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A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 1 9 7 BIOLEACHING HOLDS PROMISE FOR EXTRACTING RARE EARTHS A research team led by Idaho National Laboratory and Rutgers Uni- OMG! OUTRAGEOUS MATERIALS GOODNESS versity with support from the Critical Materials Institute recently examined a method to extract rare-earth elements (REEs) from mining waste. REEs are dif- ficult to obtain and the U.S. currently does not produce a domestic supply. However, large amounts of REEs exist in phosphogypsum (PG), a waste product from producing phosphoric acid from phosphate rock. Researchers estimate that over a billion tons of PG waste are sitting in piles at storage sites across the U.S., particularly in Idaho and Florida. To test whether REEs could be obtained from PG, the team doped synthetic phospho- gypsum with six REEs—yttrium, cerium, neodymium, samarium, europium, and ytterbium. Then they studied various solutions that could be used to extract the elements. One solution in particu- lar, a mixture of chemicals produced by the bacterium Gluconobacter oxydans, Researchers doped synthetic phospho- gypsumwith six REEs and studied solu- tions that could extract the elements. was especially intriguing for REE recov- ery. Gluconobacter is a common bacte- rium found readily in the environment, including on rotting fruit. Gluconobacter produces organic acids such as gluconic acid that dissolve the REEs from the surrounding material and pulls them into solution in a pro- cess called bioleaching. The REEs could then be precipitated from the solution and purified for industrial use, although two major challenges exist. First, PG is often mildly radioactive. Second, PG is classified as a waste material, which may cause regulatory agencies to re- strict access to PG piles. Still, the inter- est in tapping this potential source of REEs is high. Mining companies have already begun inquiring about the pro- cess. inl.gov.