 • Selective • REEs are leached with sodium sulphates (at o Nguyen, et al. 2002 Sulphate   precipitation and pH 1.5) o Schüler, et al. 2011 precipitation   recovery of the rare • Precipitation reaction: o Kul, et al. 2008 earth sulphates into Re3+ +Na+ + 2 SO42-  NaRe(SO4)2 o Abreu and Morais 2010 sulphate precipitate • Rare earth carbonates are leached with hydrochloric acid (HCl) • Transformation of • The carbonates are transformed to rare earth o Schüler, et al. 2011 Acid  Leaching   rare earth carbonate chlorides precipitate into rare o Huang, et al. 2005 earth chlorides • Chlorination reaction NaRe(SO4)2 + HCl  ReCl3 + Na+ + 3 H+ + 2 SO42-41
  42. 42. Life Cycle assessment (LCA) 7. Life cycle assessment methodology A cradle-to-gate methodology rather than full cradle-to-grave life cycle assessment (LCA) was used since it allowed restriction of the scope of this study. The cradle to gate approach defines the boundaries as “from raw material to factory gate”. In this case, it was indeed from raw material to REO output, without consideration of the fate of the numerous products made with REEs. In conformity with LCA methodology, this LCA is composed of the following sections: - Goal and Scope definition - Life Cycle Inventory - Life Cycle Impact Assessment - Life Cycle Interpretation Firstly, the goal and scope section exposes the reasons why the LCA is carried out as well as defines the boundaries of the LCA. Secondly, the life cycle inventory aims at determining the inputs and outputs of material or energy that are required by the different processes. This phase is based on a meticulous modelling of these processes. Thirdly, the life cycle impact assessment classifies and characterises the results of the life cycle inventory to come up with a quantitative estimate of environmental impacts. Finally, the life cycle interpretation draws conclusion on the LCA based on the three first steps. It helps analysing the results as well as the gaps in the study. 8. Goal definition and scope 8.1. Goal of the life cycle assessment The goal of the LCA is to establish baseline information for the processes taking place in the two biggest deposits of light REEs and resulting in the production of REO. This baseline consists of energy and chemical requirements, waste generation and pollution. This study should be looked at as starting points for people aiming at: - carrying out the full life cycle assessment of lanthanum, cerium, praseodymium or neodymium products - studying the environmental impacts of a product containing these REEs - studying the two deposits that are scrutinised here - carrying out a similar study for a different mineral - gaining knowledge about REEs The intended audience is whoever is interested in the requirements and impacts of producing REOs.42
  43. 43. 8.2. Level of specificity Although this study focuses precisely on two mines, it uses specific data whenavailable and average data otherwise. Due to the lack of available information, a highlevel of accuracy is not to be expected. The results should rather be considered as givingrealistic orders of magnitude of the energy and chemical consumption, waste generationand pollution emissions. 8.3. Display of results Throughout the LCA, the results are expressed “per tonne of REOs” (except whereotherwise stated). This means that the amounts are estimated for a final production of onetonne of REO. 8.4. Scope of the life cycle assessment The study is not a full life cycle assessment, it is composed of two stages: rawmaterial acquisition and materials manufacture. It focuses on the mining, beneficiationand refining operations to obtain REOs. These boundaries are in accordance with thescope defined in section 4. Besides, the study takes into consideration only primary activities that contribute toextracting and transforming the mineral. It does not considerate activities that contributeto making the primary activities possible. 8.5. Guideline to life cycle assessment methodology In order to carry out this study according to international standards, a mainguideline was followed as meticulously as possible: - Life cycle assessment: principles and practice by the U.S. Environmental Protection Agency (Curran 2006)9. Process Modelling: The processes described in the previous sections were modelled in order to calculatethe amount of inputs and outputs required by the production of REOs. In order to simplify the understanding, the processes of Bayan Obo were firstlymodelled and then the processes of Maoniuping were modelled. 