Method for comprehensive treatment of electrolytic manganese production wastewater containing medium-high concentration of ammonia nitrogen

Abstract

The present application relates to the technical field of manganese industry wastewater treatment device, and particularly discloses a comprehensive treatment method for electrolytic manganese production wastewater containing medium and high concentration ammonia nitrogen, which comprises the steps of removing manganese, solid-liquid separation of manganese removal wastewater, adding a precipitant for precipitation reaction, etc.; according to the characteristics of electrolytic manganese production wastewater containing manganese, ammonia nitrogen, calcium, magnesium, sulfate ions, etc., by fully utilizing the magnesium ions in water, more than 95% of the manganese ions and all the phosphate radicals in water can be selectively removed by using slurry of quicklime, without introducing excessive calcium ions, effectively reducing the dosage of magnesium salt and phosphoric acid reagent, reducing the treatment cost, so that the electrolytic manganese production wastewater containing medium and high concentration ammonia nitrogen with ammonia nitrogen > 50 mg / L can be completely treated to reach the standard by using the ammonium magnesium phosphate precipitation method, and the indexes of manganese, ammonia nitrogen, phosphate radical and pH value after treatment can all reach the first standard limit value requirement of the Comprehensive Sewage Discharge Standard (GB 8978-1996), and the manganese, ammonia nitrogen and magnesium resources in the wastewater can be recovered.

Description

Technical Field

[0001] This invention belongs to the technical field of manganese industry wastewater treatment methods, and in particular relates to a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. Background Technology

[0002] Electrolytic manganese is an important ferrous metallurgical industry in my country. Since 2000, my country has become the world's largest producer, consumer, and exporter of electrolytic manganese. The electrolytic manganese production process generates wastewater in stages such as filtration, cleaning, cooling, passivation, and slag storage. Most of this wastewater contains manganese, ammonia nitrogen, calcium, and magnesium ions, with ammonia nitrogen being the most challenging to treat. Ammonia nitrogen levels in electrolytic manganese production wastewater are generally high, often exceeding 50 mg / L, and ammonia nitrogen is a crucial indicator for total water pollution control in my country. The "Technical Policy for Pollution Prevention and Control in the Electrolytic Manganese Industry" (Huanfa

[2010] No. 150), implemented on December 30, 2010, lists manganese and ammonia nitrogen as key pollutants for pollution control in the electrolytic manganese industry, proposing requirements such as advanced treatment for ammonia nitrogen removal from wastewater, and encouraging the adoption of ammonia nitrogen recycling technology and the development of advanced technologies for recovering and utilizing ammonia nitrogen. Therefore, under the requirements of cleaner production, energy conservation, and emission reduction, researching comprehensive treatment technologies for ammonia nitrogen and other pollutants in electrolytic manganese production wastewater is of great significance.

[0003] Common methods for treating medium- to high-concentration ammonia nitrogen wastewater include stripping, chemical precipitation, and membrane treatment. Stripping is a simple process, but pretreatment to remove calcium and magnesium is required; otherwise, scaling and clogging of the equipment can occur, resulting in low efficiency. Huang Jun et al. (2013) found that the ammonia nitrogen in the effluent after treatment with a 9-stage series stripping tower was only around 65 mg / L. Membrane treatment has promising prospects, but it requires stringent influent conditions and involves significant initial investment. Chemical precipitation mainly involves magnesium ammonium phosphate precipitation, also known as struvite precipitation. Theoretically, n(M g The 1:1:1 ratio of P to N is a mature emergency treatment method with advantages such as low initial investment, rapid reaction, and recyclable precipitate products. It can also effectively remove magnesium from wastewater, and the resulting magnesium ammonium phosphate is a good compound slow-release fertilizer. However, the precipitation method is mainly used for the treatment of high-concentration (≥200mg / L) ammonia nitrogen wastewater, and the treated wastewater generally still contains a small amount of ammonia nitrogen and unreacted phosphate (i.e., residual phosphorus), which needs to be treated in combination with low-concentration ammonia nitrogen wastewater treatment technology and residual phosphorus treatment technology.

