Indian Journal of Chemical Technology Vol. 9, May 2002. pp. 251-255

Articles

The phosphine oxides Cyanex-921, Cyanex-923 and Cyanex-925 as extractants for Pb(II) from aqueous media

J N Iyer, S D Pawar & PM Dhadke*

Department of Chemical Technology, University of Mumbai, Matunga, Mumbai 400 019, India

Received 19 June 2001; revised received 27 January 2002; accepted I March 2002

The behaviour of neutral phosphine oxides Cyanex-921, Cyanex-923 and Cyanex-925 in the extraction of Pb(II) from nitrate media is described. The extraction of Pb(II) was found to be quantitative in the pH range 8.0-9.0 with these extractants. From the metal loaded organic phases for these extractants, Pb(II) was stripped back with 0.5 M H2S04• The effects of pH, temperature, equilibrium time, diluents, diverse ions and stripping ability using various acids on the extraction of Pb(II) have been studied. The methods are also extended for the analysis of real samples.

Industrial waste effluents often contain considerable amount of heavy metals which endanger public health and environment if discharged without adequate treatment. Heavy metals include elements such as lead, mercury, chromium, nickel, cadmium, zinc, etc, which have high densities and which are usually in toxic forms 1• Among these the Pb which has been used by man is a long-standing environmental contaminant2

.

Very few extraction methods are reported for Pb(II). In 6.0 M HCI with MIBK, Pb(II) is poorly extracted3

, while with TBP the highest extraction from 2.0-4.0 M HCI is less than 50%4

. Isoamyl alcohol extracts only 25-30% from 0.5 to 0.7 M thiocyanate solution5

. With 5% tri-isooctylamine in xylene, the extraction from 1.0 M HCl is about 50% and it decreases with the mcrease in acid concentration6

. With chelating extractants like acetylacetone, the extraction of Pb(II) is less than 75%7

-9

, but with 0.01 to 0.1 M oxine in chloroform the extraction is quantitative between pH 6.0-10.0 10

•

Pb(II) was also extracted quantitatively using 5% LIX51 in MIBK 11

• Acidic reagents like di(2-ethylhexyl) phosphoric acid extract Pb(II) but the reagent concentration required is 50% 12

. A yellow­green coloured complex of Pb(II), is extracted in chloroform with pyridine-2-acetaldehyde salicylo­hydrazone in the pH range 8.6-9.3 13

. Among crown ethers DB 18C6 was used for the solvent extraction of Pb(II) at pH 5.6 14

• Even Calix(6)arene and Calix(4)arene bis(N-X sulphonyl) carbamide were used also for the extraction of Pb(II) 15

·16

•

*For correspondence (Fax: 91-22-4145614)

Cyanex -921, Cyanex -923 and Cyanex -925 produced by Cytec Industries Inc., Canada are trade names for industriaVcommercial extractants which contain trialkylphosphine oxides as the active substances. Cyanex-921 is a new trade name for the previous TOPO. It contains trialkylphosphine oxide as the active substance 17

.

Cyanex-923 extractant is a mixture of four trialkylphosphine oxides, with general formula R3PO (14%), R2R'PO (42%), RR'2PO (31 %) and R'3PO (8% ), in which R denotes n-octyl and R' stands for n­hexyl groups 18

•

Cyanex-925 is a mixture of trialkylphosphine oxides containing normal and branched octyl group 19

.

Alguacil et al. have reported it as a mixture of only two compounds with formula R3PO and R2R'PO, where R=2,4,4-trimethylpentyl and R'=n-octyl20

.

These extractants extract many metal ions significantly from different systems and therefore they find numerous applications as solvating reagents. They have been used to extract many metals including acids.

Experimental Procedure Apparatus and reagents

The extractants, Cyanex-921, Cyanex-923 and Cyanex-925 supplied by Cytec Industries Inc. , Canada were used without further purification . A known amount of Pb(N03h was dissolved in a minimum quantity of HN03 and diluted to 1 L with double distilled water and standardised by known method21

• All other chemicals used were of analytical grade. Elico model Li-120 pH meter with combined electrode was used for H+ ions concentration studies

Articles

and GBC UV Visible 9IIA spectrophotometer with IOmm cortex quartz cuvettes for absorbance measurements.

