Method for producing sodium bicarbonate and gypsum using sodium sulfate

Abstract

The method for producing sodium bicarbonate and gypsum according to the present invention comprises: a first solid-liquid separation step for generating and recovering a sodium sulfate solution containing sodium ions from a mixture of an eluent and a sodium sulfate-containing substance; a second solid-liquid separation step in which carbon dioxide and ammonia are introduced into the sodium sulfate solution to produce and recover sodium bicarbonate (NaHCO3); a third solid-liquid separation step in which the sodium bicarbonate is recovered and a calcium-containing substance is introduced into the residual filtrate to produce and recover low-purity gypsum having an SO3 content of less than 40 wt%; an ammonia recovery step of recovering the low-purity gypsum and heating the residual filtrate to generate and recover ammonia; and a high-purity gypsum treatment step of recovering the ammonia and adding sulfuric acid and the low-purity gypsum recovered in the third solid-liquid separation step to a residual filtrate, thereby producing a high-purity gypsum product by using a sodium sulfate-containing mineral, a sodium sulfate by-product, and a sodium sulfate-containing substance of desulfurized waste discharged from a steel plant or a power plant. According to the present invention, sodium bicarbonate is produced and gypsum is produced using a waste liquid, thereby reducing the landfill ratio of waste generated after desulfurization, and carbon dioxide is stably fixed as a carbonate, thereby having a carbon neutral expected effect for a CCU technology using carbon dioxide, and high-purity gypsum having a high SO3 content is highly refined from low-purity stone having a low SO3 content, thereby reducing the production cost. Therefore, the utilization value of the gypsum can be improved.

Description

Technical Field

[0001] The present invention relates to a method for producing sodium bicarbonate and gypsum using sodium sulfate. Background Art

[0002] Flue gas desulfurization refers to the removal of sulfur (S), especially sulfur dioxide (SO2), from exhaust gases discharged from steel mills, thermal power plants, etc. With the development of industry, sulfur oxides (SO x ) and other harmful gases, resulting in serious air pollution and causing respiratory diseases, asthma, lung cancer and other diseases to the human body. Today, the desulfurizers used in steel mills are sodium bicarbonate (NaHCO3), activated carbon, calcium hydroxide (Ca(OH)2), etc. It is known that when sodium bicarbonate is dispersed in high-temperature exhaust gas, the specific surface area is greatly increased, thereby showing excellent absorption efficiency. At this time, sodium sulfate (Na2SO4) waste is generated as a by-product of the desulfurization process.

[0003] Recently, with the expansion of electric vehicles, the demand for lithium as a raw material for the second battery has increased. The main byproducts produced when producing lithium are silicon dioxide (SiO2) and sodium sulfate (Na2SO4). As the demand for lithium increases in the future, the amount of sodium sulfate byproduct is expected to increase. Therefore, in order to popularize the second battery, the development of technology that can reuse sodium sulfate must be advanced.

[0004] The by-products generated today are dissolved in water and then treated as wastewater or directly landfilled, which causes both treatment costs and secondary environmental problems. As a method for effectively utilizing the by-product, sodium sulfate, there is a method of dissolving sodium sulfate in water and injecting carbon dioxide and ammonia to regenerate sodium bicarbonate.

[0005] The technology underlying this method is the Solvay process, which uses dried water from concentrated seawater to produce sodium bicarbonate as a byproduct in the process of producing sodium carbonate and calcium chloride. However, the Solvay process does not include the treatment of sulfate (SO4 2- ) process, therefore, there is a need for the development of matching technologies that can solve this situation. It is expected that the current amount of sodium sulfate will continue to increase. Therefore, there is an urgent need for resource recovery or recycling solutions for by-products such as sodium sulfate. Summary of the invention

[0006] Issues to be resolved

[0007] One aspect of the present invention is to provide a method for producing sodium bicarbonate and gypsum using a substance containing sodium sulfate, which can treat environmentally friendly sodium sulfate waste and simultaneously produce sodium bicarbonate using carbon dioxide to meet the social demand for carbon neutrality.

