analysis 100,000 total counts were accumulated, thus limiting the standard error in counting rate to around 0.3%. All comparative counting determinations must be carried out under exactly reproducible conditions of geometry. Variations in the vertical and horizontal relationship of the source, sample cell, and detector to one another must be minimized. Variations in base stock composition -Le., changes in the normal proportions of lorn atomic number matrix elementsand in density from sample to sample will affect the accuracy of results obtained by use of the working curve. Accordingly, the method has been applied only to the analysis of technical grade and finished products. The x-ray method was applied to the determination of chlorine in a large number and variety of organic samples, and the results were then compared with those obtained by the conventional bomb combustion-titration procedure. As shown in Table I, the agreement between the two methods was generally within the standard deviations of the results. Esperience in this laboratory has shown the x-ray absorption technique to be more reliable because of minimized sample handling and minimized inadvertent sample contamination. The minimum concentration of chlorine detectable by x-ray absorption is around 0.01%. For the analysis of homogeneous liquid samples, results are normally accurate to within *0.02% chlorine a t concentrations below 0.5%.
At concentrations in the 10% range, an accuracy to within %O.Zoj, chlorine can be espected. The pressed-plate, solid-sampling technique suffers in precision because of difficulty in reproducing sample geometry exactly. Normal variations in geometry limit the analytical precision to about k0.05yO chlorine at concentrations below 0.5%. Since the sensitivity advantage of direct solid sample analysis is offset by geometrical imprecision, solid samples are preferably analyzed after dissolving them in a suitable solvent. Whenever possible, a solvent is used which contains the low atomic number matrix elements in approximately the same proportions as does the samplr material being analyzed. Speed. T h e usual time of analysis, including sample preparation, counting, and calculation of results is less than 5 minutes. Because of the high counting rates attainable by proportional counting Tyithout detector resolution losses, the counting time required for a given statistical counting precision is only a fraction of t h a t required by Geiger counting. T h e advantages of higher speed counting for ultimate analytical precision appear to outweigh the marginal gain in sensitivity which is obtained by increasing sample size Cost. T h e cost of the facilities described, including radioactive source, is on the order of $2500. This is less than the cost of a commercial version of the less flexible apparatus described by earlier workers.
Table 1.
Comparative Chlorine Analyses'
Iron-55 X-Ray 0.02 i 0.01 0.03 & 0.01 0.08 & 0.01 0.23 f 0.01 0 . 5 0 i 0.02 1.05 i 0.03 9.6 i0.2 a
CombustionTitration 0.02 f 0.01 0.04 f 0 . 0 1 0.10 f 0.01 0.21 f 0.01 0.45 rt 0.02 1.00 f 0.02 9.4 k 0.1
Weight per cenIt.
Radiation Safety. T h e installation described presents no radiation hazard, provided normal handling precautions are followed. T h e only appreciable radiation is directed upward in a conical beam from the source. Horizontal radiation toward the operator is absorbed by the sides of the counting cup holding the source. The removable shelves can be easily manipulated in and out of Ihe counting chamber without esposure to the radiant beam. The heavy door of the shield is normally closed except during sample changing . LITERATURE CITED
(1) Hughes, H. K., Wilczemski, J. W., -4N.4L. CHEM. 26, 1889 (19541. (2) Seaman, IT., Lawrence, H. C., Craig, H. C., Ibid., 29, 1631 (1957).
RECEIVEDfor review September 5 , 1961. A4ccepted February 16, 1962. Division of Analytical Chemistry, 139th Meeting, .4CS, St. Louis, Mo., March 1961.
Determination of Niobium and Tantalum in Minerals, Ores, and Concentrates Using Ion Exchange SlLVE KALLMANN, HANS OBERTHIN, and ROBERT LIU Research Division, ledoux & Co., Teaneck, The hydrochloric-hydrofluoric acid system was found suitable for the determination of niobium and tantalum in various minerals and ores b y ion exchange procedures. No preliminary separations are required, and the ion exchange steps provide cleancut separations from virtually all elements with which niobium and tantalum are associated. Tin, antimony, and bismuth require minor modifications of the procedure. The decomposition of the sample depends to some degree on its composition; a hydrochloric-hydrofluoric acid attack under light pressure i s suitable in most instances.
