Teor e distribuição de elementos terras raras e comparação de métodos de extração de elementos traço em solos brasileiros

• Ano de defesa: 2014
• Autor(a) principal: Paye, Henrique de Sá
• Orientador(a): Mello, Jaime Wilson Vargas de
• Banca de defesa: Abrahão, Walter Antônio Pereira , Bellato, Carlos Roberto , Caldeira, Claudia Lima
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Solos e Nutrição de Plantas
• Departamento: Fertilidade do solo e nutrição de plantas; Gênese, Morfologia e Classificação, Mineralogia, Química,
• País: BR
• Palavras-chave em Português: Terras raras; Lantanídeos; Padrões de qualidade; Extratores
• Palavras-chave em Inglês: Rare earths; Lanthanides; Quality standards; Extractors
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO
• Link de acesso: http://locus.ufv.br/handle/123456789/1665

Rare earth elements (REEs) are strategic for the country. They form a group of 17 elements with similar chemical, magnetic and fluorescence properties, which make them irreplaceable inputs in high technology. Considering the rapid increase in REEs for industrial usage, environmental contamination is also likely to increase in the near future. In this case, knowing the natural concentration or background concentration of REEs and other trace elements (TE) in soil is crucial for monitoring the impacts of human activity and understanding the extent of the anthropogenic influence on the environment. In Brazil, regional studies on the natural concentration of some trace elements in soils have been used to establish guide values for monitoring the environmental quality. However, studies on rare earth elements (REEs) content in Brazilian soils are scant and no REE background level has been determined yet. In addition, several inquiries regarding the correct selection of the trace elements extraction method have been recurrent in environmental studies. Thereby, the present study aims at determining the natural REEs content and distribution in 144 Brazilian soil samples, investigating the relationship among elements distribution and soil properties and establishing the background. Furthermore, two extraction methods, hotplate HNO3+HF (total digestion) and EPA 3050B (pseudo total digestion), were compared for digestion of one standard reference material-SRM and 30 soil samples for establishing soil quality standards. Sixteen REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and 10 TE (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sb, Zn) were analyzed using an inductively coupled plasma mass spectrometry (ICP-MS). The results showed wide variability in REE content between soil samples. Soils that developed from alkaline igneous rocks showed the highest average content of REEs followed by sedimentary rocks, unconsolidated clay sediment, metamorphic rocks, basic igneous rocks, unconsolidated sand and silt sediments, and acid igneous rocks. REE contents were more significantly correlated (p < 0,05) with, Fe, Al, Ti, Mn oxides, clay and OM than other soil properties. Graphical inspection using exploratory data analysis tools as Q-Q normal plot and boxplot was effective to recognize data patterns and isolate discrepant population data to determine threshold values and thus defining the range of the background variation for REEs. Regarding extraction methods, precise analysis was achieved for all trace elements for both methods in SRM (coefficient of variation < 4 %), with the total digestion method having better precision averaged (0.58 %) over all elements. Regarding to accuracy, high recoveries (91 103 %) for all trace elements except Sb (83 %) and Mo (47 %), were obtained by total digestion method in the SRM. However, elemental recoveries for EPA 3050B method generally were low (4 79 %). In average, significant differences (p < 0.05) were observed between content of all elements extracted for hotplate HNO3 + HF method and EPA 3050B in soil samples. The hotplate HNO3 + HF method was capable to extract the largest amounts of all trace elements. The methods differed statistically (p < 0.05) by the use of regression, although they were correlated with all elements, excepted Ba. Quality reference values (QRV) for ET established from hotplate HNO3 + HF dataset were above of the EPA 3050B for all elements. In addition, several QRV showed themselves above the prevention values established by CONAMA.