Resource utilization method and system for phosphorus and fluorine chemical wastewater electric flocculation sludge

Abstract

The invention provides a resource utilization method and system of phosphorus and fluorine chemical wastewater electric flocculation sludge, and the method comprises the following steps: carrying out electric flocculation treatment on phosphorus and fluorine chemical wastewater to obtain electric flocculation produced water and scum; precipitating and separating the electric flocculation produced water and the scum to obtain electric flocculation sludge and tail water; sequentially carrying out centrifugation, suction filtration and drying operation on the electric flocculation sludge to obtain dry sludge; kOH particles and deionized water are added into the dry sludge, an alkaline replacement reaction is carried out under the condition of a constant-temperature water bath, separation is carried out after the reaction is completed, and filter residues and mother liquor containing phosphorus and fluorine are obtained; step-by-step crystallization is carried out on the mother liquor containing phosphorus and fluorine, and KF crystals and K3PO4 crystals are obtained; the filter residues are sequentially subjected to deionized water cleaning, drying, cooling and grinding, and the iron-based coagulant is obtained; the iron-based coagulant is added into tail water to participate in reaction for sewage treatment, so that comprehensive resource utilization of the phosphorus and fluorine chemical wastewater is realized. The method realizes resourceful treatment of the phosphorus-fluorine chemical wastewater, and reduces the ecological risk of the water body.

Description

Technical Field

[0001] This invention relates to the fields of wastewater treatment and solid waste resource utilization, and particularly to a method and system for the resource utilization of electrocoagulated sludge from phosphorus and fluorine chemical wastewater. Background Technology

[0002] Phospho-fluorine chemicals are a key sector supporting global agricultural production (phosphate fertilizer supply) and high-end new materials industries (fluorinated refrigerants, polytetrafluoroethylene, etc.). However, their production process generates a large amount of waste. When this waste is directly dumped in the open, it is washed away and seeped out by rainwater. Phosphorus (mainly phosphates and polyphosphates), fluorine (mainly fluoride ions), free acids, and trace heavy metals (arsenic, cadmium, etc.) contained in the waste will dissolve, forming typical phospho-fluorine chemical wastewater. This causes the surrounding soil, water, and atmosphere to be polluted by phosphorus, fluorine, sulfates, and other trace elements.

[0003] The hazards of phosphate and fluoride chemical wastewater are multi-dimensional and long-term. Current mainstream technologies for treating this wastewater, both domestically and internationally, such as chemical precipitation, adsorption, electrocoagulation, and membrane processes, all generate large amounts of phosphate and fluoride sludge while removing pollutants from the water. This sludge has a complex composition, not only enriched with phosphorus and fluoride ions from the wastewater but also containing flocculant residues such as iron and aluminum, as well as trace amounts of heavy metals like arsenic and cadmium. Improper disposal of this sludge can cause secondary pollution that is even more difficult to treat than the wastewater itself. From an ecological and environmental perspective, existing processes often involve directly dewatering and landfilling phosphorus and fluoride sludge. Phosphorus in the sludge is easily leached into the soil by rainwater, exacerbating eutrophication of surrounding water bodies. Fluoride ions and heavy metals continuously migrate to groundwater layers, leading to inhibited soil microbial activity, reduced crop yields, and pollution of drinking water sources. From a safety perspective, phosphorus and fluoride sludge is acidic and long-term storage can corrode treatment facilities. Furthermore, the heavy metal content in the sludge often approaches or exceeds the limits for hazardous waste, requiring disposal according to hazardous waste standards, which carries the risk of environmental accidents caused by heavy metal leaching. From an economic cost perspective, companies must bear high costs for sludge dewatering, transportation, and hazardous waste landfill. Taking electrocoagulation as an example, treating 1,000 tons of phosphorus and fluoride wastewater generates approximately 5-10 tons of sludge, with annual disposal costs reaching several million yuan, significantly increasing the operational and maintenance burden on companies.

[0004] While existing technologies have been attempted for the disposal and resource utilization of phosphorus and fluorine sludge, they generally suffer from the problem of "emphasizing treatment over resource utilization," failing to achieve synergy between "treating waste with waste" and resource recycling. Patent CN115677852A discloses a method for electrocoagulation treatment of phosphorus and fluoride wastewater. Although it can effectively remove pollutants, it only treats the generated sludge as solid waste for dewatering and landfilling, without exploring the resource value of iron and phosphorus components in the sludge. This results in resource waste and increases the cost of solid waste disposal. Patent CN112321568A uses a four-stage chemical precipitation method to treat phosphogypsum leachate. Although it achieves preliminary recovery of phosphorus and fluoride, the process is complex and generates a large amount of sludge. The purity of the recovered product is low, and it does not address the core need of "treating waste with waste". Patent CN114014523A uses modified biochar as an adsorbent to treat phosphorus and fluoride wastewater. The adsorbent regeneration requires high-temperature calcination, which consumes a lot of energy and reduces the adsorption capacity by more than 30% after regeneration, which does not conform to the concept of green treatment. Patent JP6987654B2 solidifies the electrocoagulated sludge of phosphorus and fluoride wastewater, directly converting the recoverable iron and phosphorus resources into inert materials, completely wasting the potential resource value. This patent addresses the challenge of treating electrocoagulated sludge from wastewater by innovatively employing an "alkali replacement-coagulant molding" process. This process transforms iron-phosphorus and iron-fluoride compounds in the sludge into a highly efficient iron-based coagulant. This coagulant can be directly used for the advanced treatment of phosphorus and fluoride wastewater, and phosphorus and fluoride can be fully utilized as resources. This achieves synergy between "sludge resource utilization" and "deep wastewater treatment," truly putting into practice the concept of "treating waste with waste." Summary of the Invention

