KR102199389B1 - Fractional production method of metal carbonate using industrial wastewater - Google Patents

Abstract

The present invention relates to a method for fractional production of metal carbonates using industrial wastewater, and the method for fractional production of metal carbonates using industrial wastewater of the present invention relates to the capture and utilization of carbon dioxide. At the same time, it is economical and eco-friendly in that it can treat wastewater. In addition, since metal carbonates can be directly fractionated and produced from industrial wastewater in which various metal ions exist, an additional fractionation process is not required, which is efficient.

Description

Fractional production method of metal carbonate using industrial wastewater

The present invention relates to a method for fractionating metal carbonates using industrial wastewater.

After the Industrial Revolution, the use of fossil fuels such as petroleum and coal has released a large amount of carbon dioxide into the atmosphere. In general, the Earth's average temperature is kept constant due to the greenhouse effect. However, if the concentration of carbon dioxide in the atmosphere is too high, the thermal balance between the solar radiation and the Earth's radiant energy is broken, causing the Earth's surface to rise. To prevent this phenomenon, many advanced countries are developing technologies that can prevent carbon dioxide emissions. There are other types of greenhouse gases that will cause the greenhouse effect and climate change, but carbon dioxide is considered a major cause of climate change and global warming due to its enormous emissions.

Various CCS (Carbon Capture and Storage) technologies are being developed to prevent the emission of carbon dioxide produced from fossil fuel-based industrial facilities into the atmosphere. In the well-known wet absorption process, carbon dioxide is separated through wet absorbents such as alkanolamines or metal hydrates. When the wet absorbent is saturated with carbon dioxide, the absorbed carbon dioxide is transferred to a desorption device that is separated by the heat of hot steam, and the separated carbon dioxide is compressed and transferred to a storage location for separation.

However, the wet absorption process has several disadvantages. First, it requires a large amount of energy to operate the entire process. In particular, high-temperature steam is used in the desorption process for separating carbon dioxide from the absorbent solution, and the energy used in this process is known to account for 70 to 80% of the total operating energy of the CCS process.

Second, many countries lack storage space for the process. In Europe, since there are no huge underground energy sources such as oil or natural gas, underground storage of carbon dioxide is not possible. In addition, since the main component of the continental crust is lime, it reacts with carbon dioxide to form calcium bicarbonate, which is easily soluble in water, which can weaken the ground. In addition, in some countries located in the Pacific Rim, it is difficult to ensure the stability of underground storage of carbon dioxide due to active earth movement.

Therefore, a new method of treating carbon dioxide by converting carbon dioxide into a useful material has been required, and this is generally referred to as CCU (Carbon Capture and Utilization).

CCU can be largely divided into two types: a process that produces organic matter and a process that produces inorganic matter.

The organic production process converts carbon dioxide into diesel, plastic, and other organic chemicals. However, since this process is a very stable material of carbon dioxide, a large amount of energy is required to cause the reaction. Although a catalyst can be used, it is difficult to commercialize because it is too expensive.

The process of producing inorganic materials produces inorganic materials such as metal carbonates. By applying a wet adsorption process to an inorganic material production process, a large amount of carbon dioxide can be captured and converted with the absorbent and carbon dioxide absorption characteristics.

When carbon dioxide is absorbed by the alkanolamine solution absorbent, the primary and secondary amines cause the following reaction:

^{_{RR'NH + CO 2 ↔ RR'NH + COO}} - (zwitterion)

^{RR'NH + COO - + RR'NH → RR'NCOO} - + RR'NH 2 +

^{_{2RR'NH + CO 2 ↔ RR'NCOO - (}} carbonate) + RR'NH 2 +

For tertiary amines:

_{CO 2 + R 3 N + H} 2 O ↔ HCO 3 - (bicarbonate) + R 3 NH +

As can be seen from the above chemical reaction equation, carbon dioxide exists in the form of reactive carbon dioxide (ri-CO ₂ ) reacting with a metal cation, so that large-scale CO ₂ capture and formation of metal carbonates can be achieved.

In addition, this process does not require heat to separate the entrapped carbon dioxide from the absorbed solution because most of the CO ₂ is removed as it precipitates in the form of metal carbonates. The produced metal carbonate can be used in cement, paper and various other industrial fields.

