JP2020045260A - Method of recovering calcium from steelmaking slag - Google Patents

Abstract

To provide a method of recovering calcium from steelmaking slag that enables calcium eluted in a COaqueous solution from steelmaking slag to be precipitated by a simpler method.SOLUTION: The method of recovering calcium from steelmaking slag according to the present invention includes a step of bringing the steelmaking slag into contact with the COaqueous solution, which is an aqueous solution containing carbon dioxide, and a step of spraying the COaqueous solution having been in contact with the steelmaking slag.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for recovering calcium from steelmaking slag.

  Steelmaking slag (such as converter slag, pretreatment slag, secondary refining slag, and electric furnace slag) generated in the steelmaking process is used in a wide range of applications including cement materials, roadbed materials, civil engineering materials, and fertilizers (non-patented). References 1 to 3). In addition, some steelmaking slag not used for the above applications is landfilled.

  Steelmaking slag includes calcium (Ca), iron (Fe), silicon (Si), manganese (Mn), magnesium (Mg), aluminum (Al), phosphorus (P), titanium (Ti), chromium (Cr), It is known that elements such as sulfur (S) are contained. Among these, the element most contained in the steelmaking slag is calcium used in a large amount in the steelmaking process, and usually contains Fe second most. Usually, about 20% to 50% by mass of the total mass of the steelmaking slag is calcium, and about 1% to 30% by mass is Fe.

Calcium in the steelmaking slag is formed by free lime (CaO) supplied in the steelmaking process remaining as it is, or free lime precipitated during the solidification of the steelmaking slag, and free lime reacting with water vapor or carbon dioxide in the air to form hydroxide. Calcium (Ca (OH) ₂ ) or calcium carbonate (CaCO ₃ ), or calcium silicate (Ca ₂ SiO ₄ or Ca ₃ SiO ₅ etc.) or calcium oxide generated by reacting CaO with Si or Al during solidification iron aluminum _{(Ca 2 (Al 1-X} Fe X) 2 O 5) are present in a form such as (collectively compounds containing calcium, also referred to as "calcium compounds".).

  Calcium carbonate and calcium oxide are the main slag forming materials in the iron making process and the steel making process during the iron making process, and are used as modifiers for the basicity and viscosity of the slag, and as dephosphorizers from molten steel. I have. Further, calcium hydroxide obtained by adding water to calcium oxide is used as a neutralizing agent such as an acid in a drainage process. Therefore, it is expected that if the calcium compound contained in the steelmaking slag is recovered and reused in the ironmaking process, the cost of ironmaking can be reduced.

  In the future, it is expected that the number of civil engineering works to use steelmaking slag as roadbed material, civil engineering material, cement material, etc. will decrease, and the land where steelmaking slag can be landfilled will be reduced. . From this viewpoint, it is expected that the calcium compound contained in the steelmaking slag is recovered to reduce the volume of the steelmaking slag to be reused or landfilled.

  Calcium in the steelmaking slag can be recovered by eluting it in an acidic aqueous solution such as hydrochloric acid, nitric acid or sulfuric acid. However, the salt of calcium and the above-mentioned acid produced in this method is difficult to reuse. For example, calcium chloride generated by eluting calcium in steelmaking slag with hydrochloric acid can be reused by heating to form an oxide, but there is a problem that the processing cost of harmful chlorine gas generated during the heating is high. . Further, if calcium in the steelmaking slag is eluted and recovered in an acidic aqueous solution, there is a problem that the cost of purchasing the acid and disposing of the acid after the elution treatment is high.

On the other hand, if calcium is eluted and recovered from steelmaking slag in an aqueous solution containing carbon dioxide (hereinafter, also simply referred to as “CO ₂ aqueous solution”), it is expected that the above problem caused by the use of acid can be solved. (See Patent Documents 1 to 3). It should be noted that carbon dioxide is contained in a large amount in the exhaust gas, and after desulfurization and denitration of the exhaust gas, almost carbon dioxide gas is obtained except for air and water vapor. Industrially, as shown in Non-Patent Document 4, a technique for extracting carbon dioxide from exhaust gas has been put to practical use.

  Patent Literature 1 describes a method in which carbon dioxide is blown into an aqueous solution in which calcium in a converter slag is eluted to recover precipitated calcium carbonate. At this time, the lower limit of the pH is maintained at about 10 in order to suppress the generation of calcium hydrogen carbonate having high solubility in water. Patent Literature 1 does not describe a specific method for maintaining the pH at 10 or more, but it is thought that the pH is maintained at 10 or more by adjusting the amount of carbon dioxide blown.

  Patent Document 2 discloses that a crushed steelmaking slag is separated into an iron-enriched phase and a phosphorus-enriched phase, and a calcium compound in the phosphorus-enriched phase is dissolved in washing water in which carbon dioxide is dissolved. A method is described in which calcium bicarbonate in washing water is precipitated as calcium carbonate by heating to about ° C. and recovered.

  Patent Literature 3 describes a method of recovering a calcium compound from steelmaking slag by eluting the calcium compound in a plurality of times. In this method, it is described that by immersing steelmaking slag (pretreatment slag) in water into which carbon dioxide has been blown a plurality of times, a 2CaO.SiO2 phase and phosphorus dissolved in this phase are preferentially eluted. .

Patent Literature 4 discloses a method of contacting steelmaking slag with an aqueous solution of CO ₂ to elute calcium and phosphorus, and then removing carbon dioxide from the aqueous solution to precipitate a calcium compound and a phosphorus compound, thereby recovering calcium. Are listed. Patent Literature 4 describes that the method can elute a larger amount of calcium more easily than the methods described in Patent Literatures 1 to 3 and increase calcium recovery efficiency. Patent Document 4 discloses a method for removing carbon dioxide from an aqueous solution in which calcium and phosphorus are eluted, by adding one or more gases selected from the group consisting of air, nitrogen, oxygen, hydrogen, argon, and helium into the aqueous solution. Is described.

  On the other hand, Fe in the steelmaking slag is present as iron-based oxides, calcium iron aluminum oxide, and, to a lesser extent, metallic iron. Among them, the iron-based oxide contains Mn or Mg and also contains a small amount of elements such as Ca, Al, Si, P, Ti, Cr and S. Calcium iron aluminum oxide also contains a small amount of elements such as Si, P, Ti, Cr and S. In the present specification, iron-based oxides also include compounds in which a part of the surface has been changed to hydroxides or the like by water vapor in the air, and calcium iron aluminum oxide also includes water vapor in the air and carbon dioxide. And a compound in which a part of the surface has been changed to a hydroxide or a carbonate.

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

Among these, the wustite-based oxide and the hematite-based oxide can be separated from the steelmaking slag by magnetic separation because the magnetite-based oxide (Fe ₃ O ₄ ), which is a ferromagnetic material, is dispersed therein. In addition, a magnetite-based oxide alone or coexisting with another iron-based oxide can also be separated from steelmaking slag by magnetic separation.

  Patent Documents 5 to 7 disclose a method of modifying a wustite-based oxide into a magnetite-based oxide by an oxidation treatment or the like in order to separate more iron-based oxides by magnetic separation.

  Since the calcium iron aluminum oxide is magnetized to become a magnetic material, it can be separated from steelmaking slag by magnetic separation.

  Iron-based oxides and calcium iron aluminum oxide (hereinafter collectively referred to as “iron-based compounds. Calcium iron aluminum oxide is both a calcium compound and an iron-based compound.) Since it is as small as 0.1% by mass or less, it can be used as a raw material for a blast furnace or sintering if it is separated and recovered from steelmaking slag by the above-described magnetic separation or the like.

  Metallic iron is Fe entrained in the slag in the steelmaking process and minute Fe precipitated during solidification of the steelmaking slag. Larger pieces of metallic iron are removed by magnetic separation or other methods during a dry process of crushing or grinding steelmaking slag in the atmosphere.

JP-A-55-100220 JP 2010-270378 A JP 2013-142046 A WO 2015/114703 JP-A-54-87605 JP-A-52-125493 JP-A-54-88894

Masao Nakagawa, "Situation of Effective Utilization of Steel Slag", Textbook of the 205th and 206th Nishiyama Memorial Technical Lecture, Japan Iron and Steel Association, June 2011, p. 25-56 "Environmental Materials Iron and Steel Slag", Iron and Steel Slag Association, January 2014 Takayuki Futatsuka et al., "Effects of elution of components from steel slag into artificial seawater", Iron and Steel, Vol. 89, no. 4, January 2014, p. 382-387 Masaki Iijima et al., "CO2 recovery technology as a global warming countermeasure technology", Mitsubishi Heavy Industries Technical Report, Vol. 47, no. 1, 2010, p. 47-53

  According to the method described in Patent Document 4, it is expected that the amount of eluted calcium 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 is expected to be further enhanced.

In view of the above problems, the present invention can be precipitated calcium eluted into CO ₂ solution from steelmaking slag in a more simple method, to provide a method for recovering calcium from steel slag, and an object .

In view of the above object, the present invention includes a step of contacting the CO ₂ steelmaking in an aqueous solution slag is an aqueous solution containing carbon dioxide, and a step of spraying the CO ₂ aqueous solution the steelmaking slag in contact, steelmaking slag For recovering calcium from lime.

According to the present invention, it is possible to precipitate calcium eluted into CO ₂ solution from steelmaking slag with a simpler method, a method of recovering is provided calcium from steelmaking slag.

