Method for producing sodium bicarbonate and gypsum using materials containing sodium sulfate

Abstract

A method for producing sodium bicarbonate and gypsum, according to one embodiment of the present invention, comprises: a step of obtaining a sodium sulfate mixed solution by mixing an eluent and a material containing sodium sulfate (Na2SO4); a sodium bicarbonate producing step of producing sodium bicarbonate (NaHCO3) by mixing ammonia and carbon dioxide with the sodium sulfate mixed solution; a first gypsum producing step of producing gypsum by mixing a filtrate remaining after the sodium bicarbonate producing step with a calcium-containing material; an ammonia producing step of obtaining ammonia by mixing a filtrate remaining after obtaining first gypsum from the first gypsum producing step with sodium carbonate (Na2CO3); and a second gypsum producing step of producing second gypsum by mixing the first gypsum obtained from the first gypsum producing step, a filtrate remaining after obtaining ammonia from the ammonia producing step, and sulfuric acid.

Description

Method for manufacturing sodium bicarbonate and gypsum using a substance containing sodium sulfate

[0001] The present invention relates to a method for producing baking soda (sodium bicarbonate, NaHCO3) and gypsum (calcium sulfate, CaSO4) using a material containing sodium sulfate.

[0002] Flue gas desulfurization refers to the removal of sulfur (S) components, particularly sulfur dioxide (SO2), from exhaust gases emitted from sources such as steel mills and thermal power plants. With industrial development, sulfur oxides (SO2) emitted from various factories, thermal power plants, and incinerators... x Harmful gases such as sodium sulfate cause severe air pollution and induce various diseases in the human body, including respiratory diseases, asthma, and lung cancer. Currently, desulfurizing agents used in steel mills include sodium bicarbonate (NaHCO3), activated carbon, and calcium hydroxide (Ca(OH)2). In particular, sodium bicarbonate is known to exhibit excellent adsorption efficiency when sprayed into high-temperature flue gas, as its specific surface area is maximized. During this process, waste sodium sulfate (Na2SO4) is generated as a byproduct of the desulfurization treatment.

[0003] Furthermore, with the recent expansion of electric vehicle adoption, the demand for lithium, a raw material for secondary batteries, is increasing. Since the main byproducts generated during lithium production include silica (SiO2) and sodium sulfate (Na2SO4), it is expected that the amount of sodium sulfate byproducts will also increase in line with the growing demand for lithium. Therefore, the development of technology to recycle sodium sulfate is an essential prerequisite for the widespread adoption of secondary batteries.

[0004] Currently, by-products are either dissolved in water and treated as wastewater or landfilled as is, which simultaneously causes treatment costs and secondary environmental problems, so there is a need for a method to recycle them.

[0005] One embodiment of the present invention can provide a method for producing sodium bicarbonate and gypsum that can efficiently obtain sodium bicarbonate and gypsum from sodium sulfate byproducts.

[0006] One embodiment of the present invention can provide a method for producing sodium sulfate and soda ash that can process sodium sulfate byproducts while simultaneously realizing high added value of sodium sulfate.

[0007] One embodiment of the present invention can provide a method for manufacturing baking soda and gypsum, which increases the compatibility of gypsum by adjusting the purity of the gypsum as needed.

[0008] One embodiment of the present invention may provide a method for manufacturing baking soda and gypsum, which recovers ammonia from the remaining liquid after manufacturing baking soda and gypsum.

[0009] A method for manufacturing sodium bicarbonate and gypsum, which is an embodiment of the present invention, comprises: a step of obtaining a sodium sulfate mixture by mixing a substance containing sodium sulfate (Na2SO4) and an eluent; a sodium bicarbonate manufacturing step of manufacturing sodium bicarbonate (NaHCO3) by mixing ammonia and carbon dioxide with the sodium sulfate mixture; a first gypsum manufacturing step of manufacturing gypsum by mixing a calcium-containing substance with the filtrate remaining after obtaining the sodium bicarbonate manufacturing step; an ammonia manufacturing step of obtaining ammonia by mixing sodium carbonate (Na2CO3) with the filtrate remaining after obtaining the gypsum in the first gypsum manufacturing step; and a second gypsum manufacturing step of manufacturing gypsum by mixing the gypsum obtained in the first gypsum manufacturing step, the filtrate remaining after obtaining the ammonia in the ammonia manufacturing step, and sulfuric acid.