[0004] The wastewater from electrolytic manganese production mainly contains manganese, ammonia nitrogen, calcium, magnesium, and sulfate ions. Qiu Jiang (2015) used magnesium ammonium phosphate precipitation to treat manganese slag leachate. Under the conditions of initial manganese and ammonia nitrogen of 530 mg / L and 339.2 mg / L, respectively, magnesium chloride and disodium hydrogen phosphate as precipitants, reaction time of 3 h, pH = 8.0, and n(Mg):n(P):n(N) = 1.5:1:1, the ammonia nitrogen after treatment was 10.2 mg / L. However, the treatment did not consider the removal of manganese and the unused magnesium in the water, nor did it consider the treatment of residual phosphorus. Furthermore, the introduction of chloride ions would be detrimental to water recycling. Li et al. (2017) treated intermediate water from manganese slag treatment with an initial ammonia nitrogen concentration of 1000 mg / L using struvite precipitation. Under the conditions of disodium hydrogen phosphate and magnesium sulfate as precipitants, reaction pH = 10, n(P):n(N) = 1.6:1, and n(Mg):n(N) = 1.6:1, the ammonia nitrogen removal rate was 93.8%, but 62 mg / L of ammonia nitrogen remained unremoved, and the treatment of residual phosphorus was not considered. Xue et al. (2018) used struvite precipitation on electrolytic manganese wastewater after manganese removal. Under the conditions of initial ammonium, magnesium, and calcium concentrations of 875 mg / L, 1200 mg / L, and 560 mg / L respectively, disodium hydrogen phosphate as the precipitant, reaction time of 30 min, pH = 9.0, and n(P):n(N) = 1.1:1, the ammonium recovery rate was 80%, and the residual phosphorus was 20.34 mg / L, indicating that 240 mg / L of ammonia nitrogen remained in the treated wastewater. g The ammonium content was / L, and the treated wastewater was not subjected to phosphorus removal treatment.

[0005] In summary, current research on precipitation treatment of electrolytic manganese production wastewater mainly targets wastewater with high ammonia nitrogen concentrations (>200 mg / L). Most studies fail to fully utilize magnesium ions and remove manganese ions, resulting in high phosphate and magnesium salt dosages. Even when these are considered, ammonia nitrogen levels are often insufficient to below 15 mg / L, requiring additional treatment methods to meet standards. Furthermore, residual phosphorus treatment is not considered, impacting wastewater reuse. Nitrogen and phosphorus are major elements in water eutrophication and also affect electrolytic manganese production; residual phosphorus removal is a crucial consideration, with relevant standards requiring levels below 0.5 mg / L. Therefore, precipitation treatment of electrolytic manganese production wastewater should fully utilize existing ions in the water, reduce reagent dosages, lower treatment costs, and employ cost-effective methods to remove introduced phosphate ions, optimizing process conditions to ensure that wastewater with ammonia nitrogen concentrations >50 mg / L meets treatment standards. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. This method addresses the existing problems of insufficient utilization of magnesium ions, large phosphate dosage, untreated residual phosphorus, and difficulty in achieving compliance with standards for treating wastewater containing medium to high concentrations of ammonia nitrogen during the current precipitation method for treating such wastewater. Simultaneously, it achieves effective recovery of manganese, ammonia nitrogen, and magnesium resources, and features rapid reaction, reduced treatment costs, and complete compliance with effluent standards.

[0007] To achieve the above objectives, the technical solution of the present invention is: a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen, comprising the following steps:

[0008] (1) Stir the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen, add lime slurry at a uniform rate, adjust the pH to 9.5 to 9.7, continue stirring the reaction, let it stand, and obtain manganese-removed wastewater;

[0009] (2) The manganese-removing wastewater is subjected to solid-liquid separation to obtain filtrate 1 and manganese-containing slag; the manganese-containing slag is transferred to the electrolytic manganese production process for use.

[0010] (3) Add precipitant to the filtrate 1 according to n(Mg):n(N):n(P)=(0.47~0.6):1:(1.2~1.3), stir the reaction, maintain the pH of the reaction solution at 9.5~10 with NaOH solution during the reaction, continue stirring to crystallize, and let stand after crystallization to obtain the settled reaction solution;

[0011] (4) The reaction liquid is separated into solid and liquid components to obtain filtrate 2 and filter residue 2; the filter residue 2 is washed with washing water to obtain filter residue 2 washing liquid; the washing water is a sodium hydroxide solution with pH = 9.4 to 9.6;

[0012] (5) Dry the filter residue 2 at a temperature below 40°C to obtain magnesium ammonium phosphate product;

[0013] (6) Add the washing liquid of the filter residue 2 to the filtrate 2, mix evenly, then add lime milk to adjust the pH to 11-12.5, stir to react and remove phosphorus, then separate the solid and liquid to obtain filtrate 3 and filter residue 3.

