1988
A N A L Y T I C A L CHEMISTRY
hydrochloric acid method and those by the proposed method is believed to be due to glucuronide-containing hemicelluloses. Pectic substances can be extracted from fruits with dilute hydrochloric acid, oxalate, Verseqe, or other extractants. Chemical agents require heating to be effective as pectin extractants. One-gram samples of 40-mesh dried fruit pulp were extracted with 200 ml. of boiling hydrochloric acid a t p H 2 for 60 minutes; with 200 ml. of boiling 3% ammonium oxalate a t p H 7 for 60 minutes; and with 200 ml. of boiling 0.5% Versene solution a t p H 7 for 60 minutes. The extracted pectic substances were deesterified in solution by holding at pH 11.5 for 30 minutes, neutralized, diluted to 250 ml., and filtered. The first few milliliters of the filtrates were discarded, 2 mi. of each was diluted t o 100 ml., and 2-ml. aliquots were taken for anhydrouronic acid analysis by the carbazole method. The results are summarized in Table I and compared with results of the carbon dioxide and Versene-pectinase extraction. Hydrochloric acid extracts most of the pectic Substances from fruit pulps under the conditions of the experiment. Pectate pulp contains pectates which are insoluble in the acid medium and only a small fraction is extracted. Boiling oxalate or Versene solution extracted pectic substances almost as completely as the pectinase method. Boiling T’ersene solution extracted 95% of the pectic substances from dried 40-mesh pectate, raspberry, cranberry, and apricot pulp in 30 minutes. N o significant increases were obtained beyond 6 0 minutes’ heating. Pectic substances were extracted from 150-mesh apricot and grapefruit pulp by boiling Versene solution for 30 minutes, but raspberry and cranberry pulp still required 60-minute extractions. Versenepectinase is recommended, since heating is unnecessary and the method appears to be specific for extracting pectic substances from fruits. Fresh fruit and orange concentrate were analyzed for anhydrouronic acid by the carbazole method after extraction with Versene-pectinase and boiling 0.5% Versene. The results, presented in Table 11, show that boiling o.5Y0 Versene solution
Table 11. Analysis of Undried Fruit Pulp and Frozen Orange Concentrate For total pectic substances Material Analyzed Apple pulp Apricot halves Orange concentrate, Calif., total Orange concentrate, Calif.. serum Orange concentrate, Florida, total Orange concentrate, Florida, serum On fresh-weight basis.
Anhydrouronic Acida, % VerseneVersene pectinase 0.51 0.54 n 0.60 0 . 62 62 0.14 0.14 0.05 0.05 0.26 0.26 0.05 0.05
a t pH 7 for 60 minutes extracted the same amount of pectic substances from the undried pulps and frozen orange concentrates as the Versene-pectinase procedure and would serve as an alternative extraction procedure. LITERATURE CITED
(1) Carson. J. F., and Maclay, W. D., J . Am. Chem. Soc., 70, 293 (1948). (2) Jansen, E. F., and MacDonnell, L. R., Arch. Biochem., 8 , 97 ( 1945). ( 3 ) Kekess; Z. I., “The Pectic Substances,” pp. 99-104, New York, Interscience Publishers, Inc., 1951. (4) McComb, E. A., and McCready, R. h i . , ~ ~ N A LCHEN., . 24, 1630 (1952). (5) hIcCready, R. M., Swenson, H. S., and Maclay, W. D., IND. EAG.CHEN.,ANAL.ED., 18, 290 (1946). (6) Meade, R. C., Fish, 1‘. B., and Dustman, R. B., Plant Phgsiol., 23, 98 (1948). (7) Owens, H. S., McCready, R. &I., Shepherd, 8.D., Schultz, T. H., Pippen, E. L., Swenson, H. A , , hfiers, J. C., Erlandsen, R. F., and Maclay, W. D., Western Regional Research Lab., Albany, Calif., Bureau of d g r . Ind. Chem., U. S. Dept. of Agr., AtC-340 (mimeographed) 1952. RECEIVED for review June 30, 1952. Accepted August 28, 1952. Mention of manufacturers and commercial products does not imply t h a t they are endorsed or recommended by the department over others of a similar nature not mentioned.
