A method for treating wastewater containing magnesium sulfate and ammonium sulfate

Abstract

This invention discloses a method for treating wastewater containing magnesium sulfate and ammonium sulfate. The method includes: evaporating and concentrating the wastewater containing magnesium sulfate and ammonium sulfate, then cooling and crystallizing it, followed by solid-liquid separation to obtain magnesium ammonium sulfate crystals and a mother liquor containing ammonium sulfate; reacting the magnesium ammonium sulfate crystals with an ammonium salt that can generate carbonate ions and water to undergo a precipitation reaction, followed by solid-liquid separation to obtain 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 stripped water containing ammonium sulfate and an ammonium carbonate fraction; both the mother liquor containing ammonium sulfate and the stripped water containing ammonium sulfate can be evaporated and crystallized to obtain ammonium sulfate product; the ammonium carbonate fraction can be recycled for precipitation reactions. This invention can effectively separate magnesium and ammonium from wastewater, and the separated magnesium carbonate and ammonium sulfate products have high purity and good quality, and can be used directly as products.

Description

Technical Field

[0001] This invention relates to a wastewater treatment method, specifically a method for treating wastewater containing magnesium sulfate and ammonium sulfate, belonging to the field of industrial wastewater treatment technology. Technical Background

[0002] In the treatment of wastewater from the production of iron phosphate, electrolytic manganese, etc., many production wastewaters contain a large amount of cations such as ammonia, iron, magnesium, manganese, and calcium, and anions such as phosphoric acid and sulfuric acid. Through treatment and recovery of heavy metals such as iron, magnesium, manganese, and calcium, and non-metals such as phosphate, a type of wastewater containing magnesium sulfate and ammonium sulfate will eventually be produced.

[0003] Magnesium sulfate and ammonium sulfate in wastewater containing magnesium sulfate and ammonium sulfate will form magnesium ammonium sulfate precipitate after concentration, which is difficult to separate. Traditional methods include direct reuse or high-temperature separation. Direct reuse of magnesium ammonium sulfate has limited applications, while high-temperature separation consumes a lot of energy and is difficult to operate in order to recover high-temperature gas.

[0004] Currently, some researchers are synthesizing 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 uses of magnesium hydrogen phosphate are relatively narrow, resulting in high processing costs.

[0005] In conclusion, it is of great significance to invent a method for treating wastewater containing magnesium sulfate and ammonium sulfate that is efficient, energy-saving, and low-cost. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a wastewater treatment method containing magnesium sulfate and ammonium sulfate. This method is simple, effectively separates magnesium and ammonium, and yields high-purity, high-quality magnesium carbonate and ammonium sulfate products. It achieves "turning waste into treasure," is low-cost, environmentally friendly, and meets the requirements of sustainable development.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for treating wastewater containing magnesium sulfate and ammonium sulfate. The method involves evaporating and concentrating the wastewater containing magnesium sulfate and ammonium sulfate, then cooling and crystallizing it, followed by solid-liquid separation to obtain magnesium ammonium sulfate crystals and a mother liquor containing ammonium sulfate. The magnesium ammonium sulfate crystals are then reacted with an ammonium salt that can generate carbonate ions and water to undergo a precipitation reaction, followed by solid-liquid separation to obtain magnesium carbonate product and a mixture containing ammonium sulfate and ammonium carbonate. The mixture containing ammonium sulfate and ammonium carbonate is stripped to obtain stripped water containing ammonium sulfate and an ammonium carbonate fraction. Both the mother liquor containing ammonium sulfate and the stripped water containing ammonium sulfate can be evaporated and crystallized to obtain the ammonium sulfate product. The ammonium carbonate fraction can be recycled for precipitation reactions. The mass concentration of ammonia nitrogen in the wastewater is not less than twice the magnesium content.

[0008] This invention first concentrates, cools, and crystallizes wastewater to precipitate relatively pure magnesium ammonium sulfate crystals. Excess ammonium sulfate and other impurities are separated from the crystallization mother liquor. This mother liquor can then be further evaporated and crystallized to obtain a high-purity ammonium sulfate product. In the magnesium ammonium sulfate crystallization, the molar ratio of magnesium sulfate to ammonium sulfate is close to 1:1. When it reacts with ammonium salts that can generate carbonate ions, it results in a higher purity magnesium carbonate precipitate, which can be used directly as a product. The ammonium sulfate and ammonium carbonate solutions separated after the precipitation reaction can be stripped to obtain high-purity ammonium sulfate and ammonium carbonate products. In this invention, the magnesium sulfate content in the wastewater is much lower than that of ammonium sulfate, which ensures 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 embodiment, the mass concentration of magnesium in the wastewater is 0.2~3 g / L.

