Laboratory synthesis of goethite and ferrihydrite of controlled particle sizes

Resumen

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, N2 adsorption BET specific surface area, transmission
electron microscopy, attenuated total reflectance Fourier transform
infrared spectroscopy, and maximum Cr(VI) adsorption.