Separation and Determination of Thorium and Aluminum CHARLES V. BANKS and R. E. EDWARDS] Iowa State College, Ames, Iowa Aluminum Chloride Solution. A stock solution, prepared from a recrystallized reagent grade aluminum salt, was standardized by precipitation with ammonia as well as by with . precipitation . . 8-quinolhol. Dimethyl Oxalate, Fisher Scientific Co., C.P. reagent. Mesitvl Oxide, The Matheson Co. Ethyl&ediaminetetraacetic Acid. d stock solution was prepared by dissolving the recrystallized free acid in deionized water d o n g with enough sodium hydroxide to raise the pH to 5 . This solution vas standardized against the above thorium nitrate solution by spectrophotometric titration and found to be 0.03956.V. The exact concentration of this solution is not required, since the same volume of this solution is used in each determination as is used in preparing the calibration curve. Chrome Azurol S (C. I. 723). The indicator solution was prepared by dissolving 0.1 gram of Chrome Azurol S in 100 ml. of water. .ill other chemicals were of reagent grade quality unless otherxise qiecified.
Methods are presented which are applicable to the accurate analysis of an occasional thorium-aluminum mixture or to the rapid and accurate analysis of many thorium-aluminum mixtures on a routine basis. The latter method involves a combination of a modified mesityl oxide extraction of thorium w-ith a unique modification of the usual spectrophotometric titration. This unique modification eliminates the construction of all but the initial calibration curve, requires only one standard solution, only one initial pH adjustment, and the measurement of one absorbance for each thorium determination. This modification would seem to he generally useful in adapting similar spectrophotometric titrations to a routine basis.
R
E C E S T L Y a simple and rapid method for analyzing thorium-aluminum mixtures was required in connection with a study of the metallurgical properties of thorium-aluminum alloys. The literature indicated that little work has been done on the analysis of such mixtures. Grundmann ( 2 ) has determined thorium in aluminum and some aluminum alloys by means of a rather long method involving the use of sodium hydroxide, henzenearsonic acid, and oxalic acid. Fritz and Ford ( f ) reported that thorium could be titrated with ethylenediaminetetraacetic acid in the presence of small quantities of aluminnin but that major quantities of aluminum must be removed. The present method consists of separating thorium from aluminum either by precipitation from homogeneous solution as the oxalate ( 5 ) ,after which it may be determined gravimetrically, or by estraction into mesityl oxide ( d ) , after which it may lie determined by spectrophotometric titration. I t was found that sufficient oxalate must be present to comple\r the aluminum as well as to precipitate the thorium. Lithium nitrate was found to serve admirably as the salting-out, agent in the extraction of thorium, thus permitting one to detcrinine aluminum in the reniaining aqueous phase. T h e proposed spectrophotometric titration for thorium eliininates the p H adjustment' as the end point, is approached. as is required \I>- the method of Fritz and Ford, and; in addition, increases the accuracy of locating the end point by eliminating the disadrsntage of subtle color changes 11-hich often accompany visual iritlicntor~. The aluminum is determined, after thorium is separated, I I:>precipitation with 8-quinolinol ( 3 ) . APPARATUS A S D REAGENTS
Spectrophotometers. A Beckman Model DU spectrophotom. eter was used for constant nyave-length studies, r h i l e absorption spectrum measurements were obtained with a Cary Model 12 spectrophotometer. Two-centimeter matched Corex absorption cells were used. Separatory Funnels. The Squibb-type 250-ml. separator\funnels were given a n inside coating with Dow Corning DC-200 silicone fluid. Thorium Nitrate Solution. A stock solution was prepared by dissolving about 23 grams of spectrographically pure thorium nitrate tetrahydrate in 1 liter of deionized water. The pH Kat: adjusted t o 1.7 with nitric acid. This solution was standardized by precipitation with dimethyl oxalate as well as Tith ammonia and found to be 0.04170M. The exact concentration of this solution must be known. Ammonium Hydroxide. Anhydrous ammonia was hubbleJ into deionized water, and the solution stored in a polyethylene bottle.
