4-(5-nonyl)pyridine extraction of platinum from different aqueous solutions

Journal o f Radioanalytical Chemistry, Vol. 27 (1975} 15-24

4 - ( 5 - N O N Y L ) P Y R I D I N E E X T R A C T I O N

OF P L A T I N U M F R O M D I F F E R E N T A Q U E O U S S O L U T I O N S

REACTOR PRODUCTION OF CARRIER-FREE 199Au

M. IQBAL, M. EJAZ

Nuclear Chemistry Division, Pakistan Institute of Nuclear Science and Technology, P. O. Nilore, Rawalpindi (Pakistani

(Received February 25, 1975)

The partition of tracer-level (<10 =~ mole/l) platinum between various 4-(5-nonyl)-pyridine phases and aqueous nitric, hydrochloric, and sulphuric acid phases has been studied radiometrically as a function of the amine and acid concentrations. The effects of salting- out agents and some anions on the extraction of the metal are reported. The extraction data is compared with that of gold and conditions are established for the separation of daughter J99Au from neutron irradiated platinum. The distribution coefficients of various metal ions are given for the 4-(5-nonyl)pyridine - 10M HCI system and their factors for separation from platinum estimated.

Introduction

We studied the extractability of various metal ions 1-s with a high molecular weight

pyridine amine, 4-(5-nonyl)pyridine (NPy), elucidated compositions of extracted spe-

cies, and reported the conditions for the separation of these metals from fission prod- ucts, base metals, etc. using different mineral acid solutions. The work described in this communication constitutes part of a continued investigation of tl{e use of 4-(5- -nonyl)pyridine as a liquid anion exchanger and summarizes the results on the extrac-

tion studies of platinum from various aqueous solutions by the same reagent. A method is suggested for the production of carrier-free 199Au formed by the/J.decay

of 199pt which in turn is produced by the thermal neutron irradiation of platinum.

198pt(n,~/)199pt 30rain ~ 199A u ( T = 3 . 4 d ) O-

Though 199Au can also be produced by the successive neutron capture of 197Au

via 19SAu (0 c = 26000 barn) but the product thus obtained is not carrier-free. Var-

J. Radioanal. Chem. 2 7 {1975) 15

M. IQBAL, M. EJAZ: 4-(5-NONYL)PYRIDINE EXTRACTION

ious methods for the separation of gold from platinum are reported in the literature MALESZEWSKA and DYBZYNSKI 6 separated 199Au from 199pt with cation ex-

change resin and FIDELIS et al. 7 applied extraction chromatography using T B P - HC1 system, while RAKOVSKI et ai. 8 effected the separation using triphenylguani-

dinium chloride as extracting agent. All these methods either make use of high acid

concentration or are tedious and time consuming. The present communication makes use of 0.25M hydrochloric acid + 0.2M sodium thiosulphate for the separation of 199Au from 199pt by 0.1M 4-(5-nonyl)pyridine/benzene.

Experimental

Partition system

Glass vials of about 25 ml were utilized for partition ana the volumes of the aqueous and benzene phases were 2 ml each. The duration of contact between the phases was 5 min. This time was proved to be sufficient to reach equilibrium. The

"/-radioactivity of the samples from both the phases was measured with a well-type scintillation counter [NaI(Tl)]. The distribution ratio was obtained as follows:

Morg(total ) 7-count-rate per ml organic phase

Maq(total ) 7-count-rate per ml aqueous phase

where M stands for the metal.

All the extraction studies were made at room temperature (22 -+ 2 ~ Each ex- periment wai done in duplicate and the average values are reported.

Materials

4-(5-nonyl)pyridine (K & K Labs) was purified by distillation before use. As reported earlier 1'2 it is pale yellow oily liquid having a b.p. of 94 ~ at 0.8 Hgmm,

2o of 1.485 and d 2~ of 0.9208 g/cm 3. Its solubility in water is 1.2 g/1. Radio- n D active 197+199pt and 198+199Au tracers were obtained by irradiation of spectro-

chemically pure metals in the reactor PARR in a flux of 1.5 �9 10x an �9 cm -2 �9 sec - t .

