- Email: [email protected]
A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell
Accepted Manuscript Title: A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell Authors: Maryam Kasaie, Hossein Bahmanyar, Mohammad Ali Moosavian PII: DOI: Reference:
S2213-3437(17)30263-4 http://dx.doi.org/doi:10.1016/j.jece.2017.06.013 JECE 1675
To appear in: Received date: Revised date: Accepted date:
30-9-2016 5-6-2017 7-6-2017
Please cite this article as: Maryam Kasaie, Hossein Bahmanyar, Mohammad Ali Moosavian, A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell, Journal of Environmental Chemical Engineeringhttp://dx.doi.org/10.1016/j.jece.2017.06.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell Maryam Kasaie, Hossein Bahmanyar*, Mohammad Ali Moosavian
Surface Phenomena and Liquid-liquid Extraction Research Laboratory, School of Chemical Engineering, College of Engineering, University of Tehran, P. O. Box 11365/4563, Tehran, Iran
*
Corresponding author Tel.: +98 21 61112213; fax: +98 21 88221116. E-mail addresses: [email protected]
1
Highlights
The influence of operating parameters on the copper extraction rate was studied.
The rate equations were specified by the Lewis cell technique.
The diffusion is the predominant mechanism at the interface.
Mechanism of extraction was represented based on an interface reaction.
ABSTRACT
The reactive extraction of Cu(II) from a sulfate aqueous solution using Cupromex-3302 as a new extractant was investigated using a Lewis cell to reveal the mechanism of extraction. Various affecting parameters such as stirring speed, temperature, interfacial area, extractant concentration, Cu(II) concentration and aqueous phase pH were studied. The rate of copper extraction was found to be directly proportional to the concentrations of Cu(II) and extractant and inversely proportional to the concentration of H+. The extraction rate of Cu(II) increased with an increase in specific interfacial area demonstrated that the rate determining step of Cu(II) extraction by Cupromex-3302 was reactive extraction at the interface. Also, extraction rate increased with increasing the temperature. The activation energy (E) was calculated to be 15.2 kJ/mol. This value suggested that extraction of Cu(II) in this system is controlled by diffusion mechanism.
Keywords: Reaction kinetics; Solvent extraction; Lewis cell technique; Copper; Cupromex-3302.
2
Nomenclature a,b,c
Reaction orders with respect to [Cu2+], [RH] and [H+] respectively
A
Interfacial area through which mass transfer occurs; m2
ΔH
Enthalpy of activation; kJ/mol
ΔS
Entropy of activation; J/mol k
Ea
Activation energy; kJ/mol
F
Mass transfer flux of Cu(II); Kmol/ m2s
h
Planck's constant =6.6252*10-37 kJ s
kB
Boltzman constant =1.38*10-26 kJ/deg
kf
Forward extraction rate constant
mtv
Amount of mass transferred; Kmol
t
Phase contact time; s
T
Absolute temperature; K
R
Universal gas constant
Subscripts aq
Aqueous phase
org
Organic phase
f
Forward extraction
ad
Adsorbed at the liquid−liquid interface
int
Two phase interface
1. Introduction
3
Demand for copper continues to increase because of its different technological applications which include electrical materials, power generation, telecommunications, transportation, petroleum refining and industrial machinery parts [1,2]. Elimination of this metal from different wastes and solutions not only from the point of environmental aspects but also in terms of high value is very important because of the reduction of world’s high grade resources and metals high prices [3]. There is a strong tendency to research and develop the new technologies for copper extraction such as hydrometallurgical methods from the standpoints of environmental protection and resource recycling which can be competitive with conventional pyrometallurgical processes [4,5]. Nowadays, more than 20% of the world's total copper production is through solvent extraction (SX) as a desirable process for metal winning from the viewpoints of natural resources and energy conservation [5,6]. Hydroxyoximes have been the most important and applicable extractants for copper extraction among other types. Today modified aldoximes and aldoxime–ketoxime mixtures are the most widely used copper extractant systems [3, 6-13].
Kinetic investigations are of major importance for the optimization and control of extraction processes to reveal the mechanism of the extraction process [14,15]. Finding methods to improve the extraction rate via the investigation on kinetics is interesting. In addition, design of commercial solvent extraction process needs detailed and exact information about extraction kinetics [15].
Several techniques for studying metal extraction kinetics have been developed such as shake out method, [16] rotating diffusion cell, [17] Hahn cell (with a constant interfacial area non stirred cell), [18,19] single drop (falling/rising), [14,20] the AKUFVE apparatus (highly stirred tank),
4
[21] constant interfacial area stirred (Lewis) cell [15,22-26] and attenuated total reflection spectroscopy (ATR) [27].
Unfortunately, all these techniques have some disadvantages along with their advantages. Moreover, extraction mechanism sometimes shows different results due to the differences in experimental technique and concentration of reactants [15]. For example, shakeout method and the AKUFVE apparatus are now abolished due to unknown interfacial area involved. The Hahn cell is only applicable for very fast reactions. The application of the rotating diffusion cell is also limited in use because of complicated construction and expensive accessories [20].
Among mentioned methods Lewis cell with a constant interfacial area stirred cell and the single drop apparatus are easy to construct and permit the interfacial area to be calculated easily whereas in Lewis cell the stirring speed can be varied in a wide range. The major limitation of Lewis cell is that the interfacial turbulence is not well defined and varies with equipment. Nevertheless, reproducible data can be obtained by using well-designed equipment and careful operation [14, 15, 22-26].
One of the new commercial hydroxyoxime extractants for copper extraction is developed by SNF FLOMIN with trade name Cupromex-3302. This extractant was proved to be promising for copper separation [28]. Cupromex extractants are based on familiar chemistries which are highly-selective in removing a wide range of Cu concentration at various levels of acidity. According to the above description and considering notable characteristics such as being inexpensive and available, Cupromex-3302 has been used in this work.
5
In the present study, the effect of various parameters on kinetic features of copper extraction with the new extractant Cupromex-3302 applying Lewis cell were systematically investigated. Findings of this work would be useful to study the contrast between the two phenomena of mass transfer and reaction rate and proponed the exact kinetic equation for the mentioned system. This study is very important for a deep understanding of the process, and then for selection, design of the extraction equipments and for a reliable scale-up of the process.
It is worth mentioning that one of the goals we investigate the copper extraction is applying the extraction columns such as rotating disc contactor (RDC) and pulsed columns. Performance evaluation of extraction columns in the copper recovery by new extractants cupromex-3302 in order to enhance the extraction efficiency has been performed and related results are under published. Whereas copper extraction process is accompanied by a chemical reaction, so a careful research to investigate the reaction kinetics and find the exact kinetics equation has been done at this time.
2. Materials and methods
2.1. Chemicals and reagents
The commercial extractants Cupromex-3302 (mixture of 2-hydroxy-5-nonylsalicylaldoxime and TXIB (2,2,4-Trimethylpentanediol diisobutyrate) were purchased from SNF FLOMIN. The extractants were dissolved in commercial kerosene to achieve the required concentration. Kerosene was a product of Tehran refinery, which was colorless and mostly aromatic free. The aqueous working solutions were prepared by dissolving copper sulfate pentahydrate (CuSO4.5H2O, Merck, 6
99.9% purity) in deionized water. The initial copper concentration in aqueous phase and initial concentration of extractant were maintained respectively at 1 g/L and 10% (v/v).
2.2. Analytical methods
The copper concentration in aqueous solutions was analyzed by atomic absorption spectrometry (Perkin Elmer-AAnalyst 400). The aqueous phase pH measurement was done using a Lutron pH201 pH meter calibrated daily with standard buffer solutions. The pH of aqueous solutions was adjusted by adding dilute H2SO4 (Merck, 99.9% purity).
