Method for preparing high-purity magnesium hydroxide from by-products of refined salt preparation process by using chemical equilibrium simulation

Abstract

The present invention relates to a method for preparing high-purity magnesium hydroxide from by-product waste (hereinafter, sea bittern of refined salt) of a refined salt preparation process, and provides a method for preparing high-purity magnesium hydroxide from seawater or sea bittern of refined salt, the method comprising: (a) a purification step of filtering out organic and inorganic impurities contained in seawater or sea bittern of refined salt; (b) a precipitation step of adding an alkali material to the seawater or sea bittern of refined salt, that passed through the purification step, and calculating the hydrogen ion concentration index (pH) of the seawater or sea bittern of refined salt within a range calculated by means of a chemical equilibrium simulation, so as to determine, on the basis thereof, the amount of the alkali material that corresponds to the hydrogen ion concentration index (pH), and adding same to the seawater or sea bittern of refined salt so as to selectively precipitate only magnesium (Mg) ions, thereby forming magnesium hydroxide (Mg(OH)2); and (c) a drying step of drying washed magnesium hydroxide.

Description

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

[0001] The present invention relates to a method for producing high-purity magnesium hydroxide from by-product waste (hereinafter, refined salt brine) of a refined salt manufacturing process using computer simulation. More specifically, the present invention relates to a method for producing high-purity magnesium hydroxide (Mg(OH)2) by selectively precipitating only magnesium (Mg) ions by adding an alkaline substance containing a hydroxyl group (OH) including at least one selected from among hydroxides of ammonium hydroxide, sodium hydroxide, and decarboxylated limestone / dolomite to the purified salt brine, which is generated as a by-product in the process of electrochemically recovering salt (hereinafter, refined salt), to the purified salt brine during the stirring process.

[0002] Magnesium hydroxide is used in a variety of fields, including environmental applications such as water treatment, desulfurization, and soil amendments; pharmaceutical applications such as antacids; animal feed; and as a receptor in chemical processes requiring chemical resistance. Magnesium hydroxide, particularly for flame retardant applications in wire coverings, requires high purity. Demand for high-purity magnesium hydroxide, a raw material for electronic and optical materials utilizing its insulating and dielectric properties, is also growing.

[0003] The main natural resources that serve as raw materials for these magnesium hydroxides and oxides include magnesite (MgCO3), brucite (Mg(OH)2), and seawater, sea bittern, or brine. Natural minerals such as magnesite and brucite have the advantage of being easily manufactured through simple processes such as heat treatment and grinding, but it is difficult to remove impurities inherent in the minerals, such as iron (Fe2O3), alumina (Al2O3), and silicon dioxide (SiO2), making it difficult to manufacture high-purity magnesium hydroxide and magnesium oxide. On the other hand, seawater or sea bittern or brine, which are 20 to 30 times more concentrated than seawater, have a very low content of the above-mentioned impurities, making it easy to manufacture high-purity magnesium hydroxide and magnesium oxide.

[0004] Conventional high-purity magnesium hydroxide has low solubility (9.6×10 -4 g / 100mL H2O, 20℃) is added to seawater, brine and salt water, and at least one alkaline substance containing a hydroxyl group (OH) selected from among ammonium hydroxide, sodium hydroxide and hydroxides of decarboxylated limestone / dolomite is added. In addition, a method of using magnesium chloride as a magnesium source and adding the alkaline substance thereto to produce high-purity magnesium hydroxide is also widely practiced.

[0005] However, these seawater, brine and salt water are complex systems composed of more than four components, including magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), sodium chloride (NaCl) and water (H2O), and the biggest problem in producing high-purity magnesium hydroxide from them is as follows.

[0006] The pH range formed during the process of precipitating magnesium (Mg) ions into hydroxide by adding hydroxyl groups (OH) is similar to the pH range in which a large amount of calcium (Ca) ions coexisting in seawater, brine, and salt water can cause precipitation. As a result, calcium (Ca) ions have low solubility (0.17 g / 100 mL H2O, 20℃) in the pH range, and calcium hydroxide (Ca(OH)2) precipitates simultaneously with magnesium hydroxide. In this situation, it is difficult to control calcium (Ca) impurities mixed into magnesium hydroxide.

