Method for recovering phosphorus and fluorine from sludge containing phosphorus and fluorine

Abstract

The invention discloses a method for recovering phosphorus and fluorine from sludge containing phosphorus and fluorine. The method is used for resourceful treatment of the sludge containing phosphorus and fluorine in the phosphorus chemical industry. The method comprises the steps that sludge containing phosphorus and fluorine and experimental water are mixed in proportion to obtain sludge slurry, the sludge slurry is fully stirred so that the sludge slurry can be evenly dispersed, and the experimental water is consistent with field water of phosphorus chemical enterprises and is slag field return water or preparation process water; adjusting the solid content of the sludge slurry to 20%-30%; adding sulfuric acid as a reaction reagent into the sludge slurry, and carrying out a stirring reaction to obtain a mixture; carrying out solid-liquid separation on the mixture through a filtering system, and collecting filtrate containing soluble phosphorus and fluorine and solid-phase residues obtained through separation; and recovering the filtrate for a phosphorus chemical production process to realize phosphorus and fluorine resource recovery, and carrying out subsequent treatment on the solid-phase residue to realize sludge residue reduction.

Description

Technical Field

[0001] This application relates to the field of chemical production technology, and in particular to a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge. Background Technology

[0002] In recent years, with the large-scale development of the phosphate chemical industry, the amount of phosphorus- and fluorine-containing sludge generated during phosphate mining and deep processing has been increasing year by year. Its resource recovery and harmless disposal have become core aspects of the industry's green transformation. Direct landfilling or stockpiling of phosphorus- and fluorine-containing sludge generated during phosphoric acid production not only results in a serious waste of phosphorus and fluorine resources but may also cause soil and groundwater pollution due to fluoride leakage, which does not comply with national circular economy policies.

[0003] Existing treatment processes for phosphorus and fluoride recovery from phosphorus and fluoride-containing sludge have significant limitations and are fragmented. They first use pure water or tap water to prepare the sludge slurry, without considering the common issues of slag yard return water and process water preparation in phosphate chemical plants. Then, sulfuric acid is added to the slurry arbitrarily without specifying the range of solid content. Often, if the solid content is below 20%, the reaction system volume is too large, increasing the equipment load, or if it is above 30%, the slurry becomes pasty and unevenly mixed, resulting in insufficient contact between sulfuric acid and sludge. The phosphorus and fluoride conversion rate can only reach 30%-50%, which cannot achieve efficient recovery of phosphorus and fluoride from sludge.

[0004] In addition, after the reaction, solid-liquid separation is carried out by a conventional plate and frame filter press. If the separated filtrate is to be reused, additional equipment is required for purification and impurity removal. It cannot be directly connected to the phosphorus chemical production process. The resulting solid residue also needs to be transported to a landfill for disposal separately. This not only fails to reduce sludge volume but also creates a redundant process, increases enterprise costs, and makes it difficult to guarantee the stability of the treatment effect. Summary of the Invention

[0005] This application discloses a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge, which can be used for the resource-based treatment of phosphorus- and fluorine-containing sludge in the phosphorus chemical industry.

[0006] This application discloses a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge, including: Phosphorus- and fluorine-containing sludge was mixed with experimental water in a certain proportion to obtain sludge slurry. The sludge slurry was then thoroughly stirred to ensure uniform dispersion. The experimental water was the same as the on-site water used in the phosphate chemical plant, which was either slag yard return water or prepared process water. The solids content of the sludge slurry is adjusted to 20%-30%; Sulfuric acid is added as a reactant to the sludge slurry, and the mixture is stirred to obtain a mixture. The mixture is subjected to solid-liquid separation through a filtration system, and the resulting filtrate containing soluble phosphorus and fluorine and solid residue are collected. The filtrate is recycled for use in phosphorus chemical production processes to achieve the recovery of phosphorus and fluorine resources, and the solid residue is further disposed of to reduce the amount of sludge.

[0007] Optionally, the amount of sulfuric acid added is 1.2 to 1.5 times the total molar amount of phosphate in the sludge slurry.

[0008] Optionally, the sulfuric acid has a density of 1.8 g / ml and is added in batches, with the first addition being 60%-70% of the total amount, and the remaining amount added after an interval of 1-2 hours.

[0009] Optionally, the phosphorus pentoxide content in the phosphorus- and fluorine-containing sludge is 12%-14.86% on a dry basis, and the fluorine content is 3.04%-10.92%.

