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Feb 23, 2016 - The recovery of W from urban mines has become increasingly warranted because of the growing demand for W in the manufacturing of advanc...
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Selective Biosorption and Recovery of Tungsten from an Urban Mine and Feasibility Evaluation Takashi Ogi,*,† Takahiko Makino,‡ Kikuo Okuyama,† Wendelin J. Stark,§ and Ferry Iskandar∥ †

Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagamiyama, Hiroshima 739-8527, Japan Cutting Tool R&D Division, Kyocera Corporation, Kagoshima Sendai Plant, 1810 Taki-cho, Satsumasendai, Kagoshima 895-0292, Japan § Institute for Chemical and Bioengineering, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland ∥ Department of Physics, Institute of Technology Bandung, Ganesha 10, Bandung, 40132 West Java, Indonesia ‡

S Supporting Information *

ABSTRACT: Tungsten (W) is present in the waste products of used scrap metal. The recovery of W from urban mines has become increasingly warranted because of the growing demand for W in the manufacturing of advanced materials and for use within key industries (e.g., the automotive industry). In this study, processes involving the biosorption of W from urban mines by microbes (e.g., Escherichia coli and beer yeast) were evaluated for their adoptability as an environmentally friendly recycling process. Selective biosorption of W and molybdenum (Mo) ions from multicomponent metal solutions containing W, Mo, and vanadium(V) ions was successfully achieved by controlling the concentration of both cells (2.58 × 108 cells/mL) and the solution pH (1.4). These biosorption tests were also applied to a real waste solution composed of used scrap comprising tungsten carbide (WC). It was shown that E. coli cells and beer yeast successfully and preferentially adsorbed the W ion from the real waste solution. To confirm the feasibility of the biosorption process to practical applications, the recycling of WC tips from real waste products was demonstrated using beer yeast biosorption methods. The required costs, equipment (e.g., tanks), and facilities for application of the biosorption process were also evaluated.

1. INTRODUCTION Tungsten (W) is one of the most important metals used in the support of key industries (e.g., the automotive industry). W has widespread applications for high-tech materials such as machine-part cutting tools, mill rollers, electric lamp filaments, thermal shield plates, and catalysts for the removal of organic materials.1−5 In 2012, the global production of W was 73000 t, with over 80% of W (62000 t) being produced in China. The price of W has escalated since 2010, with the current prices of ammonium paratungstate and ferrotungsten generally in the ranges of $30−50/kg and $40−55/kg,6 respectively. It is anticipated that the global demand for W will continue to increase in the future because of a growing global population and the development of the automotive industry. On the basis of this demand, as well as economic and geopolitical concerns, there is an increased need for the recycling of W. To do this, W has been traditionally recovered from wastewater via various methods, including solvent extraction,7,8 ion-exchange techniques,9 and hydrometallurgical methods.5 However, these methods not only require high reagent and/or energy requirements but also generate toxic sludge and other waste products. Therefore, the development of more effective and environmentally friendly technologies for the recovery of W is essential for ensuring a sustainable supply of W. © 2016 American Chemical Society

Biosorption methods were identified as being a candidate for use in the recovery of soluble metal ions. The use of biosorption methods minimizes the volume of chemical sludges that require handling, while also being highly efficient in detoxifying effluents.10−12 Many researchers have undertaken biosorption tests on various metal ions, including silver(I), gold(III), chromium(VI), copper(II), iron(II), indium(III), nickel(II), lead(II), palladium(II), platinum(IV), rhodium(III), uranium(VI), rhenium(VII), and zinc(II), using bacterial species.12−18 Malekzadeh et al. conducted a thorough investigation of the biosorption of W using a Bacillus sp., as well as studying the effects of parameters such as the pH, initial W and cell concentration, live activity, and addition of other cations on the adsorption capacity.19 However, little research has been undertaken on W biosorption to date. Recently, our group reported the biosorption of W by Escherichia coli.20 Through adjustment of the cell concentration and pH of the W solution, our group successfully recovered 100% of W from the single-component W model solution. However, the selective Received: Revised: Accepted: Published: 2903

