Table 111.
Inherent Viscosities of Sodium Cellulose Acylate Sulfates in DMSO-1 % KI
Sodium cellulose acylate sulfates Butyrate Propionate Acetate Propionate Acetate Acetate Acetate Propionate Acetate Acetate Acetate Acetate Acetate Acetate Acetate Acetate Acetate Acetate
% Acyl
% NaSOp
39.0 34.4 34.0 27.0 31.0 30.7 27.4 26.1 30.0 29.0 27.5 20.7 23.2 18.7 24.2 18.7 17.0 12.9
17.0 15.1 16.1 15.4 18.3 19.3 17.5 18.0 19.6 20.5 20.5 17.0 21.8 22.9 31.7 30.8 29.8 40.8
Wt. ratio Inherent viscosityb acyl/NaS03 DMSO-l% KI” 2.3 2.3 2.1 1.8 1.7 1.6 1.6 1.5 1.5 1.4 1.3 1.2 1.1 0.8 0.8 0.6 0.6 0.3
1.05 3.15 3.10 2.84 1.60 1.74 1.63 2.62 1.77 1.88 2.97 1.89 2.58
Insolubled Insolubled Insolubled Insolubled Insolubled
Recalculated from per cent combined sulfur. Concentration on a cellulose basis. The last 7 samples were insoluble in DMF-l% KI. Insoluble in DMSO:H20(85:15)-l% KI.
of 27 samples of cellulose as determined by Glegg and Poillon (2). These points conform t o the line within a standard error of *0.05. The points superimposed on this line are for similar determinations of four sodium cellulose acetate sulfates dissolved in FeTNa after correcting for the weight of substituents. The samples contained from 5.2% to 21.6% XaSO3. This close agreement between the cellulose and cellulose derivative viscosities suggests that the complex formation of FeTNa with cellulose is not basically altered by the presence of sulfate groups. Figure 5 shows the relationship between these values in FeTNa and those in DAMSO-l% K I (Table 111). This straight-line relationship passing through the origin suggests that the sulfated polymers are probably well dispersed in the DMSO-l% K I and that the viscosity values can be used as a n indication of the degree of polymerization. LITERATURE CITED
DMSO-1OJ, K I without added water. Therefore, cellulose ester sulfates with varying acyl and sulfate contents were tested (Table 111). Samples having a weight ratio of acyl/NaS03 of 1.1 and greater were soluble over a wide viscosity range. Samples with a weight ratio of 0.3 t o 0.8 were insoluble. (Similar insolubility was found in DMF-l% KI for t h e same series but extended t o a ratio of 1.2.) I n addition, samples containing only ionizable substituents (sodium carboxymethylcellulose and sodium cellulose sulfate) were insoluble in both solutions. Therefore,
the solubility is dependent on a balance between organic and ionizable substituents on the cellulose structure. Inherent viscosities for the sodium acylcellulose sulfates listed in Table 111 were also determined in iron-sodium tartrate (FeTNa). I n this strongly alkaline solution the acyl but not the sulfate groups are removed. Therefore, the viscosities in FeTNa are determined on a sodium cellulose sulfate. The line in Figure 4 sbows the relationship between the relative viscosity in FeTNa, at 0.4% concentration, and the intrinsic viscosity determined by extrapolation
( 1 ) Flory, P. J., “Principles of Polymer Chemistry,” p. 629-37, Cornel1 Univertjitg Press, Ythaca, N. Y., 1953. (2) Glegg, R. E., Poillon, W. N., un-
published data, Eastman Kodak Co., Rochester 4, N. Y., 1958. (3) Mench, J. W., unpublished data, Eastman Kodak Co.. Rochevter 4, N. Y.,
1950. (4) Strauss, U. P., FUOSS, R. hl., J. Polymer Sci. 4 , 4.57 ( I 949). ( 5 ) Taoford, C., “Physical Chemistry of Macromolecules,” pp. 489-508, Wiley, New York, 1961.
RECEIVED for review September 23, 1963. Accepted December 5, 1963. Division of Cellulose, Wood and Fiber Chemistry, 145th Meeting, ACS, Kew York, N. Y., September 1963.
