Process for removing ammonia nitrogen and synchronously recovering ammonium fluoride by circulating air stripping method

Abstract

The invention relates to the technical field of wastewater treatment and resource recycling, in particular to a process for removing ammonia nitrogen and synchronously recycling ammonium fluoride by a circulating air stripping method. Comprising the following steps: adjusting the pH value of the ammonia-nitrogen-containing wastewater to 11.5-13.0 to obtain alkaline wastewater; the method comprises the following steps: introducing the alkaline wastewater into an ammonia nitrogen stripping tower, and stripping by taking air as carrier gas, so that ammonia nitrogen in the wastewater is converted into gaseous ammonia; the stripped waste gas enters an ammonia gas absorption tower and is sprayed and absorbed by adopting a hydrofluoric acid solution with the concentration of 5-15% to generate an ammonium fluoride solution; tail gas discharged by the ammonia gas absorption tower enters an acid mist absorption tower, and a potassium hydroxide solution is adopted to spray and absorb residual hydrofluoric acid to generate a potassium fluoride solution; and adjusting the pH value of the stripped wastewater to 6-9, and discharging the wastewater after reaching the standard. The invention provides a circulating stripping process system integrating efficient removal of ammonia nitrogen, synchronous recovery of fluorine resources and deep purification of wastewater, and synergistic interaction of pollution treatment and recycling is realized through directional conversion of gaseous ammonia and cooperative control of acid mist.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment and resource recycling technology, and in particular to a circulating stripping process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride. Background Technology

[0002] Ammonia nitrogen wastewater treatment is a key environmental challenge for industries such as chemical and metallurgy. Especially in the treatment of high-concentration ammonia nitrogen wastewater (such as mother liquor from ammonium chloride production and wastewater from potassium fluorotantalate production), traditional stripping methods are widely used due to their simplicity and low cost. This method adjusts the wastewater to an alkaline environment and uses air or steam to transfer free ammonia from the liquid phase to the gas phase, achieving initial removal of ammonia nitrogen. However, existing stripping technologies mostly focus on the removal of single pollutants, lacking a systematic design for the resource recovery of ammonia in the waste gas and the synergistic treatment of other pollutants, making it difficult to meet the industrial upgrading needs of green production and resource recycling.

[0003] Current industrial ammonia nitrogen wastewater treatment faces the following bottlenecks: Gaseous ammonia generated during stripping is typically discharged directly or treated with simple acid washing, failing to be effectively converted into high-value-added products (such as ammonium fluoride), resulting in nitrogen resource loss. When the absorption process is imperfect, residual hydrofluoric acid and other volatile pollutants easily form acid mist and escape, leading to fluoride diffusion pollution. For complex mixed wastewater (such as wastewater containing fluoride / ammonia / heavy metal ions), existing technologies struggle to simultaneously achieve efficient ammonia nitrogen removal, fluoride resource recovery, and deep purification, often requiring multiple independent units connected in series, increasing treatment costs. Even after stripping, the wastewater still contains trace amounts of ammonia nitrogen and impurity ions (such as sulfate and heavy metals), lacking an economically effective guarantee for deep treatment, making it difficult to consistently meet stringent emission standards. Summary of the Invention

[0004] This invention provides a circulating stripping process system that integrates efficient ammonia nitrogen removal, simultaneous fluoride resource recovery, and deep wastewater purification. Through the directional conversion of gaseous ammonia and the synergistic control of acid mist, it achieves synergistic effects in pollution control and resource utilization.

[0005] The technical solution adopted in this invention is: a process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping, comprising the following steps:

[0006] Step 1: Adjust the pH of the ammonia nitrogen-containing wastewater to 11.5–13.0 to obtain alkaline wastewater;

[0007] Step 2: Pass the alkaline wastewater into the ammonia nitrogen stripping tower and use air as the carrier gas to strip the ammonia nitrogen in the wastewater into gaseous ammonia.

[0008] Step 3: The stripped waste gas enters the ammonia absorption tower and is absorbed by spraying with a 5-15% hydrofluoric acid solution to generate ammonium fluoride solution.

[0009] Step 4: The exhaust gas from the ammonia absorption tower enters the acid mist absorption tower, where residual hydrofluoric acid is absorbed by spraying with potassium hydroxide solution to generate potassium fluoride solution.

