185
Znd. Eng. Chem. Res. 1991,30, 185-190 Gehrhardt, H. M.; Kyle, B. G. Fixed Bed, Liquid Phase Drying with Molecular Sieve Adsorbent. Ind. Eng. Chem. Process Des. Dev. 1967,6 (3),265. Gester, G. C. Design and Operation of a Light Hydrocarbon Distillation Drier. Chem. Eng. Prog. 1947,43, 117. Goto, C.; Joko, I.; Tokunaga, K. Dynamic Drying of Liquids with Zeolite-A Synthesized from Halloysite. Nippon Kagakukai 1972, 11, 2070. Goto, M.; Mataumoto, S.; Yang, B. L.; Goto, S. Dynamic Drying of Benzene with Ion-Exchange Resin. J. Chem. Eng. Jpn. 1986,19 (5),466. Gregor, H. P.; Gutoff, B. F.; Broadley, R. D.; Baldwin, D. E.; Overberger, C. G. Studies on Ion Exchange Resins. Capacity of Sulphonic Acid Cation Exchange Resins. J . Colloid. Sci. 1951a,6, 20. Gregor, H. P.; Gutoff, B. F.; Bergman, J. I. Studies on Ion Exchange Resins. I1 Volumes of Various Cation Exchange Resin Particles. J . Colloid. Sci. 1951b,6, 245. Gregor, H. P.;Held, K. M.; Bellin, J. Determination of the External Volume of Ion Exchange Resin Particles. Anal. Chem. 1951c,23, 620. Gregor, H. P.; Sundheim, B. R.; Held, K. M.; Waxman, M. H. Studies on Ion Exchange Resins. V Water Vapor Sorption. J. Colloid Sci. 1952,7,511. Gregor, H. P.; Nobel, D.; Gottleib, M. H. Studies on Ion Exchange Resins. XI1 Swelling in Mixed Solvents. J . Phys. Chem. 1955, 59, 10. Jain, L. K.; Gehrhardt, H. M; Kyle, B. G. Liquid Phase Adsorption Equilibria with Molecular Sieve Adsorbent. J. Chem. Eng. Chem. 1965,I O , 202. Joshi, S.R. Adsorptive Drying of Organic Liquids. Ph.D. Dissertation, The University of Texas at Austin, 1987.
Joshi, S. R.; Fair, J. R. Adsorptive Drying of Toluene. Znd. Eng. Chem. Res. 1988,27,2078. Lees, F. P. Desorption into a Dry Gas for Drying Organic Liquids. Br. Chem. Eng. 1969,14 (21,173. Moseman, M. H.; Bird, G. Desiccant Dehydration of Natural Gasoline. Chem. Eng. Prog. 1982,78 (2),78. Mundale, V. D.; Lohokare, S. R.; Ravimohan, A. L. CATAD Liquid Drying Processes. Chem. Eng. World 1979,14 (9),103. Polak, J.; Lu, B. C. Y. Mutual Solubilities of Hydrocarbons and Water at 0 OC and 25 OC. Can. J . Chem. Eng. 1973,51, 4018. Sirkar, S.;Meyen, A. L.; Molstad, M. C. Adsorption of Dilute Solutes From Liquid Mixtures. Trans. Faraday SOC.1970,66,2354. Starshov, I. M.; Ivanova, G. Y.; Minnibaeva, L. I. Neftepererab. Neftekhim. 1973,2,31. Stuckhov, G.; Petrenko, D. S.; Geyid, Y. P.; Keltsev, N. B. Khim. Technol. 1975,I , 16. Suzuki, K.; Monoi, Y. Practical Designing of an Adsorption Apparatus V. Kapaku Sochi 1976.18.52. Teo, W. K.; Rithven, D. M. Adsorption of Water from Aqueous Ethanol Using 3A Molecular Sieves. Znd. Eng. Chem. Prod. Des. Dev. 1986,25, 17. Waxman, M. H.; Gregor, H. P.; Sundheim, B. R. Studies on Ion Exchange Resins. VI Water Vapor Sorption by Polystyrenesulphonic Acid Resins. J . Phys. Chem. 1953,57,969. Wymore, C. E. Sulphonic-Type Cation-Exchange Resins As Desiccants. Znd. Eng. Chem. Prod. Res. Dev. 1962,1 (31,173. Wymore, C.E. Dynamic Water Sorption From Organic Liquids by Anion and Carboxylic Acid Resins. J. Znorg. Nucl. Chem. 1964, 26,855. Received for reoiew July 16,1990 Accepted August 1, 1990