N. 1.
0
the niobium and tantalum bearing minerals, columbite and tantalite (FeJIn) (Kb,Ta)z06are most important. Depending on the origin, these minerals are contaminated with varying amounts of titanium, tin, zirconium, calcium, and tungsten. Since the amount of available columbite/tantalite ore is limited, increasing amounts of pyrochlore, KaCaKb20s, and microlite, (SaCa)zTa206(0,0H,F), are being processed which, besides other calcium bearing minerals, frequently contain some rare earths. Simpsonite, rllnTa20s,is also being used while the rarer euxenite, (Y,Ca,Ce,U,Th)F
(?Jb,Ta,Ti)206 and samarskite, (Y,Er,-
Ce,U,Ca,Fe,Pb,Th)(Nb,Ta,Ti, 3m) 2 0 8 , because of their high uranium content, are desirable only if a recovery of the uranium is also envisaged. A comprehensive reviem- of methods available for the analysis of niobium and tantalum bearing ores and concentrates iyas published in 1952 ( 1 ) . Rlost methods represented modifications of the original Schoeller procedure (28, SO, 31, 36), which is based on a preliminary collection of the combined oxides of niobium, tantalum, titsnium, zirconium possibly contaminated by tungsten and phosphorus. After removal of titanium VOL. 34,
NO. 6, MAY 1962
609
($a,
(3Q)and tungsten the now classical tannin procedure is carried out ($7). The original procedure which involves a great number of fractionating steps bas been imnroved hv several modifications (6, 3;). The- determination of niobium and tantalum in ores based on cellulose chromatography (3, 4,$2, 88) has become popular in Europe, less so in the United States. A shortened chromatographic procedure is also available (15, $1). Chemical separations are avoided in several procedures based on the colorimetric determination of niobium by thiocyanate (8, 19, 55) or hydrogen peroxide ($4) and of tantalum by pyrogallol (7, $0). In addition to the above chemical methods, niobium and tantalum can also he determined spectrographically in the mixed oxides (16) or in a portion of the original sample ($6). X-ray fluorescence methods have also been published (5,%'?). It is surprising that the literature scarcely mentions ion exchange as a technique applicable to ores and concentrates, although the feasibility of a n n o r o t k n lyyvlulll ninhihm y"yuIy"'116
anrl tywllyyl"ly nntol7.m
yllu
".,
hri
this approach has been amply substantiated. b u s , Moore, and Neison introduced the HF-HCI system and showed that niobium and tantalum can be separated from each other under various conditions (17, 18). The absorption of a number of elements from HC1-HF mixtures by Dowex-1 resin has been thoroughly studied (Q), and the separation of macro amounts of niobium and tantalum from each other and from a number of associated elements in miixtures alloys (18, 87) has been demonstrated. The hydrochloric acjid-oxa1ic acid system has been studied (1% 34) and applied to the analysis of high temperature alloys (3). EXPERIMENT!91
.-.
Apparatus ana xesm. IONExCHANGE COLUMNS. The columns are made of polystyrene and are 15 inches long and 1 inch i.d. If a number of determinations are carried out, i t is desirable to arrange the columns SO that a number can he operated with a minimum of attention. Plastic columns suitable for such a n assembly were developed b y Ledoux & Co. and are equipped with Dole-type fittings of polystyrene. Inlet and outlet tubes are of polyethylene. Flexible connections are made of Tygon tubing. The flow of solutions can he controlled by hose-cock clamps on these flexible connections (Figure 1). RESIN. Dowex-1, 100-200 mesh, 8 to 10% divinyl-benzene crosslinkage is ed. While the initial work reported #re was carried out with -270 to 320 mesh resin, in line with the commendations of Hague and Mach1 (IS)),recent tests carried out in our 10
ANALYTICAL CHEMISTRY
