Boletín de la Sociedad Geológica Mexicana
Volumen 67, núm. 3, 2015, p. 433-446
Laboratory synthesis of goethite and ferrihydrite of controlled particle sizes
Milton Villacís-García1, Mariana Ugalde-Arzate1, Katherine Vaca-Escobar1, Mario Villalobos1,*, Rodolfo Zanella2, Nadia Martínez-Villegas3
1 Environmental Bio-Geochemistry Group, Earth Sciences Graduate Program, Geochemistry Department, Instituto de Geología, Universidad Nacional Autónoma de México (UNAM), Coyoacán, Ciudad Universitaria, México 04510, D.F.
2 Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México (UNAM), Coyoacán, Ciudad Universitaria, México 04510, D.F.
3 IPICyT, Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San José No. 2055, Col. Lomas 4a Secc., 78216 San Luis Potosí, SLP, México.
Iron oxyhydroxides, such as goethite and ferrihydrite, are highly abundant and ubiquitous minerals in geochemical environments. Because of their small particle sizes, their surface reactivity is high towards adsorption of anions and cations of environmental relevance. For this reason these minerals are extensively studied in environmental geochemistry, and also are very important for environmental and industrial applications. In the present work, we report the synthesis and characterization of goethite and ferrihydrite of controlled particle sizes. It has been shown that surface reactivity of these minerals is highly dependent on crystal sizes, even after normalizing by specific surface area. In order to investigate the reasons for this changing reactivity it is necessary to work with reproducible particle sizes of these minerals. We investigated here the experimental conditions to synthesize goethite samples of four different specific surface areas: ca. 40, 60, 80 and 100 m2 g-1, through the controlled speed of hydroxide addition during hydrolysis of acid Fe(III) solutions. In the case of 2-line ferrihydrite, samples with two different particle sizes were prepared by changing the aging time under the pH conditions of synthesis (pH = 7.5). The synthesized minerals were identified and characterized by: X-ray diffraction, N2adsorption BET specific surface area, transmission electron microscopy, attenuated total reflectance Fourier transform infrared spectroscopy, and maximum Cr(VI) adsorption.
Keywords: synthesis, iron oxides, specific surface area, goethite, ferrihydrite, particle size.