Solvent extraction and separation of Cd(II), Ni(II) and Co(II) from chloride leach liquors of spent Ni–Cd batteries using commercial organo-phosphorus extractants

Hydrometallurgy 77 (2005) 253 – 261 www.elsevier.com/locate/hydromet

Solvent extraction and separation of Cd(II), Ni(II) and Co(II) from chloride leach liquors of spent Ni–Cd batteries using commercial organo-phosphorus extractants B. Ramachandra ReddyT, D. Neela Priya, S. Venkateswara Rao, P. Radhika Inorganic Chemistry Division, Indian Institute of Chemical Technology (CSIR), Uppal Road, Hyderabad-500 007, India Received 26 November 2004; received in revised form 7 February 2005; accepted 8 February 2005

Abstract Development of a flow sheet for the solvent extraction, separation and recovery of cadmium(II), cobalt(II) and nickel(II) from chloride leach liquors of spent Ni–Cd batteries by hydrometallurgical route was investigated. Cyanex 923 showed selective separation of cadmium(II) from nickel(II) and cobalt(II). Two-stage counter-current extraction at 1:1 phase ratio and three stages of stripping with distilled water at an aqueous to organic (A:O) phase ratio of 1.75:1 gave N 99.9% Cd extraction and stripping efficiency. Studies on the separation of cobalt from nickel from the cadmium raffinate indicated Cyanex 272 as the best extractant with a separation factor N 4700. Cobalt(II) extraction efficiency of ~ 99.9% was achieved with 0.03 M Cyanex 272 in three counter-current stages at an A:O ratio of 1.5:1. Complete stripping of metal from the loaded organic containing 0.33 g/L Co was carried out at pH 1.5 in 2 stages at an O:A ratio of 2:1. The enrichment of cobalt was about 4.7 times. More than 99% Ni recovery was achieved with 1 M TOPS 99 as the extractant from the cobalt raffinate. A complete flow sheet of the process for the separation and recovery of Cd(II), Co(II) and Ni(II) as chlorides was demonstrated. D 2005 Elsevier B.V. All rights reserved. Keywords: Spent batteries; Chloride leach; Solvent extraction; Cadmium(II); Cobalt(II); Nickel(II); Organo-phosphorus extractants

1. Introduction Nickel–cadmium batteries are used in many portable electronic devices, military and defense

T Corresponding author. E-mail address: [email protected] (B.R. Reddy). 0304-386X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2005.02.001

applications, but are classified as hazardous waste (Sharpek, 1995) because of the presence of toxic cadmium. Recycling of spent batteries is important, both from an environmental and economic point of view. In several European countries the collection rates of spent batteries vary between 32% and 54% of battery sales. However, there appears to be no data available on directions for issuing legislation on the

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disposal and recycling of spent Ni–Cd batteries in India. Several years ago attempts were made to replace Ni–Cd batteries with Ni-MH batteries because of toxic nature of cadmium. A review of the literature reveals that both pyrometallurgical/or hydrometallurgical operations have been tried to recover metal values from spent batteries. The pyrometallurgical method basically consists of selective volatilization of metals at elevated temperatures (~ 900 8C) followed by condensation to recover cadmium with N 99% purity. But most valuable metals such as nickel and cobalt are not usually recovered (David, 1995; Anulf, 1990; Hanewald et al., 1992; Liotta et al., 1995). The hydrometallurgical route is based on crushing the spent battery followed by a physical separation of the structural elements, dissolution of Ni–Cd materials in acid and separation of metals by solvent extraction/ion exchange/cementation (Frohlich and Sewing, 1995; Bartolozzi et al., 1995; Xue et al., 1992; Nogueira and Delmas, 1999). Gupta et al. (2001) reported the use of Cyanex 923 for the extraction of cadmium from synthetic solutions. In our earlier studies, we have extensively applied organo-phosphorus extractants for SX separation as well as for the determination of Co and Ni (Sarangi et al., 1999; Reddy and Bhaskara Sarma, 1994, 2001; Bhaskara Sarma and Reddy, 2002; Ramachandra Reddy et al., 2004a,b,c). Solvent extraction studies on the extraction behavior of cadmium(II), cobalt(II) and nickel(II) from spent battery leach liquors for the determination of species at macro level concentrations has been recently communicated (Ramachandra Reddy et al., 2004b). In this paper we report studies to develop a complete hydrometallurgical process flow sheet for the separation and recovery of Cd(II), Co(II) and Ni(II) as metal chlorides from chloride leach liquors of spent nickel–cadmium batteries using commercial organo-phosphorus extractants, Cyanex 923, TOPS 99, PC 88A and Cyanex 272 diluted in kerosene. This is the first report on the application of Cyanex 923 for the selective Cd(II) separation from such solutions. The parameters studied to optimize extraction and separation conditions are: selection of extractant, effect of equilibrium pH, extractant concentration, phase ratios, extraction and stripping isotherms, counter-current extraction and stripping simulations.

