Acknowledgment
Thanks are due to M. Sanyasi Reddy for his help and cooperation. literature Cited
Allerton, J., Strom, B. O., Treybal, R. E., Trans. Am. Znst. Chem. Engrs. 39, 361 (1943). Colburn, A. P., Trans. Am. Znst. Chem. Engrs. 35, 211 (1939). Colburn, A. P., Welsh, D. G., Trans. Am. Ztut. Chem. Engrs. 38, 179 (1942). Elgin, ‘J. C.; Browning, F. M., Trans. Am. Znst. Chem. Engrs. 31, 639 (1935); 32, 105 (1936). Garner, F. H., Ellis, S. R. M., Fosbury, D. W., Trans. Znst. Chem. Eners. (London) 31. 348 (1953). Gar&, F. H., Ellis, S. R. M:, Hill, J. W., A.Z.Ch.E. J. 1, 185 11955’1. \----,-
Garner, F. H., Ellis, S. R. M., Hill, J. W., Trans. Znst. Chem. Engrs. (London) 34, 223 (1956). Krishna Murtv. R.. D. Sc. thesis. “Studies on Perforated-Plate Liquid-Liquid Extraction Towers,” Andhra University, Wal-
tair, India, 1965 (copies available from author, Andhra University Library, I.N.S.D.O.C., New Delhi). Krishna, Murty R., unpublished data, 196513. Laddha, G. S., Smith, J. M., Chem. Eng. Progr. 46, 195 (1950). Mayfield, F. D., Church, W. L., Znd. Eng. Chem. 44,2253 (1952). Morello, V. S., Beckmann, R. B., Znd. Eng. Chem. 42, 1078 (1950). Moulton, R. W., Walkey, J. E., Trans. Am. Znst. Chem. Engrs. 40, 695 (1944). Nandi, S. K., Ghosh, S. K., J. Indian Chem. Soc., Znd. News Ed. 13, 93, 103 (1950). Pyle, C., Colburn, A. P., Duffey, H. R., Znd. Eng. Chem. 42, 1042 (1950). Row, S. B., Koffolt, J. H., Withrow, J. R., Trans. Am. Inst. Chem. Engrs. 37, 559 (1941). Treybal, R. E., “Liquid Extraction,” 1st ed., McGraw-Hill New York, 1951. Treybal, R. E., “Liquid Extraction,” 2nd ed., McGraw-Hill New York, 1963. Treybal, R. E., Dumoulin, F. E., Znd. Eng. Chem. 34,709 (1942). RECEIVED for review October 14, 1966 ACCEPTED AUGUST3, 1967
STEADY-STATE SOLVENT EXTRACTION CALCULATIONS FOR CURIUM RECOVERY I . D. EUBANKS’AND J. T. LOWE Savannah River Laboratory, E. Z. du Pont de Nemours @ Co., Aiken, S. C .
29801
A numerical method has been programmed in FORTRAN IV for calculating steady-state phase concentrations in countercurrent liquid-liquid extractors. An integral number of stages, cocurrent mass transfer efficiencies, and compositions of multiple feed streams are included in the input data. Distribution data are represented b y mathematical expressions for the specific process computed. Stage concentrations for as many as seven mutually dependent distributing components can be calculated from a single set of input data. Computed and experimental concentration profiles are compared for flowsheets used to purify curium.
