Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 518–523Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Enhancement of uranium ion flux by consecutive extraction via hollow fiber supported liquid membrane A.W. Lothongkum a, P. Ramakul b, W. Sasomsub c, S. Laoharochanapan d, U. Pancharoen c,* a Department of Chemical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Ladkrabang, Bangkok 10520, Thailand Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand c Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Patumwun, Bangkok 10330, Thailand d Office of Atoms for Peace, Bangkok, Thailand Institute of Nuclear Technology (Public Organization) 10900, Thailand b A R T I C L E I N F O A B S T R A C T Article history: Received 6 September 2008 Received in revised form 23 March 2009 Accepted 27 March 2009 The enhancement of uranium separation from trisodium phosphate, a by-product, from monazite processing through a supported liquid membrane system by a consecutive extraction using the synergistic extractants is first time demonstrated in this work. Feed solution was trisodium phosphate solution containing uranium ions of 45 ppm, and the stripping solution was nitric acid solution. The effects of types and concentrations of the extractants, concentration of HNO3, flow rates of feed and stripping solutions and the numbers of cycles on extraction efficiency were investigated. D2EHPA, Cyanex 923, TBP, TOA and Aliquat 336 dissolved in kerosene were used as the extractants. The results showed that by using the synergistic extractant of Aliquat 336 mixed with TBP, the percentages of extraction and stripping or recovery considerably increased higher than those obtained by a single extractant. For the seventh-cycle separation by one-module operation using 0.1 M Aliquat 336 and 0.06 M TBP mixture, 0.5 M HNO3, and equal flow rates of feed and stripping solutions at 100 mL/min, the percentages of extraction and stripping reached 99 and 53 in 350 min. The amount of uranium ions remaining in trisodium phosphate solution was 0.22 ppm, which stayed within the standard value of technical grade trisodium phosphate of 3 ppm. ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Uranium Trisodium phosphate Liquid membrane Hollow fiber Synergistic extraction 1. Introduction Monazite ore is a yellow to reddish-brown natural phosphate of the rare earths, mainly the cerium and lanthanum metals, usually with some uranium and thorium. Yttrium, calcium, iron, and silica are frequently present. The monazite processing to separate the desired rare earths for use is shown in Fig. 1, which generates a byproduct, trisodium phosphate. Two grades of trisodium phosphate, a food grade and a technical grade, are extensively used. Food grade is used as an additive in cheese processing. The technical grade is for many applications, e.g., in boiler-water treatment, testing of steel parts after cleaning or pickling, industrial detergents such as degreasers for steel, and heavy-duty domestic cleaners for toilets and floors (http://www.thaipoly.com). The monazite processing is composed of five essential units: 1. ore digestion unit, 2. trisodium phosphate crystallization unit, 3. dissolution unit, 4. initial precipitation unit, and 5. cerium separation unit. Monazite was digested with concentrate NaOH solution at a temperature of 140– 150 8C to convert phosphate compounds of rare earths to * Corresponding author. Tel.: +66 2 218 6891; fax: +66 2 218 6877. E-mail address:
[email protected] (U. Pancharoen). hydroxide compounds. The hydroxide compounds of uranium, thorium and other rare earths, and a by-product trisodium phosphate were separated by filtration. Trisodium phosphate was sent to the crystallization unit, whereas the hydroxide compounds were then dissolved with HCl to remove the gangue and undigested components. The uranium and thorium in chloride solution were selectively precipitated with NaOH solution at pH 4.5–5.0 and the remaining mixed rare earths were all precipitated into mixed hydroxide cake at pH 11. Cerium in mixed hydroxide cake was later separated by leaching with HNO3 (Suanmamuang and Laoharochanapan, 2002). Unfortunately, uranium has high solubility in water, therefore, filtration is not a suitable technique to separate