Preparation and Adsorptive Properties of Membrane-Type Adsorbents

Continuous lithium mining from aqueous resources by an adsorbent filter with a .... separable magnetite–lithium manganese oxide nanocomposites as re...
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Ind. Eng. Chem. Res. 2002, 41, 4281-4287

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Preparation and Adsorptive Properties of Membrane-Type Adsorbents for Lithium Recovery from Seawater Aya Umeno,* Yoshitaka Miyai, Norio Takagi, Ramesh Chitrakar, Kohji Sakane, and Kenta Ooi* National Institute of Advanced Industrial Science and Technology, 2217-14 Hayashi-cho, Takamatsu 761-0395, Japan

A membrane-type adsorbent of spinel-type manganese oxide was prepared by a solvent exchange method using poly(vinyl chloride) (PVC) as a binder. PVC was dissolved in N,N-dimethylformamide (DMF) solution, after which spinel-type lithium manganese oxide was mixed with the DMF solution. The suspension was spread into a thin film and immersed in water to solidify the PVC. The membrane was treated with an HCl solution to extract lithium, resulting in a membrane-type adsorbent. The preparation conditions were studied by changing the initial PVC concentration versus DMF and lithium manganese oxide content. The membrane thickness, manganese oxide content, and tensile and abrasion strengths were measured for each membrane. A new type of adsorption cell was designed for obtaining a parallel seawater flow along the membrane-type adsorbents. The lithium adsorption experiment was carried out using natural seawater at a linear velocity of 1.25 cm/min. Placing the membrane between spacers was found to be effective in raising the lithium adsorption rate. The adsorption rate depended on the preparation conditions. The membrane prepared from an initial PVC concentration of 8%, and a PVC additive content of 20% is optimum for the adsorption of lithium in seawater. The adsorbed lithium could be easily eluted by treating with an HCl solution. Introduction Interest in lithium sources has been increasing because of wide applications of the metal in high-energy storage lithium batteries and its compounds in other fields.1 Seawater is considered to be an important future source of lithium, although the concentration of lithium is very low (0.17 mg/dm3). We are interested in technologies for the recovery of lithium from seawater, for which there have already been several studies.2-4 Among the various methods for element separation, the adsorption method is the most promising for the lithium/ seawater system from economic and environmental viewpoints. We have developed a manganese oxide adsorbent for lithium in seawater.5-7 It is obtained by the topotactic extraction of lithium from Li1.33Mn1.67O4 spinel with acid. The H+/Li+ exchange reaction progresses during the acid treatment maintaining the spinel structure to form lithium ion-sieve sites.8,9 The adsorbent (H1.33Mn1.67O4) shows highly selective adsorption for lithium in seawater, although seawater contains over 10 000 times more sodium than lithium ions. The adsorption progresses by the Li+/H+ exchange reaction because seawater is slightly alkaline (pH 8). Recently, we have developed a novel adsorbent based on a Li1.6Mn1.6O4 precursor,10 capable of a lithium uptake of 40 mg/g from seawater,11 which corresponds to a lithium content (8% as Li2O) exceeding that of lithium ores. A column adsorption method is generally more appropriate than a batch method for the recovery of a diluted element from solution. We have carried out column adsorption studies using manganese oxide adsorbents.12,13 The manganese oxide powders were granulated with poly(vinyl chloride) (PVC) as a binder, and * Corresponding authors. E-mail: [email protected], a-umeno@ aist.go.jp.

