Method for regenerating iron phosphate by treating ferrophosphorus slag with iron reducing bacteria

Abstract

In order to solve the problems existing in the current mainstream ferrophosphorus slag treatment process, the invention provides a method for preparing regenerated iron phosphate by biologically leaching ferrophosphorus slag in a low-oxygen inert atmosphere, low-temperature and organic acid environment. The method specifically comprises the following steps: (1) adding organic acid into ferrophosphorus slag slurry, adjusting the oxygen concentration in a system, and then adding iron reducing bacteria for reduction leaching; (2) after the reaction is completed, carrying out solid-liquid separation to obtain solid waste residues and ferrophosphorus liquid; and (3) removing impurities from the ferrophosphorus liquid, sequentially adding an oxidizing agent and an alkaline substance, and carrying out solid-liquid separation to obtain iron phosphate.

Description

Technical Field

[0001] The invention belongs to the field of battery recycling, and in particular relates to a method for regenerating iron phosphate by treating ferrophosphorus slag with iron-reducing bacteria. Background Art

[0002] With the rapid development of the new energy vehicle industry, the demand for power lithium batteries is increasing, which is bound to bring a large number of waste batteries. Waste batteries contain a large number of non-renewable valuable resources (such as lithium, nickel, etc.), as well as toxic and harmful substances (fluorine-containing electrolytes, etc.). If waste batteries are left alone, it will cause a large waste of valuable resources and serious environmental pollution. Therefore, the recycling of waste batteries is imminent.

[0003] At present, the recycling of waste batteries is mainly divided into pyrolysis and hydrolysis, among which the hydrolysis is more widely used. Selective leaching is the most mature process in wet recycling. This process can extract more than 90% of lithium, but it will leave a large amount of ferrophosphorus slag. After the selective leaching process, the ferrophosphorus slag changes from olivine type to α-quartz type. The crystal is composed of FeO6 octahedron and PO4 tetrahedron through shared PO-Fe bonds to form a spatial skeleton. This construction method makes the ferrophosphorus slag have high stability and generally low solubility in inorganic acid. It is difficult to dissolve when acid leaching is used in the subsequent treatment. The current mainstream ferrophosphorus slag treatment process is a "concentrated acid + reducing substance" system, which reduces Fe(III) in the ferrophosphorus slag to Fe(II) to achieve the dissolution of the ferrophosphorus slag for the preparation of subsequent products, such as patent CN115196609B. This process has the disadvantages of low leaching rate and high cost, so how to dissolve iron phosphate efficiently and at low cost has become a major problem. Summary of the invention

[0004] In order to solve the problems of low leaching rate and high cost in the prior art, the present application provides a method for leaching ferrophosphorus slag by microorganisms, which can avoid the large-scale use of acid while ensuring the leaching rate of iron and phosphorus elements, greatly reducing the process cost.

[0005] Specifically, this application adopts the following technical solutions:

[0006] A method for regenerating ferric phosphate by treating ferrophosphorus slag with iron-reducing bacteria, characterized in that it comprises the following steps:

[0007] (1) adding organic acid to the ferrophosphorus slag slurry, adjusting the oxygen concentration in the system, and then adding iron-reducing bacteria to perform reduction leaching;

[0008] (2) after the reaction is completed, solid-liquid separation is performed to obtain solid waste residue and ferrophosphorus liquid;

[0009] (3) Remove impurities from the ferrophosphorus liquid, add an oxidant and an alkaline substance in sequence, and separate the solid and liquid to obtain ferric phosphate.

[0010] Iron-reducing bacteria is a microorganism that converts Fe(III) in the system into Fe(II). It is a strict anaerobic bacteria or facultative anaerobic bacteria and is suitable for living in a normal temperature, slightly acidic or neutral environment. Applying iron-reducing bacteria to the ferrophosphorus slag reduction leaching system can avoid the use of a large amount of acid, while ensuring the leaching rate of iron and phosphorus elements, greatly reducing the process cost.

