Chlorine-containing and cod-containing phosphoric acid waste liquid resource treatment method

Abstract

This invention discloses a method for the resource-based treatment of chlorine- and COD-containing phosphoric acid waste liquid, comprising the following steps: (1) vacuum distillation: passing the phosphoric acid waste liquid into a vacuum distillation device for vacuum distillation treatment; (2) blending: adding water to the blending vessel for dilution treatment; (3) neutralization; (4) settling and stratification: the neutralized waste liquid is settling and stratified in an oil separator; (5) one-step impurity removal reaction and filtration; (6) two-step impurity removal reaction and filtration; (7) synthesis of dihydrate ferric phosphate; (8) water washing and aging; (9) drying and calcination. This invention, through multi-stage treatment, can efficiently remove high chloride ions and high COD from phosphoric acid waste liquid, with a removal rate of over 98%; at the same time, through further processing, a 30% hydrochloric acid solution product and a sodium phosphate solution are obtained, and after further reaction and treatment, a qualified anhydrous ferric phosphate product is obtained, enabling the waste to be recycled and reused. This invention has outstanding effects, simple process equipment, convenient operation, and is easy to apply in industrial production.

Description

Technical Field

[0001] This invention relates to the field of waste phosphoric acid treatment, and more particularly to a method for the resource-based treatment of chlorine- and COD-containing phosphoric acid waste liquid. Background Technology

[0002] Phosphoric acid is widely used in industries such as chemical, agricultural, pharmaceutical, electronics, and materials, but its use generates a large amount of phosphoric acid waste liquid. For example, in chemical production processes, phosphate fertilizer manufacturing, and pharmaceutical processes, phosphoric acid is often used as a raw material for the production of chemicals such as potassium dihydrogen phosphate and sodium glycerophosphate. During the production process, due to the addition of other auxiliary materials, it often contains impurities such as hydrochloric acid and COD. The recovery and treatment of this high-COD mixed phosphoric acid has always been a challenge for the industry.

[0003] Invention patent CN113683235A discloses a method for treating and recycling low-concentration phosphoric acid waste liquid. This method uses phosphorus and sulfur-containing strongly acidic production wastewater from pharmaceutical intermediates as raw materials to prepare ferric phosphate dihydrate and magnesium sulfate heptahydrate, thereby recovering resources and avoiding environmental pollution from wastewater. However, this method utilizes three steps—iron-carbon micro-electrolysis, Fenton oxidation, and full oxidation with hydrogen peroxide—to remove COD, making the process cumbersome and requiring the addition of multiple reagents, which increases costs and operational difficulty.

[0004] Chinese invention patent CN106395777A discloses a method for the comprehensive utilization of phosphoric acid waste liquid. The method includes: heating the phosphoric acid waste liquid to 40-60°C, adding activated carbon while stirring at 50-80 rpm, stirring for 1-2 hours, filtering while hot, and collecting the decolorized phosphoric acid waste liquid; heating the decolorized phosphoric acid waste liquid to 60-80°C, adding sodium hydroxide waste liquid dropwise; adding sodium carboxymethyl cellulose to the reaction solution, stirring for 1-2 hours, filtering, and collecting the filtrate; concentrating the filtrate under reduced pressure at 40-60°C to obtain crude trisodium phosphate; dissolving the crude trisodium phosphate in purified water at 90-100°C, cooling to 20-30°C, adding ethanol, allowing to stand, filtering, washing the filter cake with ethanol, and drying at 220-240°C. The preparation method of this invention has a relatively simple process flow and operation, realizing the transformation of phosphoric acid waste liquid into a valuable resource. However, this method requires the use of a large amount of activated carbon, and the adsorbed activated carbon is difficult to recover and reuse, generating a large amount of secondary hazardous waste. Summary of the Invention

[0005] The main objective of this invention is to provide a method for the resource-based treatment of phosphoric acid waste liquid that can efficiently remove high chloride ions and high COD from the waste liquid.

