TW202012643A - Method for recovering calcium from steelmaking slag - Google Patents

Abstract

An object of the invention is to provide a method for recovering calcium from steelmaking slag which can make calcium eluted from steelmaking slag into a CO₂ aqueous solution deposit by a much simpler method. The invention for achieving the above purpose is related to a method for recovering calcium from steelmaking slag. The above method has a process which is to make steelmaking slag contact with a CO₂ aqueous solution containing carbon dioxide, and a process which is to spray the CO₂ aqueous solution contacted by the steelmaking slag.

Description

Method for recovering calcium from steel-making slag

The invention relates to a method for recovering calcium from steel-making slag.

Steelmaking slag (converter slag, pretreatment slag, secondary refining slag, electric furnace slag, etc.) generated in the steelmaking process is used in a wide range of applications including cement materials, roadbed materials, civil engineering materials and fertilizers ( Refer to Non-Patent Documents 1 to 3). In addition, some steel-making slag that is not used in the above-mentioned applications is landfilled.

Known steelmaking slag contains calcium (Ca), iron (Fe), silicon (Si), manganese (Mn), magnesium (Mg), aluminum (Al), phosphorus (P), titanium (Ti), chromium (Cr ), sulfur (S) and other elements. Among these, the most contained element in the steelmaking slag is calcium used in large amounts in the steelmaking process, and usually iron is the second most contained. Generally, among all the masses of steel-making slag, about 20% to 50% by mass is calcium, and about 1% to 30% by mass is iron.

The calcium in the steelmaking slag is generated by reacting the free lime (CaO) input in the steelmaking process as it is, or the free lime precipitated during the solidification of the steelmaking slag, free lime reacts with water vapor or carbon dioxide in the air Calcium hydroxide (Ca(OH) ₂ ) or calcium carbonate (CaCO ₃ ), or calcium silicate (Ca ₂ SiO ₄ or Ca ₃ SiO ₅ etc.) or calcium oxide produced by the reaction of CaO with Si or Al during solidification Iron and aluminum (Ca ₂ (Al _1-x Fe _x ) ₂ O ₅ ) and the like exist (hereinafter, compounds containing calcium are also collectively referred to as “calcium compounds.”).

Calcium carbonate and calcium oxide are the main slag forming materials in the iron making process and steel making process of the iron making process, and are used as an adjuster for the alkalinity and viscosity of the slag, as well as a dephosphorizing agent from molten steel, etc. . In addition, calcium hydroxide obtained by adding water to calcium oxide is used as a neutralizing agent such as an acid in the drainage process. Therefore, if the calcium compound contained in the steel-making slag is recovered and reused in the iron-making process, it can be expected that the cost of iron-making can be reduced.

In addition, it is expected that the number of civil engineering projects for using steel-making slag as roadbed materials, civil engineering materials, cement materials, etc. will be reduced in the future, and the land that can be filled with steel-making slag will be reduced. From this point of view, it is also expected that the calcium compound contained in the steel-making slag is recovered to reduce the volume of the steel-making slag for reuse or landfill treatment.

The calcium in the steel-making slag can be eluted and recovered in an acidic aqueous solution such as hydrochloric acid, nitric acid, or sulfuric acid. However, the salts of calcium and the above acids produced in this method are difficult to reuse. For example, calcium chloride produced by dissolving calcium in steelmaking slag in hydrochloric acid is reusable if heated to form oxides, but there is a problem in that the treatment cost of the harmful chlorine gas generated during the above heating is high. In addition, when attempting to elute and recover calcium in the steelmaking slag in an acidic aqueous solution, there is also a problem that the cost of purchasing the acid and discarding the acid after the dissolution treatment is high.

On the other hand, if calcium is eluted and recovered from the steel-making slag in an aqueous solution containing carbon dioxide (hereinafter, also simply referred to as "CO ₂ aqueous solution"), it is expected that the above-mentioned problems caused by the use of acid can be solved (refer to the patent References 1 to 3). In addition, a large amount of carbon dioxide is contained in the exhaust gas. After desulfurization and denitration of the exhaust gas, in addition to air and water vapor, a gas that is almost carbon dioxide can be obtained. Industrially, as shown in Non-Patent Document 4, technology for extracting carbon dioxide from exhaust gas is being put into practical use.

Patent Document 1 describes a method of recovering precipitated calcium carbonate by blowing carbon dioxide into an aqueous solution that has eluted calcium in the converter slag. At this time, in order to suppress the generation of calcium bicarbonate having high solubility in water, the pH value is maintained at a lower limit of about 10. Although Patent Document 1 does not describe a specific method of maintaining the pH at 10 or more, it is considered that the pH is maintained at 10 or more by adjusting the amount of carbon dioxide injected.

Patent Document 2 describes that the crushed steel-making slag is separated in the iron-concentrated phase and the phosphorus-concentrated phase, and the calcium compound in the phosphorus-concentrated phase is dissolved in the wash water in which carbon dioxide has been dissolved, and then the wash water is heated to 50 ~60°C, a method of recovering calcium bicarbonate in washing water as calcium carbonate.

Patent Document 3 describes a method in which calcium compounds are eluted and recovered from the steel-making slag multiple times. In this method, it is described that the steelmaking slag (pretreatment slag) is impregnated with carbon dioxide water for many times, and the 2CaO•SiO ₂ phase has been solid-dissolved and the phosphorus in this phase is preferentially eluted.

Patent Document 4 describes a method of contacting a CO ₂ aqueous solution with a steel-making slag to dissolve calcium and phosphorus, then removing carbon dioxide from the aqueous solution to precipitate calcium compounds and phosphorus compounds, and recovering calcium. Patent Document 4 describes that by this method, it is easier to elute a larger amount of calcium than the methods described in Patent Documents 1 to 3, and the calcium recovery efficiency can be improved. Patent Document 4 describes that as a method for removing carbon dioxide from an aqueous solution in which calcium and phosphorus have been dissolved, a selected one selected from the group consisting of the atmosphere, nitrogen, oxygen, hydrogen, argon, and helium is blown into the aqueous solution. Or two or more gas methods.

On the other hand, Fe in the steel-making slag exists as iron-based oxides, calcium iron-aluminum oxide, and although a very small amount of metallic iron. Among these, the iron-based oxide contains elements such as Ca, Al, Si, P, Ti, Cr, and S in addition to Mn or Mg in small amounts. In addition, calcium iron iron aluminum also contains a small amount of elements such as Si, P, Ti, Cr, and S. In addition, in the present specification, the iron-based oxide also includes a compound whose part of the surface is changed to hydroxide or the like due to water vapor in the air, and calcium iron aluminum oxide also includes water vapor and carbon dioxide due to air A part of the surface is changed to a compound such as hydroxide or carbonate.

Most of the above iron-based oxides exist as wurtzite-based oxides (FeO), and others also exist as hematite-based oxides (Fe ₂ O ₃ ) or magnetite-based oxides (Fe ₃ O ₄ ) .

Among these, the skutterite-based oxide and the hematite-based oxide are dispersed in the magnetite-based oxide (Fe ₃ O ₄ ) as a ferromagnetic body, so they can be removed from the steelmaking slag by magnetic separation Separate. In addition, magnetite-based oxides alone or in combination with other iron-based oxides can also be separated from the steel-making slag by magnetic separation.

In addition, Patent Document 5 to Patent Document 7 describe a method of reorganizing a wurtzite-based oxide into a magnetite-based oxide by oxidation treatment or the like in order to separate a larger amount of iron-based oxide by magnetic separation.

The above-mentioned calcium iron iron aluminum becomes a magnetic material because of magnetization, so it can still be separated from the steel-making slag by magnetic separation.

Iron-based oxides and calcium-iron-aluminum oxides (hereinafter, these are also referred to as "iron-based compounds." Calcium-iron-aluminum oxides are calcium compounds and also iron-based compounds.) Because their phosphorus content is 0.1% by mass or less Since it is a trace amount, it can be used as a raw material for blast furnace or sintering if it is recovered from the steel-making slag by magnetic separation or the like.

The metallic iron is Fe that is caught in the slag in the steel-making process or fine Fe that is precipitated in the solidification of the steel-making slag. The large metallic iron among the metallic iron is removed by other methods of magnetic separation in the dry process of crushing or crushing the steel-making slag in the atmosphere. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 55-100220 [Patent Document 2] Japanese Patent Laid-Open No. 2010-270378 [Patent Document 3] Japanese Patent Laid-Open No. 2013-142046 [Patent Document 4] PCT International Publication No. 2015/114703 [Patent Document 5] Japanese Patent Laid-Open No. 54-87605 [Patent Document 6] Japanese Patent Laid-Open No. 52-125493 [Patent Document 7] Japanese Patent Laid-Open No. 54-88894 [Non-patent literature]

[Non-Patent Document 1] Yasuo Nakagawa, "The State of Effective Utilization of Steel Slag", 205th and 206th Nishiyama Memorial Technical Lecture Speech Text, General Association Japan Iron and Steel Association, June 2011, p.25-26 [Non Patent Document 2] "Environmental Materials Steel Slag", Iron and Steel Slag Association, January 2014 [Non-Patent Document 3] Takarazuka et al., "Dissolution Behavior of Components from Steel Slag to Artificial Seawater", Iron and Steel, Vol.89, No. 4, January 2014, p. 382-387 [Non-Patent Document 4] Masaki Ishima, etc., "CO ₂ recovery technology as a global warming countermeasure technology", Mitsubishi Heavy Industries Technology News, Vol. 47, No. 1 , 2010, p.47-53

[Problem to be solved by invention]

According to the method described in Patent Document 4, it is expected that the amount of calcium eluted can be easily increased, and the calcium recovery efficiency can be further improved. Therefore, if the eluted calcium can be more easily precipitated, the recovery efficiency of calcium can be expected to be further improved.

In view of the above problems, an object of the present invention is to provide a method for recovering calcium from steel-making slag, which can precipitate calcium that has been eluted from the steel-making slag into the CO ₂ aqueous solution by a simpler method. [Means to solve the problem]

In view of the above-described object, the present invention relates to the method of steelmaking slag recovery of calcium, which has a CO ₂ steelmaking slag contacted with an aqueous solution of step, the solution is an aqueous solution containing a CO ₂ carbon dioxide; and the atomizing steelmaking slag in contact The process of this CO ₂ aqueous solution. [Effect of the invention]

According to the present invention, a method for recovering calcium from steel-making slag that can be precipitated from the steel-making slag into the CO ₂ aqueous solution by a simpler method is provided.

