KR20130077122A - Recovery of silver from wastewater coupled with power generation using a microbial fuel cell - Google Patents

Abstract

PURPOSE: A collection of silver metal from wastewater and an electric power generation method using a microbial fuel cell are provided to collect a silver, and to manufacture an electric power with an efficient cost by using a silver ion like a silver ion effluent as a cathode electron-receptor of a microbial fuel cell. CONSTITUTION: A collection of silver metal from wastewater and an electric power generation method using a microbial fuel cell comprise the following steps: an anode electrolyte which is ammonium hydroxide and potassium perchlorate, and a buffer solution which is 4 - (2- hydroxyethyl) -1- piperazine - ethanesulfonic acid and 4 - (2- hydroxyethyl) -1- piperazine - ethanesulfonic acid sodium salt compound are manufactured for a nutritional fluid necessary for microorganism and used; and perchlorate is used for a cathode electrolyte.

Description

Recovery of silver metal from wastewater using microbial fuel cell and power generation method {RECOVERY OF SILVER FROM WASTEWATER COUPLED WITH POWER GENERATION USING A MICROBIAL FUEL CELL}

The present invention relates to a method for producing electric power while recovering silver metal using a high performance microbial fuel cell (MFC) using silver-containing heavy metal wastewater as an electron acceptor and organic wastewater as an electron donor.

Recently, the recovery and removal of silver has been actively studied due to the demand as a precious metal.

Silver is not an expensive metal like gold or platinum, but it is present in a limited amount in nature, as is the more expensive precious metal.

Moreover, current environmental reference conditions require the removal of metal ions from the industrial wastewater to ppm levels (de Radigues, Q., Santoro, R., Proost, J., 2010. Kinetic transitions during Ag and Cu electrorecovery on reticulated vitreous carbon electrodes in flow-by mode.see Chem. Eng. J. 162, 273-277).

Some silver compounds have been found to be extremely toxic to aquatic organisms including fish at high concentrations (Naddy, RB, Gorsuch, JW, Rehner, AB, McNerney, GR, Bell, RA, Kramer, JR, 2007. Chronic toxicity of silver nitrate to Ceriodaphnia Dubia and Daphnia Magna, and potential mitigating factors.See Aquat.Toxicol. 84, 1-10).

Also of interest is the potential toxicity resulting from the interaction between silver and essential nutrients, especially selenium, copper, vitamin E and B12 (Afzali, D., Mohadesi, AR, Jahromi, BB, Falahnejad, M.). Separation of trace amount of silver using dispersive liquid-liquid based on solidification of floating organic drop microextraction.Anal. Chim.Acts 684, 54-58.

Given this background, there is a need to effectively recover or reclaim silver from wastewater.

Silver recovery is based on electrical and electronic supplies discarded after use (Aktas, S., 2010. Silver recovery from spent silver oxide button cells, see Hydrometallurgy 104, 106-111) and mine wastewater (Koseoglu, H., Kitis, M. , 2009. The recovery of silver from mining wastewaters using hybrid cyanidation and high-pressure membrane process.See Mineral Eng. 22, 440-444).

Biosorption is a cost-effective way of recovering silver (see Das, N., 2010.Recovery of precious metals through biosorption-A review. Hydrometallurgy 103, 180-189). There is this.

Precipitated AgCl is converted to 99.99% pure silver by reduction with metal zinc powder (see Aktas, S., 2010.Silver recovery from spent silver oxide button cells. Hydrometallurgy 104, 106-111). Secondary pollution causes additional costs.

Electrochemical precipitation was applied to recover electrochemical silver from nitric acid solution (Raju, T., Chung, SJ, Moon, IS, 2009. Electrochemical recovery of silver from waste aqueous Ag (I) / Ag (II) redox mediator solution used in mediated electrooxidation process.See Korean J. Chem. Eng. 26 (4), 1053-1057).

This method has a problem of requiring high electrical energy at a rate of 3.81 KWh per kilogram of silver produced.

Meanwhile, microbial fuel cells generate electrons by transferring electrons generated when microorganisms in a cathode part decompose organic substances, which are substrates, to the anode part, and have been recently used to purify pollutants such as waste water and sediments.

For example, Korean Patent Laid-Open Publication No. 2003-0038240 (2003. 05. 16) discloses a fuel cell type biochemical oxygen demand meter using a low nutritional electrochemically active microorganism and a biochemical low concentration oxygen demand measuring method using the same. have.