[0010] The step of obtaining the sodium sulfate mixture may include a first solid-liquid separation step of separating impurities from a solution mixed with a substance containing sodium sulfate and an eluent and obtaining a filtrate.

[0011] The step of obtaining the above sodium sulfate mixture may involve mixing a substance containing sodium sulfate and an eluent at 40 to 60°C.

[0012] The above sodium sulfate manufacturing step may include a crystallization step of heating and crystallizing a solution mixed with the sodium sulfate mixture, ammonia, and carbon dioxide; and a second solid-liquid separation step of obtaining crystallized sodium sulfate from the solution obtained in the crystallization step.

[0013] The heating temperature of the crystallization step above may be 40 to 70°C.

[0014] The first gypsum manufacturing step may include a third solid-liquid separation step of separating gypsum from a mixture in which a calcium-containing substance is mixed with the filtrate remaining from the sodium bicarbonate manufacturing step and obtaining the filtrate.

[0015] The above calcium-containing material may be calcium oxide (CaO).

[0016] In the first gypsum manufacturing step above, the pH of the mixture mixed with the calcium-containing material may be 10 or higher.

[0017] The above ammonia manufacturing step may include a fourth solid-liquid separation step of obtaining calcium carbonate (CaCO3) from a mixture of sodium carbonate (Na2CO3) and the filtrate remaining after obtaining gypsum in the first gypsum manufacturing step, and a heating step of obtaining ammonia by heating the filtrate remaining after separating calcium carbonate (CaCO3).

[0018] The second gypsum manufacturing step may include a fifth solid-liquid separation step for separating gypsum from a mixture of the first gypsum obtained in the first gypsum manufacturing step, the filtrate remaining after obtaining ammonia in the ammonia manufacturing step, and sulfuric acid.

[0019] A method for producing baking soda and gypsum, which is an embodiment of the present invention, can efficiently obtain baking soda and gypsum from sodium sulfate byproducts.

[0020] A method for manufacturing sodium bicarbonate and gypsum, which is an embodiment of the present invention, can process sodium sulfate byproducts while simultaneously realizing high added value of sodium sulfate.

[0021] A method for manufacturing baking soda and gypsum, which is an embodiment of the present invention, can increase the compatibility of gypsum by adjusting the purity of the gypsum as needed.

[0022] A method for manufacturing baking soda and gypsum, which is an embodiment of the present invention, can improve economic efficiency by recovering ammonia from the liquid remaining after manufacturing baking soda and gypsum.

[0023] FIG. 1 is a flowchart schematically illustrating a method for manufacturing sodium bicarbonate and gypsum according to one embodiment of the present invention.

[0024] FIG. 2 is a flowchart schematically illustrating a method for manufacturing sodium bicarbonate and gypsum according to another embodiment of the present invention.

[0025] Figure 3 is a graph showing the form of carbon dioxide present in the solution according to pH when carbon dioxide is dissolved.

[0026] Figure 4 is a graph showing the change in ammonia and ammonium ions according to pH.

[0027] Figure 5 is a graph showing the XRD pattern of the gypsum produced in Example 1 of the present invention.

[0028] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0029] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0030] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0031] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0032] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0033] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0034] In this specification, terms such as 'top', 'upper', 'upper surface', 'lower', 'lower surface', 'lower surface', and 'side surface' are based on the drawings and may actually vary depending on the direction in which the elements or components are arranged.

[0035] Additionally, throughout the specification, when it is said that one part is 'connected' to another part, this includes not only cases where they are 'directly connected,' but also cases where they are 'indirectly connected' with other elements in between.

[0036] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0037] The present invention relates to a method for producing baking soda (sodium bicarbonate, NaHCO3) and gypsum (calcium sulfate, CaSO4) using sodium sulfate (Na2SO4) byproducts. Specifically, by producing baking soda and gypsum from sodium sulfate byproducts remaining after using baking soda removers to remove sulfur oxides in steel mill sintering plants, etc., it is possible to reduce carbon emissions and treat sodium sulfate byproducts in an eco-friendly manner and increase their value. Furthermore, the purity of the produced gypsum can be controlled to increase commercial viability, and the ammonia used in the production of baking soda can be recovered.