Analytical Chemistry of Niobium and Tantalum Atmospheric Chlorination of Hydrolyzed Oxide Precipitates C. F. HISKEY, LEONARD NEWMAR’, AND R. H. ATKINSON2 Polytechnic ZnstitzAte of Brooklyn, Brooklyn, N. Y . ?: A recent group of papers ( I ) , a method was presented for the
I atmospheric chlorination of some oxides associated with niobium and tantalum in their minerals. The method proposed employed octachloropropane as the chlorinating agent. A 3hour reaction time and a temperature of 275” C. were required. Following chlorination, titanium and tin were separated quantitatively by means of a distillation procedure. This separative process applied to the analysis of niobites and tantalites avoids many of the precipitations and reprecipitations of the Schoeller method ( 2 ) . It is particularly advantageous because definite molecular entities are involved rather than colloidal oxides. Therefore, the separation is clear cut and requires only one operation. Another important feature is the simplification introduced in any analytical scheme by titanium removal. I n most analytical reactions the properties of titanium compounds are intermediate to those of niobium and tantalum, making their separation from each other or their determination uncertain and difficult, These considerations indicate the desirability of introducing the chlorination-distillation step into separative schemes. 1 Present address, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass. 2 Present address, Westinghouse Electric Co., Bloomfield, K.J.
As previously indicated ( I ) , the chlorination procedure was developed for synthetic oxide mixtures prepared from pure, freshly ignited oxides. It was thought that these mixtures would have a reactivity comparable with any oxide mixture regardless of method of preparation. The usual methods for gathering the earth oxides and titania include hydrolysis in ammoniacal sohtion or tannin precipitation from a weakly acid tartrate solution. The precipitates so formed are filtered and ignited a t high heat in order to drive off water and burn off the filter paper. It was anticipated that these mixtures would chlorinate as readily as the synthetic ones. This did not prove to be the case, however. It was found that the chlorination failed in most cases when applied to oxide mixtures prepared from aqueous solution. I t became necessary to study this problem in an attempt to devise ways to circumvent this new difficulty. That investigation is the subject of this paper. EXPERIMENTAL PROCEDURES
The oxide mixtures used in this study were prepared from the same analytical grade ovides referred to in the initial communication ( 1 ) . Appropriate portions of each of the various oxides under test were separately ignited and weighed into a tared porcelain crucible (Coors S o . 0). Roughly, fifteen times as much
V O L U M E 24, N O . 12, D E C E M B E R 1 9 5 2
1989
potassium pyrosulfate was added and the mixture was gently heated t o the melting point of the pyrosulfate t o avoid any spattering. This was followed by a period of vigorous ignition until a clear melt resulted. T h e cooled melt was then extracted with 100 ml. of boiling 2 iV hydrochloric acid, which dissolved the potassium salts and hydrolyzed the earth acid sulfates t o their corresponding oxides. When tantalum and titanium are both present, considerable quantities of tantalum remain in solution. In the absence of titanium, the tantalum is nearly quantitatively precipitated a t this point. The acid slurries were next made strongly ammoniacal in order t o precipitate the hydrous oxides completely. After filtration (Whatman Paper No. 41), the oxides are resuspended in hot 2 N hydrochloric acid solution and reprecipitated with ammonia in order to free them completely of potassium salts. After drying a t 110' C. t o volatilize the ammonium chloride, the precipitates were ignited in porcelain crucibles a t 800" t o 1000" C. for 1 hour. A fluffy, amorphous-appearing oxide mixture resulted except when tantalum was present in high concentrations. In such cases the apparent density \vas greater. With exceptions noted here, the chlorination-distillation oper-