In addition, Japanese Patent Application Laid-Open No. 2008-0066460 (2008. 07. 16), by limiting the growth of microorganisms by converting the energy from the process of decomposition of organic matter in the waste water by the microorganisms in the microbial fuel cell reaction tank to electrical energy, A device for reducing the sludge production accordingly is disclosed.

Patent Publication No. 2010-0109234 (October 08, 2010) discloses a dechlorination method using a bioelectrochemical system, and Patent Publication No. 2010-0137766 (December 31, 2010) discloses a lower layer such as an appeal. The present invention discloses a microbial fuel cell that indirectly oxidizes organic matter in a sediment layer using microorganisms by installing a cathode on a sediment layer deposited on the sediment and an anode on a water surface, and a method of reducing greenhouse effect using the same.

However, techniques for removing heavy metals or recovering precious metals using microbial fuel cells are not known.

The present inventors have applied for a method for removing heavy metals with a microbial fuel cell as Korean Patent Application No. 2011-42226.

However, the patent uses an excessive amount of phosphoric acid compounds (KH ₂ PO ₄ , K ₂ HPO ₄ ) as a buffer solution, and uses a compound containing chlorine ions (NH ₄ Cl) as an electrolyte, so that silver ions are precipitated as metals. Precipitation is also produced with chloride (AgCl) or phosphate, which leads to a problem that the efficiency of recovery is significantly reduced.

An object of the present invention is to overcome the problems in consideration of the pollution and cost problems of the conventional silver recovery technology, and by using the microbial fuel cell used to purify contaminants such as waste water and sediments, it is incidentally produced power To provide a method for recovering silver from silver-containing wastewater economically without by-products.

In order to achieve the above object, in the present invention, in a microbial fuel cell having a separator between the anode and the cathode, and both electrode chambers, ammonium hydroxide (NH ₄ OH) and the anode and the cathode are used as electrolytes in the anode. Perchlorate (KClO ₄ , NaClO ₄ ) and 4- (2-hydroxyethyl) -1-piperazine-ethanesulfonic acid (HEPES), HEPES sodium salt, etc. in buffer do not form precipitates of Ag ⁺ The present invention provides a method of recovering silver metal from silver-containing wastewater using an anaerobic microorganism, which produces and uses these compounds as a nutrient solution required for microorganisms, while simultaneously producing electric power.

The above buffers can be used as 2- [N-morholino] ethane sulfonate (MES), piperazine-N, N'bis [2-ethanesulfonate] (PIPES), boric acid, 4-nitrophenol , Cysteamine, 1H-imidazole, pyridine, 2-pyridine amine, 2-chloro phenol, 3-chloro phenol, 2-nitro phenol, 4-nitro phenol, methoxy pyridine, 2,3-dimethyl pyridine , 2,4-dimethyl pyridine, 2,4,6-trimethyl pyridine, tyrosine amide, nicotine, N, N-diethyl aniline, N- (2-hydroxyethyl) piperazine-N '(4-butane sulphate Phonic acid) (HEPBS), N- (2-hydroxyethyl) piperazine-N '(2-hydroxypropane sulfonic acid) (HEPPSO) and the like may be further used.

These buffer solution systems are applicable to a system for generating electric power through the construction of a microbial fuel cell comprising a cathode using Ag ⁺ as a cathode electrode and an anode using organic materials and microorganisms.

Anaerobic microorganisms that can be used in the microbial fuel cell of the present invention are Alpha, Beta, Delta-proteobacteria, Clostridia, Shewanella oneidensis MR-1, DSP-10, Shewanella putrefaciens SR-21, IR-1, MR-1, Geobacter sulfurreducens, Geobacter sulfurreducens KN400, Ochrobactrum anthropi YZ-1, Brevibacillus sp. PTH1, E. coli K12 HB101, Aeromonas hydrophila, Corynebacterium sp. MFC03, Leptothrix discophora SP-6, Bacillus licheniformis, Bacillus thermoglucosidasius, Spirulina platensis, Bacillus subtilis, Enterococcus gallinarum, Acetobacter aceti and Gluconobacter roseus.

The present invention provides a method for recovering silver metal while generating power from a cathode chamber by using silver ions such as silver ion wastewater as a cathode electrode acceptor of a microbial fuel cell.

According to the present invention, while producing electrical energy from wastewater using a two-chamber microbial fuel cell, it is possible to economically recover silver metal without generating precipitates.

The hypothetical mechanism of the microbial fuel cell device according to the present invention is as follows.

