- Email: [email protected]
Ionic pumping in a cadmium, ortho phosphoric acid-phosphate tributyl-ammonium carbonate system: Chemical study of compartments
Desalination 206 (2007) 554–559
Ionic pumping in a cadmium, ortho phosphoric acid-phosphate tributyl-ammonium carbonate system: Chemical study of compartments F. Hassaine-Sadi*, H. Bouchabou Laboratory of Electrochemistry–Corrosion, Metallurgy and Inorganic Chemistry, Chemistry Faculty, University of Sciences and Technology Houari Boumediene, BP N° 32 El-alia, Bab-Ezzouar, Algiers, Algeria Tel. el/Fax : +213 (21) 24 73 11; email: [email protected] Received 30 May 2006; Accepted 5 June 2006
Abstract An ionic pump has been devised thanks to liquid–liquid extraction/reextraction where the extraction compartment and the reextraction compartment are put in contact with one another through the membrane composed of a mediator diluted in kerosene. We have applied this process to a system of cadmium, ortho phosphoric acid–phosphate tributyl, kerosene–ammonium carbonate. Interesting performances have been realized for diluted solutions (100 ppm). The study chemical parameters allowed to obtain the variables giving the extraction and reextraction efficiencies optimum. For the extraction compartment, the competition of orthophosphoric acid has been found. The study of the chemical variables of the reextraction compartment has demonstred that the nature and the concentration of a desactivation cosolute is very important and determinant for the formation of the non extractibles species. A chemical modelization has allowed to identify the extraction mecanisms. The classical behaviour obtained in agitated surroungings has been found again. The membrane can work thanks to the “activation” by the cosolute of the transportor at one interface and to the “deactivation” at other interface, both of these mechanisms of the active transport creating real ionic pumping. Keywords: Ionic pumping; Cadmium; Active transport mechanisms; Contra-transport; Coupling
*Corresponding author.
Presented at the EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21–25 May 2006. 0011-9164/07/$– See front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.desal.2006.06.009
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
555
1. Introduction Environment and pollution, these two words which evoked a long time in the spirits of the contradictory concepts, seem forever dependent. Humanity has been for a few years in front of an alarming growth of the water pollution by the organic matter, the toxic pesticides, detergents, substances, the carcinogenic hydrocarbons, substances, heavy metals (Pb, Hg, Zn , Cd) and sees to worsen the difficulties of the drinking water supply. Cadmium is a metal of a silver plated white, shining but which tarnishes, it is malleable and ductile, it almost always appears in a divalent state. It is a rather rare element, it is distributed uniformly in the earth’s crust, or its average concentration would be 0.15 to 0.2 mg.kg [1]. It is used in various industries: hydrometallurgy, in the manufacture of the pigments, of textiles, plastics stabilized with cadmium or nickelcadmium batteries [2]. Within the framework of our work we were interested in the liquid–liquid extraction of cadmium by phosphate tributyl starting from an orthophosphoric acid medium. The study of the variables of extraction made it possible to determine some chemical parameters giving of the outputs of optimum extraction. A chemical modelling can identify the mechanism of extraction.
2. Experimental The scheme of the extraction/reextraction combined [3,4] is drawn on Fig. 1. The first great interest of such disposition is also to allow processing of little clarified solutions and to get benefit from gravity phenomena which allow the interface to remain intact. The unclogging problems will thus be reduced considerably. The second great interest is to avoid the regeneration of the solvent wich is intact at the end of operations.
Fig. 1. Scheme of combined extraction/reextraction. (a) extraction compartment. (b) reextraction compartment. (c) organic phase: membrane.
The aqueous phases are realized from orthophosphoric acid at 95% and from solutions of cadmium (CdSO4.2H2O) (Merck) obtained by dissolving in distilled water. We have set the initial concentration of the feeding phase at 0.1 M in Cd(II). The total concentration in phosphates ions when it is maintained constant by addition of sodium (Merck). The organic phase is made of an extractant phosphate tributyl in a kerosene diluent. Regular samples have been made with the help of pipettes (2 ml) from aqueous solutions. The tests have been realized at room temperature. We have determined the cadmium concentrations in the feeding phase. The dosings have been made by atomic emission spectroscopy with plasma induced by high frequency or plasma flare (ICP) [5–7].
