**Heavy Metal Ion Extraction Using Organic Solvents: An Application of the Equilibrium Slope Method**

Tjoon Tow Teng, Yusri Yusup and Ling Wei Low *Universiti Sains Malaysia Malaysia* 

### **1. Introduction**

120 Stoichiometry and Research – The Importance of Quantity in Biomedicine

Shehata, M.R., Shoukry, M.M., Nasr, F.M.H. and van Eldik, R. (2008) Complex-formation

Shoukry, A., Rau, T., Shoukry, M., and van Eldik, R., (1998) Kinetics and mechanisms

Shoukry, M.M., Shehata, M.R., Abdel-Razik, A., Abdel-Karim, A.T. (1999) Equilibrium

Sigel, H. and Martin, R.B. (1982) Coordinating properties of the amide bond. Stability and

Sigel, H., Massoud, S.S., Corfu, N.A. (1994) Comparison of the extent of macrochelate

Tercero-Moreno, J.M., Matilla-Hernandez, A., Gonzalez-Garcia, S. and Niclos-Gutierrez, J.

Zekany, L. and Nagypal, I. (1985) in Leggett, D.J. (Ed.), Computational methods for the determination of formation constants. Plenum Press, New York, P. 71.

in metal ion-nucleic base recognition. J. Am. Chem. Soc. 116, 2958–2971 Tauler, R. Casassas, E. and Izquierdo-Ridorsa, A. (1991) Self-modelling curve resolution in

Labilization induced by S-donor chelates. Dalton Trans 779-786.

palladium(II). J Chem Soc Dalton Trans. 3105-3112.

385-426.

Anal Chim Acta. 248, 447-458.

Drugs. Chem. Rev. 99, 2451.

and Some bioligands. Monatsh Fur Chem. 130, 409-423.

reactions of dicholoro(S-methyl-L-cysteine)palladium(II) with bio-relevant ligands.

of the ligand substitution reactions of bis(amine)(cyclobutane-1,1-dicarboxylato)

studies of mixed ligand complexes involving (1,2-diaminopropane)-Palladium(II)

structure of metal ion complexes of peptides and related ligands. Chem Rev 82,

formation in complexes of divalent metal ions with guanosine (GMP2−), inosine (IMP2−), and adenosine 5́-monophosphate (AMP2−). The crucial role of N-7 basicity

studies of spectrometric titrations of multi-equilibria systems by factor analysis.

(1996) Hydrolytic species of the ion cis-diaqua(ethylenediamine) palladium(II) complex and of cis-dichloro(ethylenediamine) palladium(II): fitting its equilibrium models in aqueous media with or without chloride ion. Inorg Chim Acta. 253, 23. Wong, E. and Giandomenico, C.M. (1999) Current Status of Platinum-Based Antitumor The separation procedure of a chemical species from a matrix is essentially based on the transportation of the solute between the two involved phases, generally an organic and an inorganic one. Specifically, solvent extraction uses the concept of unique solute distribution ratios between two immiscible solvents. However, there are several situations where solutes have been observed to completely move from the inorganic to the organic phase (Anthemidis and Ioannou, 2009).

Organic solvent extraction is the transport of solutes, e.g. heavy metal ions, from an inorganic (or aqueous) phase to an organic phase. Solvents used comprise of an extractant + diluent combination. The roles of each are as follows: 1) the extractant, as a specific metal ion extractant; 2) the diluent, as a solvent condition controller, i.e. hydrophobicity, which can affect the molecules extractability (Watson, 1999; Cox, 2004). Occasionally, a phase modifier can be added to solve the problem of emulsion formation, aside from improving the phase demarcation process in an aqueous organic system (Cox, 2008).

Solvent extraction is widely applied to processes of metal ions recovery, ranging from aqueous solutions in hydrometallurgical treatment to environmental applications. It is also considered a useful technique to increase the initial concentration of the solute, commonly used in the separation processes of analytical applications (Reddy et al., 2005).

