Radiometric titration of rare elements

International Journal of Applied Radiation and Isotopes, 1957, Vol. 2, pp. 117-128, Pergamon Press Ltd., London

Radiometric Titration of Rare Elements DETERMINATION OF BERYLLIUM, AND THALLIUM

ZIRCONIUM

I. P. ALIMARIN, I. M. GIBALO, and I. A. SIROTINA Moscow State University, V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry of the Academy of Sciences of the U.S.S.R.

(Received 15 March 1957) The paper contains experimental data on the volumetric determination of beryllium, zirconium, and thallium by a radiometric titration method. In titration of beryllium and zirconium, diammonium phosphate and phosphoric acid were used as the reagent. Titration of thallium was carried out with potassium iodide, potassium chromate, phosphotungstic acid and sodium tetraphenylboron. New volumetric techniques were developed for determining beryllium, zirconium, and • thallium in industrially important products. The composition of precipitates formed was studied. It was shown that it is possible to determine the equivalence point by calculation from two known points of the radiometric titration curve.

DOSAGE R A D I O M E T R I Q U E DES E L E M E N T S RA RES D E T E R M I N A T I O N DU BERYLLIUM, DU Z I R C O N I U M ET DU T H A L L I U M Ce m5moire prdsente des donn6es expdrimentales sur la d6termination volum6trique du b5ryllium, du zirconium et du thallium par une mSthode de dosage radiomStrique. Pour le dosage du b5ryllium et du zirconium, les r6actifs utilisSs sont le phosphate de diammonium et l'acide phosphorique. Le dosage du thallium est effectu6 avec l'iodure de potassium, le chromate de potassium, l'acide phosphotungstique et le t6traph6nyl borylsodium. De nouvelles techniques volum~triques ont 5t6 mises au point pour la d6termination du b6ryllium, du zirconium et du thallium darts des produits d'importance industrielle. On dtudie la composition des pr~cipitSs form6s. On montre la possibilit5 de d6terminer par le calcul le point d'6quivalence ~ partir de deux points connus de la courbe de dosage radiomdtrique. PA~HOMETPHLIECHOE T H T P O B A H H E P E ~ H H X 3JIEMEHTOB (Onpe~e~eH~e 6epHsxnHR, tI~pKOHnn H TaJIJIID:I) B CTaTbe nss~ara~oTc~ ~aH~sie ~HcnepHMeHTaab~LIX pa60T no 06~eMHOMy onpe;~eae~mo 6epHnann, nigpRoHrrn ~ Ta~zIH~ I~IeTO~OMpa~oMeTpHqecKoro TtlTpoBaItH~I. ~JI~ TrITp0BaHH~ 6epna~nA ~ I~pHoHrm B Ka~eCTBe peaHTHBa npriMeHm~ ~;BysaMem~eHHbIri~oC~aT aMMOHH~I n 4pOC~popHyto RHCaOTy. T a n ~ r i THTpOBaaU ~ O ~ O M ~annn, xpo~aTOM, ¢OC~OpHOBOabdppa~lOBOi~ ~C~IOTO~ ~ TeTpa~peH~a6opHaTpHeM. P a a p a 6 o T a ~ ~oB~m o6~e~m,m ~eTO~BI onpei~eae~H~ 6 e p n n ~ , /414p~oHHn n TaJI~fn B TexHHqecH~ BamHhPA o6%eHTaX. I/Isyqeg COCTaB o6pa3ymn~Hxcn oca~Ho8. ~oHa3aHa

BO3MO~HttO CTB

onpe~eJieggg

MoMeltTa

DHBHB aJIeHTHOCTH

nyTeM no ~ByM TOtIHaM HpHBOI] pa2~noMeTpnqecHoro THTpOBaHrIH. I17

MaTeMaTHqeCHHM

118

L P. Alimarin, L M. Gibalo, and L A. Sirotina

GENERAL REMARKS

A ~ww radiometric technique for volumetric analysis has come into use in recent years~a,2,3,4,5, 6) along with such physicochemical techniques as conductometry, potentiometry, and amperometric titration. This technique can be used primarily in such cases where a very slightly soluble compound with constant composition can be obtained and where a suitable radioactive tracer can be selected for determining the equivalence point. In many cases the substance can be extracted from the solution with organic solvents. This technique, together with precipitation and complex formation, can considerably increase the field of use of radiometric titrations. ~7) Titration is carried out as follows: A solution of the reagent is added by drops while stirring to a beaker containing the initial solution (Fig. 1). One or both of 'To