[0006] To achieve the above objectives, the present invention provides a method for the resource-based treatment of chlorine- and COD-containing phosphoric acid waste liquid, comprising the following steps: (1) Vacuum distillation: Phosphoric acid waste liquid is passed into a vacuum distillation apparatus for vacuum distillation treatment to obtain distilled hydrochloric acid and concentrated waste phosphoric acid. The concentrated waste phosphoric acid is then passed into a mixing kettle. (2) Blending: Water is added to the blending kettle for dilution treatment to obtain blended waste acid, which is then introduced into the neutralization kettle; (3) Neutralization: Add sodium hydroxide solution to the neutralization vessel to adjust to alkalinity, then keep it warm to obtain neutralized waste liquid, which is then pumped into the oil separator. (4) Settling and stratification: The neutralized waste liquid is settled and stratified in the oil separator. Then, the upper layer is released as floating oil and the lower layer is released as sodium phosphate solution. (5) One-step impurity removal reaction and filtration: Add precipitant to sodium phosphate solution, stir and react, then filter to obtain one-step impurity removal filtrate; (6) Two-step impurity removal reaction and filtration: Add ferrous sulfate and hydrogen peroxide to the filtrate from the first-step impurity removal, stir and react, then filter to obtain the impurity-removed sodium phosphate solution; (7) Synthesis of ferric phosphate dihydrate: The purified sodium phosphate solution is passed into the reaction vessel, hydrogen peroxide and ferrous sulfate are added, the reaction is stirred, and then aged. Finally, the solid and liquid are separated to obtain crude ferric phosphate. (8) Water washing and aging: The crude ferric phosphate is washed and aged to obtain wet ferric phosphate dihydrate; (9) Drying and calcining: The wet ferric phosphate dihydrate is dried to obtain solid ferric phosphate dihydrate. The solid ferric phosphate dihydrate is then calcined at high temperature to obtain anhydrous ferric phosphate product.

[0007] Furthermore, in step (1), a falling film evaporator is selected as the vacuum distillation device, the temperature conditions for vacuum distillation are 70-90℃, the negative pressure conditions are -0.85--0.95MPa, and the vacuum distillation is carried out until the phosphoric acid concentration reaches more than 60wt%.

[0008] Furthermore, in step (2), the amount of water added is such that the phosphoric acid concentration reaches 13-20 wt%. Process water can be used in step (2).

[0009] Furthermore, in step (3), the concentration of the sodium hydroxide solution is 30 wt%, and the addition rate is 0.8–1.3 m / s. 3 Adjust the pH to 8.0–8.5 per hour, and keep warm at 60–80°C for 20–30 minutes.

[0010] Furthermore, in step (4), the settling process is to settling for 2 to 3 hours. After the settling is completed, the floating oil layer is released from the upper layer first, and then the sodium phosphate solution is released from the lower layer.

[0011] Further, in step (5), the precipitant is any one or more of aluminum sulfate, polyaluminum sulfate, aluminum chloride, polyaluminum chloride, ferric sulfate, ferric chloride, and alum mixed in any proportion, and the amount added is 0.1 to 1% of the mass of the sodium phosphate solution. The stirring reaction is carried out at room temperature for 30 minutes.

[0012] Further, in step (6), the amount of ferrous sulfate added is 0.5 to 2% of the mass of the filtrate from the first step of impurity removal, the concentration of hydrogen peroxide is 30%, the amount added is 0.5 to 1 times the mass of ferrous sulfate, and the stirring reaction is carried out at room temperature for 30 minutes.

[0013] Further, in step (7), ferrous sulfate is added in a Fe:P molar ratio of 1:0.95 to 1.05, hydrogen peroxide concentration is 30%, and the amount added is in a FeSO4:H2O2 molar ratio of 1:1.2 to 1.5. The stirring reaction is carried out at 80 to 95°C for 30 min, and the aging treatment is carried out at 50 to 60°C for 2 to 4 h.

[0014] Further, in step (8), the washing and aging process includes a first washing, an aging reaction, and a second washing. During the first washing, the washing is repeated 3 to 4 times, with pure water added each time at a mud-to-water ratio of 2 to 3:1. The pulping and washing process lasts 30 to 45 minutes, followed by filtration. The specific operation of the aging reaction is to add pure water at a mud-to-water ratio of 2 to 3:1 and pulp again, then add phosphoric acid until the pH of the pulp is 1.8 to 2.0, heat to 80 to 90°C and stir for 2 to 4 hours, followed by filtration. During the second washing, the washing is repeated 3 to 4 times, with pure water added each time at a mud-to-water ratio of 2 to 3:1. The pulping and washing process lasts 30 to 45 minutes, followed by filtration, and finally, wet ferric phosphate dihydrate is obtained.

