Method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater and magnesium sulfate wastewater treatment method

Abstract

The invention discloses a method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater, which comprises the following steps: preparing a mixed precipitator by using ammonia water and ammonium bicarbonate in a mass ratio of (0.1-1): 1; the method comprises the following steps: adding a seed crystal and a mixed precipitator into magnesium sulfate wastewater, carrying out a precipitation reaction at 35-55 DEG C for 30-130 min, and filtering, washing and drying the precipitate after the precipitation reaction is finished to obtain magnesium carbonate. The invention also discloses a magnesium sulfate wastewater treatment method. According to the method, resources such as magnesium elements in the wastewater are recycled, and the problems of generation of a large amount of waste residues and secondary pollution can be avoided.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater and a method for treating magnesium sulfate wastewater. Background Technology

[0002] Magnesium carbonate, as an important inorganic functional material, has wide applications in flame retardant materials, pharmaceutical and food additives, environmental adsorbents, and industrial fillers due to its controllable thermal decomposition, porous structure, mild alkalinity, and excellent chemical stability. Currently, the industrial preparation methods for magnesium carbonate mainly fall into the following two categories:

[0003] One type is the ore-based method, which uses magnesite (MgCO3) as raw material. Magnesium oxide is produced by high-temperature calcination, followed by hydration and carbonation reactions to prepare magnesium carbonate. Chinese Publication No. CN1789133A describes a method for producing light magnesium carbonate from magnesite tailings, the specific process of which is as follows:

[0004] 1) The ore is crushed to a particle size of 5-30cm and then fed into a lime kiln for calcination;

[0005] 2) Grind the calcined magnesite blocks to 150-200 mesh;

[0006] 3) Take the ground MgO powder, add water and digest it to form a magnesium hydroxide emulsion;

[0007] 4) The magnesium hydroxide emulsion is carbonized with CO2 to form a magnesium carbonate emulsion from the Mg(OH)2 emulsion.

[0008] 5) Place the reacted magnesium carbonate emulsion into a settling tank for settling and filter to obtain heavy magnesium water;

[0009] 6) Hydromagnesia solution pyrolyzes at 95-105℃ to form small crystalline particles;

[0010] 7) Filter and dry to obtain the finished product.

[0011] However, this technology still has significant limitations, as follows:

[0012] (1) Reliance on non-renewable mineral resources;

[0013] (2) The calcination process has high energy consumption (calcination temperature > 800℃) and high carbon emission intensity;

[0014] (3) The purity of the product is greatly affected by impurities in the tailings (such as Ca and Fe).

[0015] Another type is the chemical synthesis method, which involves reacting soluble magnesium salts (such as magnesium chloride and magnesium sulfate) with sodium carbonate or ammonium bicarbonate to precipitate magnesium carbonate. Although the traditional precipitation method is simple, the product has a high specific surface area (40–70 m²).2 Due to its porous structure and porous nature, magnesium carbonate is prone to problems such as poor dispersibility and deteriorated processing performance during polymer modification. Chinese Patent Publication No. CN115818679A proposes a method for the direct CO2 mineralization of magnesium-containing wastewater to prepare magnesium carbonate, including:

[0016] Magnesium-containing wastewater and alkaline solution are added to a carbonate-bicarbonate buffer solution to control the pH value to 9.9-10.9, while simultaneously introducing CO2 gas for stirring and mineralization. The mixture is then allowed to settle and separate into layers, and finally dried and solidified to obtain magnesium carbonate. However, this technology still has the following drawbacks:

[0017] (1) The reaction pH window is narrow, and the conditions are sensitive;

[0018] (2) The product has low added value and is difficult to meet the needs of high-end applications;

[0019] (3) For coexisting calcium impurities (such as Ca) 2+ The removal effect of ) is limited, which affects the purity of the product.

[0020] Therefore, how to provide a method that can efficiently separate calcium and magnesium and prepare high-purity magnesium carbonate is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0021] The purpose of this invention is to provide a method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater and a method for treating magnesium sulfate wastewater. This method not only realizes the recovery and utilization of resources such as magnesium in the wastewater, but also avoids the generation of large amounts of waste residue and secondary pollution problems.

[0022] To achieve the above objectives, the technical solution used in this invention is:

[0023] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater, characterized by comprising:

[0024] A mixed precipitant was prepared using ammonia and ammonium bicarbonate, with a mass ratio of ammonia to ammonium bicarbonate of (0.1-1):1.