Existing inorganic production processes have generally been able to produce some building materials such as waste concrete using metal cations from natural resources such as limestone. However, considering economic feasibility, it is inappropriate to treat waste gas using natural resources. In addition, since waste concrete contains many coagulants that can be reused after separation, there is a problem that a complicated pretreatment process must be preceded before metal cations are used.

On the other hand, industrial wastewater contains a large amount of metal cations, but is discharged to seawater without special purification. Unrefined wastewater can have a negative impact on coastal ecosystems if discharged to the shore.

S. Shen, Y. -N. Yang, Y. Bian, Y. Zhao, Environ. Sci. Technol. 2016, 50, 2054 Anand B. RaO, Edward S. Rubin, Environ. Sci. Technol. 2002, 36, 4467

Therefore, the technical problem to be solved by the present invention is to provide a standalone high-pressure hydrogen production system capable of producing hydrogen without external energy supply.

One aspect of the present invention is the step of (A) precipitating and recovering magnesium hydroxide by adding a pH adjusting agent to industrial wastewater; (B) precipitating and recovering calcium hydroxide by adding a pH adjusting agent to industrial wastewater from which the magnesium hydroxide has been recovered; And (C) reacting the recovered calcium hydroxide and magnesium hydroxide with an aqueous solution of an amine-based absorbent absorbing carbon dioxide to produce calcium carbonate and magnesium carbonate.It provides a method for fractionating metal carbonate using industrial wastewater comprising.

The pH adjusting agent in steps (A) and (B) may be a base selected from any one selected from NaOH, KOH, and LiOH, or a mixture of two or more.

The pH of step (A) may be adjusted to 7.0 to 10.0.

The pH of step (B) may be adjusted to 11.0 to 13.0.

The amine-based absorbent may be any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyl diethanolamine, and triethanolamine.

The amine-based absorbent is monoethanolamine, and the monoethanol amine may be contained in an amount of 20 to 40% by weight in the aqueous amine-based absorbent solution.

The amine-based absorbent solution that has absorbed carbon dioxide may be saturated with carbon dioxide.

The method for fractionating metal carbonate using industrial wastewater may include (D) reacting the industrial wastewater from which the calcium hydroxide and magnesium hydroxide is recovered with an aqueous amine absorbent solution that absorbs carbon dioxide to produce sodium bicarbonate; .

The amine-based absorbent solution absorbing carbon dioxide in the step (D) may contain 3 M or more of Na ions.

The amine-based absorbent in step (D) may be any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine.

The amine-based absorbent in step (D) is monoethanolamine, and the monoethanol amine may be contained in an amount of 20 to 40% by weight in the aqueous amine-based absorbent solution.

The amine-based absorbent solution absorbing carbon dioxide in the step (D) may be saturated with carbon dioxide.

The method for fractionating metal carbonates using industrial wastewater of the present invention relates to the capture and utilization of carbon dioxide, and is economical and eco-friendly in that the collected carbon dioxide is used to produce metal carbonates and wastewater treatment is possible. In addition, since metal carbonates can be directly fractionated and produced from industrial wastewater in which various metal ions exist, an additional fractionation process is not required, which is efficient.

1 is a schematic diagram showing a purified salt production process.
2 is a schematic diagram of an experimental apparatus according to an embodiment of the present invention.
3 is a graph showing the amount of sodium hydroxide added and the amount of separated calcium hydroxide and magnesium hydroxide according to an embodiment of the present invention.
4A is a graph showing the results of XRD analysis of calcium hydroxide isolated according to an embodiment of the present invention.
4B is a graph showing the XRD analysis results of magnesium hydroxide separated according to an embodiment of the present invention.
5 is a graph showing TGA analysis results of calcium hydroxide and magnesium hydroxide separated according to an embodiment of the present invention.
6 is a graph showing a carbon dioxide absorption-conversion-desorption curve of a 30 wt% MEA absorbent solution according to an embodiment of the present invention.
7A is a graph showing the result of XRD analysis of calcium carbonate precipitated according to an embodiment of the present invention.
7B is a graph showing the XRD analysis results of magnesium carbonate precipitated according to an embodiment of the present invention.
8A is an SEM image of calcium carbonate precipitated according to an embodiment of the present invention.
8B is an SEM image of magnesium carbonate precipitated according to an embodiment of the present invention.
9 is an IR spectroscopic analysis result of a 30 wt% MEA aqueous solution saturated with CO ₂ and a 30 wt% MEA aqueous solution containing 3 M sodium chloride saturated with CO ₂ according to an embodiment of the present invention.
10 is a graph showing the XRD analysis results of sodium bicarbonate precipitated according to an embodiment of the present invention.
11 is an image showing SEM analysis results of sodium bicarbonate precipitated according to an embodiment of the present invention.
12 is a schematic diagram showing a carbon dioxide resin according to an embodiment of the present invention.