bench-scale studies were carried out with a cone-shaped tank in a fluidized-bed state. Lithium was recovered effectively from seawater, and lithium carbonate of a reagent grade could be obtained.13 From an economic standpoint, it is necessary to use natural seawater flow instead of a pumped flow. Natural seawater flow has the characteristic of low hydraulic pressure, although the velocity is relatively high. However, although the column method is disadvantageous for natural seawater flow, because it requires a high pressure to achieve the fluidized state which is needed for the granules to contact seawater water effectively, a membrane-type adsorbent is a promising candidate for this application. When the membranes are set in a parallel arrangement in a cell, seawater can flow smoothly between the membranes with a small loss of head pressure, even in such low pressure differential conditions. A membrane-type adsorbent has an additional merit in that the adsorption module can be constructed easily by stacking or coiling membranes. The present paper describes the preparation of a membrane-type adsorbent and its lithium adsorptive properties from seawater. The membrane-type adsorbent was prepared by the solvent-exchange method using PVC as a binder. The preparation conditions were investigated changing the PVC additive content and initial PVC/DMF concentration. A new type of adsorption cell was designed for obtaining a parallel seawater flow along membrane-type adsorbents. The adsorption experiment was carried out using natural seawater. Experimental Section Preparation of Membrane-Type Adsorbent. A membrane-type adsorbent was prepared using poly(vinyl chloride) (degree of polymerization: 780 ( 20) as a binder, as is shown in Figure 1. After a known weight

10.1021/ie010847j CCC: $22.00 © 2002 American Chemical Society Published on Web 07/27/2002

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Figure 1. Synthesis of membrane-type adsorbent.

of PVC was dissolved in 30 g of N,N-dimethylformamide (DMF), the precursor powder Li1.33Mn1.67O4 was added to the solution and mixed vigorously. The suspension was set on a support of film-making equipment (Tester Sangyo, type Pl-1210z film coater) and spread at a speed of 10 mm/s. After the spreading run ended, the membrane was immersed in water to remove DMF and solidify the PVC, followed by water washing. The membrane was treated with an HCl solution to extract lithium, resulting in a membrane-type adsorbent. Two preparation conditions, the initial PVC concentration ([PVC]ini) and the binder additive content (Cbind), were examined in detail. These were calculated as follows:

initial PVC concentration (%) ) 100 PVC (g)/DMF (30 g) binder additive content (%) ) 100 PVC (g)/[PVC (g) + Li1.33Mn1.67O4 (g)] The samples are designated as M-8-15(Li) and so forth for the precursors and M-8-15(H) and so forth for the acid treated membranes, where the first number indicates the intial PVC concentration and the second the binder additive content. PVC was purchased from Shin Dai-Ichi Vinyl Co, Ltd. and Li1.33Mn1.67O4 powders from Nihon Juka Co. Ltd. The other reagents used were of reagent grade. Adsorption Studies. Lithium adsorptive properties in filtered natural seawater (CLi ) 0.17 mg/dm3) were investigated at 303 K using parallel-flow adsorption cells separated into five compartments. The adsorption apparatus is shown schematically in Figure 2. To equalize the seawater flow in each lane, two kinds of barriers, A (a perforated board) and B (V-shaped wiers), were fitted. Three sheets of membrane-type adsorbent (15 × 40 mm) were set longitudinally in each compartment, with or without spacers, and the seawater flushed through at a velocity of 50 cm3/min (linear velocity: 1.25 cm/min). The three adsorbents were taken out together at a predetermined time, and the lithium uptake was determined and calculated by averaging the three. Adsorption isotherms for powdered and membranetype adsorbents were obtained with lithium-enriched seawater (CLi ) 5 mg/dm3) at 303 K. From the previous

study for granulated adsorbent,12 the LiCl-enriched seawater (CLi ) 5 mg/dm3) was found to be the appropriate solution for determining the adsorptive capacity of the adsorbent in a short period of time, with only small influence of lithium chloride addition on adsorptive capacity. The maximum uptakes of Li+ ion were evaluated by extrapolating the experimentally determined values to the concentration of Li+ ion in natural seawater. In a batch-type study, a known weight of adsorbent was added to the lithium-enriched seawater and stirred for 20 days. After stirring, the lithium concentration in the supernatant solution was determined by atomic absorption spectrometry. The lithium uptake was calculated from the concentration decrease relative to the initial concentration. The uptakes of other alkali and alkaline earth metal ions by the same kind of membrane-type adsorbent after flushing with seawater for 15 days were also examined. The concentration factor (CF) for the metal ions was calculated as follows:

