Conclusions
A loss-in-weight method was used to determine the reduction characteristics of C.P. grade of Fez03 and samples of two very different types of ores. Being continuous and accurate, comparisons were readily made. T h e addition of N a 2 0 in the form of N a H C 0 3 to (c.P. grade) F e ? 0 3 results in a decrease in the reduction rate with pure hydrogen as the reducing agent. .A similar addition of NaZO to a Cuban lateritic hematite containing alumina, silica, and chromia as impurities results in an increased reduction rate. An increase in rate upon the addition of S a 2 0 is also obtained for a dense, crystalline, Cornwall magnetite ore. T h e alkali apparently reacts with the impurities in the ores, thus freeing the iron oxide for reduction; i t does not appear to act as a "promoter" in the accepted sense of the word. 'The reduction rate of iron oxide is extremely sensitive to the presence of water vapor. There is some indication that the mechanism may be described as reduction by weakly adsorbed hydrogen, inhibited by a strongly adsorbed product, Ivater vapor. literature Cited
(1) Barrett, E. P., U. S. Bur. Mines, Bull. 519 (1954). (2) Barrett, E. P., U. S. Bur. Mines, Rep. Invest. 4402 (February 1949). (3) Bakett, E. P., IYood, C. E., IND. ENG. CHEM...ANAL. ED. 18, 285 (1946).
(4) Bitsianes, G., Joseph, T. L., J . Metals 5, A I M E Trans. 197, 1641 (1953). (5) Ibid.. 6, A I M E Trans. 200, 150 (1954). (6) Brunauer. S., Emmett, P. H., Teller, E., J . A m . Chem. Soc. 60. 309 (1938). (7) C h u f a k . G. I., .4verbukh. B. D., Tatievskaya, E. P., Antono\, V. K., Zhur. Fzz. Khzm. 28, 490 (1954). (8) Darken. L. S.. Gurry, R. \V., J . A m . Chem. SOC.67, 1398
,-,
i l C)A\\ ,",.
(9) Edstrom, J. O., J . Iron Steel Znst. (London) 175, 289 (1953). (10) Edstrom, J. O., Bitsianes, G.? J . Metals 7, A I M E Trans. 203,
760 (1955). (11) Emmett, P. H., Schultz, J. F., J . A m . Chem. SOC. 55, 1376 (1933). (12) Franklin, .4. D.: Campbell, R. B., J . Phys. Chem. 59, 65 (1957). (13) Kondakov, V. V., Chukanov, Z. F., Doklady Akad. LVaui; S.S.S.R. 106, 697 (1956). (14) Krieger. K. A.. IND.ENG.CHEM...\NAL. ED. 16. 398 (1944). (15) Langmuir: I., 2. A m . Cheni. SOC. 38, 2263 (1916j. (16) Moskvicheva. A. G.. Chufarov, G. I., Doklady Akad. LVauX S.S.S.R. 105, 510 (1955). (17) Olmer. F.. J . Phys. Chem. 47, 317 (1943). (18) Ralston. 0. C.. U. S. Bur. .\.lines. Bull. 296 (1929). (19) Roiter. V. A , , Yuza. V. .4.,Kutznetzov. .4.N., Zhur. Fiz. ' k h i m . 25, 960 (1951). (20) Rostovtsev. S. T., Trudy SozNeshchaniya Inst. M e t . Ural. Filiala Akad. -Yauk S.S.S.R. i .Magnitogorsk. -5fet. Kombinat. 1955, p. 65. (21)- Rostovtsev. S. T., Fiz.-h-him. Osnovy Pritoodstva Stali. Akad. AVauk S.S.S.R.. Ins!. M e t . im. .4. A. Baikova, Trudy 3 4 Konf., ~Moscow,1955, 191. (22) Rostovtsev, S. T., Em, .4.P., Doklady Akad. Nauk S.S.S.R. 93, 131 (1953). (23) Smith, J. L.. -Inn. Chem. Pharm. 159, 82 (1871). (24) IVetherill, \l'. N.: Furnas, C. C., IND.ENG. CHEM.26, 983 (1934). (25) \ l X a m s , C. E., Ragatz, R. A , ! Ihid., 28, 130 (1936). I
,
RECEIVED for review August 18, 1960 ACCEPTED January 25, 1962
FRACTIONATION OF FISSION ELEMENTS BY ELECTRODIALYSIS G . J .
