Table 1. m
0.001 0.005 0.01 0.025 0.05 0.075 0.1 0.2 0.5 1.0
25' 3.02 2.33 2.04 1.67 1.38 1.22 1.10 0.82 0.42 0.09
Values of the pH of Hydrochloric Acid Solution, " C. 60" 90" 125' 150" 175" 200' 225" 250' 3.02 3 . 0 2 3.02 3 . 0 2 3.03 3.03 3 . 0 3 . 1 2 . 3 4 2 . 3 4 2.34 2.34 2.35 2.35 2 . 4 2 . 4 2.05 2.05 2.05 2.06 2.06 2.07 2 . 1 2 . 1 1.67 1.67 1.68 1.68 1.69 1.69 1 . 7 1 . 7 1.39 1.39 1 . 4 0 1.41 1.41 1.42 1 . 4 1 . 5 1.22 1.23 1.24 1.25 1.26 1.27 1 . 3 1 . 3 1.11 1.12 1.13 1 . 1 4 1.15 1.16 1 . 2 1 . 2 0.83 0.84 0 . 8 6 0 . 8 8 0.88 0 . 9 0 0 . 9 1 . 0 0.44 0 . 4 6 0 . 4 8 0 . 5 0 0 . 5 2 0.55 0 . 5 0 . 5 0 . 1 2 0.15 0.18 0 2 0 0 . 2 1 0 2 3 ... ...
molal HCI or one of the other solutions listed in Table I to calibrate p H meters at elevated temperatures appears to be feasible though perhaps not convenient, particularly since the hydrogen electrode is the only pH-sensitive electrode yet proved at such temperatures. Bates (1) has discussed the errors inherent in Equation 2 and in the measurement of pH. Considering the errors in the original electromotive force work
and Laura M e e n for aid in making the calculations. 275" 3.1 2.4 2.1 1.7 1.5 1.3 1.2 0.9 0.5
LITERATURE CITED
(1) Bates, R: G;:
"Electrometric pH Determinations, pp. 16-33, 62-90, Wiley, New York, 1954. (2) Ibid., p. 87. (3) Greeley, R. S., Smith, W. T., Jr., Stoughton, R. W., Lieteke, M. H., J . Phys. C h . 64, 652 (1960). (4) Zbid., in press. (5) Guggenheim, E. A., Zbid., 34, 1758 (1930). (6) Owen, B. B., Brinkley, S. R., Jr., Chem. Revs. 29, 461 (1941).
(3) and the inherent errors of Equation 2, an uncertainty in the values of Table I of =t0.03 unit at 25' to 90" C., ~ t 0 . 0 5 unit at 125' to 200' C., and f 0.1 unit at 225" to 275" C. has been established. It was estimated from data given by Owen and Brinkley (6) that the effect of the high water vapor pressure a t elevated temperatures on the p H was negligible in relation to these errors. The author thanks Gerald North
RICHARD S. GREELEY' Chemistry Division Oak Ridge National Laboratory Oak Ridge, Tenn. 1 Present address, The Mitre Corp., Bedford. Mass.
TAKEN in part from the Ph.D. thesis of Richard S. Greeley, University of Tennessee, June 1959.
Preparation of Organic Concentrate from Green River Oil Shale SIR: Like other oil s h l e s of the world, those of the Green River formation present difficult analytical problems. However, determination of the organic elementary compositions is essential to studies intended to increase the usefulness of oil shales. T o obtain accurate values for the elemental composition of the organic material in oil shale, complex corrections for the interfering effects of the mineral components are required on direct analysis of shale. The procedure presented here substantially reduces these interference problems by concentrating the organic matter. Although the organic and mineral components were not completely separated, the procedure concentrates oil-shale organic matter almost nonselectively in quantities sufficient for extensive study of its properties. Concentration was accomplished by modifying a coal beneiiciation treatment called the Trent amalgamation process. Seven pounds of organic concentrate were prepared at this laboratory using the modified procedure. The concentrate contained only about 16% mineral matter which was accounted for analytically. Concentration Procedure. Green River oil shale, ground to pass a 100-mesh screen, was leached with a hot 5% acetic acid solution until destruction of the carbonate minerals was complete. The washed residue from filtration of the acetic acid suspension was then dried thoroughly at 105' C. in a nitrogen atmosphere, 1718
ANALYTICAL CHEMISTRY
placed in a porcelain ball mill, and made into a paste by adding n-cetane in small quantities until the paste had the consistency of bread dough. Water was added to the ball mill, and the twophase mixture was agitated. The water phase was removed and replaced periodically as it became charged with separating mineral matter. When the amount of material suspended in the water phase became insignificant, the final water charge was removed. The paste was dried with methanol, dispersed in benzene, and filtered. The filter cake was washed with benzene. The concentrate was dried at 105" C. in a nitrogen atmosphere and then crushed to pass a 1Wmesh screen.
Analysis of Concentrate. Organic concentrate was prepared by this method from a raw shale containing about 75y0 mineral material. Analysis of this concentrate by routine methods gave the following results, where all d a t a are in weight per cent of the concentrate: Ash
Carbon Hydrogen Nitrogen Sulfur, organic Sulfur, pyritic Wt. gain on pyritic Fe on ashing Tot,al determined Oxygen, organic, by difference
15.24 64.98 8.74 2.00 1.14 1.23 (33 33 - 0.46 93.87 i. 13
Total organic matter \vas 83.99 wight ycof the concentrate, thc mineral
matter including pyrite was 16.01 weight %, and the organic matter had the following ultimate composition in weight per cent of organic matter: Carbon Hydrogen Nitrogen Sulfur Oxygen Total
77.36 10.41 2'. 38 1.36 8 49 100.00
Oxide- analysis on the ash obtained a t 1000" C. from the concentrate gave the following results in weight per cent of conrentrate :
Total Ash. 1OOO" C.