laboratory proved that comparable elution characteristics can he obtained by using more of the coarser resin. The resin as received from the manufacturer is transferred to a polyethylene beaker and washed several t i e s with 200 mi. of 3M nitric acid with intermittent decantations. Subsequently, the resin is washed with water and with hydrochloric acid and hydrochlorichydrofluoric acid mixtures. It is finally transferred to the columns, containing a circle of Orlon or equivalent HFresistant cloth, until a settled resin bed of 10 inches has been obtained. Before the sample is introduced into the columns, the resin is treated several times with the 5 to 4 to 11 HC1-HFH,O mixture. 5 to 4 to 11 Mixture. Reagents. Add 250 ml.of hydrochloric acid (12iM) to 300 ml. of water, then add 200 ml. of hydrofluoric acid ( 2 4 M ) and dilute to 1 liter with water. NHCI-HF Solution. Dissolve 140 grams of ammonium chloride in 500 ml. of water. Add 40 mi. of hydrofluoric acid and dilute to 1 liter with water. N&CI-NH,F Solution. Dissolve 140 grams of ammonium chloride in 500 ml. of water. Add 40 ml. of hydrofluoric acid. Adjust the acidity to a pH. of 6 with ammonium hydroxide and dilute to 1liter with water. Cupferron Solution. Dissolve 6 grams of cupferron in 80 ml. of cold water. Filter and dilute to 100 ml. Prepare fresh and keep cooled to 5' C. PROCEDURE
Decomposition - of .Sample. . WF._ . H U ATTACK. 'Transfer 0.5 gram of high-grade material to a 200- to 400-ml. polyethylene beaker. Add 25 ml. of hydrochloric acid, 20 ml. of hydrofluoric acid, and cover with a thin sheet of polyethylene wrap which is held tightly to the sides of the beaker with a rubber hand. Place on a steam heth and heat for several hours, with occasional mixing of the solution by swirling, until the sample has completely decomposed. Disregard any undissolved cassiterite and/or zircon. Remove the wrap, add 55 ml. of water, and introduce the solution into the column. SODIUMBISULFATEFUSION OF SAMPLE. The bisulfate attack is as efficient as the HF-HC1 decomposition. However, it is more time-consuming and requires more attention. Transfer sodium bisulfate (fused) to a 100-ml. porcelain crucible. Heat until effervescence stops. Pour the molten salt into a quartz crucible. About 10 grams are ample for a 0.5- to I-gram sample. Transfer the sample on top of the cold bisulfate. Heat the covered crucible, first with a small flame, finally for about half an hour with the full heat of a Bunsen burner. Allow the fusion to cool and solidify. Loosen the melt by a light tapping of the crucible and transfer to a polyethylene beaker. Rinse the quartz crucible and cover with the 5 to 4 to 11 mixture and add to the polyethylene beaker. Add sufficient 5 to 4 to 11mixture to provide
Figure 1. Assembly of columns used for ion exchange of niobium and tanta-
lum
.
.
.
."-
1
"
.
approxlmately I U U ml. 01 volume. Cover with polyethylene wrap, a6 was indicated ahove, and place on steam bath until the melt has completely dissolved. Then transfer the cooled solution onto the resin bed. SODIUMPEROXIDE FUSION OF SLAGS, RDSIDUES,AND OTHER LOW-GRADE SUBSTANCES.Fuse a 0.5 to 2-gram sample in a nickel crucible in the usual way with 5 to 10 grams of sodium peroxide. Leach the cooled melt in a polyethylene beaker with 50 ml. of water, Rinse the crucible with hot water and add to the main solution. Carefully neutralize with 18N sulfuric acid to a pN of 5 to 7 . Dilute with water to 110 ml., add 50 ml. of hydrochloric acid and 40 ml. of hydrofluoric acid, and heat on a steam bath until a clear solution results. If a black residue of nickel oxide persists, add a few drops of hydrogen peroxide and continue heating until the solution is clear. Transfer the cooled solution ontotheresinbed. Elution of Impurities. Wash the beaker w-ith 5 to 4 to 11 mixture and transfer the washings to the column, allowing the solution to drain to the top of the resin each time. Finally wash down the sides of t h e column with the same solution, and allow 300 ml. of eluate to pass through the resin bed. This may be done manually by adding from time to time new eluant, allowing the solution to drain to the top of the resin each time or by automatic delivery (Figure 1). The flow-rate of the column is about
