Metal mobilization from lithium-ion battery black mass under rhizospheric conditions: implications for secondary critical raw material recovery

The growing demand for critical raw materials (CRMs), such as lithium, nickel, manganese, and cobalt, is increasing the importance of secondary resources derived from lithium-ion battery recycling. At the same time, improper management of end-of-life batteries may pose potential environmental risks. Understanding the processes controlling metal mobilization from battery-derived materials is therefore crucial, both for assessing their environmental impacts and for developing safe and responsible strategies for CRM recovery.

This study investigates metal mobilization from lithium-ion battery black mass under rhizospheric conditions, characterized by variable pH and the presence of organic compounds. Batch leaching experiments were conducted over seven days using two particle size fractions (<250 µm and >1 mm). The material was exposed to artificial root exudates and demineralized water, both at pH 3.5 and 6.7. Concentrations of Mg, Fe, Cu, Zn, Al, Mn, Ni, Co, and Li in leachates were determined using ICP-OES. In addition, SEM-EDS was applied to characterize particle morphology and elemental distribution before and after leaching.

The results demonstrate that acidic conditions combined with organic compounds significantly enhance metal mobilization, particularly for Al and Cu, which reached extraction levels of up to ~75% and ~55% respectively, while Ni, Mn, and Co exhibited lower but still measurable extraction efficiencies up to 4.33%, 5.52%, 4.08% respectively. In artificial root exudates at pH 3.5, the concentrations of several elements were one to several orders of magnitude higher than those obtained in demineralized water. Leaching factors (ARE/H₂O) reached 32.5 for Cu and 22.5 for Al in the fine fraction, and increased to 4099 for Al and 2127 for Ni in the coarse fraction. Despite these higher factors in the coarse fraction, a clear particle-size effect was observed, with the fine fraction generally exhibiting higher relative extraction, while coarse particles occasionally released greater absolute metal amounts. In contrast, lithium displayed consistently high mobility across all tested media, pH levels and particle sizes, with comparable extraction of ~15-20%, and leaching factors ranging between ~1.0 and 1.6.

These findings demonstrate that rhizospheric processes strongly affect the release of critical elements from lithium-ion battery black mass. While such mobilization represents an environmental risk in the case of uncontrolled disposal, it also provides insights into chemical processes that may be exploited for the recovery of critical raw materials from secondary resources, contributing to more responsible raw material supply chains.

References

Miśta, G. (2025). Environmental effects of uncontrolled waste disposal: the example of batteries. MSc thesis, University of Wrocław