Lithium cobalt oxide battery recovery system and method based on electric field driven membrane distillation

Abstract

The invention relates to a lithium cobalt oxide battery recovery system and method based on electric field driven membrane distillation, and belongs to the technical field of battery material recovery and resource regeneration. In order to solve the problems of long flow, high acid and alkali consumption and low metal separation efficiency in the existing wet recovery process, efficient reduction of Co (NH3) 6 and CoCOdirectional precipitation are realized through the action of a direct current or pulsed electric field, and meanwhile, crystallization separation of lithium and cyclic regeneration of an ammonia medium are realized by combining thermal decomposition driving and membrane distillation technologies. The device integrates an electrochemical reactor, a membrane separation module and a dynamic regulation and control system, micro-groove enhanced mass transfer, electrodes and multi-parameter linkage feedback control are adopted, the metal direct recovery rate (Co is larger than or equal to 80%, and Li is larger than or equal to 80%) is remarkably increased, and comprehensive energy consumption is reduced. The method is particularly suitable for efficient and green recovery of the black powder of the power battery, and has the technical advantages of short flow, high medium circulation rate and high product purity.

Description

Technical Field

[0001] The present invention belongs to the field of battery material recovery and green metallurgy, and specifically relates to a method for efficiently recovering valuable metals from retired lithium cobalt oxide batteries by coupling electrochemical reduction with hydrophobic membrane separation technology. The method, based on a thermal-electric field synergistic drive strategy, achieves the selective extraction and separation of cobalt (Co) and lithium (Li), while simultaneously completing the cyclic regeneration of the ammonia medium. The technical solution covers key processes such as directional ion migration regulation, complex electrochemical reduction, gas film mass transfer separation, and lithium salt crystallization, and is suitable for the short-process recovery of valuable metals (Co, Li) from retired power batteries and consumer electronic batteries. Background Art

[0002] The current hydrometallurgical recovery process for retired lithium cobalt oxide batteries generally uses a strong acid system (such as sulfuric acid and hydrochloric acid) to leach valuable metals. The reaction conditions are severe and it is easy to produce sulfur / chlorine-containing waste gas and heavy metal waste liquid, facing severe environmental compatibility challenges. Although the ammonia leaching method is selective for leaching cobalt (forming Co(NH3)6 3+ While ammonia can be recycled as a green resource, offering green advantages, subsequent cobalt-lithium separation relies on multi-stage precipitation or solvent extraction, a lengthy process prone to impurities. Furthermore, the recovery of the ammonia medium relies on traditional distillation or gas stripping techniques, which pose issues such as high energy consumption and the risk of ammonia escape. Existing technologies have yet to effectively address the synergistic control challenges of direct electrochemical reduction of cobalt complexes, simultaneous lithium enrichment, and ammonia regeneration in ammonia leaching systems, limiting the process's potential for industrial application. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the problems of lengthy process, high acid and alkali consumption and low metal separation efficiency in the wet recovery process, the purpose of the present invention is to provide a lithium cobalt oxide battery recovery system and method based on electric field driven membrane distillation. The method selectively dissolves cobalt through an ammonia leaching system and forms hexaammine cobalt (Co(NH3)6 3+ ) complex ions, lithium in free state Li + In the membrane distillation system, a negative electrode plate (such as IrO2-Ti mesh electrode) and a positive electrode plate (such as Pt electrode) are placed in parallel in the feed liquid side channel, and a DC electric field (50-200 V / m) is applied to drive Co(NH3)6 3+ A reduction reaction occurs at the negative electrode interface (potential -0.8 to -1.2 V vs. SHE), generating Co in situ 2+ And the CO3 released by thermal decomposition (50-70℃) of ammonium bicarbonate (NH4HCO3) in the liquid 2- Combine to form high-purity CoCO3 precipitation; after the cobalt is completely precipitated, the remaining CO3 2- Directly with Li +Combined with the rapid crystallization of Li2CO3, the pH is controlled (pH ≥ 9.5). At the same time, the NH3 / NH4 + Under the synergistic effect of the electric field and the proton gradient (ΔpH ≥ 8), it migrates toward the acid side (containing 0.1-0.2 mol / L H2SO4) through the hydrophobic PTFE membrane (pore size 0.22-0.45 μm, porosity ≥ 80%) and is regenerated into (NH4)2SO4.

