CN110265676B

CN110265676B - Method for leaching lithium cobaltate by using microbial fuel cell

Info

Publication number: CN110265676B
Application number: CN201910380181.8A
Authority: CN
Inventors: 刘维平; 孙扬; 徐杰
Original assignee: Jiangsu University of Technology
Current assignee: Jiangsu University of Technology
Priority date: 2019-05-08
Filing date: 2019-05-08
Publication date: 2021-07-02
Anticipated expiration: 2039-05-08
Also published as: CN110265676A

Abstract

The invention relates to a method for leaching lithium cobaltate by utilizing a microbial fuel cell, which comprises the steps of on one hand, modifying an anode by carbon powder to increase the surface activity of the anode and greatly quickening the biochemical reaction process of the surface of an electrode, on the other hand, adopting a sodium chloride solution to ensure that secondary pollution is not generated in a cathode chamber, combining the anode and the cathode to improve the electron transfer efficiency and the electric energy of an MFC system, wherein the open-circuit voltage of the constructed MFC is more than 0.724V, and the power density is more than 6822.76²The leaching rate of cobalt in the lithium cobaltate is more than 48 percent; the method disclosed by the invention is mild in operation condition, simple in process flow, free of secondary pollution, high in power generation performance, free of other chemical leaching reagents in the leaching process, and is an energy-saving and environment-friendly method for recycling the waste lithium battery by using waste to treat waste.

Description

Method for leaching lithium cobaltate by using microbial fuel cell

Technical Field

The invention relates to the technical field of waste lithium battery recovery, in particular to a method for leaching trivalent cobalt in lithium cobaltate and reducing the trivalent cobalt into divalent cobalt by using a microbial fuel cell.

Background

Lithium cobaltate is widely applied to the anode material of the lithium ion battery, and the lithium ion battery has the characteristics of high energy density, long service life, small volume, light weight, wide application range and the like, and is widely applied to the fields of electronic products, automobiles, aerospace and the like. Due to the influence of the update cycle of electronic products and the service life of lithium ion batteries, a large number of waste lithium batteries are produced in recent years. The waste lithium battery contains a large amount of heavy metal and toxic electrolyte, and the harmless treatment of the waste lithium battery and the recovery of valuable metal have important significance.

At present, scientific researchers at home and abroad develop a great deal of research and discussion on the problem of leaching lithium cobaltate from the anode material of the waste lithium battery. In the patent (200910059707.9), the lithium cobaltate waste battery positive electrode material is placed in a corrosion-resistant closed container, sulfuric acid and nitric acid are poured into the container, and the waste battery positive electrode material is leached under the condition that industrial pure oxygen is introduced into the container.

In the patent (CN200910304134.1), the anode active material obtained by splitting the waste lithium ion battery is leached by sulfuric acid-hydrogen peroxide mixed solution in a multi-stage countercurrent mode, and the residual residues are leached by hydrochloric acid. Although the method has high leaching efficiency, the method consumes a large amount of chemical reagents and is accompanied by Cl₂And the environment is polluted due to generation.

The patent (CN101871048A) separates aluminum sheet with alkali solution, and dissolves the fallen powder containing lithium cobaltate with sulfuric acid and then adopts Na₂SO₄Or Na₂SO₃Or adding concentrated sulfuric acid into Fe powder for reduction and dissolution, then adopting 3-6mol/L sulfuric acid for high-acid dissolution, and finally removing alkaline earth impurities by using a precipitator. The method has low consumption of auxiliary materials and high metal recovery rate, but the extraction and back extraction are needed to separate various metal solutions in the recovery process, the amount of the used acidic solution is large, and the treatment cost of various chemical reagents is high.

The patent (CN 201210432185.4) strips aluminum foil from the lithium battery positive electrode material by electrolysis, and obtains a positive electrode active material lithium cobalt leachate. Although the method has simple process, the method needs to provide an external voltage and consumes electric energy.

Most of the existing methods for recycling the waste lithium battery anode materials adopt methods such as acid leaching, organic acid leaching, alkali leaching and electrolysis to selectively or completely leach the anode lithium cobalt oxide, and the middle steps of extraction, precipitation, distillation and the like are accompanied, so that a large amount of chemical reagents are consumed, the problems of air pollution and waste liquid discharge are caused, the steps are complicated, and the operation requirement is high.

