Magnetita e sua transformação para hematita em um solo derivado de esteatito

Santana, G. P.; Fabris, J. D.; Goulart, A. T.; Santana, D. P.

doi:10.1590/S0100-06832001000100004

Resumos

O presente trabalho objetivou caracterizar o mineral magnético e identificar suas rotas pedogenéticas de transformação em um solo formado sobre esteatito, de Minas Gerais, Brasil. O óxido de ferro isoestrutural ao espinélio foi identificado e caracterizado por análises químicas, difração de raios X, espectroscopia Mössbauer e medidas de magnetização de saturação. Na rocha fresca, foi encontrada magnetita estequiométrica e bem cristalizada, com parâmetro da rede cúbica, a o = 0.8407(5) nm. Nas frações areia e silte, foram detectadas magnetita parcialmente alterada e hematita estequiométrica e bem cristalizada, com parâmetros da rede hexagonal, a = 0.5036(3) nm e c = 1.375(4) nm. A ocorrência dessas hematitas deveu-se principalmente à oxidação do Fe2+ a Fe3+, no sítio octaédrico da magnetita, durante a pedogênese. Esse processo foi caracterizado pelo aparecimento de pequena quantidade de Fe3+ eletronicamente desacoplada, encontrada nas magnetitas parcialmente oxidadas, cujas fórmulas para as diferentes estequiometrias foram propostas. Verificou-se também pequena quantidade de ilmenita nas amostras de rocha e de solo.

Espinélios ricos em ferro; óxido de ferro; pedra-sabão; solo magnético; espectroscopia Mössbauer

The main objective of this work was to characterize the magnetic minerals and to identify their pedogenic transformation on a steatite-forming soil of Minas Gerais, Brazil. The iron-rich spinel phase was characterized by chemical analysis, powder X-ray diffraction, Mössbauer spectroscopy, with and without an externally applied magnetic field of 6 tesla, and saturation magnetization measurements. Nearly stoichiometric and well-crystallized magnetite was the only magnetic mineral actually detected. The cubic unit cell parameter of the fresh rock magnetite was found to be a o = 0.8407(5) nm. Hematite (hexagonal cell; a = 0.5036(3) nm, c = 1.375(4) nm) was detected in the altered rock and in the sand-soil and silt-soil fractions. Magnetite is assumed to transform into hematite during pedogenesis through progressive oxidation of structural Fe2+ to Fe3+. In partially oxidized magnetites, a relatively small proportion of Fe3+ was interpreted as being uncoupled from the Fe2+-Fe3+ charge transfer system, in octahedral sites of the spinel structure. Compositional formulae of magnetite with different degrees of non-stoichiometry are proposed. Ilmenite was found in minor proportions in the magnetically extracted portions from both rock and soil samples.

Iron-rich spinel; iron oxide; soapstone; magnetic soil; Mössbauer spectroscopy

SEÇÃO II - QUÍMICA DO SOLO

Magnetite and its transformation to hematite in a soil derived from steatite(¹ (1 ) This work is part of the thesis of the first author, presented to the Departmento de Química of the Universidade Federal de Minas Gerais, Brazil, as a partial requirement to obtain the title of Doctor in Science - Chemistry. It was originally planned and supervised by the late Professor Milton Francisco de Jesus Filho. )

Magnetita e sua transformação para hematita em um solo derivado de esteatito

G. P. Santana^I; J. D. Fabris^II; A. T. Goulart^III; D. P. Santana^IV

^IAssociate Professor, Departamento de Química, Universidade do Amazonas - UA. CEP 69077-000 Manaus (AM)

^IIProfessor of Chemistry, Departamento de Química, Universidade Federal de Minas Gerais - UFMG. CEP 31270-901 Belo Horizonte (MG), Brazil

^IIIAssociate Professor (presently, retired), Departamento de Química, Universidade Federal de Viçosa - UFV. CEP 36571-000 Viçosa (MG)

^IVResearcher, EMBRAPA/CNPMS, Caixa Postal 151, CEP 35701-970 Sete Lagoas (MG)

SUMMARY

The main objective of this work was to characterize the magnetic minerals and to identify their pedogenic transformation on a steatite-forming soil of Minas Gerais, Brazil. The iron-rich spinel phase was characterized by chemical analysis, powder X-ray diffraction, Mössbauer spectroscopy, with and without an externally applied magnetic field of 6 tesla, and saturation magnetization measurements. Nearly stoichiometric and well-crystallized magnetite was the only magnetic mineral actually detected. The cubic unit cell parameter of the fresh rock magnetite was found to be a_o = 0.8407(5) nm. Hematite (hexagonal cell; a = 0.5036(3) nm, c = 1.375(4) nm) was detected in the altered rock and in the sand-soil and silt-soil fractions. Magnetite is assumed to transform into hematite during pedogenesis through progressive oxidation of structural Fe²⁺ to Fe³⁺. In partially oxidized magnetites, a relatively small proportion of Fe³⁺ was interpreted as being uncoupled from the Fe²⁺-Fe³⁺ charge transfer system, in octahedral sites of the spinel structure. Compositional formulae of magnetite with different degrees of non-stoichiometry are proposed. Ilmenite was found in minor proportions in the magnetically extracted portions from both rock and soil samples.