BUB, J.
D. V I E , ' AND W .
H. W E B B
Department of Chemical Engineerinf and Chemistry, C-nimsity of Missouri, School of .Mines and Metallurgy, Rolla, .\lo, Electrodialysis methods employing Permutit cation exchange membranes 3 142 and anion exchange membranes 31 48 were feasible for the fractionation of some of the radioactive fission products. The methods are based on the characteristics of anionic, cationic, and radiocolloidal materials formed in the presence of complexing agents with adjustment of acidity. Fractionations of radioactive cerium, cesium, promethium, strontium, and zirconium, in equilibrium with their daughter decay products, were made. Studies were made with three-cell and seven-cell units. Best results were obtained with ammonium acid fluoride solutions using a seven-cell unit with a flowing system.
of aqueous solutions of irradiated reactor fuel elements for the recovery of fissionable materials by solvent extraction leaves a radioactive waste solution containing the fission products. This solution also contains various acids ("03, H F ? etc.) depending on the method of dissolution of the fuel elements. The acid is recovered, leaving a waste solution containing the fission products. The nuclei formed by fission have mass numbers from 72 to 158 (70). There have been many suggestions for the disposal of this waste solution-some include recovery techniques for certain fission elements. 'The volume is usually reduced and the conHE PROCESSING
' Present address, Mallinckrodt Spring, MO.
Chemical Works. \Veldon
centrate stored until the radiological hazard is reduced. T h e presence of cesium-1 37 and strontium-90 prolongs this storage. Electrodial!sis has been proposed by several investigators as a means of volume reduction and acid or electrolyte recovery (5-8). The electrodialysis process is accompanied by electroendosmosis. \\ater transport. Zirconium can be sorbed on silicage1 and recovered with oxalic acid ( 3 ) . Cesium and strontium can be fixed on siliceous materials ( 7). Other fission elements can be recovered by ion exchange or solvent extraction (2. 3 ) . These are only a few of the methods employed to treat the fission product solution and recover some of the radioelements. Since some of the fission elements are in demand for radiochemical and medical research, a single operation for separation and recovery would be most desirable. VOL. 1
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Electrodialysis studies performed in this laboratory on some of the more significant fission elements indicated that this might be a method for their recovery and purification as well as the recovery of acids. These studies were performed with a three-cell electrodialysis unit previously described by Bub and Webb ( 4 ) . This unit \vas equipped with ion transfer membranes which consist of thin sheets of cation or anion exchange materials exhibiting high selectivity to the electrical transfer of cations or anions and have high electrical conductivity. T h e radiation level used in this investigation caused no apparent damage to the membranes. T h e damage to ion exchange membranes by greater radiation dosages was reported by Mason and Parsi ( 7 ) . Three radioactive elements were used in the initial studies;
1
f
I\
I\
X
r
+ 4 + " 1
2
A
3
C
4
A
5
C
6
A
Experimental
7
C
I
I I I HN03 I
I
Figure 1. unit A. C.
F.
q n n
IWW
80
Flow sheet for seven-cell electrodialysis Anion wash solution Cation wash solution Feed solution containing radioactive isotope
I
n
k! CL
w
m
60
z
Q
K
k
2
40
W
0 L1: W
a 20
0 0
1
2
3
4
5
TIME, HOURS
Figure 2. Transfer of CS-BaI3' in 0.5, 1 .O, and 2.ON nitric acid 226
CsX37,Zrgj, and Celu. I n fluoride media, Cs migrated through the cation membrane into the cathode cell, Z r migrated as the ZrFs+ ion through the anion membrane into the anode cell, and C e remained in the feed cell (center) as radiocolloidal CeF3. Later studies in the same media showed that SrgO migrated to the cathode cell and Pm'47 remained in the center cell as radiocolloidal PmF3. Electrodialysis studies of mixed isotopes, Cs'", Zrgj, and Ce144,gave nearly 10070 separation of these three isotopes. These results show that the fission product solution can be fractionated in fluoride media by electrodialysis into three fractions : anionic, cationic, and radiocolloidal. The anionic fraction consists of those radioelements which are present as negative ions or negatively charged complexes in fluoride solution. T h e cationic fraction consists of those present as positive ions. The radiocolloidal fraction will contain yttrium and the rare earth elements. These elements form insoluble fluorides and \vi11 exist as radiocolloids at concentrations less than that required for precipitation ( 9 ) .
