and the unadsorbed branched and cyclic paraffins from wax B were charged to the gas chromatographic column. The resulting combined chromatograms (Figure 5 ) show distinct peaks for the normal paraffins from C19 to Cal. The identity of the peaks mas established by superimposing the peaks of standard Czo,C B , and CS2 paraffins on the wax chromatogram. The peaks representing the branched and cyclic fraction are not designated as specific carbon numbers, since the actual molecular weight is not known. Generally, a t a given carbon number, branched paraffins tend to boil lower and
cyclic paraffins tend to boil higher than normal paraffins. Since branched and cyclic paraffins could not be resolved by this column, each peak probably contained paraffins of different molecular weight. Since the thermal conductivities for normal paraffins between C20 and C32 do not differ appreciably, it is possible to measure accurately the relative amount of each paraffin present by integrating the area under each peak, then calculating the ratio of all areas, and normalizing these ratios to the amount of normal paraffin or branched and cyclic paraffin in the original wax (Table 11),
ACKNOWLEDGMENT
The authors are grateful to .’ “ggeshal’ and R* E‘ Snyder for many suggestions* LITERATURE CITED
( 1 ~ . ~ ~ ~ L . R ~ ~ ( 2 ) Hood, A., clerc, R. J., ~ ” ~ 11. ~ lJ.,, J . Inst. Petrol. 45, 168 (1959). (3) O’Connor, J. G., Norris, M.s., ANAL. 329
701 (lg60)*
R~~~~~~~ for review ~~l~ 31, 1961. Accepted November 9, 1961.
Spectrographic Determination of Thorium in Uranium O r e ROY KO and M. R. WEILER Hartford Atomic Products Operation, General Elecfric Co., Richland, Wash.
b The analytical chemistry of thorium is, at best, a complicated matter. Determination in uranium ores is further complicated b y the refractory nature of ores and the occurrence of thorium in trace amounts in the presence of gross amounts of other elements with difficult analytical problems. Thorium in uranium ores was separated and purified b y lanthanum fluoride precipitation and TTA extraction. After the purification, zirconium internal standard was added and the thorium determined b y emission spectrometry. Successful determinations were made on 1 gram of uranium ore containing as little as 0.1 p.p.m. of thorium with a n average Th234 tracer recovery of 85%. The precision of the method expressed as a relative standard deviation was f124/, a t the 1 -p.p.m. level.
T
HE general analytical chemistry of thorium is vie11 known. Excellent reviews are available (1, 7 , 11, IS). Trace analysis parhcularly in ores, is less well known. The refractory nature of ores and the presence of gross amounts of other elements with difficult analytical problems further complicate the analysis. Separation of thorium from the chemically complex ore solution is required. The chemical determination of thorium for the most part in the hundred to thousand parts per million range in various ores and monazite sands ( 2 , 6, 15, 16), and one determination as low
as 10 p.p.m. in uranium ore (9), have been reported. Spectrochemical methods have also been applied to the analysis of thoriumbearing ores and minerals containing more than 1000 p.p.m. of thorium (4, 10, 14). Only a few applications to ores containing as little as 10 p.p.m. have been made (8,17). The thorium content of uranium ores may be less than 10 p.p.m. A sensitive method is therefore required. This paper describes the emission spectrographic determination of thorium in uranium ores after separation and purification by lanthanum fluoride precipitation and thenoyltrifluoroacetone (TT-4) extraction. EXPERIMENTAL
Apparatus. Spectra were recorded on a Jarrell-Ash 3.4-meter Radsworth grating spectrograph. Power was supplied from a n -4pplied Research Laboratories Multisource unit. Transmittance measurements were made on a Jarrell-Ash recording microphotometer. Ion exchange columns were borosilicate glass tubes 1 em. in diameter and 14 cm. long. Reagents and Materials. Reagent grade chemicals were used. Lanthanum carrier mas prepared by dissolving lanthanum nitrate in water to contain 10 mg. of lanthanum per ml. Zirconium internal standard was prepared by dissolving zirconyl nitrate in 1 M HC1 to contain 0.7 mg. of zirconium per ml. Thorium standards ranging from 1 to 100 fig. per ml. in 0.1M HCl were prepared from a 1000-
