Recycling treatment method of lithium iron phosphate waste liquid

Abstract

The invention discloses a resourceful treatment method of a lithium iron phosphate waste liquid, which comprises the following steps: filtering the lithium iron phosphate waste liquid to obtain a lithium iron phosphate filtrate; adding an oxidizing agent into the lithium iron phosphate filtrate until the redox potential value reaches a potential preset value to obtain redox liquid; adding phosphate into the redox solution for precipitation, and filtering to obtain an iron phosphate crystal product and a lithium ion filtrate; adding sodium carbonate into the lithium ion filtrate for precipitation, and filtering to obtain a lithium carbonate crystal product and wastewater. According to the method, redox reaction and chemical precipitation are combined, effective resource utilization of the lithium iron phosphate waste liquid is achieved, iron elements and lithium elements are subjected to fractional precipitation, the resource recovery rate can be effectively increased, the resource recovery benefit is high, the recovery purity can be effectively improved, the operation difficulty is low, and the method is suitable for industrial production. And the recovery cost and the equipment cost can be effectively saved.

Description

Technical Field

[0001] The present invention relates to the field of resource utilization of waste liquid, and particularly to a method for resource treatment of lithium iron phosphate waste liquid. Background Art

[0002] With the wide application of lithium-ion batteries, lithium iron phosphate is favored as a cathode material due to its high safety, long cycle life and environmental friendliness. However, a large amount of waste liquid is generated during the production and use of lithium iron phosphate batteries, and these waste liquids contain lithium iron phosphate, lithium ions and other impurities.

[0003] Traditional treatment methods often cannot effectively recover valuable elements therein. If the waste liquid is directly discharged, it will not only cause waste of resources, but also environmental pollution. In related technologies, the treatment methods of lithium iron phosphate waste liquid mainly include chemical precipitation method, ion exchange method and membrane separation method, etc. However, these methods have problems such as low recovery rate, complex operation and high recovery cost. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. For this purpose, the present invention provides a method for resource treatment of lithium iron phosphate waste liquid, which has a high resource recovery rate, simple operation and can save the recovery cost.

[0005] A method for resource treatment of lithium iron phosphate waste liquid according to an embodiment of the present invention includes:

[0006] Filtering the lithium iron phosphate waste liquid to obtain a lithium iron phosphate filtrate;

[0007] Adding an oxidant to the lithium iron phosphate filtrate until the oxidation-reduction potential value reaches a preset potential value to obtain an oxidation-reduction liquid;

[0008] Adding a phosphate to the oxidation-reduction liquid for precipitation, and filtering to obtain a lithium iron phosphate crystal product and a lithium ion filtrate;

[0009] Adding sodium carbonate to the lithium ion filtrate for precipitation, and filtering to obtain a lithium carbonate crystal product and waste water.

[0010] In this embodiment, filtering the lithium iron phosphate waste liquid to obtain a lithium iron phosphate filtrate includes:

[0011] Performing primary filtration on the lithium iron phosphate waste liquid through a first filter screen to obtain a lithium iron phosphate pretreatment liquid;

[0012] Adding an acid-base regulator and a flocculant to the lithium iron phosphate pretreatment liquid until the pH reaches a first preset pH value to obtain a lithium iron phosphate regulating liquid;

[0013] Performing secondary filtration on the lithium iron phosphate waste liquid through the first filter screen to obtain a lithium iron phosphate filtrate.

[0014] In this embodiment, the first preset acid-base value is 6-8.

[0015] In this embodiment, an oxidant is added to the lithium iron phosphate filtrate until the oxidation-reduction potential value reaches a preset potential value, obtaining an oxidation-reduction solution, including:

[0016] Add the oxidant to the lithium iron phosphate filtrate according to a preset dropping rate, and detect the oxidation-reduction potential value;

[0017] When the oxidation-reduction potential value is greater than the preset potential value, stop adding the oxidant to obtain an oxidation-reduction solution, wherein the preset potential value is 771 mV.

[0018] In this embodiment, adding phosphate to the oxidation-reduction solution for precipitation, and filtering to obtain lithium iron phosphate crystal products and a lithium ion filtrate, including:

[0019] Add phosphate to the oxidation-reduction solution, and perform stirring precipitation at a first preset temperature and a first preset stirring speed to obtain a lithium iron phosphate precipitation solution;

[0020] Filter the lithium iron phosphate precipitation solution by pressure filtration to obtain lithium iron phosphate crystal products and a lithium ion filtrate.

