WO2025110411A1 - Apparatus and method for continuously producing vaterite crystalline calcium carbonate using greenhouse gas - Google Patents

Abstract

The present invention relates to an apparatus and a method for continuously producing vaterite crystalline calcium carbonate using a greenhouse gas and, more specifically, to a method for continuously producing vaterite crystalline calcium carbonate using a greenhouse gas, whereby it is possible to continuously produce high-quality vaterite crystalline calcium carbonate while utilizing carbon dioxide, which is a greenhouse gas, by using a carbonation reaction of seawater and alkaline industrial by-products.

Description

Continuous production device and method for calcium carbonate in the form of vaterite crystals utilizing greenhouse gases

The present invention relates to a device and method for continuously producing calcium carbonate in the form of vaterite crystals utilizing greenhouse gases, and more specifically, to a device and method for continuously producing calcium carbonate in the form of vaterite crystals utilizing greenhouse gases while utilizing carbon dioxide, a greenhouse gas, through a carbonation reaction of seawater and alkaline industrial by-products.

CCUS (Carbon Capture Utilization and Storage) refers to carbon dioxide capture technology and the technology to utilize or store it. Recently, due to geographical or environmental issues, the limitations of mass storage of captured carbon dioxide have been highlighted, and research and development are actively being conducted on technologies to utilize captured carbon dioxide as an alternative to storing captured carbon dioxide. Among them, mineral carbonation technology is attracting attention as a technology to stably and permanently store carbon dioxide generated in large quantities at industrial sites.

Mineral carbonation proceeds through the stages of securing raw materials, carbonation reaction, and product separation. Among inorganic carbonates, precipitated calcium carbonate (PCC) has secured a domestic market of 150,000 tons per year and is used in various fields such as paper, rubber, plastics, paints/coatings, and adhesives/sealants.

This calcium carbonate can crystallize from amorphous calcium carbonate in the early stage of the reaction into three crystal structures: calcite, vaterite, and aragonite. Among them, the vaterite crystal phase is a hydrophilic material with a large porous surface area, and can be used more widely as an expensive inkjet dye, calcium supplement, artificial bone, etc. than the other two crystal types of calcium carbonate. However, it is thermodynamically unstable, and as the reaction continues, it recrystallizes on its own and transforms into a stable calcite crystal phase, so mass production is currently impossible, and only small quantities are being produced.

Accordingly, Korean Patent Nos. 1490389 and 1551896 disclose a method for producing calcium carbonate in the form of vaterite crystals by supplying carbon dioxide to an ammonia solution mixed with desulfurized gypsum to carbonate it and then filtering it.

However, these methods are indirect carbonation methods that manufacture calcium carbonate by reacting carbon dioxide in an ammonia solution containing desulfurized gypsum. Unlike direct carbonation, solvents or chelates must be used to dissolve calcium in the desulfurized gypsum. In addition, since carbon dioxide has very limited solubility in an ammonia solution containing calcium ions, the carbonation reaction progresses slowly, which inevitably lengthens the manufacturing time of calcium carbonate, making it difficult to secure economic feasibility. In addition, due to the continuous vaporization of ammonia water, there are environmental problems in process operation, and it is difficult to control the size and particle shape of calcium carbonate produced in the continuous manufacturing process, and there is a problem of poor particle uniformity.

[Prior art literature]

[Patent Document]

(Patent Document 1) Korean Patent No. 1490389 (Publication Date: 2015.02.05.)

(Patent Document 2) Korean Patent No. 1551896 (Publication Date: 2015.04.03.)

The main purpose of the present invention is to solve the above-mentioned problems, and to provide a device and method for continuously producing calcium carbonate in the form of vaterite crystals by utilizing the carbonation reaction of seawater and alkaline industrial by-products, while effectively utilizing carbon dioxide, a greenhouse gas, by conversion into calcium carbonate.

In order to achieve the above object, one embodiment of the present invention comprises: a calcium elution unit which adds seawater to an alkaline industrial by-product to produce a calcium elution solution in which magnesium is precipitated in a solid state; a first separation unit which separates the calcium elution solution produced in the calcium elution unit by centrifugation to separate a magnesium precipitate; a reaction unit which receives the calcium elution solution from which the magnesium precipitate is separated from the first separation unit, and supplies carbon dioxide-containing gas in the form of microbubbles having an average diameter of 1 mm to 2.5 mm to the supplied calcium elution solution from which the magnesium precipitate is separated, to obtain a reactant in which calcium carbonate is precipitated; a second separation unit which dehydrates the reactant obtained in the reaction unit to obtain a calcium carbonate cake; And the present invention provides a continuous production device for vaterite crystal-phase calcium carbonate, characterized by including a drying unit for producing vaterite crystal-phase calcium carbonate by simultaneously drying and crushing the calcium carbonate cake through particle collision by rotation while spraying hot air of 100° C. to 550° C. on the calcium carbonate cake obtained from the second separation unit.

In a preferred embodiment of the present invention, the seawater may be characterized as being selected from the group consisting of normal seawater, seawater desalination concentrate, brine, bittern, and mixtures thereof.

