I n d . Eng. Chem. Res. 1987, 26, 621-627
temperatures except in the case of K z which shows relatively high errors. The results in Ay of Adachi et al. (1983) at three investigated temperatures (310.9,344.3 and 377.6 K) are similar to ours. Methane-n-Pentane. In this system, as shown in Table IV, the best results again are obtained with the optimal interaction parameters. Adachi et al. (1983) gave only one comparable isotherm (344.3 K) with better agreement with experiments, while our results are slightly better than those of Paunovii: et al. (1981). Finally it can be concluded that in cases of VLE predictions of supercritical methane with some light and heavy alkanes, all correlations must be performed with the temperature-dependent interaction parameter Kij of the Soave equation optimized for each available isotherm.
Nomenclature f = fugacity p = pressure
T = absolute temperature molar volume z = liquid mole fraction y = vapor mole fraction z = compressibility factor u =
Greek Symbols { = fugacity coefficient w = acentric factor Subscripts c = critical i, j = component Superscripts
L = liquid phase V = vapor phase Registry No. CHI, 74-82-8.
Literature Cited Adachi, Y.; Lu, B. C.-Y.; Sugie, H. Fluid Phase Equilib. 1 9 8 3 , I l , 29. Chang, T.; Rousseau, R. VI.;Ferrell, J. K. Ind. Eng. Chem. Process Des. Dev. 1983, 22, 462. Elliot, J. R.; Daubert, T. E. Ind. Eng. Chem. Process Des. Deu. 1985, 24, 743. Evelein, K. A.; Moore, R. G. Ind. Eng. Chem. Process Des. Dev. 1979, 18, 618. Graboski, M. S.; Daubert, T. E. Ind. Eng. Chem. Process Des. Deu. 1978a, 17, 443.
621
Graboski, M. S.; Daubert, T. E. Ind. Eng. Chem. Process Des. Deu. 1978b,17,448. Graboski, M. S.; Daubert, T. E. Ind. Eng. Chem. Process Des. Deu. 1979, 18, 300. Hiron, M. J. Chem. Eng. Sci. 1976, 31, 837. Hiron, M. J.; Dufour, G.; Vidal, J. Fluid Phase Equilib. 1977/1978, 1, 247. Joffe, J. Ind. Eng. Chem. Process Des. Deu. 1981,20, 168. Kabadl, V. N.: Danner, R. P. Ind. Eng. - Chem. Process Des. Deu. 1985; 24, 537. Kuester, J. L.; Mize, J. H. Optimization Techniques with Fortran; McGraw-Hill: New York, 1973: D 286. Lielmezs, J.; Howell, S. K.; Campbe-11,H. D. Chem. Eng. Sci. 1983, 38, 1293. Lin, H. Ind. Eng. Chem. Process Des. Dev. 1980, 19, 501. Oellrich, L.; Plocker, K.; Knapp, H.; Prausnitz, J. Chem. Ing. Technol. 1977, 49, 955. PaunoviE, R.; JovanoviE, S.; Mihajlov, A. Fluid Phase Equilib. 1981, 6, 141. Pedersen, K. S.; Thomassen, P.; Fredenslund, A. Ind. Eng. Chem. Process Des. Deu. 1984, 23, 163. Plocker, K.; Knapp, H.; Prausnitz, J. Ind. Eng. Chem. Process Des. Dev. 1978, 17, 324. Reamer, H. H.; Sage, B. H.; Lacey, W. N. Ind. Eng. Chem. 1950,42, 534. Sage, B. H.; Hicks, B. L.; Lacey, W. N.Ind. Eng. Chem. 1940, 32, 1085. Sage, B. H.; Reamer, H. H.; Olds, R. H.; Lacey, W. N. Ind. Eng. Chem. 1942, 34, 1108. soave, G. Chem. Eng. Sci. 1972,27, 1197. SerbanoviE, S.; DjordjeviE, B.; GrozdaniE, D.; MitroviE, A. Presented at the 2nd Yugoslav-Italian-Austrian Chemical Engineering Conference, Ljubljana, Sept 15-18, 1980; p 71-79; Glas. Hem. Drus. Beograd. 1981a, 46, 35. SerbanoviE, S. Ph.D. Dissertation, University of Belgrade, 1981b. SerbanoviE, S.; DjordjeviE, B. Teor. Osn. Khim. Tekhnol. 1984a, 18, 511. SerbanoviE, S.; DragojloviE, B.; DjordjeviE, B. Glas. Hem. Drus. Beograd. 1984b, 49, 217. Teja, A. S. Chem. Eng. Sci. 1978a, 33, 609. Teja, A. S.; Patel, N. C.; Ng, N. H. Chem. Eng. Sci. 1978b, 33, 624. Wenzel, H.; Rupp, W. Chem. Eng. Sci. 1978,33, 683. Wong, D. C. H.; Sandler, S. I.; Teja, A. S. Ind. Eng. Chem. Fundam. 1984, 23, 38.
