FeII induced mineralogical transformations of ferric oxyhydroxides into magnetite of variable stoichiometry and morphology

Abstract

a b s t r a c tThe Mössbauer spectroscopy was used to monitor the mineralogical transformations of ferrihydrite (F), lepidocrocite (L) and goethite (G) into magnetite as a function of aging time. Ferric oxyhydroxides were reacted with soluble Fe II and OH -in stoichiometric amounts to form magnetite at an initial pH of $ 9.7. Observed transformation extent into magnetite followed the order: F 4 L 4G with almost 30% of untransformed G after 1 month. The departure from stoichiometry, d, of magnetite (Fe 3 À d O 4 ) generated from F (d $ 0.04) and L (d $ 0.05) was relatively low as compared to that in magnetite from G (d$ 0.08). The analysis by transmission electron microscopy and BET revealed that generated magnetite was also different in terms of morphology, particle size and surface area depending on the nature of initial ferric oxyhydroxide. This method of preparation is a possible way to form nano-sized magnetite.

Effect of NaBH 4 on properties of nanoscale zero-valent iron and its catalytic activity for reduction of p -nitrophenol

“…112 NZVI was dried and stored in the anaerobic chamber. Other iron minerals were synthesized and characterized in the context of previous works (goethite (α-Fe III OOH) [23], magnetite (Fe II 1 III 2O4) [24] and hematite (α-Fe III 2O3) [24]). Maghemite was purchased from Sigma- NaBH4 solution (100 mM) twice by magnetic separation as described above.…”

Sorption of nalidixic acid onto micrometric and nanometric magnetites: Experimental study and modeling

“…Among them, two (M1 and M2) were prepared in lab, while third one (M3) was purchased from Prolabo. M1 and M2 were formed by mineralogical transformations of 2-line ferrihydrite and lepidocrocite (γ-FeOOH), respectively as previously reported [12]. Prior to reactivity tests, all magnetites were analyzed by X-ray powder diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared spectrometer (FTIR) as described previously [2].…”

“…Magnetite can also be formed by reacting aqueous Fe II with ferric oxides inducing their structural modifications and bulk phase transformations [12,13]. The morphology, crystallography and specific surface area of natural or synthetic magnetite can vary widely.…”

The role of dissolved Fe(II) concentration in the mineralogical evolution of Fe (hydr)oxides during redox cycling

“…Under anaerobic conditions, the products of Fe(II) catalyzed transformation of poorly crystalline Fe(III) (hydr)oxides have been well characterized and are determined by the concentration of dissolved Fe(II); a low molar ratio of Fe(II): ferrihydrite (≥0.072) leads to the formation of lepidocrocite and goethite while a high molar ratio (≤0.72) leads to the formation of goethite and magnetite. (Boland et al, 2014(Boland et al, , 2013Handler et al, 2014Handler et al, , 2009Hansel et al, 2005Hansel et al, , 2004Jeon et al, 2003;Latta et al, 2012;Liu et al, 2007;Pedersen et al, 2005;Postma, 1993;Usman et al, 2012;Yang et al, 2010;Yee, 2006). Here, we observe similar mineralogical transformations during the initial Fe(II) catalyzed transformation of ferrihydrite; however, as short redox cycles continue we observe that the limited reaction time between dissolved Fe(II) and Fe(III) (hydr)oxides results in limited mineralogical transformation.…”