selective removal of dissolved uranium in drinking water by nanofiltration
TRANSCRIPT
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WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 1 1 6 0 – 1 1 6 6
0043-1354/$ - see frodoi:10.1016/j.watres
�Corresponding autE-mail address: f
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Selective removal of dissolved uranium in drinking waterby nanofiltration
A. Favre-Reguillona,�, G. Lebuzitb, D. Muratb, J. Foosb, C. Mansourc, M. Drayed
aLaboratoire de Chimie Organique (UMR CNRS 7084), CNAM, 2 rue Conte, 75003 Paris, FrancebLaboratoire des Sciences Nucleaires, CNAM, 2 rue Conte, 75003 Paris, FrancecLaboratoire d’Electrochimie et de Chimie Analytique (UMR CNRS 7575), ENSCP, 11 rue Pierre et Marie Curie, 75005 Paris, FrancedLaboratoire de Chimie Moleculaire et Environnement (EA 1651), Universite de Savoie, Polytech’Savoie,
73376 Le Bourget du Lac Cedex, France
a r t i c l e i n f o
Article history:
Received 30 March 2007
Received in revised form
28 August 2007
Accepted 29 August 2007
Available online 7 September 2007
Keywords:
Uranium
Nanofiltration
Remediation
Drinking water
Membrane
Rejection mechanism
nt matter & 2007 Elsevie.2007.08.034
hor. Tel.: +33 472448507; [email protected] (A. Fav
a b s t r a c t
A procedure for the selective removal of uranium traces dissolved in drinking water has
been studied. Plate module membrane filtration equipment was operated to evaluate the
performance and selectivity of three different nanofiltration flat-sheet membranes.
Experiments were carried out using various commercial mineral waters with distinct
physicochemical compositions. The membranes were first discriminating by their ability to
reject uranium in the presence of the main cations found in mineral waters, using a
2 mg L�1 (2000 ppb) concentration of uranium. The rejection of U(VI) was dependent on the
uranyl speciation and the ionic strength. Second, removal of uranium traces (0.02 mg L�1,
20 ppb) was performed using the nanofiltration membrane showing the highest selectivity
for uranium toward alkaline and alkaline-earth ions. The results showed a high
performance of the nanofiltration membrane, Osmonics DL, for selective uranium rejection
at low pressure (1 bar), illustrating the advantage of nanofiltration for the selective removal
of uranium from drinking water.
& 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Natural uranium occurs in very small amounts in many soil
and rock types. The average uranium concentration in the
Earth’s crust is about 3 mg/kg. In addition, the formation of
uranium accumulations is a normal geological process,
especially in granites and sedimentary rocks, two widely
occurring rock types.
Assessment of the risk of impact from most radionuclides
is based on the total radiological dose rate. However, for
uranium, there can be a greater risk from chemical toxicity
than radiological toxicity. Chemical toxicity of uranium is
dependent on several environmental parameters (Grenthe
et al., 1992; Sheppard et al., 2005). Although uranium has
r Ltd. All rights reserved.
ax: +33 472431408.re-Reguillon).
oxidation states of (III)–(VI), the two major oxidation states
are (VI) and (IV). The latter is readily oxidized to (VI) as UO2þ2 ,
the most prevalent form of uranium in the environment.
U(VI) readily complexes with carbonate, phosphate or sulfate
ions and in these forms is soluble and easily transported
(Cheng et al., 2004; Zhou and Gu, 2005).
The maximum admissible concentrations (MACs) of ura-
nium for drinking water depend on each public authority
(Reimann and Banks, 2004). Although there is no defined MAC
in western European legislation, the US Environmental
Protection Agency has promulgated a MAC of 0.03 mg L�1
(30 ppb) and the World Health Organization (WHO) has
suggested a guideline value of 0.002 mg L�1 (2 ppb) (Reimann
and Banks, 2004). In recent investigations of drinking water
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Table 1 – Determined composition of the mineral waterafter the addition of uranyl nitrate
Sample Composition (mg L�1) pH
Na+ K+ Mg2+ Ca2+ UO22+
A 11.2 6.2 7.9 12.0 2.0 or
0.002
7.0
B 7.0 1.5 26.3 81.4 2.0 7.2
C 5.7 2.8 43.5 218.0 2.0 7.0
Table 2 – Composition of the mineral water as specifiedby the producers
Sample Composition (mg L�1) Dryresidue
Cl� NO3� SO4
2� HCO3� SiO2
A 13.5 6.3 8.1 71.0 31.7 130.0
B 4.5 3.8 10.0 357.0 13.5 309.0
C 0.0 4.6 336.0 400.2 0.0 841.0
Table 3 – General properties of Osmonics membranes
Membrane Molecular weight cut-off (Da) pI
G10 2500a 3.7b
DL 150–300c –
DK 150–300c 4.0d
a Afonso et al. (2001).b Sbai et al. (2003).c Supplied by GE Water & Process Technologies.d Tanninen and Nystrom (2002).
