Bioresource Technology xxx (2014) xxx–xxx

Contents lists available at ScienceDirect

Bioresource Technology journal homepage: www.elsevier.com/locate/biortech

Biosorbents for recovery of precious metals Sung Wook Won a, Pratap Kotte b, Wei Wei b, Areum Lim c, Yeoung-Sang Yun b,c,⇑ a Department of Marine Environmental Engineering and Institute of Marine Industry, Gyeongsang National University, 38 Cheondaegukchi-gil, Tongyeong, Gyeongnam 650-160, Republic of Korea b School of Chemical Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea c Department of Bioprocess Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea

h i g h l i g h t s  Biosorbents for the recovery of PMs were introduced.  The sources, existing media and recovery methods of PMs were summarized.  The required specifications of biosorbents for the recovery of PMs were presented.  Various strategies for powerful biosorbents were suggested and highlighted.

a r t i c l e

i n f o

Article history: Available online xxxx Keywords: Biosorbent Biosorption Precious metal Recovery Strategy

a b s t r a c t Biosorption is a promising technology not only for the removal of heavy metals and dyes but also for the recovery of precious metals (PMs) from solution phases. The biosorptive recovery of PMs from waste solutions and secondary resources is recently getting paid attractive attention because their price is increasing or fluctuating, their available deposit is limited and maldistributed, and high-tech industries need more consumption of PMs. The biosorbents for recovery of PMs require specifications which differ from those for the treatment of wastewaters containing heavy metals and dyes. In this review, the previous works on biosorbents and biosorption for recovery of PMs were summarized. Especially, we discuss and suggest the required specifications of biosorbents for recovery of PMs and strategies to give the required properties to the biosorbents. We believe this review will provide useful information to scientists and engineers and hope to give insights into this research frontier. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction In today’s world, the rapid development of industries generates a huge amount of toxic pollutants such as heavy metals, dyes, and precious metals (PMs) into the environment. In order to achieve effective removal of these environmental contaminants, several traditional methods including chemical precipitation, chemical coagulation, ion-exchange, electrochemical technology, membrane process and ultrafiltration were employed (Das, 2010). However, the materials applied in the above methods generally need a high cost. In contrast, biosorption has been considered as a promising technology to remove heavy metals or anionic/cationic dyes or to recover PMs from aqueous solutions and wastewaters. This is because of the its advantages including low cost, high efficiency, ⇑ Corresponding author at: School of Chemical Engineering, 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).

the minimal generation of chemical or biological sludge, regenerability, and possible recovery of metals by desorption (Vijayaraghavan and Yun, 2008). Over the last few decades, biosorption has been widely and successfully studied for removal of heavy metals and ionic dyes by using various types of biomasses such as bacteria, fungi, algae, agricultural and industrial byproducts, and other biomaterials (Vijayaraghavan and Yun, 2008; Park et al., 2010a). PMs including platinum group metals (PGMs) such as Ru, Rh, Pd, Os, Ir, and Pt are widely used in a variety of industries due to their unique physical and chemical properties. An increasing demand but a limited availability of PMs has led to great rises or fluctuations in their price. Thus it is urgent but attractive to recover PMs from secondary resources. In recent years, some researchers have tried to utilize biomasses in order to recover PMs, in particular Au, Pt, Pd and Ru. Table 1 summarizes the various types of biosorbents used for PMs biosorption. Generally, the raw biomasses showed low sorption capacities for PMs compared to commercial sorbents like activated carbons

http://dx.doi.org/10.1016/j.biortech.2014.01.121 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

2

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

Table 1 Biosorption of precious metals using different biosorbents. Metal

Biosorbent

Qmax (mg/g)

Sorption condition

References

Au(I)

Seaweed (Sargassum fluitans) Fungal (Penicillium chrysogenum) Bacterial (Bacillus subtilis)

pH pH pH pH

Niu Niu Niu Niu

L-Cysteine-loaded

P. chrysogenum

0.63 1.42 1.58 2.8

2 2 2 2

L-Cysteine-loaded

S. fluitans

0.92

pH 2

and and and and

Volesky Volesky Volesky Volesky

(1999) (1999) (1999) (2000)

Niu and Volesky (2000)

B. subtilis Acid-washed Ucides cordatus (waste crab shells) Hen eggshell membrane PEI-modified bacterial biosorbent fiber PEI-modified chitosan fiber PEI-modified C. glutamicum biomass Decarboxylated C. glutamicum biomass

4.04

pH 2

Niu and Volesky (2000)

33.48 147 421.1 251.7 361.76 86.16

pH pH pH pH pH pH

3.4 3 5.5 5.5 3.0 2.5

Niu and Volesky (2003) Ishikawa et al. (2002) Park et al. (2012) Park et al. (2012) Kwak and Yun (2010) Kwak and Yun (2010)

Au(III)

Cladosporium cladosporioides Strain 1 C. cladosporioides Strain 2 Streptomyces erythraeus Spirulina platensis Sulfur derivative of chitosan Glutaraldehyde cross-linked chitosan Dealginated seaweed waste Hen eggshell membrane Ca-alginate beads

94.2 104.3 6 5.55 630.29 571.2 78.79 618 290

pH pH pH pH pH pH pH pH pH

4.0 4.0 4.0 4.0 3.2 1.6 3.0 3 2

Pethkar et al. (2001) Pethkar et al. (2001) Savvaidis (1998) Savvaidis (1998) Arrascue et al. (2003) Arrascue et al. (2003) Romero-Gonzalez et al. (2003) Ishikawa et al. (2002) Torres et al. (2005)

Pt(IV)

Desulfovibrio desulfuricans D. fructosivorans D. vulgaris Thiourea derivative of chitosan Glutaraldehyde cross-linked chitosan Poly(allylamine hydrochloride)-modified E. coli PEI-modified E. coli

62.5 32.3 40.1 386.9 304.1 348.8 108.8

pH 2.0 pH 2.0 pH 2.0 pH 2.0 pH 2.0 pH 2.5 Pt-containing ICP wastewater

de Vargas et al. (2004) de Vargas et al. (2004) de Vargas et al. (2004) Guibal et al. (2000) Guibal et al. (2000) Mao et al. (2010) Won et al. (2010)

Pd(II)

EN-lignin Bayberry tannin immobilized collagen fiber membrane Racomitrium lanuginosum

22.7 33.4 37.2 109.5

0.5 M HCl 1 M HCl pH 5 pH 2.0

Parajuli et al. (2008) Ma et al. (2006) Sari et al. (2009) Fujiwara et al. (2007)

120.4 180 265.3 277.5 287.4 352 176.8

pH 2.0 pH 2 pH 3 pH 2 pH 2 pH 2 0.1 M HCl

Ramesh et al. (2008) Ruiz et al. (2000) Park et al. (2010b) Guibal et al. (2002) Guibal et al. (2002) Guibal et al. (2002) Won et al. (2011)

47.1 34.4 110.5 16

Ru-containing Ru-containing Ru-containing Ru-containing

L-Cysteine-loaded

L-lysine modified cross-linked chitosan resin Glycine modified cross-linked chitosan resin Chitosan (glutaraldehyde cross-linked) Polyallylamine hydrochloride-modified E. coli biomass Chitosan (thiourea derivative) Chitosan (glutaraldehyde cross-linked) Chitosan (rubeanic acid derivative) PEI-modified C. glutamicum biomass

Ru

Decarboxylated PEI-modified C. glutamicum biomass PEI-modified C. glutamicum PEI-modified C. glutamicum biosorbent fiber C. glutamicum biomass

and ion-exchange resins. Thus research interest has been focused on enhancing the sorption capacity of a biomass using different surface modification methods. In this present review, previously reported papers on biosorptive recovery of PMs are analyzed. Especially required specifications of biosorbents for recovery of PMs are discussed in depth. 2. PMs occurring media and conventional recovery methods 2.1. PMs The rare, naturally existing metallic chemical elements of high economic value are termed as PMs. The natural sources of these metals are seldom available and maldistributed. They include, but not limited to, Au, Pt, Pd and Ag which are internationally regarded as currency under the act of ISO 4217 and other PGMs (Ru, Rh, Os and Ir). The spectacular physical and chemical properties such as lustrous, ductile and non corrosive and high stability made them indispensable in high technology industries of the modern world. As a result of their increasing demand and lack of availability, acquired skyrocketing prices are never seemed to be come down. Hence the title ‘precious’ is given to them.