Adsorption and Elution in Hollow-Fiber-Packed Bed for Recovery of Uranium from Seawater Toshiya Takeda, Kyoichi Saito,* Kazuya Uezu, and Shintaro Furusaki Department of Chemical Engineering, Faculty of Engineering, University of Tokyo, Hongo, Tokyo 113, Japan
Takanobu Sugo and Jiro Okamoto Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Takasaki, Gunma 370-12, Japan
A 0.9-m-high fixed bed charged with hollow fibers containing amidoxime groups was placed on the coast of the Pacific Ocean for the recovery of uranium from seawater. Continuous flow of seawater a t a superficial velocity of 4 cm/s provided an averaged uranium content of 0.97 g of U/kg in the amidoxime hollow fiber along the bed after 30 days contact. An elution curve having a 230 g of U/m3 peak concentration and a 45 g of U/m3 integrated concentration of uranium was obtained at a superficial velocity of 1N HC1 of 0.0125 cm/s. The required cross-sectional area of the amidoxime hollow fiber-packed bed to produce 10 kg of U per annum was calculated as 9.4 m2 with a 0.9-m bed height.
Introduction The concentration of uranium in seawater is remarkably constant at 3.3 mg of U/m3. A total uranium content of 4.6 X logtons, dissolved in the world's oceans, is almost a 1000-fold larger than the terrestrial resources of reasonable concentrations. The molar concentration of uranium, 1.4 X lomsmol/m3, is about 1part in 4 X lo6of that of magnesium representative of bivalent cations in seawater. Extensive efforts have been continued to develop an adsorbent capable of separating uranium selectively from the other elements (Schenk et al., 1982; Kobuke et al., 1987; Egawa et al., 1988). At present, a resin containing an amidoxime group, which can be prepared by reaction of cyano groups (-CN)with hydroxylamine (NH,OH), is
promising in view of the adsorption rate, capacity, durability, and production cost. The recovery process of uranium from seawater consists of three systems: (1)adsorption from seawater using an amidoxime resin, (2) purification of the eluate with another chelating resin, and (3) further concentration of uranium using an anion-exchangeresin. An example of the recovery process is shown in Figure 1. Since an adsorbent is required to contact a tremendous volume of seawater in the first step, various effective contacting systems have been suggested and evaluated. The adsorption system in the recovery process of uranium from seawater can be classified with respect to three items: (1)the shape of the adsorbent, spherical or fibrous; (2) the mode of the adsorption bed,
0888-5885/91/2630-0185$02.50/00 1991 American Chemical Society
186 Ind. Eng. Chem. Res., Vol. 30, No. 1, 1991 Seawater
I
1'
HCI
Table 11. Summary of Uranium Adsorption Rate of Amidoxime Adsorbent bed superficial adsorption length, velocity, rate,' g of cm cm/s researcher U/kg 44 0.29-1.36 0.19 Astheimer et al., 1983 0.044-0.44 50 0.14 Omichi et al., 1986 0.34 0.3 1.8 GIRIS, 1980 0.125-1 0.11 30 Uezu et al., 1988 0.25-1 0.26 Saito et al., 1988 30 1 0.24 Saito et al., 1990 3 4 0.51 90 this study 10-day contact.
Y e l l o w cake Figure 1. Recovery process of uranium from seawater.
