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Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration
Bioresource Technology 137 (2013) 400–403
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration Sung Wook Won a, Areum Lim b, Yeoung-Sang Yun a,b,c,⇑ a
Department of BIN Fusion Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea Department of Bioprocess Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea c School of Chemical Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea b
h i g h l i g h t s The combined method of biosorption and incineration was used for the recovery of Pd. Temperature and Pd amount modulated the recovery efficiency and purity of Pd. Higher temperature up to 800 °C showed higher recovery efficiency and purity of Pd. Pure metallic Pd was recovered at 900 °C and 136.9 mg/g of Pd uptake.
a r t i c l e
i n f o
Article history: Received 11 January 2013 Received in revised form 18 March 2013 Accepted 20 March 2013 Available online 27 March 2013 Keywords: Recovery Palladium Biosorption Incineration
a b s t r a c t This work reports a direct way to recover metallic palladium with high purity from Pd(II)-sorbed polyethylenimine-modified Corynebacterium glutamicum biosorbent using a combined method of biosorption and incineration. This study is focused on the incineration part which affects the purity of recovered Pd. The incineration temperature and the amount of Pd loaded on the biosorbent were considered as major factors in the incineration process, and their effects were examined. The results showed that both factors significantly affected the enhancement of the recovery efficiency and purity of the recovered Pd. SEMEDX and XRD analyses were used to confirm that Pd phase existed in the ash. As a result, the recovered Pd was changed from PdO to zero-valent Pd as the incineration temperature was increased from 600 to 900 °C. Almost 100% pure metallic Pd was recovered with recovery efficiency above 99.0% under the conditions of 900 °C and 136.9 mg/g. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Platinum group metals (PGMs), such as palladium (Pd), are very important resources in a variety of industries, such as the electrical and electronics industry, jewelry and ornaments, medicine, catalysis, and the petroleum industry, due to their specific physical and chemical properties (Ramesh et al., 2008). However, Pd ions have high mobility in aquatic environments because of their water solubility, and exposure leads to serious harmful effects on biota (Kielhorn et al., 2002; Hoppstock and Sures, 2004). Therefore, the negative environmental effects and high demand for Pd from various industries have increased the interest in Pd recovery from PGM-containing waste solutions. The hydrometallurgical methods include adsorption by ion exchange resin, solvent extraction, and precipitation of PGMs by ⇑ Corresponding author at: Department of BIN Fusion Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea. Tel.: +82 63 270 2308; fax: +82 63 270 2306. E-mail address: [email protected] (Y.-S. Yun). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.03.143
reducing reagents (Lee et al., 1998). These methods have been used more frequently than the pyrometallurgical methods to recover PGMs. Compared with these methods, the hydrometallurgical method is more exact, predictable, and more easily controlled (Syed, 2012). However, both of these recovery methods are expensive and require extensive labor and time. Moreover, since various chemicals are used for precipitation and reduction processes, large quantities of secondary wastes are generated (Das, 2010). Therefore, there is necessity to develop an alternative method for the direct recovery of PGMs from waste solutions. In this study, a combined method of biosorption and incineration was evaluated as an alternative method able to take advantages of both hydrometallurgy and pyrometallurgy. The metallic gold with over 77.42% of purity was recovered from Au-loaded polyethylenimine (PEI)-modified bacterial biosorbent fiber using this method (Park et al., 2012). Biological processes have many advantages over traditional physicochemical treatments, as they do not require the use of large quantities of toxic chemicals. Biosorption is a promising alternative
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S.W. Won et al. / Bioresource Technology 137 (2013) 400–403
technique for recovering PGMs from aqueous and non-aqueous solutions. It has been used to separate and concentrate metals using various biomasses, such as bacteria, fungi, and algae (Vijayaraghavan and Yun, 2008). For example, Corynebacterium gltamicum biomass, which is a waste generated from microbial fermentation industries, is very cheap compared to commercial sorbents like ion exchange resins, and is available in large quantities. However, these raw materials have shown not enough uptakes of metals in aqueous solutions. In our previous work, we developed a PEI-modified Corynebacterium glutamicum biomass (PEIB) to increase metal sorption capacity, and proved its significantly improved uptake of Pd(II) in a batch system (Won et al., 2011). The present study is a continuation of previous work concerning applications of the PEIB for the recovery of palladium from hydrochloric acid solutions. To recover high-purity metallic Pd, a combined method of biosorption and incineration is suggested. This method can significantly reduce the working volume to be handled. The main factors affecting recovery efficiency and purity are incineration temperature and the amount of Pd sorbed on the PEIB. Therefore, the effects of these factors on the recovery efficiency and purity of Pd are investigated.
