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American Mineralogist; April 2008; v. 93; no. 4; p. 584-590; DOI: 10.2138/am.2008.2608
© 2008 Mineralogical Society of America
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Structure and reactivity of synthetic Co-substituted goethites

Mariana Alvarez1,*, Elsa E. Sileo2 and Elsa H. Rueda1

1 Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, B8000CPB, Bahía Blanca, Argentina
2 INQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina


Figure 1
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  		FIGURE 1. Changes in morphology with the Co content for samples (a) G3, (b) G5, (c) G7, and (d) G10 (50 000x).

 

Figure 2
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  		FIGURE 2. Particle size distribution (from SEM analyses) of (a) G3, (b) G5, and (c) G7.

 

Figure 3
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  		FIGURE 3. SEM images for samples (a) G0 and (b) G10 (magnification 100 000x).

 

Figure 4
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  		FIGURE 4. DTA traces of the particles formed with different values of Co/Fe.

 

Figure 5
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  		FIGURE 5. X-ray diffraction patterns of pure and Co-substituted goethites. * in sample G10 indicate minor peaks at 30.2 and 35.7° corresponding to a separate phase.

 

Figure 6
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  		FIGURE 6. Unit-cell parameters vs. Co concentration.

 

Figure 7
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  		FIGURE 7. Arrangement of polyhedra in the structure of goethite, the octahedra share edges within the rows, and vertices between chains.

 

Figure 8
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  		FIGURE 8. Representative dissolution curves for synthetic goethites in 4 mol/dm3 HCl at 40 °C vs. time, as affected by Co substitution

 

Figure 9
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  		FIGURE 9. Plot of xCo vs. xFe dissolved in 4 M HCl for sample G5.

 

Figure 10
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  		FIGURE 10. Activation energy determination from the Arrhenius equation in its linear form for G0 and G7 samples.

 




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