OUNTERCURRENT
solvent extraction is normally used to
C process irradiated nuclear material because a product of high purity is attainable, the process chemicals are relatively stable to ionizing radiation, the quantity of solid radioactive wastes is minimal, and the processing equipment may be operated remotely (Haas, 1961). Stage concentrations in solvent extraction processes are calculated from distribution coefficients and material balance ex1 Present address, Department of Chemistry, Oklahoma State University, Stillwater, Okla. 74074
172
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
pressions. The concentrations can be determined either numerically (Siddall, 1958) or graphically (Codding et al., 1958). Although the graphical method has been widely accepted for flowsheet design and interpretation, extensive calculations are required to design optimum flowsheets and to establish permissible fluctuations in process variables. If two components influence each other’s distribution, graphical solutions require lengthy trial-and-error procedures (Haas, 1958) ; a numerical method for a computer is therefore preferable. A limited number of previous treatments of similar problems have been reported. Mills (1965) reviewed several programs
to calculate solvent extraction concentration profiles for the tributyl phosphate (TBP)-HNO3 system. Olander (1961) wrote a program to calculate the approximate number of theoretical stages required for a desired separation. H e assumed a n ideal complexing reaction between the distributing component and TBP ; activity coefficients were neglected. Burton and Mills (1963) used a n empirical relationship for distribution data. Their mathematical model assumed that no distributing component was lost to the raffinate; stage concentrations were predicted only for the extraction section. DiLiddo and Walsh’s program (1961) treated dynamics and control in pulse columns. T h e program of Hanson et al. (1962) utilized activity data to calculate distribution coefficients, but iterations corrected the flow profile rather than the concentration profile. This paper describes a computer method that can predict stage concentrations for any solvent extraction system in which distribution behavior is known. Iterations correct concentration profiles from supplied process conditions. T h e program was developed specifically as a n aid in designing flowsheets to recover americium and curium. For this system, the agreement between calculated and experimental results was excellent. T h e actual program listing is on deposit in the AD1 Auxiliary Publications Project. Computational Method
T h e model for calculation of steady-state concentrations in countercurrent solvent extraction contactors is shown in Figure 1. Batch contacts are assumed in each stage, which approximates performance in mixer-settlers in which organic and aqueous flow is countercurrent to the mixing chamber of a stage and cocurrent to the settling chamber of that stage (Figure 2). Equations are given below for a single distributing component concentrated in the organic exit stream. T h e equations for a concentrated aqueous exit stream are similar. T h e organic and aqueous flow rates from adjacent stages, O j and A j , are calculated as the sum of all feed flow rates into all preceding stages, including the stage under consideration :
ORGANIC FEED STREAMS ORGANIC EXIT
.
*
Model of solvent-extraction contactor
N+/
.
N
.
-1
.
ok’
k=j
T h e concentration of the distributing component leaving the contactor in the organic phase is given by
Initially, the aqueous exit stream concentration, X,, is assumed to be zero unless stage concentrations have been supplied to the program. Equilibrium behavior around each stage is determined from the distribution coefficient expression, v en
(3) Since the distribution coefficient may be a function of X j e ain Equation 3, the iterations are made around each stage until two successive distribution coefficient calculations agree within 1%. Actual stages in mixer-settlers do not correspond exactly to theoretical stages, because equilibrium is not achieved in practice. Cocurrent mass transfer efficiency, defined as the ratio of the amount of material transferred to the amount that would be transferred a t equilibrium, is used to correct the theoretical concentrations. T h e mass transfer efficiency for a system is determined by mixer-settler design and the mechanism of transfer for the distributing component. T h e efficiency, E , is defined in terms of either aqueous concentrations,
(4) or organic concentrations,
(5) For the case of the distributing component concentrated in the organic exit stream, the aqueous concentration in stage j is corrected for efficiency by solving Equation 4 for X j . T h e value for X j is substituted into the material balance expression,
OjYj
+ AjXj = Oj+lYj+l + Aj-1x3--1 + Aj’Xj’ + Oj’Yj’
yjen
N+Z
=
(6)
solved for Yj+l. For j = N , Yj+l = 0, and for j = 1, Xj-, = 0. T h e calculations in Equations 3 through 6 are made sequenIf tially for values o f j from 1 to N , ending with a value for X,$,. this calculated value for X,. differs by more than 1% from the assumed value for X,. used in Equation 2, a new value for X, is chosen and the calculations through the contactor are repeated. Divergence is prevented by restricting the value between successively narrower limits. If more than half of the component leaves the contactor in the aqueous exit stream, Equation 2 is rearranged to calculate X,, and Y I is assumed to be zero for the initial iteration. Y t nis determined by
AQUEOUS FEED STREAMS
Figure 1
N oj
4-2
=
D1Xeq 3
(7)
Efficiency corrections are made, and Xjp1 is calculated by Equation 6. Calculations for Several Distributing Components
----_b Organic Flow
-Aqueous
Figure 2.