[0025] Seed crystals and a mixed precipitant are added to magnesium sulfate wastewater. The precipitation reaction is carried out at a temperature of 35-55℃ for 30-130 minutes. After the precipitation reaction is completed, the precipitate is filtered, washed, and dried to obtain magnesium carbonate.

[0026] Furthermore, the concentration of the mixed precipitant is 1-6 mol / L, which is the total concentration of ammonia and ammonium bicarbonate.

[0027] Furthermore, the mass ratio of ammonia to ammonium bicarbonate in the mixed precipitant is 1:1, the concentration of the mixed precipitant is 5 mol / L, the precipitation reaction temperature is 40℃, and the time is 120 min.

[0028] Furthermore, the mass ratio of the mixed precipitant to the magnesium ammonia ions in the magnesium sulfate wastewater is (0.1-1.3):1.

[0029] Furthermore, the mass ratio of the mixed precipitant to the magnesium ammonia ions in the magnesium sulfate wastewater is (1.1-1.3):1.

[0030] Furthermore, the seed crystal is magnesium carbonate, and the amount of seed crystal added is 5-10% of the mass of the magnesium sulfate solution. The mass of the magnesium sulfate solution is calculated in terms of oxide, i.e., MgO.

[0031] Furthermore, calcium oxide is added to the magnesium sulfate wastewater to neutralize and remove impurities by adjusting the pH and temperature of the magnesium sulfate wastewater. The pH value is 7.5-8.0, the neutralization temperature is 30-50℃, and the neutralization time is 30-90 minutes.

[0032] Further, after neutralization and impurity removal, the filter residue containing oil and rare earth elements is removed by plate and frame filtration. A mixed precipitant is added to the filtrate after filtration. The precipitate generated by the first precipitation reaction is filtered through plate and frame filtration to remove magnesium carbonate. The filtrate is then added to the mixed precipitant for a second precipitation reaction. The precipitate obtained from the second precipitation reaction is filtered through plate and frame filtration to remove magnesium carbonate and calcium carbonate. The filtrate is then concentrated and crystallized to obtain ammonium sulfate.

[0033] Furthermore, the concentration of magnesium oxide in magnesium sulfate wastewater is 1-60 g / L.

[0034] Methods for treating magnesium sulfate wastewater, including the preparation of high-purity magnesium carbonate from magnesium sulfate wastewater.

[0035] The technical effects of this invention include:

[0036] This invention provides an efficient, environmentally friendly, and economically feasible solution for the treatment of magnesium sulfate wastewater. It not only achieves the recovery and utilization of resources such as magnesium in the wastewater, reducing resource waste and potential environmental pollution risks, but also creates additional economic value, further enhancing the overall benefits of this wastewater treatment method. By converting magnesium sulfate wastewater into high-purity magnesium carbonate, this method not only achieves the recovery and utilization of resources such as magnesium in the wastewater, reducing resource waste and potential environmental pollution risks, but also creates additional economic value. Compared with traditional wastewater treatment methods, this method avoids the generation of large amounts of waste residue and secondary pollution problems. Furthermore, the high-purity magnesium carbonate product obtained has broad application prospects and can be used in multiple industries such as rubber, plastics, coatings, and pharmaceuticals, further enhancing the overall benefits of this wastewater treatment method.

[0037] The process of this invention is relatively simple, the operating conditions are easy to control, the equipment requirements are not high, and it is easy to promote large-scale industrial application. It has good market application prospects and social and environmental benefits. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater in this invention;

[0039] Figure 2 This is a scanning electron microscope image of the high-purity magnesium carbonate crystals prepared in Example 2 of the present invention. Detailed Implementation

[0040] The following description fully illustrates specific embodiments of the present invention to enable those skilled in the art to practice and reproduce it. To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention.

[0041] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0042] like Figure 1 The diagram shown is a process flow chart of the method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater in this invention.

[0043] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater includes the following steps:

[0044] Step 1: Prepare a mixed precipitant using ammonia and ammonium bicarbonate, with a mass ratio of ammonia to ammonium bicarbonate of (0.1-1):1;

[0045] The mixed precipitant is a mixture of ammonia and ammonium bicarbonate, with a mass ratio of ammonia to ammonium bicarbonate of (0.1-1):1, more preferably 1:1. When the mass ratio of ammonia to ammonium bicarbonate is greater than 1, a mixture of magnesium carbonate and basic magnesium carbonate is formed; when the ratio is less than or equal to 1, magnesium carbonate is formed. The yield of magnesium carbonate is highest when the molar ratio of the two is equal to 1.