December 21, 2015 February 20, 2016 February 23, 2016 February 23, 2016 DOI: 10.1021/acs.iecr.5b04843 Ind. Eng. Chem. Res. 2016, 55, 2903−2910

Article

Industrial & Engineering Chemistry Research recovery of W from multicomponent metal ions in an aqueous solution is essential for a realistic application. Used tungsten carbide (WC) scrap contains various metals such as molybdenum (Mo), vanadium (V), cobalt (Co), titanium (Ti), chromium (Cr), tantalum (Ta), and nickel (Ni). Among them, Ti, Cr, Ta, and Ni can be removed by solid− liquid separation; however, Mo and V remain in solution with W. V causes a significant decrease in the toughness of the hard metal tools made from recycled WC; therefore, it should be separated and removed from W. Selective biosorption tests for the multicomponent aqueous solutions containing W, Mo, and V ions have not been reported to date. On the basis of the above background information, this study focused on selective biosorption methodologies from modeled or real waste solutions containing W, Mo, and V ions, using microorganisms such as E. coli cells and beer yeast. To confirm the feasibility and environmentally friendly application of the W recovery process using the biosorption methodology, the microbial biosorption test was undertaken on a real W waste solution and then a fabricated cemented carbide tip. To maximize W recovery, beer yeast was used as the biosorbent because it was easy to obtain in large quantities at a relatively low cost. This paper presents the first examination of the recycling of W from urban mines using biosorption processes.

Table 1. Metal Components of (a) Used WC Scrap Powder Measured by XRF and (b) a Solution from Used WC Scrap Measured by ICP W

Mo

V

Co

Na

O

K

(a) Used Scrap Powder of WC (wt %; Measured by XRF) 34 2.5 0.6 0.1 27 36 0 (b) Solution of Used Scrap of WC (×10−4 ppm; Measured by ICP) 39 0.3 0.1 0.1 26 36 0.1

was prepared through alkali extraction of the used WC scrap. After alkali extraction was complete, the W filtrate was dried in a drying oven at 80 °C for 12 h. The dried powder was then diluted in a prescribed volume of ultrapure water. The concentrations of the metals in the real waste solution were measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES; SII, S-3000, Seiko Instruments Inc., Chiba, Japan), as shown in Table 1b. 2.4. Biosorption Testing of W, Mo, and V Ions Using E. coli Cells. For single-component solutions, 5 mL of an E. coli cell suspension was added to 30 mL of each aqueous Na2WO4, Na2MoO4, and V2O5 solution. The pH solution was adjusted from 1.08 to 6.90 using HCl. Unless otherwise stated, the initial metal-ion concentrations were constant at 0.8 mmol/L. For multicomponent model solutions, 5 mL of an E. coli cell suspension was added to 30 mL of aqueous Na2WO4, Na2MoO4, and V2O5 solutions, and the pH was adjusted from 1.03 to 2.03 using HCl. The initial metal-ion concentrations were constant at 0.8 mmol/L. For the real waste solution, the E. coli cell suspension or beer yeast powder was added to 30 mL of the real waste solution, and the pH was adjusted from 1.36 to 1.84 using HCl. The initial metal-ion concentrations in the real waste solution are summarized in Table 1b. All experiments were conducted at 25 °C, and the cell concentration in the mixed solution ranged from 2 × 108 to 2 × 1010 cells/mL. The number of E. coli cells in the solution was determined in a Petroff−Hausser counting chamber (Hausser Scientific, Horsham, PA) using a microscope (VHZ450, Keyence, Osaka, Japan). To follow the time course of the microbial adsorption of W, Mo, and V ions, aliquots of the solution were periodically withdrawn, and the concentration of each metal was determined using ICP-AES, as previously reported.20 The calculated errors of the experimental results were less than 1.0%. The effects of the pH on the ζ potential of E. coli were investigated using a Zetasizer (Nano ZS, Malvern Instruments Ltd., Worcestershire, U.K.). A total of 1 mL of a bacterial suspension was added to a sample bottle containing 14 mL of water. The pH of the solution was then adjusted from 1.16 to 7.23 with 1.0 mol/L HCl and 1.0 mol/L NaOH solutions. To investigate the main functional groups responsible for metal adsorption and the chemical nature of the binding processes between W, Mo, and V ions and E. coli cells, dried E. coli cells and W-, Mo-, or V-adsorbed E. coli cells were analyzed by Fourier transform infrared (FTIR) spectroscopy (PerkinElmer, Spectrum One System). For FTIR analysis, the biomass was centrifuged and dried at 90 °C, after which 10 mg of finely ground biomass was used to make pellets. 2.5. Preparation of W Concentrates. The W concentrate of tungsten oxide (WO3, obtained from the W-adsorbed microbe) was prepared through a staged heating process. After exposure to the metal solution, the E. coli cells were centrifuged and dried in a drying oven at 120 °C for 4 h. The dried sample was then heated in a furnace to 1000 °C for 2 h under