Direct Determination of Sulfur Forms in Green River Oil Shale JOHN WARD SMITH, NEIL B. YOUNG, and DALE 1. LAWLOR laramie Petroleum Research Center, Bureau of Mines,
b Pyrite, organic, and sulfate sulfur in Green River oil shale are determined directly by the method presented. Quantitative, interferencefree chemical separations are performed consecutively on the same sample. Key to the determination is a new method for decomposition of pyrite by lithium aluminum hydride reduction. For pyrite sulfur, the relative standard deviation of the determination i s about =tl.5% of the determined value, and for organic With this new sulfur about *6%. method, forms of sulfur in Green River oil shale can be determined with 618
0
ANALYTICAL CHEMISTRY
U. S.
Department of the Inferior, laramie, Wyo.
precision and accuracy satisfactory for composition studies. The classical Powell and Parr method produces erroneous results.
0
SHALES of the Green River formation in Colorado, Utah, and Wyoming represent a tremendous reserve of fossil fuel energy, equivalent to more than 1 trillion barrels of oil ( 7 ) . The Federal Bureau of Mines, under its policy of encouraging development of this energy resource, is characterizing Green River oil shales. I n this study, a knowledge of the forms IL
and amounts of sulfur present in the rock is vital for determining the composition, heating value, and thermal degradation properties of the oil shales. In Green River oil shale, sulfur occurs in both inorganic and organic combinations. The rocks, essentially siliceous dolomites containing various amounts of organic matter ( I I ) , were formed from sediments accumulated in thermally stratified Eocene lakes (3). I n the reducing environment produced by this stratification, hydrogen sulfide was generated by bacterial attack on organic matter and sulfates in the ooze. Thia hydrogen sulfide precipitated
microgranular pyrite from iron dissolved in the lake watzr (S). Sulfur in the oil-shale rock occurs in pyrite and in the residual organit: matter. Small amounts of sulfate sulfur are also present in samples (12, 19, 20). Determining sulfur forms in carbonaceous rocks anc coals requires quantitative separation of the sulfate, pyrite, and organic sulfur. Separation and determination methods in the literature were developed primarily for coals, Sulfate sulfur can be separated and determined by extraction with dilute acids and subsequent precipitation as barium sulfate (4, 14, 16). Two separate chemi1:al routes, oxidative and reductive decomposition, are open for separation of pyrite. Both depend on the premisc: that iron disulfide is more reactive t h m organic sulfur. The first, oxidative decomposition, produces sulfate and ferric ions from pyrite, either of whicsh may then be determined. The nitric acid extraction method developed by Powell and Parr ( I F ) has been widely accepted for use on coals and other solid fuels. Although the original method has been much modified ( I S , 15,21), its basic chemistry is unchanged. Becausl? Green River oil shale contains much more inorganic matter than does coal, interferences are more probable. The second chemical route to pyrite decomposition is reductive attack, producing sulfides or hydrogen sulfide. Pyrite sulfur contentrs determined by reductive treatment generally have been believed to be low and of limited reliability (P), although, by adding metallic chromium to a zinc-hydrochloric acid reductive treatment, Radmacher and Mohrhauer (17) achieved pyrite results on German coals equivalent to oxidatively determined values. Organic sulfur con1 ent usually has been obtained as the difference between total sulfur and the sum of the determined pyrite and sulfate sulfur. hlthough calculation of organic sulfur by difference may be adelpate for control work, it is not certain enough for constitution and charactwization studies. Oil shales assaying 30 to 50 gallons of oil per ton contain only 1 5 to 2591, organic matter; consequently errors in organic sulfur values are multi died 4 to 6 times when converted to an organic basis for composition studies. If the residue after mineral sulfur removal can be recovered without interfering contamination or alteration, organic sulfur can be determined directly by combustion procedures. The key to direct determination of sulfur forms in carbonaceous rocks is the pyrite decomposition method. Reductive decomposition uffers advantages of direct titrimetric determination of hydrogen sulfide from pyrite and lack of
