ANALYTICAL CHEMISTRY
70 mixture than on pure silicic acid. Actually, Rj values for these compounds on the various mixtures fell between R/ values measured on the pure components. Evidently, the acidic nature of one of the two absorbents is enhanced by the presence of the other. The nature of the interaction vhich brings about increased acidity has not been determined. Use can be made of this characteristic, however, to separate aliphatic amines, certain N-substituted and I ing substituted aromatic amines. The following general method is offered for the separation: Sample size and column length will have to be adjusted to the relative concentrations of the individual constituents. The sample is first disPolved in benzene and applied to a silicic acid column employing benzene as developer. N-hlkyl-substituted aromatic amines and certain ring-substituted aromatic amines pass into the filtrate while the aliphatic amines are held firmly near the top of the column. The filtrate is then concentrated by evaporation and introduced into a column of 50% by weight of boron oxide-silicic acid where the iV-alkyl substituted aromatic amines remain a t the top of the column and the ring substituted aromatic amines pass into the filtrate. The amines to which this method has been applied are: N-alkyl-substituted aromatic amines-methylaniline, ethllaniline, dimethylaniline, and diethylaniline. Ring-substituted aromatic amines-+ and p-nitroaniline, oand pchloroaniline, and 0- and p-methylaniline. Aliphatic amines-butylamine, amylamine, and decylamine.
Those mixed adsorbents which share the adsorption of organic molecules, thus exhibiting R f values intermediate between those measured on the pure adsorbents, should afford the practic,al chromatographer a wider choice of adsorbents. ACKNOW LEDGMEhT
The authors wish to express their appreciation to the Phillips Petroleum Co., Bartlesville, Okla., for the generous financirll grant under which this work was powible. LITERATURE CITED
(1) Cassidy, H. G., "Technique of Organic Chemistry: Adsorption and Chromatography," Vo1. V, pp. 28-39, 188-206, Ititerscience Publishers, Inc., S e w York, 1951. (2) Iddles, H. A., Lorn, rl. W., Iiosen, B. D., and H a r t , R. I.. I s n . ENG.CHEM., ANAL. ED., 11, 102 (1939). (3) LeRosen, A. L . , Alonaghan, P. H., Rivet, C. A, Smith, E. I)., a n d Suter, H. A., ilx.4~.CHEY.,22, 809 (1950). (4) LeRosen, A. L., Moravek, R. T.. and Carlton, J. K . , Ibid.. 24, 1335 (1952). (5) Smith, E. D., and LeRosen, -4.L.. Ibid., 26, 928 (1954). (6) Strain, H . H., "Chromatographic Adsorption Analysis," pp. 47-63, Interscience Publishers, Inc.. Yew York, 1942. (7) Trueblood, K. K.,and N a l m h e r g . E. W., ANAL.CHEY.,21, 1055 (1949).
R E C E IE!D for review June 19, 1954. Accepted October 13, 1951
Separation of Protactinium and Niobium by liquid-liquid Extraction FLETCHER L. MOORE O a k Ridge National Laboratory, Carbide
& Carbon Chemicals Co., O a k Ridge, Tenn.
The extraction behavior of protactinium and niobium in several liquid-liquid systems is described. Niobium carrier in oxalic acid markedly inhibits the extraction of protactinium; a method of circumventing this difficulty is given. Sulfuric acid enhances the extractability into diisobutylcarbinol of protactinium from dilute hydrochloric acid and of niobium from dilute hydrochloric or hydrofluoric acid. A rapid and effective separation of protactinium from niobium is described; niobium is extracted into diisobutylcarbinol from a dilute hydrofluoric acid-sulfuric acid solution and protactinium remains in the aqueous phase.