[0005] In view of the above situation, the main objective of this invention is to propose a method and system for the resource utilization of electrocoagulated sludge from phosphorus and fluorine chemical wastewater. By constructing an integrated process of "electrocoagulation treatment - pretreatment - sludge collection - alkaline replacement - coagulant molding - leachate treatment", sludge containing iron-phosphorus and iron-fluorine compounds is converted into a high-efficiency iron-based coagulant, while achieving the standard treatment of phosphorus and fluorine chemical wastewater (effect water / raw water), thus achieving the goal of "treating waste with waste, reducing costs and increasing efficiency".

[0006] This invention proposes a method for the resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater, the method comprising the following steps: Electrocoagulation treatment was performed on phosphorus and fluorine chemical wastewater to obtain electrocoagulated water and scum. The electrocoagulation permeate and scum are settled and separated to obtain electrocoagulation sludge and effluent. The electrocoagulated sludge was centrifuged to obtain wet sludge; The wet sludge is sequentially filtered and dried to obtain dry sludge. Add KOH granules to the dry sludge, then add deionized water and stir until the KOH is completely dissolved to obtain a mixture. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; The phosphorus and fluorine-containing mother liquor was subjected to stepwise crystallization to obtain KF crystals and K3PO4 crystals, which were then recovered. The filter residue was sequentially washed with deionized water, dried, cooled, and ground to obtain an iron-based coagulant. Iron-based coagulants are added to the effluent to participate in the reaction and treat the wastewater, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0007] This invention also proposes a resource utilization system for electrocoagulation sludge from phosphorus and fluorine chemical wastewater, wherein the system applies the resource utilization method for electrocoagulation sludge from phosphorus and fluorine chemical wastewater as described above, and the system includes: The electrolytic flocculation reactor, connected to the inclined plate sedimentation tank, is used for: Electrocoagulation treatment was performed on phosphorus and fluorine chemical wastewater to obtain electrocoagulated water and scum. Inclined plate sedimentation tank, connected to the sludge pretreatment unit, is used for: The electrocoagulation permeate and scum are settled and separated to obtain electrocoagulation sludge and effluent. The sludge pretreatment unit, connected to the alkali replacement unit, is used for: The electrocoagulated sludge was centrifuged to obtain wet sludge; The wet sludge is sequentially filtered and dried to obtain dry sludge. The alkali displacement device, connected to the filter press, is used for: Add KOH granules to the dry sludge, then add deionized water and stir until the KOH is completely dissolved to obtain a mixture. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The filter press, connected to the alkali replacement unit, is used for: The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; The mother liquor collection tank, connected to the filter press, is used for: The phosphorus and fluorine-containing mother liquor was subjected to stepwise crystallization to obtain KF crystals and K3PO4 crystals, which were then recovered. The coagulant forming device, connected to the filter press, is used for: The filter residue was sequentially washed with deionized water, dried, cooled, and ground to obtain an iron-based coagulant. A filter, installed at the front end of the dosing device, is used for: Remove foam and tiny impurities from the effluent; Dosing device, used for: Iron-based coagulants are added to the effluent to participate in the reaction and treat the wastewater, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention first uses electrocoagulation technology to treat phosphorus and fluorine chemical wastewater, and then transforms the obtained electrocoagulated sludge from solid waste into a high-efficiency coagulant, thereby increasing the sludge utilization rate and avoiding secondary pollution caused by landfill.

[0009] 2. This invention can remove pollutants such as fluorine and phosphorus from fluorine chemical wastewater, producing water that meets discharge requirements. It solves the problems of difficult treatment of fluorine chemical wastewater and environmental pollution caused by reinjection, realizes the resource-based treatment of fluorine chemical wastewater, and further reduces the ecological risk of water bodies. It is especially suitable for the treatment of leachate with high pollution load during the rainy season, effectively avoiding the industry pain points of high sludge moisture content and easy leakage of pollutants during the rainy season.

[0010] 3. The coagulant prepared in this invention has an effect on F － With a removal rate of ≥97.5% and a TP removal rate of ≥92.2%, this coagulant ensures that phosphorus and fluorine chemical wastewater fully meets discharge standards, significantly improving treatment efficiency. Furthermore, using sludge as raw material, the coagulant utilizes an alkaline displacement process to convert iron into an insoluble solid, separating impurities. The reaction solution is then pressure-filtered to obtain filter residue, which is subsequently washed to remove impurities, resulting in a substantial increase in the purity of iron in the remaining filter residue.

