842
ANALYTICAL CHEMISTRY
as by the Karl Fischer titration or by a materials balance on the reaction. Complete cross-comparisons for each of several mixtures by all the available methods showed that when by-products appeared discrepancies were evident on application of any one of the single check methods represented in Table 111. ACKNOWLEDGMENT
The support of a generous grant from the Research Corp. is gratefully acknowledged. Appreciation is due George J. Stockburger, who made some of the experimental measurements. LITERATURE CITED
(1) Bates, F. J., Natl. Bur. Standards, Circ. C440, 671 (1942). (2) Batscha, J., and Reanek, S., J . Assoc. Ofic. Agr. Chemists, 20, 107 (1937). (3) Bennett, C. T., and Garratt, D. C., Perfumery and Essentl. Oil Record, 16,18 (1925); International Critical Tables, Vol,. VII, p. 68, New York, McGraw-Hill Book Co., 1930. (4) Bingham, E. C., and Jackson, R. E., B u r . Standards Bull., 14, 59 (1919). (5) Brunel, R. F., J . Am. Chem. SOC.,45, 1334 (1923). (6) Carr, C., and Riddick, J. A., I n d . Eng. Chem., 43, 692 (1951). (7) Dorosaewskii, A. G., and Dworsancayk. S. V., Tables annuelles internationales de constantes e t donnkes nurneriques, Vol. 11, p. 756, Paris, 1913; International Critical Tables, Val. VII. p. 68, New York, McGraw-Hill Book Co., 1930. (8) Driesbach, R. R., and Nartin, R. A,, I n d . Eng. Chem., 41, 2875 (1949).
(9) Frere, F. J., Ibid., p. 2365. (10) International Critical Tables, Vol. 111, p. 120, New York, McGraw-Hill Book Co., 1930. (11) Kretschmer, C. B., and Wiebe, R., J . Am. Chem. Soc., 74, 1276 (1952). (12) Langdon, W. M., and Keyes, D. B., I d . Eng. Chem., 35, 459 (1943). (13) Lebo, R. B., J . Am. Chem. SOC.,43, 1005 (1921). (14) -Miller, H. C., and Bliss, H., I n d . E n g . Chem., 32, 123 (1940). (15) Olsen, A. L., and Washburn, E. R., J . Am. Chem. SOC.,57, 303 (1935). (16) Olsen, A. L., and Washburn, E. R., J . Phys. Chem., 42, 275 (1938). (17) Parks, G. S., and Kelley, K. K., Ibid., 29, 727 (1925). (18) Perry, J. H., “Chemical Engineers’ Handbook,” 3rd ed., p. 191, New York, McGraw-Hill Book Co., 1950. (19) Schurnacher, J. E., and Hunt, H., I n d . Eng. Chern., 34, 701 (1942). (20) Snyder, H. B., and Gilbert, E. C., Ibid., 34, 1519 (1942). (21) Timmermans, J., and Delacourt, Y., J . chim. phys., 31, 105 (1934). (22) Trew, V. C. G., and Watkins, G. M. C., Trans. Faraday Soc., 29, 1310 (1933). (23) Vogel, A. I., J . Chem. Soc., 1948, 616. (24) Washburn, E. R., Brockway, C. E., Graham, C. L., and Deming. P., J . Am. Chem. Soc., 64, 1886 (1942). (25) Whitman, J. L., and Hurt, D. M., Ibid., 52, 4762 (1930). (26) Wilson, A., and Simons, E. L., I n d . Eng. Chem., 44, 2214 (1952). RECEIVED for review November 16, 1953.
Accepted February 3, 1954.