[0021] In this embodiment, filtering the lithium iron phosphate precipitation solution by pressure filtration to obtain lithium iron phosphate crystal products and a lithium ion filtrate, including:

[0022] Input the lithium iron phosphate precipitation solution into a pressure filtration device and filter it at a preset filtration pressure to obtain lithium iron phosphate particles and a lithium ion filtrate;

[0023] Wash the lithium iron phosphate particles with deionized water in a first preset volume for a first preset number of times to obtain clean lithium iron phosphate;

[0024] Dry the clean lithium iron phosphate at a second preset temperature to obtain lithium iron phosphate crystal products.

[0025] In this embodiment, after drying the clean lithium iron phosphate at a second preset temperature to obtain lithium iron phosphate crystal products, it further includes:

[0026] Dissolve the lithium iron phosphate crystal products, and filter after cooling and crystallization to obtain purified lithium iron phosphate crystals.

[0027] In this embodiment, adding sodium carbonate to the lithium ion filtrate for precipitation, and filtering to obtain lithium carbonate crystal products and wastewater, including:

[0028] Add liquid caustic soda to the lithium ion filtrate to adjust the acidity and alkalinity to a second preset acid-base value to obtain a lithium ion adjustment solution;

[0029] Add sodium carbonate to the lithium ion regulating solution and stir and precipitate at a second preset temperature and a second preset stirring speed to obtain a lithium carbonate precipitation solution;

[0030] Filter and purify the lithium carbonate precipitation solution to obtain lithium carbonate crystal products and wastewater.

[0031] In this embodiment, filtering and purifying the lithium carbonate precipitation solution to obtain lithium carbonate crystal products and wastewater includes:

[0032] Filter the lithium carbonate precipitation solution to obtain lithium carbonate particles and wastewater;

[0033] Wash the lithium carbonate particles with deionized water in a second preset volume for a second preset number of times to obtain clean lithium carbonate;

[0034] Dry the clean lithium carbonate at a third preset temperature to obtain lithium carbonate crystal products.

[0035] In this embodiment, the second preset pH value is 8.5 - 9.0.

[0036] The embodiments of the present invention have at least the following beneficial effects:

[0037] Through the method combining redox reaction and chemical precipitation, the iron element and lithium element in the lithium iron phosphate waste liquid can be efficiently recovered. The obtained iron phosphate crystal products and lithium carbonate crystal products can be used as raw materials for products such as lithium ion batteries, realizing the effective resource utilization of the lithium iron phosphate waste liquid. Recycling resources while treating wastewater can effectively reduce the exploitation and input of new resources, meeting the requirements of sustainable development; adopting the step-by-step precipitation method for iron element and lithium element, first oxidizing the ferrous ions in the lithium iron phosphate filtrate to ferric ions by an oxidant and then recovering the ferric ions can effectively improve the resource recovery rate, with high resource treatment efficiency and high resource recycling benefits. Moreover, the iron element is precipitated and recovered in the form of iron phosphate, which can effectively improve the recovery purity, thereby effectively increasing the added value of the resource recycling products; in addition, the progress of the oxidation reaction is monitored and inferred through the oxidation reduction potential value. The monitoring operation is convenient and the monitoring and judgment results are reliable. After reaching the preset potential value, the ferric ions and lithium ions are precipitated by phosphate and sodium carbonate respectively, which can effectively simplify the treatment process, with low operation difficulty, effectively saving the recovery cost and equipment cost, and further improving the economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0039] Figure 1 is a flow schematic diagram of the resource treatment method for the lithium iron phosphate waste liquid of the embodiment of the present invention;

[0040] Figure 2 A specific process schematic diagram of step S100 provided by an embodiment of the present invention; Figure 1 in

[0041] Figure 3 A specific process schematic diagram of step S200 provided by an embodiment of the present invention; Figure 1 in

[0042] Figure 4 A specific process schematic diagram of step S300 provided by an embodiment of the present invention; Figure 1 in

[0043] Figure 5 A specific process schematic diagram of step S320 provided by an embodiment of the present invention; Figure 4 in