[0008] Solution to the problem

[0009] According to one aspect of the present invention, there is provided a method for producing sodium bicarbonate and gypsum, which comprises: a first solid-liquid separation step, generating and recovering a sodium sulfate solution containing sodium ions from a mixture of an eluent and a substance containing sodium sulfate; a second solid-liquid separation step, adding carbon dioxide and ammonia to the sodium sulfate solution to generate and recover sodium bicarbonate (NaHCO3); a third solid-liquid separation step, recovering the sodium bicarbonate and adding a substance containing calcium to a residual filtrate to generate and recover low-purity gypsum having an SO3 content of less than 40% by weight; an ammonia recovery step, recovering the low-purity gypsum and heating the residual filtrate to generate and recover ammonia; and a high-purity gypsum step, recovering the ammonia and adding sulfuric acid to the residual filtrate and the low-purity gypsum recovered in the third solid-liquid separation step.

[0010] In the high-purity gypsum production step, a step of recovering high-purity gypsum having an SO3 content of 40 wt% or more may be additionally performed.

[0011] The mass ratio of the sodium sulfate-containing substance and the eluent put into the first solid-liquid separation step can be 1:1.4 to 1:3.

[0012] In the second solid-liquid separation step, ammonia (NH3) / sodium (Na + ) can have a molar ratio of 0.8 to 1.3.

[0013] The pH value of the second solid-liquid separation step may be maintained at 7.5 to 9.0.

[0014] The second solid-liquid separation step may further include: a sodium bicarbonate washing step, washing the sodium bicarbonate to improve the recovery rate of sodium bicarbonate.

[0015] The washing solution used in the sodium bicarbonate washing step may be reused from the eluent in the first solid-liquid separation step.

[0016] The method may further include a sodium bicarbonate drying step after the sodium bicarbonate washing step, in which the sodium bicarbonate is dried.

[0017] Effects of the Invention

[0018] According to one embodiment of the present invention, sodium sulfate-containing minerals, sodium sulfate by-products, and sodium sulfate-containing substances in desulfurization waste discharged from steel mills or power plants are used to manufacture sodium bicarbonate and waste liquid is used to produce gypsum, thereby reducing the landfill ratio of waste generated after desulfurization, and stably fixing carbon dioxide as carbonate, thereby achieving the expected effect of carbon neutrality for CCU technology using carbon dioxide.

[0019] According to another embodiment of the present invention, high-purity gypsum with a high SO3 content is refined from low-purity ore with a low SO3 content, thereby improving the utilization value of the gypsum. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram showing a method for producing sodium bicarbonate and gypsum according to one embodiment of the present invention.

[0021] Figure 2 This is a graph showing the form of carbon dioxide present in a solution according to pH when carbon dioxide is dissolved.

[0022] Figure 3 It is shown that in the second solid-liquid separation step, according to the mass ratio of the substance containing water and sodium sulfate and NH3 / Na + A graph showing the change in sodium bicarbonate recovery rate in desulfurized waste with different molar ratios.

[0023] Figure 4 It is shown that in the second solid-liquid separation step, according to NH3 / Na + Graph showing the variation of sodium bicarbonate purity with molar ratio.

[0024] Figure 5a : is a graph showing the change in the purity of sodium bicarbonate according to the supply amount of water in the sodium bicarbonate washing step.

[0025] Figure 5b is a graph showing the purity of the sodium bicarbonate as an XRD pattern after the sodium bicarbonate washing step.

[0026] Figure 6a : is a graph showing the SO3 carbon content (XRF) of gypsum according to the input amount of quicklime (CaO) slurry in the third solid-liquid separation step.

[0027] Figure 6b The graph shows the temperature change rate according to the input amount of quicklime (CaO) slurry according to the reaction time in the third solid-liquid separation step.