[0014] (7) The pH of the filtrate 3 is adjusted to 7.5-9 using dilute sulfuric acid to obtain effluent that meets the standards; the filter residue 3 is returned to step (6) for further phosphorus removal.

[0015] Further, in step (1), the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen is stirred, lime slurry is added at a uniform rate, the pH is adjusted to 9.5 to 9.7, the reaction is continued for 25 to 35 minutes, and then it is allowed to stand for 7 to 9 hours to obtain manganese-removed wastewater; the lime slurry is obtained by stirring quicklime slurry, and the quicklime concentration is 18 to 22 wt%.

[0016] Furthermore, in step (2), a plate and frame filter press is used as the solid-liquid separation device.

[0017] Furthermore, the precipitant in step (3) includes phosphate and magnesium salt, wherein the phosphate is phosphoric acid, sodium dihydrogen phosphate or disodium hydrogen phosphate, and the magnesium salt is magnesium sulfate.

[0018] Further, in step (3), a precipitant is added to the filtrate 1 in the ratio of n(Mg):n(N):n(P) = (0.47~0.6):1:(1.2~1.3), and the mixture is stirred at 280~320r / min for 28~32min. During the reaction, the pH of the reaction solution is maintained at 9.5~10 with 1.8~2.2mol / L NaOH solution. The mixture is stirred and crystallized at 130~170r / min for 28~32min. After crystallization, the mixture is allowed to stand for 10~20min to obtain the settled reaction solution.

[0019] Further, in step (4), the filter residue 2 is washed with washing water to obtain a washing liquid for filter residue 2; the amount of washing water used per kilogram of filter residue 2 is 15 to 20 L.

[0020] Further, in step (5), the filter residue 2 is dried at 36-40°C to obtain magnesium ammonium phosphate product.

[0021] Further, in step (6), the washing liquid of filter residue 2 is added to the filtrate 2, mixed evenly, and then lime milk is added to adjust the pH to 11-12.5. The mixture is stirred for 28-32 minutes to remove phosphorus, and then solid-liquid separation is performed to obtain filtrate 3 and filter residue 3.

[0022] Furthermore, in step (7), the pH of the filtrate 3 is adjusted to 7.5-9 using dilute sulfuric acid with a concentration of 0.45-0.55 mol / L, thus obtaining effluent that meets the standards.

[0023] Furthermore, the effluent in step (7) meets the Class I standard limit requirements of the Integrated Wastewater Discharge Standard (GB8978-1996), namely, manganese ≤2mg / L, ammonia nitrogen ≤15mg / L, phosphate (as P) ≤0.5mg / L, and pH = 6-9. The effluent is directly discharged or reused.

[0024] This invention discloses a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. Based on the characteristics of electrolytic manganese production wastewater containing manganese, ammonia nitrogen, calcium, magnesium, and sulfate ions, this method fully utilizes the magnesium ions in the water. By using quicklime to form a slurry, it can selectively remove over 95% of the manganese ions and all of the phosphate ions in the water simultaneously, without introducing excessive calcium ions. This effectively reduces the dosage of magnesium salts and phosphate reagents, lowering treatment costs. It also enables the use of ammonium magnesium phosphate precipitation to treat electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen (>50 mg / L) to fully meet standards. After treatment, the manganese, ammonia nitrogen, phosphate, and pH values ​​all meet the Class I standard limits of the "Integrated Wastewater Discharge Standard" (GB 8978-1996). Furthermore, it allows for the recovery of manganese, ammonia nitrogen, and magnesium resources from the wastewater.

[0025] This invention provides a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen, which has the following advantages:

[0026] (1) The method of the present invention is designed for the characteristics of manganese, ammonia nitrogen, calcium, magnesium and sulfate ions in the wastewater of electrolytic manganese production. It uses lime milk to selectively remove manganese ions and makes full use of magnesium ions in the water. The addition ratio of magnesium salt is only 0.47 to 0.6 times (<1) of the molar number of ammonia nitrogen, and does not introduce excessive calcium ions. It effectively reduces the amount of magnesium salt and phosphate reagent used and lowers the treatment cost. At the same time, lime milk is used to remove unreacted phosphate ions, which does not require additional material storage, is inexpensive, safe and effective.

