Treatment method of iron phosphate waste filter cake

Abstract

The invention relates to the technical field of iron phosphate production, in particular to a treatment method of an iron phosphate waste filter cake. The invention discloses a treatment method of an iron phosphate waste filter cake, which comprises the following steps: step 1, pulping the iron phosphate waste filter cake to obtain waste slurry; 2, the waste slurry is filtered and deironed, and deironed slurry is obtained; step 3, carrying out solid-liquid separation, drying and sintering on the iron-removed slurry to obtain a sintered material; step 4, dissolving the sintered material by using sulfuric acid to obtain an acid-soluble material liquid; step 5, carrying out reaction on the acid-soluble material liquid and auxiliary materials to prepare an iron phosphate semi-finished product; and step 6, reacting the iron phosphate semi-finished product with phosphoric acid to prepare an iron phosphate product. According to the treatment method disclosed by the invention, useful components (such as iron and phosphorus) in the waste filter cake are reconverted into an iron phosphate product with a high additional value, so that the resource utilization rate is increased, and the production cost of an enterprise is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of ferric phosphate production, and in particular to a method for treating waste ferric phosphate filter cakes. Background Art

[0002] With the rapid growth of the new energy vehicle market and increasingly stringent requirements for environmental protection, lithium-ion batteries have been widely used as one of the key components for clean energy storage. Among them, lithium iron phosphate batteries are highly favored for their high safety, long life and environmental friendliness. As an important component of the positive electrode material of lithium iron phosphate batteries, the demand for iron phosphate has also increased significantly. In the production process of iron phosphate, in order to meet the market's requirements for high-quality products, the production process is continuously optimized, the level of automation is continuously improved, and the production efficiency is significantly improved.

[0003] However, in the pursuit of efficient production, a certain amount of waste is inevitably generated. For example, leakage during equipment maintenance, materials discharged during tank cleaning, and slurry discarded due to substandard quality will enter the ditch or become semi-finished product waste. These wastes not only occupy valuable storage space, but may also pollute the environment due to improper disposal. Therefore, how to effectively recycle these wastes has become a common concern within and outside the industry.

[0004] The current waste iron phosphate filter cake has the following technical problems:

[0005] 1. Waste of resources: Due to the lack of effective treatment methods, a large amount of iron phosphate waste is directly scrapped, which not only causes waste of raw materials but also increases the operating costs of enterprises.

[0006] 2. Environmental pollution: Improperly treated iron phosphate waste contains heavy metals and other harmful substances. If it is discharged into the environment at will, it may cause pollution to the soil, water and even the air.

[0007] 3. Economic considerations: Traditional processing methods often require a large amount of additional capital investment for the purchase of special equipment and technology research and development, which is a considerable expense for some small and medium-sized enterprises, affecting their enthusiasm for adopting advanced processing technologies.

[0008] 4. Process complexity: The existing recycling process is usually complicated, involving multiple steps such as washing, filtering, drying, etc., and each link requires precise control of parameters to ensure the quality of the final product, which places high demands on the professional skills of the operators.

[0009] To this end, the present application proposes a method for treating waste iron phosphate filter cake. Summary of the invention

[0010] The treatment method of iron phosphate waste filter cake described in this application, through a series of technological steps such as pulping, filtering, iron removal, drying, sintering, dissolution, and chemical reaction, re-converts the useful components (such as iron, phosphorus, etc.) in the waste filter cake into iron phosphate products with high added value, avoids the direct discard of the waste filter cake, reduces the waste of raw materials, improves the resource utilization rate, and reduces the production cost of enterprises.

