Ind. Eng. Chem. Res. 1990, 29, 2273-2277
2273
Recovery of Uranium from Seawater. 7. Concentration and Separation of Uranium in Acidic Eluate Hiroaki Egawa* and Takamasa Nonaka Department of Applied Chemistry, Faculty of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860, Japan
Morio Nakayama Faculty of Pharmaceutical Sciences, Kumamoto University, Oe-Honmachi 5-1, Kumamoto 862, Japan
Macroporous chelating resins (RSP, RSPO, RCSP, and RCSPO) containing dihydroxyphosphino and/or -phosphono groups were examined for the concentration and separation of uranium from acidic eluates of macroporous chelating resin containing amidoxime groups. RSP and RSPO had a high adsorption capacity for uranium even in 0.25-0.50 m o l ~ d m -H2S04. ~ Uranium adsorbed on the resins was eluted easily as a uranyl carbonate complex by use of 0.25 m o l ~ d m Na2C03. -~ In this effluent, other metal ions were hardly present. The use of RSP and RSPO was very effective in concentrating uranium from seawater and separating it from most other elements.
Introduction It is already reported that macroreticular chelating resin (RNH) containing amidoxime groups had a high capacity and selectivity for uranium in seawater (Egawa and Harada, 1979; Egawa et al., 1980a). It was demonstrated that not only inorganic adsorbents present as hydrous titanium oxide but also organic adsorbents make it possible to recover uranium in seawater (Egawa et al., 1980b). Collection of uranium in seawater has been done with various organic adsorbents by other workers (Sugasaka et al., 1981; Schwochau et al., 1982; Saito et al., 1987). The adsorption rate and capacity of uranium on these amidoxime-type resins were superior to that of granulated hydrous titanium oxide. However, the purity and concentration of uranium eluted from RNH with acidic solution were not sufficient for the preparation of the yellow cake utilized in industry. In this study, macroporous chelating resins (RSP, RSPO, RCSP, and RCSPO) containing dihydroxyphosphino and/or -phosphono groups were examined for the second concentration process of uranium from acidic eluates of macroporous chelating resin (RNH) amidoxime groups (Figure 1). Experimental Section Preparation of RNH. Macroreticular acrylonitriledivinylbenzene (DVB, 10 mol 70)copolymer beads (RNs) were synthesized by suspension polymerization in the presence of toluene (80 vol % per monomer) as diluent. RNs with desired diameter (32-60 mesh) were selected, and amidoxime groups were introduced by the reaction of RNs with 3% hydroxylamine methanolic solution for 2 h at 80 "C. RNH was characterized by the method reported previously (Egawa et al., 1987a,b; Nakayama et al., 1988). Preparation of RSP, RSPO, RCSP, and RCSPO. Macroreticular styrene-DVB (10 mol 70)copolymer beads (RS) were synthesized by suspension polymerization in the presence of 2,2,4-trimethylpentane (100 vol % per monomer) as diluent. RS or its chloromethylated derivatives (RCS) were heated under reflux for 6 h in a mixture of phosphorus trichloride and aluminum chloride. The phosphorylated resins (RSP and RCSP, Figure 2) was obtained by washing these resins in ice water. RSP and RCSP were oxidized with concentrated nitric acid at room temperature for 24 h to obtain the resins (RSPO and RCSPO, Figure 2) that contained only phosphono groups. These resins were characterized by the method reported previously (Egawa et al., 1984). 0888-5885f 90 f 2629-2273W2.50f 0
