Extraction of palladium (II) from nitric acid medium by imidazolium nitrate immobilized resin

Hydrometallurgy 86 (2007) 221 – 229 www.elsevier.com/locate/hydromet

Extraction of palladium (II) from nitric acid medium by imidazolium nitrate immobilized resin K.A. Venkatesan, B. Robert Selvan, M.P. Antony, T.G. Srinivasan ⁎, P.R. Vasudeva Rao Fuel Chemistry Division, Chemical Group, Indira Gandhi Centre For Atomic Research, Kalpakkam 603 102, India Received 31 July 2006; received in revised form 20 November 2006; accepted 21 November 2006 Available online 26 January 2007

Abstract Imidazolium nitrate functional groups (Im–NO3) were anchored onto a polystyrene–divinylbenzene resin matrix, and investigated for the extraction of palladium (II) from nitric acid medium. The rate of extraction and distribution coefficient, Kd, mL/g, of palladium (II) were measured as a function of extent of functionalization, and concentrations of nitric acid, sodium nitrate and palladium nitrate. Kd values of palladium (II) show a maximum in 3.0 M–4.0 M nitric acid. Slope analysis of the distribution data obtained at various aqueous phase nitrate concentrations and resin phase exchanging capacity suggest the involvement of anion exchange mechanism for the extraction of palladium (II) from nitric acid medium. The ion exchange isotherm was fitted using Langmuir adsorption model and the apparent ion exchange capacity (b = 88 mg/g) was determined. The performance of the resin under dynamic conditions was evaluated by following a breakthrough curve and the data was fitted using Thomas model. © 2006 Elsevier B.V. All rights reserved. Keywords: Ion exchange; Anchoring; Fission palladium; Imidazolium nitrate resin; Langmuir adsorption

1. Introduction The concept of by-product utilization arising from nuclear industry evolved in the 1950s. Potentially useful and strategic by-products are produced during fission of fissile elements (Ache et al., 1989, 1993). The PUREX process (Swanson, 1984) aims to recover strategic elements leaving a raffinate containing all the other fission products in 3–4 M nitric acid medium. The long-lived radioactive elements such as 137 Cs (t1/2 = 30.1a) and 90 Sr (t1/2 = 28.5 a) in addition to some non-radioactive platinum group metals are produced, in significant quantities, as by-products of fission (Ache et al., 1989, 1993). These were regarded as wastes a few decades ago ⁎ Corresponding author. Fax: +91 44 27480065. E-mail address: [email protected] (T.G. Srinivasan). 0304-386X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2006.11.006

but are now being targeted for recovery, owing to the upsurge in the utilization of these radioisotopes in the area of medicine (Brans et al., 2006; Woo and Sandford, 2002), food irradiation (Diehl, 2002; Lacroix and Ouattara, 2000; Sivinski, 1983) and sewage treatment (Borrely et al., 1998). Furthermore, the potential application of platinum group metals in various industries is wellestablished (Ache et al., 1989; Jenson et al., 1984, 1980; Kolarik and Renard, 2005). Most of the fission palladium isotopes in the spent nuclear fuel are non-radioactive or very weakly radioactive. It comprises of stable isotopes 104Pd (17 wt.%), 105 Pd (29 wt.%) 106Pd (21 wt.%) 108Pd (12 wt.%) 110Pd (4 wt.%) and a radioactive 107 Pd (17 wt.%) isotope, which has a half-life of 6.5 × 106 y. The intrinsic radioactivity of 107Pd (soft β-emittor with Emax of 35 keV) is very weak and it can be tolerated for many industrial