[First Embodiment] FIG. 1 is a flowchart of a method of recovering calcium from steel-making slag in a first embodiment of the present invention. In the present embodiment, steel-making slag is prepared (step S110), and the prepared steel-making slag is brought into contact with an aqueous solution containing carbon dioxide (hereinafter, also simply referred to as "CO ₂ aqueous solution") (step S120) and atomized The above-mentioned CO ₂ aqueous solution contacted with the steel-making slag (step S130), and thereafter, a solid component containing precipitated calcium is recovered (S140).

(Step S110: Preparation of steelmaking slag) In this process, steel-making slag is prepared.

The steel-making slag is not particularly limited as long as it is discharged in the steel-making process. Examples of steelmaking slag include converter slag, pretreatment slag, secondary refining slag, and electric furnace slag.

The size of the structure of calcium silicate, free lime, and iron-based compounds contained in the steel-making slag is about 1000 μm or less. Therefore, the steel-making slag is preferably crushed or pulverized after being discharged in the steel-making process (hereinafter, also simply referred to as "crushing, etc.") to become granular slag particles.

The maximum particle size of the crushed or crushed slag particles is preferably a size equal to or less than the structure of calcium silicate, free lime, and iron-based compounds, and more preferably 1000 μm or less. When the above-mentioned maximum particle diameter is 1000 μm or less, because the surface area per unit volume of the slag particles becomes larger, the CO ₂ aqueous solution can sufficiently penetrate into the inside of the slag particles, or because calcium silicate and free lime can be used as The individual particles are present, so calcium is easily eluted in the process described later. From the same viewpoint, the maximum particle size of the slag particles is preferably 500 μm or less, more preferably 250 μm or less, and still more preferably 100 μm or less. The slag particles can be further pulverized by a pulverizer including a hammer mill, a roll mill, a ball mill, or the like, and the maximum particle size of the slag particles can be reduced to the above-mentioned range.

In addition, the above-mentioned steel-making slag may also be a filtering residual slag. This filtering residual slag is put in a steel-making slag in a container with existing water to perform leaching of free lime and calcium hydroxide, and leaching of calcium from the surface layer of the calcium compound After that, the resulting filtered residual slag. By using the filtering residual slag, it is possible to use slag in which calcium has been eluted to a certain extent, so the load when eluting calcium can be reduced by contact with the CO ₂ aqueous solution. At this time, the calcium leached filtered water that is available at the same time is a highly alkaline aqueous solution with a pH value of 11 or higher (hereinafter, also simply referred to as "high alkali leaching water."). In the second embodiment, the high-alkali leaching water can be used as a calcium-based alkaline substance for further increasing the pH of the CO ₂ aqueous solution.

(Step S120: Contact with CO ₂ aqueous solution) In this step, the steel-making slag is brought into contact with the CO ₂ aqueous solution, and the steel-making slag is brought into contact with the CO ₂ aqueous solution to dissolve calcium.

In this step, the steel-making slag may be immersed in water in which carbon dioxide has been dissolved in advance, or after the steel-making slag is immersed in water, the carbon dioxide may be dissolved in water. However, when calcium is eluted into the CO ₂ aqueous solution, since calcium reacts with carbon dioxide and water-soluble calcium bicarbonate is generated, the carbon dioxide in the CO ₂ aqueous solution decreases with the dissolution of calcium. Therefore, from the viewpoint of improving the elution efficiency of calcium, it is preferable to introduce carbon dioxide into the CO ₂ aqueous solution that the steel-making slag is in contact with to continuously elute the calcium. In addition, while the steel-making slag is immersed in the aqueous solution, it is preferable to stir these solutions from the viewpoint of improving the reactivity.

Carbon dioxide can be dissolved in water by foaming (blowing) of a gas containing carbon dioxide, for example. From the viewpoint of improving the dissolution of calcium from the steel-making slag, it is preferable to dissolve 30 ppm or more of non-ionized carbon dioxide (free carbonic acid) in the aqueous solution. In addition, the amount of free carbon dioxide that may be contained in general tap water is 3 mg/L or more and 20 mg/L or less.

The gas containing carbon dioxide may be pure carbon dioxide gas, or a gas containing components other than carbon dioxide (for example, oxygen or nitrogen). This example of a gas containing carbon dioxide includes a mixed gas of exhaust gas after combustion and carbon dioxide, atmospheric air, and water vapor. From the viewpoint of increasing the concentration of carbon dioxide in the aqueous solution and increasing the dissolution of the calcium compound (calcium silicate, etc.) from the steel-making slag to the aqueous solution, the gas containing carbon dioxide is preferably contained at a high concentration (for example, 90%) carbon dioxide.

At this time, the steel-making slag that is in contact with the CO ₂ aqueous solution may also be crushed. By crushing the steelmaking slag, which is in contact with the CO ₂ aqueous solution, a new surface is continuously formed. This new surface is a hydroxide, carbonate, or hydroxide of silicon, aluminum, and iron that is difficult to dissolve in the CO ₂ aqueous solution. A new surface where hydrates have not yet remained or have not precipitated. This makes it easier for the CO ₂ aqueous solution to penetrate into the steel-making slag from the continuously formed surface, or the contact area of the CO ₂ aqueous solution and the slag particles becomes larger, and it is also possible to make calcium easier The steelmaking slag is eluted.

Also, at this time, the steel-making slag may be settled in the CO ₂ aqueous solution, and the slurry containing the slag particles having a larger particle size and easily settled may be filtered out from the deep side of the CO ₂ aqueous solution, selectively crushed, etc. Slag particles taken out. Because the proportion of water that has been taken out is reduced, the slag particles to be crushed and the like are easily crushed more efficiently. By reintroducing the steel-making slag that has been pulverized or the like in this way into the above-mentioned CO ₂ aqueous solution, the efficiency of pulverization of the steel-making slag and the like can be improved, and a larger amount of calcium is easily eluted from the steel-making slag.

FIG. 2 is a schematic diagram showing the structure of an apparatus for eluting calcium (hereinafter, also simply referred to as “elution apparatus”) that can be used in the present embodiment.

The elution device 100 has an elution and sedimentation tank 110, a pulverizing section 120, a carbon dioxide introduction section 130, and a slurry flow path 140. The dissolution and settling tank 110 accommodates the slurry containing the steel-making slag and the CO ₂ aqueous solution, and settles the steel-making slag (shaded area in the figure) in the slurry; the crushing section 120 crushes etc. from the bottom of the dissolution and settling tank 110 Steel-making slag contained in the slurry taken out from the side; the carbon dioxide introduction part 130 introduces carbon dioxide into the slurry; the slurry flow path 140 introduces the slurry that has been taken out from the dissolution and sedimentation tank 110 into the crushing part 120, and Then, the slurry containing the steel-making slag crushed in the crushing unit 120 and the like is introduced into the elution and settling tank 110.

The dissolution and settling tank 110 is a container for containing slurry. The elution and settling tank 110 has a slurry extraction port 112 on the bottom side, and has a slurry reintroduction port 114 on the upper side (liquid surface side) of the slurry extraction port 112 to reintroduce the slurry from the crushing unit 120. In order to easily take out the accumulated steel-making slag, the bottom surface of the elution and settling tank 110 is an inclined surface that inclines deeper toward the slurry extraction port 112.

In order to easily take out the steel-making slag deposited on the bottom surface, the dissolution and settling tank 110 has an impeller 118 that agitates the slurry near the bottom surface. In order to facilitate the removal of the steelmaking slag deposited on the bottom surface due to these operations even if the dissolution and settling tank 110 is enlarged, the impeller 118 is preferably rotated by passing through the slurry flow path 142 The rod 119 is supported and rotated from the bottom surface side of the elution and sedimentation tank 110. In addition, in order not to hinder the settlement of the steel-making slag on the upper side, the impeller 118 is preferably arranged only on the bottom surface of the dissolution and settlement tank 110.

The pulverizing section 120 communicates with the slurry extraction port 112 of the elution and sedimentation tank 110 through the slurry flow path 142, and communicates with the slurry reintroduction port 114 of the elution and sedimentation tank 110 through the slurry flow path 144.

The pulverizing unit 120 pulverizes the steel-making slag contained in the slurry introduced from the slurry flow path 142 or the like. For example, the pulverizing unit 120 causes a conventional ball used in a ball mill and a conventional ball used in a bead mill, etc. (hereinafter, also simply referred to as "pulverizing medium") to be thrown into the pulverization container by stirring. Flowing, the flowed and rotating crushing medium contacts the slag particles and slides the slag particles to crush the slag particles. The pulverizing unit 120 may be a continuous pulverizing device that pulverizes the steelmaking slag contained in the slurry such as the slurry while circulating the slurry, or may be a steelmaking slag contained in the slurry such as the temporary storage of the slurry and pulverization , Batch type crushing device.

The carbon dioxide introduction unit 130 introduces carbon dioxide supplied from an external carbon dioxide supply source into the slurry. The carbon dioxide introduction unit 130 may also introduce carbon dioxide into the slurry in any one of the elution and sedimentation tank 110, the slurry channel 142 (refer to FIG. 2), the crushing unit 120, and the slurry channel 144. The carbon dioxide introduction unit 130 may also have a bubble refining device for refining bubbles of carbon dioxide.

The slurry flow path 140 has a slurry flow path 142, a slurry flow path 144, and a pump 146. The slurry flow path 142 takes out the slurry whose concentration of the steel-making slag has been increased by the sedimentation of the steel-making slag from the elution and settling tank 112, and introduces it into the pulverizing section 120; the slurry flow The path 144 then introduces the slurry into the dissolution and settling tank 110. This slurry contains the steel-making slag crushed in the crushing unit 120, etc.; the pump 146 makes the slurry flow.