[0007] Research on methods to improve these problems has been conducted in various ways, and patent document 1 discloses a method of selectively removing calcium (Ca) ions in the form of insoluble gypsum dihydrate (CaSO4·2H2O, solubility 0.26 g / 100 mL H2O, 20°C) by adding sulfuric acid to the effluent from a refined salt manufacturing process containing a large amount of calcium (Ca) ions and magnesium (Mg) ions simultaneously.

[0008] In addition, Patent Document 2 discloses a method for recovering magnesium components by precipitating magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl) contained in brine in the form of carnallite (KCl·MgCl2·6H2O) by adjusting the molar ratio of potassium chloride and magnesium chloride to 0.8 to 1.1. However, this method also has a problem in that the load in the washing process increases because potassium chloride (KCl), which must be ultimately removed by washing to increase the purity of magnesium hydroxide in order to form carnallite (KCl·MgCl2·6H2O), must be added.

[0009] The pH range, which is a key indicator for selectively recovering magnesium components from complex systems containing four or more components, such as seawater, brine, and salt water, can be referenced to the Eh-pH (aka Pourbaix) diagram, which shows the relationship between pH and the potential at which metal ions in an aqueous solution thermodynamically exist stably. However, this is for cases where a single component exists in an aqueous solution, and there is a problem in that accurate quantitative application is difficult in cases where four or more chemical species coexist, such as seawater and refined salt brine.

[0010] The present invention has been made to solve the above problems, and the purpose of the present invention is to provide a method for rapidly producing high-purity magnesium hydroxide (Mg(OH)2) by selectively precipitating only magnesium (Mg) ions, by adding an alkaline substance containing a hydroxyl group (OH) to purified salt brine, which is a complex system containing magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl), etc., which is generated as a by-product in the process of electrochemically recovering salt from seawater, and determining the pH range of the seawater or purified salt brine containing the added alkaline substance, and deriving the ionic strength based on the accurate concentrations of four or more kinds of metal salts contained in the purified salt brine, and adding an amount of an alkaline substance in a range corresponding to the pH range determined within the range calculated by chemical equilibrium computational simulation, to the purified salt brine while stirring, thereby excluding the construction of complex equipment or the performance of complex intermediate processes.

[0011] In order to achieve the above object, the present invention provides a method for producing high-purity magnesium hydroxide from seawater or purified salt brine, characterized by comprising: (a) a purification step of filtering organic and inorganic impurities contained in seawater or purified salt brine; (b) a precipitation step of adding an alkaline substance to the seawater or purified salt brine that has undergone the purification step, calculating the pH of the seawater or purified salt brine within a range calculated by a chemical equilibrium computational simulation, and determining the amount of the alkaline substance to be added corresponding to the pH based on the pH, and adding this to the seawater or purified salt brine to selectively precipitate only magnesium (Mg) ions to form magnesium hydroxide (Mg(OH)2); and (c) a drying step of drying the magnesium hydroxide.

[0012] It is preferable that the above step (b) be performed at room temperature.

[0013] After the above step (b), it is preferable to further include a (b-2) filtering step of separating the magnesium hydroxide formed by the precipitation into solid and liquid through a filter; and a (b-3) washing step of washing the magnesium hydroxide separated from solid and liquid with ion-exchanged water.

[0014] It is preferable that the above filter have a pore size of more than 0 and less than 1㎛.

[0015] It is preferable that the above filter have a pore size of greater than 0 and less than 0.45㎛.

[0016] If the alkaline substance is added at a rate such that the pH of the purified salt water or seawater is maintained at 12.2 or lower, the alkaline substance may be ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and hydrate of decarboxylated limestone or dolomite (Ca(OH) 2· It is preferable to include at least one selected from the group consisting of Mg(OH)2).

[0017] If the alkaline substance is added without speed limitation, it is preferable that the alkaline substance includes ammonium hydroxide (NH4OH).

[0018] It is preferable that the concentration of the above alkaline substance is in the range of 3.4 to 25 wt%.

[0019] It is preferable that the pH range of the seawater or purified salt brine calculated by chemical equilibrium simulation be 8.8 to 12.2.

[0020] It is preferable to add the alkaline substance so that the pH calculated by the chemical equilibrium simulation of the purified salt brine is maintained in the range of 9.0 to 11.5.