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

In the present invention, industrial wastewater was used as a source of metal cations. 1 is a schematic diagram showing a purified salt production process, and in FIG. 1, it can be seen that the wastewater concentrated in the salt production process is produced as a by-product. Metal cation, which is abundantly present in the industrial wastewater, can be reacted with captured carbon dioxide to produce metal carbonate, and at the same time, environmentally problematic wastewater can be treated. That is, the production method of metal carbonate using industrial wastewater of the present invention relates to the capture and utilization of carbon dioxide, and at the same time, the industrial wastewater can be treated using the collected carbon dioxide, and at the same time, it is possible to produce metal carbonates that are useful in industry. So it is eco-friendly and economical.

One aspect of the present invention is the step of (A) precipitating and recovering magnesium hydroxide by adding a pH adjusting agent to industrial wastewater; (B) precipitating and recovering calcium hydroxide by adding a pH adjusting agent to industrial wastewater from which the magnesium hydroxide has been recovered; And (C) reacting the recovered calcium hydroxide and magnesium hydroxide with an aqueous solution of an amine-based absorbent absorbing carbon dioxide to produce calcium carbonate and magnesium carbonate.

The industrial wastewater refers to water discharged after being used in industrial activities such as agriculture, forestry, fishing, and mining. In particular, the industrial wastewater may be seawater-based industrial wastewater, and the seawater-based industrial wastewater refers to water or seawater-based liquid industrial waste that is discharged after being used in seawater desalination, refined salt production processes, etc.

According to an embodiment of the present invention, the pH adjusting agent in steps (A) and (B) may be a base selected from any one selected from NaOH, KOH, and LiOH, or a mixture of two or more. NaOH is a strongly basic substance, and it exists in an ionic state in water, and is preferable in that it can serve as a source of Na ions in the step of preparing sodium bicarbonate, which may be added later. In addition, NaOH used may be produced through electrolysis of seawater-based liquid industrial waste, such as seawater, seawater desalination wastewater, and wastewater generated from the refined salt production process.

According to another embodiment of the present invention, the pH of step (A) may be adjusted to 7.0 to 10.0, and the pH of step (B) may be adjusted to 11.0 to 13.0.

The industrial wastewater contains a large amount of magnesium ions and calcium ions, and when a base is added to the industrial wastewater as a pH adjuster, magnesium hydroxide and calcium hydroxide are produced, respectively. The magnesium hydroxide and calcium hydroxide can be separated by adjusting the pH, and the magnesium hydroxide is precipitated at pH 7.0 to 10.0, and the calcium hydroxide is precipitated at pH 11.0 to 13.0. This is due to the difference in solubility of magnesium hydroxide and calcium hydroxide depending on the pH. Therefore, first, magnesium hydroxide precipitated in the pH range of 7.0 to 10.0 may be recovered by adding a basic pH adjuster, and calcium hydroxide precipitated in the range of 11.0 to 13.0 may be recovered by additionally adding a pH adjusting agent.

On the other hand, amine-based materials have a property of absorbing carbon dioxide well and are used as carbon dioxide absorbers in industry. When carbon dioxide is absorbed by the alkanolamine solution absorbent, the primary and secondary amines cause the following reaction:

^{_{RR'NH + CO 2 ↔ RR'NH + COO}} - (zwitterion)

^{RR'NH + COO - + RR'NH → RR'NCOO} - + RR'NH 2 +

^{_{2RR'NH + CO 2 ↔ RR'NCOO - (}} carbonate) + RR'NH 2 +

For tertiary amines:

_{CO 2 + R 3 N + H} 2 O ↔ HCO 3 - (bicarbonate) + R 3 NH +

As can be seen from the above chemical reaction equation, carbon dioxide exists in the form of reactive carbon dioxide (ri-CO ₂ ) that reacts with metal cations. Since such reactive carbon dioxide (ri-CO ₂ ) can react with a metal cation to produce a metal carbonate, an amine-based absorbent saturated with carbon dioxide can be reacted with the separated magnesium hydroxide and calcium hydroxide to produce magnesium carbonate and calcium carbonate. have.