Electron-emitting microorganisms attached to the anode oxidize organic matter and reduce NAD ⁺ to NADH in the cytoplasm through catalytic metabolism (Du, Z., Li, H., Gu, T., 2007. A state of the art review on microbial fuel cells: A promising technology for wastewater treatment and bioenergy.See Biotech.Adv. 25, 464-482).

The emitted electrons are transferred to the anode through as many different types of redox as possible.

When a potential difference occurs in the circuit between the anode and the cathode, the free electrons move freely through the load resistor from the anode to the cathode.

The transferred electrons are consumed to reduce the oxidation type of the redox element in the cathode.

These unique, new and cost-effective microbial fuel cell devices can be used for wastewater treatment, economical recovery of precious metals and the production of electricity.

On the other hand, the battery operating voltage (Voper) is Osman, MH, Shah, AA, Walsh, FC, 2011. Recent progress and continuing challenges in bio-fuel cells.Part I: Enzymatic cells.Biosensors and Bioelectronics 26, 3087- 3102) and Vincent et al. (See Vincent, CA, Scrosati, B., Lazzari, M., Bonino, F., 1984. Modern Batteries.Edward Arnold, London). Given by 1).

- ηmem, (1)Voper = Voc- [ηact, c + ηconc, c]-[ηact, a + ηconc, a] -J

-ηmem, (1)

Where Voc is the open circuit voltage measured in the absence of current, ηact, c is the cathode activation overvoltage, ηconc, c is the cathode material transfer overvoltage, ηact, a is the anode activation overvoltage, and ηconc, a is the anode material. The transfer overvoltage, J is the current density, rho is the resistivity, l is the distance between the electrodes, and ηmem is the membrane overvoltage.

Voc is given by the following equation (2).

Voc = Vtherm-Vpar (2)

Where Vtherm is the thermodynamic cell voltage and Vpar is due to the crossover of internal current and fuel.

The Vtherm can be calculated by the Nernst equation.

If [Ag +] = 0.00927 M (1000 ppm), the thermodynamic cathode potential (Vca) is 0.799 V-(RT / F) ln (1 / 0.00927) or 0.679 V.

If [NADH] / [NAD +] = 0.1 and pH = 7 (see Logan, BE, 2008. Microbial Fuel Cells. John Wiley & Sons, New Jersey), the anode potential (Van) will equilibrate at -0.291. .

Accordingly, the thermodynamic cell voltage Vtherm can be calculated as follows: Vtherm = 0.679 V-(-0.291 V) or 0.970 V.

That is, potentially high Voc and power are obtained while recovering the silver metal.

In the present invention, the results obtained from factors such as the initial silver ion concentration, the reaction time for the recovery efficiency, the electrical properties were evaluated.

According to the invention, is a metal ion are ^{2 +} Cu, Cu ^+, Au ^{3 +,} Au +, Pd ^{3+, 4 +} Pt, Pt, Fe ^{6+ + 3,} Fe ^{+ 2,} Rh ^{+ 3,} Ir used in addition ^{3 +} , Ru ^{3 +} , Os ^{3 +} , Re ^{3 +} , Cr ^{6 +} , Cr ^{3 +} , Hg ^{2 +} .

Table 1 below shows the reduction potentials of the elements that can be used to remove organic waste in microbial fuel cells.

Cr
-0.424
-0.79
1.29a Mn
-1.18
1.695b
Fe
0.771
-0.440
Co
1.95
-0.287
Ni
-0.236

Cu
0.337
0.521
Zn
-0.763

Ga
-0.45
-0.53
As
0.559i
-0.68j
Mo
-0.200

Tc


Ru
0.25
0.46
Rh
0.758

Pd
0.915
1.29d
0.59e Ag
0.799

CD
-0.403

In
-0.338

W


Re
0.300

Os


Ir
1.16
0.86c
Pt
1.320
1.011f0.847g Au
1.50
1.68
1.154h Hg
0.911
0.796
Tl
1.28
-0.336
Pb
-0.126

The values below the element in Table 1 above represent the potential for the hydrogen reference electrode that is deposited as a metal.