Procedure

An aliquot containing 50 f.lg of Pb(II) in I OmL was taken and equilibrated separately with equal volume of Cyanex-92 I , Cyanex-923 and Cyanex-925 in toluene fo r the required shaking time of 5 min after adjusting their aqueous solution to the required pH with dilute HN03 and NH3. The aqueous to the organic phase ratio was maintained at I : I. The metal loaded organic phase was back extracted with the acid and was determined spectrophotometrically by the PAR method22 at 510 nm. All the experiments were carried out at room temperature except the effect of temperature.

Results and Discussion

EffectofpH Lead(Il) was extracted in pH range of 1.0-I 0 .0 with

Cyanex-92I , Cyanex-923 and Cyanex-925 in toluene (Fig. 1 ). The quantitati ve extraction of Pb(II) was found in pH range 8.0-9.0 with all the three extractants. Hence all the experiments were carried out at pH 8.0 with these reagents.

Effect of reagent concentration

Extraction of Pb(II) was also carried out by varying the reagent concentration (l x i0-2 to 0.125xl0·3 M) while keeping other parameters like pH, period of equilibration, diluent and temperature constant. Extraction was found to increase with increase with increase in reagent concentration. The extraction of Pb(II) was quantitative with 2.5x l0·3 M Cyanex-92I and 5x l0·3 M Cyanex-923 and Cyanex-925 respectively in toluene.

Effect of diluents

Various diluents like toluene, chloroform, carbon tetrachloride, benzene, cyclohexane, n-hexane and xylene were employed for the extraction of Pb(II). The extraction of Pb(II) with all three extractants was found to be quantitative with toluene and n-hexane and in addition to this carbontetrachloride also showed quantitative extraction with Cyanex-921. However, there was incomplete extraction with other diluents. Toluene was used as best diluent because of better phase separation (Table 1 ).

252

120

100

80 .

UJ 60 <f.

40

20

0

0 2

Indian J. Chern. Techno!. , May 2002

6

pH

,_.._Cya-921 1

1

-+- Cya-923 1 --cya-925

J 10 12

Fig. 1-Effect of p H on the percentage ex tract ion of Pb(l l) using Cyanex-92 1, Cyanex-923 and Cyanex-925

Table 1- Effec t of diluents on percentage extracti on of Pb(ll )

Loading: 50 J..lg

Diluent Percentage extraction (%E) of Pb(ll ) Cyanex- Cyanex- Cyanex-

92 1 923 925

Toluene 99 .9 99 .9 99.9

Xylene 57.5 40 .5 22.0

Chloroform 90.2 94.0 80.4

Benzene 8 1.4 93 .6 84.3

Hexane 99.9 99.9 99.6

Carbontetrachloride 99.9 98.3 89.7

Cyclohexane 94.6 95 .7 97.2

Effect of various stripping agents Lead(II) was stripped out from its loaded organic

phases with different strength mineral acids like HCI , HN03, H2S04 and HCI04. It was quantitatively stripped only with 0.5-1.0 M H2S04 from Cyanex-92I extracted phase, while with Cyanex-923 extracted phase was quantitatively stripped with 0.5-1.0 M H2S04, 1.5-2.0 M HN03, and I .S M HCI. However from Cyanex-925 organic phase it was completely stripped using 0.5 M H2S04 and 2.0 M HN03.

Therefore, 0.5 M H2S04 was preferred as stripping agents for Pb(II) for all the three reagents (Table 2) .

Nature of extracted species It was necessary to evaluate the distribution

coefficient (D) while varying the extractant concentration to ascertain the nature of extracted species. The composition of the extracted species are ascertained from graph of log D versus log R at fixed pH. The slopes obtained are 2. I, 2.04 and 1.80 with

lyer et al.: eyanex-921, eyanex-923 and eyanex -925 as Extractants for Pb(ll) Articles

Cyanex-921, Cyanex-923 and Cyanex-925 in toluene respectively (Fig. 2). Hence the probable composition of the extractable species of Pb(ll) in all the three cases is l :2.