Disclosure of Invention

In order to solve the technical problems that chemical leaching reagents are used more frequently, the microbial fuel cell is low in electricity generation quantity and power density, and the leaching rate of cobalt is low in the prior art, a method for leaching lithium cobaltate by using the microbial fuel cell is provided.

The invention is realized by the following technical scheme, and the method for leaching lithium cobaltate by utilizing the microbial fuel cell comprises the following steps:

constructing a double-chamber microbial fuel cell (hereinafter referred to as MFC) which comprises a cathode chamber and an anode chamber, wherein the cathode chamber and the anode chamber are separated by a proton exchange membrane; the cathode chamber comprises a cathode made of carbon paper loaded with lithium cobaltate particles, the anode chamber comprises an anode made of carbon paper loaded with modified carbon powder, and a resistor is connected between the cathode and the anode; adding a NaCl solution into the cathode chamber in a full chamber, and inoculating acclimatized activated sludge in the anode chamber by taking the sodium acetate solution as a substrate; and the MFC runs to generate electricity to form an electrified loop, and the cobalt in the lithium cobaltate is leached.

Further, the carbon paper is pretreated and then loaded; the pretreatment process comprises the following steps: it was placed in a concentration of 30% H₂O₂Soaking in the solution for 15-30 min to remove impurities on the surface of the carbon paper, repeatedly washing the surface of the carbon paper with water after soaking until the pH value of the surface of the carbon paper is constant, and finally drying the carbon paper.

Further, the preparation method of the carbon paper loaded with lithium cobaltate particles comprises the following steps: and mixing the lithium cobaltate particles with the adhesive, stirring under ultrasonic waves to form a first dispersion, coating the first dispersion on the surface of the carbon paper, and drying to obtain the carbon paper loaded with the lithium cobaltate particles.

Wherein the density of the lithium cobaltate particles in the first dispersion is 0.125-0.25 g/mL.

Further, the preparation method of the carbon paper modified by the loaded carbon powder comprises the following steps: and mixing carbon powder and a bonding agent, stirring under ultrasonic wave to form a second dispersion, coating the second dispersion on the surface of the carbon paper, and drying to obtain the carbon paper modified by the loaded carbon powder.

Wherein the density of the carbon powder in the second dispersion is 0.125-0.25 g/mL.

Wherein the adhesive is one of polytetrafluoroethylene emulsion, water-based epoxy resin emulsion and water glass with the mass fraction of 30-50%. The adhesive needs to meet the characteristics that after the carbon powder or lithium cobaltate is well adhered to the carbon paper, the carbon powder or lithium cobaltate can be insoluble in water, the thickness of the carbon paper is thin after curing, and the carbon paper can be tightly contacted with the carbon powder or lithium cobaltate.

Further, the distance between the anode and the cathode is 4-8 cm. Too large or too small an electrode spacing has an effect on the electricity generation performance of the system, and can affect the transfer of protons and electrons.

Further, the concentration of the NaCl solution is 4-5 g/L; the concentration of the sodium acetate solution is 2 g/L.

Further, the domesticated activated sludge is obtained by domesticating in a domestication liquid at the normal temperature of 25 ℃ in a dark and anaerobic environment for 6-8 days; the inoculation amount of the domesticated activated sludge in the anode chamber is 0.3-0.35 times of the volume of the anode chamber, and the volume ratio of the domesticated activated sludge to the substrate is 1: 2. The domestication is to obtain the electrogenic strains under certain conditions, the environmental factors influencing the microbial electrogenesis comprise temperature, pH, dissolved oxygen and concentration, the electrogenic bacteria activity is higher at the normal temperature of 25 ℃, and the survival rate can be influenced when the temperature is too low or too high; secondly, the process of culturing the strains should avoid illumination; the anaerobic state is maintained in order to keep the dissolved oxygen and the redox potential at a low level.

Wherein each 1L of the domestication solution contains: 0.2 to 0.4g of sucrose, 0.2 to 0.4g of monopotassium phosphate, 0.2 to 0.4g of dipotassium phosphate, 0.1 to 0.2g of triammonium citrate, 0.1 to 0.3g of sodium chloride, 0.3 to 0.4g of ammonium chloride, 0.3 to 0.4g of magnesium chloride and 0.1 to 0.2g of calcium chloride.

