Method for treating wastewater containing magnesium sulfate and ammonium sulfate

Abstract

The invention discloses a method for treating wastewater containing magnesium sulfate and ammonium sulfate. The method comprises the following steps: evaporating and concentrating wastewater containing magnesium sulfate and ammonium sulfate, cooling and crystallizing, and carrying out solid-liquid separation to obtain ammonium magnesium sulfate crystals and crystallization mother liquor containing ammonium sulfate; carrying out precipitation reaction on the ammonium magnesium sulfate crystal, ammonium salt capable of generating carbonate and water, and then carrying out solid-liquid separation to obtain a magnesium carbonate product and a mixed solution containing ammonium sulfate and ammonium carbonate; carrying out steam stripping on the mixed solution containing ammonium sulfate and ammonium carbonate to obtain steam stripping water containing ammonium sulfate and an ammonium carbonate fraction; the ammonium sulfate-containing crystallization mother liquor and the ammonium sulfate-containing stripping water can be subjected to evaporative crystallization to obtain an ammonium sulfate product; the ammonium carbonate fraction can be circularly used for precipitation reaction. Magnesium and ammonium in the wastewater can be effectively separated, and magnesium carbonate and ammonium sulfate products obtained through separation are high in purity and good in quality and can be directly used as products.

Description

Technical Field

[0001] The invention relates to a wastewater treatment method, in particular to a wastewater treatment method containing magnesium sulfate and ammonium sulfate, and belongs to the technical field of industrial production wastewater treatment. Technical Background

[0002] In the process of treating production wastewater such as iron phosphate and electrolytic manganese, many production wastewaters contain a large amount of cations such as ammonia, iron, magnesium, manganese, calcium, and anions such as phosphate and sulfuric acid. By treating and recovering heavy metals such as iron, magnesium, manganese, calcium, and non-metals such as phosphate, a wastewater containing magnesium sulfate and ammonium sulfate will eventually be produced.

[0003] After the magnesium sulfate and ammonium sulfate in the wastewater containing magnesium sulfate and ammonium sulfate are concentrated, magnesium ammonium sulfate precipitate is produced, which is difficult to separate. The traditional method adopts the method of direct reuse or high-temperature separation. The direct reuse of magnesium ammonium sulfate has a narrow application, the high-temperature separation consumes a lot of energy, and the recovery of high-temperature gas is difficult to operate.

[0004] At present, some researchers have synthesized magnesium hydrogen phosphate by adding an external phosphorus source to separate magnesium ions. The magnesium hydrogen phosphate produced by this method can be reused in agricultural production, etc. However, the cost of adding a phosphorus source is high, and the use of magnesium hydrogen phosphate is relatively narrow, resulting in high processing costs.

[0005] In summary, it is of great significance to invent a method for treating wastewater containing magnesium sulfate and ammonium sulfate with high efficiency, energy saving and low cost. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for treating wastewater containing magnesium sulfate and ammonium sulfate. The method is simple, can effectively separate magnesium and ammonium, and the obtained magnesium carbonate product and ammonium sulfate product have high purity and good quality, realizing "turning waste into treasure", low cost, green and environmentally friendly, and meeting the requirements of sustainable development.

[0007] In order to achieve the above technical purpose, the present invention provides a method for treating wastewater containing magnesium sulfate and ammonium sulfate. The method comprises the following steps: evaporating and concentrating the wastewater containing magnesium sulfate and ammonium sulfate, cooling and crystallizing the wastewater, and then performing solid-liquid separation to obtain magnesium sulfate ammonium crystals and a crystallization mother liquor containing ammonium sulfate; subjecting the magnesium sulfate ammonium crystals to a precipitation reaction with an ammonium salt capable of producing carbonate and water, and then performing solid-liquid separation to obtain a magnesium carbonate product and a mixed solution containing ammonium sulfate and ammonium carbonate; stripping the mixed solution containing ammonium sulfate and ammonium carbonate to obtain a stripping water containing ammonium sulfate and an ammonium carbonate fraction; both the crystallization mother liquor containing ammonium sulfate and the stripping water containing ammonium sulfate can be evaporated and crystallized to obtain an ammonium sulfate product; the ammonium carbonate fraction can be recycled for precipitation reaction; and the mass concentration of ammonia nitrogen in the wastewater is not less than twice that of magnesium element.