Effect of diverse ions The effect of various diverse ions on the extraction

of Pb(Il) was studied for these three extractants (Table 3). The tolerance limit of individual foreign ions was set so that error in percentage recovery was not more than ±2%. It was found that E. D. T. A and di-Na-tartarate highly interfere while alkali and alkaline earth metals are highly tolerated.

Effect of temperature on the extraction of Pb(ll)

0 (J) 0 -'

..

·4 -3.5 -3 -2.5 ·2

Log R

Slope cy-921 = 2.19

Slope cy-923 = 2.04 2

Slope cy-925 = 1.81 1.5

0.5

0

·0.5

-1

-1 .5 -1 -0.5 0

The extraction of Pb(II) with all the three extractants in toluene at pH was carried out at

Fig. 2-Effect of reagent concentration on the distribution ratio of Pb(ll) using eyanex=92 1, eyanex=923 and eyanex=925

Table 2-Effect of strippi ng agents on the percentage recovery of Pb (II)

Loading: 50 J..lg

Extractant Acid Percentage Recovery (% R) 0.5 M I .O M 1.5 M 2.0M

He! 65 .2 74.1 84.5 89.7 eyanex-92 1 H2S04 99.9 99.9 95.2 91.4

HN03 50.4 61.2 69.3 76.8

Hei04 32.7 25.1 15 .7 12.5

He I 73.3 83.3 99.9 89.0 eyanex-923 H2S04 99.9 99.9 99.3 94.0

HN03 74.4 87.2 99.9 99.9

Hei04 35.2 32.3 29.5 27.4

He I 44.6 69.2 77.4 82.4 eyanex-925 H2S04 99.9 96.2 82.4 50.3

HN03 40.3 55 .3 70.4 99.9 Hel04 52. 1 45.6 34.9 22.5

Table 3-Effect of various diverse ions on the extraction of Pb(ll)

Loading: 50 J..lg

Tolerance Limit (J..lg)

Interfere strongly

EDTA, Na-tartarate, Sn+4

EDTA, Na-tartarate, Sn+4

EDTA, Na-tartarate, Sn+4

1:20

Na•, Li+, K•, Mg•2

, ea•2

Na•, Li•, K•, Mg•2

Na•, Lt, K•, Mg•2

1:15

eyanex-921

Al+3, Ga•3, ln•3, Tl+3, SeN-, Mo+6

eyanex-923

ea•2, In•3, Tt•3, seN-, Mo•6

eyanex-925

ea•2, ln•3, Tt•3, seN- , Mo•6

1:10 1:5

Pd•2, Pt+4, Rh•3, er•3, Ni+2, Mn•2, Hg•2, Br-, 1, Cl- Fe+3

Pd+2, Pt+4, Rh+3, er•3, Ni•2, Mn•2,

Hg•2, Br-, 1, Cl- , At•3, Ga•3

Fe•3, zn•2

Pd+2, Pt+4, Rh•3, er•3, Ni•2, Mn•2,

Hg•2, Br-, r , Cl-, zn+2

At•3, Ga•3

1:3

zn•2, es·, eu·2,

Sb•3, Bi+3

es•, eu•2, Sb•3, Bi+3

es•, eu•2, sb•3

,

Bi+3, Fe•3

253

Articles

different temperatures (upto 70°C). The extraction was found to decrease with increase in temperature (Table 4). From Yan't Hoff equation

!J.H LogDrb=- +C

2.303RT

where Drb represents the distribution ration of Pb(II), llH is the enthalpy change for the extraction and C a constant. The slopes obtained from the plots of logD versus loglOOO/T are 2.3, 1.6, and 1.5 for Cyanex-921, Cyanex-923 and Cyanex-925 respectively . The llH values obtained with Cyanex-921, Cyanex-923 and Cyanex-925 are -44.03 kJ/mole, -30.63 kJ/mole and - 28.72 kJ/mole respectively. These values indicate that the reactions are exothermic in nature and the rate of reaction is in the order Cyanex-921> Cyanex-923> Cyanex-925 (Fig . 3).