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 1 1 6 0 – 1 1 6 6 1161
quality in the USA and Europe, high concentrations of
uranium (up to 1.2 mg L�1, 1200 ppb) were detected in some
water samples collected from private wells (Hakonson-Hayes
et al., 2002; Orloff et al., 2004). Utilization of water from these
wells has raised concerns of potential radiological and
toxicological risks to human consumers. The alternative
sources of potable water are commercially bottled water or
those after water treatment. The water treatment techniques
that have been used to reduce uranium concentration to less
than the MAC are chemical coagulation–flocculation (Gafvert
et al., 2002), activated carbon (Coleman et al., 2003), ion
exchange (Barbette et al., 2004; Barton et al., 2004; Bryant
et al., 2003; Gu et al., 2004; Vaaramaa et al., 2000), ultrafiltra-
tion assisted by complexation (Kryvoruchko et al., 2004) and
reverse osmosis (Hsiue et al., 1989; Huikuri et al., 1998; Lin
et al., 1987; Raff and Wilken, 1999).
Membrane separation processes have been used for several
years to concentrate or fractionate suspended particles and
dissolved substances. Reverse osmosis (RO), now in wide-
spread use to prepare irrigation water from briny waters, and
ultrafiltration (UF) both constitute a valuable aid for the
fractionation and concentration of colloidal substances.
Nanofiltration (NF) membranes have intermediate molecular
weight cut-offs (MWCOs) between UF and RO membranes. NF
has been found to be very useful in recent years for water and
wastewater treatment. NF membranes have been shown to be
able to remove hardness as well as a fraction of dissolved
salts. Some micropollutants, such as pesticides (Bellona et al.,
2004; Causserand et al., 2005; Kiso et al., 2001), endocrine-
disrupting compounds and pharmaceutically active com-
pounds (Kimura et al., 2003; Zhang et al., 2006), can be
effectively removed by NF membranes.
The purpose of this study was to evaluate the possibilities
of NF for the selective removal of U(VI) from well water. We
first selected the most appropriate membrane that showed
the highest U(VI) rejection and the highest selectivity toward
alkaline and alkaline earth ions. The ability of various
membranes to selectively reject U(VI) was then evaluated
using three different types of mineral water and a U(VI)
concentration of 2 mg L�1 (2000 ppb). Next, the membranes
showing the highest U(VI) selectivity were evaluated with
mineral water containing U(VI) traces (0.02 mg L�1, 20 ppb).
2. Materials and methods
2.1. Mineral water samples
Commercially available mineral water samples, in plastic
bottles, were obtained through the normal distribution
channels. Uranyl nitrate (UO2(NO3)2 � 6H2O) was added to the
water samples to obtain concentrations of 2 or 0.02 mg L�1.
Table 1 lists the cation concentration present in water
samples and Table 2 lists the main anion concentration and
dry residues as specified from the producers.
2.2. Membrane
The three flat membranes, obtained from Osmonics (GE
Water & Process Technologies), were all constituted of
polyamide filtering layers with a membrane surface area of
155 cm2. DK, DL and G10 membranes are polymeric flat thin
film composite membranes in which a polyamide selective
layer is supported on a polysulfone layer (Favre-Reguillon
et al., 2007; Mazzoni and Bandini, 2006; Sbai et al., 2003). The
MWCOs are between 150 and 2500 Da and the isoelectric
points (pI) are close to 4 (Table 3). For all membranes, the
dependence of the volumetric water flux on the transmem-
brane pressure was determined with deionized water. In
general, a pressure increase from 1 to 3 bar leads to a linear
volumetric water flux volume versus transmembrane pres-
sure. The pure water permeability results suggest that the DK
membrane is the most compact membrane, whereas the G10
and DL membranes have the most open structures.