2.3. Procedure with Lewis cell
The extraction rate of Cu(II) was measured using a constant interface stirred cell (Lewis cell) that construction of it as well as the working procedure is similar to that reported in the literature [23,29].
The characteristics of the Lewis cell used in the experiments are presented in Table 1. It consists of a cylindrical jacketed glass vessel having two flat-blade paddles in each phase, which allows the equal individual mixing of each phase without disturbing the interface. Variation of the interfacial area has been performed with putting the rings with the variable inner surfaces that produced the different interfacial areas.
Table 1.
Identical aliquots (100 mL) of the aqueous phase solution containing Cu(II) ions at a desired pH and organic phase containing Cupromex-3302 were introduced into the cell with minimum disturbance of the interface. The stirring speed was kept to be in range of 100-700 rpm with 7
neglecting disturbance of the interface by waves. After a predetermined time, 3 mL of the aqueous phase was withdrawn from the cell for analysis. The amount of copper transferred into the organic phase was estimated from the copper content in the liquid phase. In most of the experiments, the interfacial area was kept at 7.1 cm2 to evaluate interfacial area. Change of interfacial area was done by setting circular rings within the cell where the interface is formed. All experiments were carried out at 298 K, unless for tests related to evaluating temperature effects.
2.4. Method of determining of reaction rate
Following stoichiometric equation is used to describe the extraction reaction of Cu(II) by Cupromex-3302 that is a salicylaldoxime derivative [6,7]. + 2RH(org) + Cu2+ (aq) ↔ R 2 Cu(org) + 2H(aq)
(1)
Where RH is the extractant, R2Cu is the complex in the organic phase and the subscripts aq and org refer to aqueous and organic phases, respectively [6].
At the initial contact time, concentration of the complex in the organic phase was low and the reaction was far away from equilibrium, so the reverse reaction was considered negligible. Concentration of the reactant species at the reaction sites is a significant parameter on kinetics of the metal extraction [30].
Rate of liquid- liquid extraction of a metal ion by an acidic extractant like a heterogeneous system depends on the interfacial area, the concentration of the reactants involved and temperature. The extraction rate of Cu(II) at constant temperature can be expressed as:
8
d[Cu2+ ]a d[Cu2+ ]o rate = − ( )=( ) = k f A[Cu2+ ]a [RH]b [H + ]c dt dt
(2)
Where the subscripts (a), (o) represent the aqueous, organic phase, kf is the forward extraction rate constant and a, b, c are the reaction orders with respect to [Cu2+], [RH] and [H+], respectively. Flux (F) method is applied for rate analysis. The average mass flux (F) through the liquid–liquid interface can be measured by dividing the amount of copper transferred (Kmol) into the organic phase to the product of area (m2) and time of extraction (s). So: F = mt v ⁄Adt
(3)
Which is proportional to [Cu2+]a, [RH]b and [H+]c as shown below: F = k f [Cu2+ ]a [RH]b [H + ]c
(4)
With taking logarithm, Eq. (4) can be rewritten as: log(F) = log(k f ) + a × log ([Cu2+ ]) + b × log([RH]) + c × log([H + ])
(5)
That can be used to find the orders a, b and c and the rate constant in such a way that by keeping two variable concentrations constant, the order with respect to the third variable concentration can be obtained from the slope of the log–log plot of F functions to third variable concentration. The value of kf can be obtained from the intercept of the plots. It is worth noting that the rate of mass transfer is proportional to interfacial area but the flux is independent of interfacial area. Therefore, for investigating the kinetics of the liquid–liquid extraction of metal ions, the flux method is premiere because no interfacial area specification is necessary to represent the experimental data [19].
9
It should be mentioned that all reported results has been plotted according to the average values and repeatability of experiments. The uncertainties of the tests (including instrument and personal errors) have been 1-4% that is shown in Fig. 1 as an example. 3. Results and discussion
3.1. Effect of stirring speed
In Lewis cell technique, the basic criterion to distinguish the controlling mechanism of extraction is the dependency of the extraction rate on the stirring speed of the two phases [26]. Generally, the rate controlling mechanisms of the extraction include three basic regimes: diffusional regime, chemical reaction regime and mixed regime. In diffusional regime the extraction rate is controlled by the mass transfer. On the other hand, the rate of extraction increases with increasing the stirring speed [26]. But in the chemical reaction regime the kinetics of extraction is dependent on chemical reaction rather than mass transfer. Indeed there is nearly no effect on the extraction rate governed by chemical reaction. For mixed regime, the mass transfer and chemical reaction control the extraction rate together [15].
In a solvent extraction system, the process of extraction consists mainly of the transport of chemical specious from aqueous phase into the organic phase through the interface. Therefore, the nature of the interface and the interfacial phenomena must be greatly considered when studying solvent extraction reactions [31]. It is quite conceivable that changing the stirring speed may cause the change of concentration gradient across a diffusion layer between the bulk solution and interface and effects on transfer rates [15].
10
On this basis stirring speed as the most important parameter determining the mechanism of copper extraction was studied early in the range of 100−700 rpm, the maximum stirrer speed is just chosen not to disturb the interface.
The plot of copper extraction values vs. stirring speed is shown in Fig. 1. As shown, the increase in the stirring speed of the two phases increases the extraction rate in a diffusion controlled systems due to reduction of resistant and stagnant diffusion layers till it reaches a plateau region 500–700 rpm. In this region the rate remains constant with further increase in the stirring speed. So in this region, the effect of diffusion is minimized and the extraction process is assumed to be mainly controlled by chemical reactions in the bulk phase or at the interface.
Figure 1.
3.2. Effect of interfacial area
The chemical reaction can occur either in the bulk phases or at the interface. When the chemical reaction occurs in the bulk, the rate of extraction is independent of the interfacial area. In contrast, the extraction rate increases with the increase in the interfacial area when the chemical reaction occurs at the interface [32]. The effect of the interfacial area was studied as the most important parameter to distinguish chemical reaction taking place in the bulk phase or at the interface. Experiments were carried out by changing interfacial area in the range of 3.8−13.1 cm2 while keeping constant the volume of each phase at 100 ml. The plot of the extraction rate of copper vs. the interfacial area is shown in Fig. 2. This figure shows a straight line through the origin of axes demonstrates an interfacial reaction and it is observed that the reaction rate is linearly proportional to the interfacial area.
11
Figure 2.
3.3. Effect of temperature
The effect of temperature on the extraction of copper ions from aqueous solutions was investigated in the range of 298–338 K, and the results are presented in Fig. 3. It was observed that the extraction increases with the increase in temperature throughout the studied temperature range.
The plot of log F vs. 1000/T yields a straight line with slope -0.79. The activation energy was calculated from the slope of this line and determined to be 15.2 kJ/mol according to the Arrhenius equation: −E
a log F = 2.303RT
(6)
Where R is the universal gas constant that equals to 8.3145 J/K.mol [23]. It should be noted that value of F is considered as the reaction rate value in the equation 6 (Arrhenius equation).
The activation energy represents the temperature effects on extraction rate. Generally, this parameter in diffusion control process is less than where the reaction rate is controlled by chemical reaction and in the former case does not usually exceed 20.9 kJ/mol [23,25]. The calculated value of activation energy is within the value of diffusion controlled systems. It justifies that the extraction of Cu(II) in this system is controlled by diffusion mechanism.
Figure 3.
The enthalpy and entropy of activation is calculated from activated complex theory by the following equation: 12
k=
RT ∆S −∆H e R e RT Nh
(7)
Where N is the Avogadro's number (6.022×1023 molecules mol−1), h is the Plank's constant (6.626×10−34 J s) and kB (Boltzman constant) is used instead of R/N [23].
Fig. 4 shows the log Fh/kBt vs. 1000/T plot for a set of experiments in the same temperature range that fall on a straight line. From the slope and intercept of this line ∆H and ∆S values are calculated 12.6 kJ/mol and -268 J/mol.K respectively.