^a Cr ₂ O ₇ ^2- + 14 H ⁺ + 6e = 2Cr ³⁺ + 7H ₂ O;

_{^{b MnO 4 - + 4H + +}} 3e = MnO 2 (s) + 2H 2 O;

_{^{c IrCl 6 3- + 3e = Ir}} (s) + 6Cl -;

_{^{d PdCl 6 2- + 2e- = PdCl}} 4 2- + 2Cl -;

_{^{e PdCl 4 2- + 2e- = Pd}} (s) + 4Cl -;

^f [PtCl ₆ ] ^2- + 2e = [PtCl ₄ ] ^2- + 2Cl ⁻ ;

_{^{g [PtCl 4] 2- + 2e}} = Pt (s) + 4Cl -;

_{^{h [AuCl 2] - + e}} = Au (s) + 2Cl -;

ⁱ H ₃ AsO ₄ (aq) + 2H ⁺ + 2e = HAsO ₂ (aq) + 2H ₂ O;

_{^{j AsO 2 - (aq) +}} 2H 2 O + 3e = As (s) + 4OH -.

According to the present invention, by using silver ions such as silver ion wastewater as a cathode electrode acceptor of a microbial fuel cell, silver metal can be recovered while producing electric power at an efficient cost.

That is, a high recovery rate of silver metal of 99.91 ± 0.00% to 98.26 ± 0.01% can be achieved at an initial Ag + concentration of 50 ppm to 200 ppm after reaction for 8 hours with a load resistance of 1000 kPa. From the silver ion wastewater, a maximum power of about 4.25 W / m 2, a maximum voltage of 0.749 V, a maximum current density of 5.67 A / m 2, and a fill factor (FF) of 0.626 can be obtained.

Further, according to the present invention, after the conventional leaching process, silver recovery processes, that is, precipitation by KCl and substitution of silver chloride by zinc powder are omitted, thereby enabling economic saving and preventing secondary water pollution.

In addition, by using a microbial fuel cell, silver ions can be economically recovered by preventing precipitation of silver ions during recovery of silver ions.

1 is a graph showing the voltage vs. current density (VJ) curve of a microbial fuel cell obtained at different initial Ag + concentrations (50 ppm, 100 ppm, 200 ppm, 500 ppm and 1000 ppm) in a cathode electrolyte wastewater. A) and graph (B) showing the power versus current density (PJ) curve.
FIG. 2 shows the residual concentration of Ag ^{+ in} the cathode electrolyte wastewater (RC) with different initial Ag ⁺ concentrations (50 ppm, 100 ppm and 200 ppm) and the recovery efficiency of silver metal from the waste water (RE: A graph showing recovery efficiency (A), and a graph showing discharge curves of microbial fuel cells having different initial Ag ⁺ concentrations (50 ppm, 100 ppm and 200 ppm) in the wastewater, respectively.
3 is a scanning electron microscopy (SEM) photograph of silver metal deposited on a carbon cloth electrode after 3 hours of microbial fuel cell reaction in a cathode electrolyte wastewater containing 200 ppm AgNO ₃ and 0.20 M NaClO ₄ (pH 7). X) (A) and EDS (enerty dispersive X-ray spectometry) analysis results (B).

The anode electrolyte of the present invention is an electron donor per liter of 1 to 10 g (12.2 to 122 mM) of sodium acetate (CH ₃ COONa), 0.1 to 10 g of ammonium hydroxide (NH ₄ OH), 0.001 to 1 g of potassium phosphate (K ₂ HPO ₄ ) (mass ratio of nitrogen to phosphorus = 5: 2), 10-1000 mM potassium perchlorate (KClO ₄ ), 10-1000 mM 4- (2-hydroxyethyl) -1-piperazine-ethanesulfur A nutrient solution consisting of phonic acid (HEPES), 1 to 1000 mM HEPES sodium salt and 0.1 to 20 g yeast extract is used.

The cathode electrolyte uses perchlorate salt (KClO ₄ , NaClO ₄ ) in an amount of 0.01 to 2M as an electrolyte component.

Hereinafter, the present invention will be described in more detail with reference to Examples.

The following is an example showing the recovery of the silver contained in the heavy metal wastewater is only an illustration of the present invention, the scope of the present invention is not limited thereto.

[Example]

(1) microbial fuel cell type

One double chamber microbial fuel cell used in this example was fabricated with an acrylic cuboid seal with each electrode chamber maintaining 112 mL (7 cm long, 4 cm wide, 4 cm high), with an effective volume of 100 on both sides. mL.

The electrode chambers were separated by anion exchange membrane (AEM, AMI-7001, Membrane International, Inc. USA) having a surface area of 16 cm 2 (4 cm × 4 cm).

AEM is pretreated by Wang et al. (Wang, Z., Lim, B., Choi, C., 2011. Removal of Hg2 + as electron acceptor with power generation using a microbial fuel cell.Biores.Tech. 102, 6304 See description of -6307, hereinafter referred to as 'Wang et al.'), A carbon brush anode (length 2.5 cm, diameter 2.5 cm) was prepared by twisting carbon fibers (PANEX # 35, Zoltek, USA) with titanium.

