Acta Chim. Slov. 2003, 50, 663-675. 663 EXTRACTION OF COBALT AND LEAD FROM WASTE WATER USING A LIQUID SURFACTANT MEMBRANE EMULSION Saliha Bouranene, Mohamed El-Hadi Samar Faculté des Sciences de l ’Ingénieur, Département des Génies des Procédés, Université Badji-Mokhtar, B. P. 12, El-Hadjar, Annaba (23200), Algeria, E-mail: Samarmh@yahoo.fr Azzedine Abbaci* Faculté des Sciences, Département de Chimie, Université Badji-Mokhtar, B. P. 12, El-Hadjar, Annaba (23200), Algeria, Tél:+213-38-86-49-94, Fax: +213-38-86-85-10, E-mail: abbaci_a2002@yahoo.fr Received 12-03-2003 Abstract The applicability of the Liquid Surfactant Membrane (LSM) process for the removal and the concentration of lead and cobalt was investigated. The aim of this work is to find a process for the purification of wastewater, which contains cobalt and lead. A complete study of the metal extraction by the liquid membrane process using HDEHP as extractant and SPAN 80 as surfactant is performed in terms of extraction and stripping efficiencies, emulsion breaking and swelling. The results show that it is possible to recover 98.83% of cobalt and 94.21% of lead in the inner phase after 2 minutes of contacting time with a concentration factor of 50 for lead and 50 for cobalt. Introduction The aim of this work is to find a process for the purification of wastewater, which contains lead and cobalt. The pH of these solutions depends on their origin. A bibliographic survey has led us to select acidic reagents as the extractant, " and the surfactants enhance emulsions water into oil (HLB < 4) as a stabilizer that gives very good emulsions stability during the transfer even at low concentration. In order to choose the most suitable surfactant, we made a comparison between several commercialised surfactants compounds, which consist of SPAN 80 (monooleate of sorbitan), TWEEN 20 (21.22.etho-Sorbitan monolaurate), the NP4, and the Marlophen (Nonylphenol polyoxyethylene). In the extraction we used the cationic exchanger, namely, a phosphoric acid (di-2-ethylhexyl phosphoric acid or HDEHP). This latter extracts metallic cations present in aqueous solutions. The cations are exchanged for protons that are released in the aqueous phase leading to its acidification. S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... 664 Acta Chim. Slov. 2003, 50, 663-675. The surfactant liquid membrane process introduced by Li was used because of two major advantages: the first one is its possibility of treating diluted solutions and the second one is its high concentration factors. Their principles are described in details in many papers. " Experimental and Materials The selected membrane used in this work, is constituted of an extractant, that is HDEHP (di-2-ethylhexylphosphoric acid). It is the product of the Daihachi Chemical Ind. Co., Ltd., Osaka, Japan, with 95% purity. It was further purified by precipitation as a copper complex from ether and acetone solution, and then dissolved in ether and a sulphuric acid solution of 4 kmol m" . According to the procedure of Partridge and Jensen the Kerosene (Dodecane) used as a diluent was supplied by Union Chemical Works Ltd., Taiwan. Several surfactants have been tested such as the SPAN 80 (monolaurate of sorbitan) surfactant non-ionic enhancing water emulsions into oil used in liquid membranes technology, for its accentuated lipophilic character (Kao-Atlas), the TWEEN 20 (21.22.etho-sorbitan monolaureate), the NP4, and the MARLOPHEN (Nonylphenol poly-oxyethylene at 100% active matter over greasy alcohols). The external aqueous phase is obtained by dissolving the nitrate of cobalt into water Co(N03)26H20 and the nitrate of lead Pb(N03)2. The internal aqueous is a sulphuric acid or a hydrochloric acid solution which concentration will be one of the parameters to optimise. The reason for the choice of these ions is that there is an industrial relevance due to the dumping into the regional rivers and lakes of the industrial wastewater by the Giant steel industry of El-Hadjar, Annaba