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

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

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

[0013] As a preferred embodiment, the cooling crystallization temperature is 20~40℃. Controlling the cooling crystallization temperature within 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 precipitate together, affecting the purity of magnesium ammonium sulfate.

[0014] As a preferred embodiment, when the ammonium sulfate-containing crystallization mother liquor is crystallized by evaporation to produce ammonium sulfate product, the evaporation temperature is 100~120℃ and the crystallization temperature is 20~40℃.

[0015] As a preferred embodiment, the molar ratio of the magnesium ammonium sulfate crystals to the ammonium salt that can generate carbonate is 1:1 to 2. Controlling the amount of ammonium salt that can generate carbonate added within a suitable range is beneficial to improving the yield of magnesium carbonate products. If the amount added is too low, magnesium cannot be completely precipitated and separated, while if the amount added is too high, it will result in raw material waste and increase costs.

[0016] As a preferred embodiment, 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 approach a solid-phase reaction, resulting in a relative decrease in the purity of the magnesium carbonate product.

[0017] As a preferred embodiment, the ammonium salt that can generate carbonate includes ammonium carbonate and / or ammonium bicarbonate.

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

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

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

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

[0022] As a preferred embodiment, the stripping process uses steam as the stripping gas.

[0023] As a preferred embodiment, the stripping is performed by a stripping tower, wherein the bottom temperature of the stripping tower is 100~110℃, the bottom pressure is 0.32~0.34MPa, the top temperature is 90~100℃, and the top pressure is 0.3~0.31MPa.

[0024] As a preferred embodiment, the steam stripping water containing ammonium sulfate undergoes preliminary evaporation crystallization and solid-liquid separation to obtain an ammonium sulfate solution and magnesium ammonium sulfate crystals. The ammonium sulfate solution is then further evaporated and crystallized to obtain the ammonium sulfate product. The magnesium ammonium sulfate crystals are returned to the precipitation reaction process. Since a small amount of magnesium remains in the steam stripping water, the magnesium can be separated into magnesium ammonium sulfate crystals through preliminary evaporation crystallization, thereby purifying the ammonium sulfate solution. Simultaneously, the separated magnesium ammonium sulfate crystals can be returned to the precipitation process to prepare magnesium carbonate, further improving the separation and recovery efficiency of magnesium.

[0025] As a preferred embodiment, the initial evaporation temperature is 100~120℃, and the initial crystallization temperature is 20~40℃.

[0026] As a preferred embodiment, the evaporation temperature of the ammonium sulfate solution for evaporation and crystallization is 100~120℃, and the crystallization temperature is 20~40℃.

[0027] As a preferred embodiment, the ammonium carbonate fraction is cooled, crystallized, and subjected to solid-liquid separation to obtain the ammonium carbonate product. This ammonium carbonate product can be directly recycled for precipitation reactions.

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

[0029] (1) In this invention, relatively pure magnesium ammonium sulfate crystals are first precipitated by evaporation, concentration and cooling crystallization, and then magnesium is separated from the magnesium ammonium sulfate crystals by ammonium carbonate salts. The resulting 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 mixture obtained by 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 fertilizer.

[0030] (2) Magnesium and ammonium have high separation efficiency, simple separation steps, low cost, and are suitable for industrial production. Attached Figure Description

[0031] Figure 1 This is a flow chart of the wastewater treatment process containing magnesium sulfate and ammonium sulfate in Example 1 of the present invention. Detailed Implementation

[0032] Example 1

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

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

[0035] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.27% magnesium, 7.32% ammonia nitrogen, and 50.19% sulfate.

