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Extraction of Rare Earth Elements from Phospho-Gypsum: Concentrate Digestion, Leaching, and Purification

1
Department of Mineral and Waste Processing, Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics, Clausthal University of Technology, Walther-Nernst-Str. 9, 38678 Clausthal-Zellerfeld, Germany
2
New Energy Vehicle Research Center, Qingdao University, Ningxia Road No. 308, Qingdao 266071, Shan Dong, China
3
Department of Mineralogy, Geochemistry, Salt Deposits, Institute of Disposal Research, Clausthal University of Technology, Adolph-Roemer-Str. 2A, 38678 Clausthal-Zellerfeld, Germany
*
Author to whom correspondence should be addressed.
Metals 2020, 10(1), 131; https://doi.org/10.3390/met10010131 (registering DOI)
Received: 5 December 2019 / Revised: 2 January 2020 / Accepted: 10 January 2020 / Published: 15 January 2020
Rare earth-bearing gypsum tailings from the fertilizer industry are a potential source for an economically viable and sustainable production of rare earth elements. Large quantities are generated inter alia in Catalão, Brazil, as a by-product in a fertilizer production plant. Hitherto, the gypsum has been used as soil conditioner in agriculture or was dumped. The cooperative project, “Catalão Monazite: Economical exploitation of rare earth elements from monazite-bearing secondary raw materials,” intends to extract rare earth elements from these gypsum tailings. In this paper, a chemical process route to obtain a mixed rare earth carbonate from a monazite concentrate, was investigated. The results of the digestion, leaching, and precipitation experiments are presented and discussed herein. This includes reagent choice, process parameter optimization through experimental design, mineralogical characterization of the feed material and residues, purification of the leach solution, and precipitation of the rare earth as carbonates. The results showed that a rare earth extraction of about 90% without the mobilization of key impurities is possible during a sulfuric acid digestion with two heating stages and subsequent leaching with water. In the following purification step, the remaining impurities were precipitated with ammonium solution and the rare earth elements were successfully recovered as carbonates with a mixture of ammonium solution and ammonium bicarbonate. View Full-Text
Keywords: hydrometallurgy; rare earth elements; monazite; phosphogypsum; design of experiment; digestion; leaching; precipitation hydrometallurgy; rare earth elements; monazite; phosphogypsum; design of experiment; digestion; leaching; precipitation
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Brückner, L.; Elwert, T.; Schirmer, T. Extraction of Rare Earth Elements from Phospho-Gypsum: Concentrate Digestion, Leaching, and Purification. Metals 2020, 10, 131.

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