Platinum was freed from gold by reversed-phase partition chromatography according to the method' of FIDELIS et al. 7 The tracers were taken up in different acid so-

lutions by dissolving the irradiated metals in hot aqua regia and then by repeated evaporation with the corresponding acids. The other chemicals used were of ana-

lytical-reagent grade.

16 J. RadioanaL Chem. 27 {1975)


'+~ |

i

- 1

,g E~+d],- -2

2 ~

Fig. 1. Effect o f mineral acid concentrat ions on the extract ion o f p la t inum by 0.1M 4-(5-nonyl)-

pyridine/benzene. Curves: 1 - HC1; 2 - HNO3; 3 - H 2 SO+

Results and discussion

The influence 'of the acidity of the aqueous phase on the extraction of platinum was studied in the range of 10 -2 - 10M hydrochloric, nitric, and sulphuric acid concentrations. It was found that in the nitrate and sulphate systems the maximum extraction of platinum into the organic phase is attained by extractions of acid concentrations close to 0.1M. With the increase in the concentration of nitric and sulphuric acids in the aqueous phase, the degree of extraction decreases (Fig. 1) appar- ently due to the competing action of the acids. A study of the dependence of the extraction of platinum from hydrochloric acid solutions shows that after the first maximum at 0.5M HC1 the partition coefficient slightly decreases and then starts increasing again from 5M HC1 indicating that two different complexes of the metal are being extracted. In dilute acid concentrations, platinum species of the type H2PtCI6_n(OH) n are probably extracted which are converted to more extractable hydrochloroplatinic acid 9 (H2PtC16) with the subsequent increase of the hydrochloric acid concentration in the aqueous phase.

Extraction of platinum with 0.1M 4-(5-nonyl)pyridine/benzene was investigated as a function of aqueous phase sodium chloride, nitrate, and sulphate concentrations from constant aqueous phase acidity of the corresponding acids. The results presented in Fig. 2 show that, in nitrate and sulphate media, no enhancement in the extrac-

J. Radioanal. Chem. 27 (1975) 17 2


x

2

I J

kJD

f

- 2 r~

Ig lotion], M -1 0

~ O

Fig. 2. Variation of the distribution coefficient of platinum with the concentration of salting- out agents at constant acidity by 0:IM 4-(5-z/onyl)pyridine/benzene. Curves: 1 - NaC1 (0.25M HC1); 2 - NaNO a (0.25M HNOa); 3 - Na2SO 4 (0.25M H2SO4)

i IgD

Fig. 3. Extractant dependence of platinum extraction from solutions of constant acidity. Curves: 1 - 0.25M HCI; 2 - 0.25M HNOa; 3 - 0.25M H2SO ,

tion is realized, when neutral salts are added to the aqueous nitric and sulphuric acid

solutions of 0.5M each. The addition of the chloride ions to a solution of hydro-

chloric acid of constant concentration (0.25M) leads to a slight decrease in the dis-

tribution coefficient up to about 0.5M sodium chloride solutions. A further increase

in the concentration of the sodium chloride added leads to a continuous increase

in the distribution coefficient. This could be due to the formation of more extract-

able complexes of platinum formed at high chloride concentrations.

18 J. Radioanal. Chem. 27 (1975)


12----- o ~ " X \

Fig. 4. Dependence of the distribution coefficient of platinum as a function of the concentration of different ions added to 0.25M hydrochloric acid. Curves: 1 - acetate; 2 - citrate; 3 - oxalate; 4 - ascorbate; 5 - thiocyanate; 6 - thiosulphate

The composition of the compounds entering the organic phase on extraction

from hydrochloric, nitric, and sulphuric acid solutions (0.25M each) was determined graphically by plotting lg D against lg [NPy]. The linear parts of the curves gave the

value of tg a = 1 indicating that a compound with Pt : NPy ratio ~1 is formed in

all the cases. (The distribution coefficient deviates from linearity when the amine

is diluted below 5 �9 10-2Iv!. This could be associated with the contribution of the

diluent itself towards extraction.)