ml. of 10% barium chloride solution, boil 10 minutes, and let stand 4 hours. Remove the barium sulfate by filtering through dense, ash-free paper, wash with 10% HCI and then with hot water five times, and ash to constant weight a t 1000" C. Compute the sulfate sulfur content from the weight, using the following equation: Sulfate sulfur, wt. pct. = wt. BaS04 X 13.737 (1) sample weight
-REACTION
H-
FLASK
HOT PLATE AND
MAGNETIC STIRRER
Figure 1. pa ratus
Pyrite determination ap-
interfering attack on organic sulfur groups. Quantitative pyrite removal from oil-shale organic concentrates by lithium aluminum hydride (LAH) was recently demonstrated by Lawlor, Fester, and Robinson (IO). The method presented here for determining sulfur forms in oil shale was developed around reductive decomposition of pyrite by LAH. EXPERIMENTAL
The amounts of sulfate, pyrite, and organic sulfur in oil shale are determined by three consecutive analyses. First, sulfate sulfur, extracted with perchloric acid, is precipitated and determined gravimetrically. This procedure is patterned after Mott's (13) modification of the Powell and Parr method. Perchloric acid is used for extraction because it does not distill from dilute solutions. I n addition, it is a highly active acid and forms very soluble salts. Second, pyrite sulfur is reduced to sulfide by LAH treatment. Hydrogen sulfide evolved by acidification is determined by titration of the free acid formed in a neutral CdSO, absorbing solution (18). Third, organic sulfur is determined gravimetrically by Eschka fusion of the residue after mineral sulfur forms are extracted (14). To aid in evaluating the method, total sulfur content also is determined by Eschka fusion ( I ) . Sulfate Sulfur. From a n oil-shale specimen ground to pass a 100-mesh screen and dried a t 105" C. for 2 hours, weigh a sample of approximately 1 gram to the nearest 0.1 mg. R e t the powder with methanol. add 100 ml. of 10% perchloric acid, and boil gently for 30 minutes. Filter the slurry through ashless, sulfur-free filter paper and mash five times with hot water. Reserve the water-washed residue for subsequent analysis. To the filtrate, add 5 to 10 ml. of bromine water, boil to expel excess bromine, and evaporate to 100 to 150 ml. Add 10
Pyrite Sulfur. Dry the residue and filter paper from sulfate sulfur determination a t 85" C. and a pressure of less than 25 mm. Hg (about 2 hours) and then shred the paper into a two-necked reaction flask. Add approximately 1 gram of LAH dissolved in 50 ml. of tetrahydrofuran. [As a convenience, prepare, store, and dispense a stock solution of LAH in tetrahydrofuran by the Dillard method ( 5 ) . ] Assemble the reaction apparatus for refluxing and then reflux for 30 minutes with continuous magnetic stirring, gradually increasing applied heat as the vigor of the reaction decreases. Cool the reaction flask in an ice bath, and assemble the pyrite reduction apparatus for H2S evolution, as shown in Figure 1. Start a slow flow of nitrogen through the system, pour 250 ml. of cadmium sulfate solution (9 grams of 3CdS04.8H20 in 250 ml. H 2 0 ) into the gas scrubber, connect the outlet to a vacuum pump, and adjust the nitrogen flow rate so that excessive foaming does not occur in the scrubber. With the reaction flask still in the ice bath, add water carefullv to the LAH mixture through the serum cap. Adding water by drops and constant stirring are necessary in decomposing excess LAH. When the violent reaction has subsided (after adding about 5 ml. of H 2 0 ) , add the balance of 50 ml. of water to the reaction mixture. Remove the ice bath and add 50 ml. of 30'% perchloric acid to the reaction mixture through the serum cap. To complete the evolution of H2S, heat the mixture to boiling with constant stirring, and continue boiling for about 1 / 2 hour. (Completion of H2S evolution may be demonstrated by applying a syringe full of system gas to lead acetate paper.) Disconnect the gas scrubber from the system, and transfer the cadmium sulfate solution, now yellow from suspended cadmium sulfide, to a 600-ml. beaker. Titrate the sulfuric acid formed in the absorption reaction HZS
+ CdS04
-P
+ CdS 4
with 0.1.V sodium hydroxide to a p H of 5.25. Near the equivalence point add standard base by drops, waiting 20 seconds between each addition to ensure completion of the reaction. Compute pyrite sulfur content by the following equation: Pyrite sulfur, wt. % = ml. XaOH X normality NaOH X 1.6033 sample weight (2) VOL. 36,
NO. 3, MARCH 1964
619