acetic acetic acetic acetic

acid acid acid acid

wastewater wastewater wastewater wastewater

Song et al. (2013) Song et al. (2013) Kwak et al. (2013) Kwak et al. (2013)

2.2. Sources of PMs The content of the PMs in secondary sources (i.e., electronic and catalytic waste) was found to be far higher than their content in natural ores. The average concentration of the PMs found in actual and chief natural ores is about 1–30 ppm while secondary sources have higher concentrations around 1–2000 ppm. Hence the spent catalysts, electronic wastes and other secondary sources are also named as the urban mines of the PMs. Secondary sources of PMs are summarized in Table 2. Although PMs are found even in the atmosphere (as a particulate matter) and street/road sides which are from the automotive exhausts, the sources contain extremely low concentration of PMs. Therefore the present review focuses on the feasible sources of PMs where biosorption can be applied. 2.2.1. Solid wastes Different solid materials contain PMs. A huge quantity of solid materials containing PMs is generated and considered as wastes. The PMs contained in the solid wastes cannot be recovered directly by using biosorption. Leaching PMs from the solid matrices by using appropriate solvents should be prerequisite. Conventional

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx Table 2 Precious metal existing sources. Source

Ways of origin for the existence of precious metals

Atmospheric air

Automotive catalyst exhaust Incineration of precious metal vapors Volcanic eruption ashes

Solid wastes

Spent automotive catalysts Waste electric and electronic equipment Printed circuit boards Street dust and roadside soil Municipal solid waste Sediments of rivers Vegetation

Liquid wastes

Effluents of precious metal refineries Effluents of automotive catalyst waste recycle industries Effluents of the WEEE and/or PCB refinery industries Effluents from precious metal as catalyst in manufacturing processes Jewelry processing/making industry waste waters Run off street water due to rain Hospital sewage Municipal sewage

leaching methods will be reviewed in the later part. Typical types of solid wastes of interest are summarized as follows. 2.2.1.1. Municipal solid waste (MSW). It is a collection of different solid wastes by municipalities from different house hold activities used for comfortable and sustainable living of the human kind. This includes biodegradable waste, recyclable material, inert waste (construction goods, dirt, rocks etc.), electrical and electronic waste, composite waste like clothing, hazardous waste (paints, spray, chemicals etc.) and medical waste. The information about the quantities of PMs in MSW to be recovered was reported recently (Morf et al., 2013). From their studies, 1 kg of MSW contains 0.4, 5.3, 0.059, 0.000092 and 0.0005 mg of Au, Ag, Pt, Rh and Ru, respectively. This is a low concentration but far higher than their natural ores in cases of Au and Pt. Muchova et al. (2009) investigated the presence of Au, Ag, Pt, Pd and other heavy metals in the incineration bottom ash of MSW. The 2–6 mm fraction of ashes contains approximately 100, 1500–4000 and 14 ppm of Au, Ag and Pt, respectively. Bakker et al. (2007) found a useful data on Ag, Au and Pt in bottom ash fractions of incinerated municipal solid waste. Similarly a considerable amount of Ag and Au were found in the MSW melting plants in Japan. 2.2.1.2. Waste electrical and electronic equipment (WEEE). In general electronic waste (e-waste) comprises a broad range of electronic and electrical products including large household appliances like refrigerators, air conditioners, washing machines, vacuum cleaners, television sets, tape recorders and hand held equipments like cellular phones, personal stereos, personal computers, printers and consumer electronics. The economic growth increases the ownership of electronics, decreases simultaneously the life span of the electronic goods, and eventually leads to rapid growth in the amounts of unwanted and obsolete electronics. The estimated rate of global WEEE generated was approximately 40 million tons per year (Huismann et al., 2007). On the other hand, electronics are the major sources of valuable and/or rare materials such as Au, Ag, Pd, Pt, and Ir etc. The WEEE contains more PMs than their typical metal mines. The recovery of PMs obtained from the WEEE was studied by many researchers (Cui and Zhang, 2008). When comparing the amount of Au extracted from the primary and its secondary source, 1 ton of a scrap of computers has higher gold than that can be extracted from 17 tons of ore (Park and Fray,

3

2009). Therefore it is strongly advised to recover PMs from their secondary sources. The printed circuit boards (PCBs) have a significant value portion even though the PCBs cover only 6% of the weight of WEEE. The worth of Au and Pd recovered from 1 ton of PCBs was estimated to be $15,200 and $1850, respectively (Wang and Gaustad, 2012). In addition PCBs also contain a considerable value of other PMs. 2.2.1.3. Heterogeneous catalytic wastes. End-of-life vehicles (ELVs) create a worldwide problem. The discarded vehicles by its registered owner as wastes come under ELV. This is regarded as a great environmental problem, as this kind of waste includes many precious and hazardous metals. Moreover, according to the expectations of survey the scrap of ELVs ready to discard will be 1.85 and 3.71 billion tons by 2030, respectively (Paul, 2009). Therefore, there should be a strong motivation to properly process the flow of these materials. Out of the total 568,000 kg PGMs automotive catalysts, only 10% has been recovered and the remaining was thrown as waste in USA alone. In various chemical industries, PMs-containing catalysts are being used. Heterogeneous catalysts with Ru, Ir and Pd are effective for oxidation–reduction reactions. Spent heterogeneous catalysts are also a important solid source of PMs. 2.2.2. Liquid wastes Biosorption can be directly applied for recovery of metals which are present in the liquid phases, particularly when metals are of ionic form. Most available liquid wastes containing PMs are summarized as follows. 2.2.2.1. Spent electroplating and other solutions. Electroplating is extensively used for coating metal objects with a thin layer of a different metal. Spent electroplating solutions are typically from washing, rinsing and batch dumps. These contain soluble form of the various PMs and base metals. The PMs in electronic industries are used as key materials in connectors, switches, relay contacts, soldered joints, connecting wires and connecting strips (Cui and Zhang, 2008). There is an integration of different steps like electroplating, etching, rinsing and chemical and mechanical polishing (CMP) while manufacturing and processing of those electronic parts. The water and other liquids used during those processes come out in the form of waste solutions containing various PMs which requires recycling. It is well known that the waste from the semiconductor electronic industry is one of the major contributions of the PMs in surface water. 2.2.2.2. Waste solutions from hydrometallurgy. The industrial recovery of PMs from the ores and secondary sources was done by different hydrometallurgical techniques after leaching. Hydrometallurgical methods include ion exchange, solvent extraction, reduction, precipitation (Das, 2010). During these processes, a large quantity of secondary waste is generated with low concentrations of dissolved PMs needed to be recovered. 2.2.2.3. Spent homogenous catalysts. Unlike heterogeneous catalysts, homogeneous catalysts act in the same phase as the reactants. Because the homogeneous catalysts are difficult to be separated from the reaction media, they are often found in the product and waste solution streams. For example, the industrial preparation of acetic acid generally involves the PM catalyst (Ru, Ir and Rh) which proceeds through the carbonylation of the methanol. The runoff from these industries is therefore highly acidic with acetic acid and the waste solution contains the PMs complexes with organic materials (Kwak et al., 2013).

