A S H L E Y ON T H E D E C O M P O S I T I O N OF CLAYS mechanical separations1 has been deeply impressed by their practical utility. Existewe of Exceedivtgly Fine Mineral Crystals Doubtful.-Certain writers are of the opinion that the minerals found in clays and soils do not retain the crystal condition, but pass over to the colloid state when slightly under 0.001mm. in diameter. If such is the case, it is a sad fallacy to assume, calculate, and give preponderance to the size of crystal grains under 0.001 mm. in diameter. Seger’s smallest does not unduly exalt this fine matter fraction, 0.01-0, in the surface factor. Effect of Size o n Physical Properties of Clay Warns.-Clays containing large amounts of residue above 0.04 mm. in size are too coarse for fine pottery. China clays containing considerable amounts of the 0.0400.025 mm. size are the “safest” used in potting. Most of the commercial English china clays have practically no residues coarser than 0.02j mm., while if they have but slight residues coarser than 0.010mm., they are exceedingly liable to cause big losses from cracked ware. Purdy’s mechanical analyses of paving brick clays show a general agreement with this conclusion. The coarsest clays made the toughest brick and the finest clays the weakest brick. The experimental work of this paper was done before our laboratory was transferred from the Technologic Branch of the Geological Survey to the Bureau of Standards. SUMMARY.
I t is inaccurate to express the size of microscopic mineral grains in “diameters,” unless the term is carefully defined. The volumes calculated from microscopic measurement require multiplication by correction factors. The distribution of sizes in any fraction of clay obtained by mechanical analysis may follow several laws; hence, the various formulas proposed for calculating the mean size are all liable to error. A simple empirical correction factor to the arithmetical mean is apparently as accurate as any more elaborate calculation.
W 5+ W -2 + -2 + . . . ,), or dn do
Melior's surface factor,-6s (d,
(TI+ w +-+ . . . . .
Wo d , do best represent the results of a mechanical analysis. The surface factors become uncomparable if different size limits are used in calculations for the smallest sizes. It is advocated t h a t Seger’s limits-0.04, 0.02j , 0.010and o mm.-give results of most value to clay workers. Purdy’s
simpler
form,
-
-2
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THE DECOMPOSITION OF CLAYS, AND THE UTILIZATION OF SMELTER AND OTHER SMOKE IN PREPARING SULPHATES FROM CLAYS. By HARRISON E. ASHLEY.~ Received December 27, 1910.
In Ost’s “Technische Chemie,” edition of 1890,p. 129, is the statement t h a t a t a Silesian smelter the fumes 1 Trans. A m . Cer. SOC.,11, 543-547. 4 8 9 4 9 2 (1909); 12, 277-293, 441-442, 445, 779-782, 795-799 (1910); U. S. Geol. Survey, Bull. 388, 48-51 (1909). 2 Published by permission of the Director of the Bureau of Standards.
