JP7303430B2 - Collection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a recovery method for recovering calcium compounds contained in steelmaking slag discharged from steelmaking.

Steelmaking slag (converter furnace slag, pretreatment slag, secondary refining slag, electric furnace slag, etc.) generated in the steelmaking process contains elements such as calcium (Ca) and iron (Fe). Ca contained in steelmaking slag is water generated by reaction of free lime (CaO) input during the steelmaking process or free lime precipitated during solidification of steelmaking slag with water vapor or carbon dioxide in the air. It exists in the form of calcium oxide (Ca(OH) ₂ ) or calcium carbonate (CaCO ₃ ). Alternatively, calcium silicate (such as Ca ₂ SiO ₄ or Ca ₃ SiO ₅ ) or calcium iron aluminum oxide (Ca ₂ (Al _1-X Fe _X ) ₂ O ₅ ) (hereinafter, the compounds containing calcium present in steelmaking slag are collectively referred to as “calcium compounds”).

Calcium carbonate and calcium oxide are major steelmaking slag formers in the steelmaking process, and are used as an agent for adjusting the basicity and viscosity of the steelmaking slag and as a dephosphorization agent from molten steel. Calcium hydroxide, which is obtained by adding water to calcium oxide, is used as a neutralizing agent for acids and the like in the wastewater treatment process. Therefore, if the calcium compounds contained in the steelmaking slag are recovered and reused in the ironmaking process, it is expected that the cost of ironmaking can be reduced.

As a method for recovering calcium compounds from steelmaking slag, for example, a step of subjecting steelmaking slag to magnetic separation to remove iron-containing compounds from the steelmaking slag, and contacting the magnetically separated steelmaking slag with an aqueous solution containing carbon dioxide. Patent Document 1 discloses a method for eluting a large amount of calcium compounds from steelmaking slag into an aqueous solution containing carbon dioxide by performing a step of allowing the steelmaking slag to dissolve.

Japanese Patent Application Laid-Open No. 2018-115366 (published on July 26, 2018)

For efficient solid-liquid separation of the steelmaking slag used, it is necessary to increase the speed at which each component contained in the steelmaking slag settles (sedimentation speed). In particular, it is considered essential to increase the sedimentation velocity of the calcium compound, which has a relatively slow sedimentation velocity among the above components. However, conventionally, attention has been paid to the sedimentation velocity of the above components, and there has been no knowledge about techniques for increasing the sedimentation velocity.

One aspect of the present invention has been made in view of the above problems, and an object thereof is to increase the sedimentation speed of each component contained in steelmaking slag during solid-liquid separation of steelmaking slag.

In order to solve the above-described problems, a recovery method according to one aspect of the present invention is a recovery method for recovering calcium compounds contained in steelmaking slag discharged during steel production, wherein the steelmaking slag is pulverized into A magnetic separation step of collecting a first compound containing iron from the generated slurry; a first collection step of collecting a first supernatant liquid containing the calcium compound from the slurry remaining after the magnetic separation step; A second collection step of collecting a second supernatant different from the first supernatant from the slurry remaining after the first collection step, and a sedimentation step of sedimenting the calcium compound contained in the first supernatant. , In the first collection step, the second collection step and the sedimentation step, as additives, an inorganic flocculant containing a second compound represented by the following general formula (1), and the following general formula At least one of the organic flocculants containing the third compound represented by (2) is used.

[Al ₂ (OH) _n Cl _6-n ] _m (1)
(n is an integer of 1 or more and 5 or less, and m is an integer of 10 or less.)

・・・（２）
（前記有機凝集剤の分子量は、カチオン系で１００万以上であるか、またはアニオン系で３００万以上である。）
前記構成によれば、無機凝集剤または有機凝集剤を用いることにより、前記製鋼スラグに含まれる成分と前記凝集剤とのフロックが形成される。これにより、前記成分の沈降速度を速めることができる。

... (2)
(The molecular weight of the organic flocculant is 1,000,000 or more for a cationic type, or 3,000,000 or more for an anionic type.)
According to the above configuration, by using an inorganic flocculant or an organic flocculant, flocs are formed by the components contained in the steelmaking slag and the flocculant. Thereby, the sedimentation velocity of the said component can be accelerated.

