From Sulfur to Salvage: Bacteria and Battery Recycling

You have probably been told not to throw old batteries in the trash as improperly disposing them carries several environmental and safety risks. Spent batteries also contain valuable materials and recycling them thus has several economic benefits.

Depending on their makeup, lithium-ion batteries contain metals such as lithium, cobalt, nickel, and manganese (Harper et al. 2019). Recovering these metals requires separating batteries into their components and processing electrode materials; which is a relatively complicated task (Harper et al. 2019).

Acidithiobacillus thiooxidans is an acidophile: an organism that grows best in acidic conditions. Extreme acidophiles thrive in environments lower than pH 3, where high concentrations of hydrogen ions tend to disrupt cellular function (González-Rosales et al. 2022). Acidophiles possess mechanisms to restrict the ability of hydrogen ions to enter and remove/neutralize excess protons, helping to maintain a neutral cell interior (González-Rosales et al. 2022). This compartmentalization between inner and external conditions allows for their cellular machinery to function in acidic surroundings.

Yet, A. thiooxidans also contributes to the acidity of its environment through its metabolic processes. The bacterium obtains energy by oxidizing reduced sulfur compounds. When elemental sulfur is supplied, its conversion to sulphate generates hydrogen ions (H⁺). Although the reaction occurs through several enzymes and intermediaries, the overall reaction can be summarized as follow (Camacho et al. 2020):

Naseri and Mousavi (2024) investigated whether this biogenic acid could extract lithium and manganese from spent batteries. They grew A. thiooxidans in a medium rich with elemental sulfur, removed the cells, and then applied to acidic liquid in stages as the extraction proceeded. One initial reaction releases lithium and some manganese into solution while leaving manganese dioxide behind (Naseri and Mousavi 2024):

The researchers reported dissolution of 93% of lithium within six days and 53% of the manganese within eight days. Subsequent chemical treatment recovered these dissolved metals as solid compounds (Naseri and Mousavi 2024). Compared to the study’s direct bioleaching method, which retained bacteria and the battery material, staged acid addition increased metal dissolution (Naseri and Mousavi 2024). Removing the cells also separated production from extraction, allowing the metabolic products to be useful without requiring the organisms to tolerate battery waste (Naseri and Mousavi 2024).

For the bacterium, oxidizing sulfur provides energy, much as breaking down food does for us. Within a recycling process, the products of that metabolism become industrially useful chemical reactants.

Studying organisms with unique metabolisms, such as A. thiooxidans can reveal chemical capabilities shaped by natural selection that researchers can harness and adapt to human purposes. Traits that evolved to support survival in particular environments can become tools for recovering materials and developing more sustainable chemical processes. Their future applications thus depend on learning and understanding how these organisms function, while exploring how their chemistry might serve a different purpose. Battery recycling thus shows how exploring life’s diverse ways of meeting its own needs can reveal new ways to address our own.

References

Acidithiobacillus Thiooxidans Sulfur Metabolism through Coupled Gene Expression, Solution Chemistry, Microscopy, and Spectroscopy Analyses.” Frontiers in Microbiology Volume 11 – 2020 https://doi.org/10.3389/fmicb.2020.00411.

González-Rosales, Carolina, Eva Vergara, Mark Dopson, Jorge H. Valdés, and David S. Holmes. 2022. “Integrative Genomics Sheds Light on Evolutionary Forces Shaping the Acidithiobacillia Class Acidophilic Lifestyle.” Frontiers in Microbiology Volume 12 – 2021 https://doi.org/10.3389/fmicb.2021.822229.

Harper, Gavin, Roberto Sommerville, Emma Kendrick et al. 2019. “Recycling Lithium-Ion Batteries from Electric Vehicles.” Nature 575 (7781):75–86. https://doi.org/10.1038/s41586-019-1682-5.

Naseri, Tannaz, and Seyyed Mohammad Mousavi. 2024. “Improvement of Li and Mn Bioleaching from Spent Lithium-Ion Batteries, Using Step-Wise Addition of Biogenic Sulfuric Acid by Acidithiobacillus Thiooxidans.” Heliyon 10 (18):e37447. https://doi.org/https://doi.org/10.1016/j.heliyon.2024.e37447.