2. Experimental 2.1. Apparatus A Perkin Elmer Model A 300 Atomic Absorption Spectrophotometer (AAS) and a digital Digisun pH meter (model DI 707) were used for the measurement of metal concentration and pH in the aqueous phase. 2.2. Reagents The spent Ni–Cd batteries were prismatic shaped batteries supplied by HBL-NIFE Industries, Hyderabad, India. These are low rate cells with a capacity of 7 A and 1.2 V. The battery package was dismantled to remove the battery materials. Leaching of the dried material with dilute HCl under optimum conditions (HCl = 1.5 M; temperature 85 8C; solid/liquid ratio 4; time 6 h) resulted in the leach liquor (LL) with the following composition: Cd = 6.27 g/L; Ni = 21.56 g/L; Co = 0.14 g/L at pH 1.0 (Ramachandra Reddy et al., 2004b). Cyanex 923, a mixture of four trialkyl-phosphine oxides (R3P= O, R2RVP= O, R3VP= O, R2VR P= O, where R=hexyl and RV = octyl); and Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid), were obtained from Cytec Canada, & TOPS 99, (an equivalent of di-2-ethylhexyl phosphoric acid) was obtained from Heavy Water Plant, Talchar, India and PC 88A (2-ethylhexyl phosphonic acid mono-2 ethyl hexyl ester) from Daihachi Chemical Industry, Japan. All reagents were used without further purification. Cyanex 923 is mainly used for the separation of Nb from Ta, bulk recovery of rare earths, recovery of Cd from H3PO4/HCl solutions, and the extraction of mineral acids (Cytec Industries, Technical Brochure, 1999). Distilled kerosene (b.p.: 160–200 8C) with 96.2% aliphatic and 3.8% aromatic contents (as determined by NMR spectra), was used as the diluent. All other chemicals were Analar grade. 2.3. Solvent extraction procedure Suitable volumes of aqueous (leach liquor) and organic phases were contacted for 5 min after initial experiments had showed that equilibrium was reached within 1 min. The phases were separated and the metal concentration in the aqueous phase (raffinate)

B.R. Reddy et al. / Hydrometallurgy 77 (2005) 253–261

255

Thiele plot (Fig. 1) shows that quantitative Cd(II) extraction is achievable in two counter-current (C-C) stages at A:O phase ratio of 1:1. Analysis of the organic phases indicated no extraction of Ni(II) and Co(II), which shows clear separation of Cd(II) from Ni(II) and Co(II).

was estimated directly by AAS. The loaded organic (LO) phases were stripped three times with 1 M HCl, and the combined strip solutions analysed for metal values by AAS. All the experiments were carried out at room temperature (30 F 1 8C). The distribution ratio, D, was calculated as the concentration of metal present in the organic phase to that part in the aqueous phase at equilibrium.

3.1.2. Counter-current batch simulation studies for cadmium extraction To confirm the extraction isotherm prediction data, a two-stage counter-current extraction simulation (CCES) test was carried out at the A:O phase ratio of 1:1. Aqueous (raffinate) and organic (LO) outlet streams were collected after the third cycle onwards and analysed for metal values. The raffinate contained 0.005 g/L Cd corresponding to 99.9% extraction efficiency. Co-extraction of nickel and cadmium was nil.