Organic Sulfur. Filter the cooled mixture from t h e pyrite determination, washing the residue thoroughly with water. Dry t h e residue and filter paper a t 85’ C. a n d a pressure of less t h a n 25 mm. Hg. Shred the filter paper and residue into a 40-ml. porcelain crucible, mix thoroughly with about 4 grams of Eschka mixture [2 parts AIgO, 1 part anhydrous SazCOaby weight (,$)I, and then cover with a layer of Eschka mixture. Heat the crucible, gently a t first, to 825’ to 850’ C. for 1 hour or until the black carbon specks have disappeared from the calcined mass. Transfer the mixture to a beaker, washing the crucible with hot water. Add about 200 ml. of hot water to the calcined mixture, bring to a gentle boil, then filter and wash five times with hot water. Acidify the filtrate carefully with 1 to 1 hydrochloric acid, add 5 to 10 ml. of bromine water, and boil t o expel the excess bromine. Add 10 ml. of 10% barium chloride solution, boil for 10 minutes, and let stand for 4 hours. Filter the barium sulfate through a dense, ashfree filter paper; wash with 10% HCl, then five times with hot water; ash a t 1000’ C. to constant weight; and determine the weight of barium sulfate. Correct this weight for the blank value of the Eschka mixture, and compute the organic sulfur content of the sample, using the relationship given in Equation l . EVALUATION OF METHOD
To be valid, the proposed method must yield reproducible results on Green River oil shale and must determine the quantity of sulfur in each form without interference from the other forms. Direct evaluation of the method by analysis of a known sample is not possible, because production of a known sample comparable to the natural rock is impractical. Radmacher and l l o h r -
Table I. Sulfur Form Determinations Weight per cent raw shale
Sulfate 0.01 0.02 0.02 0.02 0.02
0.02 0.02
0.02
0.03 0.02 0.02 0.03 0.03 0.02 0.03 0.03 0.02 0.00 0.00 0.00
620
Pyrite Organic Sample 1 0.54 0.18 0.52 0.16 0.53 0.17 0.54 0.16 0.55 0.19 0.18 0.53 0.54 0.19 0.54 0.17 0.53 0.17 0.53 0.16 Sample 2 1.63 0.32 1.64 0.30 1.61 0.29 1.63 0.33 1.64 0.30 1.64 0.30 1.64 0.30 1.62 0.31 1.64 0.29 1.64 0.29
ANALYTICAL CHEMISTRY
Total 0.73 0.70 0.72 0.72 0.76 0.73 0.75 0.73 0.73 0.71 1.97 1.97 1.93 1.98 1.97 1.97 1.96 1.93 1.93 1.93
hauer (17‘) proved their reductive pyrite determination on coals by comparing results with those obtained by oxidative methods. When applied to oil shales, however, oxidative methods yield uncertain pyrite results. Consequently, evaluation of this method’s merit required separate evaluation of its reproducible application to oil shales and of its ability to achieve interference-free, quantitative separations. Two oil-shale samples representing typical Green River oil shales and containing different amounts of pyrite and organic sulfur were chosen as demonstration samples. Both were taken from the Mahogany zone, the high oilyielding section of the Green River formation. The Mahogany zone has been extensively studied because its oil shales probably will be the first to be exploited commercially. Descriptions of the samples are given below. Sample 1 was a composite sample, yielding about 25 gallons of oil per ton, and representing the Mahogany zone in sec. 5, T. 6 S., R. 96 IT., Garfield County, Colo. Description of the compositing method is given by Smith (19). Total sulfur content determined by Eschka fusion was 0.72 0.011 wt. % of the raw shale (average of five determinations with 95% confidence limits of the mean). Sample 2, taken from a bed 15 feet below the Mahogany marker a t the Bureau of Mines demonstration mine yielded I), more near Rifle, Colo. (% than 50 gallons of oil per ton. Total sulfur content by Eschka fusion was 1.96 f 0.016 wt. % of the raw shale (average of five determinations with 95% confidence limits of the mean). Confidence limits for the means were ts computed from the data as f--~ *‘A’
where N is the number of determinations included in the average, s in the standard deviation, and t is the usual value derived from “Student’s” t distribution for 95% confidence and N - 1 degrees of freedom (6). Use of these 95’% confidence limits permits comparison of averages from different but small numbers of determinations a t the same level of confidence. The resulting limits indicate that average values determined by another set of runs on the same sample will lie within these limits %yoof the time. Ten determinations by the method under examination were made on each of these samples. Results reported in Table I include total sulfur, calculated as the sum of the determined sulfur forms. Average values, having 95% confidence limits for each mean in weight per cent of raw shale were: for Sample I , sulfur forms: sulfate, 0.020 f 0.003; pyrite, 0.535 i 0.006; organic, 0.173 k 0.008; and total 0.728 0.013.
