For more
[Cr(VI)], mol dm-3
concentrated aqueous solutions of chromium(VI), i.e.
Fig. 7. Plot of an initial flux vs. chromium(VI) concentration in above 0.010 mol dm3, the predominant form of Cr(VI)
the source phase. Conditions as in Fig. 6.
is Cr
2
2O7 . As it can be seen from Table 1, the initial flux
decreases
at
Cr(VI)
concentration
higher
than
0.01 mol dm3. This is due to the membrane saturation
with metal complex species and as a consequence the
a permissible limit in drinking water, the third run was
lowering of the chromium(VI) transport flux is ob-
carried out, with volume of source/receiving phase
served.
reduction equal to 30:1. After 40 h of PIM process, the
Generally, the rate of transferred mass of chromium
Cr(VI) concentration in source aqueous phase was
(VI) through PIM depends on the equilibrium of Cr(VI)-
reduced to 0.0028 ppm, which is below the permissible
TOA in the aqueous phase/membrane boundarylayer,
limit for drinking water.
and also on the source/receiving phase volume ratio.
With the source/receiving phase volume ratio equal to
3.3. Recovery of chromium(VI) and other metal ions
1.0 it was possible to reduce the Cr(VI) concentration
from waste waters
from 54.0 to 1.0 ppm in 6 h of PIM process (Table 2).
This content of Cr(VI) in the aqueous phase, however, is
Effluents containing chromium(VI) are produced by
still too high as compared to permissible limits in waste
industries such as chemical industry, which uses Cr(VI)
water and drinking waters [1,20]; these limits are equal
as an oxidizing agent, textile dyeing and metal finishing
to 0.5 and 0.003 ppm, respectively.
industry, which apply Cr(VI) for chromium plating,
In the next two runs, the initial concentration of
chromate conversion coating, and anodizing of alumi-
chromium(VI) in the aqueous source phase was equal to
num. Dried sludge, formed during galvanic waste-water
the concentration of Cr(VI) in the residual aqueous
treatment in the settling tanks is considered as a solid
solution of receiving phase obtained in run no. 1, i.e.
waste product. This sludge contain also zinc, cadmium
1.0 ppm. Results of run no. 2, where the source/receiving
and iron. To studythe recoveryof metal ions from the
phase volume ratio was 10:1, show the possibilityto
industrial solutions, the aqueous solution was prepared
reduce Cr(VI) concentration 50 times, i.e. to 0.02 ppm
byleaching of 10.0 g of sludge in 1.0 dm3 of deionized
after 3 h of PIM process. To reduce Cr(VI) concentra-
water, and the residual solid phase was separated. The
tion in the aqueous source phase to 0.003 ppm, which is
concentration of metal ions in the initial solution at pH
C.A. Kozlowski, W. Walkowiak / Water Research 36 (2002) 4870–4876
4875
Table 2
Chromium(VI) removal from a source phase (volume: 50 cm3) containing 0.10 mol dm3 HCl in PIM transport with TOA Number
Initial
Volume of
Volume ratio of
Time of
Residual Cr(VI)
concentration
of run
of Cr(VI) in the
Source phase
source/receiving
process (h)
Concentration in
source phase
(cm3)
phase
the source phase
(ppm)
(ppm)
1
54.0
50
1:1
6
1.0
2
1.0
500
10:1
3
0.020
3
1.0
1500
30:1
40
0.0028
Membrane: 0.80 cm3 ONPPE/1.0 g CTA, 1.45 mol dm3 TOA; receiving phase: 0.1 mol dm3 NaOH.
4. Conclusions
99%
30%
Chromium(VI) can be effectivelyremoved from acidic
chloride aqueous solutions bytransport through PIMs
with
tri-n-octylamine
as
an
ion
carrier
into
0.10 mol dm3 sodium hydroxide as a receiving phase.
Cd(II)
Fe(III)
The optimal PIMs content for chromium(VI) was found
to be 41 wt% of CTA as the support, 23 wt% of tri-n-
octylamine as the ion carrier, and 36 wt% of ONPPE as
99%
the plasticizer. The linear relationship between initial
83%
flux of Cr(VI) and pH of source aqueous phase was
found. Also linear relationship (in log–log scale)
between initial metal flux and Cr(VI) concentration in
Cr(VI)
Zn(II)
the source aqueous phase was observed. The slope value
was equal to 0.96, which indicates a first order of Cr(VI)
Fig. 8. Recoveryfactor (%) of metals from waste water in PIM
reaction with ionic carrier at the membrane/aqueous
process transport. Membrane: 0.80 cm3 ONPPE/1.0 g CTA,