I L E C PROCESS DESIGN A N D DEVELOPMENT
Electrodialysis as used for this study consisted of the migration of cations and anions through ion exchange membranes under an applied potential. Ion exchange membranes are thin sheets of either cation or anion exchange resins bound to a n inert plastic matrix, and are therefore, respectively, selective to the migration of cations and anions. I n the electrodialysis process, ion exchange membranes allow the continuous transfer of ions trom one solution to another by the expenditure of electrical energy. T h e migrating ions carry water across the membranes which results in solution volume changes. T h e water flow does not prevent efficient operation. The transfer of water usually increases with decreasing electrolyte concentration (6, 8). Three-Cell Unit. This unit consists of three Plexiglas cells separated by cation and anion exchange membranes, which form a cathode cell, an anode cell, and a feed cell. (The membranes were manufactured by T h e Permutit Co., New York, N. Y.. Cation S o . 3142 and Anion No. 3148.) The cathode and anode cells were equipped with platinum electrodes attached to a variable control direct current power source. T h e anode and cathode cells have 100-ml. capacities whereas the feed cell has a 50-ml. capacity. T h e unit is held together by end blocks and tie rods. Carrier-free radioisotopes were obtained from Oak Ridge National Laboratory. They are in equilibrium with their daughter products as Zr95-Nb96, C S ' ~ ~ - B ~and ' ~ ~ Ce144-Pr14. , The Zr-Nb95 oxalate radioisotope solution was refluxed for 12 hours with nitric acid and hydrogen peroxide to destroy the oxalate and diluted with nitric acid. The C S - B ~ ' ~and ~ Ce-Pr14' chloride radioisotope solutions were also diluted with nitric acid. Electrodialysis studies were performed using the three-cell unit. T h e feed cell was filled with a radioactive isotope solution of known activity and acid concentration. T h e cathode and anode cells were filled with the same acid solution. A current of 1 amp. (125 ma. per sq. current density) was passed through the unit for the desired time period. During this time period the voltage was increased from 10 to 25 volts to maintain a constant current. The resistance to current flow increased with electrodialysis time owing to the removal of acid ions from the center cell. One milliliter of each solution was then removed for acidity analysis, and 1 ml. from each cell was analyzed for radioactivity content. Electrodialysis separations were performed using the threecell unit and employing the same technique described above. I n this case, a mixture of the radioactive isotopes Cs-Baln,
Cs-Bal3' was studied in 2.0, 1.0, and 0.5N nitric acid solutions. T h e Cs+ and Ba+* ions were transferred to the cathode cell a t increasingly faster rates with lower acid concentrations as shown in Figure 2. The increased transfer rates of radioactive ions from the feed solutions with lower acid concentrations is a phenomenon characteristic of all electrodialysis studies during this investigation. This is caused by the competitive transfer of acid ions. Ce-Pr'JJ was studied in 4.0, 2.0, 1.0, and 0.5,1: nitric acid solutions. Most of the Ce-Pr14J remained in the feed cell at high acid concentrations but some was transferred to the cathode cell at low acid concentrations. Most of the Ce-Pr"' adhered to the cation exchange membrane. Because of the complex nature of both Zr-Sbgj and Ce-Pr"' in nitric acid, separation did not appear to be practical in this acid. Oxalic Acid. Electrodialysis studies of Zr-Sbgj were performed in 2.0 and 1.3Soxalic acid. The rate of Zr-Sbgj transfer to the anode cell increased with decreasing acid concentration. Sixty-five per cent of the Zr-NbgS was transferred to the anode cell in 1' '2 