[0011] In this application, the Fe in the ferrophosphorus slag is trivalent. At this time, the compound FP formed by Fe and P has a stable spatial structure and is difficult to dissolve in common acids. The trivalent Fe is reduced to divalent Fe by using microorganisms, iron-reducing bacteria, which destroys the spatial structure of FP and makes it soluble in organic acids. Finally, an oxidant is added to fine-tune the iron-phosphorus ratio, and iron phosphate is synthesized in a direction.

[0012] In a specific embodiment of the present application, the ferrophosphorus slag slurry is obtained by the following method:

[0013] (1.1) Pre-treating the ferrophosphorus slag after extracting lithium from the black powder of waste lithium iron phosphate batteries;

[0014] (1.2) Add appropriate amount of deionized water to the pre-treated ferrophosphorus slag, perform homogenization, and stir at room temperature to obtain the product.

[0015] Specifically, the ferrophosphorus slag slurry is obtained by the following method:

[0016] Pre-treating the waste lithium iron phosphate battery black powder ferrophosphorus slag, wherein the pre-treatment includes but is not limited to one or more of grinding, crushing, and screening to obtain ferrophosphorus slag powder with a particle size of ≤100 mesh;

[0017] Add an appropriate amount of deionized water to the ferrophosphorus slag powder after the previous treatment, perform homogenization treatment, and stir for 30 minutes to 1 hour at room temperature to obtain the ferrophosphorus slag slurry.

[0018] In a specific embodiment of the present application, the organic acid is selected from one or more of lactic acid, pyruvic acid, acetic acid, citric acid, and oxalic acid.

[0019] In a specific embodiment of the present application, the adjusting of the oxygen concentration in the system specifically includes: controlling the pH of the system to be stable at 3.0-6.5, and then introducing an inert gas into the system using an aeration device to adjust the oxygen concentration in the system to <0.1%.

[0020] The inert gas may be conventional in the art, such as nitrogen, carbon dioxide, argon, etc. The presence of the inert gas can provide a weak oxygen or anaerobic environment for the iron-reducing bacteria and avoid secondary oxidation of the raw materials during the acid leaching process.

[0021] In a specific embodiment of the present application, the amount of iron-reducing bacteria added is 10-20% of the mass of the ferrophosphorus slag slurry.

[0022] In a specific embodiment of the present application, the reduction leaching in step (1) specifically includes: maintaining a dark light environment for reaction at room temperature, regularly sampling and measuring the Fe(II) concentration in the system, and stopping the reaction after the concentration becomes constant.

[0023] The normal temperature during reduction leaching in step (1) refers to a temperature range of 20 to 30°C.

[0024] In the present application, the solid waste residue mainly includes unreacted ferrophosphorus slag and carbonaceous materials that do not participate in the reaction.

[0025] In the present application, the ferrophosphate slag is treated with iron-reducing bacteria to reduce the insoluble crystalline ferric phosphate into ferrous ions and phosphate radicals. At this time, the ferrophosphate slag can be dissolved in the liquid phase to form ferrophosphate liquid.

[0026] In a specific embodiment of the present application, the solid waste residue in step (2) is subjected to leaching treatment, and the iron-reducing bacteria attached to the surface of the solid waste residue are repeatedly cultured.

[0027] In a specific embodiment of the present application, the impurity removal process in step (3) specifically includes:

[0028] (3.1) adding a precipitant to the ferrophosphorus solution, and then adding a flocculant to accelerate the precipitation rate of the impurity elements;

[0029] (3.2) adding alkali solution to adjust the pH of the system to 2.0-3.0, and filtering to remove the insoluble impurity precipitate;

[0030] (3.3) Adding acid to the solution obtained above to adjust the system pH to <1.1, thereby obtaining a ferrophosphorus solution after impurities are removed. Specifically, the impurity removal process in step (3) specifically includes:

[0031] Add a precipitant to the ferrophosphorus liquid, stir for 10 to 30 minutes at room temperature, then add a small amount of flocculant to accelerate the precipitation rate of impurity elements, further remove impurities, and finally slowly add alkali solution to adjust the pH of the system to about 2.0 to 3.0. After continuing the reaction for 10 to 30 minutes, filter out the insoluble impurity precipitate (mainly aluminum and copper impurities), and then add a small amount of acid to adjust the system pH <1.1 to obtain the ferrophosphorus liquid after impurities removal.

