A method for producing high purity magnesium hydroxide from by-products of a refined salt manufacturing process using chemical equilibrium computer simulation

Abstract

The present invention provides a method of producing high-purity magnesium hydroxide from seawater or refined salt brine, which comprises: a) a purification step of filtering organic and inorganic impurities contained in seawater or refined salt brine; b) a precipitation step of calculating a hydrogen ion concentration index of the seawater or refined salt brine within a range calculated by a chemical equilibrium computer simulation, determining an amount of an alkali substance corresponding to the hydrogen ion concentration index based on the calculation, and adding the alkali substance to the seawater or refined salt brine subjected to the purification step, thereby selectively precipitating only magnesium ions to form magnesium hydroxide; and c) a drying step of drying the magnesium hydroxide.

Description

Technical Field

[0001] This invention relates to a method for producing high-purity magnesium hydroxide from a byproduct waste (hereinafter referred to as refined salt bittern) of a refined salt manufacturing process using computer simulation. Specifically, it relates to a method for producing high-purity magnesium hydroxide (Mg(OH)2), wherein the byproduct (i.e., refined salt bittern) generated during the electrochemical recovery of salt (hereinafter referred to as refined salt) from seawater is stirred, and magnesium hydroxide is recovered by adding an alkaline substance containing hydroxyl (OH) to the stirred refined salt bittern. The alkaline substance includes at least one of ammonium hydroxide, sodium hydroxide, and hydroxides of calcined limestone or calcined dolomite. In the recovery process, the alkaline substance is quantitatively added while the hydrogen ion concentration index (pH) is within a range calculated by chemical equilibrium computer simulation based on the accurate concentration of four or more alkali metal and alkaline earth metal chlorides contained in the refined salt bittern, thereby selectively precipitating only magnesium ions. Background Technology

[0002] Magnesium hydroxide is used in various fields, such as environmental applications like water treatment, desulfurization, and soil improvement; pharmaceutical applications like acid stabilizers; animal feed; and as a carrier in chemical processes requiring chemical resistance. In particular, high-purity magnesium hydroxide is required for flame-retardant materials used in wire sheathing, and its demand is increasing as a raw material for high-purity magnesium hydroxide (used in electronic and optical materials utilizing insulating and dielectric properties).

[0003] Natural resources used as raw materials for magnesium hydroxide and magnesium oxide include magnesite (MgCO3), brucite (Mg(OH)2), and seawater, sea bittern, or brine. Natural minerals such as magnesite and brucite can be produced through simple processes such as heat treatment and grinding, but it is difficult to remove the impurities inherent in the minerals, such as iron oxide (Fe2O3), aluminum oxide (Al2O3), and silicon dioxide (SiO2), making it difficult to produce high-purity magnesium hydroxide and magnesium oxide. In contrast, seawater or brucite or brine, which is concentrated to 20 to 30 times the volume of seawater, contains extremely low levels of the above-mentioned impurities, making it easy to produce high-purity magnesium hydroxide and magnesium oxide.

[0004] The conventional method for manufacturing high-purity magnesium hydroxide is as follows: utilizing its low solubility (9.6 × 10⁻⁶) -4Magnesium hydroxide (Mg(OH)) is produced by adding an alkaline substance containing hydroxyl groups (g / 100mL H2O, 20℃) to seawater, bittern, or brine. The alkaline substance is selected from at least one of ammonium hydroxide, sodium hydroxide, and hydroxides of calcined limestone or calcined dolomite. Alternatively, a widely used method involves using magnesium chloride as a magnesium source and adding the aforementioned alkaline substance to produce high-purity magnesium hydroxide.

[0005] However, seawater, bittern, and brine are complex systems composed of four or more components, such as magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), sodium chloride (NaCl), and water (H2O). The following problems exist when producing high-purity magnesium hydroxide from these components.