then incinerated in air at 900 °C for 3 h in an electric furnace. All other experimental conditions were the same as in the incineration temperature experiment. Each experiment was performed in triplicate. 2.3. Measurement of uptake, recovery efficiency and purity The Pd(II) uptake of PEIB and the recovery efficiency and purity of Pd in ashes were calculated from the following equations:
Uptake : q ¼
ðC i C f ÞV M
Recovery efficiency ð%Þ ¼
ð1Þ Pd weight in ash ðmgÞ Initially sorbed Pd weight ðmgÞ 100
Purity ð%Þ ¼
Pd weight in ash ðmgÞ 100 Ash weight ðmgÞ
ð2Þ ð3Þ
where q is the Pd(II) uptake (mg/g), Ci and Cf are the initial and final Pd(II) concentrations (mg/L), respectively, and V is the working volume (L). M represents the weight of the sorbent used (g).
2. Methods 2.4. Analytical tools 2.1. Materials and surface modification The C. glutamicum biomass was obtained as a spray-dried powder form from the L-arginine fermentation industry (Daesang, Gunsan, Korea). Industrial-grade PEI (M.W.: 70,000; purity: 50 ± 1%) was purchased from Habjung Moolsan Co., Ltd. (Seoul, Korea). Glutaraldehyde (GA; 25% solution) and PdCl2 (99.0%) were purchased from Junsei Chemical and Kojima Chemicals Co., Ltd., respectively. Other chemicals used in this study were of reagent grade. PEIB was prepared according to our previous method (Won et al., 2011). Briefly, raw C. glutamicum biomass (10 g) was suspended in 100 mL of distilled water containing 3 g of PEI for 2 h, and GA (0.6 mL) as a cross-linker was added to the mixture and stirred further for 2 h. Then, the modified biomass was centrifuged, washed with distilled water four times, and lyophilized for 24 h. 2.2. Incineration experiments for recovery of Pd Biosorption experiments were carried out by placing 0.1 g of PEIB with 30 mL of 0.1 M HCl solution and 108.1 mg/L of Pd(II) concentration in 50-mL polypropylene conical tubes. The tubes were then kept at 160 rpm and 25 °C for 24 h in a shaker. After biosorption equilibrium was attained, PEIB was separated by centrifugation at 9000 rpm for 5 min. The Pd(II) concentration in the supernatant was measured using inductively coupled plasmaatomic emission spectrometry (ICP-AES; ICPS-7500, Shimadzu, Japan) after appropriate dilution. The settled PEIB was washed with distilled water several times to remove unsorbed solutes, and dried at 60 °C for 24 h in an oven. The dried Pd(II)-sorbed biosorbent was placed in alumina crucibles and incinerated in air at different temperatures (600–1000 °C) for 3 h in an electric furnace (LEF-115S, Labtech, Korea) to evaluate the effect of incineration temperature. The weight of the resultant ashes was measured, and the Pd in the ash was dissolved in 30 mL of aqua regia for 24 h. The mixture was then centrifuged to separate the residual solids. Finally, the Pd concentration in aqua regia solution was estimated by ICP-AES after proper dilution. To examine the effect of the Pd amount, samples with various Pd(II) uptakes were prepared with initial Pd(II) concentrations in the range of 44.4–181.1 mg/L and 1 g/L of PEIB. The samples were
Four samples, such as PEIB, Pd(II)-sorbed PEIB, Pd-containing ash incinerated at 600 °C, and Pd-containing ash incinerated at 900 °C, were examined using scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX; JSM-5900, JEOL, Japan). Before analyzing, all samples were coated in an Auto Fine Coater fitted with a Pt target. The surface components of samples were also analyzed by SEM-EDX at 15 keV. To verify the crystallized form of Pd in the ash, the X-ray diffraction spectrum was obtained using 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°. 3. Results and discussion 3.1. Effect of incineration temperature on Pd recovery The present study considered incineration temperature as one of the most important factors for enhancing the recovery efficiency and purity of Pd from Pd(II)-loaded PEIB because incineration temperature is a crucial heat source for the oxidative thermal decomposition of the biosorbent. To evaluate the effect of incineration temperature, Pd(II)-sorbed PEIBs were prepared in advance with 108.1 mg/L initial Pd(II) concentration and 0.1 g of PEIB. The Pd(II) uptake of the biosorbents was 25.0 ± 0.2 mg/g. Then, these samples were incinerated in air at temperatures in the range of 600–1000 °C. After incineration, all samples showed the presence of metallic Pd in ashes. The recovery efficiency and purity of Pd recovered at different incineration temperatures were calculated using Eqs. (2) and (3). The results are presented in Fig. 1, which shows that the Pd in ash recovered at 600 °C exhibited the lowest recovery efficiency and purity. This was because of the formation of palladium oxide (like PdO) during incineration, which is rarely soluble in aqua regia, and the part of that is not contained in the calculation of the recovery efficiency and purity. Park et al. (2010) reported that after incineration at 600 °C for 2 h, the Pd recovered from Pd(II)-sorbed polyallylamine hydrochloride (PAH)-modified Escherichia coli biomass showed the recovery efficiency and purity of 42.3% and 36.9%, respectively, which are similar to the values of the present study. The metallic Pd was obtained in two forms, palladium oxide (PdO) and zero-valent Pd (Pd0). XRD analysis was
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Fig. 1. The effect of incineration temperatures for the recovery efficiency and purity of Pd recovered from Pd(II)-loaded PEIB.