3. Results and discussion Choice of a system: extraction by solvatation [8,9]: In order to study the physicochemical behaviour of the reactor, we have chosen system Extraction compartment/organic phase/reextraction compartment Cd 2+ , H + , PO3-4 Interface I
/
TBP
/
(NH 4 ) 2 CO3
Interface II
Every compartment and every interface were made the object of the examination. We have computed the extraction efficiencies (amount of cadmium related to the initial amount
556
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
Fig. 2. Influence of the concentration in orthophosphoric acid. Extraction compartment: [Cd]0 = 100 ppm.
remaining in the extraction compartment) and the reextraction efficiencies (amount of cadmium in the reextraction compartment related to initial cadmium amount). 3.1. Influence of the concentration in H3PO4 Fig. 2 presents the results obtained. The efficiency of the extraction is of the order of 60% in Cd for a concentration H3PO4 2N. 3.2. Influence of the concentration in TBP We have represented the variation of the extraction and reextraction efficiences as a function of the concentrations in TBP. Fig. 3 indicates the results obtained. We find back the influence of the concentration of the solvatation agent. For the weak concentrations in phosphate tributyl, we observe a slower exaltation of the efficiency of the cadmium extraction. Note that both compartments have a symmetric behavior.
3.3. Influence in ammonium carbonate of the concentration of the reextraction phase We have studied the influence of the concentration of (NH4)2CO3 of the reextraction phase on the reextraction efficiencies. Fig. 4 presents the results and illustrates the increase of the cadmium reextracted amount when the ammonium carbonate concentration increases. One recovers the symmetry of the behaviour of the two compartments with weaker outputs. These values cannot be explained except by the intervention of the NH4+ cation. It implies the influence of one cation of the compartment backwashing at interfaces it of the compartment extraction. This means that the molecular (NH4)2 HPO4 types are transferred and limit the extraction. We are in presence of a transport, counter-transport.
3.4. Mechanisms of extraction We used for this system the traditional methods of linearization of the curves of extrac-
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
557
Fig. 3. Influence of the concentration in the phosphate tributyl.
Fig. 4. Influence of the concentration in ammonium carbonate.
tion. We calculated for variable times of the curves log D = f (log [TBP]T). Slopes observed in Fig. 5 are in conformity with those known heart the traditional.
3.4.1. Extraction compartment (a) Extraction of the cadmium(II) by the phosphate tributyl (TBP):
558
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
3.4.2. Reextraction compartment The ion cadmium (II) is re-extracted according to the equation
( CdHPO4 ) , ( TBP )
+ 3 ( NH 4 )2 CO3
⇔ Cd ( CO3 )3 + 4NH +4 + TBP 4−
(3)
+ ( NH 4 )2 HPO 4 Fig. 5. Variation of log D according to the logarithm of the total concentration phosphate tributyl. Extraction compartment: [H3PO4] = 30%. Membrane: [TBP] = 0.1 M in the kerosene.
CdHPO 4 + TBP ⇔
( CdHPO4 ) , ( TBP ) (1)
(b) The orthophosphoric acid presents the competitive following reaction:
H 3O + , H 2 PO-4 + TBP ⇔ ⎡⎣ H 3O + , H 2 PO-4 , TOPO ⎤⎦
(2)
3.5. Mechanismes of transport [9] The mechanismes of active transport are represented in Fig. 6. The diffusion of the cadmium ions Cd2+ by the activation of cosolute HPO42! at interface I, we have the migration of complex formed across the membrane by active transport and we have the deactivation of the molecular complex at interface II. The diffusion at interface II of cation NH4+ which is affected in a sense opposed that it is does by the countertransport of the two ammonium ions at interface I.
Fig. 6. Schematic representation of the mechanisms of transport.
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
3.6. Foreseeable pump type — complex “ionic” pump This puts in play the interfaces I and II of the total reactions. It is the case of the system
Cd 2+ , H + , PO3-4 / TBP / NH 4+ , CO3-mechanism
mechanism
solvatant
anion exchanges
At interface I, the total reaction maintains the concentration of the constant source and the “pumping” of the extractible species; at interface II, the total reaction maintains the elevated and constant concentration pressure gradient. It is about a real activation of the system that assures a forced convection and a real “chemical” agitation thanks to the constant renewal of interface II. The nature is completely different of the forbidden backwashing mechanism the existence of balances at interfaces II: backflow check valve.