According to another embodiment of the present invention, the amine-based absorbent may be any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine. Among these, monoethanolamine (MEA) is preferable in that it has high reactivity with carbon dioxide and the absorbent can be regenerated without additional energy input in the process of forming carbonate precipitates by reaction with metal ions. In addition, compared to other alkanolamine-based absorbents, the unit price is low and the solubility in water is high, so it is easy to control the concentration.

According to another embodiment of the present invention, the amine-based absorbent is monoethanolamine, and the monoethanol amine may be contained in an aqueous solution of the amine-based absorbent in an amount of 20 to 40% by weight, more preferably 25 to 35% by weight. May be used. When the monoethanol is contained in an amount of 20 to 40% by weight, it is preferable in that it can exhibit a high carbon dioxide absorption capacity.

According to another embodiment of the present invention, the amine-based absorbent solution that has absorbed carbon dioxide may be saturated with carbon dioxide. In the case of using an amine-based absorbent solution saturated with carbon dioxide, reactive carbon dioxide (ri-CO ₂ ) that produces metal carbonates can be easily desorbed and is preferable in that a large amount of metal carbonates can be produced.

According to another embodiment of the present invention, the method for fractionating metal carbonate using industrial wastewater comprises: (D) sodium bicarbonate by reacting the industrial wastewater obtained by recovering the calcium hydroxide and magnesium hydroxide with an aqueous amine absorbent solution absorbing carbon dioxide. It may include a; step of manufacturing.

After the calcium and magnesium components are separated in steps (A) to (C), sodium ions and chlorine anions are the most abundant ions in the remaining solution. Sodium bicarbonate can be produced by reacting sodium ions in the remaining solution with carbon dioxide captured by an amine-based absorbent as a source of metal ions.

However, in order to prepare sodium bicarbonate, it is preferable that the carbon dioxide saturated amine absorbent in step (D) contains 3 M or more of Na ions. It was confirmed that a high concentration of sodium ions should be included in order for carbon dioxide absorbed by the absorbent to form a form of bicarbonate ions rather than carbonates. That is, when the carbon dioxide saturated amine absorbent contains 3 M or more of Na ions, bicarbonate ions can be formed, and sodium bicarbonate can be produced by reacting with sodium ions.

The amine-based absorbent in step (D) may be any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine. Among these, monoethanolamine (MEA) is preferable in that it has high reactivity with carbon dioxide and the absorbent can be regenerated without additional energy input in the process of forming carbonate precipitates by reaction with metal ions. In addition, compared to other alkanolamine-based absorbents, the unit price is low and the solubility in water is high, so it is easy to control the concentration.

The amine-based absorbent in step (D) is monoethanolamine, and the monoethanol amine may be contained in an amount of 20 to 40% by weight in the aqueous amine-based absorbent solution. More preferably, 25 to 35% by weight may be included and used. When the monoethanol is contained in 20 to 40% by weight, it is preferable in that it can exhibit high carbon dioxide absorption capacity.

The amine-based absorbent solution absorbing carbon dioxide in the step (D) may be saturated with carbon dioxide. In the case of using an amine-based absorbent solution saturated with carbon dioxide, reactive carbon dioxide (ri-CO ₂ ) that produces metal carbonates can be easily desorbed and is preferable in that a large amount of metal carbonates can be produced.

Hereinafter, a preferred embodiment is presented to aid the understanding of the present invention. However, these examples are for describing the present invention in more detail, and the scope of the present invention is not limited thereto, and various changes and modifications are possible within the scope and spirit of the present invention. It will be self-evident to those who have knowledge.

Example. Fractional production of metal carbonates

Materials used

Seawater-based concentrated wastewater was provided by Hanju Salt Corp. (Ulsan, Korea), and sodium hydroxide used to separate calcium and magnesium was purchased from Sigma-Aldrich. Monoethanolamine was purchased from Sigma-Aldrich, diluted with distilled water, and used as a 30% by weight solution, and the concentration was confirmed using a gas analyzer (Gas Master, Sensoronic) using carbon dioxide and nitrogen gas (purity 99.9 vol%). .

Separation of calcium and magnesium

Calcium and magnesium ions can react with hydroxide ions, respectively, to form calcium and magnesium hydroxides. However, when calcium and magnesium ions are mixed, the pH must be adjusted through a pH swing process in order to separate each ions in the form of hydroxide.