[0044] Figure 6 A specific process schematic diagram of step S400 provided by an embodiment of the present invention; Figure 1 in

[0045] Figure 7 A specific process schematic diagram of step S430 provided by an embodiment of the present invention; Figure 6 in

[0046] Figure 8 A specific process schematic diagram of the resource treatment method of lithium iron phosphate waste liquid in the recovery of iron phosphate provided by an embodiment of the present invention;

[0047] Figure 9 A specific process schematic diagram of the resource treatment method of lithium iron phosphate waste liquid in the recovery of lithium carbonate provided by an embodiment of the present invention. Detailed implementation manners

[0048] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0049] In the description of the present invention, it should be understood that the orientation or positional relationship involved, such as up, down, left, right, front, back, etc., indicates the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention.

[0050] In the description of the present invention, if the first and second are described only for the purpose of distinguishing technical features, they should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features or implicitly specifying the sequence of the indicated technical features.

[0051] In the description of the present invention, unless otherwise clearly defined, terms such as "set", "installed", "connected", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0052] With the wide application of lithium-ion batteries, lithium iron phosphate is favored as a cathode material due to its high safety, long cycle life and environmental friendliness. However, a large amount of waste liquid is generated during the production and use of lithium iron phosphate batteries, and this waste liquid contains lithium iron phosphate, lithium ions and other impurities. Traditional treatment methods often cannot effectively recover the valuable elements therein. If the waste liquid is directly discharged, it will not only cause waste of resources, but also environmental pollution.

[0053] Therefore, it is of great significance to develop an efficient and environmentally friendly resource treatment method for lithium iron phosphate waste liquid. In related technologies, the treatment methods for lithium iron phosphate waste liquid mainly include chemical precipitation method, ion exchange method, membrane separation method, etc. However, these methods have problems such as low recovery rate, insufficient recovery purity, complex operation and high recovery cost. For example, although the chemical precipitation method is simple and easy to implement, it is difficult to achieve efficient separation of iron elements and lithium elements; although the ion exchange method and the membrane separation method can achieve a relatively high separation efficiency, the equipment cost is high, the operation is complex, and it is easily affected by impurities in the waste liquid. Therefore, there is an urgent need for a new treatment method that can efficiently recover the valuable elements in lithium iron phosphate waste liquid while reducing the treatment cost and the impact on the environment.

[0054] The resource treatment method for lithium iron phosphate waste liquid provided by the embodiments of the present invention has a high resource recovery rate, is simple to operate, and can save the recovery cost.

[0055] The following will further elaborate on the embodiments of the present invention in conjunction with the attached Figures 1 to 9 , drawings.

[0056] A resource treatment method for lithium iron phosphate waste liquid in this embodiment, as shown in Figure 1 The resource treatment method includes but is not limited to the following steps:

[0057] S100. Filter the lithium iron phosphate waste liquid to obtain a lithium iron phosphate filtrate;

[0058] S200. Add an oxidant to the lithium iron phosphate filtrate until the oxidation-reduction potential value reaches a preset potential value to obtain an oxidation-reduction liquid;

[0059] S300. Add phosphate into the redox solution for precipitation, and filter to obtain iron phosphate crystal products and lithium ion filtrate;

[0060] S400. Add sodium carbonate into the lithium ion filtrate for precipitation, and filter to obtain lithium carbonate crystal products and wastewater.

[0061] Through the method combining redox reaction and chemical precipitation, the iron element and lithium element in the lithium iron phosphate waste liquid can be efficiently recovered. The obtained iron phosphate crystal products and lithium carbonate crystal products can be used as raw materials for products such as lithium ion batteries, realizing the effective resource utilization of the lithium iron phosphate waste liquid. While treating the wastewater, resource recovery and utilization are carried out, which can effectively reduce the exploitation and input of new resources, meeting the requirements of sustainable development. The chemical reagents used in this resource treatment process are all non-toxic or low-toxic substances, which can avoid secondary pollution; the iron element and lithium element are precipitated step by step. First, the ferrous ions in the lithium iron phosphate filtrate are oxidized to ferric ions by an oxidant, and then the ferric ions are recovered, which can effectively improve the resource recovery rate. The recovery rate of valuable elements can reach more than 90%. The resource treatment efficiency is high, and the resource recovery benefit is high. Moreover, the iron element is precipitated and recovered in the form of iron phosphate, which can effectively improve the recovery purity, thereby effectively increasing the added value of the resource recovery products; in addition, the progress of the oxidation reaction is monitored and inferred through the oxidation reduction potential value. The monitoring operation is convenient, and the monitoring and judgment results are reliable. After reaching the preset potential value, iron ions and lithium ions are precipitated by phosphate and sodium carbonate respectively, which can effectively simplify the treatment process, with low operation difficulty, effectively saving the recovery cost and equipment cost, and further improving the economic benefit.