1i.p.m. stock solution, which was obtained by dissolving thorium nitrate in water and standardizing gravimetrically by igniting to the oxide. TTA mas used as a 10% solution in benzene. Th234tracer was obtained from natural uranium following the procedure of Perkins and Kalkwarf (IS). Graphite electrodes were x 11/* inch flattops supplied by National Carbon Co. They were waterproofed with a 1% solution of Apiezon grease in petroleum ether. Exposures were made on Kodak spectroscopic plates, Type 111-0. Dowex 1-X4, 50-100-mesh anion exchange resin was used. Procedure. DISSOLUTION Weigh into a n 100-ml. Erlenmeyer flask 1 gram of sample ground to 60 to 80 mesh. Add Th234 tracer. Heat 4 hours on low heat in 50 ml. of 8-V HN03-0.OlA1f (NH4)2SiF6. Add 50 ml. of 8M HC1-O.OlM (NH&SiF6 and heat 4 hours again. Four-hour leaching is sufficient; although most of our samples were leached overnight to leave room for other work during the day. Wash the residue with 1X HNOB until washings are clear. Combine solution and washings and evaporate to 10 ml. LANTK4NCM FLUORIDE-TTASEPARATION. Transfer the evaporated solution to a 100-ml. Lusteroid tube. Add lanthanum carrier and hydrofluoric acid to precipitate lanthanum fluoride. Centrifuge and decant the supernate. Wash the precipitate with 1M HF0.5M “ 0 3 . Dissolve the precipitate in 16M HT\’Os. Reprecipitate and wash as above. Slurry into a 100-m1. beaker lvith 16M “ 0 3 . ,4dd 5 ml. of 1 2 H HC10,. Evaporate to near dryness. Transfer to a 60-ml. separatory funnel. VOL. 34, NO. 1, JANUARY 1962
85
~
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~
Make the final solution 0.1M in nitric acid and 20 ml. in volume. Extract with 20 ml. of TTA solution. Wash the Backbenzene layer with 0.lM "OB. extract thorium into 2M HN03. SPECTROGRAPHIC ANALYSIS. Add 70 pg. of zirconium to the final solution from the lanthanum fluoride-TTA procedure. Evaporate to 0.5 ml. Transfer to a 1-dram screw-cap vial. Make up to 3 ml. with 0.1JP HCl. Count Th234 0.093-m.e.v. gamma in a 3 X 3 inch NaI well-type crystal on a gamma spectrometer. Standardize with a kno\Yn amount of Th234 counted in the same manner. Correct the final thorium result for separation losses as measured by the Th234tracer recovery. Transfer a suitable aliquot of the solution in the vial to a pair of graphite electrodes waterproofed with Apiezon solution. Evaporate under the heat lamp. Expose on 111-0 emulsion in
Table I. Extraction of Thorium from Ores b y Acid Leach and b y Acid Leach Plus Fusion
Thorium Found (P.P.M.) after Acid leach Acid leach plus fusion 13,000 16,000
Sample 1 2
8.3 12 14 3.2 3.2 12.4
3 4 5 6
7
8.6 10 10 3.0 2.5 12.1
Table II. Thorium Recovery from Various Purification Steps Following LaF3 Precipitation
Th-234 Recovery, % Mesityl Ion oxide exchange TTA
Sample
100 105 106 93 108 98 98
1 2 3 4 5 6 AV.
Table 111.
92 62 64 45 25 42 55
Analysis of Uranium Ores for Thorium by LaF3-TTA
Sample
Thorium Found, P.P.M. Spectrographic Colorimetric 1.5 2.2
1 2 3 4 5 6 7 8
5.3
1.9
1.3 1.4
8.3
0.2
Turbid. Color faded.
86
e
96 67 96 54 95 100 85
ANALYTICAL CHEMISTRY
2.6 5.0" 1.4b 2.2 2.6 1 5.70.
the 3800- to 5200--4. wave length region under the following or equivalent conditions: 50-micron slit, multisource 240-pulse-per-second high voltage controlled undirectional spark discharge of 20,000 volts with 150-volt primary input voltage, 360-ph. inductance, 3mm. analytical gap, and 30-second exposure. Measure the transmittances of T h 4381.9 A. and Zr 4366.4 A. lines. Convert to intensity ratios using zirconium as internal standard. Convert to thorium concentration using a working curve. Prepare the working curve by adding 700 pg. of zirconium to 1 ml. of each thorium standard. Transfer 100 pl. t o a pair of graphite electrodes. Evaporate and expose on the spectrograph under the same conditions listed above.