Moreover, the recovery method according to one aspect of the present invention may further include an aggregation step of adding the organic coagulant to the slurry to aggregate components contained in the slurry.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, when the steelmaking slag is subjected to solid-liquid separation, the sedimentation speed of each component contained in the steelmaking slag can be increased.

4 is a flow chart showing an example of the process flow of a calcium compound recovery method. It is a schematic diagram which shows an example of the flow of a process of a 1st isolation|separation process. A diagram indicated by reference numeral 301 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram indicated by reference numeral 302 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram indicated by reference numeral 303 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram indicated by reference numeral 304 is an image showing the results of Example 1. FIG. A diagram indicated by reference numeral 401 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram indicated by reference numeral 402 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram indicated by reference numeral 403 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram indicated by reference numeral 404 is an image showing the results of Example 1. FIG. A diagram indicated by reference numeral 501 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram indicated by reference numeral 502 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram indicated by reference numeral 503 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram denoted by reference numeral 504 is an image showing the results of Example 1. FIG. A diagram denoted by reference numeral 505 is an image showing the results of Example 1. FIG. A diagram indicated by reference numeral 601 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram indicated by reference numeral 602 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram indicated by reference numeral 603 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram indicated by reference numeral 604 is an image showing the results of Example 2. FIG. The figure denoted by reference numeral 701 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram denoted by reference numeral 702 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram denoted by reference numeral 703 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram denoted by reference numeral 704 is an image showing the results of Example 2. FIG. A diagram indicated by reference numeral 801 is a graph showing the relationship between the sedimentation rate and the amount of coagulant added. A diagram indicated by reference numeral 802 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. A diagram indicated by reference numeral 803 is a graph showing the relationship between the floc diameter and the amount of coagulant added. A diagram denoted by reference numeral 804 is an image showing the results of Example 2. FIG.

[1. Composition of Steelmaking Slag]
A method for recovering a calcium compound will be described below with reference to FIGS. 1 and 2. FIG. FIG. 1 is a flow chart showing an example of the process flow of the calcium compound recovery method according to the present embodiment. As shown in FIG. 1, the method for recovering calcium compounds in this embodiment includes a magnetic separation step (S1), a first separation step (S2), a second separation step (S3) and a sedimentation step (S4).

(Magnetic separation process)
The magnetic separation step S1 is a step of separating (collecting) the first compound containing iron from the slurry produced by crushing the steelmaking slag. The steelmaking slag in this step is slag discharged from steel production.

The type of the steelmaking slag to be supplied to this step is not particularly limited as long as it is slag discharged during steel production. Examples of the steelmaking slag include converter slag, pretreatment slag, secondary refining slag and electric furnace slag.

The steelmaking slag used is crushed after being discharged during steel production. The steelmaking slag used in this process is dispersed in water and slurried before magnetic separation. In other words, the steelmaking slag is pulverized to produce a slurry prior to magnetic separation. Slurry tends to disperse slag particles depending on the polarity of water molecules and water flow, so iron-based compounds and metallic iron are likely to be selectively captured by magnetic force.

The steelmaking slag is preferably heat-treated before magnetic separation. When the steelmaking slag is heat-treated, the magnetization of the iron-containing first compound is increased, and a larger amount of the iron-containing first compound can be removed by magnetic separation.

This step can be performed using, for example, a known magnetic force sorter. The type of magnetic separator used in this step is not particularly limited. In addition, the magnetic sorter can be appropriately selected from drum type, belt type, fixed magnet flow type, etc., but it is easy to handle and it is easy to increase the amount of magnetic separation by increasing the magnetic force. It is preferable to adopt a drum type. Moreover, the magnet used by the magnetic force sorter may be a permanent magnet or an electromagnet.

The magnetic flux density of the magnets provided in the magnetic force sorter is sufficient as long as it can selectively capture iron-containing compounds and metallic iron from other compounds contained in the steelmaking slag. The time and number of times this step is performed are appropriately selected depending on the impact on the production cost.

The slurry remaining after removing the first compound in the magnetic separation step S1 is subjected to solid-liquid separation in the first separation step described later.

The first separation step (first collection step) S2 is a step of separating (collecting) a first supernatant liquid from the slurry remaining after removing the first compound. Here, the first separation step S2 will be explained using FIG. FIG. 2 is a schematic diagram showing an example of the process flow of the first separation step S2.