Fig. 2. The effect of Pd amounts sorbed on the PEIB for the recovery efficiency and purity of Pd in ash incinerated in air at 900 °C.
performed to confirm the form of Pd in ash incinerated in air at 600 °C. The XRD pattern indicated the existence of both PdO and Pd0 in ash. The predominant phase in the ash was in the form of PdO, showing major PdO diffraction peaks at 2h of 33.8° (1 0 1), 41.9° (1 1 0), 54.6° (1 1 2), 60.1° (1 0 3), and 71.3° (2 0 2) (Datye et al., 2000; He and Gao, 2010; Li et al., 2008). The peaks at 2h of 40.1°, 46.5°, and 68.0° correspond to the diffraction from the (1 1 1), (2 0 0), and (2 2 0) planes of the face-centered cubic (fcc) crystalline Pd phase as an inferior phase (Datye et al., 2000; Li et al., 2008). These results indicate that the Pd in the ash incinerated in air at 600 °C consists of PdO as a predominant phase and Pd0 as an inferior phase. As the incineration temperature increased from 600 to 800 °C, the recovery efficiency and purity of Pd in ash were enhanced from 42.1% and 24.5% to 84.9% and 84.6%, respectively. This may mean that the palladium phase changes from PdO to Pd0 at higher incineration temperatures below 800 °C. On the other hand, the recovery efficiency and purity of Pd were reduced at temperatures above 800 °C. Consequently, the incineration temperature has a significant effect on the enhancement of the recovery efficiency and purity of Pd.
ash incinerated at 900 °C was higher than that of the Pd-containing ash incinerated at 600 °C. The microstructure of the Pd-containing ash incinerated at 600 °C was composed of submicron particles forming large agglomerations. On the other hand, the Pd-containing ash incinerated at 900 °C was made up of much larger agglomerates than the Pd-containing ash incinerated at 600 °C. Results similar to ours were reported in the literature for Pd-based catalyzes (Datye et al., 2000; Hinokuma et al., 2010; Kucharczyk et al., 2004). Since Pd easily undergoes reduction or oxidation at high temperature, Pd occurs either in metallic or oxide form. Although the palladium oxide form, particularly PdO, is thermodynamically stable below 780 °C, the variation of PdO into metallic Pd starts at above 780 °C and ends at 850 °C (Farrauto et al., 1992). From these general facts, the major Pd form in the ash can be considered as PdO (600 °C) and metallic Pd (900 °C) according to the incineration temperature.
