1. Without delay, data from the International Telecommunication Union shows that the amount of e-waste in 2019 was as high as 53.6 million tons. That number is expected to rise to 74 million in 2030. The structure of electronic products is complex, and the metals in them are difficult to extract, so the recycling rate of electronic waste is only 20%. ■ 2. Extraction method, the electronic chip is rich in rare earth elements. After peeling off its plastic film, the chip was crushed to increase the contact area of the chip with the bacterial solution to maximize leaching of metals. ■ 3. As a result of extraction, the metal is “attacked” by bacteria and begins to dissolve. After the chemical reaction is over, the solid residue in the solution is filtered to obtain a liquid containing various metal salts.
Acidophilus ferrooxidans and Sulfolobus have been dormant for 40 years in the French Geological and Mineral Survey. What can these bacterial microbes do? They thrive in extremely acidic environments, dissolving metals. “I hate bacteria more than I love it,” jokes research engineer Agat Huybaud. For years, she has been watching bacteria, or putting them in a “dead place.” Don’t get me wrong, Agaté is not a “sadist”, she just wants to use bacteria to extract useful metals from electronic waste in a strong acid environment.
| What is Biometallurgy? |
There are so many metals in our everyday products that researchers have even described e-waste as an “urban mine.” In 2019, the amount of e-waste in France reached 854,906 tons, and the word “mine” is not an exaggeration. Among them, on the electronic chip covered with circuits, the metal content ratio is extremely high, even higher than the metal content ratio of the underground mine. Better ways to reuse this e-waste could reduce the need to “mine new mineral resources”. After all, the depletion of mineral resources is a major concern.
At present, the mainstream method of electronic waste reprocessing is pyrometallurgy, that is, obtaining useful metals by heating electronic chips and circuit components at high temperatures. However, this method consumes a lot of energy, and there is still a lot of metal in the residue, so the consumption is relatively large.
The bacteria cultivated by the French Geological and Mineral Survey can dissolve metals such as cobalt, zinc, and nickel, and each bacteria has its own preferred metal. We call this technology “biometallurgy”, also known as “bioleaching technology”. “.
Bacteria cultured by the French Geological and Mineral Survey were harvested from acidic liquids in drains near the mine. In order for a strain to dissolve a metal, the researchers put the bacteria in a nutrient solution that contains biometallurgically leaching metals, such as cobalt, nickel, and zinc. Next, the researchers will observe how the bacteria will act on the e-waste. In the initial stage, bacteria dissolve metals slowly. If the bacteria adapt to the chemical environment, the dissolution process will gradually accelerate. “But in extreme environments, such as overacidity or overheating, even the most resistant bacteria will die. Therefore, be sure to prepare supplementary bacteria and store them in a suitable environment for later use.” Yu Bo explained road.
| The Problem of Biometallurgy |
Scientists have been studying microbes as early as the 1920s. Today, biometallurgical techniques are used to extract metals, which depend on 25% of global copper production and 5% of gold production. “We are trying to apply this technology to more complex metal parts, such as electronic chips,” said Yu Bo. The researchers first broke the e-waste into particles smaller than a millimeter and poured these particles into a solution containing bacteria. Under the action of microorganisms, metals are oxidized and dissolved. After 48 hours, the solution can be subjected to a precipitation operation to obtain a metal salt, or the solution can be electrolyzed to obtain a metal block.
However, there are two difficulties in the experimental stage. “Bacteria can only dissolve a small amount of metal.” Yu Bo said angrily. Up to 40 grams of metal can be dissolved per liter of microbial solution. Obviously, such an order of magnitude is difficult to reach the standard of large-scale industrial production. The second difficulty is economic efficiency. Currently, the microorganisms of the Bureau of Geology and Minerals Survey can only extract base metals. However, e-waste also contains a lot of precious metals. Yu Bo pointed out: “The economic benefit of this metallurgical method depends on the type of metal extracted by bacteria. If you want to extract precious metals, you need to use expensive special bacteria.” It can be seen that the chemical metallurgy method with lower cost on the market is biometallurgy. strong competitor.
To crack the puzzle, the researchers plan to conduct a larger pilot study using hundreds of liters of solution to extract the metal. However, the recycling market is still immature, the order has not yet been formed, and it is difficult to obtain financial support. “From metal production to metal recycling, a professional industrial chain should be formed,” said Patrick Deuger, project manager of the “Mineral Resources and Circular Economy” project of the Bureau of Geological and Mineral Survey. Compared with pyrometallurgy, biometallurgy is more environmentally friendly and may become a link in the chain. However, biometallurgy is not a panacea either. “Recycling and reusing metals can only reduce the pressure on the supply of mineral resources, but it cannot produce the amount of metal we need in our daily lives.” De Hugue said. Achieving a circular economy is not simple in a society with a growing economy. The introduction of new regulations and requirements for metal recovery in electronic equipment will greatly increase the value of biometallurgical research. François Gross, a graduate of the Ecole Polytechnique with a research direction of “The role of recycling in the economic system,” affirms: “In this way, people will The value of research projects is judged on the basis of economic efficiency criteria. Recycling as much metal from electronic devices as possible will be the biggest goal in the future.”