2. MATERIALS AND METHODS 2.1. Preparation of Microbial Biosorbents. E. coli cells were selected as one of the microbial biosorbents for this study because the cells were easy to obtain, inexpensive, and safe and had a rapid cultivation rate. E. coli (ATCC-PTA-3137) cells were obtained from the American Type Culture Collection (ATCC) and inoculated in a 500 mL Erlenmeyer flask containing 250 mL of Luria−Bertani broth. The flask was then sealed with an absorbent cotton stopper and incubated in a temperature-controlled shaker for 14 h at 37 °C and a rate of 110 rpm.20 E. coli cells were harvested by centrifugation (24310g for 10 min), resuspended in distilled water, and then reformed into pellets by centrifugation. This procedure was repeated twice, after which the washed cells were resuspended in distilled water and immediately used in the biosorption experiments. Various microbial biosorbents such as beer yeast (Shizen Kenkosha Co., Ltd., Kyoto, Japan), shochu lees (Yamamoto Shuzo, Satsumasendai, Japan), and koji (Aspergillus spp.) mold, spores, and mycelium (Akita Konno Co., Ltd., Daisen, Japan) were also used for W recovery in practical application tests. 2.2. Preparation of W, Mo, and V Ion Model Solutions. Biosorption experiments were conducted using modeled bulk and real waste solutions. For the modeled bulk solution, a representative metal solution containing W, Mo, and V ions was prepared by dissolving the corresponding weights of sodium tungstate(VI) dihydrate (Na2WO4·2H2O), sodium molybdate(VI) dihydrate (Na2MoO4·2H2O), and vanadium oxide(V) (V2O5) (Kanto Chemical Co., Inc., Tokyo, Japan) in distilled water. The pH of each of the test solutions was adjusted to the required value using 1.00 mol/L HCl (Kanto Chemical Co., Inc.) prior to addition of the biosorbent. A biosorbent-free solution was also prepared as a control. 2.3. Preparation of the Real W Waste Solution. A real waste solution prepared from used WC scrap was obtained from Kyocera Corp. Table 1a shows the metal components present in the used WC scrap powder, as measured by X-ray fluorescence (XRF; ZSX Primus II Rigaku). The waste solution 2904

DOI: 10.1021/acs.iecr.5b04843 Ind. Eng. Chem. Res. 2016, 55, 2903−2910

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Figure 1. (a) Relationship between the pH and removal ratio of each metal. (b) ζ potential of E. coli as a function of the pH. (c and d) ζ-potential distributions of E. coli at pH 7.00 and 1.79.

