Method for efficient separation and recovery of graphite in lithium iron phosphate battery

Abstract

The application provides a method for efficiently separating and recovering graphite in a lithium iron phosphate battery, and belongs to the technical field of lithium iron phosphate batteries. The method comprises the following steps: mixing iron-carbon residue and water to prepare pulp, and performing ultrasonic pretreatment; adding an inhibitor, a collector and a foaming agent into the pretreated pulp, performing air flotation, and separating to obtain graphite foam and iron residue pulp; performing dehydration, drying and high-temperature heat treatment on the graphite foam to obtain a battery-grade artificial graphite material; performing dehydration and concentration on the iron residue pulp to obtain rich iron residue pulp; adding acid and a reducing agent into the rich iron residue pulp to perform leaching reaction, and performing solid-liquid separation to obtain an iron-containing solution and low-quality waste residue; and washing the low-quality waste residue to obtain an acidic washing liquid, which is reused in step S4 or step S1. The method improves the grade and recovery rate of the graphite, greatly reduces resource consumption, and realizes the grading and directional reuse of the filtrate and the washing liquid.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium iron phosphate batteries, in particular to a method for efficiently separating and recovering graphite in a lithium iron phosphate battery. BACKGROUND

[0002] Lithium iron phosphate batteries have become the leading technology in the new energy vehicle and energy storage markets due to their high safety, low cost, long life and other advantages. With the large-scale application of lithium iron phosphate batteries in the new energy vehicle and energy storage fields, the recycling industry has also experienced rapid development. Waste batteries contain elements such as lithium, iron and phosphorus, and if not properly treated, they may pollute the environment. At the same time, the supply of key materials such as lithium and phosphorus is limited, and recycling can alleviate resource pressure.

[0003] The patent with the authorized publication number CN115784187B relates to an iron and phosphorus recovery process: (1) alkali leaching of phosphorus iron carbon residue to separate phosphorus, iron carbon residue; (2) secondary acid leaching of carbon inclusions in iron carbon residue to separate iron and carbon.

[0004] The iron carbon residue contains about 60% carbon residue (coated carbon, negative electrode graphite, conductive carbon black, etc. in the synthesis process of lithium iron phosphate), in order to maintain the solid ratio and pH of the iron dissolution liquid in the secondary acid leaching process, the consumption of industrial water and strong acid is increased, more acid waste gas and waste liquid increase the treatment capacity of the tail gas and water treatment system, and more alkali liquor is needed for absorption and neutralization and precipitation; and the iron in the alkaline iron carbon residue is easily hydrolyzed to form iron hydroxide colloid in the alkaline environment during the secondary acid leaching slurry preparation process, which increases the viscosity of the slurry and reduces the separation efficiency in the secondary acid leaching process; the high viscosity of the slurry requires an enlarged liquid-solid ratio and water dilution, in order to maintain the acid leaching pH, the acid consumption is increased, and the waste liquid and waste gas treatment pressure is large; a large amount of acid carbon residue is washed and neutralized, and the cost of hazardous waste to solid waste treatment is large.

[0005] Therefore, it is urgent to develop an efficient and resource-saving method for separating iron carbon residue. SUMMARY

[0006] The application is made in view of the high cost problem of the prior art, and aims to provide a method for efficiently separating and recovering graphite in a lithium iron phosphate battery.

[0007] Specifically, the first aspect of the application provides a method for efficiently separating and recovering graphite in a lithium iron phosphate battery, comprising the following steps:

[0008] S1. Ultrasonic pretreatment and slurry preparation: mixing the iron carbon residue obtained by recycling the lithium iron phosphate battery with water to prepare a slurry, and using an acid adjusting agent to control the pH of the slurry in the alkaline range, while performing ultrasonic pretreatment;

[0009] S2. Enhanced flotation separation: adding a collector, a frother and a composite inhibitor containing silicate and a bio-based organic inhibitor to the pretreated slurry, performing aeration flotation to separate graphite foam and iron residue slurry;

[0010] S3. Product processing: dehydrating, drying and high-temperature heat treating the graphite foam to obtain a battery-grade artificial graphite material; dehydrating and concentrating the iron residue slurry to obtain an iron-rich residue slurry, and the dehydrated filtrate is returned to the pulp preparation in step S1;

[0011] S4. Enhanced acid leaching: adding acid and a reducing agent to the iron-rich residue slurry to perform leaching reaction, and performing solid-liquid separation after reaction to obtain an iron-containing solution and a low-quality waste residue;

[0012] S5. Closed-loop processing: washing the low-quality waste residue to obtain an acidic washing liquid, which is returned to the acid leaching process in step S4 or the pH adjustment in step S1.