[0027] (2) In the method of the present invention, the calcium ion concentration in the untreated electrolytic manganese wastewater is generally 350-550 mg / L, which is basically saturated. Adding lime milk to adjust the pH to about 9.5 can selectively remove more than 95% of the manganese ions in the wastewater while retaining magnesium. However, since the calcium ions may be supersaturated, after standing for a period of time, the supersaturated calcium ions will react with the sulfate ions present in the solution to form calcium sulfate and precipitate. A small amount of unreacted manganese ions will also precipitate under alkaline conditions. After precipitation, the calcium ion concentration in the water can basically reach or approach the concentration before untreated treatment, without introducing too much calcium ion. In addition, during the manganese precipitation process, a peristaltic pump is used to add lime milk to the stirred wastewater at a uniform speed, which can effectively improve the utilization rate of lime and reduce the treatment cost and reduce the amount of slag.

[0028] (3) In the phosphorus removal process of the present invention, phosphate and calcium ions can react completely at pH=11. Lime milk can effectively remove unreacted phosphate in water. However, quicklime needs to react with water to form ionic calcium hydroxide before it can react with phosphate in water. If quicklime is not emulsified in advance, the calcium phosphate or hydroxyapatite generated during the reaction will cover the surface and affect the continuous reaction of calcium oxide, resulting in poor phosphorus removal effect. In addition, the lime that has not fully reacted during the phosphorus removal process can be returned for phosphorus removal. Therefore, emulsifying lime in advance and returning the lime that has not fully reacted can improve the utilization rate of lime and reduce the treatment cost.

[0029] (4) The method of the present invention specifies in detail the steps of manganese precipitation, ammonia removal, and phosphorus removal, as well as the reagent treatment method. It is highly operable and after treatment, the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen (>50 mg / L) meets the first-class standard limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996). It can also effectively recover manganese, ammonia nitrogen, and magnesium resources in electrolytic manganese wastewater. It has the advantages of rapid reaction, reduced treatment cost, and complete compliance of effluent standards.

[0030] This invention discloses a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. In the precipitation reaction process of step (3) of this invention, a rapid reaction is first carried out, followed by a reduction in the reaction rate to 130-170 r / min, and then settling. This is conducive to the crystallization of magnesium ammonium phosphate and effectively improves the precipitation efficiency of magnesium ammonium phosphate, so that electrolytic manganese production wastewater with an ammonia nitrogen concentration of 50-200 mg / L can also meet the standards by precipitation. During solid-liquid separation, washing with water with pH = 9.4-9.6 can prevent the precipitated magnesium ammonium phosphate from redissolving. After three washings, a better magnesium ammonium phosphate product can be obtained. The main components of the magnesium ammonium phosphate product are magnesium ammonium phosphate and calcium phosphate, both of which are important phosphate fertilizers and can be used as agricultural phosphate fertilizers. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0032] Figure 1 This is a flowchart of the comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to the present invention. Detailed Implementation

[0033] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0034] The present invention provides a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. In step (1), the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen contains manganese, ammonia nitrogen, calcium, magnesium and sulfate ions, wherein the ammonia nitrogen content is >50mg / L.

[0035] Example 1

[0036] Wastewater sample 1 from an electrolytic manganese plant was tested and found to contain 1217.00 mg / L manganese, 1600.00 mg / L ammonia nitrogen, 368.34 mg / L calcium, 1039.49 mg / L magnesium, and pH 6.50. 20% lime slurry, which had been stirred for 1 hour, was added uniformly to the stirred wastewater using a peristaltic pump until the pH reached approximately 9.5. Stirring continued for 25 minutes. After stirring, the manganese concentration in the solution was measured to be 50.2 mg / L and the calcium concentration to be 511.85 mg / L. After standing for 8 hours, solid-liquid separation was performed, yielding filtrate 1 and manganese-containing slag. The manganese-containing slag was returned to the electrolytic manganese production. Filtrate 1 contained 20.22 mg / L manganese, 1031.00 mg / L ammonia nitrogen, 348.32 mg / L calcium, and 901.20 mg / L magnesium, indicating a manganese removal rate of 98.34% and a magnesium content in the water that was 0.51 times that of ammonia nitrogen. Phosphoric acid and magnesium sulfate were added to filtrate 1 in a ratio of n(Mg):n(N):n(P) = 0.6:1:1.3, and the mixture was stirred at 300 rpm for 30 minutes. A 2 mol / L... The NaOH solution was maintained at pH 9.5, and then the mixture was stirred at 170 r / min for 28 min to crystallize. After crystallization, the mixture was allowed to stand for 20 min, and then solid-liquid separation was performed to obtain filtrate 2 and filter residue 2. The phosphate content (as P) in filtrate 2 was measured to be 60.0 mg / L. Filter residue 2 was then washed three times with sodium hydroxide solution at pH 9.5 (washing water volume was 15 L / kg of residue). The washed filter residue 2 was dried at a low temperature of 36℃ to obtain magnesium ammonium phosphate product. Lime milk was added to filtrate 2 and the washed water to bring the pH to 12. After stirring for 30 min, solid-liquid separation was performed. The resulting filtrate 3 was adjusted to pH 7.5-9 with 0.45 mol / L dilute sulfuric acid to complete the treatment. The resulting filter residue 3 was returned for further phosphorus removal. Analysis showed that the main products of magnesium ammonium phosphate are magnesium ammonium phosphate and calcium phosphate. The effluent contained 0.09 mg / L manganese, 8.12 mg / L ammonia nitrogen, 0.3 mg / L phosphate (as P), and pH = 7.71, which met the Class I standard limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996).