in Algeria. Procedure Emulsions are manufactured by means of an ULRA-TURAX disperser T18-10. The two phases (organic and internal aqueous) are placed into a beaker with a well-cut shape obtained by a vigorous agitation. The disperser is introduced and positioned at the interface level; we maintain the stirring at 2000 revolutions per minute (as a maximal speed) during 5 minutes. This was realized by spreading a certain volume of emulsion in a given aqueous phase volume, so that we can treat the metal to be extracted using a helical stirrer, turning at 250 revolutions per minute. S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... Acta Chim. Slov. 2003, 50, 663-675. 665 The aqueous phase pH is adjusted by adding ammonia followed by spectrometry with an electrode glass. After extraction, the depleted aqueous phase is separated from the emulsion by simple decantation. The emulsion is then broken by adding octanol, which is heated to 40 °C. The proportion of metal (cobalt to lead) is made by spectrometry (Shumadzu Japan) using the PAR (4-pyridyl-2-azorésorcinol) as complexant. The lead is proportioned by visible spectrophotometry with the presence of PAR at pH 11 and with a wavelength of 530 nm. The same method is used for the cobalt with the presence of PAR at pH 3 and with a wavelength of 530 nm. The mixture, cobalt-lead is performed by the PAR at pH 3 and a wavelength of 590 nm (visible spectrophotometry); we also performed lead-cobalt mixture by the EDTA (tetra-di-acetic-acid) at pH 11 and a wavelength of 240 nm (ultraviolet spectrophotometry). Results and discussion Breaking off the emulsion This phenomenon was measured by contacting the emulsion with an external phase composed of pure water. The variation of the pH of this phase with tirne is an indication of the emulsion breaking. The breaking rate “BR” defined by eq. (1) represents the fraction in percent of the expulsed internal phase volume to the external phase by the breaking volume Vr to the initial volume of the internal phase Vint.. The volume Vr is calculated by the material balance from the external phase pH measure, before and after the contact, so that; V r , BR (%) =— ×l00 (1) int with 10 ® - 10"^ T = 6Xt------------------------------- (2) 1A- pH 10 Where Vext. is the initial external phase volume, pHo is the pH of the initial external phase, pH is the pH of the external phase being in contact with the emulsion S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From Waste Water... [H ] i 666 Acta Chim. Slov. 2003, 50, 663-675. after a certain time of agitation, and [H+]i the protons initial concentration in the internal phase. Choice of surfactant The surfactant agent is the first factor that enhances the formation of the water emulsion into oil (W/O). For this reason, we have tried some commercial surfactants (SPAN 80, TWEEN 20, NP 4, and the MARLOPHEN). Breaking rates are calculated after 7 minutes of contact between the emulsion and external phase. Table 1. Choice of surfactant giving the lower breaking rate “ BR” in the same experimental conditions. Surfactant concentration 2% NP4 TWEEN 20 MARLOPHEN 53.59 SPAN 80 BR (%) 20.77 39.27 5.39 Working conditions The working condition are summarized as follows: Emulsion volume = 30 mL, external phase volume = 300 mL, membrane volume/internal phase volume = 2, emulsification speed = 2000 rpm, (HDEHP) = 2%, (H2SO4) = 0.5 mol/L, diluent = heptane, Stirrer speed = 350 rpm, emulsification tirne = 5 minutes, and the SPAN 80 seems to be the best because its breaking rate “BR“ is the lowest that offers us the capacitv of forming stable emulsions W/0. Study of water emulsion stabilitv in oil using SPAN 80 as a surfactant The effect of several parameters was studied. These parameters are the following: SPAN 80 concentration, HDEHP concentration, ratio volume membrane/volume inner phase, sulphuric-acid concentration, rotating speed in the transfer step, emulsification rotating speed, and emulsification tirne. Influence of the emulsification rotating speed Experiments were performed with HDEHP 2%, SPAN 80 2%, sulphuric acid of 0.5 mol/L, heptane 96%, a ratio membrane volume/internal phase of 2, rotating speed of 350 rpm, 7 minutes of contact, emulsion volume 10 mL and the external phase volume of 100 mL, the temperature of 25°C and different emulsification rotating speed. An S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and LeaclFrom Waste Water... Acta Chim. Slov. 2003, 50, 663-675. 