Al-Khwarizmi  

Engineering   
Journal  

Al-Khwarizmi Engineering Journal,  Vol. 7, No. 2, PP 68 - 74 (2011)  

  

Extraction of Zn (II) and Cu (II) Ions Using 
PEG (300) - KCl Salt Aqueous Two-Phase Systems

Saad H. Ammar *      Waqar Abdul-Wahid Abdul-Nabi **  
Musaab Khadem Rasheed ***

*, ** Department of Chemical Engineering/ University of Al-Nahrain
* Email: saad_cheminet@yahoo.com

*** Technical Institute/ Baghdad

(Received!21 October 2010; accepted 19 April 2011)

Abstract

In this paper the process of metal ions extraction (Zn(II) and Cu(II)) was studied in PEG-KCl aqueous two phase 
system was investigated without using an extracting agent. The experimental runs were performance at constant 
temperature (25 oC), constant mixing time (30 min), and constant PH of the solution (about 3). The effect of KCl salt 
concentration (from 10% to 25%), volumetric phase ratio of PEG solution to KCl solution (from 0.5 to 2), and the initial 
metal ion concentration (from 0.25 ml to 2 ml of 1 gm/L solution) were investigated on the percent extraction of Zn(II) 
and Cu(II). The results indicated that the percent extraction of metal ions increase with increasing of salt concentration 
and phase ratio, and slightly decrease with increasing of initial metal ion concentration.

Keywords: Liquid-liquid extraction, aqueous two phase system, metal ions, waste water.

1. Introduction

Aqueous two-phase systems formed when a 
water soluble polymer is mixed with a certain 
inorganic salt (e.g. (NH4)2SO4, Na2SO4, 
Na2CO3, K2HPO4, KCl), may represent an 
alternative for metal ions extraction processes in 
industrial separation, as well as environmental 
remediation applications. (Laura Bulgariu, 2008)

Many different water soluble polymers may be 
utilized to form aqueous two-phase systems 
(ATPS), poly ethylene glycol (PEG) is 
exclusively used because it is non-toxic, non-
flammable and non-volatile (Graber, T.A at. el., 
2000).

Rogers et al. classified metal ion extractions in 
the aqueous two-phase` systems into three 
categories: (1) extraction using a water-soluble 
extractant; (2) extraction of metal complexes of 
inorganic anions and (3) extraction by the PEG-
rich phase alone without an extractant. Among 
these three categories, the second type of metal 
extraction will find wide application to soft metal 
ions, which form complexes with halide or 

pseudohalide anions (Rogers, 1993 and Rogers, 
1995).

The extraction of a metal ion Mm+, with a 
complexing anion, X−, can be described as 
(Shibukawa at. el., 2001):

                                                                                       

                              …(1)                        

                     …(2)

Where β and KD are the stability constant and 
the distribution coefficient of the metal complex, 
respectively.

Most of the metal ions studied are extracted as 
anionic complexes as so that sodium ion or 
potassium ion may distribute into the top phase as 
their counter ion. A preliminary experiment 
showed that the dependence of the distribution of 
metal ions on the amount of H2SO4 added was 

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Saad H. Ammar                                    Al-Khwarizmi Engineering Journal, Vol. 7, No. 2, PP 68 - 74 (2011)

69

very small. This result suggests that the co-
extraction of hydrogen ion with the anionic 
complexes can be neglected. Sulphate ion has the 
ability to form complexes of a number of metal 
ions so that the complexation reaction of the metal 
ions with SO4

2− may not be negligible especially 
in the Na2SO4-rich phase:

                    …(3)

         …(4)

Consequently the distribution ratio of a metal ion, 
D, defined as the ratio of the metal concentration 
in the PEG-rich phase to that in the Na2SO4 rich 
phase can be given by

     …(5)

It is reasonable to assume that [M(SO4)x
2x−m]PEG << [MXn

n−m]PEG since the metal ions are 
scarcely extracted into the PEG-rich phase in the 

absence of  SCN− or I−. This may be due to small 
KD values of the metal sulphate complexes. 
Therefore, Eq. (2.25) can be rewritten as:

