INVESTIGADORES
ALVAREZ Mariana
congresos y reuniones científicas
Título:
Structural changes of a series of synthetic goethites obtained in basic solutions containing Mn(II) and Co(II)
Autor/es:
ELSA E. SILEO; MARIANA ALVAREZ; ELSA H. RUEDA
Lugar:
Campinas
Reunión:
Workshop; Latin American Workshop on Applications of Powder Diffraction; 2007
Institución organizadora:
Laboratorio Nacional de Luz Sincrotrón
Resumen:
Lateritic soils and manganese nodules found on the ocean floor are important sources for extraction of metal ions such as manganese and cobalt. Both contain iron oxides and oxyhydroxides such as hematite (Fe2O3) and goethite (a-FeOOH), and part of the Mn and Co cations are incorporated in the oxide and oxyhydroxide matrixes. Previous studies indicate that samples of goethite aged in basic Mn(II)- or Co(II)-containing solutions, form substituted a-FeOOH where the substituting metal is incorporated as Me(III). The oxidation-incorporation mechanism starts with: i) dissolution of the ferrihydrite precursor with the formation of Fe(OH)4 −  and Me(OH)3− ions, ii) adsorption of Me(OH)3−  species on the recently formed goethite nuclei; iii) oxidation of Me(II) to Me(III) on the nuclei surface; iv) and growth of goethite with Me(III) incorporation. The incorporation of Me(III) changes the structural and chemical properties of goethite. In this work we have analyzed the structural characteristics of two series of Mn- and Co-goethites. Crystallite size, atomic and cell parameters were obtained by the Rietveld refinement of XRD data. The cell parameters in Mn-goethite orthorhombic, Pbnm space group) change with the degree of Fe-for-Mn incorporation. The a- and c-parameters decrease and the b-parameter increases. These features may be ascribed to the electronic configuration of Mn(III), that presents a tetragonally distorted coordination polyhedron. In the case of Co-goethites, all cell parameters decrease with the cobalt incorporation, indicating the presence of Co(III). The changes in the cell parameters and intercationic distances in both series are analyzed and compared with those of a previous work. 2O3) and goethite (a-FeOOH), and part of the Mn and Co cations are incorporated in the oxide and oxyhydroxide matrixes. Previous studies indicate that samples of goethite aged in basic Mn(II)- or Co(II)-containing solutions, form substituted a-FeOOH where the substituting metal is incorporated as Me(III). The oxidation-incorporation mechanism starts with: i) dissolution of the ferrihydrite precursor with the formation of Fe(OH)4 −  and Me(OH)3− ions, ii) adsorption of Me(OH)3−  species on the recently formed goethite nuclei; iii) oxidation of Me(II) to Me(III) on the nuclei surface; iv) and growth of goethite with Me(III) incorporation. The incorporation of Me(III) changes the structural and chemical properties of goethite. In this work we have analyzed the structural characteristics of two series of Mn- and Co-goethites. Crystallite size, atomic and cell parameters were obtained by the Rietveld refinement of XRD data. The cell parameters in Mn-goethite orthorhombic, Pbnm space group) change with the degree of Fe-for-Mn incorporation. The a- and c-parameters decrease and the b-parameter increases. These features may be ascribed to the electronic configuration of Mn(III), that presents a tetragonally distorted coordination polyhedron. In the case of Co-goethites, all cell parameters decrease with the cobalt incorporation, indicating the presence of Co(III). The changes in the cell parameters and intercationic distances in both series are analyzed and compared with those of a previous work.