Distribution of Strontium within Barium Sulfate Precipitated from Homogeneous Solution LOUIS GORDON, CARL C. REIMER’, and BENJAMIN P. BURTT Department of Chemistry, Syracuse University, Syracuse 70,
The coprecipitation of strontium with barium sulfate is reported. Fractions of the carrier were precipitated from homogeneous solution by the hydrolysis of methyl sulfate in methanol-water medium. Residual barium was determined by a complexometric titration procedure using tetrasodium ethylenediamine tetraacetate as titrant. Strontium measurements were made using an equilibrium mixture of strontium-90 and daughter yttrium-90; Kirby’s equation was used for the interpretation of all counting rates. Evidence is presented for the existence of a supersaturated condition during the initial stages of the precipitation. A comparison of the conventional precipitation procedure with the homogeneous method indicates that the latter more nearly approaches equilibrium formation of the carrier compound. Over initial barium to strontium concentration ratios of 1.3 to 2700, strontium appears to be heterogeneouslydistributed throughout the solid phase; the heterogeneous distribution coefficient, A, in the Doerner-Hoskins equation was found to be 0.030 0.004 at 83”. This investigation emphasizes the problems involved in obtaining results in studies of this type of derichment system.
+
N. Y.
In 1926, Hahn (1.2)pointed out that “an element will only be precipitated from dilute solutions with a crystalline precipitate if it is bound with the crystal structure of the precipitate so that mixed crystals can form.” Later Hahn (11) classified carrying processes under several general headings including coprecipitation via isomorphous or isodimorphous replacement, adsorption, and internal adsorption. The distribution of a trace ion incorporated into host lattices usually conforms to either of two limiting laws. The first, describing the homogeneous distribution of a tracer ion within the solid carrier compound, is the familiar Berthelot-Kernst distribution law for the equilibrium partition of a solute between two immiscible phases. This law has been expressed by Henderson and Kracek ( I S )in a related form ( 3 )which permits the direct use of measured quantities of the tracer and carrier materials:
(?er) =D(%) carrier carrier solid
solution
This distribution law is assumed to be valid for the case where the ions in solution are in equilibrium with all of the ions in the entire solid phase. A heterogeneous distribution law was derived by Doerner and Hoskins ( 5 )for use in a study of the coprecipitation of radium in barium sulfate:
W
H E N an ion is separated from solution in the form of an insoluble salt, foreign ions are invariably removed as well. The term “coprecipitation” is used here to represent the simultaneous deposition of normally soluble foreign substances with a precipitate. 1
Present address, E. I. du Pont de Nemours & Co., Waynesboro, Va.
Doerner and Hoskins expected that this logarithmic distribution law would hold for any isomorphic salts formed by two similar elements with a common ion under experimental conditions
V O L U M E 26, NO, 5, M A Y 1 9 5 4 where each crystal layer, when formed, was in equilibrium with the solution at that time. Diffusion within the solid phase was discounted. I n enrichment systems, where A is greater than 1, the tracer would be found concentrated in the center of the crystallites with progressively smaller amounts found nearer the periphery of the crystals. I n derichment systems, where A is less than 1, the reverse is expected. A moderate number of salt systems have been studied to determine the distribution coefficient of the tracer ion chosen. Riehl(22), Chlopin ( 4 ) ,and Bonner and Kahn ( 3 ) have published reviews of distribution studies. Few distribution studies have been made using insoluble salts as carrier compounds. Merkulova (19) has studied the radiumbarium chromate, radium-lead sulfate, and radium-barium sulfate systems. In each case it was concluded that the tracer was homogeneously distributed throughout the carrier compound. Henderson and Kracek (13) and Salutsky et al. (24) have also studied the radium-barium chromate system. The latter workers found the tracer ion to be heterogeneously distributed throughout barium chromate which was precipitated from homogeneous solution.
24
40
.$E?