[0021] It is preferable to filter magnesium hydroxide (Mg(OH)2) by separating solid and liquid through a filter including a centrifugal filter.

[0022] It is preferable to wash magnesium hydroxide (Mg(OH)2) through a filter including a centrifugal filter.

[0023] The above chemical equilibrium computer simulation preferably includes the steps of: selecting a chemical species expected to participate in a reaction among seawater or purified salt brine; 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 purified salt brine.

[0024] According to the present invention, in the process of electrochemically recovering salt (purified salt) from seawater, an alkaline substance containing a hydroxyl group (OH) is added to a complex system of purified salt brine containing magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl), which is generated as a by-product, and the pH range of the seawater or purified salt brine containing the added alkaline substance needs to be determined, and the ionic strength is derived based on the exact concentrations of four or more kinds of metal salts contained in the purified salt brine, and an amount of the alkaline substance in a range corresponding to the pH range determined within the range calculated by chemical equilibrium computational simulation is added to the purified salt brine while being stirred, thereby selectively precipitating only magnesium (Mg) ions without constructing complex equipment or performing complex intermediate processes, thereby enabling the rapid production of high-purity magnesium hydroxide (Mg(OH)2).

[0025] Figure 1 is a graph showing the results of a computer simulation of the stability of each chemical species according to the pH of the chemical species contained in the purified salt solution according to one embodiment of the present invention.

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

[0027] Figure 3 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 is a process flow diagram for manufacturing high-purity magnesium hydroxide according to Example 3 of the present invention.

[0029] Figure 5 is a flowchart illustrating the equilibrium concentration and pH simulation for the production of high-purity magnesium hydroxide according to one embodiment of the present invention. In the present invention, the simulation was performed at room temperature (25°C) and atmospheric pressure. The equilibrium constant was determined using the database built into the simulation software at room temperature and pressure.

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the following embodiments are provided to enable those of ordinary skill in the art to fully understand the present invention. They may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0031]

[0032] When it is said in the detailed description or claims of an invention that one component "includes" another component, this is not to be construed as being limited to that component alone, unless specifically stated to the contrary, and should be understood to mean that it may further include other components.

[0033]

[0034] FIG. 1 is a graph showing the results of a computer simulation of the stability of each chemical species according to the pH of the chemical species contained in the purified salt brine according to an embodiment of the present invention, FIG. 2 is a graph showing the change in pH during a precipitation reaction upon addition of ammonia water according to an embodiment of the present invention, FIG. 3 is a graph showing the change in pH during a precipitation reaction upon addition of sodium hydroxide according to an embodiment of the present invention, FIG. 4 is a process flow chart for manufacturing high-purity magnesium hydroxide according to an embodiment of the present invention, and FIG. 5 is a computer simulation flow chart of equilibrium concentration and pH for manufacturing high-purity magnesium hydroxide according to an embodiment of the present invention.

[0035]

[0036] Refined salt brine is a multicomponent complex substance composed of at least four types of metal salts, including magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), sodium chloride (NaCl), and water (H2O).

[0037] The present invention provides a method for producing high-purity magnesium hydroxide from refined salt brine, including: a purification step of filtering and removing organic impurities such as microorganisms and inorganic impurities such as fine sand floating in refined salt brine, which is a by-product of a refined salt manufacturing process; a precipitation step of adding an appropriate amount of an alkaline substance containing a hydroxyl group (OH) at room temperature to the refined salt brine while being stirred, within a range of a pH calculated by a chemical equilibrium simulation, to selectively precipitate only magnesium (Mg) ions in the form of magnesium hydroxide (Mg(OH)2); a filtering step of separating the precipitated magnesium hydroxide into solid and liquid through a filter; a washing step of washing the solid-liquid-separated magnesium hydroxide with ion-exchanged water; and a drying step of drying the washed magnesium hydroxide.

[0038] In addition, the filter for filtering impurities is used to filter out organic impurities such as microorganisms floating in seawater and inorganic impurities such as fine sand, and preferably has a pore size of 1 ㎛ or less, and a membrane filter having a pore size of 0.45 ㎛ or less is more preferable.