Figure 4.
3.4. Effect of Cu(II) concentration
In Fig.5 the influence of the initial copper concentration in aqueous phase on the extraction rate of Cu(II) by Cuppromex-3302 is illustrated while extractant concentration was kept at 10%(v/v). It is found that extraction percentage increases with the increase in copper concentration. The plot of log extraction rate vs log [Cu(II)] yields a line with a slope of a , the order for Cu(II) in kinetic relation. The slope of linear regression line, namely the value of a in Eq. (2), was determined to be 0.97.
The slope of almost unity indicates that the rate of copper extraction from aqueous to organic phase is directly proportional to the copper concentration. Reduction of rate order at high concentration of Cu(II) can be related to change of adsorption rate of saturated complexes at interface. This suggested that the diffusion mechanism at higher concentrations of Cu(II) is predominant.
Figure 5.
13
3.5. Effect of Cupromex-3302 concentration
Similar to previous section, a set of experiments were performed to change the initial concentration of Cupromex-3302 in the range of (5-12% v/v) while keeping the initial copper concentration at 1 g/L. The variation of extraction rates with different Cupromex-3302 concentrations is shown in Fig.6. It could be interpreted that the rate of copper transfer to organic phase by cupromex-3302 is directly proportional to the extractant concentration in the organic phase.
From the slope of given line, the value of order b in reaction Eq. (2) is determined to be 1.01. The nearly first order with respect to Cupromex-3302 concentration is consistent to the interfacial reactions with saturation at the interface.
Figure 6.
3.6. Effect of aqueous pH The influence of H+ concentration on the rate of extraction by Cupromex-3302 is shown in Fig.7. It was found that the plot of log extraction rate vs. Log [H+] gives slope of -0.78 that is equals to order c in reaction Eq. (2). The rate is inversely proportional to the H+ concentration in the aqueous phase. The low extraction rate is achieved in high acidity because the reaction is shifted preferentially in the back extraction reaction which is equivalent to stripping of the loaded organic phase.
Figure 7.
3.7. Reaction rate and mechanism
14
From the intercepts of the curves in Figs. 5 to 7, the average log (kf) value evaluated is -3.44 and the rate of copper extraction from sulphate solution by Cupromex-3302 can be expressed as following relation: r = 3.63 × 10−4 [Cu]0.97 [H + ]−0.78 [RH]1.01
(8)
Based on several researchers' findings, if the reaction takes place at the interface involving the adsorbed oxime molecules, it can be described by the following equations [33]: 2RHorg ↔ (RH)2,org
(9)
RHorg ↔ RHad ↔ RHaq
(10)
+ + Cu2+ aq + RHad ↔ CuR ad + Haq
(11)
+ CuR+ad + RHint ↔ CuR 2−ad + Haq
(12)
CuR 2−ad ↔ CuR 2−org
(13)
At first, dimerization of hydroxime molecules at the organic phase occurs with the first reaction. Also, the equilibrium reaction between monomeric hydroxime molecules adsorbed at the interface (because of their interfacial activity) and the molecules present in the organic and the aqueous phase is a fast step. Adsorbed reactant molecules react with the copper ions at the interface of two phases. The concentration of these adsorbed reactant molecules with their hydrophilic and chemically active groups are much higher than concentration of molecules in both phases. Above summary of reaction mechanism have been explained briefly just to make it clear for the readers. This method has not been utilized to obtain the empirical order form of the final kinetic equation. 15
Being charged and partially hydrated causes to increase the hydrophilicity of adsorbed molecules and diffuse to the aqueous phase film. This leads to react with another reactant molecule in the aqueous phase that is the slowest step. Then the neutral and dehydrated complex leaves the interface rapidly by other reactant molecules. At higher concentration of reactant in the organic phase the interface is saturated with adsorbed molecules and concentration of them is constant. Therefore the reaction order 1 in Eq. 8 regarding to concentration of extractant is justified.
Because of applying the cupromex-3302 extractant in kinetically investigation of copper extraction for the first time, comparison of the present study with other existing literature have not been done due
to
copper
recovery
from
different
solutions
with
different
conditions.
4. Conclusions
In this research, the effect of operating variables on the extraction rate of copper from sulfate solution with new extractant Cupromex-3302 in the Lewis cell was studied. The rate equation for the mentioned system was obtained by changing different parameters such as concentration of Cu(II), Cupromex-3302, and H+ while keeping other variables constant. It was found that reactive extraction of copper by Cupromex-3302 was a diffusion controlled system with a change in interfacial area.
The effect of chemical reaction resistance on extraction rate was negligible when the stirring speed of two phases was kept at 300 rpm. Extraction rate increased with an increase in temperature. The activation energy (E) was calculated to be 15.2 kJ/mol.
References 16
[1] L. R. Lemos, I. J. B. Santos, G. D. Rodrigues, L. H. M. Silva, M. C. H. Silva, Copper recovery from ore by liquid–liquid extraction using aqueous two-phase system, , Journal of Hazardous Materials 237– 238 (2012) 209– 214. [2] S. Meterfi, A.H. Meniai, M. Chikhi, Elimination of Cu(II) from Aqueous Solutions by Liquidliquid Extraction. Test of sodium diethyldithiocarbamate (SDDT) as an Extracting Agent. Energy Procedia (2012) 18:1165–1174. [3] E. Bidari, M. Irannejad, M. Gharabaghi, Solvent extraction recovery and separation of cadmium and copper from sulphate solution, Journal of Environmental Chemical Engineering 1 (2013) 1269–1274. [4] L.R. Lemos, I.J.B. Santos, G.D. Rodrigues, L.H.M. Silva, M.C.H. Silva, Copper recovery from ore by liquid–liquid extraction using aqueous two-phase system. Journal of Hazardous Materials (2012) 237– 238:209– 214. [5] H. Asghari, M.S. Safarzadeh, G. Asghari, D. Moradkham, The effect of impurities on the extraction of copper from sulfate medium using LIX-984N in kerosene. Russian Journal of NonFerrous Metals (2009) 50:89–96. [6] S. Rao, N.B. Devi, B.R. Reddy, Solvent extraction of copper from sulphate medium using MOC 45 as extractant. Hydrometallurgy (2000) 57:269–275. [7] Sh. Agarwal, A.E. Ferreira, S.M.C. Santos, M.T.A. Reis, M.R.C. Ismael, M.J.N. Correia, J.M.R. Carvalho, Separation and recovery of copper from zinc leach liquor by solvent extraction using Acorga M5640, International Journal of Mineral Processing (2010) 97:85–91.
17
[8] J. Szymanowski, E. Krzyzanowska, R. Cierpiszewski, K. Prochaska, Equilibrium and kinetics of copper extraction from acidic sulfate solutions with isome 1-(2'-Hydroxy-5'-alkyl-phenyl)-I – alkanone (E)-oximes. Journal of Radioanalytical and Nuclear Chemistry (1991) 150 (2): 335-350. [9] A. Deep, P. Kumar, J.M.R. Carvalho, Recovery of copper from zinc leaching liquor using ACORGA M5640. Separation and Purification Technology (2010) 76:21–25. [10] Sh. Agarwal, M.T.A. Reis, M.R.C. Ismael, M.J.N. Correia, J.M.R. Carvalho, Modeling of the extraction equilibrium of copper from sulfate solutions with ACORGA M5640. Solvent Extraction and Ion Exchange (2012) 30:536–551. [11] F.J. Alguacil, A. Cobo, M. Alonso, Copper separation from nitrate/nitric acid media using Acorga M5640 extractant Part I: solvent extraction study. Chemical Engineering Journal (2002) 85:259–263. [12] H. Asghari, M.S. Safarzadeh, G. Asghari, G. Moradkham, The effect of impurities on the extraction of copper from sulfate medium using LIX-984N in kerosene. Russian Journal of NonFerrous Metals (2009) 50:89–96. [13] K. Ochromowicz, T. Chmielewski, Solvent extraction of copper (II) from concentrated leach liquors. Physicochem. Probl. Miner. Process (2013) 49:357-367. [14] N.E. El-Hefny, S.I. El-Dessouky, Equilibrium and kinetic studies on the extraction of gadolinium (III) from nitrate medium by di-2-ethylhexylphosphoric acid in kerosene using a single drop technique. J Chem. Technol. Biotechnol. (2006) 81:394-400.