Index terms: Iron-rich spinel, iron oxide, soapstone, magnetic soil, Mössbauer spectroscopy.

RESUMO

O presente trabalho objetivou caracterizar o mineral magnético e identificar suas rotas pedogenéticas de transformação em um solo formado sobre esteatito, de Minas Gerais, Brasil. O óxido de ferro isoestrutural ao espinélio foi identificado e caracterizado por análises químicas, difração de raios X, espectroscopia Mössbauer e medidas de magnetização de saturação. Na rocha fresca, foi encontrada magnetita estequiométrica e bem cristalizada, com parâmetro da rede cúbica, a_o = 0.8407(5) nm. Nas frações areia e silte, foram detectadas magnetita parcialmente alterada e hematita estequiométrica e bem cristalizada, com parâmetros da rede hexagonal, a = 0.5036(3) nm e c = 1.375(4) nm. A ocorrência dessas hematitas deveu-se principalmente à oxidação do Fe²⁺ a Fe³⁺, no sítio octaédrico da magnetita, durante a pedogênese. Esse processo foi caracterizado pelo aparecimento de pequena quantidade de Fe³⁺ eletronicamente desacoplada, encontrada nas magnetitas parcialmente oxidadas, cujas fórmulas para as diferentes estequiometrias foram propostas. Verificou-se também pequena quantidade de ilmenita nas amostras de rocha e de solo.

Termos de indexação: Espinélios ricos em ferro, óxido de ferro, pedra-sabão, solo magnético, espectroscopia Mössbauer.

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Full text available only in PDF format.

ACKNOWLEDGMENTS

To Drs. Eddy De Grave (Department of Subatomic and Radiation Physics, Laboratory of Magnetism, University of Gent, Belgium) and Geraldo Magela da Costa (Universidade Federal de Ouro Preto, Brazil) for the Mössbauer measurements with applied magnetic field. To Professor John Michael David Coey (Trinity College Dublin, Ireland) for his helpful discussion and constructive suggestions. Work financially supported by CNPq, FINEP and FAPEMIG (Brazil).