[0008] The present invention first concentrates and cools the wastewater for crystallization to precipitate relatively pure magnesium ammonium sulfate crystals, and the excess ammonium sulfate and other impurities are separated out by the crystallization mother liquor, and the crystallization mother liquor can also obtain a high-purity ammonium sulfate product by evaporation and crystallization, and in the magnesium ammonium sulfate crystals, the molar ratio of magnesium sulfate to ammonium sulfate is close to 1:1, and when the magnesium ammonium sulfate crystals are subjected to precipitation reaction with ammonium salts that can produce carbonate radicals, the obtained magnesium carbonate precipitation purity can be made higher, and the magnesium carbonate can be directly used as a product. The ammonium sulfate and ammonium carbonate solution separated after the precipitation reaction can obtain high-purity ammonium sulfate and ammonium carbonate products by stripping. The content of magnesium sulfate in the wastewater of the present invention is much lower than that of ammonium sulfate, so that it can be ensured that relatively pure magnesium ammonium sulfate crystals are precipitated by evaporation and cooling crystallization, thereby improving the purity of the magnesium carbonate product.

[0009] As a preferred solution, the mass concentration of magnesium in the wastewater is 0.2~3g / L.

[0010] As a preferred solution, the mass concentration of ammonia nitrogen in the wastewater is 6-14 g / L.

[0011] As a preferred solution, the molar concentration of sulfate ions in the wastewater is 1 to 1.1 times the total concentration of magnesium sulfate and ammonium sulfate.

[0012] As a preferred solution, the temperature of the evaporation concentration is 100-120° C., and the concentration multiple is 4-20 times. The ammonia nitrogen content in the concentrated solution is 45-60 g / L. Controlling the concentration multiple within a suitable range is beneficial to improving the yield and purity of magnesium ammonium sulfate crystals. If the concentration multiple is too low, magnesium ammonium sulfate crystals cannot be precipitated to the greatest extent. If the concentration multiple is too high, other impurities may be precipitated together, affecting the purity of magnesium ammonium sulfate.

[0013] As a preferred solution, the temperature of the cooling crystallization is 20-40° C. Controlling the cooling crystallization temperature in a suitable range is beneficial to improving the yield and purity of magnesium ammonium sulfate crystals. If the cooling crystallization temperature is too high, magnesium ammonium sulfate crystals cannot be precipitated to the maximum extent. If the cooling crystallization temperature is too low, other impurities may be precipitated together, affecting the purity of magnesium ammonium sulfate.

[0014] As a preferred solution, when the ammonium sulfate-containing crystallization mother liquor is subjected to evaporation crystallization to prepare the ammonium sulfate product, the evaporation temperature is 100-120°C and the crystallization temperature is 20-40°C.

[0015] As a preferred solution, the molar ratio of the ammonium magnesium sulfate crystals to the ammonium salt that can generate carbonate is 1: 1 to 2. Controlling the addition amount of the ammonium salt that can generate carbonate within a suitable range is conducive to improving the yield of the magnesium carbonate product. If the addition amount is too low, magnesium cannot be completely precipitated and separated. If the addition amount is too high, it will cause a waste of raw materials and increase costs.

[0016] As a preferred solution, the amount of water added is 1 to 2.5 times the mass of magnesium ammonium sulfate crystals. Controlling the amount of water added within a suitable range can ensure separation efficiency. If the amount of water added is too high, the precipitation reaction cannot be close to the solid phase reaction, resulting in a relatively lower purity of the magnesium carbonate product.

[0017] As a preferred embodiment, the ammonium salt capable of generating carbonate ions includes ammonium carbonate and / or ammonium bicarbonate.

[0018] As a preferred solution, the conditions of the precipitation reaction are: the pH value of the reaction system is 8.5-9.5, the temperature is 20-40°C, and the time is 5-8 hours. Controlling the pH value of the system within an appropriate range is conducive to improving the yield and purity of the magnesium carbonate product. If the pH value is too low, the yield of the magnesium carbonate product will decrease relatively. If the pH value is too high, magnesium hydroxide impurities will be generated, affecting the purity of the magnesium carbonate.

[0019] When ammonium bicarbonate is added, ammonia is used to adjust the pH. The precipitation reaction principle is as follows:

[0020] Mg(NH4)2(SO4)2+(NH4)2CO3→MgCO3↓+2(NH4)2SO4 Formula (1);

[0021] Mg(NH4)2(SO4)2+NH4HCO3+NH3 •H2O→MgCO3↓+2(NH4)2SO4+H2O Formula (2).

