A unique bacterium that thrives in highly acidic environments feeds on spent battery "waste", making it a promising new method for self-sufficient battery recycling, according to new research from Boston College chemists.
The bacterium, Acidithiobacillus ferrooxidans (Atf), has a natural metabolic cycle that produces protons capable of leaching electrode materials from spent batteries, Professor of Chemistry Dunwei Wang, Associate Professor of Biology Babak Momeni, and colleagues reported recently in the journal ACS Sustainable Resource Management.
"This is a critical step forward by examining the possibility of growing the bacteria using materials already present in spent batteries as a food source," said Wang. "More specifically, we used iron which is commonly employed as a casing material in batteries. Our results showed that the bacteria can indeed thrive with this new food source, and the resulting solution is highly active for recycling spent batteries."
In an increasingly electrified society, the widespread use of batteries to power tools, toys and gadgets points to a two-fold crisis: the ever-expanding need to produce more batteries and the rapid accumulation of spent batteries.
Efforts to solve these two problems have encountered high energy use or require the transport and use of toxic chemicals.
Wang, working in collaboration with Momeni, decided to explore whether Atf could use the iron content in spent batteries as a food source. In addition, could Atf-inspired solutions successfully leach cathode materials from spent batteries?
Momeni, whose research interests include microbial ecology and mathematical modeling of biological systems, undertook the cultivation of the bacteria. Wang, a physical chemist whose work focuses on clean energy, used the culture for battery cathode leaching. Additional co-authors were research associate Wei Li, graduate student Brooke Elander, and undergraduates Mengyun Jiang and Mikayla Fahrenbruch.
Building on other research, the team wanted to specifically see if they could replace sulfate, which is another critical component in the food source.
"Our results suggest that the activity of the bacteria does not depend on the presence of sulfate," said Wang. "This is an important finding because it indicates that for future implementations, one could do away with the need for the transportation of large quantities of one toxic material."
In addition, Wang said the team tested the possibility of using stainless steel as a food source, which is far more common in real world batteries. Their experiments showed it worked even better than pure iron.
"The finding that stainless steel worked better than pure iron was indeed a surprise," said Wang. "This is because stainless steel is a complex mixture. We didn't expect it to work so well. But this is a notable unexpected development as stainless steel is more commonly encountered in real batteries."
The team is now working on evolving the bacteria to improve the recycling efficiencies. They are also working on building prototype batteries with the recycled materials to prove that they offer the same performance advantages as traditional batteries constructed from new materials.