[0011] The technical solution adopted by this application to solve its technical problems is:

[0012] A treatment method of iron phosphate waste filter cake includes the following steps:

[0013] Step 1. Pulp the iron phosphate waste filter cake to obtain waste slurry;

[0014] Step 2. Filter and remove iron from the waste slurry to obtain iron-removed slurry;

[0015] Step 3. Perform solid-liquid separation, drying, and sintering on the iron-removed slurry to obtain sintered material;

[0016] Step 4. Use sulfuric acid to dissolve the sintered material to obtain acid-soluble material liquid;

[0017] Step 5. React the acid-soluble material liquid with auxiliary materials to prepare semi-finished iron phosphate;

[0018] Step 6. React the semi-finished iron phosphate with phosphoric acid to prepare iron phosphate products.

[0019] In some specific embodiments, in Step 1, the solid content of the waste slurry is 15-25%.

[0020] In some specific embodiments, in Step 2, a 100-200 mesh sieve is used for filtering to exclude large particles.

[0021] In some specific embodiments, in Step 2, an electromagnetic iron remover is used for circulating demagnetization to exclude magnetic substances and obtain iron-removed slurry.

[0022] In some specific embodiments, in Step 3, a flash dryer is used to dry the filter cake until the water content is 4-5% to obtain dried material.

[0023] In some specific embodiments, in Step 4, the dried material is sintered in a rotary kiln.

[0024] In some specific embodiments, in Step 4, the dry loss rate of the sintered material is less than 0.5%.

[0025] In some specific embodiments, in Step 5, the auxiliary materials are oxidized ferric sulfate and monoammonium phosphate, or ferrous sulfate, monoammonium phosphate, and hydrogen peroxide.

[0026] In some specific embodiments, in step 6, the iron phosphate semi-finished product is washed until the conductivity of the washing water is < 5000 us / cm.

[0027] In some specific embodiments, in step 6, the iron phosphate semi-finished product and phosphoric acid are reacted at 90 - 100 °C.

[0028] The beneficial effects of this application are as follows:

[0029] The treatment method described in this application, through systematic recycling treatment, converts the useful components in the waste filter cake into iron phosphate products with high added value, reduces resource waste, and improves resource utilization rate; and optimizes the process flow, reduces operation steps, lowers the professional skill requirements for operators, improves the feasibility and operability of the process, ensures the purity and performance of the final iron phosphate product, and meets the requirements of battery-grade materials.

[0030] The treatment method described in this application, by removing heavy metals and harmful substances in the waste filter cake, prevents environmental pollution caused by them. At the same time, by adopting an efficient process flow, it reduces equipment costs and energy consumption, improves the economic efficiency of the process, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention will be further described below with reference to the drawings and embodiments.

[0032] Figure 1 SEM image of the iron phosphate prepared in Example 1 of this application;

[0033] Figure 2 SEM image of the iron phosphate prepared in Example 2 of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] In order to make the technical problems to be solved, technical solutions and beneficial effects of this application clearer, the following further describes this application in detail with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application.

[0035] In this application, the term "and / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0036] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single item or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple respectively.

[0037] It should be understood that in various embodiments of this application, the magnitude of the serial numbers of the above processes does not mean the sequence of execution. Some or all steps can be executed in parallel or sequentially. The execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0038] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application. The singular forms "a", "the", and "said" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0039] The weight of the relevant components mentioned in the specification of the embodiments of this application can not only refer to the specific content of each component, but also represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the specification of the embodiments of this application is scaled up or down proportionally, it is within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass described in the specification of the embodiments of this application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0040] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0041] Term Explanation:

[0042] Conductivity: It is a physical quantity used to describe the conductivity of a substance. In the text, the conductivity of the washing water < 5000 μs / cm is an index to measure the residual degree of impurity ions in the filter cake after washing. The lower the conductivity, the lower the concentration of impurity ions.

[0043] The trench material filter cake refers to the waste generated during the production of iron phosphate due to equipment maintenance, leakage, or tank cleaning. These wastes usually enter the trench and are collected to form a filter cake.

[0044] A plate and frame, usually referring to a plate and frame filter press, is a device used for solid-liquid separation.