    …(6)

The extraction of metal ions in presence of 
inorganic extractants, with aqueous PEG–
inorganic salt two-phase systems, can be 
represented by a succession of equilibriums, 
schematically presented in Fig. (1). The metal ion, 
initially present in salt-rich phase as anionic or 
neutral species (MAm

y−; A –phase-forming anion) 
will interact with inorganic extractants, most 
probably at interface, and the formed species 
(MXn

x−) will be then partitioned into PEG rich 
phase. The formation of extractable species occurs 
step by step, until his hydration degree becomes 
comparable with the hydration environment of 
PEG-rich phase from extraction system. In 
function of the stability of metallic species formed 
with phase-forming anion (βMAy− m) and with 
inorganic extractant (βMXnx−), the following three 
situations are possible (Laura Bulgariua, at. el.,
2008).

Fig.1. Schematic Representation of Equilibriums Involved in Metal Ions Extraction with Inorganic Extractants, 
in Aqueous PEG–Inorganic Salt Two-Phase Systems. (A− –Phase-Forming Anion; X− – Inorganic Extractant) 
(Laura Bulgariua, at. el., 2008).

After inorganic extractants addition, the metal 
ions from this category form, even in salt-rich 
phase, halide species with the mention that the 

number of halide ions from metallic species is 
minimum. These species are marginalized in the 
salt-rich phase, due to their low hydration, and 

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Saad H. Ammar                                    Al-Khwarizmi Engineering Journal, Vol. 7, No. 2, PP 68 - 74 (2011)

70

remitted at interface. Here, they will interact with 
more halide ion extractants and will form anionic 
complexes with higher number of halide 
extractant in molecule. Because the hydration 
degree of these anionic complexes is lower and 
compatible with the hydration environment of 
PEG-rich phase, their partition occurs 
immediately and this is quantitative one. The 
anionic species formed at interface, cross like they 
are into PEG-rich phases, where they will interact 
predominantly by ionic forces with the other 
oxygen atoms from PEG molecules. These 
interactions affect only the bridging water 
molecules.

Fig.2. Schematic Representation of Anionic 
Complexes (MXn

x−) Extraction in Aqueous PEG–
Inorganic Salt Two-Phase System (Laura 
Bulgariua, at. el., 2008).

The breaking of hydrogen bonds between PEG 
chains and water molecules determined the 
decrease of polymer chains interaction and the 
modification of water molecules binding way on 
polymer macromolecules. The formation of 
ordinate micro-domains is due to the interaction 
of anionic extracted species with PEG molecules, 
which determined a linearization of polymer 
chains. Probably, a plane square geometry of 
metal species is preferred due to this reason.

In the same time with the transfer of anionic 
species into PEG- rich phase, the forming-phase 
anions (SO4

2-) that have accompanied the 
formation and the separation of the two aqueous 
phases are expulsed in salt-rich phase, due to the 
incompatibility of hydration environment, and the 
phases are maintained neutral from electrical 
point of view.  

The IR spectra and microscopic images 
indicate that the extracted species, indifferently by 
their type (anionic complexes or neutral 
molecules) cross in PEG-rich phase of extraction 
system and are “fixed” by characteristic 
interactions. Thus, in case of anionic species 
extraction, the IR spectra show that between metal 

extracted species and PEG molecules strong 
interactions occur, and the bridging water 
molecules are used as intermediary. Here, the 
PEG-rich phases are formed predominantly, from 
micro-domains with high ordination degree. In 
case of neutral molecules extraction, the changes 
observed in IR spectra can be attributed to the 
formation of some new hydrogen bonds between 
extracted species and PEG chains. In 
consequence, the microscopic images show that in 
the solidified PEG-rich phases of these systems 
the micro-domains with a lower ordination degree 
are predominant, which has an organization way 
and some characteristics similar to the colloidal 
systems.