Tovocuurn

FIG. 1. A p p a r a t u s for radiometric titration. 1 - - t o atmosphere; 2 - - t o v a c u u m llne.

the reactants must be radioactive. A slightly soluble precipitate is formed. After a certain amount of the reagent has been added, the solution is drawn up into the jacket of counter A through a filtering tube and the activity is measured. The result of the measurement is multiplied by the factor

K_Vo+ V0 V

V0 is the initial volume of the

solution and Vis the volume of reagent added. The solution is then returned to the beaker. Titration is being continued and the solution activity measured from time to time. After the equivalence point is reached, a small excess of the reagent will lead to a sharp rise in the solution activity, which will be registered by the counter. A titration curve is plotted, using the obtained activity data. The equivalence point is found either graphically, from the point of intersection of straight lines, or is calculated from two known points. This technique should find wide use in laboratory practice on account of the great variety of precipitation reactions, the possibility of determining the equivalence point from two known points, and the simple apparatus required. A silicon-organic compound, methylchlorosilane, should be recommended as hydrophobing agent to prevent the adsorption of radioactive materials on glass surfaces during radiometric titration. ~s) A 1 per cent solution of methyl-chlorosilane in carbon tetrachloride was used in the experiments. The surface to be hydrophobed should be cleaned and thoroughly degreased. Therefore all the beakers, flasks, burettes, pipettes, etc., were meticulously cleaned with a sodium dichromate solution, then washed with water, acetone, and benzene. The cleaned and dried glassware was then rinsed with 1 per cent solution of methyl-chlorosilane in carbon tetrachloride and dried at 120 to 140°C for 11 to 2 hours. After such treatment the glass is not wetted by water and almost completely ceases to adsorb radioactive substances. The aim of this investigation was to determine beryllium and zirconium with a phosphate, and thallium with iodide, chromate, phosphotung.stic acid, and sodium tetraphenylboron in xmportant industrial materials, using the radiometric titration method. M a n y very slightly soluble phosphates are known, but only few of them are used in

119

Radiometrie titration of rare elements

analytical chemistry on account of their varying compositions, poor filtering properties of the precipitates, and poor selectivity of the reagent. The use of phosphates for radiometric titration has already been described in

OF B E R Y L L I U M

DETERMINATION

Most volumetric methods for quantitative estimation of beryllium are based on the hydrolytic decomposition of its salts.~1°,n,~2,13~ Potentiometric and amperometric techniques have also been suggested.a4,15~ These are based on the ability of beryllium to form complex fluorides. A disadvantage of the volumetric methods is that they can be applied only to pure beryllium salt solutions. There are no volumetric methods for determining beryllium in the presence of other elements (Fe, AI).

TABLE 1.

literature, g A N G E R (1,~,3) used this method for determination of magnesium in an ammonium hydroxide medium and MOELLER a n d SCHWEITZER (9) estimated thorium in the presence of yttrium and the rare earth elements in acid medium.

buffer acetate solutions at pH values from 5 to 5.5. Titration of solutions of equal molar concentration (0.1 M, 0"05 M, 0.01 M) showed that both in direct and back titration 3 volumes of beryllium sulphate solution take two volumes of diammonium phosphate of the same molar concentration. I t leads to the conclusion that berylliumorthophosphate and not berylliumammonium phosphate is formed in titration, according to reaction

Composition of precipitates formed by Be+2 and PO4 -s ions in the process of radiometric titration

Be weight in sample (mg)

Theoretical amount of Bes(PO4) 2 (mg)

Be3 (PO4) 2 found (mg)

6.2 7.6 8.9

49.72 60.94 71.37

49.51 59.48 70.67

BeO (mg)

]

P,Os (mg)

Theoretical amount

Found

Theoretical amount

Found

17-20 21.08 24.69

17.27 21.37 24.36

32'52 39"86 46"68

32"64 40.43 47"91

It has already been stated that hydrolysis prevents the achievment of constant composition of the compound when beryllium phosphate is precipitated. ~16~ GORYNSmNA(m and HUR¢~and his co-workers ~18~determined beryllium in alloys and in minerals in the form of beryllium ammonium phosphate (BeNH4PO4), using the masking effect of trylon B, and attained satisfactory results. We made a detailed study of conditions necessary for quantitative precipitation of beryllium by phosphate and also of the composition of compounds formed by the Be +2 and PO4 -3 ions. The large amount of data obtained allowed us to establish that beryllium is precipitated quantitatively from