[0015] Furthermore, in step (9), the drying temperature is 90-110°C, the high-temperature calcination temperature is 600-800°C, and the time is 1.5-3h.

[0016] The beneficial effects of this invention are reflected in: This invention first removes chlorine from phosphoric acid waste liquid by vacuum distillation, and the distillate is condensed to obtain hydrochloric acid solution. The concentrated waste phosphoric acid is then diluted with water to facilitate the next step. Next, sodium hydroxide solution is added for neutralization, converting the phosphoric acid waste liquid into sodium phosphate. The neutralized waste liquid is allowed to settle and separate in an oil separator. The upper layer, containing a floating oil layer, removes approximately 90% of the COD. The remaining lower layer is a sodium phosphate solution, whose main component is sodium phosphate, containing small amounts of COD and chloride ion impurities. Then, a precipitant is added to the sodium phosphate solution to react, utilizing flocculation, precipitation, and adsorption to further remove residual COD from the solution. Finally, ferrous sulfate and hydrogen peroxide are added to the first-step impurity removal filtrate to remove COD through the Fenton reaction. Simultaneously, due to the action of ferric hydroxide colloids, any incompletely precipitated metal ions introduced by the precipitant in the previous step are carried out.

[0017] This invention, through multi-stage treatment, efficiently removes high chloride ions and high COD from phosphoric acid waste liquid, achieving a removal rate exceeding 98%. Simultaneously, further processing yields a 30% hydrochloric acid solution and a sodium phosphate solution. Further reactions and treatments produce a qualified anhydrous ferric phosphate product, enabling the resource-based recycling of waste. This invention offers outstanding results, a simple process apparatus, and convenient operation, facilitating industrial production applications. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of the resource utilization method for phosphoric acid waste liquid containing chlorine and COD according to the present invention. Detailed Implementation

[0019] To enable those skilled in the art to more clearly understand the technical solution described in this invention, the following embodiments are provided for illustration. The process flow diagram of the resource recovery treatment method for chlorine- and COD-containing phosphoric acid waste liquid of this invention is shown below. Figure 1 As shown. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by the present invention.

[0020] Unless otherwise specified, the raw materials, reagents or devices used in the following embodiments can be obtained from conventional commercial sources or by existing known methods; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art, and the speed of each "stirring" operation in the process of the present invention is in the range of 800 to 1200 r / min, and 1000 r / min is specifically selected in the following embodiments.

[0021] Example 1 Resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid This embodiment treats 1000L of phosphoric acid waste liquid, which has a phosphoric acid content of 15wt%, a chloride ion content of 50,000ppm, and a COD of 3000ppm. The treatment process is as follows: (1) Vacuum distillation: The waste phosphoric acid liquid is pumped from the waste liquid tank into a falling film evaporator equipped with a water ring vacuum pump. It is distilled for 2 hours under negative pressure of -0.95MPa and temperature of 70℃ to concentrate the phosphoric acid to a concentration of 60wt% to obtain concentrated waste phosphoric acid. The concentrated waste phosphoric acid is passed into a mixing kettle. After the fraction is condensed, it becomes hydrochloric acid solution, which is then concentrated and adjusted to a concentration of 30wt%.

[0022] (2) Blending: Turn on the stirrer of the blending vessel, then add water to it and adjust the phosphoric acid concentration to 13wt% to obtain blended waste acid, which is then introduced into the neutralization vessel.

[0023] (3) Neutralization: Turn on the stirrer of the neutralization vessel and pump 30wt% sodium hydroxide solution into the neutralization vessel through the sodium hydroxide solution feed pump at a rate of 0.8m / min. 3 / h, when the pH is 8.0, turn off the sodium hydroxide solution feed pump, heat to 60℃ and keep warm for 30 minutes to obtain neutralized waste liquid, and immediately pump it into the oil separator.

[0024] (4) Settling and stratification: The neutralized waste liquid is settling in the oil separator for 2 hours. After stratification, the oil is separated. First, the floating oil layer is released from the upper layer, and then the sodium phosphate solution is released from the lower layer.

[0025] (5) One-step impurity removal reaction and filtration: Add 0.1% of polyaluminum sulfate to sodium phosphate solution, stir and react for 30 min at room temperature, and filter to obtain one-step impurity removal filtrate.