[0037] Example 2

[0038] Wastewater sample 2 from an electrolytic manganese plant was tested and found to contain 1366.00 mg / L manganese, 1240.00 mg / L ammonia nitrogen, 355.38 mg / L calcium, 1137.09 mg / L magnesium, and pH 6.98. 22% lime slurry, which had been stirred for 1 hour, was added uniformly to the stirred wastewater using a peristaltic pump until the pH reached approximately 9.7. Stirring continued for 35 minutes. After stirring, the manganese concentration in the solution was measured to be 36.13 mg / L and the calcium concentration to be 476.40 mg / L. After standing for 9 hours, solid-liquid separation was performed, yielding filtrate 1 and manganese-containing slag. The manganese-containing slag was returned to the electrolytic manganese production. Filtrate 1 contained 14.27 mg / L manganese, 1088.00 mg / L ammonia nitrogen, 376.40 mg / L calcium, and 988.62 mg / L magnesium, indicating a manganese removal rate of 98.96% and a magnesium content in the water that was 0.53 times that of ammonia nitrogen. Disodium hydrogen phosphate and magnesium sulfate were added to filtrate 1 in a ratio of n(Mg):n(N):n(P) = 0.47:1:1.2. The mixture was stirred at 320 rpm for 32 minutes, using 2.2 mol / L... The NaOH solution was maintained at pH 9.6, and then the mixture was stirred at 150 r / min for 30 min to crystallize. After crystallization, the mixture was allowed to stand for 20 min, and then solid-liquid separation was performed to obtain filtrate 2 and filter residue 2. The phosphate content (as P) in filtrate 2 was measured to be 74.0 mg / L. Filter residue 2 was then washed three times with sodium hydroxide solution at pH 9.4 (washing water volume was 20 L / kg of residue). The washed filter residue 2 was dried at a low temperature of 40℃ to obtain magnesium ammonium phosphate product. Lime milk was added to filtrate 2 and the washed water to bring the pH to 12.5. After stirring for 32 min, solid-liquid separation was performed. The resulting filtrate 3 was treated by adjusting the pH of the wastewater to 7.5-9 with 0.55 mol / L dilute sulfuric acid. The resulting filter residue 3 was returned for further phosphorus removal. Analysis showed that the main products of magnesium ammonium phosphate are magnesium ammonium phosphate and calcium phosphate. The effluent contained 0.06 mg / L manganese, 10.33 mg / L ammonia nitrogen, 0.06 mg / L phosphate (as P), and pH = 8.61, which met the Class I standard limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996).