As shown in FIG. 2, the slurry is subjected to an agglomeration step. After the slurry is transferred to the first inflow tank 1, the slurry is transferred by the pump 2 to the second inflow tank 3 into which various types of waste water discharged during steelmaking flow. After transfer, the slurry is transferred from the second inflow tank 3 to the stirring device 5 by the pump 4 .

In this step, an inorganic flocculant is added to separate the first supernatant from the slurry. The inorganic additive has the effect of neutralizing and condensing negatively charged colloidal particles contained in the slurry, and contains at least a compound represented by the following general formula (1) (second compound): include.

[Al ₂ (OH) _n Cl _6-n ] _m (1)
Here, n is an integer of 1 or more and 5 or less, and m is an integer of 10 or less.

The inorganic flocculant used in this step may contain only the compound represented by the general formula (1), or may contain other components. Examples of such components are not particularly limited as long as they do not inhibit the effect of neutralizing and aggregating negatively charged colloidal particles. Examples include ferrous sulfate, polyferric sulfate, aluminum sulfate [ aluminum sulfate: Al ₂ (SO ₄ ) ₃ ] and ferric chloride solution [FeCl ₂ .4H ₂ O]. The ferric polysulfate is represented, for example, by the following general formula (2).

[Fe ₂ (OH) _n (SO ₄ ) _3−n/2 ] _m (0<n≦2, m=f(n)) (2)
The concentration of the compound represented by the general formula (1) with respect to the whole inorganic flocculant is not particularly limited. For example, the compound represented by the general formula (1) may be contained in the inorganic flocculant so that about 10% of aluminum oxide is contained in the entire inorganic flocculant.

Further, the respective concentrations of the ferrous sulfate or the polyferric sulfate with respect to the entire inorganic flocculant are not particularly limited. For example, the concentration of ferrous sulfate may be such that iron ions (Fe ²⁺ ) are contained in an amount of 4.0% or more with respect to the whole inorganic flocculant. Further, the concentration of the ferric polysulfate may be such that iron ions (Fe ³⁺ ) are contained by 11% or more.

Moreover, the respective concentrations of the aluminum sulfate and the ferric chloride solution relative to the entire inorganic coagulant are not particularly limited. For example, the concentration of aluminum sulfate may be such that 8% or more of Al ₂ O ₃ is contained in the inorganic flocculant as a whole. Further, the concentration of the ferric chloride solution may be such that FeCl ₂ is contained in an amount of 37% or more with respect to the whole inorganic flocculant. In this step, the device used for adding the inorganic flocculant is not particularly limited. In the present embodiment, a stirring device has been described as an example of the device.

Fine flocs (hereinafter referred to as fine flocs) are formed by the inorganic flocculant added in this step. The first slurry containing the fine flocs is optionally transferred to the agglomerator 6 .

The first supernatant liquid separated in this step contains calcium compounds eluted from the steelmaking slag. Specifically, the first supernatant is a highly alkaline aqueous solution containing a calcium compound. Here, the method for eluting the calcium compound from the steelmaking slag is not particularly limited. The first supernatant is subjected to a subsequent sedimentation step.

After adding the inorganic flocculant, in this step, an organic flocculant is added to the first slurry containing the fine flocs. Examples of organic flocculants include anionic/acrylamide polymer flocculants (hereinafter simply referred to as “polymer flocculants”).
By adding the organic flocculant to the first slurry, a plurality of the fine flocs are agglomerated to form coarse agglomerated flocs.

The organic flocculant used in this step contains at least a compound (third compound) represented by the following general formula (3). The molecular weight of the organic flocculant is 1,000,000 or more for a cationic type, or 3,000,000 or more for an anionic type.

・・・（３）
また、前記有機凝集剤は、前記一般式（３）で示される化合物の他に、例えば、アクリル酸ナトリウムを含む高分子化合物、アクリル酸を含む高分子化合物などが好適に用いられる。

... (3)
In addition to the compound represented by the general formula (3), for example, a polymer compound containing sodium acrylate, a polymer compound containing acrylic acid, and the like are preferably used as the organic flocculant.