[0028] Figure 7 : is a graph showing the ammonia recovery rate according to the temperature of quicklime (CaO) slurry in the third solid-liquid separation step.

[0029] Figure 8 : is a graph showing the ammonia recovery rate according to the pH of the quicklime (CaO) slurry in the third solid-liquid separation step.

[0030] Figure 9a This is a graph showing the SO3 content (XRF) of gypsum according to the amount of sulfuric acid input.

[0031] Figure 9bThis is a graph showing the XRD analysis results of gypsum according to the amount of sulfuric acid input. DETAILED DESCRIPTION

[0032] Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. In addition, the embodiments of the present invention are provided for a more complete description to those skilled in the art. In the accompanying drawings, the shapes and sizes of the elements may be exaggerated for a clearer description.

[0033] The present invention relates to a method for producing sodium bicarbonate (NaHCO3) and gypsum (CaSO4), and specifically provides a method for producing sodium bicarbonate and gypsum, wherein sodium bicarbonate is produced by recovering sodium (Na) from a substance containing low-purity sodium sulfate such as sodium sulfate waste or natural minerals, and recovering sodium (Na) from SO4 2- High-purity gypsum is produced from waste liquid, thereby reducing the landfill ratio of waste generated after desulfurization, and carbon dioxide is stably fixed as carbonate, which has the expected effect of carbon neutrality for CCU technology using carbon dioxide.

[0034] According to one embodiment of the present invention, a method for producing sodium bicarbonate and gypsum can be provided, which comprises: a first solid-liquid separation step (S2), generating and recovering a sodium sulfate solution containing sodium ions from a mixture of an eluent and a substance containing sodium sulfate; a second solid-liquid separation step (S5), adding carbon dioxide and ammonia to the sodium sulfate solution to generate and recover sodium bicarbonate (NaHCO3); a third solid-liquid separation step (S7), recovering the sodium bicarbonate and adding a substance containing calcium to the residual filtrate to generate and recover low-purity gypsum having an SO3 content of less than 40% by weight; an ammonia recovery step (S8), recovering the low-purity gypsum and heating the residual filtrate to generate and recover ammonia; and a high-purity gypsum step (S9), recovering the ammonia and adding sulfuric acid to the residual filtrate and the low-purity gypsum recovered in the third solid-liquid separation step.

[0035] Figure 1 1 is a schematic diagram showing a method for producing sodium bicarbonate and gypsum according to one embodiment of the present invention, according to which the present invention may include a first solid-liquid separation step (S2), a second solid-liquid separation step (S5), a third solid-liquid separation step (S7), and an ammonia recovery step (S8).

[0036] The first solid-liquid separation step (S2) is a step of generating and recovering a sodium sulfate solution from a substance containing sodium sulfate by an eluent. The first solid-liquid separation step (S2) may further include a stirring step (S1) of mixing the substance containing sodium sulfate and the eluent before the separation step. The first solid-liquid separation step (S2) may further include a stirring step (S1) of mixing the substance containing sodium sulfate and the eluent before the separation step. Since the eluent contains almost no sodium ions, a sodium sulfate solution can be easily generated from a substance containing sodium carbonate.

[0037] The sodium sulfate-containing material put into the first solid-liquid separation step (S2) can be a low-purity sodium sulfate-containing material such as sodium sulfate waste or natural minerals. For example, the sodium sulfate-containing waste can be generated by desulfurizing waste gas containing sulfur oxide (SOx) components with sodium bicarbonate, or it can be waste generated by by-products in a lithium production plant. For example, it can be generated by using sodium bicarbonate to desulfurize waste gas generated by combustion in thermal power plants, factories, incineration plants, etc., or by treating waste gas generated by electric dust collection in a sintering plant of a steel plant. In addition to sodium sulfate, the sodium sulfate-containing waste also contains impurities such as K, Ca, Fe, Cl, etc., so that the solid impurities generated after the stirring can be removed in the first solid-liquid separation step (S2).