100 to 125 ml. per hour. To rctluce the evaporation of HC1 and H F , the eluate may be recrivecl coni-enicntly in polyethylene bottles (qui h as empty H F bottles). Discard the eluate unlebs determinations of other constitumts of the sample are desired. Elution of Niobium. Replace the beaker or flask with a 400- to 600-111l. polyethylene beaker and pass through the column 350 ml. of NHdCl-HF solution maintaining the technique and flow-rate described before. The eluate contains all the niobium. contaminated possibly by traces of tin and/or antimony. Elution of Tantalum. l g a i n change beakers and pass 350 ml. of NH4C1-NH4F eluant through the resin bed. T h e eluate contains only the tantalum, with the exception of the rare bismuto tantalite. Determination of Niobium. If the sample contains considerable cassiterite, a small amount of tin is rendered soluble by the HF-HCl attack or by the S a H S 0 4 fusion. If a iTa202fusion IWS employed. all the tin is introduced in the column and significant amounts may accompany the niobium. Antimony need only be considered in the case of the rare stibiotantalite. I t may partly dissociate in the column and accompany the niobium. Unless the absence of tin and/or antimony is known or established, it is therefore always advisable to remove these two elements by a hydrogen sulfide separation. Add to the niobium eluate 15 grams of tartaric acid and 15 grams of boric acid. Stir until dissolved. Pass a brisk stream of hydrogen sulfide into the cold solution for 15 minutes. If necessary, filter and wash with cold 5y0 (v./v.) sulfuric acid containing a little tartaric acid and hydrogen sulfide. Discard the precipitate. Expel the hydrogen sulfide by gentle boiling. Cool the solution to below 10” C., add 60 ml. of hydrochloric acid follon-ed by 60 rnl. of cupferron, and some filter pulp, and filter preferably using mild vacuum. If the niobium content is known or suspected to be below 5 mg., use 10 mg. of sirconium in the form of zirconium sulfate and only 10 ml. of cupferron solution t o collect the niobium. Wash the precipitate throughly with 5% (v./v.) hydrochloric acid containing a little cupferron. Ignite in a tared platinum dish or crucible, first a t a low temperature, and finally to constant weight a t l l O O o C., and weigh as niobium pentoxide. If a photometric determination of the niobium is desired, the ignited precipitate is treated as described by Hague and hiachlan (12). Determination of Tantalum. Only in the rare case that the sample contains bismuth is it necessary to carry out an H2S separation. In the absence of bismuth, add to the c h h e containing the tantalum 60 ml. of hydrochloric acid and 15 grams of boric acid. Stir until dissolved. Pre(zipitate the tantalum with cupferron, filter, wash, and ignite as described for
Table
I.
130 50 450 5 500
0.
*
Separation of Niobium andTantalum from Each Other and from Titanium, Zirconium, and Tungsten
0
0 0
0 0
2dO 50 450 4
9 4 8
7“
1 0
1 1“
500 0 1 0
500 8 1 00
250 450 50 500 5
0 0 0 0 0 500 0 1 0
249 3 449 2 50 4
50 100
5 3b 501 3 0 9b 1 I*
50 100
100 50 50
100
100 50 50 50
100
50
1 0 50 50 Siohium determined photometrically by hydroquinone method. Tantalum determined photometrically by pyrogallol method. Phosphorus added in form of Sa2HP04.
niobium. Weigh as tantalum pentoxide. If a photometric determination of the tantalum is desired, the ignited precipitate is treated as described by Hague and Machlan ( I d ) . Determination of Impurities. Since the first eluate contains various constituents of the original sample (Fe, Ti, W,Mo, U, and Mn, also Zr, if a NazOz attack mas used), it can be employed for the determination of one or the other elements. Some can be collected with cupferron after complexing the hydrofluoric acid with boric acid; others are more conveniently determined after expulsion of the hydrochloric and hydrofluorie acids by evaporation with sulfuric acid. Regeneration of Resin. After the elution of tantalum, the resin can be readied for the next sample by passing two column volumes (about 75 ml.) of the 5 to 4 to 11 mixture through the column. To avoid contamination of the resin with undecomposed cassiterite and zircon, it is advisable to prevent the transfer of these insoluble substances onto the column. I n extreme cases, the solution can be introduced onto the resin bed by filtration. There is virtually no limit to the number of separations which can be carried out with the same resin. The columns illustrated in Figure 1 have been in uninterrupted use since 1954, and each column has accommodated more than 300 samples. It should also be noted that no “hydrofluoric acid burns” were experienced by the chemists and technicians carrying out the ion exchange separations. DISCUSSION