The concentration of the compound represented by the general formula (3) with respect to the entire organic flocculant is not particularly limited. For example, the concentration may be such that about 90% of the compound represented by the general formula (3) is contained in the entire organic flocculant. Further, when the polymer compound containing sodium acrylate is included, the concentration relative to the entire organic flocculant is, for example, a polymer compound containing acrylic acid or sodium acrylate with respect to the entire organic flocculant. The concentration may be such that about 90% of the polymer compound is contained.

The organic flocculant used as a flocculant in this step may contain only the compound represented by the general formula (3), or may further contain other components. Examples of the component may be an anionic polymer, a cationic polymer, or a nonionic polymer. It is appropriately selected according to the pH of the target liquid to which the organic flocculant is added. Among the above polymers, the anionic polymer functions as a flocculating agent regardless of whether the liquid has a weakly acidic, neutral or alkaline pH. Therefore, in this step, it is preferable to use an anionic polymer as the organic flocculant.

The type of the flocculating device 6 used in this step is not particularly limited as long as it can be added to the liquid to which the organic flocculant is added.

The recovery method for recovering the flocs described above is not particularly limited. It is possible to separate the

Turbidity may be measured on the first supernatant. The turbidity can be measured by, for example, a turbidity meter. Specifically, as shown in FIG. 2, the first supernatant liquid is transferred to the third inflow tank 7 according to an arbitrary configuration. After transfer, by measuring the turbidity of the first supernatant with a turbidity meter provided in the third inflow tank 7, the turbidity of the liquid is the turbidity that can be used in subsequent steps. It is possible to check whether or not

Further, the pH of the first supernatant may be measured by providing pH measuring means in the third inflow tank 7 .

The pH of the first supernatant may be any pH that allows it to be subjected to the process subsequent to the flocculation process.

By bringing an aqueous solution of carbon dioxide into contact with the slurry to which the organic coagulant has been added, calcium contained in the slurry is eluted into the carbonated water. Here, the method of eluting calcium into carbonated water is not particularly limited. The slurry obtained after elution is optionally transferred to a subsequent second separation step (second collection step) S3.

The processing in the second separation step S3 will be described below. In this step, the aggregation step is performed on the slurry obtained after the elution. Details of the aggregation step are the same as the procedure described in the first separation step S2. Briefly, an inorganic flocculant is added to the slurry obtained after said elution. Fine flocs are formed by adding an inorganic flocculant. After that, an organic flocculating agent is added to aggregate the fine flocs to form coarse flocs.

As a result of solid-liquid separation of the slurry by adding each flocculant, a second supernatant liquid different from the first supernatant liquid is separated (collected) from the slurry. Here, the second supernatant is a carbon dioxide aqueous solution containing a calcium compound. Said second supernatant is optionally transferred to a subsequent sedimentation step.

The sedimentation process will be briefly described below. The sedimentation step S4 is a step of sedimenting the calcium compound contained in the first supernatant. In this step, mixing the second supernatant and the first supernatant raises the pH of the carbon dioxide aqueous solution. That is, the amount of hydrogen ions (H ⁺ ) in carbon dioxide decreases. Since the amount of hydrogen ions (H ⁺ ) in carbon dioxide decreases, hydrogen carbonate ions (HCO ₃ ⁻ ) are combined with hydrogen ions (H ⁺ ) and carbonate ions (CO ₃ ²⁻ ) in the equilibrium equation (A) below. Equilibrium moves in the direction of separation.

HCO ₃ ⁻ →H ⁺ +CO ₃ ²⁻ (A)
The increased carbonate ions (CO ₃ ²⁻ ) combine with calcium ions to precipitate sparingly soluble calcium carbonate (CaCO ₃ ).

In the above step, the purpose is to reduce the concentration of CO ₂ in the mixture of the first supernatant and the second supernatant, and the step is performed by increasing the pH of the mixture. This is one method of reducing the _CO2 concentration in the water and precipitating calcium. In addition, the technique for precipitating calcium is not limited to the technique of the above steps. For example, there is another method of blowing air into the mixed solution or spraying the mixed solution into the air to remove CO ₂ and precipitate calcium dissolved in the CO ₂ solution. Also, the above methods may be combined.