91
were made to extract alum from shale clay. I cannot find the statement in the 1898 edition of Ost, from which the inference is t h a t the process has been abandoned. A post-mortem examination is not usually inspiring, but as we still have smelter and industrial smokes containing considerable percentages of sulphuric acid, and as clays are found everywhere, the subject is likely to be revived a t any time. An uneconomic process of a past decade often develops into a profitable industry of the present through the more definite knowledge of the conditions to be met. During the past few years some notable physicochemical data on the properties of clays t h a t are involved in such a utilization of clays have appeared in publications inaccessible to many of you, and, together with some original data, are summarized in this paper. Considering their economic importance, the clays are very imperfectly known as to decomposition and other critical points, as indicated by loss of water, heat absorption and evolutions, specific gravity changes, and solubility in acids. An incorrect notion that the combined water of kaolin is given off in two stages is very prevalent. Hillebrandr described a sample of pure crystal kaolinite (sp. gr. 2.611) and said “None of the water escapes a t a temperature of 330’ C.; it is therefore probably all basic water. . . . . . Frenzelz has described a variety of kaolin (myelin) which loses none of its water until a very high temperature is reached.” Purdy and Moore3 said: “The majority pf clays are dehydrated completely when subjected to heat a t 500-600° C., others not.” The only experimental figures with which we are acquainted, that show the actual losses in weight on heating clays to different temperatures, are those of A. E. Barnes4 and W. M. K e n n e d ~ ,a~ pupil of Orton’s. The details of these two tests are given in Fig. I. Purdy and Moore’s statement was likely based upon these testse Le Chatelier? made some determinations t h a t appear to have been accepted by all French authorities. He heated tests of typical hydrous minerals in a 5mm. platinum cone opening in a large crucible filled with calcined magnesia and heated by a Forquignon furnace, taking only I O min. to reach I O O O ~ . He states that variation of the speed had little effect. Our investigations show t h a t whatever the cause, his results were IOO to Ij o o C. too high. His results on the decomposition of calcium carbonate have been shown in error by a similar amount.8 On the basis of the observed retardations and accelerations, Le Chatelier divided the clays into 5 types : 1
U. S Geol Survey, Bull. 20, 98 (1885).
* Naumann-Zirkel, “Mineralogie,” 11th Ed., p. 676. Trans. A m . Cer SOC., 9, 213 (1907). Clayworker, 23, 705 (June, 1895). Trans. A m Cer. Soc., 4, 152 (1902). I have since learned that Ellis Lovejoy published in the Clayworker, 1886 or 1887, the loss of weight at the melting points of different metals, and found the decomposition near the meltina voint of antimonv. 624OC. ‘2.physik. Chemie, 1 , 396 (1887). C o m ~ i rendus, ~s 104, 1443, 1517. Zavriev, J . chzm. phys., 7 , 31-57; Chew. Abs., 3, 1112 (1909). 3
4
’
T H E JOURNAL OF INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y .
92
Allophane, Al,O,.zSiO,.Aq. Retardation between and z z o O . 1 A sudden acceleration a t I O O O O . Halloysite, A1,O,.zSiO2.zH,O.Aq.-Marked retardation ending a t 7 o o o . A sudden acceleration at I O O O O . Crystal Kaolin,Al,O8.2Si0,.2H,O.-Decided retardation, ending at 7 7 0 ' . A slight acceleration at I O ~ O O , "due to colloidal clay always present in kaolin." Pyrophyllite, Al,O,.qSiO,.H,O.-Retardation ending A doubtful retardation a t 850'. a t 700'. Montmorillonite, A1,0,.4SiO,.H20.Aq.--A considerable pause at 2 0 0 ° , one less sharp at 7 7 0 ° , a doubtful one a t 950'. He stated that the halloysite group is the most important, including all the sedimentary and most of the "chemical" clays. 150
with temperature-time coordinates. is a summary: Clay. End English china clay, No. 1.. North Carolina kaolin . , , No. 1 fire-clay ........ , No. 2 Ere-clay ,. .. . Paving brick shale.. . . . . . , English ball clay.. . . . I . . , Tenn. No. 3 ball clay.. , ,,
,
~
,
~
~
~
Remarks.
582, 574
578
Scceleration at 940'.
592 597 583 581 583
*4cceleration from 900 to 9700.
612 595 590 574 552, 567 574 617, 614
., An individual test is shown in Fig.
N. Dakota, highly colloidal
1911
The following
of retardation.
~. 573',
.. . . ... " . ... . . . ... . . . .. . ... N. J. saggar clay. . . . . , , ~.. . . Ohio surface clay.. , . . . . , , . , illbany, N. Y . , slip clay.. . . . Illinois joint clay., , . , . . . . . . Another Illinois joint clay.. i . Minn., highly colloidal., . ,
Feb.,
Indistinct. 2.
