Application of modified counter-current technique to the determination of tungsten in molybdenum

Andyiita CLimica At&a EIscvfcr PubIiahinq Company,

Printed

29

Anrstcrdam

in The Nrtlwxlands

APPLICATION OF MODIFIED COUNTER-CURRENT DETERMINATION OF TUNGSTEN IN MOLYBDENUlM

S. ICA1.IAIANI4U’. E. W. HOBART

AND H. Ii. OBEIITHIN

Ledorrx & Company,

07666 (U,S.A

(Rcceivcct

August

Te’eurreck.N.J.

Sth,

TECHNIQUE

TO THE

.)

I 9G7)

Counter-current extraction techniques have been frequently used in biochcmistry and organic chemistry to perform separations that wuuld be difficult, if not impossible, by other means. However, little if any use has been made of this techniclue in inorganic analysis. The mathematics of the double withdrawaf counter-current extraction technique have been prcscntecl by HIBBITS 1. ‘13ecausc of the potential of the counter-current technique to the field of analytical chemistry, the application of thcmcthod to a rather difficult inorganic analytical problem was examined asdcscribccl below. The determination of tungsten in molybdenum appears to be such a problem. Its direct determination (no separation) is not feasible by the dithiol procedure2 because of the large concentration of molybdenum. Separations, such as removal of molybdenum as the sulfide in a tartaric-sulfuric acid medium”, arc tedious and cumbersome. Adsorption of molybdenum (clution of tungsten) on an anion-exchange column is feasiblc4, but it is time-consuming and is restricted to a sample of about I 6. After this manuscript was written, a method by NEBI’ ASD DOGE~ was published which is based on the different be11avior of molybdenum and tungsten toward reducing agents prior to the extraction of the respective thiocyanate complex. The anion-exchange elution data of HAGUE et ~2:~ indicate a difference in the stabilities of the chloride-fluoride complexes of tungsten and molybdenum. It was hoped that this difference could be utilized by replacing the anion-exchange resin by a suitabk organic extractant, and that a solvent estraction procedure would allow the handling of larger quantities of molybdenum than is possible by the anionexchange procedure, DXPENIMEXTAL

The following procedure indicates the application of a modified countercurrent extraction technique to the determination of 5 p.p.m. or more of tungsten in 0.5-2.0 g of molybdenum. Procedwe Transfer a sample, weighed to the nearest mg, containing at least 5 pg of tungsten, to a polyethylene beaker. Add 2 ml of water, 15 ml of 40% hydrofluoric acid and, dropwise, concentrated nitric acid until complete dissolution of the sample is obtained. Evaporate to dryness on a water bath. Add 3 ml of the hydrofluoric acid and again evaporate to dryness. Dissolve the salts by gentle heating for I min with 90 ml of 6 M hydrochloric acid-z.4 M hydrofluoric acid. Anal.

Skim. AC&, 4x (1968)

29-34

S. KALLMASN,

30

E. W. HOBART,

H. K. ORERTHIN

In a l~olycthylcne separatory funnel shake 200 ml of methyl isobutyl ketone (MIBK) with CJOml of the mixed 6 M-2.4 M acid solution. A few drops of methyl orange added to the acid aids in readily recognizing the liquid interface in the translucent plastic separatory funnel. Discard the acid layer. In order to follow the procedure, it will be necessary to refer to Figs. I and 2. Transfer the sample to the scparatory funnel with a total of 90 ml of the mixed acid solution. Shake vigorously for I min. Call this funnel (a). . lJrc-ecluilibratc zoo ml of MIBK with 90 ml of the mixed acid in another separntory funnel (h), discarding the acid layer. Transfer the acid layer from funnel (a) to funnel (I]), shake for I min and allow the layers to separate. Add cp ml of new mixed acid solution to funnel (a) and now label this funnel (c). Shake vigorously for Acid

(a)

Pig. 1.

l’ypicnl

phase@)

)

(b)

flow

pattern for rnoclificcl counter-current

cxtmction.

