Advancing the Economic and Environmental Sustainability of Rare Earth Element Recovery from Phosphogypsum

Abstract

Transitioning to green energy technologies requires more sustainable and secure rare earth elements (REE) production. The current production of rare earth oxides (REOs) is completed by an energy and chemically intensive process from the mining of REE ores. Investigations into a more sustainable supply of REEs from secondary sources, such as toxic phosphogypsum (PG) waste, is vital to securing the REE supply chain. However, conventional solvent extraction to recover dilute REEs from PG waste is inefficient and has high environmental impact. In this work, we propose a treatment train for the recovery of REEs from PG which includes a bio-inspired adsorptive separation to generate a stream of pure REEs, and we assess its financial viability and environmental impacts under uncertainties through a "probabilistic sustainability" framework integrating life cycle assessment (LCA) and techno-economic analysis (TEA). Results show that in 87% of baseline scenario simulations, the internal rate of return (IRR) exceeded 15%, indicating that this system has the potential to be profitable. However, environmental impacts of the system are mixed. Specifically, the proposed system outperforms conventional systems in ecosystem quality and resource depletion, but has higher human health impacts. Scenario analysis shows that the system is profitable at capacities larger than 100,000 kg*hr-1*PG for PG with REE content above 0.5 wt%. The most dilute PG sources (0.02-0.1 wt% REE) are inaccessible using the current process scheme (limited by the cost of acid and subsequent neutralization) requiring further examination of new process schemes and improvements in technological performance. Overall, this study evaluates the sustainability of a first-of-its-kind REE recovery process from PG and uses these results to provide clear direction for advancing sustainable REE recovery from secondary sources.