A carbon cloth (type w1s1005, CeTech, USA) with a diffusion layer having a surface area of 2.2 cm 2 (1.7 cm × 1.3 cm) was used as a cathode.

The back side is made of titanium yarn and silver paint (Elcoat, Type P-100, Cans, Japan), and only one side is coated with non-conductor adhesive to contact the solution. It was.

(2) Start and start microbial fuel cell

In order to remove dissolved oxygen in the 50 mL sludge and the 50 mL anode electrolyte (anolyte) used by Wang et al., Nitrogen was blown for about 30 minutes and pumped into the anode chamber.

The anode electrolyte is an electron donor per liter of 1 g (12.2 mM) CH ₃ COONa, 0.2 g NH ₄ OH, 0.018 g K ₂ HPO ₄ (mass ratio of nitrogen to phosphorus = 5: 2), 20 mM KClO ₄ , 25 mM 4- (2-hydroxyethyl) -1-piperazine-ethanesulfonic acid (HEPES), 5 mM HEPES sodium salt and 0.2 g yeast extract.

The nutrient solution is used to suppress the occurrence of precipitation by using a small amount of phosphate, NH ₄ OH and K ₂ HPO ₄ , KClO ₄ is used as a source of N, P, K, which is a nutrient source of microorganisms and an electrolyte.

After the air was blown into the cathode chamber to obtain a stable three cycle voltage, the microbial fuel cell was started, and a cathode electrolyte having a pH of 7 was charged in a batch cathode cell containing N ₂ .

For the discharge experiment, the supply of the organic donor through the anode chamber was continuously passed at a flow rate of 10 mL / min (water residence time = 10 minutes) by continuously passing the donor solution from the vessel containing the 4.9 L solution through a peristaltic pump. Maintained.

Catholyte was prepared by dissolving AgNO ₃ in distilled water as a stock solution of 1000 mg / L Ag +, diluted with distilled water to the required Ag ⁺ concentration, and 0.2 M NaClO ₄ was added to enhance the ionic conductivity of the solution. .

The cathode chamber was continuously blown with N ₂ gas (60 mL / min) during the experiment to eliminate the electron consumption effect of dissolved oxygen and to mix the solution. 1000Ω external resistance was connected.

For the V-J characteristics, the external resistance was changed from 100 Hz to 0.01 Hz, and all experiments were performed at atmospheric pressure and room temperature.

(3) calculation and analysis

Electrical properties were measured with a Lab View system (with National Instruments Models, NI-cDAQ 9172, NI 9219, and NI 9203, USA).

Voltage versus current density (V-J) curves, power density versus current density (P-J) curves, and internal resistance were obtained by the method described in Wang et al. And the cathode area was used to determine the current density.

The fill factor (F.F.) from the V-J curve is defined as the maximum power (Pmax) divided by the open circuit voltage (Voc) times the closed-circuit current density (Jsc).

Pmax is the largest area on the J axis that can be drawn below the V-J curve.

F.F. defines battery performance related to maximum power.

The silver ion concentration after the microbial fuel cell reaction is defined as the concentration of remaining silver ions ([Ag ⁺ ] remaining).

A 20 mL solution was taken from the N ₂ outlet of the cathode chamber for silver ion concentration analysis using ICP-AES at a sampling interval of 2 hours.

If silver ions are not lost as a chemical precipitation, migration or leakage from the cathode chamber, the decrease in the concentration of silver ions may be considered to accumulate on the cathode as silver metal.

Consistent measurement of the silver metal mass when changing the silver ion concentration is calculated as accumulated on the cathode and indicates that there is no loss of silver ions.

Therefore, the recovery efficiency of the microbial fuel cell can be defined as follows.

{([Ag ⁺ ] original- [Ag ⁺ ] remaining) / [Ag ⁺ ] original} × 100%

Where [Ag ⁺ ] original is the concentration of silver ions before the reaction of the microbial fuel cell, and the chemical form of the silver solid accumulated on the carbon cloth is a scanning electron microscope equipped with an energy dispersive X-ray spectrometer (EDS) (Quantax 200, Bruker, Germany). (SEM) (XL-30S FEG, Philips, Netherland).

(4) V-J and P-J curves of microbial fuel cells

In the present invention, in order to know the characteristics of the microbial fuel cell, after adding Ag ⁺ , the voltage is measured with a variable external resistance, the current density is calculated, and the voltage vs. current density (VJ) and power vs. current density (PJ) are recorded. It was.