[0011] 4. The raw material of this invention is an electrocoagulation byproduct, eliminating the need to purchase coagulants externally. This reduces the treatment cost per ton of leachate by 40% to 60%, resulting in a significant decrease in treatment costs. Furthermore, the KF crystals (purity ≥98%) and K3PO4 crystals (purity ≥96%) produced by the alkali displacement method can both be used industrially.

[0012] 5. The process of this invention has wide adaptability, capable of treating both electrocoagulation tailwater and raw water during the rainy season. It eliminates the need to adjust core equipment based on wastewater type, flexibly adapting to the treatment needs of different phosphate and fluorine chemical enterprises. Furthermore, key process parameters (such as current density 6.5 mA / cm³) are also applicable. 2 The ratio of KOH to dry sludge (0.6:1) was optimized through single-factor experiments, resulting in a specific energy consumption of only 0.56 Wh / m³. 3 It is lower than the industry average energy consumption for electrocoagulation treatment (0.8~1.2wh / m³). 3 It does not cause significant corrosion to the electrodes, extends the service life of the electrodes by more than 30%, and reduces equipment operation and maintenance costs.

[0013] 6. This invention achieves targeted high-value utilization of phosphorus and fluorine resources through "alkali replacement-step crystallization". KF crystals can be used for glass etching (etching rate up to 5.2 μm / min) or as an electrolyte additive for lithium batteries. K3PO4 crystals meet the standard of "Potassium Phosphate for Agricultural Use" (HG / T4137-2010). When applied to wheat fields, it can increase the yield by more than 15%. It truly transforms pollutants into useful resources in the fields of agriculture and new energy. It is different from the limitations of existing technologies that "simply recover low-purity products" and promotes the transformation of the phosphorus and fluorine chemical industry from "end-of-pipe treatment" to "resource recycling".

[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by means of embodiments of the invention. Attached Figure Description

[0015] Figure 1 This is a schematic diagram illustrating the optimal removal rate of wastewater treated by electrocoagulation in Example 1 of the present invention. Figure 2 This is a schematic diagram of the iron production rate under optimal conditions for electrocoagulation treatment of wastewater in Example 1 of the present invention; Figure 3 This is a diagram illustrating the architecture of the resource utilization method for electrocoagulated sludge from phosphorus and fluorine chemical wastewater proposed in this invention. Figure 4 This is a flowchart of the method for resource utilization of electrocoagulated sludge from phosphorus and fluorine chemical wastewater proposed in this invention; Figure 5 This is a schematic diagram illustrating the effect of KOH dosage on the replacement of phosphorus and fluorine in sludge. Figure 6 This is a general framework diagram of the resource utilization system for electrocoagulation sludge from phosphorus and fluorine chemical wastewater proposed in this invention. Figure 7 This is a schematic diagram illustrating the effect of the iron-based coagulant prepared in Example 1 of the present invention on the direct treatment of electrocoagulation raw water. Detailed Implementation

[0016] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0017] These and other aspects of the embodiments of the present invention will become clear from the following description and accompanying drawings. In these descriptions and drawings, some specific embodiments of the present invention are specifically disclosed to illustrate some ways of implementing the principles of the embodiments of the present invention; however, it should be understood that the scope of the embodiments of the present invention is not limited thereto.

[0018] The leachate from a phosphogypsum slag yard in a certain city during the rainy season was taken as the phosphorus and fluorine chemical wastewater sample for this embodiment. The pH was measured to be 3.4±0.2. The total phosphorus was 133.65 mg / L and the fluoride was 75.61 mg / L, as detected by inductively coupled plasma atomic emission spectrometry. The conductivity was measured to be 1650 μs / cm. The samples were divided into 4 groups for single-factor experiments.

[0019] The effect of current density on the experiment: With the initial pH fixed at 3.4, conductivity at 6300 μS / cm, electrode spacing at 2 cm, and reaction time at 20 min, current densities of 5, 6.5, and 10 mA / cm were set. 2 Three sets of variables were used in an electrocoagulation reactor. After the reaction, the supernatant was filtered through a 0.45 μm aqueous filter membrane, and TP and F were measured by ICP-OES. － Concentration. Results showed: current density 6.5 mA / cm². 2 At that time, the TP removal rate was 98.47%, and the F... － Removal rate 64.07%, specific energy consumption 0.56wh / m³ 3 Compared to 5mA / cm 2 10mA / cm 2 Even better, the preliminary current density is determined to be 6.5 mA / cm². 2 This is the preferred value.