Determination of Uranium and Other Metal Ions. Uranium and other metal ions were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) with Jarrell ash ICPA mark 11. Uranium was also determined by spectrophotometry with Arsenazo I11 or H202. Adsorption of Metal Ions from Seawater on RNH. Natural seawater (uranium concentration: 2.8-3.1 ~ g d m - ~ ) was passed through a plastic column (65 mm in diameter) packed with 200 cm3of RNH (wet resin) at a space velocity (SV) of 120 h-l. After 4 cm3 of RNH was picked up from the column, metal ions on RNH were eluted by passing 10 bed volumes of 0.5 m ~ l e d m H2S04 -~ through the glass column at a SV of 3 h-l, and the concentration was determined. Preparation of Acidic Eluate. RNH contacted with natural seawater for a long time was taken out of the plastic column. After RNH was thoroughly washed with 3% NaCl solution, 150 cm3 of RNH was packed in a glass column (15 mm in diameter). H2S04solution (0.5 moldm-3) was passed through the column at a SV of 3 h-l, and several fractions of acidic eluate were preserved for the second concentration. Adsorption of Uranium from Acidic Solution by the Column Method. RSP, RSPO, RCSP, or RCSPO (4 cm3, H form) was contacted with 1 m o l ~ d m -Na2C03 ~ for a day and then packed in a glass column (a diameter of 1 cm). After these resins were washed by passing NaCl solution and pure water through the column, a 200-1000 m g ~ d m U022+ -~ solution in 0.25-0.5 m ~ l - d m H2S04 -~ was passed through the column at a S V of 10 or 15 h-l. the uranium in the effluent was determined with Arsenazo I11 or H202. After the resin was washed with 10 bed volumes of pure water, the uranium adsorbed was eluted with 0.25 m o l ~ d m -NazC03. ~ The uranium in the eluate was determined with ICP-AES. Concentration of Uranium in Acidic Eluate. RSP and RSPO (1cm3,H form) were contacted with 1 mol~dm-~ NaZCO3for a day and then packed in a glass column (a diameter of 6 mm). After these resins were washed with NaCl solution and pure water, the acidic eluate was passed through the column at a SV of 15 h-l. The metal ions in the effluent were determined by ICP-AES. The resins were washed with 10 bed volumes of pure water, and then the metal ions adsorbed on the resins were eluted with 0.25 mol~dm-~ Na2C03. The uranium, thorium, and iron in the effluent were determined by ICP-AES. 0 1990 American Chemical Society
2274
Ind. Eng. Chem. Res., Vol. 29, No. 11, 1990 After these resins were washed by passing 5 cm3 of 1 m o l ~ d m -NaCl ~ and pure water through the column, a solution of 100 mgdm-3 uranium and 20 m g ~ d m -iron ~ in 0.25 m o l ~ d m -HzS04 ~ was passed through the column at a SV of 15 h-l. The uranium and iron leakage was determined by ICP-AES. The uranium and iron adsorbed on the resins were eluted with 0.25 mol~dm-~ Na2C03and 6.0 m ~ l - d m HCl, - ~ respectively. Each metal ion in the eluate was determined by ICP-AES. After the elution, RSP and RSPO were washed with water until the wash water became neutral, and then the sorption-elution procedure was repeated.
natural seawater 1
L.
The first concentration process
amidoxime groups
,
4
- - - 3 - - - _ ._ -
Acidic eluate, U0,2+
I
The second concentration process I
-
Carbonate eluate ,U 0 2 ( CO,
)
4-
The third concentration process
Figure 1. Concentration process of uranium in seawater. G-CH2G-CH2-
6 - C H 2 G - C H 2-
P(OH)2-CH-CH2-
P (OH) -CH-CH -
RSP -
RSPO
'0
-CH-CH -CH-CH2(oH12P-o YH2
2
II
0
-CH-CH
2
'0
-CH-CH -CH-CH2(OHI2PQ II
-
CH -CH-CH21 2 P(OHl2 It
0
0
RCSP -
RCSPO
Figure 2. RSP, RSPO, RCSP, and RCSPO. Table I. Adsorption of Metal Ion on RNH from Natural Seawater concna in metal ion seawater, adsorbed, concn factor element mg.dm-3 mg/ kg resin 3.5 x 104 cu 0.003 105 4.5 x 104 Fe 0.01 455 Mn 2.0 x 105 0.002 399 5.5 x 105 Ni 0.002 1101 V 1.7 x 105 0.002 338 2.6 x 104 Zn 0.01 260 92.7 1.9 X lo6 Th 0.00005 U 1520 5.1 x 105 0.003 Ca 400 1.2 x 10 4730 1350 3.9 5260 Mg Sr 8.0 7.1 56.9 OShigematsu, T. Kaisuishi 1968, 21, 221.