In the elution and settling tank 110, the slurry containing the steel-making slag and the CO ₂ aqueous solution is thrown in, or the steel-making slag and the CO ₂ aqueous solution are thrown in separately to become a slurry. The steel-making slag in the above-mentioned slurry starts to settle from the slag particles with a larger particle size. The slurry containing the settled steel-making slag is stirred by the impeller 118 to improve the fluidity, and is taken out from the slurry take-out port 112 and introduced into the slurry flow path 142 by the pump 146 In the crushing section 120. The slurry including the steel-making slag crushed in the crushing unit 120 and the like is reintroduced into the elution and sedimentation tank 110 from the slurry channel 144. At this time, carbon dioxide is continuously introduced from the carbon dioxide introduction part 130 in the slurry. By circulating the slurry in the elution and sedimentation tank 110, the slurry flow path 142, the pulverizing section 120, and the slurry flow path 144, the steel making slag and CO are efficiently made while pulverizing the steel making slag, etc. _{2 The} aqueous solution is in contact, and calcium can be eluted from the steelmaking slag into the CO ₂ aqueous solution.

Thereafter, the slurry is filtered, or the slurry is allowed to stand and the supernatant after precipitation of the steel-making slag is recovered, and the CO ₂ aqueous solution in which calcium has been dissolved and the steel-making slag can also be separated. However, as long as it does not significantly affect the atomization of the next step, it is not necessary to separate the CO ₂ aqueous solution from which calcium has been dissolved from the steel-making slag.

(Step S130: Atomization of CO ₂ aqueous solution) In this step, the CO ₂ aqueous solution that has been in contact with the steel-making slag is atomized.

By the above atomization, carbon dioxide is removed from the CO ₂ aqueous solution, and the pH value of the CO ₂ aqueous solution increases. Accordingly, because the reduction of hydrogen ions (H ⁺⁾ CO ₂ solution in an amount of, in the following equilibrium formula (Formula 1), bicarbonate ions (HCO ₃ ^-) and calcium ions (Ca ²⁺⁾ binding, to balance The direction in which hydrogen ions (H ⁺ ) and poorly soluble calcium carbonate (CaCO ₃ ) are generated moves. In this step, it is considered that calcium precipitates in this way. ^{_{HCO 3 - + Ca 2+ ⇔ H}} + + CaCO 3 ( Formula 1)

In addition, the calcium precipitated in this step is not limited to calcium carbonate, but also includes precipitated calcium carbonate hydrate, basic calcium carbonate, calcium hydroxide, and the like.

In this step, since the area of contact between the CO ₂ aqueous solution and the surrounding atmospheric gas can be increased by atomization, the removal of carbon dioxide from the CO ₂ aqueous solution to the surrounding atmospheric gas can be performed easily and in a short time The resulting precipitation of calcium. In addition, carbon dioxide having the same partial pressure as the carbon dioxide partial pressure of the surrounding atmospheric gas remains in the atomized CO ₂ aqueous solution.

Atomization can be carried out in the form of a spray or in the form of a mist. Either way, from the viewpoint of changing the contact area of the CO ₂ aqueous solution with the surrounding atmospheric gas to be larger and promoting the precipitation of calcium due to the removal of carbon dioxide, the atomization is preferably an atomized CO ₂ aqueous solution. The droplets have a diameter of 5000 μm or less, more preferably the diameter is 1000 μm or less, still more preferably the diameter is 500 μm or less, and particularly preferably the diameter is 200 μm or less. Although the lower limit of the above diameter is not particularly limited, it can be 0.1 μm. The diameter of the above-mentioned droplets can be adjusted by the size of the discharge port or nozzle for atomizing the CO ₂ aqueous solution.

From the viewpoint of further promoting the precipitation of calcium due to the removal of carbon dioxide, atomization can also be performed multiple times. On the other hand, if a sufficient amount of calcium is precipitated, atomization may be performed only once. The number of atomization times can be determined based on the pH value (described later) of the CO ₂ aqueous solution after atomization.

From the viewpoint of promoting the precipitation of calcium due to the removal of the carbon dioxide, the atomization preferably has a partial pressure of carbon dioxide, which is lower than the equilibrium pressure of carbon dioxide in the CO ₂ aqueous solution that has been in contact with the steel-making slag. Ambient gas space.

Although the atmosphere gas is not particularly limited, it is preferably a gas having low reactivity with a CO ₂ aqueous solution or not reacting with gas (chlorine gas and sulfurous acid gas) that reacts with water to generate ions. When the gas reacts with water to generate ions, the generated ions react with calcium ions in the CO ₂ aqueous solution to form salts, and the precipitation efficiency of calcium decreases, or when the removal of salts is difficult, after the precipitation of calcium It takes time to recycle the CO ₂ aqueous solution. Accordingly, the above-mentioned gas atmosphere is a low reactivity or non-reactive gas and CO ₂ aqueous solution, in particular salts such as ion gas is preferably contacted with an aqueous solution of CO ₂ does not generate calcium ions.

The gas with low or no reactivity with the CO ₂ aqueous solution may be an inorganic gas or an organic gas. Among these, since there is little possibility of burning and explosion when leaking to the outside, it is preferably an inorganic gas. Among the above-mentioned examples of the inorganic-based gas, it is more preferable to include a gas including atmosphere, nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen (H ₂ ), argon (Ar), and helium (He), and a mixture of these gas. In addition, the atmosphere may be an atmosphere of an atomized environment containing nitrogen (N ₂ ) and oxygen (O ₂ ) in a ratio of about 4:1. Examples of the above-mentioned organic gases include methane (CH ₄ ), ethane (C ₂ H ₆ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), propane (C ₃ H ₈ ), and Fluorocarbon gas (C _n H _m F _2n+2-m ), etc.

From the viewpoint of recovering carbon dioxide removed from the CO ₂ aqueous solution in this step and easily reusing it, atomization is preferably performed in a closed container. The recovered carbon dioxide can be used for introduction into the CO ₂ aqueous solution when, for example, the steel-making slag is brought into contact with the CO ₂ aqueous solution (process S120).

Further, when atomized in a closed vessel, since when the carbon dioxide is removed from the CO ₂ concentration of the aqueous solution of carbon dioxide increases closed vessel, carbon dioxide from the CO ₂ removal rate of the aqueous drop or become not removed, The precipitation efficiency of calcium decreases. Therefore, it is preferable to introduce the above-mentioned atmospheric gas into the closed container, and to perform the atomization of the CO ₂ aqueous solution while discharging the gas containing carbon dioxide from the closed container.

In addition, at this time, the solubility of carbon dioxide in water may also be reduced by reducing the pressure or heating the inside of the sealed container. With this, the removal efficiency of carbon dioxide from the CO ₂ aqueous solution can be improved, and the precipitation efficiency of calcium can also be improved. In addition, by heating the inside of the sealed container, the solubility of calcium carbonate and the like in water decreases, so that the precipitation efficiency of calcium can be improved. At this time, the internal pressure of the closed container is preferably atmospheric pressure (about 0.1 MPa) or lower. At this time, the internal temperature of the closed container is preferably such that the vapor pressure of water does not exceed the atmospheric pressure, and more preferably is not higher than normal temperature. 100°C (when the inside of the closed container is at atmospheric pressure). The above-mentioned decompression and heating may be carried out either or both.

FIG. 3 is a schematic diagram showing the structure of an apparatus for atomizing a CO ₂ aqueous solution in a closed container (hereinafter, also simply referred to as “atomizing apparatus”) that can be used in the present embodiment.

Atomizing device 200 having a CO ₂ aqueous solution is atomized hermetic container 210, the atomizing nebulizer aqueous CO ₂ 220 is introduced into the gas atmosphere inside the hermetic container 210 gas introduction portion 230, from the interior of the sealed container 210 is discharged comprises The gas discharge part 240 of carbon dioxide gas, the pump 250 inside the decompressed airtight container, and the heater 260 heating the inside of the airtight container.

The sealed container 210 is a container in which the CO ₂ aqueous solution that has been in contact with the steel-making slag is atomized inside. The sealed container 210 has a CO ₂ aqueous solution outlet 212 for taking out the CO ₂ aqueous solution that has been atomized on the bottom side. In order to easily take out the CO ₂ aqueous solution that has been atomized and reached the bottom surface, the bottom surface of the sealed container 210 is an inclined surface that becomes deeper toward the CO ₂ aqueous solution extraction port 212.

The atomizer 220 has a CO ₂ aqueous solution flow path 222 that flows through the CO ₂ aqueous solution that has been in contact with the steel-making slag in the previous step (step S120), and is used to atomize the CO ₂ aqueous solution flow path 222 The CO ₂ aqueous solution is a shower head 224 in the form of a shower. The shower head 224 is provided on the upper side of the sealed container 210 from a plurality of openings toward the bottom side of the sealed container 210, and discharges droplets of the CO ₂ aqueous solution. In addition, although the atomizer 220 in FIG. 3 has only one shower head 224, the atomizer 220 may also have multiple shower heads.

Further, in FIG. 3, CO ₂ in an aqueous solution while the sealed container becomes inclined surface of the bottom side of the reservoir 210 has been atomized, but may not be stored CO ₂ solution, it is atomized as it is an aqueous solution of CO ₂ from the CO ₂ The aqueous solution extraction port 212 is discharged.

The gas introduction part 230 introduces the above-mentioned atmospheric gas into the sealed container 210. In this case, the bottom side of the container, from an aqueous solution of CO ₂ has been removed atomized carbon dioxide concentration of CO (carbon dioxide equilibrium pressure) ₂ aqueous solution is lowered, it becomes difficult to remove carbon dioxide from an aqueous solution of CO _2. Therefore, the gas introduction part 230 preferably introduces the above-mentioned atmospheric gas from the bottom side of the sealed container 210 to reduce the carbon dioxide concentration (partial pressure of carbon dioxide) in the atmospheric gas on the bottom side of the sealed container 210.

In addition, although only two gas introduction parts 230 are provided for the sealed container 210 in FIG. 3, a plurality of gas introduction parts 230 may be arranged at equal intervals in the circumferential direction along the outer circumference of the sealed container 210. The atmosphere gas is introduced into the bottom side of the inside of the inside uniformly, so that the entire carbon dioxide concentration on the bottom side is evenly lowered.

