Methods for fixing carbon dioxide

Abstract

A method for fixing carbon dioxide, comprising: (a) Treatment of natural mineral or steel slag with an acid to extract metal ion components; (b) Injecting carbon dioxide into an extraction solution containing the extracted metal ion components from (a) to carbonize them; (c) Transferring a solution in which the resulting carbonates from (b) are dissolved into a dissolved carbonate storage tank and storing the same; and (d) Transferring the stored, dissolved carbonates to a carbonate separation / purification tank and adjusting the pH to 7 or higher to separate the carbonates, wherein the pH of the extraction solution is not adjusted before the introduction of the carbon dioxide in (b) and the carbonation in (b) takes place without the supply of additional heat and additional pressure, characterized by the fact that The carbonization process is carried out at a carbon dioxide feed rate of 2 l / min and is completed after 5 minutes.

Description

BACKGROUND(a) Technical field

[0001] The present invention relates to a method for fixing carbon dioxide. In particular, the disclosure relates to a method for fixing carbon dioxide using natural minerals or steel slag produced in ironworks, in order to reduce the emission of carbon dioxide into the atmosphere. (b) State of the art

[0002] Carbon dioxide emissions are rising sharply due to increased consumption of fossil fuels and are recognized as a major cause of global warming. Therefore, many countries around the world have made efforts and tightened regulations to reduce carbon dioxide emissions.

[0003] Reducing carbon dioxide emissions can be achieved either through reduced use of fossil fuels themselves or through a process that separates, collects, and fixes the carbon dioxide produced from them. In the past, the latter has involved using the separated and collected carbon dioxide as a source for methanol synthesis, or fixing it by depositing it in the ocean or by using carbonate minerals.

[0004] For example, one process fixes carbon dioxide using carbonate minerals. In this process, the alkaline substances found in minerals (CaO, MgO, K2O, Na2O, etc.) are reacted with carbon dioxide to produce carbonates (CaCO3, MgCO3, Na2CO3, K2CO3, etc.) in order to fix the carbon dioxide emitted by industrial plants.

[0005] Slag produced during steelmaking includes molten iron pretreatment slag, converter slag, stainless steel slag, electric arc furnace slag, and similar materials. This steel slag is usually buried, except in limited cases as cement or aggregate for road or building construction. Numerous methods have been proposed for the utilization of discarded steel slag, as finding suitable landfill sites for disposal is becoming increasingly difficult.

[0006] KR 10 2002 050 429 A, entitled "Pretreatment Method of Steel Slag by Using Carbon Dioxide," proposes a method for fixing carbon dioxide to the surface of steel slag, which is used in port construction or artificial fish banks. Another approach to carbon dioxide disposal using slag, KR 10 2006 023 206 A, entitled "A Method for Fixing of Carbon Dioxide," proposes fixing carbon dioxide to the surface of slag containing a certain amount of water by reacting it with carbon dioxide. However, the methods described in both patents require excessively long reaction times because the efficiency of the reaction between carbon dioxide and the slag is low and therefore economically impractical.

[0007] KR 10 0 891 551 B1, entitled "Solidification Method of Carbon Dioxide by a Mineral Carbonation of Slag Generated in an Iron Industry, Capable of Improving Reaction Efficiency," proposes a method for solidifying carbon dioxide by carbonating alkaline components extracted from steel slag with gaseous carbon dioxide via a hydrothermal reaction under pressure or a hydrothermal reaction at normal pressure. However, the hydrothermal reaction consumes a great deal of energy, and there is no clear description of how the carbon dioxide is fixed after the carbonation of the alkaline components.

[0008] The German patent application KR 10 0 801 542 B1, entitled "Method For Converting Talc For Mineral Carbonation By Removing Water Molecules And Hydroxyl Groups, And A Method For Mineral Carbonation Of Carbon Dioxide Using Talc Obtained Thereby," proposes a method for fixing carbon dioxide using the natural mineral talc. However, since a particle size of 125 µm or smaller is required, excessive energy is needed for pulverizing the mineral. Furthermore, after the alkaline components are treated with a weakly acidic solvent, such as acetic acid, for extraction, some metal ions (e.g., Ca) react. 2+ ), when the pH is increased for carbon dioxide fixation by carbonation, with hydroxide ions (OH) -) and milky lime (Ca(OH)2) forms, leading to a suspension. Therefore, an additional precipitation or filtration process is necessary. Since the precipitated carbonate remains suspended in the solution, separation is difficult, and establishing an industrially applicable, continuous process is not straightforward.