3.2. SEM-EDX analysis The morphologies of four types of samples, such as PEIB, Pd(II)-sorbed PEIB, Pd-containing ash incinerated at 600 °C, and Pd-containing ash incinerated at 900 °C, were examined using SEM-EDX. Comparing the magnified SEM microphotograph of PEIB to Pd(II)-sorbed PEIB, Pd(II)-sorbed PEIB showed a very similar surface morphology to that of PEIB. The morphological difference between PEIB and Pd(II)-sorbed PEIB was not clearly found from SEM images. However, the change of the superficial elements was distinctly observed from EDX results. The EDX spectrum of the PEIB indicated the existence of C, O, Cl, and Pt elements, while that of the Pd(II)-sorbed PEIB additionally showed a Pd element peak along with the others. The advent of Pd element indicates that Pd(II) ions covered the surface of Pd(II)-sorbed PEIB. The Pt element peak was caused by coating the sample in an Auto Fine Coater fitted with a Pt target. In the case of the Pd-containing ashes incinerated at 600 and 900 °C, the surface morphologies showed forms entirely different from those of the PEIB and Pd(II)-sorbed PEIB. Comparing the PEIB and Pd(II)-sorbed PEIB to the Pd-containing ashes, the Cl peak vanished, the peaks of C and O sharply decreased, and the peak of the element Pd increased in the EDX spectra of the Pd-containing ashes. In addition, the intensity of the Pd peak of the Pd-containing
3.3. Effect of Pd amount The Pd amount on the biosorbent was considered as another major factor to increase the recovery efficiency and purity of Pd in the incineration process. To estimate the effect of the Pd amount, samples with different Pd amounts were prepared through sorption experiments carried out with various initial Pd(II) concentrations. The uptakes on the PEIBs were estimated to be 25.0, 35.5, 78.9, and 136.9 mg/g. Each sample was then incinerated in air at 900 °C for 3 h, and silver-white metallic Pd was obtained after incineration. The results of recovery efficiency and purity of Pd are presented in Fig. 2. As shown in Fig. 2, the recovery efficiency of Pd was rapidly increased until 78.9 mg/g of Pd uptake, while there was quite a bit of enhancement above 78.9 mg/g of Pd uptake. The purity of Pd gradually increased for all Pd uptakes. Compared with the recovery efficiency and purity of Pd, 136.9 mg/ g of Pd uptake showed more interesting results than that of 78.9 mg/g of Pd uptake. Both of them exhibited similar recovery efficiencies, but the purity was increased from 91.5% to almost 100% as the Pd uptake increased from 78.9 to 136.9 mg/g. This can mean that the impurities in the ash can be completely removed at higher Pd amounts, such as with 136.9 mg/g of Pd uptake. In addition, the maximum recovery efficiency and purity of Pd was observed at 136.9 mg/g of Pd uptake, and were both above 99.0%. It indicates that the amount of Pd loaded on the biosorbent plays an important role in further enhancing the recovery efficiency and purity of Pd during incineration. Therefore, high-purity metallic Pd can be recovered through controlling the incineration temperatures and Pd uptake. The most appropriate operation
S.W. Won et al. / Bioresource Technology 137 (2013) 400–403
conditions for the recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbent were 900 °C and 136.9 mg/g of Pd uptake in the experimental range. 4. Conclusions The recovery efficiency and purity of Pd recovered from loaded PEIB was enhanced as the incineration temperature increased from 600 to 800 °C. The Pd amount on the biosorbent also affected the enhancement of the recovery efficiency and purity of Pd. The recovery efficiency was significantly increased until 78.9 mg/g of Pd uptake and the purity was enhanced from 91.5% to almost 100% as the Pd uptake increased from 78.9 to 136.9 mg/g. Therefore, both the incineration temperature and Pd uptake are key factors to enhance the recovery efficiency and purity of Pd from Pd(II)-sorbed biosorbents. Acknowledgements This work was supported by the Korean Government through NRF (NRL 2008-0060070), KEITI (The Eco-Innovation project), and KETEP (20115020100060) Grants. S.W. Won was supported by research funds of Chonbuk National University in 2013. References Das, N., 2010. Recovery of precious metals through biosorption – a review. Hydrometallurgy 103, 180–189. Datye, A.K., Bravo, J., Nelson, T.R., Atanasova, P., Lyubovsky, M., Pfefferle, L., 2000. Catalyst microstructure and methane oxidation reactivity during the PdMPdO transformation on alumina supports. Appl. Catal. A 198, 179–196.