[0010] Optionally, the filtration system consists of a Buchner funnel, a suction flask, and a vacuum pump.

[0011] Optionally, the temperature of the stirring reaction is 20℃-80℃; The stirring reaction time shall not be less than 30 minutes.

[0012] Optionally, when phosphorus is preferentially recovered, the temperature of the stirring reaction is 20°C; When both phosphorus and fluorine are to be recovered, the temperature of the stirring reaction is 80°C.

[0013] Optionally, the stirring speed of the sludge slurry is 200-300 r / min, and the stirring time is 15-20 minutes to ensure uniform dispersion.

[0014] Optionally, when the filtrate is reused in the phosphorus chemical production process, it is preferentially used as process water for wet phosphoric acid production or as water for preparing phosphate rock slurry, wherein the soluble phosphorus concentration in the filtrate is ≥50g / L.

[0015] Optionally, the method further includes: The solid residue is tested after the solid-liquid separation. When the phosphorus pentoxide content in the solid residue is ≤3% and the fluorine content is ≤1%, the solid residue can be used as building material auxiliary material or disposed of safely in landfill. If the standard is not met, the solid residue will be returned to the sludge slurry preparation step for reprocessing.

[0016] As can be seen from the above technical solutions, the embodiments of this application have the following advantages: This application uses recycled water from the slag yard or prepared process water, consistent with that used in phosphate chemical plants, to prepare the sludge slurry. This avoids discrepancies between laboratory and industrial application results caused by differences in water usage, saving additional water treatment costs. Simultaneously, it utilizes the existing background phosphorus and fluoride levels in the on-site water to enhance recovery efficiency. The sludge slurry's solids content is precisely controlled at 20%-30%, avoiding problems such as excessively large reaction system volume and increased equipment load due to low solids content, while resolving issues like slurry paste formation and uneven mixing caused by excessive solids content. This ensures sufficient contact between sulfuric acid and sludge, improving phosphorus and fluoride conversion rates. Through efficient solid-liquid separation via a filtration system, the resulting filtrate containing soluble phosphorus and fluoride can be directly reused in phosphate chemical production processes, eliminating the need for additional purification steps. Solid residue is reduced through subsequent treatment, forming a closed-loop process of "recovery-reuse-reduction." This reduces enterprise costs while ensuring stable production results, achieving sludge reduction and efficiency improvement, lowering sludge disposal costs, reducing resource waste, and enhancing both economic and environmental benefits for the enterprise. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic flowchart of an embodiment of a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge provided in this application; Figure 2 A schematic flowchart of an embodiment that clarifies the optimal reaction parameters for the optimized reaction conditions provided in this application; Figure 3 This is a schematic flowchart of an embodiment of the filtration system and post-solid-liquid separation processing provided in this application. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Based on this, this application discloses a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge, which can be used for the resource-based treatment of phosphorus- and fluorine-containing sludge in the phosphorus chemical industry.

[0021] Please see Figure 1 This application provides an embodiment of a method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge, comprising: 101. Mix phosphorus- and fluorine-containing sludge with experimental water in a certain proportion to obtain sludge slurry. Stir the sludge slurry thoroughly to ensure uniform dispersion. The experimental water is the same as the on-site water used in the phosphorus chemical enterprise, which is either slag yard return water or prepared process water. First, phosphorus- and fluoride-containing sludge generated during the production process of a phosphate chemical enterprise is selected as the raw material for treatment. Then, it is mixed with experimental water according to a predetermined ratio. It is important to note that the experimental water is not ordinary tap water, but rather water consistent with the on-site water used by the phosphate chemical enterprise. Specifically, recycled water from the enterprise's slag yard or process water used for production can be used. This reduces water consumption and avoids interference from external water quality in subsequent reactions. During the mixing process, the lumpy or agglomerated phosphorus- and fluoride-containing sludge is thoroughly stirred using a stirring device to transform it into a uniformly dispersed slurry until the sludge is completely dispersed, forming a sludge slurry with no obvious lumps and a uniform texture.

[0022] 102. Adjust the solids content of the sludge slurry to 20%-30%; Solid content is a key parameter affecting the efficiency of subsequent reactions and the solid-liquid separation effect. This step precisely adjusts the solid content of the sludge slurry prepared in step 101 to 20%-30%. During operation, based on the initial solid content of the sludge slurry, the concentration is gradually adjusted by adding experimental water from step 101 (if the solid content is too high) or by moderately concentrating it (if the solid content is too low). During the adjustment process, a professional solid content detection device is used to monitor the state of the sludge slurry in real time to ensure that the final solid content of the sludge slurry is stable within the range of 20%-30%.