CF (dm3/kg) ) metal ion uptake (mg/kg)/ metal ion concentration in seawater (mg/dm3) Chemical Analysis. The lithium, manganese, and other metal ion contents of the membrane were determined with a Shimadzu AA-760 atomic adsorption spectrometer after dissolving in a 0.5 M HCl solution containing hydrogen peroxide. The lithium and other metal ion uptakes could be calculated from these values. Physical Properties. The tensile strength of the membranes was measured in accordance with the Japan Industrial Standard (JIS P8135: determination of tensile strength after immersion in water) using a test piece 4 × 8 mm2. Elastic modulus and maximum point stress were determined for each membrane. Abrasion loss by shaking was determined by the same method as that reported for granular adsorbent in a previous paper,13 whereby water (50 cm3) and nylon balls (9.5 mm φ, 20 pieces) were put into a separation funnel (100 cm3) along with a membrane (15 × 40 mm) and shaken for 2 h. Abraded manganese oxide powders were separated, and the remaining membrane was weighed. The abrasion strength was calculated as the ratio of the weight of the residual membrane to that of initial membrane. Membrane thickness was measured by micrometer. SEM observation was carried out on a Hitachi-type S-2460N scanning electron microscope. Results and Discussion Preparation and Properties of Membrane-Type Precursors. The properties of the membrane-type adsorbents obtained under different conditions are given in Table 1. First, the effect of initial PVC concentration was examined at a binder additive content of 20%. A membrane could not be obtained at [PVC]ini ) 6% because of low viscosity. The membrane prepared at [PVC]ini ) 15% had an elastic modulus too low to measure. The preliminary adsorption experiment showed that the rate of lithium adsorption increased with a decrease of [PVC]ini. Therefore, the condition [PVC]ini ) 8% was deemed most suitable for the preparation of the membrane-type adsorbent. The effect of binder additive content was examined at [PVC]ini ) 8%, changing the binder content in the region between 10% and 30%. Specific membrane area

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Figure 2. Schematic representation of parallel flow adsorption equipment. Table 1. Properties of Precursor Membranes tensile strength sample

specific membrane area/cm2 g-1

M-6-20(Li) M-8-20(Li) M-15-20(Li) M-8-10(Li) M-8-15(Li) M-8-20(Li) M-8-25(Li) M-8-30(Li)

90 63 56 63 90 98 120

membrane thickness/mm

manganese oxide content/mg g-1

unobtainable membrane 0.24 ( 0.01 470 ( 20 0.28 ( 0.03 550 ( 20 0.28 ( 0.01 560 ( 10 0.26 ( 0.02 520 ( 20 0.24 ( 0.01 470 ( 20 0.23 ( 0.03 420 ( 40 0.20 ( 0.04 380 ( 50

per unit weight, membrane thickness, and manganese oxide content are given in Table 1. Mean manganese oxide content decreased while dispersion of the manganese content increased with an increase in the binder content. Specific membrane area increased with an increase in the binder content, due to the decrease of membrane thickness. Because the viscosity of the suspension increases with manganese oxide content for a fixed PVC concentration, the decrease of membrane thickness can be ascribed to the decrease of the viscosity due to the lower manganese oxide content. The elastic modulus and maximum point stress increased with binder content. All samples showed abrasion strength above 90%, but the supernatant solutions after the abrasion test became more turbid for the samples with binder content less than 15%, due to the abrasion of a small amount of manganese oxide powder. SEM images of M-8-20(Li) and M-15-20(Li) are given in Figure 3. The cross-sectional images show that the manganese oxide powders are more loosely packed for sample M-8-20(Li). The membrane surfaces of neither sample were uniform. The surfaces derived from the air/ membrane interface of the film are smooth with small pores of around 1 µm. The surfaces derived from the membrane/support interface, however, are relatively rough and have many large pores between 2 and 10 µm in size. Usually, membranes obtained by the solvent exchange method have nonuniform surfaces due to solvent evaporation during film spreading.15 The formation of the smooth close surface of the air/membrane interface may be due to the evaporation of DMF and