The beneficial technical effects are as follows: according to the invention, on one hand, the surface activity of the anode is increased through carbon powder modification, the biochemical reaction process of the electrode surface is greatly accelerated, on the other hand, secondary pollution is not generated by adopting a sodium chloride solution in the cathode chamber, the electron transfer efficiency and the electric energy of an MFC system are improved by combining the anode and the cathode, the open-circuit voltage of the constructed MFC is greater than 0.724V, and the power density is greater than 6822.76mW/m²The leaching rate of cobalt in the lithium cobaltate is more than 48 percent; according to the carbon paper of the modified anode by using the carbon powder, on one hand, microorganisms in the activated sludge degrade organic matters and release electrons to enable electrogenic bacteria to accumulate in the modified anode, the modified anode is more favorable for the growth of the microorganisms, so that the generated electrons are more easily transferred to the surface of the anode, chemical energy is converted into electric energy, and cobalt in the lithium cobaltate serving as the anode material of the waste lithium battery is leached; the other partyThe method disclosed by the invention is mild in operation condition, simple in process flow, free of secondary pollution, high in power generation performance, free of other chemical leaching reagents in the leaching process, and is an energy-saving and environment-friendly method for recycling the waste lithium battery by using waste to treat waste.

Drawings

FIG. 1 is a schematic diagram of an MFC device constructed by the method of the present invention.

Fig. 2 is a graph showing the voltage change with time of the microbial fuel cells constructed in example 1 and comparative example 1.

Fig. 3 is a power density graph of the microbial fuel cells constructed in example 1 and comparative example 1.

Fig. 4 is SEM images of the surfaces of the anode made of the modified carbon paper loaded with carbon powder in example 1 and the anode made of the carbon paper not loaded with carbon powder in comparative example 1.

Fig. 5 is a graph showing the pore size distribution of the anode made of the modified carbon paper loaded with carbon powder in example 1 and the anode made of the carbon paper not loaded with carbon powder in comparative example 1.

Detailed Description

The invention is further described below with reference to the figures and specific examples, without limiting the scope of the invention.

Example 1

(1) Modification of carbon paper:

preprocessing carbon paper: selecting 0.2cm thick 6cm x 6cm carbon paper as anode and cathode electrode material, placing the carbon paper in 30% H₂O₂Soaking in the solution for 20min to remove impurities on the surface, repeatedly washing the surface with deionized water until the pH value of the surface is constant, and drying for later use.

Modification: a. preparing an anode: pouring 0.5g of 200-mesh carbon powder and 4mL of polytetrafluoroethylene emulsion with the mass fraction of 30% into a beaker, placing the beaker into an ultrasonic cleaning machine, ultrasonically stirring and dispersing for 10min until a sample is sticky to form a second dispersion body, uniformly coating the second dispersion body on the surface of carbon paper, and adopting a drying and bonding method until the carbon powder is uniformly and stably loaded on the surface of the carbon paper to prepare carbon powder-loaded modified carbon paper which is used as an anode. b. Preparing a cathode: dispersing 0.5g of lithium cobaltate powder in 4mL of polytetrafluoroethylene emulsion with the mass fraction of 30% by the same method to form a first dispersion, and loading the first dispersion on the carbon paper treated by the step I to prepare the carbon paper loaded with lithium cobaltate particles and using the carbon paper as a cathode.

(2) Constructing a microbial fuel cell:

the schematic diagram of the MFC device is shown in FIG. 1, and comprises a cathode chamber and an anode chamber, wherein the effective volumes of the cathode chamber and the anode chamber are both 500mL, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and the effective area of the proton exchange membrane is 9cm²(ii) a The cathode chamber comprises a cathode made of carbon paper loaded with lithium cobaltate particles, the anode chamber comprises an anode made of carbon paper loaded with carbon powder modification, and only a resistor is connected between the cathode and the anode; 500mL of NaCl solution with the concentration of 4g/L is added into the cathode chamber, and 160mL of domesticated activated sludge is inoculated in the anode chamber by using 320mL of sodium acetate solution with the concentration of 2g/L as a substrate; the distance between the two electrodes is 6 cm; and the MFC starts to operate to form an electrifying loop, and the cobalt in the lithium cobaltate starts to leach.

