Selective Precipitation of High-Quality Rare Earth Oxalates or Carbonates from a Purified Sulfuric Liquor Containing Soluble Impurities
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The purity of rare earth products depends on the ability of the reagents used to selectively promote the precipitation of the rare earth elements (REE) from impurities present in sulfuric liquors. The present study aims at investigating the conditions required to precipitate REE, either as rare earth oxalates or carbonates, from purified rare earth sulfuric liquor with a low Al3+ and UO22+ and a very high Ca2+, Mg2+, Mn2+, and SO42− impurity content. The rare earth sulfuric liquor was obtained in a previous study by the reaction of a rare earth ore with sulfuric acid, pyrolysis at 700 °C/2 h, cooling at 20 °C, and water leaching. The impurities such as Fe3+, Th4+, and PO43− were completely removed from the liquor in two consecutive neutralization steps. In order to recover the REE, the purified rare earth liquor was then treated with oxalic acid and sodium carbonate. Rare earth oxides (REO) precipitated with oxalic acid displayed a very high purity (99.2% w/w) and low impurity content. In contrast, the rare earth carbonates precipitated with sodium carbonate presented a comparatively lower REO content (68.5% w/w) and 94.2% of purity, but with a higher content of impurities. Better precipitating conditions were achieved at 60 °C, compared with 20 °C, and under stoichiometric reagent consumption, with REE precipitation efficiencies higher than 96%. The dosage above the stoichiometric condition caused the precipitation of calcium oxalates and co-precipitation of rare earth sulfates when oxalic acid is used, and precipitation of calcium, manganese, and uranium carbonates and also a co-precipitation of rare earth sulfate when sodium carbonate were used. An integrated flowsheet to produce a high-quality rare earth product from rare earth sulfuric liquor containing some impurities is proposed.
KeywordsSulfuric liquor Rare earth oxalates Rare earth carbonates Remove impurities Precipitation
The authors would like to thank Vale S.A., especially Patrice Mazzoni, Cássia Souza, and Keila Gonçalves for authorizing the publication of this work. The authors are also thankful to the technicians from Mineral Development Centre’s Vale engaged in this study. We also would like to thank Daniel Saturnino, Marcus Simões, and Julius W. Martins for proofreading the paper. Éder Oliveira and Carlos Morais acknowledge the support from CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico), CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), and FAPEMIG (Fundação de Amparo à Pesquisa de Minas Gerais).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
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