Effect of pH on the Formation of Goethite and Hematite from Ferrihydrite

Abstract

Abstraet~Storage of ferrihydrite in aqueous suspensions at 24~ and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. The crystallinity of both products, as indicated by X-ray powder diffraction line broadening and magnetic hyperfine field values and distribution widths, was poorer, the lower the proportion of the corresponding product in the mixture. The existence of two competitive formation processes is suggested: goethite is formed via solution, preferably from monovalent Fe(III) ions [Fe(OH)z § and Fe(OH)4-], and hematite by internal rearrangement and dehydration within the ferrihydrite aggregates. This concept relates the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution, and implies that conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa.

Transformation of Akaganéite Into Goethite and Hematite in the Presence of Mn

“…The transformation of akaganrite to goethite and hematite is slow, even in 0.01 M KOH and at 70~ (Cotnell and Giovanoli, 1990); at pHs close to those in natural systems, the reaction may require years to reach completion, particularly in the presence of retarding species. Transformation of a related iron oxyhydroxide, ferrihydrite, to hematite and goethite at room temperature and pH 7-8, required over one year to reach completion (Schwertmann and Murad, 1983). Therefore, to obtain transformation products within a reasonable time period and also to facilitate comparison with the previous study of the transformation of akaganrite alone (Cornell and Giovanoli, 1990), the majority of experiments was carried out at high pH.…”

Fossilized iron bacteria reveal a pathway to the biological origin of banded iron formation

“…4f). The predominance of haematite points to circumneutral depositional/diagenetic conditions, where haematite tends to be abundant between pH 7 and 8, with ferrihydrite as the precursor 25 .…”

Geochemical study of groundwater in the Sho river fan, Toyama Prefecture for heat usage by geothermal heat pump

“…Ferric ion will precipitate in the well and piping. Ferrihydrite (Fe(OH) 3 ) and goethite (FeOOH) are commonly observed in the scale of groundwater wells (e.g., Schwertmann and Murad, 1983;Charette and Sholkovitz, 2002). In this study, iron concentrations in waters were analyzed (Tables 2, 4).…”