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Efficiency of organic ligands in adsorptive dissolution and photoreductive dissolution of hematite
Mukherjee, P. & Gao, Y.
Abstract
Organic ligands, especially oxalate, play an
important role in iron dissolution from iron-containing
minerals. To study the effects of organic acid ligands on
the dissolution of iron-containing minerals, the dissolution
kinetics of hematite in the presence of oxalate, acetate, and
formate were studied under ultraviolet radiation with
varying ligand concentrations (10–3 mM). The results
indicate that for adsorption dissolution, oxalate is the
dominating ligand for producing soluble iron (III) from
hematite; for photoreductive dissolution under ultraviolet
radiation and in oxic conditions, the production of iron (II)
is highly proportional to the concentrations of oxalate,
whereas the effects of varying concentrations of formate
and acetate are not significant. At low oxalate concentrations
(10–500 µM), the photoreductive dissolution of iron
(II) is substantially low, while at high oxalate concentrations
(3 mM), oxalate is equally effective as formate and
acetate for producing photoreduced iron (II) from hematite.
Combining with field data from other works, it is likely that
the ratios of oxalate to total iron need to be higher than a
threshold range of ~1.2–5.5 in order for oxalate to
effectively produce photoreduced iron (II) from hematite.
This study demonstrates that the iron (II) yield from photoreduction
of hematite is significantly lower when the
hematite surface is pre-coated with organic ligands versus
when it is exposed to ultraviolet radiation instantaneously.
Keywords
Dissolution; Hematite; Organic ligands; Photoreduction
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