nitrogen, and oxygen, the hydrogen-hydrocarbon vapor ratio in the catalyst bed changed with time, being a t a minimum when the shale first reached the desired operating temperature, or where the liquid hourly space velocity was a maximum. In view of these factors attributable to a batch reactor, caution is advisable in trying to project the results reported to a continuous process operating a t similar conditions. Apparently, a net quantity of hydrogen was consumed during operation of the reactor. T h e quality of the product was an indication of this, as was the increase in the concentration of the helium tracer element in the earlier runs where gas samples collected from the off-gas stream were analyzed by mass spectrometry. An even better indication was obtained where the wet-test meter was used during a run. Wet-test meter readings taken every 5 or 10 minutes made it possible to observe increases and decreases in the hydrogen flow rate. For runs where both the wet-test meter and the thermal-conductivity detector unit were used, it was possible to observe the hydrogen flow rate going through a minimum value as the concentration of hydrocarbon vapors in the off-gas stream was going through a maximum. These values occurred a t the point where the shale temperature just reached the operating level. T h e economics of this process in relation to existing process concepts has yet to be studied to the authors’ satisfaction. T h e apparent advantages of this novel approach have been mentioned. Possible additional values might be added through ammonia production and the possible recovery and sale of sulfur or sulfuric acid from hydrogen sulfide. T h e noncondensable hydrocarbon vapors generated also constitute a credit either as a source of replacement hydrogen or as fuel to provide process heat requirements. Any product advantages obtained by mixing shale and catalyst could be offset by materials handling problems. T h e limited results obtained so far appear sufficiently interesting, however, to prompt further study. For coal, an added consideration exists-namely, that in addition to producing a product of high value, a coal char low in sulfur may also be possible at a time when low-sulfur fuels
for power plants are in demand. Additional experimental work is needed to confirm this possibility, and to explore how wide a variety of coals can be treated in this manner. Conclusions
T h e exploratory experiments reported here suggest the technical feasibility of producing a liquid hydrocarbon product, gasoline-like in properties, by catalytic treatment of vapors evolved from oil shale or coal which was heated in a flowing stream of hydrogen under moderate pressure. Further experimental work is needed before the economic value of such a process can be properly assessed. Acknowledgment
T h e authors thank Morgan G. Huntington for permission to publish these preliminary results and acknowledge his support of this work. literature Cited
Allred, V. D., Chem. Engr. Progr. 62 (8), 55-60 (1966). Chem. Eng. News 44, 79 (Oct. 17, 1966). Chem. Eng. News 45, 14 (Feb. 27, 1967). Chem. Week 100 (6), 29-35 (Feb. 11, 1967). Chopey, N. P., Chem. Eng. 72 (18), 52-4 (1965). Clark, E. L., Pelipetz, M. G., Storch, H. H., Weller, S., Schreiber, S., Ind. Eng. Chem. 42,861-5 (1950). Fumich, G., Jr., J . Petrol. Technol. 18 ( 8 ) 939-43 (August 1966). Green, L. E., Schmauch, L. J., Worman, J. C., Anal. Chem. 36, 1512-16 (1964). Huntington, M. G. (to Pyrochem Corp.), U. S. Patent 3,244,615 (April 5, 1966). Huntington, M. G.(to Huntington Chemical Corp.), U. S. Patent 3,106,521(Oct. 8, 1963a). Huntington, M. G. (to Huntington Chemical Corp.), U. S. Patent 3,107,985(Oct. 22, 1963b). Oil Gas J . 62 ( l o ) , 72 (March 9, 1964). Prien, C. H., Znd. Eng. Chem. 56 (9), 32-40 (1964). Schlinger, W. G., Jesse, D. R., Division of Petroleum Chemistry, 152nd meeting ACS, New York, N. Y . , Sept. 11-16, 1966. for review May 29, 1967 RECEIVED ACCEPTED September 29, 1967
DIBUTYL CARBITOL SOLVENT EXTRACTION OF POLONIUM-210 FROM NITRIC ACID SOLUTIONS OF IRRADIATED BISMUTH WALLACE W. SCHULZ AND GERALD L . RICHARDSON PaciJc Northwest Laboratory, Battelle Memorial Institute, Richland, W a s h . 99352
EUTRON
irradiation of bismuth produces polonium-2 10
N according to the following reaction sequence. &i209
+ on1
4
,,Biz10
(I9
5.0 d
gaPo210
(1)
Polonium-210 has a half life of 138 days and decays by emission of a 5.3-m.e.v. alpha particle to stable Pbm6. Because of its short half life and high specific activity, Po210 is a valuable isotopic power source; its use in space applications is expected to increase significantly (Rizzo, 1967). Separation and purification of curie amounts of Po210 have been performed for many years by the Mound Laboratory
