A production process for preparing iron phosphate using Fenton process sludge

Abstract

The invention relates to the field of materials and chemical technology, and in particular to a production process for preparing iron phosphate by using Fenton process sludge, comprising the following steps: S1, introducing air into the sludge after Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials; S2, introducing the iron oxide powder into industrial-grade phosphoric acid to react and precipitate iron phosphate crystals; S3, washing the iron phosphate crystals with warm water and cold water; S4, removing crystal water and free water in the washed iron phosphate crystals by high temperature; S5, sintering the iron phosphate crystals with crystal water removed by high temperature after increasing the temperature; one of the raw materials used in the invention, the sludge after Fenton reaction, is solid waste in the field of sewage treatment, has low cost and large output, and the sludge after Fenton reaction is used as a raw material to produce iron phosphate with different crystal structures, which can greatly reduce the cost of using iron phosphate as a raw material, is not only conducive to solving the problem of sludge treatment difficulties in the field of sewage treatment, but also recovers waste resources and reuses them in emerging industries with high demand, thereby achieving the purpose of resource utilization.

Description

Technical Field

[0001] The invention relates to the technical field of materials and chemical industry, and in particular to a production process for preparing iron phosphate by utilizing Fenton process sludge. Background Art

[0002] The principle of the Fenton reaction is that a mixed solution of hydrogen peroxide and ferrous ions produces hydroxyl radicals. Hydroxyl radicals have strong oxidizing ability and can be used to treat wastewater containing more difficult-to-degrade organic matter. Lithium iron phosphate is a lithium-ion battery positive electrode material with the advantages of high energy density, long cycle life, and good safety performance. In recent years, with the development of new energy vehicles and energy storage industries, the market demand for lithium iron phosphate batteries has gradually increased. As an important raw material for the preparation of lithium iron phosphate, the demand for iron phosphate will also continue to increase.

[0003] However, the existing technology has the following disadvantages when used: although the treatment effect of organic wastewater degradation through Fenton reaction is good, the addition of ferrous ions increases the amount of sludge after wastewater treatment and eventually treats it as solid waste. The Fenton process sludge contains about 55% to 75% ferric hydroxide, resulting in a large waste of iron resources.

[0004] In summary, developing a production process for preparing iron phosphate using Fenton process sludge is still a key issue that needs to be urgently addressed in the field of materials and chemical technology. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that although the treatment effect of organic wastewater degradation by Fenton reaction is good, the amount of sludge after wastewater treatment increases due to the addition of ferrous ions, and finally it is treated in the form of solid waste. The Fenton process sludge contains about 55% to 75% of ferric hydroxide, resulting in a large waste of iron resources.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a production process for preparing iron phosphate by using Fenton process sludge, comprising the following steps: S1, introducing air into the sludge after Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials;

[0008] S2, introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals;

[0009] S3, washing the iron phosphate crystals with warm water and cold water;

[0010] S4, removing crystal water and free water from the washed iron phosphate crystals by high temperature;

[0011] S5, high-temperature sintering the iron phosphate crystals from which the crystal water has been removed by increasing the temperature.

[0012] Furthermore, in step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows:

[0013] The sludge after the Fenton reaction contains a large amount of iron hydroxide, suspended solids and PAM (linear high molecular polymer). After air is introduced and high-temperature burning is carried out, the iron hydroxide is converted into iron oxide, and other substances become ash and are mixed with iron oxide. Due to the large difference in molar mass, the ash and iron oxide are separated by a hair dryer.

[0014] Furthermore, in step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows:

[0015] Temperature monitoring is performed by using a matrix temperature sensor, a control end and a heater. The temperature data of different areas in the high-temperature burning work are collected in real time by the matrix temperature sensor, and the temperature data is transmitted to the control end. The control end controls the heater according to the temperature data. The temperature monitoring formula is: Q(n, m) = W(p, l, e), where the temperature values ​​of the nth and mth points in the Q(n, m) matrix, W(p, l, e) are functions of temperature change, (p, l) are spatial positions, and e is time. The control end uses the formula: R heater =t·ΔQ, where R heater The heater power, t is the system response coefficient, and ΔQ is the difference between the target temperature and the current temperature.