In order to precipitate the precipitated calcium carbonate (calcium compound), the calcium carbonate is subjected to an aggregation step. The aggregation step is also performed in the same manner as described above. Briefly, the inorganic flocculant is added to a solution containing calcium carbonate. Fine flocs are formed by adding the inorganic flocculant. After that, the fine flocs are aggregated by adding the organic flocculating agent to form coarse flocs. Calcium carbonate agglomerated as agglomerated flocs by each aggregating agent is recovered by any configuration and reused in the production of steel.

The second slurry may be, for example, properly treated in various treatment devices and then discharged to the outside through a discharge channel, or may be reused in the production of steel.

The method for recovering a calcium compound of the present invention enables solid-liquid separation (sedimentation separation) in each step without using chemical solutions (pH-adjusting chemical solutions) used for the purpose of adjusting pH, such as mineral acids. The above configuration provides the following two effects. (1) Cost reduction due to no use of pH adjusting chemicals. (2) Precipitation of the calcium compound is facilitated compared to the case of using a mineral acid, and the steps required for the precipitation of the calcium compound are not complicated.

The method for recovering a calcium compound of the present invention can increase the sedimentation rate of each component contained in steelmaking slag (in particular, calcium carbonate (calcium compound), which is difficult to separate into solid and liquid), in the process of recovering calcium compounds from steelmaking slag. can.

In the present embodiment, an example of adding the organic flocculant after adding the inorganic flocculant in the flocculation step has been described, but the order of adding each flocculant is not limited to this. That is, for example, the inorganic flocculant may be added after adding the organic flocculant in the flocculation step.

Moreover, in this embodiment, the example using the said inorganic flocculant and the said organic flocculant was demonstrated. However, in the calcium compound recovery method of the present embodiment, at least one of the inorganic flocculant and the organic flocculant may be added in the flocculation step. According to the above configuration, by adding the inorganic flocculant or the organic flocculant alone, it is possible to omit a device for adding the flocculant that is not added, and it is possible to reduce the facility area, the initial cost, and the running cost.

Furthermore, as described above, the calcium compound recovery method of the present invention does not use a pH-adjusting chemical solution. Therefore, it is possible to omit a device for adding the pH-adjusting chemical solution, thereby reducing the installation area, initial cost and running cost.

Examples of the present invention are described below. First, 500 ml of slag (steel-making slag) was obtained by performing a steel-making process.

After adding a flocculant to the slag after the slurrying and magnetic separation processes, a stirring device (device name: EUROSTAR 200 digital, manufactured by IKA and a PTFE propeller stirring bar (propeller diameter: 52 mm, number of propellers: 3) Specifically, when the polymer flocculant was used as the flocculant, the flocculant was rapidly stirred for 1 minute with a stirring device (250 rpm After that, slow stirring was performed for 3 minutes (150 rpm), and after 2 minutes and 30 seconds from the start of the slow stirring, the particle diameter of the obtained flocs (hereinafter referred to as floc diameter) was visually confirmed. Regarding the visual confirmation of the floc diameter, specifically, a plurality of patterns of particle drawings with a scale of 1:1 compared to the floc diameter to be measured were prepared in advance in a certain particle distribution range. The closest thing was taken as the floc diameter.

After the slow stirring, the sample was removed from the stirrer and allowed to stand for 3 minutes. The time for the flocs to settle toward the bottom of the container into which each sample was poured was measured. Specifically, the time required for the flocs to reach a position 40 mm downward from the liquid surface of each sample was measured. The sedimentation velocity was calculated from the measurement results. After measurement, the supernatant of each sample was collected and filtered. The material obtained after filtration was weighed.

On the other hand, when the inorganic flocculant was used as the flocculant, the flocculant was added, followed by slow stirring (150 rpm) for 3 minutes with a stirring device. Two minutes and 30 seconds after the slow stirring was started, the particle size of the obtained flocs was visually confirmed. After the slow stirring, the sample was removed from the stirrer and allowed to stand for 3 minutes. After that, experiments were conducted in the same procedure as in the case of using the polymer flocculant as the flocculant.

Furthermore, when the inorganic flocculant and the organic flocculant were added as flocculants, the organic flocculant was added after the inorganic flocculant, and then rapidly stirred for 1 minute with a stirring device (250 rpm). Slow stirring was then carried out for 3 minutes (150 rpm).