elastic modulus/GPa longitudinal

lateral

0.07 0.08 not determined 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 0.11 0.12

maximum point stress/MPa longitudinal

lateral

abrasion strength/%

1.36 1.50 1.00 1.19 1.36 1.60 1.83

1.72 1.80 1.22 1.43 1.72 1.90 2.24

99.4 99.8 99.2 99.3 99.5 99.6 99.8

the decrease of manganese oxide powders at the surface during spreading. The pores are advantageous for the diffusion of metal ions into the membrane. The diffusivity in the solid phase is generally described as D ) Dsol/k2, where  is porosity, Dsol is diffusivity in aqueous phase, and k2 is tortuosity factor. Therefore, the diffusivity increases with porosity; the pores are advantageous for lithium diffusion in the solid phase. Of course, the diffusivities of other metal ions increase with an increase in the porosity, but there are little adsorption sites for these metal ions. Most of these metal ions are removed from the membrane by only water washing. Lithium Extraction from the Precursor. The membrane-type adsorbent can be prepared by the H+/ Li+ exchange of the precursor with acid. The lithium extraction behaviors from the precursors were investigated batchwise using HCl solutions with different concentrations. The amounts of lithium extracted and manganese dissolved from M-8-20(Li) by acid treatment for 2 days are summarized in Table 2. Lithium extraction was consistently above 90% and tended to increase slightly with an increase in HCl concentration but decrease with the solid-to-solution ratio. The amount of manganese dissolved was below 4% at a HCl concentration less than 0.75 M but became higher (6.8%) at 1 M. The rate of lithium extraction is fast due to availability of large number of H+ ions; a treatment for 15 h is sufficient to reach equilibrium (Figure 4). Because the proton concentration (0.75 M) is extremely higher than the Li concentration (0.000 024 M) of seawater, the extraction can progress fast. Treatment of the mem-

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Figure 3. SEM images of M-8-20(Li) and M-15-20(Li). Table 2. Lithium Extraction from the Precursora HCl concn M

solid-to-soln ratio mg cm-3

amount of Li extracted %

amount of Mn dissolved %

0.25 0.50 0.75

3 3 3 6 8 10 3

95 96 98 96 95 93 98

3.3 3.5 3.6 3.6 3.6 3.6 6.8

1.00 a

Precursor membrane: M-8-20(Li).

Figure 5. Adsorption isotherms for powdered (b) and membranetype (2) adsorbents; adsorbent: 20-200 mg; seawater: 1 dm3; time: 20 days; temperature: 303 K; (O) extrapolated value to the concentration of Li+ in seawater for powdered type adsorbent; (4) for membrane-type adsorbent.

Figure 4. Time courses of lithium extraction from M-8-20(Li); weight: 720 mg; solution: 0.75 M HCl; 0.3 dm3.

brane precursors with a 0.75 M HCl solution rarely changed their physical properties. Lithium Adsorption Isotherm. Adsorption isotherms for both the powdered and membrane-type adsorbents follow Freundlich’s equation12 with nearly equal slopes (2.4 and 2.1 dm3/g, respectively) (Figure 5). The equilibrium lithium uptakes from seawater can be evaluated by extrapolating the equations to the

lithium concentration (0.17 mg/dm3) of seawater; they are 22 and 16 mg/g, respectively. The latter corresponds to 20 mg/g of MnO2 based on manganese oxide powder. The membrane-type adsorbent retains good adsorptive capacity with little influence from the PVC binder. Adsorptive Properties from Seawater. In the case of a parallel flow system, the lithium adsorptive properties depend largely on the nature of seawater flow at the surface of the membrane. The flow is laminar in the absence of spacers between the membranes. When spacers are set on both sides of each membrane, the seawater flow at the surface of the membrane becomes turbulent, and the membrane can contact fresh seawater more effectively. We carried out the adsorption studies using two kinds of spacers, as shown in Figure 6. The lithium uptake curves show that the spacers effectively increase the adsorption rate, with the flexible polypropylene-net type spacer (Type A) more effective than the hard thin-honeycomb type spacer (Type B).