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BIGHAM, J.M.; GOLDEN, D.C.; BOWEN, L.H.; BUOL, S.W. & WEED, S.B. Iron oxide mineralogy of well-drained utilsols and oxisols: I. Characterization of iron oxides in soil clays by Mössbauer spectroscopy, X-ray diffractometry and selected chemical techniques. Soil Sci. Soc. Am. J., 42:816-830, 1978.
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COEY, J.M.D.; MORISH, A.H. & SAWATZKY, G.A. A Mössbauer study of conduction in magnetite. J. Phys., C1:271-273, 1971.
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COEY, J.M.D.; GUGAT, O.; MCCAULEY, J. & FABRIS, J.D. A portable soil magnetometer. R. Fis. Ap. Instr., 7:25-30, 1992.
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CURI, N. & FRANZMEIER, D.P. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci. Soc. Am. J., 51:153-158, 1987.
DEMATTÊ, J.L.I. & MARCONI, A. Effects of drainage on the mineralogy of soils developed from diabase in Piracicaba, State of São Paulo, Brazil. R. Bras. Ci. Solo, 15:1-8, 1991.
DORIGUETTO, A.C.; GOULART; A.T.; JESUS FILHO, M.F.; FABRIS, J.D. & SANTANA, G.P. Ilmenite of a soil system developing on amphibolite. Europ. J. Soil Sci., 49:541-546, 1998.
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FABRIS, J.D.; JESUS FILHO, M.F.; COEY, J.M.D.; MUSSSEL, W.N. & GOULART, A.T. Iron-rich spinels from Brazilian soils. Hyperfine Interac., 110:23-32, 1997a.
FABRIS; J.D.; MUSSEL, W.N.; COEY; J.M.D.; JESUS FILHO; M.F. & GOULART, A.T. Mg-rich iron oxide spinels from Tuffite. Hyperfine Interac., 110:33-40, 1997b.
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FONTES, M.P.F.; OLIVEIRA, T.S.; COSTA, L.M. & CAMPOS, A.A.G. Magnetic separation and evaluation of magnetization of Brazilian soils from different parent materials. Geoderma, 96:81-99, 2000.
FYSH, S.A. & CLARK P.E. Aluminous hematite: a Mössbauer study. Phys. Chem. Miner., 8:257-267, 1982.
GONÇALVES, M.; JESUS FILHO, M.F. & GARG, V.K. Mössbauer study of Brazilian soapstone. Hyperfine Interac., 67:437-442, 1991.
GOULART, A.T.; JESUS FILHO, M.F.; FABRIS, J.D. & COEY, J.M.D. Characterization of a soil ilmenite developed from basalt. Hyperfine Interac., 91:771-775 1994.
GOULART, A.T.; FABRIS, J.D.; JESUS FILHO, M.F., COSTA, G.M. & DE GRAVE, E. Iron oxides in a soil developed from basalt. Clays Clay Miner., 46:369-378, 1998.
JACKSON, M.L. Soil chemical analysis: advanced course. 3.ed. Madison,1969. p.894.
JCPDS - Joint Committee on Powder Diffraction Standards, International Center for Diffraction Data, Mineral Powder Diffraction Files Data Book. Swarthmore, Pensilvania, 1980. 1168p.
JEFFERY, P.G. & HUTCHISON, D. Chemical methods of rock analysis, 3.ed. Oxford, Pergamon Press Oxford, 1981. 379p.
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KÄMPF, N. & SCHWERTMANN, U. Concentration treatment for iron oxides in soils. Clays Clay Miner., 30:401-408, 1982.
LADEIRA, E.A.; ROESER, H.M.P. & TOBSCHALL, H.J. Petrogenetic evolution of the green rock belt, Rio das Velhas, Quadrilátero Ferrífero, Minas Gerais. SYMPOSIUM ON THE GEOLOGY OF MINAS GERAIS, 2., Belo Horizonte, 1983. Proceedings. Belo Horizonte, 1983. p.149-159.
LAGOEIRO, L.E. Transformation of magnetite to hematite and its influence on the dissolution of iron oxide minerals. J. Metam. Geol., 16:415-423, 1998.
McKEAGUE, J.A. An evaluation of 0.1 M pyrophosphate and pyrophosphate-dithionite in comparison with oxalate as extractants of the accumulation products in Podzols and some other soils. Can. J. Soil Sci., 47:95-99, 1966.
MEHRA, O.P. & JACKSON, M.L. Iron oxide removal from soils and clay by a dithionite-citrate system buffered with sodium bicarbonate. In: SWINEFORD, A., ed. NATIONAL CONFERENCE ON CLAYS AND CLAY MINERALS, 7., Washingt on, 1958. Proceedings. London, Pergamon Press, 1960. p.317-327.
MIJOVILOVICH, A.; MORRAS, H.; SARAGOVI, C.; SANTANA, G.P. &. FABRIS, J.D. Magnetic fraction of an Ultisol from Misiones, Argentina. Hyperfine Interac. (C), 3:332-335, 1998.
MOUKARIKA, A.; O'BRIEN, F. & COEY, J.M.D. Development of magnetic soil from ferroan dolomite. Geophy. Res. Letters, 18:2043-2046, 1991.
MURAD, E. & SCHWERTMANN, U. The influence of Al substitution and crystallinity on the room-temperature Mössbauer spectrum of hematite. Clays Clay Miner., 34:1-6, 1986.
MUSSEL; W.N.; FABRIS, J.D.; COEY, J.M.D.; SANS, L.M.A. & LELIS, M.F.F. Compositional and structural variability of Mg-rich iron oxide spinels from tuffite. R. Bras. Ci. Solo, 23:791-798, 1999.
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RESENDE, M.; SANTANA, D.P.; FRANZMEIER, D.P. & COEY, J.M.D. Magnetic properties of Brazilian Oxisols. In: INTERNATIONAL SOIL CLASSIFICATION WORKSHOP, Rio de Janeiro, 1988. Proceedings. Rio de Janeiro, 1988. p.78-108.
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(1

) This work is part of the thesis of the first author, presented to the Departmento de Química of the Universidade Federal de Minas Gerais, Brazil, as a partial requirement to obtain the title of Doctor in Science - Chemistry. It was originally planned and supervised by the late Professor Milton Francisco de Jesus Filho.

