Recovery of metallic palladium from hydrochloric acid solutions by a combined method of adsorption and incineration

Chemical Engineering Journal 218 (2013) 303–308

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Recovery of metallic palladium from hydrochloric acid solutions by a combined method of adsorption and incineration Sung Wook Won a, Yeoung-Sang Yun a,b,⇑ a b

Department of BIN Fusion Technology, Chonbuk National University, Jeonbuk 561-756, Republic of Korea School of Chemical Engineering, Chonbuk National University, Jeonbuk 561-756, Republic of Korea

h i g h l i g h t s " The maximum uptake of Pd(II) by TP 214 was 241.1 mg/g. " A metallic Pd was recovered through the combined method of adsorption and incineration. " Incineration temperature and Pd content affected the recovery efficiency and purity.

a r t i c l e

i n f o

Article history: Received 9 October 2012 Received in revised form 14 December 2012 Accepted 17 December 2012 Available online 29 December 2012 Keywords: Lewatit MonoPlus TP 214 Ion exchange resin Adsorption Incineration Metallic palladium

a b s t r a c t This study evaluated the recovery of palladium (Pd) by ion exchange resins from hydrochloric acid solutions using a combined method of adsorption and incineration. Lewatit MonoPlus TP 214 was selected as a representative commercial ion exchange resin and its adsorption performance was evaluated. Kinetic and isotherm experiments revealed that Pd(II) adsorption equilibrium was reached within 21 h, and the maximum uptake estimated by the Langmuir model was 241.1 ± 11.6 mg/g. To recover Pd as a solid form, the Pd ions-loaded resin was incinerated. The effects of incineration temperature and Pd amount were examined to enhance the recovery efficiency and purity of the recovered Pd. SEM–EDX and XRD analyses were used to confirm existence of Pd phase in ash incinerated in air at 600 °C and 900 °C. Both the incineration temperature and Pd amount significantly affected the recovery efficiency and purity. The form of Pd was changed from PdO to Pd0 as the incineration temperature was increased from 600 °C to 900 °C. At 900 °C and 258.5 mg/g of Pd(II) uptake, metallic Pd was successfully recovered with 99.0% of recovery efficiency and 96.1% of purity. Consequently, it can be claimed that the sorption–incineration process is likely an effective way enabling simple and fast recovery of precious metals as a metallic form from waste solutions. Ó 2012 Elsevier B.V. All rights reserved.

1. Introduction Precious metals, especially platinum group metals (PGMs) such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt), are of great significance in various industries due to their specific physical and chemical properties. They are widely used in many fields, such as catalysts in various chemical processes, electrical and electronic componentry, medicine, and jewelry. As a result, the demand and commercial value of PGMs are steadily increasing, but as natural resources, they are limited all over the world and are becoming depleted [1–3]. Therefore, the recovery of PGMs from primary sources (minerals)

⇑ Corresponding author at: Department of BIN Fusion Technology, Chonbuk National University, Jeonbuk 561-756, Republic of Korea. Tel.: +82 63 270 2308; fax: +82 63 270 2306. E-mail address: [email protected] (Y.-S. Yun). 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.12.052

and secondary sources (PGM-containing waste solutions) is of great economic interest, and the recovery techniques are becoming more important [4]. Processes for the recovery of PGMs from various wastes include hydrometallurgical and pyrometallurgical processes. The hydrometallurgical processes have been used successfully for the recovery of PGMs, and they have been used more frequently than the pyrometallurgical processes. The hydrometallurgical methods include solvent extraction, precipitation, adsorption and ion exchange to separate and recover PGMs in high-level liquid waste [5]. Moreover, platinum and palladium in spent petroleum catalysts can be recovered through various hydrometallurgical methods. Among these methods, the adsorption of noble metals by ion exchange resins is one of the most promising methods for the recovery of PGMs from aqueous solutions. This is due to the high efficiency and selectivity of ion exchange resins towards PGMs [6]. However, ion exchange resins are rarely used for