ation was performed as previously described ( 1 ) . Still pot residues and the distillation column holdups were combined and analyzed for total titania present, for the quantity of R205t h a t had been chlorinated and sometimes for total Rz05. The determination of titania in the residues as well as in the distillate receiver has been described ( 1 ) . The procedure used for determining the amount of R205 that was chlorinated was as follows: After the distillation operation was complete, the still pot was cooled to room temperature while the column was kept hot. This served t o condense the volatile chlorides in the still pot. The still pot was then disconnected from the column. Tu-enty-five milliliters of a mixture of 95% chloroform and 5% absolute ethyl alcohol mere poured in and swirled about t o dissolve the chlorides and excess octachloropropane. The resulting solution containing charred products and the unreacted oxides was filtered. The washing operation was repeated about three times more using smaller portions of the solvent. In addition, the column was washed d o a n several times. The last traces of unreacted oxides were removed with solvent and a rubber policeman. A411of the filtered washings were combined. The solution was concentrated by evaporation t o about 15 ml. The organic matter was then destroyed with a boiling mixture of 25 ml. of concentrated sulfuric acid and 50 ml. of concentrated nitric acid. T h e n a clear solution resulted, the nitric acid was removed by boiling down t o fumes of sulfur trioxide followed by diluting with water and refuming. After dilution with rrater the solution was neutralized with an excess of ammonia and filtered. The precipitate was then ignited a t 800" t o 1000" C. and weighed. The unreacted oxides mere determined by igniting the filter paper containing them along with any .charred products which may have been present, and then weighing. The total ovides represented the sum of the weights of the chlorinated earth oxides, the unreacted oxides, and the titania distilled as the tetrachloride. Modification of Still Pot. A new modification of the still pot was required for the handling of oxide mixtures which were t o be dried in it. This new still pot is illustrated in Figure 1 and differs from the previous one in the following way:
A-
Table I.
A male tapered ground-glass joint (10/30) is sealed t o the bottom. At the periphery of the seal a number of small holes are provided t o allow movement of liquid from the interior of the flask up through the male joint. This may be used as a filtering flask simply by attaching a female ground-glass joint t o Tvhich suction is applied. The preparation of a mat for this filtration flask is as folloms: About 2 ml. of pure silica sand or pulverized borosilicate glass is first dropped into the bottom t o provide a'support for the asbestos mat. The procedure for forming the mat is similar t o t h a t for a Gooch crucible. The mat is washed thoroughly t o free it of loose particles. Then, still maintaining suction, a h>drolyzed oxide suspension is poured in and filtered. It is washed with 1 M ammonium chloride solution t o free it of adsorbed salts. Finally the ammonium rhloride is washed out with pure distilled water. The precipitate is then sucked as dry as possible, after ( nhich the female member is removed. It may now be subjected t o any drying schedule that the operator wishes. The advantage Figure 1. Diagram of Still Pot of this filterinn flask is that it aermits low temaerature dehvdra-tions without the difficulties 01 transferring the precipitate from a filtering crucible. Filter paper may not be used in this operation because it would react with the chlorinating agent resulting in exTitanium Separation from Hydrolyzed and Ignited Oxide cessive charring and oxychloride formation. Rlixtures
Sample Composition, Grams of Each TiOz TazOa ZrO2 SnOz
KO. KbzOb 1 2 3 4 5 6 7 8 9 10 11
12 13 14 15
a
b
0.7501 0.0335 .... 0.6366 0.0684 .... .... 0.3956 0.0732 0.1037 .... 0.2953 0.0482 0.1697 .... 0.3028 0.0646 0 . 3 1 1 1 .... 0.2014 0.0663 0.4025 .... 0.3149 0.0595 0,1900 0.0315 0.2971 0.0502 0.1512 0.0318 0.222 0.039 0.206 0,085 .... 0.2940 0.0501 0.1677 0.3016 0.0517 0.1492 .... .... 0.3936 0.0710 0 . 1 1 7 1 .... 0.3879 0 . 0 6 7 6 0.2039 0.5326 0.0704 0.2667 .... .... 0.3912 0.0688 0.2333 G r a m of ZrO2 in unreacted residue. G r a m of SnOz in unreacted residue.
