In a surprising twist, a recent study has revealed that recycling nickel-metal hydride (NiMH) batteries for rare earth elements (REEs) may result in higher reported CO₂ emissions compared to extracting these elements from primary ores. This finding, published in the journal Metals, suggests that the environmental benefits of recycling might not be as straightforward as previously thought.
Conducted by researchers Daniel Sánchez Piloto and Denise Crocce Romano Espinosa from the University of São Paulo, along with Amilton Barbosa Botelho Junior from the Norwegian University of Science and Technology, the study reviews life cycle assessments (LCAs) comparing the climate impacts of producing rare earth oxides (REO) from primary ores versus recovering REEs from end-of-life NiMH batteries. Their analysis indicates that recycling could report CO₂ emissions approximately 4 to 9 times higher per kilogram of REE than primary extraction, depending on allocation choices.
Understanding the Nuances of Recycling Emissions
The authors caution that these results should not be interpreted as evidence that recycling is inherently worse for the environment. The comparison is complicated by the fact that recycling systems are multifunctional, recovering multiple metals such as nickel and cobalt alongside REEs. These systems also vary by geography, energy mix, and system boundaries, making direct comparisons challenging.
“Recycling systems recover multiple metals and use different functional units, which makes the comparison not apples-to-apples,” the authors note.
Study Approach and Methodology
This structured literature review involved screening studies from major databases like Scopus and ScienceDirect, focusing on LCAs that report climate impacts in terms of global warming potential (GWP) and CO₂-equivalents. For primary extraction, the authors selected studies reporting emissions per kilogram of mixed REO from bastnäsite and monazite pathways. For recycling, they prioritized industrial-scale studies, supplementing with lab-scale research as needed.
The review highlights a significant gap: there is no harmonized, direct industrial-to-industrial LCA comparison of primary REO production versus NiMH REE recovery, which limits the ability to make definitive conclusions.
Key Findings and Limitations
The study found that emissions from primary extraction are primarily driven by energy- and reagent-intensive chemical processing and separation steps. In contrast, recycling appears to have higher carbon emissions when impacts are allocated mainly to REEs, as NiMH recycling typically targets multiple co-products.
Several recycling LCAs were not designed to isolate process-specific emissions for REE recovery, requiring approximate allocations from whole-system results. The authors emphasize that differences in functional units, system boundaries, and regional electricity mixes materially constrain comparability.
“The reported ranges are best viewed as directional magnitudes under specific modeled contexts, not a definitive verdict on the inherent sustainability of recycling,” the study concludes.
Implications and Future Directions
This review challenges the simplistic narrative that recycling is automatically lower-carbon under current industrial configurations. However, recycling remains strategically valuable as it diversifies supply, reduces reliance on concentrated mining geographies, and could offer larger net benefits when co-product credits and avoided primary production are properly accounted for.
Moving forward, the authors call for harmonized LCAs with consistent functional units, transparent industrial datasets, and scenarios reflecting cleaner energy grids and advancements in “green solvent extraction” and improved separation techniques.
As the world continues to grapple with climate change, understanding the true environmental impact of recycling versus primary extraction is crucial. This study serves as a reminder of the complexities involved in assessing the sustainability of industrial processes and the need for nuanced, comprehensive evaluations.