coli cells as a function of the pH value. From ζ potential analysis, it was found that the surface of the E. coli cells had a positive charge in the pH range of 1.00−3.00 and a negative charge above pH 3.00. According to previous studies,9,21 the W and Mo ions under low pH conditions were anion species, including tungsten polyacid ions ([HW6O21]5−, [W12O39]6−, and [W12O4]10− in the range of 2.00 < pH < 7.00) and molybdenum polyacid ions ([Mo7O21(OH)3]3−, [Mo7O22(OH)2]4−, [Mo7O23(OH)]5−, and [Mo7O24]6− in the range of 2.00 < pH < 5.00). At low pH levels (in the range of pH 1.00−3.00), high removal ratios of the W and Mo ions were attained because of the attractive force between the W or Mo ions and the surface of the E. coli cells. When the pH was greater than 3.00, a repulsive force between the surface of the cells and the metal ions resulted in a decrease in the removal ratios of W or Mo ions. The reason for the slight decrease in the removal ratio of W and Mo ions at pH 1.0 is attributed to the chlorine (Cl) complex ions from HCl addition. The lower the pH, the higher the concentration of Cl− brought into the solution through HCl addition, and that, in turn, could compete with the negatively charged tungsten polyacid ions for the binding sites. Niu and Volesky reported a similar phenomenon for anionic species biosorption onto waste crab.22 In contrast, the V ions were identified as cationic species (VO2+ pervanadyl ion) in the pH range of 0.80−3.00 and anionic species (vanadium polyacid ion: [V10O26(OH)2]4−, [V10O27(OH)]5−, and [V10O28]6−) in the pH range of 3.00− 7.00.21 Therefore, a low V ion removal ratio could be observed in the pH range of around 1.00−3.00 because of the repulsive force. However, small quantities of V ions were also observed to be removed in the pH range of 2.0−3.0. To determine the reason for the removal of V ions at pH 2.0−3.0, we focused on the ζ-potential distribution of the E. coli cells at pH 7.00 and 1.79 (Figure 1c,d. It was found that the E. coli cells had a partial negative charge at pH 1.79, although the average value of the ζ

atmospheric (air) conditions. The concentration of W in the concentrate was measured using ICP spectroscopy. The crystal structure of the obtained powder sample after heating was also investigated using powder X-ray diffraction (XRD; Rigaku, Tokyo, Japan, RINT 2200 V) with Cu Kα radiation. 2.6. Demonstration of the Recycling of W from Waste Scrap and the Fabrication of W. Various microbial biosorbents such as beer yeast, shochu lees, and koji mold, spores, and mycelium were used to demonstrate the practical application of the W adsorption test. The experimental procedure used for the biosorption test was the same as that for E. coli unless otherwise stated. To prepare the W concentrates, the W-adsorbed biosorbents in the real waste solution were dried at 80 °C for 12 h. A WO3 powder was obtained through the calcination of W concentrates, at 800 °C for 4 h in an air atmosphere. The WO3 powder was then reduced at 900 °C for 6 h under hydrogen and nitrogen flow. The WC powder was obtained through a carbonization process, which involved heating of a mixed powder of reduced W and carbon black at 1600 °C for 3 h in a vacuum. The crystal structure and chemical components of the obtained powder samples were determined using XRD and XRF.

3. RESULTS AND DISCUSSION 3.1. Biosorption of W, Mo, and V Ions from a SingleComponent System Using E. coli Cells. Figure 1a shows the removal ratios of W, Mo, and V ions as a function of the pH, following a 7 h test at 25 °C using resting E. coli cells. The concentration of the E. coli cells was kept constant at (1.1−1.8) × 109 cells/mL. As shown in Figure 1a, the aqueous concentrations of the W and Mo ions exhibited high removal ratios within a pH range of 1.00−3.00. These removal ratios rapidly decreased when the pH of the solutions was higher than 3.00. This phenomenon may be attributed to the surface charge of the cell. Figure 1b shows the ζ potential behavior of the E. 2905

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Figure 2. (a) Time course of soluble W-, Mo-, and V-ion concentrations during biosorption using resting cells of E. coli at pH 1.03. (b) Effect of the cell concentrations on the quantities of removal of W, Mo, and V ions during biosorption and using resting cells of E. coli in the pH range of 1.44− 1.53.

