The transformation of ferrihydrite in the presence of trace Fe(II): The effect of the anionic media

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

“…Magnetite can also be formed by interactions of ferric minerals with aqueous Fe II that induce their structural modifications and bulk phase transformations. These solid state transformations are controlled by various factors like molar ratio x(Fe II )¼Fe II /[Fe II þFe III ] [15][16][17][18], pH [18,19], anionic media [20], OH À /Fe ratio [17,21] and structure of initial iron oxyhydroxide substrate [22]. The interaction of iron oxides with aqueous Fe II may lead to their transformations into ferric and/or mixed Fe II -Fe III phases.…”

“…Due to its poor cristallinity, solid state transformations of ferrihydrite are more widely reported. In the presence of low concentration of Fe II species, ferrihydrite was transformed either into goethite [14,[18][19][20]23], lepidocrocite [18,20,22] or hematite [18,24]. At high Fe II amount, mixed Fe II -Fe III minerals such as magnetite [15][16][17][18]22,25] or green rust [17,26] were formed from ferrihydrite or lepidocrocite.…”

Controlled phase formation of nanocrystalline iron oxides/hydroxides in solution – An insight on the phase transformation mechanisms

“…The conversion of ferrihydrite is slow at the catalyst absence, but its transformation can be accelerated by the addition of strong reductants [11]. Some additives, like Fe 2þ , due to its strong reducing capacity, can induce the transformation of ferrihydrite into other phases [1].…”

“…Liu et al [5,9e14], found that the presence of iron(II) can clearly accelerate the transformation of ferrihydrite into different iron phases. High pH and fast heating rates favor the topotactic transformation of ferrihydrite in solution as well as the formation of hematite, while a low pH and low heating rates favor the dissolution/re-precipitation mechanism of ferrihydrite as well as the formation of goethite [11].…”

Understanding abiotic ferrihydrite re-mineralization by ferrous ions

“…It is also well established that the iron (III)(hydr)oxide system is redox sensitive; one iron oxide transforming into another depending on various conditions such as pH, temperature, presence of ferrous ions, anions such as chloride, sulfate, and oxyanions such as arsenic (Liu et al 2005(Liu et al , 2008aPedersen et al 2005;Yee et al 2006;Mukiibi et al 2008;Das et al 2011aDas et al , 2011b. In natural and engineered environments, reductive dissolution of the ferric minerals is commonly cited as a primary mechanism causing arsenic mobilization (Pedersen et al 2006;Ghosh et al 2006;Jing et al 2008;Nguyen and Itoi 2009;Borch et al 2010;Halim et al 2010;Burnol and Charlet 2010;Maity et al 2011).…”