667 efficient emulsification gives a good dispersion of internal phase drops into the membrane. The fact that these drops become smaller will take much more time to coalesce. This procedure has led to a higher stability of the emulsion. The optimal emulsification speed was found to reach the value of 2000 rpm with a breaking rate BR of 3.5%. Table 2. Variation of the breaking rate with the emulsification speed. Emulsification rotating speed (rpm) 1000 1400 2000 BR (%) 11.79 4.86 3.35 Emulsification time The conditions used here are the same conditions used previously, the emulsification speed is 2000 rpm, the emulsification time is insufficient (t = 2 min) so that the breaking rate is great because the internal shearing is high and drops remain small enough for a long emulsion time (more than 5 minutes), so that the breaking rate is high. As shown in Table 3, the lower breaking rate is obtained for emulsion time of 5 minutes. Table 3. Effect of emulsification time on the breaking rate. Emulsion time (min) 2 5 7 10 BR (%) 12.36 3.35 7.23 11.26 Effect of rotating speed in the transfer step As expected the stability depends greatly on the rotating speed when the external interfacial area is increased by an increased rotating speed so that the ejection of the internal phase is facilitated. This can be seen on the following table with a contacting tirne of 7 minutes. In terms of stability the rotating speed must not exceed 250 rpm. Table 4. Effect of rotating speed in the transfer step on the breaking rate. Rotating speed (rpm) 150 200 250 300 350 BR (%) 4.54 4.34 2.73 3.13 3.35 S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... 668 Acta Chim. Slov. 2003, 50, 663-675. Effect of HDEHP concentration The concentration of HDEHP has an unfavourable influence on the stability of the emulsion. This may be due to the interfacial properties of HDEHP, which favors 0/W emulsions and is therefore opposed to the SPAN 80 action. Table 5. Variation of breaking rate with the HDEHP concentration. HDEHP (%) 2 4 6 8 BR (%) 2.73 4.04 6.14 7.39 Effect of sulfuric-acid concentration When the sulphuric-acid concentration increases, the stability of the emulsion decreases. This may be due to a reaction of the acid with SPAN 80 (2%), resulting in a partial loss of its surfactant properties. This can be seen in the following table. Table 6. Variation of breaking rate with the sulphuric-acid concentration. H2SO4 (mol/L) 0.25 0.5 0.75 1.0 BR (%) 1.12 2.73 12.77 20.22 From the stability point of view a concentration of sulphuric acid greater than 0.5 mol/L is prohibited. Effect of the ratio membrane/internal phase The stability increases slightly with increasing the membrane/inner phase as can be seen on Table 7. This result is expected because the ejection of the internal phase is easier when its proportion in the emulsion is higher. It should be mentioned that in these experiments, the contacting tirne was 60 minutes with SPAN 80 of 2%. Table 7. Variation of breaking rate with the ratio membrane volume /internal phase volume. Membrane/inner phase 1 2 3 4 BR (%) 6.04 3.77 2.09 2.06 Effect of SPAN 80 concentration Different concentrations of SPAN 80 have been tried, as expected the stability of the emulsion increases with SPAN 80 concentration, but the differences are limited showing that the two concentrations of SPAN 80 are convenient: 5% and 6%. S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... Acta Chim. Slov. 2003, 50, 663-675. 