and V ions) solution, the sorption order among tungstate polyacid, vanadate polyacid, and W−V heteropolyacid ions to the cell surface should be considered. This study focused on the cell concentration to improve the sorption preference of the tungstate polyacid ion. Figure 2b shows the removal ratio of W, Mo, and V ions in a threecomponent system as a function of the cell concentration of E. coli cells in the pH range of 1.44−1.53. Although the removal ratios of the W and Mo ions decreased as the cell concentration decreased, no adsorption of V ions was observed under a cell concentration of 2.58 × 108 cells/mL. This result indicates that that tungstate and molybdate polyacid ions have a higher affinity for adsorption to the E. coli cell surfaces compared with W−V heteropolyacid ions. A schematic diagram of the mechanism of selective adsorption of W and Mo ions is shown in Figure S2 (Supporting Information). At high cell concentrations, all types of metal ions can be adsorbed to the E. coli cells because of the large cell surface area (enough adsorption site). However, a decrease in the cell concentration resulted in less adsorption sites on the cell surface, causing tungstate and molybdate polyacid ions to be preferentially adsorbed to the E. coli cells. These results indicate that a decrease in the cell concentration, as a result of the biosorption process, may enable selective recovery of W and Mo ions from the three-component system containing W, Mo, and V ions (V/W = 0.028 and V/Mo = 0.031). 3.3. Biosorption of W, Mo, and V Ions from a Real Waste Solution Using E. coli Cells and the Preparation of W Concentrates. Figure 3a shows the time course of soluble W-, Mo-, and V-ion concentrations during biosorption using resting cells of E. coli for the real waste solution of used scrap (WC concentrations are shown in Table 1). The cell concentration was maintained at 2.4 × 109 cells/mL and a pH of 0.95. The aqueous concentration of W ions was decreased, and an 86% removal ratio was attained at 420 min, as shown in Figure 3a. The amount of each metal removed was 9.2 mg (W), 0.6 mg (Mo), and 0.09 mg (V). These values are comparable to 93.1 wt % (W), 6.0 wt % (Mo), and 0.9 wt % (V) and reveal that the biosorption process using E. coli is applicable for the selective recovery of W ions from a real waste solution. The calculated maximum sorption capacity of the W ions was 5.7 × 10−16 mol wt/cell for the E. coli cell (=0.89 mmol wt/gdry E. coli cell). This value is comparable to the adsorption properties (0.5−0.8 mmol wt/gadsorbent) of the anion-exchange resin (SA-10A), as shown in Figure S3

potential was positive. These results provide some explanation as to why small quantities of anionic ions, specifically V ions, were adsorbed by the E. coli cells. FTIR spectroscopy of the E. coli cells was conducted before and after W, Mo, and V biosorption to understand the involvement of the main functional groups in the binding of metals (Figure S1 in the Supporting Information). A substantial decrease in the absorption intensities of the amino groups in the spectra of the W- and Mo-adsorbed cells, suggested interactions of W or Mo with amino groups (−NH2, NH, or −NH3+). At lower pH levels, the function of NH on the bacterial surface may result in a change to NH3+. However, in the case of V, no significant difference in the absorption intensities was observed either before or after biosorption. 3.2. Biosorption of W, Mo, and V Ions from a ThreeComponent System Using E. coli Cells. On the basis of the above results (Figure 1a), biosorption tests for a threecomponent system (W, Mo, and V ions) were conducted at pH 1.03 to separate the V ion from the W and Mo ions. Figure 2a shows the time course of soluble W-, Mo-, and V-ion concentrations during a biosorption test, using resting E. coli cells at pH 1.03. All initial metal-ion concentrations were measured at 0.8 mmol/L, and the concentration of the E. coli cells was maintained at 8.7 × 109 cells/mL. After the E. coli cells were included in the three-component solution, the W- and Mo-ion concentrations rapidly decreased within 10 min. After 420 min, high removal ratios were attained for W (99.5%) and Mo (91.2%). However, small amounts of V ions (18%) were also adsorbed by the E. coli cells. Despite the fact that the removal ratio of V ions in a single-component system was less than 3%, the removal ratio of the V ions in the threecomponent system increased up to 18%. This indicated that the state of the V ions in the three-component system was different from that in the single-component system. Within the singlecomponent system, isopolyacids such as tungstate, molybdate, and vanadate were formed through condensation of each oxoacid anion of W, Mo, and V ions under low pH conditions. In the case of the three-component system, the W−V heteropolyacid ([W3V3O19]5−) may have formed through condensation of the W and V ions. In the biosorption test of the three-component system undertaken in the current study, the W−V heteropolyacid was considered to be adsorbed on the cell surface. This resulted in an increase in the removal ratios of the V ions compared with the single-component cases. Thus, to realize selective biosorption from a three-component (W, Mo, 2906