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

4

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

2.3. Conventional methods for recovery of PMs PMs are being recovered by commercially available methods including pyrometallurgy and hydrometallurgy. 2.3.1. Pyrometallurgy The pyrometallurgical process has been used to recover PMs in last two decades. Generally they include the process of incineration, smelting in a blast furnace or plasma arc furnace, drossing, melting, sintering and reactions in a gas phase at high temperatures. The mechanically crushed fine samples are burned with coke in a furnace or in a molten bath. This process follows the removal of plastics and separation and drowning of the slag phase consists of refractory oxides together with some metal oxides (Cui and Zhang, 2008). The PGMs separately collected at collector phase (with copper in case of PCBs) were dissolved in aqua regia, and subjected to the purification to get pure form of PMs. The main drawback for pyrometallurgy is associated with a long settling time required for the separation of slag and metal collector. In addition, operating temperatures for this method in the blasts are in very higher range of 1800–2000 °C. Pyrometallurgical process accounts for the partial separation of PMs, resulting in a limited upgrading of the metal value. Hydrometallurgical techniques and electrochemical processing or their combination are consequently necessary. 2.3.2. Hydrometallurgy Nowadays the industrialists as well as researchers are opted and preferred hydrometallurgical method for recovery of PMs. Operation flexibility, ease, clean working conditions, low capital requirement, low emission of toxic gases etc. are some of the advantages of the process. In case of liquid PM sources, hydrometallurgy can be directly applied. However, in case of solid PM sources, extracting a soluble constituent from a solid substance by using suitable solvents, termed as leaching, is needed prior to hydrometallurgy. This is the initial and crucial step in the hydrometallurgy process. Various reagents are used for chemical leaching. Common leaching agents include aqua regia, hydrogen peroxide, cyanide, halide, thiourea, thiosulfate, and so on. Cyanide dissolves maximum of the PMs from the secondary sources so it is widely used in the PM recovery process in earlier days. However, cyanide is toxic and causes severe contamination of natural and drinking water resources. Therefore, other leaching agents such as thiourea, thiosulfate and halides have been employed as an alternative to cyanide in case of PMs (Cui and Zhang, 2008). In case of halide leaching, all the halides except fluorine and astatine are used for the Au extraction while only chlorine/chloride has been applied to recover all PMs industrially on a significant scale. Thiosulfate (S2 O3 2 ) is also used as a substitute of cyanide in PM leaching by many researchers (Cui and Zhang, 2008). In recent years, a highly benign method has been adapted in practice that uses hydrochloric acid containing chlorine gas (Cl2/HCl) (Shen et al., 2011). This made the hydrometallurgical process more attractive and advantageous in the PMs recovery from secondary solutions. Because this leach liquor contains high chloride concentrations, PMs are present in the form of chloro complexes. PMs can be separated largely using a series of precipitation. However, the process has many drawbacks such as relatively poor selectivity for many of the precipitation steps, lengthy refining time, and labor intensive processes. Solvent extraction method is popularly used to achieve high purity of PMs. The process includes three basic steps (1) a selective extraction step to a particular metal; (2) scrubbing step (removal of co-extracted metals); and (3) a stripping step to remove the extracted metal from the organic phase. The advantages of this

method include high selectivity, high purity and complete removal of metals by multi stage extraction, short operation times and low production costs. The solid phase extraction method is an alternative of solvent extraction method which was relatively recently introduced into the PM recovery industry. Ligand exchange and ion-exchange are generally involved mechanisms, where the selectivity has been attributed to a high level of molecular recognition of solid resins. If powerful biosorbents are developed, the biosorbents can be used instead of the synthetic resins. 2.4. State of PMs after leaching PMs are in various forms of chloro-metal complexes when leached with the acids such as aqua regia, concentrated HCl in presence of chlorine gas, etc. (Bernardis et al., 2005; Cui and Zhang, 2008; Jha et al., 2013). In general, the chloro-metal complexes are anionic and their typical examples include [RuCl6]3 , [RuCl5 (H2O)]2 , [RuCl4(H2O)2] , [RuCl3(H2O)3], [RuCl6]2 , [Ru2OCl10]4 , [Ru2OCl8(H2O)2]2 , [RhCl6]3 , [RhCl5(H2O)]2 , [RhCl4(H2O)2] , [RhCl6]2 , [PdCl4]2 , [PdCl6]2 , [OsCl6]2 , [IrCl6]3 , [IrCl5(H2O)]2 , [IrCl4(H2O)2] , [PtCl4]2 , [IrCl6]2 , [PtCl6]2 and [AuCl4] . PMs in the leached solutions can form complexes with halide, cyanide, thiosulphate, etc. such as [PtI6]2 , [PtBr6]2 , [Pt(CN)4]2 , [Au(CN)4] , [Pd(CN)4]2 , [Au(S2O3)2]2 (Cui and Zhang, 2008; Jha et al., 2013). Out of different leaching agents, acidic chloride medium is an inexpensive medium in which most of PMs can form soluble chloro complexes and has been extensively studied as model species. Considering that most of PMs are of anionic form in the liquid phases, it is obvious that the biosorbents for recovery of PMs should be able to effectively bind the anionic species.

3. Required specifications of biosorbents for metal recovery purpose The conventional processes suffer with incomplete metal removal, high capital costs, high energy requirement and a disposal of the secondary wastes generated (Mack et al., 2007). These disadvantages lead to use of a feasible biosorption process as an alternative and effective method for the recovery of PMs from the waste solutions. Here we would like to consider the required specifications of biosorbents for PM recovery. 3.1. Process applicability Biosorbents, especially by microorganisms, has shown good sorption capacities towards PMs. However, the microorganismbased biosorbents have many drawbacks such as low density, small particle size, poor mechanical strength and little rigidity, difficulty in solid–liquid separation, sometimes swelling, and severe pressure drop in the column system. The small size of powder form of microorganisms leads to clogging of the column in real application. If excessive pressure applies to overcome the pressure drop, disintegration of free biomass may occur. The solution for such problems is attained by the immobilization technique. The immobilization is the main technique to make the biosorbents effective. Immobilization provides a biosorbent the right size, mechanical strength, rigidity and good porosity which enhance the sorption performance in practical processes. Immobilization needs appropriate supporting materials including alginate, polyacrylamide, polyvinyl alcohol, polysulfone, polyurethane, silica gel, cellulose, chitosan and so on (Vijayaraghavan and Yun, 2008). The immobilized biosorbents are supposed to be the alternates of ion exchange resins and activated carbons.

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

There are some successful examples of immobilized biosorbents. Au was recovered from a simulated Au-bearing process solution containing AuCl4, CuCl2, FeCl2 and ZnCl2 by Ca-alginate entrapped cells of Chlorella vulgaris and Sargassum platensis in fluidized beds (Vieira and Volesky, 2000). Similarly Pt and Pd were recovered from their sources using immobilized C. vulgaris, bayberry tannin immobilized collagen fiber (BTICF) membrane, cross-linked chitosan resin chemically modified with L-lysine, and polyethylenimine (PEI)-modified Escherichia coli (Fujiwara et al., 2007; Ma et al., 2006; Won et al., 2010). In addition to immobilized microorganisms, bead-type biomaterials like chitosan have successfully used for recovery of PMs. Au was recovered by using glutaraldehyde cross-linked and sulfur grafted chitosan, chemically modified chitosan with magnetic properties, and L-lysinemodified cross-linked chitosan (Arrascue et al., 2003; Fujiwara et al., 2007). However, the immobilization process may bring two practical problems i.e., additional process cost in immobilization and mass transfer limitation between the solute and the immobilized sorbent (Vijayaraghavan and Yun, 2008). Regarding the slow binding problem of immobilized biosorbents, a thin fiber type of biosorbent may give the solution, which will be discussed later. The cost effectiveness is critical issue especially in the case of treatment of wastewaters contaminated with heavy metals and dyes. However, because PMs are extremely expensive and conventional PM recovery processes are costly, the price of biosorbents for recovery of PMs is not as serious issue as that for treatment of wastewaters. Instead of price, the superior sorption performances of biosorbents to synthetic resins are more important specifications which include high sorption capacity, fast kinetics, and selectivity (Table 3). 3.2. High sorption capacity The high sorption capacity is one of the most important specifications for PM biosorbents. According to the biosorption mechanisms, the way to enhance the sorption capacity may change. The sorption process by dead biomasses or biomaterials is of physical nature because it is independent of metabolism. PM biosorption mechanism is generally regarded as physicochemical interactions between metal ions and the functional groups present on the surface of biosorbent. This includes electrostatic interactions, ion exchange and metal ion chelation or complexation, microprecipitation and reduction. Carboxyl, hydroxyl, amine and phosphoryl functional groups present in the biomass or the immobilizing agents account for such type of interactions. 3.2.1. Electrostatic interaction/ion exchange If electrostatic interactions are the main forces responsible for the sorption process, the amine sites holding positive charge exert electrostatic attractions with the anionic PM complexes in chloride-rich acidic conditions, because PMs in secondary sources are

Table 3 The required specifications of biosorbents according to their purpose. Purpose