Wherein the domesticated activated sludge is obtained by domesticating in domesticating liquid at normal temperature of 25 ℃ for 7 days in a dark anaerobic environment; wherein each 1L of the domestication solution contains: 0.38g of sucrose, 0.21g of monopotassium phosphate, 0.21g of dipotassium phosphate, 0.12g of triammonium citrate, 0.17g of sodium chloride, 0.4g of ammonium chloride, 0.4g of magnesium chloride and 0.12g of calcium chloride.

The MFC works on the principle as shown in FIG. 1, and utilizes the microbes in the acclimatized activated sludge to act on the anode substrate and oxidize the anode substrate to generate electrons e^－Proton H⁺And a metabolite; generation of e^－Transferring from the microbial cells to the surface of the anode to reduce the electrode; e.g. of the type^－To the cathode via an external circuit; generation of H⁺The proton exchange membrane in the anode chamber and the cathode chamber is used for transferring to the cathode chamber and reaches the surface of the cathode; h transmitted from the cathode and the lithium cobaltate particles on the surface of the cathode in the cathode chamber⁺And e^－And carrying out reduction reaction on the surface of the cathode to form a complete current loop.

Measuring open circuit voltage after MFC operation and calculating workSpecific density and determination of Co in leach solution²⁺And (4) concentration.

Comparative example 1

The comparative example is the same as the preparation method of example 1, and is different in that carbon powder is not added in (1) and (a), and carbon paper (collectively referred to as unmodified carbon paper) treated in (1) is directly applied to an anode to prepare the microbial fuel cell.

Measuring open circuit voltage after MFC operation and calculating power density and determining Co in leaching solution²⁺The concentrations, data are shown in table 1.

TABLE 1 data for example 1 and comparative example 1

	Open circuit voltage (V)	Power Density (mW/m)²)	Co²⁺Concentration (mg/L)	Co²⁺Leaching rate (%)
					Example 1	0.724	6822.76	479.6	48
Comparative example 1	0.569	4406.46	326.5	33

After the MFC was started, the open circuit voltage of example 1 and comparative example 1 was measured, and the data of example 1 and comparative example 1 are shown in fig. 2, and the voltage of MFC reached a stable value after 2 to 3 days, at this time, the maximum open circuit voltage of MFC composed of the carbon paper electrode that was not modified in comparative example 1 was 0.569V, and the maximum open circuit voltage of MFC composed of the carbon paper electrode that was modified with the carbon powder in example 1 was 0.724V. The open circuit voltage after modification is 1.27 times that without modification.

The power densities of example 1, comparative example 1 and comparative example 2 were calculated by a steady state discharge method after measuring the voltage, the data of example 1 and comparative example 1 are shown in FIG. 3, and it can be seen from FIG. 3 that the MFC maximum power density composed of the carbon powder modified carbon paper electrode of example 1 is 6822.76mW/m²Comparative example 1 the maximum power density of the MFC consisting of the unmodified carbon paper electrode was 4406.46mW/m². The power density after modification was 1.55 times that without modification.

Co in lithium cobaltate after MFC operation³⁺Leaching is started and after about 4-5 hours the material is reduced to stable Co²⁺Measuring Co in solution by atomic absorption spectrometry²⁺Concentration, measured as the catholyte Co of the MFC consisting of the unmodified carbon paper electrode in comparative example 1²⁺The concentration is 326.5mg/L, and the leaching rate is 33 percent; example 1 carbon powder modified carbon paper electrode consisting of MFC catholyte Co²⁺The concentration is 479.6mg/L, the leaching rate is 48 percent, and the leaching rate after modification is 1.45 times that after modification.

In the electrode made of carbon powder modified carbon paper in example 1 and the electrode made of unmodified carbon paper in comparative example 1, SEM images of the surfaces of the two are shown in fig. 4, the electrode made of unmodified carbon paper in fig. 4(a) has smaller surface roughness and less and smoother wrinkle degree, but after carbon powder is loaded on the surface thereof by a drying and bonding method, the surface in fig. 4(b) shows a stacking morphology of a plurality of fine particles, the stacked small particles have compact structures, and a large number of pores are formed between the stacked small particles, so that the carbon powder modified carbon paper is superior to the unmodified carbon paper in the aspects of pore structure, surface roughness and wrinkle degree, and is more favorable for attachment of microorganisms to enable the carbon powder modified carbon paper to show higher activity.