[0023] 103. Add sulfuric acid as a reactant to the sludge slurry and stir to obtain a mixture; By introducing chemical reagents to react with the sludge slurry, phosphorus and fluorine in the sludge are converted into soluble forms, facilitating subsequent separation and recovery. During operation, sulfuric acid is selected as the reaction reagent and is slowly and evenly added to the sludge slurry adjusted in step 102. During the addition process, the stirring equipment is continuously turned on to ensure sufficient contact and mixing of the sulfuric acid and sludge slurry, forming a mixture. During the stirring reaction, the reaction temperature and stirring rate are carefully controlled (specific parameters can be adjusted according to the actual production scale and sludge characteristics) to ensure that the phosphorus and fluorine compounds in the sludge react fully with the sulfuric acid, maximizing the conversion of phosphorus and fluorine into soluble phosphates, fluorides, and other substances.

[0024] 104. The mixture is passed through a filtration system for solid-liquid separation, and the filtrate containing soluble phosphorus and fluorine and the solid residue obtained from the separation are collected. The liquid and solid components of the mixture formed after the reaction are separated to obtain filtrate containing soluble phosphorus and fluoride and solid residue, respectively. Specifically, the reaction mixture is transported to a filtration system (such as a plate and frame filter press or vacuum filter suitable for phosphorus chemical sludge treatment). The filtration equipment is started, and the liquid in the mixture (i.e., the filtrate containing soluble phosphorus and fluoride) passes through the filter medium using pressure difference or vacuum suction and enters the filtrate collection device; while the solid particles in the mixture (i.e., the solid residue) are trapped on the surface of the filter medium, forming a filter cake. During the separation process, the operating status of the filtration equipment needs to be checked regularly to ensure the filtration effect. After filtration is completed, the pure filtrate containing soluble phosphorus and fluoride and the solid residue are collected separately.

[0025] 105. The filtrate is recycled for use in the phosphorus chemical production process to achieve the recovery of phosphorus and fluorine resources, and the solid residue is disposed of in subsequent processes to reduce the amount of sludge.

[0026] This step is the final stage for achieving resource recycling and sludge reduction, and it consists of two parts: filtrate recovery and solid residue disposal. The collected filtrate, containing soluble phosphorus and fluoride, can be directly supplied to the production system of phosphate chemical enterprises as a supplementary raw material, thus achieving the recycling of phosphorus and fluoride resources, reducing the enterprise's dependence on external phosphorus and fluoride raw materials, and simultaneously reducing wastewater discharge. As for the separated solid residue, since most of the phosphorus and fluoride resources have been extracted, its total amount is significantly reduced compared to the original sludge. Depending on the composition and characteristics of the residue, it can be further disposed of in a standardized manner, such as being sent to a professional solid waste treatment facility for safe landfill, or further processed into building materials, ultimately achieving the reduction, harmlessness, and resource utilization of phosphorus and fluoride-containing sludge.

[0027] In this embodiment, sludge slurry is prepared using recycled water from the slag yard or process water consistent with that used in phosphate chemical plants. This avoids discrepancies between laboratory and industrial application results caused by differences in water usage, saving additional water production costs. Simultaneously, the existing phosphorus and fluoride background values ​​in the on-site water are utilized to enhance recovery efficiency. The solids content of the sludge slurry is precisely controlled at 20%-30%, avoiding both excessively low solids content leading to an overly large reaction system and increased equipment load, and excessively high solids content causing slurry paste-like consistency and uneven mixing. This ensures sufficient contact between sulfuric acid and sludge, improving phosphorus and fluoride conversion rates. Through efficient solid-liquid separation via a filtration system, the resulting filtrate containing soluble phosphorus and fluoride can be directly reused in phosphate chemical production processes, eliminating the need for additional purification steps. Solid residue is reduced through subsequent treatment, forming a closed-loop process of "recovery-reuse-reduction." This reduces enterprise costs while ensuring stable production results, achieving sludge reduction and efficiency improvement, lowering sludge disposal costs, reducing resource waste, and enhancing both economic and environmental benefits for the enterprise.

