Recovery of Pd(II) from hydrochloric solution using polyallylamine hydrochloride-modified Escherichia coli biomass
Introduction
Precious metals are extensively used in many fields such as catalysts in various chemical processes, electrical and electronic componentry, medicine and jewellery. Platinum group elements are available at low concentration in the earth's crust, and the demand for precious metals is increasing [1]. The demand and production of palladium have recently increased rapidly, despite a decreasing tendency since 2000 [2]. The recovery of precious metals from aqueous and waste solutions is therefore of great economic interest.
Although several methods are used to recover precious metals from aqueous solution, such as ion exchange, liquid–liquid extraction, membrane filtration, and adsorption, they are expensive, slow and difficult [3]. Therefore, a low-cost, highly efficient, eco-friendly process needs to be developed for the recovery of precious metals from aqueous solution with the generation of little secondary waste.
Biosorption is a promising technology for the removal and recovery of precious metals from aqueous and waste solutions. Biosorption has been used to bind and concentrate precious metals from even very dilute aqueous solutions using certain types of inactive, dead biomass. These biomasses are comparatively inexpensive and available in copious quantities. The rate of biosorption is usually rapid since a number of metabolism-independent processes take place in the cell wall [4]. According to previous reports, various functional groups exist on the surface of the biomass, including carboxyl, hydroxyl, amine and phosphonate groups [5], [6]. Specifically, amine groups are very effective at removing anionic metal species through electrostatic interaction or hydrogen bonding [7]. Many studies have been undertaken to find low-cost biosorbents from fungi, bacteria and algae. However, such raw biosorbents have generally demonstrated a low uptake of precious metals. Many alternative methods have therefore been suggested for increasing the sorption capacity of raw biomass [8], [9], [10]. Polyallylamine hydrochloride (PAH) is composed of a large number of primary amine groups in a molecule. Kioussis et al. [11] synthesized PAH hydrogels, and this sorbent showed good sorption ability for the perchlorate (ClO4−) anion.
In this study, industrial waste biomass of Escherichia coli, from the l-phenylalanine fermentation industry, was used as a raw material. PAH was cross-linked onto the biomass of E. coli through a simple process. As a result, PAH-modified E. coli biomass was developed as a novel biosorbent and used for the removal of Pd(II) as a model anionic precious metal. In addition, the palladium was recovered from the Pd-loaded biosorbent by incineration methods.
Section snippets
Materials
The fermentation wastes (E. coli biomass) were obtained in a dried powder form from an l-phenylalanine fermentation industry (Daesang, Gunsan, Korea). The raw biomass was dried for 24 h using a spray-drying process and stored in a desiccator. For PAH cross-linking, 20 g of the dried E. coli biomass was suspended with 10 g of PAH in distilled water at pH 8.5 for 150 min, after which 2 mL of epichlorohydrin solution (99%) was added as a cross-linker and stirred for 2 h. The modified biomass was
Characterization of biosorbent
AFM is an ideal tool for determining changes in cellular morphology. In this study, AFM was used to investigate the cell surface morphology of raw and PAH-modified biomasses. The surface morphology of biomass was prone to change when it was modified by cross-linking reaction with polymer. As shown in Fig. 1, the surface of the PAH-modified biomass was clearly differentiated from that of the raw biomass. The surface of PAH-modified biomass appeared to be composed of granules. This superficial
Conclusions
The following conclusions were drawn regarding the recovery of Pd(II) from aqueous solution through sorption-incineration process using the PAH-modified E. coli biomass.
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A novel biosorbent, PAH-modified E. coli biomass, was evaluated to have satisfactory affinity toward chloro-complex of Pd(II).
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The pH edge experiments were performed at pH < 5 and indicated that the uptake of Pd(II) by the PAH-modified biomass increased with increasing the solution pH.
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Kinetic studies showed that Pd(II) biosorption
Acknowledgements
This work was supported by the Korea Science and Engineering Foundation (KOSEF) NRL Program grant funded by the Korea government (MEST) (No. R0A-2008-000-20117-0) and, in part, by Ministry of Environment as “The Eco-Technopia 21 Project” and KOSEF through AEBRC at POSTECH.
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