A recovery system for preparing magnesium sulfate using sulfuric acid waste liquid

Abstract

A recovery system for preparing magnesium sulfate using sulfuric acid waste liquid is provided. [Solution] The recovery system for preparing magnesium sulfate using sulfuric acid waste liquor according to the present invention comprises a reactor 1, a crystallizer 3, a dehydrator 4, and a dryer 5. The reactor 1 removes hydrogen peroxide from the sulfuric acid waste liquor and produces a magnesium sulfate solution. The crystallizer 3 continuously recrystallizes the magnesium sulfate solution by lowering its temperature, obtaining magnesium sulfate crystals and their mother liquor. The dehydrator 4 removes the mother liquor, and the dryer 5 dries the solution at different temperatures to obtain magnesium sulfate hydrates containing different amounts of water of crystallization.

Description

[Technical Field]

[0001] The present invention relates to the field of waste liquid recovery technology, and more particularly to a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid. [Background technology]

[0002] In an era where sulfuric acid has become a commonly used acid in industrial production and the circular economy is becoming mainstream, the industry is focusing on how to treat the sulfuric acid solution waste generated after production.With the rise and development of Taiwan's semiconductor industry, semiconductor wafers are very sensitive to micro-contaminants, so in order to achieve the goal of eliminating contaminants from the wafer surface, it was necessary to perform surface cleaning steps multiple times to remove contaminants attached to the surface. Summary of the Invention [Problem to be solved by the invention]

[0003] Conventional wafer cleaning technology primarily relies on wet cleaning, which requires the use of large amounts of a mixed solution of sulfuric acid and hydrogen peroxide. The resulting waste solution from wafer cleaning has a lower concentration than the original sulfuric acid and hydrogen peroxide, making it difficult to reuse in semiconductor manufacturing. This results in the generation of large amounts of sulfuric acid waste, which, due to its extremely high concentration, can be used as a raw material in the steel and metal industries. However, the hydrogen peroxide contained in the waste solution causes side reactions, increasing raw material consumption and limiting its usefulness in other industries. Furthermore, the amount of sulfuric acid waste generated in various industries currently far exceeds domestic market demand. Therefore, a new, robust recycling channel must be developed to address the problem of excessive sulfuric acid waste in China.

[0004] In addition, the magnesium sulfate market is widely used in various industrial applications, such as electroplating, environmental protection, building materials, fire retardant materials, artificial fibers, papermaking, leather finishing agents, magnesium stearate, etc. It is also widely used in agriculture, such as fertilizers and feed, so there is room for potential development.

[0005] Therefore, the problem that needs to be solved at this stage is to remove impurities from sulfuric acid waste liquid generated in the domestic semiconductor industry, produce magnesium sulfate with various specifications, meet market demand, and achieve the important mission of circular economy, energy saving, and carbon emission reduction.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a recovery system for producing magnesium sulfate from sulfuric acid waste liquor, which uses sulfuric acid waste liquor containing hydrogen peroxide as the main raw material for producing magnesium sulfate, removes hydrogen peroxide from the sulfuric acid waste liquor through a reactor, and effectively removes impurities through a filtration device to obtain high-purity magnesium sulfate crystals, which are then crystallized through a continuous recrystallization method, thereby shortening the production time, improving the treatment efficiency of sulfuric acid waste liquor, conforming to a circular economy, and achieving the effects of energy conservation and carbon emission reduction. [Means for solving the problem]

[0007] In order to achieve the above object, a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid, which is one embodiment of the present invention, comprises: a reactor configured to remove hydrogen peroxide from the sulfuric acid waste liquid and promote a reaction between the sulfuric acid waste liquid and a magnesium-based neutralizing agent to produce a magnesium sulfate solution; a crystallization device arranged to continuously recrystallize the magnesium sulfate solution while decreasing its temperature, thereby obtaining magnesium sulfate crystals and a crystal mother liquor thereof; a dehydration device connected to the crystallization device for removing the crystallization mother liquor to obtain magnesium sulfate crystals; and a drying device that is connected to the dehydrating device and controls the drying temperature to obtain magnesium sulfate hydrate containing 0 to 7 crystal waters.