FIG. 1 is a flowchart of a method for recovering calcium from steelmaking slag according to the first embodiment of the present invention. FIG. 2 is a schematic diagram showing a configuration of an apparatus for eluting calcium that can be used in the first embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a configuration of an apparatus that sprays 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 schematic diagram showing another configuration of a device for spraying a CO ₂ aqueous solution in a closed container that can be used in the first embodiment of the present invention. FIG. 5 is a flowchart of a method for recovering calcium from steelmaking slag in the second embodiment of the present invention. FIG. 6 is a schematic diagram showing a configuration of an apparatus which can be used in the second embodiment of the present invention and which can be used for spraying an aqueous solution of CO _{2 in} a closed container and charging it into a calcium-based alkaline substance. FIG. 7 shows the concentrations [H ₂ CO ₃ ^* ] of carbon dioxide (CO ₂ ) and carbon dioxide (H ₂ CO ₃ ), the concentrations [HCO ₃ ⁻ ] of hydrogen carbonate ions (HCO ₃ ⁻ ), and the carbonate ions in the aqueous solution. and the abundance ratio of the concentration _[CO ^{3 2-]} of _(CO ^{3 2-),} is a graph showing the relationship between the pH. FIG. 8 is a flowchart of a method for recovering calcium from steelmaking slag in the third embodiment of the present invention. FIG. 9 is a flowchart of a method for recovering calcium from steelmaking slag according to a fourth embodiment of the present invention.

[First Embodiment]
FIG. 1 is a flowchart of a method for recovering calcium from steelmaking slag according to the first embodiment of the present invention. In the present embodiment, steelmaking slag is prepared (step S110), and the prepared steelmaking slag is brought into contact with an aqueous solution containing carbon dioxide (hereinafter, also simply referred to as “CO ₂ aqueous solution”) (step S120). There was sprayed with the CO ₂ solution in contact (step S130), then, recovering the solid component comprising calcium deposited (step S140).

(Step S110: Preparation of steelmaking slag)
In this step, steelmaking slag is prepared.

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

  The size of the structure such as calcium silicate, free lime, and iron-based compounds contained in the steelmaking slag is about 1000 μm or less. Therefore, it is preferable that the steelmaking slag is crushed or pulverized (hereinafter, also simply referred to as “pulverization or the like”) after being discharged in the steelmaking process to be formed into particulate slag particles.

The maximum particle size of the crushed or pulverized slag particles is preferably about the same as or less than the structure of calcium silicate, free lime, iron-based compounds, and the like, and more preferably 1000 μm or less. When the maximum particle size is 1000 μm or less, the surface area per volume of the slag particles becomes larger, so that the CO ₂ aqueous solution can sufficiently penetrate into the inside of the slag particles, or calcium silicate and free lime are used alone. Since calcium can be present as particles, calcium is easily eluted in the steps described below. 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 even more preferably 100 μm or less. The slag particles can be reduced to such an extent that the maximum particle size falls within the above range, for example, by further crushing the crushed slag particles with a crusher including a hammer mill, a roller mill, a ball mill and the like.

In addition, the steelmaking slag is obtained by putting steelmaking slag in a container filled with water, leaching free lime and calcium hydroxide, and leaching calcium in the surface layer of a calcium compound, and then filtering the slag. It may be slag. Since the slag from which calcium has been eluted to some extent can be used by using the filtration residual slag, the load when eluting calcium by contact with the CO ₂ aqueous solution can be reduced. At this time, the filtered water from which calcium is leached is a highly alkaline aqueous solution having a pH of 11 or more (hereinafter, also simply referred to as “highly alkaline leached water”). The highly alkaline leachate can be used as a calcium-based alkaline substance for further increasing the pH of the aqueous CO ₂ solution in the _second embodiment.

(Step S120: Contact with CO ₂ aqueous solution)
In this step, the steelmaking slag is brought into contact with a CO ₂ aqueous solution. The steel slag elutes calcium by contact with CO ₂ solution.

In this step, the steelmaking slag may be immersed in water in which carbon dioxide is dissolved in advance, or the carbon dioxide may be dissolved in water after immersing the steelmaking slag in water. However, when calcium elutes into the CO ₂ aqueous solution, calcium and carbon dioxide react with each other to produce water-soluble calcium bicarbonate. Therefore, the amount of carbon dioxide in the CO ₂ aqueous solution decreases with the dissolution of calcium. Therefore, from the viewpoint of improving the calcium elution efficiency, it is preferable to introduce carbon dioxide into the CO ₂ aqueous solution in contact with the steelmaking slag to continuously elute calcium. Note that, while the steelmaking slag is immersed in the aqueous solution, it is preferable to stir the slag from the viewpoint of increasing reactivity.

  Carbon dioxide can be dissolved in water, for example, by bubbling a gas containing carbon dioxide. From the viewpoint of improving the dissolution of calcium from steelmaking slag, it is preferable that 30 ppm or more of non-ionized carbon dioxide (free carbonic acid) is dissolved in the aqueous solution. In addition, the amount of free carbonic acid that can 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 (eg, oxygen or nitrogen). Examples of the gas containing carbon dioxide include exhaust gas after combustion, and a mixed gas of carbon dioxide, air, and water vapor. From the viewpoint of increasing the concentration of carbon dioxide in the aqueous solution to enhance the dissolution of calcium compounds (such as calcium silicate) from the steelmaking slag into the aqueous solution, the gas containing carbon dioxide has a high concentration of carbon dioxide (for example, 90%).

At this time, the steelmaking slag that is in contact with the CO ₂ aqueous solution may be pulverized. The steelmaking slag in contact with the CO ₂ aqueous solution by grinding or the like, a new silicon hardly dissolved in CO ₂ aqueous solution, a hydroxide such as aluminum and iron, carbonates or hydrates yet to remain or deposit Surface is continuously formed. Thus, with or larger contact area with the or, CO ₂ aqueous solution and slag particles easily infiltrated CO ₂ aqueous solution from the surface to be the continuously formed to the inside of the steel slag, calcium from steelmaking slag Can be more easily eluted.

At this time, allowed to settle steelmaking slag in CO ₂ aqueous solution, taken out by selecting a slurry containing precipitated easily slag particles than larger particle size from the deep side of the CO ₂ aqueous solution, the retrieved slag particles You may selectively grind etc. Since the extracted slurry has a small proportion of water, the slag particles to be pulverized or the like are more easily pulverized or the like. By re-introducing the steelmaking slag pulverized in this manner into the CO ₂ aqueous solution, the efficiency of the pulverization of the steelmaking slag and the like can be increased, and a larger amount of calcium can be easily eluted from the steelmaking slag.

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

The dissolution apparatus 100 contains a slurry containing a steelmaking slag and an aqueous solution of CO _2, and dissolves the steelmaking slag (hatched area in the figure) in the slurry, and removes the steelmaking slag from the bottom side of the dissolution and sedimentation tank 110. A crushing unit 120 for crushing steelmaking slag contained in the obtained slurry, a carbon dioxide introduction unit 130 for introducing carbon dioxide into the slurry, and a slurry taken out from the elution / sedimentation tank 110 to the crushing unit 120, and And a slurry flow path 140 for re-introducing the slurry containing the steelmaking slag pulverized in the pulverizing section 120 into the elution / sedimentation tank 110.

  The elution / sedimentation tank 110 is a container that stores the slurry. The elution / sedimentation tank 110 has a slurry outlet 112 on the bottom side, and a slurry re-introduction port 114 for re-introducing the slurry from the pulverizing section 120 on the upper side (liquid level side) of the slurry outlet 112. . The bottom surface of the elution / settling tank 110 is an inclined surface that is inclined so as to become deeper toward the slurry outlet 112 in order to easily take out the deposited steelmaking slag.

  The elution / sedimentation tank 110 has an impeller 118 that stirs the slurry near the bottom surface in order to easily take out the steelmaking slag deposited on the bottom surface. The impeller 118 is rotated by a rotating rod 119 disposed through the slurry flow path 142 so that even when the dissolution and settling tank 110 is enlarged, the steelmaking slag deposited on the bottom surface by the operation thereof can be easily removed. It is preferable that the sedimentation tank 110 be rotated while being supported from the bottom side. Further, it is preferable that the impeller 118 is disposed only on the bottom surface of the elution / settling tank 110 so as not to prevent the steelmaking slag from settling on the upper side.

  The pulverizing unit 120 communicates with the slurry outlet 112 of the elution / settling tank 110 by a slurry flow path 142, and communicates with the slurry reintroduction port 114 of the elution / settling tank 110 by a slurry flow path 144.

  The crushing unit 120 crushes steelmaking slag contained in the slurry introduced from the slurry flow channel 142. For example, the pulverizing section 120 causes a known ball used in a ball mill and a known bead used in a bead mill (hereinafter, also simply referred to as a “pulverizing medium”), which are put into a pulverizing container, to flow by stirring, and to flow and rotate. The slag particles are smashed by the slag particles sliding on the slag particles when the crushing medium comes into contact with the slag particles. The crushing unit 120 may be a continuous crushing device that crushes steelmaking slag included in the slurry while flowing the slurry, or may temporarily store the slurry and crush the steelmaking slag included in the slurry. Or a batch-type pulverizer.