50
843 The filtering tube was made of 2-mm. bore borosilicate glass capillary tubing, the lower end of which was fitted with a Corning filter having a filtering area of about 28 sq. cm. Samplers similar to E in the figure were also constructed of borosilicate glass. Container C was graduated a t 10-ml. intervals from 100 to 160 ml. and a reference line was marked on the sampler tube as shown. These samplers were calibrated a t the reaction temperature. In each of the experimental runs approximately one fifth of the supernatant liquid was removed for analysis. Portions of this sample were analyzed for residual barium and strontium content.The constant temDerature bath was controlled to 5 0 . 3 ” C. Radiochemical Equipment. All measurements of strontium-90 were made with an end, mica-window Geiger-Muller tube connected to an appropriate scaling circuit. Chemicals. Except where otherwise noted, C.P. Baker’s analyzed chemicals were used without further purification. All barium solutions were prepared from barium chloride dihydrate which had been recrystallized twice from water. Standard solutions of barium and strontium were prepared by dissolving the purified barium salt or strontium chloride hexahydrate, respectively, in distilled water. The concentrations of these solutions were determined by evaporating a known volume in a platinum dish in the presence of a slight excess of sulfuric acid, igniting to constant weight - a t 800’ C., and weighing the precipaated sulfate. Methyl sulfate, Baker and Adamson Chemical Co., was purified by distillation, the fraction boiling between 186’ and 189’ C. being collected. All active solutions were prepared using carrier-free strontium90. -411 stock “hot” solutions were prepared with inactive standard strontium solutions. -
I
PRECIPITATION OF BARIUM SULFATE FROM HOMOGENEOUS SOLUTION
Elving and Van Atta’s procedure (6) for the precipitation of barium sulfate from homogeneous solution was modified so that it could be used in this distribution study. This method utilizes the slow hydrolysis of methyl sulfate in 20% methanoI-SO% water medium. Preliminary studies showed that approximately 0.4 to 0.8 mi. of methyl sulfate in a total volume of 150 ml. of the alcohol-water solution would cause the precipitation of appreciable fractions of 150 mg. of barium in from 8 to 12 hours. With this slow precipitation rate, liquid samples could be removed during the run, cooled, and diluted without any further observable precipitation. ANALYTICAL METHODS
Figure 1. Reaction Vessel and Sampler
This paper reports a study of the distribution of strontium between solution phase and barium sulfate using the technique of precipitation from homogeneous solution (9, 26) to allow slow precipitation of the solid phase. The barium-strontium sulfate system was chosen for two reasons. First, crystallographic evidence indicates isomorphism; Grahmann ( 1 0 ) and Bolton and Kelley (2) have reported that these salts form solid solutions. Secondly, the availability of strontium-90 facilitated the analytical measurements.
Barium. All residual barium determinations were made using essentially the titration procedure of Manns et al. (17), which is a modification of the Schwarzenbach (1)water-hardness titration procedure. Since the chelating agent, tetrasodium ethylenediamine tetraacetate, complexes both barium and strontium, each titration yielded the combined residual strontium and barium contents in the supernatant sample. Residual strontium concentrations were determined radiochemically; thus, the small volumes of titrant required for strontium chelation could be subtracted from the total volume used in a given titration. The remaining volume of tetrasodium ethylendiaminetetraacetate was ascribed to barium content. Strontium. Strontium measurements were made radiochemically using strontium-90 obtained from the Atomic Energy Commission. This nuclide does not disintegrate directly to a stable product but has a radioactive daughter:
APPARATUS AND MATERIALS
Reaction Equipment. This was designed so that known fractions of the supernatant liquid could be withdrawn a t constant temperature through a frit. A typical reaction vessel is shown in Figure 1. It contained a working volume of about 180 ml. and was provided with the various features as shown. The reaction vessel consisted of two sections, B and C. A small water-cooled condenser could be inserted a t A to maintain constant solution volume. Stirring could be provided when required by inserting a glass rod through the condenser. Samples were withdrawn through the filtering tube, D, into sampler, E.
