ANALYTICAL CHEMISTRY
432 (68) Shive, B., Roberts, S. AI., llahan, R., and Bailey, J. R., Ibid., 64, 909 (1942). (69) Smith, C. W., and Norton, D. G., private communication. (70) Stauffer, J. C., dissertation, “The Nitrogen Compounds in Colorado Shale Oil.” Columbia Universitv. New York. 1926. (71) Thompson, R. B., Chenicek, J. A,, Druge,”L. W., and Symon, T., Ind. Eng. Chem., 43, 935 (1951). (72) Thompson, W.C., J . Am. Chem. Soc., 53, 3160 (1931). (73) Thompson, W. C., and Bailey. J. R.. Ibid., 53, 1002 (1931). (74) Treibs, A,, Ann., 509, 103 (1934); 510, 42 (1934); 517, 172 (1935); 520, 144 (1935); dngew. Chern., 49, 682 (1936). (75) C. S. Bur. Mines, Rept. I ? L w s ~4457, . 49 (1949). (76) Ibid., 4652, 63 (1950). (77) Van Meter, R., Bailey, C . T., Smith, ,J. R., XIooie, R. T.,
Allbright, C. S., Jacobson, I A , , Hylton. 1‘. hI., and Ball, J. S., ANAL.CHEM.,24, 1758 (1952). (78) Voge, H. H., Good, G. M., and Greensfelder. B S., Proc. Third World Petroleum Congress, The Hague, See. IV, p. 124, 1951. (79) Williams, C. G., J. Chem. Soc., 7 , 97 (1855). (80) Filson, H. N., J . SOC.Chem. Ind., 67, 237 (1948). (81) Whittmann, G., Angew. Chem., 60A, 330 (1948). (82) Yoshida, T., and Sotani, H., J . Chem. S o r . Japan, Iird. C h e w Sect., 52, 98 (1949). RECEIVED for review June 17, 1952. Accepted Soveniber 24, 1952. Presented before the Division of Refining, American Petroleum Instltrite San Francisco, Calif., 1952.
Method for Determination of Small Amounts of Rare Earths and Thorium in Phosphate Rocks CLAUDE L. WARING AND HENRY MELA, JR. U . S . Geological Survey, Washington, D. C. In laboratory i n \ estigations, interest developed in the possible rare-earth content of phosphate samples from Florida and the northwestern United States. Because of the difficult? of making chemical determinations of traces of individual rare earths, a combined chemical-spectrographic method was investigated. After reniobal of iron by the extraction of the chloride with ether, the rare earths and thorium are concentrated by double oxalate precipitation, using calcium as a carrier. The rare earths are freed from calcium by an ammonium hydroxide precipitation with a fixed amount of aluminum as a carrier. The aluminum also serves as an internal standard in the final spectrographic analysis. The method will determine from 0.02 to 2 mg. of each rare earth with an error no greater than 10%. The investigation has resulted in a fairly rapid and precise procedure, involving no special spectrographic setup. The method could be applied to other types of geologic materials with the same expected acciirac?.
T
HE analysis of phosphate rock samples containing rare-earth elements from the Bone Valley formation of Florida and from the Phosphoria formation of the northwestern United States has resulted in the development of a combined chemical and spectrographic procedure. This procedure has been applied to the deternunation of cerium, yttrium, praseodymium, gadolinium, neodymium. samarium, lanthanum, dysprosium, europium, ytterbium, and thorium. The remaining rare earths were not tested because of the lack of materials, but the fact that all rareearth gi oups are represented indicates that the method may be applied to all of them. Because of the similarity of their chemical properties, the rare earths have seldom been separated by strictly chemical means. Separations have been made by fractional crystallization and ion exchange methods, but these methods are not useful for quantitative analyses. The rare-earth elementa emit complex spectra \Then excited in the direct current arc. Also a continuous background on the spectrographic plate is caused by the excitation of the rare earth in the direct current arc, and this makes analysis very difficult. However, it is possible to attain a sensitivity of O . O O l ~ ofor the ref-
erenccd rare earths by using the direct current arc under the conditions described in this paper. The principal lines of the rare-earth elenirnts were not selected for the det,erniinations because ninny of them fall in that part of the spectrum where molecular banding and continuum interfere. Instead, other lines of desired sensitivity were selected in the ultraviolet portion of the spectrum, where interferences are insignificant. This method of analysis n’ap developed on behalf of the Division of Raw IIaterids of the Atomic Energy Commission. PREVIOUS RELATED STUDIES Most. methods of determining the rare earths described in the
