Method for thermally decomposing magnesium ammonium phosphate crystal and regenerating and cyclically precipitating ammonia

Abstract

The invention discloses a magnesium ammonium phosphate crystal thermal decomposition and regenerative cycle ammonia precipitation method, and belongs to the technical field of wastewater treatment. The method comprises the following steps: (1) preparing simulated wastewater, adding a precipitant in proportion, carrying out hydrothermal synthesis reaction, stirring, standing, carrying out suction filtration to obtain magnesium ammonium phosphate crystals, washing with water, and drying for later use; (2) fully grinding and mixing the magnesium ammonium phosphate crystal and sodium hydroxide in proportion, and pyrolyzing to obtain a pyrolysis product; and (3) controlling conditions to dissolve the soluble substances in water to obtain a soluble substance dissolving solution, and filtering and separating the insoluble substances. And (4) carrying out acidolysis on the insoluble substance to obtain an insoluble substance dissolving solution. And (5) respectively adding the soluble substance dissolving solution and the insoluble substance dissolving solution into wastewater, replenishing a precipitator according to the proportion of the medicament in the step (1), stirring, standing, carrying out suction filtration to obtain magnesium ammonium phosphate crystals, and washing, drying and recycling the magnesium ammonium phosphate crystals. And (6) repeating the steps (2)-(5), and carrying out circulating ammonia removal on the high-concentration ammonia-nitrogen wastewater. The method disclosed by the invention has the advantages of lower wastewater ammonia removal cost and stable ammonia removal effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and specifically relates to a method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and circulation of ammonia precipitation, which can efficiently and stably remove ammonia in wastewater and is mainly used for treating wastewater containing high concentration of ammonia nitrogen such as industrial coking. Background Art

[0002] With the rapid development of industrial and agricultural production, water consumption and drainage are increasing every year, leading to increasingly serious water pollution problems.

[0003] In particular, wastewater from the coking industry contains harmful substances such as phenol, cyanide and oil, which greatly damage the water environment. Among them, ammonia nitrogen pollution is of particular concern. It not only makes drinking water smell bad, but also may cause lakes to dry up, seriously affecting the natural ecology. Therefore, it is particularly important to properly treat industrial wastewater containing ammonia to prevent it from being discharged directly into the environment without treatment.

[0004] In the 1990s, chemical precipitation began to develop and has been applied in countries such as Japan and the United States. Despite this, my country has not yet widely adopted magnesium ammonium phosphate precipitation in engineering projects. In the precipitation process of magnesium ammonium phosphate, a large amount of magnesium salts and phosphates are required. Therefore, a new magnesium ammonium phosphate circulation method for treating ammonia nitrogen wastewater is urgently needed to reduce the cost of reagents. Summary of the invention

[0005] In order to overcome the problems existing in the prior art, the object of the present invention is to provide a method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration cycle ammonia precipitation, and magnesium ammonium phosphate is thermally decomposed under alkaline conditions. In this process, the pyrolysis product is separated by insoluble matter and acid hydrolyzed, and then the reagent is supplemented and put into the wastewater again to perform hydrothermal synthesis reaction ammonia precipitation. The generated ammonia gas can be recovered in the form of high-concentration ammonia water, and the product of thermal decomposition can also be used as a reagent for ammonia nitrogen treatment. This method realizes the efficient recycling of magnesium ammonium phosphate, solves the problem of reagent use cost in ammonia nitrogen wastewater treatment, and responds to the challenge of decreased ammonia nitrogen removal rate caused by increasing the number of cycles of magnesium ammonium phosphate precipitation.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for thermal decomposition and regeneration of magnesium ammonium phosphate to precipitate ammonia, which is used for removing ammonia nitrogen from high-concentration ammonia-containing wastewater, comprises the following steps:

[0008] Step (1): preparing simulated wastewater with an ammonia concentration of 1000-2000 mg / L;

[0009] Step (2): under room temperature conditions, phosphate and magnesium salt precipitant are sequentially added to simulated wastewater to carry out hydrothermal synthesis reaction, during the reaction, the pH value of the reaction system is adjusted with NaOH, the mixture is stirred evenly and then allowed to stand, and then filtered to obtain magnesium ammonium phosphate crystal precipitate, which is rinsed with deionized water for multiple times, and then placed in an oven for drying, and collected for later use;

[0010] Step (3): fully grinding and mixing the washed and dried magnesium ammonium phosphate crystals and sodium hydroxide solid particles, and subjecting the uniformly mixed solid powder to a pyrolysis reaction to release ammonia and water vapor, thereby obtaining pyrolysis products of sodium magnesium phosphate, magnesium phosphate and magnesium hydroxide;