[0016] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0017] The iron oxide powder is introduced into industrial-grade phosphoric acid, and the pH value is controlled by the amount of iron oxide and phosphoric acid during the reaction to gradually precipitate iron phosphate from the solution to form iron phosphate crystals.

[0018] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0019] The target pH value range is set to 6.0-7.0 by combining the pH sensor and the automatic titration device. The automatic titration device automatically adds either iron oxide or phosphoric acid based on the pH value data of the solution detected by the pH sensor in real time. The pH control formula is: pH = -log 10 [H + ], where [H +] is the concentration of hydrogen ions in the solution, pH is the acidity or alkalinity of the solution, and the real-time pH control formula is: Δ(pH) = pH target -pH current , where Δ(pH) is the deviation between the current pH value and the target pH value, which is used to guide the direction and amplitude of the adjustment. target is the target pH, pH current is the actual pH of the solution currently measured, and the volume calculation formula for acid / base solution is: where Y add is the volume of either iron oxide or phosphoric acid that needs to be added, is the amount of either hydrogen ion or hydroxide ion that needs to be neutralized, U acid / base is the concentration of either iron oxide or phosphoric acid added, It can be calculated based on the hydrogen ion concentration and volume of the current solution: where Y solution is the volume of the solution, is the current hydrogen ion concentration of the solution, is the hydrogen ion concentration of the target solution.

[0020] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0021] The iron phosphate crystals are separated from the solution by filtering, and the water on the surface of the iron phosphate crystals is further removed by centrifugal dehydration.

[0022] Further, in step S3, the method of washing the iron phosphate crystals with warm water and cold water is:

[0023] The iron phosphate crystals obtained in step S2 are placed in warm water at a temperature between 40° C. and 60° C., and soluble impurities on the surface of the iron phosphate crystals or inside the iron phosphate crystals are dissolved and removed by washing 3 to 5 times.

[0024] Further, in step S3, the method of washing the iron phosphate crystals with warm water and cold water is:

[0025] During the 3-5 washing processes, a gradual transition from warm water to cold water is required, such as 40℃-60℃→30℃-40℃→0℃-20℃. 0℃-20℃ is cold water washing, which is used to completely remove the remaining water-soluble impurities in the solution and prevent the dissolution and loss of iron phosphate.

[0026] Further, in step S4, the method of removing the crystal water and free water in the washed ferric phosphate crystals by high temperature is:

[0027] The water in the structure of the washed iron phosphate crystals is removed by heating the washed iron phosphate crystals at a temperature of 210° C. to 230° C.

[0028] Further, in step S5, the method of high-temperature sintering the iron phosphate crystals from which the crystal water is removed by increasing the temperature is as follows:

[0029] At a high temperature of about 500° C.-1000° C., the iron phosphate crystals from which the crystal water has been removed are sintered at a high temperature, so that the crystal structure of the iron phosphate changes and is transformed into a hexagonal crystal structure at a high temperature of about 900° C.

[0030] Beneficial Effects

[0031] Compared with the known public technology, the technical solution provided by the present invention has the following advantages:

[0032] Beneficial effects:

[0033] One of the raw materials used in the present invention is the sludge after Fenton reaction, which is a solid waste in the sewage treatment field. It has low cost and large output. Using the sludge after Fenton reaction as a raw material to produce iron phosphate with different crystal structures can greatly reduce the cost of using iron phosphate as a raw material. It is not only beneficial to solve the problem of sludge treatment difficulties in the sewage treatment field, but also achieves the purpose of resource utilization by recycling waste resources and reusing them in emerging and high-demand industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of a production process for preparing iron phosphate using Fenton process sludge according to the present invention;

[0035] Figure 2 The present invention is a simplified process diagram of a production process for preparing iron phosphate using Fenton process sludge. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0037] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0039] Example:

[0040] like Figure 1 As shown, the present invention provides a production process for preparing iron phosphate using Fenton process sludge, comprising the following steps: S1, introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials;

[0041] Furthermore, in step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows:

[0042] The sludge after the Fenton reaction contains a large amount of iron hydroxide, suspended solids and PAM (linear high molecular polymer). After air is introduced and high-temperature burning is carried out, the iron hydroxide is converted into iron oxide, and other substances become ash and are mixed with iron oxide. Due to the large difference in molar mass, the ash and iron oxide are separated by a hair dryer.