literature are concerned with the rareearth elements in rare-earth minerals. RTcCart,y el QZ. (8) presented such a method, using zirconium as the internal standard. They suggested that bett’er results could be expected if a rare-eart.h line of the major component were used as the internal standard. Fassel ( 2 ) applied this suggestion in determining yttrium and gadolinium in rareearth mixtures. He reported a standard deviation of =k2.5%. The use of one rare earth as an internal st.andard for the others was described by Lopez de Azcona ( 7 ) and Fassel and Wilhelm ( 3 ) . Moeller and Brantley (9) made spectrophotometric studies of salt solutions of the rare earths but were limited by the equipment used. Sahama and Vahatalo (11) described a chemical method for concentrating the rare earths, mostly from silicate rocks. The final analysis x a s not, spectrographic but spectrophotometric. Pifia de Rubies and Doetsch (10) applied an arcing enrichment procedure for small amounts of rare earths in lead minerals. The major constituents were first volatilized to leave the rare-earth concentrates. The concentrates were arced under more strenuous conditions. I t is doubtful that this procedure can be applied to samples conhining such elements as calcium, magnesium, silicon. and aluminum because these elements tend to linger in the crater. EXPERIMENTAL CHEMICAL D T I
Preparation of Standards. The rare-earth c.lements that are accessible in this laboratory in salt or oxide form are cerium, gadolinium, lanthanum, neodymium, praseodymium, samarium, yttrium, dysprosium, europium, ytterbium, and thorium. They include members of the lanthanum group, yttrium group, and the erbium group. T o prepare the standard solutions, each rare earth is weighed on a microbalance, dissolved in water or acid, and made to 25 ml.
V O L U M E 25, NO. 3, M A R C H 1 9 5 3
433
in volume. An aliquot is taken to dryness and ignited a t 1000° C.
The oxides are tested for purity by spectrographic procedures. The purity of these oxidep is approximately 98%. The solutions are then diluted to make 1 ml. equivalent to 0.005 gram, 1 ml. equivalent to 0 0005 gram, and 1 ml. equivalent to 0.00005 gram of the oxide. .iluminum oxide n a s selected to be the chemical carrier and also to serve as the esperimeiital internal standard for the spectrographic analysis. The ideal internal standard should have vaporization characteristics close to those of the unknown element. In this respect aluminum is not ideal, but the results of the tests indicate that aluminum can be used successfully as an internal standard. To determine whether rare-earth mixtures will produce spectrographic working curves similar to those of single rare-earth standards, composite standards were prepared and arced. Points obtained from the composite standards fall in approximately the same location on Ihe curve as those obtained from similar percentages in the single rare-earth standards. Aluminum nitrate is dissolved in water and nitric acid and made to volume so that 1 ml. is equivalent to 0.005 gram of aluminum oxide. An aliquot is evaporated, ignited to 1000" C., and tested spectrographically for purity. These solutions are used to prepare the spectrographic standards. Each rare-earth solution is pipetted into a porcelain crucible and aluminum nitrate solution is added to give the ratios of aluminum oxide to rare-earth oxides shown in Table I. The solutions are evaporated to dryness on a steam bath, ignited a t 1000° C., gently ground in an agate mortar, and submitted for spectrographic study. Tests were conducted to determine the rare-earth recovery of precipitates from calcium phosphate solutions that simulate phosphate rock samples.
Table I. Ratios of Rare-Earth and Aluminum Oxides Used in Preparing Solutions for Spectrographic Standards Rare-Earth Oxide, Gram 0.00002 0.00004 0.00008
0.00014 0.0002 0.0008 0.0014 0.002
Aluminum Oxide, Gram 0.01 0.01 0.01 0.01 0.01 0.01
0.01 0.01
A solution of calcium phosphate is prepared, and aliquots equivalent to a rock sample are taken. Each rare earth, in three concentrations, is added to three of the calcium phosphate aliquota. The solutions are made to about 400 ml., and 2 grams of ammonium oxalate in solution are added. The p H is then adjusted to 3, using a p H meter and adding silicon-free ammonium hydroxide. This acidity was selected because previous experiments indicated that an increase in the basicity toward a definite blue of bromophenol blue causes iron to precipitate. After digestion for 1 hour on the steam bath and after several hours of cooling, the samples are filtered through No. 2 Whatman paper, washed with 0.1% ammonium oxalate solution, and gently ignited until the paper is completely charred. Then the samples are heated to approximately 1000" C. in a muffle furnace, cooled, a few milliliters of water are added, and then 5 ml. of.nitric acid (1 to 1). The solutions are tranferred to 600-ml. beakers, and the oxalate is again precipitated, filtered, ignited, and dissolved in the manner previously described. The solutions are then transferred to 150-ml. beakers, made to approximately 50 ml., and 2 ml. of the aluminum solution is added (10 mg. of aluminum oxide). The hydroxides are precipitated with silicon-free ammonium hydroxide, using 2 ml. in excess per 100 ml. of solution after the phenolphthalein end point. Filter pulp is added, and the samples are allowed to remain on the steam bath until the precipitates coagulate, then are filtered through No. 40 Whatman paper. After gentle charring of the paper and ignition a t 1000° C., the samples are ready for spectrographic study. Table I1 shows the rareearth additions and recoveries.