Flow in a mixer-settler
Flow
Agreement is obtained for mutually dependent distributing components by recalculating stage concentrations for previous components, if necessary, every time a new concentration proVOL 7
NO. 2
APRIL 1968
173
file is calculated. Recalculation is necessary if the stage concentrations of a previously calculated component are affected by the stage concentrations of the latest component. T o speed convergence, the concentration profiles are calculated in order of decreasing salting effect. For cases in which the distribution coefficients of two or more components are mutually dependent, a n initial estimate for the stage profiles may be made, if desired, to speed convergence. Results
The program was used in the development of solvent extraction processes to recover curium produced by irradiating plutonium (Eubanks and Burney, 1966; Groh et al., 1965). 244Cmis potentially a good isotope for power sources because of its long half life, high specific power, and potential availability. A crude americium-curium fission product nitrate solution is isolated during chemical processing of the irradiated elements (Henry, 1965). Further processing includes a step to convert this nitrate solution to a chloride solution and a step to remove lanthanide fission products (primarily cerium) from the curium product stream. I n the nitrate-to-chloride conversion step, a mixture of noctyl and n-decyl tertiary amine nitrates in diethylbenzene extracts curium and cerium from a n aqueous solution of lithium
nitrate, aluminum nitrate, and hydrazine. Nitric acid also extracts, but lithium, aluminum, and hydrazine do not. Distribution coefficients of curium, cerium, and nitric acid depend on the concentrations of lithium, aluminum, and hydrazine in the aqueous phase and cerium and nitric acid in the organic phase. The curium concentration is too low (-0.004M) to affect distribution coefficients. T h e empirical analytical expressions which relate distribution coefficients to concentrations are given in Table I. These expressions were obtained by a least squares fit of experimentally determined distribution data. Following the extraction step, curium and lanthanide fission products are back-extracted from the tertiary amine with hydrochloric acid. All the distribution coefficients are very low in this step. After feed adjustment, a mixture of n-octyl and n-decyl tertiary amine chlorides in diethylbenzene is used to extract curium from cerium in an aqueous lithium chloride solution. Hydrochloric acid also extracts, but again lithium does not. Distribution coefficients of curium, cerium, and hydrochloric acid depend on the concentration of lithium in the aqueous phase, and hydrochloric acid and tin (a feed additive) in the organic phase. T h e empirical analytical expressions for distribution coefficients, obtained as above, are given in Table 11. T h e curium, now free of cerium fission product, is back-
-
0 Observed Stage Concentrations
Calculated Stage Concentrations
75% Mass Transfer Efficiency
0 Feed Compositions Aqueous
0
- Stage
LiN03
7.8M
Aqueous
- Stage
.AI(N03)3 "03 Lanthanides Curium
I (IAS)
9 (IAF) 2.4 M 0.36 M 0.44 M
0.8 g/l
Organic - Stage 1 6 (IAX) R3N"N03 in diethylbenzene HN03 0.03M
1
Figure 3. 174
=Relative Flow
Curium stage concentrations in organic phase of conversion step
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
Table 1.
Equations for Distribution Coefficients in NitratatoChloride Conversion Stepanb
Table 11.
Equations for Distribution Coefficients in the Cerium-Curium Separation StepQ
Nitric Acid
Hydrochloric Acid
In D = -0.239 - 7.07(H0) f 0.517(NOa-) - l.O6(Al) 15.4(CeO)- 3.26(N~Ha) 3.27(H0)(A1)
+
-
In D = -8.89
Ceriumc In D = 7.55
- 5.77(H0) f
l.O6(LiCl)
Cerium
- 14.1(H0) - 46.9(Ce0)
In D = -22.5
-
12.O(H0)
+ 1.9(LiCl)
Curium In D where D H, NO3A1 Ce, N2Hl
=
-4.41
- 16.4(H0)- 37.9(Ce0) f
Curium
1.29(NOa-)
+
= distribution coefficient
In D = -18.5 - 9.11(H0) 1.89(LiC1) - 11.5(SnO) where D = distribution coefficient H, = free hydrochloric acid molarity in organic phase LiCl = lithium chloride molarity in aqueous phase Sn, = tin molarity in organic phase
= free nitric acid molarity in organic phase = = = =
nitrate molarity in aqueous phase (excluding "08) aluminum molarity in aqueous phase cerium molarity in organic phase hydrazine molarity in aqueous phase
0 Organic phase. 30% tertiary amine nitrates in diethylbenrene. Derived from experimental distribution data. Aqueous phase. 8M LiNO3.