The types of flocculants used in this example are shown in Table 2 below. Table 1 shows the concentration of the flocculant used in this example. "Slurry pH" in Table 1 intends "liquid pH of slurry". "Slurry particle diameter D90% diameter [mu]m" indicates the particle diameter when 90% of the total particles are reached by accumulating the number of particles from the smallest particle diameter. Here, the "slurry particle diameter D90% diameter [mu]m" was measured using a known particle size distribution measuring method based on a laser diffraction method. Also, the "slurry pH" was measured by a known glass electrode method. In addition, "magnetic separation slag" in Table 1 and Table 3 below is the slurry remaining after the first separation step, "final remaining slag" is the slurry remaining after the second separation step, and "Ca carbonate" is Calcium compounds that precipitate in the precipitation process are contemplated.

The experiments described above were performed in each step of the first separation step, the second separation step and the sedimentation step.

The results of this test in the first separation step will be described below with reference to FIG. The diagram indicated by reference numeral 301 in FIG. 3 is a graph showing the relationship between the particle size of flocs and the amount of coagulant added. As shown in the diagram 301 in FIG. 3, when either the polymer flocculant or the PAC is added, the comparative example (specifically, the slurry obtained when no flocculant is added) , "slurry particle diameter D90% diameter μm"), the floc diameter increased.

The diagram indicated by reference numeral 302 in FIG. 3 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. Here, the above "SS" was calculated by sampling 100 cc of the supernatant, filtering the supernatant, weighing the separated solid content, and converting the weight to mg/L. As shown in the diagram labeled 302 in FIG. 3, the addition of either the polymer flocculant or PAC compared to the slurry turbidity (target value of 50 mg/L) measured when no flocculant was added. Low SS was confirmed in all cases where

The diagram indicated by reference numeral 303 in FIG. 3 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As shown in the diagram indicated by reference numeral 303 in FIG. 3, compared to the sedimentation velocity (target value of 3 m / hr) measured when no flocculant was added, the result of adding a polymer flocculant or PAC also had a high sedimentation velocity.

The figure indicated by reference numeral 304 in FIG. 3 is an image showing the results of this test. As shown by reference numeral 304 in FIG. 3, sedimentation of flocs was observed when each flocculant was added compared to when no flocculant was added.

The results of this test in the second separation step will be described below with reference to FIG. The diagram indicated by reference numeral 401 in FIG. 4 is a graph showing the relationship between the floc diameter and the amount of coagulant added. As shown by reference numeral 401 in FIG. 4, when either the polymer flocculant or PAC was added, the floc diameter increased in both cases compared to the comparative example. In addition, even when the polymer flocculant and PAC were added, the floc diameter increased compared to the comparative example.

The diagram indicated by reference numeral 402 in FIG. 4 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. As shown in the diagram indicated by reference numeral 402 in FIG. 4, SS lower than the slurry turbidity (target value of 50 mg / L) measured when no flocculant was added, either polymer flocculant or PAC When either was added, it was confirmed in both cases. Similar results were also obtained when a polymer flocculant and PAC were added.

The diagram indicated by reference numeral 403 in FIG. 4 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As shown by reference numeral 403 in FIG. 4, as a result of the addition of the polymer flocculant or PAC, a higher sedimentation rate was confirmed especially when the polymer flocculant was added. Moreover, even when the polymer flocculant and PAC were added, a sedimentation velocity higher than the target value of 3 m/hr was confirmed.

A diagram indicated by reference numeral 404 in FIG. 4 is an image showing the results of this test. As shown by reference numeral 404 in FIG. 4, sedimentation of flocs was observed when each flocculant was added compared to when no flocculant was added.

The results of this test in the sedimentation process will be described below with reference to FIG. The diagram indicated by reference numeral 501 in FIG. 5 is a graph showing the relationship between the floc diameter and the amount of coagulant added. As shown by reference numeral 501 in FIG. 5, when PAC was added, the floc diameter increased compared to when no flocculant was added. In addition, as shown in the diagram indicated by reference numeral 501 in FIG. 5, when the polymer flocculant was added, the floc diameter increased compared to the case where the flocculant was not added, similarly to the case where PAC was added. .

The diagram indicated by reference numeral 502 in FIG. 5 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. As shown in the diagram indicated by reference numeral 502 in FIG. 5, SS lower than the slurry turbidity (target value of 50 mg/L) measured when no flocculant was added indicates that either the polymer flocculant or the PAC When either was added, it was confirmed in both cases.