[0032] Wherein, the precipitant is selected from one or more of sodium fluoride, sodium carbonate, sodium silicate, and iron powder. In the precipitation reaction, the main components of the liquid phase are ferrous ions, phosphates, lithium ions, etc., and a portion of metal impurity ions (Ca, Mg, Cu, Al, etc.). The precipitant is added to form an insoluble metal salt precipitate, and finally the impurity metal ions are removed by adjusting the pH.

[0033] The added mass of the precipitant is 1 to 1.5 times the total mass of the impurity elements Ca, Mg, Cu and Al in the ferrophosphide liquid.

[0034] Wherein, the flocculant is selected from one or more of polyacrylamide (PAM), polyaluminium chloride (PAC) and alum.

[0035] Wherein, the alkali solution is selected from one or more of sodium hydroxide, ammonia water and sodium carbonate.

[0036] In a specific embodiment of the present application, the oxidant in step (3) is selected from one or more of sodium peroxide, hydrogen peroxide, and potassium permanganate.

[0037] In a specific embodiment of the present application, the amount of the oxidant added is 1 to 1.5 times the Fe(II) content in the ferrophosphide liquid.

[0038] In a specific embodiment of the present application, the alkaline substance in step (3) is selected from one or more of sodium hydroxide, ammonia water, and sodium carbonate.

[0039] In a specific embodiment of the present application, in step (3), the alkaline substance is added to increase the pH of the system to 2.0-3.0, followed by a reaction for 10 min-1.5 h, and crude iron phosphate is obtained after solid-liquid separation.

[0040] In a specific embodiment of the present application, the specific steps after the solid-liquid separation in step (3) include:

[0041] After washing the obtained iron phosphate with pure water, a small amount of phosphoric acid is added to adjust the system pH to 1.6-1.8, the temperature is raised to 80-90°C and the reaction is continued for 1-2 hours, and the dihydrate iron phosphate product is obtained by filtration;

[0042] The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0043] Among them, the purpose of adding a small amount of phosphoric acid is:

[0044] ① Provide an acidic environment. The conversion of iron phosphate crystals needs to be carried out in an environment of pH = 1.6 to 1.8;

[0045] ② Provide phosphate. The synthesized crude iron phosphate has an imbalance in the iron-phosphorus ratio. Phosphate needs to be supplemented to promote the crystal reorganization of the amorphous crude iron phosphate. The final synthesized product is crystal-stable iron phosphate.

[0046] The present application is to solve the problems existing in the current mainstream ferrophosphorus slag treatment process, and considers biological leaching of ferrophosphorus slag under low oxygen (inert atmosphere), normal temperature, and organic acid environment, and the obtained leaching solution is used to prepare regenerated iron phosphate. This method can not only efficiently leach iron and phosphorus elements, but also suppress the dissolution of impurity elements. In addition, microbial bacteria can be recycled and regenerated, and only a small amount of nutrients need to be provided. Therefore, this method has the advantage of low cost and is a green, efficient and sustainable process.

[0047] Beneficial effects:

[0048] 1. The present application adopts iron-reducing bacteria to reduce and leach phosphorus iron slag, avoiding the large-scale use of inorganic acids (hydrochloric acid, nitric acid, sulfuric acid), and the iron-reducing bacteria can be reused, effectively reducing the process cost;

[0049] 2. The impurity removal part of the present application can effectively remove copper and aluminum impurities in the slag after the selective leaching process, and the impurity precipitation can further extract high-purity copper powder;

[0050] 3. This application can achieve an iron and phosphorus leaching rate of >99% in ferrophosphorus slag, and the indicators of the prepared regenerated iron phosphate meet the battery grade standard. The product has high added value and obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic diagram of a process flow diagram provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0053] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0054] In the description of the present invention, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0055] Reference Figure 1 The present invention provides a method for regenerating ferric phosphate by treating ferrophosphorus slag with iron-reducing bacteria, which specifically comprises the following steps:

[0056] (1) subjecting waste lithium iron phosphate battery black powder to selective leaching treatment to obtain lithium extraction solution and ferrophosphorus slag, and subjecting the ferrophosphorus slag to pre-treatment, wherein the pre-treatment includes but is not limited to one or more of grinding, crushing, and screening to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0057] (2) adding an appropriate amount of deionized water to the ferrophosphorus slag powder for homogenization, and stirring at room temperature for 30 minutes to 1 hour to obtain a ferrophosphorus slag slurry;

[0058] (3) slowly adding an organic acid (one or more of lactic acid, pyruvic acid, acetic acid, citric acid, and oxalic acid) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 3.0 to 6.5, and then introducing an inert gas, such as one or more of nitrogen, carbon dioxide, and argon, into the system using an aeration device to provide a weak oxygen or anaerobic environment for the iron-reducing bacteria and avoid secondary oxidation of the raw materials during the acid leaching process;

[0059] (4) After the oxygen concentration in the system is less than 0.1%, add 10-20% of the mass of the ferrophosphorus slag slurry of iron-reducing bacteria, maintain a dark light environment at 20-30°C for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction after the concentration is constant, and filter and separate the solid waste slag and the ferrophosphorus liquid. The solid waste slag can be repeatedly leached, and the iron-reducing bacteria attached to the surface of the solid waste slag can be repeatedly cultured;

[0060] (5) adding a precipitant (one or more of sodium fluoride, sodium carbonate, sodium silicate, and iron powder) to the ferrophosphorus liquid, stirring at room temperature for 10 to 30 minutes, then adding a small amount of flocculant to accelerate the precipitation rate of impurity elements, further removing impurities, and finally slowly adding an alkali solution (one or more of sodium hydroxide, ammonia water, and sodium carbonate) to adjust the pH of the system to 2.0 to 3.0, continuing the reaction for 10 to 30 minutes, filtering to remove insoluble impurity precipitates (mainly aluminum and copper impurities), adding a small amount of acid to the filtrate to adjust the pH to less than 1.1, and obtaining a ferrophosphorus liquid after impurities removal;

[0061] (6) adding an oxidant (one or more of sodium peroxide, hydrogen peroxide, and potassium permanganate) to the above impurity-removed ferrophosphorus liquid, and then adding an alkaline substance (one or more of sodium hydroxide, ammonia water, and sodium carbonate) to raise the pH of the system to 2.0-3.0, reacting for 10 minutes to 1.5 hours, and filtering and separating to obtain crude ferric phosphate;

[0062] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto, the temperature is raised to 80-90° C. and the reaction is continued for 1-2 hours, and the iron phosphate dihydrate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0063] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0064] The present invention is further described in detail below through specific examples.

[0065] The iron-reducing bacteria used in the specific examples were cultivated in the laboratory, specifically:

[0066] (1) Enrichment culture of iron-reducing bacteria: Under nitrogen atmosphere, the bacteria (from the iron bacteria culture bottle of Beijing Zhongxi Huada Technology Co., Ltd.) were added to 10 mL of ferrihydrite suspension (containing about 15.7 g / L of Fe) and 500 mL of distilled water, and the culture was kept at 30°C in a dark environment for 1 week for recovery culture;

[0067] (2) Isolation and purification of iron-reducing bacteria: The soil suspension is centrifuged, inoculated, and selected to obtain strains capable of reducing ferric citrate. The strains are transferred to a culture medium containing a ferrihydrite suspension, and the iron reduction rate is identified by measuring the Fe(II) content, and the efficient strains are further screened out;

[0068] (3) Further culture and amplification until iron-reducing bacteria are obtained in an amount that meets the process requirements.