In the biomedical field, supported liquid membrane methodology was used for trace analytes determination by facilitating chromatogram differentiation between samples, water and blood plasma (Jonsson and Mathiasson, 1999). It is also used to enrich human wastes (e.g. urine) with heavy metals prior to concentration determination using atomic absorption spectroscopy (AAS) (Lindegrade et al., 1992; Djane et al., 1997a; Djane et al., 1997b).

### **1.1 Organic solvents**

Numerous organic solvents have been utilized to remove heavy metals (Leopold et al., 2010; Rafighi et al., 2010; Chang et al., 2011; Fu et al., 2011; Mishra and Devi, 2011). Most of them are, in part, made from petroleum. Recently, solvents such as vegetable oil (Venkateswaran

Heavy Metal Ion Extraction Using




and the aqueous phase (Eq. 2).

**2.2 Application of the equilibrium slope methodology** 

����

ions reported in literature is presented.

extractant, *x*.

**2.2.1 Cu (II)** 

Eq. (5).

where,

sequence, is listed below.

Organic Solvents: An Application of the Equilibrium Slope Method 123

The equilibrium constant, *Keq*, can be experimentally determined. In turn, *Keq* is a function of *Deq*, which is the equilibrium distribution ratio of the metal ion concentration in the organic

��� =����������

During the experiment, the ionic strength and the correlated activity coefficient, *a*, is needed to be kept constant by adding inert chemicals or substances such as salts. A plot of lg *Deq* against pHeq can be drawn to determine the valency of the extracted metal ion. This information can also be used to ensure the experiment validity by cross-checking the actual valency of the studied metal ion to the slope of the drawn plot. In addition, a plot of lg *Deq* versus lg [extractant], will reveal the value of the stoichiometric coefficient of the

In this section a separated study on the equilibrium slope method applied to different metal

Cu(II) extraction from aqueous solutions using different organic solvents have been studied extensively. Combination of extractants and solvents used to extract Cu(II) from an aqueous solution in literature include D2EHPA + soybean oil (Chang et al., 2010; Chang et al., 2011), LIX 84 + kerosene (Agrawal et al., 2008), Cyanex 921 + kerosene (Leopold et al., 2010; Mishra and Devi, 2011), and Cyanex 272 + kerosene (Mohapatra et al., 2007; Agrawal et al., 2008; St

The steps required to determine the stoichiometric coefficient of the extractant are somewhat similar between the extractant + solvent combinations. Thus, the general technique, in

The relevant reaction equation can be written as Eq. (3), where *Keq* is defined as Eq. (4) and

���

��� <sup>=</sup> [����][��]

�� ��������� � ���

�

John et al., 2010). The solvents employed are mostly non-polar in nature.

���� � ��������

������� �

��

(2)

���� (3)

[����][��]� (4)

et al., 2007; Chang et al., 2010), were exploited as alternatives to replace the commonly used petroleum-based organic solvents. Additionally, a family of "specialist" extractants, known as the organo-phosphorous compounds, are also employed as metal extractants (Sainz-Diaz et al., 1996).

Some examples of solvents applied in heavy metals extraction are:


### **2. Stoichiometry of heavy metals extracted using organic solvents: Equilibrium slope method**

The equilibrium slope method has been used by many researchers to determine the stoichiometry of various metal–organic complexes in organic solvents (Nagaosa and Yao, 1997; Wang and Nagaosa; 2001; Mansur et al., 2002; Kumar et al., 2009). Most of its applications deal with extracting metal ions from aqueous solutions. It has proven a very useful technique of its ease of use, and its accuracy when validated by other methods, such as numerical and quantitative analysis from Fourier Transform Infrared Spectroscopy (FTIR).

### **2.1 General equilibrium slope methodology**

Following this methodology, the extractant form in the organic solvent would need to be estimated first. Subsequently, the formulation of a balanced reaction equation would be derived. A general form of the reaction equation is shown below (Eq. 1). Some applied assumptions include that the solubility of the extractant and the metal-extractant complex in the aqueous phase is small, and that the extracted metal ions are not associated to one another.