[0045] A flash dryer, a device that uses high-speed hot air flow to instantaneously dry materials.

[0046] The dry loss rate refers to the percentage of moisture or other volatile components lost during the sintering process of materials.

[0047] ND (Not Detected) indicates "not detected" or "below the detection limit" in the test results.

[0048] A method for treating waste filter cake of iron phosphate, comprising the following steps:

[0049] Step 1. Pulping the waste filter cake of iron phosphate to obtain a waste slurry;

[0050] Step 2. Filtering and iron removal of the waste slurry to obtain an iron-removed slurry;

[0051] Step 3. Solid-liquid separation, drying, and sintering of the iron-removed slurry to obtain a sintered material;

[0052] Step 4. Dissolving the sintered material with sulfuric acid to obtain an acid-soluble material solution;

[0053] Step 5. Reacting the acid-soluble material solution with auxiliary materials to prepare a semi-finished iron phosphate product;

[0054] Step 6. Reacting the semi-finished iron phosphate product with phosphoric acid to prepare an iron phosphate product.

[0055] Specifically, in Step 1, the solid content of the waste slurry is 15-25%.

[0056] In the above technical solution, the waste filter cake of iron phosphate usually has a high solid content and poor fluidity, and problems such as caking and blockage are likely to occur during direct treatment. Through pulping treatment, the filter cake is mixed with a liquid (such as demineralized water) to form a slurry with certain fluidity, which is convenient for subsequent operations such as filtration and impurity removal.

[0057] Specifically, in Step 2, a 100-200 mesh sieve is used for filtration to remove large particle solids. Then, an electromagnetic iron remover is used for cyclic demagnetization to remove magnetic substances to obtain an iron-removed slurry.

[0058] In the above technical solution, the waste slurry may contain impurities with relatively large particles (such as metal particles generated by equipment wear), and these impurities will affect the subsequent process effects such as drying and sintering. These large-particle impurities can be removed through filtration to ensure the purity of the slurry.

[0059] Magnetic metal is one of the common impurities in the production of iron phosphate, and its presence will affect the purity and safety performance of the iron phosphate product. Through the iron removal operation, the magnetic impurities in the slurry can be removed to improve the product quality.

[0060] It can be understood that a 100-200 mesh sieve is used to filter the slurry, and the large-particle impurities are intercepted by the aperture size of the sieve, thereby removing the large-particle impurities.

[0061] It can be understood that an electromagnetic iron remover adsorbs magnetic metal impurities in the slurry by generating a strong magnetic field. When the slurry passes through the electromagnetic iron remover, magnetic substances (such as Fe, Co, Ni, etc.) will be adsorbed and separated by the magnetic field, thereby achieving the purpose of iron removal.

[0062] Specifically, in step 3, a flash dryer is used to dry the filter cake at 300-400 °C until the moisture content reaches 4-5% (preferably 4.1-4.9%) to obtain a dried material. The dried material is sintered in a rotary kiln at 450-500 °C to obtain a sintered material. The dry loss rate of the sintered material is less than 0.5% (preferably 0.1-0.3%), and the content of S in the sintered material is usually ≥300 ppm.

[0063] In step 3, after the iron-removed slurry undergoes pulping and iron removal treatment, it still contains a large amount of water. The purpose of solid-liquid separation and drying is to remove the excess water and make the material reach a dryness suitable for subsequent sintering. Through drying and sintering, the slurry is transformed into a sintered material with certain strength and chemical stability, providing suitable raw materials for the subsequent dissolution and reaction steps.

[0064] It can be understood that solid-liquid separation is usually carried out by filtration or centrifugal separation methods.

[0065] The drying process removes the moisture in the material through heat energy. In the present invention, a flash dryer is used, and its principle is to instantaneously dry the material by using a high-speed hot air flow. Flash drying has the advantages of fast drying speed, high efficiency, and short heating time of the material, and is suitable for treating slurries with a relatively high water content.