T
HE purpose of this investigation was to develop a method for the separation of protactinium from niobium. The chemistry of these two elements is very similar and it has been found that protactinium follows through the standard radiochemical ( 3 ) method for the determination of niobium. Solvent extraction n-as considered as a separation technique because a rapid method was needed that could be adapted to remote control, if necessary. The extraction of protactinium from aqueous solutions into organic solvents has been investigated by several atomic energy project workers. Hyde and Wolf (4)and Kraus and Van Winkle ( 5 ) used diisopropyl ketone to extract protactinium from aqueous nitrate solutions. Kraus and Van Winkle (6) found diisopropylcarbinol to be a more efficient extractant than diisopropyl ketone for protactinium; also, they demonstrated that protactinium readily extracted from hydrochloric acid solution into diisopropylcarbinol. They found that protactinium in macro concentrations tended to hydrolyze to a nonextractable polymer in nitric acid solution and that hydrochloric acid prevented the hydrolysis. Overholt and Steahly (8) and Hudgens, Warren, and Moore ( 2 ) employed diisopropylcarbinol to extract protactinium tracer
from aqueous nitrate solutions. Gresky and Brandt ( 1 ) found diisobutylcarbinol superior to diisopropylcarbinol for the extraction of protactinium from aqueous nitrate solutions. Thr superiority of the hydrochloric acid system over the nitric acid system was verified by Reynolds, who devised an analytical method (7) for the extraction and determination of protactinium It was found that niobium extracted to some extent, thus interfering in the determination of protactinium. Because of the obvious advantage of the hydrochloric acid system, it was decided to investigate the extraction behavior of protactinium and niobium in hydrochloric acid solutions. EXTRACTION OF PROTACTINIUM AND NIOBIUM FROM HYDROCHLORIC ACID SOLUTIONS
I n order to find an effective organic extractant for protactinium, several liquid-liquid systems that are used occasionally ai the Oak Ridge National Laboratory m r e compared in the following manner. Equal volumes (6 ml.) of the aqueous phasc that contained protactinium-233 and of the organic phase were miwd for 15 minuteq. The total amount of protactinium-233
Tal~le I. Extraction of Protactinium-233 Tracer from Aqueous Solutions of .4cids into Various Organic Reagents Activity Extracted. %
Pa238
.iqueous Phase (1 1 .1 HCI (1.11 HCI HJI HCI 2.111 HC1 6.M H E 0 3
a
Organic Phase 5 % MDO.ia-xylene 5 7 , XIDOAa-chloroform 0.5.M TT.ib-xy1ene 0 . 5 M TTAb-xylene Diisopropylcarbinol (saturated with 6.1f HCLj Diisopropylcarbinol (saturated A M HCI with 6.V HCIj 6.1.1 HCI Diisobutylcarbinol (saturated with 6.M HCli Di-n-octylniethylaniine
b
Tlienoyltrifluoroacetone.
95.0 88.5 88.5 95.8 89 . 5
99.6 99.9
V O L U M E 2 7 , N O . 1, J A N U A R Y 1 9 5 5
71
radioactivity originally in the aqueous phase was 9.9 X lo6 gamma counts per minute. Aliquots of each phase were counted for gamma radioactivity by use of a scintillation counter having a sodium iodide rrystal (thallium activated). The results of the preliminary tests are shown in Table I. Each value is t3he average of the results of a t least two determinations. Because djisobutylcarbinol was indicated to be the best extractant and is readily available in high purity, it was selected for further study. From exploratory experiments (Table 11),it was ohserved that the extraction of protactinium-233 tracer from 6 M hydrochloric acid into various organic reagents was inhibited markedly by the presence of niobium carrier. Equal volumes (6 ml.) of the aque0u.s and the organic phases were mixed for 15 minutes. The total amount of protactinium-233 radioactivity originally in the aqueous phase was 5.7 x lo6 gamma counts per minute. The d:tta of Table I1 show that oxalic acid, in a solution of which n i o l h m carrier is usually prepared, does not inhibit the estraction of protactinium-233 tracer from 6M hydrochloric acid solut ion into diisopropylcarbiriol or diisobutylcarbinol, but that niobium carrier in oxalic acid does inhibit greatly the extraction ot' protactinium-233 into these solvents and into 0.5M thenoyltritluoroacetone xylene. The sitnie general effect was observed when 6 X nitric acid was substituted for 6 M hydrochloric acid. \\-hen 10 mg. of zirconium carrier (in dilute nitric acid solution) IT:\- substituted for the niobium (in oxalic acid solution), it, wa3 pos+Ie to extract the protactinium-233 quantitatively. .ilso, when t,he niobium carrier \vas introduced into the sydeni in liydrochloric acid solution (no oxalic acid in the system), it was possible to extract 80 to 90% of the protactinium-233 tracer into diinohutylcarbinol from an aqueous phase that contained 10 mg. of niobium carrier in 6M hydrochloric acid. However, :tpprosini:itt,ly 15% of the niobium \v:ts ext,racted also. The addition of oxalate-romplexing metals, such as airconiuni or aluminum, to the system under the conditions given in Table I1 (experiment 6) was olisrrved to increase the amount of protac~inium-233 tracer estr:tctrd to approximately 38%. -4 similar increase in the amount of protactinium-233 tracer extracted was possible when the aqueous phase was made 1 O J l i n hydrochloric acid. Protactinium rornplesing anions, such a i fluoride, sulfate, or phosphate. were not detected in the reagent..
Table IT. Effect of Niobium Carrier on the Extraction of Protactinium-233 Tracer in Several Systems Pa233 -.____ Aqueous Phase Activity l,:x1)t. \-