Table I. Summarv of AdsorDtion Svstem Suggested shape of adsorption force transporting researcher adsorbent bed seawater Best, 1980 bead fixed Pump Driscoll, 1983 cloth fixed Pump Kanno, 1983 bead fluidized Pump bead Suzuki et al., 1985 fluidized Pump Koske et el., 1983 bead loop Pump current bead fixed Okazaki et al., 1988 Hirai et al., 1988 bead fixed current Nobukawa et al., 1989 fiber fixed current bead fluidized current Bitte et al., 1983 Chihara et al., 1987 bead fluidized current Nakamura, 1989 bead loop current Forberg et al., 1983 bead fixed wave Suzuki et al., 1987 bead fluidized wave this study hollow fixed Pump fiber
fixed or fluidized; and (3) the method for moving the seawater, pumping or ocean current. The system is constituted by a combination of the three items. The previous studies on the adsorption system are summarized in Table I. Our study deals with a fixed bed charged with amidoxime hollow fibers through which seawater flows driven by a pump. The concentration factor (CF) of uranium defined by (1)has been reported to be more than lo6 for the amidconcentration factor = (the amount adsorbed on the adsorbent) /(the concentration in natural seawater) (1) oxime resin for 10 days (Takagi et al., 1989). The adsorption isotherm in seawater is difficult to obtain experimentally because of a much higher CF than a conventional adsorbent (Hori et al., 1987);i.e., a much longer time is required to attain equilibrium. Thus, the theoretical analysis of the adsorption rate cannot be done definitely and the adsorption rate should be measured directly. To design the adsorption bed, data correlating the amount of uranium adsorbed with the flow velocity through a bed of a given length are required. Previous data on the adsorption rate for the amidoxime resin are summarized in Table 11. Most of these studies have been oriented toward screening or improving the adsorbent and not toward designing the bed using the amidoxime resin. For example, the data measured with a shallow bed of 0.3 cm under a high flow velocity are not practical and do not serve as design data. The conditions of the adsorption experiment in our study are depicted in Figure 2, compared with previous studies. This study covers longer bed and higher flow velocity. We have suggested in an earlier study (Saito et al., 1988) a novel adsorption system using amidoxime hollow fibers
This
work
0
0.11, 1
,
, , ,
, 10
,
, , ,
,
,
-j
100
Length of adsorbent column [ cm I Figure 2. Map of experimental range of adsorption: 1, Saito et al. (1990); 2, Saito et al. (1988); 3, Astheimer et al. (1983).
prepared by radiation-inducedgrafting of acrylonitrile onto polyethylene hollow fiber and subsequent chemical conversions. The fixed bed charged with hollow fibers has a significant advantage in that it has a lower pressure drop than a bed charged with spherical adsorbents (Uezu et al., 1988). Moreover, hollow fibers are easier to handle and do not suffer from compaction during passage of seawater as compared with the fibrous adsorbents. The objectives of our study were 3-fold: (1)to obtain the adsorption rate using coastal seawater in the extended range, (2) to elute the uranium adsorbed on the bed charged with hollow fibers, and (3) to design a plant to produce 10 kg of uranium per annum based on the data obtained.
Experimental Section Preparation of Adsorbent. Porous polyethylene hollow fiber (Mitsubishi Rayon Co., Ltd., Japan) was used as a trunk polymer for grafting. The inner and outer diameters of this hollow fiber are 0.027 and 0.038 cm with 60% porosity. The filtration module loaded with the bundle of the hollow fibers has been commercially used as a water purification device. The preparation process of the amidoxime hollow fibers (AO-H fiber) consists of the following three steps: (1)radiation-induced grafting of acrylonitrile onto porous hollow fibers, (2) amidoximation, and (3) alkaline treatment. The optimum preparation conditions have been reported elsewhere (Saito et al., 1990). The properties of the resulting AO-H fibers are summarized in Table 111. Prior to the adsorption experiment, the AO-H fibers were immersed in 1 N hydrochloric acid at ambient temperature for 1h and washed repeatedly with deionized water. Adsorption of Uranium from Seawater. A continuous-flow experimental setup placed on the coast of the Pacific Ocean is shown in Figure 3. Seawater was first filtered through a sand filter and a subsequent pleated
Table 111. Properties of AO-H Fiber and Adsorption Bed AO-H fiber degree of grafting density of A 0 group i.d. 0.d. apparent density adsorption bed i.d. length void fraction bulk density a
h
.
A
g
I
1
I
I
I
L= 0.9 m u= 4 cm/s
Q,
1 cm
F l >
90 cm
1
-
125% 11.3 mol/kg base polymer 0.37 mm 0.49 mm 0.51 kg of resin (HCl)”/L of resin (KOH)b Q,
0.75 0.13 kg of resin (HCl)/L of bed
HC1 adsorbed AO-H fiber. bKOH treated AO-H fiber.
Fixed-Bed Column Charged with Amidoxime Hollow Fibers
II
OO
10
20
30
Time [dl Figure 5. Uranium uptake from seawater as a function of contact time.
h
-w
-
Ind. Eng. Chem. Res., Vol. 30,No. 1,1991 187
IB I t
Sand Bed
Seawater
Figure 3. Experimental setup of adsorption.