Required specifications

Media

Removal of heavy metals and dyes

Cost-effectiveness Abundant amount Regenerability

Aqueous solution

Recovery of precious metals

High uptake

Cl -rich acidic aqueous solution Organic solution

Fast kinetics Selectivity Acid stability Solvent stability

5

found in the form of anionic metal complexes (Mack et al., 2007). Hence there are two ways to increase the sorption performance: (1) by increasing amine/positive sites on the biosorbent and (2) by removing/minimizing/neutralizing the repulsive sites (i.e., anionic carboxyl groups). Success addition of positive ion binding sites was shown by Won et al. (2010). Similarly in case of ion exchange mechanism, the same strategically approach was possible to enhance the biosorption process (Ramesh et al., 2008). 3.2.2. Chelation/complexation mechanism A sorption process in which complex/chelation formations, substitution reactions, or strong acid base interactions play major role in the interactions between biosorbent and PMs is known as complexation. In those conditions, the functional groups/elements/ atoms with soft basic nature responsible for complexation should be increased on the surface of biosorbent by chemical treatments. In parallel the removal/minimization of interfering sites can enhance the sorption capacity. For example, glutaraldehyde cross-linked chitin derivates grafted with PEI and thiourea showed an increased sorption of Pt and Pd due to the additional sulfur group (Das, 2010). Esterified biomass to remove interfering carboxyl groups could increase the sorption uptakes of PMs (Song et al., 2013). 3.2.3. Reduction/precipitation mechanism The sorption processes where the reduction of metal ions happens in the presence of oxidizing groups in the biosorbent are said to be reduction-coupled sorptions. In this situation, the oxidizing functional groups present in the biosorbent or in the immobilized matrix should be increased. For example, glutaraldehyde crosslinked chitosan beads increased the sorption performance of Au by increasing the dose of glutaraldehyde, which acted as a reducing agent (Park et al., 2013). 3.3. Fast kinetics While concerned with the biosorption kinetics, it depends on the mass transfer of the metal ions from bulk solution phase to the binding sites at the surface of or inside the solid biosorbents. Combination of film diffusion in the aqueous phase and intraparticular diffusion in the adsorbents is termed as mass transfer. Out of them, intraparticular diffusion is often the rate determining step in the sorption process. Therefore modifying the biosorbent to make the intraparticular diffusion faster is an efficient way for achieving faster binding kinetics. Although the fast binding property is one of important specifications required for practically effective biosorbents, there have been only a few studies on this specification (Kanai et al., 2008; Kwak et al., 2013). 3.4. Selectivity The separation and purification of a PM from the mixture are time consuming and cost associated process. As long as selective sorbents are available, the separation and purification of PM become very simple and cost effective. However, developing selective sorbents is still a challenging task. Several examples of selective biosorbents will be introduced and strategies to enhance selectivity will be discussed in the next section. 3.5. Stability As discussed earlier sections the PMs exist generally in chloride-rich acidic aqueous solutions or organic solvent media (Table 3). Therefore the biosorbents for recovery of PMs should have enough stability in acids and organic solvents. The previously developed immobilizing matrices for biosorbents are mostly

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

6

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

chitosan or its derivatives, chitin, cellulose and alginate. But the performance of chitosan in the acidic solutions tends to be not good because it can be swollen and even dissolved in the acid solutions. Similarly some of the immobilization polymers were soluble in organic solutions. To achieve acid tolerance of biosorbents, the selection of immobilization matrix is critical. The synthetic polymers such as polysulfone and polyurethane are known to have high mechanical strength and acid stability (Zhou et al., 2009). However they do not have any functional groups responsible for binding the anionic PMs. A new method to introduce the binding sites to acid-tolerant polymers was recently suggested by Won et al. (2013). The cationic polymer-coated polysulfone-based biosorbent fiber was effective for the recovery of Pt(IV) even from 1 M HCl solutions. 4. Strategies for enhancing the biosorption capacity A number of raw biomasses or biomaterials have been mainly used for the removal of heavy metals or anionic/cationic dyes from aqueous media over the last decades. Various surface modification techniques were also designed and developed to enhance the sorption capacity of the biomasses (Fig. 1). In order to design and develop powerful biosorbents for PMs, we therefore need to consider a variety of surface modification techniques applied to biosorbents for heavy metals and/or dyes as well as PMs. 4.1. Pretreaments The purpose of pretreatment of biomass is to remove impurities from the raw biomass and/or to activate the binding sites. Pretreatment of a biomass can be largely divided into physical and chemical pretreatments. Physical pretreatments respectively contain autoclaving, steaming, thermal drying, lyophilization, cutting,

grinding, etc. In general, physical pretreatments are very simple and low-cost, but are less effective than chemical pretreatments (Park et al., 2010a). Common chemical pretreatments can be done with acids, alkalis, organic solvents and other chemicals. These chemical pretreatments have been preferred because of their simplicity and efficiency (Vijayaraghavan and Yun, 2008). The effect of chemical pretreatment on Cu biosorption by Marrubium globosum leaves using several agents was reported (Yazici et al., 2008). In this report, the pretreated biomass showed enhanced biosorption capacities compared to the raw biomass. Especially, alkali pretreatments with laundry detergent, NaOH and NaHCO3 were more effective than other pretreatments. Some researchers also reported that enhancement of sorption capacity was possible by alkali pretreatments of biomasses, such as Aspergillus flavus (Akar and Tunali, 2006). This may be because of a rupture on the surface wall of the biomass and formation of additional functional groups for metal binding. Remaining alkalinity might also cause hydrolysis of various metals (Yazici et al., 2008). In case of acid pretreatment of a biomass, many researchers revealed that acid pretreatment can improve the capacity of biosorbents for cationic metals or basic dyes, because some of the impurities and ions blocking the binding sites can easily be eliminated. In contrast, Yan and Viraraghavan (2001) reported that acid pretreatment of Mucor rouxii biomass greatly decreased the biosorption of heavy metals and the pretreatment also resulted in a loss of biomass by 11–16%. Thus, it is needed to look for a suitable chemical pretreatment for a certain biomass because the effect of chemical pretreatment strongly depends on the type of biomass. 4.2. Increasing the binding sites Specific functional groups on a biomass surface can be substituted for desirable functional groups by various chemical surface

Fig. 1. Schematic of simplified surface modification methods. (A) Increasing the binding sites; (B) eliminating the interfering sites; (C) coating the biosorbent with ionic polymers.

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

modification methods. Particularly, addition of binding sites to the biomass surface can lead to enhancement of the sorption capacity. Amine, carboxyl, phosphonate, sulfonate, and hydroxyl groups can act as binding sites for target ions (Vijayaraghavan and Yun, 2008). Thus, these groups can be newly introduced or increased through a proper modification method. A variety of chemical surface modifications are available for increase in the binding sites. For example, amine sites which are responsible for binding of anionic solutes were introduced to the carboxyl groups (inhibition sites) of the brown macroalga Stoechospermum marginatum biomass by reacting with propylamine (Kousha et al., 2012). The uptake of acid orange II by the aminated biomass was approximately two times higher than that by the untreated biomass. It was also reported that the ethylene diamine-treated biomasses showed the improvement of biosorption capacity of PM (Elwakeel et al., 2013). The binding sites of cationic solutes (i.e., carboxyl or phosphonate groups) could also be successfully introduced to the biomass surface. For instance, anhydrous citric acid was employed to modify the biomass because it combined with the hydroxyl groups of the biomass to form an ester linkage, introducing carboxyl groups to the biomass surface (Marshall et al., 1999). Some biomasses such as soybean hull (Marshall et al., 1999) and corncob (Vaughan et al., 2001) were modified by treatment with citric acid. It is obvious that the addition of carboxyl groups to the surface of biomass lead to the enhancement of sorption capacity of cations. Vijayaraghavan et al. (2008) utilized succinic anhydride to modify the surface of Corynebacterium glutamicum biomass. The succinated biomass was developed by chemically replacing the amine groups to carboxyl groups. They reported that the succinated biomass exhibited the enhanced uptake (337.5 mg/g) of cationic dye, methylene blue, compared to the raw biomass (207.3 mg/g) at pH 9. Some studies have been tried to convert hydroxyl groups on the biomass to phosphonate groups via phosphorylation. Klimmek et al. (2001) prepared phosphated algal biomass and they particularly reported that the phosphorylated Lyngbya taylorii showed the maximum uptakes of 2.52 mmol Cd/g, 3.08 mmol Pb/g, 2.79 mmol Ni/g, and 2.60 mmol Zn/g, which were much higher than the natural algae. Vaughan et al. (2001) reported a similar result that the phosphorylation of corncob helped to improve its natural sorption capacity of heavy metals. The biosorption of basic dyes by rice strew was also increased by modification of it with phosphoric acid (Gong et al., 2007). Through the brief review, it can be noted that the chemical surface modification methods to increase the PM binding sites can be applied to develop the biosorbents able to bind more PMs. 4.3. Eliminating the interfering sites Raw biomass has several functional groups and certain groups can interfere with the binding of target PM ions. For example, amine groups play a role as binding sites for anionic metals through electrostatic interaction, whereas negatively charged carboxyl groups may refuse anions through electrostatic repulsion. Therefore, elimination of interfering sites from the biomass could produce better biosorbents (Vijayaraghavan and Yun, 2008). From the previous literature, four cases for the elimination of interfering sites were found: (i) methylation of amine groups, (ii) acetylation of amine and hydroxyl groups, (iii) esterification of carboxyl groups, and (iv) esterification of phosphonate groups. Gong et al. (2005) tried to remove carboxyl groups from the peanut hull by methylation of amino group, esterification of carboxyl group and acetylation of amino and hydroxyl groups. The three modified biomasses were compared with untreated biomass. As a result, methylation of amino groups hardly affected the sorption capacity of ionic dyes, but esterification of carboxyl group largely influenced