2.3. Nanofiltration experiments
NF experiments were performed with an Osmonics Sepa CF
lab-scale membrane cell and the lab-scale membrane system
as already described (Sorin et al., 2006). The feed is
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WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 1 1 6 0 – 1 1 6 61162
maintained at constant composition during the experiments
by totally recycling the permeate and the feed.
Mineral waters were filtered on membranes in a cross-flow
mode. During membrane filtration, the metal ions in the feed
water are convectively driven to the membrane surface, thus
forming a concentrated polarization boundary layer near the
membrane. This layer involves a reduction in charge density of
the membrane and consequently attenuates the electrostatic
repulsions between the metal ions in solution and the charge of
the membranes (Bian et al., 2000), leading to a decrease in the
rejection (Bacchin et al., 2002; Bhattacharjee et al., 1999; Schaep
et al., 1998). The accumulation at the membrane surface is a
function of the back-transport of the complex into the bulk
solution. To decrease the accumulation at the membrane
surface, the tangential velocity (Jr) at the membrane surface
is maintained at a constant value of 145 mm s�1.
2.4. Rejection measurements
NF tests were carried out by filtering mineral water on the
membrane using a transmembrane pressure of 1–4 bar, a
tangential velocity of 145 mm s�1 and at a constant tempera-
ture of 25 1C. The pH of the solution was constant during the
nanofiltration process. The permeate flux was measured and
samples of permeate and feed were taken 30 min after each
stage of operation. Each experiment was repeated 3 times to
improve the reliability of the results.
Rejection of metal ions was evaluated from the determined
feed and permeate concentration of samples collected during
the course of the experimental tests. The rejection Ri (%) of a
substance i was calculated according
Ri ¼Cf
i � Cpi
Cfi
!� 100, (1)
where Cfi is the concentration of i in the feed and Cp
i is the
concentration of i in the permeate.
The transmission Ti (%) of a solute i is the ability of solute i
to pass through the membrane and can be expressed as
Ti ¼Cp
i
Cfi
� 100. (2)
The membrane selectivity of two solutes i and j, MSi=j, can
be expressed by the ratio of their transmission and thus may
be expressed as the function of the concentrations of i and j in
the permeate and in the feed as
MSi=j ¼Ti
Tj¼
Cpi
Cfi
�Cf
j
Cpj
. (3)
Metal ion concentrations were determined by ICP-AES with
a Spectro D ICP spectrometer. U(VI) concentration at trace
levels was determined by ICP-MS with a FINIGAN-MAT
element mass spectrometer.
3. Results and discussion
3.1. U(VI) speciation in water samples
Uranium is known to easily form stable complexes with both
organic and inorganic ligands in natural aquatic environ-
ments (Krepelova et al., 2006). There is extensive literature on
equilibria involved in the uranyl–carbonate systems (Clark
et al., 1995; Grenthe et al., 1992). These are usually quite
complex in that they consist of several different complexed
ions in rapid equilibria with one another and the hydrolyzed
species (Barton et al., 2004; Grenthe et al., 1992). It is therefore
important to quantitatively predict the reactions that are
likely to occur between uranyl and the anions present in the
aqueous media in order to understand the rejection of
aqueous species by the nanofiltration membranes. This
information is provided by speciation calculations using
chemical thermodynamic data. The speciation of uranyl as
a function of the water composition was evaluated using the
speciation code CHESS (van der Lee, 2002), which is a
speciation model specifically developed to simulate the
equilibrium state of complex aquatic systems (Fig. 1).
In the presence of carbonate and when the uranyl
concentration does not exceed the carbonate concentration,
the monomeric uranyl carbonate species UO2(CO3),
UO2(CO3)22� and UO2(CO3)3
4� are expected to dominate depend-
ing on pH (Grenthe et al., 1992). For water samples, at pH close
to 7, uranyl speciation distribution in the aqueous media
showed that UO2(CO3)22� and UO2(CO3)3
4� should be the major
individual components. For a lower concentration of carbo-
nate (water sample A, Fig. 1), the uranyl dihydroxid specie
UO2(OH)2 should be one of the major individual components.