[0013] Further, the frequency of the ultrasonic pretreatment in step S1 is 20-40 kHz, the power density is 0.3-0.5 W / mL, and the treatment time is 5-15 min.

[0014] Further, the pH of the slurry is controlled at 8.0-9.0, and the temperature is controlled at 60-70℃.

[0015] Further, the mass ratio of the iron-carbon residue to water in step S1 is 1:10-12.

[0016] Further, the acidic regulator is dilute sulfuric acid or the acidic washing liquid returned from step S5.

[0017] Further, the silicate in step S2 is sodium silicate, the bio-based organic inhibitor is sodium phytate, and the composite inhibitor is compounded from sodium silicate and sodium phytate, and the mass ratio of sodium silicate to sodium phytate is 3-5:1.

[0018] Further, the addition amount of sodium silicate is 2000-3000 g / t based on the dry basis mass of the iron-carbon residue, and the addition amount of sodium phytate is 500-800 g / t.

[0019] Further, the collector in step S2 is an oxidant pretreated fatty acid collector; and / or the frother is a sulfonate frother.

[0020] Further, the process of the oxidant pretreatment is: mixing the fatty acid collector with hydrogen peroxide at a mass ratio of 100:2-5, stirring and reacting at 40-60℃ for 20-40 min.

[0021] Further, the high-temperature heat treatment in step S3 is graphitization treatment at 2500-3000 DEG C for 2-4 hours under the protection of an inert atmosphere.

[0022] Further, the solid-liquid mass ratio of the iron-rich slag slurry after dehydration and concentration in step S3 is controlled at 1:4-5.

[0023] Further, the reducing agent in step S4 is hydrogen peroxide or sodium sulfite, and the addition amount is 0.5%-2% based on the mass of dry iron slag.

[0024] Further, the acid is industrial sulfuric acid, and the mass ratio of dry iron slag to industrial sulfuric acid is 1:1.0-1.3.

[0025] Further, the temperature of the leaching reaction in step S4 is 85-95 DEG C, and the time is 1-2 hours.

[0026] The method has the following beneficial effects:

[0027] The method of the present application realizes the efficient separation and recovery of graphite in iron-carbon slag through a series of steps such as ultrasonic pretreatment pulping and enhanced flotation separation. In the ultrasonic pretreatment pulping stage, the action of ultrasonic can make the iron-carbon slag mix better with water, and at the same time control the pH of the slurry in the alkaline range, avoiding the problem of iron hydrolysis to form iron hydroxide colloid to wrap carbon slag in alkaline environment, reducing the viscosity of the slurry, and laying a good foundation for the subsequent separation steps. In the enhanced flotation separation step, a composite inhibitor containing silicate and a bio-based organic inhibitor is used, and the combination of sodium silicate and sodium phytate can effectively inhibit impurities and improve the flotation effect. The combination of fatty acid type collector pretreated by oxidizing agent and sulfonate type foaming agent makes the graphite foam and iron slag slurry more efficiently separated. In the product processing link, the graphite foam is dehydrated, dried and high-temperature treated to obtain battery-grade artificial graphite material, realizing the high-value utilization of carbon resources. The iron-rich slag slurry is obtained by dehydration and concentration of the iron slag slurry, and the dehydration filtrate is reused for pulping, reducing the consumption of industrial water and embodying the recycling of resources. In the enhanced acid leaching step, sulfuric acid and a reducing agent are added for leaching reaction, which can effectively leach iron from the iron-rich slag slurry to obtain an iron-containing solution. By selecting appropriate reducing agents and the types and amounts of acids, and controlling the temperature and time of the leaching reaction, the leaching efficiency and product quality are ensured. The closed-loop processing step reuses the acidic washing liquid after washing the low-quality waste slag, further reducing the consumption of acid and the discharge of waste, and reducing the production cost and the impact on the environment.

[0028] The method not only improves the separation and recovery efficiency of graphite in iron-carbon slag, but also saves resources and reduces environmental pollution, has significant economic and environmental benefits, and provides strong technical support for the sustainable development of the lithium iron phosphate battery recycling industry. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0030] Figure 1 This is a process flow diagram of the present invention.