[0009] A method for fixing carbon dioxide is also described in US 2009 / 0301352 A1. Further techniques for fixing carbon dioxide are disclosed in US 2005 / 0180910 A1, US 2005 / 0002847 A1, and WO 2009 / 039393 A2. SUMMARY

[0010] The present invention provides a method for fixing carbon dioxide with the features of claim 1 and a method for fixing carbon dioxide with the features of claim 5. The invention thus provides a method capable of overcoming the problems present in conventional methods, successfully fixing carbon dioxide, and applicable to current processes. Carbon dioxide can be fixed by a liquid-phase reaction, and it exhibits improved reaction efficiency at normal temperature and pressure, thereby reducing energy consumption. Furthermore, the present invention eliminates the need for pH adjustment during carbon dioxide fixation, preventing the formation of suspended milky lime and allowing for a continuous process. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The above-mentioned and other tasks, features and advantages of the present invention will now be described in more detail with reference to certain exemplary embodiments thereof, which are illustrated in the accompanying drawings, which are shown below for illustrative purposes only and thus do not limit the disclosure, and wherein: Fig. Figure 1 shows an existing method for fixing carbon dioxide using slag; and Fig. Figure 2 shows a method for fixing carbon dioxide using natural minerals or steel slag according to an exemplary embodiment of the present invention.

[0012] It is understood that the attached drawings are not necessarily to scale and thus represent a simplified depiction of various preferred features illustrating the basic principles of the disclosure. The specific design features of the disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, are determined by the intended application and the environment in which it is used. DETAILED DESCRIPTION

[0013] The following section refers in more detail to the various embodiments of the invention, examples of which are illustrated in the accompanying drawings and described as below.

[0014] The present invention provides a method for fixing carbon dioxide, comprising (a) treating natural mineral or steel slag with an acid to extract metal ion components; (b) feeding carbon dioxide into an extraction solution containing the metal ion components obtained in step (a) to carbonate them; (c) transferring and storing a solution in which the carbonates resulting from step (b) are dissolved into a dissolved carbonate storage tank; and (d) transferring the stored dissolved carbonates into a carbonate separation / purification tank and adjusting the pH to approximately 7 or higher to separate the carbonates.

[0015] In step (a), the natural mineral is preferably not restricted. For example, peridotite, basalt, talc, serpentinite, wollastonite, etc., which contain a high amount of calcium oxide and magnesium oxide, can be used. The calcium oxide and magnesium oxide content of serpentinite and wollastonite is shown in Table 1 as an example.

[0016] And, in step (a), the steel slag can be slag, electric arc furnace slag, or converter slag, which is produced, for example, in ironworks during blast furnace, converter, or oxygen blowing processes. Steel slag is mostly used as cement or aggregate for road or building construction. The chemical composition of various steel slags is also shown in Table 1. Table 1 CaO (wt%) MgO (wt%) Natural mineral Serpentinite 0 40 Wollastonite 48 0 steel slag blast furnace slag 41 10 Converter slag 46 2 electric arc furnace slag 20 5 Pan slag 54 10

[0017] Since the natural mineral and the steel slag contain a large proportion of metal oxides, including calcium oxide and magnesium oxide, they exhibit high basicity. The metal components of the metal oxides are released into the solution through acid treatment, thus exhibiting alkaline properties. The metal ion components are predominantly Ca 2+ and Mg 2+ , and the rest can K + , N / a + , etc.

[0018] In particular, acid treatment can be carried out at pH 3–5. For this purpose, an acidic compound such as acetic acid, sodium acetate, hydrochloric acid, etc., can be used at a sufficient concentration. Thus, the solution containing the metal ions, for example, calcium, has a pH of 3–5. 2+ , Mg 2+ etc., contains an acidic pH value after acid treatment.

[0019] According to the existing procedure, the pH of the extraction solution is adjusted to approximately 12, and then carbon dioxide is introduced to form a carbonate precipitate for fixation by carbonation. During this process, some of the dissolved metal ions (e.g., Ca) react. 2+ , Mg 2+ , etc.) with hydroxide ions (OH - ) to form milky lime, which thus leads to a suspension. If the suspended solid is not effectively separated, it becomes difficult to fix carbon dioxide using a continuous process. As a result, large-scale carbon dioxide treatment is impossible.