Ien Exchange Separations Involving Combined Oxides. Based on work by Kraus and hioore (17) and Hague, Bron-n, and Bright (11),known amounts of the oxides of niobium, tantalum, titanium, zirconium, tungsten, and phosphorus in various proportions representing the usual “combined oxides,” were fused in sodium bisulfate. Since subsequent operations involved hydrofluoric acid, potassium bisulfate could not be used because of the insolubility of K2TaFi. The bisulfate melt was
50 100 100 50 50
25. 25
50 50 50
dissolved in 100 ml. of a 5 to 4 to 11 mixture of hydrochloric acid, hydrofluoric acid, and water, the solution was transferred to a polystyrene column (15 x 1 inch i d . ) containing 10 inches of 100-200 mesh Dowex-1 resin, 8 to 10% crosslinkage. Titanium, tungsten, and/or zirconium mas removed by elution with 350 ml. of the same HC1HF-H20 acid mixture. Subsequently, the niobium was eluted by passing 350 ml. of a 14% ammonium chloride (w./v.) -4% hydrofluoric acid (v./v.) mixture through the column. Tantalum was then eluted with 350 ml. of the 14% iYH4C1-470 H F solution after neutralization with ammonia to a pH of 6. In their respective fractions, niobium and tantalum were collected with cupferron after complexing the hydrofluoric acid with boric acid and adjusting the acidity with hydrochloric acid. Ten milligrams of zirconium in the form of a zirconium sulfate solution was added as collecting agent when the amount of niobium andjor tantalum was below 5 mg. The results are presented in Table I. The data in Table I indicate that the HC1-HF system introduced by Kraus and Moore (17) and Hague et al. (11) provides a cleancut separation of niobuim and tantalum from each other and from the usual components found in the combined oxides. Ion Exchange Separations Involving a Bisulfate Fusion of Original Sample. I n addition to the elements usually and occasionally collected in the combined oxides, such as niobium, tantalum, titanium, zirconium, tungsten, and phosphorus (Table I),niobium and tantalum bearing ore? and concentrates frequently contain the following oxides as part of the mineral structure or as contaminants: FeO, 3 to 25%; bInO, 0.2 to 13%; SiOn, 0.5 to 20%; &03, 0.5 to 10%; CaO, 0.2 to 22%; Na20, 0.1 to 10%; SnOz, 0.05 to 15%; U3O8, 0.01 to lo%$; YzOa, 0.01 to 1570; F, 0 to 10%. Samarskite type minerals may contain considerable amounts of various rare earths; the VOL 34, NO. 6, MAY 1962
61 1.
Table 11.
Separation of Niobium and Tantalum from Each Other and Other Elements as Found in Ores, Concentrates, and Artificial Mixtures" Characterization Xb205, % Ta2O5, % b Oxides of Other Elements Known t o Be Present of Compound Present Found Present Found >lo% 1-10% 0.1-1% O.0l-O.lgJ
Columbite Columbite-Tantalite Tantalite Tantalite Samarskite Euxenite Pyrochlore
66.18 44.25 11.25 7.14 36.75 22.47 53.14
66.23 44.19 11.26 7.22 36.63 22.50 52.98
5.19 28.74 68.42 45.79 18.65 3.47 0.75
5.23 28.63 68.54 45.88 18.53 3.50 0.7lb
Microlite 6.33 6.25 67.15 67.30 Ilicrolite-Simpsonite 3.87 64.59 3.80 64.65 All results based on average of duplicate determination. Tantalum determined by pyrogallol color procedure.
rarer stibiotantalite and bismutotantalite always contain substantial quantities of antimony and bismuth respectively. Small amounts of other elements, such as magnesium, potassium, molybdenum, vanadium, and lead, may be present in the sample as part of associated elements. In subjecting 0.5-gram samples of k n o m niobium and tantalum content (analyzed by several organizations using different methods) containing part or all of the abore elements to a sodium bisulfate fusion and leaching the melt in a polyethylene beaker with 100 ml. of the 5 to 4 to 11 niivture of hydrochloric acid-hydrofluoric acid-water. the follon ing observations were made. A clear solution is obtained unless the sample contains tin, zirconium, and or rare earth elements. Calcium, even in amounts occurring in microlite, does not precipitate as a fluoride because of the high chloride concentration. Tin occurs in Xb-Ta minerals in the form of cassiterite, which is only slightly attacked by the bisulfate fusion and the HF-HCl solvent. Zirconium occurs
Table Ill.