In a preferred embodiment of the present invention, the alkaline industrial by-product may be selected from the group consisting of paper sludge ash (PSA), cement kiln dust (CKD), quicklime kiln dust, fuel ash, bottom ash, fly ash, de-inking ash, steelmaking slag, waste concrete, and mixtures thereof.

In a preferred embodiment of the present invention, the weight ratio of the alkaline industrial by-product and seawater may be 1:5 to 100.

In a preferred embodiment of the present invention, the microbubbles may be characterized by having an average diameter of 1 mm to 2.5 mm.

In a preferred embodiment of the present invention, the flow rate of the carbon dioxide containing gas may be 0.71 L/min to 2.14 L/min per 1 L of the calcium leached solution from which the magnesium precipitate is separated.

Another embodiment of the present invention provides a method for continuously producing vaterite crystal-phase calcium carbonate, comprising the steps of: (a) adding seawater to an alkaline industrial by-product to produce a calcium leached solution in which magnesium is precipitated in a solid state; (b) centrifuging the produced calcium leached solution to separate a magnesium precipitate from the calcium leached solution; (c) supplying a carbon dioxide-containing gas in the form of microbubbles having an average diameter of 1 mm to 2.5 mm to the calcium leached solution from which the magnesium precipitate is separated to obtain a reactant in which calcium carbonate is precipitated; (d) dehydrating the obtained reactant to obtain a calcium carbonate cake; and (e) drying and pulverizing the calcium carbonate cake through particle collision by rotation while spraying hot air of 100°C to 550°C to the obtained calcium carbonate cake to produce calcium carbonate in a vaterite crystal-phase.

In another preferred embodiment of the present invention, the seawater in step (a) may be characterized by being selected from the group consisting of normal seawater, seawater desalination concentrate, brine, bittern, and mixtures thereof.

In another preferred embodiment of the present invention, the alkaline industrial by-product of step (a) may be selected from the group consisting of paper sludge ash (PSA), cement kiln dust (CKD), quicklime kiln dust, fuel ash, bottom ash, fly ash, de-inking ash, steelmaking slag, waste concrete, and mixtures thereof.

In another preferred embodiment of the present invention, the weight ratio of the alkaline industrial by-product and seawater in step (a) may be 1:5 to 100.

In another preferred embodiment of the present invention, the microbubbles may be characterized by having an average diameter of 1 mm to 2.5 mm.

In another preferred embodiment of the present invention, the flow rate of the carbon dioxide containing gas may be characterized as being 0.71 L/min to 2.14 L/min per 1 L of the calcium leached solution from which the magnesium precipitate is separated.

According to the present invention, since seawater and alkaline industrial by-products are used as starting materials, the amount of limestone, a natural resource, can be reduced, thereby enabling resource conservation, the raw material for calcium carbonate in the form of vaterite crystals can be economically supplied, and calcium contained in alkaline industrial by-products can be extracted with high efficiency using magnesium contained in seawater, and at the same time, magnesium in seawater, which hinders the production of high-purity calcium carbonate using alkaline industrial by-products, is continuously separated and removed by a centrifugal method, thereby increasing the purity of calcium carbonate, and by utilizing seawater instead of an expensive solvent, there is the effect of improving the economic feasibility of carbon dioxide storage and calcium carbonate production.

In addition, according to the present invention, by applying a centrifugal separation method and a rotary impact drying method using hot air to produce calcium carbonate in a vaterite crystal phase, scale-up is easy, and during drying, grinding and classification can be performed simultaneously, and there is an effect of being able to continuously produce calcium carbonate in a vaterite crystal phase at a high yield.

Figure 1 is a schematic diagram illustrating a continuous production device for calcium carbonate in the form of vaterite crystals according to one embodiment of the present invention.

Figure 2 is a flow chart showing a method for continuously producing calcium carbonate in a vaterite crystal phase according to one embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a drying unit according to one embodiment of the present invention.

Figure 4 shows the results of X-ray diffraction analysis of calcium carbonate manufactured in examples and comparative examples of the present invention.

Figure 5 shows the results of SEM analysis of calcium carbonate manufactured in Examples 1 to 7 of the present invention.

Figure 6 shows the results of SEM analysis of calcium carbonate in Comparative Examples 1 to 12 of the present invention.

[Explanation of symbols]

100 : Calcium release zone

200 : 1st Separation Section

210 : Centrifuge

300 : Reaction section

310: Microbubble device

400: 2nd Separation Section

410 : Filter press

500 : Drying part

510 : Rotary Impact Dryer

520: Hot air supply unit

521, 540 : Blower

522 : Heater

530 : Capture Unit

550 : Chimney

1000: Continuous production device for calcium carbonate in vaterite crystal phase

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

The terms “comprising,” “including,” or “having” used in this specification indicate the presence of features, values, steps, operations, components, parts, or combinations thereof described in the specification, and do not exclude the possibility that other features, values, steps, operations, components, parts, or combinations thereof that are not mentioned may be present or added.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, in describing the present invention, descriptions of functions or configurations already known will be omitted in order to clarify the gist of the present invention.

