EUROMEMBRANE 2004, Session 5 (S05-P-06), Hamburg, Germany (28 September-01 October, 2004)
Solvent Extraction of Concentrated Co(II) from Chloride Solutions with
Aliquat 336 in Membrane Contactors
Hsiang-Chien Kao and Ruey-Shin Juang*
Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li 320, Taiwan
*Fax: +886-3-4559373
E-mail: rsjuang@ce.yzu.edu.tw
Abstract
Extraction of Co(II) from high concentration chloride solutions in a hollow fiber module to the
kerosene solutions of Aliquat 336 was studied, in which the extracted Co(II) was simultaneously
stripped in another module to a HCl or H2SO4 solution. The aqueous feed or stripping phase flowed
in the tube side of the modules and the organic phase were always flowed across the shell side.
Experiments were conducted as a function of the initial feed Co2+ concentration (0.3-0.5 mol/dm3),
carrier concentration (0.2-0.75 mol/dm3), and stripping acidity (0.5-3 mol/dm3). In contrast to 4 N
HCl strip phase, the slightly higher extraction efficiency for Co(II) (31% vs. 28%) and comparable
stripping efficiency (30%) are found using 1 N HCl over the whole operating time (10 h). When the
strip phase was 1 N HCl and H2SO4, comparable stripping efficiency (23%) are found using H2SO4
in the whole operating time (10 h).
INTRODUCTION
Solvent extraction of cobalt from aqueous chloride solutions have been of practical interest to
researchers for a long time, the separation of both metals has been achieved in materials such as
oxide ores, nickel laterite, scraps, copper converter slag, and spent catalysts are dissolved using HCl
under pressurized or atmospheric conditions [1]. The removal of heavy metal ions from aqueous
solutions by solvent extraction (SX), in their anionic forms such as CrO42-, ZnCl42-, MoO42-, and
UO2(SO4)22-, using quaternary amines such as Aliquat 336 (tri-n-octylmethylammonium chloride)
has been shown to be promising, mainly due to high extraction efficiency [2-5].
In this work, the extraction and stripping of Co2+ from chloride solutions to a stripping HCl or
H2SO4 solution in two hollow-fiber membrane contactors (HFMC) using Aliquat 336 as carriers
were examined. Batch extraction experiments were also conducted to obtain the stoichiometry of
extraction reactions. The measured fluxes were compared with the simulated results considering the
mass transfer resistances including diffusion in aqueous layer, membrane, and organic layer. The
mass transfer characteristics of this process were discussed.
MATERIALS AND METHODS
Aliquat 336, trioctylmethylammonium chloride (Aldrich Co.), and kerosene (Union Chem. Co.,
Taiwan) were used as received. The organic solution typically contained 10 vol% of Aliquat 336
and 3 vol% of n-decanol (Merck) in kerosene. n-Docanol was added as the phase modifier to avoid
third phase formation. The feed phase consisted of CoCl2 and HCl, and the stripping phase was HCl
or H2SO4 solution.
In batch experiment, equal volumes of the organic and aqueous phases (20 cm 3 each) were
placed in 100-cm3 glass-stoppered flasks, and agitated with a magnetic stirrer at 300 rpm for 24 h.
After phase separation, Co(II) metal concentrations were analyzed by a Varian atomic absorption
1
spectrophotometer (220FS). In HFMC experiments, both phases were contacted in a countercurrent
(parallel flow) and full recirculating mode. In both modules, the aqueous phase flowed through the
tube side (3.7 cm3/s) while the organic phase flowed through the shell side (3.5 cm3/s). The volumes
of the three phases were all 1.0 L. Pressure gauges and valves were used to control the flow rates
and to ensure that a positive pressure of 2~5 psig was maintained on the aqueous sides of the
membranes [6]. The aqueous phase in the extraction module was then replaced by the feed solution.
At this moment, the experiment was started. The dilution effect of feed phase with deionized water
was corrected (about 8%). The aqueous feed and strip samples (2 cm3) were taken at preset time
intervals and the concentrations of metals were analyzed in a Varian AAS.
RESULTS AND DISCUSSION
Batch solvent extraction
Figure 2 show that the extraction efficiencies of Co from 3 N HCl with Aliquat 336. In this case,
basic extractants are used because metals form the following chloro-complexes in concentrated
chloride solutions [7].
Me 2  iCl   MeCli2i (i  0 ~ 4)
(1)
Aliquat 336 (NR4Cl) could provide an acceptable Co extractability (Fig. 2a). Such two quantities
remain constant at the entire pH range tested, except when aqueous phase is free of pH adjustment
(pH -0.55). The pH-independent extractability can be understood since H+ is not involved.
MeCl42  2 NR4 Cl  MeCl4 ( NR4 ) 2  2Cl 
(2)
The extractability for Co(II) is further enhanced by addition of chloride ions such as NaCl in
aqueous solution (Fig. 2b). Therefore, Aliquat 336 is recommended because there are no needs of
extractant modification and aqueous pH adjustment. However, kerosene consisting of 4 vol%
n-decanol and 0.2 M, rather than 0.75 M, of Aliquat 336 is chosen as the organic phase due to its
less viscous characteristics.