[0038] FIG. 1 is a flowchart schematically illustrating a method for manufacturing sodium bicarbonate and gypsum according to one embodiment of the present invention, and FIG. 2 is a flowchart schematically illustrating a method for manufacturing sodium bicarbonate and gypsum according to another embodiment of the present invention, which may be a specific example of FIG. 1.

[0039] Referring to FIG. 1, one embodiment of the present invention may include a step (S10) of obtaining a sodium sulfate mixture by mixing a substance containing sodium sulfate (Na2SO4) and an eluent; a sodium sulfate manufacturing step (S20) of manufacturing sodium sulfate (NaHCO3) by mixing ammonia and carbon dioxide with the sodium sulfate mixture; a first gypsum manufacturing step (S30) of manufacturing gypsum by mixing a calcium-containing substance with the filtrate remaining after obtaining the sodium sulfate manufacturing step (S20); an ammonia manufacturing step (S40) of obtaining ammonia by mixing sodium carbonate (Na2CO3) with the filtrate remaining after obtaining the first gypsum in the first gypsum manufacturing step (S30); and a second gypsum manufacturing step (S50) of manufacturing a second gypsum by mixing the first gypsum obtained in the first gypsum manufacturing step (S30), the filtrate remaining after obtaining ammonia in the ammonia manufacturing step (S40), and sulfuric acid.

[0040] The above-mentioned sodium sulfate-containing material may be a sodium sulfate byproduct after undergoing a desulfurization process at a steel mill, a sodium sulfate byproduct generated from a secondary battery material, etc. The above-mentioned sodium sulfate byproduct may contain some impurities such as iron and calcium, and for example, the sodium sulfate byproduct remaining after removing sulfur dioxide from a sintering plant at a steel mill may contain 10 to 15 weight percent of impurities in addition to sodium sulfate. Therefore, an additional process to remove impurities may be required to increase the purity of the sodium sulfate produced from the material containing sodium sulfate.

[0041] Accordingly, one embodiment of the present invention may include a step (S10) of obtaining a sodium sulfate mixture by mixing a leaching agent with a substance containing sodium sulfate to obtain a sodium sulfate mixture. In the step (S10) of obtaining the sodium sulfate mixture, impurities may be leached out, and the purity of the sodium sulfate and gypsum produced from the sodium sulfate mixture after the impurities are leached out may be high.

[0042] The step (S10) of obtaining the sodium sulfate mixture may be a step of mixing a substance containing sodium sulfate and a leachate at 40 to 60°C. Since sodium sulfate may have the highest solubility at 40 to 60°C, if mixing is carried out at the above temperature, the concentration of sodium sulfate may be high. Meanwhile, in the step of obtaining the sodium sulfate mixture, if the temperature is below 40°C, the sodium sulfate may not dissolve sufficiently, and if it exceeds 60°C, energy may be consumed more than necessary.

[0043] In the step (S10) of obtaining the sodium sulfate mixture, the substance containing the sodium sulfate is not particularly limited, but, for example, the content of sodium sulfate may be 50% by weight or more relative to the total weight of the substance containing the sodium sulfate. In the substance containing the sodium sulfate, substances other than sodium sulfate may be impurities such as calcium and iron.

[0044] FIG. 2 is a flowchart schematically illustrating a method for manufacturing sodium bicarbonate and gypsum according to another embodiment of the present invention. Referring to FIG. 2, in another embodiment of the present invention, the step (S10) of obtaining the sodium sulfate mixture may include a first solid-liquid separation step (S11) of separating impurities from a solution mixed with a substance containing sodium sulfate and an eluent and obtaining a filtrate.

[0045] The first solid-liquid separation step (S11) above may be a step of removing impurities eluted in the step (S10) of obtaining the sodium sulfate mixture and obtaining the sodium sulfate mixture as the filtrate. At this time, the method of the first solid-liquid separation step (S11) is not particularly limited, but may be performed, for example, by centrifugation or a filter press method.