[0039] Example 3

[0040] Wastewater sample 3 from an electrolytic manganese plant was tested and found to contain 21.69 mg / L manganese, 67.30 mg / L ammonia nitrogen, 464.41 mg / L calcium, 120.19 mg / L magnesium, and pH 6.47. 18% lime slurry, which had been stirred for 1 hour, was added uniformly to the stirred wastewater using a peristaltic pump until the pH reached approximately 9.6. Stirring continued for 30 minutes. After stirring, the manganese concentration was measured to be 0.06 mg / L and the calcium concentration to be 470.47 mg / L. After standing for 7 hours, solid-liquid separation was performed, yielding filtrate 1 and manganese-containing slag. The manganese-containing slag was returned to the electrolytic manganese production. Filtrate 1 contained 0.04 mg / L manganese, 62.65 mg / L ammonia nitrogen, 424.63 mg / L calcium, and 79.37 mg / L magnesium, indicating a manganese removal rate of 99.82% and a magnesium concentration 0.74 times that of ammonia nitrogen. Sodium dihydrogen phosphate and magnesium sulfate were added to filtrate 1 in a ratio of n(Mg):n(N):n(P) = 0.6:1:1.3. The mixture was stirred at 280 rpm for 28 minutes. During the reaction, 1.8 mol / L... The NaOH solution was maintained at pH 10, and then the mixture was stirred at 130 r / min for 32 min to crystallize. After crystallization, the mixture was allowed to stand for 10 min, and then solid-liquid separation was performed to obtain filtrate 2 and filter residue 2. The phosphate content (as P) in filtrate 2 was measured to be 15.10 mg / L. Filter residue 2 was then washed three times with sodium hydroxide solution at pH 9.6 (washing water volume was 18 L / kg of residue). The washed filter residue 2 was dried at a low temperature of 38℃ to obtain magnesium ammonium phosphate product. Lime milk was added to filtrate 2 and the washed water to bring the pH to 11.0. After stirring for 28 min, solid-liquid separation was performed. The resulting filtrate 3 was treated by adjusting the pH of the wastewater to 7.5-9 with 0.5 mol / L dilute sulfuric acid. The resulting filter residue 3 was returned for further phosphorus removal. Analysis showed that the main products of magnesium ammonium phosphate are magnesium ammonium phosphate and calcium phosphate. The effluent contained 0.01 mg / L manganese, 6.59 mg / L ammonia nitrogen, 0.1 mg / L phosphate (as P), and pH = 8.40, which met the Class I standard limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996).

[0041] Comparative Example 1

[0042] Compared to Example 1, in Comparative Example 1, after adding lime slurry to precipitate manganese and stirring, the mixture was not allowed to stand, but directly filtered and then subjected to precipitation treatment. Wastewater 1 from an electrolytic manganese plant was taken and its concentrations were measured to be 1217.00 mg / L manganese, 1600.00 mg / L ammonia nitrogen, 368.34 mg / L calcium, 1039.49 mg / L magnesium, and pH = 6.50. 20% lime slurry, which had been stirred for 1 hour, was added uniformly to the stirred wastewater using a peristaltic pump until the pH reached approximately 9.5. Stirring continued for 25 minutes. After stirring, solid-liquid separation was performed, yielding filtrate 1 and manganese-containing slag. The manganese-containing slag was returned to the electrolytic manganese production process. The concentrations of manganese, ammonia nitrogen, calcium, and magnesium in filtrate 1 were measured to be 50.2 mg / L, 1199.67 mg / L, 511.85 mg / L, and 977.46 mg / L, respectively. Therefore, the manganese removal rate was 95.88%, and the magnesium content in the water was 0.48 times that of ammonia nitrogen. Phosphoric acid and magnesium sulfate were added sequentially to filtrate 1 in a ratio of n(Mg):n(N):n(P) = 0.6:1:1.3. The mixture was stirred at 300 rpm for 30 minutes. During the reaction, 2 mol / L... The NaOH solution was maintained at pH 9.5, and then the mixture was stirred at 170 r / min for 28 min to crystallize. After crystallization, the mixture was allowed to stand for 20 min, and then solid-liquid separation was performed to obtain filtrate 2 and filter residue 2. The phosphate content (as P) in filtrate 2 was measured to be 17.0 mg / L. Filter residue 2 was then washed three times with sodium hydroxide solution at pH 9.5 (washing water volume was 15 L / kg of residue). The washed filter residue 2 was dried at a low temperature of 36℃ to obtain magnesium ammonium phosphate product. 20% lime milk that had been stirred for 1 h was added to filtrate 2 and the washed water to bring the pH to 12. After stirring for 30 min, solid-liquid separation was performed. The resulting filtrate 3 was treated by adjusting the pH of the wastewater to 7.5-9 with 0.45 mol / L dilute sulfuric acid. The resulting filter residue 3 was returned for further phosphorus removal. Analysis revealed that the main products of magnesium ammonium phosphate were magnesium ammonium phosphate and calcium phosphate. The effluent contained 0.07 mg / L manganese, 39.64 mg / L ammonia nitrogen (>15), 0.2 mg / L phosphate (as P), and pH = 7.80, which did not meet the Class I standard limit requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0043] Comparative Example 2