[0062] It can be understood that, as shown in Figure 2 After filtering the lithium iron phosphate waste liquid to obtain the lithium iron phosphate filtrate, step S100 includes but is not limited to the following steps:

[0063] S110. Filter the lithium iron phosphate waste liquid once through the first filter screen to obtain the pretreated lithium iron phosphate solution;

[0064] S120. Add an acid-base regulator and a flocculant into the pretreated lithium iron phosphate solution until the pH reaches the first preset pH value to obtain the adjusted lithium iron phosphate solution;

[0065] S130. Filter the lithium iron phosphate waste liquid twice through the first filter screen to obtain the lithium iron phosphate filtrate.

[0066] Pretreatment filtration is carried out before adding acid-base regulators and flocculants, which can effectively reduce the dosage of acid-base regulators and flocculants, effectively save the material cost of resource treatment, and thus effectively improve the efficiency of resource treatment. And before carrying out recovery treatments such as oxidation-reduction, the flocculant is used to further coagulate and precipitate fine particles, and the acid-base regulator is used to adjust the pH value of the wastewater to stabilize the iron ions and lithium ions in the wastewater, which can effectively ensure the concentration of the lithium iron phosphate filtrate obtained after secondary filtration, effectively improve the effectiveness of subsequent treatment steps, reduce the dosage of materials required for resource treatment, and thus effectively improve the efficiency of resource treatment. Among them, the first filter screen can use a filter screen with a mesh size of 50-100, which can filter out large particle impurities. According to different actual situations, filter screens with different mesh numbers can also be used for filtration treatment; the flocculant can use polyacrylamide.

[0067] It can be understood that the first preset acid-base value is 6.0-8.0. Among them, the acid-base regulator can use sulfuric acid or sodium hydroxide.

[0068] It can be understood that with reference to Figure 3 As shown, an oxidant is added to the lithium iron phosphate filtrate until the oxidation-reduction potential value reaches the potential preset value to obtain an oxidation-reduction solution. Step S200 includes but is not limited to the following steps:

[0069] S210. Add the oxidant to the lithium iron phosphate filtrate according to the preset dropping speed, and detect the oxidation-reduction potential value;

[0070] S220. When the oxidation-reduction potential value is greater than the potential preset value, stop adding the oxidant to obtain an oxidation-reduction solution, where the potential preset value is 771 mV.

[0071] It should be noted that the oxidant can be a hydrogen peroxide solution with a molar concentration of 30%, and the dropping speed can be 1000-2000 ml / min, which can be specifically determined according to the flow rate of the lithium iron phosphate filtrate and the concentration of ferrous ions.

[0072] The chemical reaction formula for oxidation-reduction in the lithium iron phosphate filtrate is:

[0073] 2Fe 2+ +H2O2+2H + =2Fe 3+ +2H2O

[0074] In the same chemical reaction, the reaction rate ratio of various substances is equal to the stoichiometric ratio in the chemical reaction formula, that is

[0075] υ(Fe 2+ ):υ(H2O2):υ(Fe 3+ )=2:1:2

[0076] Assume that the input flow rate of the lithium iron phosphate filtrate is Q = 1 L / min, and Fe 2+ = 0.1 mol / (L·min), then the dropping rate of hydrogen peroxide is:

[0077] υ0(H2O2) = 0.5υ(Fe 2+ ) = 0.5×0.1 mol / (L·min) = 0.05 mol / (L·min)

[0078] When the molar concentration of the added hydrogen peroxide solution is 30%, the dropping rate of the required hydrogen peroxide solution is:

[0079] υ1(H2O2) = 0.05 mol / (L·min)·(2×16×2) g / mol / 30% = 10.67 g / (L·min)

[0080] According to the above inference method, the concentration and dropping rate of the oxidant can be specifically calculated under different situations.