[0006] Therefore, when the pH range of the hydrogen ion concentration index formed during the precipitation of magnesium (Mg) ions into hydroxide by adding hydroxyl (OH) is similar to the pH range of the hydrogen ion concentration index that precipitates large amounts of calcium (Ca) ions coexisting in seawater, bittern, and brine, calcium (Ca) ions have low solubility (0.17 g / 100 mL H₂O, 20 °C) within this pH range, calcium hydroxide (Ca(OH)₂) precipitates simultaneously with magnesium hydroxide. Under these circumstances, it is difficult to control the calcium (Ca) impurities incorporated into magnesium hydroxide.

[0007] To improve this problem, various methods have been studied. Patent document 1 discloses a method for selectively removing calcium ions in the form of insoluble gypsum dihydrate (CaSO4·2H2O, solubility 0.26g / 100mL H2O, 20℃) by adding sulfuric acid to wastewater from a refined salt manufacturing process that contains large amounts of calcium and magnesium ions.

[0008] Furthermore, Patent Document 2 discloses a method for recovering magnesium components by adjusting the molar ratio of magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and potassium chloride and magnesium chloride in sodium chloride (NaCl) contained in bittern at 0.8 to 1.1, thereby precipitating them as carnallite (KCl·MgCl2·6H2O). However, this method increases the load on the washing process because potassium chloride should ultimately be removed in the washing process to obtain high-purity magnesium hydroxide, while this method requires the addition of potassium chloride (KCl) to form carnallite (KCl·MgCl2·6H2O).

[0009] For complex systems containing four or more components, such as seawater, bittern, and brine, the main indicator for selectively recovering magnesium is the hydrogen ion concentration index (pH) range. This can be referenced using the Eh-pH (also known as the Pourbaix) chart, which graphically represents the relationship between the potential and pH of metal ions in an aqueous solution when they are thermodynamically stable. However, it is suitable for situations where a single component exists in the aqueous solution. When four or more chemical species coexist (e.g., seawater, refined salt, bittern, etc.), it is difficult to perform accurate quantitative analysis. Summary of the Invention

[0010] Technical issues To address the aforementioned problems, this invention provides a method for rapidly producing high-purity magnesium hydroxide. Specifically, for refined bittern, a complex system containing magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl), which is a byproduct generated during the electrochemical recovery of salt from seawater, an alkaline substance containing hydroxyl (OH) groups is added. The method requires determining the pH range of the hydrogen ion concentration index of the seawater or refined bittern containing the added alkaline substance. The ionic strength is derived based on the accurate concentrations of four or more metal salts contained in the refined bittern. An amount of alkaline substance corresponding to the pH range determined through chemical equilibrium computer simulation is added to the stirred refined bittern. Therefore, without constructing complex equipment or eliminating complex intermediate processes, magnesium ions are selectively precipitated.

[0011] Problem-solving methods To achieve the above objectives, the present invention provides a method for producing high-purity magnesium hydroxide from seawater or refined bittern, comprising: a) a purification step, filtering organic and inorganic impurities contained in the seawater or refined bittern; b) a precipitation step, calculating the hydrogen ion concentration index of the seawater or refined bittern within a range calculated by a chemical equilibrium computer simulation, determining the amount of alkaline substance to be added based on the hydrogen ion concentration index, and adding it to the seawater or refined bittern after the purification step, thereby selectively precipitating only magnesium ions to form magnesium hydroxide; and c) a drying step, drying the magnesium hydroxide.

[0012] Preferably, step b) is performed at room temperature.

[0013] Preferably, after step b), the method further includes the following steps: b-2) a filtration step, in which the magnesium hydroxide formed after solid-liquid separation is separated by a filter; and b-3) a washing step, in which the magnesium hydroxide after solid-liquid separation is washed with ion-exchanged water.

[0014] Preferably, the filter has a pore size greater than 0 and less than or equal to 1 μm.

[0015] Preferably, the filter has a pore size greater than 0 and less than or equal to 0.45 μm.

[0016] Preferably, if the alkaline substance is added at a rate that maintains the pH of the refined bittern or seawater at 12.2 or less, the alkaline substance comprises at least one selected from the group consisting of ammonium hydroxide, sodium hydroxide, and hydroxides of calcined limestone or calcined dolomite.