$$\text{M}^{n+}\text{(aq)} + \text{xHR}\_{\text{(org)}} \xleftrightarrow{\text{K}\_{eq}} \text{MR}\_{\text{x}\_{\text{(org)}}} + \text{x} \text{H}^{+}\text{(aq)}\tag{1}$$

where,


The equilibrium constant, *Keq*, can be experimentally determined. In turn, *Keq* is a function of *Deq*, which is the equilibrium distribution ratio of the metal ion concentration in the organic and the aqueous phase (Eq. 2).

$$D\_{eq} = \left(\frac{\mathcal{M}^{n+}\!\_{\left(org\right)}}{\mathcal{M}^{n+}\!\_{\left(aq\right)}}\right)\_{eq} \tag{2}$$

During the experiment, the ionic strength and the correlated activity coefficient, *a*, is needed to be kept constant by adding inert chemicals or substances such as salts. A plot of lg *Deq* against pHeq can be drawn to determine the valency of the extracted metal ion. This information can also be used to ensure the experiment validity by cross-checking the actual valency of the studied metal ion to the slope of the drawn plot. In addition, a plot of lg *Deq* versus lg [extractant], will reveal the value of the stoichiometric coefficient of the extractant, *x*.

### **2.2 Application of the equilibrium slope methodology**

In this section a separated study on the equilibrium slope method applied to different metal ions reported in literature is presented.

### **2.2.1 Cu (II)**

122 Stoichiometry and Research – The Importance of Quantity in Biomedicine

et al., 2007; Chang et al., 2010), were exploited as alternatives to replace the commonly used petroleum-based organic solvents. Additionally, a family of "specialist" extractants, known as the organo-phosphorous compounds, are also employed as metal extractants (Sainz-Diaz

a. Di-2-ethylhexylphosphoric acid (D2EHPA), extensively used as an extractant for the separation of Cu(II) from aqueous solutions (Gherrou et al., 2002; Ren et al., 2007; Cox, 2008). Other applications of this popular extractant include the removal of Cd(II) (Kumar et al., 2009), Zn(II) (Vahidi et al., 2009), Fe(III) and Ti(IV) (Silva et al., 2008); b. Tributylphosphate (TBP), used to act as a phase modifier in Cu(II) extraction (Cheng, 2000). The extractant and phase modifier are diluted at certain ratios in the petroleumbased organic diluents such as kerosene and chloroform (Ak et al., 2008; Ren et al., 2008), cumene (Svendsen et al., 1990), dichloromethane (Memon et al., 2003), isododecane (Mortes and Bart, 2000), n-dodecane (Simonin et al., 2003), n-decanol (Lin et al., 2005), n-

heptane (Morais and Mansur, 2004), and n-hexane (Valenzuela et al., 2002);

**2. Stoichiometry of heavy metals extracted using organic solvents:** 

d. Cyanex 921, used to extract Cu(II) from HCl (Mishra and Devi, 2011);

in kerosene, used to extract Cu(II) (Fu et al., 2011).

c. LIX 84 and Cyanex 272, applied to extract Cu(II), Ni(II), and Al(III) (Mohapatra et al.,

e. Miscellaneous organic solvents such as I) 1-phenyl-3-heptyl-1,3-propanedione, II) 1 phenyl-4-ethyl-1,3-octanedione, III) 1-(4'-dodecyl) phenyl-3-tert-butyl-1,3-propanedione

The equilibrium slope method has been used by many researchers to determine the stoichiometry of various metal–organic complexes in organic solvents (Nagaosa and Yao, 1997; Wang and Nagaosa; 2001; Mansur et al., 2002; Kumar et al., 2009). Most of its applications deal with extracting metal ions from aqueous solutions. It has proven a very useful technique of its ease of use, and its accuracy when validated by other methods, such as numerical and quantitative analysis from Fourier Transform Infrared Spectroscopy

Following this methodology, the extractant form in the organic solvent would need to be estimated first. Subsequently, the formulation of a balanced reaction equation would be derived. A general form of the reaction equation is shown below (Eq. 1). Some applied assumptions include that the solubility of the extractant and the metal-extractant complex in the aqueous phase is small, and that the extracted metal ions are not associated to one

ርሮ ܯܴ௫ሺሻ ܪݔା

ሺሻ (1)

ܯାሺሻ ܪݔܴሺሻ

Some examples of solvents applied in heavy metals extraction are:

et al., 1996).

