Losses of Volatile Matter in Coal by Standard Method Water of Hydration and Carbon Dioxide of Mineral Matter W. A. SELVIGAND W. D. POHLE, Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
vv
ATER of hydration and carbon dioxide occurring in the mineral matter of coal are disturbing factors in coal analysis. They have been given considerable study by coal chemists, especially in connection with the use of analyses for purposes of coal classification (2, S ) , as here it is desirable to know the composition of the pure coal substance-that is, of the coal free from its ash-forming minerals. If proximate analyses are used as a basis for coal classification, the determination of volatile matter becomes important. Parr (5) proposed a system of coal classification based on volatile matter and B. t. u. of coal free of mineral matter. He applied corrections to the volatile matter as determined on the assumption that this volatile matter includes as a noncoal constituent the water of hydration of the shaley constituent of the ash-forming mineral matter. The tests described herein were made to determine whether the water of hydration and the carbon dioxide of the mineral matter occurring in coal are driven off in the standard method for determination of volatile matter (1). I n this determination the coal is heated for 7 minutes in a furnace maintained at a temperature of 950" C. The principal source of carbon dioxide in coal is calcite. As carbon dioxide is not usually determined in coal analysis, there is not much information as to its amount in various coals. Parr (6) determined carbon dioxide in about four hundred coals of Illinois and found that approximately 9 per cent of these coals contained less than 0.1 per cent of carbon dioxide; nearly 50 per cent of the coals showed carbon dioxide in excess of 0.5 per cent; 20 per cent more than 1.0 per cent of carbon dioxide; and 3 per cent over 2 per cent of carbon dioxide. The highest content of carbon dioxide found in these coals was 4.4 per cent. Fish and Addlestone (4) analyzed samples of coal from ten Virginia coal beds and found carbon dioxide ranging from 0.03 to 1.41 per cent. They also analyzed twenty-eight samples of coal from the Merrimac bed of Virginia and found from 0.26 to 5.4 per cent of carbon dioxide. Unpublished analyses of eighty-five coals from various parts of the United States, made a t the Pittsburgh Experiment Station of the U. S. TABLEI. Loss
OF
Bureau of Mines, show carbon dioxide ranging from 0.0 to 2.38 per cent, with an average of 0.53 per cent.
EXPERIMENTAL DATA A number of minerals containing water of hydration were selected for test. They were pulverized to pass a 60-mesh sieve, and a 1-gram sample was placed in a 10-cc. platinum crucible provided with a capsule cover. The crucible and contents were heated in an electric volatile-matter furnace for 7 minutes at 950' C. These conditions are the same as those used for the standard determination of volatile matter in coal. The loss in weight was compared to the loss obtained on igniting the minerals to constant weight in a muffle furnace. A number of the minerals were also analyzed for moisture, and the water of hydration was determined by the Penfieldtube method. Table I shows the results of these tests. A comparison of the losses in weight as determined in the volatile-matter furnace with the ignition losses to constant weight shows that the water of hydration was completely removed for all minerals tested with the exception of zoisite, This mineral showed a loss of 4.51 per cent on heating to constant weight a t 950" C. As the zoisite specimen contained 2.72 per cent carbon dioxide, the ignition loss of 4.51 per cent includes carbon dioxide and water of hydration. The loss on heating the zoisite in the volatile-matter furnace for 7 minutes at 950' C. was 3.41 per cent, showing that all of the volatile constituents were not driven off. A determination of water of hydration by the Penfield-tube method of the mineral after the 7-minute ignition in the volatile-matter furnace showed that 0.97 per cent of the water of hydration remained in the sample, and as the original sample had 1.76 per cent water of hydration it is apparent that this water was only partly removed by heating for 7 minutes a t 950" C. The sample of allanite contained ferrous iron which oxidized on ignition and the increase in weight due to oxidation accounts for the figures for the ignition losses being lower than the water actually determined in the sample. All the water of hydration of this mineral was driven off on heating for 7 minutes a t 950' C. It appears safe to assume from these tests that the water of hydration of the mineral matter
WATEROF HYDRATION OF VARIOUS MINERALS HEATEDIN STANDARD VOLATILE-M ATTER FURNACE LOSS IN
MINERAL
NATURE OF IMPURITIES
I 2
Serpentine Serpentine Prochlorite Allanite Epidote Zoisite a Not determined.
nuuw
32: none: sulfides, present
3 none z COS: none COz present as calcium and magnesium carbonate COz, small amount Ferrous iron, present: COz, none; sulfides, none COz none. sulfides, none COI: 2.72 6er cent ~
MOISTURE WATEROF 105O C. HYDRATION
AT
z
z
u.oa 0
60:. a a
-
__
u.77
0.10 0.05
239
TOTAL WATEB
%
%
9.81 13.57 14.63 3.44 5;81
10.58 13.76 14.76 3.28 6.33 3.75 1.68 14.06
a
1;IO
la66
a
(I
a
a
. _. 1.81 1.76
4.24
IQNITION Loss TO CONSTANT WEIQHT 750' C. 950' C.