The gas discharge part 240 discharges the atmosphere gas from the inside of the sealed container 210. Since the atmosphere gas containing carbon dioxide discharged by atomizing an aqueous solution of CO ₂ and CO ₂ is removed from the aqueous solution, the concentration of carbon dioxide becomes higher. According to the present embodiment, at this time, the atmospheric gas having a carbon dioxide concentration of 5% by volume or more can be discharged from the gas discharge part 240. By continuously supplying a certain amount of CO ₂ aqueous solution, the carbon dioxide concentration and amount of the discharged atmospheric gas can be kept constant from the initial stage to the final stage of atomization. It is easy to obtain industrially reusable carbon dioxide with a carbon dioxide concentration of 99% by volume or more by industrially recovering and purifying carbon dioxide from such atmospheric gas. In this way, in the present embodiment, an atmosphere gas with a high carbon dioxide concentration can be obtained, and the reuse of carbon dioxide is easy.

The pump 250 is arranged in the pipeline of the gas discharge part 240, adjusts the discharge amount of the atmosphere gas from the inside of the sealed container 210, and decompresses the inside of the sealed container 210. The pump 250 not only improves the removal efficiency of carbon dioxide from the CO ₂ aqueous solution that has been atomized by the above decompression, but also reduces the pressure by the gas discharge part 240 disposed on the upper side of the sealed container 210 to promote The movement of carbon dioxide from the lower side of the sealed container 210 to the upper side makes the concentration of carbon dioxide in the sealed container 210 easily lower.

The heater 260 may be any conventional heater such as a jacket heater for heating the inside of the sealed container 210. By heating the inside of the sealed container 210 by the heater 260 and depressurizing the inside of the sealed container 210 by the pump 250, the removal efficiency of carbon dioxide from the CO ₂ aqueous solution can be improved. In addition, by heating the inside of the sealed container 210 by the heater 260, the precipitation efficiency of calcium from the CO ₂ aqueous solution can also be improved. Furthermore, by using both the heating of the inside of the sealed container 210 by the heater 260 and the decompression of the inside of the sealed container 210 by the pump 250, even if it is used to improve the above-described carbon dioxide removal efficiency and calcium The heating temperature of the precipitation efficiency is not so high, and the precipitation efficiency of calcium can be sufficiently improved efficiently.

In addition, the heater 260 may heat the atmospheric gas introduced from the gas introduction part 230.

FIG. 4 is a schematic diagram showing the structure of another atomizing device 200a in the present embodiment. The atomizing device 200a has a nozzle 226 that atomizes the CO ₂ aqueous solution into a mist form by the atomizing device 220a. Even such an atomizing device 200a can similarly efficiently remove carbon dioxide from a CO ₂ aqueous solution and efficiently precipitate calcium. In addition, although the atomizing device 220a has only one nozzle 226 in FIG. 4, the atomizing device 220a may also have multiple nozzles.

When calcium is precipitated in this manner, a small amount of iron (Fe), manganese (Mn), phosphorus (P), and the like contained in the CO ₂ aqueous solution are also precipitated at the same time. Therefore, in the present embodiment, the aqueous solution after calcium precipitation can be simplified or without waste water treatment, and the cost of waste water treatment can be suppressed.

In addition, the residual aqueous solution after precipitation of calcium hardly contains elements such as calcium (Ca), iron (Fe), manganese (Mn), aluminum (Al), and phosphorus (P), and carbon dioxide, so it is Reuse is possible. Therefore, the present embodiment can reduce the amount of drainage generated by the treatment.

(Step S140: Recovery of solid content) In this step, a solid content including calcium precipitated by the atomization of the CO ₂ aqueous solution is recovered. The above-mentioned solid component can be recovered by a conventional method including a sedimentation method and a pressure filtration. This solid component contains calcium derived from steel-making slag.

(Effects) According to the method for recovering calcium from the steel-making slag described above, it is possible to recover calcium eluted into the CO ₂ aqueous solution by an easier method.

[Second Embodiment] FIG. 5 is a flowchart of a method for recovering calcium from steel-making slag in a second embodiment of the present invention. In this embodiment form, as in the first embodiment form, steel-making slag is prepared (step S110), the prepared steel-making slag is brought into contact with a CO ₂ aqueous solution (step S120), and the atomized steel-making slag is brought into contact The aforementioned CO ₂ aqueous solution (step S130). Thereafter, in the present embodiment, a calcium-based alkaline substance is added to the CO ₂ aqueous solution (step S150), and a solid component containing precipitated calcium is recovered (step S140). In addition, step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and therefore repeated descriptions are omitted.

(Step S150: Calcium-based alkaline substance input) FIG. 6 is a diagram showing the atomization of a CO ₂ aqueous solution (step S130) and the injection of a calcium-based alkaline substance into a CO ₂ aqueous solution in the present embodiment. (Step S150) A schematic diagram of the structure of the atomizing device.

The atomizing device 200b has an alkaline substance input port 270 for feeding a calcium-based alkaline substance into the CO ₂ aqueous solution inside the sealed container 210a, and the sealed container 210a has a CO ₂ aqueous solution that agitates the calcium-based alkaline substance that has been charged. Stirring blade 214, and a rotating rod 216 that rotates the stirring blade 214. In addition, the other structure of the atomizing device 200b is the same as that of the atomizing device 200 shown in FIG. 3, and therefore repeated description is omitted.

The alkaline substance input port 270 inputs the calcium-based alkaline substance into the closed container 210a and makes it contact with the CO ₂ aqueous solution. In FIG. 6, the alkaline substance input port 270 inputs the calcium-based alkaline substance into the CO ₂ aqueous solution atomized and accumulated at the bottom of the closed container 210 a.

As described above, in the atomization of the CO ₂ aqueous solution (step S130), the pH of the CO ₂ aqueous solution is increased by the removal of carbon dioxide, and calcium is precipitated from the CO ₂ aqueous solution. However, when the pH of the aqueous solution of CO ₂ exceeds about 8.5, since the carbon dioxide it can not exist in a CO ₂ already an aqueous solution, so that an increase in pH of an aqueous solution of CO ₂ caused by the atomization of about 8.5 as a boundary. On the other hand, in a CO ₂ aqueous solution, a pH of 8.5 or more even if there bicarbonate ion (HCO ₃ ^-), and this balance bicarbonate ions calcium ions (Ca ²⁺⁾ also remains. In contrast, by adding calcium-based alkaline substances to the CO ₂ aqueous solution in which carbon dioxide has been (partly) removed due to atomization, the pH of the CO ₂ aqueous solution can be further increased, and the above-mentioned residual Calcium ions are precipitated as calcium carbonate and the like.

The concentration of [HCO ₃ ^-], and carbonate ions ^(- In more detail, FIG. 7 is [H ₂ CO ₃ *], bicarbonate ion (HCO ₃₎ shows the concentration of the aqueous solution of carbonic acid (H ₂ CO ₃₎ of The graph of the relationship between the ratio of the concentration of CO ₃ ^2- ) [CO ₃ ^2- ] and the pH value. Here, [H ₂ CO ₃ *] is a concentration in which the concentration of carbon dioxide [CO ₂ ] and the concentration of carbonic acid [H ₂ CO ₃ ] have been combined. In addition, the ratio of [CO ₂ ] to [H ₂ CO ₃ ] in the aqueous solution ([CO ₂ ]/[H ₂ CO ₃ ]) is about 650, and the proportion of carbon dioxide (CO ₂ ) is higher than that of carbonic acid (H ₂ CO ₃ ) is overwhelmingly large. As is apparent from FIG. 7, when the pH value exceeds about 8.5, [H ₂ CO ₃ *] is approximately 0, and carbon dioxide hardly exists in the aqueous solution. In addition, FIG. 7 is described in a conventional document (for example, "Corrosion and Corrosion Prevention Manual" Association of Corrosion and Corrosion Prevention, 2000, p. 155).

Here, in the above-described respective kinds carbonate aqueous solution _{(CO 2, H 2 CO 3} , HCO 3 -, and CO ₃ ^2-) in the present state of equilibrium in the following formula (Formula 2) to balance the formula (Formula 4 ) Is shown. Specifically, when the pH value is lower than about 8.5, the equilibrium relationship expressed in the balance formula (Formula 2) and the balance formula (Formula 3) is established, and when the pH value is higher than about 8.5, the balance formula (Formula 3) and The balance relationship expressed in the balance formula (Equation 4) is established. _{CO 2 + H 2 O ⇔ H} 2 CO 3 ( Formula _{2) H 2 CO 3 ⇔ H} + + HCO 3 - ( Formula ^{_{3) HCO 3 - ⇔ H +}} + CO 3 2- ( Formula 4)

When the CO ₂ in the aqueous solution is reduced to about pH 8.5, in order to compensate for the decrease in CO ₂ , the balance of (Equation 2) shifts to the left, and H ₂ CO ₃ decreases. When H ₂ CO ₃ decreases, to compensate for it, the balance of (Equation 3) shifts to the left, H ⁺ decreases and the pH value of the aqueous solution increases. Also, when the H ⁺ reduction, balanced equilibrium (Equation 5) is shifted to the right, a calcium ion (Ca ²⁺⁾ and bicarbonate ions (HCO ₃ ^-) The reaction to produce insoluble calcium carbonate (CaCO ₃₎ And precipitate calcium. At this time, the above-mentioned change in the concentration of H ⁺ due to the movement of each balance also causes the equilibrium movement of the water of the equilibrium equation (Equation 6). Therefore, the pH value can be used as an indicator of the progress of the overall reaction. ^{_{Ca 2+ + HCO 3 - ⇔ H}} + + CaCO 3 ( Formula ^{_{5) H 2 O ⇔ H +}} + OH - ( Formula 6)

Because the above-mentioned several equilibrium states move simultaneously, when removing carbon dioxide from the CO ₂ aqueous solution, immediately after the removal, the equilibrium of (Equation 3) moves to the left due to the reaction shifted to the right with respect to (Equation 5) The shifted reaction is dominant, so the pH rises and a small amount of calcium carbonate precipitates. After that, since the reaction of shifting the balance of (Equation 5) to the right becomes an advantage, the pH value drops and a large amount of calcium carbonate (CaCO ₃ ) precipitates. After that, the reaction shifted to the left in (Equation 3) becomes superior to the reaction shifted to the right in (Equation 5) again, and the pH value increases. At this time, calcium carbonate is continuously precipitated by the reaction shifted to the right in (Equation 5). In this way, until the carbon dioxide in the CO ₂ aqueous solution is absent at a pH value of about 8.5, precipitation of calcium carbonate due to the equilibrium shift of (Formula 2), (Formula 3), and (Formula 5) proceeds.