[0026] (6) Two-step impurity removal reaction and filtration: 0.5% by mass of ferrous sulfate and 0.5 times the mass of ferrous sulfate, 30% hydrogen peroxide were added to the filtrate from the first-step impurity removal. After stirring and reacting for 30 minutes at room temperature, the solution was filtered to obtain a purified sodium phosphate solution. The measured values ​​were: chloride ion 1000 ppm (removal rate 98%); COD 27 ppm (removal rate 99.1%).

[0027] (7) Synthesis of ferric phosphate dihydrate: The purified sodium phosphate solution was passed into the reaction vessel, ferrous sulfate was added at a Fe:P molar ratio of 1:0.95, and hydrogen peroxide with a concentration of 30% was added at a FeSO4:H2O2 molar ratio of 1:1.2. The reaction was stirred at 80℃ for 30 min, and then heated to 50℃ and aged for 2 h. Finally, the solid and liquid were separated to obtain crude ferric phosphate.

[0028] (8) Water washing and aging: First water washing, aging reaction and second water washing. During the first water washing, the water washing is repeated 3 times. Each time, pure water is added at a mass ratio of 2:1 (mud to water). The pulp is washed for 30 minutes and then filtered. The specific operation of the aging reaction is to add pure water at a mass ratio of 2.5:1 (mud to water) and pulp again. Then, phosphoric acid is added until the pH of the pulp is 1.8. The temperature is raised to 80℃ and kept at that temperature for 2 hours. The pulp is then filtered. During the second water washing, the water washing is repeated 3 times. Each time, pure water is added at a mass ratio of 2:1 (mud to water). The pulp is washed for 30 minutes and then filtered to obtain wet ferric phosphate dihydrate.

[0029] (9) Drying and calcination: The wet ferric phosphate dihydrate was dried at 90°C for 2 hours, and then calcined at 600°C for 1.5 hours to obtain anhydrous ferric phosphate. The product indicators were tested, and chloride ions were not detected, and the COD content was 1 ppm.

[0030] Example 2 This embodiment treats 1000L of phosphoric acid waste liquid, which has a phosphoric acid content of 60wt%, a chloride ion content of 100,000ppm, and a COD of 50,000ppm. The treatment process is as follows: (1) Vacuum distillation: The waste phosphoric acid liquid is pumped from the waste liquid tank into a falling film evaporator equipped with a water ring vacuum pump. It is distilled for 1.5 hours under negative pressure of -0.90MPa and temperature of 80℃ to concentrate to a phosphoric acid concentration of 70wt% to obtain concentrated waste phosphoric acid. The concentrated waste phosphoric acid is passed into a mixing kettle. After the fraction is condensed, it becomes hydrochloric acid solution, which is then concentrated and adjusted to a concentration of 30wt%.

[0031] (2) Blending: Turn on the stirrer of the blending vessel, then add water to it and adjust the phosphoric acid concentration to 16wt% to obtain blended waste acid, which is then introduced into the neutralization vessel.

[0032] (3) Neutralization: Turn on the stirrer of the neutralization vessel and pump 30wt% sodium hydroxide solution into the neutralization vessel through the sodium hydroxide solution feed pump at a rate of 1.0m. 3 / h, when the pH is 8.2, turn off the sodium hydroxide solution feed pump, heat to 70℃ and keep warm for 25 minutes to obtain neutralized waste liquid, and immediately pump it into the oil separator.

[0033] (4) Settling and stratification: The neutralized waste liquid is settling in the oil separator for 2.5 hours. After stratification, the oil is separated. First, the floating oil layer is released from the upper layer, and then the sodium phosphate solution is released from the lower layer.

[0034] (5) One-step impurity removal reaction and filtration: Add 0.5% of ferric chloride to the sodium phosphate solution, stir and react for 30 min at room temperature, and filter to obtain the one-step impurity removal filtrate.

[0035] (6) Two-step impurity removal reaction and filtration: 1.3% ferrous sulfate and 0.8 times the mass of ferrous sulfate 30% hydrogen peroxide were added to the filtrate from the first-step impurity removal. After stirring and reacting for 30 minutes at room temperature, the solution was filtered to obtain a purified sodium phosphate solution. The measured values ​​were: chloride ion 5000 ppm (removal rate 95%) and COD 120 ppm (removal rate 99.76%).