3.2. Rejection of U(VI) by nanofiltration membranes
The effectiveness of NF membranes in removing uranium in
water was tested on U(VI) artificially enriched water samples.
Uranyl nitrate, UO2(NO3)2, was added to the water samples to
obtain uranium concentration of 2 mg L�1. Membrane perfor-
mance was measured in terms of U(VI) rejection (Fig. 2) and
U(VI)/alkaline or alkaline-earth cation selectivities.
Nanofiltration membranes are electrically charged in aqu-
eous media due to the type of material or the adsorption of
charged species. Hence, size and charge of solutes influence
the extent of rejection by nanofiltration membranes, though
the precise mechanism of rejection will depend on the type of
membrane used (Bellona et al., 2004). Predictably, the highest
cut-off membrane exhibits the lowest solute rejection for the
same water composition. The rejection of U(VI) with water
sample A was found to be 40% with G10, and 95% and 99% for
DL and DK membranes, respectively. The same trend was
observed for the rejection of alkaline and alkaline-earth ions.
The difference in rejection observed between DL and DK
membranes could be explained by a slightly lower mean pore
radius for DK than for DL (Bargeman et al., 2005).
The high rejection of cations may be attributed to the
Donnan exclusion model (Bowen et al., 1997). NF membranes
used in the work show amphoteric behavior. The isoelectric
points (pI) of DK, DL and G10 membranes are close to 4
(Table 3) and thus the electric charge density of the NF
membranes at pH 7, above the pI, is negative. In the Donnan
exclusion model, the rejection of the multicharge anions
by a negatively charged membrane is highest, whereas that of
the bivalent or monovalent cations is the lowest. The higher
rejection of Mg2+ compared with Ca2+ may be due to the
fact that magnesium ions, although smaller, display larger
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A C
0
10
20
30
40
50
60
70
80
90
100G 10
Reje
ction (
%)
Na+
K+
Mg2+
Ca2+ UO2
2+
A C
0
10
20
30
40
50
60
70
80
90
100DL
Reje
ction (
%)
Na+
K+
Mg2+
Ca2+ UO2
2+
A C
0
10
20
30
40
50
60
70
80
90
100DK
Reje
ction (
%)
Na+
K+
Mg2+
Ca2+ UO2
2+
B
B
B
Fig. 2 – Rejection coefficient of sodium, potassium,
magnesium, calcium and uranium as a function of water
samples and membrane; U(VI) ¼ 2 mg L�1 (water
composition, see Table 1 and Table 2). Experimental
conditions: T ¼ 20 1C, DP ¼ 1 bar, Jr ¼ 145 mm s�1.
4 6 8
0
20
40
60
80
100
UO2(OH)3-
UO2(CO3)22-
UO2(CO3)34-UO2(OH)2
UO2CO3
UO2OH-
UO2SO4
UO22+
Ura
nyl specie
s in w
ate
r A
(%
)
pH
4 8
0
20
40
60
80
100
UO2(CO3)34-UO2(OH)2
UO2SO4
UO2OH-
UO2(CO3)22-UO2CO3
UO22+
Ura
nyl specie
s in w
ate
r B
(%
)
pH
4 6 8
0
20
40
60
80
100
UO2(CO3)
Ura
nyl specie
s in w
ate
r C
(%
)
pH
CaUO4
UO2OH+
UO22+
UO2SO4
UO2(OH)2
UO2(CO3)34-
UO2(CO3)22-
5 7
5 6 7
75
Fig. 1 – Aqueous U(VI) speciation distribution as the function
of pH and water composition evaluated using CHESS
(van der Lee, 2002).
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 1 1 6 0 – 1 1 6 6 1163
hydrated diameters (0.80 nm) than those of calcium ions
(0.46 nm) (Rios et al., 1996).
An interesting membrane selectivity was observed with the
DL membrane for the three water samples studied. In all
cases, U(VI) rejection was high (490%), whereas the rejection
of the monovalent ions and divalent cations was low, o25%
and o40%, respectively, for water sample A, o10% and o20%,
respectively, for water sample B, and o25% and o50%,
respectively, for water sample C, which has the highest
mineral content. Under those conditions, high U(VI)/Na+ and
U(VI)/Mg2+ membrane selectivity could be obtained (Table 4).