Table 11.
Rare-Earth Recoveries from Calcium Phosphate Solutions Oxidea Added, Recovered, % Cerium
0.1 0.01 0.001
Yttrium
0.1
Praseodymium Gadolinium
0.01
0,001 0.07 0.01 0.001 0.07
0.01
0,001
Seodymium Samarium Lanthanum Thorium Dysprosium Europium Ytterbium
0.07
0.01 0.001 0.07 0.01 0.001 0.07 0.01 0.001 0.07 0.01 0.001 0.08 0,001
0.07 0.01 0.001 0.07 0.01 0.001
0.09 0.012 0.0011 0.09 0.012 0.0008 0.077 0.009
0.001 0.08 0.012 0.0007 0.08 0.011 0.001 0.056 0.01 0,0009
0.072
0.011
0.0008 0,062 0.011
0.0008
0.09 0 0013 0.06 0.01 0.001 0.07 0.009 0 0007
Treatment of Phosphate Rock Samples. A phosphate rock from the Florida land-pebble field and a western phosphate from the Phosphoria formation were selected for the initial rock testa. The Sam les were dissolved in 10 ml. of nitric acid (1 to I), 3 ml. of perchEric acid, and 5 ml. of hydrofluoric acid and heated to copious fumes of perchloric acid to break up all fluorides. They were cooled. taken up in nitric acid and water, and made to 400 ml., and the procedure as given above for the simulated s r t ~ p l e ~ was completed. Inspection of the spectra showed that a sufficient amount of iron had precipitated with the rare earths to interfere with the lines selected. Accordingly, an additional step was introduced in the chemical procedure to remove iron a t the start by extraction of the chloride with diethyl ether. Another set of samples was treated as above, heated to the copious fumes of perchloric acid, cooled, and taken up in 20 ml. of hydrochloric acid (1 to 1); a few drops of 30% hydrogen peroxide were added to keep titanium in solution, and then the solutions were transferred to 125-ml. separatory funnels. Two diethyl ether extractions mere made, using 20-ml. portions of ether. The aqueous layers were drawn into 600-ml. beakers, and any ether present was volatilized on the steam bath. Volumes were then made to 400 ml., and the procedure was carried out as stated previously. The results of spectrographic analyses applied to these sampIea are shown in Table 111. When rerun tests were conducted, with additional amounts of rare earths introduced, the results were as shown in Table IV.
Table 111. Rare-Earth Content of Two Phosphate Rock Samples Phosphate Rock from Florida Western Phosphate Land-Pebble Field, (Phosphoria Formation), Rare-Earth Oxides Cerium Yttrium Samarium Gadolinium Praseodymvum Lanthanum Neodymium Thorium Europium Ytterbium Dysprosium
%
%
0.01 0,0025 0.001 Not detected N o t detected
0.001 0.005 0,0025
0.005 0,001
Not detected Y > Eu > Pr (Odd atomic numbers) DETAILED PROCEDURES
Weigh 2.000 grams of sample, transfer to a TO-ml. platinum dish, and heat to destroy organic matter. Add 10 ml. of nitric acid ( 1 to l), 3 ml. of perchloric acid, and 5 ml. of hydrofluoric acid, and take down to perchloric acid on the steam bath, then to copious perchloric fumes on a hot plate. Drive off as much perchloric acid as possible. Cool and take up in 20 m]. of hydrochloric acid (1 to l), add several drops of 30oJ, hydrogen peroxide, cover, and boil gently. If the sample has been decomposed and a hydrolytic precipitation remains, filter the sample, wash the precipitate with hydrochloric acid (1 to l), and discard the material remaining in the filter paper. Transfer the clear solution to a separatory funnel, and wash the beaker with hydrochloric acid (1to 1).