[0039] In addition, the alkaline substance containing a hydroxyl group (OH) may be a substance containing at least one hydroxyl group (OH) among ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and hydroxides of decarboxylated limestone or decarboxylated dolomite (Ca(OH)2 / Mg(OH)2). At this time, the concentration of the aqueous solution of the alkaline substance is preferably 3.4 to 25 wt%. When the concentration of the alkaline substance is 3.4 wt% or less, the volume of the vessel for the precipitation process becomes too large compared to the production yield, which lowers the productivity, and when the concentration of the alkaline substance is 25 wt% or more, the viscosity of the reaction solution becomes too high, so the stirring speed must be increased to at least 500 rpm or more, which is a problem in that the load on the reaction stirring device becomes too high.

[0040] In addition, in a special aqueous solution system composed of four or more alkaline / alkaline earth metal salts, the calculation of the pH range for selectively precipitating only magnesium (Mg) ions in the form of magnesium hydroxide (Mg(OH)2) can be performed using the MEDUSA-HYDRA program developed by the Royal Institute of Technology in Sweden or other commercial aqueous solution-based chemical equilibrium simulation software. In addition, in the case of the purified salt brine, the pH range calculated by the chemical equilibrium simulation is preferably 8.8≤pH≤12.2, and more preferably 9.0≤pH≤11.5.

[0041] In addition, although a filter having a conventional filter can be used for filtration of the precipitated magnesium hydroxide, it is more preferable to use a continuous centrifugal filter having a relative centrifugal force (G-force) of 250 or more, which can continuously perform filtration of the precipitation reaction filtrate and subsequent washing process.

[0042] In addition, the washing of the magnesium hydroxide separated from the high-liquid phase naturally increases the impurity removal rate as the amount of ion-exchange water used increases, but considering the trade-off between the washing process time and cost and the final purity, it is preferable to wash with ion-exchange water that is within 20 times the amount of dried magnesium hydroxide (Mg(OH)2) expected to be obtained.

[0043]

[0044] In the graph of Figure 1, 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, in order to prevent mixing due to precipitation of calcium hydroxide, the pH value during the precipitation reaction must be maintained in the range of 8.8 to 12.2.

[0045]

[0046] In a preferred embodiment of the present invention, the results of component analysis of the purified salt brine and seawater used are compared and shown in Table 1. The Mg / Ca ion ratios in the seawater and purified salt brine are 3.25 and 2.36, respectively, indicating a high content of Ca ions. Due to this high content of Ca ions, when magnesium (Mg) ions are selectively precipitated by controlling the pH, a large amount of calcium (Ca) ions coexisting with the magnesium (Mg) ions have a low solubility (0.17 g / 100 mL H2O, 20°C) in a range similar to the pH range corresponding to the magnesium (Mg) ions. Therefore, when magnesium hydroxide (Mg(OH)2) is precipitated, calcium hydroxide (Ca(OH)2) is simultaneously precipitated, resulting in the mixing of calcium (Ca) impurities into the magnesium hydroxide, and there is a problem in that it is difficult to control these impurities.

[0047]

[0048] Item Purification Salt Water pH 6.2 7.9 Specific Gravity [g / cc] 1.25 1.02 Ion Content [%] Cl - 18.723.00K + 3.560.04Mg 2+ 3.310.13Na + 2.481.07Ca 2+ 1.400.04SO4 2- 0.050.27Mg 2+ / Ca 2+ 2.363.25Total 29.523.48Content by compound [%]MgCl212.980.92KCl6.780.06NaCl6.312.03CaCl23.810.13CaSO40.07-Total 29.953.14

[0049]

[0050] The precipitation reaction to selectively precipitate only magnesium (Mg) ions in the form of magnesium hydroxide (Mg(OH)2) can occur as follows: either only Mg ions are precipitated (Reaction Scheme 1) or both Mg and Ca ions are precipitated simultaneously (Reaction Scheme 2), depending on the hydrogen ion concentration index (pH) of the precipitation reaction system.

[0051]

[0052] [Reaction Scheme 1: For appropriate pH by adding precipitants NaOH and NH4OH]

[0053] Mg 2+ (+Ca 2+ (Contained in the water) + (Precipitant) + Cl - → Mg(OH)2↓ + CaCl2(aq)

[0054] [Reaction Scheme 2: In case of high pH due to excessive addition of precipitants NaOH and NH4OH]

[0055] Mg 2+ (+Ca 2+ (Contained in the water) + (Precipitant) + Cl - → Mg(OH)2↓ + Ca(OH)2↓

[0056] Here, ↓ represents precipitation, and (aq) represents a dissolved state in an aqueous solution.