[0036] (7) Synthesis of ferric phosphate dihydrate: The purified sodium phosphate solution was passed into the reaction vessel, ferrous sulfate was added at a ratio of Fe:P molar ratio of 1:1.00, and hydrogen peroxide with a concentration of 30% was added at a ratio of FeSO4:H2O2 molar ratio of 1:1.3. The reaction was stirred at 90℃ for 30 min, and then heated to 55℃ and aged for 3 h. Finally, the solid and liquid were separated to obtain crude ferric phosphate.

[0037] (8) Water washing and aging: First water washing, aging reaction and second water washing. During the first water washing, the water washing is repeated 3 times. Each time, pure water is added at a mass ratio of 2.5:1 for mud and water. The pulping and washing is carried out for 35 minutes and then filtered. The specific operation of the aging reaction is to add pure water at a mass ratio of 2:1 for mud and water and pulp again. Then, phosphoric acid is added until the pH of the pulp is 1.9. The temperature is raised to 85℃ and kept at the temperature for stirring and aging for 3 hours. Then, the pulping is carried out and filtered. During the second water washing, the water washing is repeated 4 times. Each time, pure water is added at a mass ratio of 2.5:1 for mud and water. The pulping and washing is carried out for 40 minutes and then filtered to obtain wet ferric phosphate dihydrate.

[0038] (9) Drying and calcination: The wet ferric phosphate dihydrate was dried at 100°C for 2 hours, and then calcined at 700°C for 2.5 hours to obtain anhydrous ferric phosphate. The product indicators were tested, and chloride ions were not detected, and the COD content was 1 ppm.

[0039] Example 3 This embodiment treats 1000L of phosphoric acid waste liquid with a phosphoric acid content of 90wt%, a chloride ion content of 150,000ppm, and a COD of 100,000ppm. The treatment process is as follows: (1) Vacuum distillation: The waste phosphoric acid liquid is pumped from the waste liquid tank into a falling film evaporator equipped with a water ring vacuum pump. It is distilled for 1 hour under negative pressure of -0.85MPa and temperature of 90℃ to concentrate the phosphoric acid to a concentration of 80wt% to obtain concentrated waste phosphoric acid. The concentrated waste phosphoric acid is passed into a mixing kettle. After the fraction is condensed, it becomes hydrochloric acid solution, which is then concentrated and adjusted to a concentration of 30wt%.

[0040] (2) Blending: Turn on the stirrer of the blending vessel, then add water to it and adjust the phosphoric acid concentration to 20wt% to obtain blended waste acid, which is then introduced into the neutralization vessel.

[0041] (3) Neutralization: Turn on the stirrer of the neutralization vessel and pump 30wt% sodium hydroxide solution into the neutralization vessel through the sodium hydroxide solution feed pump at a rate of 1.3m / min. 3 / h, when the pH is 8.5, turn off the sodium hydroxide solution feed pump, heat to 80℃ and keep at that temperature for 20 minutes to obtain neutralized waste liquid, which is then immediately pumped into the oil separator.

[0042] (4) Settling and stratification: The neutralized waste liquid is settling in the oil separator for 3 hours. After stratification, the oil is separated. First, the floating oil layer is released from the upper layer, and then the sodium phosphate solution is released from the lower layer.

[0043] (5) One-step impurity removal reaction and filtration: Add 1% alum by mass to the sodium phosphate solution, stir and react for 30 min at room temperature, and filter to obtain the one-step impurity removal filtrate.

[0044] (6) Two-step impurity removal reaction and filtration: 2% ferrous sulfate and 30% hydrogen peroxide (1 times the mass of ferrous sulfate) were added to the filtrate from the first-step impurity removal. After stirring and reacting for 30 minutes at room temperature, the solution was filtered to obtain a purified sodium phosphate solution. The measured values ​​were: chloride ion 7000 ppm (removal rate 95.34%); COD 107 ppm (removal rate 99.89%).

[0045] (7) Synthesis of ferric phosphate dihydrate: The purified sodium phosphate solution was passed into the reaction vessel, ferrous sulfate was added at a ratio of Fe:P molar ratio of 1:1.05, and hydrogen peroxide with a concentration of 30% was added at a ratio of FeSO4:H2O2 molar ratio of 1:1.5. The reaction was stirred at 95℃ for 30 min, and then heated to 60℃ and aged for 4 h. Finally, the solid and liquid were separated to obtain crude ferric phosphate.