Sr90t
~ =j 25 ~ years0.6 m.e.v. P -
ysot l j 2 = 65 hours 2.2 m.e.v. p -
,Zr$o(stable)
Strontium could not be measured preferentially because of the presence of active daughter. However, a useful solution to this type of mother-daughter activity problem has been published by Kirby (16), who describes a method for the determination of tracers in the presence of their active daughters. This method was used in the present work
844
ANALYTICAL CHEMISTRY
small fractions of precipitated barium sulfate. ill1 other experiments reported in Tables 111, IV, and V were conLength ducted nith stirring throughout the Precip- Sr PrecipTime of Run, Initial Initial Sr ++, Ba Ba-7, hip. hlg. itated, Sr, itated, Stirred, % Hours X D entire run except as otherwise noted 204.0 4.91 21.5 7.4 29 6 0 31 0.29 Large fractions of barium sulfate weie 173.4 4.91 18.2 6.3 40 5 0.28 0.26 204.0 4.91 24.2 6.6 40 7 0 24 precipitated in the experiments listed in 0.22 122.4 4 91 33.8 4.9 ?IO 6 0.12 0.10 Table IV. I n some of these, the solua T = 83' C. tions were stirred only for the first 5 minutes. I t was anticipated that these Table 11. Effect of Stirring Reaction Mixture during Entire Precipitation Period" would show increased coprecipitation of strontium over similar experiments Xet Counting Rate *kpparent % Initial Ba ++, Initial S r + + , Ba * - Precip- Time of Sample, Count standard, Strontiuni with stirring. ;ilthough several of the hlg. XIg. itated, "0 Run, Hrs. counts/min. counts/min. Carried experiments (cf. 5b and 6, l l b and 8, 183,F 6.98 20.9 5.6 6015 5949 -1.1 102.0 48.7 38 9 5.3 602 1 5975 -0.7 13b and 15) show greater strontium 174.2 2.00 49,s 8.5 4430 4414 -0.3 coprecipitation for the unstirred runs, 174.2 2 00 86.3 6 0 4457 4414 -0.9 174.2 2 00 28 2 4 4 4487 4440 -1.0 the distribution constants for the latter a T = 83' C. are in general agreement with those obtained where stirring was provided. From this it might be concluded that I t was empirically found that the corrections for self-absorption the strontium carried by the initial fractions of precipitated were negligible. barium sulfate was ultimately ejected from the solid ph:ise through some exchange process. EXPERIMENTAL PROCEDURE LahIer and Dinegar (16) have made a quantitative study of the supersaturation of barium sulfate under conditions in which the For each precipitation eyperiment the following procedure was precipitating ion was generated homogeneously within the followed : reaction solution. They concluded that the equilibrium value for the solubility of barium sulfate was exceeded approximately Appropriate volumes of the standard barium and the stock hot strontium ion solutions were placed in the reaction vessel. twentyfold before precipitation occurred. The data in Table I After the addition of 30 ml. of methanol and dilution to about support the observations of 1,aPller and Dinegar-Le., the pres150 ml. with distilled water, a small measured volume of methyl ence of a supersaturated condition even in the controlled type of sulfate was added to the cell. The reaction vessel was then precipitation used here thermostated in the bath; stirring was provided except where otherwise noted. After a known reaction time, the volume of Distribution Obtained Using Conventional Barium Sulfate solution in the reaction vessel was recorded and a sample of the Precipitation Method. The procedure paralleled that presupernatant liquid was removed. After cooling, this sample was viously described. Known volumes of the standard barium and quantitatively transferred to a 50-ml. volumetric flask and diluted strontium ion solutions were placed in the reaction vessel and to volume. A 40-ml. portion of this solution was removed and titrated for residual barium and strontium content. Four 1-ml. diluted to approximately 140 ml. with distilled water; methanol portions of the diluted sample were removed and dispensed into was not added. The reaction vessel was then thermostated. specimen vials where they were evaporated for subsequent After temperature equilibrium R as established, a 10- to 15-nd. counting. solution containing about 1.2 millimoles of sulfuric acid was slowly Comparison counting standards were similarly prepared from solutions containing known amounts of the equilibrium stronadded to the cell contents. During the careful addition of this tium-9Gyttrium-90 mixture. The counting rate and the Kirby precipitating agent, the reaction mixture was vigorously agitated. equation (15) were used to calculate the residual strontium in the The stirring was terminated several minutes after all of the SUIsolution after making appropriate volume corrections. From a furic acid solution had been added. knowledge of the fraction of total reaction solution analyzed for barium content and the value obtained from this titration, the residual amounts of barium could be calculated. From the initial and final amounts of barium and strontium in the reaction Table 111. Strontium Distribution within Barium Sulfate solution, calculations were made of the distribution coefficients, Precipitated from IIeterogeneous Solution The data are given in Tables I through V. D and A. Time of Table I.