669 Table 8. Variation of breaking rate with the SPAN 80 concentration. SPAN 80 (%) 2 3 4 5 6 BR (%) 6.14 2.85 2.01 1.79 1.07 Choice of diluent The di-2-ethylhexylphosphoric (HDEHP) acid dissolves in several organic solvents such as hexane, heptane, benzene and dodecane. With ali parameters previously optimised, and following the same procedure used above, we were able to control the variation of emulsion breaking rate prepared in dodecane and heptane (Figure 1). The dodecane efficiency seems to be better than that of heptane. Optimal conditions The optimal conditions can be summarized as follows: SPAN 80 = 5%, HDEHP = 6%, Dodecane = 89%, membrane /inner phase = 4, rotating speed of the transfer step = 250 rpm, sulphuric-acid concentration = 0.5 mol/L, emulsification rotating speed = 200 rpm, emulsification tirne = 5 min, the diluent is dodecane, and the temperature = 25 °C. 2,5 - 2 1,5 1 0,5 - 0 0 10 20 30 40 50 60 70 Time (min) Figure 1. Plot of BR (%) versus time for different diluents with SPAN 80 concentration of 5%. Extraction of cobalt by membrane liquid emulsion Cobalt was studied more precisely than the other metals in order to find out the optimal conditions for a good transfer. These conditions were aftenvards tested on the other metals such as lead, nickel, mercury. The experiments were generally performed under the following conditions: Initial cobalt concentration = 100 mg/L, concentration of S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From Waste Water... -Ll— Heptane ¦Q— Dodecane 670 Acta Chim. Slov. 2003, 50, 663-675. HDEHP = 6% (in weight), concentration of SPAN 80 = 5%, dodecane = 89%, stripping phase: sulphuric acid = 0.5 mol/L, volume of the aqueous phase to be purified = 100 ml/L, emulsion volume = 10 mL, membrane volume/internal phase volume = 4, and the rotating speed during the transfer step = 250 rpm. During the transfer of cobalt, the pH of the aqueous external phase was kept to the desired value by addition of ammonium acetate. Several chemical and operating parameters were studied as follows: Effect of external phase pH The experiments were performed for different values of pH, as shown in Figure 2. In the following figures (Co)ext is the concentration of cobalt in the aqueous external phase at tirne t. The kinetic of extraction increases with increasing pH. The extraction is indeed slower for pH 2.29, the cationic exchange being more difficult when the aciditv increases. In contrast, the extraction is very satisfactory between pH values of 3.09 and 4.6. At a pH 6.11 the emulsion is no more stable. The optimal range of pH is then between 3 to 4.6. Subsequently, ali the following experiments were performed at pH 4.6. Effect of extractant concentration The cobalt concentration in the external phase decreases with tirne and an increasing HDEHP concentration (up to 8%). Above this concentration the emulsion is not stable. These results are presented in Figure 3. 110 90 - 70 50 30 10 -10 10 15 Time (min) 20 ApH = 2.29 ©pH = 3.09 pH = 4.6 pH = 6.11 25 Figure 2. Plot of Cobalt concentration versus time at various pH. 0 5 S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... Acta Chim. Slov. 2003, 50, 663-675. 671 Effect of the rotating speed in the transfer step In this experiments, concentrations of HDEHP and SPAN 80 are respectively 6% and 5%. As expected the greater the rotating speed is, the better the extraction as shown in Figure 4. Indeed, the greater agitation results with a higher external interfacial area and then a quicker transfer. However, it is not possible to increase the rotating speed over 250 rpm without having a significant breaking of emulsion. Therefore, an intermediate value of the rotating speed must be adopted between the values of 200 to 300 rpm. Effect of the volume ratio of the aqueous external and emulsion This ratio (B) was varied from the value of 5 to the value of 15. The contacting tirne is 5 minutes; this is because it is the interval tirne where the membrane is very stable. 160 140 120 100 j 80 60 40 20 0 77 —JK— [HDEHP] = 6 % O [HDEHP] = 8 % O —V— [HDEHP] = 9 % r _—v 7* Cf —¦—&—^=$\ i=r-?