(96f) Advancing the Economic and Environmental Sustainability of Rare Earth Element Recovery from Phosphogypsum Using a Selective Bio-Based Adsorptive Separation

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 (beneficiation, leaching, separation by solvent extraction, and refinement) 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. PG is a waste byproduct of fertilizer production produced at hundreds of millions of tonnes per year. With a minimum REE content of ~0.02 wt% REEs, PG has the potential to meet the annual REE consumption within the United States (~9,000 tons REE/year). Additionally, PG is stored indefinitely in ‘stacks’ which are vulnerable to the release of toxic and radioactive waste into the environment. The extraction of REEs from this waste may make remediation feasible. However, it is unclear how to recover the dilute REEs from PG waste (conventional solvent extraction is inefficient and has high environmental impact). In this work, we propose a treatment train (technological readiness level < 3) for the recovery of REEs from PG which includes a bio-inspired adsorptive separation to generate a stream of pure REEs. We assessed its financial viability and life cycle environmental impacts via life cycle assessment (LCA), techno-economic analysis (TEA), and identify targeted improvement opportunities through global uncertainty/sensitivity analysis and scenario analysis. We determined that this system can be profitable (net present value of $200 million, internal rate of return of 17%, and minimum selling price (MSP) of $48/kg REO) and shows reduced environmental impact in several ReCiPe 2016 impact categories (land use, ecotoxicity, eutrophication, ionizing radiation, material resource depletion, and human toxicity) when compared to conventional REO production and PG stacking. However, the system underperforms in other impact categories (climate change, terrestrial acidification, ozone depletion, photochemical oxidant formation, particulate matter formation, and fossil resource depletion). The endpoint analysis shows that the system outperforms conventional REO production in ecosystem quality (93.0% of the impact) and resource depletion (96.2% of the impact) but underperforms in human health (213% of the impact). The life cycle environmental impacts and financial viability are primarily driven by chemical consumption in the leaching, concentration, and wastewater treatment process sections ($15/kg REO). In addition to high chemical costs, the large capital cost of the selective adsorption resin ($18/kg REO) limits profitability. Scenario analysis shows that the system is profitable at capacities larger than 100,000 kg/hr 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.