Relationship between Stirring Time and Amount of Strontium Coprecipitateda + +
Ba +a Preoipitated, %
Sr + b Preoipitated, %
78.4 76.9 75.3 76.6 77.2
12.0 13.8 13.9 15.3 20.6
+
RESULTS AND DISCUSSION
Effect of Stirring on Coprecipitation of Strontium with Barium Sulfate Precipitated from Homogeneous Solution. For the initial coprecipitation studies, stirring was allowed until some time after nucleation had taken place. After a moderate amount of the carrier compound had precipitated, stirring was discontinued. Some hours later, after additional precipitation had occurred, a sample of the supernatant solution was removed and analyzed. I n each of these experiments 0.6 ml. of methyl sulfate was added. The several runs are summarized in Table I; the data indicate a striking parallel between the amount of strontium coprecipitated and the amount of agitation used. With these small fractions of precipitated barium sulfate, less strontium was carried with longer stirring periods. The results show, a others have found, that the distribution coefficient is dependent upon experimental conditions. Later, a number of runs were conducted with stirring throughout the complete precipitation period. These results, given in Table 11, show negligible strontium coprecipitation in the case of
a
b
+
Digestion, Hours 0 1 15 40
0 0 , .j
h
D
0.083 0.10 0.11 0.12 0 16
0.038 0.048
0.053 0.068 0 077
Initial BE'+ 174.2 mu. Initial Sr +,'2.00mg.= +
I n the several experiments conducted, the separated solid was allowed to digest in the mother liquor for varying periods of time before samples were removed for analysis. The results of this series of heterogeneous precipitation runs are summarized in Table 111. Because of the well-known disadvantages of conventional precipitation methods, one would expect the resulting distribution coefficients to reflect B nonequilibrium partition of the microcomponent. A comparison of the data of Tables I11 and I V indicates the marked inferiority of the heterogeneous precipitation. Because the strontium precipitated in the experiments in Table
V O L U M E 2 6 , N O . 5, M A Y 1 9 5 4 .
~
...
~
~
845
~
in runs where 0.6 or 0.8 ml. of methyl sulfate was used, it is evident that the use of 1.0 ml. of methyl sulfate caused a \ l e thy1 Initial +Moles + Sulfate ~i~~ of sr*+ noticeablc decrease in the several con---Ba..-.-.~Used, Run, Carried, PrecipiInitial Initial stants obtained. Larger amounts of R u n Ra+', hlg Sr'+, 116'. 1Ioles S r f t XI1. Hours 70 tsted, Yo X D barium were present. 1 102.0 48.7 1.3 8 0.6 3.0 57.5 0.035 0 023 2 102.0 48.7 1.3 0.6 10 3.8 70.1 0.032 0.017 I t is apparently difficult correctly to 3 102.0 48.7 1.3 0.6 9.25 4.6 72.0 0.037 0.019 4b 290.3 2.00 94 1.0 12.25 2.5 73.4 0.019 0.0094 predict the cffcct of an increase in the 5b 174.2 0.0400 2700 10.25 0.8 5.1 78.2 0.034 0.015 precipitation rate on the value of the ti 174.2 0.0400 2700 0.8 10 3.7 79.2 0.024 0.010 7 102.0 48.7 1.3 0.6 12 4.0 82.2 0.024 0.0091 distribution coefficient. While some 8 174.2 2.00 56 0.8 12 3.6 82.9 0.021 0.0077 9 173.4 2.00 56 0.8 11.5 5,2 84.1 0.029 0.010 authors (5,WS) have reported that an in10 174.2 0.0400 2700 0.8 11.5 5.4 84.5 0,030 0.010 creased precipitation rate causes a de174.2 Ilb 2.00 56 0.8 12 6.9 87.0 0,035 0.011 12 153.0 4.00 24 0.8 10 4.7 88.5 0.022 0.0065 crease in the constant (for an enrichmcnt 290.3 61 6 3.0 1.0 14 136 3.6 88.8 0.017 0.0048 102.0 48.7 1.3 0.6 12 5.7 89.5 O.O~F, 0.0071 system), llunibrauer (20) found the 290.3 61.6 3.0 15.25 3.6 94.4 o.013 0.0022 reverse to be the case. However, there T = 83OC. is an inconsistency between the results b Stirred only for first 5 minutes. . ~. .~ .