[0044] Compared with Example 3, Comparative Example 2 used quicklime that was not pre-stirred and emulsified for manganese and phosphorus removal, and the amount of quicklime used for manganese and phosphorus removal was the same as in Example 3. Wastewater 3 from an electrolytic manganese plant was taken and measured to have the following concentrations: manganese 21.69 mg / L, ammonia nitrogen 67.30 mg / L, calcium 464.41 mg / L, magnesium 120.19 mg / L, and pH 6.47. Lime powder was added to the stirred wastewater until the pH reached approximately 9.6. Stirring continued for 30 minutes. After stirring, the manganese concentration was measured to be 1.20 mg / L and the calcium concentration to be 475.37 mg / L. After standing for 7 hours, solid-liquid separation was performed, yielding filtrate 1 and manganese-containing slag. The manganese-containing slag was returned for use in electrolytic manganese production. Filtrate 1 contained 0.70 mg / L manganese, 58.21 mg / L ammonia nitrogen, 413.30 mg / L calcium, and 76.29 mg / L magnesium, indicating a manganese removal rate of 96.77%. The magnesium ion concentration in the water was 0.76 times that of ammonia nitrogen. Sodium dihydrogen phosphate and magnesium sulfate were added to filtrate 1 in a ratio of n(Mg):n(N):n(P) = 0.6:1:1.3. The mixture was stirred at 280 rpm for 28 minutes. During the reaction, 1.8 mol / L sodium sulfate was used. The NaOH solution was maintained at pH 10, and then the mixture was stirred at 130 r / min for 32 min to crystallize. After crystallization, the mixture was allowed to stand for 10 min, and then solid-liquid separation was performed to obtain filtrate 2 and filter residue 2. The phosphate content (calculated as P) in filtrate 2 was measured to be 25.80 mg / L. Filter residue 2 was then washed three times with sodium hydroxide solution at pH 9.5 (washing water volume was 18 L / kg of residue). The washed filter residue 2 was dried at a low temperature of 38℃ to obtain magnesium ammonium phosphate product. Lime powder was added to filtrate 2 and the washed water, and the pH value was only reduced to 10.4. After stirring for 28 min, solid-liquid separation was performed. The resulting filtrate 3 was treated by adjusting the pH of the wastewater to 8.32 with 0.5 mol / L dilute sulfuric acid. The resulting filter residue 3 was returned for further phosphorus removal. Analysis revealed that the main products of magnesium ammonium phosphate were magnesium ammonium phosphate and calcium phosphate. The effluent contained 0.01 mg / L manganese, 13.35 mg / L ammonia nitrogen, 4.1 mg / L phosphate (as P) (>0.5), and pH = 8.32, which did not meet the Class I standard limit requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0045] Table 1 below shows the treatment effects of the comprehensive treatment methods for electrolytic manganese wastewater containing medium to high concentrations of ammonia nitrogen in Examples 1-3 and Comparative Examples 1-2.

[0046] Table 1 shows the experimental conditions and treatment effects in the case studies.

[0047]

[0048] As shown in Table 1, after treatment by the method of this invention, the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen (>50 mg / L) meets the Class I standard limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996). It also effectively utilizes the existing magnesium ions in the wastewater, reduces the amount of reagents added, and recovers manganese, ammonia nitrogen, and magnesium resources from the electrolytic manganese wastewater. In Comparative Example 1, after adding lime slurry to precipitate manganese and stirring, the water was directly filtered without settling, followed by precipitation treatment. The calcium content in the water was significantly higher than after settling, resulting in increased phosphate consumption and a poorer ammonia nitrogen removal effect. Furthermore, the ammonia nitrogen content was also significantly higher than after settling, requiring more phosphate under the same conditions. In Comparative Example 2, the lime was used directly without stirring or emulsification. With the same amount of lime, the manganese removal effect was slightly worse, and the phosphorus removal effect was significantly affected. In the presence of a large amount of hydroxide ions, more stable hydroxyapatite and other substances were formed, covering the lime surface and making it difficult to dissolve, resulting in a relatively poor phosphorus removal effect.