[0011] Step (4): putting the pyrolysis product into deionized water, controlling the temperature, adjusting the pH value of the solution with hydrochloric acid so that the easily soluble sodium magnesium phosphate is dissolved in the water, stirring and standing, and then filtering and separating, the easily soluble sodium magnesium phosphate is dissolved in the water to obtain an easily soluble solution, and the insoluble magnesium phosphate and magnesium hydroxide are separated;

[0012] Step (5): acid hydrolyzing the insoluble magnesium phosphate and magnesium hydroxide, wherein the acid hydrolysis process is as follows: putting the insoluble material into deionized water, controlling the temperature, and adjusting the pH value of the solution with hydrochloric acid so that the insoluble material is dissolved in the deionized water to obtain a solution of the insoluble material; 95% to 100% of the insoluble material is converted into magnesium ions and phosphate ions by acid hydrolysis;

[0013] Step (6): pouring the readily soluble solution obtained in step (3) and the sparingly soluble solution obtained in step (4) into simulated wastewater respectively, then adding phosphate and magnesium salt precipitants respectively according to the ratio of the hydrothermal synthesis reaction reagents in step (2), adjusting the pH value of the reaction system with NaOH, stirring and standing, and placing the obtained crystal precipitate in an oven to dry, collecting and recycling it, thereby removing ammonia nitrogen from the wastewater;

[0014] Step (7): Repeat steps (3)-(6) to circulate and remove ammonia from the high-concentration ammonia nitrogen wastewater.

[0015] Preferably, in step (2), magnesium salt: simulated wastewater: phosphate is added in a molar ratio of magnesium ion: ammonium ion: phosphate ion of (0.9-1):1:(1.1-1.2); in step (2) and step (6), the molar concentration of sodium hydroxide is 1-5 mol / L, and the pH value of the reaction system is adjusted to 8.5-9.5.

[0016] Preferably, the magnesium ammonium phosphate crystals formed in step (2) are orthorhombic and have a particle size of 5 to 15 μm, and the excess magnesium ammonium phosphate generated is sold as a slow-release fertilizer.

[0017] Preferably, the ammonia removal rate of the hydrothermal synthesis reaction in step (2) and step (6) is not less than 90%.

[0018] Preferably, in step (3), the molar ratio of magnesium ammonium phosphate to sodium hydroxide is 1:1-1:2, the pyrolysis reaction temperature is 100°C-110°C, and the pyrolysis reaction time is 2-3h; the ammonia released by the pyrolysis reaction is recovered and converted into ammonia water with economic value, thereby reducing the secondary pollution problem of ammonia.

[0019] Preferably, the mass proportion of the soluble magnesium ammonium phosphate in the pyrolysis product obtained in step (3) is 50%-60%.

[0020] Preferably, the temperature for separating the soluble matter in step (4) is 20-25° C., and the pH value is adjusted to 7-8.

[0021] Preferably, the acid hydrolysis temperature in step (5) is 100-110° C., and the pH value is adjusted to 1-1.3.

[0022] Preferably, in step (2), the mixture is stirred evenly with a magnetic stirrer and then allowed to stand; in step (3), the evenly mixed solid powder is spread in a corundum crucible and placed in a tubular furnace for pyrolysis reaction.

[0023] The method of the invention is used for removing ammonia nitrogen from high-concentration ammonia-containing wastewater.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The present invention adopts magnesium ammonium phosphate hydrothermal synthesis method to deammonify, and circulates and treats high ammonia nitrogen wastewater by thermal decomposition of magnesium ammonium phosphate. This technical scheme not only reduces the cost of the reagent in the magnesium ammonium phosphate chemical precipitation method, but also enables the generated excess magnesium ammonium phosphate to be sold as a slow-release fertilizer, thereby achieving economic benefits. In addition, by adding sodium hydroxide powder during the pyrolysis process of magnesium ammonium phosphate, the release rate of ammonia nitrogen is significantly improved. In the circulation process, adding the step of separating insoluble substances can separate the substances with weak ammonia nitrogen adsorption capacity in the pyrolysis product. Subsequently, these insoluble substances are released into magnesium ions and phosphate ions through acid hydrolysis treatment, and a precipitant of a corresponding proportion is supplemented as needed, thereby effectively solving the problem of decreased ammonia nitrogen removal rate when the number of magnesium ammonium phosphate precipitation ammonia increases.