Acid 1%0%!(s)

( 11)

& !z

L

1

(b)

atiw 1m1o-

72.25w 2.25Mo-

01.41w 0*34M”-

1 (C) 12.75W 12.75Mo-

1 (cl) 21.08W 3.u3mJ-

1

1

27.G4W 0.85Mo

31.32W 0.17Mo’

33.28W O.O32Mo-

1 l.OlW lO.M4Mo-

1 ‘4.UlW 4.UBM; -

a.zow 1.45Mo

11.74w 0.3UMo-

c 14.07w _17.82W O.OBMo O.O17Mo-

0.2ow D.ZlMo-

1 o.nuw 2.53Mo

2.07W l.GlMo-

1 O.O425W_ 7.83Mo

4 0.18W 3.32Mo-

1

-

82.2aw O.O3Mo-

-

1

1

I 0.47w 1.87Mo

-

-

1

1

44.37w 0.00lm101

i

5.24W 0.15hlo

1 0.03w 0.7GMo-

4 1.58W 0.24Mo-

32.05W 0.000Mo’

1 33.05w 0. OOOMo-

33.87W O.OOlMo-

1 32.71W O.OOlMo

1 20.2OW O.O03Mo-

1 22.07W O.OOlMo

4

4

3.53w O.!XMo-

37.71w o,002M”-

-

1

1

27.24W O.OOOMo

1

7.12W o.o37Mo-

0.08W O.OODMo-

11.03w 0.002Mo

I 2.4lW o.o07ni0-

J 3.41w O.O17Mo-

4.5GW O.OO’JMo

1

rig. 2. Fkxv pattern for pcrccntagcs (of the original nnlount prcscnt) of tungsten and ~nolybclcnun~ in the acid phase following the flow diagram of Fig. I. See text for explanation of n, b, c, and d.

Anal. Glrim. A&n,

41

(rgG8) 29-34

COUNTER-CURREKT

SEPARATION

OF

MO

AND

1’

31

I min and allow’the layers to separate. Transfer the acid layer from (c) and the MIBK layer from (b) to a new funnel (d), shake for I min and allow the layers to separate. The essential features of the procedure have now been given. By following the flow diagrams of Figs. I and 2, the analyst can either use the scheme presented in this paper, or devise one of his own. All new MIBK portions should be pre-equilibrated with the mixed acid mixture, before USC in the procedure. Combine all the acid layers in the far right-hand column of the flow pattern (labeled x, y, z in Fig. I). Add 14 ml of I:: I sulfuric acid and evaporate the solution to fumes of sulfur trioxidc. Add I ml of nitric acid and fume again. Repeat, if necessary, the addition of nitric acid and fuming, until all organic matter is destroyed. Wash down the sides of the beaker wit11 water, add I g of ammonium hydrogen sulfate and evaporate to strong fumes of sulfur trioxida. Continue with the removal of r&dual molybdenum and the development of the tungsten color as described in the litcrnturcfi. RESULTS

AND

UISCUSSION

The optimum medium for the separation of tungsten and molybdenum was evaluated by individually determining the distribution of the two elcmcnts between and MIBK. Data for this evaluation are solutions of varying acid concentration presented in Table I.

DISTRII3UTION SOLUTIONS

IiCl

(M)

OY AND

TUNGSTISN

AND

~IOLYIJDENUM

I-II:

1.2

0.2

1.2

Z..#

3.6

0.2

MO

_...-

CIILORlDl?-FLUORIDE

55 50 75 70

IV .--^ 45 40 25

3.6

1

3.0

4

GO

15

6.0

0.2

94

25

6.0

90

20

6.0

1.5 2.‘)

8.0

0.2

85 80

8.0

2.4

75

Pcrccnt

AQUIIOUS

o/o Extrrrctcdn

(M) .----

6

HRTWISISN

hI1131;

cxtroctcd

by

200

ml of MlUK

20

‘5

27 18 from CJOml of the acid mixture.

Because of the significant difference in the percentage extractions of tungsten and molybdenum in a 6 M hydrochloric acid - 2.4 M hydrofluoric acid (IS and 850/O, respectively), the separation of the two mctalsbycounter-current extraction is feasible. Theoretical values of the amount present in the combined aclueous phases using the double-withdrawal counter-current extraction technique’, are shown in Table II. These data indicate that quantitative separations can be obtained using the doublewithdrawal technique. However, it was hoped that a modified counter-current technique could be used which would require significantly fewer extractions and yet permit a quantitative determination of small amounts of tungsten in molybdenum. The extraction scheme evaluated is shown in Fig. I. Asal.