[0066] Sintering is to heat-treat the dried material at a high temperature to cause physical and chemical reactions between its particles to form a sintered material with certain strength and stability. The sintering process can remove organic substances and make the chemical composition of the material more uniform.

[0067] Specifically, in step 4, the sintered material contains effective components such as iron phosphate, which can be converted into soluble substances through sulfuric acid dissolution, facilitating subsequent chemical reactions and separation.

[0068] Specifically, in step 5, the auxiliary materials are oxidized ferric sulfate and monoammonium phosphate, or ferrous sulfate, monoammonium phosphate, and hydrogen peroxide.

[0069] The iron ions (such as Fe 3+ or Fe 2+ ) in the acid-dissolved liquor react with the phosphate ions (PO 4 3- ) in the auxiliary materials to form a precursor of iron phosphate.

[0070] By adjusting the pH value of the reaction system (such as using ammonia water), the precipitation process of iron phosphate can be controlled to form uniform precipitation within a suitable pH range. The adjustment of the pH value is crucial for controlling the particle size and purity of the precipitation.

[0071] In step 6, the semi-finished iron phosphate is washed until the conductivity of the wash water < 5000 us / cm (preferably). The semi-finished iron phosphate and phosphoric acid are reacted at 90 - 100 °C. After the reaction, filtration is carried out, followed by drying, sintering, and packaging to obtain the iron phosphate product.

[0072] After the reaction, by washing (such as the conductivity of the wash water < 5000 us / cm), the impurity ions (such as sulfate ions, ammonium ions, etc.) that may remain during the reaction process can be removed to further improve the purity of the product.

[0073] The semi-finished iron phosphate (basic iron phosphate) reacts with phosphoric acid (H 3 PO 4 ) to form iron phosphate dihydrate (FePO 4 ·2H 2 O) or other forms of iron phosphate compounds. This reaction further optimizes the chemical composition and crystal structure of iron phosphate by providing additional phosphoric acid.

[0074] Thermodynamic and kinetic control: The reaction is carried out at a temperature of 90 - 100 °C. The high temperature helps to increase the reaction rate and promote the crystallization process of iron phosphate. At the same time, the control of temperature can avoid the occurrence of side reactions and ensure the purity and quality of the product.

[0075] Through the following examples and comparative examples, a method for treating waste filter cake of iron phosphate described in this application is further elaborated.

[0076] Example 1

[0077] A method for treating waste filter cake of iron phosphate includes the following steps:

[0078] Prepare the gutter material filter cake to be processed and make a pulp with demineralized water. Detect the solid content of the filter cake. Its moisture content is 47%. Add 30 cubic meters of demineralized water into the tank and put in 18 t of filter cake. Calculate that the theoretical solid content is about 19.9%.

[0079] Circulate the slurry by itself and use a 150-mesh sieve to intercept large particles. Clean the sieve many times until there is no obvious intercepted material on the sieve and then stop the circulation.

[0080] Circulate the material through an electromagnetic iron remover for demagnetization. When the circulation time is ≥2 h, stop the circulation. Use a plate and frame for solid-liquid separation. Flash dry the filter cake at 400 °C until the moisture content is 4.1%, and then sinter it. Set the sintering temperature at 500 °C for 2 h.

[0081] Detect the sintered material. The dry loss rate is 0.2% and the S content is 2000 ppm. Use sulfuric acid with a mass concentration of 15% to completely dissolve the sintered material. When controlling the feeding during dissolution, the solid content is 15%. After dissolution treatment, a complete solution is obtained.

[0082] During synthesis, add 300 ml of the complete solution, add 200 ml of 1.5 mol / L oxidized ferrous sulfate, add 200 ml of 1.5 mol / L monoammonium phosphate, slowly add ammonia water to adjust the pH to 1.98. After reacting for 1 h, wash until the conductivity of the washing water is 4736 us / cm.