  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 introduce carbon dioxide into the slurry in any of the elution / sedimentation tank 110, the slurry flow path 142 (see FIG. 2), the crushing unit 120, and the slurry flow path 144. The carbon dioxide introduction unit 130 may have a bubble miniaturization device for miniaturizing carbon dioxide bubbles.

  The slurry flow path 140 takes out the slurry whose concentration of the steelmaking slag is increased by the sedimentation of the steelmaking slag from the slurry outlet 112 of the elution / sedimentation tank 110 and introduces the slurry into the pulverizing unit 120; It has a slurry flow path 144 for re-introducing a slurry containing steelmaking slag pulverized at 120 into the elution / sedimentation tank 110 and a pump 146 for flowing the slurry.

Elution-sedimentation tank 110, or a slurry containing steelmaking slag and CO ₂ solution is introduced, or steel slag and CO ₂ aqueous solution is separately introduced to a slurry. The steelmaking slag in the slurry settles from slag particles having a larger particle size. The slurry containing the settled steelmaking slag is stirred by the impeller 118 to increase the fluidity, taken out from the slurry outlet 112, and introduced into the pulverizing unit 120 through the slurry flow path 142 by the pump 146. The slurry containing the steelmaking slag pulverized in the pulverizing section 120 is re-introduced into the elution / sedimentation tank 110 from the slurry channel 144. At this time, carbon dioxide is continuously introduced into the slurry from the carbon dioxide introduction unit 130. By circulating the slurry through the elution / sedimentation tank 110, the slurry channel 142, the pulverizing section 120, and the slurry channel 144, the steelmaking slag is efficiently brought into contact with the CO ₂ aqueous solution while the steelmaking slag is being pulverized. Calcium can be eluted from the steelmaking slag into the CO ₂ aqueous solution.

You can then filtered slurry, slurry or recovered standing supernatant after precipitation of steelmaking slag and may be separated and CO ₂ aqueous calcium eluted with steelmaking slag. However, as long as there is no significant effect on the spray of the next step, it is not necessary to separate the CO ₂ aqueous calcium eluted with steelmaking slag.

(Step S130: Spray of CO ₂ aqueous solution)
In this step, the CO ₂ aqueous solution that has come into contact with the steelmaking slag is sprayed.

By the spray, carbon dioxide is removed from the CO ₂ aqueous solution, pH of the CO ₂ aqueous solution is increased. As a result, the amount of hydrogen ions (H ⁺ ) in the CO ₂ aqueous solution decreases, so that in the following equilibrium equation (Equation 1), hydrogen carbonate ions (HCO ₃ ⁻ ) are associated with calcium ions (Ca ²⁺ ), and hydrogen ions The equilibrium shifts in the direction in which (H ⁺ ) and poorly soluble calcium carbonate (CaCO ₃ ) are generated. In this step, it is considered that calcium was thus precipitated.
^{_{HCO 3 - + Ca 2+ ⇔ H}} + + CaCO 3 ( Equation 1)

  The calcium precipitated in this step is not limited to calcium carbonate, and calcium carbonate hydrate, basic calcium carbonate, calcium hydroxide, and the like may be precipitated.

In this step, since the contact area between the CO ₂ aqueous solution and the surrounding atmosphere gas can be increased by spraying, precipitation of calcium by removing carbon dioxide from the CO ₂ aqueous solution to the surrounding atmosphere gas can be performed easily and in a short time. Can be done with It should be noted that carbon dioxide of the same level as the partial pressure of carbon dioxide in the surrounding atmospheric gas remains in the sprayed CO ₂ aqueous solution.

Spraying may be performed in the form of a shower or in the form of a mist. In any case, from the viewpoint of increasing the contact area between the CO ₂ aqueous solution and the surrounding atmosphere gas to further promote the precipitation of calcium by removing carbon dioxide, the spray is performed by spraying the droplets of the CO ₂ aqueous solution. Is preferably performed so that the diameter is 5000 μm or less, more preferably performed so that the diameter is 1000 μm or less, further preferably performed so that the diameter is 500 μm or less, and the diameter is 200 μm or less. It is particularly preferred that the process be performed as follows. The lower limit of the diameter is not particularly limited, but may be 0.1 μm. The diameter of the droplet can be adjusted according to the size of a discharge port or a nozzle for spraying the CO ₂ aqueous solution.

Spraying may be performed multiple times from the viewpoint of further promoting the precipitation of calcium by removing carbon dioxide. On the other hand, if a sufficient amount of calcium is deposited, spraying may be performed only once. The number of times of spraying can be determined based on the pH of the CO ₂ aqueous solution after spraying (described later) and the like.

From the viewpoint of promoting the precipitation of calcium by removing the carbon dioxide, spraying is performed in a space having an atmosphere gas having a partial pressure of carbon dioxide lower than the equilibrium pressure of carbon dioxide in the aqueous CO ₂ solution in contact with the steelmaking slag. It is preferable to perform it.

The atmosphere gas is not particularly limited, but is preferably a gas that has lower reactivity with or does not react with a CO ₂ aqueous solution than gases (chlorine gas and sulfur dioxide gas) that react 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 a salt, and when the precipitation efficiency of calcium decreases or when it is difficult to remove the salt, Reuse of the aqueous solution of CO ₂ after the precipitation of calcium may be troublesome. Therefore, the atmosphere gas is a gas that has low reactivity or does not react with the CO ₂ aqueous solution, and in particular, is a gas that does not generate ions that form salts with calcium ions by contact with the CO ₂ aqueous solution. Is preferred.

The gas having low or no reactivity with the CO ₂ aqueous solution may be an inorganic gas or an organic gas. Of these, inorganic gases are preferred because they are less likely to burn and explode when leaked to the outside. Examples of the inorganic gas include air, a gas containing nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen (H ₂ ), argon (Ar), helium (He), and the like, and a mixed gas thereof. Is more preferable. Note that the atmosphere may be an atmosphere containing nitrogen (N ₂ ) and oxygen (O ₂ ) at a ratio of about 4: 1 and in an environment where spraying is performed. Examples of the organic gas 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) , and the like.

The spraying is preferably performed in a closed container from the viewpoint of recovering the carbon dioxide removed from the aqueous CO ₂ solution in this step and making it easier to reuse. The recovered carbon dioxide, for example, can be used to introduce the CO ₂ aqueous solution (step S120) when contacting the steel slag in CO ₂ solution.

Incidentally, sealed when performing spray in the container, the carbon dioxide concentration in the sealed container with carbon dioxide removed from the CO ₂ aqueous solution increases, or the rate of removal of carbon dioxide from the CO ₂ aqueous solution is reduced, or removed And the calcium deposition efficiency may decrease. Therefore, it is preferable to spray the CO ₂ aqueous solution while introducing the above atmospheric gas into the closed container and discharging the gas containing carbon dioxide from the closed container.

At this time, the solubility of carbon dioxide in water may be reduced by reducing or heating the inside of the sealed container. Thereby, the removal efficiency of carbon dioxide from the CO ₂ aqueous solution can be increased, and the precipitation efficiency of calcium can also be increased. Further, by heating the inside of the sealed container, the solubility of calcium carbonate or the like in water is reduced, so that the calcium deposition efficiency can be increased. At this time, the pressure inside the sealed container is preferably equal to or lower than the atmospheric pressure (about 0.1 MPa), and the temperature inside the sealed container at this time is such that the vapor pressure of water does not exceed the atmospheric pressure. The temperature is more preferably room temperature or higher and lower than 100 ° C. (when the inside of the closed container is at atmospheric pressure). Either one of the pressure reduction and the heating may be performed, or both may be performed.

FIG. 3 is a schematic diagram illustrating a configuration of a device (hereinafter, also simply referred to as “spray device”) for spraying a CO ₂ aqueous solution in a closed container that can be used in the present embodiment.

Spraying device 200 includes a sealed container 210 that CO ₂ aqueous solution is sprayed, the spray device 220 to spray the CO ₂ aqueous solution, a gas inlet 230 for introducing the atmospheric gas inside the sealed container 210, from the interior of the sealed container 210 It has a gas discharge part 240 for discharging gas containing carbon dioxide, a pump 250 for reducing the pressure inside the sealed container, and a heater 260 for heating the inside of the sealed container.

The closed container 210 is a container into which the CO ₂ aqueous solution that has come into contact with the steelmaking slag is sprayed. The closed container 210 has a CO ₂ aqueous solution outlet 212 for taking out the sprayed CO ₂ aqueous solution on the bottom side. The bottom surface of the sealed container 210 is an inclined surface that is inclined so as to become deeper toward the CO ₂ aqueous solution outlet 212 in order to easily take out the CO ₂ aqueous solution that has reached the bottom surface after being sprayed.

Nebulizer 220, before the CO ₂ solution passage 222 CO ₂ aqueous solution in contact with the steelmaking slag in step (step S120) is Nagareoku, the CO ₂ aqueous solution is Nagareoku from CO ₂ aqueous solution passage 222 like a shower Shower head 224 for spraying. The shower head 224 is installed on the upper side of the closed container 210, and discharges a droplet of the CO ₂ aqueous solution from a plurality of openings toward the bottom side of the closed container 210. In FIG. 3, the sprayer 220 has only one shower head 224, but the sprayer 220 may have a plurality of shower heads.