5.01 2.01 1.81
14.86 10.10 3.67 1.07 2.70
% Q
a (I
a a a e a 0
a
3.70 2.24 4.51
VOLATILBMATTER FURNACE 7 MINUTB'B AT 950° C.
% 10.64 13.89 14.94 3.36 6.44 3.92 1.75 14.24 15.19 10.23 4.63 2.24 3.41
ANALYTICAL EDITION
240
TABLE11. Loss MINERAL
OF
Vol. 5 , Yo. 4
CARBON DIOXIDE FOR CALCITE MINERALSHEATED IN STANDARD VOLATILE-MATTER FURNACE NATUREOF IMPURITIES
IGNITIONLoss" TO 7 Min CON~TAN WEIQHT T 960' C'.
%
Loss I N VOLATILE-MATTER FURNACE 10 Min 960° C.'
16 Min 960' C'.'
%
%
Ignition
IOEB
in coal is completely driven off with the volatile matter of the coal substance when volatile matter is determined by the standard method, with the exception of minerals such as zoisite which require intense ignition for complete removal of water of hydration. Three minerals which are essentially calcium carbonate were tested for loss of carbon dioxide when subjected to the standard method used for volatile matter in coal. All the carbon dioxide was not driven off from these minerals when heated in the volatile-matter furnace for 7 minutes at 950" C., so additional tests were made by heating for 10 and 15 minutes a t 950" C., and for 7 and 10 minutes a t 1000" C. Table I1 shows the results of these tests. The calcite minerals gave erratic results in individual determinations when heated a t 950" C. The figures shown in the table for these values are the averages of a number of determinations. Seven determinations were made for the ordinary calcite; the individual determinations ranged from 30.4 to 36.6 per cent, with an average of 33.3 per cent. Six determinations were made for the Iceland spar; these ranged from 27.1 to 30.7 per cent, with an average of 28.9. I n case of the limestone six determinations were made; these ranged from 28.5 to 35.5, with an average of 32.5 per cent. The table shows that heating for 10 minutes a t 950" C. does not remove all the carbon dioxide and that it is removed completely by heating for 15 minutes a t this temperature. At a temperature of 1000" C. the carbon dioxide is not completely removed when heated for 7 minutes but it is all removed by heating for 10 minutes. A sample of dolomite (calcium magnesium carbonate) was also used in the tests but is not included in Table 11. This mineral when heated for 7 minutes a t 950" C. decomposed so rapidly that there was considerable mechanical loss of mineral particles, as evidenced by particles being ejected from the crucible and collecting on top of the crucible lid. On account of this mechanical loss of particles the loss in weight in the volatile-matter furnace was higher by approximately 2 per cent than the loss on slow ignition in a muffle furnace, which latter indicated a carbon dioxide content of 47.4 per cent. A sufficient amount of the limestone was added to a Pittsburgh-bed coal to give a carbon dioxide content of approximately 5 per cent, The exact amount of carbon dioxide was determined by analysis. This mixture was then run for volatile matter by the standard method used in coal analysisthat is, by heating 1-gram samples for 7 minutes a t 950" C. The residual carbon dioxide remaining in the residue from the volatile matter determination was determined by analysis. The results showed that approximately 70 per cent of the carbon dioxide was expelled with the volatile matter of the coal. The standard method for determination of volatile matter in coal specifies that the sample shall be heated for 7 minutes a t a temperature of 950" C. =t 20" C. According to this specification the temperature may range from 930" to 970" C. Tests made on coal have shown that this variation in temperature will not cause any significant difference in the determination of volatile matter of the coal substance, Tests were made by heating 1-gram samples of the limestone for 7 min-
43.4
41.0
43.9
%
Not determined 42.77 33.3 36.4 N o t determined 43.67 28.9 32.7 SlOr 0.1; AbOs, 0.1 F e d , 0.4; MgO, 0.9 43.66 32.6 38.3 determined by heating in a muffle furnace to constant weight at approximately QOOo C.