[0004] The recovery system adopted in the present invention adopts a single-sided integrated electrode design, eliminates the traditional anode and cathode chamber separation structure, and achieves direct recovery rates of cobalt and lithium metals of 98.5% and 96.8% respectively through gradient temperature control (50-70°C on the liquid side and 10-20°C on the acid side) coupled with electric field-membrane mass transfer, an ammonia recycling rate of ≥93% and a comprehensive energy consumption reduction of 55% to 62%.

[0005] Technical solution: In order to achieve the above-mentioned invention objectives, the present invention adopts the following technical solution:

[0006] A lithium cobalt oxide battery recovery method based on electric field driven membrane distillation, the steps are as follows:

[0007] Step 1: Ammonia leaching selective dissolution

[0008] The lithium cobalt oxide (LiCoO2) cathode material was crushed and reacted with a mixed solution containing ammonia (NH3·H2O), ammonium bicarbonate (NH4HCO3) and sodium sulfite (ammonia concentration 3-5 mol / L, NH4HCO3 concentration 1-3 mol / L, sodium sulfite concentration 0.5-1 mol / L) under ultrasound-assisted conditions for 24-48 hours. Cobalt was converted to Co(NH3)6 3+ The complex ions are dissolved and lithium is free in the liquid in the form of Li+. The reaction equation is as follows:

[0009]

[0010] Step 2: Electrochemical reduction and cobalt precipitation

[0011] The ammonia-impregnated feed solution was introduced into the feed solution side channel of the direct contact membrane distillation system. A negative electrode plate (IrO2-Ti mesh electrode) and a positive electrode plate (Pt electrode) were placed in parallel in the channel. The following electric field conditions were applied:

[0012] (1) DC mode: electric field strength 50~200V / m, cathode potential -0.8~-1.2V (vs.SHE), driving Co(NH3)6 3+ A non-equilibrium reduction reaction occurs at the negative electrode interface:

[0013]

[0014] (2) Pulse mode: pulse frequency 10-50Hz, duty cycle 20%-80%, peak electric field strength 500-300V / m, through intermittent high field strength acceleration Reduction kinetics.

[0015] Step 3: Simultaneous thermal decomposition and precipitation

[0016] Maintain the liquid temperature at 50-70℃ and a certain pH environment to promote the decomposition of NH4HCO3 to generate NH3 and

[0017]

[0018] Co 2+ and Combined to form high purity CoCO3 precipitate (purity ≥ 99.5%, see the actual picture Figure 1 ), and the precipitate was recovered by centrifugation.

[0019]

[0020] Step 4: Ammonia recovery through membrane

[0021] NH4 on the liquid side + Deprotonation (NH4 + →NH3+H + ), while the thermally decomposed NH3, driven by the concentration difference, migrates to the acid side through the hydrophobic PTFE membrane (pore size 0.22-0.45μm, porosity ≥80%). A 0.1-0.2mol / L H2SO4 solution is introduced into the acid side channel with a flow rate controlled at 0.5-2.0m / s, flushing the membrane surface in a turbulent state (Re≥3000), rapidly absorbing NH3 to generate (NH4)2SO4 (see the ammonia recovery mass transfer flux at different temperatures for details). Figure 2 shown):

[0022] NH3+H2SO4→(NH4)2SO4

[0023] Step 5: Lithium crystal precipitation recovery

[0024] After separating the cobalt, the pH of the liquid was adjusted to 10-12, and the residual Or introduce CO2 gas to generate With Li + The reaction generates Li2CO3 crystals (Li2CO3 crystals and XRD analysis diagram, see Figure 3 shown):