The chemical reactions described below can be carried out at room temperature unless otherwise specified, and can be carried out under normal chemical reaction conditions without any additional additions. However, it should not be interpreted in a way that goes beyond what is clear to those skilled in the art.

In general, calcium carbonate in the vaterite crystal phase is thermodynamically unstable, so as reactions continue, it recrystallizes on its own and transforms into a stable calcite crystal phase. Therefore, continuous mass production is currently impossible, and only small quantities are being produced.

Accordingly, in the present invention, it was confirmed that high-quality vaterite crystal-phase calcium carbonate can be continuously produced while utilizing carbon dioxide, a greenhouse gas, by utilizing the carbonation reaction of seawater and alkaline industrial by-products and applying a centrifugal separation method and a rotary impact drying method using hot air, thereby completing the present invention.

FIG. 1 is a schematic diagram illustrating a continuous production apparatus for calcium carbonate in vaterite crystal phase according to one embodiment of the present invention, and FIG. 2 is a flow chart illustrating a continuous production method for calcium carbonate in vaterite crystal phase according to one embodiment of the present invention. With reference to these, the continuous production apparatus and method for calcium carbonate in vaterite crystal phase according to the present invention will be described.

Referring to FIGS. 1 and 2, a continuous production device (1000) for calcium carbonate in the form of vaterite crystals according to the present invention includes a calcium elution unit (100), a first separation unit (200), a reaction unit (300), a second separation unit (400), and a drying unit (500).

The above calcium elution unit (100) adds seawater to alkaline industrial by-products to precipitate magnesium present in seawater, and at the same time elutes calcium ions present in the alkaline industrial by-products to produce a calcium elution solution.

At this time, the alkaline industrial by-product may be used without limitation as long as it is an alkaline industrial by-product containing calcium, and examples thereof may include paper sludge ash (PSA), cement kiln dust (CKD), quicklime kiln dust, fuel ash, bottom ash, fly ash, de-inking ash, steelmaking slag, waste concrete, and mixtures thereof, and preferably, cement kiln dust having a CaO content of 40 wt% or more and a particle size of 10 ㎛ to 1,000 ㎛, and which can be used directly as a carbonation reaction raw material without pretreatment such as grinding or crushing.

Meanwhile, seawater can be used without limitation as long as it is seawater capable of extracting calcium from the alkaline industrial by-product, and examples thereof include general seawater, seawater desalination concentrate, brine, bittern, etc., and seawater filtered using a membrane filter, etc., can be used to filter out impurities present in the seawater.

The above seawater contains salts such as NaCl, MgCl ₂ , MgSO ₄ , CaSO ₄ , and K ₂ SO _{4 .} When alkaline industrial by-products are added to the seawater containing such salts, magnesium present in the seawater is precipitated and calcium ions present in the alkaline industrial by-products are dissolved. The magnesium precipitation and calcium ion dissolution reaction can be expressed as shown in the following reaction scheme 1, and this is a reaction whose equilibrium toward the forward reaction is very strong and can become the driving force for the calcium ion dissolution reaction.

[Reaction Formula 1]

CaO(s) + Mg ²⁺ (aq) + H ₂ O(l) → Mg(OH) ₂ (s) + Ca ²⁺ (aq)

Meanwhile, magnesium contained in seawater acts as a factor that increases the efficiency of the reaction in the dissolution of calcium ions as shown in Reaction Scheme 1, but acts as an interfering factor in the subsequent step of generating calcium carbonate by injecting carbon dioxide-containing gas. That is, magnesium ions (Mg2 ⁺ ) react with carbon dioxide supplied to seawater to form magnesium carbonate ( _MgCO3 ), thereby competitively inhibiting the formation of calcium carbonate ( _CaCO3 ) resulting from the reaction between calcium ions (Ca2 ⁺ ) and carbon dioxide, and forming magnesium carbonate, which is an impurity, which becomes an obstacle in the production of high-purity vaterite crystal-phase calcium carbonate. Therefore, seawater containing magnesium could not be considered as a solvent in the reaction for producing high-purity calcium carbonate until now, even though it has a high calcium dissolution efficiency.

However, when alkaline industrial by-products are reacted with seawater to extract calcium, the pH of the seawater increases as the calcium oxide or calcium hydroxide of the alkaline industrial by-products dissolves in the seawater, and at high pH, magnesium in the seawater reacts with OH and precipitates in the form of Mg(OH) ₂ . This precipitation reaction of Mg(OH) ₂ can be expressed as shown in the following reaction scheme 2, and since this is a forward reaction and corresponds to a reaction in which equilibrium is dominant (K≒ ¹⁰¹¹ ), most of the magnesium ions present in seawater can be precipitated in the form of Mg(OH) ₂ .

[Reaction Formula 2]

Mg ²⁺ + 2OH ^- → Mg(OH) ₂ (s)

Therefore, according to the present invention, by adding seawater to an alkaline industrial by-product, magnesium present in the seawater can be precipitated and removed, so seawater can be used as a solvent in a reaction for producing high-purity calcium carbonate.