18
[15] P. Xing, Ch. Wang, Sh. Xu, Zh. Ju, Kinetics of cobalt(II) extraction from sulfate aqueous solution by sodium salt of di-decylphosphinic acid (DDPA). Trans. Nonferrous Met. Soc. China (2013) 23:517−523. [16] B. Wionczyk, Kinetic modeling of chromium (III) extraction with ALIQUAT-336 from alkaline aqueoussolutions containing chlorides. Physicochem. Probl. Miner. Process. (2013) 49(2):587−605. [17] M.A. Hughes, R.K. Biswas, The kinetics of manganese (II) extraction in the acidic sulphateD2EHPA-n-hexane system using the rotating diffusion cell technique. Hydrometallurgy (1993) 32:209-221. [18] R.K. Biswas, M.G.K. Mondal, Kinetics of Mn (II) extraction by D2EHPA. Hydrometallurgy (2003) 69:145–156. [19] R.K. Biswas, M.A. Habib, M.G.K. Mondal, Kinetics of stripping of VO–D2EHPA complex from toluene phase by aqueous sulphate–acetate solution. Comparison of Lewis and Hahn cells. Hydrometallurgy (2004) 73:257–267. [20] R.K. Biswas, M.R. Ali, A.K. Karmakar, M. Kamruzzaman, Kinetics of solvent extraction of copper(II) by Bis-(2, 4, 4-Trimethylpentyl) phosphonic acid using the single drop technique. Chem. Eng. Technol. (2007) 30(6):774–781. [21] K.O. Ipinmoroti, M.A. Hughes, The mechanism of vanadium (IV) extraction in a chemical kinetic controlled regime. Hydrometallurgy (1990) 24:255-262.
19
[22] K. Inoue, M. Goya, Taniguchi M. Extraction equilibrium and extraction kinetics of nickel from aqueous ammonium nitrate solution with vatic 10 in n-hexane. Hydrometallurgy (1984) 13:155-167. [23] S. Javanshir, M. Abdollahy, H. Abolghasemi, A. Khodadadi Darban, Kinetics of Au (III) extraction by DBC from hydrochloric solution using Lewis cell. International Journal of Mineral Processing (2011) 98:42-47. [24] X. Yang, X. Wang, Ch. Wei, Sh. Zheng, Q. Sun, D. Wang, Extraction kinetics of tantalum by MIBK from pulp using Lewis cell. Hydrometallurgy (2013) 131-132:34–39. [25] N.E. El-Hefny, Kinetics and mechanism of extraction and stripping of neodymium using a Lewis cell. Chemical Engineering and Processing (2007) 46:623–629. [26] N.E. El-Hefny, Kinetics and mechanism of extraction of Cu(II) by CYANEX 302 from nitrate medium and oxidative stripping of Cu(I) using Lewis cell technique. Chemical Engineering and Processing (2010) 49:84–90. [27] J.K. Mcculloch, J.M. Perera, E.D. Kelly, L.R. White, G.W. Stevens, F. Grieser, A Kinetic Study of Copper Ion Extraction by Kelex 100 at a Heptane–Water Interface. Journal of Colloid and Interface Science (1996) 184:406–413. [28] B.M. Torres, M.M. Torres, Q.C. Salgado, P.H. Bravo, O.J. Fernández, CuPRO-MEX extractants as equivalent alternatives for copper recovery. IN: Copper International Conference; (2013).
20
[29] R.K. Biswas, M.A. Habib, M.R. Ali, M.Z. Haque, Kinetics of Mn (II) extraction in the acidic chloride–D2EHPA–kerosene system using the constant interfacial area stirred cell technique. Pak. J. Sci. Ind. Res. (1998) 41:121–127. [30] A. Irabien, I. Ortiz, E.S. Perez de Ortiz, Kinetics of metal extraction: Model discrimination and parameter estimation. J. Chem. Eng. Process (1990) 27(1):13−18. [31] H.F. Aly, J.A. Daoud, Over view on extraction kinetics of metal adducts. Journal of Radioanalytical and Nuclear Chemistry (1996) 208(1):47-74. [32] J. Rydberg, M. Cox, C. Musikas, G.R. Choppin, Principles and Practices of Solvent Extraction. New York: Marcel Dekker Inc. (1992). [33] J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy. London: CRC Press (1993).
21
Figure captions: Fig. 1. Effect of stirring speed on initial extraction rate, [Cu2+](aq-ini)=1 g/L, [Cupromex-3302]= 10 (v/v), interfacial area= 7.1 cm2, aqueous phase pH=1.8 and T= 298 K.
Fig. 2. Effect of interfacial area on initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and T= 298 K.
Fig. 3. Effect of temperature on initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 4. Effect of temperature on log (Fh/kBT), initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 5. Effect of [Cu2+] on extraction rate, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 6. Effect of [Cupromex-3302] on extraction rate, [Cu2+](aq-ini)= 1 g/L, stirring speed= 300 rpm aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 7. Effect of [H+] on extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm and interfacial area=7.1 cm2.
22
12
(10-4 mol / L.min)
Copper extraction
10 8 6 4 2 0 0
100
200
300 400 500 Stirring speed (rpm)
Figure 1.
23
600
700
800
8
6
-4
(10 mol / L.min)
Copper extraction rate
7
5 4 3 2 1 0 0
2
4
6
8
10
12 2
Specific interfacial area (cm )
Figure 2.
24
14
-3.5 -3.6 -3.7
y = -0.7937x - 1.5879 R² = 0.947
Log ( F )
-3.8 -3.9 -4 -4.1 -4.2 -4.3 -4.4 -4.5 3
3.05
3.1
3.15
3.2
3.25
103 K/T
Figure 3.
25
3.3
3.35
3.4
-16.8
Log ( Fh / kT )
-16.85
y = -0.658x - 14.836 R² = 0.9251
-16.9 -16.95 -17 -17.05 -17.1
3
3.05
3.1
3.15
3.2 103 K/T
3.25
Figure 4.
26
3.3
3.35
3.4
-3.2
Log ( F )
-3.4 y = 0.9706x - 2.5383 R² = 0.9752
-3.6 -3.8 -4 -4.2 -4.4 -2
-1.7
-1.4 -1.1 Log [Cu(II)]
Figure 5.
27
-0.8
-0.5
-3.8 -3.9 -4 y = 1.0136x - 3.7781 R² = 0.9916
Log ( F )
-4.1 -4.2 -4.3 -4.4 -4.5 -4.6 -0.9
-0.7
-0.5
-0.3
Log [Cupromex-3302]
Figure 6.
28
-0.1
-4 y = -0.786x - 5.6902 R² = 0.9804
-4.2
Log ( F )
-4.4 -4.6 -4.8 -5 -5.2 -2.5
-2.2
-1.9
-1.6 Log [H+]
-1.3
Figure 7.