2007; Agrawal et al., 2008);

**Equilibrium slope method** 

**2.1 General equilibrium slope methodology** 

(FTIR).

another.

where,

Cu(II) extraction from aqueous solutions using different organic solvents have been studied extensively. Combination of extractants and solvents used to extract Cu(II) from an aqueous solution in literature include D2EHPA + soybean oil (Chang et al., 2010; Chang et al., 2011), LIX 84 + kerosene (Agrawal et al., 2008), Cyanex 921 + kerosene (Leopold et al., 2010; Mishra and Devi, 2011), and Cyanex 272 + kerosene (Mohapatra et al., 2007; Agrawal et al., 2008; St John et al., 2010). The solvents employed are mostly non-polar in nature.

The steps required to determine the stoichiometric coefficient of the extractant are somewhat similar between the extractant + solvent combinations. Thus, the general technique, in sequence, is listed below.

The relevant reaction equation can be written as Eq. (3), where *Keq* is defined as Eq. (4) and Eq. (5).

$$\text{Cu}^{2+} \text{(aq)} + \text{xHR}\_{\text{(org)}} \overset{\text{K}\_{aq}}{\leftrightarrow} \text{CuR}\_{\text{x(org)}} + \text{xH}^{+} \text{(aq)}\tag{3}$$

where,

$$K\_{eq} = \frac{[\text{Cu}R\_x][H^+]^x}{[\text{Cu}^{2+}][HR]^x} \tag{4}$$

$$D\_{eq} = \left(\frac{\mathbb{C}u^{2+}\!\_{\left(org\right)}}{\mathbb{C}u^{2+}\!\_{\left(aq\right)}}\right)\_{eq} \tag{5}$$

$$K\_{eq} = D\_{eq} \frac{[H^+]^x}{[HR]^x} \tag{6}$$

$$K\_{eq} [HR]^\mathbf{x} = D\_{eq} [H^+]^\mathbf{x} \tag{7}$$

$$
\lg K\_{eq} + \varkappa \lg \text{[HR]} = \lg D\_{eq} + \varkappa \lg \text{[H}^+\text{]}\tag{8}
$$

$$
\pi \text{xlg}[H^+] = -\text{xp}H\_{eq} \tag{9}
$$

$$
\log D\_{ea} = \mathfrak{x}pH\_{ea} + \lg K\_{ea} + \mathfrak{x}\lg\{HR\} \tag{10}
$$


$$\text{Ni}^{2+}(aq) + \text{xHR}\_{(org)} \overset{\text{K}\_{aq}}{\longleftrightarrow} \text{NiR}\_{\text{x(org)}} + \text{xH}^{+}(aq) \tag{11}$$

$$K\_{eq} = \frac{[NlR\_{\overline{x}}][H^{+}]^{\overline{x}}}{[Nl^{2}"][HR]^{\overline{x}}} \tag{12}$$

$$\left(M^{n+}\right)\_{(aq)} + (n+p)/2 \overline{\left(\overline{H\_2} \overline{R\_2}\right)}\_{org} \overset{\kappa\_{eq}}{\leftrightarrow} \overline{\left(\overline{M\_n} \overline{\left(\overline{H} \overline{R\_n}\right)}\_{pg}\right)\_{org}} + nH^+\_{aq} \tag{13}$$

$$\text{Cr}^{3+}(aq) + \text{xHR}\_{\text{(org)}} \xleftrightarrow{\text{K}\_{aq}} \text{CrR}\_{\text{x(org)}} + \text{xH}^{+}(aq) \tag{14}$$

$$K\_{eq} = \frac{[CrR\_{\chi}][H^{+}]^{\text{x}}}{[Cr^{3+}][HR]^{\text{x}}} \tag{15}$$

$$D\_{eq} = \left(\frac{\mathcal{C}r^{3\*}\,\_{(org)}}{\mathcal{C}r^{3\*}\,\_{(aq)}}\right)\_{eq} \tag{16}$$

$$K\_{eq} = D\_{eq} \frac{[H^\*]^\mathbf{x}}{[HR]^\mathbf{x}} \tag{17}$$

$$K\_{eq} \lbrack HR \rbrack^\mathbf{x} = D\_{eq} \lbrack H^+ \rbrack^\mathbf{x} \tag{18}$$