uranium from trisodium phosphate solution, and it contaminates in the crystal of trisodium phosphate. The contaminated uranium is traditionally separated from trisodium phosphate solution by either ion-exchange or chemical precipitation. In general, uranium is a radioactive element which is useful at the front and back ends of the nuclear fuel cycle. However, uranium is known to cause serious environmental damage and acute toxicological effects in mammals, and its compound are potential carcinogens (Agency for Toxic Substances and Disease Registry, 2000; Clayton and Clayton, 1994). Due to safety and economic considerations, therefore, finding a new method to 1876-1070/$ – see front matter ß 2009 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jtice.2009.03.010 The carrier-mediated transport through an organic membrane is used largely for the separation objectives (Araki and Tsukube... For the latter. Yamini et al. The work of Merceddes and Jose (2001) reported a transportation of niobium (V) using TBP-Alamine 336 supported liquid membrane and the work of Maysa for uranium extraction using Alquat 336 by a liquid emulsion membrane process (Maysa. 2004. Noble and Way. Juang. Acidic ligands are frequently used as the extractantcarriers for separation of metal ions (Bromberg et al. 2007).. Lothongkum et al. Gu.. Theory The hollow fiber module shown in Fig. for example. low energy and extractant consumption. the consecutive extraction via HFSLM was used to enhance uranium ion flux by using a single extractant and a mixture of two extractants in liquid membrane known as the synergistic extractant. 1989) and electrostatic pseudo liquid membrane (EPLM) (Gu. Zhang et al. 2006).. Office of Atoms for Peace. 2003). Main types of liquid membrane systems include emulsion liquid membrane (ELM) (Li. In this work. This kind of transport is called facilitated transport or carrier-mediated transport (Boyadzhiev and Lazarova. the hollow fiber supported liquid membrane (HFSLM) is excellent to extract ions in highly-diluted solution at part per trillion (ppt) concentration levels. 2002. Monazite processing (Suanmamuang and Laoharochanapan.. and it benefits a non-equilibrium mass transfer and up-hill effect.out Cs. tetravalent and trivalent lanthanide ions (Pancharoen et al. The potential advantages of LM techniques over traditional separation techniques and solid membrane technique are low capital and operating costs. and the accumulation of extracted species in the configuration of hollow fiber module. 1990. Trisodium phosphate solution contains mainly uranium ions of about 45 ppm. 1997.. bulk liquid membrane (BLM). 2002). 1992. Sastre et al. Kondo et al. The liquid membrane acts as a solvent for a transported solute which is governed by the solubility in the liquid membrane. LMs can carry out simultaneous extraction and stripping processes in the same stage. Especially. flowing liquid membrane (FLM) (Teramoto et al. 2002). The hollow fiber supported liquid membrane (HFSLM) provides a large surface area per volume and also integrates the advantages of fiber membrane extraction process. 2006). / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 518–523 Nomenclature Cf. and a trace of rare earths. In this work. 2005) and the separation of uranium ions from nitrate media (Ramakul et al. 2006. supported liquid membrane (SLM) (Bloch and Finkelstein. The selectivity in this technique is controlled by both the extraction/back-extraction equilibrium at the interfaces and the kinetics of the transported species under a non-equilibrium mass transfer process (Yang and Fane. 1998.. Thailand. 2006. 1987). a selective separation of cerium (IV). Fonta`s et al. However. where the solute can move from low-to-high concentration solutions (Franken. Ramakul et al. the separation of ions with very low concentration has been focused on liquid membrane (LM) techniques. (2000) reported that their HSLM system could be effectively used for the preconcentration of Rh(III) from diluted solutions and thus the possibility to apply it in the analysis of this metal at low level concentrations. HFSLM has some disadvantages primarily due to the lack of their long-time stability and larger membrane resistance. 