[0081] It should be further noted that adding an oxidant to the lithium iron phosphate filtrate can oxidize the possible ferrous ions in the lithium iron phosphate filtrate to ferric ions, and at the same time detect the redox potential value of the lithium iron phosphate filtrate to ensure that the oxidation reaction is complete.

[0082] In the redox reaction of the lithium iron phosphate filtrate,

[0083] For H2O2 + 2H + + 2e - = 2H2O, its standard electrode potential is E 0 = 1.776 V.

[0084] For Fe 3+ + e - = Fe 2+ , its standard electrode potential is E 0 = 0.771 V.

[0085] According to the Nernst equation: E = E 0 -(0.0592 / n)lgQ, where n is the number of electrons transferred in the reaction and Q is the reaction quotient, to calculate the actual electrode potential in the redox reaction.

[0086] According to the chemical reaction formula of redox in the lithium iron phosphate filtrate: 2Fe 2+ + H2O2 + 2H + = 2Fe 3+ + 2H2O, it can be seen that n = 2, and the reaction quotient Q = ([Fe 2+ 2 ·[H2O2]·[H​+ 2 ) / [Fe 3+ 2 , when the forward reaction proceeds completely, ferrous ions react completely, and the reaction quotient Q approaches 0. According to the Nernst equation, lgQ approaches -∞, and E approaches E 0 , for the reduction reaction of hydrogen peroxide, its electrode potential as long as it is greater than Fe 3+ / Fe 2+ electrode potential can make the reaction proceed forward. In actual operation, to make the redox reaction proceed completely forward, the redox potential needs to be greater than 771 mV.

[0087] By detecting that the redox potential value is greater than 771, it is determined that the redox reaction proceeds completely forward. It can be inferred that all ferrous ions are oxidized to ferric ions, which can effectively increase the recovery amount of iron phosphate obtained by the resource treatment of lithium iron phosphate, thereby effectively improving the efficiency of resource treatment and having a high resource utilization rate.

[0088] It can be understood that, as shown in Figure 4 , adding phosphate to the redox solution for precipitation, and filtering to obtain iron phosphate crystal products and lithium ion filtrate. Step S300 includes but is not limited to the following steps:

[0089] S310. Add phosphate to the redox solution and stir and precipitate at the first preset temperature and the first preset stirring speed to obtain an iron phosphate precipitation solution;

[0090] S320. Filter the iron phosphate precipitation solution by pressure filtration to obtain iron phosphate crystal products and lithium ion filtrate.

[0091] Among them, the phosphate can be sodium phosphate precipitant, which can make ferric ions precipitate in the form of iron phosphate; the first preset temperature can be 40 - 60 °C, and specifically can be set to 50 °C, which can effectively improve the precipitation efficiency; the first preset stirring speed can be set to 88 rpm, and the solution is stirred and mixed at a suitable speed by the stirring paddle inside the reaction kettle, which can effectively avoid generating too many bubbles and affecting the precipitation effect while ensuring the mixing and precipitation speed; preferably, the stirring time can be set to 1 hour. The chemical reaction formula for the reaction of phosphate with ferric ions in the redox solution to make ferric ions precipitate in the form of iron phosphate is: Fe 3+ +PO4 3+ →FePO4↓.

[0092] It can be understood that, as shown in Figure 5 , filtering the iron phosphate precipitation solution by pressure filtration to obtain iron phosphate crystal products and lithium ion filtrate. Step S320 includes but is not limited to the following steps:​​

[0093] S321. Input the iron phosphate precipitation solution into a pressure filtration device and filter it at a preset filtration pressure to obtain iron phosphate particles and a lithium ion filtrate;

[0094] S322. Wash the iron phosphate particles with deionized water in a first preset volume for a first preset number of times to obtain clean iron phosphate;

[0095] S323. Dry the clean iron phosphate at a second preset temperature to obtain an iron phosphate crystal product.