[0046] (8) Water washing and aging: First water washing, aging reaction and second water washing. During the first water washing, the water washing is repeated 4 times. Each time, pure water is added at a mass ratio of 3:1 (mud to water). The pulp is washed for 45 minutes and then filtered. The specific operation of the aging reaction is to add pure water at a mass ratio of 3:1 (mud to water) and pulp again. Then, phosphoric acid is added until the pH of the pulp is 2.0. The temperature is raised to 90℃ and kept at the temperature for 4 hours with stirring. The pulp is then filtered. During the second water washing, the water washing is repeated 4 times. Each time, pure water is added at a mass ratio of 3:1 (mud to water). The pulp is washed for 45 minutes and then filtered to obtain wet ferric phosphate dihydrate.

[0047] (9) Drying and calcination: The wet ferric phosphate dihydrate was dried at 110°C for 2 hours and then calcined at 800°C for 3 hours to obtain anhydrous ferric phosphate. The product indicators were tested and no chloride ions were detected, and the COD content was 1 ppm.

[0048] Comparative Example 1 The phosphoric acid waste liquid and treatment method used in this comparative example are the same as in Example 3, except that sodium hydroxide solution is added in step (3) to adjust the pH to 7.0. The treatment result is as follows: The obtained sodium phosphate solution after purification was tested and found to have a chloride ion content of 7000 ppm, with a removal rate of 95.34%; however, its COD content was 60000 ppm, with a removal rate of only 40%. The obtained anhydrous ferric phosphate product was tested and found to have no detectable chloride ions and a COD content of 10000 ppm.

[0049] It is evident that the addition of alkali in step (3) is extremely important for pH control. When the pH is not within the range of the present invention, the COD removal rate will be greatly reduced, and the product that meets the requirements cannot be obtained.

[0050] Comparative Example 2 The phosphoric acid waste liquid and treatment method used in this comparative example are the same as those in Example 3, except that the process of keeping it at 80°C for 20 minutes in step (3) is omitted. The treatment result is as follows: The obtained sodium phosphate solution after purification was tested and found to have a chloride ion content of 7000 ppm, with a removal rate of 95.34%; and a COD content of 8000 ppm, with a removal rate of 92%. The obtained anhydrous ferric phosphate product was tested and found to have no detectable chloride ions and a COD content of 360 ppm.

[0051] It can be seen that if the heat preservation step in step (3) is cancelled, the COD removal rate will be relatively poor, and a lot of COD will remain in the final product, thus affecting the product quality.

[0052] Comparative Example 3 The phosphoric acid waste liquid and treatment method used in this comparative example are the same as those in Example 3, except that step (5) is omitted. The treatment result is as follows: The obtained sodium phosphate solution after purification was tested and found to have a chloride ion content of 7000 ppm, with a removal rate of 95.34%; and a COD content of 5600 ppm, with a removal rate of 94.4%. The obtained anhydrous ferric phosphate product was tested and found to have no detectable chloride ions and a COD content of 280 ppm.

[0053] It is evident that if the impurity removal process is eliminated, the COD removal rate will be relatively poor, and a large amount of COD will remain in the final product, thus affecting product quality.

[0054] Comparative Example 4 The phosphoric acid waste liquid and treatment method used in this comparative example are the same as in Example 1, except that step (6) is omitted. The treatment result is as follows: The obtained sodium phosphate solution after purification was tested and found to have a chloride ion content of 7000 ppm, with a removal rate of 95.34%; and a COD content of 6400 ppm, with a removal rate of 93.6%. The obtained anhydrous ferric phosphate product was tested and found to have no detectable chloride ions, a COD content of 300 ppm, and residual aluminum ions of 50 ppm.