The pore size distribution of the electrode made of carbon paper modified with carbon powder of example 1 and the electrode made of unmodified carbon paper of comparative example 1 were observed, and as shown in FIG. 5, it can be seen from FIG. 5(a) that the specific surface area of the electrode of unmodified carbon paper is 230.331m²Per g, pore volume of 0.209cm³(g), from FIG. 5(b), it is known that the specific surface area of the carbon paper electrode modified by the supported carbon powder is 917.610m²Per g, pore volume of 0.668cm³The modification of the carbon powder can increase the specific surface area and pore volume of the carbon paper, is more favorable for the attachment of microorganisms to enable the carbon paper to show higher activity, has lower cost and is more favorable for the industrial application of MFC.

Example 2

(1) Modification of carbon paper:

preprocessing carbon paper: selecting 0.2cm thick 6cm x 6cm carbon paper as anode and cathode electrode material, placing the carbon paper in 30% H₂O₂Soaking in the solution for 15min to remove impurities on the surface, repeatedly washing the surface with deionized water until the pH value of the surface is constant, and drying for later use.

Modification: a. preparing an anode: 0.5g of 200-mesh carbon powder and 2mL of water glass with the mass fraction of 40% are poured into a beaker, the beaker is placed into an ultrasonic cleaning machine to be ultrasonically stirred and dispersed until a sample is sticky to form a second dispersion body, the second dispersion body is uniformly coated on the surface of carbon paper, a drying and bonding method is adopted until the carbon powder is uniformly and stably loaded on the surface of the carbon paper, and the carbon paper loaded with the carbon powder modification is prepared and used as an anode. b. Preparing a cathode: dispersing 0.5g of lithium cobaltate powder in 2mL of water glass with the mass fraction of 40% by the same method to form a first dispersion, and loading the first dispersion on the carbon paper treated by the first step to prepare the carbon paper loaded with lithium cobaltate particles and using the carbon paper as a cathode.

(2) Constructing a microbial fuel cell:

the schematic diagram of the MFC device is shown in FIG. 1, and comprises a cathode chamber and an anode chamber, the effective volumes of the two chambers are both 500mL, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and the effective area of the proton exchange membraneIs 9cm²(ii) a The cathode chamber comprises a cathode made of carbon paper loaded with lithium cobaltate particles, the anode chamber comprises an anode made of carbon paper loaded with carbon powder modification, and only a resistor is connected between the cathode and the anode; 500mL of NaCl solution with the concentration of 4.5g/L is added into the cathode chamber, and 320mL of sodium acetate solution with the concentration of 2g/L is used as a substrate and inoculated with 160mL of acclimatized activated sludge in the anode chamber; the distance between the two electrodes is 4 cm; and the MFC starts to operate to form an electrifying loop, and the cobalt in the lithium cobaltate starts to leach.

Wherein the domesticated activated sludge is obtained by domesticating in domesticating liquid at normal temperature of 25 ℃ for 7 days in a dark anaerobic environment; wherein each 1L of the domestication solution contains: 0.2g of sucrose, 0.4g of monopotassium phosphate, 0.4g of dipotassium phosphate, 0.1g of triammonium citrate, 0.1g of sodium chloride, 0.3g of ammonium chloride, 0.3g of magnesium chloride and 0.1g of calcium chloride.

The maximum open circuit voltage of the embodiment is 0.731V, and the maximum power density is 6870.32mW/m²(ii) a Co in leaching solution²⁺The leaching rate was 49%.

Example 3

(1) Modification of carbon paper:

preprocessing carbon paper: selecting 0.2cm thick 6cm x 6cm carbon paper as anode and cathode electrode material, placing the carbon paper in 30% H₂O₂Soaking in the solution for 30min to remove impurities on the surface, repeatedly washing the surface with deionized water until the pH value of the surface is constant, and drying for later use.