llIETIlOD I
Determination of Thorium. Thorium Can be quantitatively precipitat)ed as the oxalate in the presence of major amounts of siuminuni, provided suffirient dimethyl oxalate and oxalic arid are present to complex the aluiiiinum and react with the thorium. Determination of Aluminum. Aluminum can be conveniently precipitated from the above filtrste with 8-quinolinol after the oxalate has been destroyed h y evaporation with nitric and pprchloric acids. Recommended Procedure. The following procedure is recoinmended if only a few- thorium-aluminum mixtures are to he analyzed. The sample is prepared as s nitric acid, perchloric acid, or hydrochloric acid solution containing from 50 to 200 mg. of thorium. The volume of solution is adjusted to about 125 nil. Concentrated ammonium hydroside, free from silica, is added dropwise m-ith stirring to the appearance of a permanent turbidity, whereupon 10 ml. of concentrated hydrochloric acid is added with mixing, and the solution i p allowed to stand for 5 to 10 minutes. Dimethyl oxalate, 12 grams, is added, the solution ip placed on a low temperature hot plate, and mechanically stirred for 30 minutes. A hot osalic acid solution containing 16 grams of oxalic acid in 280 ml. of water is added, and the stirring and heat'ing are continued for another 30 minutes. The solution is cooled to room temperature, filtered through a medium porosity filter paper, and washed 10 times with a 27, oxalic acid solut,ion containing 40 ml. of concentrated hydrochloric acid per liter. The precipitate and filter paper are transferred to a porcelain crucible which has been ignited a t 1000" C. and weighed to constant weight. The filter papers are charred by gentle ignition and finally ignited to const,ant weight' a t 1000' C. The thorium is 1%-eighedas the dioxide. T h o 2 . The filtrate from the oxalate precipitation is treated with 50 ml. or' concentrated nitric acid and 50 ml. of concentrated perchloric. acid and evaporat'ed nearly to dryness. After dilution the aluniinum is precipitated with 8-quinolinol according to the procedure of Ii-nlthoff and Sandell ( 3 ) . Typical results obtained by the use of the above procedure for the separation and determination of thorium and aluminum arc summarized in Table I. IIETIIOD I1
Determination of Thorium. The fact that thorium cat1 he quantitatively extracted into mesityl oxide when aluminum nitrate is used as a salt'ing-out agent suggested the possibility of using some other salting-out agent when aluminum is also to be determined, and perhaps even for other applications where aluminum may be an undesirable interference. Thorium was found to be quantit,atively extracted into mesityl oxide from
947
ANALYTICAL CHEMISTRY
948 Table I. NO. of
Trials
Taken 0.2180 0.1090
3 3
0.6
Recovery of Thorium and Aluminum from Synthetic Samples ThOn, Gram Found, av. 0.2181 i. 0.0001 0.1093 i 0.0004
AlzOa, Gram Taken 0.1205
0.1208
Found, av. 0.1207 =t0.0002 0.1206 i 0.0001
c
0.5
-
0.4
-
4
-
-
H 503 m
I
8
point should not exceed the end point by more than about 0.7 ml. The solutions are diluted to volume and shaken well, and the absorbances are measured, just after shaking, in 2-cm. Corex cells a t 585 mp vs. a blank of distilled water. The slit width is not too critical, a setting of 0.05 to 0.08 mm. being satisfactory. The pH of each solution decreases to 2.00 f 0.05 in the vicinity of the end point, since the final volume and amount of ethylenediaminetetraacetic acid are constant. The fact that no p H adjustment is needed as the end point is approached is a distinct advantage for a rapid routine method. The sample is prepared as a nitrate solution containing from 50 t o 100 mg. of thorium. The volume of the solution is adjusted to about 20 ml. and the acidity adjusted to be 1144 nitric acid. Sixteen grams of lithium nitrate are added, the solution is warmed to effect solution, and is allowed t o cool to room temperature. This solution is vigorously shaken with 25 ml. of mesityl oxide for about 20 seconds. The extract is washed three times with 20-ml. portions of 1N nitric acid solution saturated with lithium nitrate. These washings are combined with the original aqueous phase for the determination of aluminum. The organic phase is extracted three times n-ith 20-ml. portions of distilled water, and these aqueous extracts are combined for the determination of thorium.
2 L,
a Z02-
Table 11. Recovery of Thorium and -Aluminum from Synthetic Samples
0
01 "
1
0.0 0
T h , G'ram n
I I I1 5 IO 15 M i . OF 0.04170 M THORIUM NITRATE
Figure 1. Typical titration of ethylenediaminetetraacetic acid solution with standard thorium
solutions nearly saturated 73 ith lithium nitrate, while incomplete extractions were obtained from solutions saturated with sodium nitrate. A simple, rapid, and accurate method of measuring the extracted thorium, which could at the same time be readily adapted to the routine determination of a large number of samples, was desired. The following method, in which an initial spectrophotometric titration of ethylenediaminetetraacetic acid with a standard thorium solution is used as a calibration curve for all subsequent thorium determinations, seemed to meet all these requirements. It consists simply of adding the unknown amount of thorium t o a flask containing the same quantities of ethylenediaminetetraacetic acid and indicator as were present in the initial titration, and then titrating t o a point beyond the end point with the same standard thorium solution. The total thorium corresponding to the absorbance of this solution is readily obtained from the calibration curve. From the total thorium present and the volume of the standard thorium solution added, the unknown amount of thorium is determined. This method requires only one standard solution, only one initial p H adjustment, and the measurement of a single absorbance for each thorium determination. Determination of Aluminum. Aluminum can be quantitatively precipitated from the aqueous phase with 8-quinolinol subsequent to the extraction of the thorium. Recommended Procedure. The following procedure is recommended for the rapid and accurate analysis of many thoriumaluminum mixtures on a routine basis.