H Figure 4. Cross-sectional area of AO-H fiber packed bed (marker = 1 mm).
cartridge fiiter having a nominal pore size of 10 pm (TC-10, Toyo Roshi Co., Ltd., Japan) and then passed upward through the AO-H fiber packed bed. The temperature of the seawater was kept a t 299-303 K. A bundle of 230 AO-H fibers, 15 cm in length, was charged in a 1-cm-i.d. column that was 15 cm in length. The cross section across the column is pictured in Figure 4. Seawater flows through both the lumen and shell parts of the AO-H fiber set in a direction parallel to the flow and does not permeate across the hollow fiber wall. The void fraction of the bed was calculated to be 76%, and the ratio of the inner (lumen) part to outer (shell) part of the AO-H fiber was 7/10. The bundle of the hollow fibers functions as a packed adsorbent which exhibits a relatively low pressure drop, and not as a filtration membrane. The connection of six columns afforded a 90-cm-high column. The superficial velocity of the seawater was set to be 4 cm/s and controlled precisely. After specific time intervals, the uranium concentration in the seawater sampled from the inlet and
outlet of the bed was determined by an established method (Shijo and Sakai, 1982). The concentration difference in the liquid was converted into the averaged amount of uranium adsorbed on the AO-H fibers along the column. To understand the distribution of uranium along the bed, after 30 days contact, five pieces of the AO-H fibers were taken from each of the six columns. They were then soaked in 1N hydrochloric acid to elute uranium and other elements adsorbed. The uranium content in the eluates was determined colorimetrically (Motojima et al., 1969). Other metals in the eluates were determined by atomic absorption spectometry. Elution of Uranium from AO-H Fiber Packed Bed. Elution was done according to the following procedures: (1)washing with deionized water to remove the surface seawater, (2) preelution with 0.01 N HC1 to elute weakly bonded elements such as magnesium and calcium (Suzuki et al., 1986), and (3)elution with 1N HC1 to elute uranium. Each liquid was passed upward through the 90-cm-high AO-H fiber packed column at a prescribed velocity. The effluent was collected continuously with a fraction collector until a prescribed bed volume was attained. Bed volume (BV) may be defined as the volume of the bed, 70.7 cm3. The elution curve was measured at ambient temperature. Elution Equilibrium. The elution equilibrium, i.e., the adsorption equilibrium in an eluate, was obtained by means of batch experiments. Prior to the elution, the fibers taken out of the column were immersed in an excess volume of 0.01 N HC1. Various amounts of the AO-H fibers were allowed to reach equilibrium with a known volume of 1N HC1 in sealed Erlenmeyer flasks. The flasks were placed in a constant-temperature shaker bath kept at 298 K. After equilibration, liquid samples were withdrawn and analyzed. Subsequent complete elution provided the initial content of adsorbed uranium.
Results and Discussion Adsorption of Uranium from Seawater. Seawater was introduced over 30 days through a 90-cm-high AO-H fiber packed bed at a superficial velocity of 4 cm/s, which corresponds to 22.5 s of mean residence time. The averaged amount of uranium adsorbed on the AO-H fibers along the bed is shown in Figure 5 as a function of contact time. We have obtained an uranium uptake of 0.97 g of U/kg of the AO-H fibers and a recovery ratio of 31% after 30 days contact for a superficial velocity of 4 cm/s. The resulting uranium content of the AO-H fibers is approximately equivalent to that of terrestrial low-grade uranium ores. The recovery ratio is defined as follows: recovery ratio = (total amount adsorbed along the bed)/(total amount flowed through the bed) (2)
188 Ind. Eng. Chem. Res., Vol. 30, No. 1, 1991 300
I
I
I , , , > j
5 a P
I
,
oo
(
,
,
30
60 Height [cml
90
Effluent volume I BV
I
Figure 8. Elution curve of uranium.
Figure 6. Uranium distribution adsorbed along the bed.
Figure 7. Ca and Mg distribution adsorbed along the bed.