Magnesium hydroxide was precipitated in a pH range of 7 to 10, and calcium hydroxide was precipitated and separated in a pH range of 11-13. This difference in pH and solubility was used to separate cations and obtain a solid phase, and each precipitate and the remaining solution were separated by vacuum filtration using a glass fiber filter (Whatman, GF/F, pore size 0.7 micron). After filtration, the precipitate was washed with 99.9% ethanol to remove sodium chloride and other polar and soluble impurities.

Specifically, in order to separate calcium and magnesium, a pH swing method was applied to separate calcium and magnesium components into calcium hydroxide and magnesium hydroxide. The separation process used 1000 mL of seawater-based industrial wastewater without further treatment. The initial distribution of the components is shown in Table 1 below, and the concentration of metal cations in natural seawater is also indicated.

Natural seawater Industrial wastewater Metal cation Concentration (ppm) Metal cation Concentration (ppm) Ca ²⁺ 400 Ca ²⁺ 21985.7 Mg ²⁺ 1270 Mg ²⁺ 50231.2 Na ⁺ 10550 Na ⁺ 22631.5 Ba ²⁺ 0.05 Ba ²⁺ 0.7

3 is a graph showing the amount of 4 M NaOH added and the weight of the precipitate in each pH range. As can be seen in FIG. 3, precipitation of magnesium hydroxide mainly occurred in the range of pH 8-10. On the other hand, precipitation of calcium hydroxide mainly occurred in the range of pH 11 to 13. After separation, the precipitate was washed with 99.9% ethanol to remove remaining sodium chloride and other polar and soluble impurities. Then, it was dried for 72 hours to remove the ethanol solvent. After washing and drying, 117.7 g of magnesium hydroxide and 38.9 g of calcium hydroxide precipitate were obtained. XRD and TGA analysis were performed to confirm that the precipitated solid was actually magnesium carbonate and calcium carbonate.

Through the XRD analysis results shown in FIG. 4, it was confirmed that the precipitate separated in the pH range of 8 to 10 was magnesium hydroxide, and the precipitate separated in the pH range of 11 to 13 was calcium hydroxide. Next, TGA analysis was performed to measure the purity of calcium hydroxide and magnesium hydroxide salts. Based on the TGA and DTG curves shown in FIG. 5, the purity of the calcium hydroxide and magnesium hydroxide salts were 92.9% by weight and 83.7% by weight, respectively. Separation yields of magnesium and calcium ions were calculated as 81.7% and 88.7%, respectively, on a molar basis (Table 2). This precipitate was used to produce calcium carbonate and magnesium carbonate by combining each precipitate with ri-CO ₂ .

Types of metal cation Separated Form Initial Cation Concentration
(mg/L) The amount of
metal hydroxide
separated
(g) Conversion Yield
(%) Magnesium (Mg ²⁺ ) Magnesium Hydroxide
(Mg(OH) ₂ ) 50231.2 117.7 81.7 Calcium
(Ca ²⁺ ) Calcium Hydroxide
(Ca(OH) ₂ ) 21985.7 38.9 88.7

CO ₂ Absorption and precipitation of calcium carbonate, magnesium carbonate

The precipitates separated from the 30% by weight MEA aqueous solution were chemically converted to calcium and magnesium carbonate.

Absorption experiments were performed in 800 mL aqueous solution. In this process, a simulated flue gas containing 15 vol% carbon dioxide and 85 vol% nitrogen gas was used so that the flow rates were 310 mL/min and 1820 mL/min for each of carbon dioxide and nitrogen gas.

Using the experimental apparatus shown in FIG. 2, the absorption solution was saturated and mixed with calcium hydroxide and magnesium hydroxide, respectively, and then stirred for 24 hours to promote chemical conversion. 200 mL of an absorbent solution was used for the conversion of calcium and magnesium.

The degree of saturation of the sorbent was determined using a gas analyzer that analyzes the concentration of gas coming out of the reactor. After the conversion step, the precipitate was separated using vacuum filtration and then dried in a convection oven for 72 hours.

Specifically, as shown in FIG. 6, 400 mL of a 30% by weight MEA aqueous solution was used for CO ₂ absorption. The absorbent solution was saturated with CO ₂ over time, and the amount of CO ₂ absorbed by the absorbent solution was calculated through the following equation.