[0017] Preferably, if the alkaline substance is added at an unrestricted rate, the alkaline substance comprises ammonium hydroxide.

[0018] Preferably, the concentration range of the alkaline substance is 3.4 wt% to 25 wt%.

[0019] Preferably, the hydrogen ion concentration index of the seawater or refined bittern, calculated by computer simulation of chemical equilibrium, is in the range of 8.8 to 12.2.

[0020] Preferably, the alkaline substance is added while maintaining the hydrogen ion concentration index of the refined bittern, calculated by computer simulation of chemical equilibrium, in the range of 9.0 to 11.5.

[0021] Preferably, magnesium hydroxide is filtered by solid-liquid separation using a filter that includes a centrifugal filter.

[0022] Preferably, the magnesium hydroxide is washed through a filter containing a centrifugal filter.

[0023] Preferably, the chemical equilibrium computer simulation includes the following steps: selecting chemical species predicted to participate in the reaction in seawater or refined bittern; inputting the concentration of the chemical species; calculating and inputting the ionic strength of the chemical species; calculating and inputting the equilibrium constant of the chemical species; and calculating the equilibrium concentration and hydrogen ion concentration index of seawater or refined bittern.

[0024] Beneficial effects According to the present invention, for the byproducts generated during the electrochemical recovery of salt (refined salt), namely, refined salt bittern containing magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl) as a complex system, an alkaline substance containing hydroxyl (OH) is added to it. It is necessary to determine the range of hydrogen ion concentration index (pH) of the seawater or refined salt bittern containing the added alkaline substance. The ionic strength is derived based on the accurate concentration of four or more metal salts contained in the refined salt bittern. An amount of alkaline substance corresponding to the range of hydrogen ion concentration index (pH) determined by chemical equilibrium computer simulation is added to the stirred refined salt bittern. Therefore, without the need to construct complex equipment or eliminate complex intermediate processes, only magnesium ions are selectively precipitated, thereby rapidly producing high-purity magnesium hydroxide (Mg(OH)2). Attached Figure Description

[0025] Figure 1 This is a graph showing the results of computer simulations of the stability of each chemical species contained in refined bittern at different pH values ​​according to an embodiment of the present invention.

[0026] Figure 2 This is a graph showing the pH change during the precipitation reaction when ammonia is added according to Example 2 of the present invention.

[0027] Figure 3 This is a graph showing the pH change during the precipitation reaction when sodium hydroxide is added according to Example 3 of the present invention.

[0028] Figure 4 This is a process flow diagram for manufacturing high-purity magnesium hydroxide according to Example 3 of the present invention.

[0029] Figure 5 This is a computer simulation flowchart of the equilibrium concentration and pH for producing high-purity magnesium hydroxide according to an embodiment of the present invention. In this invention, the temperature and pressure are fixed at room temperature (25°C) and atmospheric pressure, respectively, before computer simulation. The equilibrium constants used are derived from the database built into the computer simulation software at room temperature and atmospheric pressure.

[0030] Best mode Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are intended to enable those skilled in the art to fully understand the present invention and to allow for various other modifications; the scope of the present invention is not limited to the following embodiments.

[0031] In the detailed description or claims of this invention, when one constituent element is described as "comprising" another constituent element, it should not be construed as being limited to the constituent element, but should be understood as potentially including other constituent elements, unless otherwise expressly stated.

[0032] Figure 1 This is a graph showing the computer simulation results of the stability of each chemical species contained in refined bittern at different pH values ​​according to an embodiment of the present invention. Figure 2 This is a graph showing the pH change during the precipitation reaction when ammonia is added according to Example 2 of the present invention. Figure 3 This is a graph showing the pH change during the precipitation reaction when sodium hydroxide is added according to Example 3 of the present invention. Figure 4 This is a process flow diagram for manufacturing high-purity magnesium hydroxide according to Example 3 of the present invention. Figure 5 This is a computer simulation flowchart of the equilibrium concentration and pH for producing high-purity magnesium hydroxide according to an embodiment of the present invention.