[0037] (3) The above filtrate (crystallization mother liquor) is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature is controlled at 20℃. Ammonium sulfate product is obtained by separation. 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) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0038] (4) Take 78.11g of the above magnesium ammonium sulfate crystals and mix them with 31.43g of ammonium carbonate. At the same time, add 180mL of pure water, stir in a water bath at 30℃ for 5h, filter, and obtain ammonium sulfate-ammonium carbonate mixed solution and filter residue. Wash the filter residue with pure water and dry it at 105℃ to obtain magnesium carbonate product. After testing, the magnesium carbonate product has a magnesium content of 23.37%, an ammonia nitrogen content of 0.00125%, and a sulfate content of 0.0946%. The purity meets the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000) with a magnesium content ≥22.92%. Among them, the magnesium concentration in the ammonium sulfate-ammonium carbonate mixed solution is 3854.87mg / L.

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

[0040] (6) Cool the ammonium carbonate solution fraction to crystallize, and control the crystallization temperature to 30°C to obtain the ammonium carbonate product.

[0041] (7) The steam extracted from the water is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature at 30℃. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 for magnesium-ammonia separation. The ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain the ammonium sulfate product. The ammonium sulfate product is tested and found to contain 92.6% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0042] Example 2

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

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

[0045] (1) 12L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 9.2 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.68% magnesium, 7.80% ammonia nitrogen, and 53.49% sulfate.

[0047] (3) The above filtrate (crystallization mother liquor) is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature is controlled at 20℃. Ammonium sulfate product is obtained by separation. 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) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0048] (4) Mix 33.2g of the above-mentioned magnesium ammonium sulfate crystals with 13g of ammonium carbonate, add 90mL of pure water, stir in a water bath at 30℃ for 5h, filter, and obtain a mixed solution of ammonium sulfate and ammonium carbonate and filter residue. Wash the filter residue with pure water and dry it at 105℃ to obtain magnesium carbonate product, with a magnesium content of 23.11%, an ammonia nitrogen content of 0.00175%, and a sulfate content of 0.0852%. The purity meets the requirements of "Industrial Hydrated Basic Magnesium Carbonate" (HGT2959-2000) for magnesium content ≥22.92%. The magnesium concentration in the ammonium sulfate-ammonium carbonate mixed solution is 3734.76mg / L.

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

[0050] (6) Cool the ammonium carbonate solution fraction to crystallize, and control the crystallization temperature to 30°C to obtain the ammonium carbonate product.

[0051] (7) The steam extracted from the water is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature at 30℃. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 for magnesium-ammonia separation. The ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain the ammonium sulfate product. The ammonium sulfate product contains 91.5% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0052] Example 3

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

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

[0055] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.56 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.36% magnesium, 7.24% ammonia nitrogen, and 50.26% sulfate.

[0057] (3) The above filtrate (crystallization mother liquor) is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature is controlled at 20℃. Ammonium sulfate product is obtained by separation. 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) with nitrogen ≥19.0% and sulfur ≥21.0%.

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

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

[0060] (6) Cool the ammonium carbonate solution fraction to crystallize, and control the crystallization temperature to 30°C to obtain the ammonium carbonate product.

[0061] (7) The steam extracted from the water is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature at 30℃. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 for magnesium-ammonia separation. The ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain the ammonium sulfate product. The ammonium sulfate product contains 90% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0062] Example 4

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

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

[0065] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.27% magnesium, 7.32% ammonia nitrogen, and 50.17% sulfate.

[0067] (3) The above filtrate (crystallization mother liquor) is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature is controlled at 20℃. Ammonium sulfate product is obtained by separation. 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) with nitrogen ≥19.0% and sulfur ≥21.0%.

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

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

[0070] (6) Cool the ammonium carbonate solution fraction to crystallize, and control the crystallization temperature to 30°C to obtain the ammonium carbonate product.

[0071] (7) The steam extracted from the water is evaporated and crystallized. The evaporation temperature is controlled at 100℃ and the crystallization temperature is controlled at 30℃. Magnesium ammonium sulfate crystals and ammonium sulfate solution are separated. The magnesium ammonium sulfate crystals are returned to step 4 for magnesium-ammonia separation. The ammonium sulfate solution is returned to step 3 for evaporation and crystallization to obtain the ammonium sulfate product. The ammonium sulfate product contains 94.2% ammonium sulfate, and the purity meets the requirements of "Fertilizer Grade Ammonium Sulfate" (GB / T535-2020) with nitrogen ≥19.0% and sulfur ≥21.0%.

