Researchers have created a protein sensor that lights green when it comes into contact with the rare earth element terbium, which might stimulate the development of U.S. acid mine drainage rare earth element mining.
So far, no luminescence-based sensor has measured terbium at low concentrations in an acidic and complicated environmental sample. If commercialized, it might help prospectors find the commercially valuable ingredient in abandoned mine tailings.
Rare earth elements are vital in wind turbines and electric automobiles. Federal research funds in the United States are being used to develop technologies for mining low-grade sources of rare earths, such as coal by-products, electric waste, and mine effluents.
Joseph Cotruvo, who invented the sensor with two colleagues at Pennsylvania State University, stated, “It’s a straightforward technology, and it has a sensitivity that is comparable to state of the art.” This new tool is still under development, as accurate as of today’s most advanced laboratories’ equipment, yet quicker and more user-friendly.
However, “if the sensor can be mass-produced or reused, that would greatly reduce characterisation costs for domestic rare-earth manufacturing,” said Scott Crawford, a contractor with the National Energy Technology Laboratory in Pittsburgh who was not involved in the sensor’s creation. According to him, increasing the domestic production of rare earths is critical for the country’s economy, ecology, and security.
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Another group of scientists is also working on new methods for detecting rare earth metals. For example, scientists at Idaho National Laboratory are developing a luminous sensor that may be used in liquids.
To create the novel sensor, scientists looked to the soil-dwelling bacteria Methylorubrum extorquens and a protein it produces. For example, if terbium is found in acid mine drainage, the sensor might notify workers on the ground.
Lanmodulin can detect terbium even in the presence of other rare earths or heavy metals. To excite terbium, the scientists utilized tryptophan, a photosensitizer that absorbs light more effectively than terbium. As a result, terbium produces a wide range of light colors, the most intense of which is a greenish hue at 545 nanometers. As the concentration of terbium increases, so does the luminescence’s intensity.
The sensor worked well in acid mine drainage from the Lower Kittanning coal seam, even with low terbium concentrations (parts per billion) and high concentrations of other rare earths and heavy metals.
Metals can only be detected in a liquid solution since the U.V. light might be blocked by solids, according to Cotruvo. After five years of development, he expected the sensor to be completely functional and capable of detecting other critical rare earths.
The U.S. Department of Energy (DOE) is now sponsoring more than 30 programs to extract rare earth elements from coal mining and related waste products. Coal ash, waste rock, immature lignite coal, sludge, and acid mine drainage are rich sources of rare earth elements, but practical extraction methods have yet to be developed.
Water from underground mines is a source of acid mine drainage. Acidic water is created when sulfur-bearing minerals in the rock dissolve in it. On the other hand, Acidic water dissolves heavy metals (such as rare earths) in stone. Drinking water sources are at risk because of the water’s high corrosion potential.
According to Earthworks, in 2013, 17–27 billion gallons of contaminated water were produced yearly by 40 hard-rock mines in the United States. However, the Department of Energy and the National Energy Technology Laboratory (NETL) has prioritized turning waste into money. Two coal and coal ash locations in America might produce millions of tonnes of rare earth elements, considerably over the domestic requirement of 100,000 tonnes yearly, according to a study to the U.S. Congress in 2017.
When it comes to the last few years, the U.S. Geological Survey estimates that China has generated and supplied 90% of the world’s rare earth elements. During trade tensions with the Trump administration in 2019, the nation threatened to reduce supplies.