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Figure 6. Time courses of lithium uptake with different kinds of spacers; membrane: M-8-20(H); seawater flow: 1.25 cm/min; (O) with spacer A; (0) with spacer B; (4) without spacer.

Figure 7. Time courses of lithium uptakes for samples with different initial PVC concentrations; (y) M-8-20(H); (!) M-12-20(H); (5) M-15-20(H).

These results show that spacers are advantageous for membrane-type adsorbents in a parallel flow cell. The control of seawater flow at the surface of the membrane is important in designing an efficient membrane-type adsorbent system. We used the Type A spacer in subsequent adsorption studies. Time courses of lithium adsorption for the membranes derived from different [PVC]ini values are given in Figure 7. The adsorption rate based on unit weight depends on the initial PVC concentration. The adsorbent obtained at a lower [PVC]ini value shows a higher adsorption rate, probably due to the higher porosity of the membrane, as is shown in the SEM images. The present membrane consists of two components, manganese oxide and PVC. Manganese oxide has many Li specific sites, but PVC does not have adsorption sites. The pores that are observed by SEM are spaces between PVC polymers; therefore, they facilitate lithium migration but not lithium “adsorption”. Lithium ions as well as seawater can migrate more smoothly into the membrane with higher porosity, but specific lithium adsorption progresses only in the manganese oxide particles.

Figure 8. (a) Effect of binder additive content on lithium adsorptivity based on adsorbent weight; (b) M-8-10(H); (9) M-820(H); (2) M-8-30(H). (b) Effect of binder additive content on lithium adsorptivity based on adsorbent area; (b) M-8-10(H); (9) M-8-20(H); (2) M-8-30(H).

Because the membrane was not obtained at [PVC]ini ) 6%, the most suitable [PVC]ini value is estimated to be 8%. Effect of Binder Additive Content on Lithium Adsorptivity. The effect of binder content on lithium adsorptivity was investigated using membranes with different Cbinder values (10%, 20%, and 30%). Time courses of lithium adsorption are given in Figure 8a. The lithium uptake per unit of adsorbent weight does not depend largely on the binder content, unlike the case of granular adsorbent where the adsorption rate decreased considerably with an increase in binder content.12 In the membrane-type adsorbent, the specific membrane area per unit weight changes considerably depending on binder content (Table 1). Therefore, the lithium uptake per unit area was plotted as a function of adsorption time in Figure 8b. The adsorption curves show that the adsorption rate per unit area increases markedly with a decrease of binder content, similar to the case of granular adsorbent. Our results show that the increase of PVC content results in the decrease of manganese content, while it

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Table 3. Metal Ion Uptakes by Membrane-Type Absorbenta metal ion

uptake/ mg g-1

concn in seawater/ mg dm-3

concn factor/ dm3 kg-1

Li+ Na+ K+ Mg2+ Ca2+ Sr2+

10.6 4.3 0.4 10.8 5.3 0.5

0.17 10 500 380 1350 400 8

62 000 0.4 1.1 8.0 13.0 62.0

a

M-8-20(H): 90 mg; absorption time: 15 days.

