Effect of acetate on ferrihydrite crystallization

Abstract

M6ssbauer spectroscopy was used to follow the aging of ferrilaydrite with different amounts of acetate, to achieve more crystalline products. M6ssbauer spectra of fresh samples did not show any magnetic components. After two years aging, the solids presented crystalline fractions. Hematite formation was inhibited as acetate content increased in solids. For an acetate/iron molar ratio equal to 0.63 goethite was formed instead of hematite. X-ray diffraction confirmed these results. This work shows that synthetic samples can be used for elucidating the "anti-bematitic" effect of organic matter already detected in soils.

Effects of Adsorbed Arsenate on the Rate of Transformation of 2-Line Ferrihydrite at pH 10

“…15,24À29 Although sulfate adsorbs onto ferrihydrite in a much weaker fashion than silicate and phosphate, it still retards the rate of ferrihydrite transformation and promotes hematite formation akin to silicate and phosphate. 30 In addition to the inorganic anions discussed above, organic ligands such as oxalate, 31 carboxylic acid, 32 acetate, 33 and simple sugars 34 also inhibit ferrihydrite transformation.…”

“…Although goethite is expected to be the only stable product under pristine alkaline conditions, formation of surface complexes (adsorbed solutes) promotes dehydration followed by transformation to hematite rather than the dissolution and reprecipitation pathway to goethite. ,− Although sulfate adsorbs onto ferrihydrite in a much weaker fashion than silicate and phosphate, it still retards the rate of ferrihydrite transformation and promotes hematite formation akin to silicate and phosphate . In addition to the inorganic anions discussed above, organic ligands such as oxalate, carboxylic acid, acetate, and simple sugars also inhibit ferrihydrite transformation.…”

Occurrence and Constitution of Natural and Synthetic Ferrihydrite, a Widespread Iron Oxyhydroxide

“…The aging of ferrihydrite in the presence of different amounts of acetate was monitored for two years, mainly by Mo ¨ssbauer spectroscopy, using ferrihydrite powders that had been dried at 120 °C after washing with ammonium acetate solutions of different concentrations. 284 High acetate concentrations led to the crystallization of goethite, whereas hematite was formed at low levels. Thus, acetate was concluded to inhibit the crystallization of hematite in favor of goethite.…”

Effect of citrate on the local Fe coordination in ferrihydrite, arsenate binding, and ternary arsenate complex formation

“…Natural Fhs are often associated with significant amounts of organic C (e.g., Murad et al, 1988;Rancourt et al, 2001) but only few studies exist which focus on the effect of high or low molecular weight organic compounds on the structure and reactivity of Fh (Varela et al, 1994;Rancourt et al, 2005;Schwertmann et al, 2005;Eusterhues et al, 2008;Berquó et al, 2009). Especially low molecular weight organic compounds like polyhydroxycarboxylates (PHC) such as oxalate, citrate, and fumarate are omnipresent in natural systems, but to the best of our knowledge, there is no systematic study investigating their effect on the local (i.e., <4 Å ) Fe coordination in Fh.…”