A conceptual model to predict uranium removal from aqueous solutions in water–rock systems associated with low- and intermediate-level radioactive waste disposal
File(s)
Published version
Author(s)
Kenney, J
Kirby
Cuadros, J
Weiss
Type
Journal Article
Abstract
Global stores of radioactive waste are housed in surface stores where actinides are
susceptible to environmental release. It is imperative that waste disposal facilities
are built to safely contain this waste. However, to do this we must ensure that the
e
ngineered and natural barriers are sufficient to prevent the buried materials from
migrating through to the surface. Solutions migrating from repositories (ILW and
LLW) will have a wide range of chemical compositions and conceptual models
constraining the
key mineral
-
water interactions with realistic lithologies are
urgently needed. To this end, we conducted experiments to study U removal from
solution via mineral
-
surface interactions with quartz, sandstone, and volcanic rock
over a pH range of 2
-
12, with
varying concentrations of U (10 ppb, 0.1 ppm, 1 ppm,
and 10 ppm) and with and without bicarbonate added (2 mM) with 0.1 M NaCl
electrolyte. We observed that the U concentration in solution had little effect on the
extent of U removal from solution as a fu
nction of pH or bicarbonate concentration
2
with quartz and sandstone but was important for volcanic rocks, where removal of
U, due to adsorption, decreased with increasing U concentration between pH 4 and
8. When bicarbonate was added to solution then the
quartz, sandstone, and volcanic
rock geomaterials acted similarly in their abilities to immobilize uranium, with an
adsorption envelope from pH 4
-
8 followed by an increase in U removal, likely via
precipitation, at high pH. When bicarbonate was not added,
the removal of U from
solution was more controlled by the geomaterial. Bicarbonate addition at pH 6
-
10
lowered adsorption. However, the addition of bicarbonate in experiments with 10
ppm U at pH 10
-
12 allowed for precipitation of U at the rock surface
, making
bicarbonate an immobilizing factor. Therefore, our conceptual model shows that U
is immobilised from radioactive waste
-
like solutions in a bimodal distribution, both
at low (6) and high (11) pH.
susceptible to environmental release. It is imperative that waste disposal facilities
are built to safely contain this waste. However, to do this we must ensure that the
e
ngineered and natural barriers are sufficient to prevent the buried materials from
migrating through to the surface. Solutions migrating from repositories (ILW and
LLW) will have a wide range of chemical compositions and conceptual models
constraining the
key mineral
-
water interactions with realistic lithologies are
urgently needed. To this end, we conducted experiments to study U removal from
solution via mineral
-
surface interactions with quartz, sandstone, and volcanic rock
over a pH range of 2
-
12, with
varying concentrations of U (10 ppb, 0.1 ppm, 1 ppm,
and 10 ppm) and with and without bicarbonate added (2 mM) with 0.1 M NaCl
electrolyte. We observed that the U concentration in solution had little effect on the
extent of U removal from solution as a fu
nction of pH or bicarbonate concentration
2
with quartz and sandstone but was important for volcanic rocks, where removal of
U, due to adsorption, decreased with increasing U concentration between pH 4 and
8. When bicarbonate was added to solution then the
quartz, sandstone, and volcanic
rock geomaterials acted similarly in their abilities to immobilize uranium, with an
adsorption envelope from pH 4
-
8 followed by an increase in U removal, likely via
precipitation, at high pH. When bicarbonate was not added,
the removal of U from
solution was more controlled by the geomaterial. Bicarbonate addition at pH 6
-
10
lowered adsorption. However, the addition of bicarbonate in experiments with 10
ppm U at pH 10
-
12 allowed for precipitation of U at the rock surface
, making
bicarbonate an immobilizing factor. Therefore, our conceptual model shows that U
is immobilised from radioactive waste
-
like solutions in a bimodal distribution, both
at low (6) and high (11) pH.
Date Issued
2017-01-23
Date Acceptance
2017-01-18
Citation
RSC Advances, 2017, 7, pp.7876-7884
ISSN
2046-2069
Publisher
Royal Society of Chemistry
Start Page
7876
End Page
7884
Journal / Book Title
RSC Advances
Volume
7
Copyright Statement
© The Royal Society of Chemistry 2017. Open access article. This article is licensed under a CC-BY 3.0 (https://creativecommons.org/licenses/by/3.0/)
Sponsor
Natural Environment Research Council (NERC)
Grant Number
NE/L000660/1
Subjects
Science & Technology
Physical Sciences
Chemistry, Multidisciplinary
Chemistry
SORPTION BEHAVIOR
SELLAFIELD AREA
IONIC-STRENGTH
HUMIC-ACID
ADSORPTION
COMPLEXES
PH
CALCIUM
MONTMORILLONITE
SPECTROSCOPY
Publication Status
Published