hours. C e - P P 4 in oxalic acid \vas distributed in all cells and therefore eliminated oxalic acid as a separation media. Hydrofluoric Acid. I n 1.0 and 0.j1V hydrofluoric acid solution. nearly 90y0 of the Zr-Sbgj \vas transferred to the anode cell in l1 ' 2 hours. Because of the formation of insoluble rare earth fluorides. Ce-PrId4 \vi11 be radiocolloidal and remain in the feed cell in fluoride media but \vi11 not precipitate since the concentration is not high enough to overcome the solubility product. I n fluoride solution, Cs-Bal3' exist as simple Cs+ and Ba+? ions and are transferred to the cathode cell. T h e transfer of Ba13; ma)- be reduced somewhat by radiocolloidal formation of BaF?, which is less soluble than CsF. T h e results of the electrodialysis studies of Zr-Nbsj in fluoride solution and the chemistry of Ce-Prl44 and Cs-Bal3; indicate that separation of these isoropes is possible in fluoride solution Separations were performed using the three-cell unit in 1.23-V hydrofluoric acid and 1.20F (formula weights per liter of solution) ammonium acid fluoride solutions. Table I sholvs the results of the separation of Cs-Bal37, Zr-Nb,gj and Ce-Prld4 in hydrofluoric acid solution and the results in am-
Zr-Nbgj? and Ce-Pr'?' was placed in the feed cell. T h e Cs-Ba13i and Zr-Sbgj isotope radioactivities were measured using a gamma energy, single channel spectrometer with a shielded gamma scintillation well counter. T h e Ce-Pr14' isotope radioactivity was determined using a shielded beta scintillation counter \vith a n absorber for the Zr-Nbgj and Cs13' beta activities. Per cent error of measurement of the Zr-Nblgj and Cs-Ba13: radioactivities was approximately 5Yoj while that for Ce-Prld4 \vas approximately 2%. Corrections were made for background counts and counting efficiency. All radioactivities are reported as the equilibrium mixture of parent and daughter elements. Although both the parent and daughter elements have different diffusion coefficients, and thus have different electrodialysis rates. no distinction was made between the ratio of parent-to-daughter radioactivities in the unelectrodialyzed feed solution and the ratio in the resulting solutions. Seven-Cell Unit. 'This unit was constructed from 8-inch diameter poly(viny1 chloride) pipe and was held together by end blocks and tie rods. Alternate anion and cation exchange membranes separated the cells? forming five working cells and t\vo electrode cells. T h e electrodes were 8-inch diameter graphite disks. Each cell had a capacity of 815 ml. Figure 1 shows the flow sheet for this unit. Operation of this unit was similar to that of the three-cell unit except the solutions were continuously recycled through the cells, and the current density was 50 m a . per sq. cm. T h e voltage across the cells had to be varied to maintain constant current. T h e seven-cell unit was emplo!-ed for the separation of Cs-Ba'Z7 and Zr-Sbgj and for electrodialysis studies of Sr-YB, Pml47>and Ce-Pr"?. Results and Discussion
Electrodialysis studies were performed in nitric, oxalic, and hydrofluoric acids using the three-cell electrodialysis unit. Nitric Acid. Zr-Sbgj was studied in 3.0, 2.0, and 1 . 0 S nitric acid solurions. Results shoiv that in nitric acid solution Zr-NbQj predominates in the feed cell and very little is transferred to eirher the anode or cathode cells. This indicates that Zr-\-b55 \vas present in radiocolloidal form in this nitric acid range. Experiments in lower nitric acid concentrations gave unsatisfactory results. This system is being investigated more thoroughly by this laborator)-.
Table 1.
Initial Isotope Activity in Feed Cell, U.P.S.a
Isotope
Cs-Ba13: Zr-KbQj Ce-Pr144 Total, D.P.S.5 Recovery b Final acidity, .V
46,125 21,550 37,500 105,175 80.970
Separation of Cs-BaI3', Zr-Nbg5, and Ce-Pr"?