[0020] Experiment on the effect of initial pH: fixed current density 6.5 mA / cm² 2 The conductivity was 6300 μS / cm, the electrode spacing was 2 cm, and the reaction time was 20 min. Three initial pH values ​​were adjusted to 3.4, 5.5, and 8.5. After the reaction, the removal rate of TP was 98.47% at an initial pH of 3.4, and F... － The removal rate was 64.07%, and the pH of the solution rose to 7.28 after the reaction; the initial pH was 5.5 when F... － The removal rate dropped to 58.32%. At the initial pH of 8.5, electrode passivation was obvious, and the TP removal rate dropped to 86.21%. Therefore, the initial pH of 3.4 was determined to be the preferred value.

[0021] Experiment on the effect of conductivity: fixed current density 6.5 mA / cm² 2 The initial pH was 3.4, the electrode spacing was 2 cm, and the reaction time was 20 min. Three groups were adjusted to conductivity of 6300, 7100, and 8400 μS / cm. Results showed that at a conductivity of 7100 μS / cm, the TP removal rate was 98.47%, and the F removal rate was... － Removal rate 64.07%, specific energy consumption 0.56wh / m³ 3 When the conductivity is 6300 μS / cm, the specific energy consumption increases to 0.99 Wh / m. 3 F at 8400 μs / cm －The removal rate dropped to 60.15%, so the conductivity of 7100 μs / cm was determined to be the preferred value.

[0022] Effect of reaction time on experiment: fixed current density 6.5 mA / cm² 2 The initial pH was 3.4, conductivity was 7100 μS / cm, and electrode spacing was 2 cm. Three reaction times were set: 20, 25, and 30 min. Results showed that at 25 min, the TP removal rate was 98.47%, and the F removal rate was... － Removal rate 64.07%, specific energy consumption 0.56wh / m³ 3 TP did not reach stability after 20 minutes of reaction, and the specific energy consumption increased to 0.72 Wh / m³ after 30 minutes. 3 Therefore, a reaction time of 25 min was determined to be the preferred value.

[0023] Therefore, the optimal condition is a current density of 6.5 mA / cm². 2 The initial pH was 3.4, the conductivity was 7100 μS / cm, the reaction time was 25 min, and the electrode spacing was 2 cm, which is the scheme of Example 1 of this invention. The results are as follows... Figure 1 and Figure 2 As shown, Figure 1 The curves showing the removal rates of TP and F under these conditions over time are shown. Figure 2 The data above shows the changes in iron production during the electrocoagulation process. The data indicates that Example 1 of this invention operates under conditions of a current density of 6.5 mA / cm², a conductivity of 7100 μs / cm, and a reaction time of 25 min. This ensures that the iron content in the electrocoagulated sludge matches the iron content required for subsequent alkaline replacement and coagulant formation, avoiding excessive iron entering the solid phase and causing resource waste and increased energy consumption. A balance is achieved between removal efficiency, energy consumption, and sludge properties for subsequent resource utilization.

[0024] Example 1 Please see Figure 3 and Figure 4 This embodiment provides a method for the resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater, the method comprising the following steps: For phosphorus and fluorine chemical wastewater at a current density of 6.5 mA / cm² 2 Electrocoagulation was carried out under the conditions of conductivity 7100 μs / cm, reaction time 25 min, and electrode spacing 2 cm; electrocoagulation permeate and scum were obtained. The electrocoagulation permeate and scum were settled and separated to obtain electrocoagulation sludge and effluent. The TP removal rate in this part reached 98.47%, and F... － The removal rate reached 64.07%, and the specific energy consumption was only 0.56Wh / m³, resulting in electrocoagulated sludge enriched with iron, phosphorus, and fluorine. The electrocoagulation sludge was centrifuged and stirred at 3000 rpm for 10 min at room temperature to obtain wet sludge and supernatant. The supernatant was returned to the electrocoagulation treatment for subsequent generation of electrocoagulation sludge. The wet sludge was dried at 105℃ for 2 hours to obtain dry sludge. Under a mass ratio of 0.6:1, KOH was mixed with dry sludge, then deionized water was added, and the mixture was stirred until the KOH was completely dissolved to obtain a mixed solution. The effect of KOH dosage on the replacement of phosphorus and fluorine in the sludge was investigated. Figure 5 As shown in the figure, phosphorus (F) is initially displaced into the solution. When the fluorine displacement reaction slows down, phosphorus is displaced into the solution in large quantities. However, further increases in KOH dosage after reaching a certain value do not significantly enhance the displacement of phosphorus and fluorine. Therefore, a mass ratio of 0.6:1 effectively transfers phosphorus and fluorine from the sludge to the liquid phase for subsequent KF and K3PO4 recovery, while avoiding excessive alkali leading to increased chemical consumption and subsequent neutralization burden. This approach balances phosphorus and fluorine recovery efficiency and economic viability in the alkali displacement stage, distinguishing it from existing sludge resource recovery processes that do not quantitatively optimize alkali dosage. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; Take 50L of phosphorus and fluoride-containing mother liquor, filter it through a 0.45μm aqueous filter membrane, and centrifuge it at 3000rpm for 10min to remove suspended impurities, obtaining a clear mother liquor. Place the clear mother liquor in a constant temperature water bath and vacuum evaporate it at 65℃ and -0.08MPa to concentrate it to a solid content of 35%. Then cool it to 20℃ and let it stand for 2h to allow KF to crystallize. After centrifugation again, wash the crystals three times with deionized water and dry them in a drying oven at 105℃ for 3h to obtain 0.44kg of KF product.