On the other hand, at a pH value of about 8.5 or more where carbon dioxide almost disappears from the aqueous solution, when the pH value increases and the H ⁺ in the aqueous solution decreases, the balance of (Equation 5) shifts to the right by calcium ions (Ca ²⁺⁾ and bicarbonate ions (HCO ₃ ^- reaction) to generate the insoluble calcium carbonate (CaCO _3), for precipitation of calcium. By this equilibrium movement, almost all calcium in the aqueous solution is precipitated up to pH 10.

However, as described above, in the removal of carbon dioxide from a CO ₂ aqueous solution, the pH value of the aqueous solution can be raised only until the pH value at which carbon dioxide does not exist in the aqueous solution is around 8.5. In contrast, by adding calcium-based alkaline substances to the CO ₂ aqueous solution after removing carbon dioxide to a certain extent, the calcium concentration and pH value in the CO ₂ aqueous solution are increased, and the balance of (Equation 5) is easier to the right Deviation, and can promote the precipitation of calcium carbonate.

In addition, the lower the carbon dioxide concentration of the CO ₂ aqueous solution, the lower the efficiency of further removal of carbon dioxide from the CO ₂ aqueous solution. Therefore, when attempting to increase the pH value of the CO ₂ aqueous solution by atomization (removal of carbon dioxide), it is necessary to exponentially extend the distance traveled by the atomized CO ₂ aqueous solution. On the other hand, the removal of carbon dioxide from the CO ₂ aqueous solution due to atomization is stopped to the extent that a certain degree of carbon dioxide remains in the CO ₂ aqueous solution, and then calcium is promoted by the input of calcium-based alkaline substances The precipitation of can suppress the complexity of processing caused by the enlargement of the atomizing device or the increase in the number of atomizations. For example, atomization is preferably performed until the pH value of the CO ₂ aqueous solution becomes 6.5 or more and 8.0 or less, preferably until the pH value of the CO ₂ aqueous solution becomes 6.6 or more and 7.5 or less, and thereafter, a calcium-based alkaline substance is added to the CO _{2 in} aqueous solution.

Although the calcium-based alkaline substance may be an alkaline substance containing calcium, it is preferable to include calcium hydroxide (Ca(OH) from the viewpoint of easily increasing the pH value and increasing the amount of precipitated calcium. ₂ ) The composition, or a composition that generates calcium hydroxide when it is put in water (hereinafter, also simply referred to as "calcium hydroxide-based composition."). The calcium hydroxide-based composition may be an aqueous solution in which calcium hydroxide is dissolved, or a slurry in which solid calcium hydroxide is dispersed. Alternatively, the substance containing calcium hydroxide may be solid calcium hydroxide. Alternatively, the calcium-based alkaline substance may be solid calcium oxide (CaO) that changes into calcium hydroxide when it is put into a CO ₂ aqueous solution.

Among these, an aqueous solution in which calcium hydroxide is dissolved can be easily obtained in each step of the process of recovering calcium from steel-making slag. For example, the above-mentioned aqueous solution in which calcium hydroxide is dissolved may be high-alkali leaching water obtained in the process of preparing the steel-making slag when filtering residual slag is obtained, or it may be after hydration treatment in the third embodiment described later The obtained hydration treated water may also be magnetic separation water obtained after wet magnetic separation in the fourth embodiment described below. In addition, in this specification, the liquid component obtained by the contact of the steel-making slag and water like the above-mentioned high-alkali leaching water, hydration treatment water, and magnetic separation water is also called slag leaching water.

The slag leaching water can be obtained in the previous treatment step by contacting the steel-making slag that precipitates calcium by atomization of a CO ₂ aqueous solution (step S130) and the input of a calcium-based alkaline substance (step S150). The slag leaching water may also be the slag leaching water obtained in the treatment process in contact with other steel-making slag. In this step, slag leaching water is added to the CO ₂ aqueous solution, and it is preferable from the viewpoint of effective utilization of the slag leaching water discharged in each step for recovering calcium from the steelmaking slag.

Alternatively, the aqueous solution in which calcium hydroxide is dissolved may be a waste liquid obtained in a process other than the process of recovering calcium from steel-making slag. Examples of the above waste liquid include waste water solutions generated when calcium carbide (Calcium carbide) and water are reacted to produce acetylene. The above wastewater solution is roughly composed of water and calcium hydroxide. Therefore, by using the above-mentioned waste water solution, it is possible to reduce the mixing amount of impurities into the solid content containing the precipitated calcium.

In addition, instead of the above-mentioned calcium-based alkaline substance, a sodium-based substance containing sodium hydroxide or the like and an ammonia-based substance containing ammonia or the like may be added to the CO ₂ aqueous solution. However, the solid content containing the precipitated calcium obtained by inputting these contains sodium which may shorten the life of the refractory contained in the sintering furnace or blast furnace or ammonia which may generate toxic ammonia gas by heating. Therefore, it is preferable to promote the precipitation of calcium by the input of the calcium-based alkaline substance.

In FIG. 6, the alkaline substance input port 270 directly inputs the calcium-based alkaline substance into the CO ₂ aqueous solution accumulated at the bottom of the closed container 210 a. However, the method of adding the calcium-based alkaline substance is not limited to this. For example, the above-mentioned calcium-based alkaline substance may be added to the CO ₂ aqueous solution in a barrel tank provided on the downstream side of the closed container 210a, or may be arranged in a flow path in which the closed container 210a communicates with the barrel tank. A mixer in which the above-mentioned calcium-based alkaline substance is added and mixed into a CO ₂ aqueous solution. However, the above-mentioned calcium-based input like a basic substance in a sealed container 210a CO ₂ aqueous solution is atomized while the atomization of the aqueous solution ₂ and CO to CO ₂ has been atomized aqueous alkaline substance calcia Because it is possible to shorten the time required for processing and to complete the device structure more easily, it is preferable.

After the calcium-based alkaline substance is added, it is preferable to stir the CO ₂ aqueous solution to uniformly disperse or uniformly mix the calcium-based alkaline substance. In FIG. 6, the closed container 210 a includes a stirring blade 214 that stirs a CO ₂ aqueous solution into which a calcium-based alkaline substance has been added, and a rotating bar 216 that rotates the stirring blade 214.

Further, in FIG. 6, although shown as having a spray atomizer CO ₂ aq shaped atomizing device atomizer, but also be used as an aqueous solution having a CO ₂ spray mist atomizing device atomizer, The calcium-based alkaline substance is input in the same manner.

(Effects) According to the method for recovering calcium from the steel-making slag described above, it is possible to recover calcium that has been eluted into the CO ₂ aqueous solution by an easier method.

[Third Embodiment] Fig. 8 is a flowchart of a method for recovering calcium from steel-making slag in a third embodiment of the present invention. In the present embodiment, the steel-making slag is prepared in the same manner as in the first embodiment (step S110), and thereafter, a hydration treatment is performed on the steel-making slag (step S160). Thereafter, the steelmaking slag that has been subjected to the hydration treatment is brought into contact with an aqueous solution of CO ₂ (step S120), the aqueous solution of CO ₂ that has been contacted with the atomized steelmaking slag (step S130), and a solid containing precipitated calcium is recovered Ingredients (Step S140). In addition, step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and therefore repeated descriptions are omitted.

The above-mentioned hydration treatment may be carried out by a method or condition in which the calcium compound contained in the steel-making slag is sufficiently hydrated.

As mentioned above, the calcium in the steelmaking slag acts as free lime, calcium hydroxide (Ca(OH) ₂ ), calcium carbonate (CaCO ₃ ), calcium silicate (Ca ₂ SiO ₄ , Ca ₃ SiO ₅ ) and calcium iron aluminum Calcium compounds such as (Ca ₂ (Al _1-x Fe _x ) ₂ O ₅ ) exist.

When hydration treatment is applied to this steel-making slag, for example, calcium silicate hydrate and calcium hydroxide (Ca(OH) ₂ ) are generated from calcium silicate by the reaction represented by the following (Equation 7), or Calcium oxide hydrates are generated from calcium iron iron aluminum oxide by the reaction represented by the following (Formula 8) (hereinafter, the compounds including calcium that can be generated by hydration treatment are also collectively referred to as "calcium hydrates.") . 2(2CaO•SiO ₂ ) + 4H ₂ O → 3CaO•2SiO ₂ • 3H ₂ O + Ca(OH) ₂ (Equation 7) 2CaO•1/2(Al ₂ O ₃ • Fe ₂ O ₃ ) + 10H ₂ O → 1/2(4CaO•Al ₂ O ₃ •19H ₂ O) + HFeO ₂ (Formula 8) ((Formula 8) is expressed in calcium iron aluminum oxide (Ca ₂ (Al _1-x Fe _x ) ₂ O ₅ ) Example of the case of X=1/2.).

The calcium hydrate produced by the above reaction and the like is easily dissolved in the CO ₂ aqueous solution. Therefore, by performing hydration treatment, calcium derived from calcium silicate, calcium oxide, iron, aluminum oxide, and the like contained in the steelmaking slag can be more easily eluted.

In addition, although free lime is easily dissolved in an aqueous solution of CO ₂ , it usually contains less than about 10% by mass in steel-making slag. In contrast, calcium silicate usually contains about 25% to 70% by mass in the steelmaking slag, and calcium iron iron aluminum usually contains about 2% to 30% by mass in the steelmaking slag. Therefore, if calcium contained in calcium silicate, calcium iron iron aluminum, etc. is more easily eluted into the CO ₂ aqueous solution by hydration treatment, the amount of calcium eluted from the steelmaking slag to the CO ₂ aqueous solution can be increased, and It is thought that it is possible to recover calcium from the steelmaking slag in a shorter time.