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Farrauto, R.J., Hobson, M.C., Kennelly, T., Waterman, E.M., 1992. Catalytic chemistry of supported palladium for combustion of methane. Appl. Catal. A 81, 227–237. He, H., Gao, C., 2010. A general strategy for the preparation of carbon nanotubes and graphene oxide decorated with PdO nanoparticles in water. Molecules 15, 4679–4694. Hinokuma, S., Fujii, H., Okamoto, M., Ikeue, K., Machida, M., 2010. Metallic Pd nanoparticles formed by Pd–O–Ce interaction: a reason for sintering-induced activation for CO oxidation. Chem. Mater. 22, 6183–6190. Hoppstock, K., Sures, B., 2004. Platinum-group metals. In: Merian, E., Anke, M., Ihnat, M., Stoeppler, M. (Eds.), Elements and Their Compounds in the Environment. Wiley-VCH, Weinheim, pp. 1047–1074. Kielhorn, J., Melber, C., Keller, D., Mangelsdorf, I., 2002. Palladium – a review of exposure and effects to human health. Int. J. Hyg. Environ. Health 205, 417–432. Kucharczyk, B., Tylus, W., Ke˛pin´ ski, L., 2004. Pd-based monolithic catalysts on metal supports for catalytic combustion of methane. Appl. Catal. B 49, 27–37. Lee, S.H., Kim, K.R., Kim, Y.S., Paek, S.W., Yoo, J.H., Chung, H., 1998. Ion exchange characteristics of platinum group metals from nitric acid solution by anion exchangers. J. Ind. Eng. Chem. 4, 58–63. Li, K.-T., Hsu, M.-H., Wang, I., 2008. Palladium core-porous silica shellnanoparticles for catalyzing the hydrogenation of 4-carboxybenzaldehyde. Catal. Commun. 9, 2257–2260. Park, J., Won, S.W., Mao, J., Kwak, I.S., Yun, Y.-S., 2010. Recovery of Pd(II) from hydrochloric solution using polyallylamine hydrochloride-modified Escherichia coli biomass. J. Hazard. Mater. 181, 794–800. Park, S.-I., Kwak, I.S., Bae, M.A., Mao, J., Won, S.W., Han, D.H., Chung, Y.S., Yun, Y.S., 2012. Recovery of gold as a type of porous fiber by using biosorption followed by incineration. Bioresour. Technol. 104, 208–214. Ramesh, A., Hasegawa, H., Sugimoto, W., Maki, T., Ueda, K., 2008. Adsorption of gold(III), platinum(IV) and palladium(II) onto glycine modified crosslinked chitosan resin. Bioresour. Technol. 99, 3801–3809. Syed, S., 2012. Recovery of gold from secondary sources – a review. Hydrometallurgy 115–116, 30–51. Vijayaraghavan, K., Yun, Y.-S., 2008. Bacterial biosorbents and biosorption. Biotechnol. Adv. 26, 266–291. Won, S.W., Park, J., Mao, J., Yun, Y.-S., 2011. Utilization of PEI-modified Corynebacterium glutamicum biomass for the recovery of Pd(II) in hydrochloric solution. Bioresour. Technol. 102, 3888–3893.
Contents lists available at SciVerse ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration Sung Wook Won a, Areum Lim b, Yeoung-Sang Yun a,b,c,⇑ a
Department of BIN Fusion Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea Department of Bioprocess Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea c School of Chemical Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea b
h i g h l i g h t s The combined method of biosorption and incineration was used for the recovery of Pd. Temperature and Pd amount modulated the recovery efficiency and purity of Pd. Higher temperature up to 800 °C showed higher recovery efficiency and purity of Pd. Pure metallic Pd was recovered at 900 °C and 136.9 mg/g of Pd uptake.
a r t i c l e
i n f o
Article history: Received 11 January 2013 Received in revised form 18 March 2013 Accepted 20 March 2013 Available online 27 March 2013 Keywords: Recovery Palladium Biosorption Incineration
a b s t r a c t This work reports a direct way to recover metallic palladium with high purity from Pd(II)-sorbed polyethylenimine-modified Corynebacterium glutamicum biosorbent using a combined method of biosorption and incineration. This study is focused on the incineration part which affects the purity of recovered Pd. The incineration temperature and the amount of Pd loaded on the biosorbent were considered as major factors in the incineration process, and their effects were examined. The results showed that both factors significantly affected the enhancement of the recovery efficiency and purity of the recovered Pd. SEMEDX and XRD analyses were used to confirm that Pd phase existed in the ash. As a result, the recovered Pd was changed from PdO to zero-valent Pd as the incineration temperature was increased from 600 to 900 °C. Almost 100% pure metallic Pd was recovered with recovery efficiency above 99.0% under the conditions of 900 °C and 136.9 mg/g. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction Platinum group metals (PGMs), such as palladium (Pd), are very important resources in a variety of industries, such as the electrical and electronics industry, jewelry and ornaments, medicine, catalysis, and the petroleum industry, due to their specific physical and chemical properties (Ramesh et al., 2008). However, Pd ions have high mobility in aquatic environments because of their water solubility, and exposure leads to serious harmful effects on biota (Kielhorn et al., 2002; Hoppstock and Sures, 2004). Therefore, the negative environmental effects and high demand for Pd from various industries have increased the interest in Pd recovery from PGM-containing waste solutions. The hydrometallurgical methods include adsorption by ion exchange resin, solvent extraction, and precipitation of PGMs by ⇑ Corresponding author at: Department of BIN Fusion Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea. Tel.: +82 63 270 2308; fax: +82 63 270 2306. E-mail address: [email protected] (Y.-S. Yun). 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.03.143
