Environmental Engineering Reference
In-Depth Information
2000
1800
1600
1400
1200
1000
800
600
400
200
0
Hb1/1 U
Hb1/1 TDS
Upstream, U
0
500
1000 1500
Days after starting the monitoring on the site
2000
2500
3000
3500
4000
4500
FIGURE 9.7
Long-term performance of the PRB near Pécs: uranium concentration and total dissolved solid
(TDS) in the observation well Hb1/1 (15 m downstream of the PRB). (From CsÖvári, M. 2009,
personal communication.)
Ion-exchange processes (see Reaction 9.9) or surface sorption using HAP
(two possible surface groups, Reactions 9.10 and 9.11) are described by the
following equations (Wu et al. 1991, Leyva et al. 2001).
≡
Ca
2
+
+
UO
2
+
≡
UO
2
+
+
Ca
2
+
(9.9)
2
2
2
+
+
+
≡+ ≡
OH
UO
O-UO
+
H
(9.10)
2
2
+
2
+
2
+
+
≡
OP-OH
+
O
≡
O P-O-UO
+
H
(9.11)
3
2
3
2
In the work of Fuller et al. (2002) autunite and chernikovite have been
identified as solid phases after adding uranyl ions to a saturated solution
of hydroxyapatite. Evidence for adsorption of U(VI) to hydroxyapatite sur-
faces as an inner-sphere complex was found for certain concentration ratios.
Similarly uranium phosphates have been found in laboratory experiments
on uranium removal from artificial groundwater (Simon et al. 2008), see
Fig u re 9.8.
Uranium can also be removed by adsorption on surfaces. Morrison
and Spangler (1992) have evaluated a range of uranium and molybdenum
adsorption tests using a variety of materials. Good removal results have
been obtained using lime, hematite, peat, ferric oxyhydroxide, phosphate,
and TiO
2
while clays exhibited low sorption potential. Precipitation and
adsorption onto a surface are processes that can simultaneously occur in a
chemical barrier. The sorption of uranium from groundwater was studied
in a series of publications (Morrison and Spangler 1992, 1993, Morrison et al.
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