[0033] Refined bittern is a complex multi-component system composed of four or more metal salts, including magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), sodium chloride (NaCl), and water (H2O).

[0034] This invention provides a method for producing high-purity magnesium hydroxide from refined bittern, comprising: a purification step, removing organic impurities such as microorganisms and inorganic impurities such as fine sand floating in the refined bittern (a by-product waste of the refined salt manufacturing process) by filtration; a precipitation step, adding an appropriate amount of an alkaline substance containing hydroxyl (OH) groups to the purified bittern being stirred at room temperature and with the pH index within a range calculated by a chemical equilibrium computer simulation, thereby selectively precipitating magnesium (Mg) ions only as magnesium hydroxide (Mg(OH)2); a filtration step, separating the precipitated magnesium hydroxide through a filter; a washing step, washing the separated magnesium hydroxide with ion-exchanged water; and a drying step, drying the washed magnesium hydroxide.

[0035] Furthermore, the purpose of the filter used to filter impurities is to filter out organic impurities such as microorganisms and inorganic impurities such as fine sand floating in seawater. Its pore size is preferably less than or equal to 1 μm, and more preferably a membrane filter with a pore size less than or equal to 0.45 μm.

[0036] Furthermore, the alkaline substance containing hydroxyl (OH) can be at least one of ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and hydroxides of calcined limestone or calcined dolomite (Ca(OH)2 / Mg(OH)2). In this case, the concentration of the aqueous solution of the alkaline substance is preferably between 3.4 wt% and 25 wt%. When the concentration of the alkaline substance is less than or equal to 3.4 wt%, the container volume used for the precipitation process is too large relative to the yield, leading to a decrease in productivity. When the concentration of the alkaline substance is greater than or equal to 25 wt%, the viscosity of the reaction solution is too high, requiring the stirring speed to be increased to at least 500 rpm, thus overloading the reaction stirring device.

[0037] Furthermore, the range of hydrogen ion concentration index (pH) can be calculated using the MEDUSA-HYDRA program developed by the Royal Institute of Technology in Sweden or other commercially available aqueous solution-based chemical equilibrium computer simulation software. This range is used to selectively precipitate magnesium (Mg) ions only as magnesium hydroxide (Mg(OH)2) in a specific aqueous solution system composed of four or more alkali metal salts or alkaline earth metal salts. Moreover, for the purposes of this refined bittern, the range of hydrogen ion concentration index (pH) calculated by chemical equilibrium computer simulation is preferably 8.8 ≤ pH ≤ 12.2, more preferably 9.0 ≤ pH ≤ 11.5.

[0038] In addition, conventional filters equipped with filters can be used; however, it is preferable to use a continuous centrifugal filter with a relative centrifugal force (G-force) greater than or equal to 250, which can continuously perform filtration of the precipitate reaction filtrate and subsequent washing processes.

[0039] Furthermore, regarding the washing of the solid-liquid separated magnesium hydroxide, the impurity removal rate increases with the amount of ion-exchange water used. However, considering the time and cost required for the washing process and the trade-off with the final purity, it is preferable to use no more than 20 times the amount of dried magnesium hydroxide (Mg(OH)2) expected to be obtained for washing.

[0040] exist Figure 1 In the chart, magnesium hydroxide (Mg(OH)2) begins to precipitate at pH 8.8, and calcium hydroxide (Ca(OH)2) begins to precipitate at pH 12.2. Therefore, the pH value needs to be maintained in the range of 8.8 to 12.2 to prevent calcium hydroxide precipitation from causing incorporation.

[0041] In a preferred embodiment of the present invention, the component analysis results of the refined bittern and seawater used are shown in Table 1. The ratio of Mg to Ca ions in seawater and refined bittern are 3.25 and 2.36, respectively, with a high Ca ion content. Due to the high Ca ion content, when magnesium ions are selectively precipitated by controlling the hydrogen ion concentration index (pH), a large number of calcium ions coexisting with the magnesium ions have low solubility (0.17 g / 100 mL H2O, 20 °C) within a similar range of hydrogen ion concentration index (pH) to those of the magnesium ions. Therefore, when magnesium hydroxide (Mg(OH)2) precipitates, calcium hydroxide (Ca(OH)2) precipitates simultaneously, resulting in calcium (Ca) impurities being incorporated into the magnesium hydroxide, thus posing a problem of difficulty in controlling this impurity.