7

the biosorption of basic dyes. Acetylation of amino and hydroxyl groups extremely decreased the biosorption ratios of both cationic and anionic dyes. Han and Yun (2007) reported that the maximum uptake of Reactive Red 4 at pH 4 by the esterificated biomass of C. glutamicum was 105.8 mg/g, which was 2.74 times higher than that by the protonated biomass. Therefore, elimination of carboxyl groups by esterification can be an attractive strategy to design powerful biosorbents for recovery of PMs, because carboxyl groups should interfere with the binding of anionic chloro complexes of PM. 4.4. Coating the biosorbent with ionic polymers Another efficient strategy to introduce the binding sites is coating the biosorbent with ionic polymers possessing a lot of binding sites for PM ions. If an ethanolamine molecule combines with the biomass, it just creates one amine site on the biomass surface. However, if PEI combines with the biomass, it can create a huge amount of amine groups. PEI consists of plenty of primary and secondary amine groups in a molecule. Increase on the amine sites should lead to large enhancement of sorption capacity of PMs. Deng and Ting (2005a) prepared a modified fungal biomass of Penicillium chrysogenum by grafting PEI onto the biomass surface. The PEI-modified biomass exhibited good biosorption capacity for Cr(VI) at a pH range of 4.3–5.5. However, this grafting procedure is complicated, and requires expensive and toxic chemicals such as pyridine, 4-bromobutyryl chloride and chloroform. Deng and Ting (2005b) improved their method to be simple, in which methanol was used as a solvent when PEI was attached onto P. chrysogenum biomass. However, their method still remains in some problems. The residual methanol should be removed following biosorbent preparation, which may cause cost-ineffectiveness and environmental pollution. This leads to further development of cheaper and environmentally friendlier method for PEI-coated biosorbents. Mao et al. (2011) used water as a solvent instead of methanol and optimized the modification process using response surface methodology. The biosorption capacity of PEI-coated bacterial biosorbent was enhanced 4.52 times compared to that of raw biomass. By using the similar method suggested by Mao et al. (2011), thin fiber type of bacterial biosorbent was coated with PEI and the PEI-coated biosorbent fiber showed 16.5 times higher sorption capacity of Ru in the actual waste solution from Samsung-BP Chemical (Ulsan, Korea) than synthetic resin being used in the company (Kwak et al., 2013). Acrylic acid was copolymerized onto the surface of biomass to increase the amount of carboxyl groups. It resulted in five and seven times improvements for the biosorption capacity of copper and cadmium, respectively, in comparison to pristine biomass (Deng and Ting, 2005c). Yu et al. (2007) prepared poly(amic acid)-grafted Baker’s yeast biomass by the reaction with pyromellitic dianhydride and thiourea. As a result, 15- and 11-fold enhanced uptake of Cd and Pb, respectively, could be achieved. Won et al. (2009) utilized the modification method, which was suggested by Yu et al. (2007), to prepare poly(amic acid)-modified C. glutamicum biomass for basic dyes. The maximum uptake by the modified biomass was 173.6 mg/g while that by the raw biomass was 52.8 mg/g. As a simple method, Mao et al. (2013) tried to electrostatically coat the C. glutamicum biomass with anionic polymer poly(acrylic acid) in water and then cross-link it with glutaraldehyde to reinforce the stability of the physically coated polymer. The modified biomass recorded the maximum Cd uptake of 139.8 mg/g, which corresponds to 3.2 times enhancement. This work indicates that physical sorption followed by cross-linking can be a green route to make powerful biosorbents. Moreover, the fusion of chemical modification and polymer coating can be a good choice to further enhance the biosorption capacity. For instance, Song et al. (2013) esterified

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

8

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

the remaining carboxyl groups in PEI-coated C. glutamicum biomass. The esterified PEI-coated biosorbent showed further enhanced uptake of Ru in the actual acetic acid waste solution. 4.5. Genetic cell surface modification The genetically engineered microorganisms have been considered as potential biosorbents especially for removal of metal ions from the solution phases. Genetic engineering is expected to give a possible solution to design powerful biosorbents which have high affinity and selectivity towards target metal ions (Singh et al., 2008). According to previous reports, there are two main processes involved in the removal of metal ions by recombinant organisms, including (1) intracellular accumulation by living microorganisms and (2) surface sorption by engineered cells (Kuroda and Ueda, 2003). Resting cell suspensions of Desulfovibrio desulfuricans NCIMB 8307 was studied for recovery of Pd. The maximum uptake of Pd was 196 mg Pd/g dry cells (Yong et al., 2002). The recombinant E. coli was performed for Ni bioaccumulation (Deng et al., 2013). Recombinant strains expressing both nickel-affinity transmembrane proteins and metallothioneins (MTs) showed good tolerance to Ni and the maximum Ni uptake reached 83.33 mg/g. Singh et al. (2008) introduced Arabidopsis thaliana PC synthase to the yeast Saccharomyces cerevisiae which showed six times higher accumulation of As than the control strain. The accumulation capacity and tolerance towards metal ions can be significantly enhanced by intracellular metal-binding proteins. Nonetheless, the main disadvantage of intracellular accumulation is the reusability. The recovery of metal ions after accumulation needs to break the cells as a general rule. For the easy recovery of metal ions, genetic surface modification of microorganisms can be considered as an alternative method to intracellular accumulation (Kuroda and Ueda, 2003). Multitudinous metal-binding proteins and peptides were successfully displayed on the different type of cells and these surface modified cells were successfully used as biosorbents for metal ions (Fujiwara et al., 2007). Yeast MT and hexa-His were displayed on the yeast-cell surface by a-agglutinin-based cell-surface engineering and it showed superior adsorption and recovery of Cd (Kuroda and Ueda, 2003). By serial selection, the screened peptide sequences were displayed on the surface of E. coli cell, showing the enhanced binding affinity and specificity towards Zn (Kjærgaard et al., 2001). Therefore, considering adsorption and recovery of PMs, the cells surface adsorption was potentially more appropriate than intracellular accumulation. In addition, because the binding sites are exposed to the cell surface, fast sorption kinetics can also be expected. 5. Strategies for enhancing biosorption kinetics Biosorbents with fast sorption kinetics would be more practical especially in scaled-up adsorption processes. PMs are less reactive hence termed as noble metals due to their resistant to general oxidation and reduction conditions. In a similar manner the chloro complexes of PM are also less reactive than that of other base metal ions. The oxidation state of the PM and the nature of the ligand control the reactivity of the PMs. The ligands containing soft donor atoms react in a little faster manner than those containing hard donor atoms and the second row PMs are more reactive than the third row PMs. PM with divalent oxidation state shows several order magnitude faster reactions than that of higher oxidation state with the soft donor ligands by readily participating in substitution reactions. In case of biosorption of PMs, the mechanism is a combination in most of the biosorbents used. In acidic solutions, the electrostatic interactions dominate with a miner contribution of the complexation mechanism. In the case of heavy metals, the

reactions are fast and so the other factors responsible due to the biosorption process are neglected. On the other hand, as PM kinetics is slow, the other factors controlling the reactions due to the biosorption process is of high importance. The immobilized biosorbents depending on the immobilizing agent can be made in the form of flakes, beads, capsules, hollow beads and highly porous beads, sheets and fibers (Guibal, 2004). To offer fast kinetics to the immobilized biosorbents, we need to reduce their size because a decrease in the size of an immobilized biosorbent generally leads to an increase in the rate of PM biosorption (Ruiz et al., 2000). Among them, thin fiber type of biosorbents can have high surface area and short migration path length of metal ions. Since a thin biosorbent fiber is long enough, it can be used in the practical adsorption column without severe pressure drop and column clogging problem. In addition to fiber type, highly porous biosorbents can have fast kinetics. Some of the studies confirmed that the biosorbent fiber (Kwak et al., 2013) and highly porous biosorbents (Kanai et al., 2008) were able to bind PMs with fast kinetics.