*
Sample 2, sulfur forms: sulfate, 0.018 f 0.009; pyrite, 1.633 i: 0.008; organic, 0.303 f 0.010; and total 1.954 -f 0.015. These means are reported to the third decimal place to illustrate computation of confidence limits. I n practice only two places should be reported. Relative standard deviations of the pyrite determinations for samples 1 and 2 were 1.6 and 0.7%, respectively. For organic sulfur these were 6.5 and 4.6%, and for total sulfur 2.3 a,nd 1.1%. Determining sulfur forms in oil shales with reproducibility adequate for composition studies is indicated by these results. Quantitative sulfur recovery by the t hree-st ep met hod is demonstrated. The total sulfur values, calculated as the sum of determined sulfur forms, are equivalent to values determined by Eschka fusion within confidence limits of the determinations. Although these results are precise, they only indicate the quantitative, interference-free determination of the sulfur forms. Quantitative, interference-free separation and determination of sulfur forms could only be demonstrated indirectly. Two separate proofs were necessary: That LAH did not produce hydrogen sulfide from organic sulfur groups present in oil shale, and that pyrite was totally reduced and determined by LAH treatment. I n his study of reduction of organic materials with complex metal hydrides, Gaylord ( 8 ) indicates that the first requirement would be met. To gain additional evidence concerning this requirement the LAH reduction procedure was performed on 2-gram samples of organic sulfur compounds chosen to represent possible sulfur groupings present in the insoluble organic matter of oil shale. The following compounds were tested: 1decanethiol, 1-octadecanethiol, thiacyclohexane, 2-methylthiophene, benzo( b )thiaphene, dibenzothiaphene, and di-a-naphthyldisulfide. Only in the cases of 1-decanethiol and thiacyclohexane were visible precipitates of cadmium sulfide formed, and these were trace amounts requiring only one drop (0.03 ml.) of standard base to pass the neutralization point, Since 0.03 ml. of 0.1.V base represents only 0.002 per cent sulfur from 2 grams of a pure organic sulfur compound, these yields were not significant. Consequently, LAH treatment does not produce hydrogen sulfide from organic sulfur compounds at a level interfering with sulfur form determination. To test the second requirement, the L h H reduction procedure was applied to a sample prepared by mixing quartz and pyrite to produce a sample containing about 4y0pyrite. The components were ground to pass a 100-mesh screen, leached with hydrochloric acid, and dried before mixing. Total sulfur
content on this sample was determined by Eschka fusion. .Irerage results of five pyrite and four total sulfur determinations in weight per cent of the prepared sample were 2.282 i 0.004 and 2.290 =k 0.023, rqiectively, with the 95% confidence limits computed from the data. A statistical test for inequality of these mezns (6) yielded a t test value of 1.09. The critical t test value a t 95% confidence was about 2.86; thus, the difference between the means is not significant. The close agreement between di:termined pyrite sulfur and total sulfur indicates complete pyrite reduction and sulfur determination. Because tests of the method yield reproducible determinations on oil shale and indicate complettb separation and determination of pyrite without significant attack on organic sulfur groups, it is concluded that the method affords valid determinti tion of the sulfur forms in oil shale. DISCUSSION
Failure of the modified l l o t t method (21) to determine accurately the sulfur