0
Strike position 12 (=kO.5) (d.c. arc) 300
21-foot Wadsworth mounted grating SA-1 4 minutes at 18' & 0.5' C., D-19 25 microns 35%
After the plates were processed the transmission values of the rare earth and aluminum internal standard (3059.997 A , ) in the first spectral order were recorded. PHOSPHATE FROM
EMULSION CALIBR4TION
LAND -PEBBLE
A two-step method was used in calibrating the emulsion. 4 similar method has been described by Harvey (6). This method was developed with the expectation of eliminating or reducing stroboscopic effects and intermittency effects common to the sector wheel methods. The method does not require highly critical adjustments of optics. The gamma may be checked on any production plate if the iron content of the samples is greater than 0.1%.
PHOSPHATE NORTHWESTERN
FLORIDA FIELD
FROM
UNITED
STATES
C.4 LCU LATIONS
Practices similar to those described by Churchill (1) were used in making the final calculations. The analytical curves were prepared by two methods, straight transmission and logarithm intensity ratios. The analytical curves based on logarithm intensity ratios were drawn by applying the internal standard aluminum line at 3059.997 A. and the analytical lines falling b e tween 2837.229 and 3306.372 A. In the very low percentage ranges of cerium, neodymium, and praseodymium, the straight
Figure 1.
Mutual AbundanceRelationships of Rare-Earth Elements in Phosphate Rock Samples
V O L U M E 25, NO. 3, M A R C H 1 9 5 3 Table V. Element Cerium
a
435
.4rc Lines Used in Quantitative Tests ( 5 ) Wave Length, A. 4222,599 3256.682
Element Praseodymium
Wave Length, A. 4241.019 4226.327 3245.462
Dysprosiuni
3251,260 3232.642
Samarium
Europium
3262.263 3306.372
3280. 682a 2906.676
Thorium
Gadolinium
3046,480 3034,059
2870.413 2837.299
Yttrium
3195,615 3179.418
Lanthanum
3246.120 3215 813
Ytterbium
Neodymium
4247 367 3275,218
3261.609 3031.110 2859.800
Aluminum
3069.997 (internal standard line)
Not listed in Gatterer and Junkes table ( 4 )
of the aluminum solution from a buret, several drops of phenolphthalein, then silica-free ammonium hydroxide until the end point. Add 2 ml. of ammonium hydroxide in excess, and place on a steam bath until the precipitate coagulates. Add paper pulp, filter through a 9-cm. KO.40 Whatman paper, and wash with a 2% ammonium nitrate solution. Place the sample in a small previously ignited and weighed porcelain crucible, gently char the paper, then ignite in a muffle furnace a t 1000” C. for 15 to 20 minutes. Cool in a desiccator, weigh, gently grind and mix with a pestle, and reserve for spectrographic analyses. Weigh 10 mg. of the sample, mix with 20 mg. of graphite, and place all of the material in a number 8 pure graphite electrode (0.25-inch outside diameter cut to 0.22 inch; inside diameter 0.19 inch; depth of crater, 0.24 inch; depth of shoulder, 0.24 inch). The upper 0.25-inch diameter electrode is of pure graphite cut to hemispherical 0.06-inch radius. Arc the sample following the previously described s ectrographic conditions. Develop the plate 4 minutes a t 18’ with D-19 developer. Fix, wash, and dry the plate. Place the late in the densitometer and read line transmissions (Table V). &omplete ralculations.
8.
LITERAI‘URE CITED
Make two diethyl ether extractions, using 20-ml. portions each time, and drain the aqueous layer into a 600-ml. beaker. Place the beaker on the steam bath and volatilize theether. Evaporate the solution to approximately 20 ml. A4ddseveral drops of 30% hydrogen peroxide to keep the titanium in solution, make to 400 ml., add a solution containing approximately 2 grams of ammonium oxalate, and adjust the p H to 3 on a p H meter with ammonium hydroxide. Place the beaker on the steam bath for 1 hour, cool for 4 hours, and filter on an 11-cm. No. 42 Whatman paper. Wash with a cool 0.1% ammonium oxalate solution. Gently ignite in a porcelain crucible until the filter paper is charred, then in a muffle furnace a t 900’ to 1000” C. for 15 to 20 minutes. After the oxide has cooled, carefully moisten it with several milliliters of distilled water, then add 5 ml. of nitric acid (1 to 1). If complete solution is not obtained, add several drops of hydrogen peroxide, transfer from the crucible to a 600-ml. beaker, and warm gently. Repeat the procedure starting with the addition of 30y0 hydrogen peroxide and ammonium oxalate steps. Transfer the solution to a 150-ml. beaker. Heat if necessary to dissolve all the oxide: make to approximately 50 ml. : add 10 ml.
