J.RADZOANAL;NUCL.CHEM.,LETTERS 103 /3/ 167-176 /1986/

SOLVENT EXTRACTION OF SILVER/I/ FR~ DILUTE CYANIDE SOLUTIONS WITH 2,4-DIHYDROXYACETOPHENONE

THIOSEMICARBAZONE

A.V. Reddy, G.S. Reddy x, Y.K. Reddy

Department of Chemistry, S.V. University, Tirupati - 517 502, India

XDepartment of Chemistry, S.V. University, Post-Graduate Centre, Cuddapah, India

Received 18 October 1985 Accepted 30 October 1985

The solvent extraction of silver/I/ has been carried out in O.5M nitric acid in presence of cyanide by 2,4-dihydroxyacetophenone thio- semicarbazone /DATS/. Ethyl acetate has been used as a solvent and quantitative recovery is made possible with 12.5-fold excess of the reagent in a single extraction. In this medium silver/I/ forms a 2:2 complex /metal:ligand/ with DATS. The effect of diverse ions on the extraction of silver/I/ has been investigated.

INTRODUCTION

2,4-Dihydroxyacetophenone thiosemicarbazone /DATS/ has

been prepared by Admann and Fikrat I and they used it as

a photometric reagent for the determination of copper and

cobalt. This reagent has also been used for the spectro-

photometric determination of nickel/II/2. In this labora-

tory this reagent has been utilized for the extraction

167 s Sequoia $. A., Lausanne Akaddmiai Kiad6, Budapest

REDDY et al.: SOLVENT EXTRACTION OF SILVER/I~

and radiometric determination of cobalt/II/ from ammonium

chloride - ammonium hydroxide medium 3 and silver/I/ from

acetic acid - sodium acetate buffer 4. Preliminary studies

indicated that the metal could also be extracted from

dilute nitric acid and under these conditions the recovery

is not affected by the presence of considerable amounts

of cyanide. Hence a detailed investigation has been car-

ried out to study the possibilities of recovering silver/I/

in presence of cyanide using the same reagent.

EXPERIMENTAL

All the reagents and chemicals used were of analytical

grade or chemically pure as necessary. DATS was synthesized

according to the procedure described earlier I. llOmAg was

obtained from the Isotope Group, Bhabha Atomic Research

Centre, Bombay and its radiochemical purity was ascertained

by y-ray spectrometry. The various solutions required in

the experiment were prepared from the solvents pre-equi-

librated with each other.

Solvent extraction procedure

The aqueous phase was 0.5M nitric acid, except in

experiments on the role of acid concentration. 2.0 ml of

aqueous phase containing the tracer llOmAg and 2.0 ml of

organic phase were taken and equilibrated for 30 min in

a thermostat at 330~I K /equilibrium could be attained

within 2 min/. The two phases were allowed to separate

and then pipetted out for the estimation of the metal by

counting the activity using a Y-scintillation counter with

a well-type NaI/TI/ crystal. The distribution coefficient,

D, was taken as the ratio of the activity of the tracer

168

REDDY et al. : SOLVENT EXTRACTION OF SILVER/I/

TABLE 1

Effect of nitric acid on the extraction of silver/I/

EDATS3 = 1.17xlO-3M, lAg/I/] = 4.7xlO-4M

Acid strength, D Extraction, M %

1.00 6.45 86.58

0.75 10.20 91.07

0.50 12.42 92.55

0.25 10.32 91.17

0.I0 6.96 87.45

0.05 3.21 76.25

0.O1 1.13 53.11

in the organic phase to that in the aqueous phase. Duplicate

experiments were performed; the distribution values

agreed within +2%.

RESULTS AND DISCUSSION

Effect of acid strength

The percent of extraction of silver/I/ increased slight-

ly as the acid strength decreased from 1.0 to 0.75M and

"D" remained almost constant in the region of 0.75-O~

"D" decreased rapidly as the acid strength was decreased

gradually from O.25M. Hence, further studies were carried

out in 0.5M nitric acid /Table i/.

Effect of reagent cqncentration

Effect of reagent concentration was studied by vary-

ing the DATS concentration in ethylacetate from 1.0 to

15.0 fold that of silver/I/ concentration. Silver/I/

169

REDDY et al. : SOLVENT EXTRACTION OF SILVER/It

TABLE 2

Effect of reagent concentration on the extraction of silver/I/

lAg/I/3 = 4.7xlO-4M, Acid strength = O.5M

Concentratio 9 D Extraction, of DATS, xlO ~ %

0.47 1.25 55.33

1.17 13.33 93.02

2.35 48.56 97.98

3.52 181.00 99.45

4.69 704.20 99.86

5.87 I00.00

7.04 ~ i00.00

was extracted to the extent of 98% when the reagent

concentration was in 5-fold excess to that of metal ion

and quantitative recovery was possible at and above

12.5-fold excess of reagent /Table 2/.

Composition of the complex

Composition of the complex is determined by molar

ratio and slope analysis methods.

From molar ratio method it is observed that two moles

of reagent are participating in the complex formation

/Fig. i. /.