In addition, the total volume of the compound generated by the hydration treatment is usually larger than the total volume of the compound before the reaction. Furthermore, in the hydration treatment, part of the free lime in the steel-making slag is eluted into the water for treatment. Therefore, when the hydration treatment is performed, cracks are generated inside the slag particles, and the slag particles are easily disintegrated using the cracks as a starting point. In this way, when the slag particles are disintegrated, the particle diameter of the slag particles becomes smaller, the surface area per unit volume becomes larger, and because water or CO ₂ aqueous solution can sufficiently penetrate into the interior of the steel-making slag, a large amount of hydrate can be hydrated in this step Calcium compound. In addition, when the steelmaking slag is brought into contact with the CO ₂ aqueous solution thereafter (process S120), a larger amount of calcium can be eluted.

Therefore, the hydration treatment is preferably carried out using a method and conditions in which calcium silicate or calcium iron oxide aluminum contained in the steelmaking slag can be hydrated.

Specific examples of the hydration treatment include the treatment of steel-making slag that settles down after being immersed in water (hereinafter, also simply referred to as "immersion standing"), the treatment of steel-making slag that has been immersed in water, such as stirring or crushing (Hereinafter, also simply referred to as "dipping and stirring".), the treatment of standing the paste containing water and slag particles (hereinafter, also simply referred to as "slurrying and standing"), and the treatment with a sufficient amount of steam Disposal of steel-making slag standing in the container (hereinafter, also referred to as "wet standing"), etc. According to these methods, the steel-making slag and water can be sufficiently contacted. The hydration treatment may be performed by only one of the above-mentioned immersion standing, immersion stirring, slurrying standing, wet standing, and the like, or two or more of these may be carried out in any order. From the viewpoint of more sufficient hydration treatment to the inside of the slag particles to make calcium easier to elute, the hydration treatment by immersion stirring is preferred.

The immersion stirring may stir the steel-making slag immersed in water in a container with a stirring impeller, or may be crushed while stirring the steel-making slag by a ball mill. From the viewpoint of more fully hydrating the inside of the slag particles to make calcium easier to elute, the immersion stirring is preferably pulverized while stirring the steel-making slag.

The above-mentioned reaction by the hydration treatment is caused by the contact of the calcium compound with water near or inside the surface of the steel-making slag. Here, although a certain amount of water penetrates into the steel-making slag, the amount of contact with water near the surface is large. Therefore, calcium hydrate is more likely to be generated near the surface of the steel-making slag. In addition, when the components contained in the steel-making slag are dissolved in the water used in the hydration treatment, in the same manner as the above-described dissolution in the CO ₂ aqueous solution, silicon, aluminum, iron, and manganese, or hydroxides and carbonates of these And hydrates, etc. remain or precipitate on the surface of steel-making slag. When these remaining or precipitated substances hinder the penetration of water inside the steel-making slag, calcium hydrate becomes difficult to form inside the steel-making slag.

On the other hand, in the hydration process, the surface area of the slag particles is increased by crushing steel-making slag that has been immersed in water, and the contact area between the water and the slag particles can be further increased. In addition, by crushing steel-making slag, which has been immersed in water, a new surface on which the above-mentioned substances have not remained or have not been precipitated is continuously formed, and since the surface from which the water is continuously formed penetrates into the steel-making slag, so Calcium hydrate can be formed more easily even inside the steel-making slag. Further, by grinding the surface of the steel-making slag, the above-mentioned remaining or precipitated substances are removed, the contact area between water and slag particles is changed to a large extent, and water can penetrate into the steel-making slag more easily.

Hydration process water used, preferably comprises a non-ionized free ionized carbonate and bicarbonate ions (HCO ₃ ^-) and the like of carbon dioxide levels less than 300 mg / L. When the content of the above carbon dioxide is less than 300 mg/L, since calcium compounds other than free lime and calcium hydroxide are difficult to dissolve into the water used in the hydration process, it can be in contact with the CO ₂ aqueous solution (step S120) , So that most of the calcium contained in the steelmaking slag is eluted into the CO ₂ aqueous solution, and the recovery of calcium is difficult to become complicated. In addition, when there is a large amount of carbon dioxide in water, although calcium dissolved from free lime, calcium hydroxide, etc. reacts with carbon dioxide to form and precipitate calcium carbonate, covering the surface of the slag particles, and the hydration reaction becomes difficult to proceed, but when carbon dioxide When the content is less than 300 mg/L, the above hindrance of the hydration reaction caused by the precipitation of calcium carbonate is difficult to occur. In addition, the content of carbon dioxide in industrial water is usually less than 300 mg/L. Therefore, the water used in the hydration treatment by immersion standing or immersion stirring is preferably industrial water that does not intentionally add or contains carbon dioxide.

The temperature of water used in the hydration treatment may be a temperature at which water does not evaporate violently. For example, when hydration treatment is performed on steelmaking slag at approximately atmospheric pressure, the temperature of water is preferably 100° C. or lower. However, when the hydration treatment is performed using an autoclave at a higher pressure, the temperature of the water may be 100° C. or higher in the range below the boiling point of the water at the pressure during the hydration treatment. Specifically, the temperature of the water when the hydration treatment is performed by immersion standing or immersion stirring is preferably 0°C or higher and 80°C or lower. When an autoclave is used to perform hydration treatment at a higher pressure, although the upper limit of temperature is not particularly limited, it is preferably 300° C. or less from the pressure resistance and economic aspects of the device. In addition, the temperature when the hydration treatment is performed by gelatinization and standing is preferably 0°C or higher and 70°C or lower.

The duration of the hydration treatment can be arbitrarily set by the average particle diameter of the slag and the temperature of the hydration treatment (temperature of air including water or steam). For the duration of the hydration treatment, the smaller the average particle diameter of the slag, the shorter the time, and the higher the temperature for the hydration treatment, the shorter the time.

For example, when the hydration treatment by immersion standing or immersion stirring is performed at room temperature on steel-making slag with a maximum particle size of slag particles of 1000 μm or less, the duration of the hydration treatment can be about 8 hours in a row, preferably 3 More than 30 hours. When the above-mentioned hydration treatment is performed by immersion in water of 40°C or more and 70°C or less, the duration of the hydration treatment is preferably 0.6 hours or more and 8 hours or less continuously.

In addition, when the hydration treatment by immersion and stirring carried out at the same time by crushing and the like is performed on the steel-making slag, and the steel-making slag is a steel-making slag having a maximum particle size of 1000 μm or less, the duration of the hydration treatment is It is preferably 0.1 hours or more and 5 hours or less, and more preferably 0.2 hours or more and 3 hours or less. Alternatively, when the hydration treatment by immersion and agitation performed at the same time at normal temperature is performed, the duration of the hydration treatment is preferably performed until the maximum particle size of the slag particles becomes 1000 μm or less, preferably 500 μm or less, more preferably It becomes 250 μm, and more preferably becomes 100 μm or less.

In addition, the hydration treatment is preferably performed to the extent that calcium silicate sufficiently becomes a hydrate and calcium hydroxide, and/or the calcium iron iron aluminum oxide sufficiently becomes a calcium oxide-based hydrate. For example, the hydration treatment is preferably applied until the amount of calcium silicate contained in the steel-making slag is 50% by mass or less, or the amount of calcium iron aluminum oxide is 20% by mass or less.

Although the steel-making slag after the hydration treatment can be used as it is for contact with an aqueous solution of CO ₂ (step S120), when the steel-making slag is in the form of a slurry, it is preferable to perform solid-liquid separation to separate the steel-making slag and liquid components Separate. The solid-liquid separation can be performed by a conventional method including reduced pressure filtration and pressure filtration. The liquid component obtained by the above solid-liquid separation (also referred to as "hydration treated water" in this specification), because it contains not only water that has been used for hydration treatment but also eluted from the steel-making slag Calcium, so it becomes alkaline. Therefore, the above hydration treated water can be used as the calcium-based alkaline substance for further increasing the pH of the CO ₂ aqueous solution in the second embodiment.

In addition, in this embodiment mode, similar to the second embodiment mode, after atomizing the CO ₂ aqueous solution contacted with the steel-making slag, a calcium-based alkaline substance may be added to the CO ₂ aqueous solution (process S150), and thereafter, the solid content containing the precipitated calcium is recovered (step S140).

(Effects) According to the above method for recovering calcium from steel-making slag, calcium is more easily eluted from the steel-making slag into the CO ₂ aqueous solution, and the recovery efficiency of calcium from the steel-making slag can be further improved.

[Fourth Embodiment] FIG. 9 is a flowchart of a method of recovering calcium from steel-making slag in a fourth embodiment of the present invention. In this embodiment mode, the steel-making slag is prepared in the same manner as the first embodiment mode (step S110), and thereafter, magnetic separation is performed on the steel-making slag (step S170). After that, the steelmaking slag that has been subjected to magnetic separation is brought into contact with an aqueous solution of CO ₂ (step S120), the aqueous solution of CO ₂ that has been contacted with the atomized steelmaking slag (step S130), and a solid component containing precipitated calcium is recovered (Step S140). In addition, step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and therefore repeated descriptions are omitted.

By performing magnetic separation on the steelmaking slag, the inhibition of contact with the CO ₂ aqueous solution on the surface of the steelmaking slag caused by the compound containing iron remaining or precipitated on the surface of the steelmaking slag, or the inclusion of It is considered that the crushing or grinding in contact with the CO ₂ aqueous solution caused by the iron compound having relatively high hardness can prevent the calcium compound in the steel-making slag from being eluted into the CO ₂ aqueous solution more easily.

In addition, the calcium-iron-aluminum oxide contained in the steel-making slag is difficult to be magnetized after Ca is eluted by contact with the CO ₂ aqueous solution, and recovery by magnetic separation is not easy. In contrast, by performing magnetic separation before contact with the CO ₂ aqueous solution, calcium iron aluminum in the steelmaking slag can also be recovered, and it is considered that iron derived from calcium iron aluminum can also be more easily reused.