[0025] Application scenarios: This KF product can be used in glass etching processes, with an etching rate of 5.2 μm / min in a 20% HF system, which can meet the basic requirements of industrial glass surface treatment; it can also be used as an auxiliary raw material to prepare fluorine-containing chemicals, realizing the recycling of fluorine resources.

[0026] The remaining 30L of mother liquor after KF crystallization was mixed with an appropriate amount of Ca(OH)2 powder and stirred for 30min to precipitate impurity ions. After centrifugation at 3000rpm for 10min, the mixture was filtered through a 0.45μm filter membrane to obtain a purified mother liquor. The purified mother liquor was placed in a constant temperature water bath and vacuum evaporated at 65℃ and a vacuum degree of -0.08MPa to concentrate it to a solid content of 50%. Then, it was allowed to stand at 60℃ for 3h to precipitate K3PO4 crystals. After solid-liquid separation, the product was washed three times with 95% ethanol and dried in a drying oven at 105℃ for 3h to obtain 2.43kg of K3PO4 product.

[0027] Application scenarios: This product has been tested and meets the standard of "Agricultural Potassium Phosphate" (HG / T4137-2010), with a K2O content of 61.2% and a water-soluble phosphorus content of 30.8%. When applied to wheat fields, it can increase the yield by more than 15%. As a high-efficiency phosphorus and potassium fertilizer, it can effectively improve soil fertility and realize the agricultural resource utilization of phosphorus resources.

[0028] The residual liquid after crystallization (containing a small amount of potassium salt) is returned for multi-effect vacuum evaporation to improve the recovery rate (total potassium salt recovery rate ≥85%). The filter residue was washed with deionized water until the pH of the effluent was approximately 7. The cleaned filter residue is then placed in a 105℃ oven and dried for 2 hours. After being removed, it is ground to a fineness of 100 mesh to obtain the iron-based coagulant product. Iron-based coagulants are added to the wastewater, and after stirring and reacting at 25°C, solid-liquid separation is performed, and the treated water that meets the standards is discharged to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0029] Example 2 Please refer to the following embodiment, which provides a method for the resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater. The method includes the following steps: For phosphorus and fluorine chemical wastewater at a current density of 6.5 mA / cm² 2 Electrocoagulation was carried out under the conditions of conductivity 6300 μs / cm, reaction time 20 min, and electrode spacing 2 cm; electrocoagulation permeate and scum were obtained. The electrocoagulation permeate and scum were settled and separated to obtain electrocoagulation sludge and effluent. The TP removal rate in this part reached 99.85%, and F... － The removal rate reached 64.81%, with a specific energy consumption of 0.98Wh / m³, and electrocoagulated sludge enriched with iron, phosphorus, and fluorine was obtained; The electrocoagulation sludge was centrifuged and stirred at 2500 rpm for 10 min at room temperature to obtain wet sludge and supernatant. The supernatant was returned to the electrocoagulation treatment for subsequent generation of electrocoagulation sludge. The wet sludge was dried at 100°C for 2 hours to obtain dry sludge. Under the condition of a mass ratio of 0.45:1, KOH and dry sludge are mixed, then deionized water is added and stirred until KOH is completely dissolved to obtain a mixed solution. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; Take 50L of phosphorus and fluoride-containing mother liquor, filter it through a 0.45μm aqueous filter membrane, and centrifuge it at 2500rpm for 15min to remove suspended impurities, obtaining a clear mother liquor. Place the clear mother liquor in a constant temperature water bath and vacuum evaporate it at 60℃ and -0.07MPa to concentrate it to a solid content of 30%. Then cool it to 20℃ and let it stand for 2.5h to allow KF to crystallize. After centrifugation again, wash the crystals twice with deionized water and dry them in a drying oven at 100℃ for 2h to obtain 0.4kg of KF product.

[0030] Application scenarios: This KF product can be used in glass etching processes, with an etching rate of 5.2 μm / min in a 20% HF system, which can meet the basic requirements of industrial glass surface treatment; it can also be used as an auxiliary raw material to prepare fluorine-containing chemicals, realizing the recycling of fluorine resources.

[0031] The remaining 30L of mother liquor after KF crystallization was mixed with an appropriate amount of Ca(OH)2 powder and stirred for 20min to precipitate impurity ions. After centrifugation at 2500rpm for 15min, the mixture was filtered through a 0.2μm filter membrane to obtain a purified mother liquor. The purified mother liquor was placed in a constant temperature water bath and vacuum evaporated at 65℃ and a vacuum degree of -0.07MPa to concentrate it to a solid content of 45%. Then, it was allowed to stand at 65℃ for 3.5h to precipitate K3PO4 crystals. After solid-liquid separation, the product was washed four times with 97% ethanol and dried in a drying oven at 100℃ for 4h to obtain 2.09kg of K3PO4 product.