-~ ------D^= ^=8 10 12 Time (min) Figure 3. Plot of cobalt concentration versus time at different HDEHP concentration. 120 100 80 60 40 20 0 468 Time (min) Figure 4. Plot of cobalt concentration versus time at different rotating speed in the transfer step. S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... 672 Acta Chim. Slov. 2003, 50, 663-675. D—V /V =15 ex em o—V /V =10 ex em A—V /V =5 ex em 0 123 456 7 Time (min) Figure 5. Plot of cobalt concentration versus time at different ratio of the aqueous external and emulsion. As was expected the cobalt extraction slightly increases when the studied ratio decreases, this is mainly due to the greater volume of the emulsion as can be seen on the following in Figure 5, where (Co) is the concentration of metal remaining in the external phase after 2 minutes, but the differences are very limited in this range of values of the ratio (B). The optimal value of the ratio is 10. Optimal conditions The optimal conditions were taken to be: SPAN 80 = 5%, HDEHP = 6%, dodecane = 89%, membrane volume/internal phase volume = 4, external phase volume/emulsion volume = 10, contacting time = 1 min, stirrer speed = 250 rpm, and the extracting efficiencv (Rext.) is calculated from the following equation as Rext. = (quantity of extracted cobalt/quantity of initial cobalt): ext. ~ x~,0ext/ 0ext. -^ fext/ fext. ^0ext. ' ^0ext/ 0ext. /*!"" \->) where Coext. is the initial concentration of cobalt in the external aqueous, Cfext. is the final concentration of cobalt in external aqueous phase, Vrjext. the initial volume of the external aqueous phase, Vfext. is the final volume of the external aqueous phase, the value of Rext. was found to be equal to 99.15% for a contact time of 1 minute. Cobalt stripping In this čase, the parameter we studied was the concentration of inner phase (sulphuric acid). The other conditions were: HDEHP = 6%, SPAN 80 = 5%, dodecane = i 100 i 80 - 60 - 40 - 20 - n^-= V,^—- S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... Acta Chim. Slov. 2003, 50, 663-675. 673 89%, the ratio volume of the emulsion/inner phase = 4, the rotating speed in the transfer step = 250 rpm, the contacting tirne = 5 minutes, pH of the external phase is 4.6, the external phase volume /emulsion volume = 10, and the initial concentration of cobalt = 100 mg/L. Effect of the sulphuric-acid concentration In this čase, the value of the ratio membrane/inner phase is taken to be equal to 4. For the acid concentration between the values of 0.5 and 1.5 mol/L, the stripping of cobalt is greater or equal to 60%. However, for a concentration of sulphuric acid greater than 1.5 mol/L, the emulsion swells up due to the osmosis, which provokes the dilution of the internal phase by the transfer of water from the external phase, resulting in a less effective stripping. In addition, the emulsion stabilitv is poorer. The optimal stripping efficiencv Rdes. is found to be equal to 63.29% for a sulphuric-acid concentration of 1 mol/L. Čase of lead In the previouslv determined conditions, a study of the extraction of lead versus the pH of the external phase was performed. At a value of pH 4, the extraction of lead is very satisfactory, and the extraction yield for pH 4 is 99.13%. The de-extraction efficiency (Rdes) as defined in eq. (5) is calculated from the following material balance: Initial quantity of lead in the external phase = quantity of extracted lead + quantity of remaining lead: ^0ext/ 0ext. ~ ^wlo ^fext/ fext. v ' where XVw/o represents the lead quantity, which has been moved from the external phase to the emulsion W/0. This quantity has a concentration X of lead in a volume Vw/o of emulsion, Rdes. = (Quantity of de-extracted lead by the membrane/quantity of moved lead from the external phase to the emulsion) xl00 defined by des. ~ v-^/int. /int. ' ^elh /*!"" ~ V-/int. /int. ^0ext.0ext. fext. fext. /*!"" \y) where Cfint. is the final lead concentration as internal phase, Vfint. is the internal phase final volume, Cfext is the final lead concentration as external, Vfext. is the external phase final volume, Coext. is the initial lead concentration as external phase, and Voext. is the S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From Waste Water... 