In FIG. 3, the sprayed CO ₂ aqueous solution is stored on the bottom surface side of the closed container 210 having an inclined surface, but the CO ₂ aqueous solution is not stored, and the sprayed CO ₂ aqueous solution is used as it is. _{The second} aqueous solution outlet 212 may be discharged.

The gas introduction unit 230 introduces the above atmospheric gas into the closed container 210. In this case, the bottom side of the container, is removed carbon dioxide from the atomized CO ₂ aqueous solution have reduced concentration of carbon dioxide in the CO ₂ aqueous solution (the equilibrium pressure of carbon dioxide), carbon dioxide from the CO ₂ aq It is difficult to remove. Therefore, it is preferable that the gas introduction unit 230 introduces the above-mentioned atmosphere gas from the bottom side of the closed vessel 210 to lower the concentration of carbon dioxide (partial pressure of carbon dioxide) in the atmosphere gas on the bottom side of the closed vessel 210. .

  In FIG. 3, only two gas introduction units 230 are provided for the closed container 210, but a plurality of gas introduction units 230 are arranged at equal intervals in the circumferential direction along the outer periphery of the closed container 210. The above-mentioned atmospheric gas may be uniformly introduced to the bottom side inside the closed vessel 210, and the carbon dioxide concentration on the bottom side may be uniformly reduced as a whole.

The gas discharge unit 240 discharges the atmospheric gas from the inside of the closed container 210. Atmosphere gas discharged is because it contains carbon dioxide removed from the CO ₂ aqueous solution by spraying the CO ₂ aqueous solution, carbon dioxide concentration is high. 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 unit 240. By continuously supplying a constant amount of the CO ₂ aqueous solution, the concentration and the amount of carbon dioxide in the discharged atmospheric gas can be kept constant from the beginning to the end of spraying. From such an atmospheric gas, it is easy to obtain industrially reusable carbon dioxide having a carbon dioxide concentration of 99% by volume or more by industrially recovering and purifying carbon dioxide. is there. Thus, in the present embodiment, an atmosphere gas having a high carbon dioxide concentration can be obtained, and the carbon dioxide can be easily reused.

The pump 250 is disposed in the pipe of the gas discharge unit 240, and adjusts the discharge amount of the atmospheric gas from the inside of the closed container 210 to reduce the pressure inside the closed container 210. The pump 250 increases the efficiency of removing carbon dioxide from the CO ₂ aqueous solution sprayed by the above-described depressurization, and also reduces the pressure from the gas discharge unit 240 disposed on the upper side of the closed vessel 210 to thereby reduce the lower side of the closed vessel 210. And promotes the movement of carbon dioxide from above to the upper side, so that the concentration of carbon dioxide inside the closed container 210 is easily reduced.

The heater 260 may be a known heater such as a jacket heater for heating the inside of the closed container 210. By heating the inside of the sealed container 210 with the heater 260 and depressurizing the inside of the sealed container 210 with the pump 250, the efficiency of removing carbon dioxide from the CO ₂ aqueous solution can be increased. In addition, by heating the inside of the closed container 210 by the heater 260, the efficiency of calcium precipitation from the CO ₂ aqueous solution can be increased. Further, by using both the heating of the inside of the sealed container 210 by the heater 260 and the depressurization of the inside of the sealed container 210 by the pump 250, the heating temperature for increasing the carbon dioxide removal efficiency and the calcium deposition efficiency is reduced. Even if not so high, the calcium deposition efficiency can be efficiently and sufficiently increased.

  In addition, the heater 260 may heat the atmosphere gas introduced from the gas introduction unit 230.

FIG. 4 is a schematic diagram illustrating a configuration of another spraying device 200a according to the present embodiment. The spraying device 200a has a nozzle 226 that causes the sprayer 220a to spray the CO ₂ aqueous solution in a mist state. Also in such a spraying device 200a, similarly, carbon dioxide can be efficiently removed from the CO ₂ aqueous solution, and calcium can be efficiently precipitated. In FIG. 4, the spray device 220a has only one nozzle 226, but the spray device 220a may have a plurality of 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 simultaneously precipitated. For this reason, in the present embodiment, the aqueous solution after the precipitation of calcium can simplify or eliminate wastewater treatment, and can suppress the cost of wastewater treatment.

  Further, since the remaining aqueous solution after the precipitation of calcium hardly contains elements such as calcium (Ca), iron (Fe), manganese (Mn), aluminum (Al), and phosphorus (P), and carbon dioxide, , And can be reused in the process. Therefore, the present embodiment can reduce the amount of wastewater generated by the treatment.

(Step S140: Recover solid component)
In this step, a solid component containing calcium precipitated by spraying the CO ₂ aqueous solution is recovered. The solid component can be recovered by a known method including a sedimentation precipitation method and pressure filtration. This solid component includes calcium derived from steelmaking slag.

(effect)
According to the method for recovering calcium from steelmaking slag described above, calcium eluted in the CO ₂ aqueous solution can be recovered by an easier method.

[Second embodiment]
FIG. 5 is a flowchart of a method for recovering calcium from steelmaking slag in the second embodiment of the present invention. In the present embodiment, as in the first embodiment, to prepare the steelmaking slag (step S110), contacting the steel slag prepared for CO ₂ aqueous solution (step S120), the CO ₂ aqueous solution steelmaking slag in contact Is sprayed (step S130). Thereafter, in the present embodiment, a calcium-based alkaline substance is introduced into the CO ₂ aqueous solution (Step S150), and a solid component containing precipitated calcium is recovered (Step S140). Step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and thus redundant description will be omitted.

(Step S150: Injection of calcium-based alkaline substance)
Figure 6 is a schematic diagram showing the structure of a spray apparatus that can be used for spraying of CO ₂ solution in this embodiment (step S130) and turned into calcium-based CO ₂ aqueous solution of an alkaline material (step S150).

Spray apparatus 200b has an alkaline substance inlet 270 to introduce an alkaline substance calcium system in the interior of the CO ₂ aqueous solution of the sealed container 210a, the sealed container 210a is a CO ₂ aqueous solution is charged with alkaline substance calcium-based It has a stirring blade 214 for stirring and a rotating rod 216 for rotating the stirring blade 214. The other configuration of the spraying device 200b is the same as that of the spraying device 200 shown in FIG.

The alkaline substance introduction port 270 introduces a calcium-based alkaline substance into the inside of the closed container 210a and makes the calcium-based alkaline substance come into contact with the CO ₂ aqueous solution. In FIG. 6, the alkaline substance inlet 270 injects a calcium-based alkaline substance into the CO ₂ aqueous solution that has been sprayed and collected at the bottom of the closed container 210a.

As described above, in the spraying of the CO ₂ aqueous solution (step S130), the pH of the CO ₂ aqueous solution is increased by removing carbon dioxide, and calcium is precipitated from the CO ₂ aqueous solution. However, when the pH of the CO ₂ aqueous solution exceeds about 8.5, carbon dioxide can no longer exist in the CO ₂ aqueous solution, and therefore, the rise of the pH of the CO ₂ aqueous solution by the above spraying is limited to about 8.5. It is. On the other hand, hydrogen carbonate ions (HCO ₃ ⁻ ) exist in the CO ₂ aqueous solution even at a pH of 8.5 or more, and calcium ions (Ca ²⁺ ) remain in equilibrium with the hydrogen carbonate ions. On the other hand, by introducing a calcium-based alkaline substance into the CO ₂ aqueous solution from which carbon dioxide has been (partially) removed by spraying, the pH of the CO ₂ aqueous solution is further raised, and the remaining calcium ions are carbonated. It can be precipitated as calcium or the like.

More specifically, FIG. 7 shows the concentration [H ₂ CO ₃ ^* ] of carbonic acid (H ₂ CO ₃ ), the concentration [HCO ₃ ⁻ ] of hydrogen carbonate ion (HCO ₃ ⁻ ), and the concentration of carbonate ion (CO ₂ ) in the aqueous solution. ₃ ²⁾ and the abundance ratio of the concentration _[CO ^{3 2-],} and is a graph showing the relationship between the pH. Here, [H ₂ CO ₃ ^* ] is the combined concentration of the concentration of carbon dioxide [CO ₂ ] and the concentration of carbon dioxide [H ₂ CO ₃ ]. Note that the ratio of [CO ₂ ] and [H ₂ CO ₃ ] in the aqueous solution ([CO ₂ ] / [H ₂ CO ₃ ]) is about 650, and carbon dioxide (CO ₂ ) is higher than carbon dioxide (H ₂ CO ₃ ). ₂ ) The existence ratio is overwhelmingly large. As is clear from FIG. 7, when the pH exceeds about 8.5, [H ₂ CO ₃ ^* ] is almost 0, and carbon dioxide hardly exists in the aqueous solution. FIG. 7 is described in a known document (for example, "Corrosion and Corrosion Protection Handbook", Corrosion and Corrosion Protection Association, 2000, p. 155).

