Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites

Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn i...

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Autor principal:	Sileo, Elsa Ester
Publicado:	2006
Materias:	Acid dissolution Mn-goethite Mn-hematite Rietveld refinement Thermal transformation dehydroxylation geochemistry goethite hematite hydrolysis phase transition
Acceso en línea:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00092541_v231_n4_p288_Alvarez http://hdl.handle.net/20.500.12110/paper_00092541_v231_n4_p288_Alvarez
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	paper:paper_00092541_v231_n4_p288_Alvarez
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spelling	paper:paper_00092541_v231_n4_p288_Alvarez2023-06-08T14:33:38Z Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites Sileo, Elsa Ester Acid dissolution Mn-goethite Mn-hematite Rietveld refinement Thermal transformation dehydroxylation geochemistry goethite hematite hydrolysis phase transition Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn in the dehydroxylation process was investigated using X-ray diffraction (XRD) and the Rietveld refinement of XRD data together with scanning electron microscopy (SEM), differential thermogravimetric analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). In all cases, the formed hematites retained the acicular shape of the precursor goethite. The dehydroxylation temperature increased with the increase of the Mn content in the parent goethite. The cell parameters of both phases decreased with the thermal treatment, however the decrease in the goethite b-parameter was more pronounced. This fact could be attributed to the distortion in the goethite structure by the presence of manganese. The band shifts in the FT-IR spectra of the goethites with different Mn substitution were analysed. The intensities of the hydroxyl vibrations were indicative of the degree of dehydroxylation. The chemical reactivity of all the samples, before and after the thermal treatment, was also studied. The kinetic experiments were carried out at 40 °C in 4 mol dm- 3 HCl. The acid dissolution of all Mn-goethites showed a congruent behavior indicative of a homogeneous distribution of Mn in the goethite crystals, this trend was not observed in the formed hematites presenting a high Mn content. The dissolution rate in goethites increased with the increase of Mn content, the opposite effect was observed in the corresponding hematites. The activation energy in both phases was also obtained and indicated that the Mn substitution produces an opposite effect on goethite- and hematite-phases. Different kinetic laws were applied in order to explain the dissolution behavior, but the modified first-order Kabai equation described the dissolution data best. © 2006 Elsevier B.V. All rights reserved. Fil:Sileo, E.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2006 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00092541_v231_n4_p288_Alvarez http://hdl.handle.net/20.500.12110/paper_00092541_v231_n4_p288_Alvarez
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Acid dissolution Mn-goethite Mn-hematite Rietveld refinement Thermal transformation dehydroxylation geochemistry goethite hematite hydrolysis phase transition
spellingShingle	Acid dissolution Mn-goethite Mn-hematite Rietveld refinement Thermal transformation dehydroxylation geochemistry goethite hematite hydrolysis phase transition Sileo, Elsa Ester Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
topic_facet	Acid dissolution Mn-goethite Mn-hematite Rietveld refinement Thermal transformation dehydroxylation geochemistry goethite hematite hydrolysis phase transition
description	Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn in the dehydroxylation process was investigated using X-ray diffraction (XRD) and the Rietveld refinement of XRD data together with scanning electron microscopy (SEM), differential thermogravimetric analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). In all cases, the formed hematites retained the acicular shape of the precursor goethite. The dehydroxylation temperature increased with the increase of the Mn content in the parent goethite. The cell parameters of both phases decreased with the thermal treatment, however the decrease in the goethite b-parameter was more pronounced. This fact could be attributed to the distortion in the goethite structure by the presence of manganese. The band shifts in the FT-IR spectra of the goethites with different Mn substitution were analysed. The intensities of the hydroxyl vibrations were indicative of the degree of dehydroxylation. The chemical reactivity of all the samples, before and after the thermal treatment, was also studied. The kinetic experiments were carried out at 40 °C in 4 mol dm- 3 HCl. The acid dissolution of all Mn-goethites showed a congruent behavior indicative of a homogeneous distribution of Mn in the goethite crystals, this trend was not observed in the formed hematites presenting a high Mn content. The dissolution rate in goethites increased with the increase of Mn content, the opposite effect was observed in the corresponding hematites. The activation energy in both phases was also obtained and indicated that the Mn substitution produces an opposite effect on goethite- and hematite-phases. Different kinetic laws were applied in order to explain the dissolution behavior, but the modified first-order Kabai equation described the dissolution data best. © 2006 Elsevier B.V. All rights reserved.
author	Sileo, Elsa Ester
author_facet	Sileo, Elsa Ester
author_sort	Sileo, Elsa Ester
title	Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
title_short	Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
title_full	Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
title_fullStr	Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
title_full_unstemmed	Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites
title_sort	structural characterization and chemical reactivity of synthetic mn-goethites and hematites
publishDate	2006
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00092541_v231_n4_p288_Alvarez http://hdl.handle.net/20.500.12110/paper_00092541_v231_n4_p288_Alvarez
work_keys_str_mv	AT sileoelsaester structuralcharacterizationandchemicalreactivityofsyntheticmngoethitesandhematites
_version_	1768544347998912512

Structural characterization and chemical reactivity of synthetic Mn-goethites and hematites

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