[0069] Example 1

[0070] This embodiment provides a method for regenerating iron phosphate by treating ferrophosphorus slag with iron-reducing bacteria, the method comprising the following steps:

[0071] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0072] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0073] (3) slowly adding a lactic acid aqueous solution (50 wt%) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 5.5, and then introducing nitrogen into the system using an aeration device;

[0074] (4) When the oxygen concentration in the system is less than 0.1%, add 10% of the iron-reducing bacteria by mass of the ferrophosphorus slag slurry, maintain a dark environment at 25°C for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction after the concentration is constant, filter and separate the solid waste slag and the ferrophosphorus liquid. Repeat the leaching of the solid waste slag, and repeatedly culture the iron-reducing bacteria using the iron-reducing bacteria attached to the surface of the solid waste slag;

[0075] (5) adding a precipitant (sodium fluoride, iron powder) to the ferrophosphorus liquid, stirring for 10 minutes at room temperature, adding a small amount of flocculant, and finally slowly adding a sodium hydroxide solution (32 wt%) to adjust the pH of the system to 3.0, continuing the reaction for 10 minutes, filtering, and adding a small amount of acid to the filtrate to adjust the pH to less than 1.1 to obtain a ferrophosphorus liquid after impurities removal;

[0076] (6) adding hydrogen peroxide to the impurity-removed ferrophosphorus liquid, wherein the concentration of hydrogen peroxide is 20% and the added mass is 1.3 times the Fe(II) content in the ferrophosphorus liquid, and then adding sodium hydroxide solution (32 wt %) to raise the pH of the system to 2.0, reacting for 10 min and filtering to obtain crude iron phosphate;

[0077] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto to adjust the system pH to 1.8, the temperature is raised to 90° C. and the reaction is continued for 1 hour, and the dihydrate iron phosphate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0078] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0079] The anhydrous ferric phosphate product in this example was analyzed for element content, and the results were as follows:

[0080] Table 1 Elements and content analysis

[0081]

[0082] Example 2

[0083] This embodiment provides a method for regenerating iron phosphate by treating ferrophosphorus slag with iron-reducing bacteria, the method comprising the following steps:

[0084] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 180 mesh;

[0085] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0086] (3) slowly adding oxalic acid / lactic acid mixed acid (lactic acid: oxalic acid = 1:3, mass ratio) to the ferrophosphorus slag slurry, controlling the pH of the system to be stable at 6.5, and then introducing a mixed gas of argon and nitrogen (Ar: N2 = 1:5) into the system using an aeration device;

[0087] (4) When the oxygen concentration in the system is less than 0.1%, add 20% of the iron-reducing bacteria by mass of the ferrophosphorus slag slurry, maintain a dark environment at 30°C for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction when the concentration is constant, and filter and separate the solid waste slag and the ferrophosphorus liquid;

[0088] (5) adding a precipitant (sodium fluoride, iron powder) to the ferrophosphorus liquid, stirring at room temperature for 30 minutes, adding a small amount of flocculant, and finally slowly adding a sodium hydroxide solution (32 wt%) to adjust the pH of the system to 2.5, continuing the reaction for 30 minutes, filtering, and adding a small amount of acid to the filtrate to adjust the pH to 1.0 to obtain a ferrophosphorus liquid after impurities removal;

[0089] (6) adding hydrogen peroxide to the impurity-removed ferrophosphide liquid, the added mass being 1.3 times the Fe(II) content in the ferrophosphide liquid, and then adding sodium hydroxide solution (32 wt%) to raise the pH of the system to 2.5, reacting for 10 min, and filtering and separating to obtain crude ferric phosphate;

[0090] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto to adjust the system pH to 1.8, the temperature is raised to 90° C. and the reaction is continued for 1.5 h, and the dihydrate iron phosphate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0091] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0092] The anhydrous ferric phosphate product in this example was analyzed for element content, and the results were as follows:

[0093] Table 2 Elements and content analysis

[0094]

[0095] Note: "-" in the table means that the element is below the detection limit of the instrument and is not detected (ND)

[0096] Example 3

[0097] Referring to Example 1, the main difference between this example and Example 1 is that the inorganic acid is different, and the specific operation is as follows:

[0098] This embodiment provides a method for regenerating iron phosphate by treating ferrophosphorus slag with iron-reducing bacteria, the method comprising the following steps:

[0099] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0100] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0101] (3) slowly adding a citric acid aqueous solution (60 wt%) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 3.5, and then introducing nitrogen into the system using an aeration device;

[0102] (4) When the oxygen concentration in the system is less than 0.1%, add iron-reducing bacteria in an amount of 10% of the mass of the ferrophosphorus slag slurry, maintain a dark light environment at room temperature for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction after the concentration becomes constant, filter and separate the solid waste slag and the ferrophosphorus liquid. Repeat the leaching of the solid waste slag, and repeatedly culture the iron-reducing bacteria using the iron-reducing bacteria species attached to the surface of the solid waste slag;

[0103] (5) adding a precipitant (sodium fluoride, iron powder) to the ferrophosphorus liquid, stirring for 10 minutes at room temperature, adding a small amount of flocculant, and finally slowly adding a sodium hydroxide solution (32 wt%) to adjust the pH of the system to 3.0, continuing the reaction for 10 minutes, filtering, and adding a small amount of acid to the filtrate to adjust the pH to less than 1.1 to obtain a ferrophosphorus liquid after impurities removal;

[0104] (6) adding hydrogen peroxide to the impurity-removed ferrophosphorus liquid, wherein the concentration of hydrogen peroxide is 20% and the added mass is 1.3 times the Fe(II) content in the ferrophosphorus liquid, and then adding sodium hydroxide solution (32 wt %) to raise the pH of the system to 2.0, reacting for 10 min and filtering to obtain crude iron phosphate;

[0105] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto to adjust the system pH to 1.8, the temperature is raised to 90° C. and the reaction is continued for 1 hour, and the dihydrate iron phosphate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0106] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0107] The anhydrous ferric phosphate product in this example was analyzed for element content, and the results were as follows:

[0108] Table 3 Elements and content analysis

[0109]

[0110] Note: "-" in the table means that the element is below the detection limit of the instrument and is not detected (ND)

[0111] Comparative Example 1

[0112] This comparative example provides a method for regenerating ferric phosphate by treating ferrophosphorus slag with iron-reducing bacteria, the method comprising the following steps:

[0113] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0114] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0115] (3) slowly adding a sulfuric acid aqueous solution (20 wt%) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 5.5, and then introducing nitrogen into the system using an aeration device;

[0116] (4) When the oxygen concentration in the system is less than 0.1%, add 10% of the iron-reducing bacteria by mass of the ferrophosphorus slag slurry, maintain a dark light environment at room temperature for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction after the concentration is constant, filter and separate the solid waste slag and the ferrophosphorus liquid. Repeat the leaching of the solid waste slag, and repeatedly culture the iron-reducing bacteria using the iron-reducing bacteria attached to the surface of the solid waste slag;

[0117] (5) adding a precipitant (sodium fluoride, iron powder) to the ferrophosphorus liquid, stirring for 10 minutes at room temperature, adding a small amount of flocculant, and finally slowly adding a sodium hydroxide solution (32 wt%) to adjust the pH of the system to 3.0, continuing the reaction for 10 minutes, filtering, and adding a small amount of acid to the filtrate to adjust the pH to less than 1.1 to obtain a ferrophosphorus liquid after impurities removal;

[0118] (6) adding hydrogen peroxide to the impurity-removed ferrophosphorus liquid, wherein the concentration of hydrogen peroxide is 20% and the added mass is 1.3 times the Fe(II) content in the ferrophosphorus liquid, and then adding sodium hydroxide solution (32 wt %) to raise the pH of the system to 2.0, reacting for 10 min and filtering to obtain crude iron phosphate;

[0119] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto to adjust the system pH to 1.8, the temperature is raised to 90° C. and the reaction is continued for 1 hour, and the dihydrate iron phosphate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0120] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0121] The anhydrous ferric phosphate product in this example was analyzed for element content, and the results were as follows:

[0122] Table 4 Elements and content analysis

[0123]

[0124] Note: "-" in the table means that the element is below the detection limit of the instrument and is not detected (ND)

