Huijing Deng
University of California Davis
Ph.D student in Transportation Technology and Policy, University of California, Davis. Research topics including vehicle electrification, and LCA on MFA on rare earth elements.
Clean energy technologies, such as electric vehicles and wind turbines, have increased demand for permanent magnets, and particularly Nd-Fe-B rare earth magnets, that are used in the electric motors and generators. These are... [ view full abstract ]
Clean energy technologies, such as electric vehicles and wind turbines, have increased demand for permanent magnets, and particularly Nd-Fe-B rare earth magnets, that are used in the electric motors and generators. These are foreseen to be the dominant type of permanent magnets because of their significantly stronger magnetic fields than other types of magnets, thus the constituent rare earth elements (REEs) will need to be supplied at an increasing rate with the growth of clean energy technologies. Because REEs are critical to clean energy, it is important to understand the environmental impacts resulting from their production, and the factors that influence their environmental impacts. Both light REEs (LREEs, e.g. Neodymium) and heavy REEs (HREEs, e.g. Dysprosium) are required in permanent magnets. However, among the handful of life cycle assessment (LCA) studies on REEs, most of them consider only sites that use bastnasite and monazite ores that primarily produce LREEs, and little attention has been paid to sites that mainly produce HREEs. Thus, there is a significant gap in LCAs of HREEs.
China plays a dominant role in REE mining and production, producing about 95% of the world’s REEs. The ion-adsorption clay deposits in southern China are the world’s primary source of HREEs. REEs in ion-adsorption ores are adsorbed on the surface of clay minerals with rare earth oxide (REO) concentrations ranging from 0.05–0.2%. The ion state of REEs in these ores makes extraction and processing easier and more economical than mining from bastnasite and monazite.
This presentation reports the results of a detailed LCA based on original data acquired from 4 local rare earth mining sites in Jiangxi Province, southern China. Among the sites investigated, in situ leaching has become the major technology, replacing heap leaching and pool leaching due to its improved environmental performance. The process involves injecting fluid into the ground and pumping out a liquid mixture. When leaching is complete, fresh water is injected to drive out the remaining REE-bearing solution.
The functional unit in this study is 1 kg of mixed REOs produced from ion-adsorption clays, using the technology of in situ leaching. Since the mining happens in China, the Chinese Life Cycle Database (CLCD) and Ecoinvent 3.0 database were used together to conduct inventory analysis. Allocation based on economic value is proposed to partition impacts to the constituent REEs due to the different market price of each HREE and its concentration in ion-adsorption clays. Allocation based on mass is also presented for comparison. Energy use, ecotoxicity, acidification, resource depletion, and global warming potential resulting from the production of REOs in ion-adsorption clays in southern China is reported.
• Sustainable energy systems , • Products and services, design for the environment, product declarations and labelling , • Sustainable consumption and production