Initial Isotope Actioity in Feed Cell, D .PS.a
Isotope Actiaity ajter 2-Hr. Electrodialysis, D.P.S.5 Anode cell Feed cell Cathode cell Experiment 1 0.0 19,920 0.0 19,920
1.36
In 1.23.V Hydrofluoric Acid 585 45,000 46,900 465 0.0 21,900 19,100 0.0 35,300 20,150 45,000 104,100 82.8% 0.21 0.96
Isotope Activity after 2-Hr. Electrodialysis, D.P.S.a Anode cell Feed cell Cathode cell Experiment 2
650 475 21,800 22,925
0.0
17,200 0.0 17,200 1.37
46,100 0.0 0.0
46,100
0.21
0.97
I n 1.20F Ammonium Acid Fluoride. Cs-Ba137
Zr-Nbgj Ce-Pr144 Total, D.P.S.a Recovery b Final acidity, S a Disintegrationsper
38,050 11,475 39,350 88,875 90.4% second.
0.0 10,050 0.0 10,050
905 510 32,300 33,715
36,550
48,000 14,600 39,400 102,000 88.1%
0.0 0.0
36,550
1.93 0.33 0.72 Losses due to sorption on ion exchange membranes.
c
1,050 985 31,700 33,735
0.0
11,420 0.0
11,420
1.92 Formula weightsper liter of solution.
VOL. 1
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44,700
0.30
JULY 1 9 6 2
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227
rnonium acid fluoride. Almost 100% separation \vas accomplished in these solutions with a current density of 125 ma. per sq. cm. for 2 hours. Five to 207, of the Zr-Sbg3 and 40 to joyo of the Ce-PrlG was sorbed on the ion exchange membranes in hydrofluoric acid. I n ammonium acid fluoride solution, the sorption of Ce-Pr144 \vas reduced to 18 to 20% and 10 to 15% of the Zr-Kbgj \vas sorbed. This sorption is not desirable and should be kept to a minimum. T h e best separation of Cs-Ba137 and Zr-Y-bYj was accomplished in hydrofluoric acid media.
loo
'
80
60
5 W
40
0 U
te
T h e ammonium acid fluoride system was also studied by employing the seven-cell unit. Results of these experiments are shown in Tables I 1 and 111. These results show that it is possible to separate these elements i n ammonium acid fluoride using the seven-cell unit. T h e use of a flowing system reduced the sorption of Zr-Nbyj and Ce-Prr4i. Figure 3 shoxvs the transfer rates of Cs-Ba and137 Zr-Nbgj in O . . W and 1.OF ammonium acid fluoride solutions. T h e waste solution is usually about 2 S in nitric acid, a n d the nitric acid can be recovered by electrodialysis leaving the waste solution about 0.05.V in nitric acid (6). Since nitric acid is present in the waste solution, several experiments ivere performed in a mixture of 0.5F ammonium acid fluoride and 0.5.T nitric acid. T h e effects of nitric acid present in the feed solution on the transfer rates of Cs-Bal37 and Zr-Sbgj are shown in Figure 4. Figure 4 also shoivs the transfer of Sr-YYO. I t is expected that greater transfer of S r - F can be accomplished with a longer electrodialysis time. T h e mixed nitric acid and ammonium acid fluoride system \vas employed for the separation of C S - B ~ ' ~and ' Zr-SbSj, and electrodialysis studies of Sr-YgO, Pmlri? and Ce-Pr144 using the seven-cell unit. T h e results of these experiments are summarized in Table IV. T h e continuous recycling of the solutions through the seven-cell unit reduced the sorption of ZrSb'j on the membranes to 3 to 6y0and that of Ce-Pr144to 2%. T ~ v oper cent of the PmI47 was sorbed. Cs--BaI37 and Sr-Yga showed 99 to 100% recovery. Separation \vas not as complete with thc seven-cell unit as it !vas \vith the three-cell unit. Better separation can be expected by increasing the current density and electrodialysis time. The results obtained in this laboratoi how that a n electrodialysis process, employing ion exchange membranes, can be developed to separate and recover some of the more significant fission elements from radioactive waste solutions. Research is now being conducted to develop a n electrodialysis technique to separate the three fractions produced into individual components. Studies are in progress to separate the radiocolloidal fraction: consisting primarily of Ce, Pr, Pni? and Y! using a technique of employing t\vo or more chelating agents Ivith overlapping stability constants. T h e electrodialysis units for these studies are equipped with cation exchange membranes, S e p t o n CR-6 1, and anion exchange membranes? S e p t o n AR-111.4. supplied by Ionics. Inc., Cambridge. lfass.
