Comparative Life Cycle Assessment of NdFeB Permanent Magnet

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Comparative Life Cycle Assessment of NdFeB Permanent Magnet Production from different Rare Earth Deposits Andrea Schreiber, Josefine Marx, Petra Zapp, and Frank Walachowicz ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b04165 • Publication Date (Web): 22 Mar 2018 Downloaded from http://pubs.acs.org on March 22, 2018

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ACS Sustainable Chemistry & Engineering

Comparative Life Cycle Assessment of NdFeB Permanent Magnet Production from different Rare Earth Deposits Josefine Marx,† Andrea Schreiber,*† Petra Zapp,† Frank Walachowicz‡ †

Forschungszentrum Jülich, Institute of Energy and Climate Research – Systems Analysis and Technology Evaluation

(IEK-STE), D-52425 Jülich, Wilhelm-Johnen-Straße, Germany ‡

Siemens AG Corporate Technology, Research in Energy and Electronics, 13629 Berlin, Siemensdamm 50, Germany

[email protected], [email protected], [email protected], [email protected] Supporting information

Abstract Neodymium, praseodymium and dysprosium are rare earth elements often used in high performance magnets. Environmental impacts during the production of 1 kg neodymium iron boron (NdFeB) magnet from three major deposits are quantified using life cycle assessment (LCA). The scope of the assessment includes the largest rare earth oxide (REO) production in Bayan Obo (China), the second largest at a mine in Mount Weld (Australia), and a third mine in Mountain Pass (US) that closed production in 2015. Consecutively impacts from metal refining and final magnet production are added. Environmental impacts along the magnet production life cycle are dominated by the production of rare earth components (50 – 99.9%). Using REOs from the American mine shows best overall environmental performance due to improved handling of chemicals. Biggest differences to the worst Chinese pathway can be found in freshwater and terrestrial ecotoxicity, acidification, freshwater eutrophication, particulate matter and human toxicity. The smallest differences are observed for climate change, resource depletion and marine eutrophication. For the first time an LCA for the three largest rare earth producers was performed under the same frame conditions and methodological assumptions. This approach is a step towards getting a consistent picture of environmental impacts. Keywords: rare earth permanent magnets, Bastnaesite, Monazite, life cycle assessment

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[email protected]

Introduction In 2016 world rare earth mine production was 126,000 metric tons rare earth oxide (REO) equivalents predominately in China (105,000 t).1 Several rare earth elements (REEs) are used for the transformation of the fossil era into a decarbonized energy sector. REEs are essential for wind and solar energy, electric and hybrid vehicles or low-energy lighting. Approx. 20% of the REEs are used for magnets in motors and generators.2 Rare earth iron boron magnets (NdFeB) are among the strongest permanent magnets. Basis for the technical properties of magnets are the use of the specific REEs neodymium (Nd), praseodymium (Pr) and dysprosium (Dy). A typical NdFeB magnet used in wind turbines consists of approx. 65% iron, 32% RE metals, 2% cobalt and 1% boron. Today, REEs are produced in two major supply chains.3 China represents the largest REEs producer worldwide (85%) and Bayan Obo is the largest Chinese REE deposit;4 Australia is the second biggest producer (8%) and the most prominent one of the Western World.5 The Mount Weld deposit is the biggest known REE deposit outside of China. The United States have been the third largest producer worldwide (3%).5 Its Mountain Pass mine is an important REE deposit but production was stopped in 2015 for the time being due to financial problems. The three deposit sites do not only vary in their locations, with different environmental legislation or infrastructures, they also present different mineral types. While Bayan Obo is a mixture of bastnaesite and monazite, the other two deposits are dominated by a single mineral (bastnaesite in Mountain Pass, monazite in Mount Weld). REE production is often associated with high ecological damage, as previous life cycle assessment (LCA) studies have shown.5-20 Most of them consider the production of (mixed) REOs from the bastnaesite/monazite ore of Bayan Obo.5-6, monazite.9,

12, 18

9, 13-16

A few studies analyze REO production from

Four studies focus on REEs production from ion adsorption clays (IACs) in

Southern China.8, 11, 21-22 Only two studies analyze NdFeB magnet production.6, 23 However, even for studies based on the Bayan Obo deposit, the environmental impacts differ considerably. Reasons are different assumptions about technical parameters (e.g. ore concentration, yield, 2 Environment ACS Paragon Plus

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efficiency of beneficiation), allocation procedures as well as databases and life cycle impact assessment (LCIA) methods. Most of the studies based on Bayan Obo use outdated unit processes for RE production from the ecoinvent database16 (see SI for detailed discussion of ecoinvent process for rare earth production). This study performs a comparative LCA for the production of a 1 kg NdFeB magnet which can be used in direct drive wind generators. Three different production pathways are distinguished with Nd and Pr obtained from the Mount Weld, Mountain Pass and Bayan Obo deposits. Dy is obtained from Chinese IACs for all pathways. The subsequent metal processing steps and the NdFeB magnet production take place in China. For the first time the three RE process routes can be compared directly because consistent frame conditions such as system boundary settings, level of detail, market allocation methods (based on the same market prices), inclusion of waste and waste water treatment with comparable assumptions, same software and database have been employed.