The above magnetic separation can be performed using a conventional magnetic separator. The magnetic separator can be dry or wet, and can be selected according to the state of the steelmaking slag (dried state or slurry state). In addition, although the magnetic separator can be appropriately selected from the drum type, the belt type, and the flow type between fixed magnets, etc., particularly because the screening of the steelmaking slag contained in the slurry is easy, and the magnetic force is increased, it is easy to increase the amount of magnetic separation , So the drum type is preferred. In addition, the magnet used in the magnetic separator may be a permanent magnet or an electromagnet.

The magnetic flux density caused by the magnet is sufficient if it can selectively capture iron-based compounds and metallic iron from other compounds contained in the steel-making slag, for example, it can be 0.003 T or more and 0.5 T or less. It is preferably 0.005 T or more and 0.3 T or less, and more preferably 0.01 T or more and 0.15 T or less.

Moreover, magnetic separation does not need to be performed to remove all the iron-based compounds and metallic iron contained in the steel-making slag. Even if the amount of the iron-based compound removed from the steel-making slag by magnetic separation is a small amount, the effect of the present embodiment in which calcium becomes easier to be eluted into the CO ₂ aqueous solution compared to conventional ones can be achieved. Therefore, the time and frequency of magnetic separation can be appropriately selected according to the influence of magnetic separation on the manufacturing cost.

In addition, the steel-making slag is preferably heat-treated before performing magnetic separation. When the steel-making slag is heat-treated, the magnetization of iron-based compounds and metallic iron is increased, and a larger amount of iron-based compounds can be removed by magnetic separation. The above heat treatment is preferably performed at 300°C or more and 1000°C or less for 0.01 minutes or more and 60 minutes or less.

In the magnetic separation, the steel-making slag may be in a dried state, but it is preferably in the form of slurry dispersed in water. Slurry-like steel-making slag is easily dispersed by the polarity of water molecules, water flow, or other slag particles, so it is easy to selectively capture iron-based compounds and metallic iron by magnetic force. In particular, when the particle size of the slag particles is 1000 μm or less, in a gas such as air, the liquid crosslinking force caused by the condensation of water vapor in the atmosphere, the van der Waals force between the slag particles, and the slag particles The slag particles are easily aggregated due to electrostatic forces, etc., but they can be sufficiently dispersed by becoming a slurry. In addition, although the metal iron in the steel-making slag is tiny, it is difficult to capture when the steel-making slag is dried, but when the steel-making slag becomes a slurry, the metal iron dispersed in water by magnetic separation also becomes Must be easy to capture.

The slurry after removing iron-based compounds and metallic iron by magnetic separation can be used as it is for contact with an aqueous solution of CO ₂ (step S120), but when the steel-making slag is in the form of slurry, it is preferably solidified Liquid separation separates the steelmaking slag from the liquid components. The solid-liquid separation can be performed by a conventional method including reduced pressure filtration and pressure filtration. The liquid component obtained by the above solid-liquid separation (also referred to as "magnetic separation water" in this specification), because it contains not only the water used for slurrying but also the eluted from the steelmaking slag Calcium, so it becomes alkaline. Therefore, the above-mentioned magnetic separation water can be used as a calcium-based alkaline substance for further increasing the pH of the CO ₂ aqueous solution in the second embodiment.

In addition, the magnetic separation to remove the slag from the steelmaking slag by magnetic separation contains a large amount of Fe compounds including iron-based compounds and metallic iron as described above, so it can be reused as a raw material for blast furnace or sintering.

The steelmaking slag is preferably heat-treated before performing magnetic separation. When the steel-making slag is heat-treated, the magnetization of the iron-based compound is increased, and a larger amount of the iron-based compound can be removed by magnetic separation. The above heat treatment is preferably performed at 300°C or more and 1000°C or less for 0.01 minutes or more and 180 minutes or less.

In addition, in this embodiment mode, similar to the second embodiment mode, after atomizing the CO ₂ aqueous solution contacted with the steel-making slag, a calcium-based alkaline substance may be added to the CO ₂ aqueous solution (process S150), and thereafter, the solid content containing the precipitated calcium is recovered (step S140).

In addition, in this embodiment mode, as in the third embodiment mode, the steel-making slag before the hydration treatment (step S160) before contact with the CO ₂ aqueous solution may be performed. In the present embodiment, when the hydration treatment is further performed on the steel-making slag, either hydration treatment or magnetic separation may be performed first, or the magnetic separation by the wet method or the magnetic separation by the wet method may be performed. The slurry circulates while performing both parties. In the case where any of these is carried out first, when the hydration treatment (especially the hydration treatment by immersion stirring) is performed first and then the magnetic separation is performed, especially when the apparatus has been enlarged, in addition to the recovery rate of calcium In addition to improvement, there is also the ability to perform overall processing in a shorter time. [Example]

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, these examples do not limit the scope of the present invention to the specific methods described below.

[Experiment 1] Steel-making slag having the composition ratio described in Table 1 was prepared. In addition, the composition of steel-making slag is measured by chemical analysis.

[Table 1] Table 1: Composition of Steelmaking Slag

After pulverizing the steel-making slag shown in Table 1 to a diameter of 8 mm or less, it was heated at 750°C for 20 minutes. After heating, the steelmaking slag air is cooled to normal temperature. After further crushing the steel-making slag, the part that has passed through the sieve with a pore size of 106 μm was used in the subsequent treatment.

In the following experiments, the calcium concentration of each aqueous solution was measured by chemical analysis after filtering the slurry and separating the slag.

In addition, in the following experiments, the pH values of the respective aqueous solutions and slurries were measured by the glass electrode method.

[Experiment 1] (Hydration treatment: hydration by ball mill) A ball mill with an inner diameter of 500 mm was prepared. In this ball mill, 1 kg of steelmaking slag without magnetic separation was put in, and 1 L of water was put in to make the steelmaking slag into a slurry. Furthermore, a 6 kg alumina ball (pulverizing medium) was put into the ball mill, and the diameter of the ball was 10 mm. Thereafter, the ball mill was rotated at 50 rpm, and the rotating ball was brought into contact with the steel-making slag to pulverize the steel-making slag. By the simultaneous hydration of the crushing, the particle diameter (d90) of the slag becomes 20 μm. No carbon dioxide was introduced into the slurry-form steel-making slag.

(magnetic separation) Water is added to the slurry-formed steel-making slag that has been hydrated to make the slurry volume 40 L. The slurry was put into a drum-type magnetic separator, and magnetic separation was performed under the conditions of a maximum magnetic flux density of 0.07 T on the drum surface and a drum peripheral speed of 40 m/min. The iron concentration in the steelmaking slag after magnetic separation was measured by a chemical analysis method and a weight measurement. Among the iron elements contained in the original steelmaking slag, 41% of the mass was removed. After the magnetic separation, the residual slurry is filtered and the residual slag is separated. For the subsequent process, the magnetic separation water is retained. This magnetic separation water is an aqueous solution in which the calcium remaining after separating the residual slag has been leached, and the calcium concentration of this magnetic separation water is 480 mg/L. In addition, in the preliminary experiment beforehand, it was confirmed that the slag with a dry weight of 0.15 kg was separated by magnetic separation.

₍₂ into contact with CO.'S solution simultaneously: contacting CO.'S ₂ and pulverization of an aqueous solution) in the device structure shown in Figure 2 having. The dissolution and sedimentation tank is a cylindrical container with an inner diameter of 480 mm, and an impeller rotating along the bottom surface is provided in order to move the steel-making slag accumulated and settled to the suction port. Rotate the impeller at 40 rpm. The residual slag collected by filtration after the aforementioned magnetic separation step was put into this dissolution and settling tank without drying, and water was added to make the slurry amount 100 L. At this time, the ratio of water to slag is about 120:1. The steel-making slag collected from the bottom is transported by the pump to the crushing section, and is crushed by a continuous crushing device using a ball mill. The crushing part is a horizontal cylinder with an inner diameter of 200 mm, and a Φ10 mm ball is placed inside to 70% of the total volume. Simultaneously with this, 20 L/min of carbon dioxide was introduced into the piping section between the dissolution and sedimentation tank and the crushing section. The contact with the CO ₂ aqueous solution was performed for 30 minutes.

The slurry obtained by dissolving calcium obtained as above was filtered and separated from the slag to obtain a CO ₂ aqueous solution in which calcium was dissolved. At this time, the pH value of the CO ₂ aqueous solution was 6.6, and the calcium concentration was 1230 mg/L.

(Spray) Calcium is precipitated by the spray atomization method shown in FIG. 3. By spraying a plurality of holes with a diameter of 0.5 mm, the CO ₂ aqueous solution was atomized at a flow rate of 5 L/min from a height of 4.5 m downward in a closed container with an inner diameter of 960 mm. From the bottom side of the closed container, blow air at a flow rate of 40 L/min from two opposite places. The CO ₂ aqueous solution that has reached the bottom side of the closed container is taken out from the bottom of the closed container and introduced into the barrel tank connected to the closed container. After the primary atomization, the liquid component of the CO ₂ aqueous solution in which the calcium compound (calcium carbonate) has precipitated is recovered from the barrel tank, and atomization is performed again (total secondary atomization).

The pH value of the CO ₂ aqueous solution after the second atomization is 8.0, and the calcium concentration is 61 mg/L.

(Recovery of solid content) From the tank into which the CO ₂ aqueous solution has been atomized, the solid content containing calcium can be easily recovered.

From this result, it is known that the pH value of the CO ₂ aqueous solution increases by atomization, and calcium compounds (calcium carbonate) are precipitated from the CO ₂ aqueous solution. After the second atomization, the calcium precipitation rate at this time ((100 (%)-calcium concentration after atomization (%))/calcium concentration before atomization (%)) was about 95.0%.

[Experiment 2] By the same procedure as in Experiment 1, hydration treatment, magnetic separation, calcium elution, and separation of slag and CO ₂ aqueous solution by filtration were performed. Thereafter, calcium was recovered by the same procedure as in Experiment 1. At this time, the atomization was performed only once and at a flow rate of 8 L/min.

In addition, the carbon dioxide concentration of the gas that has been discharged from the closed container in the experiment was measured by infrared, and it was about 10%. The carbon dioxide concentration of this gas is higher than the carbon dioxide concentration (approximately 9%) in the exhaust gas from general natural gas-fired power plants, and it is easy to recover and refine.