[0046] The concentration of the mixed precipitant refers to the total concentration of ammonia and ammonium bicarbonate. The concentration of the mixed precipitant is 1-6 mol / L, more preferably 5 mol / L. When the concentration is too low, the concentration of the ammonium sulfate solution obtained from the precipitation reaction is too low, increasing the cost of further recovery and treatment. When the concentration is too high, the generated magnesium carbonate crystals will agglomerate, affecting the particle size distribution and filtration performance of the product. Furthermore, the volatilization of excessively high concentrations of ammonia will also affect the operating environment.

[0047] Step 2: Add seed crystals and mixed precipitant to magnesium sulfate wastewater. After the precipitation reaction is complete, the precipitate is filtered, washed and dried to obtain magnesium carbonate.

[0048] Magnesium sulfate wastewater originates from the extraction process in rare earth hydrometallurgical processes. The mass ratio of the mixed precipitant to the magnesium ammonia ions in the magnesium sulfate wastewater (nNH4) is... + nMg 2+ The mass ratio of the mixed precipitant to magnesium sulfate ammonia-magnesium ions (nNH4) is (0.1-1.3):1, more preferably (1.1-1.3):1. + nMg 2+ If the mass ratio (nNH4) is less than 0.1, the supersaturation is low and magnesium carbonate precipitation is not easily formed. + nMg 2+ A value greater than 1.3 will affect the purity of magnesium carbonate.

[0049] The principle of precipitation reaction is:

[0050] If the mass ratio of ammonia to ammonium bicarbonate is 1:1, the following main reactions will occur:

[0051] NH3·H2O+NH4HCO3=(NH4)2CO3+H2O;

[0052] MgSO4+(NH4)2CO3=MgCO3↓+(NH4)2SO4;

[0053] If the mass ratio of ammonia to ammonium bicarbonate is less than 1, the following reaction will mainly occur:

[0054] NH3·H2O+NH4HCO3=(NH4)2CO3+H2O;

[0055] MgSO4+(NH4)2CO3=MgCO3↓+(NH4)2SO4;

[0056] MgSO4+NH4HCO3=Mg(HCO3)2+(NH4)2SO4;

[0057] Mg(HCO3)2=MgCO3↓+H2O+CO2↑;

[0058] In this application, magnesium salts are used as seed crystals, preferably magnesium carbonate. The amount of seed crystals added is 5-10% of the mass of the magnesium sulfate solution, more preferably 6-8%, where the mass of the magnesium sulfate solution is calculated as oxide, i.e., MgO. Within the above-mentioned addition range, the positive role of the seed crystals in the precipitation reaction can be fully utilized. An appropriate amount of seed crystals can provide sufficient active sites for the growth of magnesium carbonate crystals, effectively promoting the nucleation and growth process, thereby improving the crystallinity and purity of magnesium carbonate. If the amount of seed crystals added is too small, it will not provide enough nuclei for crystal growth, resulting in slow and uneven crystal growth, affecting the quality and yield of the product; while if the amount of seed crystals added is too large, it may cause the seed crystals to compete for growth space and nutrients, which is also not conducive to normal crystal growth and may also increase production costs. During the precipitation reaction, magnesium carbonate seed crystals can provide specific nuclei and growth templates for the growth of magnesium carbonate crystals. This helps guide the magnesium carbonate crystals to grow in an orderly manner according to specific crystal forms and structures, thereby obtaining magnesium carbonate products with uniform particle size and high crystallinity. Compared to not adding seed crystals or adding other seed crystals, using magnesium carbonate seed crystals can significantly improve the purity of magnesium carbonate products, reduce the formation of impurity crystals, accelerate the precipitation reaction rate, shorten the reaction time, and improve production efficiency.

[0059] The precipitation reaction temperature is 35-55℃, more preferably 40℃, and the time is 30-130 min, more preferably 120 min. If the reaction temperature is lower than the above conditions, the yield of magnesium carbonate will decrease. If the temperature is higher than the above conditions, the carbonate ions in the mixed precipitant will decompose, and ammonia will volatilize, damaging the environment and reducing the yield of magnesium carbonate. If the reaction time is less than the above range, it will affect the yield of magnesium carbonate, and a longer reaction time will reduce the purity of magnesium carbonate.

[0060] The concentration of magnesium oxide in magnesium sulfate wastewater is 1-60 g / L, more preferably 10-30 g / L. When the concentration is too low, the supersaturation is low and magnesium carbonate precipitation is not easy, while when the concentration is too high, the resulting magnesium carbonate crystals are small in size, affecting the filtration performance and making it difficult to promote industrial application.