[0057]

[0058] In a preferred embodiment of the present invention, in a complex aqueous solution composed of four or more kinds of alkaline / alkaline earth metal salts including magnesium chloride (MgCl2), calcium chloride (CaCl2), potassium chloride (KCl), and sodium chloride (NaCl), the calculation of the pH range for selectively precipitating only magnesium (Mg) ions in the form of magnesium hydroxide (Mg(OH)2) was performed using the MEDUSA-HYDRA program (developed by the Royal Institute of Technology, Sweden) for chemical equilibrium computational simulation. However, general commercial software for the purpose of aqueous solution-based chemical equilibrium computational simulation that assumes accurate input of the concentrations of all participating ions in the system may also be used.

[0059] In the case of refined salt brine, the ionic strength based on the participating ionic species and concentration is calculated based on Equation 1, and the results calculated using a computer simulation program based on this are shown in Table 2, and the results calculated using a computer simulation program based on this are shown in Fig. 1. The pH range calculated by the chemical equilibrium computer simulation was derived as 8.8≤pH≤12.2, but it is preferably 9.0≤pH≤11.5. That is, it is good to add an alkaline substance while monitoring the concentration range of seawater or refined salt brine to which an alkaline substance has been added in the range of 8.8≤pH≤12.2 and preferably 9.0≤pH≤11.5.

[0060] [Equation 1: Calculation of ionic strength]

[0061]

[0062] Here, ci is the molar concentration of ion i, z i is the charge of ion species i

[0063]

[0064] Item MgCaNaKClOHc (molar concentration) 1.089 0.279 3.042 0.946 4.224 2.179 z (charge) +2+2+1+1-1-1 Ionic strength 0.161

[0065]

[0066] Ionic strength is defined as the product of the molar concentration of an ion and its charge, and is generally a physical quantity proportional to the concentration of a chemical species dissolved in an aqueous solution. As the ionic strength value increases, the reaction rate increases, the optimum pH decreases, and it is a factor that affects the solubility of the corresponding metal ion species existing in an aqueous solution. In a typical chemical equilibrium simulation, an ideal solution, an infinite dilution solution (ionic strength = 0), is assumed for calculation. Therefore, in the target system of the present invention, the calculation of the ionic strength based on the exact concentration and charge of cations and anions other than magnesium (Mg) ions is a very important factor in the accurate computational simulation of the system. In addition, an important input value in the chemical equilibrium simulation is temperature, and in the present invention, 25℃, which is close to room temperature, is assumed. The process of the chemical equilibrium simulation according to the present invention is shown in Fig. 5.

[0067] As illustrated in FIG. 5, the chemical equilibrium simulation includes the steps of selecting chemical species expected to participate in a reaction among seawater or purified salt brine; 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 purified salt brine.

[0068] The chemical species participating in the reaction are cations and anions, and the cation is Mg 2+ , Ca 2+ and the anion is OH - , Cl - The temperature and pressure were maintained at room temperature (25℃) and atmospheric pressure (1 atm).

[0069]

[0070] To verify the results of this chemical equilibrium computer simulation, the following experiment was performed in which brine was rapidly added to a precipitant solution of a given concentration at once.

[0071]

[0072] <Example 1>

[0073] 1 liter (~1.25 kg) of purified brine having a pH of 6.2 was filtered through a membrane filter with a pore size of 0.45 ㎛ or less to remove organic impurities such as floating microorganisms and inorganic impurities such as fine sand. 2 M (3.4 wt% concentration) ammonia water (NH4OH) as a precipitant was injected into a 3 L beaker equipped with a pH meter, and the amount of purified brine calculated according to the stoichiometric composition purified by the above method was quickly added at once while stirring at a speed of 300 rpm, and the pH before and 2 hours after adding the brine was measured using the equipped pH meter. After 2 hours of precipitation reaction, stirring was stopped, and the precipitation reaction solution was filtered through a centrifugal filter. Then, ion-exchanged water of 20 times the weight of the expected amount of magnesium hydroxide (Mg(OH)2) to be obtained was injected, and the magnesium hydroxide filtered through the centrifugal filter was immediately washed, and the magnesium hydroxide powder was finally manufactured by drying at 105℃ for 16 hours or more. The results of component analysis performed using X-ray fluorescence analysis are shown in Table 3.