[0028] Please see Figure 2 This application provides an embodiment for optimizing reaction conditions and determining optimal reaction parameters, including: 201. The amount of sulfuric acid added should be 1.2 to 1.5 times the total molar amount of phosphate in the sludge slurry; 202. The density of sulfuric acid is 1.8 g / ml, and it is added in batches. The first addition is 60%-70% of the total amount, and the remaining amount is added after an interval of 1-2 hours.

[0029] Sulfuric acid, as the core reagent for the dissolution of phosphorus and fluorine in this method, directly determines the reaction efficiency and resource recovery effect through its dosage and addition method. Specifically, the amount of sulfuric acid added must be strictly matched with the molar amount of total phosphate in the sludge slurry, controlled within the range of 1.2 to 1.5 times. This ratio is based on the following: 1.2 times the molar amount can meet the basic requirement for the full reaction of phosphorus and fluorine compounds in the sludge, while the upper limit of 1.5 times can cope with the interference of possible insoluble impurities in the sludge, ensuring the completeness of the reaction, while avoiding the waste of acid and the burden on subsequent filtrate treatment caused by excessive addition.

[0030] The selected sulfuric acid must meet the specification requirement of a density of 1.8 g / ml. This density corresponds to a sulfuric acid concentration that ensures the acidity of the reaction system, providing a suitable chemical environment for the conversion of phosphorus and fluorine from the solid phase to their soluble forms. The addition process is carried out in batches: the initial addition accounts for 60%-70% of the total addition. This proportion allows for rapid initiation of the reaction and control of the initial reaction rate. The remaining 30%-40% of the sulfuric acid is added after an interval of 1-2 hours. This avoids problems such as sudden local temperature rises and impurity precipitation caused by excessively high acid concentrations due to a single large addition. This stepwise reaction ensures a stable decrease in the pH value of the system, guaranteeing the continuous and efficient dissolution of phosphorus and fluorine ions.

[0031] 203. The phosphorus pentoxide content in phosphorus- and fluoride-containing sludge, on a dry basis, is 12%-14.86%, and the fluoride content is 3.04%-10.92%. The phosphorus- and fluoride-containing sludge processed in this embodiment has a clearly defined composition range. On a dry basis (i.e., the solid components after moisture removal), the phosphorus pentoxide content is 12%-14.86%, and the fluoride content is 3.04%-10.92%. The phosphorus pentoxide content reflects the basic reserves of recoverable phosphorus resources in the sludge, and a content of over 12% ensures the economic value of recovery. The fluctuation range of fluoride content reflects the differences in sludge from different production stages. The range of 3.04%-10.92% covers the typical fluoride content of sludge produced by processes such as phosphoric acid production and phosphate fertilizer preparation, ensuring the applicability of this method to most sludge types in the industry.

[0032] 204. The temperature for the stirring reaction is 20℃-80℃; 205. The stirring reaction time shall not be less than 30 minutes; 206. When phosphorus is recovered preferentially, the temperature of the stirring reaction is 20℃; 207. When both phosphorus and fluorine are to be recovered, the temperature for stirring the reaction is 80℃; The temperature of the stirring reaction is a key variable for controlling the leaching efficiency of phosphorus and fluorine. In this embodiment, the temperature is controlled within a wide range of 20℃-80℃, and the settings are refined according to the recovery target: when the process target is to prioritize the recovery of phosphorus, the reaction temperature is set to 20℃, at which the phosphorus leaching rate is the highest. This is because the low temperature environment can reduce the tendency of fluoride ions to form complexes with other ions, thereby reducing interference in the phosphorus leaching process. When it is necessary to simultaneously recover phosphorus and fluorine, the reaction temperature is increased to 80℃. The high temperature condition can promote the dissolution kinetics of fluoride, accelerate the release rate of fluorine from the solid sludge, and at the same time ensure that the phosphorus leaching efficiency is maintained at a high level.

[0033] The stirring reaction time must not be less than 30 minutes. The reaction time is set based on reaction kinetic studies: in the first 10 minutes, the initial reaction between sulfuric acid and sludge is vigorous, resulting in a rapid dissolution rate of phosphorus and fluorine; between 10 and 30 minutes, the reaction enters a stable phase, and the remaining sparingly soluble phosphorus and fluorine compounds gradually dissolve; after 30 minutes, the dissolution rate tends to stabilize, and further extending the time has limited effect on improving recovery efficiency. Therefore, setting a lower limit of 30 minutes ensures that the vast majority of phosphorus and fluorine compounds are converted.