reducing reagents (Lee et al., 1998). These methods have been used more frequently than the pyrometallurgical methods to recover PGMs. Compared with these methods, the hydrometallurgical method is more exact, predictable, and more easily controlled (Syed, 2012). However, both of these recovery methods are expensive and require extensive labor and time. Moreover, since various chemicals are used for precipitation and reduction processes, large quantities of secondary wastes are generated (Das, 2010). Therefore, there is necessity to develop an alternative method for the direct recovery of PGMs from waste solutions. In this study, a combined method of biosorption and incineration was evaluated as an alternative method able to take advantages of both hydrometallurgy and pyrometallurgy. The metallic gold with over 77.42% of purity was recovered from Au-loaded polyethylenimine (PEI)-modified bacterial biosorbent fiber using this method (Park et al., 2012). Biological processes have many advantages over traditional physicochemical treatments, as they do not require the use of large quantities of toxic chemicals. Biosorption is a promising alternative
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S.W. Won et al. / Bioresource Technology 137 (2013) 400–403
technique for recovering PGMs from aqueous and non-aqueous solutions. It has been used to separate and concentrate metals using various biomasses, such as bacteria, fungi, and algae (Vijayaraghavan and Yun, 2008). For example, Corynebacterium gltamicum biomass, which is a waste generated from microbial fermentation industries, is very cheap compared to commercial sorbents like ion exchange resins, and is available in large quantities. However, these raw materials have shown not enough uptakes of metals in aqueous solutions. In our previous work, we developed a PEI-modified Corynebacterium glutamicum biomass (PEIB) to increase metal sorption capacity, and proved its significantly improved uptake of Pd(II) in a batch system (Won et al., 2011). The present study is a continuation of previous work concerning applications of the PEIB for the recovery of palladium from hydrochloric acid solutions. To recover high-purity metallic Pd, a combined method of biosorption and incineration is suggested. This method can significantly reduce the working volume to be handled. The main factors affecting recovery efficiency and purity are incineration temperature and the amount of Pd sorbed on the PEIB. Therefore, the effects of these factors on the recovery efficiency and purity of Pd are investigated.
then incinerated in air at 900 °C for 3 h in an electric furnace. All other experimental conditions were the same as in the incineration temperature experiment. Each experiment was performed in triplicate. 2.3. Measurement of uptake, recovery efficiency and purity The Pd(II) uptake of PEIB and the recovery efficiency and purity of Pd in ashes were calculated from the following equations:
Uptake : q ¼
ðC i C f ÞV M
Recovery efficiency ð%Þ ¼
ð1Þ Pd weight in ash ðmgÞ Initially sorbed Pd weight ðmgÞ 100
Purity ð%Þ ¼
Pd weight in ash ðmgÞ 100 Ash weight ðmgÞ
ð2Þ ð3Þ
where q is the Pd(II) uptake (mg/g), Ci and Cf are the initial and final Pd(II) concentrations (mg/L), respectively, and V is the working volume (L). M represents the weight of the sorbent used (g).
2. Methods 2.4. Analytical tools 2.1. Materials and surface modification The C. glutamicum biomass was obtained as a spray-dried powder form from the L-arginine fermentation industry (Daesang, Gunsan, Korea). Industrial-grade PEI (M.W.: 70,000; purity: 50 ± 1%) was purchased from Habjung Moolsan Co., Ltd. (Seoul, Korea). Glutaraldehyde (GA; 25% solution) and PdCl2 (99.0%) were purchased from Junsei Chemical and Kojima Chemicals Co., Ltd., respectively. Other chemicals used in this study were of reagent grade. PEIB was prepared according to our previous method (Won et al., 2011). Briefly, raw C. glutamicum biomass (10 g) was suspended in 100 mL of distilled water containing 3 g of PEI for 2 h, and GA (0.6 mL) as a cross-linker was added to the mixture and stirred further for 2 h. Then, the modified biomass was centrifuged, washed with distilled water four times, and lyophilized for 24 h. 2.2. Incineration experiments for recovery of Pd Biosorption experiments were carried out by placing 0.1 g of PEIB with 30 mL of 0.1 M HCl solution and 108.1 mg/L of Pd(II) concentration in 50-mL polypropylene conical tubes. The tubes were then kept at 160 rpm and 25 °C for 24 h in a shaker. After biosorption equilibrium was attained, PEIB was separated by centrifugation at 9000 rpm for 5 min. The Pd(II) concentration in the supernatant was measured using inductively coupled plasmaatomic emission spectrometry (ICP-AES; ICPS-7500, Shimadzu, Japan) after appropriate dilution. The settled PEIB was washed with distilled water several times to remove unsorbed solutes, and dried at 60 °C for 24 h in an oven. The dried Pd(II)-sorbed biosorbent was placed in alumina crucibles and incinerated in air at different temperatures (600–1000 °C) for 3 h in an electric furnace (LEF-115S, Labtech, Korea) to evaluate the effect of incineration temperature. The weight of the resultant ashes was measured, and the Pd in the ash was dissolved in 30 mL of aqua regia for 24 h. The mixture was then centrifuged to separate the residual solids. Finally, the Pd concentration in aqua regia solution was estimated by ICP-AES after proper dilution. To examine the effect of the Pd amount, samples with various Pd(II) uptakes were prepared with initial Pd(II) concentrations in the range of 44.4–181.1 mg/L and 1 g/L of PEIB. The samples were