b
a Organic phase. 30% tertiary amine hydrochlorides in diethylbenrene; Based on datapresented by Roth and Henry (1965).
too
IO 0 Observed Stage Concentrations -Calculated Stage Concentrations
90% Mass Transfer Efficiency
Feed Compositions Aqueous
- Stage
LiCl
I (2AS)
11.0M
Aqueous LiCl HCI Curium SnClz
Stage IO (2AF) ll.OM 0.4M 0.8 g / l O.IM
-
Organic Stage 16 (2AX) R-N-HCI 0.6M HE1 0.04 M
10-2
m2tF0
= Relative Flow
10-3 Figure 4. Curium stage concentrations in organic phase of actinide-lanthanide separation step Organic-Stage
16, in diethylbenzene VOL. 7
NO. 2
APRIL 1968
175
0.E
Precipitation of AI and R.E. Nitrates inI IAF
>
0.5
0.I % Cm loss to IAW Flowsheet Conditions
I k' 0.4
Stream Stoge Fed Flow
9
.0" 0.3 z
Composition
I
loo+ 5%
9
2 0 0 + 5 % LiNO3, 7.8-8.2M
C
AI(NO3I3, Variable "03, Variable Lanthanide,, BD% 0
I
I
200?5%
Mass Transfer Efficiency I
1
RaN-HCI, 0.60-0.62M HCI, 0.01-0.05M
I
I
I
L i C l in 2AF, M Figure 6.
Operating region for curium-cerium separation step 2AX, in diethylbenzene
176
l & E C PROCESS DESIGN AND DEVELOPMENT
I
-
Nomenclature
Ajf
flow rate of aqueous stream entering contactor a t stage j A , = flow rate of aqueous stream leaving s t a g e j Y j = concentration of distributing component in organic stream leaving stage j X j = concentration of distributing component in aqueous stream leaving stage j 0,f = flow rate of organic stream entering contactor at stage j X,, = concentration of distributing component in aqueous stream entering contactor at stage j Y,f = concentration of distributing component in organic stream entering contactor a t stage j 0, = flow rate of organic stream leaving stage j Dj = equilibrium distribution coefficient Ar = number of stages in contactor X,~Q = equilibrium aqueous concentration of distributing component in stage j Y,eq = equilibrium organic concentration of distributing component in stage j =
Haas, W. O., “Chemical Processing of Reactor Fuels,” J. F. Flagg, ed., p. 126, Academic Press, New York, 1961. Haas, W. O., Znd. Eng. Chem. 50, 125 (1958). Hanson, D. N., Duffin, J. H., Somerville, G. F., “Computation of Multistage Separation Processes,” Reinhold, New York, 1962. Henry, H . E., “Isolating Americium and Curium from A1(K03)3NaNO--HNOq Solutions bv Batch Extraction with Tributvl Phosphgte,” E. I . du Pont de Nemours & Co., Savannah Rivdr Laboratory, USAEC Rept. DP-972 (1965). Mills, A. L., “Review of Computer Programmes for Solvent Extraction Calculations,” Reactor Group, United Kingdom Atomic Energy Authority, TRG Rept. 902 ( D ) (1965). Olander, D. R., Znd. Eng. Chem. 53, 1 (1961). Roth, J. A . , Henry, H. E., J . Chem. Eng. Data IO, 298 (1965). Schlea, C. S., Caverly, M. R., Horni, E. C., Henry, H. E., Jenkins, W.J., “Miniature Pilot Plant for Processing Irradiated Nuclear Fuel,” E. I. du Pont de Nemours & Co., Savannah River Laboratory, USAEC Rept. DP-757 (1962). Siddall, T. H., “A Rationale for the Recovery of Irradiated Uranium and Thorium by Solvent Extraction,” Proceedings of 2nd International Conference on Peaceful Uses of Atomic Energy, Vol. 17, p. 339, Geneva, 1958. RECEIVED for review January 20, 1967 ACCEPTEDOctober 12, 1967
literature Cited