[0043] Furthermore, in step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows:

[0044] Temperature monitoring is performed by using a matrix temperature sensor, a control end and a heater. The temperature data of different areas in the high-temperature burning work are collected in real time by the matrix temperature sensor, and the temperature data is transmitted to the control end. The control end controls the heater according to the temperature data. The temperature monitoring formula is: Q(n, m) = W(p, l, e), where the temperature values ​​of the nth and mth points in the Q(n, m) matrix, W(p, l, e) are functions of temperature change, (p, l) are spatial positions, and e is time. The control end uses the formula: R heater =t·ΔQ, where R heater The heater power, t is the system response coefficient, and ΔQ is the difference between the target temperature and the current temperature;

[0045] In this embodiment, the sludge formed after the Fenton reaction is introduced into the burning device and air is introduced to decompose the iron hydroxide therein at high temperature to generate iron oxide. Other components such as PAM organic matter are decomposed at high temperature and converted into ash or oxidized into carbon dioxide and water. A matrix temperature sensor is used to monitor the temperature of different areas of the burning device in real time to ensure that the temperature is evenly distributed within an appropriate range. The temperature data is transmitted to the control end through the sensor. The control end dynamically adjusts the heater output according to the set target temperature range to prevent the situation where the temperature is too high and the iron oxide is overburned or the low temperature causes incomplete oxidation. In the mixture formed after burning, the molar mass of the iron oxide powder is much greater than the ash. The air blowing separation device is used to separate the ash with lower density through air blowing to obtain the iron oxide powder. It is beneficial to ensure that the temperature is stable within the optimal range, avoid energy waste, product overburning and uneven quality, and effectively utilize waste, reduce environmental pollution, and improve the automation level of production through real-time temperature monitoring and automatic adjustment, reduce manual intervention and operation errors, and enhance the consistency and controllability of the process.

[0046] S2, introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals;

[0047] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0048] The iron oxide powder is introduced into industrial-grade phosphoric acid, and the pH value is controlled by the amount of iron oxide and phosphoric acid during the reaction to gradually precipitate iron phosphate from the solution to form iron phosphate crystals.

[0049] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0050] The target pH value range is set to 6.0-7.0 by combining the pH sensor and the automatic titration device. The automatic titration device automatically adds either iron oxide or phosphoric acid based on the pH value data of the solution detected by the pH sensor in real time. The pH control formula is: pH = -log 10 [H + ], where [H + ] is the concentration of hydrogen ions in the solution, pH is the acidity or alkalinity of the solution, and the real-time pH control formula is: Δ(pH) = pH target -pH current , where Δ(pH) is the deviation between the current pH value and the target pH value, which is used to guide the direction and amplitude of the adjustment. target is the target pH, pH current is the actual pH of the solution currently measured, and the volume calculation formula for acid / base solution is: where Y add is the volume of either iron oxide or phosphoric acid that needs to be added, is the amount of either hydrogen ion or hydroxide ion that needs to be neutralized, U acid / base is the concentration of either iron oxide or phosphoric acid added, It can be calculated based on the hydrogen ion concentration and volume of the current solution: where Y solution is the volume of the solution, is the current hydrogen ion concentration of the solution, is the hydrogen ion concentration of the target solution.

[0051] Further, in step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is:

[0052] The iron phosphate crystals are separated from the solution by filtering, and the water on the surface of the iron phosphate crystals is further removed by centrifugal dehydration;

[0053] In this embodiment, iron oxide powder is introduced into an industrial-grade phosphoric acid solution to gradually increase the pH value of the solution by adding iron oxide, the pH value of the solution is monitored in real time by a pH sensor, and any one of iron oxide or phosphoric acid is automatically added according to the data provided by the pH sensor, so that the solution is maintained under the most suitable conditions to ensure the stable precipitation of iron phosphate crystals, and then the iron phosphate crystals are separated from the solution by a filtering device, and then a centrifugal dehydration device is used to remove the water attached to the surface of the crystals. It is beneficial to avoid dissolution or impurities, improve product purity, detect and adjust pH in real time, improve process stability and consistency, reduce errors caused by manual intervention, avoid excessive use of any one of iron oxide or phosphoric acid, reduce waste, and reduce production costs.