Table IV. Comparison of Uranium Elution Performance from Amidoxime Adsorbent Suzuki Hirotsu et al. this et al. (1986) (1987) study elution bed 1 diameter, cm 1 7 150 length, cm 300 90 adsorbent hollow fiber shape bead bead 1.19 0.94 uranium adsorbed, g of U/kg 1.8 0.51 0.19 apparent density, kg/L 0.24 elution with HC1 1 concn, mol/L 1 0.5 3 0.98 space velocity, l / h 0.3 0.041 0.0125 superficial velocity, cm/s 0.025 ? upward upward direction of flow elution curve peak BV 1 2.2 1.2 0.23 peak concn, g of U/L 9 0.10
The data obtained are compared with the results of the previous studies in Table 11. The experimental conditions of the bed height and velocity in this work are more practical for designing the adsorption bed. The uranium distribution adsorbed along the AO-H fiber packed bed after 30 days contact is shown in Figure 6. Little inclination of the concentration profile was observed along the bed. This will be due to the low recovery ratio and the favorable isotherm of uranium adsorption for AO-H fibers. The distributions of magnesium and calcium are shown in Figure 7. The flat distributions in the figure are reasonable because the concentrations of their ionic species in natural seawater are much higher than that of uranium. From Figures 6 and 7, the concentration factor of each element defined by (1)can be calculated to be 280000, 29, and 49 for U, Ca, and Mg, respectively. Elution of Uranium from AO-HFiber Packed Bed. The amidoxime beads charged in the adsorption bed are required to be transported to another elution bed because the longer bed provides a higher concentration of uranium by applying chromatographic operation. In our suggested system, however, the adsorption bed is easily switched to the elution bed by having the eluate flow in place of seawater. First, water was introduced to wash the column until 18 BV is reached, where the electric conductivity is reduced from 1 X 10' of natural seawater to 24 pS. Second, preelution with 0.01 N HCl up to 50 BV was necessary to elute almost all of the Mg and Ca adsorbed on the AO-H fibers. Third, elution by 1 N HC1 was carried out. The elution curve of uranium at 0.0125 cm/s superficial velocity using 1 N HC1 solution is shown in Figure 8. The uranium concentration in the eluate was 230 g of U/m3 at the peak
point of 1.2 BV. The integrated concentration in the eluate collected in the range between 0.7 and 3.1 BV was 45 g of U/m3 with 95% recovery of uranium. Therefore, the concentration ratio in the adsorption and elution systems using the AO-H fiber packed bed can be calculated as 14000 by dividing 45 g/m3 by 3.3 mg/m3. This ratio meets the requirement for the subsequent purification and concentration system for uranium production using another chelating resin and an anion-exchange resin (Sasaki et al., 1984). The elution performance of the AO-H fiber packed bed is summarized in Table IV, compared to the previous studies using amidoxime bead packed beds. Suzuki et al. (1986) have proposed a long column elution method and reported a remarkably high concentration of uranium up to about 9000 mg of U/L at the peak value using a 3-mhigh bed charged with amidoxime resins containing an initial uranium content of 1.8 mg of U/kg. In this study, however, similar behavior was not observed. This can be explained by the following reasons. (1)The eluate flowed in both the inner and outer parts of the bundle of the AO-H fibers, so that the difference in the liquid velocity caused the residence time distribution in the bed and resulted in broadening the elution curve. (2) The different elution isotherms for the two adsorbents, i.e., amidoxime beads prepared by amidoximation of acrylonitrile-styrene copolymer (Suzuki et al., 1986) and the present amidoxime hollow fibers based on acrylonitrile-grafted polyethylene, caused the difference in the elution behavior. The elution isotherm was determined with the use of the AO-H fibers that adsorbed uranium from coastal seawater and is shown in Figure 9. The amount of uranium adsorbed on the AO-H fibers in 1 N HC1 was correlated
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1 I1
u= 4 cm/s
,
,
,
,
30 Height
,
, 60
(
90
(cml
Ind. Eng. Chem. Res., Vol. 30, No. 1, 1991 189 adsorption bed required was reduced by one order. In addition, the present adsorption-elution system has the following advantages: (1)lower pressure loss (Saito et al., 1988),Le., lower input energy for pumping, and (2) no need to transport adsorbents in switching from adsorption to elution. When the quality of coastal seawater passing through the bed is relatively poor, prefiltration of seawater is necessary to prevent fouling of the amidoxime hollow fibers. Prefiltering could negate the savings of the pressure drop in the hollow-fiber-packed bed. The effect of prefiltering on adsorption characteristics of uranium from seawater will be discussed in a later publication. Uranium concentration [ g - ~ / m ’ l Figure 9. Elution isotherm.