(1) Churchill, J. R., IND. ENG.CHEM.,ANAL.ED.,16,653-70 (1944). Fassel, V. A., J . Opt. Soc. Am., 39, 187-93 (1949).
(2) (3) (4)
Fassel, V. A., and Wilhelm, H. A., Ibid., 38, 518-26 (1948). Gatterer, A., and Junkes, J., “Spektren der Seltenen Erden,” Citta del Vaticano, Specola Vaticana, 1945. ( 5 ) Harrison, G. R., “M.I.T. Wavelength Tables,” New York, John Wiley & Sons, 1948. (6) Harvey, C. E., “Spectrochemical Procedures,” pp. 66-81, Glendale, Calif., Applied Research Laboratories, 1950. ( 7 ) Lopez de Azcona, J. M., BoZ. inst. geol. y minero EspaRa., 15 (3). 270 (1941).
McCarty, C. N., Scribner, L. R., Lawrenz, X I . , and Hopkins, B. S.,IND. ENG.CHEM.,ANAL.ED.,10, 184-7 (1938). (9) Moeller, Therald, and Brantley, C. J., Univ. Illinois Tech. Rept. NP-1105 (1949). (10) Piria de Rubies, S., and Doetsch, J., 2 anorg. allgem. Chem., 220, (8)
199 (1935). (11)
Sahama, T. G., and Vahatalo, IT.,BuZl. comm.
geo2.
Finlande,
126, 50-83 (1941). RECEIVKD for review September 3, 1962. Accepted Kovember 25, 1952. Publication authorized b y t h e Director, U. S. Geological Survey.
System Acetic Acid- Water-Dimet hylaniline Liquid Phase Behavior and Analysis LEO GARWIN‘ AND PHILIP 0. HADDAD2 Oklahoma A. and M . College, Stillwater, Okla.
D
URING the course of an investigation of the possible use of dimethylaniline for improving the separation of acetic acid and water (5),it became necessary to analyze mixtures of acetic acid, water, and dimethylaniline. To accomplish this simply, it appeared desirable to take advantage of the titratability of the acetic acid for its direct determination, as well as the difference in the refractive index of dimethylaniline and water to distinguish between these two components. This paper concerns itself with the analysis of the ternary system acetic acidwater-dimethylaniline by a combination of refractive index determination and acid titration. Liquid-liquid equilibrium data are also presented to permit the ready analysis of mixtures in the two-phase region. Angelescu has systematically studied many liquid ternary systems of the general type aromatic amine-organic acid-water (1 )) but information on the particular system under consideration has not appeared. This author has also reported selected 1 Present address, Kerr-McGee Oil Industries, Inc., Oklahoma City, Okla. 2 Present address, Daw Chemical Co., Freeport, Tex
physical properties of several binary systems of the type aromatic amine-butyric acid ( 2 ) . MATERIALS
Acetic acid, C.P. grade, assaying 99.5 weight % acetic acid by titration, was used for all mixtures containing water. For the binary system acetic acid-dimethylaniline, acid of 99.8 weight % ’ purity was obtained by drying the C.P. material over anhydrous sodium sulfate overnight, decanting the liquid, and distilling it in a three-ball Snyder column. A heart cut was collected. It possessed a refractive index, ng5, of 1.3698. The literature reports nZO , = .1,.3718 for the pure material ( 4 ) . Dimethylanllme, chemical No. 5053 (free from monomethylaniline) from the Matheson Co., Inc., boiling point 192-193” C. This was used directly. I t s refractive index, rigs, was determined as 1.5560. The literature gives a value of nZ,O = 1.5582 ( 5 ) . During the latter part of the investigation, dimethylaniline from the early runs (present in mixtures with acetic acid and water) was recovered for reuse as follows: The acetic acid was neutralized with sodium carbonate until the mixture was basic to phenolphthalein. The dimethylaniline layer was decanted, washed with water, and then steam-distilled. The purity of the dimethylaniline recovered in this way was confirmed by com-