3BeSO4 + 2(NH~)2HPO4 = Be3(PO4) 2 + 2(NH4)2SO 4 + H2SO~. The precipitate formed in the phosphate titration of beryllium was analysed for BeO and P205 contents. The results are listed in Table 1. It can be seen that in acetic acid medium in the presence of ammonium acetate at p H values from 5 to 5.5 the product formed will be beryllium orthophosphate (Bea(PO~)2). Up to the present beryllium orthophosphate has not been used for analytical purposes, but a number of authors have obtained this compound and studied its properties) 19~

I. P. Alimarin, I. M. Gibalo, and I. A. Sirotina

120

The beryllium determination was carried out as follows. 10 ml of the acetate buffer (pH 4.99-5.57) and 2.6 ml of 15 per cent ammonium acetate solution were added to 2-5 ml of beryllium sulphate (0-7-9 mg). A solution of diammonium phosphate (0.0913M). containing radioactive phosphorus-32 (activity = 20,000 to 30,000 count per minute per ml) was then added to this solution drop by drop, with energetic stirring. After a fixed volume of the solution had been added the solution was drawn up into jacket A (Fig. 1) and its activity was measured. Several points lying in front of and beyond the equivalence point were thus obtained, making allowance for the change in volume. The equivalence point was determined graphically or by calculation and the amount of beryllium in sample was computed. Plots of the curve for radiometric titration of beryllium with diammonium phosphate are given in Fig. 2 and data on quantitative estimation of various amounts of beryllium in Table 2. The table shows that beryllium can be successfully determined by radiometric titration technique. It was pointed out earlier that considerable time (about 50 min) is required for determining a number of points on the radiometric titration curve. (3) Therefore the possibility of determining the equivalence

14012

/

•~ i o o ¢

J

C

6oc 20C

O

\. 1

/

I

Table 2.

Determination of beryllium by the radiometric titration method

Be

(0.1374 M) (mg)

0"60 1"00

1"53 2"00 5-00 7"00

0.74 1-24 1.90 2.48 6.20 8-68

0.0913 M Phosphate solution used (ml) 0.59

Be

found (mg)

1.00

0-73 1.24

1.53 2"03 4-84 6.83

2'53 6.08 8.47

Deviation per cent

--1.40 4-0.0 ±0 4-1.60 --2.00 --2.43

1.90

point from two points of the radiometric titration curve was studied and an attempt was made to develop a general mathematical expression determining the equivalence point. Three types of radiometric titration curves were considered : (1) Titration with a radioactive reagent (Fig. 3a). In this case it was necessary to obtain two points beyond the equivalence point on the curve. Let A s' and A~' be the solution activity after addition of Vz and V2 millilitres of the reagent. V~' is the equivalence point. F is the background count (the laboratory background plus solution activity due to the solubility of the precipitate). From similarity of triangles A B D and A C E it follows that Ve' =

I

Sample size (rag)

V I ' ( A 2' - - F ) - - V~'(A~' - - F ) A~' - - A 1'

/ 2

3

4

5

Reagentadded

6

7

8 mt !

FIo. 2. I. Titration of 6"2 mg of beryllium with a 0.0913 M (NH4),HPO 4 solution. II. Titration of 8.48 mg of phosphorus with 0' 1375 M solution of beryllium sulphate. 1--counts per min; 2--reagent added, ml.

[

--

_-

Reagent odded FIG. 3. Radiometric titration curves. 1--counts per min; 2--reagent added, ml.

rnt

121

Radiometric titration o f rare elements

At B e : A 1 ratios of 1.5, beryllium was slowly precipitated by phosphate; quantitative precipitation was obtained only after adding a large excess of the precipitation agent. It should be pointed out that in the presence of other elements (Ca, Fe, Cu, Mg) even large amounts of aluminum do not interfere with beryllium determination. Presumably Be and AI form mixed complex compounds with E D T A (ethylene-diamine tetra-acetic acid and beryllium can be displaced from these compounds by elements forming a more stable complex. In the presence of other elements, beryllium determination was carried out as follows. An excess of three- to four-fold amount of the 7.5 per cent E D T A solution was added to a solution containing a mixture of