[0008] At least the following points will become clear from the description and drawings to be described later. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to a second embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to a fourth embodiment of the present invention. [Figure 5] 1 is a flowchart illustrating a recovery method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail the preferred embodiments of the present invention, but the present invention is not limited to these, and various modifications are possible within the scope of the description. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0011] (First embodiment) 1 is a schematic diagram showing a recovery system for preparing magnesium sulfate from sulfuric acid waste liquor according to a first embodiment of the present invention. As shown in the figure, the recovery system for preparing magnesium sulfate from sulfuric acid waste liquor according to the present invention mainly includes a reactor 1, a crystallization device 3, a dehydration device 4, and a drying device 5. Each of these will be described below.

[0012] The reactor 1 is provided with an agitation mechanism 11 for agitating the reactants in the reactor 1, and is further provided with a heating mechanism 12 for heating and maintaining the reaction temperature in the reactor 1. In this embodiment, the reactor 1 may be connected to a sulfuric acid storage tank (not shown), which is used to store sulfuric acid waste liquid and supply it to the reactor at a constant rate. The reactor 1 may be directly connected to a sulfuric acid discharge channel (not shown), or a metering device may be used to control the transport of the sulfuric acid waste liquid to the reactor 1 at a constant rate through the sulfuric acid discharge channel. The reactor 1 is further provided with a reactant supply tank 15, which is used to add a magnesium-based neutralizing agent to the reactor 1.

[0013] More specifically, the sulfuric acid wastewater recycled in this invention is sulfuric acid wastewater discharged from the semiconductor industry. Sulfuric acid wastewater contains sulfuric acid and hydrogen peroxide (H2O2). Hydrogen peroxide interferes with the subsequent magnesium sulfate process, and its removal is necessary to reduce the amount of by-products produced. In practice, taking advantage of the chemical property of hydrogen peroxide, which is easily decomposed by heat, a magnesium-based neutralizing agent, accounting for 0.1% to 10% of the weight of the sulfuric acid wastewater, is first added to the reactor. The reaction is then heated and stirred to promote the thermal decomposition of the hydrogen peroxide. The remaining hydrogen peroxide is then measured using hydrogen peroxide test paper at preset intervals, and the hydrogen peroxide is completely removed. The magnesium-based neutralizing agent is then added to reactor 1, and the solution in the reactor is stirred at a constant temperature and speed using heating mechanism 12 and stirring mechanism 11 to promote the reaction between the sulfuric acid wastewater and the magnesium-based neutralizing agent, producing a magnesium sulfate solution.

[0014] The reactor 1 is further equipped with a hydrometer 13 and a pH meter 14, which continuously monitor the changes in the specific gravity of magnesium sulfate and the pH value of the solution during the reaction process, visualize and digitize the reaction process, allowing the operator to conveniently and immediately grasp the progress of the reaction.

[0015] The crystallization device 3 is a continuous vacuum cooling crystallization device, a continuous heat exchange crystallization device, or a shower cooling crystallization device, which is used to cool the magnesium sulfate solution and continuously recrystallize it to obtain magnesium sulfate crystals and their mother liquor. 2+ +SO4 2- +nH2O→MgSO4·nH2O (n=0-7), and the cooling temperature is controlled to obtain magnesium sulfate hydrate with different waters of crystallization. In actual operation, the present invention preferably controls the cooling temperature within the range of 20°C to 67.5°C to obtain magnesium sulfate hydrate with 6-7 waters of crystallization, and controls the drying temperature to obtain magnesium sulfate hydrate with different waters of crystallization, or controls the cooling temperature to 80°C to obtain magnesium sulfate hydrate with one water of crystallization.

[0016] The crystallization device 3 may be formed by connecting multiple continuous vacuum cooling crystallization devices or multiple continuous heat exchange crystallization devices in series to increase the cooling and crystallization efficiency of the magnesium sulfate filtrate. In practice, the crystallization device 3 is preferably a shower cooling crystallization device with a controlled flow rate ranging from 1 ton (ton) / hour to 6 ton / hour, which lowers the temperature of the magnesium sulfate solution and forms magnesium sulfate crystals from the crystals, achieving high-speed continuous crystallization, shortening the crystallization process time, and reducing energy consumption.