Datas de Publicação

Publicação nesta coleção
03 Out 2014
Data do Fascículo
Mar 2001

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

[1] ALLAN, J.E.M.; COEY, J.M.D.; SANDERS, I.S.; SCHWERTMANN, U.; FRIEDRICH, G. & WIECHOWSKI, A. An occurrence of a fully-oxidized natural titanomaghemite in basalt. Mineral. Mag., 53:299-304, 1989.

[2] BIGHAM, J.M.; GOLDEN, D.C.; BOWEN, L.H.; BUOL, S.W. & WEED, S.B. Iron oxide mineralogy of well-drained utilsols and oxisols: I. Characterization of iron oxides in soil clays by Mössbauer spectroscopy, X-ray diffractometry and selected chemical techniques. Soil Sci. Soc. Am. J., 42:816-830, 1978.

[3] BLESA, M.A.; MARINOVICH, H.A.; BAUMGARTNER, E.C. & MAROTO, A.J.G. Mechanisms of dissolution of magnetite by oxalic acid-ferrous ion solutions. Inorg. Chem., 26:3713-3717, 1986.

[4] COEY, J.M.D.; MORISH, A.H. & SAWATZKY, G.A. A Mössbauer study of conduction in magnetite. J. Phys., C1:271-273, 1971.

[5] COEY, J.M.D. Magnetic properties of iron in soil oxides and clay minerals. In: STUCKI, J.W.; GOODMAN, B.A. & SCHWERTMAN, U., eds. Iron in soils and clays Minerals, Dordrecht, Reidel Publishing Company, 1988. p.397-466.

[6] COEY, J.M.D.; GUGAT, O.; MCCAULEY, J. & FABRIS, J.D. A portable soil magnetometer. R. Fis. Ap. Instr., 7:25-30, 1992.

[7] COMISSÃO DE SOLOS DO ESTADO DE SÃO PAULO - CSESP. Levantamento de reconhecimento dos solos do Estado de São Paulo. Rio de Janeiro, Serviço Nacional de Pesquisa Agropecuária 1960. (Boletim Técnico, 12)

[8] CURI, N. Lithosequence and toposequence of Oxisols from Goiás and Minas Gerais, Brazil. West Laffayette, Purdue University, 1983 (Tese de Doutorado)

[9] CURI, N. & FRANZMEIER, D.P. Effect of parent rocks on chemical and mineralogical properties of some Oxisols in Brazil. Soil Sci. Soc. Am. J., 51:153-158, 1987.

[10] DEMATTÊ, J.L.I. & MARCONI, A. Effects of drainage on the mineralogy of soils developed from diabase in Piracicaba, State of São Paulo, Brazil. R. Bras. Ci. Solo, 15:1-8, 1991.

[11] DORIGUETTO, A.C.; GOULART; A.T.; JESUS FILHO, M.F.; FABRIS, J.D. & SANTANA, G.P. Ilmenite of a soil system developing on amphibolite. Europ. J. Soil Sci., 49:541-546, 1998.

[12] EMPRESA BRASILEIRA DE PESQUISA AGROPECUÁRIA - EMBRAPA Centro Nacional de Pesquisa de Solos (Rio de Janeiro, RJ). Sistema Brasileiro de Classificação de Solos, Brasília, Embrapa Produção de informação, Rio de Janeiro, Embrapa Solos, 1999. 412p.

[13] FABRIS, J.D.; COEY, J.M.D.; QI, Q. & MUSSEL, W.N. Characterization of Mg-rich maghemite from tuffite, Am. Mineral., 80:664-669, 1995.

[14] FABRIS, J.D.; JESUS FILHO, M.F.; COEY, J.M.D.; MUSSSEL, W.N. & GOULART, A.T. Iron-rich spinels from Brazilian soils. Hyperfine Interac., 110:23-32, 1997a.

[15] FABRIS; J.D.; MUSSEL, W.N.; COEY; J.M.D.; JESUS FILHO; M.F. & GOULART, A.T. Mg-rich iron oxide spinels from Tuffite. Hyperfine Interac., 110:33-40, 1997b.

[16] FERREIRA, B.A. Caracterização físico-química de minerais ferruginosos de um pedossistema desenvolvido de basalto. Belo Horizonte, Universidade Federal de Minas Gerais, 1995. p.90 (Tese de Mestrado)

[17] FONTES, M.P.F.; OLIVEIRA, T.S.; COSTA, L.M. & CAMPOS, A.A.G. Magnetic separation and evaluation of magnetization of Brazilian soils from different parent materials. Geoderma, 96:81-99, 2000.

[18] FYSH, S.A. & CLARK P.E. Aluminous hematite: a Mössbauer study. Phys. Chem. Miner., 8:257-267, 1982.

