摘要
Rare earth (RE) metals have been widely applied in new materials, leading to their drastic production increase in the last three decades. In the production process featured by the molten-fluoride electrolysis technology, perfluorocarbon (PFC) emissions are significant and therefore deserve full accounting in greenhouse gas (GHG) emission inventories. Yet, in the ‘2006 IPCC Guidelines for National Greenhouse Gas Inventories’ no method currently exists to account for PFC emissions from rare earth metal production. This research aims to determine emission factors for industrial rare earth metals production through on-site monitoring and lab analysis of PFC concentrations in the exhaust gases from rare earth metal electrolysis. Continuous FTIR measurements and time-integrated samples (analysed off-site by high-precision Medusa GC–MS) were conducted over 24–60 h periods from three rare earth companies in China, covering production of multiple rare earth metals/alloys including Pr-Nd, La and Dy-Fe. The study confirmed that PFC emissions are generated during electrolysis, typically in the form of CF <sub>4</sub> (∼90% wt of detected PFCs), C <sub>2</sub> F <sub>6</sub> (∼10%) and C <sub>3</sub> F <sub>8</sub> (<1%); trace levels of c-C <sub>4</sub> F <sub>8</sub> and C <sub>4</sub> F <sub>10</sub> were also detected. In general, PFC emission factors vary with rare earth metal produced and from one facility to another, ranging from 26.66 to 109.43 g/t-RE for CF <sub>4</sub> emissions, 0.26 to 10.95 g/t-RE for C <sub>2</sub> F <sub>6</sub> , and 0.03 to 0.27 g/t-RE for C <sub>3</sub> F <sub>8.</sub> Converted to 211.60 to 847.41 kg CO <sub>2</sub> -e/t-RE for total PFCs, this emissions intensity for rare earths electrolysis is of lower (for most RE production) or similar (Dy-Fe production) level of magnitude to industrial aluminium electrolysis.