Modification: a. preparing an anode: pouring 0.5g of 200-mesh carbon powder and 3mL of 50% aqueous epoxy resin emulsion into a beaker, placing the beaker into an ultrasonic cleaning machine, ultrasonically stirring and dispersing until a sample is sticky to form a second dispersion, uniformly coating the second dispersion on the surface of carbon paper, and adopting a drying and bonding method until the carbon powder is uniformly and stably loaded on the surface of the carbon paper to prepare carbon powder-loaded modified carbon paper which is used as an anode. b. Preparing a cathode: dispersing 0.5g of lithium cobaltate powder in 3mL of 50% aqueous epoxy resin emulsion by the same method to form a first dispersion, and loading the first dispersion on the carbon paper treated by the step (i) to prepare the carbon paper loaded with lithium cobaltate particles and using the carbon paper as a cathode.

(2) Constructing a microbial fuel cell:

the schematic diagram of the MFC device is shown in FIG. 1, and comprises a cathode chamber and an anode chamber, wherein the effective volumes of the cathode chamber and the anode chamber are both 500mL, the cathode chamber and the anode chamber are separated by a proton exchange membrane, and the effective area of the proton exchange membrane is 9cm²(ii) a The cathode chamber comprises a cathode made of carbon paper loaded with lithium cobaltate particles, the anode chamber comprises an anode made of carbon paper loaded with carbon powder modification, and only a resistor is connected between the cathode and the anode; 500mL of NaCl solution with the concentration of 5g/L is added into the cathode chamber, and 160mL of domesticated activated sludge is inoculated in the anode chamber by using 320mL of sodium acetate solution with the concentration of 2g/L as a substrate; the distance between the two electrodes is 8 cm; and the MFC starts to operate to form an electrifying loop, and the cobalt in the lithium cobaltate starts to leach.

Wherein the domesticated activated sludge is obtained by domesticating in domesticating liquid at normal temperature of 25 ℃ for 7 days in a dark anaerobic environment; wherein each 1L of the domestication solution contains: 0.4g of sucrose, 0.3g of monopotassium phosphate, 0.3g of dipotassium phosphate, 0.2g of triammonium citrate, 0.3g of sodium chloride, 0.3g of ammonium chloride, 0.3g of magnesium chloride and 0.2g of calcium chloride.

The voltage measurement and the power density calculation were carried out by a steady-state discharge method, the maximum open-circuit voltage of this example was 0.736V, and the maximum power density was 6893.11mW/m²(ii) a Co in leaching solution²⁺The leaching rate was 49%.

Comparative example 2

2 sets of double-chamber MFC devices were constructed in the same way as in example 3, except that: the concentration of NaCl solution in the cathode chamber is 3g/L and 6g/L respectively.

By steady state discharge method, voltage measurement and Co calculation were carried out²⁺The leaching rate of (A).

The data for examples 1-3 and comparative example 2 are shown in Table 2.

TABLE 2 data for examples 1-3 and comparative example 2

As can be seen from the data in Table 2, the NaCl solution concentration can affect the electrogenesis and Co production of the microorganisms²⁺Leaching rate, concentration of NaCl solution in the range of 4-5 g/L, open-circuit voltage of MFC and Co²⁺The leaching rate is high, while in comparative example 2, too low concentration of NaCl causes low concentration of ions in the cathode chamber, affecting electron transfer, and thus affecting the leaching rate, while high concentration of salt affects microbial tolerance of the biofilm (a membranous structure formed on the electrode when the electrogenic microbes undergo a bioelectrochemical reaction), affecting biological activity, and thus causing low electrogenesis and leaching rate. In the existing research, phosphate buffer solution is adopted as MFC catholyte to improve the conductivity, but the addition of the phosphate buffer solution can increase the content of phosphorus in water, so that secondary pollution to water is caused; the invention adopts NaCl solution as catholyte, can improve the electricity generation of microorganisms in a proper concentration range, improves the electron transfer rate, and further ensures the open-circuit voltage and Co of the MFC²⁺The leaching rate is at a higher level.

Comparative example 3

3 groups of double-chamber MFC devices are built, the effective volume of the device is 500mL, the building method is the same as that of the embodiment 3, and the difference is that: the volume ratio of the activated sludge to the anode substrate in the anode chamber is 1:1, 1:3 and 1:4 respectively, and the influence of the sludge concentration on the power generation performance of the MFC is discussed.

The voltage measurement was performed by the steady state discharge method.

The open circuit voltage data for example 3 and comparative example 3 are shown in table 3.