[0025]

[0026] A lithium cobalt oxide battery recovery system based on electric field driven membrane distillation, which mainly includes:

[0027] (1) Membrane assembly: The feed side and the acid side are directly separated by a hydrophobic PTFE membrane, with a membrane flux of 10 to 30 L / (m 2 h), a micro-groove array (depth 0.1-0.5 mm, spacing 1-3 mm) is designed on the inner wall of the acid-side channel to disrupt laminar flow and enhance NH3 absorption efficiency.

[0028] (2) Electrode system: The negative electrode uses an IrO2-Ti mesh electrode (IrO2 loading 50-200nm), catalyzing Co(NH3)6 3+ Redox reaction; the positive electrode uses a mesh Pt electrode.

[0029] (3) Dynamic control module

[0030] Temperature control: 50-60°C on the liquid side (to promote decomposition and mass transfer), 25-35°C on the acid side (to maintain absorption efficiency);

[0031] Electric field-flow rate linkage: When the flow rate on the acid side is ≥1.5m / s, it automatically switches to the pulsed electric field mode (frequency 30-50Hz, duty cycle 50%-80%) to match the NH3 transmembrane flux;

[0032] Gas-liquid separation: A gas-liquid separator is set at the acid side outlet to capture unreacted NH3 and return it to the acid side for cyclic absorption.

[0033] The optimization of the process parameters of the lithium cobalt oxide battery recycling system based on electric field driven membrane distillation is summarized in Table 1:

[0034] Table 1

[0035]

[0036]

[0037] Beneficial effects:

[0038] (1) The present invention realizes Co(NH3)6 by direct current or pulse electric field 3+ The efficient reduction and directional precipitation of CoCO3 are achieved by combining thermal decomposition drive and membrane distillation technology to realize the crystallization separation of lithium and the recycling regeneration of ammonia medium.

[0039] (2) The present invention adopts an integrated electrochemical reactor, a membrane separation module and a dynamic control system, and adopts micro-grooves to enhance mass transfer, electrodes and multi-parameter linkage feedback control, which significantly improves the direct recovery rate of metals (Co ≥ 80%, Li ≥ 80%) and reduces the overall energy consumption.

[0040] (3) The present invention is particularly suitable for the efficient and green recovery of power battery black powder, and has the technical advantages of short process, high medium circulation rate (NH3≥85%) and product purity (CoCO3≥90%, Li2CO3≥90%). BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a real picture of cobalt carbonate precipitation.

[0042] Figure 2 Ammonia recovery mass transfer flux changes with temperature.

[0043] Figure 3 XRD analysis diagram of Li2CO3.

[0044] Figure 4 This is a structural schematic diagram of a lithium cobalt oxide battery recovery system based on electric field driven membrane distillation of the present invention.

[0045] Explanation of main reference numerals: 1- pump, 2- feed liquid bottle, 3- water bath, 4- titanium mesh electrode, 5- platinum mesh electrode, 6- PTFE membrane, 7- permeate side bottle, 8- balance, 9- power supply, 10- pump, 11- condenser. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings:

[0047] Reference Figure 4 As shown, a lithium cobalt oxide battery recycling system based on electric field driven membrane distillation mainly includes:

[0048] (1) A direct contact membrane distillation unit consisting of a feed side channel and an acid side channel, which are separated by a hydrophobic PTFE membrane (pore size 0.22-0.45 μm, porosity ≥80%);

[0049] (2) The negative electrode plate (IrO2-Ti mesh electrode) and the positive electrode plate (Pt electrode) are integrated in the liquid side channel, with a spacing of 5 to 20 mm; the electrode size is 3x3 cm and the thickness is 0.1 mm, which is easy to install in the device.