[0055] It is evident that if the two-step impurity removal process is cancelled, the COD removal rate will be relatively poor, and a large amount of COD will remain in the final product, thus affecting product quality; in addition, the aluminum ions introduced by the precipitant in step five to ensure complete precipitation cannot be removed, thus affecting product quality.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid, characterized in that, Includes the following steps: (1) Vacuum distillation: Phosphoric acid waste liquid is passed into a vacuum distillation apparatus for vacuum distillation treatment to obtain distilled hydrochloric acid and concentrated waste phosphoric acid. The concentrated waste phosphoric acid is then passed into a mixing kettle. (2) Blending: Water is added to the blending kettle for dilution treatment to obtain blended waste acid, which is then introduced into the neutralization kettle; (3) Neutralization: Add sodium hydroxide solution to the neutralization vessel to adjust to alkalinity, then keep it warm to obtain neutralized waste liquid, which is then pumped into the oil separator. The sodium hydroxide solution has a concentration of 30 wt% and is added at a rate of 0.8–1.3 m / s. 3 / h, adjust pH to 8.0-8.5, and keep warm at 60-80℃ for 20-30 minutes; (4) Settling and stratification: The neutralized waste liquid is settled and stratified in the oil separator. Then, the upper layer is released as floating oil and the lower layer is released as sodium phosphate solution. (5) One-step impurity removal reaction and filtration: Add precipitant to sodium phosphate solution, stir and react, then filter to obtain one-step impurity removal filtrate; (6) Two-step impurity removal reaction and filtration: Add ferrous sulfate and hydrogen peroxide to the filtrate from the first-step impurity removal, stir and react, then filter to obtain the impurity-removed sodium phosphate solution; (7) Synthesis of ferric phosphate dihydrate: The purified sodium phosphate solution is passed into the reaction vessel, hydrogen peroxide and ferrous sulfate are added, the reaction is stirred, and then aged. Finally, the solid and liquid are separated to obtain crude ferric phosphate. (8) Water washing and aging: The crude ferric phosphate is washed and aged to obtain wet ferric phosphate dihydrate; (9) Drying and calcining: The wet ferric phosphate dihydrate is dried to obtain solid ferric phosphate dihydrate. The solid ferric phosphate dihydrate is then calcined at high temperature to obtain anhydrous ferric phosphate product.

2. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (1), a falling film evaporator is selected as the vacuum distillation apparatus. The temperature conditions for vacuum distillation are 70 to 90°C, and the negative pressure conditions are -0.85 to -0.95 MPa. The vacuum distillation process is carried out until the phosphoric acid concentration reaches 60 wt% or more.

3. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (2), the amount of water added is to adjust the phosphoric acid concentration to 13-20 wt%.

4. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (4), the settling process is to let it stand for 2 to 3 hours. After the settling is completed, the floating oil layer is released from the upper layer first, and then the sodium phosphate solution is released from the lower layer.

5. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (5), the precipitant is any one or more of aluminum sulfate, polyaluminum sulfate, aluminum chloride, polyaluminum chloride, ferric sulfate, ferric chloride, and alum mixed in any proportion, and the amount added is 0.1-1% of the mass of sodium phosphate solution. The stirring reaction is carried out at room temperature for 30 minutes.

6. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (6), the amount of ferrous sulfate added is 0.5 to 2% of the mass of the filtrate from the first step of impurity removal, the concentration of hydrogen peroxide is 30%, and the amount added is 0.5 to 1 times the mass of ferrous sulfate. The stirring reaction is carried out at room temperature for 30 minutes.

7. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (7), ferrous sulfate is added in a Fe:P molar ratio of 1:0.95 to 1.05, hydrogen peroxide concentration is 30%, and the amount added is in a FeSO4:H2O2 molar ratio of 1:1.2 to 1.

5. The stirring reaction is carried out at 80 to 95°C for 30 minutes, and the aging treatment is carried out at 50 to 60°C for 2 to 4 hours.

8. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (8), the washing and aging process includes a first washing, an aging reaction, and a second washing. During the first washing, the washing is repeated 3 to 4 times, with pure water added each time at a mud-to-water ratio of 2 to 3:

1. The pulping and washing process lasts 30 to 45 minutes, followed by filtration. The aging reaction is carried out by adding pure water at a mud-to-water ratio of 2 to 3:1 and pulping again. Then, phosphoric acid is added until the pH of the pulp is 1.8 to 2.

0. The pulp is heated to 80 to 90°C and stirred for 2 to 4 hours before filtration. During the second washing, the washing is repeated 3 to 4 times, with pure water added each time at a mud-to-water ratio of 2 to 3:

1. The pulping and washing process lasts 30 to 45 minutes, followed by filtration. Finally, wet ferric phosphate dihydrate is obtained.

9. The method for resource recovery treatment of chlorine- and COD-containing phosphoric acid waste liquid as described in claim 1, characterized in that, In step (9), the drying temperature is 90-110℃, the high-temperature calcination temperature is 600-800℃, and the time is 1.5-3h.

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