[0061] After roasting rare earth concentrate with concentrated sulfuric acid, rare earth chloride and magnesium sulfate wastewater are generated through water leaching neutralization and extraction transformation. The magnesium sulfate wastewater needs to be treated and utilized.

[0062] Calcium oxide is added to magnesium sulfate wastewater to neutralize and remove impurities by adjusting the pH and temperature of the wastewater. The pH value is 7.5-8.0, preferably 7.8. If the pH value is lower than 7.5, the removal of impurity ions is incomplete, and if the pH value is higher than 8.0, the amount of neutralization residue is large.

[0063] The neutralization and impurity removal temperature is 30-50℃, and the neutralization and impurity removal time is 30-90 min; preferably, the neutralization and impurity removal temperature is 40℃, and the neutralization and impurity removal time is 60 min. If the temperature is higher than the above, there will be unnecessary energy consumption; if the temperature is lower than the above, the removal efficiency of impurity ions will be low; if the processing time is higher than the above, the reaction efficiency will be affected; if the processing time is lower than the above, the impurities will be incompletely removed.

[0064] After neutralization and impurity removal, the filter residue containing oil and rare earth elements is removed by plate and frame filtration. A mixed precipitant is added to the filtrate after filtration. The precipitate generated by the first precipitation reaction is filtered through plate and frame filtration to remove magnesium carbonate. The filtrate is then added to the mixed precipitant for a second precipitation reaction. The precipitate obtained from the second precipitation reaction is filtered through plate and frame filtration to remove magnesium carbonate and calcium carbonate. The filtrate is then concentrated and crystallized to obtain ammonium sulfate.

[0065] Magnesium carbonate can be reused in the extraction process, while magnesium carbonate and calcium carbonate can be reused in the neutralization process.

[0066] The precipitate was filtered, washed, and dried to obtain magnesium carbonate.

[0067] Magnesium sulfate wastewater originates from the wastewater obtained during the rare earth hydrometallurgical process, and its chemical composition is shown in Table 1:

[0068] Table 1

[0069] MgO CaO <![CDATA[MnO2]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> ZnO <![CDATA[SO4 2- ]]> pH g / L 20.81 1.06 0.2 0.16 0.22 0.05 45.32 2.97

[0070] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0071] Example 1

[0072] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater includes the following steps:

[0073] Ammonia water and ammonium bicarbonate were mixed at a molar ratio of 0.95:1 and the concentration was adjusted to 4 mol / L to prepare a mixed precipitant. 2.5 g of magnesium carbonate seed crystals and 150 mL of the 4 mol / L mixed precipitant were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 35 °C for 60 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 99.6% and a yield of 50.6%.

[0074] Example 2

[0075] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater includes the following steps:

[0076] Ammonia and ammonium bicarbonate were mixed at a molar ratio of 1:1 and the concentration was adjusted to 5 mol / L to prepare a mixed precipitant. 2.5 g of magnesium carbonate seed crystals and 125 mL of the 5 mol / L mixed precipitant were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 40 °C for 120 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 99.8% and a yield of 51.6%.

[0077] The contents of other metallic impurities in high-purity magnesium carbonate crystals are shown in Table 2:

[0078] Table 2

[0079]

[0080] like Figure 2 The image shown is a scanning electron microscope (SEM) image of the high-purity magnesium carbonate crystals prepared in Example 2 of this invention.

[0081] The figure shows that the generated magnesium carbonate crystals will agglomerate, and the magnesium carbonate crystals have low impurity content, high crystallinity and purity.

[0082] Example 3

[0083] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater includes the following steps:

[0084] Ammonia water and ammonium bicarbonate were mixed at a molar ratio of 0.8:1 and the concentration was adjusted to 4 mol / L to prepare a mixed precipitant. 3.0 g of magnesium carbonate seed crystals and 160 mL of the 4 mol / L mixed precipitant were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 50 °C for 115 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 99.7% and a yield of 50.9%.

[0085] Example 4

[0086] A method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater includes the following steps:

[0087] Ammonia and ammonium bicarbonate were mixed at a molar ratio of 1:1 and the concentration was adjusted to 6 mol / L to prepare a mixed precipitant. 3.0 g of magnesium carbonate seed crystals and 100 mL of the 6 mol / L mixed precipitant were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 45 °C for 130 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 99.7% and a yield of 51.3%.