[0096] Among them, the preset filtration pressure of the pressure filtration device can be set to 0.6 MPa, and the iron phosphate particles and the lithium ion filtrate can be efficiently and reliably separated through the pressure filtration device; the first preset volume of deionized water each time is twice that of the iron phosphate particles, and the first preset number of washing times can be set to at least three times. By washing the iron phosphate particles with deionized water, the impurities on their surfaces can be effectively removed, and the purity of the iron phosphate crystal product obtained in subsequent processing can be effectively improved; the second preset temperature can be set to 80 - 100 °C, and the drying time of the clean iron phosphate can be set to 2 hours.

[0097] It can be understood that after drying the clean iron phosphate at the second preset temperature to obtain the iron phosphate crystal product, that is, after step S320, it further includes but is not limited to the following steps:

[0098] Dissolve the iron phosphate crystal product, filter it after cooling and crystallization to obtain a purified iron phosphate crystal.

[0099] Select a suitable solvent such as hydrochloric acid solution to recrystallize the iron phosphate crystal product by recrystallization to achieve further purification, and a purified iron phosphate crystal with higher purity can be obtained.

[0100] It can be understood that with reference to Figure 6 as shown, add sodium carbonate to the lithium ion filtrate for precipitation, and filter to obtain a lithium carbonate crystal product and wastewater. Step S400 includes but is not limited to the following steps:

[0101] S410. Add liquid alkali to the lithium ion filtrate to adjust the pH value to a second preset pH value to obtain a lithium ion adjusted solution;

[0102] S420. Add sodium carbonate to the lithium ion adjusted solution and stir for precipitation at a second preset temperature and a second preset stirring speed to obtain a lithium carbonate precipitation solution;

[0103] S430. Filter and purify the lithium carbonate precipitation solution to obtain a lithium carbonate crystal product and wastewater.

[0104] Among them, after adding liquid caustic soda to adjust the pH value to the second preset pH value, react for 10 minutes to obtain a lithium ion adjustment solution. Adjusting the pH value first can effectively improve the efficiency of subsequent precipitation of lithium ions. Sodium carbonate can use saturated sodium carbonate solution, which can effectively improve the reaction efficiency. The second preset temperature can be set to 60-80 °C, and the second stirring speed can be set to 60 rpm, which can effectively ensure the precipitation effect of lithium carbonate. The chemical reaction formula for sodium carbonate to react with lithium ions in the lithium ion adjustment solution to precipitate lithium ions in the form of lithium carbonate is: 2Li + +Na2CO3→Li2CO3↓+2Na + .

[0105] It can be understood that, as shown in Figure 7 , filtering and purifying the lithium carbonate precipitation solution to obtain lithium carbonate crystal products and wastewater. Step S430 includes but is not limited to the following steps:

[0106] S431. Filter the lithium carbonate precipitation solution to obtain lithium carbonate particles and wastewater;

[0107] S432. Wash the lithium carbonate particles with deionized water in a second preset volume for a second preset number of times to obtain clean lithium carbonate;

[0108] S433. Dry the clean lithium carbonate at a third preset temperature to obtain lithium carbonate crystal products.

[0109] Among them, the filtration of the lithium carbonate precipitation solution can use 800-mesh polypropylene filter cloth, and plate-and-frame dehydration with a filtration pressure of 0.6 MPa is used for solidification. The solidified lithium carbonate particle cake is sent for subsequent washing and drying; the second preset volume of deionized water each time is twice that of the lithium carbonate particles, and the second preset number of washing times can be set to at least three times. Washing the lithium carbonate particles with deionized water can effectively remove the impurities on their surfaces and can effectively improve the purity of the lithium carbonate crystal products obtained in subsequent processing; the third preset temperature can be set to 100-120 °C.

[0110] After drying the clean lithium carbonate at a third preset temperature to obtain lithium carbonate crystal products, after step S433, it further includes but is not limited to the following steps:

[0111] Dissolve the lithium carbonate crystal products, filter after cooling and crystallization to obtain purified lithium carbonate crystals.

[0112] Select a suitable solvent to recrystallize the lithium carbonate crystal products by recrystallization to achieve further purification, and lithium carbonate purified crystals with higher purity can be obtained.