[0022] As a preferred solution, the stripping process uses water vapor as the stripping gas.

[0023] As a preferred solution, the stripping is completed by a stripping tower, the bottom temperature of the stripping tower is 100-110°C, the bottom pressure is 0.32-0.34 MPa, the top temperature is 90-100°C, and the top pressure is 0.3-0.31 MPa.

[0024] As a preferred solution, the stripping water containing ammonium sulfate is subjected to preliminary evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate solution and ammonium magnesium sulfate crystals; the ammonium sulfate solution is then subjected to evaporation crystallization to obtain an ammonium sulfate product; and the ammonium magnesium sulfate crystals are returned to the precipitation reaction process. Since a small amount of magnesium element still remains in the stripping water, the magnesium element can be separated out in the form of ammonium magnesium sulfate crystals through preliminary evaporation crystallization treatment, thereby achieving the purpose of purifying the ammonium sulfate solution. At the same time, the separated ammonium magnesium sulfate crystals can be continuously returned to the precipitation process to prepare a magnesium carbonate product, further improving the separation and recovery efficiency of the magnesium element.

[0025] As a preferred solution, the initial evaporation temperature is 100-120°C, and the initial crystallization temperature is 20-40°C.

[0026] As a preferred solution, the evaporation temperature of the ammonium sulfate solution evaporation crystallization is 100-120°C, and the crystallization temperature is 20-40°C.

[0027] As a preferred solution, the ammonium carbonate fraction is cooled, crystallized and solid-liquid separated to obtain an ammonium carbonate product, which can be directly recycled for precipitation reaction.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention first precipitates relatively pure ammonium magnesium sulfate crystals by evaporation concentration and cooling crystallization, and then separates the magnesium precipitate in the ammonium magnesium sulfate crystals by ammonium carbonate salts. The obtained magnesium carbonate product has high purity and can meet the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000). No secondary processing is required and it can be reused as a chemical raw material. The ammonium sulfate and ammonium carbonate mixed liquid obtained by the precipitation reaction is separated by stripping to obtain high-quality ammonium sulfate and ammonium carbonate products. The purity of the ammonium sulfate product can meet the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) and can be reused as a fertilizer.

[0030] (2) The separation efficiency of magnesium and ammonium is high, the separation steps are simple, the cost is low, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a process flow chart for treating wastewater containing magnesium sulfate and ammonium sulfate in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] Example 1

[0033] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this embodiment are as follows:

[0034] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0035] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100°C to obtain 430mL of mother liquor.

[0036] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 400 mL of filtrate and 78.11 g of ammonium magnesium sulfate crystals. The filtrate contained 120.3 mg / L of magnesium, 51416.13 mg / L of ammonia nitrogen, and 257320.8 mg / L of sulfate. The ammonium magnesium sulfate crystals contained 6.27% of magnesium, 7.32% of ammonia nitrogen, and 50.19% of sulfate.

[0037] (3) The filtrate (mother crystallization liquor) is evaporated and crystallized, and the evaporation temperature is controlled at 100°C and the crystallization temperature is controlled at 20°C to separate and obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 94.2% of ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0038] (4) 78.11 g of the above-mentioned ammonium magnesium sulfate crystals were mixed with 31.43 g of ammonium carbonate, and 180 mL of pure water was added at the same time. The mixture was stirred in a water bath at 30° C. for 5 h, and filtered to obtain an ammonium sulfate-ammonium carbonate mixed solution and a filter residue. The filter residue was washed with pure water and dried at 105° C. to obtain a magnesium carbonate product. After testing, the magnesium content of the magnesium carbonate product was 23.37%, the ammonia nitrogen content was 0.00125%, and the sulfate content was 0.0946%. The purity met the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000, magnesium content ≥ 22.92%). Among them, the magnesium concentration in the ammonium sulfate-ammonium carbonate mixed solution was 3854.87 mg / L.

[0039] (5) The ammonium sulfate-ammonium carbonate mixed solution is stripped in a stripping tower, the bottom temperature of the stripping axe is controlled to be 110°C, the top temperature of the tower is controlled to be 90°C, the gas introduced is 100°C water vapor, an ammonium carbonate solution fraction is obtained at the top of the tower, and stripping water is obtained in the bottom of the tower. The stripping water contains ammonium sulfate and magnesium sulfate.