20
0 0
1
2
TIME, HOURS Figure 3. A. 6. C.
D.
Transfer of C S - B ~ and ' ~ ~ Zr-Nbgj
CS-BO'~' in 0.5 F ammonium acid fluoride Zr-Nbg5 in 0.5 F ammonium fluoride Cs-BaI3' in 1.2 F ammonium acid fluoride Zr-Nby5 in 1.2 F ammonium acid fluoride
,""
80
Table II. Electrodialysis of Cr-BaL3', Zr-Nbg6, and Ce-Pr144 in Ammonium Acid Fluoride Solution Using the Seven-Cell Unit
40 W
V
E W
a 20 Isotope
0
0
1
2
TIME, HOURS
Figure 4.
Transfer of Cs-Bar3', Zr-Nbg5, and Sr-YgO
A. C ~ - B a ' ~ ' i n0.5F ammanium acid fluoride solution 8. Cs-Ba"' in 0.5N nitric acid and 0.5 F ammonium acid fluoride solution C. Zr-Nbg5 in 0.5F ammanium acid fluoride solution D. Sr-YyO in 0.5N nitric acid and 0.5 F ammonium acid fluoride solution E. Zr-NbS5 in O.5N nitric acid and 0.5 F ommanium acid fluoride solution 228
l&EC PROCESS DESIGN A N D DEVELOPMENT
Initial acidity Cs-BaI3' Final acidity Initial acidity Zr-Nb95
Final acidity Initial acidity Ce-Pr'44 Final acidity Flow rate, ml. /inin. '1
Initial Isotope Activity, D.P.S.u X 106
s 17 38
zY
Lv
8 35 '2' .2' 3 31 3 24
.v
Disinfqrations per second.
P f r Cen/ o j Initial Isotope dctiuity in Solutions afrer 2 - H r . Electrodialysis Anion Fwd Cation
0.69 0.0 1.49 0.53 55.3 1.62 0.65 0.0 0.0
1.10 150
1 15
26 0 0 50 1 03 40 5 0 40 0 48 99 5 98 1 0 19
109
0 62 73 7 0 14 0 54 0 0
0 0 0 0
08 48 0 0 0 26
200
Table 111. Separation of C S - B O ' ~and ~ Zr-Nbg5 in 0.5 Formal Ammonium Acid Fluoride Using the Seven-Cell Unit
I s n I 0pc
Cs-Br
I37
2 r-N
b9j
Final acidity Cs-Bal37 Zr-Nb95
Final acidity Flow rate, nil. miin.
Initial Is0 topP ..icticity, D.P.S.a X 108
Per Cent of Initial Isotop? Acticity in Solutions after l1,'2-Hr, Electrodialysis Anion Ifhed Cati 0 12 Experiment 1 2.21 0.0 18.0 81.6 1.68 63.5 34.0 0.0 -v 1.29 0.24 0.49
Experiment 2 2.07 0.0 1.74 69.7 .v 1,09 150
9.9
89.6
29.2 0.21 109
0.31 200
0.0
Disintqratiun, Po- second.
