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An unusually thermally stable magnetite from a niobium mine in Brazil

Published online by Cambridge University Press:  09 July 2018

A. C. Silva ,
M. C. Pereira ,
L. C. A. Oliveira ,
L. C. D. Cavalcante ,
J. D. Fabris  and
E. Murad
A. C. Silva
Affiliation:
Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil
M. C. Pereira
Affiliation:
Instituto de Ciência e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39803-371 Teófilo Otoni, Minas Gerais, Brazil
L. C. A. Oliveira
Affiliation:
Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil
L. C. D. Cavalcante
Affiliation:
Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil Centro de Ciências da Natureza, Universidade Federal do Piauí, 64049-550 Teresina, Piauí, Brazil
J. D. Fabris
Affiliation:
Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil Departamento de Química, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 39100-000 Diamantina, Minas Gerais, Brazil
E. Murad*
Affiliation:
Departamento de Química, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Minas Gerais, Brazil
*
*E-mail: emurad@yahoo.com
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Abstract

Magnetite-rich waste from a niobium mine near Araxá, State of Minas Gerais, Brazil, was heated to 500°C and 1000°C under an O2 atmosphere. The original waste and its oxidized products were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), room-temperature 57Fe Mössbauer spectroscopy, thermogravimetric analysis (TG) and temperature-programmed reduction (TPR).

Semiquantitative analyses by EDS and quantitative chemical analyses showed the waste to be constituted primarily of Fe with minor amounts of Ti, Ba, Al, Si, Nb, Mn, S and P. Mössbauer and XRD showed the waste to consist predominantly of magnetite and hematite. The magnetite content decreases when the temperature increases due to its direct conversion to hematite. However, at 500°C only 10 wt.% of original magnetite was converted to hematite, confirming the high stability of this magnetite, which could still be detected at 1000°C. The TG profile shows no significant weight gain on heating, indicating a high stability of the magnetite. The TPR profiles show that the hematite in the waste is sintered after treatment at 1000°C and the reduction peaks are consequently shifted to higher temperatures. This high thermal stability is attributed to a moderate isomorphous replacement of Fe by other cations present in the Nb mining waste.

Keywords

magnetitehematiteniobiumwastethermal stabilityAraxáMinas GeraisBrazil
Type
Research Article
Information
Clay Minerals , Volume 47 , Issue 1 , March 2012 , pp. 69 - 79
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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