[0040] (6) Cooling and crystallizing the ammonium carbonate solution fraction, controlling the crystallization temperature to 30° C., and obtaining an ammonium carbonate product.

[0041] (7) The above steam stripping is subjected to evaporation and crystallization, and the evaporation temperature is controlled to be 100°C and the crystallization temperature is controlled to be 30°C, and magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 to continue the separation of magnesium and ammonia, and the ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 92.6% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0042] Example 2

[0043] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this embodiment are as follows:

[0044] The wastewater contains 21.4 g / L sulfate, 6 g / L ammonia nitrogen, and 0.2 g / L magnesium.

[0045] (1) 12L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 9.2 times at 100°C to obtain 1290mL of mother liquor.

[0046] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 1260 mL of filtrate and 33.2 g of ammonium magnesium sulfate crystals. The filtrate contained 231.10 mg / L of magnesium, 53726.79 mg / L of ammonia nitrogen, and 265311 mg / L of sulfate. The ammonium magnesium sulfate crystals contained 6.68% of magnesium, 7.80% of ammonia nitrogen, and 53.49% of sulfate.

[0047] (3) The filtrate (mother crystallization liquor) is evaporated and crystallized, and the evaporation temperature is controlled at 100°C and the crystallization temperature is controlled at 20°C to separate and obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 94.2% of ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0048] (4) 33.2 g of the above-mentioned ammonium magnesium sulfate crystals were mixed with 13 g of ammonium carbonate, 90 mL of pure water was added, the mixture was stirred in a water bath at 30° C. for 5 h, and filtered to obtain an ammonium sulfate-ammonium carbonate mixed solution and a filter residue. The filter residue was washed with pure water and dried at 105° C. to obtain a magnesium carbonate product having a magnesium content of 23.11%, an ammonia nitrogen content of 0.00175%, and a sulfate content of 0.0852%. The purity met the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000, magnesium content ≥ 22.92%). The magnesium concentration in the ammonium sulfate-ammonium carbonate mixed solution was 3734.76 mg / L.

[0049] (5) The ammonium sulfate-ammonium carbonate mixed solution is stripped in a stripping tower, the bottom temperature of the stripping axe is controlled to be 110°C, the top temperature of the tower is controlled to be 90°C, the gas introduced is 100°C water vapor, an ammonium carbonate solution fraction is obtained at the top of the tower, and stripping water is obtained in the bottom of the tower. The stripping water contains ammonium sulfate and magnesium sulfate.

[0050] (6) Cooling and crystallizing the ammonium carbonate solution fraction, controlling the crystallization temperature to 30° C., and obtaining an ammonium carbonate product.

[0051] (7) The above steam stripping is subjected to evaporation and crystallization, and the evaporation temperature is controlled to be 100°C and the crystallization temperature is controlled to be 30°C. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 to continue the separation of magnesium and ammonia, and the ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 91.5% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0052] Example 3

[0053] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this embodiment are as follows:

[0054] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0055] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.56 times at 100°C to obtain 430mL of mother liquor.

[0056] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 400 mL of filtrate and 78.11 g of ammonium magnesium sulfate crystals. The filtrate had a magnesium content of 120.3 mg / L, an ammonia nitrogen content of 51416.13 mg / L, and a sulfate content of 257320.8 mg / L; the magnesium content of the ammonium magnesium sulfate crystals was 6.36%, the ammonia nitrogen content was 7.24%, and the sulfate content was 50.26%.

[0057] (3) The filtrate (mother crystallization liquor) is evaporated and crystallized, and the evaporation temperature is controlled at 100°C and the crystallization temperature is controlled at 20°C to separate and obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 94.2% of ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0058] (4) 78.11 g of ammonium magnesium sulfate crystals were mixed with 19.2 g of ammonium carbonate, 180 mL of pure water was added, the mixture was stirred in a water bath at 30° C. for 5 h, and filtered to obtain an ammonium sulfate-ammonium carbonate mixed solution and a filter residue. The filter residue was washed with pure water and dried at 105° C. to obtain a magnesium carbonate product having a magnesium content of 23.48%, an ammonia nitrogen content of 0.0022%, and a sulfate content of 0.0709%. The purity met the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000, magnesium content ≥ 22.92%). The magnesium concentration in the ammonium sulfate-ammonium carbonate mixed solution was 6508.41 mg / L.