Table IV. Summary of Results from the Seven-Cell Unit i n a Mixture of 0.5N Nitric Acid and 0.5 F Ammonium Acid Fluoride
Initial Per Cent of Initial Isotope Isotope Acticity in Solutions after Actiuity, D.P.S.O 2-Hr. Electrodialysis Is0 tofie X 106 lnion Feed Cation Experiment 1 Cs-BrI3' 1.92 0.0 9 5 90 3 Zr-l\b93 1.61 34.9 62 1 0 0 Ce-Prli4 2.11 0.0 98.0 0.0 Sr-\'90 4.43 0.0 70.0 30.0 Pm14: 3.95 0.0 98 0 0.0 Flow rate! ml. min. 150 109 200 Experiment 2 8.2 91.8 2.37 0.0 63.7 0.0 1.64 30.7 99 . 0 0.0 3.24 0.0 Sr-YgO 4.75 0.0 60.0 39.': Pm147 4.02 0.0 99.0 0 0 Flow rate: mi. min. 150 109 200 Disinfegraiio?zsper second. I
Acknowledgment
T h e authors thank C. \V. Brauer for providing some of the d a t a for various phases of this work and D. E. 'l'routner for his assistancr i n suggcsting a mixed isotope counting technique. literature Cited (1) Xmphlrtt. C . B.. Fixation of Highly Active \Vasres in Solid Form. L X ' C 5,'19. Atomic Energy Resfarch Establishment, Harwell. England. 1956. (2) Brnedict. M.. Pigford. T. H.. "Nuclear Chemical Engineeri q . " p. 204. McGraw-Hill, New York, 1957. (3) Bruce. F. K.. Fletcher, J. M.. Hyman. H . H., Katz. J. J.,eds., "Progress in Nuclrar Energy 111-Procrss Chemistry," p. 345351. McGra\\.-Hill. Nris York. 1956. (4) Bub. G. ,I.. \\.ebb. \ V . H., Rei,. Sci. Inslr. 32, No. 7, 857 (1961). (5) Durham. K. \V.. Gouldrn. P. D.: Electrodialysis of Fission Product Solutions. Chalk Rivrr, Ontario. AECL-437, CRDC614, 1957. (6) Mason. 1'. .I.,,Juda. \Valtcr: "Applications of Ion Exchange
Membranes in Electrodialysis," Chem. Eng. Progr. Symn,b. S u . 5 5 , KO.24. 155 (1959). (7) Mason. E. X.. Parsi. E. J., ".Applications of Ion Transfer Membranes in Nuclear Chemical Processing," Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva? Switzerland. .A/Conf.. 15/P/502, 1958. 18) Parsi. E. J . . "The Electrochemical Utilization of Ion Exchange Membranes in AEC ODerations." ORNL-1812. Oak Ridre National Laboratory, O a i Ridge. Tenn., 1955. (9) Schubert. J.. Conn. E. E.. .Y~icleonics4, 6 (1949). (10) Sieqel. J. M.. Rw..\fad. Phys. 18, 513-44: J . Am. Ci7rm. SUC. 68, 2411 (1946). RECEIVED for review .Iugust 21. 1961 .ACCEPTED March 12. 1962 \i-ork financially supported by V. S.Xtomic Enrrgy Commission under Contract No. .AT (1 1-1) 770.
SUPERSATURATION OF SULFATES IN ELECT ROD IA LYSIS CA R L BE RG
E R A N D R0 BERT M
.
L U R I E, Ionics, Inc., 752 Sixth St., Cambiidge. .liass.
Small quantities ( 2 5 p.p.m.) of sodium hexametaphosphate and carboxymethylcellulose stabilize calcium and magnesium sulfate solutions in electrodialysis equipment at levels up to 225% of saturation. When calcium sulfate precipitates, the salt (CaS04.2H?O) i s first found within the unit. Precipitation first occurs at stagnant zones next to the membranes, the points of highest concentraiion. Four polyphosphates and CMC appreciably extend the time before the supersaturated solutions precipitate. The synergistic effect of SHMP and CMC has been noted. Higher temperatures and low pH's hasten hydrolysis of the polyphosphate and lead to lower stability. Silica sols appear to b e effective destabilizers for supersaturated Cas04 solutions, since a slowly settling precipitate i s produced within the unit which does not clog the flow paths.
L E C T R O D I . ~ I . Y S I S has
become a kvidely used method of deIt is a n especially valuable and economic technique for deniinrralizing brackish ground waters found in desert regions around the world as \re11 as in many other locations. h-ot uncoinmonly these waters have high levels of calcium and magnesium sulfates and may even be saturated. Since the electrodialysis process electrically transfers the salt from the product stwain to a waste stream: the \vaste stream
E salting Ivater.
must necessai il! become supersaturated if the raw \\-ater is saturated. .4 further complication is the disposal of the waste stream which. if poured out on the ground. might find its way back to the original ivell. In addition. it is desirable to desalt all of the !rater rather than just a portion. T h e primary objective of this work has been the determination of rhe conditions ivhich control the allowable level of superVOL.
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