[0026] In the process of thermal decomposition of magnesium ammonium phosphate, ammonia gas is released, and the ammonia gas can be recovered and converted into ammonia water with economic value, which not only reduces the secondary pollution problem of ammonia nitrogen, but also increases economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a schematic diagram of the thermal decomposition and regeneration cycle of magnesium ammonium phosphate crystals to treat high-ammonia nitrogen wastewater. Figure 2 It is the XRD pattern of magnesium ammonium phosphate crystal precipitate. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention clearer and more concise, the present invention is further described in detail below in conjunction with the accompanying drawings and an embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] Implementation Case 1

[0030] The present embodiment provides a method for thermally decomposing magnesium ammonium phosphate crystals and regenerating and recycling ammonia in high-ammonia nitrogen wastewater, comprising the following steps:

[0031] (1) Preparation of ammonium chloride simulated wastewater: Weigh 3.819 g of ammonium chloride and dissolve it in water. Transfer it into a 1000 ml volumetric flask and add water to the scale to obtain ammonium chloride simulated wastewater with an ammonia concentration of 1000 mg / L.

[0032] (2) Under room temperature conditions, phosphate and magnesium salt precipitants were added to the simulated ammonium chloride wastewater in the molar ratio of magnesium ion: ammonium ion: phosphate ion of 0.9:1:1.1. During the reaction, the pH value of the wastewater was adjusted to 8.5 with a 5 mol / L NaOH solution. The reaction was stirred for 10 min at 25 ° C with a magnetic stirrer and then allowed to stand for 20 min. The ammonia nitrogen removal rate of the hydrothermal synthesis reaction was 91.534%. Finally, the magnesium ammonium phosphate crystal precipitate was filtered and rinsed with deionized water three times, then placed in an oven at 40 ° C for 48 h to dry, and collected for use.

[0033] (3) Then, the washed and dried magnesium ammonium phosphate and sodium hydroxide solid particles are fully ground and mixed, and the molar ratio of magnesium ammonium phosphate to sodium hydroxide is 1:1. The evenly mixed solid powder is spread in a corundum crucible and placed in a tube furnace at 100° C. for pyrolysis for 2 hours. The pyrolysis obtains 60% by weight of soluble sodium magnesium phosphate and 40% by weight of insoluble magnesium phosphate and magnesium hydroxide. At the same time, the ammonia generated by the pyrolysis reaction is recovered in the form of ammonia water and used directly.

[0034] (4) The pyrolysis product is put into 100 ml of deionized water, the temperature is controlled at 20° C., the pH value of the solution is adjusted to 7 with hydrochloric acid, and stirred for 20 minutes to dissolve the easily soluble sodium magnesium phosphate in the deionized water. After standing, the solution is filtered and separated. The easily soluble matter is dissolved in the water to obtain an easily soluble solution, and the insoluble matter is separated.

[0035] (5) Acid hydrolysis of the insoluble magnesium phosphate and magnesium hydroxide is performed. The acid hydrolysis process is as follows: the insoluble material is put into 100 ml of deionized water, the temperature is controlled at 100° C., the pH value of the solution is adjusted to 1.3 with hydrochloric acid, and stirred for 1.5 hours to dissolve the insoluble material in the deionized water. 95% of the insoluble material is dissolved in the insoluble solution in the form of magnesium ions and phosphate ions.

[0036] (6) The readily soluble solution in step (4) and the sparingly soluble solution in step (5) are respectively poured into 200 ml of ammonium chloride simulated wastewater, and then appropriate amounts of precipitants are added according to the ratio of the hydrothermal synthesis reaction reagents in step (1), and the pH value of the reaction system is adjusted to 8.5 with a 5 mol / L NaOH solution. After stirring and standing, the obtained sodium magnesium phosphate precipitate is placed in an oven to dry, collected and recycled, thereby removing ammonia nitrogen from the wastewater.

[0037] (7) Repeating steps (3)-(6) can circulate and remove ammonia from high-concentration ammonia nitrogen wastewater.

[0038] The flow chart of magnesium ammonium phosphate method for cyclic treatment of high ammonia nitrogen wastewater is shown in Figure 1 .

[0039] The method of the present invention not only greatly reduces the reagent cost of treating high-ammonia nitrogen wastewater by the magnesium ammonium phosphate method, but also maintains a relatively stable and high ammonia nitrogen removal rate in the circulating wastewater treatment. The ammonia nitrogen content of the wastewater after the separated solution is treated is below 80 mg / L, and the ammonia removal rate can be maintained at above 92%; the ammonia nitrogen content of the wastewater after the acid hydrolysis solution is treated is below 87 mg / L, and the ammonia removal rate can be maintained at above 91.3%, which is convenient for subsequent treatment of the wastewater, and the precipitated product can also be utilized as a resource.