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applications (Kolarik and Renard, 2005). Thus the separation of palladium from high level liquid waste (HLLW) may provide considerable incentives in view of its widespread applications in various chemical, pharmaceutical and electronic industries (Ache et al., 1989; Jenson et al., 1984, 1980; Kolarik and Renard, 2005). In addition, isolation of palladium from HLLW may indirectly solve some of the problems associated with the management of high level radioactive waste described elsewhere (Sundaram and Perez, 2000). Therefore, removal of PGM from HLLW is desirable before immobilization to eliminate complex problems during vitrification and also to improve the quality of final waste form. The composition of HLLW is described elsewhere (Mathur et al., 1996) and majority of the elements present in HLLW exist as cationic species in 3–4 M nitric acid medium. However, palladium (II) in HLLW exists in the form of anionic nitrate complexes (Kolarik and Renard, 2003a). Recovery of valuable PGMs from HLLW has been extensively studied in the last two decades (Ache et al., 1989; Jenson et al., 1984, 1980; Rizvi et al., 1996; Shukla et al., 1993; Mimura et al., 2001; Lee and Chung, 2000; Koizumi et al., 1993; Mezhov et al., 2002a,b) with particular interest in the separation of palladium. A recent review by Kolarik and Renard (2003a,b, 2005) details the methods and materials reported to date for the recovery of valuable PGM from spent nuclear fuel and the behavior of fission PGM in HLLW. Recently we have also investigated the separation and recovery of palladium by an electrorefining method using room temperature ionic liquids (Giridhar et al., 2006a), solid phase extraction by sulphur based resins (Venkatesan et al., 2005) and solvent extraction by ylides (Mohan Raj et al., 2006) and Aliquat-336 (Giridhar et al., 2006b). A new method of extraction-cum-electrodeposition has been developed for the recovery of palladium from nitric acid medium (Giridhar et al., 2006b). Since the target metal, palladium (II) is a soft acid, selective extraction of it is feasible with soft base extractants containing S and N as ligands or donors. Various organo-functionalized resins are also studied for the extraction of palladium and other precious metals from non-radioactive feed solution (Jermakowicz-Bartkowiak et al., 2005; Kaledkowski and Trochimczuk, 2006; Sanchez et al., 2004; Qu et al., 2006). Sulphur based extractants and resin are reported to exhibit extraordinary selectivity for palladium at all nitric acid concentrations (Rizvi et al., 1996; Shukla et al., 1993; Mimura et al., 2001); however, they are vulnerable to acid-degradation. Several conventional anion exchange resins (Kolarik and Renard, 2003a; El-Said et al., 2002;

Pokhitonov and Romanovskii, 2005; Korolev et al., 2005) containing tertiary and quaternary ammonium ions as functional groups were also reported for the separation of palladium. However, these conventional exchangers exhibit poor selectivity for palladium from nitric acid feed representing HLLW, and usually operate at higher temperatures for increasing the selectivity. Anion resin functionalized with N,N-dimethylbenzimidazole (AR-01) was reported (Lee and Chung, 2000; Kolarik and Renard, 2003a) to extract palladium from 6 M nitric acid medium and attains equilibrium after 20 h at 60 °C. However, methylimidazole anchored on polystyrene–divinylbenzene copolymer has not been studied for the extraction of palladium from nitric medium. Therefore, the objective of the present paper is to anchor 1-methylimidazole on chloromethylated resin and to study the extraction behavior of palladium (II) from nitric acid medium on it. The effects of various parameters such as time, concentration of nitric acid and palladium ion on the extraction of palladium by the resin is reported. Extraction of palladium under dynamic conditions is also reported. 2. Experimental 2.1. Materials All the reagents used in the present study were of analytical reagent grade. Chloromethylated polystyrene–divinylbenzene (4.5 mmol/g; 4% cross linkage) copolymer was purchased from M/s. Thermax (India) Pvt. Ltd., Pune, India. The chloromethylated resin was washed with methanol and acetone to remove monomers and dried in air. 1-methylimidazole was procured from Lancaster UK. Palladium (II) nitrate was procured from M/s. Otto Chemie., Mumbai. 2.2. Preparation of imidazolium nitrate anchored resin (Im–NO3) The reaction scheme adopted for the preparation of Im–NO3 is shown below in Scheme 1. It involves the immersion of chloromethylated resin (2 g = 9 mmol) in a round bottomed flask containing 50 mL of toluene and desired amount of 1-methylimidazole. The entire mixture was refluxed for the desired interval of time. The supernatant was then decanted, and the product was washed with toluene, methanol and acetone and dried in air. The amount of methylimidazole anchored on the resin was estimated by eluting the chloride ion present in the resin. Sodium nitrate solution (0.1 M, 100 mL) was passed into a column packed with 0.5 g of the anchored resin. The

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223

Scheme 1. Synthesis of imidazole anchored resin I = Chloromethylated resin; II = 1-methylimidazole; III = Imidazole anchored resin — Cl form; Im– NO3 = Imidazole anchored resin — NO3 form.

effluent and water washings were collected in a 250 mL standard flask and the chloride content in the solution was measured by Mohr's method. The entire quantity of resin was converted to nitrate form by passing sodium nitrate solution in to a column packed with the resin until the effluent is free from chloride ion (tested with acidified silver nitrate). This nitrate form of imidazolium anchored resin, Im–NO3, was used for the entire study.

10− 4 M palladium nitrate, 1.0 M nitric acid, and desired concentration of sodium nitrate. The total nitrate ion concentration in the test solution was varied from 1.0 M to 5.0 M by varying the concentrations of nitric acid and sodium nitrate. The distribution ratio of palladium was measured as described above. Similar experiments were performed with the concentration of nitric acid in the test solution 3.0 M (or) 5.0 M and the total nitrate ion concentration up to 6.0 M.