The diagram indicated by reference numeral 503 in FIG. 5 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As shown by reference numeral 503 in FIG. 5, as a result of adding PAC, a sedimentation velocity higher than the target value (3 m/hr) was confirmed. In addition, when the polymer flocculant was added, a higher sedimentation rate was confirmed than when the PAC was added.

A diagram indicated by reference numeral 504 in FIG. 5 is an image showing the results of this test. As shown by reference numeral 504 in FIG. 5, floc sedimentation was observed when each flocculant was added compared to when no flocculant was added.

The figure indicated by reference numeral 505 in FIG. 5 is an image showing the results of this test. As indicated by reference numeral 505 in FIG. 5, sedimentation of flocs was observed when the polymer flocculant was added.

In calculating the floc diameter and sedimentation velocity shown in FIG. 5, it was difficult to perform visual confirmation while the suspended particles were being stirred. Therefore, said visual confirmation was carried out by transferring the flocs to another clarified liquid and stirring again.

From the results of this example, it was confirmed that the sedimentation speed of components contained in steelmaking slag was increased by using an inorganic flocculant or an organic flocculant. Therefore, in the process of recovering calcium compounds from steelmaking slag, it was demonstrated that the process of separating calcium carbonate, which is difficult to separate into solids and liquids, does not become a bottleneck. Moreover, it was demonstrated that the calcium compound can be easily precipitated by the method for recovering the calcium compound according to the present invention.

[Example 2]
In the same procedure as described in [Example 1] above, (i) when the organic flocculant is added after adding the inorganic flocculant, and (ii) after adding the organic flocculant, the inorganic flocculant is added. The sedimentation velocity was investigated in the case of Table 3 shows the concentration of the flocculant used in this example.

Inorganic flocculants and organic flocculants used in this example are the same as the flocculants shown in Table 2.

This experiment was conducted in each step of the first separation step, the second separation step and the sedimentation step. The results of this test in the first separation step will be described below with reference to FIG. The diagram indicated by reference numeral 601 in FIG. 6 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. As shown in the diagram indicated by reference numeral 601 in FIG. 6, compared to the slurry turbidity (target value of 50 mg / L) measured when no flocculant was added, in any of (i) and (ii) above Also, a low SS was confirmed.

The diagram indicated by reference numeral 602 in FIG. 6 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As indicated by reference numeral 602 in FIG. 6, a higher sedimentation velocity was confirmed especially in the above case (i). Also in the case of (ii) above, a sedimentation velocity (3.6 m/hr) higher than the sedimentation velocity (3 m/hr) when no flocculant was added was confirmed.

The diagram indicated by reference numeral 603 in FIG. 6 is a graph showing the relationship between the floc diameter and the amount of coagulant added. As shown by reference numeral 603 in FIG. 6, in both (i) and (ii) above, the floc diameter increased compared to the case where no flocculant was added.

A diagram indicated by reference numeral 604 in FIG. 6 is an image showing the results of this test. The image on the left side of the diagram indicated by reference numeral 604 in FIG. 6 shows the results when the polymer flocculant was added after the addition of PAC. The image on the right side of the drawing indicated by reference numeral 604 in FIG. 6 shows the results when the PAC was added after the addition of the polymer flocculant. As indicated by reference numeral 604 in FIG. 6, floc sedimentation was observed in all cases.

The results of this test in the second separation step will be described below with reference to FIG. The diagram indicated by reference numeral 701 in FIG. 7 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. As shown in the diagram indicated by reference numeral 701 in FIG. 7, compared to the slurry turbidity (target value of 50 mg / L) measured when no flocculant was added, in any of (i) and (ii) above Also, a low SS was confirmed.

The diagram indicated by reference numeral 702 in FIG. 7 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As indicated by reference numeral 702 in FIG. 7, particularly in the case of (i) above, a higher sedimentation velocity was confirmed as compared to the case where no flocculant was added.

The diagram denoted by reference numeral 703 in FIG. 7 is a graph showing the relationship between the floc diameter and the amount of coagulant added. As shown by reference numeral 703 in FIG. 7, in both (i) and (ii) above, the floc diameter increased compared to the case where no flocculant was added.