[0059] (5) The ammonium sulfate-ammonium carbonate mixed solution is stripped in a stripping tower, the bottom temperature of the stripping tower is controlled to be 110°C, the top temperature of the tower is controlled to be 100°C, the gas introduced is 100°C water vapor, an ammonium carbonate solution fraction is obtained at the top of the tower, and stripping water is obtained in the bottom of the tower, the stripping water contains ammonium sulfate and magnesium sulfate.

[0060] (6) Cooling and crystallizing the ammonium carbonate solution fraction, controlling the crystallization temperature to 30° C., and obtaining an ammonium carbonate product.

[0061] (7) The above steam stripping is subjected to evaporation and crystallization, and the evaporation temperature is controlled to be 100°C and the crystallization temperature is controlled to be 30°C. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 to continue the separation of magnesium and ammonia, and the ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 90% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0062] Example 4

[0063] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this embodiment are as follows:

[0064] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0065] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100°C to obtain 430mL of mother liquor.

[0066] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 400 mL of filtrate and 78.11 g of ammonium magnesium sulfate crystals. The filtrate had a magnesium content of 120.3 mg / L, an ammonia nitrogen content of 51416.13 mg / L, and a sulfate content of 257320.8 mg / L; the magnesium content of the ammonium magnesium sulfate crystals was 6.27%, the ammonia nitrogen content was 7.32%, and the sulfate content was 50.17%.

[0067] (3) The filtrate (mother liquor for crystallization) is evaporated and crystallized, and the evaporation temperature is controlled at 100°C and the crystallization temperature is controlled at 20°C to separate and obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 94.2% of ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535 2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0068] (4) 78.11 g of ammonium magnesium sulfate crystals were mixed with 30.84 g of ammonium bicarbonate, the pH value was adjusted to 9 with ammonia water, 180 mL of pure water was added, the mixture was stirred in a water bath at 30°C for 5 h, and filtered to obtain an ammonium sulfate-ammonium carbonate mixed solution and a filter residue. The filter residue was washed with pure water and dried at 105°C to obtain a magnesium carbonate product with a magnesium content of 23.45%, an ammonia nitrogen content of 0.00235%, and a sulfate content of 0.0643%. The purity met the requirement of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000) for a magnesium content of ≥22.92%. The magnesium concentration of the ammonium sulfate-ammonium carbonate mixed solution was 3965.82 mg / L.

[0069] (5) The ammonium sulfate-ammonium carbonate mixed solution is stripped in a stripping tower, the bottom temperature of the stripping tower is controlled to be 100°C, the top temperature of the tower is controlled to be 90°C, the gas introduced is 100°C water vapor, an ammonium carbonate solution fraction is obtained at the top of the tower, and stripping water is obtained in the bottom of the tower, the stripping water contains ammonium sulfate and magnesium sulfate.

[0070] (6) Cooling and crystallizing the ammonium carbonate solution fraction, controlling the crystallization temperature to 30° C., and obtaining an ammonium carbonate product.

[0071] (7) The above steam stripping is subjected to evaporation and crystallization, and the evaporation temperature is controlled to be 100°C and the crystallization temperature is controlled to be 30°C. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 to continue the separation of magnesium and ammonia, and the ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain an ammonium sulfate product. After testing, the ammonium sulfate product contains 94.2% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) of nitrogen ≥19.0% and sulfur ≥21.0%.

[0072] Comparative Example 1

[0073] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this comparative example are as follows:

[0074] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0075] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.56 times at 100°C to obtain 430mL of mother liquor.

[0076] (2) If the mother liquor obtained by evaporation and concentration is directly filtered without cooling and crystallization, no ammonium magnesium sulfate crystals can be obtained.

[0077] Comparative Example 2

[0078] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this comparative example are as follows:

[0079] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0080] 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated to 2 times at 100°C to obtain 1L of mother liquor.

[0081] (2) The mother liquor obtained by evaporation and concentration is cooled to 33°C for crystallization and filtered. However, the concentration of ammonium magnesium sulfate in the filtrate is too high and a relatively pure ammonium sulfate product cannot be obtained.

[0082] Comparative Example 3

[0083] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this comparative example are as follows:

[0084] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0085] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100°C to obtain 430mL of mother liquor.

[0086] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 400 mL of filtrate and 78.11 g of ammonium magnesium sulfate crystals. The filtrate contained 120.3 mg / L of magnesium, 51416.13 mg / L of ammonia nitrogen, and 257320.8 mg / L of sulfate. The ammonium magnesium sulfate crystals contained 6.27% of magnesium, 7.32% of ammonia nitrogen, and 50.19% of sulfate.