2.3. Effect of nitric acid 2.5. Effect of [Im–NO3] All the experiments were carried out at 298 K. Extraction of palladium as a function of nitric acid concentration was studied by equilibrating resin with solution containing 6.2 × 10− 4 M palladium ion present in desired concentration of nitric acid. After 6h of equilibration, an aliquot was taken from the supernatant. The concentration of palladium present in the aliquot before and after equilibration was measured by spectrophotometric procedure (Rizvi and Natrajan, 1990) using Arsenazo III as coloring agent at the λmax of 627 nm. The distribution coefficient (Kd, mL/g) and the percentage of palladium extracted by the resin were calculated using Eqs. (1) and (2) respectively. Kd ¼


 ½Pdini −½Pdfin V m ½Pdfin


% Extraction ¼

1−

 ½Pdfin 100 ½Pdini

ð1Þ

ð2Þ

where V and m are respectively the volume of the solution and mass of the sorbent taken for equilibration. The kinetics of extraction were determined by sampling the above solutions at various times. 2.4. Effect of [NO3−] The effect of nitrate ion concentration on the extraction of palladium was studied by equilibrating 0.05 g of Im–NO3 resin with aqueous solution containing 6.2 ×

The influence of concentration of exchanging nitrate in the resin on the distribution coefficient of palladium was studied by equilibrating the Im–NO3 resin with aqueous solution containing 6.2 × 10− 4 M palladium nitrate dissolved in desired concentration of nitric acid. The nitrate exchange capacity was changed during preparation by using substoichiometric amounts of 1-methylimidazole. Palladium present in aqueous phase before and after extraction was determined as described above and the distribution values were calculated. 2.6. Effect of [Pd(II)] The extraction isotherm of palladium was constructed from the results of the experiments that involved equilibration of 0.05 g of the resin with aqueous phase containing desired concentration of nitric acid (3.0 M) and palladium nitrate(10− 4–10− 2 M) The concentration of Pd(II) present in the aqueous phase before and after extraction was measured and the concentration of Pd(II) in resin phase was calculated. 2.7. Column study The performance of the sorbent under dynamic condition was assessed by column breakthrough experiments. In this experiment 1.0 g (= 2 mL bed volume) of Im–NO3 was immersed in water and loaded into a glass column of radius 0.25 cm. The sorbent bed was washed

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Table 1 Variation of ion exchange capacity of Im–NO3 as a function of duration of refluxing and ratio of chloromethylated resin to 1-methylimidazole taken for synthesis Mole ratio of resin: 1-methylimidazole

Duration of refluxing (min)

Ion exchange capacity, mmol/g

1 : 10 1 : 10 1 : 10 1 : 10 1 : 10 1 : 10 1:5 1 : 1.5 1:1 1 : 0.75 1 : 0.5

40 60 120 180 300 480 300 300 60 60 60

3.56 3.59 3.60 3.70 3.99 4.00 3.98 4.06 3.43 3.01 2.80

with nitric acid of concentration equivalent to that of feed. The experimental feed solution containing 6.2 × 10− 4 M palladium ion diluted in 3.0 M nitric acid was passed at a flow rate of 0.5 mL/min. The effluent was collected at various intervals of time and analyzed for palladium. The ratio of the concentration of palladium in the effluent (C ) to that of feed (Co) was plotted against the bed volume of the solution passed through the bed to obtain the breakthrough curve. 3. Results and discussion 3.1. Preparation of Im–NO3 The results of ion exchange capacity obtained for anchoring of 1-methylimidazole on chloromethylated resin are shown in Table 1. When the mole ratio of chloromethylated resin to 1-methylimidazole is 1 : 10, rapid functionalization of methylimidazole is observed, leading to the exchange capacity of 3.5 mmol/g within 40 min of refluxing. Subsequently, the rate of functionalization is slow and a capacity of 4 mmol/g is achieved after 5 h of refluxing. Lowering of 1-methylimidazole concentration in the mixture (to 1 : 1.5) does not have much impact on the capacity values. Therefore, bulk of the resin (Im–NO3) with capacity of 4 mmol/g was prepared by refluxing 10 g of chloromethylated resin (4.5 mmol/g) with 1-methylimidazole (68 mmol) in 150 mL of toluene for 5h.

served in the initial stages of equilibration followed by the establishment of equilibrium occurring within 200 min of equilibration. The rate of uptake of palladium (d[Pd]t / dt) by Im–NO3 is given by Eq. (3). d½Pdt ¼ k1 ½Resin dt