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(Supporting Information). Figure 3b shows the removal ratios of the W, Mo, and V ions from the real waste solutions, as a function of the concentration of the E.coli cells at pH 1.03. As displayed in Figure 3b, the W ions were successfully selectively recovered from the real waste solution. The digital photographs in Figure 3c show the dried powder sample of the W-adsorbed cells. The concentration of W in the dried sample was calculated using the amount of W removed per unit of dried biomass and had a value of approximately 49.2% (w/w). This concentration was calculated to be 535 times the concentration of W in the initial solution (9.91 × 10−4 w/w). A calcination step was used to prepare the W concentrates. W-adsorbed biosorbents were heated at 800 °C for 2 h in a furnace under atmospheric conditions. After calcination, the produced powder became dark green (Figure 3d), indicating the generation of WO3 crystals.4 ICP-AES analysis revealed that the solid condensate (in powder form) contained 77.0% of W (W/ solid condensate), which was calculated to be 837 times the initial concentration of the W solution. Figure 3e shows the XRD pattern of the W-adsorbed E. coli powder sample after calcination at 800 °C. The obtained crystal structure of the sample indicated the presence of WO3 with impurities, which were likely derived from sodium and phosphate. 3.4. Demonstration of the Recycling of W from Used WC Scrap Using Biosorption. Figure 4 shows a theoretical flowchart of recycling of the WC tips. The total system includes the processes of calcination, alkali extraction, biosorption, separation, incineration, reduction, and carbonization. To demonstrate the WC recycling process using biosorption, experiments involving the biosorption performance of various types of biosorbents (i.e., dried E. coli, pure shochu lees, dried shochu lees, beer yeast, and koji mode, spores, and mycelium) were conducted. The results of the biosorption experiments indicate the recovery ratio of the W ion (Table S1 in the Supporting Information). The differences between the saturated adsorption amounts were primarily attributed to the

Figure 3. (a) Time course of soluble W-, Mo-, and V-ion concentrations during biosorption using resting cells of E. coli (cell concentration: 2.40 × 109 cells/mL) at pH 0.95. (b) Relationship between the cell concentration and removal ratio of each metal in the pH range of 1.7−1.8. (c) W-adsorbed E. coli cells after drying at 80 °C. (d) W-adsorbed E. coli cells after calcination at 800 °C. (e) XRD analysis of the powder sample of W-adsorbed E. coli cells after calcination.

Figure 4. Theoretical flowchart of recycling of the used WC tip in biosorption. 2907

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Industrial & Engineering Chemistry Research individual cell size and the chemical functions as groups on the cell surface. In this study, beer yeast was selected for demonstration of the WC recycling experiment because of its high adsorption performance (0.29 gw/gbeer yeast) and ease of handling. Figure 5

Table 2. Metal Components of Cemented Carbide Tip Fabricated from (a) a WC Powder Sample via the Biosorption Process (Beer Yeast) and (b) a Commercially Available WC Powdera W

Co

69.7

18.9

68.0

21.0

C

Al

Si

Ti

(a) From Biosorbed WC (wt %) 11.1 ND ND 0.1 (b) From Commercial WC (wt %) 11.0 0.1 0.1 0.1

Fe

Ni