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adsorption purposes, and have instead been used for preconcentrating PGMs [7]. Anion exchange resins can easily sorb PGM ions, which are present in the form of anionic chloro-complexes in wastewaters with high chloride concentrations and low pH [8]. However, low selectivity was the main problem with anion exchange resins where base metals were being eluted along with PGMs. Chelating resins are a favorable alternative to conventional anion exchange resins for the selective separation of PGMs. In contrast to typical ion exchange resins, chelating resins interact with ion exchange and complexing reaction mechanisms, exhibiting high selectivity for anionic PGM ions. The properties and ion exchange capacity of these resins particularly depend on the type and quantity of functional groups and the pH of the solution. Chelating functional groups such as thiol, thiourea, dithizone, thiosemicarbazide, 2mercaptobenzothiazole, thiohydrazide and triisobutyl phosphine sulfide are often used in chelating resins [9–11]. Lewatit MonoPlus TP 214 (shortly TP 214) with thiourea functional groups showed good Pd adsorption performance in chloride–nitrate and chloride systems [10]. Thus, TP 214 was chosen as a model ion exchange resin in this study. To recover precious metals, desorption methods are often used and evaluated using various eluting agents such as HCl, thiourea, EDTA, and NaOH [1,12,13]. The acidified thiourea in HCl solution showed high desorption efficiency from the Pd(II)-loaded sorbents. Since desorption methods require various organic chemicals, a drawback of this method is presented in the generation of secondary wastewater after the desorption process. By electrolytic deposition, Pd can be recovered from the Pd-bearing acidic thiourea solution and the resulting solution can be recycled. However, this method is still discontinuous and time-consuming [14]. In our previous work [15], we proposed a combined method of biosorption and incineration as an alternative method that can be used for the recovery of PGMs. Pt sorbed on PEI-modified Escherichia coli biomass was successfully recovered in a metallic form with a recovery efficiency and purity of over 98.7% and 56.6%, respectively, from ICP wastewater containing Pt ions. However, there have been few studies on the recovery of PGMs with high purity using the combined method of adsorption and incineration. In the present work, a combined method of adsorption and incineration was used for the separation and recovery of Pd from hydrochloric acid solutions using TP 214. Pd(II) adsorption performances on the TP 214 were evaluated through kinetic and isotherm experiments, and the effects of incineration temperature and Pd amount were investigated in order to enhance the recovery efficiency and purity of Pd. 2. Experimental 2.1. Materials Lewatit MonoPlus TP 214 was purchased from LANXESS Korea Ltd. and chosen as a representative ion exchange resin, which can sorb anionic precious metals owing to its good capacity for platinum metals, gold and silver. The general characteristics of TP 214 are as follows: cross-linked polystyrene matrix, macroporous type, thiourea functional group, 2.0 eq/L total exchange capacity, 0.55 mm bead size and 43–48% water content. Palladium(II) chloride (PdCl2, 99.0%) was supplied by Kojima Chemicals Co., Ltd. (Saitama, Japan). Other chemicals used in this study were reagent grade. 2.2. Batch adsorption experiments A 1000 mg/L Pd(II) stock solution was prepared by dissolving PdCl2 in 0.1 M HCl solution. According to the chemical equilibrium

software MEDUSA [16], palladium ions were assumed to be present in the 0.1 M HCl solution as anionic chloro-complexes 2 (PdCl4 ). The batch adsorption studies were performed at pH 1.0 and 25 °C in 50-mL polypropylene conical tubes at various Pd(II) concentrations in 0.1 M HCl solutions. The kinetic experiment was conducted with 90 mg/L of the initial Pd(II) concentration and 1.0 g/L of the sorbent at 25 ± 1 °C and 160 rpm in a multishaking incubator (HB-201MS-2R, Hanbaek, Korea). The samples were collected at different time intervals in order to determine the time when the adsorption equilibrium was attained. After centrifugation at 9000 rpm for 5 min, the collected samples were properly diluted and measured using inductively coupled plasma–atomic emission spectrometry (ICP-AES; ICPS7500, Shimadzu, Japan). The isotherm experiment was conducted with 1.0 g/L of the resin in 30 mL of the Pd(II) solution. The initial Pd(II) concentrations were altered from 0 to 570 mg/L, which resulted in different final Pd(II) concentrations after the adsorption equilibrium was achieved. After 24 h, the samples were centrifuged, and Pd(II) concentration in each of the supernatant portion was determined by ICP-AES after proper dilution. The Pd(II) uptake (q, mg/g) of the TP 214 was calculated from the following mass balance equation:

q¼

ðC i  C f ÞV m

ð1Þ

where Ci and Cf are the initial and final Pd(II) concentrations (mg/L), respectively, and V is the working volume (L). m stands for the weight of the sorbent used in this work (g). 2.3. Adsorption data modeling The adsorption kinetics was described using pseudo-first-order and pseudo-second-order models, which are represented in their non-linear forms by the following equations:

pseudo-first-order model : qt ¼ q1 ð1  expðk1 tÞÞ pseudo-second-order model : qt ¼

q22 k2 t 1 þ q2 k2 t

ð2Þ ð3Þ

where qt represents the amount of Pd(II) sorbed at any time (mg/g), q1 and q2 are the amounts of Pd(II) sorbed at equilibrium (mg/g), k1 is the pseudo-first-order rate constant (L/min) and k2 is the pseudosecond-order rate constant (g/mg min). The adsorption isotherm was described using the Langmuir isotherm model as follows:

Langmuir model : qe ¼

qmax bC e 1 þ bC e

ð4Þ

where qe is the amount of sorbed metal (mg/g), Ce is the equilibrium Pd(II) concentration (mg/L), qmax is the maximum uptake (mg/g) and b is the Langmuir equilibrium constant (L/mg). Both kinetic and isotherm data modeling were estimated by non-linear regression using SigmaPlot software (version 10.0, SPSS, USA). 2.4. Incineration experiments for Pd recovery Incineration experiments were conducted for the recovery of Pd from Pd(II)-sorbed TP 214 resins. After Pd(II) adsorption, the Pd(II)loaded resins were separated by centrifugation, and the concentrations of Pd(II) remaining in the supernatants were measured by ICP-AES. The settled resins were washed with distilled water several times and dried at 60 °C for 24 h in an oven. To evaluate the effect of incineration temperature, the dried Pd(II)-loaded resins were placed in alumina crucibles and incinerated in air at different temperatures (600–1000 °C) for 3 h in an

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Recovery efficiency ð%Þ ¼

100

80

Pd(II) uptake (mg/g)

electric furnace (LEF-115S, Labtech, Korea). The weight of the resultant ashes was measured; 30 mL of aqua regia was added to an alumina crucible with the ashes and the mixture was stirred at room temperature at 160 rpm for 24 h. Then, the mixture was centrifuged in order to separate the residual solid. Finally, the Pd concentration in the solution was measured by ICP-AES after proper dilution. To examine the effect of Pd content, samples with various Pd(II) uptakes were first prepared. These samples were then incinerated in air at 900 °C for 3 h in an electric furnace. All other conditions of these experiments were the same as those used in the above experiments. The recovery efficiency and purity of palladium recovered by incineration were calculated using the following equations:

60

40

20 pseudo-first-order model pseudo-second-order model

0

Weight of metal in ash ðmgÞ Weight of initially sorbed metal ðmgÞ

0

200

400

Purity ð%Þ ¼

Weight of metal in ash ðmgÞ  100 Weight of ash ðmgÞ

800

1000

1200

1400

1600

Time (min)

 100 ð5Þ

600

Fig. 1. Adsorption kinetics of Pd(II) uptake for the Lewatit MonoPlus TP 214. The curve was predicted using pseudo-first-order and pseudo-second-order kinetic models.

ð6Þ

2.5. Analytical methods Four types of samples, TP 214 resin, Pd(II)-sorbed TP 214 resin, Pd-containing ash incinerated at 600 °C and Pd-containing ash incinerated at 900 °C, were prepared and examined using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectrometer (EDX) (SEM–EDX; JSM-6400, JEOL, Japan). These samples were coated in an Auto Fine Coater fitted with a Pt target. The surface components of the samples as well as surface morphologies were analyzed by SEM–EDX at 20 keV. In order to verify the crystallized form of Pd in the ash, X-ray diffraction (XRD) patterns were recorded on a Rigaku D/max 2500 diffractometer equipped with Cu Ka radiation (k = 1.5406 Å) over a scanning interval (0.02°) from 20° to 80°.