~ ~- obtained in Table V using 1.0 ml. of methyl sulfate and the values for strontium carried in Table I11 in the I11 was deposited a t a coniparativel!. rapid rate, it was espected heterogeneous precipitation experiments. It can be seen in the that, prolonged digestion might effwt some purification of the latter table that thcsc rapid precipitations caused relatively solid phase. Over the 60-hour digestion period (Table 111) it is large amounts of strontium to be carried; here the distribution seen that the amount of strontium coprecipitated continually incoefficients are abnormally lnrgc. It is reasonable to cxpect creased with digestion rather than decreased. This agrees with these constants t,o be larger than those obtained from homothe qualitative observations of Fischer ( 7 ) who concluded from an gencous precipitations, since the system is not permitted to beelectron microscopy study that aging of barium sulfate crystals in come dcrichcd in strontium in an cquilibrium manner during the contact with mother liquid docs not cause any apparent drgree of format,ion of the carrier compound. Accordingly, it follows that prrfection of these crystals. thc constants ohtained from the experiments using 1.0 nil. of Precipitation from Homogeneous Solution. As thc studies in methyl sulfate should be, if anything, larger than the others Table 11 showed that the amount of st'rontium coprecipitated listed in Table V. This does not occur; it is difficult to explain with the initial fract,ions of the precipitated barium sulfate was thcse observations logically. negligible, precipitat,ion experiment.s were conducted in which -large fractions of the carrier compound were separated. In Table V. Relationships between Distribution Coefficients these experiments the initial concentration ratio of barium to and R~~~ of precipitationOin strontium Distribution strontium was varied as well as the amount of methyl sulfate. Initial Here the data are arranged Moles Bat+. T h r results are shown in Table IT'. Methyl Preoipii n the order of increasing fraction of carrier compound precipiMoles Sulfate tated, rated, without regard for the initial concentration ratio of harium S r + + L-sed, ,111. X D Sr, 1.3 0.6 0.03,j 0 053 57.5 t o strontium or the amount of methyl sulfate used. 0.032 0.011 70.1 0.037 0 019 72.0 In Table \', however, these same data are arranged to shoiv the 0.024 0.009 82.2 rcmlationship between the initial barium to strontium conccntra0.020 0,007 89.5 Av. 0.031 =t ,005 0 , 0 1 5 5 ,006 tion ratio, the rate of precipitation of barium sulfate, and thc dis24 0.8 0.022 0.0065 88.5 tribution coefficients A and D. The interpretation of the data 56 0 8 0.021 0.0077 82.9 shown in Tables IV and V is somewhat difficult because of the ah0.029 0.010 84 1 0.03.ih 0 Ollh 87 0 wncr of a clearly defined trend in eit,licr of the calculated distriAv. 0 . 0 2 8 * 005 0.0096 i. ,001 Iiution constants with changes in the fraction of barium sulfate 2700 0.8 0 034b O.Ol5b i8.2 0,024 0.010 79.2 prrcipitated. Xormally, if the Docrncr-Hoskins law is followed 0.030 0 010 84.5 h y a particular system, the valucs of X should be independent of A r . 0.029 * 001 0.012 * ,002 thr amount of carricr prrcipitated nhilc the homogeneous coeffi94 1 0 O.01Qb 0.00946 73.4 cicmts should vary. 3 0.Olib 0.0048b 88.8 3 0.013 0.0022 94.4 The data in Tables 11-and \~-orcobtained with solutions havAv. 0.016 + ,001 0 0055 3z ,003 iiig a aide range of initial conccntration ratios of barium t o strona T = 83' C. tium. According to the views of Docrner and Hoskins, if the Only for the minutes' trarib component can be isomorphous1.v incorporated within the Of all the rcsults shown in Table T', the most striking variation cairit'i compound lattice, thc system should show constancy of in Coefficient with change in the fraction of barium sulfate precipthv distribution coefficient even if thc solubility product of the itated is seen in the group of five runs performed on solutions tracer compound is cxcecdcd. Furthermore, these investigators having an initial barium to strontium concentration ratio of 1.3. bclieved that, while mixed crystal formation would occur if the Here the D values decrease, with