Here, the presence state of each of the carbonic acid species (CO ₂ , H ₂ CO ₃ , HCO ₃ ⁻ , and CO ₃ ²⁻ ) in the aqueous solution is determined by the following equilibrium equations (Equation 2) to (Equation 4). It is represented by Specifically, when the pH is lower than about 8.5, the equilibrium relationship represented by the equilibrium equation (Equation 2) and the equilibrium equation (Equation 3) holds, and when the pH is higher than about 8.5. Satisfies the equilibrium relationship represented by the equilibrium equation (Equation 3) and the equilibrium equation (Equation 4).
CO ₂ + H ₂ O⇔H ₂ CO ₃ (formula 2)
^{_{H 2 CO 3 ⇔ H + +}} HCO 3 - ( Equation 3)
^{_{HCO 3 - ⇔ H + + CO}} 3 2- ( Equation 4)

When CO ₂ in the aqueous solution is reduced, up to a pH of about 8.5, the equilibrium of (Equation 2) is biased to the left to compensate for the decrease in CO ₂ , and H ₂ CO ₃ is reduced. When H ₂ CO ₃ decreases, the equilibrium of (Equation 3) shifts to the left to compensate for the decrease, H ⁺ decreases, and the pH of the aqueous solution increases. When H ⁺ decreases, the equilibrium of the equilibrium equation (Equation 5) shifts to the right, and calcium ions (Ca ²⁺ ) and hydrogen carbonate ions (HCO ₃ ⁻ ) react to cause poorly soluble calcium carbonate (CaCO ₃ ). Occurs and calcium is precipitated. At this time, the equilibrium movement of water of the equilibrium equation (Equation 6) occurs together with the change of the concentration of H ⁺ due to the movement of each equilibrium. Therefore, pH can be used as an indicator of the progress of the whole reaction.
^{_{Ca 2+ + HCO 3 - ⇔ H}} + + CaCO 3 ( Formula 5)
^{_{H 2 O ⇔ H + + OH}} - ( Equation 6)

Since the above-mentioned several equilibrium states move simultaneously, when carbon dioxide is removed from the CO ₂ aqueous solution, immediately after the start of the removal, the equilibrium of (Equation 3) is shifted to the left side for the reaction biased to the right of (Equation 5). The pH rises due to the predominantly biased reaction, and a small amount of calcium carbonate precipitates. Thereafter, the reaction in which the equilibrium of (Equation 5) shifts to the right becomes dominant, so that the pH drops and more calcium carbonate (CaCO ₃ ) precipitates. Thereafter, the leftward reaction of (Equation 3) becomes more dominant than the rightward reaction of (Equation 5) again, and the pH rises. At this time, calcium carbonate continues to be precipitated due to the rightward reaction of (Equation 5). In this way, the precipitation of calcium carbonate by the equilibrium transfer of (Equation 2), (Equation 3), and (Equation 5) proceeds until the pH becomes about 8.5 at which carbon dioxide in the CO ₂ aqueous solution disappears.

On the other hand, at about pH 8.5 or more at which carbon dioxide has almost disappeared from the aqueous solution, when H ⁺ in the aqueous solution decreases due to an increase in pH, the equilibrium of (Equation 5) shifts to the right, and calcium ion and bicarbonate ion The formation of calcium carbonate (CaCO ₃ ), which is hardly soluble in the reaction, promotes the precipitation of calcium. Due to this equilibrium movement, almost all of the calcium in the aqueous solution precipitates by pH 10.

However, as described above, in the removal of carbon dioxide from a CO ₂ aqueous solution, the pH of the aqueous solution can be increased only to about pH 8.5 at which carbon dioxide does not exist in the aqueous solution. On the other hand, by introducing a calcium-based alkaline substance into the CO ₂ aqueous solution after removing carbon dioxide to some extent, the calcium concentration and the pH in the CO ₂ aqueous solution are increased, and the equilibrium of the equation (5) is shifted to the right. It can facilitate the precipitation of calcium carbonate.

In addition, the lower the carbon dioxide concentration of the aqueous CO ₂ solution, the lower the efficiency of further removing carbon dioxide from the aqueous CO ₂ solution. Therefore, in order to raise the pH of the CO ₂ aqueous solution by spraying (removal of carbon dioxide), it is necessary to exponentially increase the flight distance of the sprayed CO ₂ aqueous solution. On the other hand, the removal of carbon dioxide from the CO ₂ aqueous solution by spraying is stopped when a certain amount of carbon dioxide remains in the CO ₂ aqueous solution, and thereafter the precipitation of calcium is promoted by introducing a calcium-based alkaline substance. By doing so, it is possible to suppress the processing from becoming complicated due to an increase in the size of the spray device and an increase in the number of times of spraying. For example, spraying, pH of CO ₂ aqueous solution is 6.5 to 8.0, preferably continued until the pH of the CO ₂ aqueous solution is 6.6 to 7.5, after which the alkaline substance calcium-based CO ₂ It is preferable to put in an aqueous solution.

The calcium-based alkaline substance may be an alkaline substance containing calcium (Ca). From the viewpoint of increasing the pH and increasing the amount of precipitated calcium, calcium hydroxide (Ca ( OH) ₂ ) or a composition that generates calcium hydroxide when introduced into 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), which changes into calcium hydroxide when injected into a CO ₂ aqueous solution.

  Among these, the aqueous solution in which calcium hydroxide is dissolved can be easily obtained in each step of the process of recovering calcium from steelmaking slag. For example, the aqueous solution in which the calcium hydroxide is dissolved may be high alkali leaching water obtained when obtaining filtration residual slag in the step of preparing steelmaking slag, or may be hydrated in a third embodiment described later. The water may be hydration-treated water obtained after the treatment, or may be magnetic separation water obtained after wet magnetic separation in a fourth embodiment described later. In the present specification, a liquid component obtained by contacting steelmaking slag with water, such as the above-mentioned highly alkaline leaching water, hydration-treated water, and magnetic separation water, is also referred to as slag leaching water.

The slag leaching water was obtained in a previous processing step on steelmaking slag in which calcium is precipitated by spraying a CO ₂ aqueous solution (step S130) and charging a calcium-based alkaline substance (step S150). May be obtained during the process of processing other steelmaking slag. It is preferable to add the slag leachate to the CO ₂ aqueous solution in this step from the viewpoint of effective utilization of the slag leachate discharged in each step for recovering calcium from the steelmaking slag.

  Alternatively, the aqueous solution in which the calcium hydroxide is dissolved may be a waste liquid obtained by a process other than the process of recovering calcium from steelmaking slag. Examples of the waste liquid include a waste aqueous solution generated when acetylene is produced by reacting calcium carbide (calcium carbide) with water. The waste aqueous solution is substantially composed of water and calcium hydroxide. Therefore, the use of the waste aqueous solution can reduce the amount of impurities mixed into the solid component containing precipitated calcium.

Instead of the 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 components containing precipitated calcium obtained by introducing these components generate sodium and toxic ammonia gas which may shorten the life of the refractory contained in the sintering furnace and the blast furnace. May contain ammonia. Therefore, it is preferable to promote the precipitation of calcium by adding the calcium-based alkaline substance.

In FIG. 6, the alkaline substance inlet 270 directly injects the calcium-based alkaline substance into the CO ₂ aqueous solution collected at the bottom of the sealed container 210a. However, the method of adding the calcium-based alkaline substance is not limited to this. For example, in a separately provided tank downstream of the sealed container 210a, may be charged with an alkaline substance of the calcium-based on CO ₂ aqueous solution, in the flow path for communicating the sealed container 210a and the tank, CO ₂ aq A mixer for charging and mixing the above-mentioned calcium-based alkaline substance may be arranged. However, with such CO ₂ aqueous solution is charged alkaline substance of the calcium-based in a sealed container 210a to be sprayed, and the spray of CO ₂ aqueous solution, and the alkaline substance calcium system to the sprayed CO ₂ aqueous solution, simultaneously Performing the method is preferable because the time required for the processing can be reduced and the equipment configuration can be simplified.

After charging the calcium-based alkaline substance, 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 vessel 210a has a stirring blade 214 for stirring a CO ₂ aqueous solution into which a calcium-based alkaline substance is charged, and a rotating rod 216 for rotating the stirring blade 214.

Although FIG. 6 shows a spraying device having a sprayer for spraying a CO ₂ aqueous solution in a shower form, a calcium-based alkaline substance is charged by using a spraying device having a sprayer for spraying a CO ₂ aqueous solution in a mist state. May be similarly performed.

(effect)
According to the method for recovering calcium from the steelmaking slag described above, calcium eluted in the aqueous CO ₂ solution can be recovered by an easier method.

[Third Embodiment]
FIG. 8 is a flowchart of a method for recovering calcium from steelmaking slag in the third embodiment of the present invention. In the present embodiment, as in the first embodiment, a steelmaking slag is prepared (step S110), and then the steelmaking slag is subjected to a hydration treatment (step S160). Thereafter, the hydration process alms steel slag is brought into contact with CO ₂ aqueous solution (step S120), steelmaking slag is sprayed the CO ₂ solution in contact (step S130), recovering a solid component comprising a precipitated calcium (Step S140). Step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and thus redundant description will be omitted.

  The hydration treatment may be performed by a method and under conditions in which the calcium compound contained in the steelmaking slag is sufficiently hydrated.

As described above, calcium in steelmaking slag includes free lime, calcium hydroxide (Ca (OH) ₂ ), calcium carbonate (CaCO ₃ ), calcium silicate (Ca ₂ SiO ₄ , Ca ₃ SiO ₅ ) and calcium oxide. present as iron aluminum _{(Ca 2 (Al 1-X} Fe X) 2 O 5) calcium such as compounds.