Figure 3 shows the stripping efficiency of Co from the loaded Aliquat 336 phase, indicating that
it is comparable among four strip phases. Comparing to NaCl, the slightly lower efficiency with
HCl is explained by its Cl- activity [8]. The high Cl- activity virtually favors the formation of
negatively charged metal chloro-complexes, forcing them to be re-extracted to the organic phase.
HFMC experiments
Figure 4 shows the two-stage HFMC, it is observed that about 12% Co (3.0 g/L) is extracted to
organic phase after 1-h operation, and 30% Co is stripped using 1 N HCl after 5-h operation (It is
reminded that the volume of strip phase is half of that of feed or organic phase in the HFMC tests).
Figure 5 illustrates the results of one-stage HFMC tests using HCl (1, 4 N) and H2SO4 (1 N) as the
stripping agents. In contrast to 1 N HCl, the slightly higher extraction efficiency for Co (31% vs.
28%) and comparable stripping efficiency (30%) are found using 1 N HCl in the whole operating
time (10 h). When stripping phase use 1 N HCl and H2SO4, the Co extraction efficiency is same
(31%) and comparable stripping efficiency (23%) are found using H2SO4 in the whole operating
time (10 h). Just as two-stage mode, the mass transfer during the stripping step in one-stage HFMC
tests is far slower.
Three possible ways or reasons are commented here to overcome or explain such drawbacks.
The first way is to replace hydrophobic fibers used in the stripping step by hydrophilic ones.
Alexander and Callahan [9] indicated that solvent extraction with microporous fibers is more rapid
as the fiber is wetted by the phase having higher solubility for the solute being transferred. Prasad
and Sirkar [10,11] also found that for comparable membrane pore sizes and statistics, hydrophobic
membranes are to be preferred for the distribution ratio beyond 1, whereas hydrophilic membranes
2
are preferable for the ratio less than 1.0. The second factor affecting the mass transfer may be the
incomplete use of fiber area. Seibert et al. [12] have found that a significant portion of the fibers is
bypassed by the shell-side fluid and thus only 10~30% of the total fiber area is used. The final
possibility is the blocking of the aggregates of metal-Aliquat 336 complexes (and/or the extractant
itself) within the pores of the membrane. Sungpet et al. [13] found that the incorporation of metals
into the membrane reduces amine flux compared to that obtained from solution-diffusion, and
suggested that highly stable amine-metal complex forming within the intercluster regions of the
membrane leads to blocking phenomenon.
It is accepted that HFMC system provides a large contact area (103~104 ft2/ft3) compared to
traditional packed towers (102~103 ft2/ft3) [9]. This process can eliminate difficulty of small density
difference and problems of phase separation due to emulsion formation in the extraction units such
as mixers-settlers. They can also overcome the troubles such as flooding, loading, and entrainment
encountered in conventional extraction units [14,15]. However, the abnormally slow mass transfer
encountered in the present HFMC process makes this device impractical. This problem should be
solved to pursue HFMC for further practical applications.
REFERENCES
1. Ritcey G.M., Commercial processes for nickel and cobalt, in Handbook of Solvent Extraction,
Lo T.C., Baird M.H.I., Hanson C., (Eds.); Wiley, New York, 1983, pp. 673-687.
2. Rice N.M. and Smith M.R., Recovery of zinc(II), cadmium(II), and mercury(II) from chloride
and sulfate media by solvent extraction. J. Appl. Chem. Biotechnol. 25: 379-402 (1975).
3. McDonald C.W. and Lin T.S., Solvent extraction studies of zinc and cadmium with Aliquat
336-S in aqueous chloride solutions. Separ. Sci. 10: 499-505 (1975).
4. Sato T., Shimomura T., Murakami S., Maeda T. and Nakamura T., Liquid-liquid extraction of
divalent manganese, cobalt, copper, zinc and cadmium from aqueous chloride solutions by
tricaprylmethylammonium chloride. Hydrometallurgy 12: 245-254 (1984).
5. Thorsen G., Commercial processes for cadmium and zinc, in Handbook of Solvent Extraction,
Lo T.C., Baird M.H.I., Hanson C. (Eds.), Wiley, New York, pp. 709-716 (1983).
6. Prasad R. and Sirkar K.K., Membrane-based solvent extraction, in Membrane Handbook, Ho
W.S.W. and Sirkar K.K. (Eds.), Van Nostrand Reinhold, New York, 1992, pp. 727-763.
7. Sato T., Adachi K., Kato T. and Nakamura T., Extraction of divalent manganese, cobalt, copper,
zinc, and cadmium from hydrochloric acid solutions by tri-n-octylamine. Sep. Sci. Technol. 17:
1565-1576 (1982).