The concentration of silver ions in the cathode electrolyte was varied from 50ppm to 1000ppm at pH 7.

Both the anode and the cathode chambers were operated in batch injection mode while stirring the solution with a magnetic stirrer while blowing N ₂ .

An anode electrolyte based on HEPES buffer was filled in the anode chamber.

Data were obtained within 15 minutes to avoid severe concentration exhaustion when changing the load resistance from 100㏀ to 0.01㏀.

Electrochemical factors are summarized in Table 2 below.

The high square-like nature of the curve represented by the fill factor is desirable to achieve high performance of the cell.

Since peak current density (Jpeak) and closed-circuit current density (Jsc) are close to each other, the peak current density was selected instead of the closed-circuit current density due to the V-J curve distortion to calculate F.F.

The maximum voltage and the maximum current density are defined as the voltage and the current density at the maximum power point, respectively.

1 shows the voltage versus current density (VJ) curve (A) and power versus current density (PJ) of a microbial fuel cell obtained at different initial Ag ⁺ concentrations (50 ppm, 100 ppm, 200 ppm, 500 ppm and 1000 ppm) in the cathode electrolyte wastewater, respectively. It is a graph which shows the curve (B).

The voltage was measured by varying the load resistance from 100 mA to 10 mA and the supporting electrolyte was 0.2 M NaClO ₄ (pH 7).

Table 2 below shows the electrochemical parameters of the microbial fuel cell at different initial Ag ⁺ concentrations in the cathode electrolyte wastewater.

density Voc / V (a) Jpeak / Am-2 (b) Vmax / V (c) Jmax / Am-2 (d) Pmax / Wm-2 (e) Rint / O (f) F.F (g) 50 ppm 0.840 1.95 0.650 1.48 0.960 547 0.586 100 ppm 0.906 3.18 0.648 2.10 1.363 557 0.473 200 ppm 0.942 4.09 0.670 3.81 2.551 284 0.662 500 ppm 0.968 5.91 0.731 5.54 4.048 168 0.708 1000 ppm 0.995 6.82 0.749 5.67 4.250 164 0.626

(a) Voc; Open circuit voltage, (b) Jpeak; Peak circuit current density, (c) Vmax; Maximum voltage, (d) Jmax; Maximum current density, (e) Pmax; Power density, (f) internal resistance, (g) F.F. fill factor; F.F. = Pmax / Voc x Jpeak.

As shown in Table 2 above, all factors except Rint and FF have been significantly improved with the increase of Ag ⁺ concentration, and the internal resistance Rint, determined by the slope of the rising part of voltage vs. current, has a Ag ⁺ concentration of 100 ppm to 1000 ppm. When rising to 557 Ω to 164 감소, this indicates that ohmic resistance decreases in bulk on the electrolyte as more Ag ⁺ is added.

Increasing the Ag ⁺ concentration decreases the polarization resistance or the charge transfer resistance, expressed as Rp = η / J.

Where η is overvoltage and J is current density, which can be derived at low overvoltage from the Butler-Volmer equation, and these effects will lead to improvements in F.F. and maximum power.

As shown in FIG. 1 and Table 2, a high open circuit voltage (Voc) and a sharp rise in current density of 0.995 V were observed from the 1000 ppm Ag + cathode electrolyte, as defined in equation (1), and a maximum of 4.25 W / m 2. A power point, a maximum voltage of 0.749 V, a maximum current density of 5.67 A / m 2, an internal resistance of 164 mA and an FF of 0.626 were achieved.

If Vpar does not exist, then Voc will be equal to Vtherm according to equation (2).

Still Vtherm (0.995 V) is about 0.025 V higher than the thermodynamic cell voltage (Vtherm) (0.970 V) with the assumption of a ratio of [NADH / NAD ⁺ ] = 0.1 as mentioned above.

If we recalculate this ratio to fit Vtherm using Ean = -0.316 V, the [NADH / NAD ⁺ ] ratio is found to be 0.73.

This indicates that microbial fuel cells can have ratios greater than the hypothetical value of 0.1 (Logan, B.E., 2008. Microbial Fuel Cells. John Wiley & Sons, New Jersey).

(5) Effect of Initial Ag ⁺ Concentration on Ag Recovery

Since there is no possibility of adsorption or precipitation of silver ions diffused from the anode chamber, all silver ions present in the cathode electrolyte are reduced to solid silver only.