[0040] Implementation Case 2

[0041] The present embodiment provides a method for treating high-ammonia nitrogen wastewater by thermal decomposition and regeneration of magnesium ammonium phosphate crystals, comprising the following steps:

[0042] (1) Preparation of ammonium chloride simulated wastewater: Weigh 7.638 g of ammonium chloride and dissolve it in water. Transfer it into a 1000 ml volumetric flask and add water to the scale to obtain ammonium chloride simulated wastewater with an ammonia concentration of 2000 mg / L.

[0043] (2) Under room temperature conditions, phosphate and magnesium salt were added to the simulated ammonium chloride wastewater in the molar ratio of magnesium ion: ammonium ion: phosphate ion of 1:1:1.2. During the reaction, the pH value of the wastewater was adjusted to 9.5 with 1 mol / L NaOH solution. The reaction was stirred for 10 min at 25 °C with a magnetic stirrer and then allowed to stand for 20 min. The ammonia nitrogen removal rate of the hydrothermal synthesis reaction was 92.878%. Finally, the magnesium ammonium phosphate crystal precipitate was filtered and rinsed with deionized water three times, then placed in an oven at 40 °C for 48 h for drying, and collected for later use.

[0044] (3) Then, the washed and dried magnesium ammonium phosphate and sodium hydroxide solid particles are fully ground and mixed, and the molar ratio of magnesium ammonium phosphate to sodium hydroxide is 1:2. The evenly mixed solid powder is spread in a corundum crucible and placed in a tube furnace at 110° C. for pyrolysis for 3 hours. The pyrolysis obtains 50% by weight of soluble sodium magnesium phosphate and 50% by weight of insoluble magnesium phosphate and magnesium hydroxide. At the same time, the ammonia generated by the pyrolysis reaction is recovered in the form of ammonia water and used directly.

[0045] (4) The pyrolysis product is put into 100 ml of deionized water, the temperature is controlled to be 25° C., the pH value of the solution is adjusted to 8 with hydrochloric acid, and stirred for 20 minutes, so that the easily soluble sodium magnesium phosphate is dissolved in the deionized water. After standing, the solution is filtered and separated. The easily soluble matter is dissolved in the water to obtain an easily soluble solution, and the insoluble matter is separated.

[0046] (5) Acid hydrolysis is performed on the insoluble magnesium phosphate and magnesium hydroxide. The acid hydrolysis process is as follows: the insoluble material is put into 100 ml of deionized water, the temperature is controlled at 110° C., the pH value of the solution is adjusted to 1 with hydrochloric acid, and stirred for 1.5 hours to dissolve the insoluble material in the deionized water. The insoluble material is completely acid-hydrolyzed into the solution in the form of magnesium ions and phosphate ions.

[0047] (6) The readily soluble solution in step (4) and the insoluble solution in step (5) are respectively poured into 200 ml of ammonium chloride simulated wastewater, and then appropriate amounts of precipitants are added according to the ratio of the hydrothermal synthesis reaction reagents in step (1), and the pH value of the reaction system is adjusted to 9.5 with 1 mol / L NaOH solution. After stirring and standing, the obtained sodium magnesium phosphate precipitate is placed in an oven to dry, collected and recycled, thereby removing ammonia nitrogen from the wastewater.

[0048] (7) Repeat steps (3)-(6) to circulate and remove ammonia from high-concentration ammonia nitrogen wastewater.

[0049] The flow chart of magnesium ammonium phosphate method for cyclic treatment of high ammonia nitrogen wastewater is shown in Figure 1 .

[0050] like Figure 2 As shown, it is the XRD diagram of magnesium ammonium phosphate crystal precipitate. It can be seen from the figure that the characteristic peak represents the magnesium ammonium phosphate substance.

[0051] The method of the present invention significantly reduces the cost of the reagents for treating high-ammonia nitrogen wastewater by the magnesium ammonium phosphate method, while maintaining a stable removal rate of ammonia nitrogen in wastewater treatment. After the separated solution is circulated, the ammonia nitrogen content in the wastewater is reduced to below 76 mg / L, and the ammonia removal rate is above 92.4%; after the acid-hydrolyzed solution is circulated, the ammonia nitrogen content in the wastewater is reduced to below 82 mg / L, and the ammonia removal rate is above 91.8%. This not only improves the treatment efficiency and economy, but also facilitates subsequent wastewater treatment. It is worth mentioning that the precipitation product can be utilized as a resource, further promoting the goals of environmental protection and sustainable development.