DISCUSSION
Dissolution. An excellent reference on t h e dissolution a n d analysis of ores is a U. S. Geological Survey Bulletin compiled by Grimaldi et al. (5). Grimaldi recommended complete d e , composition of the sample. Experiments with a limited number of uranium ores in our laboratory indicated that acid leaching alone extracted as much thorium as leaching followed by fusion of the residue. Table I shows results obtained by successive leachings in 8 X HN03-0.01M (NH4)*SiFe and in 8 X HCI-O.OIN (SH4)&3iFG and by a combined acid leach and carbonate fusion of the residue. The ores were principally uraninite-bearing sandstones from the Colorado Plateau. Separation and Purification by Lanthanum Fluoride-TTA. Precipitation
reactions for t h e initial separation of thorium from t h e ore solution were tried. Zirconium iodate carrying looked attractive because titanium was the only other element carried ( I S ) , but was not always successful with traces of thorium. Hydroxide precipitation separated thorium from the alkali and alkaline earth elements and from zinc, nickel, copper, and silver but not from iron, uranium, and zirconium. The latter separation was made by lanthanum fluoride precipitation, which provided a n effective first separation of thorium. After fluoride precipitation, mesityl oxide and T T A extractions and anion exchange were tried to eliminate lanthanum, other rare earths, and metals coprecipitated with the lanthanum fluoride. Thorium recovery was measured with thorium-234 tracer added to the ore. Complete exchange between added tracer and thorium in the ore was assumed because of the rigorous leaching condition used. llesityl oxide has been reported to extract microgram amounts of thorium quantitatively in the presence of phosphates, arsenates, sulfates, and borates
( 5 ) . Table I1 shows the excellent recoveries of thorium obtained by mesityl oxide extraction after lanthanum fluoride precipitation. Unfortunately, colorimetric or spectrographic analysis of the extract was not practicable because of the extraction of interfering substances. Anion exchange from 8-U HKO3 and elution with 3JP HC1 gave poor recoveries after lanthanum fluoride precipitation. Thorium is strongly adsorbed by an anion exchange resin such as Dowex 1 in 7 to 821 HKOJ ( 3 ) . Yery few other elements are adsorbed. Anion exchange in nitric acid should, therefore, make an excellent purification step, but low recoveries were obtained, 8 s shown in Table 11. The cause of the lo^ recoveries Tvas not investigated. Table I1 also shows good recoveries obtained with TTA extraction after lanthanum fluoride precipitation. The extraction of thorium by TTA is quantitative above a p H of 1 (6). Thorium is separated from the alkali elements, alkaline earths, rare earths, zirconium, hafnium, protactinium, plutonium(IV), neptunium(IV), and iron(I1Ij at a p H between 1 and 2. In the isolation of trace amounts of thorium from a complex mixture, TTA extraction is an excellent final purification step. The combined lanthanum fluoride precipitation and TTL4 extraction, separation, and purification steps gave an average thorium recovery of 85y0',.Corrections for thorium losses through the separation steps were, therefore, made by measuring thoriuni234 tracer recoveries. Spectrographic Analysis. After thorium was isolated from the ore solution, zirconium internal standard was added, the solution transferred t o a pair of graphite electrocles, and thorium determined by a high voltage spark discharge. Zirconium has been shown by Dutra and l l u r a t a (4) to be a good internal standard for thorium. For our work, T h 4381.9 A. was used as the analytical line; Zr 4366.4 -1. as the internal standard line. -4tenth of a microgram of thorium or 0.1 p.p.m. based on a 1-gram sample was detected. RESULTS
Uranium ore samples separated and purified by lanthanum fluoride precipitation and TTA extraction were analyzed spectrographically. Table I11 shows some results obtained and alsu a comparison with results obtained by a Thoron colorimetric method. A standard deviation of h0.12 p . p m was estimated from six replicate measurements on one of the ore samples. About half of the results shown in Table 111, excluding those where turbidity or fading of color in the color-
imetric method occurred, agree n-ithin the precision of the measurements. I n the rest. the colorimetric results are consistently higher, indicating a positive bias probably due to the presence of other ions forming color with Thoron reagent. The spectrographic method is free from such bias and i s considered the more rrliable of thp t n o . I n both c:i\es, results were corrected for losses through the separation steps by measuring thorium-234 recovery. LITERATURE CITED
r7., Proc. Second Intern. Conf. Peaceful Uses Atomic Energy, Geneva, 28, 517 (1958).
(1) Banks, C.
(2) Banks, C. V., Byrd, C. H., h s a ~ .
CHEM.25, 416 (1953). (3) Danon, J., J . Am. Chem. SOC. 78, 5953 (1956). (4) Dutra, C. V., Murata, K. J., Spectrochim. Acta 6 , 373 (1954). (5) Grinialdi, F. S., May, I., Fletcher, 11. H., Titcomb, J., U. S. Geol. Surv. Bull. 1006 (1954). (6) Hageman, F., J . - 1 ~ 2 . Chem. Sac. 72, 768 (1950). (7) Hyde, E. IC, S a t l . Research CouncilXuclear Sci. Natl. Acad. Sci. (U. s.)> Ser. 3004 (1960). (8) Kingbury, G. K. J., Temple, R.B. F., Analyst 77, 307 (1952). (9) Laux, P. G., Brown, E. A, U. S. A t . Energy Comm. Rept. NLCO-752 ( 1958). (10) RIarinkovic. 11. D.. Bull. Inst. I;’uclear Sci, “Boris Kidrich” 9, 215 (1959).
