Separation of Co 2+ using n-alkilic alcohols based liquid membranes

Transcription

1 Separation of Co 2+ using n-alkilic alcohols based liquid membranes AURELIA CRISTINA NECHIFOR 1, 2, LACRAMIOARA NAFTANILA 2, ANDREEA RADUCU 2, VALERIU DANCIULESCU 2, STEFAN IOAN VOICU 2, EUGENIA EFTIMIE TOTU 2 1 National Institute for Microtechnologies IMT Bucharest, Str. Erou Iancu Nicolae nr. 126A, Bucharest, 2 Faculty of Applied Chemistry and Materials Sciences Politehnica University of Bucharest 1-7 Gheorghe Polizu St., Bucharest, , ROMANIA nechiforus@yahoo.com Abstract: The concentration and separation of cobalt from different effluents represented a permanent major objective for researchers due to technical, economic, environment and health importance. There are well known the results for cobalt concentration and separation through liquid membranes using kerosene and a trasporter. In this paper we promote a new type of membrane solvent, polar, biodegradable and very low soluble in water medium saturated normal alcohols (n-hexanol, n-octanol or n-decanol). The liquid membranes techniques allow the use of heavy volatile solvents because finally the interest cation will be transferred from an aqueous phase source to an aqueous receptor phase. In the paper are presented the study results for cobalt ions separation through a new type of liquid membrane depending by the nature of membrane, the nature of transporter and the operation conditions. Key-Words: - Co 2+ separation, liquid membrane 1 Introduction The concentration and removal of heavy metals from aqueous solutions is a major interest domain due to multiple applications such as decontamination techniques for environment, analytical chemistry, and biomedical applications [1-8]. Extraction of cobalt ions from acidic solutions takes place most often in the presence of rhodanate ions [9-14]. Separation of cobalt ions in the presence of rhodanate ions is performed under a ph gradient oriented in the opposite direction from that previously presented, from basic source phase. So, source phase is acid and receiving phase is basic. Usually, the most used carrier is a neutral organophosphorus compound or a fatty tertiary amine and organic phase is a hydrocarbon [15-20]: 2(C 4 H 9 O) 3 POorg +2H + aq +Co(SCN) 4 2 aq ((C 4 H 9 O) 3 PO)2H 2 Co(SCN) 4 org (1) ((C 4 H 9 O) 3 PO)2H 2 Co(SCN) 4 org +2OH aq 2(C 4 H 9 O) 3 POorg +Co(SCN) 4 2 aq+2h 2 Oaq (2) In this case, the neutral carrier, tributyl phosphate (TBP), contributes to the formation of ion-pair complex which is preferentially soluble in the liquid membrane. The transport scheme, illustrated in the scheme 1 show that both cobalt ions and protons are transported from source phase to receiving phase. This is called co-coupled transport. Fig.1 The transport scheme of Co 2+ in liquid membrane 2 Materials and methods The cobalt nitrate and cobalt sulfate (Merck), normal aliphatic alcohols, C 6, C 8 and C 10 (Merck), ammonia solution 25% (Merck), ammonium rhodanate (Merck), SPAN 20, SPAN 80, piridiniu dodecyl chloride, piridiniu tetradecyl chloride, piridiniu octadecil chloride, dodecylbenzene ISBN:

2 sulphonate, Hyamina (Merck), acid di-(2- ethylhexyl) phosphoric acid (D2EHPA) (Merck), trioctilamine (TOA), tributyl phosphate (TBP) (Merck), Ethylenediaminetetraacetic acid (EDTA) (Merck), and bidistilled water were used. The source phase, which contains cobalt ions which must be separate, was obtained by dissolving cobalt nitrate in a minimum amount of concentrated nitric acid (67%) and finally brought to the desired volume with distilled water in a volumetric flask. It has also been used a waste water containing cobalt ions, from electrochemical coating baths, with a concentration of mg/l Co 2+, into a complex composition with other electrolytes, acid ph (4.8) and a conductivity of S / cm. From literature data it is known that cobalt ion separation with the help of liquid membranes in the presence of acidic or neutral medium, occurs due to the formation of a complex with SCN - ion to form Co(SCN) Therefore, in source phase was added concentrated ammonium rhodanate (50%), to form the complexes. Membrane phase (organic phase) is presented as a reverse emulsion, which contains the dispersed receptor. The organic phase also contains the surfactant (emulsifier) and the inverse emulsion necessary as transporter. As organic phase were chosen normal aliphatic alcohols, C 6, C 8 and C 10, due to several factors, such as insolubility in water, chemical inertness, lack of toxicity, relatively low ignitability, low cost price and the fact that are used currently in classical separation processes by solvent extraction. Phase receivers used to remove cobalt ions were represented by basic aqueous solutions, which have a composition dependent on the working system chosen (eg, 2 M ammonia / ammonium sulphate and / or lithium sulphate, EDTA). 3. Results and discussions The experiments carried were carried out in order to determine the optimal parameters of cobalt extraction with acidic ph from source phase. It were identified the following factors for the influence of the process: membrane solvent nature, source phase ph, respectively, phase receivers, transporters (extracters) of membrane phase and the nature and concentration of surface-active substance used to stabilize the primary emulsion. Although the source phase has, usually, for a particular ion, an acid ph imposed, its value is not known for any cation which becomes the object of extraction. Even more needed are the experiments establishing the optimum ph, the more was determined that under conditions given by the extractant composition and temperature, it can vary significantly to some cations: Co 2+ and Ni 2+ (Fig. 2) [10,11,17]. In this paper, the experiments of extraction were performed with average normal alcohols: hexanol, octanol and decanol, the source phase with a ph between 3.5 and 6.5, using the extrac: TBP and TOA of concentration 0, 02M. Source phase contains 150 mg/l Co 2+, and ammonium rhodanate concentration was great excess 2M. The working ph is adjusted with sodium acetate / acetic acid buffer. The results presented in figures 3 and 4 show that the extraction yield is influenced favorably, but less by lower ph, especially in the case tributyl phosphate (TBP), while for trioctil amine (TOA) increased ph site, favoring the extraction, although in a measure quite different for the three alcohols tested. Influence of cobalt extraction yield falls in the range of 95 ± 3% during the study, which leads to the idea of imposing a ph of 4.8 ± 0.2, which can be maintained, relatively easily with an acetate / acetic acid buffer. Fig.2 Isothermals of extraction of the metal ions: Nickel (II), Cobalt (II) 3.1 The influence of ph of source phase Fig.3 The influence of source phase ph over the extraction of cobalt with TBP, in various normal alcohols ISBN:

3 It is interesting to observe that the three alcohols have not a similar behavior, the entire ph range studied, but to choose a ph of source phase of 4.8 ± 0.2 where of extraction yield of cobalt is practically the same for all three alcohols and two extract. 0.2 M EDTA and a ph between 7.5 and 11 made with ammonia and ammonium nitrate. Fig.5 The influence of ph of phase receivers over extraction of cobalt with TBP, in various normal alcohols. Fig.4 The influence of source phase ph over the extraction of cobalt with TOA, in various normal alcohols Alcohol which becomes the favourite for practical use is octanol, because it is the least affected by the changes of ph and the nature of extractant. It is possible that due to the low solubility of n octanol compared to n hexanol (but bigger enough compared with decanol), to be the main motivation for the behavior of its best in extraction. This may be correlate with the observation which indicate that the total insoluble membrane phase disadvantage the transport, preventing interaction with cation transporter from the aqueous medium, and very soluble organic phase, leading to losses and contamination of both of the aqueous phase The influence of ph of receiving phase In the case of cobalt extraction from acidic aqueous solutions, re-extraction is made in basic aqueous phase which contain and complex, often EDTA. Establishing the optimum basic ph is very important because a sharp increase can lead to high material consumption, both to achieve increased basic and to neutralize the environment to recover cobalt. In the figures 5 and 6 are shown the results of reextraction of cobalt from alcoholic membrane phase, for the two extractants, at a concentration of Fig.6 The influence of ph of receiving phase over extraction of cobalt with TOA in various normal alcohols. Re-extraction occurs with yields, slightly, lower and octanol behavior is less influenced by ph. The recovery of cobalt from alcoholic environment containing TOA component is more difficult, this being caused by basic larger and therefore stronger interaction with cobalt rhodanate. Optimum ph range is between 9.6 and 10, allowing easy control with ammonia buffer The effect of surfactant nature and concentration The carried out experiments had in view the surfactant selection and optimal concentration leading to a higher extraction yield. The proposed mechanism for a neutral or slightly basic carrier, does not limit the types of surfactants proposed: ISBN:

4 SPAN 20, SPAN 80, dodecylbenzene sulphonate (DDBSNa) and Hyamina (HyA) because the basic role of surfactant substance is to stabilize the primary emulsion. In the figure 7 are shown the results of extraction of cobalt from acidic source phase using in the membrane phase cationic, anionic and neutral surfactants in concentrations between 10-7 M and 10-5 M. This range includes the first critical micellar concentration of surfactant (MCC), but does not exceed the solubility limit concentration value (SLC). in source phase; ph 9,8+0,2 in receiving phase; anionic or neutral surfactants in concentrations close to the solubility limit; the cobalt ion capture agent EDTA: 0.2 M; n octanol use is preferable, since it is practically insoluble in water (0.3 g / L, 20 C) than in hexanol (5.9 g / L, 20 C) but soluble enough to ensure interactions with aqueous phases, compared to n decanol ( g / L 25 C). Acknowledgement Authors recognize the financial support from the European Social Fund through project POSDRU/89/1.5/S/63700, , Human Resource Development by Postdoctoral Research on Micro and Nanotechnologies (project which financed Aurelia Cristina Nechifor) and also through project POSDRU/89/1.5/S/54785 Postdoctoral Program for Advanced Research in the field of nanomaterials (project which financed Stefan Ioan Voicu). Fig.7 The influence of surfactants concentration from membrane phase over extraction of cobalt with TBP, in n octanol Standard working conditions have been established considering the previous experiments or literature data as follows: cobalt concentration 10-2 M, from acetate / acetic acid solution containing excess ammonium rhodanate, 2M (ph = 4.8, acetate buffer), phase receiving basic (ph = 9.8, ammoniacal buffer) containing 0.2 M EDTA, membrane based on octanol and carrier 10-2 M, TOA and, respectively TBP. The results obtained confirm the proposed mechanism and mass transfer and the anionic surfactant favors transport, while the cation does not interfere in the process. The positive effect of increasing concentration of non-ionic surfactants, SPAN type, is justified by stabilizing the primary emulsion and less through participation in cobalt transport. 4 Conclusion The extraction of cobalt, M from acidic aqueous solutions in the presence of ion rhodanate, in excess, 2M operation is required: ph 4,8+0,2 References: [1] Henry Kasaini, Fumiyuki Nakashio, Masahiro Goto, Application of emulsion liquid membranes to recover cobalt ions from a dualcomponent sulphate solution containing nickel ions, Journal of Membrane Science, vol. 146 (2), 1998, pp [2] S.I. Voicu, A.C. Nechifor, B. Serban, G. Nechifor and M. Miculescu, Formylated Polysulphone Membranes for Cell Immobilization, Journal of Optoelectronics and Advanced Materials, Vol.9, Nr. 11, 2007, pp [3] B. Şerban, M. Bercu, Ş.I. Voicu, A.C. Nechifor and C. Cobianu, Synthesis and characterization of a novel functionalized conductive beta-cyclodextrine-doped polyaniline, Revista de Chimie, 57, 2006, pp [4] G. Nechifor, S.I. Voicu, A.C. Nechifor and S. Garea, Nanostructured hybrid membrane polysulfone-carbon nanotubes for hemodialysis, Desalination, 241, 2009, pp [5] A. Sürücü, V. Eyüpoglu, O. Tutkun, Selective separation of cobalt and nickel by supported liquid membranes, Desalination, vol. 250 (3), 2010, pp [6] F.D. Balacianu, A.C. Nechifor, R. Bartos, S.I. Voicu and G. Nechifor, Synthesis and characterization of Fe3O4 magnetic particles- ISBN:

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