는 흡수제 용액에 흡수된 이산화탄소의 양이고,

는 이산화탄소의 유속이고,

는 이산화탄소 농도,

는 배기 라인에서의 이산화탄소 농도이다. 가스 분석기는 고정된 시간 간격(Δt) 30 초 동안 이산화탄소 농도를 측정하였다.

는 15 vol%로 고정하였으며,

및

는 몰 단위를 나타낸다. here,

Is the amount of carbon dioxide absorbed in the absorbent solution,

Is the flow rate of carbon dioxide,

Is the carbon dioxide concentration,

Is the carbon dioxide concentration in the exhaust line. The gas analyzer measured the carbon dioxide concentration during a fixed time interval (Δt) of 30 seconds.

Was fixed at 15 vol%,

And

Represents the molar unit.

When the absorbent solution was saturated with carbon dioxide, the absorption experiment was terminated. In order to convert magnesium hydroxide into a magnesium carbonate salt, 30 g of a magnesium hydroxide precipitate was added to 200 mL of a saturated absorbent. Likewise, 30 g of calcium hydroxide precipitate was added to 200 mL of saturated absorbent. Both reactions were stirred for 24 hours using a magnetic stirrer to achieve maximum conversion of each cation. After 24 hours, the precipitate and the remaining solution were separated using a vacuum pump and a glass fiber filter (Whatman, GF/F, pore size 0.7 micron). Thereafter, the separated precipitate was washed with 99.9% ethanol to remove the remaining amine and then dried in a convection oven for 72 hours to remove the ethanol solvent. As shown in Table 3 below, after washing and drying, the magnesium and calcium-based precipitates obtained 21.487 g and 38.191 g, respectively. 400 mL of 30 wt% MEA aqueous solution absorbed 1.6476 moles of carbon dioxide. In the conversion step, 200 mL of a saturated solution containing 0.8238 moles of ri-CO ₂ was used. 48.044 g of magnesium hydroxide was added to form magnesium carbonate, which is equivalent to 0.8238 moles of Mg ²⁺ ions required to react with ri-CO ₂ . The precipitation reaction produced 21.487 g of magnesium carbonate, which was 0.2549 mol. The conversion rate was 30.94% for magnesium carbonate and 46.36% for calcium carbonate.

Types of metal cation addition The amount of
CO ₂ absorbed
(mol) The amount of
metal hydroxide
Added
(g) The amount of
metal carbonate
formation
(g) Conversion Yield
(%) Magnesium
Hydroxide 0.8238 48.044 21.487 30.94 Calcium
Carbonate 61.038 38.191 46.36

The amount of dissolved carbon dioxide was calculated based on 200 mL of 30 wt% MEA aqueous solution, and the conversion rate was calculated based on the theoretical maximum conversion amount.

The reaction of ri-CO ₂ with magnesium / calcium ions to produce magnesium carbonate and calcium carbonate proceeds without energy consumption. However, the conversion rate of magnesium is lower than that of calcium as shown in [Table 3]. This is because the reaction for producing calcium carbonate is more energetically advantageous than magnesium carbonate. The standard formation enthalpy and Gibbs free energies for magnesium carbonate are -1113 KJ/mol and -1029.3 KJ/mol, respectively. For calcium carbonate, the standard enthalpy of formation and Gibbs free energy at 298.15 K are -1207 KJ/mol and -1129.1 KJ/mol, respectively. Therefore, in terms of energy stability, the reaction between dissolved carbon dioxide and calcium ions is more preferable, and is reflected in the high conversion rate of calcium carbonate.

XRD and SEM analysis were performed to determine whether each metal hydroxide was converted to carbonate. 7 is a graph showing an XRD analysis result according to an embodiment of the present invention, and FIG. 8 is an SEM image of calcium carbonate and magnesium carbonate according to an embodiment of the present invention. From the XRD analysis of FIG. 7, it can be seen that calcium hydroxide is converted to a calcium carbonate salt and the dominant crystal structure is calcite. Calcium carbonate has three crystal structures: calcite, vaterite and aragonite. In terms of thermodynamic stability, calcite is the most stable structure, so most of calcium carbonate is produced in the form of calcite in the presence of water. That is, since the conversion conditions were kept constant under room temperature (298.15 K) and atmospheric pressure (101.325 kPa) using 30% by weight of MEA aqueous solution, the formation of calcite is a natural result.