[0031] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0033] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0034] See Figure 1 A method for efficient separation and recovery of graphite in lithium iron phosphate batteries includes the following steps:

[0035] S1. Ultrasonic pretreatment pulping: The iron-carbon slag obtained from the recovery of lithium iron phosphate batteries is mixed with water to make pulp, and an acid regulator is used to control the pH of the pulp in the alkaline range, while ultrasonic pretreatment is carried out at the same time.

[0036] S2. Enhanced flotation separation: Add a composite inhibitor containing silicate and bio-based organic inhibitor, collector and frother to the pretreated slurry, and carry out aerated flotation to separate graphite foam and iron slag slurry;

[0037] S3. Product processing: the graphite foam is dehydrated, dried and high-temperature treated to obtain a battery-grade artificial graphite material; the iron slag slurry is dehydrated and concentrated to obtain an iron-rich slag slurry, and the dehydrated filtrate is reused for the slurry preparation in step S1;

[0038] S4. Intensified acid leaching: an acid and a reducing agent are added to the iron-rich slag slurry for leaching reaction, and after the reaction, solid-liquid separation is performed to obtain an iron-containing solution and a low-quality waste residue;

[0039] S5. Closed-loop processing: the low-quality waste residue is washed to obtain an acidic washing liquid, which is reused for the acid leaching process in step S4 or the pH adjustment in step S1.

[0040] The method of the present application realizes the efficient separation and recovery of graphite in iron-carbon slag through a series of steps such as ultrasonic pretreatment for slurry preparation and intensified flotation separation. In the ultrasonic pretreatment for slurry preparation, the action of ultrasonic can make the iron-carbon slag mix better with water, and at the same time, the pH of the slurry is controlled in the alkaline range, avoiding the problem of iron hydrolysis to form iron hydroxide colloid to wrap carbon slag in alkaline environment, reducing the viscosity of the slurry, and laying a good foundation for the subsequent separation steps. In the step of intensified flotation separation, a composite inhibitor containing silicate and a bio-based organic inhibitor is used, and the combination of sodium silicate and sodium phytate can effectively inhibit impurities and improve the flotation effect. The combination of fatty acid type collector pretreated by oxidizing agent and sulfonate type foaming agent makes the graphite foam and iron slag slurry more efficiently separated. In the product processing link, the graphite foam is dehydrated, dried and high-temperature treated to obtain a battery-grade artificial graphite material, realizing the high-value utilization of carbon resources. The iron slag slurry is dehydrated and concentrated to obtain an iron-rich slag slurry, and the dehydrated filtrate is reused for slurry preparation, reducing the consumption of industrial water and embodying the recycling of resources. In the step of intensified acid leaching, the addition of acid and reducing agent for leaching reaction can effectively leach iron from the iron-rich slag slurry to obtain an iron-containing solution. The selection of appropriate reducing agent and acid type and amount, as well as the control of leaching reaction temperature and time, ensures the leaching efficiency and product quality. In the closed-loop processing step, the acidic washing liquid after washing the low-quality waste residue is reused, further reducing the consumption of acid and the discharge of waste, and reducing the production cost and the impact on the environment.

[0041] In this embodiment, the iron-carbon slag is the iron-carbon slag after acid leaching and alkali leaching of lithium iron phosphate battery black powder to extract lithium. The main components are iron 40-60%, fixed carbon 20-40%, phosphorus 2-5%, and moisture <30%. The iron-carbon slag is preliminarily crushed by a crusher to a particle size of less than 2mm to ensure uniform slurry preparation in the subsequent steps.

[0042] The pretreated iron-carbon slag and the recycled water of step 3 are put into a pulp-making barrel with heating and stirring functions at a mass ratio of 1: (10-12). The preferred ratio is 1:11. Under slow stirring (100-200 rpm), add the acid regulator dilute sulfuric acid (concentration of 10-20 wt%) or the recycled acidic washing liquid of step S5 as the pH regulator. The acidic washing liquid is an acidic mixed salt solution rich in sulfuric acid (residual sulfuric acid from the incomplete reaction or washing down in the intensified acid leaching of step S4), ferrous sulfate (product of the reaction of iron oxides / hydroxides with sulfuric acid during acid leaching), and phosphoric acid (phosphorus in the raw material also enters the solution in the form of phosphoric acid or soluble phosphate during acid leaching), and the pH of the slurry is precisely controlled in the alkaline range of 8.0-9.0. Avoid using strong alkali to prevent the pH from being >10, which causes the iron ions to hydrolyze violently. Turn on the heating system and raise the slurry temperature to and maintain at 60-70°C.