29
-1
Tables Table 1. Characteristics of the Lewis cell Internal
Volume of each
Rings
Blades
section
diameters
distance
100 mL
2, 3, 4 cm
5.5 cm
Height of cell diameter 4.8 cm
11 cm
30
S2213-3437(17)30263-4 http://dx.doi.org/doi:10.1016/j.jece.2017.06.013 JECE 1675
To appear in: Received date: Revised date: Accepted date:
30-9-2016 5-6-2017 7-6-2017
Please cite this article as: Maryam Kasaie, Hossein Bahmanyar, Mohammad Ali Moosavian, A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell, Journal of Environmental Chemical Engineeringhttp://dx.doi.org/10.1016/j.jece.2017.06.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A kinetic study on solvent extraction of copper from sulfate solution with Cupromex-3302 using Lewis cell Maryam Kasaie, Hossein Bahmanyar*, Mohammad Ali Moosavian
Surface Phenomena and Liquid-liquid Extraction Research Laboratory, School of Chemical Engineering, College of Engineering, University of Tehran, P. O. Box 11365/4563, Tehran, Iran
*
Corresponding author Tel.: +98 21 61112213; fax: +98 21 88221116. E-mail addresses: [email protected]
1
Highlights
The influence of operating parameters on the copper extraction rate was studied.
The rate equations were specified by the Lewis cell technique.
The diffusion is the predominant mechanism at the interface.
Mechanism of extraction was represented based on an interface reaction.
ABSTRACT
The reactive extraction of Cu(II) from a sulfate aqueous solution using Cupromex-3302 as a new extractant was investigated using a Lewis cell to reveal the mechanism of extraction. Various affecting parameters such as stirring speed, temperature, interfacial area, extractant concentration, Cu(II) concentration and aqueous phase pH were studied. The rate of copper extraction was found to be directly proportional to the concentrations of Cu(II) and extractant and inversely proportional to the concentration of H+. The extraction rate of Cu(II) increased with an increase in specific interfacial area demonstrated that the rate determining step of Cu(II) extraction by Cupromex-3302 was reactive extraction at the interface. Also, extraction rate increased with increasing the temperature. The activation energy (E) was calculated to be 15.2 kJ/mol. This value suggested that extraction of Cu(II) in this system is controlled by diffusion mechanism.
Keywords: Reaction kinetics; Solvent extraction; Lewis cell technique; Copper; Cupromex-3302.
2
Nomenclature a,b,c
Reaction orders with respect to [Cu2+], [RH] and [H+] respectively
A
Interfacial area through which mass transfer occurs; m2
ΔH
Enthalpy of activation; kJ/mol
ΔS
Entropy of activation; J/mol k
Ea
Activation energy; kJ/mol
F
Mass transfer flux of Cu(II); Kmol/ m2s
h
Planck's constant =6.6252*10-37 kJ s
kB
Boltzman constant =1.38*10-26 kJ/deg
kf
Forward extraction rate constant
mtv
Amount of mass transferred; Kmol
t
Phase contact time; s
T
Absolute temperature; K
R
Universal gas constant
Subscripts aq
Aqueous phase
org
Organic phase
f
Forward extraction
ad
Adsorbed at the liquid−liquid interface
int
Two phase interface
1. Introduction
3
Demand for copper continues to increase because of its different technological applications which include electrical materials, power generation, telecommunications, transportation, petroleum refining and industrial machinery parts [1,2]. Elimination of this metal from different wastes and solutions not only from the point of environmental aspects but also in terms of high value is very important because of the reduction of world’s high grade resources and metals high prices [3]. There is a strong tendency to research and develop the new technologies for copper extraction such as hydrometallurgical methods from the standpoints of environmental protection and resource recycling which can be competitive with conventional pyrometallurgical processes [4,5]. Nowadays, more than 20% of the world's total copper production is through solvent extraction (SX) as a desirable process for metal winning from the viewpoints of natural resources and energy conservation [5,6]. Hydroxyoximes have been the most important and applicable extractants for copper extraction among other types. Today modified aldoximes and aldoxime–ketoxime mixtures are the most widely used copper extractant systems [3, 6-13].
Kinetic investigations are of major importance for the optimization and control of extraction processes to reveal the mechanism of the extraction process [14,15]. Finding methods to improve the extraction rate via the investigation on kinetics is interesting. In addition, design of commercial solvent extraction process needs detailed and exact information about extraction kinetics [15].
Several techniques for studying metal extraction kinetics have been developed such as shake out method, [16] rotating diffusion cell, [17] Hahn cell (with a constant interfacial area non stirred cell), [18,19] single drop (falling/rising), [14,20] the AKUFVE apparatus (highly stirred tank),
4
[21] constant interfacial area stirred (Lewis) cell [15,22-26] and attenuated total reflection spectroscopy (ATR) [27].
Unfortunately, all these techniques have some disadvantages along with their advantages. Moreover, extraction mechanism sometimes shows different results due to the differences in experimental technique and concentration of reactants [15]. For example, shakeout method and the AKUFVE apparatus are now abolished due to unknown interfacial area involved. The Hahn cell is only applicable for very fast reactions. The application of the rotating diffusion cell is also limited in use because of complicated construction and expensive accessories [20].
Among mentioned methods Lewis cell with a constant interfacial area stirred cell and the single drop apparatus are easy to construct and permit the interfacial area to be calculated easily whereas in Lewis cell the stirring speed can be varied in a wide range. The major limitation of Lewis cell is that the interfacial turbulence is not well defined and varies with equipment. Nevertheless, reproducible data can be obtained by using well-designed equipment and careful operation [14, 15, 22-26].
One of the new commercial hydroxyoxime extractants for copper extraction is developed by SNF FLOMIN with trade name Cupromex-3302. This extractant was proved to be promising for copper separation [28]. Cupromex extractants are based on familiar chemistries which are highly-selective in removing a wide range of Cu concentration at various levels of acidity. According to the above description and considering notable characteristics such as being inexpensive and available, Cupromex-3302 has been used in this work.
5
In the present study, the effect of various parameters on kinetic features of copper extraction with the new extractant Cupromex-3302 applying Lewis cell were systematically investigated. Findings of this work would be useful to study the contrast between the two phenomena of mass transfer and reaction rate and proponed the exact kinetic equation for the mentioned system. This study is very important for a deep understanding of the process, and then for selection, design of the extraction equipments and for a reliable scale-up of the process.
It is worth mentioning that one of the goals we investigate the copper extraction is applying the extraction columns such as rotating disc contactor (RDC) and pulsed columns. Performance evaluation of extraction columns in the copper recovery by new extractants cupromex-3302 in order to enhance the extraction efficiency has been performed and related results are under published. Whereas copper extraction process is accompanied by a chemical reaction, so a careful research to investigate the reaction kinetics and find the exact kinetics equation has been done at this time.
2. Materials and methods
2.1. Chemicals and reagents
The commercial extractants Cupromex-3302 (mixture of 2-hydroxy-5-nonylsalicylaldoxime and TXIB (2,2,4-Trimethylpentanediol diisobutyrate) were purchased from SNF FLOMIN. The extractants were dissolved in commercial kerosene to achieve the required concentration. Kerosene was a product of Tehran refinery, which was colorless and mostly aromatic free. The aqueous working solutions were prepared by dissolving copper sulfate pentahydrate (CuSO4.5H2O, Merck, 6
99.9% purity) in deionized water. The initial copper concentration in aqueous phase and initial concentration of extractant were maintained respectively at 1 g/L and 10% (v/v).
2.2. Analytical methods
The copper concentration in aqueous solutions was analyzed by atomic absorption spectrometry (Perkin Elmer-AAnalyst 400). The aqueous phase pH measurement was done using a Lutron pH201 pH meter calibrated daily with standard buffer solutions. The pH of aqueous solutions was adjusted by adding dilute H2SO4 (Merck, 99.9% purity).
2.3. Procedure with Lewis cell
The extraction rate of Cu(II) was measured using a constant interface stirred cell (Lewis cell) that construction of it as well as the working procedure is similar to that reported in the literature [23,29].