[0038] The eluent is not particularly limited as long as it can elute the substance containing sodium sulfate and sodium sulfate ions, and may be, for example, one or more selected from water, a sodium aqueous solution, and an ammonia aqueous solution.

[0039] The second solid-liquid separation step (S5) is a step of generating sodium bicarbonate (NaHCO3) from a sodium sulfate solution. The second solid-liquid separation step (S5) may include an ammoniation step (S3) of adding ammonia to the sodium sulfate solution and a carbonation step (S4) of adding carbon dioxide and then being performed.

[0040] The sodium sulfate solution may react with carbon dioxide and ammonia to generate solid-phase sodium bicarbonate through a carbonation reaction of Formula 1 below.

[0041] Na2SO4+2CO2+NH3+2H2O → 2NaHCO3+(NH4)2SO4 (1)

[0042] As shown in the above formula 1, the Gibbs' free energy of the reaction of generating calcium carbonate is expressed as a negative number of -851.0 kJ / mol, so the reaction of generating sodium bicarbonate can occur spontaneously. In addition, this reaction is an exothermic reaction, so it has the advantage of not consuming much additional energy in the process of generating sodium bicarbonate.

[0043] The reaction pressure of the carbonation reactor in which the carbonation reaction occurs can be 1-10 atm, and the reaction temperature can be below 50° C. When 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, thereby reducing the economy of the sodium bicarbonate and gypsum as the final product. The time of the carbonation reaction varies according to the injection method of carbon dioxide. When carbon dioxide is injected in the form of gas, it varies according to the presence or absence of aeration, and if aeration is performed, it can be carried out for less than 4 hours. However, the optimal pressure and reaction time can be different according to the size, space, and conditions of the reactor.

[0044] Figure 2 is a graph showing the forms of carbon dioxide present in a solution according to pH when carbon dioxide is dissolved. The chemical formula of sodium bicarbonate, also known as sodium bicarbonate, is NaHCO3, and as the bicarbonate ion (HCO3 - ) concentration increases, the production of sodium bicarbonate can be increased.

[0045] In addition, refer to Figure 2 The concentration of bicarbonate ions in the aqueous solution of the carbonate system containing carbon dioxide is the highest when the pH is 7.5-9.0. Therefore, in order to improve the recovery rate of sodium bicarbonate, it is preferred that the pH of the sodium sulfate solution is maintained at 7.5-9.0.

[0046] However, in order to produce the sodium bicarbonate, a sufficient amount of carbon dioxide is dissolved in the sodium sulfate solution, and the pH of the solution can be below 7.5. In this case, the bicarbonate ion (HCO3 - ) is converted into carbonic acid (H2CO3) to reduce the sodium bicarbonate generation rate. Therefore, before carbon dioxide is added to the sodium sulfate solution, preferably, ammonia is first added and fully dissolved, and then carbon dioxide is added.

[0047] The carbon dioxide can be one or more 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 exhaust gas, gas power plant exhaust gas, incinerator flue gas, glass dissolving exhaust gas, thermal device exhaust gas, petrochemical process exhaust gas, petrochemical process gas, pre-combustion exhaust and gasifier exhaust.

[0048] In addition, the carbon dioxide may be concentrated by one or more methods selected from the group consisting of a wet amine process, a PSA suspension process, and a separation membrane process.

[0049] Figure 3It is shown that in the second solid-liquid separation step, according to the mass ratio of the substance containing water and sodium sulfate and NH3 / Na + A graph showing the change in sodium bicarbonate recovery rate in desulfurized waste with different molar ratios.