Table V. Comparison of Designing 10 kg of U per annum Plant MMAJ model plant plant suggested in this (1988) study adsorption adsorbent Ti02.xH20-PVC,PAN amidoxime hollow fiber bed mode fluidized bed fixed bed height, cm looa 90 velocity, cm/s 0.5 4 temp, K ? 277-303 contact time, 20 30 days elution eluate 0.5-1 N HCl 1 N HCI ? space 3 velocity, l / h cycles per 10 10 annum area required, 81 9.4 m2 Estimated.
linearly with the concentration of uranium in the solution. For comparison, the data reported by Suzuki et al. (1986) are also plotted in Figure 9. Their isotherm is more favorable to elution, as discussed above. The reason for this difference is unclear. Design of 10 kg/annum Pilot Plant. A plant producing W kg of uranium with 10 adsorption-elution cycles per annum can be directly designed from the experimental results. The cross-sectional area of the adsorption bed charged with amidoxime hollow fiber can be calculated on the basis of the experimental data obtained. Thus, (3.3 X lo4)
X
A
X
u
X
30
X
24 X 3600 X 10 X va = W (3)
where A, u and ‘laare the effective cross-sectional area required (m2),superficial velocity of seawater (m/s), and recovery ratio corresponding to u,respectively. The factors 30 X 24 X 3600 and 10 indicate the contact time of 30 days in units of seconds and the cycle number, respectively. Inserting the experimental results in (3) gives the value of A = 9.4 m2. In Japan, a project to design and test a model plant producing 10 kg of uranium per annum was started in 1978 and terminated in 1985. The Metal Mining Association in Japan (MMAJ) has reported the summary of the results obtained in this project (1988). The results obtained in the present study are compared with those reported by the MMAJ in Table V. Although the effect of the chemical structure of the adsorbent, the temperature, and the quality of coastal seawater on the adsorption rate was unknown at present, obviously the size of the
Acknowledgment We thank Takeji Ohtani of the Membrane and Medical Materials Department, Mitsubishi Rayon Co., Ltd., for his help in providing the starting polymer. Special thanks are also extended to Satoru Aramaki and Yoshimitsu Aramaki of K. S. Auto Co., Ltd., for their elaborate work in manufacturing the automatic experimental apparatus. This work was supported by Grant-in-Aid for Energy Research No. 01603006 from the Ministry of Education, Science, and Culture. Registry No. U, 7440-61-1.
Literature Cited Astheimer, L.; Schenk, H. J.; Witte, E. G.; Schwochau, K. Development of Sorbers for the Recovery of Uranium from Seawater. Part 2. The Accumulation of Uranium from Seawater by Resins Containing Amidoxime and Imidoxime Functional Groups. Sep. Sci. Technol. 1983, 18, 307. Best, F. R. The Recovery of Uranium from Seawater Ph.D. Thesis, Nuclear Engineering Department, MIT, 1980. Bitte, J.; Kellner, A.; Ludwing, K. P. Comparison of Different Extraction Concepts for the Recovery of Uranium from Seawater. Proc. Int. Meet. Recovery Uranium Seawater 1983, 34. Chihara, K. Cost Estimation for Uranium Recovery from Seawater. Rep. Spec. Proj. Res. Energy 1987, 57. Driscoll, M. J. Recent Work on MIT on Uranium Recovery from Seawater. Proc. Int. Meet. Recovery Uranium Seawater 1983, 1. Egawa, H.; Nonaka, T.; Nakayama, M. Influence of Crosslinking and Porosity on the Uranium Adsorption of Macroreticular Chelating Resin Containing Amidoxime Croups. J . Macromol. Sci. Chem. 1988, A25, 1407. Forberg, S.;Langstrom, G.; Vallander, P. Recovery of Uranium from Seawater Using Wave Power. Proc. Int. Meet. Recovery Uranium Seawater 1983, 51. GIRIS (Governmental Industrial Research Institute Shikoku, Japan). Development of a Novel Adsorbent for Recovery of Uranium from Seawater. GIRIS News 1980, 34(9). Hirai, T.; Sakata, N.; Yamada, M.; Tsujitani, J.; Okazaki, M.; Tamon, H. Development of Adsorber System Utilizing Ocean Current for Uranium Recovery from Seawater. Bull. SOC.Sea Water Sci. Jpn. 1988, 42, 7. Hirotsu, T.; Takagi, N.; Katoh, S.; Sugasaka, S.; Takai, N.; Seno, M.; Itagaki, T. Selective Elution of Uranium from Amidoxime Polymer. 