[0125] Comparative Example 2

[0126] This comparative example provides a method for regenerating ferric phosphate by treating ferrophosphorus slag with iron-reducing bacteria, the method comprising the following steps:

[0127] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0128] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0129] (3) slowly adding a benzoic acid aqueous solution (50 wt%) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 5.5, and then introducing nitrogen into the system using an aeration device;

[0130] (4) When the oxygen concentration in the system is less than 0.1%, add 10% of the iron-reducing bacteria by mass of the ferrophosphorus slag slurry, maintain a dark light environment at room temperature for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction after the concentration is constant, filter and separate the solid waste slag and the ferrophosphorus liquid. Repeat the leaching of the solid waste slag, and repeatedly culture the iron-reducing bacteria using the iron-reducing bacteria attached to the surface of the solid waste slag;

[0131] (5) adding a precipitant (sodium fluoride, iron powder) to the ferrophosphorus liquid, stirring for 10 minutes at room temperature, adding a small amount of flocculant, and finally slowly adding a sodium hydroxide solution (32 wt%) to adjust the pH of the system to 3.0, continuing the reaction for 10 minutes, filtering, and adding a small amount of acid to the filtrate to adjust the pH to less than 1.1 to obtain a ferrophosphorus liquid after impurities removal;

[0132] (6) adding hydrogen peroxide to the impurity-removed ferrophosphorus liquid, wherein the concentration of hydrogen peroxide is 20% and the added mass is 1.3 times the Fe(II) content in the ferrophosphorus liquid, and then adding sodium hydroxide solution (32 wt %) to raise the pH of the system to 2.0, reacting for 10 min and filtering to obtain crude iron phosphate;

[0133] (7) After the crude iron phosphate is washed with pure water, a small amount of phosphoric acid is added thereto to adjust the system pH to 1.8, the temperature is raised to 90° C. and the reaction is continued for 1 hour, and the dihydrate iron phosphate product is obtained by filtration, and the remaining phosphorus-containing liquid is continuously reused for the next batch of crystallization operations;

[0134] (8) The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

[0135] The anhydrous ferric phosphate product in this example was analyzed for element content, and the results were as follows:

[0136] Table 5 Elements and content analysis

[0137]

[0138] Note: "-" in the table means that the element is below the detection limit of the instrument and is not detected (ND)

[0139] Experimental example

[0140] This experimental example verifies the reducing performance of the iron-reducing bacteria provided by the present invention, and specifically comprises the following steps:

[0141] (1) crushing and screening the ferrophosphorus slag after lithium extraction from waste lithium iron phosphate battery black powder to obtain ferrophosphorus slag powder with a particle size of less than 100 mesh;

[0142] (2) adding an appropriate amount of deionized water to the above-mentioned ferrophosphorus slag powder, performing homogenization treatment, and stirring at room temperature for 30 minutes to obtain a ferrophosphorus slag slurry;

[0143] (3) slowly adding a lactic acid aqueous solution (50 wt%) to the ferrophosphorus slag slurry to control the pH of the system to be stable at 5.5, and then introducing nitrogen into the system using an aeration device;

[0144] (4) When the oxygen concentration in the system is less than 0.1%, add iron-reducing bacteria in an amount of 10% by mass of the ferrophosphorus slag slurry, maintain a dark light environment at room temperature for reaction, regularly sample and measure the Fe(II) concentration, stop the reaction when the concentration is constant, and filter and separate the solid waste slag and the ferrophosphorus liquid.

[0145] The valence and content of iron in the ferrophosphorus slag and ferrophosphorus liquid in this experimental example were analyzed, and the results are as follows:

[0146] Table 6 Elements and content analysis

[0147]

[0148] It can be seen from the results in Table 6 that the iron-reducing bacteria provided by the present invention can effectively reduce iron (III) to iron (II).