The effect of different anions on the extraction of platinum by 0.1M NPy/ben-

zene from 0.25M hydrochloric, nitric and sulphuric acid solutions was studied. The

results are shown in Figs 4 - 6 , respectively. Platinum is extracted in the presence

of different ions, in a variety of ways that reflect the complexity of the aqueous

solutions of platinum. In the case o f chloride media, the partition data show a de-

creasing trend when the concentration of the added ions increases above 0.025M.

The decrease is more pronounced in the case of thiosulphate. Though there is also

a decreasing trend in the case of ascorbate and thiocyanate ions but there is no ap-

preciable decrease in the extraction. It is seen from Fig. 4 that the partition coef-

ficients of platinum shifted markedly towards higher values with the addition of

J. Radioanal. Chem. 27 (1975) 19 2*


IgO

5 .

a t.

Ig [ a n i o n ] ~ M

Fig. 5. Dependence of the distribution coefficient of platinum as a function of the concentration of different ions added to 0.25M nitric acid. Curves: 1 - acetate; 2 - citrate; 3 - oxalate; 4 - ascorbate; 5 - thiocyanate; 6 - thiosulphate

only small concentrations of thiosulphate, thiocyanate, and ascorbate ions. This could

be associated with the formation of some more extractable species at low concen-

trations of these ions and the equilibrium shifts with the increase of concentration o f these ions in the aqueous phase favouring the formation of inextractable com-

plexes. The shape of the extraction isotherms in case of acetate, oxalate, and citrate

is generally similar suggesting an identical composition of the species extracted. In

the nitrate system, the effect of ascorbic acid appears to be similar to the corre-

sponding chloride media. The e:ffect of acetate, oxalate, and citrate on the extraction

of the metal also produces results similar to the chloride media. The extraction of

platinum is quantitative even from a thiocyanate medium up to 1M while the addi-

tion of thiosulphate leads to a more rapid decrease than that resulted by other ion.

In sulphate media, the effect of the addition of ascorbate, thiosulphate, and thio-

cyanate is generally similar to the chloride media. This indicates that the extraction

is not much influenced by the nature of the anions of the supporting acids. In the

20 J. Radioanal. Chem. 27 (1975}


I

Fig. 6. Dependence o f the dis t r ibut ion coefficient o f p la t inum as a Junct ion of the concentrat ion

of different ions added to 0.25M sulphuric acid. Curves: 1 - acetate; 2 - citrate; 3 -

oxalate; 4 - ascorbate; 5 - th iocyanate; 6 - thiosulphate

llg 13

I

~ " -2 -1 0 1 -- I g [acid] , M

Fig. 7. Variation of the distr ibution coefficient of gold with the concentrat ion of aqueous acids

for extract ion by 0.1M 4-(5-nonyl)pyridine/benzene. Curves: 1 - HCI; 2 - HNO3;

3 - H 2SO,

J. Rad ioana l . C h e m . 2 7 ( 1 9 7 5 ) 21


~_~ I -2

Ig [anion], M

~ D

O ~ o - - 2

\ I

-1

Fig. 8. Dependence of the distribution coefficient of gold as a function of the concentration of different ions added to 0.25M hydrochloric acid. Curves: 1 - acetate; 2 - citrate; 3 - oxalate; 4 - ascorbate; 5 - thiocyanate; 6 - thiosulphate

case of oxalate ions, an anomalous increase in the extraction was observed at 0.1M

concentration of sodium oxalate.