At this time, the weight ratio of the alkaline industrial by-product and seawater may vary depending on the available calcium content in the alkaline industrial by-product, but preferably, the weight ratio of the alkaline industrial by-product and seawater may be adjusted to 1:5 to 100, more preferably 1:10 to 80, and even more preferably 1:10 to 50. When the content of seawater to the alkaline industrial by-product satisfies the above ratio range, there is an advantage of increasing the efficiency of calcium ion elution, and when it goes beyond the above range, problems such as a decrease in the elution efficiency of calcium ions or inability to secure a sufficient amount of calcium elution may occur.

According to a preferred embodiment of the present invention, the seawater may be characterized by having a magnesium concentration of 1,000 mg/L to 5,000 mg/L. As described above, magnesium ions in seawater act as a factor that dissolves available calcium present in the form of CaO in alkaline industrial by-products. Therefore, the higher the magnesium concentration in seawater, the more the calcium ion dissolution efficiency can be improved. However, when the magnesium concentration exceeds 5,000 mg/L, there is an advantage in that more calcium is dissolved as the magnesium concentration increases, thereby utilizing more carbon dioxide, but the time is longer than the optimal process time, so that calcium carbonate manufactured in the form of vaterite may recrystallize into calcium carbonate in the form of calcite, which is thermodynamically more stable.

Generally, seawater contains magnesium at a concentration of about 1,300 mg/L (about 0.05 M), so magnesium ions can be additionally added to increase the concentration of magnesium in seawater. At this time, the magnesium ions added can be added in the form of a magnesium salt, and are not particularly limited as long as they can supply Mg ²⁺ . In a preferred embodiment of the present invention, the magnesium salt can be MgCl ₂ ㆍ 6H ₂ O. In addition, a method of increasing the concentration of salts by using a reverse osmosis (RO) membrane can also be applied to increase the magnesium content in seawater.

The above calcium elution unit (100) may use stainless steel as a material that is resistant to salt corrosion to prevent corrosion due to the salt content of seawater, and may use double blades to perform the reaction evenly without alkaline byproducts being deposited on the bottom. The double blades may be configured to be detachable as needed to enable maintenance and replacement.

Afterwards, magnesium is precipitated in the calcium elution unit (100) and the calcium elution solution from which calcium is eluted is supplied to the first separation unit (200). The first separation unit (200) receives the supplied calcium elution solution and performs solid-liquid separation to separate the magnesium precipitate from the calcium elution solution.

The first separation unit (200) may include a centrifuge (210), and magnesium precipitated in the calcium leached solution may be separated through the centrifuge. At this time, the centrifugation rotation speed may be performed at 3,000 rpm to 5,500 rpm. If the centrifugation rotation speed is less than 3,000 rpm, the precipitated Mg(OH) ₂ may be mixed with the calcium leached solution and discharged, which may cause a problem in that the purity of the vaterite-type calcium carbonate may be lowered. If it exceeds 5,500 rpm, the obtained calcium leached solution may be small, which may cause a problem in that the calcium carbonate yield may be low.

In general, when separating magnesium precipitate from calcium leached solution, membrane filters or filter presses were used in the past, but such separation methods required re-organization after use, and continuous operation was not possible because membrane or filter cloth fastening and separation and washing processes were required. Accordingly, in the present invention, by applying a centrifugal separation method when separating magnesium precipitate from calcium leached solution, continuous operation is possible without a burden on the subsequent stage, and high-purity vaterite crystal calcium carbonate can be stably produced.

The magnesium precipitate separated from the first separation unit has a form of Mg(OH) ₂ , and the Mg(OH) ₂ separated in this manner can be stored separately and used for other purposes.

The calcium leached liquid from which the magnesium precipitate is separated is transferred to a reaction unit (300), and in the reaction unit (300), carbon dioxide-containing gas is injected in the form of microbubbles into the calcium leached liquid from which the magnesium precipitate is separated, thereby generating a reactant in which calcium carbonate is formed through a carbonation reaction as shown in Reaction Formula 3.

[Reaction Formula 3]

CO ₂ (aq) + H ₂ O ↔ H ₂ CO ₃ (aq)

H ₂ CO ₃ (aq) ↔ H ⁺ + HCO ₃ ^-

HCO ₃ ^- ↔ H ⁺ + CO ₃ ^2-

Ca ₂₊ ⁺ CO ₃ ^2- ↔ CaCO ₃

Referring to the above reaction formula 3, it can be seen that hydrogen ions are generated in the process in which carbon dioxide (CO ₂ ) dissolves in the calcium leached solution from which the magnesium precipitate has been separated to form carbonate ions (CO ₃ ^2- ). Accordingly, as carbon dioxide-containing gas is injected to form calcium carbonate, the pH of the calcium leached solution gradually decreases. At this time, NaOH is used as an additive to enable Ca ²⁺ and CO ₃ ^2- to combine through a chemical reaction.

Accordingly, according to one embodiment of the present invention, the carbon dioxide-containing gas supplied in the form of microbubbles can be supplied until the pH of the calcium solution from which the magnesium precipitate is separated becomes 7 to 8.5 to perform a carbonation reaction.