[0046] Referring to FIG. 1, one embodiment of the present invention may include the sodium bicarbonate manufacturing step (S20). The sodium bicarbonate manufacturing step (S20) may be a step of manufacturing sodium bicarbonate (NaHCO3) by mixing ammonia and carbon dioxide with the sodium sulfate mixture. Sodium ions contained in the sodium sulfate mixture may react with carbon dioxide and ammonia to produce solid sodium bicarbonate through a carbonation reaction of the following formula (1).

[0047] [Equation 1]

[0048] Na2SO 4(s) + CO 2(g) + H2O (l) + NH 3(g) → 2NaHCO 3(s) + (NH4)2SO 4(aq) (1)

[0049] As shown in Equation (1) above, the carbonation reaction that produces sodium bicarbonate is an exothermic reaction, and energy can be saved because there is not much additional energy consumed during the sodium bicarbonate production process.

[0050] As shown in Equation (1) above, in order to produce sodium sulfate from a mixture containing sodium sulfate, the solubility of carbon dioxide must be high to increase the production yield of sodium sulfate. Since carbon dioxide is an acidic gas, the pH must be raised to increase its solubility, and thus, ammonia, a basic gas, can be introduced to raise the pH.

[0051] The above sodium bicarbonate manufacturing step (S20) may have a reaction pressure of 1 to 10 atm. If the pressure of the carbonation reactor exceeds 10 atm, a sufficient amount of carbon dioxide can be dissolved, but the energy required for the carbonation reactor is high, which may reduce the economic viability of the final product, sodium bicarbonate, and if it is less than 1 atm, the amount of dissolved carbon dioxide may be low.

[0052] In the above sodium bicarbonate manufacturing step (S20), the reaction time may vary depending on the method of injecting carbon dioxide. If carbon dioxide is injected in the form of gas, it varies depending on whether aeration is performed, and if aeration is performed, it may be possible to have a reaction time of 4 hours or less. However, the optimized pressure and reaction time may vary depending on the size / space / conditions of the reactor. The method of performing aeration is not particularly limited, but it may be performed, for example, by bubbling.

[0053] Figure 3 is a graph showing the form of carbon dioxide present in a solution according to pH when carbon dioxide is dissolved. Referring to Figure 3, the concentration of bicarbonate ions in an aqueous solution of a carbonate system containing carbon dioxide can be highest when the pH is 6.0 to 10.0. Therefore, to increase the recovery rate of sodium bicarbonate, the pH of the sodium ion solution can be maintained at 6.0 to 10.0, for example, 8 to 9.

[0054] However, if a sufficient amount of carbon dioxide is dissolved in the sodium sulfate solution to produce the above-mentioned sodium bicarbonate, the pH of the solution may become 7.5 or lower. In this case, bicarbonate ions (HCO3 - Since the sodium sulfate may be converted into carbonic acid (H2CO3) and the sodium sulfate production rate may decrease, ammonia may be added first to the sodium sulfate solution to dissolve it sufficiently before carbon dioxide is added.

[0055] Referring to the above equation (1), ammonia can be mixed in a gaseous or aqueous solution state and can act as a catalyst without participating in the reaction to make the solution basic.

[0056] The carbon dioxide may be at least one selected from the group consisting of pure carbon dioxide, FINEX off gas (FOG), FINEX tail gas (FTG), blast furnace gas (BFG), converter gas, coal power plant flue gas, gas power plant flue gas, incinerator flue gas, glass melting flue gas, thermal equipment flue gas, petrochemical process flue gas, petrochemical process process gas, pre-combustion flue gas, and gasifier flue gas.

[0057] The above carbon dioxide may be concentrated by at least one method selected from the group consisting of the wet amine method, the PSA process, and the membrane process.

[0058] Referring to FIG. 2, in another embodiment of the present invention, the sodium bicarbonate manufacturing step (S20) may include a crystallization step (S21) of heating and crystallizing a solution mixed with sodium sulfate, ammonia, and carbon dioxide; and a second solid-liquid separation step (S22) of obtaining crystallized sodium bicarbonate from the solution obtained in the crystallization step (S21).