[0010] Step 5: Adjust the pH of the stripped wastewater to 6–9 before discharging it to meet standards.

[0011] The ammonium fluoride solution is returned to the production line to prepare ammonium fluoride products, and the potassium fluoride solution is reused for the production of potassium fluorotantalate.

[0012] As a further improvement of the present invention, in step one, the pH of the wastewater is adjusted to 12.0–12.8, and the adjusting agent is either sodium hydroxide or potassium hydroxide.

[0013] As a further improvement of the present invention, in step two, the operating temperature of the stripping tower is controlled at 30–60°C, and the gas-liquid volume ratio is 200:1–500:1.

[0014] As a further improvement of the present invention, in step three, the hydrofluoric acid solution is circulated and sprayed to absorb the ammonium fluoride until the concentration reaches 15-30%, and the resulting solution is concentrated and crystallized at low temperature to recover the solid ammonium fluoride.

[0015] As a further improvement of the present invention, the concentration of potassium hydroxide solution in step four is controlled at 10–25%, and the generated potassium fluoride solution is directly recycled for the potassium fluorotantalate synthesis process.

[0016] As a further improvement of the present invention, the ammonia nitrogen-containing wastewater is derived from the mother liquor of ammonium chloride production, the drainage of the ammonia stripping system, or the mixed liquor after pretreatment of alkaline miscellaneous water, with an initial ammonia nitrogen concentration ≥5000mg / L.

[0017] As a further improvement of the present invention, in step five, the wastewater is subjected to barium chloride precipitation, pyrolusite adsorption and special heavy metal adsorption resin for deep treatment before discharge to ensure that the total nitrogen is ≤35mg / L.

[0018] The beneficial effects of this invention are as follows: By coupling ammonia nitrogen stripping, directional synthesis of ammonium fluoride, and synergistic conversion of acid mist, this invention achieves synergistic effects of the three objectives of "pollution control, resource recovery, and deep purification." It converts traditionally waste gaseous ammonia into high-value-added ammonium fluoride products, while the by-product potassium fluoride solution is directly recycled into the potassium fluorotantalate production line, realizing closed-loop utilization of nitrogen and fluoride resources. The two-stage absorption tower design ensures high ammonia removal and fluoride capture rates in the tail gas, completely eliminating the risk of acid mist escape. The combination of multi-source wastewater compatible treatment and deep purification units stabilizes the total nitrogen in the effluent and reduces overall operating costs. Attached Figure Description

[0019] Figure 1 This is a flowchart of a process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride using a cyclic stripping method according to the present invention. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0021] This invention provides a cyclic stripping process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride, comprising the following steps:

[0022] Step 1: Adjust the pH of the ammonia nitrogen-containing wastewater to 11.5–13.0 to obtain alkaline wastewater;

[0023] Step 2: Pass the alkaline wastewater into the ammonia nitrogen stripping tower and use air as the carrier gas to strip the ammonia nitrogen in the wastewater into gaseous ammonia.

[0024] Step 3: The stripped waste gas enters the ammonia absorption tower and is absorbed by spraying with a 5-15% hydrofluoric acid solution to generate ammonium fluoride solution.

[0025] Step 4: The exhaust gas from the ammonia absorption tower enters the acid mist absorption tower, where residual hydrofluoric acid is absorbed by spraying with potassium hydroxide solution to generate potassium fluoride solution.

[0026] Step 5: Adjust the pH of the stripped wastewater to 6–9 before discharging it to meet standards.

[0027] Among them, ammonium fluoride solution is returned to the production line to prepare ammonium fluoride products, and potassium fluoride solution is recycled for the production of potassium fluorotantalate.

[0028] In step one of this invention, the pH of the wastewater is adjusted to 12.0–12.8, and the adjusting agent is either sodium hydroxide or potassium hydroxide.

[0029] In step two of this invention, the operating temperature of the stripping tower is controlled at 30–60°C, and the gas-liquid volume ratio is 200:1–500:1.

[0030] In step three of this invention, hydrofluoric acid solution is circulated and sprayed to absorb ammonium fluoride until the concentration reaches 15-30%. The resulting solution is then concentrated and crystallized at low temperature to recover solid ammonium fluoride.

[0031] In step four of this invention, the concentration of potassium hydroxide solution is controlled at 10–25%, and the generated potassium fluoride solution is directly recycled for the potassium fluorotantalate synthesis process.