Methods An LCA is performed to quantify the environmental impacts of Nd and Pr production from the Bayan Obo, Mount Weld and Mountain Pass deposits, Dy from IACs as well as the subsequent metal and NdFeB magnet production in China. LCA is an adequate method for a holistic evaluation of environmental effects of a product system considering the entire life cycle.24-25 Emissions, energy and material flows related to this life cycle are quantified and evaluated in terms of environmental impacts. So called foreground processes cover the entire production chain of NdFeB magnets, from mining to final magnet production, but not the incorporation of magnets into wind generators. Data is based on literature sources, producer information and expert opinions. The GaBi6.115 software26 is used combined with the Ecoinvent 3.3 database27 for background process data (e.g. supply of auxiliary material, energy, transport). The functional unit is a 1 kg NdFeB magnet. Since production of REEs is a multi-product system environmental burdens have to be allocated appropriately. In this study an allocation method based on the market prices of REOs28 is considered. To estimate uncertainties that refer to the allocation method a mass-based 3 Environment ACS Paragon Plus


allocation is undertaken as a sensitivity analysis (Table S4, Figure S1). Both allocation procedures are described in the supporting information (SI, chapter Methods). Twelve impact categories from the ReCiPe 1.08 midpoint (H) method29 are selected for LCIA: fossil depletion, climate change, terrestrial acidification, freshwater and marine eutrophication, ozone depletion, photochemical oxidant formation, human toxicity, terrestrial ecotoxicity, freshwater ecotoxicity, ionizing radiation, and particulate matter formation. To deal with data uncertainty, each single process has received a data quality indicator based on the classification system of the American Association of Cost Estimation30 applied for the Mining and Mineral Processing Industries (SI, Table S 25 and S 26), in order to evaluate the validity of the results (Table S 27).

Life Cycle Inventory In this section the production pathways are discussed. Figure 1 outlines the systems assessed, indicating the different production sites and the necessary transports between them. As no electrolysis outside of China exists, the REOs obtained from Mountain Pass and Mount Weld have to be transported to China for further metal reduction.5 Dy is obtained from IACs by in-situ leaching with ammonium sulfate in Southern China. Data for Dy production is taken from a separate paper which has been published recently.21 For magnet production three pathways are assumed: a Chinese magnet producer for the Bayan Obo process chain, a Malaysian producer (100% Japanese owned) for the Mount Weld process chain, and a Japanese producer for the Mountain Pass process chain.6, 31-32 Thus, the metals have to be transported from electrolysis in Baotou to the magnet facilities (Figure 1).


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Southern provinces (CN)

Pr6O11

Nd2O3

Mountain Pass (US)

In-situ leaching of IAC

Nd2O3

Pr6O11

Nd, Pr

transport

Kuantan (MY)

Ningbo Konit (CN)

transport

Pr6O11

magnet production

REE

reduction

Nd2O3

Baotou (CN)

Mount Weld (AUS)

REO

Kuala Lumpur (MY)

transport

Bayan Obo (CN)

separation

electrolysis Baotou (CN)

beneficiation

mining

transport

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transport

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Fukui (JP)

NdFeB

NdFeB magnet

separation

Shaoguan (CN)

Dy2O3

calciothermic Dy reaction Shaoguan (CN)

Figure 1. Production sites of the three supply chains. Rare earth metal production. A more detailed description is shown in Figure 2. Plant specific documentation, regulations, and domain specific knowledge from experts at Aachen University33-35 were considered to model the various processes. The basic proceeding for Nd and Pr production is the same at all three deposits. It is identical for Nd and Pr except for the last solvent extraction step (SX5) where both are separated (Figure 2). Therefore the following descriptions for Nd also apply for Pr.



Figure 2. Exemplary process chain of the three supply chains for the production of Nd. The process chains start with a conventional open pit mining process. Due to the lack of plant specific inventory data (e.g. energy supply, explosives), data from literature16, 36-40 is modified with mining parameters such as stripping rate, mining rate, and life time to determine the life cycle inventory data for the mining processes of each deposits. Ore composition and detailed process data are listed in SI. The beneficiation consists of different comminution steps followed by flotation. All crushing and grinding processes are similar, although the products differ in grain size (Mount Weld

Comparative Life Cycle Assessment of NdFeB Permanent Magnet

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