8. Harned H.S. and Owen B.B., The Physical Chemistry of Electrolytic Solutions, 2nd ed.,
Reinhold Publishing Co., New York, 1950, p. 547 and 601.
9. Alexander P.R. and Callahan R.W., Liquid-liquid extraction and stripping of gold with
microporous hollow fibers. J. Membr. Sci. 35: 57-71 (1987).
10. Prasad R. and Sirkar K.K., Solvent extraction with microporous hydrophilic and composite
membranes. AIChE J. 33: 1057-1066 (1987).
11. Prasad R. and Sirkar K.K., Dispersion-free solvent extraction with microporous hollow fiber
modules. AIChE J. 34: 177-188 (1988).
12. Seibert A.F., Py X., Mshewa M. and Fair J.R., Hydraulics and mass transfer efficiency of a
commercial-scale membrane extractor. Sep. Sci. Technol. 28: 343-359 (1993).
13. Sungpet A., Saithong T. and Kalapanulak S. Blocking phenomenon in permeation of amines
through perfluorosulfonate ionomer containing metal ions. J. Membr. Sci. 202: 81-87 (2002).
14. Gabelman A. and Hwang S.T., Hollow fiber membrane contactors. J. Membr. Sci. 159: 61-106
(1999).
15. Klaasen R. and Jansen A.E., The membrane contactor: Environmental applications and
possibilities. Environ. Prog. 20: 37-43 (2001).
3
50
Extraction (%)
40
Back-Extraction
Stripping
P
P
P
(a) A: 22.4 g L-1 Co + 3 M HCl
O: Aliquat 336 + 4~5 vol% dodecanol
Co-Aliquat 366 (0.75 M)
Co-Aliquat 366 (0.2 M)
30
20
10
Extraction
0
0
1
2
3
4
5
6
Initial aqueous pH
P
Flowmeter
P
Pressure gauge
Stripping
phase
Organic
phase
Extraction (%)
60
Feed
phase
40
(b) A: 22.4 g L-1 Co + 3 M HCl
O: 0.75 M Aliquat 336 + 5 vol% dodecanol
20
0
0.0
0.5
1.0
1.5
2.0
2.5
Amount of added NaCl (M)
Fig. 1. Experimental setup of the extraction and stripping in
hollow fiber membrane contactors
100
1.0
8
2.8
F (1 L): 22.5 g L-1 Co + 3 M HCl
O (1 L): 0.2 M Aliquat 336 + 4 vol% dodecanol
S (0.5 L): 1 M HCl
80
6
4
HCl
NaCl
20
2
1.6
1.2
0.8
0.8
Feed
Strip
-
HCl
NaCl
NaCl+citrate
0.4
0.7
0.0
0
0
0
0
1
2
3
2.0
-1
H2SO4
40
Cfeed/C0
60
0.9
2.4
Cstrip (g L )
(a) O: 0.2 M Aliquat 336 + 5 vol% dodecanol
+ 3.0 g L-1 Co(II)
Activity of Cl
Stripping (%)
Fig. 2. Effect of pH and NaCl concentration on the
extraction of Co from 3 N HCl using Aliquat 336
60
120
180
240
300
360
Time (min)
4
Species concentration (N)
Fig. 3. Effect of the concentrations of stripping agents on
stripping efficiencies of Co from the loaded organic phase
1.0
5.0
(a) F (1 L): 22.5 g L-1 Co + 3 N HCl
O (1 L): 0.2 M Aliquat 336 + 4 vol% dodecanol
S (0.5 L): 4 N HCl
4.0
3.0
0.8
2.0
Strip Co
0.7
1.0
0.6
1.0
4.0
3.0
0.8
2.0
Strip Co
0.7
1.0
0
60
120
180
240
300
360
420
480
540
600
(c) F (1 L): 22.5 g L-1 Co + 3 N HCl
O (1 L): 0.2 M Aliquat 336 + 4 vol% dodecanol
S (0.5 L): 1 N H2SO4
0.9
0.0
5.0
4.0
3.0
0.8
2.0
Strip Co
0.7
-1
Feed Co
Cstrip (g L )
Cfeed/C0
-1
Feed Co
Cstrip (g L )
Cfeed/C0
0.0
5.0
(b) F (1 L): 22.5 g L-1 Co + 3 N HCl
O (1 L): 0.2 M Aliquat 336 + 4 vol% dodecanol
S (0.5 L): 1 N HCl
0.9
0.6
-1
Feed Co
Cstrip (g L )
Cfeed/C0
0.9
0.6
1.0
Fig. 4. Time profiles of the extraction and stripping of
Co using two-stage HFMC (strip phase: 1 N HCl)
1.0
0
0
60
120
120
180
240
240
300
360
360
420
480
480
540
600
600
0.0
Time (min)
Fig. 5. Time profiles of extraction and stripping of Co using
one-stage HFMC (strip phase: 1; 4 N HCl and 1 N H2SO4)
4