2003. liquid film permeation process and other liquid membrane systems (Patthaveekongka et al. the percentages of extraction and stripping were highly dependent on the concentration of HNO3 in the feed solution and did not increase much because the permeabilities decreased due to membrane fouling concentration polarlization and the decrease in diffusivity of feed solution.W. 1967). 2.. In addition.in Cf. In addition. The most interesting case arises when this solubility is controlled by a chemical reaction between the transported solute and the extractant-carrier molecule to form a solute-carrier complex. and high fluxes. Zhang et al. 2(a) contains hollow fibers aligning in the horizontal and inside them the extractant is Fig. 1999). .. higher than the legislation of trisodium phosphate technical grade. 1993. its separation efficiency and recovery depends on a proper selection of the suitable extractant in the system. Bangkok.A. 1. trisodium phosphate crystal was obtained from the Rare Earth Research and Development Center.. 2003).out NR4Cl concentration of inlet feed (ppm) concentration of outlet feed (ppm) concentration of outlet striping solution (ppm) basic extractant (Aliquat 336: quaternary amine) separate uranium from either monazite processing directly or from trisodium phosphate is of interest among the researchers. 1968). to separate the contaminated uranium from trisodium phosphate solution to meet the legislation amount of trisodium phosphate technical grade. In recent years. 1994). One of the most 519 important advantages of such systems is the possibility to tune the selectivity and efficiency of the transport by controlling the pH of the aqueous feed phase and/or receiving phase or recovery phase (a stripping phase). Ren et al. 2005.. Our group also presented good results of using HFSLM. Trisodium phosphate solution was used as feed solution. high surface tension and low volatility.3 cm 20.4 m2 29. simultaneously the stripping solution was counter-currently pumped into the shell side. Thereafter. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 518–523 520 Fig.in (2) Industries Inc. 3. 4. % Extraction ¼ C f . Ltd. analytical grade. was selected as the organic solvent for high stability of liquid membrane due to its low solubility in water. feed solution was pumped into the tube side. The extractability of uranium ions in this research can be determined by the percentage of extraction.3 cm 240 In this work trisodium phosphate from monazite processing was obtained from the Rare Earth Research and Development Center. Feed and chemicals Property Description Material Inside diameter of the hollow fiber Outside diameter of the hollow fiber Pore size Porosity Contact area Area per unit volume Module diameter Module length Number of fibers Polypropylene 240 mm 300 mm 0. Kerosene. and Cyanex 923 from Cytec . were dissolved in kerosene and supplied as the extractants. 3. (a) Hollow fiber module. The structures of the extractants are shown in Fig.in (1) and the percentage of recovery is calculated by % Recovery ¼ C s. At first. which in turn led to higher mass transfer coefficient than individual fibers and they served as a support for the liquid membrane. TOA (Tri-n-octylamine).A. the JPI grade from PTT Public Co.W. 2(b).in C f . Bangkok. The schematic diagram to explain the coupled transport between uranium ions in feed solution and NO3 in the stripping solution of the HFSLM process is described by Fig. (b) flow pattern in hollow fiber supported liquid membrane and (c) a counter-transport scheme between synergistic extractant of Aliquat 336 with TBP and uranium ions. was used as the surfactant. 2.1. Aliquat 336 (Methyltrioctylammonium chloride) from Merck Ltd. The extractant is dissolved in the organic solution and behaves as the carrier to accelerate the transport of the specific component from the feed phase to the stripping phase. 1-Dodecanol from Merck Ltd. It contains mainly uranium ions of about 45 ppm and a trace of other rare earths. Office of Atoms for Peace. Hollow fiber supported liquid membrane Celgard 1x-30 240 microporous polypropylene hollow fibers were woven into fabric and wrapped around a central tube feeder that supplied the shell side fluid.out 100 C f .out 100 C f . 3.3 cm2/cm3 6. 