Claims

1. A method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration of circulating ammonia precipitation, characterized in that: Used to remove ammonia nitrogen from high-concentration ammonia-containing wastewater, including the following steps: Step (1): preparing simulated wastewater with an ammonia concentration of 1000-2000 mg / L; Step (2): under room temperature conditions, phosphate and magnesium salt precipitant are sequentially added to simulated wastewater to carry out hydrothermal synthesis reaction, during the reaction, the pH value of the reaction system is adjusted with NaOH, the mixture is stirred evenly and then allowed to stand, and then filtered to obtain magnesium ammonium phosphate crystal precipitate, which is rinsed with deionized water for multiple times, and then placed in an oven for drying, and collected for later use; Step (3): fully grinding and mixing the washed and dried magnesium ammonium phosphate crystals and sodium hydroxide solid particles, and subjecting the uniformly mixed solid powder to a pyrolysis reaction to release ammonia and water vapor, thereby obtaining pyrolysis products of sodium magnesium phosphate, magnesium phosphate and magnesium hydroxide; Step (4): putting the pyrolysis product into deionized water, controlling the temperature, adjusting the pH value of the solution with hydrochloric acid so that the easily soluble sodium magnesium phosphate is dissolved in the deionized water, stirring and standing, and then filtering and separating, the easily soluble sodium magnesium phosphate is dissolved in water to obtain an easily soluble solution, and the insoluble magnesium phosphate and magnesium hydroxide are separated; Step (5): acid hydrolyzing the insoluble magnesium phosphate and magnesium hydroxide, wherein the acid hydrolysis process is as follows: putting the insoluble material into deionized water, controlling the temperature, and adjusting the pH value of the solution with hydrochloric acid so that the insoluble material is dissolved in the deionized water to obtain a solution of the insoluble material; 95% to 100% of the insoluble material is converted into magnesium ions and phosphate ions by acid hydrolysis; Step (6): pouring the readily soluble solution obtained in step (3) and the sparingly soluble solution obtained in step (4) into simulated wastewater respectively, then adding phosphate and magnesium salt precipitants respectively according to the ratio of the hydrothermal synthesis reaction reagents in step (2), adjusting the pH value of the reaction system with NaOH, stirring and standing, and placing the obtained crystal precipitate in an oven to dry, collecting and recycling it, thereby removing ammonia nitrogen from the wastewater; Step (7): Repeat steps (3)-(6) to circulate and remove ammonia from the high-concentration ammonia nitrogen wastewater.

2. A method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration of ammonia precipitation according to claim 1, characterized in that: In step (2), magnesium salt: simulated wastewater: phosphate are added in a ratio of magnesium ion: ammonium ion: phosphate ion of (0.9-1):1:(1.1-1.2); in step (2) and step (6), the molar concentration of sodium hydroxide is 1-5 mol / L, and the pH value of the reaction system is adjusted to 8.5-9.

5.

3. The method for thermal decomposition and regeneration of magnesium ammonium phosphate crystals according to claim 1, characterized in that: The magnesium ammonium phosphate crystals formed in step (2) are orthorhombic and have a particle size of 5 to 15 μm. The excess magnesium ammonium phosphate generated is sold as a slow-release fertilizer.

4. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 1, characterized in that: The ammonia removal rate of the hydrothermal synthesis reaction in step (2) and step (6) is not less than 90%.

5. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 1, characterized in that: In step (3), the molar ratio of magnesium ammonium phosphate to sodium hydroxide is 1:1-1:2, the pyrolysis reaction temperature is 100°C-110°C, and the pyrolysis reaction time is 2-3h; the ammonia released by the pyrolysis reaction is recovered and converted into ammonia water with economic value, thereby reducing the secondary pollution problem of ammonia.

6. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 2, characterized in that: The mass proportion of the soluble sodium magnesium phosphate in the pyrolysis product obtained in step (3) is 50%-60%.

7. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 3, characterized in that: In step (4), the temperature for separating the soluble matter is 20-25° C., and the pH value is adjusted to 7-8.

8. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 4, characterized in that: In step (5), the acid hydrolysis temperature is 100-110° C., and the pH value is adjusted to 1-1.

3.

9. The method for thermal decomposition of magnesium ammonium phosphate crystals and regeneration and recycling of ammonia precipitation according to claim 1, characterized in that: In step (2), the mixture is stirred evenly with a magnetic stirrer and then allowed to stand; in step (3), the evenly mixed solid powder is spread in a corundum crucible and placed in a tubular furnace for pyrolysis reaction.

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