[0020] To overcome the limitations of existing processes, the present invention omits the step of adjusting the pH to approximately 12. By omitting the pH adjustment step, the formation of milky lime and, consequently, the formation of suspended solids can be prevented. This enables a continuous process and the large-scale treatment of carbon dioxide. According to the present invention, the pH adjustment step to predetermined alkaline ranges (for example, pH 7 or higher) for the separation of carbonates is carried out after a CO2 reaction with metal ion components has been completed. Since the metal ions have participated in reactions to form the carbonates, the probability of the formation of suspended solids through reaction with hydroxide ions is very low.The solution containing the carbonates formed by carbon dioxide fixation (step (b)) is transferred to and stored in a dissolved carbonate storage tank. After the stored dissolved carbonates are transferred to a carbonate separation / purification tank, the pH is adjusted to 7 or higher to separate the carbonates. Consequently, the carbonation and carbonate separation processes can be carried out continuously.

[0021] In the present invention, the carbonization in step (b) can be carried out at normal temperature and pressure. Here, normal temperature and pressure mean that no additional heat or pressure needs to be supplied. For example, the temperature can be between approximately 0-40°C (32-104°F), and preferably between approximately 10-25°C (50-77°F), and the pressure can be between approximately 0.1-5 atm, and preferably between 0.5-2 atm. According to the present invention, the carbonization can be completed within approximately 5 minutes, even without the energy-consuming hydrothermal reaction. That is, the carbonization reaction of step (b) can be completed within approximately 5 minutes if the carbon dioxide feed rate is, for example, 2 l / min.Since the release of the metal ion components in step (a) can be completed within approximately 2 hours, the entire process can be finished in approximately 2 hours, making it a very economical process. Thus, carbon dioxide can be effectively fixed using natural minerals or steel slag, e.g., slag, electric furnace slag, or converter slag produced in ironworks during blast furnace, converter, or oxygen blowing processes, thereby significantly reducing greenhouse gas emissions and enabling the use of previously discarded steel slag.

[0022] The carbon dioxide gas treated by the process according to the present invention can be any carbon dioxide gas, including that produced as a byproduct of industrial furnaces such as blast furnaces, lime kilns, coking furnaces, etc., or by sintering or hot rolling processes, power generation, waste heat boilers, or the like. Accordingly, if a plant is equipped with an ironworks capable of capturing the carbon dioxide produced during the steelmaking process, the steel slag produced during the process can be used to capture the gases that contribute to global warming on-site. This allows compliance with environmental regulations, and the byproducts, such as metal oxides, can be used as a new source of revenue instead of being disposed of as waste. EXAMPLE

[0023] The example and experiment will now be described. The following example and experiment serve only for illustration and are not intended to limit the scope of the revelation. [Example]

[0024] Metal ion components were extracted from steel slag with a particle size of 1–5 mm using 10 vol% acetic acid at a pH of 3–5. The weight ratio of extraction solvent to slag was 10:1, and the stirring speed was 150 rpm. The change in calcium ion concentration with extraction time is shown in Table 2. Table 2 Extraction time (hrs) 1 2 3 Calcium ion concentration (mg / L) 26000 38000 38000

[0025] As can be seen from Table 2, the extraction of the metal ions by the acid treatment was completed after approximately two hours.

[0026] Carbonization (carbon dioxide fixation) was carried out by introducing carbon dioxide into the resulting extraction solution. Carbonization was performed at 25°C (77°F) and 1 atm, with a carbon dioxide flow rate of 2 L / min. The changes in calcium ion concentration and pH during carbonation are shown in Table 3. Table 3 Carbonization time (min) 1 1.5 2 2.5 3 3.5 4 4.5 Calcium ion concentration (mg / l) 38000 22000 18000 16000 13500 13200 13000 13000 pH 3,71 3,90 3,98 4,02 4,06 4,10 4,14 4,22

[0027] As can be seen from Table 3, carbonization was completed after approximately 4.5 minutes following the injection of carbon dioxide.