[0050] Reference Figure 3 By adjusting the mass ratio of the sodium sulfate-containing substance and the water used as the eluent in the first solid-liquid separation step (S2), the recovery rate of sodium bicarbonate can be adjusted. In order to make the recovery rate of sodium bicarbonate recovered in the second solid-liquid separation step (S5) 50% (Na + The mass ratio of the sodium sulfate-containing substance to the eluent added in the first solid-liquid separation step (S2) may be 1:1.4-1:3. If the mass ratio of the sodium sulfate-containing substance to the eluent is less than 1.4, there may be a problem that the sodium sulfate is not dissolved, resulting in a loss of sodium sulfate as a residue and a reduction in the recovery rate of sodium ions. If the mass ratio of the sodium sulfate-containing substance to the eluent exceeds 3, the recovery rate of sodium ions will increase, but the concentration of sodium ions will be low, so there may be a problem that the content of sodium ions that do not react and flow out of the waste liquid becomes high, thereby reducing the production of sodium bicarbonate.

[0051] At the same time, in order to + Water concentration recovery 50 mol% sodium bicarbonate, ammonia (NH3) / sodium (Na + The molar ratio of ammonia (NH3) / sodium (Na + ) is less than 0.8, the recovery rate of sodium bicarbonate recovered in the second solid-liquid separation step (S5) is less than 50 mol %, and when it exceeds 3, the recovery rate of sodium bicarbonate increases, but the purity of sodium bicarbonate may be reduced.

[0052] The sodium bicarbonate separated in the second solid-liquid separation step (S5) is manufactured using a sodium sulfate-containing substance containing impurities, and therefore, the purity of the sodium bicarbonate is low compared to the sodium bicarbonate manufactured from pure sodium carbonate. Therefore, in order to improve the purity of the sodium bicarbonate, the second solid-liquid separation step (S5) may include a sodium bicarbonate washing step of washing the sodium bicarbonate. In the sodium bicarbonate washing step, the more the washing amount increases, the higher the purity of the generated sodium bicarbonate can be.

[0053] The washed sodium bicarbonate may further include a sodium bicarbonate drying step. If the sodium bicarbonate drying step is performed at a temperature exceeding 50°C, there is a tendency for sodium bicarbonate to decompose into sodium carbonate again, so preferably, the sodium bicarbonate is dried at a temperature below 50°C.

[0054] However, when the final target product is sodium carbonate rather than sodium bicarbonate, the produced sodium bicarbonate can be dried above 50° C. to obtain sodium carbonate. In addition, the solution used in the washing for improving the purity of sodium bicarbonate can be reused as an eluent for the first solid-liquid separation step (S2).

[0055] The third solid-liquid separation step (S7) is a step of generating and recovering low-purity gypsum generated from the residual filtrate of sodium bicarbonate recovery. The third solid-liquid separation step (S7) may include a low-purity gypsum production step (S6) of adding calcium-containing substances to sodium bicarbonate to generate low-purity gypsum with a SO3 content of less than 40% by weight. The filtrate after the carbonation reaction contains a large amount of sulfate ions (SO4 2- ), therefore, in order to produce gypsum from the sulfate ions contained in the filtrate, a calcium-containing substance may be added.

[0056] The calcium-containing substance may be one or more selected from the group consisting of waste cement, waste concrete, fly ash, fly ash, iron slag, quicklime (CaO), calcium chloride (CaCl2), wollastonite, limestone, olivine, serpentine, asbestos and deinking ash.

[0057] In order to generate the sodium bicarbonate, if calcium-containing substances are added to the optimal filtrate with a pH between 7.5 and 9.0, the pH of the filtrate rises to above 9. When the pH of the filtrate is above 9, the carbon dioxide remaining in the solution is converted into carbonate ions (CO3 2- ) exists in the form of calcium ions (Ca 2+ ) reacts with carbonate ions to produce calcium carbonate (CaCO3). In addition, at high pH, ​​the carbon dioxide remaining in the solution is released through the hydroxyl groups (OH - ) forms lime (Ca(OH)2). Therefore, the gypsum generated in the third solid-liquid separation step (S7) is a low-purity gypsum containing calcium carbonate and calcium hydroxide and having an SO3 content of less than 40% by weight.