[0034] 208. The stirring speed of the sludge slurry should be 200-300 r / min, and the stirring time should be 15-20 minutes to ensure uniform dispersion; In the sludge slurry preparation stage, uniform dispersion of the sludge is achieved through stirring to create favorable conditions for subsequent reactions. In this embodiment, the stirring speed is controlled at 200-300 r / min, and the stirring time is set at 15-20 minutes. The selection of the stirring speed is based on the following: 200 r / min can meet the basic dispersion requirements of sludge particles and avoid agglomeration; the upper limit of 300 r / min can further improve the uniformity of dispersion, while preventing problems such as slurry splashing and increased energy consumption caused by excessive speed. The stirring time of 15-20 minutes ensures that sludge particles of different sizes can be fully dispersed—for larger agglomerates, 15 minutes can achieve initial dispersal; for harder sludge components, 20 minutes can ensure that they are completely integrated into the slurry, so that the concentration of sulfuric acid is uniform throughout the reaction system when added later, avoiding incomplete local reactions.

[0035] 209. When the filtrate is reused in the phosphorus chemical production process, it should be used as process water for wet phosphoric acid production or as water for preparing phosphate rock slurry, wherein the concentration of soluble phosphorus in the filtrate is ≥50g / L.

[0036] The reuse method and quality indicators of the filtrate containing soluble phosphorus and fluoride obtained after solid-liquid separation directly affect the resource recycling efficiency. The filtrate is preferentially used as process water for wet-process phosphoric acid production or as water for preparing phosphate rock slurry. The wet-process phosphoric acid production process requires a large amount of process water and has certain requirements for phosphorus concentration. The soluble phosphorus in the filtrate can directly participate in the phosphoric acid preparation reaction, reducing the consumption of purchased phosphate rock. When used for preparing phosphate rock slurry, the phosphorus and fluoride components in the filtrate can react synergistically with the components in the slurry, enhancing the slurry's reactivity.

[0037] To ensure effective reuse, the soluble phosphorus concentration in the filtrate must be ≥50 g / L. A concentration of 50 g / L ensures that reuse of the filtrate will not negatively impact the phosphorus concentration balance of the production system, while also avoiding increased transportation and storage costs due to excessively low concentrations.

[0038] In this embodiment, by controlling the amount of sulfuric acid added to 1.2 to 1.5 times the total molar amount of phosphate in the sludge slurry, and by adding it in batches, combined with targeted temperature control of 20℃-80℃ (20℃ when prioritizing phosphorus recovery, and 80℃ when taking into account phosphorus and fluorine recovery), the phosphorus recovery rate in the sludge can reach more than 85%, and the fluorine recovery rate can reach 60%-90% depending on the target requirements. Compared to traditional processes, these optimized parameters maximize the conversion of phosphorus and fluorine in solid sludge into soluble forms, improving resource utilization and providing high-quality recycled raw materials for phosphate chemical production. Designed specifically for typical phosphate chemical sludge characteristics (12%-14.86% dry-basis phosphorus pentoxide content and 3.04%-10.92% fluorine content), the parameters directly adapt to sludge treatment needs, enabling efficient operation without additional pretreatment. Through efficient recovery of phosphorus and fluorine resources, the amount of solid residue is reduced by more than 60% compared to the original sludge, reducing the pressure on sludge landfill or disposal and minimizing the environmental pollution risks caused by phosphorus and fluorine emissions with solid waste. The closed-loop reuse of the filtrate achieves the recycling of water and phosphorus / fluorine resources, reducing wastewater discharge.

[0039] Please see Figure 3 This application provides an embodiment of a filtration system composition and post-solid-liquid separation treatment, including: 301. The filtration system consists of a Buchner funnel, a suction flask, and a vacuum pump; 302. After solid-liquid separation, the solid residue is tested; 303. When the phosphorus pentoxide content in the solid residue is ≤3% and the fluorine content is ≤1%, the solid residue shall be used as building material auxiliary material or disposed of safely in landfill. 304. If the standard is not met, the solid residue shall be returned to the sludge slurry preparation step for reprocessing.