[0074] "Added quickly" means "added the entire amount at once." The addition speed is typically the speed of pouring water into a cup, and the key point is that it was added in one go. The same applies below.

[0075]

[0076] <Comparative Example 1>

[0077] Magnesium hydroxide powder was prepared in the same manner as in Example 1, except that 2M sodium hydroxide (NaOH) was used as a precipitant, and the results of component analysis are shown in Table 3. The key point of the experiment is that it was “added quickly.”

[0078]

[0079] Comparative Example 2

[0080] A composite oxide (CaO·MgO) powder obtained by heat-treating dolomite (Ca·Mg(CO3)2) from Yeongwol Mountain, Gangwon-do at 950℃ for 1 hour was added to ion-exchanged water stirred at 300 rpm to prepare a 5 wt% composite hydroxide (Ca(OH)2·Mg(OH)2) slurry, which was used as a precipitant. Magnesium hydroxide powder was prepared in the same manner as in Example 1, and the results of component analysis are shown in Table 3. The key point of the experiment here is that it was "added quickly."

[0081]

[0082] Item Example 1 Comparative Example 1 Comparative Example 2 Precipitant 2 M-NH4OH 2 M-NaOH 5%-Ca·Mg(OH) 2 Initial pH 11.8 14.0 12.5 pH after 2 hours of reaction 11.0 13.8 12.0 Chemical composition (%) Mg(OH) 2 99.1 96.9 94.7 CaO 0.02.8 4.1 SiO 2 0.00.00.2 Al 2 O 3 0.00.20.2 Fe 2 O 3 0.00.00.1 Na 2 O 0.00.10.0 K 2 O 0.10.00.0

[0083] ※ Mg(OH)2(wt%) = 100 - (content of elements detected through XRF analysis)(wt%)

[0084]

[0085] In Example 1 and Comparative Examples 1 and 2 of the present invention, when weakly alkaline ammonia water was used as a precipitant, the pH during the precipitation reaction was 11.0 after 2 hours from the initial pH of 11.8, and as a result of maintaining the pH during the entire precipitation reaction within the range of 8.8≤pH≤12.2 as a result of computer simulation, it was possible to produce high-purity magnesium hydroxide with a Mg(OH)2 concentration of 99.1% and CaO of 0.05% (500 ppm) or less.

[0086] On the other hand, when sodium hydroxide (NaOH), which is strongly alkaline, was used as a precipitating agent, the pH during the precipitation reaction was 13.8 after 2 hours from the initial pH of 14.0, which was higher than the alkaline range of 8.8≤pH≤12.2 derived from the computer simulation during the entire precipitation reaction, and as a result, low-purity magnesium hydroxide containing impurities was produced with a Mg(OH)2 concentration of 96.9% and CaO of 2.8%.

[0087] In addition, when the strongly alkaline decarboxylated dolomite hydrate (Ca(OH)2·Mg(OH)2) was used as a precipitant, the pH during the precipitation reaction was 12.0 after 2 hours from the initial pH of 12.5, and the pH in most of the precipitation reaction except after 2 hours was maintained in an alkaline range higher than the computer simulation result of 8.8≤pH≤12.2, resulting in the production of low-purity magnesium hydroxide with an Mg(OH)2 concentration of 94.7% and CaO of 4.1%.

[0088] In particular, in the case of dolomite hydrate (Ca(OH)2·Mg(OH)2), the CaO component showed a higher value than when sodium hydroxide was used as a precipitant due to the influence of the Ca(OH)2 component added simultaneously as an inherent component of dolomite, and the purity was lower than when sodium hydroxide was used as a precipitant due to the mixing of iron oxide (Fe2O3), which is an impurity inherent in dolomite mineral.

[0089] Comparative Examples 1 and 2 illustrate that the key is not whether the alkali is strong or weak, but whether it is added quickly or slowly, as described below. In particular, the purpose of these examples is to illustrate that strong alkali should not be added quickly, as rapid addition of strong alkali can result in low purity magnesium hydroxide, as described below.