6. Strategies for selective biosorbents For recovery of PMs from actual solutions, selectivity is one of most important requirements, while for treatment of wastewaters, high sorption capacity of all (or most of) contaminants is required. However, the many reports have not focused on biosorption in multi-metal systems (i.e. actual waste solutions). We summarized the literatures concerning selective biosorption of PMs from multimetal systems (Colica et al, 2012; Ahamed et al., 2013; Elwakeel et al., 2013; Park et al., 2013), and also proposed some strategies to design selective biosorbents for recovery of PMs. According to a previous report (Colica et al, 2012), some bacteria showed ability to selectively bind metal ions. This study showed the purple non sulfur bacteria could be used as selective biosorbents for recovery of Ru from the real industrial effluents (containing Ru, Cu, Zn, Ni, and Fe). The uptake of Ru by the biomass was around 40 mg/g while the removal of other contaminant metals was not significant. Thus it is possible to find out new bacterial strains for selective recovery of a specific PM. Chitosan is obtained by deacetylation of chitin and it is one of the most abundant biopolymers in nature. Chitosan derivatives containing chelating ligands have been popularly used as selective biosorbents. Chelating groups with N and S usually have a high affinity towards PMs according to the theory of hard and soft acids and bases (HSAB) defined by Pearson (Ahamed et al., 2013). Several functional groups and ligands containing N or S donor atoms such as poly(ethylenimine) (Ahamed et al., 2013), amino acids (Fujiwara et al., 2007; Ramesh et al., 2008), ethylenediamine, and 3-amino1,2,4-triazole-5-thiol (Elwakeel et al., 2013) were introduced to chitosan for selective recovery of PMs. The complexation and chelation were the main underlying mechanisms determining the selectivity in the separation process. Ion imprinting techniques (IITs) were successfully applied in preparation of chitosan derivatives (Ahamed et al., 2013). It is worth mentioning that one type of glutaraldehyde-crosslinked chitosan beads (GA-CS) was developed for sorptive separation of Au(III) and Pd (Park et al., 2013). Interestingly, noncross-linked chitosan beads showed Pd selectivity, but GA-CS showed an increased Au(III) selectivity with increasing the GA concentration. The reason was suggested as a reduction-coupled sorption mechanism of Au(III). Furthermore, a 2-step selective desorption was introduced to give pure Pd and almost pure Au(III). Thus these findings open a way to design selectivity-tunable biosorbents with reducing agents for recovery of PMs. In the solvent extraction method, metal-selective chelating agents are available. A capsule type of biosorbent is being

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

developed by encapsulating the chelating agents inside of biopolymers and the preliminary study on it shows possibility as a new way to design selective biosorbents, which is our on-going work. 7. Strategies for stable biosorbents Stability is a key factor especially in the field of biosorptive recovery of PMs, because PMs are generally contained in highly acidic chloride-rich aqueous solutions or organic solvents (Mack et al., 2007). Under such conditions, biosorbents should be stable enough. The chitosan or its derivatives has been used as matrix of biosorbents. However, chitosan dissolves in highly acidic environments or in organic acid media. To make stable biosorbents in actual solutions containing PMs, acid- and solvent-tolerant polymers can be used as biosorbent matrices. Acid-tolerant polymers include polysulfone, polyurethane, cellulose, calcium alginate, etc. (Zhou et al., 2009). However, these polymers lack the PM-binding functional groups. The recently published study gave a solution for such problem, in which the biomass-polysulfone composite fibers were prepared and then by using the biomass functional groups (i.e. carboxyl groups), cationic polymer PEI was coated on the surface of the composite fibers. As a result, the PEI-coated biomass-polysulfone composite fibers showed high acid stability as well as high sorption capacity of Pt(IV) ions (Won et al., 2013). Another successful example is the work by Kwak et al. (2013). They made the PEI-coated biomass–chitosan composite fiber and successfully used the fiber for recovery of Ru in the water-free acetic acid waste solution generated from Samsung BP Chemicals Co., Ltd., Ulsan, Korea. Although acetic acid is known as a good solvent for dissolving chitosan, the fiber was very stable in the acetic acid waste solution. This is because the acetic acid waste solution contains no water (less than 100 ppm) and water-free acetic acid cannot dissolve chitosan.

9

Park et al. (2013) reported a new way of 2-step desorption process for selective recovery of Pd(II) and Au(III) from the glutaraldehydecrosslinked chitosan beads. In the first desorption with 5 M HCl, only Pd(II) was able to be desorbed, leading to pure Pd ions in the eluent. The second desorption with acidified thiourea could elute the zero valent gold, which was reduced from Au(III) by glutaraldehyde in the step of biosorption, as well as remaining Pd(II). As a result, pure Pd(II) solution and Au-riched solution (Au content: 97.7%) were achieved through the selective 2-step desorption process. It should be noted that the desorption method enables to recover PMs as ionic forms, which is supposed to be reduced to metallic form using appropriate reducing agents. To recover PMs as metallic forms directly, biosorption–incineration combined process can be applied, in which ionic PMs can be reduced to metallic forms along with oxidation of organic constituents during incineration (Kwak and Yun, 2010; Won et al., 2010; Park et al., 2012). Because PMs are very expensive unlike heavy metals and biosorbents are less inexpensive than synthetic resins, sorption-incineration method can be another option for recovery of PMs from the biosorbents. 9. Conclusions High-performance biosorbents can be developed by using various surface modification methods. Especially, coating ionic polymer on the surface of a biomass seems to be efficient compared to other chemical surface modifications. Moreover, there is a need to study researches about fusion of chemical surface modification and polymer coating to further enhance the biosorption capacity. Thin fiber form of biosorbents can lead to fast sorption, but we should consider polymeric matrix when prepare immobilized biosorbents to peculiarize acid and/or solvent stability. Finally, we need to make a new approach for selective biosorbents and to develop a selective biosorption process. References

8. Strategies for recovery of PMs and regeneration of biosorbents The desorption and reusing ability is one of the important properties for cost-effective biosorbent. To achieve the successful desorption process, it requires appropriate elutants which significantly depend on the type of biosorbent and the mechanism of biosorption. The properties of good elutants are as follows: (i) non destructive to the biosorbent; (ii) low cost; (iii) eco-friendly chemicals; (iv) effectivities (Syed, 2012). The following parts summarized the commonly suitable elutants using in desorption and regeneration of PMs-loaded biosorbent. Yin et al. (2013) investigated the desorption of Au(III) from the organophosphonic acid functionalized spent buckwheat hulls (OPA-BH) by using the eluent solutions of acidic thiourea. The results showed that the elution rate was up to 90.1% using the solution of 5.0% thiourea and 0.1 mol/L HCl and the sorbents retained 88.0% of original Au(III) sorption capacity after two cycles. The elution of Au(I) loaded on egg shell membrane (ESM) was successfully studied using NaOH and NaCN (Ishikawa et al., 2002). Especially, the Au(I) sorption capacity was not reduced after five consecutive sorption/desorption cycles. Recovery of Pd(II) from the PEI-modified waste biomass of C. glutamicum were carried out using the solution of 0.01–2 mol/L thiourea and 1 mol/L HCl (Won et al., 2011), showing that the desorption efficiency was higher than 96.8%. Mao et al. (2010) reported that Pt(IV) was successfully recovered by desorbing Pt(IV)-loaded poly(allylamine hydrochloride)-modified E. coli using 0.05 M acidified thiourea and the regenerated biosorbent was successfully reused up to four cycles. In general, acidified thiourea can be effective as an elutant for desorbing PMs from PMs-loaded biosorbent.