[0042] Table 1 In a precipitation reaction used to selectively precipitate magnesium ions only as magnesium hydroxide (Mg(OH)2), as shown below, depending on the hydrogen ion concentration index (pH), it is possible that only Mg ions precipitate (Equation 1), or both Mg and Ca precipitate simultaneously (Equation 2).

[0043] [Formula 1: When adding precipitating agents NaOH and NH4OH to achieve the appropriate pH] Mg 2+ (+Ca contained in bittern) 2+ ) + (precipitant) + Cl - → Mg(OH)₂↓ + CaCl₂(aq) [Equation 2: When excessive amounts of precipitating agents NaOH and NH4OH are added, resulting in excessively high pH] Mg 2+ (+Ca contained in bittern) 2+ ) + (precipitant) + Cl - → Mg(OH)₂↓ + Ca(OH)₂↓ In this context, ↓ represents precipitation, and (aq) represents the state of being dissolved in aqueous solution.

[0044] In a preferred embodiment of the invention, in an aqueous solution of a complex component system consisting of four or more alkali metal salts or alkaline earth metal salts containing magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl), the range of hydrogen ion concentration index (pH) for selectively precipitating only magnesium (Mg) ions as magnesium hydroxide (Mg(OH)2) is calculated using the MEDUSA-HYDRA program (developed by the Royal Institute of Technology in Sweden) for chemical equilibrium computer simulation. However, commercially available software for chemical equilibrium computer simulation based on accurate input of the concentrations of all participating ion species in the system can be used.

[0045] For refined bittern, the ionic strength calculated using Formula 1 based on the types and concentrations of the involved ions is shown in Table 2, and the results calculated using computer simulation are also presented. Figure 1 The hydrogen ion concentration index (pH) range calculated by computer simulation through chemical equilibrium is derived to be 8.8 ≤ pH ≤ 12.2, preferably 9.0 ≤ pH ≤ 11.5. That is, it is necessary to control the concentration range of seawater or refined bittern containing alkaline substances within 8.8 ≤ pH ≤ 12.2 (preferably 9.0 ≤ pH ≤ 11.5) while adding alkaline substances.

[0046] [Formula 1: Calculation of Ionic Strength] Where ci is the molar concentration of ion type i, and zi is the charge of ion type i.

[0047] Table 2 Ionic strength is defined as the product of the molar concentration and charge of an ion. It is a physical quantity proportional to the concentration of chemical species typically dissolved in aqueous solutions. As ionic strength increases, the reaction rate increases, the optimal pH decreases, and the solubility of that metal ion in aqueous solution is affected. In conventional chemical equilibrium computer simulations, infinitely diluted solutions (ionic strength = 0) are used as ideal solutions for calculations. In the system of this invention, the calculation of ionic strength based on the accurate concentrations and charges of cations and anions (excluding magnesium ions) is crucial for the system and for accurate computer simulations. Furthermore, an important input value in chemical equilibrium computer simulations is temperature; in this invention, the temperature is 25°C, close to room temperature. The chemical equilibrium computer simulation process according to the invention is as follows: Figure 5 As shown.

[0048] like Figure 5 As shown, the chemical equilibrium computer simulation includes: selecting the chemical species predicted to participate in the reaction in seawater or refined bittern; inputting the concentration of the chemical species; calculating and inputting the ionic strength of the chemical species; calculating and inputting the equilibrium constant of the chemical species; and calculating the equilibrium concentration and hydrogen ion concentration index (pH) of the seawater or refined bittern.

[0049] The chemical species involved in the reaction are divided into cations and anions; cations include Mg. 2+ Ca 2+ Anions include OH-, Cl-, etc. - Temperature and pressure were maintained at room temperature (25°C) and atmospheric pressure (1 atm), respectively.

