Environmental Engineering Reference
In-Depth Information
(a)
100
NpO
2
+
80
CHP
60
PC500
BQ500
40
HQ500
20
0
150
100
200
0
50
250
Exposure time (h)
(b)
100
NpO
2
+
CHP
80
HQ100
60
HQ250
40
HQ500
20
0
0
50
100
150
200
250
Exposure time (h)
Figure 29.6
Reduction and removal of Np(V) by the humic derivatives under anoxic conditions, pH 4.7, c
0
(Np) = 5.4·10
−5
m,
c
0
(HS) = 500 mg·l
−1
, Np(V):HS ratio = 1:40. (a) effect of quinonoid monomer nature incorporated into humic structure (HQ, hydroquinone;
cT, catechol; BQ, benzoquinone); (b) effect of reagent ratio (parent HA-to-quinonoid monomer) for HQ-enriched derivatives. HQ100,
HQ250, and HQ500 stand, respectively, for derivatives with reagent ratios of 100, 250, and 500 mg of HQ per 1000 mg of cHP. Reproduced
with permission from Ref. [31]. © American chemical Society.
complexes were investigated using x-ray photoelectron spectroscopy (xPS) as described by Kalmykov et al. [39]. xPS is a
powerful synchrotron technique that measures the elemental compositions, as well as chemical and electronic states of the ele-
ments that exist within a material. The xPS spectra of Np equilibrated with goethite and cHP-HQ100 at pH 3.5 and pH 7.5 are
presented in Figure 29.7. complete reduction of Np(V) to Np(IV) occurred at pH 3.5, but it remained in pentavalent state at pH
7.5. The higher reducing power of hydroquinone-enriched humic derivatives is in good agreement with what is predicted by the
Nernst equation.
The functional distribution of humic materials sorbed onto a goethite surface at different pH values was also studied using
scanning transmission x-Ray microscopy (STxm), which accommodates both a good 2D spatial resolution (up to 10 nm) and
the capability of producing high-quality spectra (NexAFS). The purpose of this study was to investigate the structure of the
humic coating on the goethite surface under different pH conditions. The sample equilibrated at pH 3.5 showed distinct
structures in the STxm c1s ratio image analysis of the selected sample regions (Fig. 29.8).
