Ferrous iron oxidation under acidic conditions – The effect of ferric oxide surfaces

Contaminant leaching from gold mining tailings dams in the Witwatersrand Basin, South Africa: A new geochemical modelling approach

“…(1)) needs to be oxidised to ferric iron. This occurs via the following reaction (Stumm and Lee, 1961;Jones et al, 2014):…”

“…However, ferric iron is soluble at a pH value below 3 (Jones et al, 2014). Therefore, until enough acidity is produced through Eq.…”

“…Therefore, until enough acidity is produced through Eq. (1) to bring the pH down from circum neutral to <3, ferric iron will precipitate as ferrihydrite according to (Jones et al, 2014): The oxidation of pyrite by ferric iron can be 2 orders of magnitude higher than oxidation by oxygen (Chandra and Gerson, 2010). However, the oxidation of ferrous to ferric iron is slow, unless the reaction is catalysed by bacteria, such as Acidithiobacillus Ferrooxidans (Gleisner et al, 2006).…”

The effect of oxidant addition on ferrous iron removal from multi-element acidic sulphate solutions

“…Also, the oxidation process has been found to occur either homogeneously in solution or heterogeneously on iron oxyhydroxides or solid particulates 25 . The form of oxidation is however, dependent on the physicochemical conditions in the system 25,[27][28][29] . Studies on the kinetics of oxidation of iron have resulted in different rate laws being proposed depending on the pH of the media.…”

Fe(II)-catalyzed transformation of ferrihydrite associated with natural organic matter

“…Some possible explanations for why fulvic acids inhibit transformation more then humic acids may be due to differences in (i) amount of Fe(II) sorption, (ii) OM molecular weights (MW), or (iii) carboxylic content of OM. Fulvic acids have higher carboxylic contents compared to humic acids ( Table 2.1) and it has been suggested that the carboxylic groups can bind strongly to ferrihydrite surfaces via ligand exchange, or associate with Fe(II) and prevent the direct complexing with structural Fe(III) and thus reduce the rate of Fe(II) oxidation (112)(113)(114)(115). Previous results with a soluble OM extracted from Ultisol with a high carboxylic content, however, resulted in substantial ferrihydrite transformation at C/Fe ratio 1.2, which suggests that carboxylic content may not be the controlling factor in whether ferrihydrite transformation occurs or not (75, 86).…”