forms is illustrated by results obtained for the typical oil-shale, samples 1 and 2. Pyrite sulfur contents ’or these samples, determined from nitric acid soluble iron by this procedure, were 0 74 =t 0.019 (10 determinations) and 1.88 + 0.051 ( 5 determinations) wt. %, respectively. The 95% confidence limits are given with the means. These results, although reproducible, are obviously in error. For sample 1, this “pyrite” sulfur exceeds the total sulfur determined independently on the sample, and, for sample 2, it is only 0.08% less than the total sulfur content, leaving no room for organic s u l f r . Such results are extremely objectionable to composition studies. Failure of the modified N o t t method, for which the basic chemistry was initial Iy developed by Powell and Parr ( I C ) , indicates the need for a new method of determining sulfur forms such as is described in this report. To adapt methods of determining sulfur forms to the speed requirements of control analysis, organic sulfur content has generally been taken as the difference between total sulfur and sulfur determined in sulfates and Consequently, the pyrite (13-16). determined organic sulfur values for the two test samples a .e compared in Table I1 with organic mlfur values computed as the difference between the Eschka total sulfur tnd the sum of pyrite and sulfate sulfur. Means for these organic sulfur values with 95% confidence limits (weight per cent raw shale) were: Sample 1, determined: 0.173 =+ 0.008, by difference: 0.165 =t 0.006; sample 2, deteimined: 0.303 i:
0,010, by difference: 0.309 f 0.012. Statistical tests for inequality (6) yield values for the t statistics of 1.76 and 0.89 for samples 1 and 2, re~ are spectively, and the critical t s values approximately 2.1. Therefore, the hypothesis of equality of the population means must be accepted. This determination does not consider propagation of error and the resulting uncertainty of the value obtained by difference. Consequently, in spite of the small confidence limits, the by-difference value is less precise than the determined value. Where less precision is acceptable, as in control work, by-difference values seem to be acceptable. Filtrate from recovery of organic sulfur after L h H treatment was tested for sulfur content in all test runs made on the demonstration samples. This tetrahydrofuran solution was oxidized with hydrogen peroxide and liquid bromine, and sulfate ion then was precipitated with barium chloride. I n most cases sulfur was not detected. The few samples yielding precipitates gave insignificant amounts-less than 0.01% of the sample. This demonstrates that organic sulfur was not dissolved from the oil-shale sample by the tetrahydrofuran, because, if solution occurred, sulfate precipitates would have appeared in all test cases. The few trace amounts of sulfur recovered probably arose from incomplete evolution of sulfide sulfur. The titration curve for the absorbing solution, p H m.volume of base added, is typical for neutralization of a strong acid by a weak base (9). This is produced by the buffering action of the salt solution. hfter sulfide absorption the p H of the absorbing solution is 2.7 to 2.8. On titration with base the p H finally stabilizes at 7.4 (past the equivalent point). Approaches to the equivalent point are curved, of course, but a sharp p H increase from 4.0 to 6.5 occurs across the neutralization point. Titration tests on CdS04 solutions containing known amounts of sulfuric acid and on solutions after H2S absorption gave virtually identical curves, whose equivalent points averaged p H 5.25 (range 5.15 to 5.35). Because the range represented only 0.002 n t . yo sulfur, the more convenient titration to a fixed p H of 5.25 was deemed sufficiently accurate. The p H values of the original absorbing solutions came in this range. While a n indicator such as chlorophenol red, changing from yellow to red over the p H range of 4.8 to 6.4 (9), might be used for this titration, the precision and the ease of reading obtained with a commercial p H meter makes the instrumental method preferable. Blank determinations on reagents for pyrite reduction and hydrogen sulfide
Table II.
