NOTES
Oct., 1957 Si02 have combined to form the SrSi03 and by the time 12 hours had passed excess silica in the amorphous form had begun to appear. Because crystalline materials found in longer experiments are rather complex mixtures only a few more analyses were made, and those simply to show the trend toward larger amounts of silica present. Table 111 contains the chemical analysis of the solutions a t several time intervals.
1439
prevent further devitrification. Where the early coating was not tightly bound the reactions proceeded without difficulty. In this manner SrSiO resembles BaSi03 which adhered so tightly that reaction was stopped completely.2
Conclusions The reactions of a dilute solution of Sr(OH)2with silica resemble closely those of Ca(OH)2 with the exception that the first insoluble silicates formed TABLE I11 have a tendency to adhere to the rod surface in the ANALYSISOF LIQUIDPHASE case of Sr(OH)z; while no such tendency was ob10 g. Si02 glass rod, 0.025 N Sr(0H)z served with Ca(OH)2. I n this respect the reactions 50% filling, 125 ml., 400°, 340 atm. of resemble those of Ba(OH)2 rather than Time at 400°,hr. SiOz, mg. SrO, mg. Ratio, SrO/SiOn Ca(OH)z. 0 3.0 46.6 15,58 After three hours a t 400" the reaction has pro4 34.0 2.89 0.085 ceeded beyond an equi-molar quantity of silica 12 51.5 3.25 .063 which would require the loss of 0.025 mole or 0.1522 48 57.5 1.71 .030 g. from the rod. Devitrification continues a t a 65 62.5 3.95 .Of33 slowly decreasing rate until 65 hours have passed, 96 44.0 1.48 .034 then a rapid increase in reaction occurs which corIt is evident from the results in Table I11 that responds with the appearance of a new crystalline although the reaction starts a t 124O, not much phase, @-cristobalite, among the solids present. strontium silicate (SrSi03) is built up in solution Unlike Ca(OH)2 the 0-cristobalite formed rapidly until several hours have passed, and then the ma- changes to a-cristobalite which is a lower energy terial in solution takes the form of a silica rich form of silica. This transformation is probably due complex rather than a simple silicate. This confirms to the higher pH of the solution.6 From a theoretical standpoint one would expect the results reported in the exploratory work2 published in THISJOURNAL. After 48 hours the mini- that because of the more basic character of Sr(OH)2 mum concentration of SrO is reached in solution, the reaction of this material should resemble more which corresponds with the slow rate of reaction, closely the reactions of the alkali metal hydroxides Fig. 1, after which the concentration of SrO in- with silica; however, the formation of the more increases in solution to 65 hours and then decreases to soluble silicates as intermediate materials in the reaction and the more acidic nature of the hydroa minimum again at 96 hours. One complicating condition that was observed lytic products of the strontium silicate, result in the during the course of these experiments was the formation of the more symmetrical and higher entendency of the insoluble strontium silicates t o ergy forms of quartz. adhere to the surface of the rod and in some cases (5) Paper No. I11 of this series, THIBJOURNAL, 61, 1432 (1957).
NOTES T H E EXTRACTION OF ALUMINUM AND SILICON FROM MUSCOVITE MICA BY AQUEOUS SOLUTIONS BY
GEORGEL. GAINES,JR.AND
c. P. RuTKowsKI
General EEectric Research Laboratory, Scheneclady, N . Y . Received M a y 9, 1867
I n connection with studies on the ion-exchange properties of natural micas, we have been concerned about the possibility of attack on the .aluminosilicate framework of the mineral by aqueous solution. The importance of this type of phenomenon in connection with the ion-exchange behavior of clays has been emphasized before.' Bradley2 has also observed interesting surface effects with acid (1) N. T. Coleman and M. E. Harward, J. A m . Chsm. Soc., 76, 6045 (1953). (2) 'R.S; Bradloy, Trans. Faradau Soc., 36, 1361 (1039).
treated mica. We wish to report here some measurements of the extraction of aluminum and silicon from ground mica samples by several aqueous solutions. Experimental Carefully fractionated samples of ground Bengal Ruby muscovite mica of various particle sizes were used for this study. The origin, preparation and analytical data for these mica samples are given in the discussion of our ionexchange studies.a The surface areas of the samples used, as determined by adsorption of krypton at -196' in the conventional B.E.T. technique, were 0.70 m.2/g. for the 20-40 mesh fraction and 2.32 m.2/g. for the 100-200 mesh fraction. Solutions were prepared from reagent grade chemicals or commercial standard volumetric solutions, using distilled, deionized water. Extractions were performed by agitating 1-g. samples of the mica with 120-ml. portions of solution in a thermostat a t 25.0" for the desired length of time, then removing the supernatant liquid for analysis. Polyethylene containers were used throughout.
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(3) G. L. Gainos, Jr., THIS JOURNAL, 61, 1408 (1957).