$$
\lg D\_{eq} = \varkappa p H\_{eq} + \lg K\_{eq} + \varkappa \lg \text{[HR]} \tag{19}
$$

$$\text{Zn}^{2+} \text{(aq)} + 1.5 \text{(H}\_2\text{R}\_2\text{)}\_{\text{(org)}} \xrightarrow{K\_{aq}} \text{ZnR}\_2\text{(HR)}\_{\text{(org)}} + 2\text{H}^+ \text{(aq)}\tag{20}$$

$$\text{Co}^{2+}(aq) + \text{xHR}\_{\text{(org)}} \xleftrightarrow{\text{K}\_{\text{eq}}} \text{CoR}\_{\text{x(org)}} + \text{xH}^{+}(aq) \tag{21}$$

$$K\_{eq} = \frac{[CoR\_x][H^+]^\chi}{[Co^{2+}][HR]^\chi} \tag{22}$$

$$D\_{eq} = \left(\frac{\mathcal{Co}^{2+}\!\_{(org)}}{\mathcal{Co}^{2+}\!\_{(aq)}}\right)\_{eq} \tag{23}$$

$$K\_{eq}[HR]^\chi = D\_{eq}[H^+]^\chi \tag{24}$$

$$
\log D\_{eq} = \text{x}pH\_{eq} + \text{lg}K\_{eq} + \text{xlg}\{HR\} \tag{25}
$$

$$\text{Co}^{2+}(aq) + \text{HR}^{1\text{(2)}}(org) + \text{Cl}^-(aq) \leftrightarrow \text{Co}R^{1\text{(2)}}\text{Cl. 3}H\_2O\_{\text{(org)}} + \text{H}^+\text{(aq)}\tag{26}$$

$$[Al^{3+} + n[HR]\_2 \overset{K\_{eq}}{\leftrightarrow} AlH\_{2n-3}R\_{2n} + 3H^+ \tag{27}$$

$$K\_{eq} = \frac{[AlH\_{2n-3}R\_{2n}][H^+]^3}{[Al^{3+}][HR]\_2^n} \tag{28}$$

$$K\_{eq} = \frac{D\_{eq} [H^+]^3}{[HR]\_2^n} \tag{29}$$

$$D\_{eq} = \frac{[AlH\_{2n-3}R\_{2n}]}{[Al^{3+}]} \tag{30}$$

$$
\log \mathcal{D}\_{eq} = \lg K\_{eq} + n \lg \text{[}HR\text{]}\_2 - 3 \lg \text{[}H^+\text{]} \tag{31}
$$

$$\mathbf{y} = \boldsymbol{\beta}\_0 + \boldsymbol{\Sigma}\_{l=1}^k \boldsymbol{\beta}\_l \mathbf{x}\_l + \boldsymbol{\varepsilon} \tag{32}$$


Heavy Metal Ion Extraction Using

Vol.358, pp.822

Organic Solvents: An Application of the Equilibrium Slope Method 131

Djane, N.K.; Bergdahl, I.A.; Ndung's, K.; Schutz, A.; Johansson, G. & Mathiasson, L. (1997a).

Djane, N.K.; Ndung'u, K.; Malcus, F.; Johansson, G. & Mathiasson, L. (1997b). Supported

Fu, W.; Chen, Q., Hu, H., Niu, C. & Zhu, Q. (2011). Solvent extraction of copper from

Gherrou, A.; Kerdjoudj, H., Molinari, R. & Drioli, E. (2002). Removal of silver and copper

Leopold, A.A.; Coll, M.T., Fortuny, A., Rathore, N.S. & Sastre, A.M. (2010). Mathematical

Li, D.Q.; Wang, L.G. & Wang, Y.G. (2003). Synergistic extraction of Zinc(II) with mixtures of CA-100 and Cyanex 272. *Separation Science and Technology*, Vol.38, pp. 2291–2306. Lin, S.H.; Kao, H.C., Su, H.N. & Juang, R.S. (2005). Effect of formaldehyde on Cu(II) removal