[0054] S3, washing the iron phosphate crystals with warm water and cold water;

[0055] Further, in step S3, the method of washing the iron phosphate crystals with warm water and cold water is:

[0056] The iron phosphate crystals obtained in step S2 are placed in warm water at a temperature between 40° C. and 60° C., and soluble impurities on the surface of the iron phosphate crystals or inside the iron phosphate crystals are dissolved and removed by washing 3 to 5 times.

[0057] Further, in step S3, the method of washing the iron phosphate crystals with warm water and cold water is:

[0058] During the 3-5 washing processes, a gradual transition from warm water to cold water is required, such as 40℃-60℃→30℃-40℃→0℃-20℃. 0℃-20℃ is cold water washing, which is used to completely remove the remaining water-soluble impurities in the solution and prevent the dissolution and loss of iron phosphate.

[0059] In this embodiment, the purity of the iron phosphate crystals is improved by removing soluble impurities on the surface or inside the iron phosphate crystals through washing, so as to provide high-quality raw materials for subsequent applications such as preparing lithium iron phosphate batteries. During 3-5 washing processes, the warm water is gradually transitioned to cold water. After each washing, the cleanliness of the water is checked. The orderly washing with warm and cold water is beneficial to avoid the continuous use of high-temperature water, save energy, and meet the requirements of green environmental protection.

[0060] S4, removing crystal water and free water from the washed iron phosphate crystals by high temperature;

[0061] Further, in step S4, the method of removing the crystal water and free water in the washed ferric phosphate crystals by high temperature is:

[0062] removing moisture from the washed iron phosphate crystal structure by heating the washed iron phosphate crystal at a temperature of 210° C. to 230° C.;

[0063] In this embodiment, water molecules bound to iron phosphate molecules in the lattice structure of the iron phosphate crystals can be removed by heating in the range of 210°C-230°C without destroying the structure of the iron phosphate crystals or causing decomposition of other components, which is beneficial to improving the purity of the iron phosphate crystals, reducing the impact of moisture on the crystal structure, and avoiding crystal deformation or reactivity changes caused by environmental changes.

[0064] S5, sintering the iron phosphate crystals after removing the crystal water by increasing the temperature;

[0065] Further, in step S5, the method of high-temperature sintering the iron phosphate crystals from which the crystal water is removed by increasing the temperature is as follows:

[0066] At a high temperature of about 500° C. to 1000° C., the iron phosphate crystals from which the crystal water has been removed are subjected to high temperature sintering, so that the crystal structure of the iron phosphate changes and is transformed into a hexagonal crystal structure at a high temperature of about 900° C.;

[0067] In this embodiment, sintering is carried out at a high temperature of 500°C-1000°C to achieve the transformation of the iron phosphate crystals from an orthorhombic crystal structure, making it suitable for different application scenarios. At the same time, it is transformed into a hexagonal crystal structure at a high temperature of about 900°C. The hexagonal crystal structure has better thermal stability, a lower specific surface area and strong chemical stability. The iron phosphate with a hexagonal crystal structure has a crystal structure that is more suitable for lithium ion embedding, which can effectively improve the capacity and charge and discharge efficiency of lithium batteries.

[0068] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A production process for preparing iron phosphate using Fenton process sludge, characterized in that: The following steps are involved: S1. The sludge after Fenton reaction is introduced into air and then burned at high temperature to obtain iron oxide powder and other ash materials; S2, introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals; S3, washing the iron phosphate crystals with warm water and cold water; S4, removing crystal water and free water from the washed iron phosphate crystals by high temperature; S5, high-temperature sintering the iron phosphate crystals from which the crystal water has been removed by increasing the temperature.

2. A production process for preparing iron phosphate using Fenton process sludge according to claim 1, characterized in that: In step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows: The sludge after the Fenton reaction contains a large amount of iron hydroxide, suspended solids and PAM (linear high molecular polymer). After air is introduced and high-temperature burning is carried out, the iron hydroxide is converted into iron oxide, and other substances become ash and are mixed with iron oxide. Due to the large difference in molar mass, the ash and iron oxide are separated by a hair dryer.