ð3Þ

where k1 is the first order rate constant and [Resin] is the residual concentration of extraction sites in the resin phase, which can be related to the concentration of palladium in the resin phase at various intervals of time by Eq. (4). ½Resin ¼ ½Pdeqm −½Pdt

ð4Þ

where [Pd]eqm and [Pd]t are the palladium loading at equilibrium and at various intervals of time respectively. Substituting Eq. (4) in Eq. (1) gives d½Pdt ¼ k1 dt ½Pdeqm −½Pdt

ð5Þ

Integration of Eq. (5) between the limits, at t = 0, [Pd]t = 0 and at t = t, [Pd]t = [Pd]t, results in Eq. (6), which is known as Lagergren equation ½Pdt ¼ ½Pdeqm ð1−e−k1 t Þ

ð6Þ

Non-linear regression of the kinetic data using Eq. (6) is also shown in Fig. 1 and the rate constant (k1) obtained from the fitting increased from 5.9 × 10− 2 min− 1 to 7.4 × 10− 2 min− 1 when the concentration of nitric acid increased from 2.0 M to 4.0 M. 3.3. Effect of [HNO3] The distribution coefficient of palladium (II) as a function of nitric acid concentration on Im–NO3 is

3.2. Kinetics of extraction The rate of uptake of palladium by Im–NO3 from nitric acid medium is shown in Fig. 1. At all nitric acid concentrations, rapid extraction of palladium is ob-

Fig. 1. Kinetics of extraction of palladium (II) by Im–NO3. V / m = 50 mL/g; T = 298 K; [Pd(II)] = 6.2 × 104 M.

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225

½PdðH2 OÞ4 2þ þ 4NO−3 () PdðNO3 Þ2− 4 ½PdðNO3 Þ4 2−

b4 ¼

ð10Þ

½PdðH2 OÞ4 2þ ½NO−3 4

The total concentration of palladium (CPd) is given by Eq. (11). CPd ¼ ½PdðH2 OÞ4 2þ þ ½PdðH2 OÞ3 ðNO3 Þþ þ ½PdðH2 OÞ2 ðNO3 Þ2  þ ½PdðH2 OÞðNO3 Þ3 − þ ½PdðNO3 Þ4 2

Fig. 2. Variation of distribution coefficient of palladium (II) with concentration of nitric acid. Equilibration time = 6 h; T = 298 K; [Pd(II)] = 6.2 × 10− 4 M.

shown in Fig. 2. It is seen that Kd values increases with increase in the concentration of nitric acid reaching a maximum value at 3.0 M nitric acid which is ideally suited for the extraction of palladium from nitric acid medium representing high level nuclear wastes. It should be noted that the distribution coefficients obtained in the case of Im–NO3 resin are 3–4 times higher than the values obtained for Dowex 1 × 4 resin (quaternary ammonium salt with nitrate exchanging ion) under similar conditions. The reason for high distribution coefficients obtained for Im–NO3 is not clear, however it could be due to the strong interaction of anionic palladium nitrate species with the imidazolium resin. The distribution trend observed in the present study indicates that palladium (II) may be forming a series of anionic complexes with nitrate ions in aqueous solution, which are likely to be extracted by Im–NO3 through anion exchange. The formation of various nitrate complexes of palladium (II) from free palladium (II) ion ([Pd(H2O)4]2+) are given below, where βn are the corresponding formation constants. 2þ

½PdðH2 OÞ4  b1 ¼

þ

NO−3

Using Eqs. (7)–(10), the total concentration of palladium, CPd, and the concentration of [Pd(H2O)(NO3)3]− can be written as

½PdðH2 OÞ3 ðNO3 Þþ ½PdðH2 OÞ4 2þ ½NO−3 

½PdðH2 OÞ4 2þ þ 2NO−3 () ½PdðH2 OÞ2 ðNO3 Þ2  ½PdðH2 OÞ2 ðNO3 Þ2  b2 ¼ ½PdðH2 OÞ4 2þ ½NO−3 2 ½PdðH2 OÞ4 2þ þ 3NO−3 () ½PdðH2 OÞðNO3 Þ3 − " ½PdðH2 OÞðNO3 Þ3  b3 ¼ ½PdðH2 OÞ4 2þ ½NO−3 3