11. Sep. Sci. Technol. 1987,22, 2217. Hori, T.; Saito, K.; Furusaki, S.; Sugo, T.; Okamoto, J. Adsorption Equilibrium of Uranium from Seawater on Chelating Resin Containing Amidoxime Group. Kagaku Kogaku Ronbunsyu 1987,23, 795. Kanno, M. MMAJ Project for the Extraction of Uranium from Seawater. Proc. Int. Meet. Recovery Uranium Seawater 1983,12. Kobuke, Y.; Tabushi, I.; Aoki, T.; Kamaishi, T.; Hagiwara, I. Composite Fiber Adsorbent for Rapid Uptake of Uranyl from Seawater. Ind. Eng. Chem. Res. 1987,27, 1461. Koske, P. H.; Ohlrogge, K.; Jager, W. Some Economic Consideration for a Pilot Plant Based on the Adsorber Loop Concept. h o c . Int. Meet. Recovery Uranium Seawater 1983, 89. MMAJ (Metal Mining Agency of Japan). Marine Resources and Its Future. MMAJ Rep. 1988. Motojima, K.; Yamamoto, T.; Kato, Y. 8-Quinolinol Extraction and Spectrophotometric Determination of Uranium with Arsenazo 111. Bunseki Kagaku 1969, 18, 208.
Ind. Eng. Chem. Res. 1991, 30, 190-196
190
Nakamura, S. Study on System for Recovery of Uranium from Seawater. Ph.D. Thesis, Technological University of Nagaoka, Nagaoka, Japan, 1989. Nobukawa, H.; Tamehiro, M.; Kobayashi, M.; Nakagawa, H.; Sakakibara, J.; Takagi, N. Development of Floating Type-Extraction System of Uranium from Seawater Using Seawater Current and Wave Power. Nippon Zosen Cakkai Ronbunsyu 1989,165,281. Okazaki, M.; Tamon, H.; Yamamoto, T. Conceptional System Design for Uranium Recovery from Seawater Utilizing Ocean Current. Bull. SOC.Sea Water Sci. Jpn. 1988,41,257. Omichi, H.; Katakai, A.; Sugo, T.; Okamoto, J. A New Type of Amidoxime-Groupcontaining Adsorbent for the Recovery of Uranium from Seawater. 111. Recycle Use of Adsorbent. Sep. Sci. Technol. 1986,21, 563. Saito, K.; Uezu, K.; Hori, T.; Furusaki, S.; Sugo, T.; Okamoto, J. Recovery of Uranium from Seawater Using Amidoxime Hollow Fibers. AIChE J . 1988,34,411. Saito, K.; Yamaguchi, T.; Uezu, K.; Furusaki, S.; Sugo, T.; Okamoto, J. Optimum Preparation Conditions of Amidoxime Hollow Fiber Synthesized by Radiation-Induced Grafting. J . Appl. Polym. Sci. 1990,39,2153. Sasaki, A.; Echigo, Y.; Yamao, M.; Suematsu, Y.; Ishikura, T.; Hirotsu, T.; Katoh, s.;Sugasaka, K. Separation and Concentration of Uranium from Acidic Eluate. Bull. SOC.Sea Water Sci. Jpn. 1984,37,341. Schenk, H. J.; Astheimer, L.; Witte, E. G.; Schwochau, K. Develop-
ment of Sorbers for the Recovery of Uranium from Seawater. Part 1. Assessment of Key Parameters and Screening Studies of Sorber Materials. Sep. Sci. Technol. 1982, 17,1293. Shijo, Y.; Sakai, K. Rapid Spectrophotometric Determination of Uranium in Seawater. Bunseki Kagaku 1982,31,E395. Suzuki, M.; Chihara, K.; Fujimoto, M.; Yagi, H.; Wada, A. Conceptual Process Design for Uranium Recovery from Sea Water. Bull. Sac. Sea Water Sci. Jpn. 1985,39,152. Suzuki, M.; Fujii, T.; Tanaka, S.; Itagaki, T.; Katoh, S. Million Fold Concentration of Uranium in Seawater by Adsorption and Long Column Desorption Using Amidoxime Resin. h o c . Eng. Found. Conf. Fundam. Adsorpt. 1986,2nd,37. Suzuki, M.; Fujii, T.; Tanaka, S. Adsorption and Desorption Process for Recovering Uranium in Seawater. Rep. Spec. Proj. Res. Energy 1987,49. Takagi, N.;Hirotsu, T.; Sakakibara, J.; Katoh, S.; Sugasaka, K. Preparation of Fibrous Adsorbent Containing Amidoxime Groups from Composite Poly(acrylonitri1e) Fiber and Its Adsorption Ability for Uranium. Bull. SOC.Sea Water Sci. Jpn. 1989,42,279. Uezu, K.; Saito, K.; Hori, T.; Furusaki, S.; Sugo, T.; Okamoto, J. Performance of Fixed-Bed Charged with Chelating Resin of Capillary Fiber Form for Recovery of Uranium from Seawater. Nippon Genshiryoku Gakkaishi 1988,30,359. Received for reuieur March 16, 1990 Accepted August 15, 1990