[0017] In this invention, a buffer tank 6 can be optionally installed. In the first embodiment, the buffer tank 6 is not installed, and the magnesium sulfate crystals discharged from the crystallization device 3 are passed through a dehydrator 4 to remove the crystal mother liquor, thereby obtaining magnesium sulfate crystals. The crystal mother liquor removed by the dehydrator is guided into a mother liquor tank 7. Since the crystal mother liquor contains free acid, it is dehydrated before being recycled into the reactor 1 as a raw material for reuse, thereby increasing the recycling rate of the sulfuric acid waste liquid. The dehydrator 4 is preferably a centrifugal dehydrator, which achieves high-speed dehydration.

[0018] Drying device 5 is connected to dehydrating device 4, and the magnesium sulfate crystals dehydrated by dehydrating device 4 are transported into drying device 5, where the drying temperature is controlled to obtain magnesium sulfate hydrate containing 0 to 7 crystal waters. Drying device 5 is a multi-stage drying device, preferably a multi-stage vibrating fluid bed dryer or a multi-stage flash dryer. To prevent dehydration due to excessively high temperatures, the bed temperature is set to between 40°C and 55°C, and drying is continued for 6 to 8 hours to obtain the finished product, magnesium sulfate heptahydrate (MgSO4 7H2O). The temperature of the bed may be controlled to between 70°C and 80°C and dried continuously for between 5 and 8 hours to obtain magnesium sulfate trihydrate (MgSO4·3H2O) as magnesium sulfate heptahydrate (MgSO4·7H2O) loses water of crystallization, or the temperature of the bed may be controlled so as not to fall below 200°C and dried continuously for between 8 and 10 hours to obtain anhydrous magnesium sulfate (MgSO4).

[0019] The magnesium sulfate hydrate (MgSO₄·nH₂O (n = 0 to 7)) containing 0 to 7 crystal water particles obtained through the above process is crushed in crushing device 8, which is connected to drying device 5, to the particle size required for general sale, and then sealed and packaged in small portions according to market sales specifications in a packaging machine.

[0020] (Second embodiment) Figure 2 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquor according to a second embodiment of the present invention. The second embodiment is an improvement on the first embodiment, and unless otherwise specified, the remaining components and arrangement are all the same as those of the first embodiment, and therefore will not be described again here. The improvement lies in the fact that a filtration device 2 is disposed between the reactor 1 and the filtration device 2, and a buffer tank 6 is disposed between the crystallization device and the dehydration device. In actual use, the crystallization device 3 is a continuous vacuum cooling crystallization device, a continuous heat exchange crystallization device, or a shower cooling crystallization device, and preferably includes a buffer tank 6.

[0021] As shown in Figure 2, filtration device 2 is connected to reactor 1. In this case, the magnesium sulfate solution in reactor 1 is guided to flow into filtration device 2 and filtered to separate solid impurities from liquid. After the impurities are reduced, the solution proceeds to the subsequent crystallization flow chart, thereby increasing the purity of the finished product. The filtered magnesium sulfate solution is guided to flow into crystallization device 3, and solid impurities are discharged from a solid outlet. Some of the solid impurities can be used as cement additives, cement products, or tile filler materials. filtration device 2 is preferably an acid-resistant frame filter press.

[0022] The buffer tank 6 is connected to the crystallization device 3 and the dehydration device 4. The crystallization device 3 discharges the magnesium sulfate crystals and their mother liquor into the buffer tank 6, where they are allowed to stand. Using the difference in density between the magnesium sulfate crystals and the mother liquor, the magnesium sulfate crystals are separated from the mother liquor and allowed to settle at the bottom of the buffer tank 6. The magnesium sulfate crystals that have stood are transported through a channel to the dehydration device 4, where the mother liquor is removed to obtain the magnesium sulfate crystals. The mother liquor is guided to be transported into the mother liquor tank 7.