If the pH of the calcium leached solution is less than 7 due to the continuous supply of carbon dioxide-containing gas supplied in the form of microbubbles, the carbonation reaction may proceed excessively, causing the formed vaterite-type crystal structure to recrystallize into calcite, and the calcite-type calcium carbonate may be further carbonated into calcium bicarbonate due to the low pH, and as the calcium bicarbonate dissolves in the solvent, the solid content yield may decrease, resulting in a problem of reduced process efficiency. In addition, if the pH of the calcium leached solution exceeds 8.5, since sufficient carbon dioxide is not supplied, calcium ions effective for the reaction do not react sufficiently and remain, resulting in a problem of reduced carbonation reaction efficiency.

At this time, the carbonation reaction can be performed at 10°C to 40°C, and when the above reaction conditions are satisfied, calcium carbonate in the form of vaterite crystals can be stably produced while preventing a decrease in the reaction rate.

The carbon dioxide-containing gas that can be used in the above carbonation reaction is not particularly limited, but may be at least one selected from the group consisting of, for example, pure carbon dioxide, FINEX off gas (FOG), FINEX tail gas (FTG), blast furnace gas (BFG), converter gas, coal-fired power plant exhaust gas, gas-fired power plant exhaust gas, incinerator exhaust gas, glass melting exhaust gas, thermal facility exhaust gas, petrochemical process exhaust gas, petrochemical process gas, post-combustion exhaust gas, and gasifier exhaust gas.

The above reaction unit (300) may include a microbubble device (310) that supplies carbon dioxide-containing gas in the form of microbubbles to the calcium leached solution from which the magnesium precipitate has been separated. The microbubble device (310) may be applied without limitation to any device capable of supplying microbubbles of carbon dioxide-containing gas to the calcium leached solution, and for example, the microbubble device may be a microbubble pump type, a pressurized dissolution type, or a microbubble device that induces the gas particles to be split into small particles by passing through a micronozzle.

The above microbubble pump type microbubble device generates a vortex in an aqueous solution, sucks in gas through the difference in pressure, and when the vortex collapses, the rotational force of the released bubbles is converted into collision energy, which microfiberizes the bubbles through the impact. This method generates microbubbles when the vortex of a liquid containing bubbles collapses, and the calcium solution from which the magnesium precipitate in the reaction section is separated is injected into the pump, thereby mixing the carbon dioxide gas and the aqueous solution by creating a vortex inside the pump.

In addition, the pressurized dissolution method microbubble device is installed at the bottom of the reaction section, and the amount of gas dissolved increases in proportion to the pressure according to Henry's law. The pressurized dissolution method can utilize this characteristic to dissolve carbon dioxide in an aqueous solution, then reduce the pressure to create a supersaturated condition, and can be designed to automatically shut off when a specific pH, such as pH 7 to 8.5, is reached through a pH meter. The time to reach a specific pH may vary depending on the flow rate conditions, and can be set so that a continuous process can be performed.

In addition, the micro-bubble device with the micro-nozzle method is installed at the bottom of the reaction section, so that the gas passing through it is evenly distributed within the reaction section, which can induce rapid dissolution. In particular, although carbon dioxide has a high solubility in water, dissolution occurs from the part that comes into contact with the liquid (water), so if the part that comes into contact with the liquid is maximized, the dissolution speed of the carbon dioxide can be increased. In a process requiring a high content of carbon dioxide, such as the present invention, the carbon dioxide injected through the micro-bubble device with the micro-nozzle method can be utilized to the maximum extent, thereby increasing process efficiency and shortening the process time.

The microbubbles formed by the above microbubble device are microbubbles with an average diameter of 1.0 mm to 2.5 mm, have less buoyancy than general bubbles in a solution, and shrink and transform into nano-sized bubbles when dissolved in a solvent, and then completely dissolve as they disappear, so not only does the contact area of the bubbles increase, but also the amount of dissolution increases, which can enhance the carbonation reactivity with a calcium solution.

Specifically, when carbonation is performed with microbubbles having an average diameter of 1.0 mm to 2.5 mm, the particle shape of the calcium carbonate produced can be formed in a vaterite crystal phase rather than a calcite or aragonite crystal phase.

Accordingly, if the average diameter of the microbubbles is less than 1.0 mm, the carbon dioxide induces a rapid reaction rate due to the high ionization rate into the calcium leached solution, making it difficult to control the end point of the reaction, which may cause a problem in that the vaterite-type calcium carbonate produced as a result is recrystallized into calcite-type calcium carbonate, and the recrystallized calcite-type calcium carbonate is re-dissolved into the calcium leached solution. In addition, if the average diameter of the microbubbles exceeds 2.5 mm, the interface where the carbon dioxide gas and the calcium leached solution come into contact is small, which reduces the dissolution power into the calcium leached solution, and as the carbonation rate is reduced, the reaction time is delayed, which may cause a problem in that the vaterite-type calcium carbonate is recrystallized into calcite-type calcium carbonate.