[0049] This invention discloses a comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen. Based on the characteristics of electrolytic manganese production wastewater containing manganese, ammonia nitrogen, calcium, magnesium, and sulfate ions, this method fully utilizes the magnesium ions in the water. By using quicklime to form a slurry, it can selectively remove over 95% of the manganese ions and all of the phosphate ions in the water simultaneously, without introducing excessive calcium ions. This effectively reduces the dosage of magnesium salts and phosphate reagents, lowering treatment costs. It also enables the use of ammonium magnesium phosphate precipitation to treat electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen (>50 mg / L) to fully meet standards. After treatment, the manganese, ammonia nitrogen, phosphate, and pH values ​​all meet the Class I standard limits of the "Integrated Wastewater Discharge Standard" (GB 8978-1996). Furthermore, it allows for the recovery of manganese, ammonia nitrogen, and magnesium resources from the wastewater.

[0050] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A comprehensive treatment method for electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen, characterized in that, Includes the following steps: (1) Stir the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen, add lime slurry at a uniform rate, adjust the pH to 9.5 to 9.7, continue stirring the reaction, let it stand, and obtain manganese-removed wastewater; (2) The manganese-removing wastewater is subjected to solid-liquid separation to obtain filtrate 1 and manganese-containing slag; the manganese-containing slag is transferred to the electrolytic manganese production process for use; (3) Add precipitant to the filtrate 1 according to n(Mg):n(N):n(P)=(0.47~0.6):1:(1.2~1.3), stir the reaction at 280~320r / min for 28~32min, maintain the pH of the reaction solution at 9.5~10 with 1.8~2.2mol / LNaOH solution during the reaction, continue stirring and crystallizing at 130~170r / min for 28~32min, and let it stand for 10~20min after crystallization to obtain the standing reaction solution; (4) The reaction liquid is separated into solid and liquid components to obtain filtrate 2 and filter residue 2; the filter residue 2 is washed with washing water to obtain filter residue 2 washing liquid; the washing water is a sodium hydroxide solution with pH=9.4~9.6; (5) Dry the filter residue 2 at a temperature below 40°C to obtain magnesium ammonium phosphate product; (6) Add the washing liquid of the filter residue 2 to the filtrate 2, mix evenly, then add lime milk to adjust the pH to 11~12.5, stir to react and remove phosphorus, then separate the solid and liquid to obtain filtrate 3 and filter residue 3. (7) The pH of the filtrate 3 is adjusted to 7.5~9 using dilute sulfuric acid to obtain qualified effluent; the filter residue 3 is returned to step (6) for further phosphorus removal.

2. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (1), the electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen is stirred, lime slurry is added at a uniform rate, the pH is adjusted to 9.5 to 9.7, the reaction is continued for 25 to 35 minutes, and then left to stand for 7 to 9 hours to obtain manganese-removed wastewater; the lime slurry is obtained by stirring quicklime slurry, and the quicklime concentration is 18 to 22 wt%.

3. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (2), a plate and frame filter press is used as the solid-liquid separation equipment.

4. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, The precipitant in step (3) includes phosphate and magnesium salt, wherein the phosphate is phosphoric acid, sodium dihydrogen phosphate or disodium hydrogen phosphate, and the magnesium salt is magnesium sulfate.

5. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (4), the filter residue 2 is washed with washing water to obtain filter residue 2 washing liquid; the amount of washing water used per kilogram of filter residue 2 is 15~20L.

6. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (5), the filter residue 2 is dried at 36~40℃ to obtain magnesium ammonium phosphate product.

7. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (6), the washing liquid of filter residue 2 is added to the filtrate 2, mixed evenly, and then lime milk is added to bring the pH to 11~12.

5. The mixture is stirred for 28~32 minutes to remove phosphorus, and then solid-liquid separation is performed to obtain filtrate 3 and filter residue 3.

8. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, In step (7), dilute sulfuric acid with a concentration of 0.45~0.55mol / L is used to adjust the pH of the filtrate 3 to 7.5~9, thereby obtaining compliant effluent.

9. The method for comprehensive treatment of electrolytic manganese production wastewater containing medium to high concentrations of ammonia nitrogen according to claim 1, characterized in that, The effluent in step (7) meets the Class I standard limit requirements of the Integrated Wastewater Discharge Standard (GB8978-1996), namely, manganese ≤2mg / L, ammonia nitrogen ≤15mg / L, phosphate (as P) ≤0.5mg / L, and pH=6~9. The effluent is directly discharged or reused.

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