To study the effect of Ag ⁺ on silver metal recovery, the concentration of silver nitrate was varied from 50 ppm to 200 ppm over time.

This example used an anode electrolyte based on HEPES buffer solution and a cathode electrolyte based on AgNO ₃ as provided in the beginning and operation of the microbial fuel cell.

The anode and cathode chambers were operated in a batch injection mode of operation.

A 20 mL solution was taken from each of the newly started cathode electrolytes at the planned reaction time, followed by ICP analysis.

FIG. 2 shows the residual concentration of Ag + in the cathode electrolyte wastewater (RC) and the recovery efficiency of silver metal from the wastewater (RE) with different initial Ag + concentrations (50 ppm, 100 ppm and 200 ppm), respectively, depending on the reaction time. A graph showing recovery efficiency (A), and a graph showing discharge curves of microbial fuel cells with different initial Ag + concentrations (50 ppm, 100 ppm and 200 ppm) in the wastewater.

The load resistance and supporting electrolyte are 1000 kPa and 0.2 M NaClO ₄ (pH 7), respectively.

ICP-AES measurements were performed in triplicate and statistically.

As shown in FIG. 2A, the recovery efficiency within 8 hours ranges from 98.26 ± 0.01% (residual concentration; 3.48 ± 0.01 ppm) at an average concentration of 99.91 ± 0.00% (residual concentration; 0.05 ± 0.00 ppm) from the initial concentration of 50 ppm to 200 ppm. It was.

The residual concentration of Ag + in the solution was higher as the initial concentration of Ag + increased. From these results, it can be seen that Ag + exhibits a fast reduction reaction and high recovery efficiency at the cathode.

The results of operating the anode chamber in continuous injection mode and the cathode in batch injection mode are similar to the operation of a batch-injected microbial fuel cell as above, indicating that the exhaustion of silver ions occurs much earlier than acetate exhaustion. .

(6) Discharge curves of microbial fuel cells with different initial Ag ⁺ concentrations

FIG. 2B shows the discharge characteristics of a microbial fuel cell having different Ag + concentrations as electron acceptors in the cathode chamber and 0.2 M NaClO ₄ as a supporting electrolyte and 1000 Ω load resistance while operating in a batch injection mode.

As shown in FIG. 1A, the anode electrolyte based on the HEPES buffer solution was passed through the anode chamber in a continuous injection mode.

As shown in FIG. 2B, the discharge voltage increased as the concentration of Ag ⁺ increased.

That is, as the initial Ag ⁺ concentration increased from 50 ppm to 200 ppm, the maximum voltage changed from 0.50 V to 0.63 V.

As the Ag ⁺ concentration increased, the voltage remained maximized for longer periods of time and showed longer burnout times.

Meanwhile, FIG. 3 is a scanning electron microscopy (SEM) photograph of silver metal deposited on a carbon cloth electrode after 3 hours of microbial fuel cell reaction in a cathode electrolyte wastewater containing 200 ppm AgNO ₃ and 0.20 M NaClO ₄ (pH 7). (10,000 ×) (A) and EDS (enerty dispersive X-ray spectometry) analysis results (B).

The surface shape of the precipitated silver crystals can be seen in FIG. 3A, and EDS analysis also shows that pure silver metal is recovered from the solution.

From the above results, the energy produced by the batch-injected microbial fuel cell when using 200 ppm AgNO ₃ to achieve 98.3% silver recovery efficiency with a load resistance of 1000 kW is calculated at a rate of 0.0143 KWh / kg silver. You will get metal and electrical energy.

On the other hand, the conventional electroprecipitation method has been reported to allow the recovery of silver metal by consuming electricity at a ratio of 3.81 KWh / kg silver at optimum conditions as described above (Raju, T., Chung, SJ, Moon, IS , 2009. Electrochemical recovery of silver from waste aqueous Ag (I) / Ag (II) redox mediator solution used in mediated electrooxidation process.See Korean J. Chem. Eng. 26 (4), 1053-1057).

This means that the microbial fuel cell system of the present invention can recover valuable metals such as silver and obtain electrical energy without generating sediment, which will be economically beneficial and will have a significant impact on the silver industry. .

The experimental conditions are similar in the sense that silver metal is obtained by reduction of the silver nitrate solution in the cathode.

In terms of electrical characteristics, when a constant concentration of 200 ppm in the cathode chamber and a constant concentration of organic electron donor are maintained in the anode electrolyte, a discharge resistance of 0.63 V and 2.86 A / It is very encouraging to have a result of 1.80 W / m 2 with a current density of 2 m 2, and it is also hopeful that the silver recovery efficiency reaches 98.3% within 8 hours.