Modeling of an Adsorption Unit Packed with Amidoxime Fiber Balls for the Recovery of Uranium from Seawater Shigeharu Morooka,*Takafumi Kato, Mitsutoshi Inada, Tokihiro Kago, and Katsuki Kusakabe Department of Applied Chemistry, Kyushu University, Fukuoka 812, Japan
Amidoxime fiber adsorbents are prepared by treating commercial poly(acrylonitri1e) fibers with NHzOH in methanol and then with an aqueous NaOH solution. The rate of adsorption of uranium from seawater is 0.1-0.3 (g of U/kg of dry fiber)/day. The fiber is placed in 2-cm-diameter spherical shells of plastic net, and these fibrous balls are packed in a column. Seawater is assumed t o flow through the packed bed by the kinetic force of the ocean current. The permeation velocity of liquid in each ball is evaluated with a small electrode that detects the electrochemical limiting current. When the permeation velocity is slow, most uranyl ions are adsorbed only in the peripheral part of the ball. A model of the packed bed adsorption unit is proposed, and a numerical calculation gives optimum values of design parameters. The recovery of uranium from seawater has been tested with various adsorbents, and derivatives of poly(acry1onitrile) known as amidoxime resin have been shown to be most promising (Egawa, 1979, 1988; Schenk et al., 1982; Astheimer et al., 1983; Egawa et al., 1988). Amidoxime resin is normally used as small spheres that are contacted with seawater in a fluidized bed (Kanno, 1983; Koske and Ohlrogge, 1983), but fibrous amidoxime adsorbent prepared with commercial poly(acrylonitri1e)fiber is also very useful (Katoh et al., 1982; Saito et al., 1988; Kobuke et al., 1988; Shirotsuka et al., 1988; Takagi et al., 1989; Morooka et al., 1990b). It is possible to increase the adsorption rate up to ca. 3.5 g/kg of dry fiber in 7 days if the tensile strength of the fiber is left out of' consideration (Takagi et al., 1989). Because the fibrous adsorbent is quite bulky, the contacting system between fiber and seawater is inherently different from that for particulate adsorbents. In the previous study (Morooka et al., 1990a), amidoxime fiber was sandwiched with plastic nets in the shape of small
* Author to whom
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mattresses 2 cm square and 2 mm thick. This type was chosen so that the fibrous adsorbent might be handled like particles. It was shown that the mattresses were fluidized smoothly when a swirling flow was imposed by means of a specially designed liquid distributor. Fluidization can be maintained by an ocean current that induces a superficial liquid velocity of 5-10 cms-' in the bed. Other designs such as streamers and filters are possible with fibrous adsorbents, but the study of their feasibility is still insufficient. Recently, Katoh and co-workers (Katoh and Sugasaka, 1987)prepared ball-type adsorbents by entangling chopped fibers during the amidoximation. These fibrous balls may be used in a fluidized or packed bed. Nobukawa et al. (1989) proposed an adsorption system using amidoxime fiber balls packed in cages of 3-5-m diameter with a thickness of 0.2-1 m. The cages are arranged in stacks below the sea surface suspended by ropes from a buoy. Seawater around the fibrous balls is exchanged by the flow due to the heaving motion of the buoy and the kinetic force of the ocean current. The production cost of uranium was estimated to be 20000 yen/kg of uranium if the fiber could 0 1991 American Chemical Society