3. TBP (Tributylphosphate). Fig. The extractant can be used singly or in combination with other extractants for the synergistic effect. D2EHPA (Di(2-ethylhexyl) phosphoric acid). without further purification. The feed and stripping solutions flow counter-currently in tube side and shell side of the HFSLM as shown in Fig. The woven polypropylene fabrics allowed more uniform fiber spacing. 3.2.. Thailand. The characteristics of the hollow fiber module are shown in Table 1. 2(c). Experimental Table 1 Properties of the hollow fiber module. The structure of the extractants.3. was used as the stripping solution. Lothongkum et al. Nitric acid (HNO3). Procedures The single-module operation is shown in Fig. embedded.. Uranium ions from trisodium phosphate solution were 3. the extractant was diluted in kerosene then added into tubes and shell of the HFSLM at the same time for 40 min to assure the extractant embedded in the micropores of hollow fibers.05 mm 30% 1. whereas the inlet stripping solution was fresh. The higher concentration above 0.3. 2 = gear pumps. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 518–523 Fig. the reaction by the synergistic extractant of Aliquat 336 and TBP are proposed in this work.. be achieved by increasing the concentration of the extractant.5 M. 9 = inlet stripping solution). 4 = outlet pressure gauges.W. This result is in agreement with the studies as demonstrated.12 M. 2(c) because a basic extractant is good for cations. the extractability abruptly decreased. It might be implied that uranium ions in trisodium phosphate solution was in [UO2(CO3)3]4. of which its extractability came after D2EHPA and as high as with the increasing operating time. stripping solution [HNO3] = 0. 6 = outlet stripping solution. 6. 8 = outlet feed solution. 6 reveals that higher extraction of uranium can Fig. Percentages of uranium extraction at different concentrations of Aliquat 336: stripping solution [HNO3] = 0. This fact can be explained by Le Chatelier’s principles that the increase in extractant concentration in the liquid membrane results in higher fluxes. (1 = inlet feed solution. while D2EHPA. (4). 4. as shown in the schematic diagram in Fig. 5. when the operating time increased. Eq. The concentration of uranium ion was measured by the inductively coupled plasma spectroscopy (ICP). ½UO2 ðCO3 Þ3 4 þ 2ðNR4 Þþ Cl @ ðNR4 Þ2 ½UO2 ðCO3 Þ2 2 þ 2Cl þ CO3 2 (3) Fig. 7. In this work. (3) shows that uranium species form the complex with Aliquat 336 in modified leaching and extraction of uranium from monazite (El-Nadi et al.1 M due to an easier concentration preparation. Aliquat 336. The synergistic effect of two extractants Because the separation efficiency and recovery by HFSLM depends on a proper selection of the suitable extractant in the system. However.14 M. Qfeed = Qstrip = 100 mL/min. The concentration of uranium ion in the outlet stripping solution was measured individually. Qfeed = Qstrip = 100 mL/min. 521 Fig. 7 and 8. the feed of the second cycle was obtained from the first outlet feed solution and so on. . 4. Percentages of uranium extraction at different concentration of coextractants mixed with 0.12 M. in the experiments the concentration of Aliquat 336 was fixed at 0. 4. Qfeed = Qstrip = 100 mL/min. Lothongkum et al.1 M different extractants. In Eq. In case the study of the numbers of cycle (the consecutive extraction).5 M. a single extractant and a mixture of two extractants in liquid membrane known as the synergistic extractant for the highest separation of uranium were reported in Figs.1. 2005). Effect of the extractant concentration The concentration of Aliquat 336 was varied in the range of 0. is good for anions form of UO22+. Effects of the type of extractant The percentage of extraction was plotted against the operating time.2. the extraction was likely decreased. moved across the liquid membrane to the stripping phase and were collected in the stripping reservoir.5 M. the flux decreases because the increase in film viscosity becomes dominant and obstructs mass transfer. Percentage of uranium extraction against operating time using 0. which acquired the extraction of uranium about 32%. Fig. an acidic extractant. 4. In this work. Schematic diagram of the one-module microporous polypropylene hollow fiber membrane. 7 = hollow fiber module. 