ð7Þ

4 X

bi ½NO−3 i g

ð12Þ

b3 ½NO−3 3 CPd 4 P 1 þ bi ½NO−3 i

ð13Þ

CPd ¼ ½PdðH2 OÞ4 f1 þ

i¼1

½PdðH2 OÞðNO3 Þ3 − ¼

i¼1

If the mechanism of extraction involves the ion exchange of [Pd(H2O)(NO3)3]− species as shown in Eq. (14), then the equilibrium constant (K) of extraction and the distribution coefficient (Kd) of palladium can be represented by Eqs. (15) and (16) respectively. Im  NO3 þ ½PdðH2 OÞðNO3 Þ3 − () Im  ½PdðH2 OÞðNO3 Þ3  þ NO−3

ð14Þ

½Im  PdðH2 OÞðNO3 Þ3 ½NO−3  ½Im  NO3 ½PdðH2 OÞðNO3 Þ3 −

ð15Þ

K¼

Kd ¼

þ

() ½PdðH2 OÞ3 ðNO3 Þ

ð11Þ

½Im  PdðH2 OÞðNO3 Þ3  CPd

ð16Þ

Substituting the value of [Pd(H2O)(NO3)3]− from Eq. (13), and combining Eqs. (15) and (16) results in Kd ¼ K½Im  NO3 

ð8Þ

b3 ½NO−3 2 4 P 1 þ bi ½NO−3 i

ð17Þ

i¼1

At low nitrate ion concentrations, ð9Þ

1NN

4 X i¼1

bi ½NO−3 i

ð18Þ

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and Eq. (17) can be simplified to Eq. (19), where the distribution coefficient (Kd) of palladium (II) varies directly with [NO3−]2. Kd ∝K½Im  NO3 ½NO−3 2

ð19Þ

At high nitrate ion concentrations, the denominator term tends towards the fourth power of nitrate ion concentration as shown in Eq. (20) and thus Kd varies inversely with [NO3− ]2 according to Eq. (21) 1þ

4 X

! bi ½NO−3 i

Y½NO−3 4

ð20Þ

i¼1

Kd ∝K½Im  NO3 ½NO−3 −2

ð21Þ

Thus, depending upon the nitrate ion concentration used in the study the slope of the plot of log Kd versus log [NO3−] should vary from 2 to − 2 according to Eqs. (19) and (21). A plot log Kd against log [NO3] is shown in Fig. 3. When the initial concentration of nitric acid is 1.0 M, and the total nitrate in the test solution is varied from 1.0 M to 5.0 M, log Kd − log [NO3] results in a slope of 0.91. The magnitude of slope decreases to 0.4 when the initial concentration of nitric acid is increased to 3.0 M and the total nitrate ion concentration is varied up to 5.0 M using sodium nitrate. Further increase in total nitrate concentration to 6.0 M, when initial concentration of nitric acid is 5.0 M, results in a negative slope of − 0.68. The results suggest that an increase in Kd values of palladium with the increase in concentration of nitric acid could be attributed to the increased formation of

Fig. 4. Variation of log Kd with log [Im–NO3] for the extraction of palladium (II) by Im–NO3. V / m = 200 mL/g; T = 298 K; equilibration time = 10 h; [Pd(II)] = 6.2 × 10− 4 M.

anionic palladium nitrate complexes, and decrease in Kd values at higher nitrate ion concentrations could be due to the shift in the equilibrium reaction (14) in the reverse direction. 3.4. Effect of [Im–NO3] At constant nitrate ion concentration, a plot of log Kd against log [Im–NO3] should result in a slope of unity, according to Eq. (17). Fig. 4 shows the plot of log Kd against log [Im–NO3] for the extraction of palladium at various initial concentrations of nitric acid. It is seen that Kd value increases with increase in the extent of functionalization. At all nitric acid concentrations, log Kd − log [Im–NO3] plot results in a slope of ∼ 1.0, which is in accordance with Eq. (14), confirming the validity of the mechanism shown in Eq. (14). Similarly, slope analysis for the extraction of palladium (II) by solvent extraction (Mohan Raj et al., 2006; Giridhar et al., 2006b) using liquid anion exchangers have resulted in a slope of 1.5. It was proposed the extraction of both [Pd(H2O)(NO3)3] − and [Pd(NO3)4] 2− is responsible for the higher magnitude. However, in the present study, the PS–DVB resin matrix being rigid, seems to prefer the extraction of [Pd(H2O)(NO3)3] − resulting in a slope of 1.0 only. 3.5. Effect of [Pd(II)]

Fig. 3. Variation of log Kd with log [NO3] for the extraction of palladium (II) by Im–NO3. V / m = 200 mL/g; T = 298 K; equilibration time = 10 h; [Pd(II)] = 6.2 × 10− 4 M.