In addition, the flow rate of the carbon dioxide-containing gas supplied in the form of the microbubbles may be 0.71 L/min to 2.14 L/min, preferably 0.71 L/min to 1.29 L/min, based on 1 L of the calcium effluent. When the flow rate of the carbon dioxide-containing gas is less than 0.71 L/min, the carbon dioxide injection speed into the calcium effluent is slow, so that the dissolving power decreases, resulting in a long reaction time, which may cause a problem that the vaterite-type calcium carbonate produced during the reaction is recrystallized into calcite-type calcium carbonate, and when it exceeds 2.14 L/min, the reaction speed is fast, making it difficult to control the reaction completion time, which may cause a problem that the vaterite-type calcium carbonate produced during the reaction is recrystallized into calcite-type calcium carbonate, and the recrystallized calcite-type calcium carbonate is re-dissolved back into the calcium effluent.

The reactant in which calcium carbonate is precipitated, obtained from the reaction unit (300) described above, is supplied to the second separation unit (400), and in the second separation unit (400), the supplied reactant is dehydrated to separate the filtrate and the calcium carbonate cake, and the separated calcium carbonate cake is obtained.

At this time, the second separation unit (400) may be equipped with a filter press (410) in which, as an example, filtration and washing discharge are automatically performed, and the reactants may be continuously dehydrated in the equipped filter press to form a calcium carbonate cake. When the filter press is used in this way, it is effective in continuously recovering a large amount of calcium carbonate cake with minimized moisture content.

The above dehydrated calcium carbonate cake is transferred to a drying unit (500), and in the drying unit (500), the transferred calcium carbonate cake is dried and crushed to produce calcium carbonate in the form of vaterite crystals.

The drying unit (500) may include, as an example, a rotary impact dryer (510) that dries and crushes calcium carbonate cake supplied from a second separation unit by spraying hot air onto the cake and causing particle collisions by centrifugal force, as shown in FIG. 3; a hot air supply unit (520) that supplies hot air to the rotary impact dryer; and a collecting unit (530) that collects dried and finely divided calcium carbonate in the rotary impact dryer.

The above rotary impact dryer (510) is a dryer that dries and crushes the supplied calcium carbonate cake by particle collision using high-speed centrifugal force while spraying hot air supplied from a hot air supply unit (520). The dryer has a crushing rotary blade formed on a wall surface and/or a rotating shaft, so that moisture contained in the calcium carbonate cake is separated and dried by strong rotational force and hot air, and at the same time, stable crushing and crushing are achieved by collision between the calcium carbonate cake particles and the dryer wall surface, the crushing rotary blade, and the calcium carbonate cake.

At this time, the rotation speed of the rotary impact dryer of the drying unit may be 5,000 rpm to 9,000 rpm.

The hot air supply unit (520) for supplying hot air to the above-described rotary impact dryer (510) is composed of a blower (521) and a heater (522) and can supply hot air of a certain temperature to the above-described rotary impact dryer. The temperature of the hot air supplied to the above-described rotary impact dryer can be 100°C to 550°C, preferably 100°C to 400°C, and more preferably 100°C to 350°C.

If the hot air temperature is less than 100°C, the moisture present in the calcium carbonate cake is not sufficiently removed, causing recrystallization of calcium carbonate due to the moisture, which may cause a deterioration in the quality of the calcium carbonate product. In addition, if the temperature exceeds 400°C, the calcium carbonate having the formed vaterite crystal phase undergoes a phase transition into a calcite crystal ^phase , and furthermore, _CO32- forming the calcium carbonate structure dissociates into _CO2 , which may cause a problem of causing a deterioration in the purity of the calcium carbonate.

In addition, the collecting unit (530) of the drying unit collects dried and finely divided calcium carbonate from the rotary impact dryer. At this time, the calcium carbonate can be collected by classifying only the finely divided calcium carbonate that is separated from the dryer by hot air. The collecting unit can be applied without limitation as long as it is a device that can collect solid particles in an air stream, and as an example, it can be a dust collecting device that collects calcium carbonate particles in an air stream using a bag-shaped filter cloth.

Meanwhile, the drying unit may be equipped with a blower (540) and a chimney (550) that can transport and discharge the air separated by the collecting unit to the outside.

Hereinafter, a method for continuously producing calcium carbonate in the form of vaterite crystals according to the present invention will be described in detail.

The continuous manufacturing method of calcium carbonate in a vaterite crystal phase according to the present invention comprises: adding seawater to an alkaline industrial by-product to generate a calcium leached solution in which magnesium is precipitated in a solid state [step (a)]; centrifuging the generated calcium leached solution to separate a magnesium precipitate from the calcium leached solution [step (b)]. Thereafter, a carbon dioxide-containing gas is supplied in the form of microbubbles to the calcium leached solution from which the magnesium precipitate has been separated to obtain a reactant in which calcium carbonate is precipitated [step (c)]; dehydrating the obtained reactant to form a calcium carbonate cake [step (d)]; then, drying and pulverizing the calcium carbonate cake through particle collision by rotation while spraying hot air on the formed calcium carbonate cake to produce calcium carbonate in a vaterite crystal phase [step (e)].

Calcium carbonate produced in this manner may have a vaterite crystal phase of 80 wt% or more, preferably 85 wt% or more, a purity of 97% or more, preferably 98%, a whiteness of 99% or more, and an average particle size of 1 ㎛ to 5 ㎛, and thus may be used as an expensive inkjet dye, a functional additive for papermaking, a rubber additive, a plastic additive, a calcium supplement, or an artificial bone.