(2) Titration of a radioactive substance with a non-radioactive reagent (Fig. 3b). Here it was necessary to obtain two points lying before the equivalence point of the curve. As can be seen from the figure, A 1

Ve --

V1

A 2 - - F - - V~--V2" After simplification, the equation is solved for 1)~, giving

Ve = V2(A1 - - F ) -- VI(A2 --F)

(2) A 1 -- A 2 (3) Titration of a radioactive substance with a radioactive agent. Both methods for determining the equivalence point can be used in this case. Two-point titration of beryllium greatly reduces the time o f analysis and gives TABLE 3. Be weight in sample 0"74 1"24 1-90 2"48 6'20

Two-point titration of beryllium with a 0.0193 M ammonium phosphate solution VI

I

A1

V2

280 542 792 1201 800

4 5 4 8 7

A2

F

V,

Be found (mg)

Deviation (per cent)

570 701 1291 3550 1435

65 60 61 61 65

0.61 1 "02 1.53

0.75 1.26 1.90 2.55 6.00

+1.4 +1.6 0 +2'8 --3'2

! i

2.06 4.84

elements (1 M concentration). An equal volume of acetate buffer (pH ---- 5.5) and a 15 per cent ammonium acetate solution in a Determination of beryllium in the presence of other volume equal to that of E D T A solution elements were then added. Titration was carried out Experiments have shown that in the with diammonium phosphate. The amount presence of E D T A (7.5 per cent) beryllium of beryllium present was determined either is precipitated quantitatively, whereas A1, graphically or by calculation, using equation Fe, Cu, Mn, Pb, Cr, Ca, Mg, Co, Ni, and (1). The results are given in Table 4. As can be seen from the table, the error in other elements remain in the solution. Special attention was given to the deter- determinations of beryllium in the presence mination of beryllium in the presence of A1, of other elements does not exceed the Fe, and Cu, as the first two are common radiometric measurement error. companions of beryllium, while copper is the chief component of beryllium bronzes. The Determination of beryllium in bronze determination of beryllium in the presence of A weighed amount (0-8-1-3 g) of bronze large amounts of aluminium was found to be was dissolved in 15 ml of cold nitric acid difficult. ( 1 : 1 ) and the solution was evaporated satisfactory results, as can be seen from Table 3.

1. P. AIimarin, I. M. Gibalo, and I. A. Sirotina

122 TABLE 4.

Determination of beryllium in the presence of other elements Weight in sample (mg)

Be

Cu

Fe [

0.62 2'48 7-44 10.00 12-0 4.00 4.96 0.50 8.50 5.00 O-25

64.0 381.0 60"0 100'0 6-4 20.O 180.0 100"0 32"0

18.05 I00.0 30.0 50.0 73.0 5.0 85.0 40.0 16.8

A1

Ca

1.3 38.0

10.0

120.0 90.0 40.0 20"0 2"0 120.0 120-0

30.0 25.0 40-0 40-0

Co

Mg

25.0 20.0 40.8

Ni

30.0 35.0 50.0

35.0 50.0

40.0

1-24

24.80

almost to dryness. Distilled water was added to the residue, and heat applied until the salt dissolved completely. After cooling, the solution was transferred to a 25 ml volumetric flask; it was neutralized with a 2 per cent a m m o n i u m hydroxide solution and distilled water was added to the mark. For beryllium determination, 5 ml aliquot portions were used. 25 ml of 7.5 per cent EDTA solution, 30 ml of acetate buffer, and 15-25 ml of 15 per cent ammonium acetate solution were added to each portion, and it was titrated with 0.0913 M (NH4)~HPO 4 solution. The results of analyses on Be in bronze are given in Table 5. Table 6 gives the results of beryllium determinations by titration, using the twopoint technique. Tables 5 and 6 show that the beryllium content of bronze can be successfully determined by this method.