[0058] The ammonia recovery step (S8) is a step of recovering low-purity gypsum and heating the remaining filtrate to generate and recover ammonia. The filtrate remaining after extracting the low-purity gypsum may contain a large amount of ammonia, so it is preferred to extract the remaining filtrate. Slurry containing low-purity gypsum is added to the ammonia recovery device of the ammonia recovery step (S8). The slurry is attached in the form of oxide scale and reduces efficiency. Therefore, it is effective to recover ammonia by adding it in the form of aqueous solution.

[0059] At this time, the molar ratio of calcium ions to sulfate ions (Ca 2+ :SO4 2-) is preferably 1:1.0-1.3. When the sulfate ion ratio exceeds 1.3, the purity of the gypsum becomes low. When the sulfate ion ratio is less than 1.0, the pH of the filtrate is too low, so there is a problem of not being able to fully recover ammonia in the ammonia stripping step.

[0060] Preferably, the pH of the ammonia recovery step (S8) is maintained above 8.0. If the pH of the ammonia recovery step (S8) is less than 8.0, there is a problem of reduced ammonia recovery rate.

[0061] In addition, the remaining filtrate is heated in the ammonia recovery step (S8), but the heated filtrate is preferably above 50° C. If the temperature of the filtrate is lower than 50° C., there is a problem that the recovery rate of ammonia is reduced.

[0062] Before the ammonia recovery step (S8), in the third solid-liquid separation step (S7), the calcium-containing substance reacts with water to generate an exothermic reaction. Therefore, a heat exchanger is further included between the sodium bicarbonate reactor and the ammonia recovery device, so that when heat is applied to the ammonia recovery equipment, the added energy consumption is reduced, thereby saving energy in the ammonia recovery step.

[0063] The recovered ammonia can be reused in the form of gas or manufactured into ammonia water again and reused.

[0064] The high-purity gypsum step (S9) is a step of adding sulfuric acid and the low-purity gypsum recovered in the third solid-liquid separation step to the filtrate remaining after recovering ammonia to generate high-purity gypsum with an SO3 content of 40% by weight or more. The filtrate remaining after recovering ammonia in the ammonia recovery step (S8) is mixed with the recovered low-purity gypsum again, and sulfuric acid is additionally injected, so that the pH of the filtrate is reduced. When the pH of the filtrate is reduced, the carbonate ions present in the filtrate are converted into bicarbonate ions to inhibit the formation of calcium carbonate, and by reducing the hydroxide ions in the solution, a high-purity gypsum with an SO3 content of 40% by weight or more can be obtained.

[0065] After the high-purity gypsum production step, a step of recovering high-purity gypsum having an SO3 content of 40 wt% or more may be further performed.

[0066] At this time, the ratio of sulfate ions added from calcium ions and sulfuric acid (Ca 2+ :SO4 2- ) is preferably 1:0.1-0.5. When the ratio of sulfate ions exceeds 1:0.5, the pH is too low and the cost of wastewater treatment increases. When the ratio of sulfate ions is less than 1:0.1, the SO3 content is insufficient and it cannot be used as industrial gypsum.

[0067] Furthermore, sulfate ions contained in the sulfuric acid can also be used as a raw material for gypsum.

[0068] In the third solid-liquid separation step (S7), high-purity gypsum can be recovered and the remaining filtrate can be discharged after being subjected to wastewater treatment.

[0069] The present invention is described in more detail below by way of specific examples. The following examples are merely examples to help understand the present disclosure, and the scope of the present invention is not limited thereto.

[0070] Example

[0071] Experimental Example 1: Measurement of the mass ratio of water / sodium sulfate and NH3 / Na + Changes in the recovery rate and purity of sodium bicarbonate in desulfurization waste with different molar ratios

[0072] Water and a substance containing sodium disulfate were added to a stirrer in different proportions, and then stirred at 40° C. for 1 hour at a stirring speed of 500 rpm, and solid-liquid separation was performed on the mixture after the stirring was completed, thereby obtaining a sodium sulfate solution.