The variation of palladium loading in Im–NO3 resin as a function of its concentration is shown in Fig. 5. The amount of palladium loaded on to the resin increases with the concentration of palladium in the aqueous phase. The linear form of the Langmuir equation relating

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227

3.6. Column experiments

Fig. 5. Ion exchange isotherm of palladium (II) extraction from 3.0 M nitric acid. V / m = 200 mL/g; T = 298 K; equilibration time = 10 h.

the amount of metal ion extracted (Cs) by the resin and the metal concentration in solution (Cf) is given by Eq. (22). Cf 1 Cf þ ¼ Cs KL b b

ð22Þ

where Cf is the equilibrium concentration of palladium (mg/L), Cs is the amount of palladium extracted by Im–NO3 (mg/g), KL is the Langmuir adsorption constant (L/mg) is related to the affinity of the resin towards the metal ion, and b is the apparent extraction capacity of palladium on Im–NO3 resin under the studied conditions. From Eq. (22), the experimental capacity (b,mg/g) and KL are obtained from the slope and intercepts of the straight line shown in Fig. 6. The apparent experimental capacity, b, was found to be 88 mg/g for the extraction of palladium (II) from 3.0 M nitric acid medium by Im–NO3 resin.

Fig. 6. Langmuir plot for the extraction of palladium from 3.0 M nitric acid. V / m = 200 mL/g; T = 298 K; equilibration time = 10 h.

The performance of the resin under dynamic loading conditions can be evaluated by following a breakthrough curve (Helfferich, 1962). Fig. 7 shows the breakthrough curve for the extraction of palladium (II) (6.2 × 10− 4 M) from 3.0 M nitric acid medium by Im–NO3. The feed solution was passed at a flow rate of 0.5 mL/min. It is seen that 10% breakthrough is obtained after passing 25 bed volumes. Various simple models have been developed to describe the dynamic behavior of extraction of metal ions in a fixed bed column (Thomas, 1944; Aksu and Gonen, 2004; Mathaialagan and Viraraghavan, 2002; Sivaiah et al., 2004). The Thomas model (Thomas, 1944) is given by Eq. (23) C 1 ¼ ðK ðBm−C T o V Þ=QÞ C0 1 þ e

ð23Þ

where, C and C0 are the concentration of palladium (in mg/L) in the effluent and in the feed (= 65 mg/L), respectively; KT is the Thomas rate constant (mL min− 1 mg− 1 ); B (in mg/g) is the maximum loading capacity of palladium under the specified conditions; m (= 1.0 g) is the mass of the sorbent taken in the column; V (in mL) is the throughput volume and Q is the flow rate in mL/min. Breakthrough data is fitted using Eq. (23) by non-linear regression and the values of KT and B were found to be 1.72 × 10 − 1 mL min − 1 mg− 1 and 8 mg/g respectively. The extracted palladium was quantitatively eluted using 25 mL of 0.05 M thiourea in 0.1 M nitric acid.

Fig. 7. Breakthrough curves for the extraction of palladium (II) by Im– NO 3 . Resin = 1 g = 2 mL; T = 298 K; [HNO3 ] = 3.0 M; flow rate = 0.5 mL/min; [Pd(II)] = 6.2 × 10− 4 M.

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4. Conclusions The kinetics of anchoring of 1-methylimidazole on chloromethylated polystyrene–divinylbenzene is rapid and leads to 80% anchoring of methylimidazolium ion on the resin matrix within 40 min of refluxing. A maximum anion exchange capacity of ∼ 4 mmol/g was obtained after 5h of the reaction. The distribution coefficient of palladium (II) in the resin increased with the aqueous phase concentration of nitric acid and reached a maximum at 3–4 M. Anion exchange of palladium nitrate species, [Pd(H2O)(NO3)3]−, present in aqueous phase with NO3− ion of Im–NO3 resin is responsible for the extraction of palladium (II) from nitric acid medium. The extraction data can be fitted to a Langmuir adsorption model and an apparent exchange capacity of 88 mg/g for palladium extraction from 3.0 M nitric acid is obtained. Breakthrough curve is followed up to the C/Co of 0.8 and 10% breakthrough is obtained after passing 25 bed volumes of the feed. Acknowledgement The authors thank Miss N. Subhashri, M.Sc. Student, Anna University for assistance. References Ache, H.J., Baetsle, L.H., Busth, R.P., Nechaev, A.F., Popik, V.P., Ying, Y., 1989. Feasibility of Separation and Utilization of Ruthenium, Rhodium and Palladium from High Level Waste. Technical Report Series, vol. 308. IAEA, Vienna. Ache, H.J., Baetsle, L.H., Busth, R., Cooperstein, R., Grigoriev, A.Y., Langley, K.F., Morita, Y., Nechaev, A.F., Popik, V.P., Wada, Y., 1993. Feasibility of Separation and Utilization of Cesium and Strontium from High Level Waste. Technical Report Series, vol. 356. IAEA, Vienna. Aksu, Z., Gonen, F., 2004. Biosorption of phenol by immobilized activated sludge in a continuous packed bed: prediction of breakthrough curve. Process Biochem. 39 (5), 599–613. Borrely, S.I., Cruz, A.C., Del Mastro, N.L., Sampa, M.H.O., Somessari, E.S., 1998. Radiation processing of sewage and sludge. A review. Prog. Nucl. Energy 33 (1/2), 3–21. Brans, B., Linden, O., Giammarile, F., Tennvall, J., Punt, C., 2006. Clinical applications of newer radionuclide therapies. Eur. J. Cancer 42 (8), 994–1003. Diehl, J.F., 2002. Food irradiation — past, present and future. Radiat. Phys. Chem. 63 (3–6), 211–215. El-Said, N., Siliman, A.M., El-Sherif, E., Borai, E.H., 2002. Separation of palladium from simulated intermediate radioactive waste/ chloroacetic acid/nitrate medium by IRA-410 and IRA-900 anion exchangers. J. Radioanal. Nucl. Chem. 251 (2), 285–292. Giridhar, P., Venkatesan, K.A., Reddy, B.P., Srinivasan, T.G., Vasudeva Rao, P.R., 2006a. Recovery of fission palladium by electrodeposition using room temperature ionic liquids. Radiochim. Acta 94 (3), 131–136.