Slobodan P. SerbanoviE,* Bojan D. DjordjeviE Faculty of Technology and Metallurgy Chemical Engineering Department University of Belgrade 11000 Belgrade, Yugoslavia Received for review November 19, 1985 Accepted September 25, 1986
Development of an Improved Two-cycle Process for Recovering Uranium from Wet-Process Phosphoric Acid An improved two-cycle separation process for the recovery of uranium from wet-process phosphoric acid by extraction with bis(2-ethylhexy1)phosphoric acid (D2EHPA) plus dibutyl butylphosphonate (DBBP) in kerosene has been developed and demonstrated successfully in bench-scale, continuous mixer-settler tests. The sulfuric acid and water scrubbing steps for the recycled extractant in the second cycle solve the problems of the contamination and dilution of the phosphoric acid by the ammonium ion and water and also avoid the formation of undesirable phosphatic precipitates during the subsequent extraction of uranium by recycled organic extractant. The advantages of the improved process are lower chemical cost, higher product purity, and better phase separation in comparison with the previous process. Although the uranium content in phosphate deposits is relatively small (50-200 ppm), it represents a significant potential source of uranium when large amounts of phosphate rock are processed. The recovery of uranium 0888-5885/87/2626-0621$01.50/0
as a byproduct from wet-process phosphoric acid has been investigated since the early 1950s, and several solvent extraction processes have been developed. Of the various extraction systems reported in the literature, only three 0 1987 American Chemical Society
622 Ind. Eng. Chem. Res., Vol. 26, No. 3, 1987 Table I. Major Compositions of Wet-Process Phosphoric Acid concentration for sample 2 1 3 composition 4.8 4.3 4.8 HJ'O,. M 1.24 1.24 2.24 0.072 0.062 0.067 1.01 1.22 1.98 0.032 0.035 0.040 3.96 4.56 2.08 1.98 1.24 0.76 0.89 0.76 1.82 3.85 5.60 5.65 0.013 0.008 0.017 0.073 0.065 0.070 6.4 5.4 6.0 0.47 0.33 0.41 0.26 0.21 0.31
are of commercial interest. They are the octylpyrophosphoric acid system (OPPA) which extracts tetravalent uranium (Cronan, 1959; Ellis, 1952; Greek et al., 1957;Long et al., 1955; Reese and Schroeder, 1981), the synergistic bis(2-ethy1hexyl)phosphoric acid-trioctylphosphine oxide system (DBEHPA-TOPO) which extracts hexavalent uranium (Berry et al., 1981; Hurst et al., 1972; Hurst and Crouse, 1973; Sialino and Francois, 1980; Steck, 1984; York, 1983),and the octylphenylphosphoric acid system (OPAP) in which tetravalent uranium is extracted (Arnold, 1978; Arnold et al., 1980; Hurst and Crouse, 1974; Hurst et al., 1977). D2EHPA-TOP0 processes based on methods developed at the Oak Ridge National Laboratory by Hurst et al. are the most promising ones which are in use at many commercial plants. Advantages claimed for the D2EHPA-TOP0 process are that the extractant combination is stable toward high acid concentration as well as the carbonate solutions used for stripping and that a high-grade product is recovered. However, the TOPO synergistic agent is expensive, and hence the total chemicals cost is higher. Another drawback is the formation of a precipitate of some kind of phosphatic compounds in the extraction stage of the second purification cycle when the organic extractant recycles directly from the ammonium carbonate stripping stage. Owing to the conversion of bis(2-ethylhexy1)phosphoricacid to a highly hydrated ammonium salt, the extracted water and NH4+transfer to the aqueous phase, when the organic extractant is returned to the uranium extraction circuit for contact with fresh phosphoric acid. The absorption of NH4+and water by the phosphoric acid results in undesirable contamination and dilution of the phosphoric acid and loss in overall efficiency of operation. Blake et al. (1958) and Murthy et al. (1970) studied the synergistic enhancement of uranium extraction by addition of neutral organophosphorus compounds to D2EHPA and showed that TOPO gave higher synergistic effect than DBBP did. However, in view of the higher cost and unavailability of TOPO in commercial quantities, DBBP seems to be a good substitute for TOPO. Detailed studies of the effect of the process variables and demonstration of a complete process flow sheet on uranium extraction with D2EHPA-DBBP have not been performed previously. In the present work, factors affecting the uranium recovery from wet-process phosphoric acid with bis(2ethylhexy1)phosphoricacid plus dibutyl butylphosphonate in kerosene were extensively examined, and an improved two-cycle separation process was developed and demonstrated in bench-scale, continuous mixer-settler tests. The addition of the sulfuric acid and water scrubbing steps for
F i r s t Cancen-
Recycle co phosphare rock l e a c h i n g circuit
!3-6 s t a g e s .
'7
It
Scrubbing r; ' c a g e s .
.J
: ,I'. P?.>dll
ca1cioation
Filtration
i
First Concentration Cycle 0 . 5 - 0 . 7 IDZEHPA-O.1-0.1II Purification C y c l e 0 . 3 - 0 . 1 \1 DZEHPA-0.Oh-0.1
Second
* Original
ifea a c i d decrease