Table 4---Effect of temperature on the percentage extraction of Pb(ll)

Loading: 50 flg

Temperature [Cyanex-921] (K) 303 0.71 313 0.58 323 0.24 333 0.11 343 0.06

D [Cyanex-923]

0.51 0.41 0.35 0.23 0. 15

[Cyanex-925]

0.48 0.33 0.18 0.14 0.10

Indian J. Chern. Technol., May 2002

Analysis of sample The proposed methods were employed for the

analysis of Pb(ll) in the samples like leaded brass, tin based white metal and solder. The experimental resu lts were found to be in good agreement with the theoretical values having R. S. D. va]ue less than 0.32 (Table 5).

Conclusion (i) The results indicate that Cyanex-921 , Cyanex-

923 and Cyanex-925, commercia lly available

0

0.-----------------------

-0.2

-0.4

Slope Cy-921 = 2.3

Slope Cy-923 = 1.6

Slope Cy-925 = 1.5

g> -0.6 --'

-0.8

-1

I• Cya-9211 . I ,· Cya-923 J t• Cya-925

-1.2 1------,-----,----~--------,---~--,----,--~--~

2.85 2.9 2.95 3 3.05 3.1 3.15 3-.2 3.25 3.3 3.35

1ffx1000

Fig. 3-Effect of temperature on distribution ratio of Pb(ll ) using Cyanex=921, Cyanex=923 and Cyanex=925

Table 5-Analysis of Pb in alloys

Extractant Sample Present Found % Recovery R.S.D

Leaded brass 2.24 2.23 99.5 0.17 (BCS385)

Cyanex-921 Tin base white metal 3.18 3. 17 99.7 0.21 (BCS 178)

Solder 67.34 67.1 99.6 0. 16

Cyanex-923 Leaded brass 2.24 2.23 99.5 0.20 (BCS385)

Tin base white metal 3.18 3.16 99.4 0.2 2 (BCS 178)

Solder 67.34 66.9 99.4 0.26

Cyanex-925 Leaded brass 2.24 2.22 99.2 0.32 (BCS385)

Tin base white metal 3.18 3.16 99.4 0.20 (BCS 178)

Solder 67 .34 66.8 99.2 0.21

254

lyer eta/.: Cyanex-921, Cyanex-923 and Cyanex -925 as Extractants for Pb(ll) Articles

phosphine oxides, extract Pb(II) quantitatively from its aqueous solution . The reagent concentration of Cyanex-921 required for extraction of Pb(Il ) is less as compared to Cyanex-923 and Cyanex-925. This may be due to the higher percentage (99. 1 %) of active component (tri-n-octyl phosphine oxide) in Cyanex-92 1 as compared to Cyanex-923 and Cyanex-925 where it is 92.4% and 65.9% respectively.

(i i) The t:.H values indicate that the extractions are exothermic In nature with all the three extractants.

(iii ) The enthalpy values also indicate that the rate of reaction is in the order Cyanex-921 > Cyanex-923 > Cyanex-925 i.e. Pb(II) gets extracted faster with Cyanex-921 as compared to the other two reagents.

(iv) The extraction with all the three reagents is found to be 100% unlike with TBP where the highest extraction from HCI (2.0-4.0 M) is less than (50%)8

.

(v) The extractant's concentration required with these reagents is less as compared to di(2-ethylhexyl) phosphoric acid (50%) 16 and dibenzo-18-crown-6 (0.01 Min nitrobenzene)23

.

(vi) The extraction takes place at lower pH as compared to diazo-18-crown, which extracts Pb(ll) at pH 11.024

.

(vii) The methods were extended to analysis of leaded brass, tin based white metal and solder alloy samples, where results were in good agreement with certified values.

Acknowledgement The authors are thankful to Cytec Industries Inc.

Canada for supplying the gift sample of Cyanex-921 , Cyanex-923 and Cyanex-925.

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