results in the marked increase of the specific surface area (Table 1). These two factors give an opposite effect to the lithium adsorption rate (the increase in the outer surface area increases the adsorption rate, while the decrease of manganese content decreases). We can introduce the parameter “effective surface area” as Seff ) RMnSm, where RMn is the fraction of manganese oxide in the membrane and Sm specific surface area; thus, Seff corresponds to the surface area occupied by manganese oxide. The lithium adsorption rate should correlate to the Seff value when the lithium diffusion in the solid phase is rate-determining step. The Seff value increases with an increase in the PVC content (50, 72, and 84 m2/g for M-8-10(H), M-8-20(H), and M-8-30(H), respectively), which agrees with an increasing order of Li adsorption rate (Figure 8a). This suggests that the diffusion in solid phase is the rate-determining step, in analogy to the case of lithium adsorptions on granular adsorbents. When the lithium adsorption rate is normalized per surface area as shown in Figure 8b, the adsorption rate correlates only to manganese oxide content; consequently, it decreases with PVC content. Therefore, the results in Figure 8, parts a and b, are not incompatible with the conclusion that the lithium diffusion in the solid phase is rate-determining step. The present results suggest that the outer surface area plays an important role in controlling the adsorption rate, regardless of the adsorbent form, granular or membrane. The lithium desorption behavior was investigated in a 0.75 M HCl solution using membranes (M-8-20(H)) treated for 15 days in seawater (lithium uptake: 9.5 mg/ g). The desorption of lithium progressed effectively; the amount of lithium desorbed reached 86% by acid treatment for only 5 h. There was no apparent degradation of the membrane adsorbent during acid treatment. In the previous paper, we have investigated the reusability of the granular adsorbent by the repetition of adsorption from seawater followed by desorption by acid.13 The seven repetitions of the adsorption-desorption cycle resulted in a slight (1.5% each) decrease of the lithium adsorption rate. A similar reusability can be expected from the present membrane, because both the adsorbents consist of the same components. Adsorption of Other Metal Ions. Alkali metal and alkaline-earth metal uptakes from seawater are given in Table 3 for membranes (M-8-20(H)) treated for 15 days in seawater. The concentration factors can be calculated using these metal uptakes and published metal ion concentrations in seawater. An extremely high CF value (62 000) is obtained for lithium ions compared with those (less than 100) for the other metal ions. Thus, the membrane-type adsorbent concentrates lithium ions effectively from seawater, although the concentration of Li+ ion is extremely low as compared to Na+, K+, Mg2+, and Ca2+ ions in natural seawater. Most of the