[0073] Then, the sodium sulfate solution and the ammonia solution with an ammonia content of 25-30% by weight were added to a 300 mL high-pressure reactor according to the ratio in Table 1 below and stirred. The temperature of the high-pressure reactor was maintained at 25° C., and carbon dioxide gas was injected to 7 bar. The high-pressure reactor was stirred at a stirring speed of 200 rpm for 8 hours, and the product after stirring was filtered for solid-liquid separation to obtain sodium bicarbonate. The obtained sodium bicarbonate was measured based on the water / waste weight ratio and NH3 / Na + The recovery rate of sodium bicarbonate in the molar ratio is shown in Figure 3 In the experiment, the NH3 / Na + The purity of sodium bicarbonate is shown in Figure 4 middle.

[0074] [Table 1]

[0075] <![CDATA[NH3 / Na + Molar ratio]]> Example 1 1.3 Example 2 1.0 Example 3 0.8 Comparative Example 1 1.5 Comparative Example 2 0.6

[0076] according to Figure 3 , it can be confirmed that NH3:Na + In Examples 1 to 3 where the molar ratio of NH3:Na is above 0.8, the recovery rate of sodium bicarbonate exceeds 50% when the weight ratio of water / waste is in the range of 1.4 to 3, and the recovery rate of sodium bicarbonate exceeds 50%. + In Comparative Example 2 in which the molar ratio of was less than 0.8, the recovery rate of sodium bicarbonate was less than 50%.

[0077] In addition, according to Figure 4 It can be confirmed that according to NH3:Na +When sodium bicarbonate is produced in Comparative Example 1 in which the molar ratio exceeds 1.3, the content of impurities such as (NH4)2SO4 increases, so the purity of sodium bicarbonate decreases to less than 80%.

[0078] Experimental Example 2: Measurement of the purity of sodium bicarbonate according to the supply amount of water used in the sodium bicarbonate washing step

[0079] The sodium bicarbonate produced by the same method as in Example 1 was washed and then dried. The change in the purity of the sodium bicarbonate was measured by ion chromatogram (IC) and by changing the amount of water supplied during the washing step, and is shown in FIG. Figure 5a middle.

[0080] In addition, the purity of the sodium bicarbonate after washing with the supply amount of water in the washing step being 83 mL was measured by an X-ray diffraction analyzer (XRD) and is shown in FIG. Figure 5b middle.

[0081] according to Figure 5a , it can be confirmed that the greater the supply amount of water supplied in the washing step, the higher the purity of sodium bicarbonate.

[0082] Experimental Example 3: Measurement of gypsum purity and reaction temperature according to the input amount of quicklime slurry

[0083] After carbonation, 100 mL of waste solution and 20, 40, 60, and 80 mL of 7M quicklime slurry were prepared and put into the gypsum reactor, stirred for 30-60 minutes, and the third solid-liquid separation was performed to recover the gypsum. After drying the recovered gypsum, the purity and yield of the gypsum were measured. The purity of the quicklime was confirmed by the SO3 content on XRF, and the results are shown in Figure 6a In addition, the production of quicklime slurry generates an exothermic reaction, and the temperature change of the solution added to the quicklime slurry is shown in Figure 6b .

[0084] according to Figure 6a As shown, when the input amount of quicklime slurry exceeds 40 mL, the pH of gypsum increases, thereby reducing the SO3 content.

[0085] according to Figure 6b As shown, it can be confirmed that the temperature of the reaction solution increases as the input amount of quicklime slurry increases.

[0086] Example 4: Measuring ammonia recovery as a function of temperature

[0087] After mixing 100 mL of the waste solution after carbonation and adding 40 mL of 7M quicklime prepared in the reactor, the mixture was reacted at room temperature for 30-60 minutes, and the gypsum was removed by the third solid-liquid separation. After the gypsum was produced, the remaining filtrate was put into the ammonia recovery device, and the heating temperature was changed in the range of 20°C to 95°C to aerate with nitrogen. The ammonia recovery rate was confirmed by IC, and the results are shown in Figure 7 middle.