(g)

Be found (per cent)

0'8363 1"0313 1"2175

2"12 2"12 2'12

2"15 2"11 2"13

0.62 2-39 7.32 10.09 11-77 3.97 4.82 0.48 8.21 5-11 0.26 1.23 25.40

0 --3.63 --1.60 +0.90 --1-88 --0.75 --2.80

--4.00 --3.40 +2.20 +4.00 --0-80 +2-40

A weighed amount of (0"5-0.7g) of beryllium concentrate was fused with a fourfold amount of sodium fluoride ~20) in a platinum crucible at a temperature of 1000-1100°C for 40 to 50 min. The product was allowed to cool and a small amount of sulphuric acid was added to the crucible, which was then heated on a sand bath. After complete decomposition of silicic acid and of fluorides, sulphuric acid was evaporated almost to dryness and the residue was dissolved in distilled water. The crucible contents were transferred to a 50 ml volumetric flask and neutralized with dilute ammonium hydroxide until the solution became slightly turbid. The particles were dissolved by 1 or 2 drops of dilute sulphuric acid and distilled water was added to the mark. For beryllium determinations, to 5 ml TABLE 6.

Be content in bronze according to specifications per cent

Deviation (per cent)

The determination of beryllium in concentrate

TABLE 5. The determination of beryllium in bronze (Equivalence point found graphically) Weight of bronze sample

Be found (mg)

Weight of bronze sample

The determination of beryllium in bronze (Equivalence point calculated)

Aa

V~

A2

F

V,

Be found (per cent)

6 / 161 12 280 6 120

14 14 14

398 } 68 330 68 360 70

2.86 3.52 4.33

2.10 2"11 2"15

V~

(g)

0-8363 1-0313 1.2513

[I

Radiometric titration o f rare elements

portions of the solution were added 10-12 ml of E D T A solution, 25 ml of acetate buffer (pH 5.13), and 15 ml of 15 per cent ammonium acetate solution, and the titration was carried out with a 0.0913 M (NH4)2HPO4 solution. The results are listed in Tables 7 and 8. Table 8 contains the results of beryllium determinations by titration, using the twopoint technique. Comparison of results for the beryllium content of concentrate as determined by radiometric titration with results of gravimetric analysis shows that the volumetric TABLE 8. Concentrate sample weight

(g)

123

method proposed can be used in analysing materials containing beryllium. TABLE 7.

The determination of beryllium in concentrate (Equivalence point found graphically) Be found

Concentrate sample weight

(g)

By volumetric analysis

By gravimetric analysis

0.6059 0.6256 0-6558

10.80 10.90

11.I0 11.01 I1.10

11-03

The determination of beryllium in concentrate by the two-point titration technique

I V1

At

V2

A2

Be found (per cent)

F ]

0.6059 0.6256 0.6558

4 4 6

268 216 340

6 5 8

459 287 483

THE DETERMINATION

Zirconium is usually determined gravimetrically by precipitation from acidic solution with ammonium phosphate or phenylarsonic acid. A number of volumetric methods for determination of zirconium, both directly121,22,23) (titration with E D T A using Eriochrome Cyanine or Alizorol Cyanone as an indicator and amperometric titration with a fluoride or Cupferron), and indirectly~24,25,26) (zirconium is separated in the form of a slightly soluble compound--selenite, iodate, or phosphate--which is dissolved, and the anion bounded with zirconium is determined volumetrically). The radiometric titration method was used for direct determination of zirconium in alloys without preliminary separation from other elements. ~7) A solution of zirconium chloride was prepared by fusing a weighed sample of ZrOz with a six- to eight-fold amount of potassium pyrosulphate and dissolving it in dilute ( 1 : 4 ) hydrochloric acid. The zirconium concentration was determined

68 66 64

By volumetric analysis

By gravimetric analysis

10-85 10-46 11 '03

11.10 11.01 11.10

!

[

OF ZIRCONIUM

by

the gravimetric phosphate method. The concentration of the phosphoric acid solution was determined with magnesia mixture. 200C 180C

140C .c

~ lO0C

\

o U

20(? ~ 0

1

2 3 4 Reagent added

5

6

7 rnL

FIo. 4. I. Titration of 13.68 mg of zirconium in 25 ml 0.05 M phosphoric acid solution. II. Titration of 19.6 mg of phosphoric acid in 25 ml of 0"05 M zirconyl chloride solution. 1--counts per min; 2--reagent added, ml.