Likewise, analysis of the magnesium hydroxide conversion shows that magnesium hydroxide was converted to magnesium carbonate, mainly in the form of magnesite. Magnesium carbonate may exist in a hydrated form such as barringtonite (dihydrate), nesequehonite (trihydrate) and lansfordite (pentahydrate). In terms of energy, nesquehonite formation is preferred over magnesite formation.

Finally, in FIG. 8, the left and right images are the precipitated calcium carbonate salt (calcite) and the precipitated magnesium carbonate salt (magnesite), respectively. From FIG. 8, the structure of a scalenohedral and rhombohedral of calcite can be confirmed.

In other words, it can be seen that calcium and magnesium cations in seawater-based wastewater are separated into hydroxide by adding sodium hydroxide, and these separated calcium magnesium and magnesium hydroxide are carbonated to produce calcium carbonate (calcite) and magnesium carbonate (magnesite) salts. there was.

Sodium bicarbonate precipitation

When calcium and magnesium components were separated from seawater-based industrial wastewater, sodium cation and chlorine anion were the most abundant ions in the remaining solution, so sodium bicarbonate was precipitated using the remaining solution after separation of calcium and magnesium.

It is known that carbon dioxide peroxide is converted into reactive ionic forms such as carbonates and carbonates and carbamates when reacting with primary amines. Based on this theoretical background, a solution obtained by separating calcium and magnesium was added to a 200 mL MEA aqueous solution to prepare a 30 wt% MEA solution containing 3 M sodium chloride, and sodium chloride was recovered therefrom. In order to saturate the MEA solution, the same absorption experiment as the CO ₂ absorption and precipitation of calcium and magnesium carbonate was applied.

Sodium bicarbonate was formed by a reaction between sodium and bicarbonate ions, and the solubility of sodium bicarbonate in water was 96 g/L at 298.15 K, so some of the sodium bicarbonate precipitated and some remained as an ionic solution.

To confirm the formation of sodium bicarbonate, the precipitate was separated by vacuum filtration and dried for 72 hours.

Specifically, a 30% by weight MEA aqueous solution containing 3 M sodium chloride was prepared so that the dissolved carbon dioxide was in the form of bicarbonate ions instead of carbonate. The high concentration of sodium ions (> 3M) affects the steric hindrance of carbonate ions, causing a reaction with water molecules to form bicarbonate. IR spectroscopy was used to determine whether or not bicarbonate ions were formed in a 30 wt% MEA aqueous solution with 3 M sodium chloride added.

9 is an IR spectroscopic analysis result of a 30 wt% MEA aqueous solution saturated with CO ₂ and a 30 wt% MEA aqueous solution containing 3 M sodium chloride saturated with CO ₂ according to an embodiment of the present invention. As can be seen in Figure 9, the stretch band corresponding to the NH bond indicates the presence of MEA molecules. The difference between the solutions containing or without sodium chloride can be seen at a wavenumber of about 1500 cm ^-1 . With the addition of 3 M sodium chloride, the transmittance of the 30% by weight MEA aqueous solution dropped sharply, showing the lowest transmittance locally at a wavenumber of 1575 cm ^-1 . On the other hand, the transmittance of the 30 wt% MEA aqueous solution to which 3 M sodium chloride was not added was almost unchanged, and the wavelength indicating this characteristic was indicated by a pink bar in FIG. 9. MEA 30% by weight aqueous solution without 3M sodium chloride has a lower transmittance in that area compared to 3M sodium chloride due to the presence of carbonate ions. From this result, it was confirmed that sodium bicarbonate formation was possible when carbon dioxide was supplied to a 30 wt% MEA aqueous solution containing 3 M sodium chloride.

Carbon dioxide absorption formed a white precipitate, which was analyzed by XRD, EDS and SEM.

10 is a graph showing the XRD analysis results of sodium bicarbonate precipitated according to an embodiment of the present invention. In FIG. 10, the XRD analysis confirmed that sodium bicarbonate was produced in the form of nahcolite mixed with sodium chloride. Since dissolved carbon dioxide was converted to bicarbonate ions, some of the sodium ions reacted with the bicarbonate salt to form sodium bicarbonate salt. Solubility of sodium bicarbonate (96 g/L, 298.15 K) was lower than that of sodium carbonate salt (300 g/L, 298.15 K), so when the solubility of sodium bicarbonate exceeded the solubility, hydrochloric acid was discharged. Since sodium carbonate was not detected by XRD analysis, the process of making sodium bicarbonate by adding sodium chloride to the primary amine was confirmed.