[0032] Application scenarios: This product has been tested and meets the standard of "Agricultural Potassium Phosphate" (HG / T4137-2010), with a K2O content of 61.2% and a water-soluble phosphorus content of 30.8%. When applied to wheat fields, it can increase the yield by more than 15%. As a high-efficiency phosphorus and potassium fertilizer, it can effectively improve soil fertility and meet the nutrient needs of crops during key growth periods.

[0033] The residual liquid after crystallization (containing a small amount of potassium salt) is returned for multi-effect vacuum evaporation to improve the recovery rate (total potassium salt recovery rate ≥85%). The filter residue was washed with deionized water until the pH of the effluent was approximately 7. The cleaned filter residue is then placed in a 105℃ oven and dried for 2 hours. After being removed, it is ground to a fineness of 100 mesh to obtain the iron-based coagulant product. Iron-based coagulants are added to the wastewater, and after stirring and reacting at 20°C, solid-liquid separation is performed, and the treated water that meets the standards is discharged to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0034] Example 3 Please refer to the following embodiment, which provides a method for the resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater. The method includes the following steps: For phosphorus and fluorine chemical wastewater at a current density of 10 mA / cm 2Electrocoagulation was carried out under the conditions of conductivity 8400 μs / cm, reaction time 30 min, and electrode spacing 2 cm; electrocoagulation permeate and scum were obtained. The electrocoagulation permeate and scum were settled and separated to obtain electrocoagulation sludge and effluent. The TP removal rate in this part reached 99.84%, and F... － The removal rate reached 59.86%, and the specific energy consumption was 1.22Wh / m³, resulting in electrocoagulated sludge enriched with iron, phosphorus, and fluorine. The electrocoagulation sludge was centrifuged and stirred at 2700 rpm for 13 min at room temperature to obtain wet sludge and supernatant. The supernatant was returned to the electrocoagulation treatment for subsequent generation of electrocoagulation sludge. The wet sludge was dried at 110℃ for 3 hours to obtain dry sludge. Under the condition of a mass ratio of 0.9:1, KOH and dry sludge are mixed, then deionized water is added and stirred until KOH is completely dissolved to obtain a mixed solution; The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; Take 50L of phosphorus and fluoride-containing mother liquor, filter it through a 0.45μm aqueous filter membrane, and centrifuge it at 2700rpm for 13min to remove suspended impurities, obtaining a clear mother liquor. Place the clear mother liquor in a constant temperature water bath and vacuum evaporate it at 70℃ and -0.09MPa to concentrate it to a solid content of 40%. Cool it to 20℃ and let it stand for 2h to allow KF to crystallize. After centrifugation again, wash the crystals four times with deionized water and dry them in a drying oven at 110℃ for 5h to obtain 0.39kg of KF product.

[0035] Application scenarios: This KF product can be used in glass etching processes, with an etching rate of 5.2 μm / min in a 20% HF system, which can meet the basic requirements of industrial glass surface treatment; it can also be used as an auxiliary raw material to prepare fluorine-containing chemicals, realizing the recycling of fluorine resources.

[0036] The remaining 30L of mother liquor after KF crystallization was mixed with an appropriate amount of Ca(OH)2 powder and stirred for 40min to precipitate impurity ions. After centrifugation at 2700rpm for 13min, the mixture was filtered through a 0.45μm filter membrane to obtain a purified mother liquor. The purified mother liquor was placed in a constant temperature water bath and vacuum evaporated at 70℃ and a vacuum degree of -0.09MPa to concentrate it to a solid content of 55%. Then, it was allowed to stand at 70℃ for 4h to precipitate K3PO4 crystals. After solid-liquid separation, the product was washed twice with 99% ethanol and dried in a drying oven at 110℃ for 2h to obtain 2.18kg of K3PO4 product.

[0037] Application scenarios: This product has been tested and meets the standard of "Agricultural Potassium Phosphate" (HG / T4137-2010), with a K2O content of 52.3% and a water-soluble phosphorus content of 40.1%. When applied to wheat fields, it can increase the yield by more than 15%. As a high-efficiency phosphorus and potassium fertilizer, it can effectively improve soil fertility and enhance the overall benefits of agriculture.