I. P. Alimarin, L M. Gibalo, and L A. Sirotina

124 TABLE 9.

Determination of zirconium by the radiometrie titration method in the presence of other elements. Amount used (mg)

Zr 2"7 16.2 19.8 5'4 10.8 18.0 29"7 27"0 4-5 6.3 2"7 10.8 18"0 26.1 8.1

Ti

Fe

A1

Co

Ni

Cu

50-0 1000.0 500.0 100-0 20-0 2.0

10.0 10.0

100.0 400-0 400.0 300.0

10.0 25"0 10.0 15'0 20.0

The radioactive isotope used was phosphorus-32 (Na2HPO 4 solution). Small amounts were added to a phosphoric acid solution. Dilute 0.1 M and 0.05 M, and 0.01/M working solutions were prepared from initial solutions. The equivalence point was found graphically by extrapolating the branches of the titration curve to the point of intersection. Fig. 4 shows the radiometric titration curves for zirconium and phosphoric acid. A large number of experiments carried out under various conditions (solution, acidity from 0.5 to 2"5 N, concentration from 0.01 to 1 mg per ml, varying order of titration) showed that 1 mole of phosphoric acid is used up in titration of 1 mole of zirconium chloride. Hence the titration reaction equation will be ZrOC12 -t- H3PO4 = Z r O H P O 4 -+- 2HC1. The precipitate composition was confirmed by chemical analysis. The zirconyl phosphate precipitate dissolves appreciably when the acidity is increased to 3.5-4 N.

Determination of zirconium in the presence of other elements To find out the possibility of volumetric estimation of zirconium by phosphoric acid

25.0 25.0 30.0 20"0 10"0 15"0

50-0 500.0 15"0 30"0 20'0 15"0

30.0 30"0 20.0 20.0 10.0 40.0

Zr found (mg)

2.7 16-1 19.9 5-46 10.89 18"0 29.5 26.6 4.4 6.25 2.65 10.9 18.1 26"0 8-05

in the presence of other elements, titrations of zirconium solutions with 0.5 M phosphoric acid solution were carried out with addition of Fe +3, A1+3, Co +2, Ni +2, Cu +2, and Ti +~. (The solution acidity was 2 N and the initial volume 25ml.) The results are listed in Table 9. The table shows that zirconium can be successfully determined in the presence of other elements. H 2 0 2 was added to the solution when the determination of zirconium was carried out in the presence of titanium.

Determination of zirconium in alloys Three samples of iron-base alloys containing various amounts of zirconium (9.51 per cent, 1.05 per cent, and 0.53 per cent) as well as large amounts (several per cent) of A1, Cu, Co, and Ni were available. The determination of zirconium was carried out as follows. A weighed sample (1-3 g) of the alloy was dissolved in 30 ml of dilute 1 : 1 hydrochloric acid heated on a sand-bath. The solution was cooled and the undissolved residue (silicic acid and part of the zirconium) was filtered off. The residue was washed on a filter two or three times with distilled water, the filter was dried and ignited at 900-I000 °.

125

Radiometric titration of rare elements TABLE 10. Alloy sample No.

Determination of zirconium in alloys

Weight of sample per 100 ml of solution (g)

Zirconium found (per cent) By radiometric titration

By gravimetric analysis

9.21; 1.10; 0.54;

9.32

1.0103 2.4820 3.1395

9.34; 1.05; 0.50;

9.51

1.06

1.05

0.55

0.53

After calcination* the precipitate was fused with potassium pyrosulphate. The product was dissolved in a small volume

(10 ml) of dilute 1 : 1 hydrochloric acid and added to the alloy solution. The alloy solution was then transferred to a i00 ml flask, and after dilution to volume with distilled water carefully mixed. 2025 ml aliquot portions were withdrawn and subjected to titration as described above with 0.05 M and 0"0l M phosphoric acid solutions containing the radioactive isotope phosphorus-32. The result of analyses are given in Table 10. The data prove that radiometric titration can be successfully employed for determination of zirconium in alloys.

THE D E T E R M I N A T I O N OF THALLIUM

The existing methods for determination of thallium (1) are based on its precipitation as a chromate or iodide.t~8, 29) Volumetric determination can be carried out in a hydrochloric acid solution with methyl orange as tracer. (3°) An amperometric technique for titration of thallium in the presence of other elements has also been suggested. ~31) A study was also made of the possibility of carrying out the determination of thallium by radiometric titration with iodide, chromate, phosphotungstic acid, and sodium tetraphenylboron.

