3 years ago

Rare Earths from Mines to Metals: Comparing Environmental Impacts from China's Main Production Pathways

Zongguo Wen, Jason C.K. Lee
Over the past decade, China has supplied over 90% of global rare earths, and in doing so bore significant environmental burdens from processing its complex ores. In this study, we used life cycle assessment to quantify environmental impacts for producing 1 kilogram (kg) of 15 rare earth elements from each major production pathway. The scope of assessment included the largest rare earth oxide (REO) production chain in Bayan Obo, as well as lesser known production chains for bastnäsite in Sichuan and in-situ leaching of kaolin clays in the Seven Southern Provinces of China. This was followed by assessing impacts from the three major metal refining processes: molten salt electrolysis, calciothermic reduction, and lanthanothermic reduction. Among 11 impact categories assessed, results were highest for human toxicity that ranged between 13.1 and 50.4 kg 1,4-dichlorobenzene-eq (equivalent)/kg of rare earth metal−1, followed by eutrophication (0.04 to 1.26 kg phosphate-eq/kg of rare earth metal−1), abiotic depletion potential of fossil fuels (592 to 1,857 megajoules per kg of rare earth metal−1), acidification (0.25 to 0.87 kg sulfur dioxide-eq/kg of rare earth metal−1), and global warming (39.1 to 109.6 kg carbon dioxide-eq/kg of rare earth metal−1) potentials. Regionally, impacts in Sichuan were lower across all key impact categories than in Bayan Obo: 32% lower for human toxicity, 67% lower for eutrophication, 58% lower for acidification, and 45% lower for global warming. A scenario analysis between the industry average and best available technologies revealed considerable potential to mitigate impacts across all production chains, particularly by improving waste treatment practices.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/jiec.12491

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