[0059] The particle size of baking soda is also commercially important. Larger particle sizes result in higher purity but may hinder dissolution, while excessively small particles can affect operations by making it difficult to control the mixing volume due to issues such as pipe clogging or air scattering. The required particle size varies depending on the application, and it is necessary to adjust the particle size accordingly. The particle size of baking soda can be controlled based on the reactor temperature. Generally, as the reactor temperature rises, the particle size increases, while as the temperature decreases, the particle size decreases. Furthermore, as the temperature increases, the solubility of the solid also increases, leading to a decrease in yield.

[0060] In order to control the particle size of the sodium bicarbonate as described above, the sodium bicarbonate manufacturing step (S20) may include a crystallization step (S21). The crystallization step (S21) is not particularly limited, but, for example, the particle size of the sodium bicarbonate can be arbitrarily controlled according to the purpose or use of the sodium bicarbonate. The crystallization step (S21) may be carried out in equipment such as a crystallizer.

[0061] The heating temperature of the crystallization step (S21) may be 40 to 70°C. Referring to FIG. 3, it can be seen that the difference in solubility between sodium sulfate and sodium bicarbonate is greatest between 40°C and 70°C. If the temperature of the crystallization step (S21) is less than 40°C, the solubility of gaseous carbon dioxide and solid phases decreases, and the yield increases; however, since not only sodium bicarbonate but also other impurities such as sodium sulfate precipitate as solids, the purity of sodium bicarbonate may decrease. In order to improve the purity of the decreased sodium bicarbonate, a washing process must be performed, which increases the amount of water used in the downstream wastewater treatment process or circulation, and may place a burden on operating costs. In addition, if the crystallization step (S21) exceeds 70°C, the solubility of sodium sulfate decreases, and the amount of leached out may decrease, and consequently, the yield of sodium bicarbonate may decrease.

[0062] The second solid-liquid separation step (S22) above may be a step of obtaining sodium bicarbonate from the solution crystallized in the crystallization step (S21). Since the sodium bicarbonate discharged in the crystallization step (S21) may be discharged in a slurry state mixed with liquid, solid-liquid separation may be performed to increase the purity of the sodium bicarbonate.

[0063] At this time, the method of the second solid-liquid separation step (S22) is not particularly limited, but can be performed by, for example, centrifugation or filter press methods.

[0064] According to one embodiment of the present invention, a first gypsum manufacturing step (S30) may be included in which a calcium-containing substance is mixed with the filtrate remaining after the baking soda manufacturing step (S20) to manufacture gypsum. The filtrate obtained after the carbonation reaction in the baking soda manufacturing step (S20) contains sulfate ions (SO4 2- Since it contains a large amount of ) calcium-containing material can be added to produce gypsum from the sulfate ions contained in the liquid.

[0065] The above calcium-containing material may be at least one selected from the group consisting of waste cement, waste concrete, coal ash, fly ash, iron slag, quicklime (CaO), calcium chloride (CaCl2), wollastonite, limestone, olivine, serpentine, asbestos, and deinking ash, and specifically may be quicklime.

[0066] The above calcium-containing material can be dissolved in water and mixed in the form of a slurry. If the above calcium-containing material is mixed in a powder state, the reaction rate is slow, so the pH enhancement efficiency may be low.

[0067] Referring to FIG. 2, in another embodiment of the present invention, the first gypsum manufacturing step (S30) may include a third solid-liquid separation step (S31) for separating gypsum from a mixture in which a calcium-containing substance is mixed with the filtrate remaining after the sodium bicarbonate manufacturing step (S20) and obtaining the filtrate. The first gypsum manufacturing step (S30) involves sulfate ions (SO4) contained in the filtrate in which the calcium-containing substance is present. 2- ) and carbonate ions (CO3 2- It can react with ) to produce gypsum (CaSO4) and calcium carbonate (CaCO3).

[0068] At this time, the method of the third solid-liquid separation step (S31) is not particularly limited, but can be performed by, for example, centrifugation or filter press methods.