The continuous manufacturing method of vaterite crystal phase calcium carbonate according to the present invention uses seawater and alkaline industrial by-products as starting materials, so that the amount of limestone, a natural resource, can be reduced, thereby enabling resource conservation, and the raw material of vaterite crystal phase calcium carbonate can be economically supplied, and the calcium contained in the alkaline industrial by-product can be highly efficiently extracted using the magnesium contained in the seawater, and at the same time, the magnesium in the seawater, which hinders the production of high-purity calcium carbonate using the alkaline industrial by-product, is separated and removed by a centrifugal method, thereby increasing the purity of the calcium carbonate, and the economic feasibility of storing carbon dioxide and manufacturing calcium carbonate can be improved by utilizing seawater instead of an expensive solvent.

In addition, the continuous production method of calcium carbonate in vaterite crystal form according to the present invention is easy to scale up by applying a centrifugal separation method and a rotary impact drying method using hot air, and can perform pulverization and sorting simultaneously with drying during drying, and can continuously produce calcium carbonate in vaterite crystal form at a high yield.

The continuous production method of calcium carbonate in vaterite crystal phase according to the present invention is the same as that mentioned in the corresponding continuous production device for calcium carbonate in vaterite crystal phase, so a person skilled in the art will be able to clearly understand the production method, and thus, the description will be omitted to avoid duplication.

Hereinafter, the present invention will be described more specifically through specific examples. The following examples are merely examples to help understand the present invention, and the scope of the present invention is not limited thereto.

<Example 1>

1-1: Calcium solution formation step

Calcium carbonate in the form of vaterite crystals was produced using the device shown in Fig. 1. 50 kg of lime kiln dust and 500 kg of seawater were supplied to the calcium elution unit and stirred at 25°C and 100 rpm for 1 hour to form a calcium elution solution in which magnesium was precipitated. At this time, the lime kiln dust had an effective particle size of 1,000 ㎛, and the results of chemical component analysis using an XRF (X-ray Fluorescence Spectrometer) device are shown in Table 1 below.

[Table 1]

In addition, seawater was collected from the east coast and concentrated using reverse osmosis. The pH of the seawater was 7.8, and the calcium and magnesium concentrations were analyzed by the Korea Ship and Ocean Research Institute, an authorized analytical institution, and were found to be 798.4 mg/L and 2,546.6 mg/L, respectively, which were similar to the components of general seawater desalination concentrate.

1-2: Magnesium precipitate separation and carbonation reaction step

In the calcium elution portion of Example 1-1, the precipitated magnesium was separated from the calcium elution liquid using a centrifuge (rotation speed 3,500 rpm). Thereafter, the calcium elution liquid from which the magnesium precipitate was separated was supplied to a reaction portion equipped with a microbubble device and stirred at a speed of 100 rpm. At this time, NaOH was injected as an additive to induce a reaction in the form of Ca(OH) ₂ through a chemical reaction with Ca2 ⁺ ions. The NaOH was added in an amount equivalent to the molar ratio that reacts with Ca2 ⁺ , and if a large amount is added, the unreacted NaOH will form _Na2CO3 through a chemical reaction with _CO2 injected in the form of microbubbles, and during the reaction, the already formed _vaterite -type calcium carbonate undergoes a phase transition to calcite, which is a more stable state, so that it may be difficult to obtain high-content vaterite-type calcium carbonate. After securing a reaction stabilization time of 5 minutes, carbon dioxide was supplied in the form of microbubbles at 20°C using the microbubble device until the pH of the calcium leached solution became 7.5. Carbon dioxide was supplied at a rate of 0.71 L/min based on 1 L of the calcium leached solution from which the magnesium precipitate was separated, to obtain a reactant in which calcium carbonate was precipitated. At this time, the average diameter of the microbubbles was 2.14 mm.

1-3: Dehydration and drying step of the reactant in which calcium carbonate is precipitated

The reactant in which calcium carbonate was precipitated in Example 1-2 was dehydrated using a filter press to form a calcium carbonate cake, and the formed calcium carbonate cake was continuously supplied at a speed of 70 kg/h to a drying section including a hot air supply section, a rotary impact dryer, and a collecting section. The calcium carbonate cake supplied to the drying section was dried and pulverized through particle collision by rotation at 7,000 rpm while spraying hot air at 300°C, and finely powdered vaterite crystals were collected and manufactured in the collecting section.

<Examples 2 to 7>

Calcium carbonate was manufactured in the same manner as in Example 1, except that the conditions of each example were changed as shown in Table 2 below.

<Comparative examples 1 to 12>

Calcium carbonate was manufactured in the same manner as in Example 1, except that the conditions of each comparative example were changed as shown in Table 2 below.

[Table 2]

[Experimental Example 1: Measurement of purity and whiteness of calcium carbonate]

The purity and whiteness of the calcium carbonate manufactured in the examples and comparative examples were measured and shown in Table 3. At this time, the purity of the calcium carbonate was calculated by measuring the weight of calcium carbonate among the solid content obtained in the examples and comparative examples, and the whiteness was measured using a chromaticity meter (CR-400, Konica Minolta).