[0088] according to Figure 7 , it can be confirmed that as the temperature increases, the ammonia recovery rate increases.

[0089] Experimental Example 5: Measurement of ammonia recovery rate according to pH of filtrate after gypsum extraction

[0090] After recovering the gypsum, H2SO4 was added to the filtrate to lower the pH, or a 7M quicklime slurry was used to adjust the pH by raising the pH, and then ammonia was recovered. The temperature during ammonia recovery was maintained at 80°C. The ammonia recovery method was the same as in Example 5, and the recovery rate results are shown in Figure 8 middle.

[0091] according to Figure 8 It was confirmed that as the pH of the filtrate increased, the ammonia recovery rate increased.

[0092] Experimental Example 6: Measuring the purity of gypsum injected with sulfuric acid

[0093] 20, 40, 60, and 80 mL of 30 wt% sulfuric acid were added in different amounts to the low-purity gypsum produced in Example 4 (40 mL of 7M quicklime slurry) and the waste liquid for recovering ammonia produced in Example 5 (temperature 80° C.) and stirred. The purity of the gypsum was confirmed by the SO3 content on XRF and XRD, and the results are shown in Figure 9a and 9b middle.

[0094] according to Figure 9a and Figure 9b It was confirmed that high-purity dihydrate gypsum (CaSO4·2H2O) can be obtained by adding sulfuric acid to low-purity gypsum and stirring.

[0095] The embodiments of the present invention are described in detail above, but the scope of the present invention is not limited thereto. Various modifications and variations can be made without departing from the technical concept of the present invention, which will be obvious to those skilled in the art.

Claims

1. A method for producing sodium bicarbonate and gypsum, comprising: A first solid-liquid separation step, generating and recovering a sodium sulfate solution containing sodium ions from a mixture of an eluent and a substance containing sodium sulfate; A second solid-liquid separation step, in which carbon dioxide and ammonia are added to the sodium sulfate solution to generate and recover sodium bicarbonate; A third solid-liquid separation step, recovering the sodium bicarbonate and adding a substance containing calcium to the residual filtrate to generate and recover low-purity gypsum with a SO3 content of less than 40% by weight; an ammonia recovery step, recovering the low-purity gypsum and heating the residual filtrate liquid to generate and recover ammonia; as well as In the high-purity gypsum production step, the ammonia is recovered and sulfuric acid and the low-purity gypsum recovered in the third solid-liquid separation step are added to the residual filtrate.

2. The method for producing sodium bicarbonate and gypsum according to claim 1, wherein: The high-purity gypsum production step is followed by an additional step of recovering high-purity gypsum having an SO3 content of 40% by weight or more.

3. The method for producing sodium bicarbonate and gypsum according to claim 1, wherein: The mass ratio of the sodium sulfate-containing substance and the eluent put into the first solid-liquid separation step is 1:1.4 to 1:

3.

4. The method for producing sodium bicarbonate and gypsum according to claim 1, wherein: In the second solid-liquid separation step, the molar ratio of ammonia to sodium is 0.8 to 1.

3.

5. The method for producing sodium bicarbonate and gypsum according to claim 1, wherein: The pH value of the second solid-liquid separation step is maintained at 7.5 to 9.

0.

6. The method for producing sodium bicarbonate and gypsum according to claim 1, wherein: The second solid-liquid separation step further comprises: The sodium bicarbonate washing step is to wash the sodium bicarbonate to improve the recovery rate of the sodium bicarbonate.

7. The method for producing sodium bicarbonate and gypsum according to claim 6, wherein: The washing solution used in the sodium bicarbonate washing step is reused from the first solid-liquid separation step by the eluent.

8. The method for producing sodium bicarbonate and gypsum according to claim 6, wherein: The sodium bicarbonate washing step also includes: The sodium bicarbonate drying step is to dry the sodium bicarbonate.

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