A.E,Barnes; brick clay 2 5g. 51 hrs. -W.M. Kennedy; Florida kaolin 30g 28 hrs. . . I -
remp 500
400
300 200
O I0 0
0
2
5
7
Per cent. IDSS o f
10
water:
12
.L
I5
Fig. 1.
We have made only what we consider preliminary tests, heating cylindrical test pieces ( 5 cm. long, 3 . 5 cm. in diam., I cm. hole half way through the center) in an electric furnace with sufficient current turned on from the start to bring the test-piece to about IOOOO in roo minutes. Usually the runs were carried to 800' only. This gives a very rapid rise for the first few hundred degrees. The results are most readily perceived when put on logarithmic plotting paper 1 Temperatures
as given by Le Chatelier.
An initial slow rate of heating is due to the water held persistently b y colloidal clay up t o zoo or 3 0 0 ' . A second retardation from about 500 to 5 7 5 ' is due to the expulsion of all the chemically combined water. A third retardation from about 8 2 5 to 9 2 5 ' is of a wholly unproved nature, possibly the transformation of quartz to tridymite. The same description, unproved, applies to the acceleration occurring a t about 92 5 O , which we suspect
4
..... .
.
A S H L E Y ON T H E DECOMPOSlTION OF CLAYS. of being due to the formation of sillimanite, a mineral which crystallizes out in clay products a t about 1350’ C. The specific gravity determinations of KnoteI a t the University of Illinois on the same sample of clay confirm our thermal results. Any attempt to
Heat Changes o f
determine from the specific gravities of sillimanite ( 3 . 2 ) , quartz ( 2 . 6 5 ) , tridymite (2.31, and corundum (4) what compounds exist a t I O O O O is futile, as the lightest possible mixture has a specific gravity of 2 . 9 5 , as opposed to Knote’s determination of 2 . 7 2 .
93
were repeated, except that the retardation a t 825 to 925’ did not appear with the clay tried (Fig. 3). I n Fig. 4 we have combined the results of Bleiningerl and Knote* on the same clay. The apparent inconsistency of their results is due to the fact t h a t Bleininger dried his sample a t 100’ and Knote a t 115’. Such differences have a profound influence on colloid behavior, as has been noted by Hillebrand, Lord, and others. Knote made no determinations
$00 200
! \ I
I
I
I
I
*.* e ”
___-----------4j;;
0
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y .
94
Extraction. Per cent.
............. ........................
Raw clay., . . . Ignited a t 600’. Ignited a t 1O0Oo.
.......................
6 44 5
Edgar ball clay ignited a t 600’ gave 70 per cent. extraction, while raw clay and I O O O O ignition also gave small extractions. Le Chatelier stated that the heat evolution a t 1000’ accompanies the change by which A1,0, becomes insoluble in acids. RiesI found a few tenths of I per cent. soluble salts in unburned clay, 4 . 5 0 per cent. in soft-burned, and Evidently the softI . 0 3 per cent. in hard-burned. burned clay took up sulphuric acid from the fuel to some extent. At sufficiently high temperatures’ silica will displace the sulphuric acid from its compound with alumina. I n this article we have compiled most of the data available, showing a t what points changes take place in the chemical nature of clays. The technical application of this data for the purpose of extracting soluble sulphates from clays by smelter smoke is outside the province of the laboratories with which we are connected. As Prof. Bleininger remarked when the writer proposed the title: “There will likely be mighty little about smelter smoke and a lot about clays in your article.” Brick-yards are sometimes much objected to because of the large amount of sulphuric acid they discharge into the atmosphere. I n Belgium lime is sometimes put on the kiln tops to capture the acid fumes. It has been noticed that wood on the top of wove or field kilns becomes impregnated with sulphuric acid, and the writer has been questioned by a manufacturer as to whether such condensed acid is finally discharged into the atmosphere. I n a certain large city, where the suppression of acid brick-yard smoke is agitated, and where the brick commonly used are but soft-fired, the amount of soluble salts is unusually large. It is inconceivable that all of these salts were originally in the clay used. Hence it would appear that the brick-makers, probably unintentionally, are delivering sulphates in bricks rather than into the atmosphere. I t appears, then, that any clay ignited between 600 and g o o 0 C. will take up acids quite readily. The methods of utilizing this fact and the economy of processes are not discussed. The retardation points given on p. 92 were determined under the direction of Prof. A. V. Bleininger by Messrs. R. K. Hursh and S. E. Young. The curves with equal temperature increments and equal energy increments were made by the writer.