[0113] It should be noted that for the wastewater after the recovery of iron phosphate crystal products and lithium carbonate crystal products, it can be returned to the front end for repeated resource treatment; or, for the wastewater after the recovery of iron phosphate crystal products and lithium carbonate crystal products, the pollutant content is detected. If it meets the discharge standard, it is directly discharged. If there are excessive pollutants detected, further biological treatment or other advanced treatment methods are adopted to make the wastewater meet the discharge standard before discharging.

[0114] It can be understood that the second preset pH value is 8.5 - 9.0. By adjusting the pH in advance for lithium ion filtration to make it alkaline, it can effectively ensure that the sodium carbonate used subsequently is effective for precipitating lithium ions, thereby effectively improving the efficiency of resource recovery treatment for lithium ions.

[0115] The following is an illustrative description of the resource treatment method for lithium iron phosphate waste liquid with specific data:

[0116] Reference Figure 8 As shown, the wastewater containing iron phosphate and lithium carbonate, that is, the lithium iron phosphate waste liquid, is conveyed to a filtering device through a conveyor belt to filter impurities. The filtering device filters the lithium iron phosphate waste liquid through an 80 - mesh stainless - steel filter screen inside it. The waste liquid flows into the primary sedimentation tank. Then, a flocculant is added according to the amount of 5 - 10 grams of polyacrylamide per ton of waste liquid, and sulfuric acid is added to adjust the pH to 7. After stirring evenly, it is left to stand and precipitate for 2 - 3 hours, and the supernatant is taken as the lithium iron phosphate filtrate.

[0117] Reference Figure 8 As shown, the lithium iron phosphate filtrate is conveyed to an oxidation reaction kettle. According to the stoichiometric ratio of ferrous ions, hydrogen peroxide, and ferric ions υ(Fe 2+ ):υ(H2O2):υ(Fe 3+ ) = 2:1:2, 1.2 times the amount of hydrogen peroxide solution is added for oxidation reaction, and it is stirred at a speed of 100 - 200 rpm. At the same time, the oxidation - reduction potential value is detected. When the voltage is stably maintained above 771 mV, it indicates that the oxidation reaction is completed; the solution is transferred to a precipitation reaction kettle, and a sodium phosphate solution is added according to 1.1 times the concentration of ferric ions for reaction precipitation. The precipitation reaction temperature is controlled at 50 °C and stirred for 1 - 2 hours. After the reaction is completed, high - pressure filtration is carried out through a vacuum filter or a pressure filtration device to obtain iron phosphate particles and a lithium ion filtrate; the iron phosphate particles are conveyed by a belt conveyor, and the iron phosphate particle precipitate is washed 3 - 5 times with deionized water, and then put into a steam dryer to be dried at 90 °C for 4 - 6 hours. The condensed water is recovered into the comprehensive regulation pool, and after obtaining the iron phosphate crystal product, it is packaged.

[0118] Reference Figure 9As shown, the lithium-ion filtrate is collected as the mother liquor and transported to the first reactor. After adding the alkali solution to the first reactor to adjust the pH value to 8.5 - 9.0, it is then transported to the second reactor. A saturated sodium carbonate solution is added at 1.05 times the lithium-ion concentration. The precipitation reaction temperature is controlled at 70°C, and stirring is carried out at a speed of 80 - 120 rpm for 1 - 1.5 hours. After the reaction is completed, lithium carbonate particles and wastewater are obtained through filtration by filtration equipment such as a precision plate and frame filter. The wastewater can be returned as the mother liquor for further resource recovery. The lithium carbonate particles are transported by a belt conveyor, washed 4 - 6 times with deionized water at 80 - 90°C for precipitation, and then placed in a steam dryer and dried at 110°C for 6 - 8 hours. The condensed water is recovered into the comprehensive regulation pool, and the lithium carbonate crystal product is obtained for product packaging.

[0119] The wastewater from which the iron phosphate crystal product and the lithium carbonate crystal product have been recovered is subjected to water quality monitoring. If indicators such as chemical oxygen demand, total phosphorus, and total lithium meet the discharge standards, it is discharged through the drain pipe; if any indicator exceeds the standard, the wastewater is introduced into the biological treatment pool and further treated through the degradation of microorganisms until it meets the standard for discharge.