[0043] Start the ultrasonic generator and immerse the ultrasonic probe 1 / 3 below the slurry liquid surface. The ultrasonic pretreatment frequency is 20-40 kHz, the power density is 0.3-0.5 W / mL, and the treatment time is 5-15 min. During ultrasonic treatment, the slurry is stirred at a rate of 300-400 rpm to ensure uniform energy distribution. This step utilizes the cavitation effect of ultrasound, which releases a huge amount of energy when the tiny bubbles collapse in an instant, breaking the agglomeration between iron-carbon slag particles and allowing the iron-carbon slag to be more fully dispersed in water. At the same time, the alkaline environment and suitable temperature and ultrasonic conditions cooperate to further prevent the hydrolysis of iron ions to form iron hydroxide colloid, effectively reducing the viscosity of the slurry and facilitating subsequent flotation separation.

[0044] In this embodiment, the pretreated slurry of step S2 is pumped into a mechanical stirring flotation machine for air flotation. The silicate is sodium silicate, the bio-based organic depressant is sodium phytate, and the composite depressant is a mixture of sodium silicate and sodium phytate, with a mass ratio of sodium silicate to sodium phytate of 3-5:1, preferably 4:1. The addition amount of sodium silicate is 2000-3000 g / t and the addition amount of sodium phytate is 500-800 g / t based on the mass of dry iron-carbon slag. First, mix sodium silicate and sodium phytate uniformly in a dosing tank to form a compounded solution, then dilute it with warm water to a concentration of 5% before adding it, and stir for 3-5 min. The depressant of the present application uses a compounded composition of sodium silicate and sodium phytate, in which sodium silicate depresses iron minerals, while sodium phytate, as a green and efficient bio-based depressant, can more preferentially and firmly chelate and adsorb on the surface of iron hydroxide / oxide particles, forming a very strong hydrophilic layer that completely suppresses the floatability of iron hydroxide / oxide, while almost not affecting the floatability of graphite.

[0045] The collector in step S2 is a fatty acid collector pretreated by an oxidant; the pretreatment process is mixing the fatty acid collector with hydrogen peroxide at a mass ratio of 100:2-5, and stirring and reacting at 40-60°C for 20-40 min. Preferably, oxidized oleic acid is used. The present application uses an oxidized and activated fatty acid collector, and the pretreatment process can generate partial hydroxyl fatty acids, which have stronger collecting ability and selectivity and can more efficiently adsorb on the surface of graphite.

[0046] The foaming agent is a sulfonate foaming agent, preferably sodium dodecyl sulfonate, and the amount used is 100-200 g / t (based on dry residue).

[0047] The aeration amount of the aeration flotation is 0.8-1.2 m 3 air / (m 2 ·min, the stirring speed is 1800-2200 rpm, and the flotation time is 12-18 min.

[0048] This step greatly improves the separation efficiency of graphite and iron slag through the synergistic effect of the composite inhibitor, the pretreated collector and the foaming agent, and reasonable control of the aeration amount, the stirring speed and the flotation time. The composite inhibitor of sodium silicate and sodium phytate can form a stable inhibition layer on the surface of the iron slag, effectively inhibiting the floating of the iron slag, while the fatty acid collector pretreated by the oxidant has good selective adsorption capacity for graphite, which can enhance the hydrophobicity of graphite, making it more easily attached to the bubbles and floated with the foam. The foam produced by the sulfonate foaming agent has moderate stability, which is conducive to the collection of graphite foam. Under such conditions, the graphite foam can quickly and massively float to the liquid surface, achieving efficient separation with the iron slag slurry, creating favorable conditions for the high-quality production of subsequent products. At the same time, the entire flotation process is carried out under relatively mild conditions, reducing energy consumption and equipment wear and tear, and reducing production costs.

[0049] In this embodiment, the graphite foam product scraped out in step S3 enters the thickener for preliminary dewatering, and the underflow is dewatered by a plate and frame filter press to obtain graphite filter cake with a water content of <25%. The filter cake is sent to a high-temperature graphitization furnace under the protection of an inert atmosphere (nitrogen or argon). The high-temperature graphitization treatment is carried out at 2500-3000°C for 2-4 h under the protection of an inert atmosphere, and the furnace is cooled to room temperature.