[0023] (Third embodiment) 3 is a schematic diagram showing a recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to the first embodiment of the present invention. The third embodiment is an improvement based on the second embodiment. Unless otherwise specified, the remaining components and arrangement are all the same as those of the second embodiment, and their description will not be repeated here. The reactor 1 is specifically improved in that it is equipped with a nitric acid feeder 16 for adding nitric acid to the reactor 1. The strong acidity of nitric acid and its reaction with hydrogen peroxide decomposes hydrogen peroxide, thereby achieving the effect of removing hydrogen peroxide from the sulfuric acid waste liquid.

[0024] (Fourth embodiment) Figure 4 is a schematic diagram of a recovery system for preparing magnesium sulfate from sulfuric acid waste liquor according to the first embodiment of the present invention. As shown in the figure, the fourth embodiment is an improvement on the first embodiment, further comprising a buffer tank 6, which is connected to the reactor 1 and the crystallization device 3, which is further connected to a milling device 8. In this embodiment, the crystallization device 3 is preferably a shower cooling crystallization device. The buffer tank 6 allows the magnesium sulfate solution to settle and separate insoluble impurities, and the magnesium sulfate solution is concentrated before being continuously crystallized at high speed in the crystallization device 3.

[0025] Based on the recovery system configured with the above-mentioned components, magnesium sulfate is prepared using sulfuric acid waste liquid by the following method. The specific steps are as follows: In step 1, sulfuric acid waste liquid containing hydrogen peroxide is transported into reactor 1, and magnesium-based neutralizing agent is added from reactant supply tank 15 into reactor 1. The reaction is continuously stirred at a constant temperature and speed to remove hydrogen peroxide and promote the reaction between the sulfuric acid waste liquid and the magnesium-based neutralizing agent, thereby producing a magnesium sulfate solution. In step 2, the magnesium sulfate solution is cooled in a crystallizer 3 to continuously precipitate magnesium sulfate crystals. In step 3, the crystal mother liquor is removed from the magnesium sulfate crystals by a dehydrator 4, and the crystals are dried at different temperatures by a dryer 5 to obtain magnesium sulfate hydrate containing 0 to 7 crystal waters.

[0026] Specifically, in step 1, if hydrogen peroxide becomes unstable due to heat or an acidic environment, different methods are employed to remove it. The first method utilizes the chemical property of hydrogen peroxide, which decomposes when exposed to heat. First, a magnesium-based neutralizer, accounting for 0.1% to 10% of the weight of the sulfuric acid waste liquid, is added from reactant supply tank 15 to reactor 1. The hydrogen peroxide is thermally decomposed by the heat generated by the reaction between the sulfuric acid waste liquid and the magnesium-based neutralizer, as well as by heating using reactor 1's heating mechanism 12. The chemical reaction for hydrogen peroxide decomposition is 2H2O2 → 2H2O + O2 (gas). Sampling is performed at predetermined intervals, and the remaining hydrogen peroxide is measured using hydrogen peroxide test paper. After the hydrogen peroxide is removed, the magnesium-based neutralizer is added and allowed to react.

[0027] The second method utilizes the strong acidity of hydrogen peroxide to add nitric acid to the sulfuric acid waste liquid in reactor 1, and achieves the effect of removing hydrogen peroxide from the sulfuric acid waste liquid through a reaction between the strongly acidic nitric acid and hydrogen peroxide. The chemical reaction formula for the reaction between nitric acid and hydrogen peroxide is 2HNO3 + H2O2 → 2NO2 (gas) + O2 (gas) + 2H2O. The nitric acid is highly concentrated, and the amount of nitric acid added accounts for 3% to 10% of the weight of the sulfuric acid waste liquid. Preferably, the amount added accounts for 7% to 9% of the weight of the sulfuric acid waste liquid. After removing the hydrogen peroxide, a magnesium-based neutralizer is added to allow the reaction to proceed.