[0069] Meanwhile, if a calcium-containing substance, which is a basic substance, is added to the filtrate whose pH has been adjusted to between 7.5 and 9.0 to produce sodium bicarbonate in the above sodium bicarbonate manufacturing step (S20), the pH of the filtrate may rise to 9 or higher. If the pH of the filtrate becomes 9 or higher, the carbon dioxide remaining in the solution becomes carbonate ions (CO3 2- Since it exists in the form of ), the input calcium ions (Ca 2+ ) can react with carbonate ions to produce calcium carbonate (CaCO3). In addition, carbon dioxide remaining in the solution under high pH conditions reacts with hydroxyl groups (OH) in the water - Calcium hydroxide (Ca(OH)2) can be produced by ). Therefore, the gypsum produced in the first gypsum manufacturing step (S30) may be low-purity gypsum containing calcium carbonate and calcium hydroxide, with an SO3 content of less than 40 weight%.

[0070] In one embodiment of the present invention, an ammonia manufacturing step (S40) may be included in which sodium carbonate (Na2CO3) is mixed with the liquid remaining after obtaining gypsum in the first gypsum manufacturing step (S30) to obtain ammonia. In the liquid remaining after obtaining gypsum in the first gypsum manufacturing step (S30), Ca 2+ Since ions remain, sodium carbonate is mixed to precipitate calcium carbonate (CaCO3), and ammonia can be recovered. The ammonia manufacturing step (S40) can improve the economic efficiency of the process by recovering the ammonia used in the sodium bicarbonate manufacturing step (S20).

[0071] Figure 4 is a graph showing the changes in ammonia and ammonium ions according to pH. Referring to Figure 4 and Equation (1) above, in the reaction to produce sodium sulfate, ammonia may exist in the solution in the form of ammonium sulfate, and specifically, ammonium ions (NH₄ 4+It can exist in the form of ). To recover ammonia existing in the form of ammonium ions, it is necessary to convert it into ammonia gas, and as can be seen in Figure 4, the higher the pH of the solution, the lower the concentration of ammonium ions and the higher the concentration of ammonia.

[0072] Accordingly, in the first gypsum manufacturing step (S30), the pH of the mixture containing calcium-containing material may be 10 or higher, specifically 11 or higher. If the pH of the mixture is less than 10, the proportion of ammonia present in the solution in the form of ammonium increases, which may result in a lower ammonia recovery rate.

[0073] At this time, the ammonium salts in the remaining liquid after obtaining sodium bicarbonate may exist in the form of ammonia gas. To recover the ammonia gas, the liquid can be transferred to an ammonia stripper facility and can be transferred in the form of a clear solution. At this time, before transferring the manufactured ammonia to the stripper, gypsum can be manufactured and separated to produce a clear solution.

[0074] Referring to FIG. 2, in another embodiment of the present invention, the ammonia manufacturing step (S40) may include a fourth solid-liquid separation step (S41) for obtaining a remaining liquid after separating calcium carbonate (CaCO3) from a mixture of the remaining liquid after obtaining gypsum in the first gypsum manufacturing step (S30) and sodium carbonate (Na2CO3), and a heating step (S42) for obtaining ammonia by heating the remaining liquid after separating calcium carbonate (CaCO3).

[0075] At this time, the method of the fourth solid-liquid separation step (S41) is not particularly limited, but can be performed by, for example, centrifugation or filter press methods.

[0076] In the heating step (S42) above, the heating means is not particularly limited and may be heated, for example, by a heat exchanger. When the filtrate remaining after separating calcium carbonate (CaCO3) is heated in the heating step (S42), gaseous ammonia can be recovered, and if necessary, the ammonia can be dissolved by convection with steam and then cooled to be recovered in the form of water ammonia. The recovered ammonia or water ammonia can be reused toward the carbonation reactor and can be utilized in other processes that require ammonia.

[0077] Meanwhile, the gypsum produced in the first gypsum manufacturing step (S30) described above may be low-purity gypsum with a weight of SO3 of less than 40% by weight. Since low-purity gypsum has little utility value, there is a need to produce high-purity gypsum with a high gypsum content.

[0078] Accordingly, one embodiment of the present invention may include a process for producing high-purity gypsum with a higher purity of the gypsum produced to increase the utility value of the gypsum, specifically having a SO3 weight of 40% or more.