metal ions adsorbed on the membrane were desorbed to the solution phase by the treatment with a 0.75 M HCl solution. The desorbed fractions were 95%, 95%, 93%, and 93% for Na+, K+, Mg2+, and Ca2+ ions, respectively. The selective lithium adsorptive property of the membrane-type adsorbent arises from the marked lithium ion-sieve property of the powdered adsorbent (H1.33Mn1.67O4) in the membrane. We have carried out basic studies on the ion selectivity of the powdered adsorbent.16 It has a high selectivity for lithium ions among alkali metal, alkaline earth metal, and transition-metal ions. Its lithium selective property can be explained by the lithium ion-sieve property of the adsorption sites formed among the crystal lattice. The sites are so narrow that metal ions other than lithium are excluded from the sites due to a large steric effect in both the dehydrated and hydrated form. Because Na+, K+, and Ca2+ ions have ionic radii larger than Li+,17 they suffer a large steric hindrance at the entrance of the sites. The Mg2+ ion, while having about the same ionic radius, has a free energy of hydration that is about 4-times higher than Li+.18 Therefore, it needs a greater amount of energy in order to be dehydrated and enter the adsorption sites. Conclusion A membrane-type adsorbent with high mechanical and chemical stabilities and good adsorptive capacity for lithium in seawater can be obtained by a solventexchange method with PVC as a binder. A parallel-flow cell with suitable spacers around the membranes is advantageous for the effective lithium recovery from seawater utilizing natural flow. Literature Cited (1) Epstein, J. A.; Feist, E. M.; Zmora, J. Extraction of Lithium from the Dead Sea. Hydrometallurgy 1981, 6, 269. (2) Dang, V. D.; Steinberg, M. Preliminary Design and Analysis of Recovery of Lithium from Brine With The Use of a Selective Extractant. Energy 1978, 3, 325. (3) Abe, M.; Chitrakar, R. Recovery of Lithium from Seawater and Hydrothermal Water by Titanium(IV) Antimonate Cation Exchanger. Hydrometallurgy 1987, 19, 117. (4) Leont’eva, G. V.; Vol’chin, V. V.; Chirkova, L. G.; Mironova, E. A. Isma-1 Cation-Exchanger and Its Sorptional Properties. Zh. Prikl. Khim. 1982, 55, p 1306-1310 (in Russian). (5) Ooi, K.; Miyai, Y.; Katoh, S. Recovery of Lithium from Seawater by Manganese Oxide Adsorbent. Sep. Sci. Technol. 1986, 21, 755. (6) Miyai, Y.; Ooi, K.; Katoh, S. Recovery of Lithium from Seawater Using a New Type of Ion-Sieve Adsorbent Based on MgMn2O4. Sep. Sci. Technol. 1988, 23, 179. (7) Miyai, Y.; Ooi, K.; Katoh, S. Preparation and Ion-Exchange Properties of Ion-Sieve Manganese Oxide Based on Mg2MnO4. J. Colloid Interface Sci. 1989, 130, 535. (8) Feng, Q.; Miyai, Y.; Kanoh, H.; Ooi, K. Li+ Extraction/ Insertion with Spinel-Type Lithium Manganese Oxides. Characterization of Redox-Type and Ion-Exchange-Type Sites. Langmuir 1992, 8, 1861. (9) Ammundsen, B.; Jones, D. J.; Burns, G. R. Mechanism of Proton Insertion and Characterization of the Proton Sites in Lithium Manganate Spinels. Chem. Mater. 1995, 7, 2151. (10) Chitrakar, R.; Kanoh, H.; Miyai, Y.; Ooi, K. A New Type of Manganese Oxide(MnO2‚0.5H2O) Derived from Li1.6Mn1.6O4 and Its Lithium Ion-Sieve Properties. Chem. Mater. 2000, 12, 3151. (11) Chitrakar, R.; Kanoh, H.; Miyai, Y.; Ooi, K. Recovery of Lithium from Seawater Using Manganese Oxide Adsorbent (H1.6 M1.6 O4) Derived from Li1.6Mn1.6O4. Ind. Eng. Chem. Res. 2001, 40, 2045.

Ind. Eng. Chem. Res., Vol. 41, No. 17, 2002 4287 (12) Miyai, Y.; Ooi, K.; Nishimura, T.; Kumamoto, J. Lithium Adsorptive Properties of a New Selective Adsorbent Derived from Li1.33Mn1.67O4. J. Seawater Sci. Jpn. 1994, 48, 411 (in Japanese). (13) Miyai, Y.; Kanoh, H.; Feng, Q.; Ooi, K. Bench Scale Studies on Lithium Recovery from Seawater. J. Seawater Sci. Jpn. 1995, 49, 226 (in Japanese). (14) Weber. Physicochemical Processes for Water Quality Control; Wiley-Interscience: New York, 1972; p 242. (15) Kesting, R. Asymmetric Cellulose Acetate Membranes. In Reverse Osmosis and Synthetic Membranes; Sourirajan, S., Ed.; National Research Council Canada: Ottawa, Canada, 1977; p 89.

(16) Ooi, K.; Miyai, Y.; Katoh, S. Lithium-Ion Sieve Property of λ-Type Manganese Oxide. Solvent Extract. Ion Exch. 1987, 5 (3), 561. (17) Shannon, R. D.; Prewitt, C, T. Acta Crystallogr. 1969, B25, 925. (18) Rosseinsky, D. R. Chem. Rev. 1965, 65, 467.

Received for review October 16, 2001 Revised manuscript received April 22, 2002 Accepted June 9, 2002 IE010847J