Organic Sulfur Determined and Computed
Organic sulfur, weight Determined By Sample 1 0.18 0.16 0.17 0.16 0.19 0.18 0.19 0.17 0.17 0.16 Sample 2 0.32 0.30 n 29 0 : 33 0.30 0.30 0.30 0.31 0.29 0.29
per cent difference 0.17 0.18 0.17 0.16 0.15 0.17 0.16 0.16 0.16 0.17
0.31 0.29 0 32 0.31 0.29 0.29 0.30 0.34 0.32 0.32
evolution produced no measurable values. Yo visible cadmium sulfide formed, and p H values of the final solution were a t the equivalence point. Small amounts of tetrahydrofuran distill over and are absorbed in the scrubber solution; however, adding even massive amounts of tetrahydrofuran did not interfere with the titration. .Ilthough this method was developed specifically for use on Green River oil shales, it probably is applicable to many other carbonaceous rocks. I n such extended applications the presence of elemental sulfur, which reacts quantitatively with L.IH to yield H2S and would be determined as pyrite, must be considered. LITERATURE CITED
(1) A. S. T. M . Book of Standards, Part 5,
pp. 959-61, Philadelphia, Pa., 1955. (2) Belcher, R., Spooner, C. E., Fuel 20, 172 (1941). (3) Bradley, W. H., U . S . Geol. Surv. Profess. Papers 168, 58 (1931). (4) Campbell, J. R., “Methods of Analysis of Fuels and Oils,” pp. 17-19, Chemical Publishing Co., S e w York, 1952. (5) Dillard, C. R., J . Chem. Ed. 29, 129 (1952). (6) Dixon, IT. J., Massey, F. J., Jr., “Introduction t o Statistical Analysis,” pp. 104-5, McGraw-Hill, New York, 1951. (7) Duncan, D. C., Ind. Petrol. Assoc. Am., pp. 22, 49-51, August 1958. (8) Gaylord, X. G., “Reduction with Complex Metal Hydrides,” pp. 832-888, Interscience, S e w York, 1956. (9) GlaFstone, Samuel, “Textbook of Physical Chemistry,” 2nd ed., pp. 10036, Van Kostrand, S e w York, 1946. (10) Lawlor, D. I,., Fester, J. I., Robinson, W.E., Fuel 42, 239 (1963). (11) Milton, C., Chao, E. C. T., Fahey, J. J., Mrose, M. E., “Report of the International Geological Congress, 21 st Session,” pp. 171-84, 1960. VOL. 36, NO. 3, MARCH 1964
621
(12) Milton, C., Eugster, H. P:, “Researches in Geochemistry,” Philip Abelson, ed., pp. 118-50, Wiley, New York, 1959. (13) Mott, R. A., Fuel 29,53 (1950). (14) Powell, A. R., Bur. Mines Tech. Paper 254,21 pp. (1921). (15) Powell, A. R., Ind. Eng. Chem. 12, 887(1920). (16) Powell, A. R., Parr, S. W., Bull. 111, Eng. Exp. Station, Univ. of Illinois, 62 pp. (1919).
(17) Radmacher, W., Mohrhauer, P., Glueckauj 89,503 (1953). (18) Scott, W. W.,“Standard Methods of Chemical Analysis,” 5th ed., N. H. Furman, ed., Vol. 1, pp. 911-12, Van Nostrand, New York, 1939. (19) Smith,. J. W., Bur. Mines Rept.
Invest. 5725, 16 pp. (1961). 120) Stanfield. K. E.. Frost. I. C.. Mc’ Auley, W.S., Smith, H. N.’, Bur. h n e s Rept. Invest. 4825, 27 pp. (1951).
(21) Van Hees, W., Early, E., Fuel 38, 425-8 (1959). RECEIVED for review September 23, 1963. Accepted November 18, 1963. Division of Petroleum Chemistry, 144th Meeting, ACS, Los Angeles, Calif., April 1963. This work was done under a cooperative agreement between the Bureau of Mines, United States Department of the Interior, and the University of Wyoming.