Elution of Iron Adsorbed on RSP and RSPO by the Batch Method. The resins (0.125 g) that adsorbed iron were shaken with 50 cm3 of HC1 solution (1.0-10.0 mol. dm-3) at 30 O C for 24 h. The amount of iron eluted from the resins was calculated from the concentration of iron in the supernatant. Recycle for Recovery of Uranium from an Acidic Solution Containing Iron. RSP and RSPO (1cm3, H form) were packed in a glass column (a diameter of 1 cm).
Results and Discussion Recovery of Uranium from Seawater with RNH. RNH, which was prepared as described in the Experimental Section, not only has high selectivity for uranium in seawater but also has high chemical and physical stabilities (Egawa et al., 1980b). The apparent anion- and cation-exchange capacities of the RNH used for the recovery of uranium from seawater were 2.7 and 1.1 mequiv. g-l, respectively. Natural seawater was passed through the column packed with this RNH for a long time; the metal ions adsorbed on RNH are listed in Table I. When the concentration factor for each metal ion was calculated on the basis of the concentration in seawater reported by Shigematsu (1968), that of uranium was more than lo5. The concentration factors for thorium, nickel, vanadium, and manganese were found to also be high. On the other hand, sodium ion that was present in natural seawater in large quantities hardly adsorbed on the RNH. Although alkali-earth metal ions such as calcium and magnesium were slightly adsorbed, the concentration factors for them were less than 10. Uranium could be easily eluted from HzS04. However, the purity the RNH with 0.5 mol~dm-~ and concentration of uranium in the eluate were not sufficient for the yellow cake utilized in industry, as described previously (Sugasaka et al., 1981). We reported that RSP, RSPO, RCSP, and RCSPO synthesized in our laboratory had an adsorption ability for uranium in a solution of pH l (Egawa et al., 1984). These resins were expected to exhibit high selectivity for uranium even in a stronger acidic solution. Adsorption of Uranium from Acidic Solution on RSP, RSPO, RCSP, and RCSPO. RSP, RSPO, RCSP, and RCSPO were examined for the adsorption of UO?+ in 0.25 mol.dmW3H2S04 by the column method. The typical characteristics of resins utilized in this investigation are listed in Table 11. H2S04was selected as the eluting agent from an economical standpoint. The breakthrough curves shown in Figure 3 indicate that all resins have an adsorption ability for UO?+ in acidic solution. In this case, when the concentration of UOz2+in the effluent arrived at 10% of the concentration in the loading solution, the amount of U022+adsorbed was regarded as the breakthrough capacity. RSP and RSPO gave a particularly sufficient breakthrough capacity for the concentration of uranium in acidic eluate. The breakthrough curves of RSP and RSPO for U022+in stronger acidic solution (0.5
Table 11. Characteristics of RSP, RSPO, RCSP, and RCSPO cation-exchange salt splitting capacity, capacity, resin meauivae-' meauivd VI." c m 3 d VQab cm3& RSP 5.2 2.3 2.3 3.0 RSPO 8.7 2.4 1.4 2.9 RCSP 6.2 1.6 2.2 3.0 RCSPO 7.2 2.1 2.1 3.2
V,? cm3.e-' 4.8 5.5 4.4 4.6
Dry volume of resin (Hform). *Wet volume of resin (Hform). Wet volume of resin (Na form).
v,
V9J 1.3 2.1 1.4 1.5
swelling ratio V J v, 2.1 3.9 2.0
V J v, 1.6 1.9 1.5
2.2
1.4
Ind. Eng. Chem. Res., Vol. 29, No. 11, 1990 2275 500
1
100
1
,
1
I
50
L
a
Y 4
i
n 100
0
Effluent volume
0
50
100 Effluent volume
150 (dm3/dm3-resin)
Figure 3. Breakthrough curves for U O:+ in acidic eluate. UO?+ concentration of loading solution: 500 mgdm-3. HzS04concentration: 0.25 m~lmdm-~. Flow rate: SV 15 h-l. Resins: RSP (O),RSPO (o),RCSP (o),RCSPO (m).
