es7b01793_si_001.pdf (553.92 kB)
Download fileFe(II) Interactions with Smectites: Temporal Changes in Redox Reactivity and the Formation of Green Rust
journal contribution
posted on 2017-10-04, 00:00 authored by Adele
M. Jones, Cassandra A. Murphy, T. David Waite, Richard N. CollinsIn
this study, temporal changes in the redox properties of three
0.5 g/L smectite suspensions were investigateda montmorillonite
(MAu-1) and two nontronites (NAu-1 and NAu-2) in the presence of 1
mM aqueous Fe(II) at pH 7.8. X-ray absorption spectroscopy revealed
that the amount of Fe(II) added quantitatively transformed into chloride-green
rust (Cl-GR) within 5 min and persisted over 18 days. Over the same
time, the reduction potential of all three suspensions increased by
50 to 150 mV to equilibrate at approximately −100 mV vs SHE.
The reduction of a model organic contaminant, 4-chloronitrobenzene
(4-CINB), also became increasingly slower over time with virtually
no 4-CINB reduction being observed after 18 days. There was a strong
correlation between reduction potential and the quantity of 4-ClNB
reduced by MAu-1, although other factors were likely involved in the
decreased redox reactivity observed in the nontronites. It is hypothesized
that the temporal increase in reduction potential results from clay
mineral dissolution resulting in increased Fe(III) contents in the
Cl-GR. These results demonstrate that long-term studies are recommended
to accurately predict contaminant management strategies.