3. Results and discussion 3.1. Separation and recovery of cadmium 3.1.1. Effect of Cyanex 923 concentration and phase ratio Increasing Cyanex 923 concentration in the range 0.1–0.6 M increased the percentage extraction of Cd(II) from the leach liquor at pH 1.0 from 29 to 96.5%. Co-extraction of Ni(II) and Co(II) was nil. To determine the number of stages required at a chosen volume phase ratio, the extraction isotherm was obtained by contacting the leach liquor and 0.6 M Cyanex 923 at different A:O phase ratios from 1 to 8; and O:A phase ratios from 1 to 5. The McCabe–

3.1.3. Stripping of cadmium from loaded organic Sufficient quantities of loaded organic phase and raffinate were generated for carrying out cadmium stripping studies. Under optimum conditions; i.e. using a feed leach liquor at pH 1.0 and 0.6 M Cyanex 923 in kerosene, a CCES test was carried out in two

14 12

8 6 1 4

r at i O pe

ng

, A: l i ne

[Cd]Feed : 6.272 g/L

[Cd] Org , g/L

10

1: 1 O=

2 2

0 0

1

2

3

4

5

6

7

[Cd] Aq , g/L Fig. 1. McCabe–Thiele plot for cadmium extraction. Organic = 0.6 M Cyanex 923. Aqueous: Cd = 6.27 g/L; Ni = 21.56 g/L; Co = 0.14 g/L; pH = 1.0.

B.R. Reddy et al. / Hydrometallurgy 77 (2005) 253–261

A:O phase ratio Cd stripping, %

1.0:1 59.8

1.5:1 77.4

1.75:1 80.6

2.0:1 84.6

stages at A: O phase ratio of 1:1. The generated LO contained 6.27 g/L Cd. Cadmium raffinate was used to optimize conditions for the separation of cobalt and nickel. As the transfer of cadmium from leach liquor to the organic phase containing Cyanex 923 follows a solvation mechanism with the association of chloride ions (Gupta et al., 2001), the stripping of cadmium was carried out with distilled water (pH 6.1) at a 1:1 phase ratio. This resulted in a stripping efficiency of 59.8% in single stage. Further studies were carried out by increasing the O:A ratio from 1:1 to 1:2, to increase the stripping efficiency to ~ 85% (Table 1). Considering the phase ratio and stripping efficiency, an O:A phase ratio of 1:1.75 and a three-stage counter-current stripping simulation (CCSS) was selected to yield a stripping efficiency of N 99% Cd. 3.1.4. Three-stage counter-current stripping simulation for cadmium A three-stage CCSS was carried out at A:O 1:1.75 to generate a representative strip solution (SS) and spent organic (SO). The combined strip solution and spent organic were collected. The SO phase was found to contain 0.005 g/L Cd corresponding to a stripping efficiency of 99.9%. The strip solution contained 3.58 g/L Cd at pH 1.9. 3.2. Processing of cadmium-free raffinate for cobalt recovery The raffinate from the cadmium extraction circuit, containing Ni = 21.56 g/L and Co = 0.14 g/L at pH 1.03, was used in optimizing conditions for cobalt recovery. 3.2.1. Selection of organo-phosphorus extractants, TOPS 99/PC 88A/Cyanex 272 for cobalt separation It is well documented in the literature that the separation factor, b (b = D Co/D Ni) for cobalt and nickel increases with the pK a values of acidic organophosphorus extractants. However, most of the reported results are basically from synthetic sulphate solutions

containing the metals at low and equal concentrations and are concerned with the extraction stoichiometry, structure of the organic complexes, equilibrium constants and selectivity (Danesi et al., 1985; Dreisinger and Cooper, 1984; Preston, 1983; Sarangi et al., 1999; Reddy and Bhaskara Sarma, 2001, Devi et al., 1998; Flett, 1987). On the other hand in the present study, the raffinate obtained after cadmium separation from the LL contains cobalt to nickel concentrations in the ratio of 1:154, which is very high. To select the best extractant with regard to efficiency of cobalt extraction over nickel, low extractant concentration and high separation factor; organo-phosphorus extractants such as TOPS 99, PC 88A and Cyanex 272 were studied

a

70 60 50

% Extraction

Table 1 Effect of A:O phase ratio on cadmium stripping from LO

40 30 20 10 0 1

2

3 4 5 Equilibrium pH

6

7

1

2

3 4 5 Equlibrium pH

6

7

b 60 0 Separation factor, fl β= Dco/DNi

256

500 400 300 200 100 0

Fig. 2. a. Equilibrium pH vs. % extraction Co and Ni with TOPS 99 (5, n—0.01 M, D, E—0.06 M and o, —0.2 M); Co (5, D, o); Ni (n,E, ). b. Variation of separation factor, b = D Co/ D Ni with equilibrium pH. (n, z, 5) 0.01 M, 0.06 M and 0.2 M TOPS 99.

