The results of this interesting experiment were published in the number 3, volume 5 of the journal MDPI Recycling. According to the data provided, an electronic plate was placed in a container filled with the bacterial solution under investigation, an aqueous solution containing the microorganism Acidithiobacillus ferrooxidans, and twenty days later, it was observed that the components of the plate had begun to detach from the circuit and fall to the bottom of the container.
Working imperceptibly at sight, this bacterium has the capacity to dissolve the solder by oxidizing the added iron, so that when the container is shaken, the components that make up the circuit, such as diodes, capacitors and resistors, are detached, leaving only the board itself, since it generally contains copper and in some cases gold.
The purpose is precisely to separate these components, since they contain strategically important elements, such as tantalum, ruthenium and gallium. Therefore, when they are separated from the plate, they can be classified later and treated separately. And from the solution, which contains the dissolved solder, the tin and silver used in the solder can also be purified in a subsequent treatment. This is why he has called the process "biodismantling".
Source: MDPI Recycling, Creative Commons Attribution License.
Rare earth recycling
This new procedure is particularly attractive because it allows to recover elements of the rare earth group, which can hardly be recovered from this type of waste using the recycling methods known so far. It also has the advantage that these rare elements are enriched by sorting and extracting them by another process, such as solvent extraction; for example, studies showed that dysprosium could be enriched by a factor of 140 by biodismantling and further sorting the components, reaching a concentration almost comparable to that of the mineral from which it is extracted.
Difference from conventional procedure
In the proven conventional processes for recycling electronic waste, printed circuit boards are shredded and chemically or thermally processed, so that in the end only those elements that were present in a high concentration can be recovered, and elements such as rare earths, present in low concentrations, can only be recovered by even more complex and expensive processes, whose energy cost simply does not make them viable.
In conclusion, this is a procedure that provides a great benefit, since instead of crushing and dissolving with some chemical all the components of the waste and only recovering some elements, the separation and subsequent classification is the most outstanding, since the components can thus be treated separately and other procedures can be applied according to each component to extract the constituent elements respectively, and they can be made available again to be used as raw material.
Hopefully, in the following stages of the research, the methods of classification and treatment of each component will be achieved, since if a way can be found to easily separate the components from the solution, this method can be used on a large scale, having for the first time an alternative with great potential to recover very important and rare elements from the electronic components.
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