(11) AIueller, T., Schweitzer, G. K., Starr, D. D., Chem. Reus. 4 2 , 63 (Febriiarv- _._. 19.58) ~ . ~
(12) Pkrkins,’-R. W., Kalkwarf, D. R., ANAL.CHEM.28, 1989 (1956). (13) Rodden, C. J.. Warf, J. Cj., “ilnalytical Chemistr; of the Manhattan Project,” pp. 160-207, AlcGraw-Hill, New York, 1950. (14) Rose, H. J., Jr., hlurata, K. J., Spectrochim. Acta 6 , 161 (1954). (15) Tillu, M. L1.$ Athavale, V. T., Anal. Chzm. Acta 11, 62 (1954). (16) Ibzd., p. 324. (li) Raring, C. L., Xela, H., Jr., ~ A L CHEY.25, 432 (1953). RECEIVEDfor review June 5, 1961. Accepted October 30, 1961. Pittsburgh Conference on Bnalytical Chemistry and Applied Spectroscopy, February 27 to illarch 3, 1961, Pittsburgh, Pa.
Spectrographic Analysis of Germanium for Traces of Arsenic and Bismuth THOMAS J. VELEKER Chemical and Metallurgical Division, Sylvania Elecfric Products Inc., Towanda, Pa.
b Traces of arsenic and bismuth are determined in germanium powder and germanium dioxide b y means of the emission spectrograph. A preconcentration step is used which extracts these elements in a chloroform sohtion of the diethyl ammonium salt of diethyl dithiocarbamic acid. The ranges of the procedure are 0.06 to 10 p p.m. of arsenic and 0.005 to 2.5 p.p.m. of bismuth. The coefficient of variation for the method is 15%.
rison and Cosgrove (3) and Smalrs and Pate ( 5 ) describe methods for some of the group V elements down to the 0.001to 1.0-p.p.m. range. However, the arsenic determination is troublesome because some of the germanium converts to its radioactive isotopes, one of which decays to an arsenic daughter. This necessitates the removal of the germanium matrix and a correction for the arsenic formed, which raises the lower limit of sensitivity. EXPERIMENTAL
T
preparation of semiconductor grade germanium requires a material of very high purity. The purer the germanium can be made, the feJyer passes are required by methods of zone refining. Impurity elements from groups I11 and V of the periodic table are particularly troublesome. The distribution coefficients of most of the group Ir elements are favorable for zone purification, with the exception of phosphorus which is 0.12. Arsenic and bismuth have coefficients of 0.04 and 0.00004, respectively (1). -1 search of the literature was not helpful in finding any suitable spectrochemical methods for determining small traces of arsenic and bismuth in germanium. Several analytical techniques were found. These included Luke and Campbell’s (2) colorimetric procedures to determine group V elements in the range of 0.1 to 1.O p.p.ni. Also, some radioactivation techniques have been described. hlorHE
It was necessary to develop a preconcentration technique to detect submicrogram quantities of arsenic and
‘09‘0 PNOOE
os
I 0
I
os
IO
I 5
CENTER
CbTHODE OISTANCE IN MILLIMETERS
Figure 1 . Intensity of radiation in the analytical g a p
bismuth. The lower limit of detection that was directly attainable on the dual spectrograph was 1 p.p.m. of arsenic and 0.1 p.p.m. of bismuth. Both gratings were used: the 30,000 in the second order for arsenic a t 2288.12 -4.and the 15,000 in the second order for bismuth at 3067.716 -4.These limits were about a magnitude better than are usually attainable for these elements. This improvement was mainly due to the use of boiler cap electrodes with a suitable buffer and the use of a n aperture before the slit to photograph the most sensitive part of the discharge. Photographing off the cathode side of the discharge increased the arsenic sensitivity; however, bismuth was not improved (Figure 1). Standard samples were prepared in two ways to determine the working curves and check the preconcentration procedure. Standard solutions of bismuth powder dissolved in nitric acid and arsenic trioxide in dilute sodium hydroxide were used for making additions. A graduated series of standard solutions was made and sufficient quantities were added to germanium dioxide and germanium poFder to give a range of 0.005 to 10 p.p.m. of arsenic and bismuth. A second series of standards was prepared by making additions to the final buffer in the range of 0.1 to 200 p.p.m. Care was taken to avoid contact between the solution and vessel containing the powders. All standards were dried a t 100’ C. and then blended to ensure homogeneity. VOL. 34, NO. 1, JANUARY 1962
87
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