Vol. 61
SOTES
1440 I
I
I
I
TABLE I
I
Al
AND
Si EXTRACTED FROM MICA IN 24 HOURS AT 25' 20-40 mesh Si,
Solution
0 . 1 N HCI 0 . 1 N KOH 0.1 N KC1
4
Irg.
Irg.
100-200 mesh AI, Si, Pg.
Pg.
85 1280 380 310 300 470 0" 0" 5" H2O 0" 5" 5" 10" "The precision of the analyses in these cases is 2~5-10
300 140 0"
Pg *
from 1 g. of 100-200 mesh mica in 24 hours by very dilute HC1 solution (pH 4.5) and NaHCOa solution (pH 8). Dependence of the extent of attack on acid or base concentration, with a minimum a t or J 0 16 24 32 40 near pH 7, is suggested. HOURS. While the present data are few and not very preFig. 1.-The extraction of aluminum and silicon from 100cise, certain relationships are interesting. Each 200 mesh Bengal Ruby muscovite by 0.1 N HCl a t 25'. flake of mica exhibits two types of surfacecleavage planes and edees. A mica flake consists CLEAVAGE SURFACE of a stack of aluminosilicate layers as shown in Fig. 2. The cleavage surfaces are tetrahedral @ aluminosilicate lattices with one A1 for every three TETRAHEDRAL LAYER - S i = A I Si (with, of course, the exchangeable potassium OCTAHEDRAL L A Y E R - A14 ions). At the edges, both tetrahedral and octahedral layers are exposed, and the over-all ratio T E T R A H E D R A L LAYER - S i AI Si/Al is unity. For our samples we can estimate the thickness and hence area of edge surface from the average sieve opening and the total surface area. On this basis, we find for the 20-40 mesh OCTAHEDRAL LAYER - A I 4 I O A " fraction an average thickness of 1.0 p and 23 cm.2 of edge surface per gram, while for the 100-200 mesh mica, the corresponding values are 0.3 EL and 130 cm.2. Thus, there is about 3 times as much cleavage surface in a gram of 100-200 mesh mateFig. 2.--The (idealized) layer structure of muscovite mica. rial as in one gram of the 2 0 4 0 mesh sample, while the edge surface is almost sixfold larger. ComAluminum was determined by the aluminon method4 parison of the amount of both A1 and Si extracted using a Beckman D U spectrophotometer a t 525 mp. The from the two fractions shows the ratio (at all times method was standardized against reagent grade KAl( SO&. 12H20. No account was taken of the possibility of error investigated-1,4,24 and 48 hours) to be in this due to Fe+++ extraction from the mica, but the extremely range-from two to five times as much of either elesmall iron content of the mica used would make any serious ment is extracted from the finer particles. Acid error from this source unlikely. extraction, however, seems to give consistently Silicon was determined colorimetrically as the silicomoIybdate complex, as described by Boltz and Mellon,6 except higher ratios between the two fractions than does that 10% oxalic acid was used instead of tartaric acid, and KOH. The atomic ratio of Si/Al extracted ranges measurements were made with the Beckman DU spectro- from 0.14 to 0.37 in the HC1 solution, and from 0.6 photometer at 800 mp. This procedure was standardized to 3.6 in 0.1 N KOH, for both particle size ranges. against sodium metasilicate which had been analyzed graviOn the basis of these considerations, it is temptmetrically. ing t o make certain postuIates. It seems likely Results and Discussion that acid attack occurs primarily a t the edges of Typical data, those for the extraction of AI and the particles, where the octahedral layer is exSi by 0.1 N HCI from 100-200 mesh mica, are posed, and it is this layer which is primarily atshown in Fig. 1. Similar time dependence was ob- tacked. Whether the tetrahedral layer is also served in all cases. The results at the end of 24 attacked directly by acid under the mild conditions hours for other solutions and particle sizes are sum- we have used, or merely comes into solution bemarized in Table I. cause of the destruction of its "underpinnings" reComplete solution of the 1-g. samples used mains a moot point. This conclusion is in agreewould yield 215 mg. of Si and 189 mg. of Al; in no ment with the observations on layer-type c1ays,E-8 case has more than 1%of the sample been dissolved. where adids also attack the octahedral layer most This is still, however, much more than enough to readily. saturate the ion-exchange sites of the mica.a With basic solutions, however, the attack seems Preliminary experiments (in which only A1 was de- to be directed primarily a t the tetrahedral layers. termined) also showed extraction of 50-200 pg. A1 (6) G . W. Brindley and R. F. Youell, Acta Cryst., 4 , 495 (1951). 8
48
-
Y
i 1
(4) E. B. Sandcll. "Colorimetric Determinations of Traces of Metals," Second Edition, Interscience Publishers, Inc., Now York, N. Y.,1950, p. 148 (procedure A). (5) D. F. Boltz and M. G. Mellon, Anal. Chem., 19, 873 (1947).