Type of Mineral Columbite Columbite Columbite-Tantalite Tantalite
Fe Mn Fe
W, S n F e Fe, U, Y Ti. Y
Ca,Fe
Ca
Al, Ca
in Nb-Ta minerals in form of zircon vr-hich also is not attacked by the NaHSO4-HF-HC1 treatment. A nuinber of cassiterite and zircon residues resulting from the attack described n-ere examined spectroscopically and were invariably found to be free from niobium and tantalum. Rare earth fluorides are practically insoluble in hydrofluoric acid media. Any solubility due to the presence of hydrochloric acid leads to the formation of cations which are not absorbed by the resin. When artificial mixtures and natural samples of known niobium and tantalum content were fused in sodium bisulfate, the melt was leached in the 5 to 4 to 11 mixture of HF-HCl-H20, and the solution mas passed through Dorex-1 resin, it was observed that all elements with the exception of niobium, tantalum, tracm of soluble tin (soluble in SnHS04HF-HCl), antimony. and bismuth eluted readily. -4ntimony occurs only rarely in the Nb-Ta minerals and TI ill be found partly in the niobium fraction, together with traces of tin. The equally rare bismuth accompanies the tantalum.
Nb205, 7c Present Found
TazOs, % Present Found
66.15 58.20 44.17 11.30 2.05 7.14 6.36 12.23
5.19 20.13 28.74 68.42 79.15 45.79 67.15 58.79
5.17 20.20 28.63 68.60 79.20 45.86 67.29 58.63
Pyrochlore
53.14 56.43
53.23 56.29
0.75 0.27
0.69O 0.300
Euxenite Samarskite Ferroniobium
22.47 36.75 57.5070
22.50 36.75 57.52%
3.47 18.65 3.68%
3.48 18.80 3.6570
49.23%
12.1470
12.19%
Nb Ferroniobium Tantalum 49.2070
h-b
Ta
Nb Ta a All results based on average of duplicate determination. See Table 11. 0 Tantalum determined photometrically. ?r'b
6 12
Zr, Si, Ca -41, Si Sn
T W
Zr, Si Unknown Ca, Pb, Mn Zr Mn. Fe. P Sn. Al. Si K, Mn,'P sn; AI'
Na, Si, Zr, Y Mn, R.E. Unknown
Hague and Machlan (IS) have shown that substitution, in the 5 to 4 to 11 mixture, of part of the hydrochloric acid by ammonium chloride causes ready elution of tin, and presumably antimony, along with the other impurities of the sample. However, it was observed in this laboratory that the introduction of the NH4Cl into the 5 to 4 to 11mixture may cause premature leakage of the niobium. It is therefore suggested to use the 5 to 4 to 11 solution in its original form and remove traces of tin and/or antimony by passing hydrogen sulfide into the niobium eluate, after the addition of boric and tartaric acids. The niobium eluant again consisted of a 14% ammonium chloride (w./v.)47, (v./v.) hydrofluoric acid mixture. Tantalum was eluted with the same solution after neutralization with amnionia to a pH of 6. Both niobium and tantalum TT-ere recovered in their respective fractions by cupferron precipitation after complexing the hydrofluoric acid with boric acid, adjusting the acidity with hydrochloric acid, and,
Determination of Niobium and Tantalum in Ores and Concentrates Following HF-HCI Attack"
66.18 58.14 44.25 11.25 2.13 i.ii 6.33 12.15
Microlite
Mn, Ti, Sn Fe, Ti, Sn, Zr, Ca Mn Mn R.E., Ti, Th U. Ca. Pb. Th.R.E. y a , Ti, Si,R'E., Zr Fe Sn, Ti, Fe, Na
ANALYTICAL CHEMISTRY
Ta
Ta
Oxides of Other Elements Known to Be Present >lo% 1-1070 0.1-170 0.01-0.1% b
b
Fe
Ti, Sn, 11n
b b
Fe b b
Ca b
Ca b b
b
b
b
Si, Zr
Ca, A1 b
b b
b
l l n , Ti b b
b b
b
Unknown
Na, Si, Fe, Mn
R.E., Y
Xa, Fe, Ti, R.E., Si
Zr, M n , Y, Ba
b
b
b' b
b b
Unknown Unknown
b b
Sn b
Sn b
b
where required, after removal of any tin and ‘’orantimony in the niobium and of any bismuth in the tantalite fraction with hydrogen sulfide. Results of these tests are presented in Table 11. Decomposition with HydrofluoncHydrochloric Acid Mixture. The attack of niobium and tantalum bearing minerals with hydrofluoric acid originally introduced by Smith ($3) is almost exclusively restricted to the riiobates and tantalates of the rare earths ( 1 4 ) . Columbite and tantalite are only slightly attacked, ex-en by repeated t,reatnients with hydrofluoric acid, wit’h or without the addition of nitric acid. However, experiments carried out in this laboratory proved that a complete attack of all niobium