[Table 3]

As shown in Table 3, the calcium carbonate manufactured in the examples and comparative examples all had a purity of 97.5% or higher and a whiteness of 99% or higher.

[Experimental Example 2: Measurement of crystal structure and whiteness of calcium carbonate]

In order to measure the crystal structure of the calcium carbonate manufactured in the examples and comparative examples, the degree of crystallization for the unique crystal structure (calcite, vaterite, aragonite) of the calcium carbonate included in the sample was calculated based on the Rietveld method from the X-ray spectrum, and the value was expressed as a percentage and calculated as a relative value of vaterite. In addition, a scanning electron microscope (JSM-IT200, JEOL Corporation) was used to analyze the particle size, and the results are shown in Figures 5 and 6 and Table 4 below.

[Table 4]

As shown in Table 4, Figures 5 and 6, it was confirmed that in the case of Examples 1 to 7, high-content vaterite-type calcium carbonate could be stably manufactured compared to Comparative Examples 1 to 12.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications may be made within the scope of the claims, the detailed description of the invention, and the attached drawings, which also fall within the scope of the present invention.

Claims (10)

A calcium extraction unit that produces a calcium extraction solution in which magnesium is precipitated in a solid state by adding seawater to alkaline industrial by-products; A first separation unit for separating a magnesium precipitate by centrifuging the calcium elution solution produced in the above calcium elution unit; A reaction unit which receives a calcium leached solution from which a magnesium precipitate is separated from the first separation unit, and supplies carbon dioxide-containing gas in the form of microbubbles having an average diameter of 1 mm to 2.5 mm to the calcium leached solution from which the magnesium precipitate is separated, thereby obtaining a reactant in which calcium carbonate is precipitated; A second separation unit for removing the reactant obtained from the above reaction unit to obtain a calcium carbonate cake; and A continuous production device for vaterite crystal-phase calcium carbonate, characterized by including a drying unit for producing vaterite crystal-phase calcium carbonate by simultaneously drying and crushing the calcium carbonate cake through particle collision by rotation while spraying hot air of 100°C to 550°C on the calcium carbonate cake obtained in the second separation unit. In the first paragraph, A continuous production device for calcium carbonate in vaterite crystal form, characterized in that the seawater is selected from the group consisting of normal seawater, seawater desalination concentrate, brine, bittern, and mixtures thereof. In the first paragraph, A continuous production device for vaterite crystal-phase calcium carbonate, characterized in that the alkaline industrial by-product is selected from the group consisting of paper sludge ash (PSA), cement kiln dust (CKD), quicklime kiln dust, fuel ash, bottom ash, fly ash, de-inking ash, steelmaking slag, waste concrete, and mixtures thereof. In the first paragraph, A continuous production device for calcium carbonate in vaterite crystal form, characterized in that the weight ratio of the alkaline industrial by-product and seawater is 1:5 to 100. In the first paragraph, A continuous production device for calcium carbonate in vaterite crystal form, characterized in that the flow rate of the carbon dioxide-containing gas is 0.71 L/min to 2.14 L/min per 1 L of calcium leached solution from which magnesium precipitate is separated. (a) a step of adding seawater to an alkaline industrial by-product to produce a calcium solution in which magnesium is precipitated in a solid state; (b) a step of centrifuging the generated calcium leached solution to separate the magnesium precipitate from the calcium leached solution; (c) a step of supplying carbon dioxide-containing gas in the form of microbubbles having an average diameter of 1 mm to 2.5 mm to the calcium leached solution from which the magnesium precipitate has been separated to obtain a reactant in which calcium carbonate is precipitated; (d) a step of dehydrating the obtained reactant to obtain a calcium carbonate cake; and (e) a step of producing calcium carbonate in the form of vaterite crystals by simultaneously drying and crushing the calcium carbonate cake through particle collision by rotation while spraying hot air of 100° C. to 550° C. on the obtained calcium carbonate cake; a continuous method for producing calcium carbonate in the form of vaterite crystals, characterized by including the step. In Article 6, A method for continuously producing calcium carbonate in vaterite crystal form, characterized in that the seawater in step (a) is selected from the group consisting of normal seawater, seawater desalination concentrate, brine, bittern, and mixtures thereof. In Article 6, A method for continuously producing vaterite crystal-phase calcium carbonate, characterized in that the alkaline industrial by-product of step (a) is selected from the group consisting of paper sludge ash (PSA), cement kiln dust (CKD), quicklime kiln dust, fuel ash, bottom ash, fly ash, de-inking ash, steelmaking slag, waste concrete, and mixtures thereof. In Article 6, A continuous method for producing calcium carbonate in vaterite crystal form, characterized in that the weight ratio of the alkaline industrial by-product and seawater in step (a) is 1:5 to 100. In Article 6, A method for continuously producing calcium carbonate in vaterite crystal form, characterized in that the flow rate of the carbon dioxide-containing gas is 0.71 L/min to 2.14 L/min per 1 L of calcium leached solution from which magnesium precipitate is separated.

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