___-_-
EXTENT AND COMPOSITION O F T H E INCRUSTATION ON SOME F I L T E R SANDS. By E. BARTOWA N D C. E. MILLAR. Received January 7, 1911
%‘hen lime is used in connection with water puri“Clays of Wisconsin.” Wisconsin Survey, Bull. 16, 22 (1906). H. A . Seger, “Collected Writings,” American Ceramic Society Translation, 2, 583, 646 (1902).
Feb.,
191I
fication there is a tendency to form an incrustation in the pipes or on the sand grains of the filters. I n some cases the sand grains have become so large that it has been necessary to put in new sand. Cases have been reported where the sand near the bottom of the filters has caked into a solid mass.1 We have investigated the sand in some filters in Illinois. Samples of sand were sent to us from Danville (2), Kankakee, Quincy, and Moline. TVe are indebted t o H. PI.Ely, Danvillc, C. H. Cobb, Kankakee, W.R. Gelston, Quincy, and to M. Olson, Moline, for information concerning the sand used. The Danville plant used Red Wing, hfinn., sand having an effective size of 0 . 3 1 and a uniformity coefficient of I . 8. During periods of low turbidity from 0 . 2 7 to 0 . 7 grain per gallon of lime and from 0 . 5 8 to I . 5 grains per gallon of iron sulphate were used. I n periods of high turbidity from 0.8 to 2 . 5 grains per gallon of lime and from 2 . 5 to 4 , o grains per gallon of iron sulphate were used. Filter KO. 8 has been in use 7 years and filter No. 6 5 years. A larger proportion of lime was used prior to the last 1 5 months. The Kankakee plant uses Mount Tom sand. The size a t the beginning is not known. The sand has been in use 9 years, but only during I year has I grain per gallon of iron sulphate and 2 grains per gallon of lime been used. During the remainder of the time alum has been the coagulant. The Quincy plant uses Red Wing, Minn., sand having an effective size of 0 . 3 8 and a uniformity coefficient of 2 . I . IVhile the sand has been in use a long time, it is not possible to tell the exact time, for about two years ago, the sand was removed from the filters, screened, and the finest replaced. It has undoubtedly been in use more than 7 years, for Quincy was the first plant in the country to use the lime and iron sulphate process. During the last 4 years an average of 2 . 0 5 grains per gallon of iron sulphate and 2 . 8 4 grains per gallon of lime were used. The Moline plant has been in operation without removal or change of the sand for five years. Alum has been used about nine months; previous t o that, lime and iron sulphate were used regularly, I grain per gallon of iron sulphate and 3 grains per gallon of lime being used. The sand received has been examined to determine the relative amount of the incrustation, the size of the incrusted grains, and the composition of the incrustation. TABLEI. Danville Danville. No. 6 . No. 8.
Kankakee.
Quincy.
351.0 238.0
383.0 330.0
325.0 49.0
330.0 94.0
113.0
53.0
276.0
236.0
~~
S a m e of sand. Weight of sand taken. 343.0 Weight of residual sand 232.0 Weight of incrustation removed. . . . . . . . . . . 112.0 Per cent. of incmstation. . . . . . . . . . . . . . . 3 2 . 4 Per cent. increase by incrustation. . . . . . . . 4 7 . 9
Moline.
32.2
13.7
84.7
71.4
45.7
15.9
633.0
249.0
1
1 Eng. and Mzn. J . May 6, 1908. I-fealth, 1908.
Report of Ohio State Board of