Titration of thallium with potassium iodide Thallium

isotope thallium-204

with

a

1600

120C

\

X w

o

Radiometric determination of thallium with 0.1 M K I

TI sample weight (rag)

KI used (ml)

T1 found (mg)

Deviation (per cent)

0.46 1.14

0.018 0.046 0.075 0.15 0.22 0.30

0 "45 1"16

--2'0 +1"7 0 0 +3"2 --2"6

1.86

1"86

3"73 5"77 7"56

~<

u 40C

TABLE 1 I.

3.73 5.59 7.76

sac

'

specific activity of 150 mc/g served as tracer. The volume of solution was 2 ml. Titration was carried out in the presence of acetic acid. Fig. 5 gives the curves obtained for radiometric titration of thallium with potassium iodide and the analysis data are listed in Table 11.

0.05 d.1o o.15 0.20 ~ e n t added rnt

Fzc-. 5. Titration of small quantities of thallium with 0.1 M

potassium iodide solution (2 ml volume). 1--counts per rain; 2--reagent added, ml.

Determination of large amounts of thallium (10 rag) can be carried out rapidly, using the two-point technique. The results obtained are given in Table 12. It is often necessary to carry out the determination of thallium in the presence of lead, which reacts similarly. To remove the interference by lead, we used a double volume of ~saturated solution of EDTA, binding the lead in a stable complex. The necessary p H value of the solution was obtained by means of an acetate buffer with

* Siliclc acid was not separated from the precipitate, since it does not interfere with the determination of zirconium.

I. P. Alimarin, I. M. Gibalo, and I. A. Sirotina

126 TABLE 12.

Radiometric titration of thallium using the two-point technique ~<

T1 sample weight (mg)

T1 found (mg)

v~

Deviation (per cent) c 120C

6"51 8"37 10.20 12.10

i

0"28 0.37 0.46 0.54

6"33 8"36 10"40 12"20

--2.8 --0.1 +2.0 +0.8

c 802 D

/

~

/

/

×

x

a p H of 4. In the presence of EDTA at a p H of 4, thallium can easily be determined even with a fiftyfold amount of lead in the solution.

402 II

V

O

Titration of thallium with potassium chromate In the presence of ammonium hydroxide, thallium yields a yellow precipitate with good filtering properties when acted on by the chromate ion. The solubility of thallium chromate is approximately of the same order as that of the iodide, and the minimum amounts that can be determined using these reagents are therefore equal. Table 13 contains results obtained for radiometric titration of various amounts of thallium with potassium chromate, using the two-point technique. It can be seen from the table that thallium titration with chromate gives a sufficient degree of accuracy.

Titration of thallium with phosphotungstic acid Determination of thallium with phosphotungstic acid was carried out with solutions TABLE 13.

Titration of thallium with 0.05 M K2CrO4 using the two-point technique

Sample weight (mg)

T1 found (mg)

Deviation (per cent)

0"46 0"84 3'72 7"23 9"40

0 +1-2 --0.3 --3.1 +1.0 +1.8 +2.1

0"46 0'83 3"73 7'46 9"30 ll'10

I 1"30

13"90

14"20

0"2 0"4 Reagent. added

0"6 ml

FIG. 6. Titration of small quantities of thallium with 0' 1 M phosphotungstic acid solution (2 ml volume) 1---counts per min; 2--reagent added, ml.

containing the radioactive tracer thallium204 and with heteropolyacid labelled with phosphorus-32. The phosphorus-32 isotope was introduced into the acid molecule during synthesis of the acid. <3e~ The composition of the precipitate formed in titration of thallium with phosphotungstic acid is similar to that of the products obtained by substituting univalent alkali methods for four hydrogen atoms of heteropolyacid.<~3341 It follows that in titration the compound T14Ha[P(W~OT) 6] is formed. Precipitation was carried out in 0.5-1 N H N O a ; a precipitate of larger particle size is obtained under these conditions. Fig. 6 contains plots of the curves for TABLE 14.

Titration of thallium with phosphotungstic acid

Sample weight (mg)

v~

0"21 0'52 0"90

0'02 0"025 0"045 0"09 0"18 0"27

1"86

3"73 5"59

T1 found (mg)

0"22 0"51 0"90 1 '86 3"73 " 5"59

Deviation (per cent)

+4"8 --1'9 0 0 0 0

Radiometric titration o f rare elements TABLE 16.