9.1. Bayan Obo deposit The calculations are explained in Appendix 4. 9.1.1. Mining On the one hand, there are two different kinds of inputs: energy to fuel themachinery and explosives. On the other hand, there are two different types of outputs:valuable minerals and waste rocks. Before modelling the mining operation, consideration is given to the mining rate. The results and assumptions are summarised in Table 7. 43
  44. 44. 9.1.1.1. Mining rate The mining rate is the rate of rock extraction, it is expressed in tonnes per day (tpd). Assuming that mining rate in the Bayan Obo deposit increased proportionally to the REO production, the mining rate of 15,000 tonnes per day (tpd) in 2006 (Castor and Hedrick 2006) can be used to estimate the mining rate in 2010. As a result, it is estimated that the Bayan Obo mining rate was about 16,200 tpd in 2010. 9.1.1.2. Energy requirement Due to a lack of public data, it was not possible to estimate the energy consumption of the mining operations directly. However, the order of magnitude of the energy consumption is provided in the Mining Engineering Handbook, which estimates that surface mining operations require 5 to 10 kWh per tonne of rock handled (Nilsson 1992). Thus, considering 7.5 kWh per tonne of rock handled (middle figure between 5 and 10 kWh), it is estimated that the annual quantity of energy consumed in the mining operations amounts to 44.3 GWh. Assuming that the mining operations are carried out with machinery (trucks, shovel…), this amount of energy is provided with fuel. 9.1.1.3. Explosives input In the same document, Nilsson estimates that surface mining operations requires 0.14 to 0.23 kg of ammonium nitrate/fuel oil (ANFO) 9 per tonne of blasted rock (Nilsson 1992). Assuming that the mining operations requires 0.2 kg of ANFO per tonne of blasted rock, the annual quantity of ANFO for the mining operations is about 1,180 tonnes. 9.1.2. Comminution This stage of the operations does not require any input but energy to grind and crush and the rock to be ground and crushed. The only output is the crushed rock. The energy requirements are estimated based on a similar rare earth mining project. This project takes place in Thor Lake (Northwest territories of Canada), it is supposed to start the production not before 2014. The company Avalon Rare Metals is carrying out this project (Eriksson and Olsson 2011). Avalon Rare Metals has estimated that 6 MW are necessary in average for the 2,000 tpd milling operations (comminution, beneficiation and hydrometallurgy) (Cox et al. 2011). As a result, it is estimated that the comminution, beneficiation and hydrometallurgy operations in Bayan Obo require 426 GWh per year. The results and assumptions of the mining and comminution sections are summarised in Table 7. 9 ANFO is an explosive composed of ammonium nitrates (NH4NO3) and oil.44
  45. 45. 9.1.3. Beneficiation During the production of concentrated bastnaesite, several different chemicals areused to obtain the right froth flotation. Unfortunately, it was not possible to identify thedifferent chemicals nor to determine how long these solutions can be used before beingdiscarded. However, two main other inputs have been identified for this stage: energy for thechemical reactions and mined minerals. The outputs are of three different types: - rare earth concentrate - other valuable minerals (such as those containing Fe or Nb) - tailings Assuming a full recovery and high selectivity of the magnetic minerals (Fe and Nb)thanks to the magnetic separation roll, the beneficiation process is described in Figure 20. 45
  46. 46. 46 Table 7: Summary of the mining and comminution processes modelling Stage   Type   Quantity   Assumptions   o proportionality to REO output o Bayan Obo represented 48% of Mining   Mining rate 16,200 tpd the production in 2006 (as in 2010)   Energy requirement 44.3 GWh per year o mining rate assumption   Explosives 1,180 tonnes per year o mining rate assumption Comminution,  Beneficiation  and   o proportionality to Thor Lake Energy requirement 426 GWh per year Hydrometallurgy   project Table 8: Summary of the beneficiation modelling Stage   Type   Quantity   Assumptions   o 75% efficiency of the Beneficiation   Rare earth concentrate produced 139,000 tonnes per year subsequent stages o 60% recovery of REEs o Full recovery and perfect 9.8 tonnes per tonne of rare earth   Waste rock generated selectivity of Fe and Nb concentrate produced minerals