11 is an image showing SEM analysis results of sodium bicarbonate precipitated according to an embodiment of the present invention. From the SEM image of FIG. 11, a monoclinic crystal structure could be confirmed. EDS analysis was performed at the point indicated by "EDS Point" in FIG. 11, and the composition is shown in Table 4 below. The ratio of sodium bicarbonate and sodium carbonate was deduced from the molar fraction of each constituent atom. From Table 4 below, it can be seen that the molar fraction of chlorine atoms is 9.94 mol%, indicating that 9.94 mol% sodium is required to form sodium chloride. Thus, the remaining atoms of Na, C and O exist in the ratio of Na:C:O = 16.45:16.23:47.43. It was confirmed that this ratio closely coincided with the stoichiometry of sodium bicarbonate, that is, Na:H:C:O=1:1:1:1:3.

Element Weight Fraction (% by weight) Mole Fraction (mol%) C 10.18 16.23 O 39.66 47.43 Na 31.72 26.39 Cl 18.44 9.94 Total 100 100

12 is a schematic diagram showing a carbon dioxide resin according to an embodiment of the present invention.

Accordingly, the method of fractionating metal carbonate using industrial wastewater of the present invention is economical and eco-friendly in that it is possible to treat wastewater while utilizing the collected carbon dioxide to produce metal carbonate. In addition, since metal carbonates can be directly fractionated and produced from industrial wastewater in which various metal ions exist, an additional fractionation process is not required, which is efficient.

The above-described Examples and Comparative Examples are examples for explaining the present invention, and the present invention is not limited thereto. Since those of ordinary skill in the art to which the present invention pertains will be able to implement the present invention by various modifications therefrom, the technical protection scope of the present invention should be determined by the appended claims.

Claims (12)

(A) adding a pH adjuster to industrial wastewater to precipitate and recover magnesium hydroxide;
(B) precipitating and recovering calcium hydroxide by adding a pH adjusting agent to industrial wastewater from which the magnesium hydroxide has been recovered; And
(C) preparing calcium carbonate and magnesium carbonate by reacting the recovered calcium hydroxide and magnesium hydroxide with an aqueous solution of an amine-based absorbent absorbing carbon dioxide to produce calcium carbonate and magnesium carbonate. The method of claim 1,
The pH adjusting agent in steps (A) and (B) is a method for fractional production of metal carbonates using a base selected from any one or a mixture of two or more selected from NaOH, KOH and LiOH. The method of claim 1,
The method of fractional production of metal carbonates using industrial wastewater in which the pH of step (A) is adjusted to 7.0 to 10.0.
The method of claim 1,
The method of fractional production of metal carbonates using industrial wastewater in which the pH of step (B) is adjusted to 11.0 to 13.0.
The method of claim 1,
The amine-based absorbent is any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine. Method for fractionation of metal carbonates using industrial wastewater.
The method of claim 1,
The amine absorbent is monoethanolamine,
The monoethanol amine is a method for fractionating metal carbonates using industrial wastewater containing 20 to 40% by weight in the aqueous amine-based absorbent solution.
The method of claim 1,
The amine-based absorbent solution absorbing carbon dioxide is saturated with carbon dioxide. A method for fractionating metal carbonate using industrial wastewater.
The method of claim 1,
The method for fractional production of metal carbonate using the industrial wastewater,
(D) preparing sodium bicarbonate by reacting the industrial wastewater from which the calcium hydroxide and magnesium hydroxide is recovered with an aqueous amine-based absorbent solution that absorbs carbon dioxide to produce sodium bicarbonate; Method for fractionating metal carbonate using industrial wastewater comprising.
The method of claim 8,
The amine-based absorbent solution absorbing carbon dioxide in the step (D) contains 3 M or more of Na ions.
The method of claim 8,
The amine-based absorbent in step (D) is any one or a mixture of two or more selected from monoethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine. Method for fractionation of metal carbonates using industrial wastewater.
The method of claim 8,
The amine-based absorbent in step (D) is monoethanolamine,
The monoethanol amine is a method for fractionating metal carbonates using industrial wastewater containing 20 to 40% by weight in the aqueous amine-based absorbent solution.
The method of claim 8,
The amine-based absorbent solution absorbing carbon dioxide in the step (D) is saturated with carbon dioxide.

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