[0087] S3: Mix 78.11 g of ammonium magnesium sulfate crystals with 30.72 g of ammonium carbonate, add 380 mL of pure water, and stir in a water bath at 30°C for 5 h. No magnesium carbonate precipitation will be produced.

[0088] Comparative Example 4

[0089] The components of the wastewater containing magnesium sulfate and ammonium sulfate in this comparative example are as follows:

[0090] The wastewater contains 55.64g / L sulfate, 12.73g / L ammonia nitrogen, and 3g / L magnesium.

[0091] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100°C to obtain 430mL of mother liquor.

[0092] (2) The mother liquor obtained by evaporation and concentration was cooled and crystallized to 33°C, filtered, and the filter residue was dried at 105°C to obtain 400 mL of filtrate and 78.11 g of ammonium magnesium sulfate crystals. The filtrate contained 120.3 mg / L of magnesium, 51416.13 mg / L of ammonia nitrogen, and 257320.8 mg / L of sulfate. The ammonium magnesium sulfate crystals contained 6.27% of magnesium, 7.32% of ammonia nitrogen, and 50.19% of sulfate.

[0093] (3) Mix 78.11 g of ammonium magnesium sulfate crystals with 30.84 g of ammonium bicarbonate, adjust the pH value to 7 with ammonia water, add 180 mL of pure water, and stir in a water bath at 30°C. The reaction pH value is too low and the magnesium carbonate product cannot be obtained.

Claims

1. A method for treating wastewater containing magnesium sulfate and ammonium sulfate, characterized in that: The wastewater containing magnesium sulfate and ammonium sulfate is evaporated and concentrated, then cooled and crystallized, and then solid-liquid separation is performed to obtain magnesium sulfate ammonium crystals and a crystallization mother liquor containing ammonium sulfate; the magnesium sulfate ammonium crystals are subjected to precipitation reaction with ammonium salt that can produce carbonate and water, and then solid-liquid separation is performed to obtain a magnesium carbonate product and a mixed solution containing ammonium sulfate and ammonium carbonate; the mixed solution containing ammonium sulfate and ammonium carbonate is subjected to steam stripping to obtain steam stripping water containing ammonium sulfate and an ammonium carbonate fraction; the crystallization mother liquor containing ammonium sulfate and the steam stripping water containing ammonium sulfate can both be evaporated and crystallized to obtain an ammonium sulfate product; the ammonium carbonate fraction can be recycled for precipitation reaction; the mass concentration of ammonia nitrogen in the wastewater is not less than twice that of magnesium element.

2. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The mass concentration of magnesium in the wastewater is 0.2-3 g / L; The mass concentration of ammonia nitrogen in the wastewater is 6-14 g / L; The molar concentration of sulfate ions in the wastewater is 1 to 1.1 times the total concentration of magnesium sulfate and ammonium sulfate.

3. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1 or 2, characterized in that: The temperature of the evaporation concentration is 100-120° C., and the concentration multiple is 4-20 times.

4. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1 or 2, characterized in that: The temperature of the cooling crystallization is 20-40°C.

5. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The molar ratio of the ammonium magnesium sulfate crystals to the ammonium salt capable of generating carbonate is 1:1-2.

6. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1 or 5, characterized in that: The amount of water added is 1 to 2.5 times the mass of the ammonium magnesium sulfate crystals.

7. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1 or 5, characterized in that: The ammonium salt capable of generating carbonate includes ammonium carbonate and / or ammonium bicarbonate.

8. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The conditions of the precipitation reaction are as follows: the pH value of the reaction system is 8.5-9.5, the temperature is 20-40° C., and the time is 5-8 hours.

9. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The stripping adopts water vapor as the stripping gas; The stripping is completed through a stripping tower, the bottom temperature of the stripping tower is 100-110°C, the bottom pressure is 0.32-0.34MPa, the top temperature is 90-100°C, and the top pressure is 0.3-0.31MPa.

10. A method for treating wastewater containing magnesium sulfate and ammonium sulfate according to claim 1 or 9, characterized in that: The water stripping of the ammonium sulfate-containing steam is subjected to preliminary evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate solution and ammonium magnesium sulfate crystals; the ammonium sulfate solution is further subjected to evaporation crystallization to obtain an ammonium sulfate product; and the ammonium magnesium sulfate crystals are returned to the precipitation reaction process.

Images