Calcite (ordinary) Calcite Iceland spar) Calcite !limestone) 0
10 Min., 1000° C.
42.3 42.9
7 Min 1000° 6. % 41.0 40.2
% .-
42.8 43.9
utes a t different temperatures varying from 930" to 970" C. Table I11 gives the results of these tests, and shows a wide range in the carbon dioxide evolved at this range of furnace temperatures, as 19.9 per cent of carbon dioxide was driven off a t 930" C. and 34.6 per cent a t 970" C. These are average values and the table shows that the individual determinations differed considerably. Assuming that the ignition loss of 43.56 shown in Table I1 consists of the carbon dioxide present, Table 111 shows that 45.7 per cent of the carbon dioxide present was removed a t 930" C. and 79.4 per cent a t 970" C. The relatively large differences in the individual determinations a t 950" C. were probably caused by small unavoidable differences in the furnace temperature, although this was maintained as uniform as possible with the standard furnace used for this determination. TABLE111. Loss OF CARBON DIOXIDE OBTAINEDBY HEATING LIMESTONE FOR 7 MINUTES IN VOLATILE-MATTER FURNACE INDIVIDUAL AVERAG~ TEMPERATURH~ DETERMINATIONSAVERAQE COa REMOVED
c.
%
%
%
22.1,18.7,18.8
19.9
46.7
940
25.0, 24.7 24.7, 26.3
24.9
67.2
960
28.5,28.8 35.1, 34.0 36.6,33.0
32.6
74.0
34.6,36.6,33.7
34.6
79.4
O
930
970
,
Because of the incomplete removal of carbon dioxide from calcite and the erratic results obtained over the temperature range of 930" to 970" C., it does not appear feasible to apply corrections to the volatile-matter determination for carbon dioxide from calcite, in coals containing relatively large amounts of mineral carbonates. With such coals it would be better practice to remove the major portion of the calcite previous to analysis by means of a float-and-sink method. The ignition losses shown in Table I1 were made by heating 1-gram samples to constant weight in a muffle maintained at a temperature of 900" C. The standard method for determination of ash in coal (1) specifies heating 1-gram samples of coal to constant weight (*O.OOl gram) a t a temperature between 700" and 750" C. Tests made by heating the three calcite minerals under these conditions show that all the carbon dioxide is removed in from 2 to 2.5 hours. These results checked closely with the loss on ignition at 900" C. as given in Table 11. It is safe to conclude that all carbonates are decomposed in the standard method for determination of ash in coal. Reference to Table I shows that approximately one-half of the water of hydration was removed by heating epidote to constant weight a t 750" C . The sample of zoisite gave a loss under these conditions of heating equivalent to the amount of carbon dioxide present as an impurity in the mineral. Analysis of this mineral after heating to constant weight a t 750" C. showed that the carbon dioxide was completely removed, but that little, if any, of the water of hydration had been removed, as a Penfield-tube test on the ignited material showed 1.54 per cent water of hydration as compared to 1.76 per cent for the original sample. These tests
July 15, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
show that minerals such as epidote and zoisite require intense ignition for complete removal of water of hydration and that this water is not removed in the standard method for determination of ash in coal by which the coal is ignited to constant weight a t a temperature between 700" and 750" C. No information is available as to the amount of such minerals that may be present in coal. ACENOWLEDGMENT The writers gratefully acknowledge the assistance of W. H. Ode, assistant chemist, Pittsburgh Experiment Station, U. S. Bureau of Mines, in making a number of the tests included in this paper.
241
LITERATURE CITED (1) Am. SOC. Testing Materials, Standards, Pt. 11, Non-Metala, pp. 689-726. 1930. (2) Fieldner, A. C., and Selvig, W. A., Trans. Am. Inst. Mining Met. Engrs., Coal Division, 597-613 (1930). (3) Fieldner, A. C., Selvig, W. A., and Gibson, F. H., Ibid., 224-35 (1932). (4) Fish, F. H., and Addlestone, 3. A,, IND.ENG.CHEM., Anal. Ed., 3, 155-8 (1931). (5) Parr, S. W., Eng. Expt. Station, Univ. Illinois, BUZZ.180 (1928). (6) Parr, 8. W., Illinois Coal Mining Investigations, Bull. 3 (1916). RECEIVEDJanuary 17, 1933. Presented before the Division of Gas and Fuel Chemistry at the 86th Meeting of the American Chemical Society, Washington, D. C., March 26 to 31, 1933. Published by permiesion of the Director, U. 8.Bureau of Mines. (Not subject to copyright.)