[0088] Comparative Example 1

[0089] The only difference from Example 2 is that the molar ratio of ammonia to ammonium bicarbonate in the mixed precipitant is 1.2:1. All other process steps and parameters are the same as in Example 2.

[0090] Specifically, the following steps are included:

[0091] Ammonia and ammonium bicarbonate were mixed at a molar ratio of 1.2:1 and the concentration was adjusted to 5 mol / L. 2.5 g of magnesium carbonate seed crystals and 125 mL of ammonia precipitant with a concentration of 5 mol / L were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 40 °C for 120 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 95.4% and a yield of 49.3%.

[0092] In the precipitation reaction, the molar ratio of the mixed precipitant ammonia water to ammonium bicarbonate exceeded the limit (0.1-1):1, which affected the yield and purity of magnesium carbonate.

[0093] Comparative Example 2

[0094] The only difference from Example 2 is that the precipitation reaction time is 150 min, and the specific steps include:

[0095] Ammonia and ammonium bicarbonate were mixed at a molar ratio of 1:1 and the concentration was adjusted to 5 mol / L to prepare a mixed precipitant. 125 mL of the 5 mol / L mixed precipitant and 2.5 g of magnesium carbonate seed crystals were added to 2 L of magnesium sulfate wastewater. The mixture was then stirred at 40 °C for 150 min. After filtration, washing, and drying, magnesium carbonate was prepared with a purity of 98% and a yield of 50.6%.

[0096] Precipitation reaction time exceeding the range of 30-130 min will reduce the purity of magnesium carbonate.

[0097] The terminology used in this invention is descriptive and exemplary, not restrictive. Since this invention can be embodied in many forms without departing from the spirit or essence of the technical solution, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A method for preparing high purity magnesium carbonate from magnesium sulfate wastewater, characterized by, The application relates to a method for treating magnesium sulfate wastewater. The mixed precipitant is prepared by using ammonia water and ammonium bicarbonate, and the mass ratio of the ammonia water to the ammonium bicarbonate is (0.1-1):1; The seed crystal and the mixed precipitant are added into the magnesium sulfate wastewater, the temperature of the precipitation reaction is 35-55 DEG C, the time is 30-130 min, and the precipitate is obtained by filtering, washing and drying after the precipitation reaction.

2. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The concentration of the mixed precipitant is 1-6 mol / L, and the concentration of the mixed precipitant is the total concentration of the ammonia water and the ammonium bicarbonate.

3. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The mass ratio of the ammonia water to the ammonium bicarbonate in the mixed precipitant is 1:1, the concentration of the mixed precipitant is 5 mol / L, the temperature of the precipitation reaction is 40 DEG C, and the time is 120 min.

4. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The mass ratio of the mixed precipitant to the magnesium-ammonia ion in the magnesium sulfate wastewater is (0.1-1.3):

1.

5. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 4, characterized in that, The mass ratio of the mixed precipitant to the magnesium-ammonia ion in the magnesium sulfate wastewater is (1.1-1.3):

1.

6. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The seed crystal is magnesium carbonate, the adding amount of the seed crystal is 5-10% of the mass of the magnesium sulfate solution, and the mass of the magnesium sulfate solution is calculated according to the oxide, i.e. MgO.

7. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The magnesium sulfate wastewater is added with calcium oxide, the pH value and the temperature of the magnesium sulfate wastewater are adjusted to carry out neutralization and impurity removal, the pH value is 7.5-8.0, the temperature of the neutralization and impurity removal is 30-50 DEG C, and the time of the neutralization and impurity removal is 30-90 min.

8. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 7, characterized in that, After the neutralization and impurity removal, the filter residue containing oil and rare earth is removed through plate-frame filtration, the filtrate is added with the mixed precipitant, the precipitate generated by the first precipitation reaction is removed through plate-frame filtration, the filtrate is added with the mixed precipitant to carry out the second precipitation reaction, the precipitate obtained by the second precipitation reaction is removed through plate-frame filtration to remove magnesium carbonate and calcium carbonate, and the filtrate is concentrated and crystallized to obtain ammonium sulfate.

9. The method for preparing high-purity magnesium carbonate from magnesium sulfate wastewater as described in claim 1, characterized in that, The concentration of the magnesium oxide in the magnesium sulfate wastewater is 1-60 g / L.

10. A method for treating magnesium sulfate wastewater, characterized by, The magnesium sulfate wastewater is treated by using the method in any one of claims 1-9.

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