Four samples, such as PEIB, Pd(II)-sorbed PEIB, Pd-containing ash incinerated at 600 °C, and Pd-containing ash incinerated at 900 °C, were examined using scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX; JSM-5900, JEOL, Japan). Before analyzing, all samples were coated in an Auto Fine Coater fitted with a Pt target. The surface components of samples were also analyzed by SEM-EDX at 15 keV. To verify the crystallized form of Pd in the ash, the X-ray diffraction spectrum was obtained using 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°. 3. Results and discussion 3.1. Effect of incineration temperature on Pd recovery The present study considered incineration temperature as one of the most important factors for enhancing the recovery efficiency and purity of Pd from Pd(II)-loaded PEIB because incineration temperature is a crucial heat source for the oxidative thermal decomposition of the biosorbent. To evaluate the effect of incineration temperature, Pd(II)-sorbed PEIBs were prepared in advance with 108.1 mg/L initial Pd(II) concentration and 0.1 g of PEIB. The Pd(II) uptake of the biosorbents was 25.0 ± 0.2 mg/g. Then, these samples were incinerated in air at temperatures in the range of 600–1000 °C. After incineration, all samples showed the presence of metallic Pd in ashes. The recovery efficiency and purity of Pd recovered at different incineration temperatures were calculated using Eqs. (2) and (3). The results are presented in Fig. 1, which shows that the Pd in ash recovered at 600 °C exhibited the lowest recovery efficiency and purity. This was because of the formation of palladium oxide (like PdO) during incineration, which is rarely soluble in aqua regia, and the part of that is not contained in the calculation of the recovery efficiency and purity. Park et al. (2010) reported that after incineration at 600 °C for 2 h, the Pd recovered from Pd(II)-sorbed polyallylamine hydrochloride (PAH)-modified Escherichia coli biomass showed the recovery efficiency and purity of 42.3% and 36.9%, respectively, which are similar to the values of the present study. The metallic Pd was obtained in two forms, palladium oxide (PdO) and zero-valent Pd (Pd0). XRD analysis was
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Fig. 2. The effect of Pd amounts sorbed on the PEIB for the recovery efficiency and purity of Pd in ash incinerated in air at 900 °C.
performed to confirm the form of Pd in ash incinerated in air at 600 °C. The XRD pattern indicated the existence of both PdO and Pd0 in ash. The predominant phase in the ash was in the form of PdO, showing major PdO diffraction peaks at 2h of 33.8° (1 0 1), 41.9° (1 1 0), 54.6° (1 1 2), 60.1° (1 0 3), and 71.3° (2 0 2) (Datye et al., 2000; He and Gao, 2010; Li et al., 2008). The peaks at 2h of 40.1°, 46.5°, and 68.0° correspond to the diffraction from the (1 1 1), (2 0 0), and (2 2 0) planes of the face-centered cubic (fcc) crystalline Pd phase as an inferior phase (Datye et al., 2000; Li et al., 2008). These results indicate that the Pd in the ash incinerated in air at 600 °C consists of PdO as a predominant phase and Pd0 as an inferior phase. As the incineration temperature increased from 600 to 800 °C, the recovery efficiency and purity of Pd in ash were enhanced from 42.1% and 24.5% to 84.9% and 84.6%, respectively. This may mean that the palladium phase changes from PdO to Pd0 at higher incineration temperatures below 800 °C. On the other hand, the recovery efficiency and purity of Pd were reduced at temperatures above 800 °C. Consequently, the incineration temperature has a significant effect on the enhancement of the recovery efficiency and purity of Pd.
ash incinerated at 900 °C was higher than that of the Pd-containing ash incinerated at 600 °C. The microstructure of the Pd-containing ash incinerated at 600 °C was composed of submicron particles forming large agglomerations. On the other hand, the Pd-containing ash incinerated at 900 °C was made up of much larger agglomerates than the Pd-containing ash incinerated at 600 °C. Results similar to ours were reported in the literature for Pd-based catalyzes (Datye et al., 2000; Hinokuma et al., 2010; Kucharczyk et al., 2004). Since Pd easily undergoes reduction or oxidation at high temperature, Pd occurs either in metallic or oxide form. Although the palladium oxide form, particularly PdO, is thermodynamically stable below 780 °C, the variation of PdO into metallic Pd starts at above 780 °C and ends at 850 °C (Farrauto et al., 1992). From these general facts, the major Pd form in the ash can be considered as PdO (600 °C) and metallic Pd (900 °C) according to the incineration temperature.