Determination of Small Amounts of Manganese in Salt Solutions NORMAN ASHWELLCLARK,Department of Chemistry, Iowa State College, Ames, Iowa
S
INCE the introduction in 1917 by Willard and Greathouse (9) of potassium periodate for the oxidation of manganese to permanganate, the method has come into general use. The color from 0.01 mg. of manganese in 50 cc. has been reported as easily checked against known standards. Recently a still more delicate color reaction has been suggested by Stratton, Ficklen, and Hough (8) using benzidine hydrochloride, with an optimum concentration for color comparison between 0.001 and 0.0001 mg. per 100 cc. Both methods have been used in these laboratories for the determination of traces of manganese in salt solutions.
POTASSIUM PERIODATE METHOD The potassium periodate method depends upon the oxidation of the manganese in acid solution to the colored manganese ion, and comparison with a standard similarly prepared, Willard and Greathouse, for 100 cc. of solution containing 2.5 or more mg. of manganese, advised 10 to 15 cc. of concentrated sulfuric acid, 20 cc. of concentrated nitric acid, 5 to 10 cc. of 85 per cent phosphoric acid, or mixtures of two or more acids. The amount of acid was shown to vary widely without influencing the results. This method was used by Bartow and Thompson ( I ) without the sulfuric acid, for manganese in potable waters. I n 1930 Richards ( 6 ) reported results on biological material that showed the desirability of controlling the acidity very accurately in order to get satisfactory results with small quantities of manganese. Sulfuric acid was used and, with the acidity from 5 to 6 per cent, no fading of the color was observed. Excess acidity prevented development of the full color or caused it to fade rapidly. I n the same year Skinner and Peterson (7) published a paper on the determination of manganese in animal tissue. They showed that 10 to 20 grams of material, when ashed in a muffle furnace a t cherry red, could be extracted with 5 cc. of 85 per cent phosphoric acid and 30 to 50 cc. of water and, after filtering, could be oxidized directly with 0.3 gram of potassium periodate without loss of color. They found that 0.01 mg. of manganese in 50 cc. gave a readable color when compared in Nessler tubes against an inverted V of white paper. I n these laboratories it became necessary to know the content of manganese fairly accurately in a number of salt solutions both separated and together, and in concentrated
and dilute solutions. The salts in which the manganese was determined included potassium nitrate, primary calcium phosphate, magnesium sulfate, ferric chloride, and later ferric citrate. I n all cases 50-cc. Nessler tubes were used for the color comparison. The tubes were carefully matched for color of glass; for this reaction, tubes with a trace of brown in their composition were found to be less delicate than others. With a good frame and milk-glass reflector, and with sky light, the comparison was as easily made as with the inverted V paper used by Skinner and Peterson. It was usually possible to detect the presence of 0.001 mg. of manganese in the 50-cc. tube; 0.002 mg. could always be seen, and there was a distinct difference in additions of 0,001 mg. Colors produced by the potassium periodate oxidation were remarkably stable; in some cases standard solutions which had been kept for 7 months in the dark showed no trace of fading. The standard solution was made from potassium permanganate of known normality, or from recrystallized potassium permanganate as suggested by Richards (6). I n both cases the solutions were reduced by sodium sulfite and sulfuric acid, and the sulfur dioxide boiled off. Various combinations of sulfuric, nitric, and phosphoric acids for the oxidation with potassium periodate showed that phosphoric acid alone was the most satisfactory. The remainder of the oxidations were made in 50 to 100 cc. of a solution containing 5 cc. of 85 per cent phosphoric acid and 0.3 gram of potassium periodate. A few minutes' boiling usually brought out the full color; the solution was then cooled and made up to 50 cc. in the Nessler tubes. A further solution was made up from the same standards and reduced with the sulfur dioxide as before, or by Bureau of Standards sodium oxalate, diluted until the content was 0.002 mg. of manganese per cc. and, when freshly oxidized by potassium periodate, used as a check on the diluted standard solutions. A few cubic centimeters of this (solution B+), before oxidation, were used with separate samples of unknowns to test for interfering substances. A liter of the distilled water used was evaporated to 50 cc., but showed no trace of manganese after oxidation. By varying the amounts of potassium periodate, this salt also was shown to contain no manganese. Samples of commercial 85 per cent phosphoric acid contained from 0.002 to 0.003 mg. in 5 cc. By recrystallizing this could be elimi-