A calibration curve of absorbance vs. volume of standard thorium solution, Figure 1, is prepared by transferring by pipet identical portions (15 ml. is convenient) of approximately 0.04M ethylenediaminetetraacetic acid solution ( p H about 5 ) to each of a series of 250-ml. volumetric flasks. Five milliliters of the Chrome Azurol S solution and 60 ml. of water are added to each of the above flasks. Varying amounts of the standard thorium solution are added, by buret, to each of the 250-ml. flasks. The series of solutions should correspond to a few points before the end point and several points beyond the end point. The last
Al, Gram
Taken
Found 0.0484 0.0482 0.0484 0,0484 0.0484 0.0483 0.0484 0.0483 0.0968 0.0970 0.0968 0.0965 0,0968 0.0967 0.0968 0,0966 0.1936 0.1939 0.1936 0.1938 0.1936 0.1939 0.1936 0.1936 0.1482 0.1483 0.1452 0.1464 0.1452 0.1463 0.1482 0.1454 Aluminum not determined.
Taken 0.1252 0.1252 0,1252 0.1232 0.1252 0.1252 0.1252 0.1262
0.0626 0.0626 0.0626 0 0626 0.1252 0 1252 0.1252 0.1252
Found 0.1254 0,1247 0.1262 0.1244 0.1257 0.1284 0.125;
....
0.0627 0,0626 0,0627 0,0628 0,1237 0,1252 0.1255 0.1287
The combined aqueous extracts. containing the thorium, are neutralized v ith concentrated sodium hydroxide solution to pH 1.7 & 0.1 using a pH meter. This solution is transferred to a 250-ml. volumetric flask containing the same volumes of standard ethylenediaminetetraacetic acid solution (15 ml. is convenient) and Chrome Azurol S solution ( 5 ml.) as were used in preparing the calibration curve. The excess ethylenediaminetetraacetic acid is then titrated with the standard thorium solution to a point beyond the end point as evidenced by a pronounced
Table 111.
Effect of Various Ions on Determination of Thorium" n-t.
Th Found, Gram 0 0968 0 1340 0 0989 Fe(N03)g 0 1010 n on5 n 09x4 0 001 0 0970 0 0908 0 010 0.0945 0 050 0 010 0 0969 0 010 0 0968 0 080 0 0968 0 040 0 0968 0 040 0 0968 0 040 0 0969 0 070 0 0968 0 010 0 0967 0 010 0 0964 0 010 0 0967 0 0968 0 010 0 010 0 0968 0 050 0 0968 0 2906 0 0960 0 290b 0 0872 a Each solution contained 0.0968 gram of thorium. b Weight of acid taken. Material Taken UOZ(NOB)% ZrO (NO3j 2
Element, Gram 0 040 0 025 0 003 0 010
Error,
70 0 0 +38 4 + 2 2 + 4 4 4-16 0.2 0.0 - 2.4 0.1 0.0 0.0 0.0
+ +
+ 000 ...001 -
-
0.1 0.4
0.1 0.0 0.0 0.0 0.2 9.9
V O L U M E 27, N O . 6, J U N E 1 9 5 5 purple color. I n general, one should not exceed the end point by more than 0.4 ml. This solution is diluted to volume, and its absorbance determined in the same manner as for the solutions used in preparing the calibration curve. The total thorium corresponding t o this observed absorbance is read from the calibration curve. From the total thorium present and the amount of thorium added as standard thorium solution, the amount of extracted thorium ip determined: Grams of T h = Thtotat - 0.23218J4 nhere V is milliliters used and M is the molarity of the standard thorium solution. Typical results obtained by Method I1 on synthetic samples are reported in Table 11. Interferences. It 4 as felt that the mesityl oxide extraction of thorium with lithium nitrate as thP salting-out agent might be useful in procedures other than the one described above, and for this reason an interference study was made. .I group of cations and two anions m-ere investigated as t o their interference in the determination of thorium by the recommended extraction-spectrophotometric titration procedure. The results of this study are shown in Table I11 and indicate strong interference from zirconium, iron, tin, and phosphate. Other anions which form stable complexes with thorium or which form insoluble compounds v, ith thorium would also be expected to interfere. Qualitative tests indicated that uranium(T'1) s-as probably eytracted quantitatively, that zirconium was about 25% eytracted and that iron(II1) vas about 10% extracted.