and tantalum bearing minerals (iTith the exception of simpsonitej can be obtained if the heating of the sample with hydrofluoric acid is carried out under mild pressure. This can be achieved by placing the sample in a polyethylene beaker of convenient size, adding a n excess of hydrofluoric acid, covering the beaker with a piece of thin polyethylene sheet, big enough so that it can be held tightly against the sides of t’he beaker with a rubber lxind. Subsequent heating on a steam bath, with a n occasional mixing of the solution by a swirling motion, invariably will lead to a complete decomposition of the sample. If the hydrofluoric acid is replaced by the acid part of the 5 to 4 to 11 mixture of hydrochloric acid-hydrofluoric acidwater-eg., 25 nil. of HC1 and 20 ml. .HF-decomposition is even more rapid, and complete solution of the sample can be ohtained in about 2 hours. This mode of attack is also very effective for ferroriiobiiim. After solution of the sample and prior to introducing the solution into the column, sufficient water is added so that the mixture has the 5 t o 4 t o 11 (HCl-HI’-H,O) specification. It should be noted that the attack discussed :{hove does not touch zircon and itcrite is attacked only to a minor esteiit. About 150 residues consisting of cassiterite, zircon, and, in some cases, some rare earth fluorides, have been ex:smined spectroscopically in this labomtor!-, and only in three instances x i s the presence of a significant amount of niobium and /or t’ant’alumindicated. In tn-o cases, incompkte decomposition of the snniple was traced back to a t’oo short heating period. In one case, the snmple contained a substantial amount of simpsonite. This rare mineral, consisting of A12T:i2O8, is incompletely attacked by the HF-HC1 mixture. When its presence is known or suspect’ed, the sample should be fused in sodium bisulfate, or preferably, in sodium peroxide. iF7hen samples of known niobium and tantalum content were decomposed
Table IV.
Determination of Niobium in Slags and Other Low-Grade Materials Following N a z O zFusion” Type of NbzO5, % TaZO6, % Oxides of Other Elements Present RIaterial Expected Found Expected Found >lo70 1-1070 Si, Ca, Fe, Na Mn, 110,Ti, Sn 5 08 Slag 4 8 4 87 5 1 Si, Ca, Fe, Na -41, Ti, Sn, Zr 7 22 Slag 8 35 8 40 7 15 Fe, Ti, Si Mn, Sn, Zr, Ca 3 49 Residue 6 5 6 53 3 4 Ti, Fe Zr, Si, Mn, Sn Rutile 3 13 7 72 3.20 7 69 Ca, S a , Fe 4 54 -11 Simpsonite 64 12 64 27 4 50 All results based on average of duplicate determinations.
with the mixed HC1-HF acids, diluted rvith water to provide a 5 t o 4 to 11 medium of HC1-HF-H20, introduced into the column, and eluted as previously described, the results recorded in Table I11 were obtained. Decomposition with Sodium Peroxide. Since sodium sulfate salts do not interfere with the ion exchange separation in a n HC1-HF medium, tests were carried out t o establish whether a melt resulting from a sodium peroxide decomposition could be treated in such a way as to make i t amenable for subsequent ion exchange separations. The sodium peroxide attack appears attractive for samples such as slags, furnace products, low-grade samples containing considerable amounts of gangue material, and even for high-grade material such as sinipsonite which does not completely yield to an HC1-HF attack. When melts resulting from a sodium peroxide fusion were leached in polyethylene beakers, acidified to neutrality n-ith 1 8 s sulfuric acid, heated to expel excess hydrogen peroxide, and adjusted with hydrochloric and hydrofluoric acids to provide a 5 to 4 to 11 medium of HCI-HF-H20, clear solutions resulted in every case. Only a limited amount of I!ork has been carried out with this system (Table IT’), Preliminary results, hon ever, indicate that the sodium peroxide melt treated, as described above, acts exactly like a sodium bisulfate melt which is dissolved in the 5 to 4 to 11 mixture. It is not permissible to acidify the sodium peroxide melt with hydrochloric acid since the addition of the excessive amount of chlorides interferes with the analytical scheme described above.