Precipitation of Submicrogram Quantities of Thorium by Barium Sulfate and Application to Fluorometric Determination of Thorium in Mineralogical and Biological Samples CLAUDE W. SILL and CONRAD P. WlLLlS Health and Safety Division, U . S. Atomic Energy Commission, ldaho Falls, ldaho
b Investigation of the toxicology and mineralogy of thorium requires its determination at extremely low concentrations in many kinds of biological and mineralogical materials. An efficient method i s required for separation of thorium from the relatively large samples employed. From 100 to pg. of thorium i s precipitated to better than 99.5% by 25 mg. of barium or other elements forming insoluble sulfates from 75-ml. volume. The separation takes place from strongly acidic solutions and i s not affected appreciably over a wide range of experimental conditions. The barium sulfate i s dissolved in alkaline DTPA and the thorium i s determined directly in the alkaline solution by a fluorometric procedure, which has been applied to the following types of samples with the detection limits indicated: rocks, 2 X bone ash, 5 X lod7%; feces, liver, and grain, 2 x IO-8%; urine, 10-11 gram per ml.; and blood, 2 X 10-lo gram per ml.
D
an investigation into the determination of radium-226 in liquid effluents from mills processing uranium ores ( I ) , results were frequently thousands of times too high when conventional procedures employing coprecipitation of radium sulfate with barium or lead sulfates were used. The extraneous activity was shown to be thorium-230. I n a subsequent investigation on the fluorometric determination of thorium using morin ( 8 ) , barium produced a serious decrease in 622
URING
ANALYTICAL CHEMISTRY
fluorescence of thorium standards due to actual physical loss of thorium in the barium sulfate precipitate. I n both procedures, precipitation of the minute quantities of thorium by barium sulfate was so efficient that the method appeared to have great potential as an analytical separation. Pyrosulfate fusion can be employed for dissolution of refractory materials and at the same time ensure complete dissolution of the thorium itself. The resulting solution containing high concentrations of sulfates is well suited for precipitation of barium sulfate, while keeping other elements dissolved in the strongly acidic solution. Accordingly, the effect of experimental conditions and other elements on the separation was investigated using thorium-234 tracer. Approximately 2 x IO5 c.p.m. and a 5-minute counting time were used on each test to permit all thorium to be accounted for with a standard deviation of 0.1%. Preparation of the tracer and its use by gamma counting in a 3-inch thallium-activated sodium iodide well crystal are described elsewhere ( 7 ) . To determine if the coprecipitation of thorium were peculiar to barium or if other elements forming insoluble sulfates would act similarly, the element being tested was fused with 3 grams each of anhydrous sodium and potassium sulfates and 2 ml. of concentrated sulfuric acid in the presence of the thorium tracer. After cooling, the cake was dissolved in 5 ml. of concentrated sulfuric acid and 70 ml. of hot water. The solution was allowed to stand for about 15 minutes and was then centrifuged at 2000 r.p.m. for 5 minutes. The aqueous supernate mas
diluted to 100 ml. and 50 ml. was counted under the conditions described. With 25 mg. of barium or a n equal number of moles of lead or lanthanum, only 0.2% of the thorium remained unprecipitated. With the same number of moles of strontium, cerium, or praseodymium, or only 5 mg. of barium, the loss was 0.7%. The efficiency is much lower with the more soluble sulfates such as calcium and the double rare earth sulfates above praseodymium. However, m-ith benzidine sulfate, 99.iyo of the thorium mas present in the filtrate, in sharp contrast to the results found with metallic sulfates. The effect of experimental conditions on the barium system was tested using the basic conditions described above, with 25 mg. of barium. The data showed that recovery of thorium is not affected significantly by type or concentration of acid or salts, temperature of precipitation, length of digestion, or order of addition of barium. Recovery of thorium is complete even after a few minutes’ digestion with barium added as preformed barium sulfate. However, a high concentration o f ’ sulfate is required. The separated barium sulfate dissolves easily in alkaline diethylenetriaminepentaacetic acid (DTP-A),from which it can be reprecipitated without coprecipitation of thorium by addition of acetic or even sulfuric acid, provided the acidity is not allowed to become higher than about pH 3. On addition of 10 ml. of 1 to 1 sulfuric acid, the thorium i. again precipitated quantitatively with the barium sulfate. Seither ortho- nor pyrophosphate has significant effect, even if present during