Ahamed, M.E.H., Mbianda, X.Y., Mulaba-Bafubiandi, A.F., Marjanovic, L., 2013. Selective extraction of gold(III) from metal chloride mixtures using ethylenediamine N-(2-(1-imidazolyl)ethyl) chitosan ion-imprinted polymer. Hydrometallurgy 140, 1–13. Akar, T., Tunali, S., 2006. Biosorption characteristics of Aspergillus flavus biomass for removal of Pb(II) and Cu(II) ions from an aqueous solution. Bioresour. Technol. 97, 1780–1787. Arrascue, M.L., Garcia, H.M., Horna, O., Guibal, E., 2003. Gold sorption on chitosan derivatives. Hydrometallurgy 71, 191–200. Bakker, E., Muchova, L., Rem, P.C., 2007. Separation of precious metals from MSWI bottom ash. Conference Proceeding from 6th International Industrial Mineral Symposium. 1–3 February, Izmir, Turkey, p. 6. Bernardis, F.L., Grant, R.A., Sherrington, D.C., 2005. A review of methods of separation of the platinum-group metals through their chloro-complexes. React. Funct. Polym. 65, 205–217. Colica, G., Caparrotta, S., De Philippis, R., 2012. Selective biosorption and recovery of Ruthenium from industrial effluents with Rhodopseudomonas palustris strains. Appl. Microbiol. Biotechnol. 95, 381–387. Cui, J., Zhang, L., 2008. Metallurgical recovery of metals from electronic waste: a review. J. Hazard. Mater. 158, 228–256. Das, N., 2010. Recovery of precious metals through biosorption – a review. Hydrometallurgy 103, 180–189. de Vargas, I., Macaskie, L.E., Guibal, E., 2004. Biosorption of palladium and platinum by sulfate-reducing bacteria. J. Chem. Technol. Biotechnol. 79, 49–56. Deng, S., Ting, Y.P., 2005a. Polyethylenimine-modified fungal biomass as a highcapacity biosorbent for Cr(VI) anions: sorption capacity and uptake mechanisms. Environ. Sci. Technol. 39, 8490–8496. Deng, S., Ting, Y.P., 2005b. Characterization of PEI-modified biomass and biosorption of Cu(II), Pb(II) and Ni(II). Water Res. 39, 2167–2177. Deng, S., Ting, Y.P., 2005c. Fungal biomass with grafted poly(acrylic acid) for enhancement of Cu(II) and Cd(II) biosorption. Langmuir 21, 5940–5948. Deng, X., He, J., He, N., 2013. Comparative study on Ni2+-affinity transport of nickel/ cobalt permeases (NiCoTs) and the potential of recombinant Escherichia coli for Ni2+ bioaccumulation. Bioresour. Technol. 130, 69–74. Elwakeel, K.Z., El-Sayed, G.O., Darweesh, R.S., 2013. Fast and selective removal of silver(I) from aqueous media by modified chitosan resins. Int. J. Miner. Process. 120, 26–34. Fujiwara, K., Ramesh, A., Maki, T., Hasegawa, H., Ueda, K., 2007. Adsorption of platinum (IV), palladium (II) and gold (III) from aqueous solutions onto L-lysine modified crosslinked chitosan resin. J. Hazard. Mater. 146, 39–50.