[0090] In Example 1 and Comparative Examples 1 and 2, all were added quickly at once. In Example 1, it was possible to achieve high purity of magnesium hydroxide by adding brine with a pH of 6.2 to ammonia water, which is weakly alkaline with a pH of 12 or less, to maintain the overall pH at 12 or less. However, in Comparative Examples 1 and 2, both were strong alkaline with a pH exceeding 12.2, and it was impossible to avoid mixing in impurities due to calcium hydroxide precipitating according to FIG. 1.

[0091] Accordingly, based on the range of 8.8≤pH≤12.2, which is the result of the computer simulation of the present invention, the following experiment was additionally performed on purified salt brine to selectively induce precipitation of only magnesium (Mg) ions, and the experiment was performed with the concentration and injection speed of the alkaline substance as variables.

[0092]

[0093] <Example 2>

[0094] Purification of the refined brine was performed in the same manner as in Example 1. 1 L (1.25 kg) of brine with a pH of 6.2 was placed in a 3 L beaker equipped with a pH meter, and 9 wt% ammonia water (NH4OH) was quickly added at once as a precipitating agent while stirring at a speed of 300 rpm as in Example 1. That is, the concentration of ammonia water was approximately 3.4 wt% in Example 1, and the experiment was performed in Example 2 with 9 wt%, which is about three times higher. Magnesium hydroxide powder was manufactured in the same manner as in Example 1, except that the precipitation reaction was performed for 2 hours while observing the pH with a pH meter equipped on the beaker. The results of component analysis performed in the same manner as in Example 1 are shown in Table 4, and the change in pH during the precipitation reaction is shown in Fig. 2. In addition, a flow chart of the magnesium hydroxide manufacturing process is shown in Fig. 4.

[0095]

[0096] <Example 3>

[0097] Purification of the refined brine was performed in the same manner as in Example 1. 1 L (1.25 kg) of the refined brine having a pH of 6.2 was placed in a 3 L beaker equipped with a pH meter, and while stirring at a speed of 300 rpm, a 25 wt% sodium hydroxide (NaOH) aqueous solution (more than three times higher concentration than the 8 wt% sodium hydroxide concentration of Comparative Example 2) as a precipitant was injected through a quantitative pump over a period of 30 minutes at sufficient intervals. Afterwards, the pH was observed with the equipped pH meter and the precipitation reaction was performed for 1 hour, and except that magnesium hydroxide powder was manufactured in the same manner as in Example 1, and component analysis was performed in the same manner. The results are shown in Table 4. The pH change during the precipitation reaction is shown in Fig. 3. In addition, a flow chart of the magnesium hydroxide manufacturing process is shown in Fig. 4.

[0098]

[0099] In a preferred embodiment 2 of the present invention, the pH of the reaction system during the precipitation reaction in which 9 wt% weakly alkaline ammonia water as a precipitant was rapidly added at once was maintained at 9.1 ≤ pH ≤ 9.4, which is within 8.8 ≤ pH ≤ 12.2 as a result of computer simulation, and as a result, it was possible to produce high-purity magnesium hydroxide with a purity of 99.49% with a CaO impurity component of 0.15 wt% or less.

[0100] In a preferred embodiment 3 of the present invention, the pH of the reaction system during the precipitation reaction in which 25 wt% of strongly alkaline sodium hydroxide as a precipitant was slowly quantitatively added at a rate of 65 ml / min over 30 minutes using a quantitative pump was maintained at 9.1 ≤ pH ≤ 9.6, which is within the range of 8.8 ≤ pH ≤ 12.2 derived from the computer simulation, and as a result, it was possible to produce high-purity magnesium hydroxide with a purity of 99.18% with a CaO impurity component of 0.23 wt% or less. In Comparative Example 2, when sodium hydroxide was rapidly added, low-purity magnesium hydroxide was produced, whereas in this Example 3, high-purity magnesium hydroxide was produced despite the strong alkali by adding it slowly.

[0101] That is, when adding an alkaline substance, high-purity magnesium hydroxide could be obtained by adding the alkaline substance slowly or over a period of 15 to 60 minutes so as to maintain the pH of seawater or purified salt water at 12.2 or lower.