To s tudy the possibility of the separation of 199Au from irradiated platinum a

comparison of the extraction data of plat inum from different mineral acid solutions

(Fig. 1) with that of gold (Fig. 7) can be made. Here Fig. 7 is reproduced from

Ref. 4 The comparison shows that it is not possible to get bo th of these elements

Separated from each other from simple mineral acid media. However, studies were

made to find the effect of different ions on the extraction of gold and plat inum

under similar conditions from 0.25M hydrochloric acid. The effect o f different ions

on the extraction of gold from 0.25M hydrochloric acid is shown in Figl 8.

22 J. Radioanal. Chem. 27 (1975)


Table 1 Distribution coefficients and separation factors of various metal ions between

0.1M 4-(5-nonyl)pyridine/benzene and 10M hydrochloric cid

Metal i o n

Cr(VI) Tc(VII) Mo(VI) Au(III) Mn(Ii)

AgO) Fe(III) Cr(III)

Concentration in the initial aqueous phase, M

5.10 -2 C.F.

10 -s 2.10 -6

10-s 10-8

10-2 5.10 -2

Distribution coefficient, D

0.014 0.091 0.022

16.0 0.10 0.006

10 0.0001

Separation factors

1.4 103 9.2 103 2.2 103 6.25 10 -1 1 102 6 104

1 10 s

A comparison of Fig. 4 and Fig. 8 indicates the possibility of the separation of gold and platinum from sodium thlosulphate solutions. The distribution coefficient of platinum from 0.25M sodium thiosulphate is 7 while that of gold is 0.01 under

similar conditions.

Separation o f t 99Au from irradiated platinum

Neutron irradiated platinum target, cooled for 4 hrs, was dissolved in hot aqua regia and then repeatedly evaporated with concentrated hydrochloric acid and fi-

nally taken up in 0.25M. hydrochloric acid. The pregnant aqueous phase was made 0.2M with respect to sodium thiosulphate and contacted 5 to 6 times with 0.1M

of 4(5-nonyl)pyridine/benzene and the organic phases were combined. The aqueous phase contained 199Aufree from platinum. Thiswas confirmed by the 7-spectrum and

the decay studies. The organic phase contained platinum with some contamination of gold which can be eliminated by washing the organic phase 2 to 3 times with

barren aqueous phase (0.25M HC1 + 0.2M Na2S203). The selectivity of the extraction separation of chromium(VI) with 0.1M NPy/

/benzene from 10M hydrochloric acid was studied. The behaviour of various base metals was examined. The results presented in Table 1 show that separation can also

be achieved from chromium(VI) and silver.

Messrs. M. SAEED and RIAZ JOSEPH gave valuable assistance on counting and calculating D values.

23 J. RadioanaL Chem. 27 (1975)


References

1. M. IQBAL, M~ EJAZ, J. Radioanal. Chem., 23 (1975) 51. 2. M. IQBAL, lVl. EJAZ, Anal. Chim. Acta, 74 (1975) 125. 3. M. IQBAL, M. EJAZ, Talanta, 22 (1975) 143. 4. M. IQBAL, kL EJAZ, Radiochim. Acta, (in the press). 5. M. IQBAL, M. EJAZ, Anal. Chem., 47 (1975) 125. 6. H. MALESZEWSKA, R. DYBZYNSKI, Nukleonika, 12 (1967) 1181. 7. I. FIDELIS, R. GWOZDZ, S. SIEKIERSKI, Nukleonika, 8 (1963) 327. 8. E. E. RAKOVSKI, B. S. ROBINOVICH, M. I. STAROZHITSKOYA, Soviet. Radiochem.,

(English transl.) 13 (1971) 144. 9. J. W. MELLOR, Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. XVI,

Lowe and Brydone Ltd., London, 1961, p. 333.

24 J. Radioanal. Chem. 27 (1975}

Documents

4-(5-nonyl)pyridine extraction of platinum from different aqueous solutions