500 400
Figure 6. Effect of U022+concentration on the breakthrough capacity. Resin: RSPO. Flow rate: SV 15 h-l. UO?' concentration of loading solution: lo00 mgdm-3 (O),500 mg.dnr3 (O),200 mg.dm-3 (0).
7 1
1
m
P
-P
200 300 (dm3/dm3-resin)
I
E
a0
-
300
D
a
Y
;200
8
m
i
Y
3
500 RSPO : 4 cm3(H-form)
8
100
3
400
C c
0 0
50
100
150
Effluent volume
200
(dm3/dm3-resin)
200 300
-
l o o0
1
I
i 0
300
:I
2
t I
Figure 4. Effect of acidity on the adsorption of UO?. UO? concentration of loading solution: 500 m ~ d m - ~Flow . rate: SV 15 h-l. H,SO, concentration: 0.25 m ~ l - d m -(-), ~ 0.5 m ~ l - d m -(-~- -) resins: RSP (O),RSPO ( 0 ) .
50 100 Effluent volume
150 200 (dm3/dm3-resin)
Figure 7. Breakthrough curves for Th" in acidic solution. Th4+ concentration of loading solution: 500 mgdm-3. Flow rate: SV 15 h-l. HzS04concentration: 0.25 m ~ l . d m -(0, ~ o ) ,0.5 m o l ~ d m -(0, ~
m) .
100
0
50
100
Effluent volume
150
200
(dm3/dm3-resin)
Figure 5. Effect of flow rate on the adsorption of UOpl+. UO? concentration of loading solution: 500 mgdm-3. Resin: RSP. Flow rate: SV 10 h-I (O),SV 15 h-l ( 0 ) .
m ~ l - d m H2S04) -~ are shown in Figure 4. Although the breakthrough capacity of RSP and RSPO decreased in 0.5 m o l ~ d m -H2S04, ~ the degree of decrease was not remarkable. Since the concentration of H2S04in acidic eluate obtained by the first concentration process is estimated to be in the range from 0.25 to 0.5 mol~dm-~ (Egawa et al., 1980b), the adsorption ability of these resins was evaluated to be enough for uranium in acidic eluate. As shown in Figure 5, if we are allowed to pass UO?+ in H$04 solution through the resin at a slower flow rate, it may be possible to increase the breakthrough capacity. Next, the breakthrough capacity for U022+was measured with U022+solutions of 1000, 500, and 200 mg.dm-3 in 0.25 m ~ l . d m - ~ H2S04. As shown in Figure 6, the breakthrough capacity was constant regardless of the UOZ2+concentration. On
the other hand, when 0.25 m~ledm-~ sodium carbonate was used as the eluting agent, more than 90% uranium adsorbed on both RSP and RSPO could be eluted with 10 bed volumes of eluent. Adsorption of Thorium from Acidic Solution on RSP and RSPO. Since thorium is also useful as an energy source, RSP and RSPO were examined for the concentration of thorium. The breakthrough curves for Th4+in 0.25 or 0.5 mol.dmT3H2S04are shown in Figure 7. The breakthrough capacities of RSP and RSPO for Th4+were lower than those for UO?', but the adsorption ability of RSP for Th4+from stronger acidic solution (0.5 molsdm" H2S04)did not exhibit any decrease. These results indicate that RSP and RSPO have a high affinity for thorium in acidic solution, and the thorium adsorbed on the resin could be eluted with sodium or ammonium carbonate. Concentration of Uranium from an Acidic Eluate of RNH. As described in the Experimental Section, after natural seawater was passed through the column packed with RNH for a long time, the metal ions on RNH were eluted by 10 bed volumes of 0.5 m ~ l - d mH$304. -~ Although calcium sulfate was observed in the acidic eluates, these precipitates did not cause blocking of the column. Six bed
2276 Ind. Eng. Chem. Res., Vol. 29, No. 11, 1990 Table 111. Concentration of Metal Ions in Acidic Eluate element
concn, mgadm-?
