A joint research project by BOKU Tulln and IMC University of Applied Sciences Krems has revealed significant potential for recovering valuable materials from electronic waste using an intriguing method.
Bacteria turn electronic waste into treasure!
The study addresses an innovative method that can sustainably and environmentally recycle critical raw materials such as rare earth elements. The rapid increase in the use of electronic devices and their short lifespans lead to large amounts of electronic waste. Although these wastes contain valuable metals and rare earth elements, current recycling methods are inadequate and cause environmental problems.
The focus of the research is the combination of two biotechnological processes known as bioleaching and bioaccumulation. Bioleaching is a natural process where microorganisms dissolve metals from metal-containing waste. Certain bacteria produce acidic compounds that effectively separate rare earth elements from complex materials like electronic waste, forming the first step necessary for the recovery of these elements.
The microorganisms used in the study, Acidithiobacillus thiooxidans and Alicyclobacillus disulfidooxidans, were isolated from an acidic mining lake in the Czech Republic and specially cultivated in the laboratory. These bacteria are known for their ability to survive in low pH environments and oxidize inorganic compounds to obtain energy.
The rare earth elements dissolved through bioleaching are then recovered using a second process called bioaccumulation. Bioaccumulation involves the selective absorption and accumulation of metals from the surrounding solution by specific microorganisms.
In this study, researchers developed a system using Escherichia coli bacteria that can efficiently accumulate rare earth elements. In this process, the bacteria act like metal sponges, trapping rare earth elements from the solution within their cells.
In laboratory experiments, researchers achieved up to 85% recovery of rare earth elements from electronic waste using this two-step method, a significantly higher efficiency compared to current chemical recycling methods.
Moreover, bioleaching and bioaccumulation stand out as environmentally friendly and sustainable recycling methods. They consume less energy, result in lower greenhouse gas emissions, and minimize hazardous waste formation compared to traditional methods.
However, despite these promising results, there are challenges to the industrial application of bioleaching and bioaccumulation-based recycling methods. The complex and variable composition of electronic waste can impact the efficiency of the process. High concentrations of other metals such as iron, copper, and aluminum can negatively affect the recovery of rare earth elements.
Researchers are working on various strategies to overcome these challenges. One approach is to “adapt” microorganisms to tolerate high metal concentrations. Using a device called a morbidostat, bacteria are gradually exposed to increasing metal concentrations to achieve adaptation. Another strategy is to use new materials such as lignin hydrogel in the bioleaching and bioaccumulation processes to reduce the concentration of interfering metals.
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