Lindegrad, B.; Jonsson, J.A. & Mathiasson, L. (1992). Liquid membrane work-up of blood

Mansur, M.B.; Slater, M.J. & Biscaia Jr, E.C. (2002). Equilibrium analysis of the reactive liquid-

Memon, S.; Akceylan, E., Sap, B., Tabakci, M., Roundhill, D.M. & Yilmaz, M. (2003). Polymer

Mishra, S. & Devi, N. (2011). Extraction of copper (II) from hydrochloric acid solution by

Mohapatra, D.; Kim, H.I., Nam, C.W. & Park, K.H. (2007). Liquid-liquid extraction of

Mortes, M. & Bart, H.J. (2000). Extraction equilibria of zinc with bis(2 ethylhexyl)phosphoric

Nagaosa, Y. & Yao, B.H. (1997). Extraction equilibria of some transition metal ions by bis(2-

and D2EHPA. *Separation and Purification Technology,* Vol.56, pp. 311-318. Morais, B.S. & Mansur, M.B. (2004). Characterization of the reactive test system

ZnSO4/D2EHPA in n-heptane, *Hydrometallurgy,* Vol.74, pp. 11–18.

acid. *Journal of Chemical Engineering Data*, Vol.45, pp. 82–85.

ethylhexyl)phosphoric acid. *Talanta*, Vol.44, pp. 327-337.

*Separation and Purification Technology*, Vol.80, pp. 52-59.

*Hydrometallurgy,* Vol.96, pp. 230–234.

*Journal of Chromatography,* Vol.573, pp.191-200.

*Chemical Engineering and Processing*, Vol.45, pp. 684-690.

Cyanex 921. *Hydrometallurgy,* Vol.107, pp. 29-33.

anions. *Journal of Polymer and Environment*, Vol.11, pp. 67–69.

Vol.182, pp. 903-911.

*Materials,* Vol.120, pp. 1–3.

Supported liquid membrane enrichment combined with atomic absorption spectrometry for the determination of lead in urine. *Analyst*, Vol.122, pp.1073-1077.

liquid membrane enrichment using an organophosphorus extractant for analytical trace metal determinations in river waters. *Fresenius' Journal of Analytical Chemistry*,

ammoniacal chloride solutions by sterically hindered β-diketone extractants.

ions acidic thiourea solutions with a supported liquid membrane containing D2EHPA as carrier, *Separation and Purification Technology,* Vol.28, pp. 235–244. Jonsson, J.A. & Mathiasson, L. (1999). Liquid membrane extraction in analytical sample preparation II: Applications. *Trends in Analytical Chemistry*, Vol.18, pp. 325-334. Kumar, V.; Kumar, M., Jha, M.K., Jeong, J. & Lee, J. (2009). Solvent extraction of cadmium

from sulfate solution with di(2-ethylhexyl)phosphoric acid diluted in kerosene.

modelling of cadmium (II) solvent extraction from neutral and acidic chloride media using Cyanex 923 extractant as a metal carrier. *Journal of Hazardous Materials*,

from synthetic complexed solutions by solvent extraction. *Journal of Hazardous* 

plasma samples applied to gas chromatographic determination of aliphatic amines.

liquid test system ZnSO4/D2EHPA/n-heptane. *Hydrometallurgy*, Vol.63, pp. 117-126. Mellah, A. & Benachour, D. (2006). The solvent extraction of zinc and cadmium from

phosphoric acid solution by di-2-ethylhexyl phosphoric acid in kerosene diluent.

supported calyx arene derivatives for the extraction of metals and dichromate

aluminium (III) from mixed sulphate solutions using sodium salts of Cyanex 272

### **4. Conclusion**

Liquid extraction of heavy metals is widely applied in many fields ranging from the environmental to the biomedical discipline. In the environmental field, some of the more prominent applications include: removal and recovery of heavy metals and dyes from wastewater. In the biomedical field, liquid extraction has been used in the determination of heavy metals in human waste (e.g. urine). However, trace analytes extraction is still a great challenge in the pharmaceutical and medical industry.