3.2. SEM-EDX analysis The morphologies of four types of samples, such as PEIB, Pd(II)-sorbed PEIB, Pd-containing ash incinerated at 600 °C, and Pd-containing ash incinerated at 900 °C, were examined using SEM-EDX. Comparing the magnified SEM microphotograph of PEIB to Pd(II)-sorbed PEIB, Pd(II)-sorbed PEIB showed a very similar surface morphology to that of PEIB. The morphological difference between PEIB and Pd(II)-sorbed PEIB was not clearly found from SEM images. However, the change of the superficial elements was distinctly observed from EDX results. The EDX spectrum of the PEIB indicated the existence of C, O, Cl, and Pt elements, while that of the Pd(II)-sorbed PEIB additionally showed a Pd element peak along with the others. The advent of Pd element indicates that Pd(II) ions covered the surface of Pd(II)-sorbed PEIB. The Pt element peak was caused by coating the sample in an Auto Fine Coater fitted with a Pt target. In the case of the Pd-containing ashes incinerated at 600 and 900 °C, the surface morphologies showed forms entirely different from those of the PEIB and Pd(II)-sorbed PEIB. Comparing the PEIB and Pd(II)-sorbed PEIB to the Pd-containing ashes, the Cl peak vanished, the peaks of C and O sharply decreased, and the peak of the element Pd increased in the EDX spectra of the Pd-containing ashes. In addition, the intensity of the Pd peak of the Pd-containing
3.3. Effect of Pd amount The Pd amount on the biosorbent was considered as another major factor to increase the recovery efficiency and purity of Pd in the incineration process. To estimate the effect of the Pd amount, samples with different Pd amounts were prepared through sorption experiments carried out with various initial Pd(II) concentrations. The uptakes on the PEIBs were estimated to be 25.0, 35.5, 78.9, and 136.9 mg/g. Each sample was then incinerated in air at 900 °C for 3 h, and silver-white metallic Pd was obtained after incineration. The results of recovery efficiency and purity of Pd are presented in Fig. 2. As shown in Fig. 2, the recovery efficiency of Pd was rapidly increased until 78.9 mg/g of Pd uptake, while there was quite a bit of enhancement above 78.9 mg/g of Pd uptake. The purity of Pd gradually increased for all Pd uptakes. Compared with the recovery efficiency and purity of Pd, 136.9 mg/ g of Pd uptake showed more interesting results than that of 78.9 mg/g of Pd uptake. Both of them exhibited similar recovery efficiencies, but the purity was increased from 91.5% to almost 100% as the Pd uptake increased from 78.9 to 136.9 mg/g. This can mean that the impurities in the ash can be completely removed at higher Pd amounts, such as with 136.9 mg/g of Pd uptake. In addition, the maximum recovery efficiency and purity of Pd was observed at 136.9 mg/g of Pd uptake, and were both above 99.0%. It indicates that the amount of Pd loaded on the biosorbent plays an important role in further enhancing the recovery efficiency and purity of Pd during incineration. Therefore, high-purity metallic Pd can be recovered through controlling the incineration temperatures and Pd uptake. The most appropriate operation
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conditions for the recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbent were 900 °C and 136.9 mg/g of Pd uptake in the experimental range. 4. Conclusions The recovery efficiency and purity of Pd recovered from loaded PEIB was enhanced as the incineration temperature increased from 600 to 800 °C. The Pd amount on the biosorbent also affected the enhancement of the recovery efficiency and purity of Pd. The recovery efficiency was significantly increased until 78.9 mg/g of Pd uptake and the purity was enhanced from 91.5% to almost 100% as the Pd uptake increased from 78.9 to 136.9 mg/g. Therefore, both the incineration temperature and Pd uptake are key factors to enhance the recovery efficiency and purity of Pd from Pd(II)-sorbed biosorbents. Acknowledgements This work was supported by the Korean Government through NRF (NRL 2008-0060070), KEITI (The Eco-Innovation project), and KETEP (20115020100060) Grants. S.W. Won was supported by research funds of Chonbuk National University in 2013. References Das, N., 2010. Recovery of precious metals through biosorption – a review. Hydrometallurgy 103, 180–189. Datye, A.K., Bravo, J., Nelson, T.R., Atanasova, P., Lyubovsky, M., Pfefferle, L., 2000. Catalyst microstructure and methane oxidation reactivity during the PdMPdO transformation on alumina supports. Appl. Catal. A 198, 179–196.
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