[0083] Add 500 ml of water to make a pulp of the filter cake, add 8 ml of 85% phosphoric acid, heat up to 95 °C for conversion for 2 h, and the filter cake becomes powdery.

[0084] Wash the filter cake, dry it in an oven (150 °C), and sinter it using a muffle furnace (500 °C) to obtain the Figure 1 phosphoferrite product as shown.

[0085] Example 2

[0086] A method for treating phosphoferrite waste filter cake, comprising the following steps:

[0087] Prepare the synthetic PH-to-high plate and frame filter cake to be processed and make a pulp with demineralized water. Detect the solid content of the filter cake. Its moisture content is 50%. Add 30 cubic meters of demineralized water into the tank and put in 16 t of filter cake. Calculate that the theoretical solid content is about 22.2%.

[0088] Circulate the slurry by itself and use a 200-mesh sieve to intercept large particles. Clean the sieve many times until there is no obvious intercepted material on the sieve and then stop the circulation.

[0089] The material is subjected to cyclic demagnetization by an electromagnetic separator. When the cycle time is ≥2 h, the cycle is stopped, and a plate-and-frame filter is used for solid-liquid separation. The filter cake is flash-dried at 400 °C until the water content reaches 4.9%, and then sintered at 450 °C for 2 h.

[0090] The sintered material is detected. The dry loss rate is 0.1%, and the S content is 445 ppm. The sintered material is dissolved with sulfuric acid with a mass concentration of 1.1%. When controlling the feeding during dissolution, the solid content is 15% to obtain a semi-liquid.

[0091] During synthesis, 300 ml of the semi-liquid is added, 200 ml of 1.5 mol / L unoxidized ferrous sulfate is added, 200 ml of 1.5 mol / L ammonium monophosphate is added, and hydrogen peroxide is slowly added to oxidize divalent iron. After reacting for 1 h, it is washed until the conductivity of the washing water reaches 4201 us / cm.

[0092] 500 ml of water is added to make a pulp of the filter cake, 8 ml of 85% phosphoric acid is added, and the temperature is raised to 95 °C for conversion for 2 h, and the filter cake becomes powdery.

[0093] The filter cake is washed, oven-dried (at 150 °C), and sintered using a muffle furnace (at 450 °C) to obtain the Figure 2 phosphoferrite product as shown.

[0094] Example 3

[0095] A method for treating waste filter cake of phosphoferrite, comprising the following steps:

[0096] Prepare the waste filter cake in the gutter to be treated and make a pulp of it using demineralized water. The solid content of the filter cake is detected, and its water content is 48%. 35 cubic meters of demineralized water is added to the tank, and 18 t of the filter cake is put in. The theoretical solid content is calculated to be about 17.7.

[0097] The slurry is circulated by itself, and a 100-mesh sieve is used to intercept large particles. The sieve is cleaned multiple times until there is no obvious intercepted material on the sieve, and then the circulation is stopped.

[0098] The material is subjected to cyclic demagnetization by an electromagnetic separator. When the cycle time is ≥2 h, the cycle is stopped, and a plate-and-frame filter is used for solid-liquid separation. The filter cake is flash-dried at 390 °C until the water content reaches 4.5%, and then sintered at 480 °C for 2 h.

[0099] The sintered material is detected. The dry loss rate is 0.3%, and the S content is 550 ppm; the sintered material is completely dissolved with sulfuric acid with a mass concentration of 10%. When controlling the feeding during dissolution, the solid content is 15%. After dissolution treatment, what is obtained is basically a completely dissolved liquid.

[0100] During synthesis, 300 ml of all-liquid solution was added, 200 ml of 1.5 mol / L peroxidized ferrous sulfate was added, 200 ml of 1.5 mol / L ammonium monophosphate was added, and ammonia water was slowly added to adjust the pH to 1.95. After reacting for 1 h, washing was carried out until the conductivity of the washing water reached 3508 us / cm.