The characteristics of the Lewis cell used in the experiments are presented in Table 1. It consists of a cylindrical jacketed glass vessel having two flat-blade paddles in each phase, which allows the equal individual mixing of each phase without disturbing the interface. Variation of the interfacial area has been performed with putting the rings with the variable inner surfaces that produced the different interfacial areas.
Table 1.
Identical aliquots (100 mL) of the aqueous phase solution containing Cu(II) ions at a desired pH and organic phase containing Cupromex-3302 were introduced into the cell with minimum disturbance of the interface. The stirring speed was kept to be in range of 100-700 rpm with 7
neglecting disturbance of the interface by waves. After a predetermined time, 3 mL of the aqueous phase was withdrawn from the cell for analysis. The amount of copper transferred into the organic phase was estimated from the copper content in the liquid phase. In most of the experiments, the interfacial area was kept at 7.1 cm2 to evaluate interfacial area. Change of interfacial area was done by setting circular rings within the cell where the interface is formed. All experiments were carried out at 298 K, unless for tests related to evaluating temperature effects.
2.4. Method of determining of reaction rate
Following stoichiometric equation is used to describe the extraction reaction of Cu(II) by Cupromex-3302 that is a salicylaldoxime derivative [6,7]. + 2RH(org) + Cu2+ (aq) ↔ R 2 Cu(org) + 2H(aq)
(1)
Where RH is the extractant, R2Cu is the complex in the organic phase and the subscripts aq and org refer to aqueous and organic phases, respectively [6].
At the initial contact time, concentration of the complex in the organic phase was low and the reaction was far away from equilibrium, so the reverse reaction was considered negligible. Concentration of the reactant species at the reaction sites is a significant parameter on kinetics of the metal extraction [30].
Rate of liquid- liquid extraction of a metal ion by an acidic extractant like a heterogeneous system depends on the interfacial area, the concentration of the reactants involved and temperature. The extraction rate of Cu(II) at constant temperature can be expressed as:
8
d[Cu2+ ]a d[Cu2+ ]o rate = − ( )=( ) = k f A[Cu2+ ]a [RH]b [H + ]c dt dt
(2)
Where the subscripts (a), (o) represent the aqueous, organic phase, kf is the forward extraction rate constant and a, b, c are the reaction orders with respect to [Cu2+], [RH] and [H+], respectively. Flux (F) method is applied for rate analysis. The average mass flux (F) through the liquid–liquid interface can be measured by dividing the amount of copper transferred (Kmol) into the organic phase to the product of area (m2) and time of extraction (s). So: F = mt v ⁄Adt
(3)
Which is proportional to [Cu2+]a, [RH]b and [H+]c as shown below: F = k f [Cu2+ ]a [RH]b [H + ]c
(4)
With taking logarithm, Eq. (4) can be rewritten as: log(F) = log(k f ) + a × log ([Cu2+ ]) + b × log([RH]) + c × log([H + ])
(5)
That can be used to find the orders a, b and c and the rate constant in such a way that by keeping two variable concentrations constant, the order with respect to the third variable concentration can be obtained from the slope of the log–log plot of F functions to third variable concentration. The value of kf can be obtained from the intercept of the plots. It is worth noting that the rate of mass transfer is proportional to interfacial area but the flux is independent of interfacial area. Therefore, for investigating the kinetics of the liquid–liquid extraction of metal ions, the flux method is premiere because no interfacial area specification is necessary to represent the experimental data [19].
9
It should be mentioned that all reported results has been plotted according to the average values and repeatability of experiments. The uncertainties of the tests (including instrument and personal errors) have been 1-4% that is shown in Fig. 1 as an example. 3. Results and discussion
3.1. Effect of stirring speed
In Lewis cell technique, the basic criterion to distinguish the controlling mechanism of extraction is the dependency of the extraction rate on the stirring speed of the two phases [26]. Generally, the rate controlling mechanisms of the extraction include three basic regimes: diffusional regime, chemical reaction regime and mixed regime. In diffusional regime the extraction rate is controlled by the mass transfer. On the other hand, the rate of extraction increases with increasing the stirring speed [26]. But in the chemical reaction regime the kinetics of extraction is dependent on chemical reaction rather than mass transfer. Indeed there is nearly no effect on the extraction rate governed by chemical reaction. For mixed regime, the mass transfer and chemical reaction control the extraction rate together [15].
In a solvent extraction system, the process of extraction consists mainly of the transport of chemical specious from aqueous phase into the organic phase through the interface. Therefore, the nature of the interface and the interfacial phenomena must be greatly considered when studying solvent extraction reactions [31]. It is quite conceivable that changing the stirring speed may cause the change of concentration gradient across a diffusion layer between the bulk solution and interface and effects on transfer rates [15].
10
On this basis stirring speed as the most important parameter determining the mechanism of copper extraction was studied early in the range of 100−700 rpm, the maximum stirrer speed is just chosen not to disturb the interface.
The plot of copper extraction values vs. stirring speed is shown in Fig. 1. As shown, the increase in the stirring speed of the two phases increases the extraction rate in a diffusion controlled systems due to reduction of resistant and stagnant diffusion layers till it reaches a plateau region 500–700 rpm. In this region the rate remains constant with further increase in the stirring speed. So in this region, the effect of diffusion is minimized and the extraction process is assumed to be mainly controlled by chemical reactions in the bulk phase or at the interface.
Figure 1.
3.2. Effect of interfacial area
The chemical reaction can occur either in the bulk phases or at the interface. When the chemical reaction occurs in the bulk, the rate of extraction is independent of the interfacial area. In contrast, the extraction rate increases with the increase in the interfacial area when the chemical reaction occurs at the interface [32]. The effect of the interfacial area was studied as the most important parameter to distinguish chemical reaction taking place in the bulk phase or at the interface. Experiments were carried out by changing interfacial area in the range of 3.8−13.1 cm2 while keeping constant the volume of each phase at 100 ml. The plot of the extraction rate of copper vs. the interfacial area is shown in Fig. 2. This figure shows a straight line through the origin of axes demonstrates an interfacial reaction and it is observed that the reaction rate is linearly proportional to the interfacial area.
11
Figure 2.
3.3. Effect of temperature
The effect of temperature on the extraction of copper ions from aqueous solutions was investigated in the range of 298–338 K, and the results are presented in Fig. 3. It was observed that the extraction increases with the increase in temperature throughout the studied temperature range.
The plot of log F vs. 1000/T yields a straight line with slope -0.79. The activation energy was calculated from the slope of this line and determined to be 15.2 kJ/mol according to the Arrhenius equation: −E
a log F = 2.303RT
(6)
Where R is the universal gas constant that equals to 8.3145 J/K.mol [23]. It should be noted that value of F is considered as the reaction rate value in the equation 6 (Arrhenius equation).
The activation energy represents the temperature effects on extraction rate. Generally, this parameter in diffusion control process is less than where the reaction rate is controlled by chemical reaction and in the former case does not usually exceed 20.9 kJ/mol [23,25]. The calculated value of activation energy is within the value of diffusion controlled systems. It justifies that the extraction of Cu(II) in this system is controlled by diffusion mechanism.
Figure 3.
The enthalpy and entropy of activation is calculated from activated complex theory by the following equation: 12
k=
RT ∆S −∆H e R e RT Nh
(7)
Where N is the Avogadro's number (6.022×1023 molecules mol−1), h is the Plank's constant (6.626×10−34 J s) and kB (Boltzman constant) is used instead of R/N [23].
Fig. 4 shows the log Fh/kBt vs. 1000/T plot for a set of experiments in the same temperature range that fall on a straight line. From the slope and intercept of this line ∆H and ∆S values are calculated 12.6 kJ/mol and -268 J/mol.K respectively.
Figure 4.