[0038] The residual liquid after crystallization (containing a small amount of potassium salt) is returned for multi-effect vacuum evaporation to improve the recovery rate (total potassium salt recovery rate ≥85%). The filter residue was washed with deionized water until the pH of the effluent was approximately 7. The cleaned filter residue is then placed in a 105℃ oven and dried for 2 hours. After being removed, it is ground to a fineness of 100 mesh to obtain the iron-based coagulant product. Iron-based coagulants are added to the wastewater, and after stirring and reacting at 30°C, solid-liquid separation is performed, and the treated water that meets the standards is discharged externally, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0039] Example 4 Please see Figure 6 This embodiment provides a resource utilization system for electrocoagulation sludge from phosphorus and fluorine chemical wastewater. The system applies the resource utilization method for electrocoagulation sludge from phosphorus and fluorine chemical wastewater as described above. The system includes: The electrolytic flocculation reactor, connected to the inclined plate sedimentation tank, is used for: Electrocoagulation treatment was performed on phosphorus and fluorine chemical wastewater to obtain electrocoagulated water and scum. Inclined plate sedimentation tank, connected to the sludge pretreatment unit, is used for: The electrocoagulation permeate and scum are settled and separated to obtain electrocoagulation sludge and effluent. The sludge pretreatment unit, connected to the alkali replacement unit, is used for: The electrocoagulated sludge was centrifuged to obtain wet sludge; The wet sludge is sequentially filtered and dried to obtain dry sludge. The alkali displacement device, connected to the filter press, is used for: Add KOH granules to the dry sludge, then add deionized water and stir until the KOH is completely dissolved to obtain a mixture. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The filter press, connected to the alkali replacement unit, is used for: The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; The mother liquor collection tank, connected to the filter press, is used for: The phosphorus and fluorine-containing mother liquor was subjected to stepwise crystallization to obtain KF crystals and K3PO4 crystals, which were then recovered. The coagulant forming device, connected to the filter press, is used for: The filter residue was sequentially washed with deionized water, dried, cooled, and ground to obtain an iron-based coagulant. A filter, installed at the front end of the dosing device, is used for: Remove foam and tiny impurities from the effluent; Dosing device, used for: Iron-based coagulants are added to the effluent to participate in the reaction and treat the wastewater, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

[0040] Figure 7 The treatment effect of coagulant on raw phosphogypsum leachate during the rainy season is shown on the x-axis, which represents the dosage of coagulant, and the y-axis represents the removal rates of TP and F as the dosage increases. To verify the effectiveness of this invention, 10L of raw phosphogypsum chemical wastewater from the rainy season was used. The initial concentration of total phosphorus (TP) was 133.65 mg / L (standard limit 10 mg / L), and the concentration of fluoride (F) was... － The initial concentration was 75.61 mg / L (standard limit 15 mg / L), the initial pH was 3.4 (acidic), the conductivity was 1650 μs / cm, and 10 g / L of the coagulant prepared in Example 2 was added.

[0041] Raw water was filtered through a 0.45 μm filter membrane to remove suspended particulate matter, then transferred to a beaker, and the iron-based coagulant prepared in Example 1 was added. The reaction was controlled using a magnetic stirrer at 25 °C, with the temperature ranging from 20 °C to 30 °C. After stirring, the mixture was allowed to settle for 30 minutes, and the supernatant was filtered through a 0.22 μm filter membrane.

[0042] Test results showed that at a dosage of 10 g / L, the TP concentration in the raw water decreased from 133.65 mg / L to 2.7 mg / L, with a removal rate of 97.97%, far below the standard limit of 10 mg / L; F － The concentration decreased from 75.61 mg / L to 6.63 mg / L, with a removal rate of 91.23%, meeting the discharge requirement of 15 mg / L. Furthermore, the pH of the solution naturally increased from the initial 3.4 to 6.8-7.2 after the reaction, requiring no additional adjustment and conforming to the pH range for wastewater discharge. It can be seen that even when the iron-based coagulant prepared in this invention is directly added to water under the same conditions without undergoing electrocoagulation, the effluent still meets the discharge standards. Therefore, the iron-based coagulant prepared in this invention has advantages in technical indicators, economy, and environmental protection.

[0043] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for the resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater, characterized in that, The method includes the following steps: Electrocoagulation treatment was performed on phosphorus and fluorine chemical wastewater to obtain electrocoagulated water and scum. The electrocoagulation permeate and scum are settled and separated to obtain electrocoagulation sludge and effluent. The electrocoagulated sludge was centrifuged to obtain wet sludge; The wet sludge is sequentially filtered and dried to obtain dry sludge. Add KOH granules to the dry sludge, then add deionized water and stir until the KOH is completely dissolved to obtain a mixture. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; The phosphorus and fluorine-containing mother liquor was subjected to stepwise crystallization to obtain KF crystals and K3PO4 crystals, which were then recovered. The filter residue was sequentially washed with deionized water, dried, cooled, and ground to obtain an iron-based coagulant. Iron-based coagulants are added to the effluent to participate in the reaction and treat the wastewater, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

2. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 1, characterized in that, The conditions for electrocoagulation treatment were: current density 6.5 mA / cm³. 2 ~10mA / cm 2 Conductivity 6300μs / cm~8400μs / cm, reaction time 20min~30min, electrode spacing 2cm.

3. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 2, characterized in that, During the centrifugation process of electrocoagulation sludge, the centrifugation conditions are: stirring at 2500~3500 rpm for 10~15 min at room temperature.

4. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 3, characterized in that, During the sequential filtration and drying process of the wet sludge, the drying conditions are 100~110℃ for 2~3 hours.

5. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 4, characterized in that, The optimal mass ratio of KOH particles to dry sludge is 0.6:1 during the process of adding KOH particles to dry sludge.

6. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 5, characterized in that, The stepwise crystallization of phosphorus- and fluorine-containing mother liquor to obtain KF crystals and K3PO4 crystals includes the following steps: The phosphorus and fluorine-containing mother liquor was filtered through a 0.2~0.45μm microfiltration membrane to remove trace suspended impurities, resulting in a clear mother liquor. The clarified mother liquor was centrifuged and then vacuum evaporated in a water bath to concentrate the mother liquor to a solid content of 30% to 40%. The liquid was then cooled to obtain KF crystals. The KF crystals were then washed and dried to obtain KF crystals. The remaining concentrate was added to Ca(OH)2 powder and stirred, then centrifuged and filtered through a 0.2~0.45μm microfiltration membrane to obtain a purified mother liquor. The refined mother liquor was vacuum evaporated again in a water bath to concentrate the solid content to 45%–55%, and K3PO4 crystals were precipitated. Then, solid-liquid separation, washing and drying were carried out in sequence to obtain K3PO4 crystals and residual liquid. The residual liquid was used to recycle to obtain KF crystals and K3PO4 crystals.

7. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 6, characterized in that, The clarified mother liquor was centrifuged and then vacuum evaporated in a water bath to concentrate it to a solid content of 30%–40%. The liquor was then cooled to obtain KF crystals, which were then washed and dried. The centrifugation parameters for obtaining the KF crystals were: 2500–3000 rpm for 10–15 min; water bath temperature: 60–70℃; vacuum evaporation: -0.07–-0.09 MPa; cooling parameters: cooling to 15–25℃ and standing for 2–3 h; washing with deionized water, 2–4 times; and drying at 100–110℃ for 2–5 h.

8. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 7, characterized in that, Add the remaining concentrate to Ca(OH)2 powder and stir. Then, centrifuge and filter through a 0.2~0.45μm microfiltration membrane in sequence to obtain the purified mother liquor. During the process, the stirring time is 20~40min; the centrifugation parameters are 2500~3000rpm and 10~15min. The refined mother liquor was vacuum evaporated again in a water bath to concentrate it to a solid content of 45%–55%, precipitating K3PO4 crystals. Solid-liquid separation, washing, and drying were then performed sequentially to obtain K3PO4 crystals and residual liquid. During this process, the water bath temperature was 60–70℃, and the mixture was allowed to stand for 3–4 hours; the vacuum evaporation vacuum degree was -0.07–-0.09 MPa; the washing process used 95–99% ethanol, washing 2–4 times; and the drying temperature was 100–110℃, with a drying time of 3–4 hours.

9. The method for resource utilization of electrocoagulation sludge from phosphorus and fluorine chemical wastewater according to claim 8, characterized in that, During the centrifugation process of electrocoagulation sludge, the resulting products also include supernatant, which is used to return to the electrocoagulation treatment.

10. A resource utilization system for electrocoagulation sludge from phosphorus and fluorine chemical wastewater, characterized in that, The system utilizes the resource utilization method for electrocoagulation sludge from phosphorus and fluorine chemical wastewater as described in any one of claims 1 to 9, and the system comprises: The electrolytic flocculation reactor, connected to the inclined plate sedimentation tank, is used for: Electrocoagulation treatment was performed on phosphorus and fluorine chemical wastewater to obtain electrocoagulated water and scum. Inclined plate sedimentation tank, connected to the sludge pretreatment unit, is used for: The electrocoagulation permeate and scum are settled and separated to obtain electrocoagulation sludge and effluent. The sludge pretreatment unit, connected to the alkali replacement unit, is used for: The electrocoagulated sludge was centrifuged to obtain wet sludge; The wet sludge is sequentially filtered and dried to obtain dry sludge. The alkali displacement device, connected to the filter press, is used for: Add KOH granules to the dry sludge, then add deionized water and stir until the KOH is completely dissolved to obtain a mixture. The mixture was subjected to an alkaline displacement reaction under constant temperature water bath conditions to obtain a reaction solution; The filter press, connected to the alkali replacement unit, is used for: The reaction solution was filtered under pressure to obtain filter residue and phosphorus- and fluorine-containing mother liquor; The mother liquor collection tank, connected to the filter press, is used for: The phosphorus and fluorine-containing mother liquor was subjected to stepwise crystallization to obtain KF crystals and K3PO4 crystals, which were then recovered. The coagulant forming device, connected to the filter press, is used for: The filter residue was sequentially washed with deionized water, dried, cooled, and ground to obtain an iron-based coagulant. A filter, installed at the front end of the dosing device, is used for: Remove foam and tiny impurities from the effluent; Dosing device, used for: Iron-based coagulants are added to the effluent to participate in the reaction and treat the wastewater, so as to achieve comprehensive resource utilization of phosphorus and fluorine chemical wastewater.

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