In slope analysis method, the extraction of metal ion

increases with increasing DATS concentration in ethyl-

acetate in 0.5M nitric acid. The ig D against ig [Reagent]

plot /Fig. 2./ is linear with a slope of 2.0. It confirms

REDDY et al. : SOLVENT EXTRACTION OF SILVER/I/

tO0 o

c 0 '-~ 80 u

*~ 60 t,U

<,0

20

0 0

I ~J I r 1 2 3 4 5

Mol. of reagent

Fig. i. Molar ratio method

o 0.4

02

0

-0.2

-04

-0.6

-I 21

-0.8

-1.0

~J -4.2 -h.0 -3.8 -3.6 -3.4 -3.2

[g[reagent]

Fig. 2. Lg-lg plots for the variation of the extraction of silver]I] with the concentration of 2,4-di- hydroxyacetophenone thiosemicarbazone /DATS/

1"II

REDDY et al.: SOLVENT EXTRACTION OF SILVER, I/

02~ ~ ~

-06

-03 E I i f l -37 -36 -3.5 -34 -3.3 -32 -31

[g [mela[]

Fig. 3. Effect of the metal concentration on the ex- traction of silver/I/ by 2,4-dihydroxyaceto- phenone thiosemicarbazone /DATS /

that two moles of reagent participate in the complex

formation.

The "D" value decreases gradually on increasing the

concentration of metal ion while keeping the DATS con-

centration constant. The ig D against ig [Metal] plot

/Fig. 3./ is also linear with a slope of 2.3 indicating

that two moles of silver/I/ are involved in the complex

formation.

The above results reveal that the ratio of metal to

ligand is 2:2 in nitric acid, unlike the case of acetate-

acetic acid medium where it is i:i. It may be due to the

formation of a dimer.

Effect of cyanide

The presence of cyanide causes no effect /Table 3/

whereas silver/I/ cannot be extracted from cyanide

solutions in acetate-acetic acid buffer 4. This may be

172

REDDY et al. : SOLVENT EXTRACTION OF SILVER/I/

TABLE 3 Effect of various ions on the extraction of silver/I/

Amount of Ag + = 101.3 uq; [DATS] = 9.39xlO-4M, acid strength = O.5M

Foreign ion Added as Tolerance limit, ug

AI/III/

As/V/

Bi/III/

Cd/II/

Ce/IV/

c o / I : / cu/::/

Fe/III/

Hg/II

Mn/II

Mo/VI

Ni/II

PblII

Pd/II

Sb/V/

Se/IV

Ti/IV/

ulvl/

v /v /

W/VIl

ZnlIIl

Fluoride

Thiocyanate

Oxalate

Citrate

Tartrate

EDTA

Thiourea

Phosphate

Sulphate

Cyanide

AI2/SO4/3./NH4/2SO4.2H20 2000

Na2As206 None

Bi/NO3/3.5H20 2000

CdlCH3COOI2.2H20 2000

/NH414Ce/SO4/4.2H20 300

COSO4.7H20 2000

CuSO4.5H2 O None

NH4Fe/SO4/2.12H20 None

Hg/NO3/2.xH20 None

MnSO4.H20 lOO0

/NH4/6Mo7024 None

/NH4/2Ni/SO4/2.6H20 iOOO

PblCH3COO/2.3H20 IOOO

Pd/CH3CO0/2 None

Sb205 None

Na2SeO3.2H2 O None

K2TiO/C204/2 300

UO2/CH3COO/2.2H20 2000

NH4VO 3 2000

Na2WO4.2H20 2000

ZnSO4.7H20 2000

NaF 3000

NH4SCN None

K2C204.H20 3000

Na3CsH507.2H20 3000

KNaC4H406.4H20 3000

Na2EDTA 3000

NH2.CS.NH 2 None

NH4H2PO 4 3000

MgSO 4 3000

KCN 6000

REDDY et al. : SOLVENT EXTRACTION OF SILVER/I]

due to the hydrolysis of cyanide yielding HCN which is

volatile. The experiments using cyanide were carried out

in a fume cupboard.

Effect of foreign ions

The effect of various foreign ions on the extraction

behaviour of silver/I/ was studied /Table 3/. The

tolerance limit was set at the amount required to

cause ~2% error in the silver/I/ recovery. Aluminium/III/,

bismuth/III/, cadmium/II/, cobalt/II/, uranium/VI/, va-

nadium/V/, tungsten/VI/ and zinc/II/ do not affect the

extraction of silver/I/ into the organic phase even

when present in 20-fold excess. Manganese/II/, nickel/II/

and lead/II/ are tolerable when present in the ratio

of i:I0 and cerium/IV/ and titanium/IV/ when present

in the ratio of 1:3. Arsenic/V~, copper/II/, iron/III/

and palladium/II/ interfere in the extraction of sil-

ver/I/. Mercury/II/, molybdenum/VI/, antimony/V/ and

selenium/IV/ also interfere by forming precipitates in

the aqueous phase.

The interference of copper and nickel can be avoided

by masking with EDTA. Similarly iron and vanadium ions

are masked with fluoride and citrate, respectively.

Oxalate, tartrate, phosphate, sulphate, citrate,

fluoride and EDTA do not interfere in the extraction of

silver/I/ even when present in 30-fold excess. Thio-

cyanate and thiourea interfere seriously.

The present method is advantageous over the earlier

procedure as this method can be applied for the recovery

of silver from plating solutions containing cyanide.

X

174

REDDY et al. : SOLVENT EXTRACTION OF SILVER/I/

The authors thank Dr. B. Rangamannar, Reader in Radio-

chemistry, S.V. University, Tirupati, for providing

facilities at the Radiochemical Laboratories and the

University Grants Commission, New Delhi, for\awarding

a research fellowship to one of them /AVR/.

REFERENCES

i. A. Admann, B. Fikrat, Chim. Acta, Turcia~, 3 /1975/ 51.

2. K.H. Reddy, D.V. Reddy, Ind. J. Chem., 22 /1983/ 824.

3. A.V. Reddy, M.L.P. Reddy, Y.K. Reddy, J. Radioanal. Nucl. Chem. Lett~, 86 /1984/ 391.

4. A.V. Reddy, G.S. Reddy, Y.K. Reddy, J. Radioanal. Nucl. Chem. Lett., 93 /1985/ 279.

a* 175