[0050] The flotation underflow (iron residue slurry) enters a high-efficiency thickener or a deep-cone thickener, and a small amount of polyacrylamide (PAM) flocculant (dosage 50-100 g / t) is added to accelerate sedimentation. The underflow concentration is controlled at 20-25% (i.e. the mass ratio of iron residue to water is about 1:4-5), and a rich iron residue slurry is obtained. All the filtrate and overflow produced by dewatering is pumped back to the pulping barrel of step 1 to completely replace fresh industrial water, achieving zero discharge. This step not only realizes further separation and productization of graphite and iron residue, but also reduces the consumption of industrial water through the reuse of filtrate, embodying the concepts of resource recycling and environmental protection. The battery-grade artificial graphite material obtained after dewatering, drying and high-temperature heat treatment of graphite meets the requirements of the battery industry in terms of purity and performance, and can be applied in the field of lithium-ion batteries, etc., improving the added value of carbon resources. The rich iron residue slurry provides suitable raw material for the subsequent iron leaching step, and prepares for the recycling of iron resources. The entire step S3 realizes efficient utilization of resources and environmentally friendly production mode while ensuring product quality, further improving the economic and environmental benefits of the method of the present application.

[0051] In this embodiment, step S4 pumps the iron-rich slag slurry into an acid-resistant reaction kettle with stirring and heating functions, adds industrial sulfuric acid with a concentration of 30%, and the mass ratio of dry basis iron slag to industrial sulfuric acid is 1:1.0-1.3. At the same time, 30% mass fraction of hydrogen peroxide or sodium sulfite is added, and the addition amount is 0.5%-2% based on the mass of dry basis iron slag. The leaching reaction temperature is 85-95 ℃, the stirring speed is 150-200 rpm, and the reaction time is 1-2 h. After the reaction is completed, the slurry is filtered by an acid-resistant plate and frame filter press to obtain an iron and phosphorus-containing leaching solution (which is sent for further recovery of phosphorus or preparation of iron phosphate) and low-quality waste residue. This step successfully leaches iron from the iron-rich slag slurry into the solution by strengthening the acid leaching reaction. In this process, industrial sulfuric acid provides an acidic environment as an acid, allowing iron to dissolve in the form of ions. Hydrogen peroxide or sodium sulfite acts as a reducing agent, which can reduce high-valence iron to low-valence iron that is more easily dissolved, thereby improving the leaching rate of iron. Controlling the appropriate reaction temperature, stirring speed and reaction time ensures the full and efficient progress of the reaction. The reaction temperature of 85-95 ℃ can accelerate the reaction rate, while avoiding the occurrence of side reactions caused by too high temperature. The stirring speed of 150-200 rpm helps to ensure that the reactants are in full contact, improving the uniformity of the reaction. The reaction time of 1-2 h is optimized to ensure sufficient leaching of iron without wasting energy. The iron and phosphorus-containing leaching solution obtained after solid-liquid separation has important recycling value. It can be further treated, such as recovering phosphorus elements or used to prepare iron phosphate and other products. Iron phosphate is an important battery material that can be used as a positive material for lithium-ion batteries, which further increases the added value of the entire recycling process. Low-quality waste residue enters the closed-loop processing step to maximize resource utilization and minimize waste emissions.

[0052] In this embodiment, the low-quality waste residue is washed twice with clean water in step S5. The first washing liquid (strongly acidic, containing a large amount of residual acid and soluble salt): preferentially pumped to the acid leaching reactor of step 4, directly used to configure a new batch of acid leaching slurry, which can replace 30-40% of fresh sulfuric acid. The second washing liquid (weakly acidic): pumped to the pulping barrel of step 1, used to replace fresh water and assist in adjusting the pH. The washed waste residue is mixed with other neutralizing agents (such as lime milk) in the factory area, neutralized to pH = 7-8, and the mud obtained after pressure filtration (mainly composed of silicates, calcium salts, and a small amount of impurities) can be used as roadbed material or building material filler for comprehensive utilization. The filtrate enters the factory area sewage treatment system. This step realizes closed-loop processing of the entire recovery process, significantly reducing production costs and environmental impact. Reusing the acidic washing liquid after washing the low-quality waste residue reduces the amount of fresh sulfuric acid used, reducing the cost of the acid leaching step. At the same time, using the second washing liquid to replace fresh water and assist in adjusting the pH further saves water resources. Using the neutralized mud as roadbed material or building material filler realizes the resource utilization of waste, reducing the discharge of solid waste. The entire closed-loop processing process not only improves the utilization rate of resources, but also follows the green and environmentally friendly concept, making this recovery method have significant advantages in both economy and environment. Through fine control and optimization of each step, the method of the present application can efficiently separate and recover graphite from lithium iron phosphate battery black powder leaching iron and carbon residue, and has good industrial application prospect and promotion value.