5.32 4.03 3.28 0.62 1.02 1.02 15.29 15.24
Discussion. This concentration method was first applied t o oil shales by Quass (2) and later by Himus and Basak (1). The latter workers noted that it did not perform equally well on all oil shales. Two modifications were necessary to adapt the process to Green River oil shale: removal of the cementing carbonate minerals prior t o thc concentration procedure, and prcparation of an oil paste with finely grotmd oil shaie bciore addition u i IvXtvr. In the Trent amalgamution process,
as used by Quass ( 8 ) ,oil was added to a slurry of powdered oil shale and water. However, no separation could be obtained unless the oil shale was wet by oil before exposure to water. Preparation of a paste of oil and oil s h d e is a necessary initial step. The carbonate minerals in Green River oil shale inhibit mineral removal by this method and must be destroyed chemically before the concentration procedure is begun. The mechanism of the concentration action is based on preferential wetting of the organic and mineral components by oil and water, respectively. As new surfaces are exposed in agitating the paste, water breaks the oil film on mineral particles, wets them, and incorporates them into suspension in the water phase. Since shearing of the paste is the action that exposes new mineral particles to the water phase, the mixing equipment should be chosen to increase this action. A laboratory model of the Szegvari Attritor, manufactured by the Union Process Co., Akron, Ohio, was used in these tests, Exact proportion of oil and shale in the paste is not critical as long as the
paste is plastic but will not slump or flow. The type of oil used is not critical. Low viscosity, nonvolatile oils will afford separation. Cetane was used in this experimental work because i t has appropriate viscosity and volatility characteristics. It provided satisfactory control of the oil effects in development of this procedure. Progress of the enrichment can be checked approximately by weighing the charged shale and then obtaining a cumulative weight of the mineral matter removed. Comparison of this weight with an amount of mineral estimated from the ash content of the carbonatefree starting material provides an estimate of the remaining mineral. I n Green River oil shale, this progress can also be folloaed by the diminishing and eventual disappearance of the x-ray diffraction peak at 28.0" 28 in the concentrate. This is the major peak of soda feldspar. a removable mineral constituent of oil shale not found in ordinary porcelains. Mineral removal by this method is not complete for two reasons. First, when particles are sufficiently small, water cannot break the oil film to wet
and remove such particles. Second, particles such as pyrite, which are readily wetted by oil, are retained in the paste and are concentrated. For this reason metal components in the mixing equipment should be avoided as a source of contamination. Material lost from porcelain equipment readily enters the water phase and is removed. This organic concentrate represents well the organic material in the raw shale. Two possible alterations in its composition are the extraction of benzcne-soluble portions and the addition of acetic acid. Since this organic concentrate can be produced in quantity and can be analyzed easily by routine methods, it provides a starting material for further study of the nature of the organic matter in Green River oil shale. LITERATURE CITED
(1) Himus, G. W., Basak, G. C., Fuel 28, 5 7 4 4 (1949). (2) Quass, F. W., J. Inst. Petrol. 25, 813-19 (1939). JOHN WARDSMITH L. WARRENHICBY
Laramie Petroleum Research Center U. S. Bureau of Mines Laramie, Wyo.
Fluorescent X-Ray Determination of Selenium in Plant Material SIR: Rapid reliable determinations of selenium in plant material are important in areas where the selenium content of forage may be deleterious to grazing animals. Wet chemical methods (8, 5-7) are sensitive enough but too slow for such survey purposes. The method reported here is similar in rationale to that suggested by Brandt and Lazar ( 1 ) but in our experience yielded somewhat more consistent results. Selenium has a K a peak at a wave length of 1.106 -4. Arsenic and bromine with KCYemissions at 1.177 and 1.041 .4.,respectively, are possible interferences, through spectral coincidence. However, with a lithium fluoride anal ~ z i n gcrystal (2d = 4.0269 A.) resolution of the three peaks is satisfactory, 3 e differences of nearly two degrees between selenium and either bromine or arsenic being obtained. The importance of matris effects in the analysis of plant material by sray fluorescent spectrography is apparrJnt in the data of Figure 1 in which the fluorcscent and scattered h-radiation from samples of t a o species, sugar beet .tnd the selenium-accumulating need, \t:inleys p i n a t a , is ompnri.6. Each -'mpli. contained 15 p.p.m. oi selenium. '!?F greater background emission obiuined with the Stank ya sampie is ac-
companied by a proportionally higher emission of selenium K a radiation. The following correction procedure was effective : The scattered primary radiation is measured at two values of 2 8, one on either side of the selenium K a peak. The estimated background radiation at the selenium K a peak is obtained from these values by linear interpolation. This background is then subtracted from the total radiation measured a t the selenium KCYpeak. The difference is due to the presence of selenium in the sample. This value must be corrected
30
further since differences in background due to differences in internal shielding of the sample will be accompanied by a nearly proportional difference in the fluorescent radiation measured. To do this one of the standards of known selenium content is selected for the reference background. The value obtained after subtraction of the estimated background is then multiplied by the ratio of the reference background to the estimated background. The procedure may be represented symbolically as follows:
1
b Figure 1 . Plot of total counts per second as function of 2 0 for plant samples, each containing 15 p.p.m. of Se
+ - + Stanleya
0 - 0 Sugar
beet
VOL. 32, NO. 12, NOVEMBER 1960
1719