Table 3 open circuit voltage of MFC built up in example 3 and comparative example 3

The results of example 3 and comparative example 3 show that: the maximum open circuit voltage is 0.403V when the sludge-to-substrate volume ratio is 1:4, 0.511V when the sludge-to-substrate volume ratio is 1:3, and 0.736V when the sludge-to-substrate volume ratio is 1:2, whereby it can be obtained that the maximum open circuit voltage increases with the increase in the sludge concentration within a suitable range because more electricity-producing bacteria can be utilized with the increase in the sludge concentration. However, the maximum open circuit voltage was 0.704V at a sludge to substrate volume ratio of 1:1 and did not increase further, probably because the substrate content decreased with increasing sludge concentration, resulting in a voltage drop.

Claims

1. A method for leaching lithium cobaltate by using a microbial fuel cell is characterized by comprising the following steps:

constructing a double-chamber microbial fuel cell, which comprises a cathode chamber and an anode chamber, wherein the cathode chamber and the anode chamber are separated by a proton exchange membrane;

the cathode chamber comprises a cathode made of carbon paper loaded with lithium cobaltate particles, the anode chamber comprises an anode made of carbon paper loaded with modified carbon powder, and a resistor is connected between the cathode and the anode;

adding a NaCl solution into the cathode chamber in a full chamber, inoculating domesticated activated sludge in the anode chamber by taking a sodium acetate solution as a substrate, enabling the two-chamber microbial fuel cell to operate to generate electricity to form an electrified loop, and leaching cobalt in lithium cobaltate; the concentration of the NaCl solution is 4-5 g/L; the concentration of the sodium acetate solution is 2 g/L;

the carbon paper is pretreated and then loaded; the pretreatment process comprises the following steps: placing the carbon paper in H with the concentration of 30%₂O₂Soaking in the solution for 15-30 min to remove impurities on the surface of the carbon paper, repeatedly washing the surface of the carbon paper with water after soaking until the pH value of the surface of the carbon paper is constant, and finally drying the carbon paper for later use;

the preparation method of the carbon paper loaded with the lithium cobaltate particles comprises the following steps: mixing lithium cobaltate particles with a binder, stirring under ultrasonic waves to form a first dispersion, coating the first dispersion on the surface of carbon paper, and drying to obtain carbon paper loaded with the lithium cobaltate particles;

the preparation method of the carbon paper modified by the loaded carbon powder comprises the following steps: mixing carbon powder and an adhesive, stirring under ultrasonic wave to form a second dispersion, coating the second dispersion on the surface of carbon paper, and drying to obtain carbon powder-loaded modified carbon paper;

the adhesive is one of polytetrafluoroethylene emulsion, water-based epoxy resin and water glass with the mass fraction of 30-50%.

2. The method for leaching lithium cobaltate by using the microbial fuel cell as claimed in claim 1, wherein the density of the lithium cobaltate particles in the first dispersion is 0.125-0.25 g/mL.

3. The method for leaching lithium cobaltate by using the microbial fuel cell as claimed in claim 1, wherein the density of the carbon powder in the second dispersion is 0.125-0.25 g/mL.

4. The method for leaching lithium cobaltate by using the microbial fuel cell as claimed in claim 1, wherein the distance between the anode and the cathode is 4-8 cm.

5. The method for leaching lithium cobaltate by using the microbial fuel cell as claimed in claim 1, wherein the acclimated activated sludge is obtained by acclimatization in an acclimatization solution at a normal temperature of 25 ℃ in a dark environment for 6-8 days; the inoculation amount of the domesticated activated sludge in the anode chamber is 0.3-0.35 times of the effective volume of the anode chamber, and the volume ratio of the domesticated activated sludge to the substrate is 1: 2.

6. The method for leaching lithium cobaltate by using the microbial fuel cell as claimed in claim 5, wherein each 1L of the acclimation solution contains: 0.2 to 0.4g of sucrose, 0.2 to 0.4g of monopotassium phosphate, 0.2 to 0.4g of dipotassium phosphate, 0.1 to 0.2g of triammonium citrate, 0.1 to 0.3g of sodium chloride, 0.3 to 0.4g of ammonium chloride, 0.3 to 0.4g of magnesium chloride and 0.1 to 0.2g of calcium chloride.