[0053] In summary, the present application completely solves the interference problem of iron hydroxide colloid: through the ultrasonic cavitation effect, the colloid is physically broken and the graphite surface is cleaned; through the complex inhibitor of sodium phytate and sodium silicate, the iron minerals are strongly inhibited from floating, creating ideal conditions for efficient flotation. Resource consumption is greatly reduced: by pre-concentrating iron through flotation, the subsequent acid leaching acid consumption is reduced by more than 40% (iron residue: acid from the conventional 1:1.5 to 1:1.0-1.2). Water consumption is reduced: the filtrate and washing liquid are classified and reused, the consumption of fresh industrial water is reduced by more than 60%, and nearly zero wastewater is discharged. Reagent saving: ultrasonic pretreatment improves the drug effect, and the dosage of collectors and inhibitors can be reduced by about 15-20%. The entire process forms a high-efficiency material circulation, the amount of solid waste is reduced, and it is a harmless building material raw material, realizing green and low-carbon recovery.

[0054] Embodiment

[0055] The present disclosure is more particularly described in the following examples that are intended purely for illustrative purposes and are not intended to limit the scope of the disclosure. Various modifications and variations will be apparent to those skilled in the art from the disclosure. Unless otherwise stated, all proportions, percentages, and ratios reported in the following examples are by weight. Unless otherwise stated, all reagents used in the examples are available commercially or are synthesized according to conventional methods and used as received without further purification. Unless otherwise stated, all equipment used in the examples is available commercially.

[0056] Example 1

[0057] A method for efficient separation and recovery of graphite from lithium iron phosphate batteries, comprising the following steps:

[0058] S1. Ultrasonic pretreatment pulping: 500 g of iron-carbon residue recovered from lithium iron phosphate batteries is mixed with 5500 g of water at a ratio of 1 : 11 to make a slurry, under stirring at 150 rpm, 15 wt% concentrated sulfuric acid or the acid washing liquid recycled from step S5 is slowly added as a pH adjuster, the slurry pH is accurately controlled at 8.5, the heating system is started, the slurry temperature is raised to and maintained at 65°C; the ultrasonic generator is started, the ultrasonic probe is immersed 1 / 3 below the slurry liquid surface, the ultrasonic pretreatment frequency is 30 kHz, the power is 700 W, and the treatment time is 10 min;

[0059] S2. Enhanced flotation separation: the slurry is transferred to a flotation machine. A composite inhibitor containing silicates and bio-based organic inhibitors is added to the pretreated slurry, where sodium silicate 2000 g / t, sodium phytate 500 g / t, mass ratio 4: 1, stirring for 3 min; then add the collector oxidized oleic acid (1000 g / t, prepared by pretreating oleic acid with 5% hydrogen peroxide at a ratio of 100:3), stir for 2 min; finally add the frother sodium dodecyl sulfonate 150 g / t, carry out aeration flotation, the aeration amount is 31.1 m 3 air / (m 2 ·min), the stirring speed is 2000 rpm, the flotation time is 15 min, and the graphite foam and iron residue slurry are separated;

[0060] S3. Product processing: the graphite foam is dehydrated, dried, and graphitized at 2800°C for 3 h under the protection of an inert atmosphere to obtain a graphite product; the iron residue slurry is added with a polyacrylamide flocculant for dehydration and concentration, and the underflow concentration is controlled at 25% to obtain an iron-rich residue slurry, and the dehydration filtrate is recycled to the pulping of step S1;

[0061] S4. Reinforced acid leaching: 300 g of iron-rich slag slurry (75 g of dry basis iron slag) was taken and 37.5 g of 30% industrial sulfuric acid was added, the mass ratio of dry basis iron slag to industrial sulfuric acid was 1:1.3; 1.0 g of 30% hydrogen peroxide was added synchronously, the leaching reaction temperature was 90°C, the stirring speed was 180 rpm, the reaction time was 1.5 h, and after the reaction, solid-liquid separation was performed to obtain an iron-containing solution and a low-quality waste residue;

[0062] S5. Closed loop processing: the dewatered filtrate is all used for slurry preparation; the washing liquid of the waste residue after acid leaching (first time) is used for acid preparation for the next acid leaching.