Burton, TV. R., Mills, A . L., ,Vucl. Eng. 8, 248 (1963). Codding, J. T$‘., Haas, LV. O., Heuniann, F. K., Znd. Eng. Chem. 50, 145 (1958). DiLiddo, B. A , , IValsh, T. J., Znd. Eng. Chem. 53, 801 (1961). Eubanks, I. D., Burney, G. A . , “Curium Process Development. I. General Process Description,” E. I . du Pont de Nemours & Co., Savannah Riler Laboratory, USAEC Rept. DP-1009 (1966). Groh, €1. J., Huntoon, R . T., Schlea, C. S., Smith, J. A., Springer, F. H., .\‘uclear Appl. 1, 327 (1965).
Information developed during work under Contract AT(07-2)-1 with the U. S. Atomic Energy Commission. Material supplementary to this article has been deposited as Document No. 9793 with the AD1 Auxiliary Publications Project, Photoduplication Service, Library of Congress, IVashington, D. C. A copy may be secured by citing the docummt number and by remitting $6.25 for photoprints or 62.50 for 35-mm. microfilm. Advance pa! ment is required. Make checks or money orders payable to Chief, Photoduplication Service, Library of Congress.
SOLVENT EXTRACTION OF THORIUM AND URANIUM FROM BERYLLIUM NITRATE FEEDS BY TRI-n-BUTYL PHOSPHATE R. C. CAIRNS, M. G. B A I L L I E , B. J. FOX, A N D R . K. R Y A N Australian Atomic E n e r a Commission Research Establishment, Sutherland, ,Yew South Wales, Australia
A solvent-extraction process is presented for the recovery of uranium and thorium from radioactive feed solutions highly salted with beryllium nitrate. By using a tri-n-butyl phosphate extractant and a split contactor system, in which the scrub raffinate and feed raffinate streams are kept separate, it was demonstrated that fission product decontamination factors greater than 1 03,and adequate uranium and thorium recoveries, can be obtained for activity levels up to 1 curie per liter.
ABORATORY
development has recently been completed a t
L Lucas Heights of flo\ysheets for the fuel cycle of a B e 0
high temperature reactor system (Cairns et al., 1966). As part of this work it \yas necessary to develop a liquid-liquid extraction process for uranium and thorium recovery from feeds highly salted with beryllium nitrate. T h e fuel element (Smith, 1966) consists of a matrix of beryllium oxide, in the form of a sphere of about I-inch diameter, containing particles of plutonium and thorium oxides in solid solution, 150 to 200 microns in diameter. T h e sphere is coated with a iayer of beryllium oxide about 0.05 inch thick. Because of the presence of beryllium oxide this fuel element poses some unique extraction problems. Aqueous head-end methods, and liquid-liquid separation techniques, were selected
for experimental study and this led to the development of a solvent-extraction process for recovering uranium and thorium from the highly salted feed solution arising from the head-end step. B e 0 High Temperature Gas-Cooled Reactor Fuel Cycle
For economic reasons it was necessary to consider the recycle of both moderator and fuel material. The fuel cycle studies were therefore based on the conceptual flowsheet given in Figure 1. In the head-end process the fuel elements are crushed and ground, and subjected to a nitric acid leaching step to dissolve the bulk of the fuel materials with as little of the B e 0 moderator as possible; the residual moderator is subsequently dissolved for further treatment. In the actinide sepaVOL. 7
NO. 2 A P R I L 1 9 6 8
177