[0040] This embodiment describes the composition of the filtration system and the specific process of solid-liquid separation and post-treatment. The filtration system consists of a Buchner funnel, a suction flask, and a vacuum pump, which work together: the Buchner funnel is lined with filter media to trap solid particles, the suction flask receives the filtrate, and the vacuum pump accelerates the separation process by generating negative pressure, achieving efficient solid-liquid separation of the reaction mixture. After solid-liquid separation, the solid residue is tested, focusing on the content of phosphorus pentoxide and fluorine. When the test results show that the phosphorus pentoxide content in the solid residue is ≤3% and the fluorine content is ≤1%, it indicates that the recoverable phosphorus and fluorine resources in the residue have been basically extracted. At this time, it can be used as building material auxiliary materials or safely landfilled, realizing both solid waste resource utilization and avoiding environmental pollution. If the test results do not meet the standards, i.e., the phosphorus pentoxide content in the solid residue is >3% or the fluorine content is >1%, it indicates that the residue still contains a lot of recoverable resources. It needs to be returned to the sludge slurry preparation step for reprocessing, and further extraction of phosphorus and fluorine is carried out through a recycling process until the residue meets the standards before final disposal. This system forms a complete closed loop from separation to detection to disposal or return, ensuring the maximization of resource recovery and the environmental friendliness of solid waste treatment.

[0041] In this embodiment, the filtration system consists of a Buchner funnel, a suction flask, and a vacuum pump. Its simple yet efficient structure enables rapid solid-liquid separation, significantly reducing separation time and effectively trapping solid particles to ensure filtrate purity, providing high-quality raw materials for subsequent resource recovery. The detection and grading mechanism for solid residue plays a crucial role: compliant residue (phosphorus pentoxide ≤3%, fluorine ≤1%) can be used as building material auxiliary materials or safely landfilled, achieving resource utilization and harmless treatment of solid waste; non-compliant residue is returned for reprocessing, avoiding resource waste, increasing the total phosphorus and fluorine recovery rate, forming a complete closed-loop process, enhancing the overall stability and reliability of the process, balancing economic efficiency and environmental protection, reducing enterprise costs while contributing to green development, and providing strong support for industrial applications.

Claims

1. A method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge, characterized in that, include: Phosphorus- and fluorine-containing sludge is mixed with experimental water in a certain proportion to obtain sludge slurry. The sludge slurry is then thoroughly stirred to ensure uniform dispersion. The experimental water is the same as the on-site water used in the phosphate chemical enterprise, which is either slag yard return water or prepared process water. The solids content of the sludge slurry is adjusted to 20%-30%; Sulfuric acid is added as a reaction reagent to the sludge slurry, and the mixture is stirred to obtain a mixture. The mixture is subjected to solid-liquid separation through a filtration system, and the resulting filtrate containing soluble phosphorus and fluorine and solid residue are collected. The filtrate is recycled for use in phosphorus chemical production processes to achieve the recovery of phosphorus and fluorine resources, and the solid residue is further disposed of to reduce the amount of sludge.

2. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The amount of sulfuric acid added is 1.2 to 1.5 times the total molar amount of phosphate in the sludge slurry.

3. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The sulfuric acid has a density of 1.8 g / ml and is added in batches. The first addition is 60%-70% of the total amount, and the remaining amount is added after an interval of 1-2 hours.

4. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The phosphorus pentoxide content in the phosphorus- and fluorine-containing sludge is 12%-14.86% and the fluorine content is 3.04%-10.92% on a dry basis.

5. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The filtration system consists of a Buchner funnel, a suction flask, and a vacuum pump.

6. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The temperature of the stirring reaction is 20℃-80℃; The stirring reaction time shall not be less than 30 minutes.

7. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 6, characterized in that, When phosphorus is preferentially recovered, the temperature of the stirring reaction is 20°C; When both phosphorus and fluorine are to be recovered, the temperature of the stirring reaction is 80°C.

8. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, The stirring speed of the sludge slurry is 200-300 r / min, and the stirring time is 15-20 minutes to ensure uniform dispersion.

9. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to claim 1, characterized in that, When the filtrate is reused in the phosphorus chemical production process, it is preferentially used as process water for wet phosphoric acid production or as water for preparing phosphate rock slurry, wherein the concentration of soluble phosphorus in the filtrate is ≥50g / L.

10. The method for recovering phosphorus and fluorine from phosphorus- and fluorine-containing sludge according to any one of claims 1 to 9, characterized in that, The method further includes: The solid residue is tested after the solid-liquid separation. When the phosphorus pentoxide content in the solid residue is ≤3% and the fluorine content is ≤1%, the solid residue can be used as building material auxiliary material or disposed of safely in landfill. If the standard is not met, the solid residue will be returned to the sludge slurry preparation step for reprocessing.

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