.

.

B.R. Reddy et al. / Hydrometallurgy 77 (2005) 253–261

a 100 80 % Extraction

under wide range of conditions. The results of extraction of cobalt and nickel as a function of equilibrium pH and extractant concentrations; and corresponding b values, are presented in Figs. 2–4. In the case of TOPS 99, the best separation factor was achieved with 0.06 M extractant at an equilibrium pH 2.94, but the cobalt extraction was only 30.5%. At higher concentrations, the b values decreased drastically due to co-extraction of nickel. With PC 88A as the extractant, the b values increases with an increase in the concentration of extractant; and highest b value of

257

60 40 20 0 1

a

2

3 4 5 Equilibrium pH

6

7

3 4 5 Equilibrium pH

6

7

b

100

5000 Separation factor,β= Dco/DNi

% Extraction

80 60 40 20 0

3000 2000 1000 0

2

1

3 5 4 Equilibrium pH

6

7

b 3000 Separation factor, β= Dco/DNi

4000

1

2

Fig. 4. a. Effect of equilibrium pH vs. %extraction Co and Ni with Cyanex 272 (5, n—0.02 M and D,E—0.03 M); Co (5, D); Ni (n, E). b. Variation of separation factor, b = D Co/D Ni with equilibrium pH. (n, E) 0.02 M and 0.03 M Cyanex 272.

2500 2000 1500 1000 500 0 1

2

3 4 5 Equilibrium pH

6

7

Fig. 3. a. Effect of equilibrium pH vs. %extraction Co and Ni with PC 88A. (5, n—0.005 M, D,E—0.01 M and o, —0.04 M); Co (5, D, o); Ni (n, E, ). b. Variation of separation factor, b = D Co/ D Ni with equilibrium pH. (n, E, ) 0.005 M, 0.01 M and 0.04 M PC 88A.

.

.

.

2714 was achieved at an equilibrium pH 5.22 with 0.04 M PC 88A. In the case of Cyanex 272, the best b value of 4728 was achieved with 0.03 M extractant at an equilibrium pH 5.78. Comparison of b values is presented in Table 2. From these studies, Cyanex 272 appears to be the best and further studies on separation of cobalt from nickel was carried out using this extractant. 3.2.2. Effect of equilibrium pH on the extraction of cobalt From the cadmium raffinate, extraction was carried out at 1:1 phase ratio in the equilibrium pH range 1.57 to 6.03 using 0.03 M Cyanex 272. The results showed

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Table 2 Comparison of separation factor (b) values with extractants Extractant, [M] Equilibrium pH D Co

D Ni10

4

b = D Co/D Ni

TOPS 99 0.01 0.06 0.20

1.18 2.94 3.55

– 1.26 0.44 7.93 0.28 667

PC 88A 0.005 0.01 0.04

5.81 2.30 5.22

0.50 0.17 7.60

12.9 1.63 83.6

387 1031 2714

Cyanex 272 0.02 0.03

5.39 5.78

1.98 31.77

15.1 67.2

3974 4728

89 555 4

that at pH 5.7, separation of cobalt could be achieved (Fig. 4). 3.2.3. Cobalt extraction from cadmium raffinate To optimize the conditions with respect to the phase ratio and number of counter-current stages required for the quantitative extraction of cobalt, extraction of metal was obtained at different A:O phase ratios from 1:1 to 2:1 (Table 3) using 0.03 M Cyanex 272 at an aqueous phase equilibrium pH 5.7. The results indicate that, cobalt extraction decreased with increase in A:O ratio. The co-extraction of nickel was in the range of 0.7–0.6%. Considering the percent extraction, phase ratio, minimum stages required for complete removal of cobalt, and at the same time possible enrichment of metal in the organic phase; an A:O phase ratio of 1.5:1 was selected in order to remove cobalt in three countercurrent stages. This was confirmed with a three-stage CCES test which resulted in a raffinate containing 0.4 mg/L of cobalt (99.9% extraction efficiency), 21.48 g/L nickel and a loaded organic containing 209.4 mg/L cobalt. The co-extraction of nickel into the loaded organic was 0.12 g/L. The loaded organic,