....
.... ....
....
.... .... .... .... ....
0.0267
0.0274
....
....
.... ....
Sample Unreacted, yo 0.0 0.8
.. ..
.. 62:O
40.6 98.0 12.2 13.8 5,9 19.5 27.9 7.6
Original Ti02 in Residue, 70 0.0 0.1 9.8 10.0 20.3 31.5 33.1 43.0
...
1.4
1.1
1.4 9.8 6.4 3.1
Notes
.....
0.0315" 0.0318Q
.....
O.Ob O.Ob
...e
...c ...e
. . .d
e Long-necked reaction flask substituted and heated t o over 400' C. for 2.5 hours. Purpose of long-necked flask was t o allow partial cooling of ball joint connecting i t t o distillation column. -4t high temperatures used here, there would have been vapor loss. d Same a s C except 30 grams of octaohloropropane CnCla used instead of usual 15 grams.
Chlorination of Hydrolyzed and Ignited Oxide Mixtures. I n the first group of experiments various oxide mixtures prepared as described above and chlorinated in the usual way, except as noted below, were tested for completeness of chlorination and of titanium removal. Some typical results obtained are given in Table I. From a n examination of these data a number of conclusions may be made and these are itemized: Mixtures of niobia and titania react quantitatively (Nos. 1 and 2). The addition of tantala t o the niobia-titania mixture hinders titania chlorination (Nos. 3-6). Even with much more severe reaction'conditions, this chlorination cannot be made quantitative, although substantial improvement results (Kos. 11-15).
1990 The addition of even small percentages of zirconia t o the oxide mixtures has a greater inhibiting effect than does the tantala upon the over-all chlorination. With 15% zirconia in the oxide mixture the chlorination is virtually prevented. The presence of stannic oxide in the mixture has a beneficial effect on the over-all process, partially overcoming the inhibiting effect of the tantala. I n general, it is apparent that such a procedure would yield quantitative results for titanium only when the sample was extremely low in tantala and zirconia. This restriction is so great however, as to render the approach worthless for most of the minerals which it was expected to analyze. Consequently, it was necessary to overcome this defect or else to abandon the chlorination step in toto. X-RAYEXAMINATION OF THE IGNITED PRECIPITATES. Since ignition of the precipitated oxide mixtures had produced such striking effects, the question arose as t o the nature of possiblr structural changes tvhich occurred during the ignition. Changes did not occur if mixtures of oxides ignited separately were combined and then reignited but appeared t o require the intimate mixing which simultaneous precipitation afforded. To make a brief study of the changes that occurred on ignition, samples were prepared of pure tantala, niobia, and titania and then of thc following mixtures (in 1 to 1 weight ratios): tantalum and niobium pentoxides, tantalum and titanium oxides, and niobium and titanium oxides. These 'ignited oxides and ignited mixtures wcrc placed in the sample holder of a recording Geiger counter x-ray spectrometer and the detecting tube was swept through an angle from 60" to 18" in units of 2 e. Analysis of the resulting curves showed that for the pure oxides markedly crystalline products resulted possessing characteristic diffraction patterns. The mixture of niobia and tantala retained the crystallinity of the two components. I t s diffraction pattern was a simple combination of the two individual patterns for the pure oxides modified only by the dilution effect which each would have on the other. In the remaining tn.0 mixtures containing titania with each of the earth oxides, a diffraction pattern could barely be distinguished indicating a poorly crystalline almost amorphous material. A few weak diffraction peaks could be observed, but these bore no relation to the diffraction patterns of the pure oxides. Instead they suggested the formation of new phases extremely difficult to chlorinate. To improve the chlorination of these ignited oxide mixtures, two general approaches were tried. One way to increase the chlorinating efficiency of the octachloropropane was to add a catalyst