[0050] To verify the results of the computer simulation of the chemical equilibrium, the following experiment was conducted in which bittern was rapidly added to an aqueous solution of a precipitant of a predetermined concentration in a single step.

[0051] <Example 1> One liter (approximately 1.25 kg) of refined bittern with a hydrogen ion concentration index (pH) of 6.2 is passed through a membrane filter with a pore size of 0.45 μm or less to remove floating organic impurities such as microorganisms and inorganic impurities such as fine sand. 2M (3.4 wt%) ammonia solution (NH4OH) is added as a precipitant to a 3L volumetric beaker equipped with a pH meter, and the mixture is stirred at 300 rpm. Simultaneously, the purified bittern purified by the above method is rapidly added in a single batch in the amount calculated according to the stoichiometric formula. The pH before adding the bittern and the pH two hours after adding the bittern are measured using the pH meter. After the precipitation reaction was carried out for 2 hours, stirring was stopped, and the precipitation reaction solution was filtered through a centrifugal filter. Ion-exchange water with a weight of 20 times that of the desired magnesium hydroxide (Mg(OH)2) was added to immediately wash the magnesium hydroxide filtered through the centrifugal filter. Then, it was dried at 105°C for 16 hours or longer. The final magnesium hydroxide powder was analyzed by X-ray fluorescence spectrometry, and the results are shown in Table 3.

[0052] "Rapid addition" means "injecting the entire dose at once." The injection speed is the same as pouring water into a cup normally, with the emphasis on injecting it all at once. The same applies below.

[0053] <Comparative Example 1> Magnesium hydroxide powder was prepared using the same method as in Example 1, except that 2M sodium hydroxide (NaOH) was used as a precipitant. The compositional analysis results are shown in Table 3. The key point is "rapid addition".

[0054] <Comparative Example 2> Dolomite (Ca·Mg(CO3)2) from Yeongwolsan Mountain in Gangwon Province, South Korea, was heat-treated at 950°C for 1 hour. The resulting composite oxide (CaO·MgO) powder was added to ion-exchange water stirred at 300 rpm to prepare a 5 wt% composite hydroxide (Ca(OH)2·Mg(OH)2) slurry, which was then used as a precipitant. Magnesium hydroxide powder was prepared using the same method as in Example 1. The compositional analysis results are shown in Table 3. The key point is "rapid addition".

[0055] Table 3 ※Mg(OH)2 (wt%) = 100 - (content of elements detected by XRF analysis) (wt%) In Example 1 and Comparative Examples 1 and 2 of the present invention, when weakly alkaline ammonia water is used as a precipitant, the initial pH of the precipitation reaction is 11.8, and the pH after 2 hours is 11.0. The pH of the overall precipitation reaction is maintained between 8.8 ≤ pH ≤ 12.2 as derived by computer simulation, which can produce high-purity magnesium hydroxide with a Mg(OH)2 concentration of 99.1% and a CaO content of less than or equal to 0.05% (500 ppm).

[0056] Conversely, when strong alkaline sodium hydroxide (NaOH) was used as a precipitant, the initial pH of the precipitation reaction was 14.0, and the pH after 2 hours was 13.8. The pH of the overall precipitation reaction was maintained in an alkaline range higher than the computer simulation results of 8.8≤pH≤12.2, and finally, low-purity magnesium hydroxide with impurities, containing 96.9% Mg(OH)2 and 2.8% CaO, was produced.

[0057] Furthermore, when using strongly alkaline calcined dolomite hydrate (Ca(OH)2·Mg(OH)2) as a precipitant, the initial pH of the precipitation reaction was 12.5, and the pH after 2 hours was 12.0. In most of the precipitation reactions except after 2 hours, the pH remained in an alkaline range higher than the computer simulation results of 8.8≤pH≤12.2, ultimately producing low-purity magnesium hydroxide with a Mg(OH)2 concentration of 94.7% and a CaO content of 4.1%.