[0079] Specifically, one embodiment of the present invention may include a second gypsum manufacturing step (S50) in which gypsum obtained in the first gypsum manufacturing step (S30), the filtrate remaining after obtaining ammonia in the ammonia manufacturing step (S40), and sulfuric acid are mixed to produce gypsum. Due to the mixing described above, the pH of the filtrate may be reduced, and carbonate ions present in the filtrate are converted into bicarbonate ions, thereby suppressing the production of calcium carbonate. Additionally, the concentration of hydroxide ions in the solution is lowered, which reduces the amount of slaked lime produced, so that high-purity gypsum with a SO3 weight of 40% or more can be produced.

[0080] At this time, the ratio of calcium ions and sulfate ions added from sulfuric acid (Ca 2+ : SO4 2-The ratio of sulfate ions is preferably 1:0.1 to 0.5. If the ratio of sulfate ions exceeds 1:0.5, the pH becomes too low, increasing wastewater treatment costs. If the ratio of sulfate ions is less than 1:0.1, the SO3 content is insufficient, making it unsuitable for use as commercial gypsum.

[0081] Referring to FIG. 2, in another embodiment of the present invention, the second gypsum manufacturing step (S50) may include a fifth solid-liquid separation step (S51) for separating gypsum from a mixture of the first gypsum obtained in the first gypsum manufacturing step (S30), the filtrate remaining after obtaining ammonia in the ammonia manufacturing step (S40), and sulfuric acid. At this time, the method of the fifth solid-liquid separation step (S51) is not particularly limited, but may be performed, for example, by centrifugation or a filter press method.

[0082] Examples

[0083] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0084] 1. Experimental Example 1

[0085] (1) Preparation of baking soda

[0086] A mixture was prepared by stirring 100 g of desulfurization waste and 200 mL of water at 40 ℃ for 1 hour, and the mixture was separated into solid and liquid using a filter press to obtain a sodium sulfate solution. The preparation of the sodium sulfate solution was repeated until 370 g of sodium sulfate solution was obtained.

[0087] 70 g of an aqueous ammonia solution of 25 to 30 wt% and 48.5 g of carbon dioxide were added to 370 g of the produced sodium sulfate solution and reacted for 4 hours at 40°C and 7 bar to obtain a slurry containing sodium bicarbonate. The slurry containing sodium bicarbonate was separated into solid and liquid using a filter press to obtain sodium bicarbonate and a filtrate.

[0088] (2) Step of manufacturing gypsum (low-purity gypsum)

[0089] 250 g of a 25 wt% quicklime (CaO) slurry was added to the filtrate remaining after separating the above sodium bicarbonate, and stirring was carried out for 1 hour. After stirring was finished, solid and liquid separation was performed using a filter press to produce gypsum, and the remaining filtrate was obtained.

[0090] (3) Step to recover ammonia

[0091] 0.5 g of sodium carbonate (Na2CO3) was added to 100 g of the filtrate remaining after preparing the above gypsum, stirred at room temperature for 30 minutes, and then the solid and liquid were separated using a filter press to obtain the solid and filtrate.

[0092] The recovered liquid was heated to 80°C and aerated using an inert gas to recover the ammonia contained in the liquid.

[0093] NH4 in the solution before and after recovery + The ammonia recovery rate was measured by measuring the amount of ions, and the ammonia recovery rate was 90 mol%.

[0094] (4) Step of manufacturing gypsum (high-purity gypsum)

[0095] The waste liquid from which ammonia had been removed by aeration was mixed again with 100 g of the first gypsum, and then 85 g of a 30 wt% aqueous sulfuric acid solution was slowly added and stirred for 1 hour to produce a slurry. Afterwards, the slurry was separated into solid and liquid using a filter press to recover the gypsum.

[0096] The purity of the gypsum produced above was measured through XRD and ICP, and as a result, the SO3 content was 93 wt%. In addition, Fig. 5 is a graph showing the XRD pattern of the gypsum produced in Example 1 of the present invention. Referring to Fig. 5, it can be confirmed that no impurities were detected in the XRD pattern.

[0097] 2. Experimental Example 2

[0098] 100 g of the filtrate obtained after solid-liquid separation following the addition of gypsum and sodium carbonate in Experimental Example 1 above was aerated using an inert gas at different pH (7 to 12) and temperature (40 to 80 ℃) to recover the ammonia contained in the filtrate, and this is shown in Table 1.