which would function more efficiently than niobium as a chlorine carrier. This approach was suggested by the beneficial effects produced by the stannic oxide. A second approach was to avoid the formation of these new chlorination-resistant phases altogether. Addition of Chlorination Catalyst. The addition of a chlorinecarrying catalyst is suggested by the data in Table I. It ill be recalled that the addition of a basic oxide like zirconia had a very deleterious effect on the chlorination. From previous Fork it was known that if such basic substances such as sodium oxalate, barium oxide, or barium carbonate were added t o the ignited oxides, chlorination could be effectively prevented. On the other hand, the addition of a more acidic oxide, like stannic oxide, had a beneficial effect. The high volatility of stannic chloride compared to the chlorides of molybdenum and tungsten suggested that these latter elements might be better additives than tin. They would be superior for three reasons: 1. Their low volatility would concentrate them in the still pot where they were needed while the stannic chloride would be refluxing in the column. 2. They were elements not commonly found with earth oxide minerals and thus need not be determined. 3. Because of their ease of separation from the earth oxides, their initial presence would not greatly disturb the analytical program.
ANALYTICAL CHEMISTRY 4 series of samples containing niobia, tantala, titania, and zirconia was prepared according t o the hydrolysis procedure given in the section on experimental procedures. Molybdenum(VI) oxide was added to these immediately prior to chlorination. I n another experiment, tungsten(V1) oxide and stannic(1V) oxide were precipitated along with the other oxides to achieve more intimate mixing The samples n-ere then subjected to the usual chlorination-distillation procedure. The results obtained are summarized in Table 11. From an examination of these results it can be seen that improvement results in all cases over \+-hat might have been expected had the acidic oxide not been added. This supports the belief that the more acid chlorides function as chlorination catalysts. Severtheless, the over-all prospective was one which gave little promise of quantitative chlorination for most oxide mixtures. Therefore, it seemed desirable t o set aside this approach temporarily in favor of one which would avoid the formation of the unreactive oxide mixtures. Low Temperature Dehydration. In this connection attempts were made to effect a dehydration of the oxide mixtures a t temperatures lower than 800" C. It n-as hoped that a temperature might be found a t which all of the m t e r could be removed without the formation of the chlorination-resistant mixtures.
Table 11. Effect of Acidic Oxides on Chlorination of Ignited Earth Oxide 3Iixtures Xb?O6, %
Taros. 7% Tior, % ZrOz, % M t. of sample, gram Added oxide, gram Original TiOz in unreacted residue, %, Wt. of unreacted residue, gram
0 5
3 4 21.5 16 7 68 0 60.5 8.2 10.6 7 3 7.1 0 5909 0 3409 -\loo3 WOS 0 5 0.2
3 8
6.7
27 2
0 0502
0.1178
56 29 9 4 0
1 2 3 45 2 3 40 7 6 9 6 8 5.3 5268 0.5166
No03
0 5
.\Io03
0 3663
35.4 0.2789
5
22.5 60.3 11.1 6.1 0.3327 SnOl 0.15 53.2 0.2815
The new filtration flask described above was utilized in these experiments. In the preliminary studies a group of simple oxide mixtures of a wide variety of compositions Tvas prepared, transferred into the filtration flasks, dehydrated under conditions of varying severity, and then chlorinated. From such studies as these it v a s soon found that dehydration overnight a t 110" C. gave satisfactory results. With the aid of vacuum, the time of dehydration could be reduced to 4 or 5 hours. The time for oxide preparation could be reduced even further when the precipitates were given a final washing with volatile organic solvents like acetone or acetone followed by diethyl ether. From among
Table 111. Chlorination of Oxide Mixtures Subjected t o Low Temperature Dehydration Samples neighed approx. 0.4 "ram. 25 Grains of octachloropropane used. Chlorination conditions: 2