3.4. Effect of Cu(II) concentration
In Fig.5 the influence of the initial copper concentration in aqueous phase on the extraction rate of Cu(II) by Cuppromex-3302 is illustrated while extractant concentration was kept at 10%(v/v). It is found that extraction percentage increases with the increase in copper concentration. The plot of log extraction rate vs log [Cu(II)] yields a line with a slope of a , the order for Cu(II) in kinetic relation. The slope of linear regression line, namely the value of a in Eq. (2), was determined to be 0.97.
The slope of almost unity indicates that the rate of copper extraction from aqueous to organic phase is directly proportional to the copper concentration. Reduction of rate order at high concentration of Cu(II) can be related to change of adsorption rate of saturated complexes at interface. This suggested that the diffusion mechanism at higher concentrations of Cu(II) is predominant.
Figure 5.
13
3.5. Effect of Cupromex-3302 concentration
Similar to previous section, a set of experiments were performed to change the initial concentration of Cupromex-3302 in the range of (5-12% v/v) while keeping the initial copper concentration at 1 g/L. The variation of extraction rates with different Cupromex-3302 concentrations is shown in Fig.6. It could be interpreted that the rate of copper transfer to organic phase by cupromex-3302 is directly proportional to the extractant concentration in the organic phase.
From the slope of given line, the value of order b in reaction Eq. (2) is determined to be 1.01. The nearly first order with respect to Cupromex-3302 concentration is consistent to the interfacial reactions with saturation at the interface.
Figure 6.
3.6. Effect of aqueous pH The influence of H+ concentration on the rate of extraction by Cupromex-3302 is shown in Fig.7. It was found that the plot of log extraction rate vs. Log [H+] gives slope of -0.78 that is equals to order c in reaction Eq. (2). The rate is inversely proportional to the H+ concentration in the aqueous phase. The low extraction rate is achieved in high acidity because the reaction is shifted preferentially in the back extraction reaction which is equivalent to stripping of the loaded organic phase.
Figure 7.
3.7. Reaction rate and mechanism
14
From the intercepts of the curves in Figs. 5 to 7, the average log (kf) value evaluated is -3.44 and the rate of copper extraction from sulphate solution by Cupromex-3302 can be expressed as following relation: r = 3.63 × 10−4 [Cu]0.97 [H + ]−0.78 [RH]1.01
(8)
Based on several researchers' findings, if the reaction takes place at the interface involving the adsorbed oxime molecules, it can be described by the following equations [33]: 2RHorg ↔ (RH)2,org
(9)
RHorg ↔ RHad ↔ RHaq
(10)
+ + Cu2+ aq + RHad ↔ CuR ad + Haq
(11)
+ CuR+ad + RHint ↔ CuR 2−ad + Haq
(12)
CuR 2−ad ↔ CuR 2−org
(13)
At first, dimerization of hydroxime molecules at the organic phase occurs with the first reaction. Also, the equilibrium reaction between monomeric hydroxime molecules adsorbed at the interface (because of their interfacial activity) and the molecules present in the organic and the aqueous phase is a fast step. Adsorbed reactant molecules react with the copper ions at the interface of two phases. The concentration of these adsorbed reactant molecules with their hydrophilic and chemically active groups are much higher than concentration of molecules in both phases. Above summary of reaction mechanism have been explained briefly just to make it clear for the readers. This method has not been utilized to obtain the empirical order form of the final kinetic equation. 15
Being charged and partially hydrated causes to increase the hydrophilicity of adsorbed molecules and diffuse to the aqueous phase film. This leads to react with another reactant molecule in the aqueous phase that is the slowest step. Then the neutral and dehydrated complex leaves the interface rapidly by other reactant molecules. At higher concentration of reactant in the organic phase the interface is saturated with adsorbed molecules and concentration of them is constant. Therefore the reaction order 1 in Eq. 8 regarding to concentration of extractant is justified.
Because of applying the cupromex-3302 extractant in kinetically investigation of copper extraction for the first time, comparison of the present study with other existing literature have not been done due
to
copper
recovery
from
different
solutions
with
different
conditions.
4. Conclusions
In this research, the effect of operating variables on the extraction rate of copper from sulfate solution with new extractant Cupromex-3302 in the Lewis cell was studied. The rate equation for the mentioned system was obtained by changing different parameters such as concentration of Cu(II), Cupromex-3302, and H+ while keeping other variables constant. It was found that reactive extraction of copper by Cupromex-3302 was a diffusion controlled system with a change in interfacial area.
The effect of chemical reaction resistance on extraction rate was negligible when the stirring speed of two phases was kept at 300 rpm. Extraction rate increased with an increase in temperature. The activation energy (E) was calculated to be 15.2 kJ/mol.
References 16
[1] L. R. Lemos, I. J. B. Santos, G. D. Rodrigues, L. H. M. Silva, M. C. H. Silva, Copper recovery from ore by liquid–liquid extraction using aqueous two-phase system, , Journal of Hazardous Materials 237– 238 (2012) 209– 214. [2] S. Meterfi, A.H. Meniai, M. Chikhi, Elimination of Cu(II) from Aqueous Solutions by Liquidliquid Extraction. Test of sodium diethyldithiocarbamate (SDDT) as an Extracting Agent. Energy Procedia (2012) 18:1165–1174. [3] E. Bidari, M. Irannejad, M. Gharabaghi, Solvent extraction recovery and separation of cadmium and copper from sulphate solution, Journal of Environmental Chemical Engineering 1 (2013) 1269–1274. [4] L.R. Lemos, I.J.B. Santos, G.D. Rodrigues, L.H.M. Silva, M.C.H. Silva, Copper recovery from ore by liquid–liquid extraction using aqueous two-phase system. Journal of Hazardous Materials (2012) 237– 238:209– 214. [5] H. Asghari, M.S. Safarzadeh, G. Asghari, D. Moradkham, The effect of impurities on the extraction of copper from sulfate medium using LIX-984N in kerosene. Russian Journal of NonFerrous Metals (2009) 50:89–96. [6] S. Rao, N.B. Devi, B.R. Reddy, Solvent extraction of copper from sulphate medium using MOC 45 as extractant. Hydrometallurgy (2000) 57:269–275. [7] Sh. Agarwal, A.E. Ferreira, S.M.C. Santos, M.T.A. Reis, M.R.C. Ismael, M.J.N. Correia, J.M.R. Carvalho, Separation and recovery of copper from zinc leach liquor by solvent extraction using Acorga M5640, International Journal of Mineral Processing (2010) 97:85–91.
17
[8] J. Szymanowski, E. Krzyzanowska, R. Cierpiszewski, K. Prochaska, Equilibrium and kinetics of copper extraction from acidic sulfate solutions with isome 1-(2'-Hydroxy-5'-alkyl-phenyl)-I – alkanone (E)-oximes. Journal of Radioanalytical and Nuclear Chemistry (1991) 150 (2): 335-350. [9] A. Deep, P. Kumar, J.M.R. Carvalho, Recovery of copper from zinc leaching liquor using ACORGA M5640. Separation and Purification Technology (2010) 76:21–25. [10] Sh. Agarwal, M.T.A. Reis, M.R.C. Ismael, M.J.N. Correia, J.M.R. Carvalho, Modeling of the extraction equilibrium of copper from sulfate solutions with ACORGA M5640. Solvent Extraction and Ion Exchange (2012) 30:536–551. [11] F.J. Alguacil, A. Cobo, M. Alonso, Copper separation from nitrate/nitric acid media using Acorga M5640 extractant Part I: solvent extraction study. Chemical Engineering Journal (2002) 85:259–263. [12] H. Asghari, M.S. Safarzadeh, G. Asghari, G. Moradkham, The effect of impurities on the extraction of copper from sulfate medium using LIX-984N in kerosene. Russian Journal of NonFerrous Metals (2009) 50:89–96. [13] K. Ochromowicz, T. Chmielewski, Solvent extraction of copper (II) from concentrated leach liquors. Physicochem. Probl. Miner. Process (2013) 49:357-367. [14] N.E. El-Hefny, S.I. El-Dessouky, Equilibrium and kinetic studies on the extraction of gadolinium (III) from nitrate medium by di-2-ethylhexylphosphoric acid in kerosene using a single drop technique. J Chem. Technol. Biotechnol. (2006) 81:394-400.
