18 NOVEMBER 2020 WorldWide Drilling Resource ® Turning Waste into a Resource Adapted from Information by Pennsylvania State University Scientists at Penn State believe they have discovered a new way to treat acid mine drainage (AMD), which could turn the waste into a domestic source of critical rare earth elements. According to Mohammad Rezaee, assistant professor of mining engineering in the College of Earth and Mineral Sciences at Penn State, “Acid mine drainage has been a significant environmental concern for many decades. This research shows we can modify existing treatment processes in a way that not only addresses environmental concerns, but at the same time recovers valuable elements and actually decreases the cost of treatment.” The team developed a two-stage treatment process which allowed them to recover higher concentrations of rare earth elements using smaller amounts of chemicals than previously possible. “This technique represents an efficient, low-cost, and environmentally friendly method to extract these valuable minerals that are used in a wide variety of consumer and industrial products,” said Sarma Pisupati, professor of energy and mineral engineering and director of the Center for Critical Minerals at Penn State. Rare earth elements are a group of 17 minerals used in advanced technologies designated as critical to the country’s economic and national security. Currently, the country imports nearly 100% of these materials. AMD occurs when pyrite rock (iron sulfide), unearthed through the mining process, interacts with water and air and oxidizes, creating sulfuric acid. This acid breaks down the surrounding rocks causing toxic metals to dissolve into the water. Typically, AMD is collected in retention ponds and chemicals are used to neutralize the pH. This causes dissolved metals to form into solids (precipitate), and settle out of the water. Up to 70% of rare earth elements can be extracted as a sludge using this process, and the rest are released along with the treated water, according to researchers. The method developed by the team of Penn State scientists uses carbon dioxide to bring the pH to neutral levels. The chemical reaction caused by adding carbon dioxide, resulted in the formation of solid minerals called carbonites. The rare earth elements bond with the extra carbonites and precipitate out of the water at lower pH values. The process, called carbon dioxide mineralization, is an emerging technology being used to remove excess carbon dioxide from the atmosphere and this study is the first time it has been used to recover large concentrations of rare earth elements from AMD. This new treatment method could make the domestic rare earth element market more competitive. “With a simple modification of existing treatment processes, industry could use less chemicals and get more value out of AMD waste,” Rezaee said. “This is the beauty of this research.” AMD from coal mining operations in Appalachia could be a promising domestic source of rare earth elements since it contains high concentrations of rare earth minerals. ENV
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