TABLE 15. Titration of T1 with a 0.1 M solution of H~[P(W20~)~] in the presence of other elements Weight in sample (mg) TI

Pb

0"93 0"93 1 "86

124

1 "86

124

Hg

Ag

Bi 10

17 1.98

5OO 200

TI found (rag)

Reagent used (ml)

TI found (mg)

Deviation (per cent)

0-23 0-46 0.93 2.79 4.65 5.58

0'036 0"067 0"14 0.40 0'67 0"82

0'24 0"46 0'95 2"72 4'56 5'58

+4"3 0 +2'1 --2"5 --2"0 0

1 '86

Determination of thallium in the presence of other elements Titration with phosphotungstic acid allows to determine thallium in the presence of elements which react in a similar fashion (Hg, Pb, Ag, Bi). In the presence of nitric acid (1 N) phos.photungstic acid does not yield a precipitate with the elements mentioned, whereas thallium titration is quantitative. Table 15 gives the results of radiometric titration of thallium in the presence of other elements. As can be seen from table, considerable amounts of accompanying elements do not interfere in the determination of thallium. In the presence of silver, thallium cannot be determined when T1 : Ag ratio reaches 1: 50.

Titration with sodium tetraphenylboron Sodium tetraphenylboron forms a white precipitate with thallium. The data on TABLE 17.

Radiometric titration of T1 with 0.05 M solution of Na[B(C~Hs)4]

Weight of T1 in sample (mg)

0"93 0'94 I "84

radiometric titration of thallium with phosphotungstic acid and Table 14 the results of analyses for small amounts of thallium.

127

titration of thallium with this reagent are listed in Table 16. Experiments showed that thallium can be successfully titrated with sodium tetraphenylboron in the presence of lead if the latter is bound in a c o m p l e x ' b y means of E D T A It was found that small amounts of thallium (0.4 rag) can be determined in the presence of 150 times the amount of lead.

The analysis of industrial products Finally industrial products were analysed containing, along with thallium, zinc, cadmium, and copper. The product was prepared for analysis by simply dissolving a weighed sample in nitric acid and neutralizing the solution to the p H required, after which titration with sodium tetraphenylboron was carried out in the presence of EDTA. The results of analyses are listed in Table 17. As can be seen from the table, radiometric titration can be successfully used for the determination of thallium in industrial products.

Analysis of industrial products TI found

Sample No.

I

II III

Composition

T1, Cd T1, Cd T1, Pb, Cd, Cu, ZnS TI, Pb, Cd, Cu, ZnS Cu, TI Cu, T1

Sample Weight (rag)

N a B(CrHs) 4

used (ml)

By radiometric titration

By chemical analysis

By spectral analysis

0.1139 0-1446 0.1039 0.1039 0.1050 0.1023

0-022 0.028 0-027 0.32 0.028 0.028

0"11 0'14 0"14 0-17 0"14 0'14

>0.12 >0"12 0-14 0-14 0-1 0'1

>0'1 >0.1 0"1 0"1 ~0-1 ~0"1

128

L P. Alimarin, L M. Gibalo, and I. A. Sirotina

CONCLUSIONS (1) A n e w v o l u m e t r i c m e t h o d has b e e n p h o s p h a t e , b e r y l l i u m o r t h o p h o s p h a t e is d e v e l o p e d for the d e t e r m i n a t i o n of b e r y l l i u m f o r m e d ; z i r c o n i u m yields z i r c o n i u m phosa n d z i r c o n i u m w i t h p h o s p h a t e a n d of p h a t e in acid m e d i u m . t h a l l i u m w i t h iodide, c h r o m a t e , p h o s p h o (3) I t was p r o v e d t h a t in r a d i o m e t r i c tungstic acid, a n d s o d i u m t e t r a p h e n y l titration the equivalence p o i n t c a n be found boron. f r o m two k n o w n points. T h e properties a n d c o m p o s i t i o n o f the (4) R a d i o m e t r i c titration o f Be, Zr, a n d p r e c i p i t a t e were studied. T1 can be successfully e m p l o y e d for the (2) I t was shown t h a t in the r a d i o m e t r i c analysis of i m p o r t a n t industrial p r o d u c t s titration of b e r y l l i u m with d i a m m o n i u m c o n t a i n i n g these elements.

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