[0102]

[0103] Item Example 2 Example 3 Precipitant 9%-NH4OH 25%-NaOH Initial pH 6.366.39 pH 9.129.59 after 1.5 hours of reaction Chemical composition (%) Mg(OH) 2 99.4999.18 CaO 0.150.23 SiO 2 0.050.04 Al 2 O 3 0.020.01 Fe 2 O 3 0.070.02 Na 2 O 0.080.18 K 2 O 0.140.34

[0104] ※ Mg(OH)2(wt%) = 100 - (content of elements detected through XRF analysis)(wt%)

[0105]

[0106] This technology for selectively precipitating only magnesium (Mg) ions in complex systems containing multi-component metal salts, such as seawater, brine, and salt water, utilizing chemical equilibrium simulations will contribute to simplifying the manufacturing process of high-purity magnesium-containing materials with improved purity and reducing manufacturing costs.

[0107] Above, the preferred embodiments of the present invention have been described in detail, but the present invention is not limited to the above embodiments, and various modifications are possible by those skilled in the art.

Claims

1. (a) A purification step for filtering out organic and inorganic impurities contained in seawater or refined salt water; (b) a precipitation step of adding an alkaline substance to seawater or refined salt brine that has undergone the above purification step, calculating the pH of the seawater or refined salt brine within a range calculated by chemical equilibrium simulation, and determining the amount of the alkaline substance to be added corresponding to the pH based on this, and adding this to seawater or refined salt brine to selectively precipitate only magnesium (Mg) ions to form magnesium hydroxide (Mg(OH)2); and (c) a drying step of drying the magnesium hydroxide; A method for producing high-purity magnesium hydroxide from seawater or refined salt water, characterized in that it comprises:

2. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or refined salt water, characterized in that the step (b) is performed at room temperature.

3. In paragraph 1, After step (b) above, (b-2) A filtration step for separating the magnesium hydroxide formed by the above precipitation into solid and liquid through a filter; (b-3) A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that it further includes a washing step of washing the high-purity separated magnesium hydroxide with ion-exchange water.

4. In paragraph 3, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the filter has a pore size of more than 0 and less than 1 ㎛.

5. In paragraph 4, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the filter has a pore size of more than 0 and less than 0.45㎛.

6. In paragraph 1, If the alkaline substance is added at a rate such that the pH of the purified salt water or seawater is maintained at 12.2 or lower, the alkaline substance is ammonium hydroxide (NH4OH), sodium hydroxide (NaOH), and hydrate of decarboxylated limestone or dolomite (Ca(OH)). 2· A method for producing high-purity magnesium hydroxide from seawater or purified salt brine, characterized in that it contains at least one selected from the group consisting of Mg(OH)2).

7. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the alkaline substance includes ammonium hydroxide (NH4OH) when the alkaline substance is added without limitation on speed.

8. In paragraph 6 or 7, A method for producing high-purity magnesium hydroxide from seawater or refined salt brine, characterized in that the concentration of the alkaline substance is in the range of 3.4 to 25 wt%.

9. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the pH range of the seawater or purified salt water calculated by chemical equilibrium simulation is 8.8 to 12.

2.

10. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or refined salt brine, characterized in that the method of adding the alkaline substance is such that the hydrogen ion concentration index (pH) calculated by the chemical equilibrium simulation of the refined salt brine is maintained in the range of 9.0 to 11.

5.

11. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the filtration of magnesium hydroxide (Mg(OH)2) is performed by separating solid and liquid through a filter including a centrifugal filter.

12. In paragraph 1, A method for producing high-purity magnesium hydroxide from seawater or purified salt water, characterized in that the washing of magnesium hydroxide (Mg(OH)2) is performed through a filter including a centrifugal filter.

13. In paragraph 1, The above chemical equilibrium simulation is, A step for selecting chemical species expected to participate in the reaction among seawater or refined salt water; A step of inputting the concentration of the above chemical species; A step of calculating and inputting the ionic strength of the above chemical species; A step of calculating and inputting the equilibrium constant of the above chemical species; and A step for calculating the equilibrium concentration and hydrogen ion concentration index (pH) of seawater or purified salt water; A method for producing high-purity magnesium hydroxide from seawater or refined salt water, characterized in that it comprises:

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