(7) B. B. Osthaus, "Clays and Clay Minerals," (Proc. of the Fourth Natl. Conf. on Clays and Clay Minerela), Publication No. 456, Natl. Acad. of hi.-Natl. Res. Council, p. 301 (1056). (8) G. T. Kerr, et al., ref. 7, g. 522.
ILTOTES
Oct., 1957
1441
While this can occur either at edges or on the cleavage surface, it appears that a t least a part of the reaction is at the cleavage surfaces. If this is so, however, the rate of attack by base there must be appreciably less than the rate of attack by acid at the edges. We are indebted t o Dr. E. H. Winslow for extensive suggestions and assistance with the analytical techniques used in this study.
F
LIQUID-VAPOR EQUILIBRIUM IN THE SYSTEM ACETIC ACID-PROPIONIC ACID AT 20'
El
BYSHERRIL D. CHRISTIAN
Fig. 1.-Liquid-vapor
Department of Chemistry, The Univerdty of Oklahoma, Norman, Oklahoma Reeeived May 4, 1867
In order to calcuIate the activities of components in solutions involving one or more of the aliphatic acids, it is necessary to know the equilibrium constants describing the vapor phase association, in addition to the vapor and liquid phase compositions and total pressure data. The purpose of this work was to determine the activities of both components in the system acetic acid-propionic acid as a function of concentration. This system might be expected to be nearly ideal, since the components are members of a homologous series, but t,he vapor phase association which must occur between like and unlike molecules should lead to an apparent non-ideal behavior. Experimental Liquid and vapor compositions and total vapor pressures were determined by means of a technique and apparatus which are an improvement of the method of Hansen and Mil1er.I A diagram of the apparatus is given in Fig. 1: A is a 300-ml. round-bottom flask which contains the sample, B is a thermostated bath controlled a t 20.0 & 0.02', C is mercury manometer, D a solenoid operated ground glass bleeder valve, E a tube in which vapor samples are frozen, F a three-way stopcock opening to vacuum or dry air, G a tube through which samples may be added or removed and H is a magnetic stirrer. With stirrer H running, stopcock F is opened to vacuum and bleeder valve D held open. When it appears that evacuation of foreign gases is complete, stopcock F is closed and a pressure readin taken. The stopcock is again opened, the system furtfer evacuated, the stopcock closed and a new pressure reading taken. When further evacuation produces no measurable pressure change it is assumed that the system is free of foreign gases, and the pressure is read to 2~0.02mm. with a Gaertner precision cathetometer. Valve D is closed and a Dry Ice-acetone bath is placed around tube E. Valve D is controlled with an on-off timer to open for about 1second every 10 seconds. When a sufficiently large sample has been condensed, tube E is sealed off with a hand torch and the condensate is analyzed refractometrically. Dry air is introduced into the system until atmos heric pressure is reached, and with valve D open, tube &is blown open using a hand torch. A liquid sample is removed with a pipet and analyzed refractometrically. The next solution increment is introduced through tube G, the tube is sealed, and the above process is repeated. It should be noted that in the ap aratus described the only greased valve is stopcock F. t h i s valve may easily be replaced by a mercury float valve in the case of systems which attack stopcock greases. Acids used were distilled through a 30-plate Oldershaw column a t reflux ratios in excess of 10 to 1, only middle fractions of the distillate being retained. Boiling ranges
-
(1) R. S. Hansen and F. A. Miller, THIS JOURNAL,68, 193 (1954).
UE
equilibrium apparatus.
10 E 9
z-
2 8
8 & 7
3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Fig. 2.-Total vapor pressure as a function of mole fraction of propionic acid; open circles are liquid points; solid circles are vapor points; curves are theoretical. of the fractions used were (corrected to 760 mm.); acetic acid, 118.1-118.2', pro ionic acid, 141.2-141.3'. A Bausch and LomE Precision Abbe refractometer was used for all solution analyses. Solutions of known concentration were pre ared from the pure starting materials by weight and a calitration curve of mole per cent. vs. refractometer scale readings was constructed. Scale readings were determined for the unknown solutions and mole per cent. read directly from the calibration curve.
Treatment of Data.-Experimental values of total pressure vs. mole fraction propionic acid in the liquid phase and mole fraction propionic acid in the vapor phase are plotted in Fig. 2. In order to determine the deviation of these data from ideal behavior it is necessary to know the vapor phase dimerization constants (neglecting higher polymerization constants at these low total pressures). An ideal solution is one for which fi = XiJO, where Xi is the mole fraction of component i in the liquid mixture and fi and $0 represent the fugacities of the component in a solution where it has a mole fraction Xi and in pure component i, respectively. Hansen, Miller and Christian2 have demonstrated that in a system where association occurs in the vapor phase the fugacity of each component is equal to the monomer pressure of that component, assuming that all the species formed individually obey the ideal gas law. Thus, in an ideal binary liquid mixture of components A and B which dimerize in the vapor phase (2) R. S. Hansen, 69, 391 (1955).
F. A. Miller and 8. D. Christian, THISJOURNAL