cu
4.3
Fe hl n Ni
23.7 28.9 63.4
Zn
13.0 13.2
v
RSPO
element Th
concn, mg.dm-3
Mg
450.6
8.3
Sr
20.5
2.1
1
-
-
RSP
RSPO
1 "F,
100
0
200
0
300
100
Ca
200
' dm3~dm3.req,1,
E f f l u e n t volume
300
400
I
Figure 10. Breakthrough curves of various metal ions in acidic eluate. Metal ions: U (0): Fe ( O ) ,T h (81,V (A). Other metal ions (a). Co: metal ion concentration in loading solution. C: metal ion concentration in effluent. RSPO
RSP
~
100
80
60
40
20
0 0
0
10
20 0
Effluent volume
10
20
ldm3/dm3-resin)
5
10
15
0
E l u t i o n volume
5
10
15
(dm3/dm3-resin)
Figure 11. Elution curves of U and Th. Metal ions: U (O), Th (0).
RSPO had a high affinity for iron. Figure 10 shows the breakthrough curves that were drawn to represent metal RSP RSPO ion leakage as the ratio of all metal ion concentrations in the effluent to that in the acidic eluate (loading solution). These results showed that RSP and RSPO have selective adsorption ability for uranium and thorium in acidic eluate 10 ? containing many metal ions. Although RSP and RSPO P had a higher adsorption ability for iron than for uranium and thorium, RSP had enough breakthrough capacity for y 100 7 uranium. Since iron adsorbed on the resins could not be eluted with 0.25 m o l ~ d m sodium -~ carbonate, it could be separated from uranium and thorium. Elution curves of RSP and RSPO for uranium and thorium are shown in Figure 11. Uranium adsorbed on RSP and RSPO could be eluted, and uranium in this eluate was concentrated 500 0 100 200 300 0 100 200 300 400 times at the first concentration process. Since uranium E f f l u e n t volume (dm31dm3-resin) the is eluted as uranyl carbonate complex, uo2(co3)34-, third concentration of uranium can be carried out easily Figure 9. Breakthrough curves for U, Th, and V in acidic eluate. by use of a strong anion-exchange resin. The separation volumes of the eluent was required for the elution of metal of thorium in this eluate is under investigation. In this ions. The H,SO, concentration of this acidic eluate was article, typical results of the first and second concentration 0.42 m ~ l - d m -and ~ , the concentration of metal ions is shown processes have been described, but a high reproducibility in Table 111. This acidic eluate was passed through the of this presented recovery process was confirmed by several minicolumn packed with RSP or RSPO. As shown in examinations. Figure 8, alkali-earth metal ions such as magnesium, Recycles for the Recovery of Uranium in Acidic calcium, and strontium and some other heavy metal ions eluate. The regeneration of these resins was investigated. were eluted at void volumes without adsorption on the Figure 12 shows the eluation of iron adsorbed on RSP and resins. Accordingly, it was suggested that the use of RSP RSPO with HC1 solution. Although iron adsorbed on and RSPO make it possible to separate uranium from most ~ it was RSPO could be eluted by use of 6 m ~ l e d m -HCl, of the metal ions in the acidic eluate. Breakthrough curves impossible to completely elute the iron adsorbed on RSP. for uranium and other metal ions that were adsorbed on In order to confirm the possibility of the reuse of RSP, the RSP and RSPO are summarized in Figure 9. The sorption-elution recycles of uranium and iron were exambreakthrough curves for iron indicated that both RSP and ined by the column method. A mixture of 100 mg.dm-3 Figure 8. Breakthrough curves for metal ions in acidic eluate.
r?
-
,-
I n d . Eng. Chem. Res. 1990,29, 2277-2288
2277
Conclusion RSP and RSPO were used for the concentration of uranium from acidic eluates of amidoxime resins, and it was very effective in concentrating uranium from seawater and separating it from most other elements. Acknowledgment This work was supported by a Grant-in-Aid for Energy Research from the ministry of Education, Science and Culture of Japan.