When this steelmaking slag is subjected to a hydration treatment, for example, calcium silicate hydrate and calcium hydroxide (Ca (OH) ₂ ) are generated from calcium silicate by a reaction represented by the following (Formula 7), A calcium oxide-based hydrate is formed from calcium iron aluminum oxide by a reaction represented by the following (formula 8) (hereinafter, calcium-containing compounds that can be formed by hydration treatment are collectively referred to as “calcium hydrate” Also called "things").
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 ( Eq. 8)
(Equation (8), calcium iron aluminum oxide _{(Ca 2 (Al 1-X} Fe X) in 2 _{O 5)} showing an example of a case of X = 1/2.)

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

Although free lime is easily dissolved in a CO ₂ aqueous solution, steelmaking slag usually contains only less than about 10% by mass. On the other hand, calcium silicate is usually contained in steelmaking slag at about 25% by mass to 70% by mass, and calcium iron aluminum is usually contained in steelmaking slag at about 2% by mass to 30% by mass. Therefore, if calcium contained in calcium silicate and calcium iron aluminum is easily eluted with the CO ₂ aqueous solution by the hydration treatment, the amount of calcium eluted from the steelmaking slag to the CO ₂ aqueous solution can be increased, It is considered that calcium can be recovered from the 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, during the hydration process, some of the free lime in the steelmaking slag elutes into the water for treatment. Therefore, when the hydration treatment is performed, cracks are generated inside the slag particles, and the slag particles are likely to collapse starting from the cracks. When the slag particles collapse in this way, the particle diameter of the slag particles decreases, the surface area per volume increases, and water or a CO ₂ aqueous solution can sufficiently penetrate into the steelmaking slag. Many calcium compounds can be hydrated, and when the steelmaking slag is subsequently brought into contact with a CO ₂ aqueous solution (step S120), a larger amount of calcium can be eluted.

  Therefore, it is preferable that the hydration treatment is performed by a method and under conditions in which calcium silicate or calcium iron aluminum oxide contained in the steelmaking slag can be hydrated.

  Specific examples of the hydration treatment include a treatment in which the steelmaking slag immersed and settled in water is allowed to stand (hereinafter, also simply referred to as “immersion stationary”), and the steelmaking slag immersed in water is stirred or crushed. Treatment (hereinafter, also simply referred to as "immersion stirring"), treatment of leaving a paste containing water and slag particles (hereinafter, also simply referred to as "pasting and standing"), and a sufficient amount of water vapor A process of leaving the steelmaking slag in the container (hereinafter, also simply referred to as “wet standing”) is included. According to these methods, the steelmaking slag and the water can be brought into sufficient contact. In the hydration treatment, only one of the above immersion stationary, immersion stirring, pasting stationary and wet stationary may be performed, or two or more of these may be performed in an arbitrary order. The hydration treatment by immersion and stirring is preferred from the viewpoint of more sufficiently hydrating the interior of the slag particles to facilitate the elution of calcium.

  The immersion stirring may be performed by stirring a steelmaking slag immersed in water inside a container having a stirring impeller, or may be performed by pulverizing the steelmaking slag while stirring it with a ball mill. From the viewpoint of hydrating more sufficiently to the inside of the slag particles to make calcium more easily eluted, it is preferable that the immersion stirring is performed by pulverizing the steelmaking slag while stirring.

The above-described reaction due to the hydration treatment occurs when the calcium compound contacts water near or inside the surface of the steelmaking slag. Here, although a certain amount of water permeates into the steelmaking slag, the amount of contact with water is greater near the surface. Therefore, calcium hydrate is more easily generated near the surface of the steelmaking slag. Further, when the components contained in the steelmaking slag is dissolved in water used for hydration, as in the case of dissolving the CO ₂ solution described above, silicon, aluminum, iron and manganese or their hydroxides, carbonates and Hydrates may remain or precipitate on the surface of the steelmaking slag. When these remaining or precipitated substances inhibit the penetration of water into the steelmaking slag, calcium hydrate is less likely to be generated inside the steelmaking slag.

  On the other hand, by grinding the steelmaking slag immersed in water during the hydration treatment, the surface area of the slag particles can be increased, and the contact area between the water and the slag particles can be further increased. In addition, by crushing the steelmaking slag immersed in water, a new surface on which the above-mentioned substance still does not remain or precipitate is continuously formed, and water is continuously transferred from the surface formed continuously to the inside of the steelmaking slag. , Calcium hydrate can be more easily generated inside the steelmaking slag. Also, by grinding the surface of the steelmaking slag, the remaining or precipitated substance is removed, the contact area between water and slag particles becomes larger, and water is more easily permeated into the steelmaking slag. can do.

The water used in the hydration treatment preferably has a carbon dioxide content of less than 300 mg / L, including free non-ionized carbonic acid and ionized bicarbonate ions (HCO ₃ ⁻ ). If the content of the carbon dioxide is less than 300 mg / L, calcium compounds other than free lime and calcium hydroxide are hardly eluted in water used for the hydration treatment, so that most of the calcium contained in the steelmaking slag is CO ₂ It can be eluted into the aqueous CO ₂ solution at the time of contact with the aqueous solution (step S120), and the recovery of calcium does not easily become complicated. Also, if the water has a high carbon dioxide content, calcium eluted from free lime or calcium hydroxide reacts with carbon dioxide, and the generated and precipitated calcium carbonate covers the surface of the slag particles, and the hydration reaction proceeds If the content of carbon dioxide is less than 300 mg / L, inhibition of the hydration reaction due to the precipitation of calcium carbonate is unlikely to occur. The content of the carbon dioxide in the industrial water is usually less than 300 mg / L. Therefore, it is preferable that the water used for the hydration treatment by immersion standing or immersion stirring is industrial water to which carbon dioxide is not intentionally added or contained.

  The temperature of the water used for the hydration treatment may be a temperature at which the water does not evaporate violently. For example, when hydrating steelmaking slag under conditions of approximately atmospheric pressure, the temperature of water is preferably 100 ° C or lower. However, when performing hydration at a higher pressure using an autoclave or the like, the temperature of the water may be 100 ° C or higher as long as the temperature is not higher than the boiling point of water at the pressure at which the hydration is performed. . Specifically, the temperature of water when performing hydration treatment by immersion standing or immersion stirring is preferably 0 ° C or more and 80 ° C or less. When the hydration treatment is performed at a higher pressure using an autoclave or the like, there is no particular upper limit on the temperature, but the temperature is preferably 300 ° C. or less from the viewpoint of the pressure resistance of the apparatus and economical aspects. The temperature at which the hydration treatment is performed by pasting and standing is preferably 0 ° C. or more and 70 ° C. or less.

  The duration of the hydration treatment can be arbitrarily set depending on the average particle diameter of the slag, the temperature at which the hydration treatment is performed (temperature of water or air containing water vapor), and the like. The duration of the hydration treatment may be shorter as the average particle diameter of the slag is smaller, and may be shorter as the temperature of the hydration treatment is higher.

  For example, when the hydration treatment by immersion standing or immersion stirring is performed at room temperature on steelmaking slag in which the maximum particle size of the slag particles is 1000 μm or less, the duration of the hydration treatment may be about 8 hours continuously. It is preferable that the heating time be 3 hours or more and 30 hours or less. When the above hydration treatment is performed by immersion in water at a temperature of 40 ° C. or more and 70 ° C. or less, it is preferable that the duration of the hydration treatment is continuously 0.6 hours or more and 8 hours or less.

  Further, when hydration treatment by immersion and stirring while pulverizing steelmaking slag having a maximum particle size of 1000 μm or less is performed at room temperature, the duration of the hydration treatment is continuously 0.1 hours or more. The time is preferably not more than 0.2 hours, more preferably not less than 0.2 hours and not more than 3 hours. Alternatively, when the hydration treatment by immersion and stirring while pulverizing or the like is performed at normal temperature, the duration of the hydration treatment is such that the maximum particle size of the slag particles is 1000 μm or less, preferably 500 μm or less, more preferably 250 μm, and still more preferably It is preferable to perform the process until the thickness becomes 100 μm or less.

  The hydration treatment is preferably carried out to such an extent that calcium silicate is sufficiently converted into a hydrate and calcium hydroxide, or calcium iron oxide is sufficiently converted into a calcium oxide hydrate. For example, the hydration treatment is preferably performed until the amount of calcium silicate contained in the steelmaking slag becomes 50% by mass or less, or until the amount of calcium iron aluminum oxide becomes 20% by mass or less.

The steelmaking slag after the hydration treatment may be used as it is for contact with a CO ₂ aqueous solution (step S120). However, when the steelmaking slag is in a slurry state, the steelmaking slag and the liquid component are separated by solid-liquid separation. Is preferred. The solid-liquid separation can be performed by a known method including filtration under reduced pressure and filtration under pressure. The liquid component obtained by the solid-liquid separation (hereinafter simply referred to as “hydration-treated water”) contains calcium eluted from steelmaking slag in addition to the water used for the hydration treatment. It has become. Therefore, in the second embodiment, the hydration-treated water can be used as a calcium-based alkaline substance for further increasing the pH of the CO ₂ aqueous solution.

In this embodiment, similarly to the second embodiment, after spraying a CO ₂ aqueous solution contacted by steelmaking slag, a calcium-based alkaline substance is introduced into the CO ₂ aqueous solution (step S150), and thereafter, The solid component containing calcium precipitated on the surface may be recovered (Step S140).