[0101] 500 ml of water was added to make a slurry of the filter cake, 8 ml of 85% phosphoric acid was added, and the temperature was raised to 98 °C for conversion for 1.5 h, and the filter cake became powdery.

[0102] The filter cake was washed, dried in an oven (150 °C), and sintered using a muffle furnace (500 °C) to obtain iron phosphate products.

[0103] Comparative Example 1

[0104] A method for treating iron phosphate waste filter cake includes the following steps:

[0105] Prepare the gutter material filter cake to be treated and make a slurry of it using demineralized water. The solid content of the filter cake was detected, and its moisture content was 47%. 30 cubic meters of demineralized water was added to the tank, 18 t of filter cake was put in, and the theoretical solid content was calculated to be about 19.9%.

[0106] The slurry was circulated by itself, and a 150-mesh sieve was used to intercept large particles. The sieve was cleaned many times until there was no obvious intercepted material on the sieve and then the circulation was stopped.

[0107] The material was circulated for demagnetization through an electromagnetic demagnetizer. When the circulation time was ≥2 h, the circulation was stopped, and a plate and frame were used for solid-liquid separation to obtain a filter cake.

[0108] The filter cake was dissolved using 20% sulfuric acid by mass, and the following occurred: the filter cake was difficult to dissolve, and it was still difficult to dissolve and filter even when the temperature was raised.

[0109] Comparative Example 2

[0110] A method for treating iron phosphate waste filter cake includes the following steps:

[0111] Prepare the gutter material filter cake to be treated and make a slurry of it using demineralized water. The solid content of the filter cake was detected, and its moisture content was 47%. 30 cubic meters of demineralized water was added to the tank, 18 t of filter cake was put in, and the theoretical solid content was calculated to be about 19.9%.

[0112] The slurry was circulated by itself, and a 150-mesh sieve was used to intercept large particles. The sieve was cleaned many times until there was no obvious intercepted material on the sieve and then the circulation was stopped.

[0113] The material was circulated for demagnetization through an electromagnetic demagnetizer. When the circulation time was ≥2 h, the circulation was stopped, and a plate and frame were used for solid-liquid separation.

[0114] The filter cake was dissolved using sulfuric acid with a mass concentration of 30%. It was found that the filter cake was difficult to dissolve, and even when the temperature was raised, it was still difficult to dissolve and filter.

[0115] The iron phosphate products obtained in Examples 1 - 3 were tested, and the test results are summarized in Table 1 below.

[0116] Table 1

[0117]

[0118]

[0119] As can be seen from Table 1, for the contents of phosphorus (P) and iron (Fe): in Examples 1 - 3, the percentage contents of P and Fe were relatively stable and mainly composed of iron phosphate.

[0120] Fe / P ratio: This ratio is close to the iron - phosphorus ratio in the theoretical chemical formula of iron phosphate, indicating that the synthesis process was well - controlled and the product had a high purity.

[0121] Sulfur (S) content: The low sulfur content indicates that sulfate was effectively removed during the treatment process, which is particularly important for battery materials because high sulfur content may affect battery performance.

[0122] Trace elements: For other trace elements such as Ca, Mg, Na, etc., their concentrations were very low, and some were even undetectable (ND), which means the product had a high purity and was suitable as the cathode material for high - performance lithium - ion batteries.

[0123] Heavy metals and other impurities: For example, the contents of elements such as Ni, Zn, Cu, Mn, Pb, Cr, Al, Ti, Co, K, etc. were also at very low levels, which helped to improve the safety and cycle life of the battery.

[0124] Figure 1 and Figure 2 Figure shows the morphology of iron phosphate particles taken by scanning electron microscope (SEM). From the figure, the particles are uniform and have a moderate particle size, which is beneficial to improving the conductivity and ion transport efficiency of the electrode material.