Literature Cited
1 0
0
2
4
Concn. of €IC1
6
0
10
(m~l-dm-~)
Figure 12. Elution of Fe adsorbed on RSP and RSPO by the batch method. Table IV. Adsorption-Elution Recycles of Uranium and Iron by the Column Method’ recyc1e U adsorbed, ~ d m - ~Fe adsorbed, pdm” 1 18.77 3.04 2 19.62 3.40 3 19.05 3.26 4 19.21 3.35 5 19.18 3.50 6 18.63 3.40 7 18.41 3.40 8 3.41 18.68 9 18.73 3.39 10 18.64 3.40 11 18.22 3.20 12 18.48 3.28 OColumn packed with 1 cm3 of RSP.
U022+and 20 m ~ d m Fe3+ - ~ in 0.25 m o l ~ d m -HzSO4, ~ as a model solution of acidic eluate, was passed through the minicolumn packed with RSP. When the 200 bed volume solution was passed through the column, the amounts of UO?+ and Fe3+adsorbed are shown in Table IV. These results show that adsorption of UOZ2+and Fe3+ did not decrease by recycles. Although Fe3+adsorbed on RSP did not eluate completely with 6.0 m ~ l a d m -HC1 ~ at the first sorption-elution cycle, the amount of iron eluted increased with an increase of recycle number, and the accumulation of iron on RSP stopped a t the seventh recycles. From these results, it was confirmed that the amount of iron accumulated on RSP was slight and did not influence the reuse for uranium recovery.
0888-5885/90/2629-2277$02.50/0
Egawa, H.; Harada, H. Recovery of Uranium from Sea Water by Using Chelating Resins Containing Amidoxime Groups. Nippon Kagaku Kaishi 1979,958-959. Egawa, H.; Harada, H.; Nonaka, T. Preparation of Adsorption Resins for Uranium in Sea Water. Nippon Kagaku Kaishi 1980a, 1767-1772. Egawa, H.; Harada, H.; Shuto, T. Recovery of Uranium from Sea Water. Nippon Kagaku Kaishi 1980b, 1773-1776. Egawa, H.; Nonaka, T.; Ikari, M. Preparation of Macroreticular Chelating Resins Containing Dihydroxyphosphino and/or Phosphono Groups and their Adsorption Ability for Uranium. J. Appl. Polym. Sci. 1984, 29, 2045-2055. Egawa, H.; nakayama, M.; Nonaka, T.; Sugihara, E. Recovery of Uranium from Sea Water. IV. Influence of Crosslinking Reagent on the Uranium Adsorption of Macroreticular Chelating Resin Containing Amidoxime Groups. J. Appl. Polym. Sci. 1987a, 33, 1993-2005. Egawa, H.; Nakayama, M.; Nonaka, T.; Yamamoto, H.; Uemura, K. Recovery of Uranium from Seawater V. Preparation and Properties of the Macroreticular Chelating Resins Containing Amidoxime and Other Functional Groups. J.Appl. Polym. Sci. 198713, 34, 1557-1575. Nakayama, M.; Uemura, K.; Nonaka, T.; Egawa, H. Recovery of Uranium from Seawater. VI. Uranium Adsorption Ability and Stability of Macroporous Chelating Resin Containing Amidoxime Groups Prepared by the Simultaneous Use of Divinylbenzene and Ethyleneglycol Dimethacrylate as Crosslinking Reagent. J . Appl. Polym. Sci. 1988, 36, 1617-1625. Saito, K.; Hori, T.; Furusaki, S.; Sugo, T.; Okamoto, J. Porous Amidoxime-Group-Containing Membrane for the Recovery of Uranium from Seawater. Znd. Eng. Chem. Res. 1987,26,1977-1981. Schwochau, K.; Asheimeier, L.; Schenk, H. J.; Witte, E. G.On the Extraction of Uranium from Sea Water by a Complexing Resin. 2. Naturforsch. 1982,37B, 214-216. Shigematsu, T. Chemical Analysis of Elements in Seawater. Kaisuishi 1968,21, 221-228. Sugasaka, K.; Katoh, S.; Takai, H.; Takahashi, H.; Umezawa, Y. Recovery of Uranium from Seawater. Sep. Sci. Technol. 1981,16, 971-985. Received for review October 18, 1989 Reuised manuscript received J u n e 19, 1990 Accepted July 11, 1990
0 1990 American Chemical Society