[0050] (3) Power module, supporting DC or pulsed electric field output (DC intensity 50-200 V / m; pulse parameters: frequency 10-50 Hz, duty cycle 20%-80%);

[0051] (4) Acid side circulation pump drives the sulfuric acid solution to flow tangentially along the membrane surface at a flow rate of 0.5 to 2.0 m / s to form a dynamically renewed liquid film.

[0052] Example 1:

[0053] A lithium cobalt oxide battery recovery method based on electric field driven membrane distillation comprises the following steps:

[0054] Step 1: Ammonia leaching selective dissolution

[0055] The discarded lithium cobalt oxide (LiCoO2) cathode material was mechanically crushed to a particle size of ≤100 μm, mixed with ammonia-ammonium bicarbonate mixture (NH3 concentration 4 mol / L, NH4HCO3 concentration 1 mol / L, reducing agent (the reducing agent used in the present invention is sodium sulfite) at a solid-liquid ratio of 10 (g / L), placed in a reactor, controlled at a temperature of 80±2°C, a stirring rate of 400 rpm, and reacted for 30 hours. After dissolution, the cobalt in the feed solution was converted to Co(NH3)6 3+ It exists in the form of lithium, lithium is free in the form of Li+, and the cobalt dissolution rate is ≥80%.

[0056] Step 2: Electrochemical reduction and cobalt precipitation

[0057] The ammonia soaked liquid was introduced into the liquid side channel (flow rate 1.2 m / s) of the electrochemical membrane distillation reactor. The positive and negative plates were arranged in parallel in the channel. The reactor parameters were as follows:

[0058] ①Electrode system: negative electrode: IrO2-Ti mesh electrode (IrO2 coating thickness 150nm, pore size 1.5mm); positive electrode: mesh Pt electrode;

[0059] ② Electric field conditions: DC mode: electric field strength 150 V / m, cathode potential -1.0 V (vs. SHE); switch to pulse mode: frequency 40 Hz, duty cycle 60%, peak electric field strength 250 V / m.

[0060] Step 3: Synchronous thermal decomposition and precipitation: Maintain the liquid temperature at 60 ° C, NH4HCO3 decomposes to produce CO32-, Co 2+ Combined with CO32- to form CoCO3 precipitate, the precipitate was centrifuged (rotation speed 4000 rpm, 15 minutes) to obtain CoCO3 powder with a purity of 90%.

[0061] Step 4: Lithium crystallization and ammonia recovery

[0062] ① Lithium recovery: adjust the pH of the liquid to above 9, add seed crystals (Li2CO3 microcrystals), stir and crystallize for 2 hours, and filter to obtain Li2CO3 crystals (purity 99.3%, direct yield 96.5%);

[0063] ② Directed migration of ammonia: Driven by the transmembrane pressure difference and proton gradient (pH feed side = 9.0, acid side = 1.0), NH3 on the feed side migrates to the acid side through the PTFE membrane (pore size 0.22μm, porosity 85%). 0.1mol / L H2SO4 solution (flow rate 1.8m / s, Re = 3500) is introduced into the acid side to absorb NH3 to generate (NH4)2SO4 solution, and the ammonia recovery rate is ≥90%.