(effect)
According to the above-described method of recovering calcium from steelmaking slag, calcium can be more easily eluted from the steelmaking slag into the CO ₂ aqueous solution, and the efficiency of recovering calcium from steelmaking slag can be further increased.

[Fourth embodiment]
FIG. 9 is a flowchart of a method for recovering calcium from steelmaking slag according to a fourth embodiment of the present invention. In the present embodiment, as in the first embodiment, a steelmaking slag is prepared (step S110), and then the steelmaking slag is subjected to magnetic separation (step S170). Then, contacting the steel slag subjected to the magnetic separator to CO ₂ aqueous solution (step S120), steelmaking slag is sprayed the CO ₂ solution in contact (step S130), recovering a solid component comprising a precipitated calcium (step S140). Step S110, step S120, step S130, and step S140 can be performed in the same manner as in the first embodiment, and thus redundant description will be omitted.

By applying a magnetic separation in steelmaking slag, with a compound containing a remaining or deposited on the surface of the steel slag iron, inhibition or contact CO ₂ aqueous solution to the surface of the steel slag, CO with a compound containing a relatively high hardness iron _It is considered that inhibition of grinding or grinding during contact with the aqueous solution ₂ can be suppressed, and the calcium compound in the steelmaking slag can be easily eluted with the aqueous CO ₂ solution.

The calcium iron aluminum oxide contained in the steelmaking slag is hardly magnetized after Ca is eluted by contact with a CO ₂ aqueous solution, and is not easily recovered by magnetic separation. On the other hand, by performing magnetic separation before contact with the CO ₂ aqueous solution, calcium iron aluminum oxide in the steelmaking slag can also be recovered, and iron derived from calcium iron aluminum can be more easily reused.

  The magnetic separation can be performed using a known magnetic separator. The magnetic separator may be either a dry type or a wet type, and can be selected according to the state of the steelmaking slag (dry state or slurry state). The magnetic separator can be appropriately selected from a drum type, a belt type, a flow type between fixed magnets, and the like.In particular, it is easy to sort steelmaking slag contained in the slurry, and the magnetic force is increased to increase the magnetic separation amount. A drum type is preferable because it is easy. Further, the magnet used by the magnetic force sorter may be a permanent magnet or an electromagnet.

  The magnetic flux density by the magnet may be such that the ferrous compound and metallic iron can be selectively captured from other compounds contained in the steelmaking slag. For example, the magnetic flux density can be set to 0.003T or more and 0.5T or less. It is preferably between 0.005T and 0.3T, and more preferably between 0.01T and 0.15T.

Further, it is not necessary to perform the magnetic separation until all of the iron-based compound and metallic iron contained in the steelmaking slag are removed. Even if the amount of the iron-based compound removed from the steelmaking slag by the magnetic separation is small, the effect of the present embodiment that calcium is more easily eluted into the CO ₂ aqueous solution than before can be obtained. Therefore, the time and the number of times of the magnetic separation may be appropriately selected according to the influence of the magnetic separation on the manufacturing cost.

  The steelmaking slag is preferably subjected to a heat treatment before the magnetic separation. When the steelmaking slag is heat-treated, the magnetization of the iron-based compound and metallic iron increases, and a larger amount of the iron-based compound can be removed by magnetic separation. The 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.

  The steelmaking slag may be in a dry state at the time of magnetic separation, but is preferably in the form of a slurry dispersed in water. Slurry-like steelmaking slag is apt to disperse slag particles due to the polarity of water molecules, water flow, and the like, so that it is easy to selectively capture iron-based compounds and metallic iron by magnetic force. In particular, when the particle diameter of the slag particles is 1000 μm or less, in a gas such as air, the slag particles are formed by a liquid bridging force due to condensation of water vapor in the atmosphere, a van der Waals force between the slag particles, an electrostatic force between the slag particles, and the like. Are easily agglomerated, but the slag particles can be sufficiently dispersed by forming the slurry. In addition, since the metallic iron in the steelmaking slag is minute, it is difficult to catch the ironmaking slag when the steelmaking slag is dry. However, when the steelmaking slag is made into a slurry, the metallic iron dispersed in water is also easily captured by magnetic separation.

The slurry from which the iron-based compound and metallic iron have been removed by magnetic separation may be used as it is for contact with a CO ₂ aqueous solution (step S120), but when the steelmaking slag is in a slurry state, it is subjected to solid-liquid separation to produce steel. Preferably, the slag and the liquid component are separated. The solid-liquid separation can be performed by a known method including filtration under reduced pressure and filtration under pressure. The liquid component obtained by the solid-liquid separation (herein, also simply referred to as “magnetically separated water”) contains calcium eluted from the steelmaking slag in addition to the water used for slurrying, and thus becomes alkaline. I have. Therefore, the 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.

  Further, the magnetically separated slag removed from the steelmaking slag by the magnetic separation contains a large amount of iron-containing compounds such as iron-based compounds and metallic iron as described above, and thus can be reused as a raw material for blast furnaces and sintering.

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

In this embodiment, similarly to the second embodiment, after spraying a CO ₂ aqueous solution contacted by steelmaking slag, a calcium-based alkaline substance is introduced into the CO ₂ aqueous solution (step S150), and thereafter, The solid component containing calcium precipitated on the surface may be recovered (Step S140).

In addition, also in this embodiment, similarly to the third embodiment, the hydration treatment (step S160) may be performed on the steelmaking slag before being brought into contact with the CO ₂ aqueous solution. When further hydration treatment is performed on the steelmaking slag in this embodiment, any of the hydration treatment and the magnetic separation may be performed first, or the wet magnetic separation is performed, or the slurry subjected to the wet magnetic separation is circulated. , May be performed simultaneously. If any of these is performed first, the hydration treatment (particularly hydration treatment by immersion and stirring) is performed first, and then magnetic separation increases the calcium recovery rate, especially when the apparatus is upsized. In addition, the entire process can be performed in a shorter time.

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

[Experiment 1]
A steelmaking slag having the component ratio shown in Table 1 was prepared. The components of the steelmaking slag were measured by a chemical analysis method.

  The steelmaking slag shown in Table 1 was pulverized to a diameter of 8 mm or less, and then heated at 750 ° C. for 20 minutes. After heating, the steelmaking slag was air-cooled to room temperature. Thereafter, the steelmaking slag was further pulverized and then passed through a sieve having an opening of 106 μm, and used for the subsequent treatment.

  In the following experiments, the calcium concentration of each aqueous solution was measured by a chemical analysis method after filtering the slurry to separate the slag.

  In each of the following experiments, the pH of each aqueous solution and slurry was measured by a glass electrode method.

[Experiment 1]
(Hydration treatment: hydration by ball mill)
A ball mill having an inner diameter of 500 mm was prepared. 1 kg of steelmaking slag not subjected to magnetic separation was charged into the ball mill, and 1 L of water was charged to turn the steelmaking slag into a slurry. Further, 6 kg of alumina balls (crushing medium) were charged into the ball mill. The diameter of the ball was 10 mm. Thereafter, the ball mill was rotated at 50 rpm, and the rotating balls were brought into contact with the steelmaking slag to pulverize the steelmaking slag and the like. By this hydration while pulverizing, the particle diameter (d90) of the slag became 20 μm. Carbon dioxide was not introduced into the slurry steelmaking slag.

(Magnetic selection)
Water was added to the hydrated slurry steelmaking slag so that the slurry volume became 40 L. This slurry was put into a drum type magnetic separator, and magnetically selected 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. When the iron concentration in the steelmaking slag after the magnetic separation was measured by a chemical analysis method and the weight was measured, 41% by mass of the iron element contained in the first steelmaking slag was removed. After the magnetic separation, the remaining slurry was filtered to separate the remaining slag. The magnetically separated water, which is an aqueous solution from which the residual calcium was leached after the residual slag was separated, was set aside for the subsequent process. The calcium concentration of the magnetic separation water was 480 mg / L. In a preliminary experiment, it was confirmed that slag having a dry weight of 0.15 kg was separated by magnetic separation.

(Contact with CO ₂ aqueous solution: Contact with CO ₂ aqueous solution while pulverizing etc.)
An apparatus having the configuration shown in FIG. 2 was used. The elution / sedimentation tank was a cylindrical container having an inner diameter of 480 mm, and was provided with an impeller that rotated along the bottom surface so that the steelmaking slag that had settled and accumulated moved to the suction port. The impeller was rotated at 40 rpm. The remaining slag collected by the filtration after the magnetic separation step was put into the elution / sedimentation tank without drying, and water was added so that the slurry amount became 100 L. At this time, the ratio of water to slag was approximately 120: 1. The steelmaking slag collected from the bottom was sent to a pulverizing unit by a pump, and was pulverized by a continuous pulverizer using a ball mill. The pulverizing part was a horizontal cylindrical shape having an inner diameter of 200 mm, and a ball of φ10 mm was placed therein at 70% of the total volume. At the same time, 20 L / min of carbon dioxide was introduced into the pipe section between the elution / settling tank and the pulverizing section. The contact with the CO ₂ aqueous solution was performed for 30 minutes.

The calcium-eluted slurry obtained as described above was filtered and separated from the slag to obtain a calcium-eluted CO ₂ aqueous solution. At this time, the pH of the aqueous CO ₂ solution was 6.6, and the calcium concentration was 1,230 mg / L.