[0099] Quicklime slurry was additionally added to adjust the pH to the level in Table 1, and the Ca in the solution 2+ Sodium carbonate was added to remove ions.

[0100] Solution pH Solution Temperature (°C) Recovery Time (min) NH3 Recovery Rate (mol%) Comparative Example 1 780 6060 Comparative Example 2 880 6070 Comparative Example 3 980 6080 Example 1 108 6090 Example 2 118 6095 Example 3 128 6097 Example 4 117 8095 Example 5 116 10095 Example 6 115 12095

[0101] Referring to Table 1, it can be seen that at least 90 mol% of ammonia is recovered when the pH is 10 or higher, while at most 80 mol% of ammonia is recovered when the pH is less than 10. Additionally, it can be seen that the recovery time is shortened as the temperature increases.

[0102] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and it will be obvious to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention as described in the claims.

Claims

1. A step of obtaining a sodium sulfate mixture by mixing a substance containing sodium sulfate (Na2SO4) and an eluent; A sodium bicarbonate manufacturing step of producing sodium bicarbonate (NaHCO3) by mixing ammonia and carbon dioxide with the above sodium sulfate mixture; A first gypsum manufacturing step of manufacturing gypsum by mixing a calcium-containing substance with the liquid remaining after the above sodium bicarbonate manufacturing step; An ammonia manufacturing step of obtaining ammonia by mixing sodium carbonate (Na2CO3) into the filtrate remaining after obtaining gypsum in the first gypsum manufacturing step; and A method for manufacturing sodium bicarbonate and gypsum, comprising a second gypsum manufacturing step of mixing the gypsum obtained in the first gypsum manufacturing step, the filtrate remaining after obtaining ammonia in the ammonia manufacturing step, and sulfuric acid to produce gypsum.

2. In Paragraph 1, A method for producing sodium bicarbonate and gypsum, wherein the step of obtaining the above sodium sulfate mixture includes a first solid-liquid separation step of separating impurities from a solution mixed with a substance containing sodium sulfate and an eluent and obtaining a filtrate.

3. In Paragraph 1, A method for manufacturing sodium bicarbonate and gypsum, wherein the step of obtaining the above sodium sulfate mixture is to mix a substance containing sodium sulfate and a leachate at 40 to 60°C.

4. In Paragraph 1, The above sodium bicarbonate manufacturing step is, A crystallization step of heating and crystallizing a solution mixed with the above sodium sulfate mixture, ammonia, and carbon dioxide; and A method for producing sodium bicarbonate and gypsum, comprising a second solid-liquid separation step for obtaining crystallized sodium bicarbonate from a solution obtained in the crystallization step above.

5. In Paragraph 4, A method for manufacturing sodium bicarbonate and gypsum, wherein the heating temperature of the crystallization step is 40 to 70℃.

6. In Paragraph 1, A method for manufacturing sodium bicarbonate and gypsum, wherein the first gypsum manufacturing step comprises a third solid-liquid separation step in which gypsum is separated from a mixture in which a calcium-containing substance is mixed with the filtrate remaining after the sodium bicarbonate manufacturing step and the filtrate is obtained.

7. In Paragraph 6, A method for manufacturing sodium bicarbonate and gypsum, wherein the calcium-containing material is calcium oxide (CaO).

8. In Paragraph 1, A method for manufacturing sodium bicarbonate and gypsum, wherein in the first gypsum manufacturing step above, the pH of the mixture of calcium-containing material is 10 or higher.

9. In Paragraph 1, A method for producing sodium bicarbonate and gypsum, wherein the above ammonia production step comprises a fourth solid-liquid separation step of obtaining a remaining liquid after separating calcium carbonate (CaCO3) from a mixture of sodium carbonate (Na2CO3) and the remaining liquid after obtaining gypsum in the above first gypsum production step, and a heating step of obtaining ammonia by heating the remaining liquid after separating calcium carbonate (CaCO3).

10. In Paragraph 1, A method for manufacturing sodium bicarbonate and gypsum, wherein the second gypsum manufacturing step comprises a fifth solid-liquid separation step for separating gypsum from a mixture of the first gypsum obtained in the first gypsum manufacturing step, the filtrate remaining after obtaining ammonia in the ammonia manufacturing step, and sulfuric acid.

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