Giridhar, P., Venkatesan, K.A., Srinivasan, T.G., Vasudeva Rao, P.R., 2006b. Extraction of fission palladium by Aliquat 336 and electrochemical studies on direct recovery from ionic liquid phase. Hydrometallurgy 81 (1), 30–39. Helfferich, F., 1962. Ion Exchange. McGraw-Hill Book Company, New York. Jenson, G.A., Rohmann, C.A., Perrigo, L.D., 1980. Recovery and Use of Fission Product Noble Metals. PNL-SA-8358. Pacific Northwest Laboratory, Richland, Washington. Jenson, G.A., Platt, A.M., Mellinger, G.B., Bjorklund, W.J., 1984. Recovery of noble metals from fission products. Nucl. Technol. 65 (2), 305–324. Jermakowicz-Bartkowiak, D., Kolarz, B.N., Serwin, A., 2005. Sorption of precious metals from acid solutions by functionalized vinylbenzyl chloride–acrylonitryle–divinylbenzene copolymers bearing amino and guanidine ligands. React. Funct. Polym. 65 (1–2), 135–142. Kaledkowski, A., Trochimczuk, A.W., 2006. Chelating resin containing hybrid calixpyrroles: new sorbent for metal cations. React. Funct. Polym. 66 (9), 957–966. Koizumi, K., Ozawa, M., Kawata, R., 1993. Electrolytic extraction of platinum group metals from dissolver solution of purex process. J. Nucl. Sci. Technol. 30 (11), 1195–1197. Korolev, V.A., Pokhitonov, Y.A., Gelis, V.M., Milyutin, V.V., 2005. Recovery of Pd from spent fuel: 2. Sorption recovery of Pd from nitric acid solutions on anion-exchange resins. Radiochemistry 47 (4), 370–373. Kolarik, Z., Renard, E.V., 2003a. Recovery of valuable fission platinoids from spent fuel, Part I: General considerations and basic chemistry. Platin. Met. Rev. 47 (2), 74–87. Kolarik, Z., Renard, E.V., 2003b. Recovery of valuable fission platinoids from spent fuel, Part II: Separation processes. Platin. Met. Rev. 47 (3), 123–131. Kolarik, Z., Renard, E.V., 2005. Potential applications of fission platinoids in industry. Platin. Met. Rev. 49 (2), 79–90. Lacroix, M., Ouattara, B., 2000. Combined industrial processes with irradiation to assure innocuity and preservation of food products— a review. Food Res. Int. 33 (9), 719–724. Lee, S.H., Chung, H., 2000. Ion exchange characteristics of palladium and rhodium from simulated radioactive liquid waste. J. Nucl. Sci. Technol. 37 (3), 281–287. Mathaialagan, T., Viraraghavan, T., 2002. Adsorption of cadmium from aqueous solution by perlite. J. Hazard. Mater. 94 (3), 291–303. Mathur, J.N., Murali, M.S., Balaramakrishna, M.V., Chitnis, R.R., Wattal, P.K., Theyyunni, T.K., Ramanujam, A., Dhami, P.S., Gopalakrishnan, P.K., 1996. Recovery of neptunium from highly radioactive waste solutions of purex origin using tributyl phosphate. Sep. Sci. Technol. 31 (15), 2045–2063. Mezhov, E.A., Kuchmumov, V.A., Druzhenkov, V.V., 2002a. Study of extraction of palladium from nitric acid solutions with nitrogen containing compounds, as applied to recovery of fission palladium from spent nuclear fuel of nuclear power plants: 1. Extraction and back washing conditions. Radiochemistry 44 (2), 135–140. Mezhov, E.A., Druzhenkov, V.V., Sirotinin, A.N., 2002b. Study of extraction of palladium from nitric acid solutions with nitrogen containing compounds, as applied to recovery of fission palladium from spent nuclear fuel of nuclear power plants: 3. Optimization of extraction process for palladium recovery and refining. Radiochemistry 44 (2), 146–150. Mimura, H., Ohta, H., Akiba, K., Onodera, Y., 2001. Selective uptake and recovery of palladium by biopolymer microcapsules enclosing cyanex 302 extractant. J. Nucl. Sci. Technol. 38 (5), 342–348.