[0063] Example 2

[0064] This example is basically the same as Example 1, except that the ultrasonic power in step S1 is 600 W and the time is 12 min.

[0065] Example 3

[0066] This example is basically the same as Example 1, except that in the inhibitor of step S2, the sodium silicate is 2400 g / t and the sodium phytate is 600 g / t.

[0067] Example 4

[0068] This example is basically the same as Example 1, except that in step S4, the acid leaching sulfuric acid ratio is 1:1.2 in terms of the mass ratio of dry basis iron slag to industrial sulfuric acid.

[0069] Comparative Example 1

[0070] 500 g of the same batch of iron-carbon slag was taken and mixed directly with 375 g of 30% sulfuric acid (dry basis slag: acid was 1:2.25), and stirred and leached at 90°C for 2 hours; after the reaction, solid-liquid separation was performed to obtain a leaching solution and a residue (mainly graphite), and the residue was washed with water and dried.

[0071] Comparative Example 2

[0072] This comparative example is basically the same as Example 1, but the ultrasonic pretreatment step is omitted and only conventional stirring slurry preparation is performed.

[0073] Comparative Example 3

[0074] This comparative example is basically the same as Example 1, but the inhibitor is only sodium silicate, and the amount used is 2500 g / t.

[0075] Comparative Example 4

[0076] This comparative example is basically the same as Example 1, but the floated graphite is only dried by dewatering and is not subjected to high-temperature graphitization treatment.

[0077] Comparative Example 5

[0078] The present comparative example is basically the same as Example 1, but all the dewatering filtrate and washing liquid are not reused, and all are treated as waste water, and fresh water is used throughout.

[0079] Experimental cases

[0080] A certain batch of lithium iron phosphate battery black powder is uniformly used to obtain iron-carbon slag after leaching lithium by acid leaching and alkali leaching, and the composition is: Fe 52.3%, C 35.1%, P 3.8%, and other (O, Li, Al, etc.) 8.8%. The iron-carbon slag graphite is efficiently separated and recovered by the methods of Examples 1-4 and Comparative Examples 1-5, and the results are shown in Table 1.

[0081]

[0082] As can be seen from Table 1, Examples 1-4 perform excellently in graphite grade and recovery rate, and all can reach a high level. In terms of graphite grade, Example 1 reaches 99.7%, Example 2 is 99.6%, Example 3 is as high as 99.8%, and Example 4 reaches 99.5%. In terms of graphite recovery rate, Example 1 reaches 93.5%, Example 2 is 92.8%, Example 3 reaches 94.1%, and Example 4 reaches 93.7%. This shows that the method of the present application can efficiently separate and recover graphite from the lithium iron phosphate battery black powder leaching iron-carbon slag under optimized process parameters, and obtain high-grade and high-recovery-rate graphite products.

[0083] Although Comparative Example 1 has a graphite recovery rate of 99.5%, the graphite grade is only 78.2%, and the acid consumption is as high as 0.45 t / t and the water consumption is 2.5 t / t, fully exposing the disadvantages of high consumption and low quality of the prior art. In Comparative Example 2, the iron hydroxide colloid cannot be effectively broken, resulting in sticky flotation foam and difficult cleaning, and the separation efficiency is sharply reduced, with a graphite grade of only 88.5% and a recovery rate of 75.3%. In Comparative Example 3, the traditional depressant sodium silicate has insufficient inhibitory ability on the iron hydroxide colloid, so that part of the fine-grained iron minerals still float with the graphite, and the graphite grade and recovery rate are both not ideal, being 92.1% and 82.6% respectively. Although the flotation separation effect of Comparative Example 4 is good, the adsorbed reagents and microcrystalline structure defects on the surface of the graphite are not removed, and the product cannot meet the battery grade standard, and the value is greatly reduced. In Comparative Example 5, since the classification and reuse strategy is not adopted, the fresh water consumption soars to 1.2 t / t, and the environmental protection and economic advantages are lost.