Table 4 Effect of pH on nickel scrubbing from LO using 0.12 g/L cobalt scrub feed Initial pH

Equilibrium pH

Co in scrub raffinate (g/L)

Ni in scrub raffinate (g/L)

3.0 4.0 4.25

5.25 5.33 5.56

0.007 Nil 0.002

0.114 0.120 0.118

thus obtained, was used for generating data on nickel scrubbing and cobalt stripping; and the raffinate was used to optimize conditions for nickel recovery. 3.2.4. Scrubbing of nickel from loaded organic Initial tests carried out on the scrubbing of coextracted nickel from LO with distilled water at 1:1 phase ratio at different initial pH from 2.05 to 5.05 (corresponding to an equilibrium pH in the range 4.60 to 5.68), gave a scrubbing efficiency of 27–35% Ni and co-scrubbing of 61–74% Co, respectively. As a result, nickel scrubbing from LO was carried out with 0.12 g/L cobalt chloride solution in the initial pH range from 3.0 to 4.25 (Table 4). The results clearly demonstrate quantitative removal of Ni from LO with a scrub feed of pH 4. The scrubbed LO contains 0.33 g/L Co corresponding to quantitative scrubbing efficiency. 3.2.5. Stripping of cobalt from the loaded organic The cobalt from the LO was stripped with dilute HCl in the pH range 1 to 2 at O:A ratios of 1:1 and 2:1 (Table 5) to determine the possible enrichment of cobalt and the number of stages needed for quantitative stripping of cobalt from LO. The results indicate optimum conditions of strip solution of pH 1.5 and O:A phase ratio 2:1 for complete stripping of metal in 2 stages. The results of a two-stage CCSS carried out under these optimum conditions verified quantitative stripping efficiency of cobalt. Table 5 Effect of pH and phase ratio on stripping of cobalt from LO

Table 3 Effect of A:O ratio on cobalt extraction A:O

Cobalt extraction, %

Co-extraction of Ni, %

Theoretical no. stages

1.0:1 1.5:1 2.0:1

97.0 89.6 68.5

0.7 0.6 0.6

2 3 6

Strip feed pH

Equilibrium pH

Phase ratio O:A

Stripping efficiency, %

Theoretical no. stages

2.0 1.5 1.0 1.5

2.23 1.60 1.16 1.60

1:1 1:1 1:1 2:1

86.5 99.3 99.2 99.3

4 2 2 2

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259

Table 6 Stripping of nickel from loaded organic at different phase ratios

3.3. Processing of cobalt-free raffinate for nickel recovery The raffinate from the cobalt extraction circuit, containing 21.48 g/L Ni at pH 5.7, was used in optimizing conditions for nickel recovery using TOPS 99 as the extractant. 3.3.1. Effect of equilibrium pH and extractant concentration Extraction of nickel from cobalt raffinate was carried out at 1:1 phase ratio in the equilibrium pH range from 1.91 to 6.27 using 1 M TOPS 99. As expected, the percentage extraction of metal increases with the rise in equilibrium pH of the aqueous phase and reaches a maximum 97.7% around pH 6.1 and remains constant thereafter. To determine the number of stages required at a chosen volume phase ratio, the extraction isotherm was obtained by contacting cobalt raffinate and 1 M TOPS 99 at different A:O phase ratios from 1:1 to 5:1 and O:A from 1:1 to 5:1 at an equilibrium pH 6.0. The McCabe–Thiele plot (Fig. 5) shows N 99% Ni extraction is achieved in two C-C stages at A:O phase ratio of 1:1.25. Based on single stage extraction data, a two-stage CCES test was carried out at A:O phase

HCl, [M]