In this chapter, the equilibrium slope method and its utility in estimating the stoichiometry of the resulting organic complexes has been reviewed for multiple heavy metal ions. The number of protons involved generally dictates the slope of the lg *Deq* versus pH plot. A slope of 2 is common for many heavy metals, thus attributing that the general organic complexes obtained from these extraction processes are in the form of dimers.

In brief other methods, numerical and FTIR quantitative analysis have been discussed and might be helpful to further corroborate the results of the equilibrium slope method.

### **5. References**


Liquid extraction of heavy metals is widely applied in many fields ranging from the environmental to the biomedical discipline. In the environmental field, some of the more prominent applications include: removal and recovery of heavy metals and dyes from wastewater. In the biomedical field, liquid extraction has been used in the determination of heavy metals in human waste (e.g. urine). However, trace analytes extraction is still a great

In this chapter, the equilibrium slope method and its utility in estimating the stoichiometry of the resulting organic complexes has been reviewed for multiple heavy metal ions. The number of protons involved generally dictates the slope of the lg *Deq* versus pH plot. A slope of 2 is common for many heavy metals, thus attributing that the general organic complexes

In brief other methods, numerical and FTIR quantitative analysis have been discussed and

Agrawal, A.; Manoj, M.K., Kumari, S., Bagchi, D., Kumar, V. & Pandey, B.D. (2008).

Ak, M.; Taban, D. & Deligoz, H. (2008). Transition metal cations extraction by ester and

Al-Zoubi, W.; Kandil, F. & Chebani, M.K. (2011). Solvent extraction of chromium and copper

*Arabian Journal of Chemistry*, Article in Press DOI:10.1016/j.arabjc. 2011.06.023 Anthemidis, A.N. & Ioannou, K.G. (2009). Recent development in homogenous and

Baba, A.A. & Adekola, F.A. (2011). Beneficiation of a Nigerian sphalerite mineral: solvent

Chang, S.H.; Teng, T.T. & Norli, I. (2010). Extraction of Cu(II) from aqueous solutions by

Chang, S.H.; Teng, T.T. & Norli, I. (2011). Efficiency, stoichiometry and structural studies of

Cheng, C.Y. (2000). Purification of synthetic laterite leach solution by solvent extraction

Cox, M. (2004). *Solvent extraction in hydrometallurgy*, In: J. Rydberg, M. Cox, C. Musikas, G.R.

Cox, M. (2008). *Liquid–liquid extraction and liquid membranes in the perspective of the twenty-first* 

using D2EHPA. *Hydrometallurgy*, Vol.56, pp. 369-386.

United States of America, pp. 457–462.

United States of America, pp. 1–19.

Extractive separation of copper and nickel from copper bleed stream by solvent

ketone derivatives of chromogenic azocalix arenes. *Journal of Hazardous Materials,* 

using Schiff base derived from terephthaldialdehyde and 5-amino-2-methoxy phenol.

dispersive liquid-liquid extraction for inorganic elements determination. A review.

extraction of zinc by Cyanex 272 in hydrochloric acid. *Hydrometallurgy*, Vol. 109,

vegetable oil-based organic solvents. *Journal of Hazardous Materials,* Vol.181, pp. 868-872.

Cu(II) removal from aqueous solutions using di-2-ethylhexylphosphoric acid and tributhylphosphate diluted in soybean oil. *Chemical Engineering Journal*, Vol.166, pp.

Choppin (Eds.), Solvent Extraction Principles and Practice, Marcel Dekker Inc., The

*century*, In: M. Aguilar, J.L. Cortina (Eds.), Solvent Extraction and Liquid Membranes Fundamentals and Applications inNewMaterials, CRC Press, the

might be helpful to further corroborate the results of the equilibrium slope method.

extraction route. *Minerals Engineering*, Vol.21, pp. 1126-1130.

challenge in the pharmaceutical and medical industry.

obtained from these extraction processes are in the form of dimers.

**4. Conclusion** 

**5. References** 

Vol.154, pp. 51-52.

pp. 187-193.

249-255.

*Talanta,* Vol.80, pp. 413-421.


**Part 3** 

**Stoichiometry in Lipids** 

**and Polymers Architecture** 