[0084] In summary, the present application effectively solves the problems existing in the prior art by fine control and optimization of each step, such as ultrasonic pretreatment pulping, enhanced flotation separation, product treatment, enhanced acid leaching and closed loop treatment, etc., and achieves the goal of efficient separation and recovery of graphite from the iron-carbon residue of lithium iron phosphate battery black powder leaching. Not only the grade and recovery rate of graphite are improved, but also the resource consumption is greatly reduced, the filtrate and washing liquid are classified and recycled, the consumption of fresh industrial water is reduced, the wastewater discharge is almost zero, the amount of reagent is saved, the whole process forms an efficient material circulation, the amount of solid waste is reduced, and the solid waste is a harmless building material, realizing green and low-carbon recovery, and having good industrial application prospect and popularization value.

[0085] It should be noted that the present application is not limited to the above-mentioned embodiments.

[0086] The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications that can be thought of by those skilled in the art, other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

1. A method for efficient separation and recovery of graphite in a lithium iron phosphate battery, characterized by, The method comprises the following steps: S1. Ultrasonic pretreatment pulping: iron-carbon slag recovered from lithium iron phosphate batteries is mixed with water to prepare a slurry, and an acidic regulator is used to control the pH of the slurry in the alkaline range, while ultrasonic pretreatment is performed; S2. Intensified flotation separation: a collector, a foaming agent and a composite inhibitor comprising silicate and a bio-based organic inhibitor are added to the pretreated slurry, and air flotation is performed to separate graphite foam and iron slag slurry; S3. Product processing: the graphite foam is dehydrated, dried and high-temperature heat treated to obtain a battery-grade artificial graphite material; the iron slag slurry is dehydrated and concentrated to obtain a rich iron slag slurry, and the dehydrated filtrate is recycled to the pulping of step S1; S4. Intensified acid leaching: an acid and a reducing agent are added to the rich iron slag slurry for leaching reaction, and after the reaction, solid-liquid separation is performed to obtain an iron-containing solution and a low-quality waste residue; S5. Closed loop processing: the low-quality waste residue is washed to obtain an acidic washing liquid, which is recycled to the acid leaching process of step S4 or the pH adjustment of step S1.

2. The method for efficient separation and recovery of graphite in lithium iron phosphate batteries according to claim 1, characterized in that, In step S1, the ultrasonic pretreatment has a frequency of 20-40 kHz, a power density of 0.3-0.5 W / mL, and a treatment time of 5-15 min; and / or The pH of the slurry is controlled at 8.0-9.0, and the temperature is controlled at 60-70℃.

3. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized in that, In step S1, the mass ratio of the iron-carbon slag to water is 1:10-12; and / or The acidic regulator is dilute sulfuric acid or the acidic washing liquid recycled from step S5.

4. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized by, In step S2, the silicate is sodium silicate, the bio-based organic inhibitor is sodium phytate, the composite inhibitor is compounded from sodium silicate and sodium phytate, and the mass ratio of sodium silicate to sodium phytate is 3-5:1; and / or The addition amount of sodium silicate is 2000-3000 g / t based on the dry mass of iron-carbon slag, and the addition amount of sodium phytate is 500-800 g / t.

5. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized in that, In step S2, the collector is an oxidant pretreated fatty acid collector; and / or the foaming agent is a sulfonate foaming agent.

6. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 5, characterized in that, The process of the oxidant pretreatment is: mixing the fatty acid collector with hydrogen peroxide at a mass ratio of 100:2-5, and stirring and reacting at 40-60℃ for 20-40 min.

7. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized by, In step S3, the high-temperature heat treatment is graphitization treatment at 2500-3000℃ for 2-4 h under the protection of an inert atmosphere.

8. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized by, In step S3, the rich iron slag slurry after dehydration and concentration has a solid-liquid mass ratio of 1:4-5.

9. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized by, In step S4, the reducing agent is hydrogen peroxide or sodium sulfite, and the addition amount is 0.5%-2% based on the dry mass of iron slag; And / or, the acid is industrial sulfuric acid, and the mass ratio of the dry mass of iron slag to the mass of industrial sulfuric acid is 1:1.0-1.

3.

10. The method of efficient separation and recovery of graphite from lithium iron phosphate batteries according to claim 1, characterized by, In step S4, the leaching reaction has a temperature of 85-95℃ and a time of 1-2 h.

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