A schematic representation of Cd(II) extraction 
in the presence of halide ions in the considered 
aqueous two –phase system is presented in fig. (3) 
according to this, for partition Cd(II), processes 
which occur at the PEG-rich phases/salt-phase 
interface are essential: Cd(II) complexation with 
halide ions and the transformation of cadmium 
halide species into complex species towards the 
PEG-rich phase have a higher affinity under the 
employed conditions (Laura Bulgariua, at. el.,
2008).

Fig.3. Schematic Representation of the Main 
Processes Involved in Cd (II) Extraction in the 
Considered Aqueous Two-Phase System (Laura 
Bulgariua, at. el., 2008).

The anionic species formed at the interface 
cross into the PEG-rich phase, where they will 
interact, predominantly by ionic forces, with the 

Top phase (rich in PEG)

Bottom phase (rich in 
inorganic salt)

In
te

rf
ac

e

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Saad H. Ammar                                    Al-Khwarizmi Engineering Journal, Vol. 7, No. 2, PP 68 - 74 (2011)

71

Atomic 
absorption 

spectrophotom
-eter

PEG 
solution

KCl 
solution

Shaking 
30 min

Metal ion 
solution

Centrifugation

Bottom 
phase

Top 
phase 

ether oxygen atoms of PEG. An equivalent ionic 
transfer process ensures the electro neutrality of 
the two phases. In case  of extraction of Cd(II) 
anionic complexes, the SO4

2- ion which are 
present in the PEG-rich phase after formation of 
the aqueous two-phase system are expelled into 
the salt-rich phase, due to the incompatibility of 
the hydration environment. Thus, the phases are 
kept neutral from an electrical point of view and 
the hydrophobicity of the PEG-rich phase is 
maintained during of extraction process.

In this study, the extraction of Zn(II) and 
Cu(II) metal ions in PEG-KCl aqueous two phase 
system was investigated without using an 
extractant. The effect of salt concentration, 
volumetric phase ratio of PEG solution to KCl 
solution, and initial metal ion concentration on the 
percent extraction of Zn(II) and Cu(II) were 
investigated.

Fig.4. Experimental Procedure Steps

2. Materials and Methods

The PEG used in this study was PEG-3000 
(average molecular weight, 3000). Stock solutions 
of 30% (w/w) PEG were prepared by dissolving 
of suitable quantity of PEG in deionized water. 
The stock solutions of inorganic salt at different 
values (10%, 15%, 20%, and 25% (w/w) KCl) 
were prepared by dissolving the required amount 

of salt in deionized water and at constant PH 
value (about 3) by adding small volumes of acids 
or bases concentrated solutions. The 1 gm/L 
solution of metal ions (Zn(II) and Cu(II)) was 
obtained by metal sulphate salt dissolving in 
deionized and distillate water, the initial metal ion 
concentration was varied by taking 0.25, 0.5, 1 
and 2 mL of the 1 gm/L metal ion solution 
prepared.

For each experiment, an aqueous two-phase 
system was prepared by mixing the prespecified 
volumetric phase ratio of PEG stock solution –
KCl salt stock solution in the range of 0.5, 1, 1.5, 
and 2

With constant pH of 3 at room temperature 
(25±2 oC). The (0.25–1.5) mL of 1 gm/L metal 
ion (Zn(II) and Cu(II)) solutions were added and 
the system was shaken for 30 minute followed by 
15 minute of Centrifugation. Equal volumes (1 
ml) for each phase were separated and measured 
for Zn(II) and Cu(II) ions by means of atomic 
absorption spectrometer (Type PERKIN –
ELMER 5000 in Ibn-Sina State Company, 
Baghdad). Figure (4) show the experimental 
procedure steps.

3. Results and Discussion

3.1. Effect of Concentration of KCl 

Figure (5) shows the percent extraction of 
metal ions (Zn(II) and Cu(II)) as a function of  
concentration of KCl in the stock solution (10%, 
15%, 20%, and 25% (w/w) KCl) at phase ratio of 
1 and initial metal ion concentration of 0.5 mL of 
1 gm/L. It is clear from this figure that the percent 
extraction of metal ions increase with increasing 
of KCl concentration in salt phase.