Chim.

Act.a,

41

(xgG8)

29-34

S. HALLMAh’X,

32

E. W. HOBART,

H. K. OBERTHIK

In this procedure, MIBK is added to the acidic solution of the sample (funnel (a)), and the phases arc shaken and permitted to separate. The MIBK phase is transferred to another separatory funnel, (c), and a fresh acid phase added. The acid phase is also transferred to another scparatory funnel, (b) and a fresh MIBK portion added. After these two funnels are shaken, the acid phase from (c) and the MIBK phase from (b) are combined in another separatory funnel (d), shaken and separated, etc.

----.._ No. cl/ .SL(l&~S -._-_-.--~--_.-..-.

_-_-. ----- ..__ _No. of cxlriictious ..--

9 11 13 15 23 -..-

_.._ -

._.._._--

I_LL.-.._-.

I.3 I r, z7

_ . ..-.--

u Ttworcticnl

.___ - .----. IV

!)7*‘3

..__-_-_

..,-_...-...........

. I... ‘;i, No

__. ., ..-....---.. 97.2 98.08 07.=3 98.15

20 20

_...-

- ._I‘yO

.

.

. __

_

0.02 z.qG. IO-if 5. IS). zo-,s 9.23*10-6 8.80* -.-.-..- ...- .

IO-@ _

rmutts.

Figure z shows the percentage of tungsten and molybdenum present in the acid phases (aflev cnc/r exlvaction) following the flow diagram of Fig. x. For example, when equilibrium is rcachcd, the acid phase from the first extraction will contain 550/O of the tungsten and 15% of the molybdenum originally present (marked (a) on Fig. 2). If the acid phase is trcatccl with a new MIIBK phase [(b) in Fig. z], after extraction and equilibriunt, the acid phase will contain 72.250/O (85% of 85%) of the tungsten ancl z.zsryO of the molybdenum originally present. If the MIl3K phase from (a) is treated with new acid C(c) in ‘Fig. 23, then, after extraction and equilibrium, this acid phase will contain 12.750/~ of the tungsten (85o/o of the 15% which remained in the MIBK phase after extraction at (a)) and 12.75% of the nlolybdenuln. If the MIBK phase from (b) is combined with the acid phase from (c) and these phases shaken and equilibrntcd [(d) in Fig. z], the acid phase will contain 2~.680/~ of the tungsten, and 3.83% of the molybdenum originally present. The following information can be obtained from Fig. 2. (I) After the first extraction of the acid phase with MIBK, if the acid phase is treated 7 times with new MII3K phases, the final acid phase will then contain 27.24% of the original tungsten present and a negligible amount of the original molybdenum. (2) Treating the original MIBK phase 5 times with fresh acid will result in 0.0425~/~ of the original tungsten and 7.83% of the original molybdenum being present in the final acid phase, It is apparent that in order to obtain quantitative recovery of the tungsten, the acid portions must be combined, Thus, in the example shown in Fig. 2, the acid phases containing 27.240/O W, o.ooo”/o MO; 32.7x0/O W, o.oor”/o MO; 22.07*/~ W, O.OOX~/~ Mo;‘xr.03% W, o.ooz”h MO; and 4.$1*/~ W, O.OO~% MO, would be combined. The total amount of tungsten in the combined acid portions equals 97.6x% of the amount originally present, together with o.oo9°/o of the amount of molybdenum originally Anal.

Ctiinz.

Rem,

41 (ztgG8) 29-34

COUNTER-CURREST

SEPARATION

OF MO ASD

w

33

present. These data can be represented more readily, if the flow scheme in Fig. 2 is called 8 “across” and 5 “down”. Table III summarizes the total percentage of the original tungsten and molybdenum obtained in the combined acid portions (combined as in the preceding example) after other combinations are calculated by computer’. Thus, when the procedure labeled G across, 3 down is used, 89.48% of the tungsten originally present should be obtained in the final acid portions, contaminated by only d.o24O/‘& of the amount of molybdenum originally present. This small amount of molybdenum does not interfere in the dithiol procedure of HOBART AXD HURLEY~.