[0058] In particular, regarding dolomite hydrate (Ca(OH)2·Mg(OH)2), due to the inherent composition of dolomite and the added Ca(OH)2 component, the content of CaO component is higher than when sodium hydroxide is used as a precipitant, and the inherent impurity iron oxide (Fe2O3) of dolomite mineral is incorporated, so the purity is lower than when sodium hydroxide is used as a precipitant.

[0059] In Comparative Examples 1 and 2, the focus is on whether the substance is added rapidly or supplied slowly (as described below), rather than whether it is a strong or weak alkaline base. In particular, the rapid addition of a strong alkaline substance results in low purity of magnesium hydroxide, thus indicating that strong alkaline substances should not be added rapidly, as described below.

[0060] In Example 1 and Comparative Examples 1 and 2, the addition was rapid and in one step. In Example 1, bittern with a pH of 6.2 was added to weakly alkaline ammonia water with a pH less than or equal to 12 to maintain the overall pH at 12 or lower, thereby achieving high-purity magnesium hydroxide. However, Comparative Examples 1 and 2 were both strongly alkaline with a pH greater than 12.2, resulting in calcium hydroxide precipitation (e.g. Figure 1 As shown in the figure, it is impossible to avoid the introduction of impurities.

[0061] Therefore, based on the results of computer simulation in this invention, which show a pH range of 8.8 ≤ pH ≤ 12.2, the following experiment was further performed on refined bittern to selectively induce only magnesium (Mg) ion precipitation, in which the concentration of alkaline substances and the injection rate were used as variables.

[0062] <Example 2> The refined bittern was purified using the same method as in Example 1. 1L (1.25kg) of bittern with a pH of 6.2 was added to a 3L beaker equipped with a pH meter and stirred at 300rpm. Simultaneously, 9wt% ammonia (NH4OH) was rapidly added as a precipitant (as in Example 1). That is, the ammonia concentration in Example 2 was 9wt%, three times higher than the approximately 3.4wt% concentration in Example 1. The pH was monitored using the pH meter installed in the beaker, and a precipitation reaction was carried out for 2 hours. Magnesium hydroxide powder was prepared using the same method as in Example 1, and component analysis was performed using the same method as in Example 1. The results are shown in Table 4. The pH changes during the precipitation reaction are as follows: Figure 2 As shown. In addition, the process flow diagram for the manufacture of magnesium hydroxide is as follows: Figure 4 As shown.

[0063] <Example 3> The refined bittern was purified using the same method as in Example 1. 1L (1.25kg) of refined bittern with a pH of 6.2 was added to a 3L beaker equipped with a pH meter, and the mixture was stirred at 300rpm. Simultaneously, a 25wt% sodium hydroxide (NaOH) aqueous solution (concentration three times or higher than the 8wt% sodium hydroxide concentration in Example 2) was added as a precipitant over a sufficient period of 30 minutes using a metering pump. The pH was then monitored using the installed pH meter, and a precipitation reaction was carried out for 1 hour. Magnesium hydroxide powder was prepared using the same method as in Example 1, and component analysis was performed using the same method as in Example 1. The results are shown in Table 4. Furthermore, the pH changes during the precipitation reaction are as follows: Figure 3 As shown. In addition, the process flow diagram for the manufacture of magnesium hydroxide is as follows: Figure 4 As shown.

[0064] In the preferred embodiment 2 of the present invention, when a weakly alkaline ammonia solution with a concentration of 9 wt% as a precipitant is added rapidly at one time, the pH of the reaction system during the precipitation reaction is maintained at 9.1 ≤ pH ≤ 9.4, which is within the range of 8.8 ≤ pH ≤ 12.2 derived by computer simulation, and the CaO impurity content is less than or equal to 0.15 wt%, ultimately producing high-purity magnesium hydroxide with a purity of 99.49%.