The rejection of cations by NF membranes is dependent on
their valence, but the structure of ions in solution must also
be taken into account. Fig. 1 shows the uranyl speciation of
the different water samples. For DL and DK membranes the
observed rejection was high (490%) whatever the water
samples, but for G10 membrane the observed rejection of
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Table 5 – Observed U(VI) rejection with G10 membranes
Watersample
U(VI)rejection (%)
Dry residue(mg L�1)
MSNaþ
UðVIÞ
A 40 130 1.5
B 21 309 1.2
C 13 841 1.1
Experimental conditions: T ¼ 20 1C, Jr ¼ 145 mm s�1, U(VI) ¼
2 mg L�1, water composition, see Table 1 and Table 2.
Table 4 – Membrane selectivity observed with DLmembrane with an uranium concentration of 2 mg L�1
(water composition, see Table 1)
Membrane selectivity Water sample
A B C
U(VI)/Na+ 16.0 8.5 7.6
U(VI)/Mg2+ 11.8 7.4 4.8
Experimental conditions: T ¼ 20 1C, DP ¼ 1 bar, Jr ¼ 145 mm s�1.
1.0 1.5 2.0 2.5 3.0 3.5 4.00
10
20
30
40
50
60
70
80
90
100
G10
Reje
ction (
%)
ΔP (bar)
Na+ K
+Ca
2+Mg
2+UO2
2+
1.0 1.5 2.0 2.5 3.0 3.5 4.00
10
20
30
40
50
60
70
80
90
100
DL
Reje
ction (
%)
ΔP (bar)
Na+ K
+Mg
2+ Ca2+
UO22+
Fig. 3 – Rejection coefficient of sodium, potassium,
magnesium, calcium and uranium as a function of
transmembrane pressure (DP) for G10 and DL membranes.
Water sample A; experimental conditions: T ¼ 20 1C,
Jr ¼ 145 mm s�1, U(VI) ¼ 2 mg L�1, water composition, see
Table 1 and Table 2.
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 1 1 6 0 – 1 1 6 61164
uranyl was lower and thus gave us the opportunity to study
the influence of speciation and ionic strength.
The different rejections of uranyl obtained with the G10
membrane are listed in Table 5. For water samples A and B, at
pH 7.0, up to 70% and 80%, respectively, of uranyl is in the
form of UO2(CO3)22�. The relatively high rejection of uranyl
species compared with alkaline and alkaline-earth observed
with water sample A could be explained by the Donnan
exclusion model. The negatively charged uranyl complexes
are rejected by the negatively charged membrane while
cations are less rejected. As can been seen in Table 5, an
increase in the concentration of salts from 130 to 309 mg L�1
decreased the observed rejection of uranyl by a factor of 2. An
increase in the electrolyte concentration shielded the mem-
brane charges by the counter-ions, causing reduced mem-
brane rejection. The alkaline and alkaline-earth rejections are
somewhat different but are also very slightly dependent on
the feed concentration. The idea of rejection on the basis of
the Donnan exclusion model is in accordance with the two
experimental findings: high rejection of negatively charged
species and rejection depends on the ionic strength.
For water sample C, up to 75% of uranyl is in the form of
(UO2(CO3)2)2� and 20% is in the form of (UO2(CO3)3)4� (Fig. 1).
However, the ionic strength is at its highest and thus
the observed rejection of uranyl using G10 nanofiltration
membrane is at its lowest. Moreover, under these conditions,
no U/Na+ or U/Mg2+ selectivity was observed.
3.3. Influence of process parameters on U(VI) rejection
The influence of the operating parameters on the rejection of
U(VI) was then studied using water sample A with mem-
branes G10 and DL. The filtration tests were carried out with a
transmembrane pressure (DP) varying from 1 to 4 bar at a
constant tangential velocity (Jr) of 145 mm s�1. The effect of
applied pressure on U(VI) rejection is shown in Fig. 3.
The permeate water flux increased linearly as the pressure
increased when the composition of feed water was kept
constant. Fig. 3 shows that the rejection of each component
increased linearly as the pressure increased. The U(VI)
rejection at 1 bar in water sample A was 40%, although at
4 bars the U(VI) rejection rose to 65%. The same increase of
rejection was observed for alkaline and alkaline-earth ca-
tions; the rejection of Mg2+ was 15% at 1 bar and 27% at 4 bar.