Fig.5. Percent Extraction (%) of Metal Ions as a 
Function of Concentration of KCl in the Stock 
Solution % (w/w) at Phase Ratio of 1 and Initial 
Metal Ion Concentration of 0.5 mL of 1 gm/L.

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Saad H. Ammar                                    Al-Khwarizmi Engineering Journal, Vol. 7, No. 2, PP 68 - 74 (2011)

72

The formation of aqueous two-phase system of 
PEG and a certain inorganic salt can be explained
on the basis of the competition for hydration 
between the two components. The addition of an 
inorganic salt increases the dehydration of the 
polymer chains, due to the salting-out effect and 
phase separation (Laura Bulgariu, 2005).

3.2. Effect of the (PEG/KCl) Phase Ratio 

Figure (6) shows the percent extraction of 
metal ions (Zn(II) and Cu(II)) with the volumetric 
phase ratio of PEG to KCl (0.5, 1, 1.5, and 2) at 
constant KCl salt concentration in stock solutions 
of 20% (w/w) and initial metal ion concentration 
of 0.5 ml of 1 gm/L.  

Fig.6. Percent Extraction (%) of Metal Ions as a 
Function of Phase Ratio at KCl Concentration in 
Stock Solutions of 20% (w/w) and Initial Metal Ion 
Concentration of 0.5 mL of 1 gm/L.

The results above indicate that the extraction 
of the metals above increases with increasing of 
PEG/KCl volumetric phase ratio. This might be 
attributed to the increase in the quantity of 
transferred metal which is related with quantity of 
the extractant that will furnish the necessary 
molecules to form the complex to reach the 
equilibrium state (Graber, T.A., 2007).

3.3. Effect of Initial Metals Concentration 

Figure (7) shows the percent extraction of 
metal ions as a function initial metal concentration 
in the salt phase at phase ratio of 1 and KCl salt 
concentration in the stock solution of 20% (w/w). 
As notices from the results that plotted in Figure 
(7), increasing the metals concentration in the 
feed, the percent extraction of metal removed 
decrease.

Fig.7. Percent Extraction (%) of Metal Ions as a 
Function of Initial Metal Ion Concentration at 
Phase Ratio of 1 and KCl Salt Concentration in the 
Stock Solution of 20% (w/w).

4. Conclusion

The process of Zn(II) and Cu(II) metal ions 
extraction was studied using aqueous PEG – KCl 
salt two phase systems without using an extractant 
agent. The process variables salt concentration in 
the salt phase, PEG/KCl volumetric phase ratio, 
and the initial metal ions concentration were 
studied on the percent extraction of metal ions. 
The results indicated that the percent extraction of 
metal ions increase with increasing of salt 
concentration and phase ratio, and slightly 
decrease with increasing of initial metal ion 
concentration. 

5. References

[1] Graber, T.A., Andrews, B.A; Asenjo, J.A., 
“Model for the partition of metal ions in 
aqueous two phase systems” J. Chromatoger., 
2000.

[2] Graber, T.A., Medina, H., "Phase equilibrium 
and partition of iodide in an aqueous biphasic 
system formed by (NH) SO+PEG+HO at 
25oC", J. of Chemical and Engineering Data, 
p1262-1267, 2007.

[3] Masami Shibukawa, Noriko Nakayama 
,Tadashige Hayashi, Daigo Shibuya,Yukihiro 
Endo, "Extraction behaviour of metal ions in 
aqueous polyethylene glycol–sodium 
sulphate two-phase systems in the presence 
of iodide and thiocyanate ions", Japan, 
Analytica Chimica Acta 427(2001)293–300.