[0032] The ammonia nitrogen-containing wastewater of this invention originates from the mother liquor of ammonium chloride production, the drainage of the ammonia stripping system, or the mixed liquor after pretreatment of alkaline miscellaneous water, with an initial ammonia nitrogen concentration ≥5000 mg / L.

[0033] In step five of this invention, the wastewater undergoes deep treatment before discharge, including barium chloride precipitation, pyrolusite adsorption, and a special heavy metal adsorption resin, to ensure that the total nitrogen is ≤35mg / L.

[0034] Example:

[0035] (I) Wastewater Sources and Water Quality Characteristics

[0036] Wastewater type: Ammonium chloride workshop mother liquor (60%) + ammonia stripping system drainage (30%) + alkaline miscellaneous water pretreatment mixture (10%).

[0037] Water quality parameters: ① Ammonia nitrogen concentration: 1850 mg / L; ② Fluoride ion: 75 mg / L; ③ SO42-: 2200 mg / L; ④ pH: 5.8; ⑤ Heavy metals (Mn) 2+ ): 12 mg / L.

[0038] (II) Process Implementation Steps

[0039] Step 1, pH adjustment:

[0040] Add 25% sodium hydroxide solution to the wastewater storage tank to adjust the pH to 12.5 (control range 12.0–12.8); after adjustment, the wastewater characteristics are: free ammonia content ≥98%, meeting the conditions for efficient stripping.

[0041] Step 2, ammonia nitrogen stripping:

[0042] Alkaline wastewater is pumped into a packed ammonia nitrogen stripping tower. Operating parameters: ① Temperature: 45℃ (control range 30–60℃); ② Gas-liquid ratio: 350:1 (control range 200:1–500:1); ③ Air velocity: 1.2m / s. 3 / min. Stripping effect: Ammonia nitrogen concentration in wastewater after stripping: 28 mg / L (removal rate 98.5%); gaseous ammonia production: 3.4 kg / m³ 3 Wastewater.

[0043] Step 3, Ammonium fluoride synthesis:

[0044] Gaseous ammonia is introduced into the ammonia absorption tower and subjected to countercurrent spraying with a 12% hydrofluoric acid solution. Absorption control: The solution is circulated and sprayed until the ammonium fluoride concentration reaches 22% (controlled range 15–30%); the solution is then transferred to an evaporation crystallization reactor, concentrated under reduced pressure at 80°C, and then cooled for crystallization. Product recovery: ① Ammonium fluoride crystals with a purity ≥99.2% are obtained; ② Nitrogen resource recovery rate: 96.3%.

[0045] Step 4, Acid Mist Control and Potassium Fluoride Recovery:

[0046] The exhaust gas is introduced into an acid mist absorption tower and sprayed with a 15% potassium hydroxide solution. Operating parameters: ① KOH solution concentration: 15% (controlled range 10–25%); ② Spray density: 8m³ / h.3 / (m 2 • h). Product destination: The generated potassium fluoride solution (concentration 19%) is directly pumped into the potassium fluorotantalate synthesis tank; fluorine recovery rate: 98.7%, acid mist elimination rate: 100%.

[0047] Step 5, advanced wastewater treatment:

[0048] After stripping, the wastewater was treated with dilute sulfuric acid to restore the pH to 7.2. Deep purification unit: ① Barium chloride precipitation: dosage 1.2 times the stoichiometric ratio, reaction time 30 min, SO42- removal rate 99.1%; ② Pyrolusite adsorption: mineral powder particle size 200 mesh, dosage 15 g / L, shake adsorption for 40 min, Mn... 2+ Removal rate 95.6%; ③ Special heavy metal adsorption resin.

[0049] The final effluent test results are shown in the table below.

[0050] parameter numerical values Emission standards Total nitrogen 26mg / L ≤35mg / L Fluoride ions 0.8 mg / L ≤10mg / L <![CDATA[SO42-]]> 42mg / L ≤400mg / L

[0051] (III) Resource utilization and economic analysis

[0052] Product revenue (based on 100m) 3 Wastewater treatment: ① Ammonium fluoride crystals: 3.1 tons (market price 6000 yuan / ton); ② Potassium fluoride solution: 4.7m³ 3 (Replacing purchased raw materials saves 12,000 yuan in costs).

[0053] The operating costs are compared in the table below.

