e. ONPPE, in CTA mem-
measured
using
one-channel
gamma
spectrometer
brane with tri-n-octylamine as an ion carrier on
(ZSG-1 type, Polon). The source phase acidity was
chromium(VI) transport was studied. Blank experi-
controlled bypH meter (multifunctional pH meter, CX-
ments, in the absence of a carrier, yielded no significant
731 Elmetron, with combined pH electrode, ERH-136,
flux across PIM with onlysupport and plasticizer. As it
Hydromet, Poland). The source aqueous phase pH was
was proved byBartsch et al. [17] there is a linear
kept constant byadding periodicallysmall amounts of
relationship between the number of carbon atoms in the
1.0 mol dm3 HCl.
alkyl group of the series of alkyl o-nitrophenyl ethers
For transport of Cr(VI) across PIM with source/
and the alkali metal cations flux of transport across the
receiving phase volume ratio higher than 1.0, another
CTA membranes. The pentyl o-nitrophenyl ether was
apparatus was applied. In this case, a membrane module
found as the best plasticizer among the alkyl o-
was used, to which both aqueous phases were pumped
nitrophenyl ethers studied. As source and receiving
with peristaltic pumps (PP1B-05A type, Zalimp, Poland)
phases, 1.0 mol dm3 HCl and 0.10 mol dm3 NaOH
working at a speed of 100 cm3 min1 from tanks contain-
aqueous solutions were used, respectively. Transport
ing source and receiving aqueous phases, respectively.
rate of Cr(VI) through PIM remained constant (Fig. 2)
Kinetics of transport process through PIM, similar to
due to the introduction of 0.80 cm3 or more of plasticizer
transport across SLM, can be described bya first-order
per 1 g of CTA. The thickness of the membrane
reaction with respect to chromium(VI) concentration [16]:
containing 0.8 cm3 of ONPPE/1.0 g CTA was equal to
c
28 mm. The resulting membrane contained 41 wt% CTA,
ln
¼ kt;
ð1Þ
23 wt% TOA, and 36 wt% ONPPE (Fig. 3). Content of
ci
plasticizer is much lower as compared to PIMs used by
where c is the chromium(VI) concentration (mol dm3) in
other authors. For instance, PIMs used byNazarenko
the source phase at a given time, ci is the initial Cr(VI)
and Lamb [13] contained 76% of octyl o-nitrophenyl
concentration in the source phase, k is the rate constant
ether. On the other hand, Bartsch and Hayashita’s
(s1), and t is the transport time (s).
membranes contained 62% octyl o-nitrophenyl ether.
To calculate the k value, a plot of ln ðc=ciÞ vs. time was
The unusuallylow content of plasticizer in PIMs used in
made. The rate constant value for the duplicate
our experiments is due to good plasticizing properties of
transport experiment was then averaged and standard
tertiaryamine, serving as an ion carrier. On the other
deviation calculated. Examples of such plots are given in
hand, PIMs containing more support (in this case CTA)
Fig. 4. This figure shows the linear relationship of
show higher stabilityand mechanical resistance. As can
ln ðc=ciÞ vs. time, confirmed byhigh values of determi-
be seen from the paper of Sugiura and Hirata [18] fluxes
nation coefficient ðr2Þ 0.9699–0.9918. The permeability
of lanthanide cations transported across PIM containing
coefficient (P) was calculated as follows:
benzoyltrifluoroacetone as a carrier and trioctyl- and
V
tridodecylmethylammonium chlorides as plasticizers
P ¼
k;
ð2Þ
A
where V is the volume of aqueous source phase, and A is
−3
the area of membrane.
2
cm3 ONPPE / 1.0 g CTA
0.4
The initial flux ðJiÞ was determined as equal to
0.8
J
, mol dm
1.6
i ¼ Pci :
ð3Þ
3
2.6
To describe the efficiencyof chromium(VI) removal
6.4
from the source phase, the recoveryfactor (RF) was
1
calculated:
c
RF ¼ i c 100%:
ð4Þ
ci
0
Cr(VI) concentration•10
0
5
10
3. Results and discussion
Time, hr
Fig. 2. Chromium(VI) concentration in source phase vs. time
3.1. Effects of organic phase content
of transport through PIMs with different plasticizer content.
Membrane phase: 0.0625 g CTA, and 0.0708 g TOA; source
PIM content, i.e. the kind of membrane support, kind
phase: 1.0 mol dm3 HCl; receiving phase: 0.10 mol dm3
and concentration of an ion carrier, as well as type and
NaOH.
C.A. Kozlowski, W. Walkowiak / Water Research 36 (2002) 4870–4876
4873
CTA (41%)
0
[TOA], mol dm-3