949 APPLICATIONS
Method I serves very satisfactorily for the analysis of an occasional thorium-aluminum alloy. Method I1 seems t o be ideally suited for the anal!-sis of many thorium-aluminum allol-s on a routine basis. The method is rapid, as it requires only one standard solution, only one initial pH adjustment, and the measurement of a single absorbance for each thorium determination. The method is accurate, as the final measurement is made spectrophotometrically rather than visually. This modification of the usual spectrophotometric titration should be very useful in adapting many other spectrophotometric titrations to a routine basis, as it eliminates the construction of all but the initial calibration curve. LITERATURE CITED
Fritz, J. S.,and Ford, J. J., AXAL.CHEM.,25, 1 6 4 0 (1953). Grundmann, H., Alz~minium,24, 105 (1942). Kolthoff, I. AI., and Sandell, E. B.. "Textbook of Quantitative Inorganic .halysis," pp. 326-7, l\lacmillan. S e w Pork, 1948. Levine, H., and Grimaldi, F. S., U. S. Atomic Energy Comm. Rept. AECD-3186 (1950). Willard, H. H., and Gordon, L., h n ~ CHEM., . 20, 1 6 5 (1945). RECEIVED for rerieiv August 2 7 , 1954. Accepted February 10, 1955. Based in part on a dissertation submitted b y R . E. Edwards in partial fulfillment of the requirements for the degree of master of science, Iowa State College, h i e s , Iowa, August 1953. Contribution S o . 372 from t h e Institute for Atomic Research and Department of Chemistry. Iowa State College, Arnes, Ioxra. Work was performed in the d m e s Laboratory of the Atomic Energy Commission.
Determination of Total Sulfur Content of Sedimentary Rocks by a Combustion Method MAYNARD E. COLLER and RICHARD K. LElNlNGER Geological Survey,
lndiana D e p a r t m e n t of Conservation, Bloomington, Ind.
Total sulfur has been determined in common sedimentary rocks b y a combustion method. Sulfur contents range from 0.001 to 5.0%. Experiments show that the combustion method can be used in analyzing sedimentary rocks in which sulfur is present as sulfide, sulfate, or both. Pulverized samples from 0.100 to 0.500 pram in weight are used in this method. Each sample is placed in a No. 6 Leco combustion boat and covered with t w o fluxes: 0.50 gram of standard ingot iron and approximately 1.0 gram of 30-mesh granular tin. The boat with sample then is placed in the combustion tube of a Burrell L-nit Package AIodel T29A tube furnace which is controlled at a temperature of 1310" to 1320" C. After the sample has been heated for 1 minute, oxygen is admitted at a rate of about 1 liter per minute. The sulfur dioxide formed is absorbed in a starch solution and is titrated with standard potassium iodate in a Leco sulfur determinator. Thirteen values obtained for National Bureau of Standards standard sample la, argillaceous limestone, range from 0.273 to 0.2i6y0 sulfur (certificate value 0.27 % by calculation),
S
I X C E 1947 the Indiana Geological Survey has made a study of the limestone and dolomite resources of Indiana and has collected many samples for analysis. Because the sulfur content of limestone is specified for many commercial uses, the development of a rapid method for its determination became de&able. The survey has also sampled many clays and shales;
the sulfur content of these materials is important because of the adverse effects of sulfur during firing or glazing of ceramic wares. The classical wet methods for sulfur, as mentioned by Hillebrand and Lundell (3) and as found in the book of -4STLI standards ( 1 ) . were too long and time-consuming since they depended upon the weighing of sulfur as barium sulfate. Combustion methods found in the literature ( 2 ) were primarily for use on steel or other metals. The Laboratory Equipment Corp. ( 4 ) had distributed instructions for the use of its sulfur apparatus, but no methods were found for nonmetallic compounds. The rapidity of the combustion method was so advantageous that the adaptation of this type of procedure to sedimentary rocks was attempted. PRELIMIXARY INVESTIGATION
An investigation of the temperature of combustion showed that 1310" to 1320" C. gave the most uniform factor, and was the easiest temperature with which to rvork-Le., there was less strain on the eyes when placing the boat in the tube and when extracting it, and there seemed to be less danger of the molten sample cutting through the boat and causing damage to the tube and its liner. Other temperatures tried were 1260") 1385", and 1425 C. rln attempt was made to obtain fusion of the sample using no fluxing material. The fusions mere sporadic and mostly incomplete, giving a wide variation in the factors obtained. Granulated tin ( 5 ) and copper strip ( d , 4 ) were tried as fluxes, but the time consumed in the determination )!as so variable as t o cause indecision as t o the completeness of the determination,