[0064] The above is only a preferred embodiment of the present invention. Those skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lithium cobalt oxide battery recovery method based on electric field driven membrane distillation, characterized in that: The following steps are involved: Step 1: crush the lithium cobalt oxide cathode material and conduct ammonia leaching reaction with a solution containing ammonia water, ammonium bicarbonate and reducing agent sodium sulfite. Cobalt is converted to Co(NH3)6 3+ Lithium dissolves in the form of complex ions, Li + It is free in the liquid and generates Co(NH3)6 3+ He Li + of liquid; Step 2: The feed liquid is introduced into the feed liquid side channel of the direct contact membrane distillation system, and the positive plate and the negative plate are arranged in parallel in the channel. A DC or pulsed electric field is applied to drive the Co(NH3)6 3+ Reduced to Co at the negative electrode interface 2+ ; Step 3: Control the liquid temperature to 50-70°C to decompose ammonium bicarbonate to generate NH3 and CO3 2- , of which CO3 2- With Co 2+ Combined to form CoCO3 precipitate; Step 4: After separation of CoCO3 precipitation, the pH of the remaining liquid can be adjusted to ≥ 9.5, and the remaining or supplemented amount of CO3 2- With Li + The reaction generates Li2CO3 crystals; Step 5: NH4 in the feed solution + Under the action of the electric field, deprotonation is accelerated to generate NH3. At the same time, the NH3 produced by thermal decomposition cooperates with the electric field to enhance mass transfer and migrates to the acid side through the hydrophobic PTFE membrane. The sulfuric acid solution flowing in the acid side channel directionally flushes the membrane surface, so that the migrated NH3 is quickly absorbed to generate (NH4)2SO4.

2. The method for recycling lithium cobalt oxide batteries based on electric field driven membrane distillation according to claim 1, characterized in that: In step 5, the concentration of sulfuric acid solution in the acid side channel is 0.1-0.2 mol / L, and the flow rate is 0.5-2.0 m / s, forming a turbulent boundary layer with the hydrophobic membrane surface. The gas-liquid contact is enhanced by Reynolds number control (Re ≥ 3000), and the NH3 absorption efficiency is ≥ 85%.

3. The method for recycling lithium cobalt oxide batteries based on electric field driven membrane distillation according to claim 1, characterized in that: In step 2, the DC electric field strength is 50 to 200 V / m, the negative electrode potential is -0.8 to -1.2 V; the pulse frequency is 10 to 50 Hz, the duty cycle is 20% to 80%, the peak electric field strength is 500 to 300 V / m, and the duty cycle of the pulse electric field is adjusted in conjunction with the acid side flow rate: when the acid side flow rate is ≥1.5 m / s, the pulse duty cycle is increased to 50% to 80% to match the NH3 transmembrane flux.

4. The method for recycling lithium cobalt oxide batteries based on electric field driven membrane distillation according to claim 1, characterized in that: In step 2, under the driving of electric field, Co(NH3)6 3+ A reduction reaction occurs at the negative electrode interface, generating Co in situ 2+ And with the CO3 released by thermal decomposition of ammonium bicarbonate in the liquid 2- Combined to form a high-purity CoCO3 precipitate.

5. A lithium cobalt oxide battery recovery system based on electric field driven membrane distillation, characterized in that: include: (1) A direct contact membrane distillation unit, comprising a feed side channel and an acid side channel, the two being separated by a hydrophobic PTFE membrane; (2) The negative and positive plates are integrated in the liquid side channel, with a spacing of 5 to 20 mm; (3) Power module, supporting DC or pulsed electric field output; (4) Acid side circulation pump drives the sulfuric acid solution to flow tangentially along the membrane surface at a flow rate of 0.5 to 2.0 m / s to form a dynamically renewed liquid film.

6. The lithium cobalt oxide battery recovery system based on electric field driven membrane distillation according to claim 5, characterized in that: The inner wall of the acid side channel is provided with a micro groove array with a depth of 0.1 to 0.5 mm and a spacing of 1 to 3 mm, which is used to destroy the laminar flow and enhance the capture capacity of the sulfuric acid liquid membrane for NH3.

7. The lithium cobalt oxide battery recovery system based on electric field driven membrane distillation according to claim 5, characterized in that: The pore size of the hydrophobic PTFE membrane is 0.22 to 0.45 μm, and the porosity is ≥80%.

8. The lithium cobalt oxide battery recovery system based on electric field driven membrane distillation according to claim 5, characterized in that: The negative electrode plate is an IrO2-Ti mesh electrode and the positive electrode plate is a Pt electrode.

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