  47. 47. Nb   1.3  kg   0%   35.1 % Fe   350  kg   Magnetic minerals 100%   Fe   6% Rare   350  kg   Earth   35%   36  kg   Gangue   60%   24  kg   Rare earth 40%   Gangue   concentrate 588.7  kg   59%   Rare   Rare   Earth   Gangue   Earth   60  kg   564.7  kg   24  kg   6%   96%   4%   Nb   58.9 % 1.3  kg   0%   Tailings Figure 20: Beneficiation process in Bayan Obo for one tonne of original rock As a consequence, the processing of one tonne of original ore results in theproduction of: - 351 kg of iron and niobium (recovered to be later refined) - 60 kg of mixed rare earth concentrate - 589 kg of tailings Considering the production of REO in 2010 (62,400 t) and assuming a 75%efficiency of the overall subsequent stages (Schüler et al. 2011), it is estimated that139,000 tonnes of mixed-rare earth concentrate were produced that year. The results and assumptions of the beneficiation process are summarised in Table 8. 9.1.4. Hydrometallurgy and separation of rare earths This stage was described in section 5.5. It is composed of several successivechemical reactions. 47
  48. 48. For both deposits, the overall recovery rate of the separation and refining processes is considered to be 75% (Schüler et al. 2011). It is considered that the five different chemical reactions each have the same recovery rate rR: ! !! =   !. 75 = 94.4% Considering that the bastnaesite/monazite ratio was 5:2 (71.4% of bastnaesite and 28.6% of monazite in Bayan Obo’s rare earth mineral) (Huang et al. 2005), each chemical reaction was scrutinised to estimate how much of every chemical is required per rare earth atom. This is described in the following section: Chemical reactions ReFCO3 RePO4 0.71 CO2 For bastnaesite: 3/2 H2SO4 0.71 HF ReFCO3  ReFO + CO2 Acidic roasting Heat 0.71 H2O 2 ReFO + 3 H2SO4 Re2(SO4)3 0.29 H3PO4 + 2HF+2 H2O For monazite: Re2(SO4)3 2 RePO4 + 3 H2SO4  Re2(SO4)3 + 2 H3PO4 3/2 (NH4)2SO4 Carbonate3 (NH4)HCO3 3/2 CO2 Re2(SO4)3+ 6 (NH4)HCO3  precipitation 3/2 H2O Re2(CO3)3 +3 (NH4)2SO4 + 3 CO2 + 3 H2O Re2(CO3)3 3 HCl Acid leaching 3/2 H2CO3 Re2(CO3)3 + 6 HCl  2 ReCl3 + 3 H2CO3 ReCl3 Heat Solvent extraction 3 (HX)2 ReCl3 + 3(HX)2  ReX6H3 + 3 HCl 3 (HX)2 ReX6H3 + 3 HCl  ReCl3 + 3(HX)2 48
  49. 49. The stoichiometric coefficients for the hydrometallurgy process are summarised in Table 9. 9.1.5. Refining Likewise, the estimation of the amounts of necessary chemicals for the refining process was carried out based on the different chemical reactions. ReCl3 Chemical reactions 2 ReCl3 + 3 C2H2O4  Re2(C2O4)3 +3/2 C2H2O4 Precipitation 3 HCl 6 HCl Re2(C2O4)3 Re2(C2O4)3+ 3/2O2 Re2O3+ 6 CO2 for Heat Oxidation 3 CO2 La, Nd & Sm 0.93 O2 Re2(C2O4)3+ 2 O2  2 ReO2 +6 CO2 for Ce 3 Re2(C2O4)3+11/2O2Re6O11+18CO2 Rare earth oxide for Pr The stoichiometric coefficients for the refining process are summarised in Table 9. 9.1.6. Stripping ratio The stripping ratio is the ratio between the mass of waste rock that is generated and the mass of mineral that goes for further processing. The calculation of the stripping ratio is composed of three steps. Firstly, the yearly mass (mY) recovered in Bayan Obo deposit in 2010 is calculated from the mining rate of the mine: !! = 16,250 ∗ 365 = 5.93  10!  !"##$% Then, the mass of mineral (mM) that is processed is calculated from the rare earth grade of the mineral rate (6%), the production of REO in 2010 (62,400 t), the beneficiation recovery (60%) and the recovery during subsequent processes (75%): !"#  !"#$%&(#)!"#! !! =   = 2.31  10! !"##$% !"#"$%&%(%)#!"#$%"!& ∗ !"#$%$%&!"#$%"!& ∗   !"#$  !"#$ℎ!"#$% Finally, the mass of waste recovered (mWaste) is calculated: !!"#$% = !! − !! = 3.62  10!  !"##!" As a result, the stripping ratio in Bayan Obo is estimated: !!"#$% !"#$%%$&  !"#$% = = 1.57 !! For each tonne of mineral that is processed in the early stages, 1.57 tonne of waste are recovered. 49

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