[0028] Specifically, the magnesium-based neutralizing agent added in step 1 is a mixture formed by mixing a magnesium-based compound and a solvent in a weight ratio ranging from 1:1 to 1:3. The magnesium-based compound is one or a combination of magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), and magnesium carbonate (MgCO3). The solvent is a mixture of one or two of water and dehydrated crystallization mother liquor. Calculated based on the weight ratio, the magnesium-based compound:water ratio is preferably 1:2.

[0029] The magnesium-based neutralizing agent is added to the reactor 1 in a fixed amount via the reagent supply tank 15. The temperature of the reactor 1 is controlled between 50°C and 90°C, and the stirring speed is set between 20 rpm and 90 rpm. The reaction is continued for 15 to 45 minutes to promote the reaction between the sulfuric acid waste liquid and the magnesium-based neutralizing agent. The main chemical reactions are (1) H2SO4 + MgO → MgSO4 + H2O, (2) H2SO4 + MgCO3 → MgSO4 + H2O + CO2 (gas), and (3) H2SO4 + Mg(OH)2 → MgSO4 + 2H2O. The reaction between the sulfuric acid waste liquid and the magnesium-based neutralizing agent forms a magnesium sulfate solution, with a specific gravity of magnesium sulfate between 1.28 and 1.72 and a pH of 5 to 8. In this case, when the sulfuric acid in the sulfuric acid waste liquid is completely consumed, the addition of the magnesium-based neutralizing agent is stopped.

[0030] In step 2, the magnesium sulfate solution is first filtered in filtration device 2 to remove solid impurities, and then cooled and recrystallized in crystallization device 3 at a temperature between 20°C and 67.5°C. The magnesium sulfate crystals and their mother liquor are transported to buffer tank 6 and allowed to stand, whereby the magnesium sulfate crystals and the mother liquor are separated, and then dehydrated in dehydration device 4 to obtain magnesium sulfate crystals. Alternatively, the magnesium sulfate crystals may be directly dehydrated in dehydration device 4 to separate them.

[0031] The technical content of the present invention will be further explained by combining the flow chart shown in FIG. 5 with the recovery system shown in FIG. <Raw materials> Sulfuric acid solution: Sulfuric acid waste liquid containing hydrogen peroxide (H2O2) generated in the semiconductor industry. The sulfuric acid content is 75% and the hydrogen peroxide content is 5%. Magnesium-based neutralizing agent: The weight ratio of magnesium-based compound to water is 1: 2. The magnesium-based compound includes magnesium oxide, magnesium hydroxide, and magnesium carbonate. <Reaction steps> In step 1, sulfuric acid waste liquor is charged into reactor 1 at a fixed rate, and a fixed amount of magnesium-based neutralizing agent is added from reactant supply tank 15. The reactor is heated to 80°C using heating mechanism 12 and then kept at a constant temperature. The stirring mechanism 11 is stirred at a stirring speed of 70 rpm, and the stirring is continued at a constant temperature and speed. During this time, the amount of hydrogen peroxide remaining in the reaction solution is measured using hydrogen peroxide test paper. When the specific gravity of magnesium sulfate in the magnesium sulfate solution measured by hydrometer 13 is 1.66 and the pH value of the magnesium sulfate solution measured by pH meter 14 is 7, the addition of magnesium-based neutralizing agent is stopped, and the reaction time is 40 minutes. In step 2, the magnesium sulfate solution is filtered to remove solid impurities using filtration device 2 (e.g., an acid-resistant frame filter press), resulting in a magnesium sulfate solution from which the solid impurities have been removed. The solid impurities are then discharged as cement additives, cement products, or tile filler material. The filtered magnesium sulfate solution is then cooled and crystallized using crystallization device 3 (a continuous heat exchange crystallization device in this case) to a crystallization temperature of 35°C, yielding magnesium sulfate heptahydrate (MgSO4·7H2O) and its crystal mother liquor, which are then discharged into a buffer tank. In step 3, magnesium sulfate heptahydrate (MgSO4·7H2O) and its mother liquor are placed in a buffer tank for solid-liquid separation, then guided to a dehydrator where the mother liquor is removed by centrifugation to obtain magnesium sulfate heptahydrate crystals (MgSO4·7H2O). The mother liquor is guided to flow into a storage tank. The magnesium sulfate heptahydrate crystals (MgSO4·7H2O) are dried at 40°C in a multi-stage vibrating fluid bed dryer to obtain magnesium sulfate heptahydrate (MgSO4·7H2O), which is then crushed and packaged to obtain the finished product.