O:A ratio

Stripping efficiency, %

0.6 0.8 1 1 2 2 2

1:1 1:1 1:1 1.25:1 2:1 2.25:1 2.5:1

53.1 81.4 99.6 81.3 99.4 92.0 93.0

ratio of 1:1.25, and the representative raffinate showed the presence of 5mg/L Ni, corresponding to an extraction efficiency of 99.98%. The LO phase contained 17.2 g/L Ni. 3.3.2. Nickel stripping from loaded organic Nickel stripping from LO containing 17.2 g/L Ni was carried out at 1:1 phase ratio with varying acid concentrations from 0.6 to 2.0 M and O:A phase ratios from 1:1 to 2.5:1 (Table 6). The results clearly indicate an increase in percent stripping with rise in acid concentration and decrease in O:A ratio. Considering the better acid utilization, minimum number of stages, better stripping efficiency and enrichment of nickel, an O:A ratio of 2:1 was selected to carry out a two-stage CCSS with 2.0 M HCl. The spent organic

40 35

25 1 20

25

:1.

e,

15

in gl

O

A:

=1

[Ni]feed : 21.48 g/L

[Ni] org, g/L

30

tin

era

Op

10 5 2 0 0

2

4

6

8

10

12

14

16

18

20

22

[Ni]Aq, g/L Fig. 5. McCabe–Thiele plot for nickel extraction. Organic = 1 M TOPS 99; Aqueous: cobalt raffinate, Ni = 21.48 g/L.

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B.R. Reddy et al. / Hydrometallurgy 77 (2005) 253–261

Leach liquor Cd: 6.2 g/L N i: 21.5 g/L Co: 0.14 g/L

0.6 M Cyanex 923 in Kerosene

Distilled water

Cd exraction 2 Stages, A:O=1:1

Cd stripping 3 Stages A:O=1.75:1

Cd L.O

Cd raffinate Ni=21.5 g/L Co=0.14 g/L 0.03 M Cyanex272 in Kerosene

Co extraction 3 Stages A:O=1.5:1

3.54 g/L cadmium chloride Scrub.feed: 0.12 g/L Co

Co L.O Co: 0.209 g/L

Ni: 0.12 g/L

Co raffinate Ni: 21.44 g/L

1 M TOPS 99 in Kerosene

Ni extraction 2 Stages A:O=1:1.25

Regenerated solvent

Co scrubbing 1 Stage, A:O=1:1 Co SLO, Co: 0.329 g/L Distilled water pH=1.5 Co stripping 2 stages O:A= 2:1

Regenerated solvent 0.66 g/L cobalt chloride 2 M HCl strip feed

Ni L.O Ni: 17.18 g/L Ni stripping 2 Stages A:O=1:2

Regenerated solvent 34.36 g/L nickel chloride

Fig. 6. Flow sheet of the process for the recovery of Cd(II), Co(II) and Ni(II). Aqueous: Cd = 6.27 g/L; Ni = 21.56 g/L; Co = 0.14g/L; pH 1.0.

contained 1.6 mg/L Ni, corresponding to a stripping efficiency of 99.98%. A complete flow sheet of the process is presented in Fig. 6.

4. Conclusions A complete hydrometallurgical process for the separation and recovery of cadmium(II), cobalt(II) and nickel(II) from chloride leach liquors of spent batteries was developed on laboratory scale by solvent extraction route using the commercial phosphorus based extractants. Cyanex 923 was selective for cadmium(II) separation. Selectivity studies for cobalt–nickel separation indicated Cyanex 272 as the best extractant. The generated chloride salts of cadmium, cobalt and nickel are in pure form with a recovery efficiency N 99.95%. The enrichment of cobalt and nickel during extraction and stripping stages was about 4.7 and 1.6 times, respectively.

Finally, the present approach demonstrates a process which could solve the environmental related issues and at the same time recover valuable metals as chlorides. Nomenclature LO Loaded organic A Aqueous O Organic CC Counter current CCES Counter current extraction simulation CCSS Counter current stripping simulation SS Strip solution SO Spent organic b Separation factor

Acknowledgements The authors express sincere thanks to the Ministry of Environment and Forests (MOEF), New Delhi,

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India for financial support under project No. 19-125/ 99-RE. Thanks are also due to Dr. J.S. Yadav, Director and Dr. B.M. Choudary, Head, Inorganic and Physical Chemistry Division, IICT, Hyderabad, for their constant encouragement and permission to publish this work. Thanks are also to Cytec Canada for Cyanex 923 free sample.

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