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

10

S.W. Won et al. / Bioresource Technology xxx (2014) xxx–xxx

Gong, R., Jin, Y., Chen, J., Hu, Y., Sun, J., 2007. Removal of basic dyes from aqueous solution by sorption on phosphoric acid modified rice straw. Dyes Pigment. 73, 332–337. Gong, R., Sun, Y., Chen, J., Liu, H., Yang, C., 2005. Effect of chemical modification on dye adsorption capacity of peanut hull. Dyes Pigment. 67, 175–181. Guibal, E., 2004. Interactions of metal ions with chitosan-based sorbents: a review. Sep. Purif. Technol. 38, 43–74. Guibal, E., Vincent, T., Mendoza, R.N., 2000. Synthesis and characterization of a thiourea derivative of chitosan for platinum recovery. J. Appl. Polym. Sci. 75, 119–134. Guibal, E., Offenberg, N., Vincent, T., Tobin, J.M., 2002. Sulfur derivatives of chitosan for palladium sorption. React. Funct. Polym. 50, 149–163. Han, M.H., Yun, Y.-S., 2007. Mechanistic understanding and performance enhancement of biosorption of reactive dyestuffs by the waste biomass generated from amino acid fermentation process. Biochem. Eng. J. 36, 2–7. Huismann, J., Magalini, F., Kuehr, R., Maurer, C., Ogilvoe, S., Poll, J., Delgado, C., Artim, E., Szlezak, J., Stevels, A., 2007. 2008 Review of directive 2002/96 on waste electrical and electronic equipment (WEEE) final report. ENV.G.4/ETU/ 2006/0032. United Nations University, Bonn, Germany, 2007, August 05. Available http://ec.europa.eu/environment/waste/weee/studies_weee_en.htm. Ishikawa, S., Suyama, K., Arihara, K., Itoh, M., 2002. Uptake and recovery of gold ions from electroplating wastes using eggshell membrane. Bioresour. Technol. 81, 201–206. Jha, M.K., Lee, J.-C., Kim, M.-S., Jeong, J., Kim, B.-S., Kumar, V., 2013. Hydrometallurgical recovery/recycling of platinum by the leaching of spent catalysts: a review. Hydrometallurgy 133, 23–32. Kanai, Y., Oshima, T., Baba, Y., 2008. Synthesis of highly porous chitosan microspheres anchored with 1,2-ethylenedisulfide moiety for the recovery of precious metal ions. Ind. Eng. Chem. Res. 47, 3114–3120. Kjærgaard, K., Schembri, M.A., Klemm, P., 2001. Novel Zn2+-chelating peptides selected from a fimbria-displayed random peptide library. Appl. Environ. Microbiol. 67, 5467–5473. Klimmek, S., Stan, H.J., Wilke, A., Bunke, G., Buchholz, R., 2001. Comparative analysis of the biosorption of cadmium, lead, nickel, and zinc by algae. Environ. Sci. Technol. 35, 4283–4288. Kousha, M., Daneshvar, E., Sohrabi, M.S., Jokar, M., Bhatnagar, A., 2012. Adsorption of acid orange II dye by raw and chemically modified brown macroalga Stoechospermum marginatum. Chem. Eng. J. 192, 67–76. Kuroda, K., Ueda, M., 2003. Bioadsorption of cadmium ion by cell surfaceengineered yeasts displaying metallothionein and hexa-His. Appl. Microbiol. Biotechnol. 63, 182–186. Kwak, I.S., Won, S.W., Chung, Y.S., Yun, Y.-S., 2013. Ruthenium recovery from acetic acid waste water through sorption with bacterial biosorbent fibers. Bioresour. Technol. 128, 30–35. Kwak, I.S., Yun, Y.-S., 2010. Recovery of zero-valent gold from cyanide solution by a combined method of biosorption and incineration. Bioresour. Technol. 101, 8587–8592. Ma, H.-w., Liao, X.-p., Liu, X., Shi, B., 2006. Recovery of platinum(IV) and palladium(II) by bayberry tannin immobilized collagen fiber membrane from water solution. J. Membr. Sci. 278, 373–380. Mack, C., Wilhelmi, B., Duncan, J.R., Burgess, J.E., 2007. Biosorption of precious metals. Biotechnol. Adv. 25, 264–271. Mao, J., Kwak, I.-S., Sathishkumar, M., Sneha, K., Yun, Y.-S., 2011. Preparation of PEIcoated bacterial biosorbent in water solution: optimization of manufacturing conditions using response surface methodology. Bioresour. Technol. 102, 1462– 1467. Mao, J., Lee, S.Y., Won, S.W., Yun, Y.-S., 2010. Surface modified bacterial biosorbent with poly(allylamine hydrochloride): development using response surface methodology and use for recovery of hexachloroplatinate(IV) from aqueous solution. Water Res. 44, 5919–5928. Mao, J., Won, S.W., Yun, Y.S., 2013. Development of poly(acrylic acid)-modified bacterial biomass as a high-performance biosorbent for removal of Cd(II) from aqueous solution. Ind. Eng. Chem. Res. 52, 6446–6452. Marshall, W.E., Wartelle, L.H., Boler, D.E., Johns, M.M., Toles, C.A., 1999. Enhanced metal adsorption by soybean hulls modified with citric acid. Bioresour. Technol. 69, 263–268. Morf, L.S., Gloor, R., Haag, O., Haupt, M., Skutan, S., Lorenzo, F.D., Böni, D., 2013. Precious metals and rare earth elements in municipal solid waste – sources and fate in a Swiss incineration plant. Waste Manage. 33, 634–644. Muchova, L., Bakker, E., Rem, P., 2009. Precious metals in municipal solid waste incineration bottom ash. Water Air Soil Pollut.: Focus 9, 107–116. Niu, H., Volesky, B., 1999. Characteristics of gold biosorption from cyanide solution. J. Chem. Technol. Biotechnol. 74, 778–784. Niu, H., Volesky, B., 2000. Gold-cyanide biosorption with L-cysteine. J. Chem. Technol. Biotechnol. 75, 436–442. Niu, H., Volesky, B., 2003. Characteristics of anionic metal species biosorption with waste crab shells. Hydrometallurgy 71, 209–215. Parajuli, D., Inoue, K., Kawakita, H., Ohto, K., Harada, H., Funaoka, M., 2008. Recovery of precious metals using lignophenol compounds. Miner. Eng. 21, 61–64. Park, D., Yun, Y.-S., Park, J.M., 2010a. The past, present, and future trends of biosorption. Biotechnol. Bioprocess Eng. 15, 86–102. Park, J., Won, S.W., Mao, J., Kwak, I.S., Yun, Y.-S., 2010b. 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. Park, S.-I., Kwak, I.S., Won, S.W., Yun, Y.-S., 2013. Glutaraldehyde-crosslinked chitosan beads for sorptive separation of Au(III) and Pd(II): Opening a way to design reduction-coupled selectivity-tunable sorbents for separation of precious metals. J. Hazard. Mater. 248–249, 211–218. Park, Y.J., Fray, D.J., 2009. Recovery of high purity precious metals from printed circuit boards. J. Hazard. Mater. 164, 1152–1158. Paul, R. 2009. End-of-life management of waste automotive materials and efforts to improve sustainability in North America. Fourth International Conference on Sustainable Development and Planning, WIT Transactions on Ecology and the Environment, vol. 120. WIT Press, pp. 853–861. Pethkar, A.V., Kulkarni, S.K., Paknikar, K.M., 2001. Comparative studies on metal biosorption by two strains of Cladosporium cladosporioides. Bioresour. Technol. 80, 211–215. 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. Romero-Gonzalez, M.E., Williams, C.J., Gardiner, P.H.E., Gurman, S.J., Habesh, S., 2003. Spectroscopic studies of the biosorption of gold(III) by dealginated seaweed waste. Environ. Sci. Technol. 37, 4163–4169. Ruiz, M., Sastre, A.M., Guibal, E., 2000. Palladium sorption on glutaraldehydecrosslinked chitosan. React. Funct. Polym. 45, 155–173. Sari, A., Mendil, D., Tuzen, M., Soylak, M., 2009. Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies. J. Hazard. Mater. 162, 874–879. Savvaidis, I., 1998. Recovery of gold from thiourea solutions using microorganisms. Biometals 11, 145–151. Shen, S., Guishen, L., Pan, T., He, J., Guo, Z., 2011. Selective adsorption of Pt ions from chloride solutions obtained by leaching chlorinated spent automotive catalysts on ion exchange resin Diaion WA21J. J. Colloid Interface Sci. 364, 482–489. Singh, S., Lee, W., DaSilva, N.A., Mulchandani, A., Chen, W., 2008. Enhanced arsenic accumulation by engineered yeast cells expressing Arabidopsis thaliana phytochelatin synthase. Biotechnol. Bioeng. 99, 333–340. Song, M.-H., Won, S.W., Yun, Y.-S., 2013. Decarboxylated polyethyleniminemodified bacterial biosorbent for Ru biosorption from Ru-bearing acetic acid wastewater. Chem. Eng. J. 230, 303–307. Syed, S., 2012. Recovery of gold from secondary sources – a review. Hydrometallurgy 115–116, 30–51. Torres, E., Mata, Y.N., Blázquez, M.L., Munoz, J.A., Gonzalez, F., Ballester, A., 2005. Gold and silver uptake and nanoprecipitation on calcium alginate beads. Langmuir 21, 7951–7958. Vaughan, T., Seo, C.W., Marshall, W.E., 2001. Removal of selected metal ions from aqueous solution using modified corncobs. Bioresour. Technol. 78, 133–139. Vieira, R.H.S.F., Volesky, B., 2000. Biosorption: a solution to pollution? Int. Microbiol. 3, 17–24. Vijayaraghavan, K., Won, S.W., Mao, J., Yun, Y.-S., 2008. Chemical modification of Corynebacterium glutamicum to improve methylene blue biosorption. Chem. Eng. J. 145, 1–6. Vijayaraghavan, K., Yun, Y.-S., 2008. Bacterial biosorbents and biosorption. Biotechnol. Adv. 26, 266–291. Wang, X., Gaustad, G., 2012. Prioritizing material recovery for end-of-life printed circuit boards. Waste Manage. 32, 1903–1913. Won, S.W., Kim, S., Kotte, P., Lim, A., Yun, Y.-S., 2013. Cationic polymer-immobilized polysulfone-based fibers as high performance sorbents for Pt(IV) recovery from acidic solutions. J. Hazard. Mater. 263, 391–397. Won, S.W., Mao, J., Kwak, I.-S., Sathishkumar, M., Yun, Y.-S., 2010. Platinum recovery from ICP wastewater by a combined method of biosorption and incineration. Bioresour. Technol. 101, 1135–1140. 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. Won, S.W., Vijayaraghavan, K., Mao, J., Kim, S., Yun, Y.-S., 2009. Reinforcement of carboxyl groups in the surface of Corynebacterium glutamicum biomass for effective removal of basic dyes. Bioresour. Technol. 100, 6301–6306. Yan, G., Viraraghavan, T., 2001. Heavy metal removal in a biosorption column by immobilized M. rouxii biomass. Bioresour. Technol. 78, 243–249. Yazici, H., Kilic, M., Solak, M., 2008. Biosorption of copper(II) by Marrubium globosum subsp globosum leaves powder: effect of chemical pretreatment. J. Hazard. Mater. 151, 669–675. Yin, P., Xu, M., Qu, R., Chen, H., Liu, X., Zhang, J., Xu, Q., 2013. Uptake of gold (III) from waste gold solution onto biomass-based adsorbents organophosphonic acid functionalized spent buckwheat hulls. Bioresour. Technol. 128, 36–43. Yong, P., Rowson, N.A., Farr, J.P.G., Harris, I.R., Macaskie, L.E., 2002. Bioaccumulation of palladium by Desulfovibrio desulfuricans. J. Chem. Technol. Biotechnol. 77, 593–601. Yu, J., Tong, M., Sun, X., Li, B., 2007. A simple method to prepare poly(amic acid)modified biomass for enhancement of lead and cadmium adsorption. Biochem. Eng. J. 33, 126–133. Zhou, L.-C., Li, Y.-F., Bai, X., Zhao, G.-H., 2009. Use of microorganisms immobilized on composite polyurethane foam to remove Cu(II) from aqueous solution. J. Hazard. Mater. 167, 1106–1113.

Please cite this article in press as: Won, S.W., et al. Biosorbents for recovery of precious metals. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/ j.biortech.2014.01.121

Biosorbents for recovery of precious metals.

Biosorption is a promising technology not only for the removal of heavy metals and dyes but also for the recovery of precious metals (PMs) from soluti...
651KB Sizes 1 Downloads 2 Views