The same trend was observed with the DL membrane (Fig. 3),
but transmembrane pressure had a small effect on U(VI)
rejection. The rejection of U(VI) with the DL membrane was
95% at 1 bar, although it was 98% at 4 bar while we observed
an increased in the Mg2+ rejection from 41% at 1 bar to 78% at
4 bar. We can thus consider this linearity as due to an absence
of concentration polarization under our conditions.
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An increase of transmembrane pressure slightly increased
the membrane selectivity for both membranes. When the
transmembrane pressure is increasing from 1 to 4 bars,
MSNaþ
UðVIÞ is increased from 1.5 to 2.8 and from 16 to 20 for G10
and DL membrane, respectively (Fig. 3). Although at higher
pressure, higher permeate flux can be obtained, there is a
limit to what operating pressure can be reached. Indeed, if the
pressure is too high, much more energy is consumed and the
concentration polarization boundary layer effect is increased.
Therefore, it is very important to optimize these factors to
obtain the most economic operating conditions in designing
the NF system. Operating a DL membrane at 1 bar was then
further investigated for the removal of U(VI) traces.
3.4. Removal of U(VI) traces by DL membranes
Uranyl nitrate, UO2(NO3)2, was added to water sample A to
obtain a uranium concentration of 0.02 mg L�1 (20 ppb). The
NF tests were carried out on the DL membrane with a
transmembrane pressure of 1 bar, a tangential velocity of
145 mm s�1 and at a temperature of 20 1C. The concentration
of the cations in the permeate and in the feed were
determined by ICP-MS for uranium and by ICP-AES for the
alkaline and alkaline-earth metal ions (Table 6).
As expected, the alkaline and alkaline-earth rejections were
lower than 45% and 25% for the respective cations. Under
these above conditions, the U(VI) trace (20 ppb) rejection was
high (95%) and the membrane selectivity was comparable to
the value observed with U(VI) at 2 mg L�1 (2000 ppb). Under
the same conditions, the U(VI) concentration in the permeate
was lower than the MAC suggested by the WHO, i.e. 2 ppb. The
choice of an membrane with a high selectivity toward the
removal of U(VI) should be emphasized. The ability of
membranes to reject inorganic cations and among then
U(VI) has already been demonstrated (Raff and Wilken,
1999). But our results show that DL membrane, under
appropriate experimental conditions, can selectively removed
U(VI) carbonate complexes with a high selectivity toward
others cations present in the feed (Table 6). Thus, the
composition of the permeate obtained using a DL membrane
Table 6 – Measured composition of the water sample A inthe feed and in the permeate
Cations Initialconc.(mg/L)
Permeateconc.(mg/L)
Rejection(%)
MScationUðVIÞ
Na+ 11.2a 8.7a 22 15.6
K+ 6.2a 4.7a 24 15.2
Mg2+ 7.9a 4.4a 44 11.2
Ca2+ 12.0a 7.3a 39 12.2
UO22+ 0.02b 0.001b 95 _
Experimental conditions: U(VI) ¼ 20 ppb; DL membrane, T ¼ 20 1C,
DP ¼ 1 bar, Jr ¼ 145 mm s�1.a Measured by ICP-AES.b Measured by ICP-MS.
does not require additional treatments to meet drinking
water standards such as hardness.
4. Conclusion
NF membranes are able to selectively reject U(VI) from
mineral water with a relatively high selectivity, despite a
high concentration of alkaline and alkaline-earth cations.
Consequently, nanofiltration equipment can be considered
suitable for reducing the U(VI) concentration in drinking
water to less than the World Health Organization (WHO)
maximum admissible concentration (MAC). The rejection
mechanism for uranyl is predominantly due to charge effects
between uranyl carbonate complexes and the charged
membrane. The general pattern was similar for all three
membranes. The rejection was dependent on the uranyl
speciation and the ionic strength. Furthermore, a mineral
water containing up to 20 ppb of U(VI) can be lowered to
0.8 ppb, which is below the MAC suggested by WHO with the
DL membrane with a transmembrane pressure of 1 bar, a
tangential velocity of 145 mm s�1 and at a temperature of
20 1C. A major advantage of membrane filtration is that
compared with ion exchange processes, it is a continuous
process that does not require further chemical products (for
example, for the regeneration of the adsorbant). Use of such a
system may therefore offer a viable and cost-effective method
for in situ water remediation.
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