Table 1 Kinetic and isotherm parameters for Pd(II) adsorption by the Lewatit MonoPlus TP 214. Kinetics Pseudo-first-order model q1 (mg/g) 82.4 (2.1)

k1 (L/min) 0.0081 (0.0008)

R2 0.984

Pseudo-second-order model q2 (mg/g) 92.3 (0.8)

k2 (g/mg min) 0.0001 (0)

R2 0.999

Isotherm Langmuir model qmax (mg/g) 241.1 (11.6)

b (L/mg) 0.387 (0.151)

R2 0.956

300

3.1. Adsorption performance

250

The adsorption kinetics in wastewater treatment is very important because it provides valuable insights into the mechanism and reaction pathways of an adsorption reaction [17]. Fig. 1 shows the Pd(II) uptakes by the TP 214 as a function of time. The kinetics of the adsorption of Pd(II) anions onto the TP 214 was very slow, with 92% removal occurring in the first 540 min. Complete adsorption equilibrium was attained after 21 h. Since TP 214 is a macroporous chelating resin with thiourea functional groups, Pd(II) anions should first penetrate into the polymeric matrix of the resin, which is a rate-controlling step. Then, they can be bound with the thiourea groups of the resin [10]. Because of this, the adsorption between the functional groups of the resin and Pd(II) anions occurs slowly, and the adsorption kinetics depends on the diffusion rate of Pd(II) anions. Slow sorption kinetics of TP 214 resin for Pd(II) in hydrochloric acid solution is an undesired characteristic. The experimental adsorption kinetic data were described by pseudo-first-order and pseudo-second-order models. Table 1 shows the parameters estimated by the two kinetic models. In the pseudo-first-order model, the calculated q1 value slightly deviated from the experimental one even though the coefficient of determination, R2, was 0.984. On the other hand, R2 for the pseudo-second-order kinetic model was 0.999, and the Pd(II) adsorption capacity (q2) calculated at equilibrium was close to the

Pd(II) uptake (mg/g)

3. Results and discussion

200 150 100 50 0 0

50

100

150

200

250

300

350

Equilibrium Pd(II) concentration (mg/L) Fig. 2. Adsorption isotherm of Pd(II) uptake for the Lewatit MonoPlus TP 214. The isotherm experimental data were plotted using the Langmuir model.

experimental value. This indicates that the pseudo-second-order kinetic model is more suitable to describe the Pd(II) adsorption kinetics on TP 214 than the pseudo-first-order kinetic model. The isotherm study was also conducted to evaluate the maximum Pd(II) adsorption capacity of TP 214. The experimental data were plotted using Langmuir isotherm model, which is shown in

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100 Recovery efficiency Purity

Percentage (%)

80

60

40

20

0 600

700

800

900

1000

Temperature (oC) Fig. 3. The effect of incineration temperatures on the recovery of Pd from Pd(II)sorbed TP 214 resins.

Fig. 2. The ratio between the Pd(II) concentration remaining in the solution and that adsorbed on the TP 214 decreased with increasing Pd(II) concentration. Consequently, the isotherm shape was a typical L-shaped adsorption isotherm, indicating progressive saturation of the solid. The Langmuir constants and the coefficient of determination, R2, are listed in Table 1. The Langmuir adsorption isotherm has traditionally been used to quantify and contrast the performance of different sorbents. It estimates the maximum uptake values that cannot be achieved in experiments [18]. The R2 value was found to be 0.956. According to the Langmuir model, the maximum Pd(II) uptake was estimated to be 241.1 ± 11.6 mg/g for the TP 214. The Langmuir equilibrium constant (b) of the TP 214 was 0.387 L/mg, representing the high affinity between Pd(II) anions and the resin. In addition, to confirm the sorption capacity level of the TP 214 resin, the maximum adsorption capacity of the TP 214 for Pd(II) was compared with various other ion exchange resins reported in the literature. The maximum Pd(II) uptake by the TP 214 was lower than that of Dowex M-4195 (342.3 mg/g), which is a chelating resin with bis-picolylamine functional groups [19]. However, TP 214 was superior to other chelating resins

Fig. 4. SEM images and EDX spectra of the TP 214 resin (a and a0 ), Pd(II)-sorbed TP 214 resin (b and b0 ), Pd-containing ash incinerated at 600 °C (c and c0 ), and Pd-containing ash incinerated at 900 °C (d and d0 ).