[0149] From the results of Tables 1 to 5, it can be seen that the method provided by the present invention for treating phosphorus iron slag with iron-reducing bacteria has a high recovery rate of phosphorus iron elements, a good iron reduction effect, and a low impurity content in the obtained anhydrous iron phosphate product. In Comparative Example 1, inorganic acid is used. Compared with the organic acid in the present invention, the inorganic acid cannot provide energy substances for the iron-reducing bacteria, so the iron-reducing bacteria are not active in the system, so the effect of Comparative Example 1 is poor; in Comparative Example 2, benzoic acid is used. Due to its weak acidity and stable benzene ring structure, it is not easy to be decomposed and absorbed, so it cannot provide a carbon source for the iron-reducing bacteria to ensure its normal reproduction, so the recovery rate of iron and phosphorus is low, and the effect is the worst.

[0150] The specific embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0151] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0152] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for regenerating ferric phosphate by treating ferrophosphorus slag with iron-reducing bacteria, characterized in that: The following steps are involved: (1) adding organic acid to the ferrophosphorus slag slurry, adjusting the oxygen concentration in the system, and then adding iron-reducing bacteria for reduction leaching; (2) after the reaction is completed, solid-liquid separation is performed to obtain solid waste residue and ferrophosphorus liquid; (3) Remove impurities from the ferrophosphorus liquid, add an oxidant and an alkaline substance in sequence, and separate the solid and liquid to obtain ferric phosphate.

2. The method according to claim 1, characterized in that The ferrophosphorus slag slurry is obtained by the following method: (1.1) Pre-treating the ferrophosphorus slag after extracting lithium from the black powder of waste lithium iron phosphate batteries; (1.2) Add appropriate amount of deionized water to the pre-treated ferrophosphorus slag, perform homogenization, and stir at room temperature to obtain the product.

3. The method according to claim 1, characterized in that The organic acid is selected from one or more of lactic acid, pyruvic acid, acetic acid, citric acid, and oxalic acid; Preferably, the adjusting the oxygen concentration in the system specifically comprises: controlling the pH of the system to be stable at 3.0-6.5, and then introducing an inert gas into the system by using an aeration device to adjust the oxygen concentration in the system to <0.1%.

4. The method according to claim 1, characterized in that: The reduction leaching in step (1) specifically includes: maintaining a dark light environment for reaction at room temperature, regularly sampling and measuring the concentration of Fe(II) in the system, and stopping the reaction after the concentration becomes constant.

5. The method according to claim 1, characterized in that The solid waste residue in step (2) is subjected to leaching treatment, and the iron-reducing bacteria attached to the surface of the solid waste residue are repeatedly cultured.

6. The method according to claim 1, characterized in that The impurity removal process in step (3) specifically includes: (3.1) adding a precipitant to the ferrophosphorus solution, and then adding a flocculant to accelerate the precipitation rate of the impurity elements; (3.2) adding alkali solution to adjust the pH of the system to 2.0-3.0, and filtering to remove the insoluble impurity precipitate; (3.3) Add acid solution to the solution obtained above to adjust the system pH to <1.1, thereby obtaining the ferrophosphorus solution after impurities removal.

7. The method according to claim 6, characterized in that The precipitant is selected from one or more of sodium fluoride, sodium carbonate, sodium silicate, and iron powder; Preferably, the flocculant is selected from one or more of polyacrylamide, polyaluminium chloride and alum.

8. The method according to claim 6, characterized in that The alkali solution in the step (3.2) is selected from one or more of sodium hydroxide, ammonia water and sodium carbonate.

9. The method according to claim 1, characterized in that: In step (3), the oxidant is selected from one or more of sodium peroxide, hydrogen peroxide, and potassium permanganate; Preferably, the alkaline substance is selected from one or more of sodium hydroxide, ammonia water and sodium carbonate.

10. The method according to claim 1, characterized in that The specific steps after the solid-liquid separation in step (3) include: washing the obtained iron phosphate with pure water, adding a small amount of phosphoric acid, heating to 80-90° C. and continuing the reaction for 1-2 hours, and filtering to obtain the iron phosphate dihydrate product; The dihydrated ferric phosphate is calcined under high temperature conditions to obtain anhydrous ferric phosphate product.

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