es7b01944_si_001.pdf (1.78 MB)
Iron Redox Transformations in the Presence of Natural Organic Matter: Effect of Calcium
journal contribution
posted on 2017-08-07, 00:00 authored by Chao Jiang, Shikha Garg, T. David WaiteThe
effects of calcium on iron redox transformations in acidic
nonirradiated and irradiated Suwannee River Fulvic Acid (SRFA) solutions
are investigated in this study. Our results reveal that, even though
calcium is redox-inert, it affects the redox transformations of iron
with increased Fe(III) reduction rates under irradiated conditions
and decreased Fe(II) oxidation rates in the dark in the presence compared
to the absence of calcium. While the exact mechanism via which the
Fe(III) reduction rate under irradiated conditions is impacted by
calcium addition is not clear, the formation of more photolabile weakly
complexed Fe(III)SRFA is most consistent with our experimental results.
An observed decline in the Fe(II) oxidation rate in nonirradiated
and previously irradiated SRFA solutions with the addition of calcium
can be rationalized by formation of more weakly bound Fe(II) and Fe(III).
The higher Fe(III) reduction rates and lower Fe(II) oxidation rates
in the presence compared to the absence of calcium will help to maintain
higher concentrations of Fe(II) thereby increasing the bioavailability
of iron in calcium-containing waters. On the basis of our experimental
results, we have developed a mathematical model that well describes
the iron redox transformations mediated by SRFA in calcium-containing
waters under irradiated and nonirradiated conditions.