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8000 PdO 101

4000 Pd 111 PdO 112 PdO 110 PdO 103 Pd 200

2000

3.2. Effect of incineration temperature for Pd recovery An incineration method can be used to recover precious metals in metallic form from precious metal-loaded sorbents [15]. In this work, the incineration temperature was considered as a major factor to affect the recovery efficiency and purity of Pd recovered. For evaluating the effect of incineration temperatures, adsorption experiments were carried out in a 30 mL solution with 108 mg/L Pd(II) concentration. Pd(II)-loaded resins were then incinerated in air in the temperature range of 600–1000 °C. The Pd(II) uptake on the resins was 32.4 mg/g, and the recovery efficiency and purity of Pd in ashes was estimated by Eqs. (5) and (6). Consequently, the metallic Pd in ash was obtained after the incineration of Pd(II)loaded TP 214 resins. The results are presented in Fig. 3. The incineration temperatures significantly affected the recovery of Pd from the Pd(II)-loaded TP 214, as shown in Fig. 3. The recovery efficiency and purity of Pd in ash was increased from 34.47% and 20.54% to 74.93% and 94.08%, as incineration temperature was increased from 600 °C to 800 °C. Above 800 °C, the change of the Pd recovery efficiency was negligible, while the purity of the Pd was slightly decreased. However, the recovery efficiency and purity of Pd in ash were lower than expected. Because the palladium recovered by incineration exists in two forms, zero-valent Pd (Pd0) and palladium oxide (PdO), palladium is readily soluble in aqua regia, but PdO is rarely soluble. Therefore, the above results may be due to the recovery efficiency and purity of Pd0. Further studies were carried out and are discussed in the following section to verify the form of the recovered Pd.

600 oC 900 oC

6000

Intensity (cps)

(Purolite S-940 (53.2 mg/g) [20], thiourea–formaldehyde resin (31.85) [21], melamine–formaldehyde-thiourea chelating resin (15.29 mg/g) [22]), weakly basic anion exchange resins (Amberlyst A-23 (173.4 mg/g) [23], Varion ADAM (121.48 mg/g) [24]), and nonionic resin (Amerlite XAD-16 (35.6 mg/g) [25]). LANXESS reports that TP 214 is special used for metal separation and recovery in hydrometallurgy and recovery of palladium catalysis from organic process streams because it has a high selectivity for PGMs [26]. Therefore, it can be concluded that TP 214 resin is promising for Pd(II) sorption from Pd(II)-bearing acidic solutions.

PdO 202 Pd 220

0 20

30

40

50

60

70

80

2 Theta (degree) Fig. 5. XRD patterns of the ashes incinerated in air at 600 °C (black line) and 900 °C (red line), respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

form at high temperature because it easily undergoes reduction or oxidation. PdO is thermodynamically stable in air up to about 780 °C, but above this temperature, the transition of PdO into metallic Pd starts, and ending at 850 °C [30]. As such, the Pd in the ash can be considered to be PdO (600 °C) and metallic Pd (900 °C) according to the incineration temperature. XRD analysis was additionally conducted to verify the form of Pd recovered at 600 °C and 900 °C the XRD patterns of which are displayed in Fig. 5. The predominant phase in the ash incinerated at 600 °C was in the form of PdO, showing major PdO diffraction peaks at 2h = 33.4° (PdO 101), 41.5° (PdO 110), 54.4° (PdO 112), 60.4° (PdO 103), and 71.0° (PdO 202) [27,31,32]. The Pd in the ash incinerated at 900 °C exhibited the characteristic peaks of face-centered cubic (fcc) crystalline Pd. The peaks at 2h = 40.2°, 46.8° and 68.1° correspond to the Pd planes (1 1 1), (2 0 0) and (2 2 0) [27,32]. These results indicate that the palladium phase changed from PdO to metallic Pd, when incineration temperature was increased from 600 °C to 900 °C.

3.3. Identification of the form of Pd recovered by incineration To confirm the form of Pd in ash, SEM–EDX and XRD analyses were conducted. Fig. 4 shows SEM–EDX results of the TP 214 resin, Pd(II)-sorbed TP 214 resin, Pd-containing ash incinerated at 600 °C, and Pd-containing ash incinerated at 900 °C. The microstructure of the surface of the TP 214 resin was similar to that of Pd(II)-sorbed TP 214 resin (Fig. 4a and b). However, the surface of the Pd(II)sorbed TP 214 resin was partially covered by the adsorption of Pd(II) anions. This superficial change was clearly observed in EDX results. As can be seen in Fig. 4a0 and b0 , the EDX spectrum of the TP 214 resin revealed the existence of C, O, S and Cl elements, while that of the Pd(II)-sorbed TP 214 resin showed a Pd element peak in addition to C, O, S and Cl elements. The surface of the Pd-containing ashes incinerated at 600 °C and 900 °C were very different from that of the Pd(II)-sorbed TP 214 resin. Comparing the Pd(II)-sorbed TP 214 resin to the Pd-containing ashes, the peak corresponding to the element sulfur disappeared in the EDX spectra of the Pdcontaining ashes (Fig. 4c0 and d0 ). This indicates that the resin was fully destroyed during incineration above 600 °C. The microstructure of the Pd-containing ash incinerated at 600 °C consisted of submicron particles forming large agglomerations (Fig. 4c). On the other hand, the Pd-containing ash incinerated at 900 °C exhibited much larger agglomerates than the Pd-containing ash incinerated at 600 °C (Fig. 4d). These results are similar to Pd-based catalyses [27–29]. Palladium occurs either in metallic or oxide