18
[15] P. Xing, Ch. Wang, Sh. Xu, Zh. Ju, Kinetics of cobalt(II) extraction from sulfate aqueous solution by sodium salt of di-decylphosphinic acid (DDPA). Trans. Nonferrous Met. Soc. China (2013) 23:517−523. [16] B. Wionczyk, Kinetic modeling of chromium (III) extraction with ALIQUAT-336 from alkaline aqueoussolutions containing chlorides. Physicochem. Probl. Miner. Process. (2013) 49(2):587−605. [17] M.A. Hughes, R.K. Biswas, The kinetics of manganese (II) extraction in the acidic sulphateD2EHPA-n-hexane system using the rotating diffusion cell technique. Hydrometallurgy (1993) 32:209-221. [18] R.K. Biswas, M.G.K. Mondal, Kinetics of Mn (II) extraction by D2EHPA. Hydrometallurgy (2003) 69:145–156. [19] R.K. Biswas, M.A. Habib, M.G.K. Mondal, Kinetics of stripping of VO–D2EHPA complex from toluene phase by aqueous sulphate–acetate solution. Comparison of Lewis and Hahn cells. Hydrometallurgy (2004) 73:257–267. [20] R.K. Biswas, M.R. Ali, A.K. Karmakar, M. Kamruzzaman, Kinetics of solvent extraction of copper(II) by Bis-(2, 4, 4-Trimethylpentyl) phosphonic acid using the single drop technique. Chem. Eng. Technol. (2007) 30(6):774–781. [21] K.O. Ipinmoroti, M.A. Hughes, The mechanism of vanadium (IV) extraction in a chemical kinetic controlled regime. Hydrometallurgy (1990) 24:255-262.
19
[22] K. Inoue, M. Goya, Taniguchi M. Extraction equilibrium and extraction kinetics of nickel from aqueous ammonium nitrate solution with vatic 10 in n-hexane. Hydrometallurgy (1984) 13:155-167. [23] S. Javanshir, M. Abdollahy, H. Abolghasemi, A. Khodadadi Darban, Kinetics of Au (III) extraction by DBC from hydrochloric solution using Lewis cell. International Journal of Mineral Processing (2011) 98:42-47. [24] X. Yang, X. Wang, Ch. Wei, Sh. Zheng, Q. Sun, D. Wang, Extraction kinetics of tantalum by MIBK from pulp using Lewis cell. Hydrometallurgy (2013) 131-132:34–39. [25] N.E. El-Hefny, Kinetics and mechanism of extraction and stripping of neodymium using a Lewis cell. Chemical Engineering and Processing (2007) 46:623–629. [26] N.E. El-Hefny, Kinetics and mechanism of extraction of Cu(II) by CYANEX 302 from nitrate medium and oxidative stripping of Cu(I) using Lewis cell technique. Chemical Engineering and Processing (2010) 49:84–90. [27] J.K. Mcculloch, J.M. Perera, E.D. Kelly, L.R. White, G.W. Stevens, F. Grieser, A Kinetic Study of Copper Ion Extraction by Kelex 100 at a Heptane–Water Interface. Journal of Colloid and Interface Science (1996) 184:406–413. [28] B.M. Torres, M.M. Torres, Q.C. Salgado, P.H. Bravo, O.J. Fernández, CuPRO-MEX extractants as equivalent alternatives for copper recovery. IN: Copper International Conference; (2013).
20
[29] R.K. Biswas, M.A. Habib, M.R. Ali, M.Z. Haque, Kinetics of Mn (II) extraction in the acidic chloride–D2EHPA–kerosene system using the constant interfacial area stirred cell technique. Pak. J. Sci. Ind. Res. (1998) 41:121–127. [30] A. Irabien, I. Ortiz, E.S. Perez de Ortiz, Kinetics of metal extraction: Model discrimination and parameter estimation. J. Chem. Eng. Process (1990) 27(1):13−18. [31] H.F. Aly, J.A. Daoud, Over view on extraction kinetics of metal adducts. Journal of Radioanalytical and Nuclear Chemistry (1996) 208(1):47-74. [32] J. Rydberg, M. Cox, C. Musikas, G.R. Choppin, Principles and Practices of Solvent Extraction. New York: Marcel Dekker Inc. (1992). [33] J. Szymanowski, Hydroxyoximes and Copper Hydrometallurgy. London: CRC Press (1993).
21
Figure captions: Fig. 1. Effect of stirring speed on initial extraction rate, [Cu2+](aq-ini)=1 g/L, [Cupromex-3302]= 10 (v/v), interfacial area= 7.1 cm2, aqueous phase pH=1.8 and T= 298 K.
Fig. 2. Effect of interfacial area on initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and T= 298 K.
Fig. 3. Effect of temperature on initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 4. Effect of temperature on log (Fh/kBT), initial extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm, aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 5. Effect of [Cu2+] on extraction rate, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 6. Effect of [Cupromex-3302] on extraction rate, [Cu2+](aq-ini)= 1 g/L, stirring speed= 300 rpm aqueous phase pH=1.8 and interfacial area= 7.1 cm2.
Fig. 7. Effect of [H+] on extraction rate, [Cu2+](aq-ini)= 1 g/L, [Cupromex-3302]= 10 (v/v), stirring speed= 300 rpm and interfacial area=7.1 cm2.
22
12
(10-4 mol / L.min)
Copper extraction
10 8 6 4 2 0 0
100
200
300 400 500 Stirring speed (rpm)
Figure 1.
23
600
700
800
8
6
-4
(10 mol / L.min)
Copper extraction rate
7
5 4 3 2 1 0 0
2
4
6
8
10
12 2
Specific interfacial area (cm )
Figure 2.
24
14
-3.5 -3.6 -3.7
y = -0.7937x - 1.5879 R² = 0.947
Log ( F )
-3.8 -3.9 -4 -4.1 -4.2 -4.3 -4.4 -4.5 3
3.05
3.1
3.15
3.2
3.25
103 K/T
Figure 3.
25
3.3
3.35
3.4
-16.8
Log ( Fh / kT )
-16.85
y = -0.658x - 14.836 R² = 0.9251
-16.9 -16.95 -17 -17.05 -17.1
3
3.05
3.1
3.15
3.2 103 K/T
3.25
Figure 4.
26
3.3
3.35
3.4
-3.2
Log ( F )
-3.4 y = 0.9706x - 2.5383 R² = 0.9752
-3.6 -3.8 -4 -4.2 -4.4 -2
-1.7
-1.4 -1.1 Log [Cu(II)]
Figure 5.
27
-0.8
-0.5
-3.8 -3.9 -4 y = 1.0136x - 3.7781 R² = 0.9916
Log ( F )
-4.1 -4.2 -4.3 -4.4 -4.5 -4.6 -0.9
-0.7
-0.5
-0.3
Log [Cupromex-3302]
Figure 6.
28
-0.1
-4 y = -0.786x - 5.6902 R² = 0.9804
-4.2
Log ( F )
-4.4 -4.6 -4.8 -5 -5.2 -2.5
-2.2
-1.9
-1.6 Log [H+]
-1.3
Figure 7.
29
-1
Tables Table 1. Characteristics of the Lewis cell Internal
Volume of each
Rings
Blades
section
diameters
distance
100 mL
2, 3, 4 cm
5.5 cm
Height of cell diameter 4.8 cm
11 cm
30