A diagram indicated by reference numeral 704 in FIG. 7 is an image showing the results of this test. The image on the left side of the diagram indicated by reference numeral 704 in FIG. 7 shows the results when the polymer flocculant was added after the addition of PAC. The image on the right side of the drawing indicated by reference numeral 704 in FIG. 7 shows the results when the PAC was added after the addition of the polymer flocculant. As indicated by reference numeral 704 in FIG. 7, floc sedimentation was observed in all cases.

The results of this test in the sedimentation process will be described below with reference to FIG. The diagram indicated by reference numeral 801 in FIG. 8 is a graph showing the relationship between the sedimentation speed and the amount of coagulant added. As indicated by reference numeral 801 in FIG. 8, a very high sedimentation velocity was confirmed especially in the above case (i). Also in the case of (ii) above, a higher sedimentation velocity (3.6 m/hr) was obtained than the sedimentation velocity (3 m/hr) when no flocculant was added.

The diagram indicated by reference numeral 802 in FIG. 8 is a graph showing the relationship between the slurry turbidity SS and the amount of coagulant added. As shown in the diagram indicated by reference numeral 802 in FIG. 8, compared to the slurry turbidity (target value of 50 mg / L) measured when no flocculant was added, in any of (i) and (ii) above Also, a low SS was confirmed.

The diagram indicated by reference numeral 803 in FIG. 8 is a graph showing the relationship between the floc diameter and the amount of coagulant added. As shown by reference numeral 803 in FIG. 8, in both (i) and (ii) above, the floc diameter increased compared to the case where no flocculant was added.

A diagram indicated by reference numeral 804 in FIG. 8 is an image showing the results of this test. The image on the left side of the diagram indicated by reference numeral 804 in FIG. 8 shows the results when the polymer flocculant was added after the addition of PAC. The image on the right side of the diagram indicated by reference numeral 804 in FIG. 8 shows the results when the PAC was added after the addition of the polymer flocculant. As indicated by reference numeral 804 in FIG. 8, floc sedimentation was observed in all cases.

From the results of this example, regardless of the order in which the inorganic flocculating agent and the organic flocculating agent were added, the sedimentation speed of the components contained in the steelmaking slag was increased by using the inorganic flocculating agent and the organic flocculating agent. confirmed. Therefore, in the process of recovering calcium compounds from steelmaking slag, it was demonstrated that the process of separating calcium carbonate, which is difficult to separate into solids and liquids, does not become a bottleneck. Moreover, it was demonstrated that the calcium compound can be easily precipitated by the method for recovering the calcium compound according to the present invention.

It should be noted that each condition (for example, the amount of coagulant added, the concentration and particle size of the slurry, etc.) of the experiment performed in this example was described as an example of the condition. Each target value described in this embodiment is also an example, and the target value differs depending on the equipment and local conditions.

S1 magnetic separation step S2 first separation step (first collection step)
S3 Second separation step (second collection step)
S4 sedimentation process

Claims (1)

A recovery method for recovering calcium compounds contained in steelmaking slag discharged from steelmaking,
a magnetic separation step of collecting a first compound containing iron from a slurry produced by pulverizing the steelmaking slag;
A first collection step of adding an organic flocculant and an inorganic flocculant to the slurry remaining after the magnetic separation step and collecting a first supernatant liquid containing the calcium compound from the slurry ;
An organic flocculant and an inorganic flocculant are added to the slurry while bringing an aqueous carbon dioxide solution into contact with the slurry remaining after the first collection step to elute calcium in the aqueous carbon dioxide solution, and from the slurry, the first A second collection step of collecting a second supernatant liquid containing the aqueous carbon dioxide solution in which the calcium is eluted, which is different from the supernatant liquid;
A sedimentation step of adding the second supernatant, an organic flocculant, and an inorganic flocculant to the first supernatant, and sedimenting the calcium compound contained in the first supernatant,
In each of the first collecting step, the second collecting step and the sedimentation step, the inorganic flocculant contains a second compound represented by the following general formula (1), and the organic flocculant contains the following general formula A recovery method including the third compound represented by (2).
[Al ₂ (OH) _n Cl _6-n ] _m (1)
(n is an integer of 1 or more and 5 or less, and m is an integer of 10 or less.)

... (2)
(The molecular weight of the organic flocculant is 1,000,000 or more for a cationic type, or 3,000,000 or more for an anionic type.)

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