[4] Laura Bulgaria, Dumitru Bulgariu, 
"Extraction of metal ions in aqueous 
polyethylene glycol –inorganic salt two 

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Saad H. Ammar                                    Al-Khwarizmi Engineering Journal, Vol. 7, No. 2, PP 68 - 74 (2011)

73

phase systems in the presence of inorganic 
Extractants: Correlation between extraction 
behavior and stability constants of extracted 
species" Journal of Chromatography A, 117-
124, 2008.

[5] Laura Bulgariu, Dumitru Bulgariu, "The 
Extraction of Zn(II) in Aqueous PEG (1550)-
(NH4)2SO4 Two Phase System Using Cl-
Ions As Extracting Agent", 2005.

[6] Laura Bulgariua , Dumitru Bulgariu , 
Extraction of metal ions in aqueous 
polyethylene glycol–inorganic salt two-phase 
systems in the presence of inorganic 
extractants: Correlation between extraction 
behaviour and stability constants of extracted 

species, Journal of Chromatography A, 
1196–1197 (2008) 117–124

[7] Laura Bulgariu and Dumitru  Bulgariu , 
“Cd(II) Extraction  in PEG(1550)–
(NH4)2SO4  aqueous  two-phase systems  
using halide extractants”,   Romania Journal 
of  the Serbian Chemical Society  73 (3) 341-
350 (2008).

[8] Rogers R.D., A.H. Bond, C.B. Bauer, Sep. 
Sci. Technol. 28, 1091 (1993).

[9] Rogers R.D., A.H. Bond, C.B. Bauer, J. 
Zhang, M.L. Jezl, D.M. Roden, S.D. Rein, 
R.R. Chomko, in: R.D. Rogers, M.A. 
Eiteman (Eds.), Aqueous Biphasic 
Separations: Biomolecules to Metal Ions, 
Plenum Press, New York, , p. 1 (1995).

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74 ، صفحة2، العدد 7مجلة الخوارزمي الھندسیة المجلد                                                              سعد حنش عمار - 68 )2011(

74

الزنك بأستخدام انظمة المحالیل المائیة ثنائیة الطوروالنحاس یوناتأستخالص أ
  ملح كلورید البوتاسیوم - ) ٣٠٠٠(بولي اثلین كالیكول المتكونة من 

  *** مصعب كاظم رشید**      وقار عبدالواحد عبدالنبي    * سعد حنش عمار
یة** ، * و یا م ی لك دسة ا ھن ن/ قسم ال ھری الن ة  مع ا   ج

  saad_cheminet@yahoo.com: رید االلكترونيالب* 
  بغداد /المعھد التقني***    

  
  
  

  الخالصة

كلورید  ملحوبولي اثلین كالیكول في أنظمة المحالیل المائیة ثنائیة الطور والمتكونة من ) الزنكو,  النحاس(أستخالص أیونات المعادن  عملیةتم دراسة 

تم  .)افة لكونھ مكون للطور الملحيحیث ان ملح كلورید البوتاسیوم یعمل كعامل أستخالص باالض(وبدون استخدام عوامل استخالص  KClالبوتاسیوم 

لمتغیرات التالیة على تم دراسة ا). 3بحدود ( المحلول ثابت  PHو ) دقیقة 30(زمن الخلط ثابت , )درجة مئویة 25(اجراء التجارب تحت درجة حرارة ثابتة 

  :نسبة االستخالص

 تركیز الملحKCl   وزنا% 25الى % 10في الطور الملحي من.

 2الى  0.5من ) طور محلول ملح كلورید البوتاسیوم/ طور محلول البولي أثیلین كالیكول(نسبة الطور الحجمیة.

 لتر/ غرام 1ملیلتر من تركیز  2الى  0.25 بینویتراوحالتركیز االبتدائي الیونات المعدن.

ح  ) النحاس والزنك(اظھرت النتائج أن النسبة المئویة الستخالص أیونات المعادن  ي     KClتزداد بصورة رئیسیة بزیادة كل من تركیز مل ور الملح ي الط ف

   .ونسبة الطور بین البولیمر والملح وتقل مع زیادة التراكیز االبتدائیة ألیونات المعادن

  

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