[0032] The magnesium sulfate heptahydrate prepared according to the above-described embodiment has the following results based on standard feed-grade quality testing: <Table 1: Quality inspection results of magnesium sulfate heptahydrate prepared according to this invention> JPEG0003253553000002.jpg66128

[0033] As can be seen from the comparison in Table 1 above, the present invention uses sulfuric acid waste liquor generated from the semiconductor industry and the composite industry as raw material, and the magnesium sulfate heptahydrate prepared meets the quality standards of magnesium sulfate feed additive specifications, effectively removes impurities in the sulfuric acid waste liquor, and the prepared magnesium sulfate heptahydrate simultaneously meets the mass requirements of multiple industries such as industry, feed industry, and agriculture.

[0034] Referring also to FIG. 4, magnesium sulfate is prepared by the recovery system according to the fourth embodiment of the present invention and the preparation system according to the prior art, respectively. The specific process flow of the fourth embodiment is described below. <Operation steps> In step 1, sulfuric acid waste liquor containing hydrogen peroxide is transported into the reactor, and a magnesium-based neutralizing agent accounting for 5% of the weight of the sulfuric acid waste liquor is first added from the reactant supply tank, and the reactor is heated to remove the hydrogen peroxide. Then, the magnesium-based neutralizing agent is added to the reactor, and the reaction is continued at a constant temperature and speed of 75°C and 72 rpm for 45 minutes. When the specific gravity of the magnesium sulfate in the reaction solution reaches 1.29 and the pH of the reaction solution reaches 7, the addition of the magnesium-based neutralizing agent is stopped to obtain a magnesium sulfate solution. In step 2, the magnesium sulfate solution is cooled in a crystallizer (here, the crystallizer is a shower cooling crystallizer) to continuously precipitate magnesium sulfate crystals. In step 3, the magnesium sulfate crystals are directly transported to a crushing facility to obtain crude magnesium sulfate crystals.

[0035] See Table 2 below for a detailed comparison between the processing system according to the prior art and the processing system according to the present invention. <Table 2: Comparison of magnesium sulfate preparation systems according to the present invention and the prior art> JPEG0003253553000003.jpg246165JPEG0003253553000004.jpg54165

[0036] As is clear from the comparison in Table 2 above, the recovery system of the fourth embodiment uses sulfuric acid waste liquor generated in the semiconductor and composite industries as a raw material to selectively and rapidly produce crude magnesium sulfate crystals. The processing time is significantly shorter than that of conventional technologies. This crude magnesium sulfate crystals can be used as a raw material, and through purification and refinement, magnesium sulfate that meets the quality standards of agriculture, industry, feed, and food industries can be produced. Furthermore, compared to conventional sulfuric acid waste liquor recovery and treatment technologies, the present invention can treat a larger amount of sulfuric acid waste liquor and has higher processing efficiency, further contributing to industrial development.

