Life-Cycle Assessment of Rare Earth Production from Monazite

Rare Earth Deposits & Mining

Browning, and 4 co-authors, reported in 2016 that the environmental life cycle impacts of conceptual rare earth production processes were assessed. An average greenhouse gas emission of 65.4 kg CO₂e/kg was estimated for the 15 rare earths produced from monazite, ranging from 21.3 kg CO₂e/kg for europium to 197.9 kg CO₂e/kg for yttrium. The average water consumption of rare earth production was 11,170 kg/kg ranging from 3,803 kg/kg for samarium and gadolinium to 29,902 kg/kg for yttrium. The average gross energy requirement for production was 917 MJ/kg, ranging from 311 MJ/kg for samarium and gadolinium to 3,401 MJ/kg for yttrium. Given the low concentration of HREE in monazite, the high impacts across all categories for yttrium and other HREE are not necessarily representative of HREE sourced from all rare earth resources. Further studies into other rare earth mineral resources (e.g. bastnasite and xenotime) are recommended to improve the overall understanding of environmental impacts from rare earth production.

The authors concluded that rare earth production from monazite produces impacts far greater in magnitude than any other metals currently investigated with a LCA. This is due to the large and complicated flowsheet with high energy consumption associated primarily with numerous solvent extraction stages and high chemical consumption due to the inherent difficulty in separating the individual rare earth elements. The GWP of titanium from the Becher and Kroll process is 35.7 kg CO₂e/kg while results from this study indicate an average GWP of 65.4 kg CO₂e/kg for monazite processing. Similar results are seen for the GER (361 MJ/kg for titanium, 917 MJ/kg rare earth average) and SWB (351 kg/kg for nickel via hydrometallurgical processing, 497 kg/kg REs average).

It is a reasonable assumption that all other impact categories investigated also display far higher impacts for rare earths than for other commodity metals. This study represents a starting point for further research into investigation of environmental effects resulting from rare earth production. Building a knowledge base of the rare earth minerals may assist in decision making for further development of the rare earth industry, and result in cleaner production of these industrially important metals.