(9) Faris, J., Brody, J., Paper S o . 34, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1961. (10) Gillis, J., Hoste, J., Cornand, P., Sueecke, A.. Meded. Vlaam. Chem. Tier. 15, 63 (1953). (11) Hague, J. L., Brown, E. D., Bright, H. A,, J . Research iYatl. Bur. Standards 5 3 . 261 (1954). (12)” ague, J. L., Machlan, L. A., Ibid., . - - - - ~ 62, 11 ( 1 Y 6 Y ) . (13) Ibid., p. 53. (14) Hillebrand, W. F., Lundell, G. E. F., “Applied Inorganic Analysis,” p. 591, Wiley. -N e- w York. - - - - - > -l%%. --(15) Hunt, C., Wells, R. A., Analyst - E. .~ 79, 345 (1Y54). (16) Ingles, J. C., Manual of Analytical Methods for the Uranium Concentrating Plant Department of Mines and Technology Surveys Monograph 866, Ottawa, , I
19.58
(17) Kraus, K. A., Moore, G. E., J. Am. Cheni. SOC.71, 3855 (1949);, 73,. 2900 (1951). (18) Kraus, K. A, Nelson, F., ASTM Special Technical Publication No. 195, 1956. (19) llarzys, A. E. O., Analyst 79, 327 ( 1954). (20) Ibid., 80, 194 (1955). (21) Mercer, R. A., Wells, R. h.,Ibid., 79,339 (1954). 122) Mercer, R. E., Williams, A. F., J . Chem. SOC.1952, 3399. (23) Mitchell, B. J., Proc. Conf. Ind. Appl. X-Ray Anal., p. 253, Denver, 1957. (24) Pickup, R., Colonial Geol. ;Ilineral C Resources 5, 144 (1955). (25) Powell, A . R., Schoeller, W. R., Jahn, C., Analyst 60, 506 (1935). (26) Rankama, K., Joensuu, O.,Bull. commiss. g8ol. Finlande Nr 138, C.r. SOC.geol. Finlande Xr 19, 8 (1946). ( 2 7 ) Schoeller, W. It., ilnalyst 57, 750 (1932). (28) Schoeller, W.R., “Analytical Chemistry of Tantalum and Niobium,” pp. 51-63, Chapman and Hall, London, n“1
lY31.
(29) Schoeller, W. R., Jahn, C., Analyst 57. i-. 1932’1. ( 30). 57,, i. 2 (1932). - ~ , (30) Schoeller, W. R., Webb, H. W., Ibzd., 54, 704 (1929). Ibid., (31) Ibid., Ibzd., p. 709. ( 3 2 ) Slavin, M., Pinto, C. M., Bol. 21, 27 (1946); C.A. 42,7674~(1948). (33) Smith, J. L., Am. Chem. J. 5, 44 i~ 1883’1 1883’1. _ _ . (34) Ppeecke, A., Hoste, J., Talanta 2, 332 (1959). (35) Ward, F. N., Marranzino, A. P., BSAL.CHEM.27, 1325 (1955). (36) Waterhouse, E. F., Schoeller, W. R., Analyst 57,284 (1932). (37) Wilkins. D. H.. Talanta 2. 355 (1959). ’ (38) Williams, A. F., J . Chem. Soc. 1952, 3158. ~
LITERATURE CITED
(1) Atkinson, R. H., Steigman, J., Hiskey,
C. F., ANAL. CHEM. 24, 477 (1952).
(2) Bandi,
W.R., Buyok, E. G., Lewis, L.
L., Melnik, L. XI.,Ibid., 33,1275 (1961). (3) Burstall, F. H., Swain, P., Williams, A. F., Wood, G. A., J . Chem. SOC.1952,
1497.
(4) Burstall, F. H Williams, A. F., Analyst 77, 983 (19b2). (5) Campbell, W. J., Carl, H. F., ANAL.
CHEM.28,960 (1956). (6) Cunningham, T. R., IND.ESG.CHEW, ANAL.ED. 10, 233 (1938). (7) Dinnin, J. I., - 4 N 4 L . CHEV.25, 1803 (1953). (8) Dobkina, B. &I., Petrova, E. I., Zazodskaya Lab. 25, 1064 (1959).
~
RECEIVED for review November 28, 1961. Accepted March 2, 1962. VOL 34, NO. 6, MAY 1962
613