[0125] The result of Comparative Example 1 was difficult dissolution; in Comparative Example 1, sulfuric acid with a mass concentration of 20% was used to dissolve the filter cake, and it was found that the filter cake was difficult to dissolve, and even when the temperature was raised, it was still difficult to dissolve and filter. This indicates that high - concentration sulfuric acid may not be suitable for directly dissolving the filter cake without pretreatment (such as sintering).

[0126] In Comparative Example 2, the situation was more serious. Sulfuric acid with a mass concentration of 30% was used, resulting in the filter cake being not only difficult to dissolve, but also unable to improve the solubility or filtration effect even when the temperature was raised.

[0127] It can be seen that the main reasons why Examples 1-3 can successfully process the iron phosphate waste filter cake while Comparative Examples 1-2 fail to achieve the same effect are as follows:

[0128] Sintering step: Example 1 includes a sintering step, which is carried out at 450-500 °C. This process causes physical and chemical changes in the components of the filter cake, forming a structure that is more easily soluble in acid. In contrast, Comparative Examples 1-2 skipped this step and directly treated the original filter cake with sulfuric acid, thus encountering problems with difficult dissolution.

[0129] Moderate sulfuric acid concentration: Example 1 selected a suitable concentration of sulfuric acid (15%), which can not only effectively dissolve the sintered material but also prevent incomplete dissolution or other side reactions due to excessive concentration. In contrast, the sulfuric acid concentrations used in Comparative Examples 1-2 are too high (20% and 30% respectively), which may lead to the formation of insoluble compounds or over-reaction, thus hindering the normal dissolution process.

[0130] Degree of drying: After being treated by a flash dryer, the water content of the filter cake in Example 1 is reduced to 4-5%. Such a degree of drying helps the subsequent sintering and dissolution steps to proceed smoothly. In contrast, Comparative Examples 1-2 may lack proper drying treatment, which affects the solubility and filtration efficiency of the filter cake.

[0131] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for treating waste ferric phosphate filter cake, characterized in that: The following steps are involved: Step 1. Slurrying the waste iron phosphate filter cake to obtain waste slurry; Step 2: filtering and removing iron from the waste slurry to obtain iron-removed slurry; Step 3. performing solid-liquid separation, drying and sintering on the iron removal slurry to obtain a sintered material; Step 4. using sulfuric acid to dissolve the sintering material to obtain an acid-soluble material solution; Step 5. reacting the acid-soluble liquid with the auxiliary materials to prepare a semi-finished ferric phosphate product; Step 6. reacting the semi-finished ferric phosphate product with phosphoric acid to prepare the ferric phosphate product.

2. The processing method according to claim 1, characterized in that: In step 1, the solid content of the waste slurry is 15-25%.

3. The processing method according to claim 1, characterized in that: In step 2, filter using a 100-200 mesh screen to remove large particles.

4. The processing method according to claim 3, characterized in that: In step 2, an electromagnetic iron remover is used to perform cyclic demagnetization to remove magnetic materials and obtain an iron-removing slurry.

5. The processing method according to claim 1, characterized in that: In step 3, the filter cake is dried using a flash dryer to a moisture content of 4-5% to obtain a dried material.

6. The processing method according to claim 5, characterized in that: In step 4, the dried material is sintered in a rotary kiln.

7. The processing method according to claim 6, characterized in that: In step 4, the dry loss rate of the sintering material is less than 0.5%.

8. The processing method according to claim 1, characterized in that: In step 5, the auxiliary materials are oxidized ferrous sulfate and monoammonium phosphate, or ferrous sulfate, monoammonium phosphate, and hydrogen peroxide.

9. The processing method according to claim 1, characterized in that: In step 6, the semi-finished ferric phosphate product is washed until the conductivity of the washing water is less than 5000 us / cm.

10. The processing method according to claim 1, characterized in that: In step 6, the semi-finished iron phosphate product and phosphoric acid are reacted at 90-100°C.

Images