(Introduction of calcium-based alkaline substances) Subsequently, in the CO ₂ aqueous solution (pH value: 7.0, calcium concentration: 190 mg/L, calcium precipitation rate: 84.5%) accumulated in the barrel tank, hydrogen hydroxide was added Calcium-based composition-1 (magnetic separation water obtained in the above-mentioned magnetic separation step), calcium hydroxide-based composition-2 (aqueous solution prepared by dissolving calcium hydroxide in water), and calcium hydroxide-based composition -3 (a slurry prepared by dispersing solid calcium hydroxide in calcium hydroxide water) while stirring the CO ₂ solution. In order to make the pH value of the CO ₂ aqueous solution after input into any one of 8.0, 8.5, 9.0, and 9.5, the input amount was adjusted separately.

Table 2 shows the pH value and calcium concentration of the calcium hydroxide-based composition-1 to the calcium hydroxide-based composition-3 that have been added. In addition, the calcium concentration of the calcium hydroxide-based composition-3 as the slurry is an average concentration that also contains solid parts.

[Table 2] Table 2: Calcium hydroxide-based composition 1~Calcium hydroxide-based composition 3

Table 3 shows the pH value, calcium concentration, and calcium precipitation rate of the CO ₂ aqueous solution after each calcium hydroxide-based composition is added (atomization and calcium concentration after the calcium hydroxide-based composition is added/before atomization) Calcium concentration).

[Table 3] Table 3: pH value, calcium concentration, calcium precipitation rate after the calcium hydroxide-based composition was put in

As is obvious from Table 3, by adding calcium hydroxide-based composition to the atomized CO ₂ aqueous solution, the calcium concentration decreased compared to the calcium concentration (190 mg/L) after one atomization, and by hydrogen The calcium oxide-based composition is input and calcium is further precipitated. The calcium precipitation rate at this time is not related to the kind of calcium hydroxide-based composition to be charged, but is roughly related to the pH value after being charged.

In addition, when the pH value of the CO ₂ aqueous solution after the calcium hydroxide injection is 8.0 or more, the calcium precipitation rate is 90% or more, and when the pH value of the CO ₂ aqueous solution after the calcium hydroxide input is 8.5 or more, then The calcium precipitation rate is 94% or more. When the pH of the CO ₂ aqueous solution after the calcium hydroxide is added is 9.0 or more, the calcium precipitation rate is 95% or more.

[Experiment 3] (Hydration treatment-1: hydration by dipping and stirring using a ball mill) A ball mill with an inner diameter of 500 mm was prepared. In this ball mill, 1 kg of steelmaking slag without magnetic separation was put in, and 1 L of water was put in to make the steelmaking slag into a slurry. Furthermore, a 6 kg alumina ball (pulverizing medium) was put into the ball mill, and the diameter of the ball was 10 mm. Thereafter, the ball mill was rotated at 50 rpm, and the rotating ball was brought into contact with the steel-making slag to pulverize the steel-making slag. By the simultaneous hydration of the crushing, the particle diameter (d90) of the slag becomes 20 μm. No carbon dioxide was introduced into the slurry-form steel-making slag.

(Hydration treatment-2: hydration by immersion and stirring) Water was added to the slurry-like slag that had been hydrated to make the amount of slurry 40 L, and stirred for 15 minutes. Thereafter, the slurry is filtered, and the slag and the hydration treated water (aqueous solution) are separated. The pH of the hydrated water is 12.5, and the calcium concentration is 470 mg/L.

(CO ₂ into contact with an aqueous solution of: contacting pulverization simultaneously with the aqueous CO ₂₎ reacting by the above-described filtered-2 hydration treatment only separated slag without drying into the same dissolution test apparatus 1 And settling tank, and add water to make the amount of slurry 100 L. At this time, the ratio of water to slag is about 100:1. The other conditions were the same as in Experiment 1, and calcium was eluted.

The slurry obtained by dissolving calcium obtained as above was filtered and separated from the slag to obtain a CO ₂ aqueous solution in which calcium was dissolved. At this time, the pH value of the CO ₂ aqueous solution is 6.7, and the calcium concentration is 1390 mg/L.

(Atomization) As in Experiment 12, the CO ₂ aqueous solution obtained above was atomized by a spray atomization method to precipitate calcium. The atomization is performed only once.

The pH value of the CO ₂ aqueous solution after one atomization is 6.9, and the calcium concentration is 230 mg/L. The calcium precipitation rate at this time was 83.5%.

(Introduction of calcium-based alkaline substance) Thereafter, calcium hydroxide-based composition-4 (hydration-treated water obtained in hydration treatment-2) was added to the CO ₂ aqueous solution accumulated in the tank, While stirring the CO ₂ solution. In order to adjust the pH of the CO ₂ aqueous solution after the injection to any one of 8.0, 8.5, and 9.0, the input amount of the calcium hydroxide-based composition-4 was adjusted.

Table 4 shows the pH value and calcium concentration of the calcium hydroxide-based composition-4 that has been added.

[Table 4] Table 4: Calcium hydroxide-based composition-4

Table 5 shows the pH value, calcium concentration, and calcium precipitation rate of the CO ₂ aqueous solution after the calcium hydroxide-based composition-4 was added (atomization and calcium concentration after the calcium hydroxide-based composition was added/before atomization) Calcium concentration).

[Table 5] Table 5: pH value, calcium concentration, calcium precipitation rate after the calcium hydroxide-based composition was introduced

As is apparent from Table 5, when the hydrated water is added to the CO ₂ aqueous solution after atomization, the calcium concentration also decreases compared with the calcium concentration (190 mg/L) after one atomization, and calcium is further precipitated.

(Recovery of solid content) From the tank into which the CO ₂ aqueous solution has been atomized, the solid content containing calcium can be easily recovered.

This application is an application claiming priority based on Japanese application No. 2018-175965 filed on September 20, 2018, and the contents described in the patent scope, specification and drawings of this application are applied to this application in. [Industry use possibility]

The present invention can precipitate calcium that has been eluted from the steel-making slag into the CO ₂ aqueous solution by a simpler method, so it is useful as a method for recovering calcium resources in iron production.

100: Dissolution device 110: Dissolution and settling tank 112: Slurry extraction port 114: Slurry reintroduction port 118: Impeller 119: Rotating rod 120: Crushing section 130: Carbon dioxide introduction section 140: Slurry flow path 142: Slurry flow Path 144: Slurry flow path 146: Pump 200, 200a, 200b: atomizing device 210, 210a: closed container 212: CO ₂ aqueous solution outlet 214: stirring blade 216: rotating rod 220, 220a: atomizing device 222: CO ₂ aqueous solution flow path 224: shower head 226: nozzle 230: gas introduction part 240: gas discharge part 250: pump 260: heater 270: alkaline substance input port S110-S170: process

1 is a flowchart of a method for recovering calcium from steel-making slag in a first embodiment of the present invention; FIG. 2 is a diagram showing a structure of an apparatus for dissolving calcium that can be used in the first embodiment of the present invention FIG. 3 is a schematic diagram showing the structure of an apparatus for atomizing a CO ₂ aqueous solution in a closed container that can be used in the first embodiment of the present invention; FIG. 4 is a first embodiment of the present invention. showing the configuration of states can be used in a closed vessel to another CO.'s ₂ aqueous atomizing device; FIG. 5 is a flowchart illustrating the method of steelmaking slag of calcium recovered in the second embodiment of the present invention patterns FIG. 6 is a schematic diagram showing the structure of an apparatus that can be used in the second embodiment of the present invention and that can be used for the atomization of a CO ₂ aqueous solution and the input of a calcium-based alkaline substance in a closed container; FIG 7 is a graph showing concentration of carbon dioxide in the aqueous solution (CO ₂₎ and carbonic acid (H ₂ CO ₃₎ is [H ₂ CO ₃ *], bicarbonate ions (HCO ₃ ^-) concentration of [HCO ₃ ^-], and carbonate FIG. 8 is a flow chart of a method for recovering calcium from steel-making slag in the third embodiment of the present invention. FIG. 8 is a graph of the relationship between the existence ratio of ion (CO ₃ ^2- ) concentration [CO ₃ ^2- ] and pH value. FIG. 9 is a flowchart of a method of recovering calcium from steel-making slag in a fourth embodiment of the present invention.

S110-S140: Process

Claims (8)

And a step of atomizing the solution CO ₂ is contacted steelmaking slag; a step to make contact with the steelmaking slag aqueous CO _2, the CO ₂ aqueous solution is an aqueous solution containing carbon dioxide: steelmaking slag to a process for recovering calcium, having . The method for recovering calcium from steel-making slag as described in claim 1, wherein before the step of atomizing the CO ₂ aqueous solution, there is a step of removing the steel-making slag from the CO ₂ aqueous solution to which the steel-making slag has been in contact. Space ₂ as an aqueous solution or an entry request from a method of recovering calcium steelmaking slag, wherein the carbon dioxide partial pressure of the CO 2 for CO.'S ₂ in the atomized solution. The method for recovering calcium from steel-making slag according to any one of claims 1 to 3, which includes from the atmosphere, nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen (H ₂ ), argon (Ar ) And the inorganic gas selected from the group consisting of helium (He) atomizes the CO ₂ aqueous solution in the space. The method for recovering calcium from steel-making slag according to any one of claims 1 to 4 includes the step of adding a calcium-based alkaline substance to the CO ₂ aqueous solution that has been atomized. The method for recovering calcium from steel-making slag as described in claim 5, wherein the calcium-based alkaline substance is input from an aqueous solution in which calcium hydroxide is dissolved, a slurry in which solid calcium hydroxide is dispersed, The calcium hydroxide-based composition selected from the group consisting of solid calcium hydroxide and solid calcium oxide. The method for recovering calcium from steel-making slag as described in claim 5 or 6, wherein the calcium hydroxide-based composition to be input is slag leaching water obtained by contacting the steel-making slag with water. The method for recovering calcium from steel-making slag according to any one of claims 5 to 7, wherein the input of the calcium-based alkaline substance is performed simultaneously with the atomization of the CO ₂ aqueous solution.

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