K.A. Venkatesan et al. / Hydrometallurgy 86 (2007) 221–229 Mohan Raj, M., Dharmaraja, A., Panchanatheswaran, K., Venkatesan, K.A., Srinivasan, T.G., Vasudeva Rao, P.R., 2006. Extraction of fission palladium (II) from nitric acid by benzoylmethylene– triphenylphosphorane. Hydrometallurgy 84 (1–2), 118–124. Pokhitonov, Y.A., Romanovskii, V.M., 2005. Palladium in irradiated fuel. Are there any prospects for recovery and application? Radiochemistry 47 (4), 370–373. Qu, R.J., Sun, C.M., Ji, C.N., 2006. Synthesis and characterization of polystyrene-supported 2,5-dimercapto-1,3,4-thiodiazole and its sorption behavior for Pd(II), Pt(IV), and Au(III). J. Appl. Polym. Sci. 101 (1), 631–637. Rizvi, G.H., Natrajan, P.R., 1990. Extraction of palladium from nitric acid medium and its spectrophotometric determination using arsenazo III. Fresenius' J. Anal. Chem. 336, 498–500. Rizvi, G.H., Mathur, J.N., Murali, M.S., Iyer, R.H., 1996. Recovery of fission product palladium from acidic high level waste solutions. Sep. Sci. Technol. 31 (13), 1805–1816. Sanchez, J.M., Hidalgo, M., Salvado, V., 2004. A comparison of the separation behavior of some new coordinating resins and commercial quaternary ammonium resins with reference to their separation of gold(II) and palladium (II) in hydrochloric acid media. Solvent Extr. Ion Exch. 22 (2), 285–303. Shukla, J.P., Singh, R.K., Sawant, S.R., Varadarajan, N., 1993. Liquid– liquid extraction of palladium from nitric acid by bis(2-ethylhexyl) sulphoxide. Anal. Chim. Acta 276 (1), 181–187.

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Sivaiah, M.V., Venkatesan, K.A., Sasidhar, P., Krishna, R.M., Murthy, G.S., 2004. Ion exchange studies of cerium (III) on uranium antimonate. J. Nucl. Radiochem. Sci. 5 (1), 7–10. Sivinski, J.S., 1983. Environmental application of cesium-137 irradiation technology: sludges and foods. Radiat. Phys. Chem. 22 (1/2), 99–118. Sundaram, S.K., Perez Jr., J.M., 2000. Noble Metals and Spinal Settlings in High Level Waste Glass Melters. PNNL-13347. Pacific Northwest National Laboratory, Richland, Washington. Swanson, J.L., 1984. PUREX process flow-sheets. In: Schulz, W.W., Burger, L.L., Navratil, J.D., Bender, K.P. (Eds.), Science and Technology of Tributyl Phosphate, vol. 3. CRC Press Inc., Boca Raton, p. 55. Thomas, H.C., 1944. Heterogeneous ion exchange in a flowing system. J. Am. Chem. Soc. 66 (10), 1664–1666. Venkatesan, K.A., Robert Selvan, B., Antony, M.P., Srinivasan, T.G., Vasudeva Rao, P.R., 2005. Extraction of palladium from nitric acid medium by various commercial resins functionalized with phosphinic acid, methylene thiol and isothiouronium moieties on polystyrene–divinylbenzene. J. Radioanal. Nucl. Chem. 266 (3), 431–440. Woo, L., Sandford, C.L., 2002. Comparison of electron beam irradiation with gamma processing for medical packaging materials. Radiat. Phys. Chem. 63 (3–6), 845–850.