674 Acta Chim. Slov. 2003, 50, 663-675. external phase initial volume. The stripping efficiency is very satisfactory when Rdes 70.23% and the internal phase concentration HC1 = 0.5 mol/L. Purification of a solution containing the two metals The initial external aqueous solutions contained 100 mg/L of Co and Pb at pH 4.6. The organic phase was composed of 6% HDEHP, 5% SPAN 80, and dodecane. The internal solution contained sulphuric acid of 1 mol/L. The volumes of the organic and the external phases were respectively 10 mL and 100 mL, the ratio membrane /internal phase was 4, the stirrer speed was 250 rpm during 5 minutes at a temperature of 25 °C, and the emulsification speed of 2000 rpm during 5 minutes. The results are presented in Figure 6. For a contacting tirne of 2 minutes, the extraction efficiencies are 98.83% for cobalt and 94.21% for lead. For de-extraction, we found an efficiency of 78.01% for cobalt and 63.44% for lead. 120 _ O lead 100 L e— cobalt 80 60 - 01234 56 time (min) Figure 6. Plot of cobalt and lead concentration versus time. Conclusion The surfactant chosen SPAN 80 is an efficient surfactant enhancing the formation of stable emulsion water in oil even at low concentration with a breaking rate equal to 1.07% for a contacting tirne of 6 minutes. The kinetic of extraction of the two metals is very quick which reduces considerably the swelling up phenomena of the membrane by osmosis. After 1 minute, the extraction efficiency of cobalt at pH 4.6 is 99.15%. For a contacting tirne of 3 minutes, the extraction efficiency of lead is 98.13% at pH 4. The de-extraction efficiency is 63.29% for cobalt and 70.23% for lead. In the čase of the mixture S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater... Acta Chim. Slov. 2003, 50, 663-675. 675 extraction, the cobalt extraction efficiency is 98.3% and 94.21% for lead for a contacting tirne of 2 minutes. Nomenclature BR.......percentage breaking rate C..........concentration, mg/L HLB ....hydrophilic-lipophilic balance LSM ....liquid surfactant membrane O.........oil V.........volume, mL W.........water References 1. R. R. Barefoot, A. Wang, J. C. Vanloon, Y. Li, Talanta 1992, 39, 1337-1341. 2. J. Draxler, W. Furst, R. Marr, I. S. E. C. 1988, 6-1, Moscow. 3. D. Hartmann, « Extraction de TUrariium contenue dans le lexiviats par membrane émulsionnée », These de 1'ecole Centrale, Pariš, 1992. 4. T. C. H. Huang, T. H. Tsai, Acta. Chem. Scand. 1991, 45, 383-391. 5. R. Kopunec, T. H. Ngomanh, J. Radioanal. Nucl. Chem. 1994, 1, 181-204. 6. N. N. Li, US Pat. 3, 410, 794, 1968. 7. M. E. H. Samar, D. Pareau, G. Durand, A. Chesne, International Symposium Hydrometallurgy, ed. Institution of Mining and Metallurgy, 1994, 635-654. 8. M. E. H. Samar, D. Pareau, G. Durand, A. Chesne, Buli. Soc. Chim. Fr. 1992, 129, 259-264. 9. A. Sato, S. Nakamura, K. Akiba, J. Radioanal. Nucl. Chem. 1994, 178, 63-71. 10. J. A. Partridge, R. C. Jensen, J. Inorg. Nucl. Chem. 1969, 31, 2587-2595. Povzetek Proučevali smo uporabnost postopka ekstrakcije v emulziji s pomočjo tekoče membrane ob dodatku površinsko aktivne snovi (Liquid Surfactant Membrane - LSM) pri procesih odstranjevanja in koncentriranja svinca in kobalta. Cilj tega dela je bil najti primeren način čiščenja odpadnih vod, ki vsebujejo kobalt in svinec. Izvedli smo obseženo študijo ekstrakcije kovin v HDEHP preko tekoče membrane, pri čemer je bil kot površinsko aktivna snov uporabljen SPAN 80. Določili smo učinkovitost ekstrakcije in stripinga ter stabilnost in nabrekanje emulzije. Rezultati so pokazali, da je možno odstraniti do 98.83% kobalta in 94.21% svinca pri kontaktnem času 2 minuti. Koncentracijska faktorja za svinec in kobalt sta bila 50. S. Bourenane, M. E. H. Samar, A. Abbaci: Extraction of Cobalt and Lead From JVaste JVater...