3 = inlet pressure gauges. But apparently above 0. was considered the most appropriate for uranium extraction.12 M. Results and discussion 4. The results from Fig. The optimum concentration was found around 0. 5 showed that D2EHPA obtained high percentage of extraction.A. 5 = outlet flow meters.1 M Aliquat 336: stripping solution [HNO3] = 0. However.02–0. stripping solution [HNO3] = 0. for a one-module operation with one-cycle separation (50 min). 9. 7.4. 11. by using the synergistic extractant (0. The highest uranium extraction from trisodium phosphate solution was obtained by synergistic extractant of 0.1 M Aliquat 336 and 0.06 M TBP) and nitric acid of 0. in the range of 0. stripping solution [HNO3] = 0. 4. Percentages of uranium extraction and stripping by synergistic extractant of 0. Effects of the flow rates of feed and stripping solutions The flow rates of feed to stripping solutions play an important role on the percentages of extraction and stripping. In addition. From Figs.1 M Aliquat 336 mixed with 0.06 M TBP was higher than those obtained by a single 0.1 M Aliquat 336 mixed with 0. the highest percentages of extraction and stripping of uranium ions about 34 and 18 were achieved.5 M.1–0. This can be explained by the principles of Le Chatelier.5 M on the stripping of uranium was examined.5. Qfeed = Qstrip = 100 mL/min. It is noted that higher percentages of extraction and stripping were obtained at lower flow rates of feed and stripping solutions. 10. However. 7 and 8.06 M TBP. 4.06 M. ½UO2 ðCO3 Þ3 4 þ 2ðNR4 Þþ Cl þ xTBP @ ðNR4 Þ2 ½UO2 ðCO3 Þ2 2 TBPx þ 2Cl þ CO3 2 (4) Fig. 8).06 M TBP. .5 M. the highest percentages of the extraction and stripping of uranium ions about 34 and 18 from one-module operation with one-cycle separation were attained. the percentages of extraction using synergistic extractants were higher than those by either a single extractant of Aliquat 336 or TBP. Percentages of uranium extraction and stripping against flow rate of stripping solution: extractant 0.A. Qstrip = 100 mL/min.1 M Aliquat 336 mixed with 0. Lothongkum et al. Qfeed = 100 mL/min. 9.06 M TBP. The extractant was 0. the minimum flow rate was not lower than 100 mL/min.06 M TBP at Qfeed = Qstrip = 100 mL/min against concentration of HNO3. Percentages of uranium extraction against extractants: stripping solution [HNO3] = 0. 8. too high flow rate. Too high flow rates of feed and stripping solutions result in less residence time or less contact time for metal ions to react in the extraction and stripping reactions in the HFSLM process.5 M as the stripping solution.5 M. a stripping solution. as seen in Fig. it can be explained that the consecutive extraction using the mixture of two extractants enhanced uranium ion flux and extraction.1 M Aliquat 336 mixed with 0. / Journal of the Taiwan Institute of Chemical Engineers 40 (2009) 518–523 522 Fig. 10 and 11 show the relationship between the percentages of extraction and stripping of uranium at different equal flow rates of feed and stripping solutions by a counter flow pattern. due to the limitation of the system in this work.5 M to avoid the degradation of polypropylene hollow fiber due to high acidic condition. Figs. The extraction increased with the concentration of TBP upto 0.1 M Aliquat 336 and TBP.W. Fig. From Fig. The nitric acid concentration was limited at 0.1 M Aliquat 336 mixed with 0. especially at 180 mL/min may deteriorate the membrane system which can be seen from poor system stability in terms of lower percentages of extraction and stripping of uranium ions. The results indicated that by using the flow rates of both feed and stripping solutions at 100 mL/min. Fig. Percentages of uranium extraction and stripping against feed flow rate: extractant 0. The optimal flow rate results by a balance between pressure drop and mass transfer rate. Effect of the stripping solution concentration The effect of the concentration of nitric acid.1 M Aliquat 336 mixed with 0. The increase in the concentration of the stripping solution in this study results in a progressive increase of the stripping of uranium.06 M TBP (Fig. Since the total percentage of uranium extraction by 0. Thailand are deeply acknowledged. Z. 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