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until the C/Fe molar ratio exceeds 1.6. For C/Fe molar ratios above 1.6, the aggregation and

deposition kinetics of HA-Fe(II) colloids under anoxic conditions are slower than those of HA-
Fe(III) colloids under oxic conditions. Further, the aggregation of HA-Fe colloids under both

anoxic and oxic conditions decreases with increasing C/Fe molar ratio from 1.6 to 23.3. This
study highlights the importance of the redox transformation of Fe(II) to Fe(III) and the C/Fe

ratio for the formation and stability of NOM-Fe colloids that occur in subsurface environments
with anoxic–oxic interfaces.

论文链接：10.1021/acs.est.7b02356.

25. Redox transformation and reductive immobilization of Cr(VI) in the Columbia
River hyporheic zone sediments
作 者 : Xu, Fen; Liu, Yuanyuan; Zachara, John; 等 .

JOURNAL OF HYDROLOGY 卷 : 555 页 : 278-287 出版年 : DEC 2017

摘 要：An experimental and modeling study was conducted to investigate the redox
transformation and reductive immobilization of groundwater contaminant Cr in hyporheic zone
(HZ) sediments from U.S. DOE’s Hanford Site, where groundwater Cr(VI) is migrating and

discharging to the nearby Columbia River. Experimental results revealed that Cr(VI) can be
reduced and immobilized by the HZ sediments in the presence/absence of O2. Anaerobic pre-

incubation of the sediments increased the effective rate of Cr reduction that was correlated with
the increase in HCl-extractable Fe(II) content in the sediments. The reduced Cr was stable when

exposed to O2 under field-relevant pH (7.5) with and without dissolved Mn(II), which might
be oxidized to form Mn(III/IV) oxides that may oxidize reduced Cr. The Cr(VI) reduction rate

showed a multi-rate behavior, apparently reflecting the presence of reductants with different
reactivity in the sediments. The results from

this study indicated that the HZ sediments
can reductively immobilize Cr and the

sediment redox capacity can be recharged
through microbial activities. The results

implied that HZ can play a role as a natural
permeable redox barrier for removing

groundwater Cr before it discharges into a river system.
论文链接：https://doi.org/10.1016/j.jhydrol.2017.10.016

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