[0028] The conversion rate of the calcium ions and the purity of the precipitated calcium carbonate are summarized in Table 4. Table 4 Calcium ion concentration (mg / l) Conversion rate of dissolved calcium ions ((AB) / A×100, %) Purity of precipitated calcium carbonate (%) Before carbonization(A) After carbonization (B) 38000 13000 65,8 99

[0029] As can be seen from Table 4, both the purity and the yield of calcium carbonate precipitation could be improved. Thus, the process proposed in the present invention, in which carbon dioxide is fixed by carbonation without pH adjustment, enables the production of high-purity carbonate in approximately two hours. Furthermore, large-scale carbon dioxide processing is possible because a continuous process is enabled.

[0030] Advantageously, the process for fixing carbon dioxide according to the present invention, wherein metal ions are extracted from natural mineral or steel slag by acid treatment, is much more efficient than the existing solid-gas reaction. Since the reaction is carried out at normal temperature and pressure without the need for an energy-intensive process such as hydrothermal synthesis, energy consumption can be reduced. Furthermore, since pH adjustment for carbon dioxide fixation is omitted, the formation of suspended, milky lime can be prevented, and a continuous process is enabled.

[0031] Furthermore, since the method for fixing carbon dioxide according to the present invention enables the reduction of carbon dioxide emissions through the use of steel slag, which is currently only used for worthless applications, it can be an effective measure to address the greenhouse gas reduction requirement imposed on steel-producing companies by enabling the recycling of discarded steel slag as carbonate.

Claims

[1] A method for fixing carbon dioxide, comprising: (a) Treatment of natural mineral or steel slag with an acid to extract metal ion components; (b) Injecting carbon dioxide into an extraction solution containing the extracted metal ion components from (a) to carbonize them; (c) Transferring a solution in which the resulting carbonates from (b) are dissolved into a dissolved carbonate storage tank and storing the same; and (d) Transferring the stored, dissolved carbonates to a carbonate separation / purification tank and adjusting the pH to 7 or higher to separate the carbonates, wherein the pH of the extraction solution is not adjusted before the introduction of the carbon dioxide in (b) and the carbonation in (b) takes place without the supply of additional heat and additional pressure, characterized by , that The carbonization process is carried out at a carbon dioxide feed rate of 2 l / min and is completed after 5 minutes. [2] The method for fixing carbon dioxide according to claim 1, wherein the treatment with the acid is carried out at pH 3 - 5. [3] The method for fixing carbon dioxide according to claim 1, wherein the carbonization is carried out at a temperature between 0-40°C under normal pressure. [4] The method for fixing carbon dioxide according to claim 1, wherein the steel slag belongs to the group consisting of slag, electric arc furnace slag or converter slag produced in ironworks during blast furnace, converter or oxygen blowing processes. [5] A method for fixing carbon dioxide, comprising: (a) Treatment of slag with an acid to extract metal ion components; (b) Injecting carbon dioxide into an extraction solution containing the extracted metal ion components from (a) to carbonize them, (c) Transferring a solution in which the carbonates resulting from (b) are dissolved into a first tank and storing the resulting carbonates in the first tank; and (d) Transferring the stored, dissolved carbonates to a second carbonate tank and adjusting the pH to a predetermined range to separate the carbonates, wherein the pH of the extraction solution is not adjusted before the introduction of the carbon dioxide in (b) and the carbonation in (b) takes place without the supply of additional heat and additional pressure, characterized by , that The carbonization process is carried out at a carbon dioxide feed rate of 2 l / min and is completed after 5 minutes. [6] The method for fixing carbon dioxide according to claim 5, wherein the treatment with the acid is carried out at pH 3 - 5. [7] The method for fixing carbon dioxide according to claim 5, wherein the carbonization is carried out at a temperature between 0-40°C and the pressure is between 0.1-5 atm. [8] The method for fixing carbon dioxide according to claim 5, wherein the carbonization is carried out at a temperature between 10-25°C and the pressure is between 0.1 and 2 atm. [9] The method for fixing carbon dioxide according to claim 5, wherein the slag is steel slag and the steel slag belongs to the group consisting of electric furnace slag or converter slag produced in ironworks during blast furnace, converter or oxygen blowing processes. [10] The method for fixing carbon dioxide according to claim 5, wherein the slag is natural mineral slag. [11] The method for fixing carbon dioxide according to claim 5, wherein the set, predetermined range for pH is 7 or higher.

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