increased fraction of carrier presolubility product of the tracer compound wst9 exceeded, precipicipitated while thc corresponding X values show no such marked tation from solutions of niodcratelv large concentrations could change. The data tend to show that the strontium distribution not he expected to obey their law. In the present investigation, within the solid phase is in accord with the Doerner-Hoskins tho solubility product of the tracrr compound was not exceedcd law. nhrrc an initial barium to strontium concentration ratio of 2700 It is significant that most reports on distribution studiee decxisttd. However, the coefficicnts for these experiments agree scribe enrichment-type systems. It was probably fortuitous n-ith others where larger initial strontium concentrations were that radium was used in many of the original distribution studies. uwd. The solubility of most radium salts is such that an enrichnicnt of Thc data as arranged in Table T shoa the effect of changes in radium within the chosen carrier compounds was permitted. tlic rate of formation of the carrier compound on the value of the Many more experimental difficulties can be expected in studies on coeffirients. While sensibly identical coefficients were obtained
Table Iv.
Relationship between Distribution Coefficients and Fraction of Carrier Precipitateda in Strontium Distribution
:: 0
~~
~
~~
~
~
~
~~
-Bc
ANALYTICAL CHEMISTRY
846
the distribution of a compound within a more insoluble solid as exemplified by the present study. By taking as the most representative values, those distribution coefficients obtained from runs in which 0.6 or 0.8 ml. of methyl sulfate was used, an average value of X = 0.030 5 0.004 is obtained. A number of authors (8, 21,25) have suggested that a relationship exists between solubilities and distribution coefficients. While solubility data are not available for barium and strontium sulfate in an ionic environment such as the methanol-water medium used here, the aqueous solubilities of these sulfates, as a function of temperature, are available (14, 18). From these data, the solubility products a t 83” C. were calculated to be 2.5 x 10-10 for barium sulfate and 8.8 X lo-’ for strontium sulfate. The solubilities of barium sulfate and strontium sulfate, in moles per 100 ml., are 1.6 X and 9.4 X 10-6, respectively. It is seen that the ratio of the solubility products, 2.8 X differs from the observed heterogeneous distribution coefficients by a factor of approximately 100. The ratio of solubilities, 0.017, on the other hand is a t least of the same order of magnitude as the distribution coefficient experimentally obtained. Actually, with the exception of the radium-barium sulfate system, there is little evidence for the existence of a simple relationship between the solubility ratio of salts and the observed distribution coefficients. CONCLUSIONS
A study of the distribution of strontium between the liquid phase and barium sulfate precipitated by several methods has shown that a homogeneous precipitation method more nearly approaches equilibrium formation of barium sulfate than does the conventional sulfate precipitation method. Strontium sulfate-barium sulfate in 20% methan01-80% water medium was observed to be a derichment system in which the strontium appears to be heterogeneously distributed throughout the solid phase. At 83” C., for initial barium t o strontium concentration ratios varying from 1.3 to 2700, the logarithmic distribution coefficient was found to be 0.030 i 0.004. Derichment systems of this type present many more experimental difficulties than do enrichment systems.
ACKNOWLEDGMENT
The authors are indebted to H. W. Kirby, Mound Laboratory, Monsanto Chemical Co., for his assistance during the radiochemical investigations. LITERATURE CITED
Biedermann, W., and Schwarzenbach, G., C h i m i a , 2, 56 (1948). Bolton, B., and Kelley, W., M.S. thesis, Syracuse University, 1947.