[0072] Comparative Example 1

[0073] The wastewater containing magnesium sulfate and ammonium sulfate in this comparative example has the following composition:

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

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

[0076] (2) If the mother liquor obtained by evaporation and concentration is filtered directly without cooling and crystallization, magnesium ammonium sulfate crystals cannot be obtained.

[0077] Comparative Example 2

[0078] The wastewater containing magnesium sulfate and ammonium sulfate in this comparative example has the following composition:

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

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

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

[0082] Comparative Example 3

[0083] The wastewater containing magnesium sulfate and ammonium sulfate in this comparative example has the following composition:

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

[0085] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.27% magnesium, 7.32% ammonia nitrogen, and 50.19% sulfate.

[0087] S3 mixes 78.11g of magnesium ammonium sulfate crystals with 30.72g of ammonium carbonate, adds 380mL of pure water, and stirs in a water bath at 30℃ for 5h. No magnesium carbonate precipitate is produced.

[0088] Comparative Example 4

[0089] The wastewater containing magnesium sulfate and ammonium sulfate in this comparative example has the following composition:

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

[0091] (1) 2L of wastewater containing magnesium sulfate and ammonium sulfate was evaporated and concentrated 4.65 times at 100℃ 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 magnesium ammonium 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 magnesium ammonium sulfate crystals contained 6.27% magnesium, 7.32% ammonia nitrogen, and 50.19% sulfate.

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

Claims

1. A method for treating wastewater containing magnesium sulfate and ammonium sulfate, characterized in that: Wastewater containing magnesium sulfate and ammonium sulfate is evaporated, concentrated, cooled, and crystallized. Solid-liquid separation is then performed to obtain magnesium ammonium sulfate crystals and a mother liquor containing ammonium sulfate. The magnesium ammonium sulfate crystals are then reacted with an ammonium salt that can produce carbonate ions and water to undergo a precipitation reaction. Solid-liquid separation is then performed to obtain magnesium carbonate product and a mixed solution containing ammonium sulfate and ammonium carbonate. The mixed solution containing ammonium sulfate and ammonium carbonate is stripped to obtain stripped water containing ammonium sulfate and an ammonium carbonate fraction. Both the mother liquor containing ammonium sulfate and the stripped water containing ammonium sulfate can be evaporated and crystallized to obtain ammonium sulfate product. The ammonium carbonate fraction can be recycled for precipitation reactions. The ammonia nitrogen concentration in the wastewater is not less than twice the magnesium content. The amount of water added is 1 to 2.5 times the mass of magnesium ammonium sulfate crystals; The conditions for the precipitation reaction are: pH value of the reaction system is 8.5~9.5, temperature is 20~40℃, and time is 5~8h.

2. The wastewater treatment method 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 in the wastewater is 1 to 1.1 times the total concentration of magnesium sulfate and ammonium sulfate.

3. A wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1 or 2, characterized in that: The evaporation and concentration temperature is 100~120℃, and the concentration ratio is 4~20 times.

4. A wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1 or 2, characterized in that: The cooling crystallization temperature is 20~40℃.

5. The wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The molar ratio of the magnesium ammonium sulfate crystals to the ammonium salt that can generate carbonate is 1:1~2.

6. A wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1 or 5, characterized in that: The ammonium salts that can produce carbonate include ammonium carbonate and / or ammonium bicarbonate.

7. The wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1, characterized in that: The stripping process uses steam as the stripping gas. The stripping is completed through a stripping tower. The bottom temperature of the stripping tower is 100~110℃, the bottom pressure is 0.32~0.34MPa, the top temperature is 90~100℃, and the top pressure is 0.3~0.31MPa.

8. A wastewater treatment method containing magnesium sulfate and ammonium sulfate according to claim 1 or 7, characterized in that: The steam-out water containing ammonium sulfate is subjected to preliminary evaporation crystallization and solid-liquid separation to obtain ammonium sulfate solution and magnesium ammonium sulfate crystals; the ammonium sulfate solution is then subjected to evaporation crystallization to obtain ammonium sulfate product; the magnesium ammonium sulfate crystals are returned to the precipitation reaction process.

Images