Indeed, there is a wastewater containing 31000 ppm of silver nitrate leached from the silver oxide button cells used (Aktas, S., 2010. Silver recovery from spent silver oxide button cells. Hydrometallurgy 104, 106-111).

A two-silicone microbial fuel cell system with AgNO ₃ , such as a leachate from a silver oxide button cell in which an organic wastewater is passed through an anode chamber and a cathode chamber is used, shows a cost-effective recovery of silver metal.

In addition, according to the present invention, after the conventional leaching process, silver recovery processes, that is, precipitation by KCl and substitution of silver chloride by zinc powder may be omitted, thereby saving economics and preventing secondary water pollution.

The drawings and the detailed description of the invention are merely illustrative of the invention and are used merely for the purpose of describing the invention and not for limiting the scope of the invention as set forth in the claims or the claims.

Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this.

Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (5)

In a method for producing power while recovering silver metal from silver-containing wastewater by using a microbial fuel cell having an anode, a cathode, and a separator between both electrode chambers,
Ammonium hydroxide and potassium perchlorate as anode electrolytes, 4- (2-hydroxyethyl) -1-piperazine-ethanesulfonic acid, 4- (2-hydroxyethyl) -1-piperazine-ethanesulfuric acid as buffer A method for recovering silver metal from silver-containing wastewater and producing electric power using a microbial fuel cell, characterized in that a sodium phosphate salt compound is prepared and used as a nutrient solution for microorganisms, and perchlorate is used as a cathode electrolyte. . The method of claim 1,
The anode electrolyte is an electron donor per liter of 1 to 10 g of sodium acetate, 0.1 to 10 g of ammonium hydroxide, 0.001 to 1 g of potassium phosphate (mass ratio of nitrogen to phosphorus = 5: 2), 10 to 1000 mM of potassium perchlorate, 10 to 1000 mM 4- (2-hydroxyethyl) -1-piperazine-ethanesulfonic acid, 1-1000 mM 4- (2-hydroxyethyl) -1-piperazine-ethanesulfonic acid sodium salt and 0.1 to 20 g of It is composed of a yeast extract, the cathode electrolyte is characterized in that the perchlorate salt (KClO ₄ , NaClO ₄ ) is used as an electrolyte component in a ratio of 0.01 to 2M, to recover the silver metal from the silver-containing wastewater using a microbial fuel cell How to produce power at the same time. The method of claim 1,
The buffer solution is 2- [N-morholino] ethane sulfonate, piperazine-N, N'bis [2-ethanesulfonate], boric acid, 4-nitrophenol, cysteamine, 1H-imidazole, Pyridine, 2-pyridine amine, 2-chloro phenol, 3-chloro phenol, 2-nitro phenol, 4-nitro phenol, methoxy pyridine, 2,3-dimethyl pyridine, 2,4-dimethyl pyridine, 2 , 4,6-trimethyl pyridine, tyrosineamide, nicotine, N, N-diethyl aniline, N- (2-hydroxyethyl) piperazine-N '(4-butane sulfonic acid), N- (2-hydro A method for recovering silver metal from silver-containing wastewater and producing power using a microbial fuel cell, characterized by using at least one of oxyethyl) piperazine-N '(2-hydroxypropane sulfonic acid). . The method of claim 1,
A microbial fuel cell, wherein the microbial fuel cell is characterized in that the microbial fuel cell is used to recover the silver metal from the silver-containing wastewater and to generate electric power. The method of claim 1,
Microorganisms used in microbial fuel cells include Alpha-proteobacteria, Beta-proteobacteria, Delta-proteobacteria, Clostridia, Shewanella oneidensis MR-1, Shewanella oneidensis DSP-10, Shewanella putrefaciens SR-21, IR-1, MR-1, Geobacter sulfurreducens , Geobacter sulfurreducens KN400, Ochrobactrum anthropi YZ-1, Brevibacillus sp. PTH1, E. coli K12 HB101, Aeromonas hydrophila, Corynebacterium sp. Silver metal from wastewater containing silver using a microbial fuel cell, characterized by at least one selected from MFC03, Leptothrix discophora SP-6, Bacillus licheniformis, Bacillus thermoglucosidasius, Spirulina platensis, Bacillus subtilis, Enterococcus gallinarum, Acetobacter aceti, and Gluconobacter roseus A method of producing power at the same time that it recovers.

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