3. A production process for preparing iron phosphate using Fenton process sludge according to claim 2, characterized in that: In step S1, the method of introducing air into the sludge after the Fenton reaction and then burning it at high temperature to obtain iron oxide powder and other ash materials is as follows: Temperature monitoring is performed by using a matrix temperature sensor, a control end, and a heater. The temperature data of different areas in the high-temperature burning work are collected in real time by the matrix temperature sensor, and the temperature data is transmitted to the control end. The control end controls the heater according to the temperature data. The temperature monitoring formula is: Q(n, m) = W(p, l, e), where the temperature values ​​of the nth and mth points in the Q(n, m) matrix, W(p, l, e) are functions of temperature change, (p, l) are spatial positions, and e is time. The control end uses the formula: R heater =t·ΔQ, where R heater The heater power, t is the system response coefficient, and ΔQ is the difference between the target temperature and the current temperature.

4. A production process for preparing iron phosphate using Fenton process sludge according to claim 3, characterized in that: In step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is as follows: The iron oxide powder is introduced into industrial-grade phosphoric acid, and the pH value is controlled by the amount of iron oxide and phosphoric acid during the reaction to gradually precipitate iron phosphate from the solution to form iron phosphate crystals.

5. A production process for preparing iron phosphate using Fenton process sludge according to claim 4, characterized in that: In step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is as follows: The target pH value range is set to 6.0-7.0 by combining the pH sensor and the automatic titration device. The automatic titration device automatically adds either iron oxide or phosphoric acid based on the pH value data of the solution detected by the pH sensor in real time. The pH control formula is: pH = -log 10 [H + ], where [H + ] is the concentration of hydrogen ions in the solution, pH is the acidity or alkalinity of the solution, and the real-time pH control formula is: Δ(pH) = pH target -pH current , where Δ(pH) is the deviation between the current pH value and the target pH value, which is used to guide the direction and amplitude of the adjustment. target is the target pH, pH current is the actual pH of the solution currently measured, and the volume calculation formula for acid / base solution is: where Y add is the volume of either iron oxide or phosphoric acid that needs to be added, is the amount of either hydrogen ion or hydroxide ion that needs to be neutralized, U acid / base is the concentration of either iron oxide or phosphoric acid added, It can be calculated based on the hydrogen ion concentration and volume of the current solution: where Y solution is the volume of the solution, is the current hydrogen ion concentration of the solution, is the hydrogen ion concentration of the target solution.

6. A production process for preparing iron phosphate using Fenton process sludge according to claim 5, characterized in that: In step S2, the method of introducing the iron oxide powder into industrial grade phosphoric acid to react and precipitate iron phosphate crystals is as follows: The iron phosphate crystals are separated from the solution by filtering, and the water on the surface of the iron phosphate crystals is further removed by centrifugal dehydration.

7. A production process for preparing iron phosphate using Fenton process sludge according to claim 6, characterized in that: In step S3, the method of washing the iron phosphate crystals with warm water and cold water is as follows: The iron phosphate crystals obtained in step S2 are placed in warm water at a temperature between 40° C. and 60° C., and soluble impurities on the surface of the iron phosphate crystals or inside the iron phosphate crystals are dissolved and removed by washing 3 to 5 times.

8. A production process for preparing iron phosphate using Fenton process sludge according to claim 7, characterized in that: In step S3, the method of washing the iron phosphate crystals with warm water and cold water is as follows: During the 3-5 washing processes, a gradual transition from warm water to cold water is required, such as 40℃-60℃→30℃-40℃→0℃-20℃. 0℃-20℃ is cold water washing, which is used to completely remove the remaining water-soluble impurities in the solution and prevent the dissolution and loss of iron phosphate.

9. A production process for preparing iron phosphate using Fenton process sludge according to claim 8, characterized in that: In step S4, the method of removing the crystal water and free water in the washed ferric phosphate crystals by high temperature is: The water in the structure of the washed iron phosphate crystals is removed by heating the washed iron phosphate crystals at a temperature of 210° C. to 230° C.

10. A production process for preparing iron phosphate using Fenton process sludge according to claim 9, characterized in that: In step S5, the method of high-temperature sintering the iron phosphate crystals after removing the crystal water by increasing the temperature is: At a high temperature of about 500° C.-1000° C., the iron phosphate crystals from which the crystal water has been removed are sintered at a high temperature, so that the crystal structure of the iron phosphate changes and is transformed into a hexagonal crystal structure at a high temperature of about 900° C.

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