3.4. Effect of Pd amount loaded on the sorbent To enhance the recovery efficiency and purity of Pd, the amount of metal was considered as another major factor in the incineration process. For this evaluation, Pd(II) adsorption experiments were conducted with initial Pd(II) concentrations of 44.4, 181.1 and 358.6 mg/L, respectively. The uptakes on the resins were appreciated to be 44.3, 173.6 and 258.5 mg/g at 44.4, 181.1 and 358.6 mg/L of initial Pd(II) concentrations, respectively. From the uptake values, the Pd amounts loaded on the TP 214 were calculated to be 1.33, 5.21 and 7.76 mg, respectively. After adsorption, these samples were individually incinerated in air at 900 °C for 3 h. Fig. 6 represents the recovery efficiency and purity of Pd in the ash. Both the recovery efficiency and purity of Pd recovered were improved at higher amounts of Pd. The maximum recovery efficiency and purity of Pd in the ash were respectively above 99.0% and 96.1% at 7.76 mg Pd content. These results reveal that the amount of Pd loaded on the sorbent plays an important role in further increasing the recovery efficiency and purity of Pd recovered by incineration. From the results of the effects of incineration temperature and Pd amount loaded on the resin, it can be concluded that metallic Pd with high purity is recovered with the conditions of high incineration temperature and high Pd amount. This means that the

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120

Percentage (%)

110 100 90 80 70

Recovery efficiency Purity

60 0

2

4

6

8

10

Pd content (mg) Fig. 6. The influence of Pd amounts loaded on the TP 214 resins for Pd recovery and purity.

combined method of adsorption and incineration can be efficiently used for the recovery of metallic precious metals from preciousmetal-bearing aqueous or waste solutions. This method is also simple and eco-friendly compared to the conventional hydrometallurgical methods, which involve multi-step extraction, precipitation and chemical reduction using toxic chemicals. 4. Conclusions The following conclusions were drawn with regard to the recovery of metallic Pd from Pd(II)-bearing hydrochloric acid solutions through the combined method of sorption and incineration by TP 214 ion exchange resin.  Kinetic and isotherm experiments showed that Pd(II) sorption equilibrium was attained at around 21 h, and the maximum Pd(II) uptake of TP 214 was 241.1 mg/g according to the Langmuir model.  The incineration temperature affected the recovery efficiency and purity of Pd recovered by incineration.  According to the SEM–EDX and XRD analyses, the Pd in ashes incinerated in air at 600 °C and 900 °C formed PdO and metallic Pd, respectively.  When Pd(II)-sorbed resins were incinerated in air at 900 °C, the amount of Pd plays an important role in enhancing the recovery efficiency and purity of Pd recovered. The maximum recovery efficiency and purity of Pd in ash were above 99.0% and 96.1%, respectively, for 7.76 mg Pd content.

Acknowledgements This work was supported by the Korean Government through NRF (NRL 2008-0060070), KEITI (The Eco-Innovation project and Converging Technology Program), and KETEP (20115020100060) grants. S.W. Won was supported by Research Professor Fellowship from Chonbuk National University in 2012. References [1] K. Fujiwara, A. Ramesh, T. Maki, H. Hasegawa, K. Ueda, Adsorption of platinum (IV), palladium (II) and gold (III) from aqueous solutions on L-lysine modified crosslinked chitosan resin, J. Hazard. Mater. 146 (2007) 39–50. [2] A. Sari, D. Mendil, M. Tuzen, M. Soylak, Biosorption of palladium (II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies, J. Hazard. Mater. 162 (2009) 874–879.

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