[19] GONÇALVES, M.; JESUS FILHO, M.F. & GARG, V.K. Mössbauer study of Brazilian soapstone. Hyperfine Interac., 67:437-442, 1991.

[20] GOULART, A.T.; JESUS FILHO, M.F.; FABRIS, J.D. & COEY, J.M.D. Characterization of a soil ilmenite developed from basalt. Hyperfine Interac., 91:771-775 1994.

[21] GOULART, A.T.; FABRIS, J.D.; JESUS FILHO, M.F., COSTA, G.M. & DE GRAVE, E. Iron oxides in a soil developed from basalt. Clays Clay Miner., 46:369-378, 1998.

[22] JACKSON, M.L. Soil chemical analysis: advanced course. 3.ed. Madison,1969. p.894.

[23] JCPDS - Joint Committee on Powder Diffraction Standards, International Center for Diffraction Data, Mineral Powder Diffraction Files Data Book. Swarthmore, Pensilvania, 1980. 1168p.

[24] JEFFERY, P.G. & HUTCHISON, D. Chemical methods of rock analysis, 3.ed. Oxford, Pergamon Press Oxford, 1981. 379p.

[25] JESUS FILHO, M.F.; FABRIS, J.D.; GOULART, A.T.; COEY, J.M.D.; FERREIRA, B.A. & PINTO, M.C.F. Ilmenite and magnetite of a tholeiitic basalt. Clays Clay Miner., 43:641-642, 1995.

[26] KÄMPF, N. & SCHWERTMANN, U. Concentration treatment for iron oxides in soils. Clays Clay Miner., 30:401-408, 1982.

[27] LADEIRA, E.A.; ROESER, H.M.P. & TOBSCHALL, H.J. Petrogenetic evolution of the green rock belt, Rio das Velhas, Quadrilátero Ferrífero, Minas Gerais. SYMPOSIUM ON THE GEOLOGY OF MINAS GERAIS, 2., Belo Horizonte, 1983. Proceedings. Belo Horizonte, 1983. p.149-159.

[28] LAGOEIRO, L.E. Transformation of magnetite to hematite and its influence on the dissolution of iron oxide minerals. J. Metam. Geol., 16:415-423, 1998.

[29] McKEAGUE, J.A. An evaluation of 0.1 M pyrophosphate and pyrophosphate-dithionite in comparison with oxalate as extractants of the accumulation products in Podzols and some other soils. Can. J. Soil Sci., 47:95-99, 1966.

[30] MEHRA, O.P. & JACKSON, M.L. Iron oxide removal from soils and clay by a dithionite-citrate system buffered with sodium bicarbonate. In: SWINEFORD, A., ed. NATIONAL CONFERENCE ON CLAYS AND CLAY MINERALS, 7., Washingt on, 1958. Proceedings. London, Pergamon Press, 1960. p.317-327.

[31] MIJOVILOVICH, A.; MORRAS, H.; SARAGOVI, C.; SANTANA, G.P. &. FABRIS, J.D. Magnetic fraction of an Ultisol from Misiones, Argentina. Hyperfine Interac. (C), 3:332-335, 1998.

[32] MOUKARIKA, A.; O'BRIEN, F. & COEY, J.M.D. Development of magnetic soil from ferroan dolomite. Geophy. Res. Letters, 18:2043-2046, 1991.

[33] MURAD, E. & SCHWERTMANN, U. The influence of Al substitution and crystallinity on the room-temperature Mössbauer spectrum of hematite. Clays Clay Miner., 34:1-6, 1986.

[34] MUSSEL; W.N.; FABRIS, J.D.; COEY, J.M.D.; SANS, L.M.A. & LELIS, M.F.F. Compositional and structural variability of Mg-rich iron oxide spinels from tuffite. R. Bras. Ci. Solo, 23:791-798, 1999.

[35] NORRISH, K. & TAYLOR, R.M. The isomorphus replacement of iron by aluminium in soil goethites. J. Soil Sci., 12:294-306, 1961.

[36] PINTO, M.C.F.; JESUS FILHO, M.F.; GOULART, A.T.; FABRIS, J.D. & SANTANA, G.P. Pedogenic stability of magnetite from amphibolite. Hyperfine Interac. (C), 2:61-66, 1997.

[37] PINTO, M.C.F.; FABRIS, J.D.; GOULART, A.T. & SANTANA, G.P. Pedogenetic instability of magnetite in mafic lithology. Hyperfine Interac. (C), 3:325 - 327, 1998.

[38] RAUEN, M.J. Mineralogical identification of a toposequence of soils from basaltic rocks in the state of Paraná, Brazil. West Laffayette, Purdue University, 1980. (MSc Thesis)

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