4. Conclusions The chemical variable survey permitted to determine the chemical parameters giving the extraction efficiencies and optimum backwashing. The competition the mechanism of extraction of the orthophosphoric acid has been recovered. The compartment backwashing destined to contain aqueous solutions of ammonium, cosoluté of “deactivation”. The results showed a total asymmetry of the behaviour of the two compartments. The working of the pump is disrupted by the formation likely of transferable molecules of ammonium. The study of the chemical parameters of the compartment backwashing showed that the choice and concentration of the deactivation cosolute are determining; so the anion will permit
559
the formation of nonextractibles and the cation will permit the counter-transportation, positive coupling. We could define the type of “complex” ionic pump when the static system operates grace a transportation, counter-transportation, positive coupling, and in other cases where one of the constants of backwashing extraction or/and is non-quantitative, we are then in the presence of a transportation, counter-transportation, negative coupling. The chemical modelizations have allowed the phenomenological characterisation of the combination that we have conceived and studied. We have proposed a complex ionic pump allowing the transfer of several species.
References [1] V. Hiatt and J.E. Huff, Int. J. Environ. Stud., 7 (1975) 277. [2] M. Fleischer and Coll, Environ. Health Perspect., 7 (1974) 253. [3] L. Sadoun and F. Hassaine-Sadi, Purification-concentration process. Desalination, 167 (2004) 159. [4] F. Hassaine-Sadi and L. Sadoun, Desalination,187 (2005) 17. [5] M.J.F. Leroy and E.M.M. Sutter, An. Fals. Exp. Chim., 718(756) (1977) 400. [6] G. Charlot, The Analytical Chemistry Method: Quantitative Analysis, Mass, Paris, 1961. [7] P. Fremaux and G. Cattin, Analytical Chemistry, 50(1) (1968) 34–39. [8] G.M. Ritcey and A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984. [9] G.M. Ritcey and A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy, Part II, Elsevier, Amsterdam, 1989. [10] F. Hassaine-Sadi, A. Benhassaine and H. Ait-Amar, Transportation of the biological membrane process to the treatments of low-grade metal effluents. Physical modelling of an ionic pump. Transport Membrane Mechanisms, Entropie, 230 (2001) 31–34.
Ionic pumping in a cadmium, ortho phosphoric acid-phosphate tributyl-ammonium carbonate system: Chemical study of compartments F. Hassaine-Sadi*, H. Bouchabou Laboratory of Electrochemistry–Corrosion, Metallurgy and Inorganic Chemistry, Chemistry Faculty, University of Sciences and Technology Houari Boumediene, BP N° 32 El-alia, Bab-Ezzouar, Algiers, Algeria Tel. el/Fax : +213 (21) 24 73 11; email: [email protected] Received 30 May 2006; Accepted 5 June 2006
Abstract An ionic pump has been devised thanks to liquid–liquid extraction/reextraction where the extraction compartment and the reextraction compartment are put in contact with one another through the membrane composed of a mediator diluted in kerosene. We have applied this process to a system of cadmium, ortho phosphoric acid–phosphate tributyl, kerosene–ammonium carbonate. Interesting performances have been realized for diluted solutions (100 ppm). The study chemical parameters allowed to obtain the variables giving the extraction and reextraction efficiencies optimum. For the extraction compartment, the competition of orthophosphoric acid has been found. The study of the chemical variables of the reextraction compartment has demonstred that the nature and the concentration of a desactivation cosolute is very important and determinant for the formation of the non extractibles species. A chemical modelization has allowed to identify the extraction mecanisms. The classical behaviour obtained in agitated surroungings has been found again. The membrane can work thanks to the “activation” by the cosolute of the transportor at one interface and to the “deactivation” at other interface, both of these mechanisms of the active transport creating real ionic pumping. Keywords: Ionic pumping; Cadmium; Active transport mechanisms; Contra-transport; Coupling
*Corresponding author.