[0065] In the preferred embodiment 3 of the present invention, when 25 wt% of strongly alkaline sodium hydroxide as a precipitant is slowly and quantitatively added over 30 minutes at a rate of 65 ml / min using a metering pump, the pH of the reaction system during the precipitation reaction is maintained at 9.1 ≤ pH ≤ 9.6, which is within the range of 8.8 ≤ pH ≤ 12.2 derived from computer simulation, and the CaO impurity content is less than or equal to 0.23 wt%, ultimately producing high-purity magnesium hydroxide with a purity of 99.18%. In Comparative Example 2, low-purity magnesium hydroxide was produced when sodium hydroxide was added rapidly, while in this Example 3, despite being strongly alkaline, high-purity magnesium hydroxide can be produced by slow addition.

[0066] That is, when adding alkaline substances, high-purity magnesium hydroxide can be obtained by slowly adding them or adding them over 15 to 60 minutes to keep the pH of seawater or refined bittern at 12.2 or lower.

[0067] Table 4 ※Mg(OH)2 (wt%) = 100 - (content of elements detected by XRF analysis) (wt%) As mentioned above, the technology of selectively precipitating magnesium ions in complex systems containing multi-component metal salts, such as seawater, bittern, and brine, through chemical equilibrium computer simulation is beneficial for simplifying the manufacturing process of high-purity magnesium materials with improved purity and reducing manufacturing costs.

[0068] The present invention has been described in detail above through preferred embodiments. However, the present invention is not limited to the above embodiments, and those skilled in the art can make various modifications thereto.

Claims

1. A method for producing high-purity magnesium hydroxide from seawater or refined bittern, comprising: a) Purification step, filtering out organic and inorganic impurities contained in seawater or refined bittern; b) In the precipitation step, within a range calculated by computer simulation using chemical equilibrium, the hydrogen ion concentration index (pH) of the seawater or refined bittern is calculated. Based on this, the amount of alkaline substance corresponding to the hydrogen ion concentration index is determined and added to the seawater or refined bittern after the purification step, thereby selectively precipitating only magnesium ions to form magnesium hydroxide; and c) Drying step: Drying the magnesium hydroxide.

2. The method according to claim 1, characterized in that, Step b) is performed at room temperature.

3. The method according to claim 1, characterized in that, The following steps are further included after step b): b-2) Filtration step, wherein the magnesium hydroxide formed after the precipitate is separated into solid and liquid components by a filter; and b-3) Washing step: Wash the magnesium hydroxide after solid-liquid separation with ion-exchanged water.

4. The method according to claim 3, characterized in that, The filter has a pore size greater than 0 and less than or equal to 1 μm.

5. The method according to claim 4, characterized in that, The filter has a pore size greater than 0 and less than or equal to 0.45 μm.

6. The method according to claim 1, characterized in that, If the alkaline substance is added at a rate that maintains the pH of the refined bittern or seawater at 12.2 or less, the alkaline substance comprises at least one selected from the group consisting of ammonium hydroxide, sodium hydroxide, and hydroxides of calcined limestone or calcined dolomite.

7. The method according to claim 1, characterized in that, If the alkaline substance is added at an unrestricted rate, the alkaline substance includes ammonium hydroxide.

8. The method according to claim 6 or claim 7, characterized in that, The concentration range of the alkaline substance is 3.4 wt% to 25 wt%.

9. The method according to claim 1, characterized in that, The hydrogen ion concentration index of the seawater or refined bittern, calculated by computer simulation of chemical equilibrium, ranges from 8.8 to 12.

2.

10. The method according to claim 1, characterized in that, The alkaline substance is added while maintaining the hydrogen ion concentration index of refined bittern, calculated by computer simulation of chemical equilibrium, in the range of 9.0 to 11.

5.

11. The method according to claim 1, characterized in that, Magnesium hydroxide is filtered by solid-liquid separation using a filter that includes a centrifugal filter.

12. The method according to claim 1, characterized in that, Magnesium hydroxide is washed through a filter that includes a centrifugal filter.

13. The method according to claim 1, characterized in that, The computer simulation of chemical equilibrium includes the following steps: Select chemical species from seawater or refined bittern that are predicted to participate in the reaction; Enter the concentration of the chemical species; Calculate and input the ionic strength of the chemical species; Calculate and input the equilibrium constant of the chemical species; and Calculate the equilibrium concentration and hydrogen ion concentration index of seawater or refined bittern.

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