of the Monsanto Research Corp. (Moyer, 1956). T h e scheme used a t the Mound Laboratory to separate Po210 from irradiated bismuth metal involves a series of deposition and redissolution steps in which the Po*lO is concentrated and purified by spontaneous deposition on unirradiated bismuth powder. This paper describes a new continuous countercurrent solvent extraction process developed as a n alternative way of separating Po210 from large amounts of associated bismuth. This solvent-extraction scheme, which employs dibutyl Carbitol [bis(2-butoxyethyl)ether] as the extractant, is a n efficient, high capacity processing technique. I t appears well suited VOL 7
NO. 1
JANUARY 1968
149
A dibutyl Carbitol (DBC) solvent-extraction process for recovery and purification of PoZl0 from nitric acid solutions of irradiated bismuth metal has been developed. It is suitable as a head end step in recovery of kilogram quantities of Po210for subsequent use in isotopic power sources. It involves countercurrent extraction of polonium from an aqueous nitric acid-bismuth nitrate feed solution containing about 4 curies per liter of Poz1' into approximately a double-volume portion of DBC. The resulting organic extract is scrubbed with 3M "03 to provide further decontamination from bismuth; polonium is then stripped into a 0.2M " 0 3 solution. In laboratory and pilot plant demonstration tests, over-all PoZl0recoveries were 98% or greater while over-all bismuth decontamination factors were typically 1500 or higher.
Process Description
Solvent Extraction. A detailed chemical flowsheet for the DBC extraction separation of Po210 from bismuth in the 1AF solution is shown in Figure 1. Principal features of the extraction process are :
Fuel Dissolution. T h e bismuth target elements currently irradiated in Hanford reactors are 6 inches long and 1.34 inches in diameter. and weigh 3.01 pounds. They are clad in an aluminum can with a 0.035-inch wall thickness. The bismuth is irradiated to yield about 6 curies (Ci.) of Po210 per pound of bismuth (about 2.5 grams of Po*1oper ton of bismuth). T h e aluminum cans are removed by dissolution in a sodium hydroxide-sodium nitrate solution according to well established techniques for decladding irradiated reactor fuel elements (Blanc0 and \$'atson, 1961). The bismuth is then dissolved in boiling dilute nitric acid to prepare extraction column feed stock (1 A F solution). A satisfactory dissolution procedure is to start the dissolution reaction in a minimum volume of 4 to 6 M " 0 3 and then add concentrated nitric acid periodically over a 1- to 2-hour period. In pilot plant tests of this technique, unirradiated bismuth target elements were completely dissolved in about 5 hours a t a n average dissolution rate of about 2 mils per minute (Richardson, 1966). About 3.5 to 4 moles of nitric acid were used per mole of bismuth dissolved; the off-gases appeared to be nitric oxide and nitrogen dioxide.
Polonium-210 is preferentially (>99%) extracted into the DBC solvent in the extraction column. About 2 to 8% of the bismuth is also extracted. Most of the extracted bismuth is removed from the DBC phase by contact with a small volume of 3 M " 0 3 in the scrub column. T h e aqueous raffinate from the scrub column is routed to the extraction column to recover the small amounts of Po2lowhich are also scrubbed from the organic phase. A dilute nitric acid solution is used in the strip column to strip the purified Po21ofrom the organic phase. The resulting aqueous solution is considered a suitable starting material for final concentration and purification of the Poz1oby chemical or electrolytic deposition techniques. The process provides for recovery of over 98% of the Po210 with an over-all bismuth decontamination factor of greater than 1500. Successful operation of the extraction process requires careful control of the nitric acid concentrations in the various aqueous and organic streams. Of particular concern is the nitric acid concentration in the extraction column, since B i O N 0 3 .HzO will begin to precipitate if the nitric acid concentration falls
for use as a head end step in the production of megacurie quantities of Po210.
. _
1AF
Bi HN03
1.67M
PO*
100% 0.3
Flow
lAFS _ 1.23M
Bi HN9 2.64M HNHzS03 0.081 Po 111% Flow 0.425
2.4M
Addition
~
Flow
t
* pO2lo Concentration
will be about 4 Ci./l. i n the 1AF
i -
Organic Extraction Column Extractant 100% DBC
Flow 1.6M 1.0
500 c.
Bi HNQ
Po Flow
I
0.125
350
Bi HNOj Po Flow
c.
I Figure 1 .
Strip Column