[0120] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and purposes of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for recycling lithium iron phosphate waste liquid, characterized in that: include: filtering the lithium iron phosphate waste liquid to obtain a lithium iron phosphate filtrate; Adding an oxidant to the lithium iron phosphate filtrate until the redox potential reaches a preset potential value to obtain a redox solution; adding phosphate to the redox solution for precipitation, and filtering to obtain an iron phosphate crystal product and a lithium ion filtrate; Sodium carbonate is added to the lithium ion filtrate for precipitation, and a lithium carbonate crystal product and waste water are obtained by filtration.

2. The method for recycling lithium iron phosphate waste liquid according to claim 1, characterized in that: The method of filtering the lithium iron phosphate waste liquid to obtain the lithium iron phosphate filtrate comprises: Filtering the lithium iron phosphate waste liquid once through a first filter screen to obtain a lithium iron phosphate pretreatment liquid; Adding an acid-base regulator and a flocculant into the lithium iron phosphate pretreatment solution until the pH reaches a first preset pH value to obtain a lithium iron phosphate regulating solution; The lithium iron phosphate waste liquid is filtered twice through the first filter to obtain lithium iron phosphate filtrate.

3. The resource treatment method of lithium iron phosphate waste liquid according to claim 2, characterized in that: The first preset pH value is 6-8.

4. The method for recycling lithium iron phosphate waste liquid according to claim 1, characterized in that: The step of adding an oxidant to the lithium iron phosphate filtrate until the redox potential reaches a preset potential value to obtain a redox solution comprises: Adding an oxidant to the lithium iron phosphate filtrate according to a preset dropwise addition rate, and detecting the redox potential value; When the redox potential value is greater than the preset potential value, the addition of the oxidant is stopped to obtain a redox solution, wherein the preset potential value is 771 mV.

5. The method for recycling lithium iron phosphate waste liquid according to claim 1, characterized in that: The step of adding phosphate to the redox solution for precipitation and filtering to obtain an iron phosphate crystal product and a lithium ion filtrate comprises: adding phosphate to the redox solution, and stirring and precipitating at a first preset temperature and a first preset stirring speed to obtain an iron phosphate precipitate solution; The iron phosphate precipitate is filtered by pressure filtration to obtain an iron phosphate crystal product and a lithium ion filtrate.

6. The method for recycling lithium iron phosphate waste liquid according to claim 5, characterized in that: The method of filtering the iron phosphate precipitate by pressure filtration to obtain an iron phosphate crystal product and a lithium ion filtrate comprises: The iron phosphate precipitate is input into a filter press and filtered at a preset filtration pressure to obtain iron phosphate particles and a lithium ion filtrate; Washing the iron phosphate particles a first preset number of times with a first preset volume of deionized water to obtain clean iron phosphate; The clean iron phosphate is dried at a second preset temperature to obtain an iron phosphate crystal product.

7. The method for recycling lithium iron phosphate waste liquid according to claim 6, characterized in that: After drying the clean iron phosphate at a second preset temperature to obtain an iron phosphate crystal product, the method further includes: The iron phosphate crystal product is dissolved, and filtered after cooling and crystallization to obtain purified iron phosphate crystals.

8. The method for recycling lithium iron phosphate waste liquid according to claim 1, characterized in that: The step of adding sodium carbonate to the lithium ion filtrate for precipitation and filtering to obtain a lithium carbonate crystal product and waste water comprises: Adding liquid alkali to the lithium ion filtrate to adjust the pH to a second preset pH value to obtain a lithium ion regulating solution; adding sodium carbonate to the lithium ion regulating solution, and stirring and precipitating at a second preset temperature and a second preset stirring speed to obtain a lithium carbonate precipitate; The lithium carbonate precipitate is filtered and purified to obtain a lithium carbonate crystal product and waste water.

9. The method for recycling lithium iron phosphate waste liquid according to claim 8, characterized in that: The method of filtering and purifying the lithium carbonate precipitate to obtain a lithium carbonate crystal product and waste water comprises: filtering the lithium carbonate precipitate to obtain lithium carbonate particles and wastewater; Washing the lithium carbonate particles a second preset number of times with deionized water in a second preset volume to obtain clean lithium carbonate; The clean lithium carbonate is dried at a third preset temperature to obtain a lithium carbonate crystal product.

10. The method for recycling lithium iron phosphate waste liquid according to claim 8, characterized in that: The second preset pH value is 8.5-9.0.

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