[0037] To sum up, the recovery system and method for preparing magnesium sulfate using sulfuric acid waste liquid according to the present invention have the following technical advances and advantages: First, the control node is installed to shorten the reaction time. The reactor of the present invention uses a hydrometer and a pH meter to monitor the progress of the neutralization reaction and control the reaction time, reducing time waste and shortening the reaction time. Second, it reduces by-products and improves the purity of magnesium sulfate. This invention removes hydrogen peroxide from sulfuric acid waste liquid by heating or adding nitric acid, which makes the treatment method simple and inexpensive, effectively removes hydrogen peroxide, reduces the generation of by-products, and obtains magnesium sulfate hydrate with high purity that meets industrial standards. Third, the treatment efficiency of sulfuric acid waste liquid is high. This invention uses a continuous crystallization method and controls the cooling temperature to rapidly lower the temperature of the magnesium sulfate filtrate and obtain magnesium sulfate hydrate with different crystal waters. The treatment volume of the magnesium sulfate filtrate is large, resulting in high production efficiency. The drying temperature is controlled using a drying device to obtain magnesium sulfate hydrate with different crystal waters. During production, the amount of crystal water in magnesium sulfate can be controlled by selecting the amount of crystal water to be contained in the magnesium sulfate during temperature-recrystallization based on the target product, or by drying at different temperatures to control the amount of crystal water, thereby increasing the flexibility of the production process. Fourth, it is compatible with the circular economy, meeting the requirements of energy conservation and carbon emission reduction. This invention uses sulfuric acid waste liquor as the reaction raw material, and by heating or adding nitric acid to cause a reaction, impurities that affect the quality of the magnesium sulfate are filtered out, and magnesium sulfate crystals containing 0 to 7 crystal water are prepared at different crystallization or drying temperatures. This efficiently treats sulfuric acid waste liquor, reduces environmental pollution and resource waste, and prepares magnesium sulfate raw material needed for industry, agriculture, and the feed industry, thereby complying with the circular economy and meeting the requirements of energy conservation and carbon emission reduction.

[0038] Although the embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design modifications and the like are also included within the scope of the present invention without departing from the gist of the present invention. [Explanation of symbols]

[0039] 1. Reactor 11 Stirring mechanism 12 Heating mechanism 13 Hydrometer 14 pH meter 15 Reactant supply tank 16 Nitric acid supply device 2 Filtration device 3 Crystallization device 4 Dehydration equipment 5 Drying equipment 6. Buffer tank 7 Mother liquor tank 8. Crushing equipment

Claims

1. a reactor configured to remove hydrogen peroxide from the sulfuric acid waste liquid and promote a reaction between the sulfuric acid waste liquid and a magnesium-based neutralizing agent to produce a magnesium sulfate solution; a crystallization device arranged to continuously recrystallize the magnesium sulfate solution while decreasing its temperature, thereby obtaining magnesium sulfate crystals and a crystal mother liquor thereof; a dehydration device connected to the crystallization device for removing the crystallization mother liquor to obtain magnesium sulfate crystals; a drying device that is connected to the dehydration device and controls the drying temperature to obtain magnesium sulfate hydrate containing 0 to 7 water of crystallization,

2. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, wherein the reactor is provided with a heating mechanism and a stirring mechanism for heating and stirring the solution in the reactor, the reactor is further provided with a hydrometer and a pH meter for continuously monitoring changes in the specific gravity of magnesium sulfate and the pH value of the solution during the reaction process, and the reactor is provided with a reactant supply tank for adding a magnesium-based neutralizing agent.

3. 3. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, wherein a nitric acid supplier is disposed in the reactor to supply nitric acid so as to promote removal of hydrogen peroxide in the sulfuric acid waste liquid.

4. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, further comprising a filtration device installed between the reactor and the crystallization device for filtering the magnesium sulfate solution discharged from the reactor and transporting it to the crystallization device, wherein the filtration device is an acid-resistant frame filter press.

5. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, wherein the crystallization apparatus is a continuous vacuum cooling crystallization apparatus, a continuous heat exchange crystallization apparatus, or a shower cooling crystallization apparatus.

6. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, further comprising a buffer tank connected to the crystallization device and the dehydration device, respectively.

7. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, further comprising a buffer tank connected to the reactor and the crystallization device, respectively, the crystallization device further connected to a grinding device, and the crystallization device is a shower cooling crystallization device.

8. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, further comprising a mother liquor tank connected to the dehydrator and the reactor, respectively, for receiving the crystallization mother liquor separated by the dehydrator, dehydrating the mother liquor, and then recycling the mother liquor to the reactor.

9. 2. The recovery system for preparing magnesium sulfate using sulfuric acid waste liquid according to claim 1, further comprising a pulverizer connected to the drying device for pulverizing the dried magnesium sulfate hydrate.

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