RISCOVISRY

OF

I’UNCTION

OF

TUNCXTISN VARYING

AND TlfIZ

-__.---_._-__-I_

I’A’CTISRN

-.--_-

I;low

$vocedttrc

.__

_...

6

~lOLY11I~I’.NUhl

l’I.OW

_.

_.__-~-.--_-_--_._._

G G

2

7

3

3 8

4 5 3

8

4

(yO)

CV

-._ ._.. - _....

3
acrow

_--..

Told _.-_-_-

nnlorblrl

hlODII’IItI>

COUNT15R-CURRE.NT

AS

A

--..-.__

MO

89.48

0.024

QG.60

o.oGr

99.01 85.92

0.128

95.00 9hI

0.013 0.030

82.02

0.002

_._

0.004

93.05 97.61

OF

TUNGSTI?.N

IN

ncici portions

using flow pattern

of sn,?lpCe (g)

IV fo1mi

p*p.?n. iv

(pg)a

-

I3

26

T.0

-

20

20

2.0

-

2.0

50

2.0

100

1.0 1.0

10 ;:

1.0

IO0 ._.-,..--corrcctcd

200

indicated.

hlOI.YRDENUhl

0.5

I.0 1.0 ---__ a lknults

X.XTHACTION

I)

n --.-.^-__.

0.004 8 5 0.009 ._-- _.-..-_ ..-_.-.-._-..--...-.------_______.-. mThcorcticnl amount present in combined

DIITERMINATION

UY (I%.

--.-______ for solubility of tungsten

44 99

22

25 25

150

34 52 74 I25 225

24 22

._._-._ .--_-_ ~_--_I-_in ivII1IJIC.

24 25 25

The method described here (G across, 3 down) was applied to the determination of tungsteninamolybdenumsamplecontainingzof3p.p.m.of tungsten (as established by cooperative work in several laboratories with the ion-exchange method) to which varying amounts of tungsten were added. The results are shown in Table IV. The successful application of this modified counter-current extraction technique to the determination of tungsten in molybdenum, will, it is hoped, stimulate Anal.

Skim.

Ada,

41 (x968)

29-34

S, KALLMANN,

34 others

to

analytical

apply this chemistry.

tcchniquc

to other

difficult

E.

W.

separation

HORART,

H.

problems

K. OBERTHIN

in inorganic

SUMllfAfiY More than trace amounts of molybdenum interfere in the determination of tungsten by the dithiol method. A simplified counter-current extraction method is described which allows the determination of 5 p.p.m. or more of tungsten in a molybdenum matrix. The optimum conditions for the separation were a 6 M HCl-2.4 M HI? medium and methyl isobutyl ketone as cxtractant; the percentage extractions in a single pass were Irs’yO anct IS’%, for molybdenum and tungsten, respectively.

Ix nlolyb~i~ne @nc clans le dosage clu tungstenc par la m&ho& au clithiol, IJn procecl6 simpfifi6 par extraction :I contrc courant cst cl&-it; it pcrmet le dosage de 5 p,p.m. 011 plus de tungstenc clans une matricc de molybdene. Lcs conditions optima sont : milieu I-ICI G M-HI; 2.4 M ct methyl isobutylcdtone comme extractant. Les *I& d’extraction clans un simple passage sont Ss’y, pour le molybdhne et 15% pour le tungstfinc. ZUSAMMENFASSUNL;

Sind mchr als Spuren Molybdtin vorhanden, so stijren sie clie J3cstimmung von Wolfram mit der Dithiol-Methoclc. Es wird ein vereinfachtes Gcgcnstromextraktionsverfahren bcschricben, clas die ~est~rnrnun~ von 5 p.p.m. oder mchr Wolfram in einer Molybdanmatrix gestattct. Die optimalen Beclingungcn zur Trennung sind ein Gemisch aus G M HCl und 2,4 M HF und Methyl-isobutylketon als Extraktionsmittel. Die prozentuale Extraktion bci cinem Schritt betrtigt 85% fur Molybdtin und ~5%

Imwgutric A ucclysis,

J.