Presented at the EuroMed 2006 conference on Desalination Strategies in South Mediterranean Countries: Cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean. Sponsored by the European Desalination Society and the University of Montpellier II, Montpellier, France, 21–25 May 2006. 0011-9164/07/$– See front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.desal.2006.06.009
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
555
1. Introduction Environment and pollution, these two words which evoked a long time in the spirits of the contradictory concepts, seem forever dependent. Humanity has been for a few years in front of an alarming growth of the water pollution by the organic matter, the toxic pesticides, detergents, substances, the carcinogenic hydrocarbons, substances, heavy metals (Pb, Hg, Zn , Cd) and sees to worsen the difficulties of the drinking water supply. Cadmium is a metal of a silver plated white, shining but which tarnishes, it is malleable and ductile, it almost always appears in a divalent state. It is a rather rare element, it is distributed uniformly in the earth’s crust, or its average concentration would be 0.15 to 0.2 mg.kg [1]. It is used in various industries: hydrometallurgy, in the manufacture of the pigments, of textiles, plastics stabilized with cadmium or nickelcadmium batteries [2]. Within the framework of our work we were interested in the liquid–liquid extraction of cadmium by phosphate tributyl starting from an orthophosphoric acid medium. The study of the variables of extraction made it possible to determine some chemical parameters giving of the outputs of optimum extraction. A chemical modelling can identify the mechanism of extraction.
2. Experimental The scheme of the extraction/reextraction combined [3,4] is drawn on Fig. 1. The first great interest of such disposition is also to allow processing of little clarified solutions and to get benefit from gravity phenomena which allow the interface to remain intact. The unclogging problems will thus be reduced considerably. The second great interest is to avoid the regeneration of the solvent wich is intact at the end of operations.
Fig. 1. Scheme of combined extraction/reextraction. (a) extraction compartment. (b) reextraction compartment. (c) organic phase: membrane.
The aqueous phases are realized from orthophosphoric acid at 95% and from solutions of cadmium (CdSO4.2H2O) (Merck) obtained by dissolving in distilled water. We have set the initial concentration of the feeding phase at 0.1 M in Cd(II). The total concentration in phosphates ions when it is maintained constant by addition of sodium (Merck). The organic phase is made of an extractant phosphate tributyl in a kerosene diluent. Regular samples have been made with the help of pipettes (2 ml) from aqueous solutions. The tests have been realized at room temperature. We have determined the cadmium concentrations in the feeding phase. The dosings have been made by atomic emission spectroscopy with plasma induced by high frequency or plasma flare (ICP) [5–7].
3. Results and discussion Choice of a system: extraction by solvatation [8,9]: In order to study the physicochemical behaviour of the reactor, we have chosen system Extraction compartment/organic phase/reextraction compartment Cd 2+ , H + , PO3-4 Interface I
/
TBP
/
(NH 4 ) 2 CO3
Interface II
Every compartment and every interface were made the object of the examination. We have computed the extraction efficiencies (amount of cadmium related to the initial amount
556
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
Fig. 2. Influence of the concentration in orthophosphoric acid. Extraction compartment: [Cd]0 = 100 ppm.
remaining in the extraction compartment) and the reextraction efficiencies (amount of cadmium in the reextraction compartment related to initial cadmium amount). 3.1. Influence of the concentration in H3PO4 Fig. 2 presents the results obtained. The efficiency of the extraction is of the order of 60% in Cd for a concentration H3PO4 2N. 3.2. Influence of the concentration in TBP We have represented the variation of the extraction and reextraction efficiences as a function of the concentrations in TBP. Fig. 3 indicates the results obtained. We find back the influence of the concentration of the solvatation agent. For the weak concentrations in phosphate tributyl, we observe a slower exaltation of the efficiency of the cadmium extraction. Note that both compartments have a symmetric behavior.
3.3. Influence in ammonium carbonate of the concentration of the reextraction phase We have studied the influence of the concentration of (NH4)2CO3 of the reextraction phase on the reextraction efficiencies. Fig. 4 presents the results and illustrates the increase of the cadmium reextracted amount when the ammonium carbonate concentration increases. One recovers the symmetry of the behaviour of the two compartments with weaker outputs. These values cannot be explained except by the intervention of the NH4+ cation. It implies the influence of one cation of the compartment backwashing at interfaces it of the compartment extraction. This means that the molecular (NH4)2 HPO4 types are transferred and limit the extraction. We are in presence of a transport, counter-transport.
3.4. Mechanisms of extraction We used for this system the traditional methods of linearization of the curves of extrac-
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
557
Fig. 3. Influence of the concentration in the phosphate tributyl.
Fig. 4. Influence of the concentration in ammonium carbonate.
tion. We calculated for variable times of the curves log D = f (log [TBP]T). Slopes observed in Fig. 5 are in conformity with those known heart the traditional.