(Spray)
Calcium was precipitated by the shower spray method shown in FIG. The above CO ₂ aqueous solution was sprayed downward at a flow rate of 5 L / min into a closed container having an inner diameter of 960 mm from a height of 4.5 m with a shower head having a plurality of holes having a diameter of 0.5 mm. From the bottom side of the sealed container, air was blown from two opposing locations at a total flow rate of 40 L / min. The CO ₂ aqueous solution that reached the bottom of the closed container was taken out from the bottom of the closed container and introduced into a tank connected to the closed container. After spraying once, the liquid component of the aqueous CO ₂ solution on which the calcium compound (calcium carbonate) was precipitated was recovered from the tank and sprayed once more (total of two sprays).

The pH of the aqueous CO ₂ solution after spraying twice was 8.0, and the calcium concentration was 61 mg / L.

(Recovery of solid components)
From the tank into which the sprayed CO ₂ aqueous solution was introduced, solid components containing calcium could be easily recovered.

From this result, it was found that the pH of the aqueous CO ₂ solution was increased by spraying, and a calcium compound (calcium carbonate) was precipitated from the aqueous CO ₂ solution. At this time, the calcium deposition rate ((100 (%)-calcium concentration (%) after spraying) / calcium concentration (%) before spraying) was about 95.0% after spraying twice.

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

  In addition, when the carbon dioxide concentration of the gas discharged from the closed container during the experiment was measured by an infrared method, it was about 10%. The concentration of carbon dioxide in this gas was higher than the concentration of carbon dioxide in exhaust gas from a general natural gas-fired power plant (about 9%), and was such that recovery and purification could be easily performed.

(Injection of calcium-based alkaline substance)
Thereafter, the calcium hydroxide-based composition-1 (the magnetic separation obtained in the above magnetic separation step) was added to the aqueous CO ₂ solution (pH: 7.0, calcium concentration: 190 mg / L, calcium deposition rate: 84.5%) stored in the tank. Water), calcium hydroxide-based composition-2 (aqueous solution prepared by dissolving calcium hydroxide in water), and calcium hydroxide-based composition-3 (solid calcium hydroxide is dispersed in calcium hydroxide water) Slurry prepared in advance) was added while stirring the CO ₂ solution. The amount of each CO ₂ aqueous solution was adjusted so that the pH of the CO ₂ aqueous solution became 8.0, 8.5, 9.0, or 9.5.

  Table 2 shows the pH and calcium concentration of the calcium hydroxide composition-1 to calcium hydroxide composition-3 charged above. In addition, the calcium concentration of the calcium hydroxide-based composition-3 which is a slurry is an average concentration including a solid content.

The pH and calcium concentration of the CO ₂ aqueous solution after the above-mentioned calcium hydroxide-based composition was charged, and the calcium deposition rate (calcium concentration after spraying and calcium hydroxide-based composition / calcium concentration before spraying) It is shown in Table 3.

As is clear from Table 3, by adding the calcium hydroxide-based composition to the CO ₂ aqueous solution after spraying, the calcium concentration is lower than the calcium concentration after spraying once (190 mg / L), It was found that calcium was further precipitated by feeding the calcium hydroxide-based composition. The calcium precipitation rate at this time was substantially correlated with the pH after the addition, regardless of the type of the calcium hydroxide-based composition to be added.

When the pH of the aqueous CO ₂ solution after the addition of calcium hydroxide is 8.0 or more, the calcium precipitation rate is 90% or more, and when the pH of the aqueous CO ₂ solution after the addition of calcium hydroxide is 8.5 or more. The calcium deposition rate was 94% or more, and the calcium deposition rate was 95% or more when the pH of the CO ₂ aqueous solution after the addition of calcium hydroxide was 9.0 or more.

[Experiment 3]
(Hydration treatment-1: Hydration by immersion stirring using a ball mill)
A ball mill having an inner diameter of 500 mm was prepared. 1 kg of steelmaking slag not subjected to magnetic separation was charged into the ball mill, and 1 L of water was charged to turn the steelmaking slag into a slurry. Further, 6 kg of alumina balls (crushing medium) were charged into the ball mill. The diameter of the ball was 10 mm. Thereafter, the ball mill was rotated at 50 rpm, and the rotating balls were brought into contact with the steelmaking slag to pulverize the steelmaking slag and the like. By this hydration while pulverizing, the particle diameter (d90) of the slag became 20 μm. Carbon dioxide was not introduced into the slurry steelmaking slag.

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

(Contact with CO ₂ aqueous solution: Contact with CO ₂ aqueous solution while pulverizing etc.)
The slag separated by the filtration after the above-mentioned hydration treatment-2 was put into a dissolution / sedimentation tank of the same apparatus as in Experiment 1 without drying, and water was added so that the slurry amount became 100 L. At this time, the ratio of water to slag was approximately 100: 1. Elution of calcium was carried out in the same manner as in Experiment 1 under other conditions.

The calcium-eluted slurry obtained as described above was filtered and separated from the slag to obtain a calcium-eluted CO ₂ aqueous solution. At this time, the pH of the CO ₂ aqueous solution was 6.7, and the calcium concentration was 1390 mg / L.

(Spray)
As in Experiment 12, to precipitate calcium by spraying the CO ₂ aqueous solution obtained above in the shower spray method. Spraying was performed only once.

After spraying once, the pH of the aqueous CO ₂ solution was 6.9, and the calcium concentration was 230 mg / L. At this time, the calcium deposition rate was 83.5%.

(Injection of calcium-based alkaline substance)
Thereafter, the CO ₂ aqueous solution collected in the tank, calcium hydroxide-based composition 4 (hydration water obtained in the hydration treatment -2) was charged with stirring CO ₂ solution. The charging amount of the calcium hydroxide-based composition-4 was adjusted so that the pH of the CO ₂ aqueous solution after the charging became any of 8.0, 8.5, and 9.0.

  Table 4 shows the pH and calcium concentration of the calcium hydroxide-based composition-4 charged above.

The pH and calcium concentration of the CO ₂ aqueous solution after the calcium hydroxide-based composition-4 was charged, and the calcium deposition rate (calcium concentration after spraying and calcium hydroxide-based composition charged / calcium concentration before spraying) It is shown in Table 5.

As is clear from Table 5, when the hydration-treated water was added to the CO ₂ aqueous solution after spraying, the calcium concentration was lower than the calcium concentration (190 mg / L) after spraying once, and It was found that further precipitation occurred.

(Recovery of solid components)
From the tank into which the sprayed CO ₂ aqueous solution was introduced, solid components containing calcium could be easily recovered.

INDUSTRIAL APPLICABILITY The present invention is useful as a method for recovering calcium resources in iron making, since calcium eluted in a CO ₂ aqueous solution from steelmaking slag can be precipitated by a simpler method.

REFERENCE SIGNS LIST 100 dissolution apparatus 110 dissolution / sedimentation tank 112 slurry outlet 114 slurry re-introduction port 118 impeller 119 rotary rod 120 pulverizing unit 130 carbon dioxide introduction unit 140 slurry flow path 142 slurry flow path 144 slurry flow path 146 pump 200, 200a, 200b spray Apparatus 210, 210a Closed vessel 212 CO ₂ aqueous solution outlet 214 Stirring blade 216 Rotating rod 220, 220a Sprayer 222 CO ₂ aqueous solution flow path 224 Shower head 226 Nozzle 230 Gas inlet 240 Gas outlet 250 Pump 260 Heater 270 Alkaline substance inlet

Claims (8)

Contacting steelmaking slag with a CO ₂ aqueous solution that is an aqueous solution containing carbon dioxide;
Spraying a CO ₂ aqueous solution contacted by the steelmaking slag;
A method for recovering calcium from steelmaking slag, comprising: Before the step of spraying the CO ₂ aqueous solution, a step of removing the steel slag from CO ₂ aqueous solution in which the steelmaking slag is in contact, a method for recovering calcium from steel slag according to claim 1. Wherein the CO ₂ to carbon dioxide partial pressure than the aqueous solution is spraying the CO ₂ aqueous solution to a lower space, and recovering calcium from steel slag according to claim 1 or 2. The CO ₂ aqueous solution is sprayed into a space containing an inorganic gas selected from the group consisting of air, nitrogen (N ₂ ), oxygen (O ₂ ), hydrogen (H ₂ ), argon (Ar), and helium (He). A method for recovering calcium from steelmaking slag according to any one of claims 1 to 3. Including sprayed the CO ₂ process of aqueous solution introduced an alkaline substance calcium system, a method for recovering calcium from steel slag according to any one of claims 1 to 4.   The introduction of the calcium-based alkaline substance is performed by selecting an aqueous solution in which calcium hydroxide is dissolved, a slurry in which solid calcium hydroxide is dispersed, solid calcium hydroxide, and water selected from the group consisting of solid calcium oxide. The method for recovering calcium from steelmaking slag according to claim 5, which is charging of a calcium oxide-based composition.   The method for recovering calcium from steelmaking slag according to claim 5 or 6, wherein the calcium hydroxide-based composition to be charged is slag leachate obtained by contacting steelmaking slag with water. Introduction of alkaline material in the calcium-based, the method of the CO ₂ solution sprayed simultaneously performed, and recovering the calcium from steel slag according to any one of claims 5-7.

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