Life cycle assessment with primary data on heavy rare earth oxides from ion-adsorption clays

Abstract

Heavy and light rare earth elements (REEs) are critical to clean energy technologies, and thus the environmental impacts from their production are increasingly scrutinized. Most previous LCAs of REE production focus on sites producing light REEs. This research addresses this gap by collecting primary data from sites producing heavy rare earth oxides (HREOs) from ion-adsorption clays, conducting an LCA, and providing open-source life cycle inventory (LCI) datasets of HREO production for the LCA community. Methods This study conducts a LCA based on acquired primary data from four mining sites in Jiangxi Province, China. The functional unit is 1 kg of mixed HREOs of 90% purity from ion-adsorption clays using the technology of in situ leaching. Previous studies have used the Ecoinvent database, relying mostly European or global life cycle inventories (LCIs). Here, the Chinese Life Cycle Database provided China-specific reference life cycle inventories (LCIs). The Ecoinvent 3 database was also used in this study, however, for electricity generation LCIs used in a scenario analysis evaluating China's changing grid mix (Wernet et al. 2016). Twelve impact categories were examined using Impact 2 2002+, USEtox 2.01 and IPCC methods. Results are provided as a bounded range, reflecting low and high estimates based on collected primary data. Results and discussion Results show 1 kg of mixed HREOs emit 258-408 kg CO2e, and consume 270-443 MJ primary energy. These values fall within the range of previous LCAs that examined both bastnaesite/monazite deposits and ion-adsorption clays using literature values. Other impact categories considered are not similar across studies, however. Differences are due to variability in resource type and quality, technology, and modeling choices, such as reference LCI sources. Mining and extraction contribute most to impacts due to large quantities of chemicals for leaching and precipitation of REOs, and electricity consumption. Among chemicals, ammonium sulfate is the largest contributor to many impact categories. When China's electricity grid mix change over time is included, environmental impacts for the whole production process can change up to 12%. Conclusions The primary contributions of this study are the collection and publication of primary data from mining companies in Jiangxi Province, China; the provision of open-source LCI datasets for mixed HREOs from ion-adsorption clays; and a comparison of results between this study and previously published studies. While the scope of this study concludes at the production of mixed HREO, which is a limitation, it provides a foundation for development of LCIs for refined heavy REEs.

Environmental impacts of rare earth production

“…Reaction equations (3)(4)(5)(6) show the cracking of pure bastnäsite with HCl. 23 The formation of large amounts of HF is avoided.…”

Towards sustainable extraction of technology materials through integrated approaches

“…per kg REO assuming a 90-92% purity 102 , whilst another provided a range between 18.8 and 33.11 kg CO 2 eq. per kg REO with a 90% purity 103 . LCAs have also been carried out on separated REE production from monazite mineral sands with an average impact of 65.4 kg CO 2 eq.…”

Exploring the REEs Energy Footprint: Interlocking AI/ML with an Empirical Approach for Analysis of Energy Consumption in REEs Production

“…In 2016, the EC for the world's deposits was analyzed, and the average was approximately 1218 GJ per 1 ton of RO [12]. The estimated EC for Ion adsorption clays to produce 1 ton of RO was 19.86 GJ in 2016 [17] and 442.60 GJ [18] in 2019. In 2019, the estimated EC for mining and mineral processing operations, to process 1 ton of mine/mill tailings, was 0.02-0.05 GJ [19,20].…”