3.4.1. Extraction compartment (a) Extraction of the cadmium(II) by the phosphate tributyl (TBP):
558
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
3.4.2. Reextraction compartment The ion cadmium (II) is re-extracted according to the equation
( CdHPO4 ) , ( TBP )
+ 3 ( NH 4 )2 CO3
⇔ Cd ( CO3 )3 + 4NH +4 + TBP 4−
(3)
+ ( NH 4 )2 HPO 4 Fig. 5. Variation of log D according to the logarithm of the total concentration phosphate tributyl. Extraction compartment: [H3PO4] = 30%. Membrane: [TBP] = 0.1 M in the kerosene.
CdHPO 4 + TBP ⇔
( CdHPO4 ) , ( TBP ) (1)
(b) The orthophosphoric acid presents the competitive following reaction:
H 3O + , H 2 PO-4 + TBP ⇔ ⎡⎣ H 3O + , H 2 PO-4 , TOPO ⎤⎦
(2)
3.5. Mechanismes of transport [9] The mechanismes of active transport are represented in Fig. 6. The diffusion of the cadmium ions Cd2+ by the activation of cosolute HPO42! at interface I, we have the migration of complex formed across the membrane by active transport and we have the deactivation of the molecular complex at interface II. The diffusion at interface II of cation NH4+ which is affected in a sense opposed that it is does by the countertransport of the two ammonium ions at interface I.
Fig. 6. Schematic representation of the mechanisms of transport.
F. Hassaine-Sadi, H. Bouchabou / Desalination 206 (2007) 554–559
3.6. Foreseeable pump type — complex “ionic” pump This puts in play the interfaces I and II of the total reactions. It is the case of the system
Cd 2+ , H + , PO3-4 / TBP / NH 4+ , CO3-mechanism
mechanism
solvatant
anion exchanges
At interface I, the total reaction maintains the concentration of the constant source and the “pumping” of the extractible species; at interface II, the total reaction maintains the elevated and constant concentration pressure gradient. It is about a real activation of the system that assures a forced convection and a real “chemical” agitation thanks to the constant renewal of interface II. The nature is completely different of the forbidden backwashing mechanism the existence of balances at interfaces II: backflow check valve.
4. Conclusions The chemical variable survey permitted to determine the chemical parameters giving the extraction efficiencies and optimum backwashing. The competition the mechanism of extraction of the orthophosphoric acid has been recovered. The compartment backwashing destined to contain aqueous solutions of ammonium, cosoluté of “deactivation”. The results showed a total asymmetry of the behaviour of the two compartments. The working of the pump is disrupted by the formation likely of transferable molecules of ammonium. The study of the chemical parameters of the compartment backwashing showed that the choice and concentration of the deactivation cosolute are determining; so the anion will permit
559
the formation of nonextractibles and the cation will permit the counter-transportation, positive coupling. We could define the type of “complex” ionic pump when the static system operates grace a transportation, counter-transportation, positive coupling, and in other cases where one of the constants of backwashing extraction or/and is non-quantitative, we are then in the presence of a transportation, counter-transportation, negative coupling. The chemical modelizations have allowed the phenomenological characterisation of the combination that we have conceived and studied. We have proposed a complex ionic pump allowing the transfer of several species.
References [1] V. Hiatt and J.E. Huff, Int. J. Environ. Stud., 7 (1975) 277. [2] M. Fleischer and Coll, Environ. Health Perspect., 7 (1974) 253. [3] L. Sadoun and F. Hassaine-Sadi, Purification-concentration process. Desalination, 167 (2004) 159. [4] F. Hassaine-Sadi and L. Sadoun, Desalination,187 (2005) 17. [5] M.J.F. Leroy and E.M.M. Sutter, An. Fals. Exp. Chim., 718(756) (1977) 400. [6] G. Charlot, The Analytical Chemistry Method: Quantitative Analysis, Mass, Paris, 1961. [7] P. Fremaux and G. Cattin, Analytical Chemistry, 50(1) (1968) 34–39. [8] G.M. Ritcey and A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984. [9] G.M. Ritcey and A.W. Ashbrook, Solvent Extraction. Principles and Applications to Process Metallurgy, Part II, Elsevier, Amsterdam, 1989. [10] F. Hassaine-Sadi, A. Benhassaine and H. Ait-Amar, Transportation of the biological membrane process to the treatments of low-grade metal effluents. Physical modelling of an ionic pump. Transport Membrane Mechanisms, Entropie, 230 (2001) 31–34.