[0054] project Traditional crafts The process of this invention Drug fees ￥8200 ￥9500 Energy fee ￥6800 ￥5200 Resource recovery benefits ￥30600 Comprehensive cost ￥15000 Net income ¥15,900

[0055] As can be seen from the above embodiments, the circulating stripping process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride in this application has significant advantages in terms of resource utilization and economy. From a resource utilization perspective, it not only successfully converts gaseous ammonia into high-value-added ammonium fluoride crystals, but also produces potassium fluoride solution as a byproduct that can be directly reused in production, achieving efficient recovery and recycling of nitrogen and fluorine resources and reducing resource waste. In processing 100m³ of ammonia... 3 During wastewater treatment, 3.1 tons of ammonium fluoride crystals and 4.7 m³ of wastewater can be obtained. 3 Potassium fluoride solution, these products bring considerable economic benefits.

[0056] From an economic perspective, although the reagent cost of this invention's process is higher than that of the traditional process, reaching 9,500 yuan, the energy cost is significantly reduced to 5,200 yuan, and a revenue of 30,600 yuan is obtained through resource utilization. In comparison, the total cost of the traditional process is 15,000 yuan, while the process of this invention can still achieve a net profit of 15,900 yuan after deducting costs. This indicates that the process of this invention can effectively reduce production costs and improve economic efficiency in the long run.

[0057] Furthermore, the advantages of this technology are also reflected in environmental protection and sustainable development. Through efficient ammonia nitrogen removal and resource recovery, it reduces the emission of pollutants such as nitrogen and fluoride, lowering the risk of environmental pollution. Simultaneously, its multi-source wastewater compatibility and deep purification capabilities ensure that all indicators of the final effluent consistently meet stringent emission standards. This provides a green, efficient, and economical solution for wastewater treatment in industries such as chemical and metallurgy, contributing to the green upgrading and sustainable development of these industries. With increasingly stringent environmental requirements and the growing acceptance of resource recycling concepts, this technology, which achieves both pollution control and economic benefits, has broad application prospects and significant promotional value.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride using a cyclic stripping method, characterized in that, Includes the following steps: Step 1: Adjust the pH of the ammonia nitrogen-containing wastewater to 11.5–13.0 to obtain alkaline wastewater; Step 2: Pass the alkaline wastewater into the ammonia nitrogen stripping tower and use air as the carrier gas to strip the ammonia nitrogen in the wastewater into gaseous ammonia. Step 3: The stripped waste gas enters the ammonia absorption tower and is absorbed by spraying with a 5-15% hydrofluoric acid solution to generate ammonium fluoride solution. Step 4: The exhaust gas from the ammonia absorption tower enters the acid mist absorption tower, where residual hydrofluoric acid is absorbed by spraying with potassium hydroxide solution to generate potassium fluoride solution. Step 5: Adjust the pH of the stripped wastewater to 6–9 before discharging it to meet standards. The ammonium fluoride solution is returned to the production line to prepare ammonium fluoride products, and the potassium fluoride solution is reused for the production of potassium fluorotantalate.

2. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, In step one, the pH of the wastewater is adjusted to 12.0–12.8, and the adjusting agent is either sodium hydroxide or potassium hydroxide.

3. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, In step two, the operating temperature of the stripping tower is controlled at 30–60℃, and the gas-liquid volume ratio is 200:1–500:

1.

4. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, In step three, the hydrofluoric acid solution is circulated and sprayed until the ammonium fluoride concentration reaches 15-30%. The resulting solution is then concentrated and crystallized at low temperature to recover the solid ammonium fluoride.

5. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, In step four, the concentration of potassium hydroxide solution is controlled at 10–25%, and the generated potassium fluoride solution is directly recycled for the potassium fluorotantalate synthesis process.

6. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, The ammonia nitrogen-containing wastewater originates from ammonium chloride production mother liquor, ammonia stripping system drainage, or a mixture of pretreated alkaline miscellaneous water, with an initial ammonia nitrogen concentration ≥5000 mg / L.

7. The process for removing ammonia nitrogen and simultaneously recovering ammonium fluoride by cyclic stripping according to claim 1, characterized in that, In step five, the wastewater undergoes deep treatment before discharge, including barium chloride precipitation, pyrolusite adsorption, and a special heavy metal adsorption resin, to ensure that the total nitrogen is ≤35mg / L.

Images