Banner, H. A., and Kahn, M., Nucleonics, 8, No. 2 , 4 6 (1951). Chlopin, V., Trav. inst. &at r a d i u m (U.S.S.R.),4 , 3 4 (1938). Downer, H., and Hoskins, W., J . Am. Chem. SOC.,47, 662 (1925).
Elving, P., and Van A t t s , R., ANAL.CHEM.,22,1375 (1950). Fischer, R., Ibid., 23, 1667 (1951). Flood, H., 2. anorg. u. allgem. Chem., 229,76 (1936). Gordon, L., . ~ N A L .CHEM.,24,459 (1952). Grahmann, W., Y e u e s Jahrb. Mineral. Geol., 1, 1 (1920). Hahn, O., “Applied Radiochemistry,” Ithaca, Cornell University Press, 1936. Hahn, O., Ber., 59B, 2014 (1926). Henderson, L., and Kracek, F., J . Am. Chem. Soc., 49, 738 (1927).
International Critical Tables, Val. 6, p. 256, New York, McGraw-Hill Book Co., 1929. Kirby, H., A N ~ LCHEY., . 24, 1678 (1952). LaLIer, V., and Dinegar, R., J . Am. Chem. Soc., 73, 380 (1951). RIanns, T., et aZ., ANAL.CHEM.,24, 908 (1952). Mellor, “Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 3, London, Longmans, Green and Co., 1923. JIerkulova, XI.,Tral;. inst. Btat r a d i u m (U.S.S.R.), 3, 141 (1937).
ilIumbrauer, R., 2. physik. Chem., A156, 113 (1931). Ratner. A, J . Chem. P h y s . , 1,789 (1933). Riehl, K.,2. p h y s i k . Chem., A177, 224 (1936). Riehl, N., and Kading, H., Ibmd., A149, 180 (1930). Salutsky, lI.,Stites, J. G., and Martin, A. W., ANAL.CHEM., 25, 1677 (1953).
Shulyatikov, B., J . P h y s . Chem. (U.S.S.R.),21,975 (1947). Willard, E., ASAL CHEM., 22, 1372 (1950). RECEIVED for review August 22. 1953. Accepted February 19, 1954. Abstracted from the thesis submitted by Carl C. Reimor to the Graduate School of Syracuse University in partial fulfillment of the requirements for the degree of doctor of philosophy, July 1953. Study supported in part by g r a n a from the Btomic Energy Commission and from the Research Corp. One of the authors (C.C.R.) was the holder of 8 Charles A. Coffin Fellowship (General Electric Co.) in 1951-52 and the Procter and Gamble Fellowship in 1952-53.
Recrystallization of Barium Sulfate from Fused Salts MORRIS GALLANT, GEORGE J. SCHMITT, and JOSEPH STEIGMAN Department o f Chemistry, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. The usual method for sulfate determination consists of the precipitation of the barium salt. The latter strongly coprecipitates many ions, and most variations of the method rely upon either counterbalancing errors or empirical weight calibrations. This investigation has shown that when appropriate precautions are taken, coprecipitated sodium and chloride ions can be quantitatively removed by one fusion of the original precipitate with alkali chlorides, allowing it to resolidify, leaching with barium chloride solution, washing, filtering, and igniting. The necessary precautions include the purification of the alkali chlorides and barium chloride and the use of an excess of barium chloride in the solution used for washing the recrystallized precipitate. The procedure is shown to be applicable to the determination of sulfate in the presence of a large excess of sodium chloride. On the other hand, nitrate is much
more difficult to remove by this procedure. The extremely strong tendency of this ion to form solid solutions in barium sulfate is demonstrated by introducing it into the precipitate from an alkali chloride melt.
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NE of the important inorganic analyses is the estimation of soluble sulfates. The most widely used method is the precipitation of the insoluble barium salt and its gravimetric determination. In many situations the accuracy is poor. Other gravimetric methods have been proposed, such as the precipitation of the lead, benzidine, or complex cobalt sulfates. These compounds, while free from certain disadvantages of the barium salt, are in general too soluble for many applications. The overwhelming bulk of sulfate analyses is still performed by precipitating, igniting, and weighing the barium salt. There are many researches in the literature, too numerous t o
