Selenium removal method and selenium removal apparatus

Abstract

An object of the present disclosure is to provide a selenium removal method that can easily remove selenium from a selenium-containing raw material.SOLUTION: A selenium removal method according to one aspect of the present disclosure includes a step of obtaining a slurry containing a selenium-containing raw material and water, a step of supplying a carbon dioxide-containing gas to the slurry obtained in the step of obtaining a slurry, a step of adding an alkaline additive to the slurry obtained in the step of obtaining a slurry to adjust the pH of the slurry to 11 or more after the step of supplying, and a step of performing solid-liquid separation on the slurry after the step of supplying and the step of adjusting.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a selenium removal method and apparatus. [Background technology]

[0002] In blast furnaces used to extract pig iron from iron ore, the use of small particle size iron ore can cause clogging, so large particle size iron ore is selected and used as the raw material for iron production. However, the proportion of small particle size iron ore is not small, and it is desirable to make effective use of this small particle size iron ore. Therefore, such small particle size iron ore is sometimes sintered to be used as the raw material for iron production in blast furnaces.

[0003] In the sintering process for producing the sintered ore, fine particles containing iron (sintering dust) are contained in the exhaust gas. Such sintering dust is separated and collected (captured) by a dust collector, but it is desired to further reduce the raw material costs of pig iron and various steel products by further utilizing this sintering dust as a sintering raw material.

[0004] On the other hand, sintering dust may contain selenium, which is undesirable for reuse as a sintering raw material. To improve the utilization rate of sintering dust, a method for removing selenium has been proposed (Japanese Patent Laid-Open Publication No. 2019-163532). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-163532 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, sinter dust and water are mixed to form a slurry, and a chemical such as sodium carbonate is added to the slurry to precipitate calcium eluted from the sinter dust as calcium carbonate in the liquid phase, thereby promoting the elution of selenium from the sinter dust. Specifically, calcium oxide in the sinter dust is dissolved by dispersing the sinter dust in water to form calcium ions, and sodium carbonate is added to precipitate the calcium ions as calcium carbonate in the liquid phase, thereby promoting the elution of selenium from the sinter dust. There is a demand for a method to more easily produce calcium carbonate so that selenium can be easily removed.

[0007] In view of the above circumstances, an object of the present disclosure is to provide a method for removing selenium that can easily remove the selenium from a raw material containing selenium. [Means for solving the problem]

[0008] A selenium removal method according to one embodiment of the present disclosure that solves the above-described problems includes the steps of obtaining a slurry containing a raw material containing selenium and water, supplying a gas containing carbon dioxide to the slurry obtained in the step of obtaining a slurry, adjusting the pH of the slurry obtained in the step of obtaining a slurry by adding an alkaline additive to the slurry obtained in the step of obtaining a slurry so that the pH of the slurry after the supplying step is 11 or higher, and performing solid-liquid separation of the slurry after the supplying step and the adjusting step. [Effects of the Invention]

[0009] The selenium removal method of the present disclosure can easily remove selenium from raw materials containing selenium. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic front view showing a selenium removal device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0012] (1) A selenium removal method according to one embodiment of the present disclosure includes the steps of obtaining a slurry containing a raw material containing selenium and water, supplying a gas containing carbon dioxide to the slurry obtained in the step of obtaining a slurry, adding an alkaline additive to the slurry obtained in the step of obtaining a slurry to adjust the pH of the slurry after the supplying step to 11 or higher, and performing solid-liquid separation of the slurry after the supplying step and the adjusting step.

[0013] In this selenium removal method, a gas containing carbon dioxide is supplied to a slurry containing a selenium-containing raw material and water, so that calcium ions dissolved in the liquid phase can be easily converted into calcium carbonate, thereby accelerating the elution of selenium from the raw material. Furthermore, an alkaline additive is added to the slurry to adjust the pH to 11 or higher, preventing the calcium carbonate from converting to calcium bicarbonate, further accelerating the elution of selenium. The slurry from which the selenium has been eluted can be subjected to solid-liquid separation to easily obtain a solid phase (the raw material) from which selenium has been removed.

[0014] (2) In the above (1), the adjusting step may be performed after the supplying step. By performing the adjusting step after the supplying step, the ease of eluting selenium in the raw material can be improved.

[0015] (3) In the above (2), the pH of the slurry may be adjusted to less than 7 in the supplying step. By adjusting the pH of the slurry to less than 7 in the supplying step, the calcium carbonate can be produced efficiently.

[0016] (4) In the above (2) or (3), the pH of the slurry may be adjusted to 11 or more in the step of obtaining the slurry. By adjusting the pH of the slurry to 11 or more in the step of obtaining the slurry, the selenium can be efficiently eluted.

[0017] (5) In any one of (1) to (4), the raw material may be sinter dust discharged from a sintering plant. That is, the selenium removal method is suitable for removing selenium from sinter dust discharged from a sintering plant.

[0018] (6) A selenium removal apparatus according to one embodiment of the present disclosure includes a slurry preparation unit that prepares a slurry containing a raw material containing selenium and water, a gas supply unit that supplies a gas containing carbon dioxide to the slurry prepared in the slurry preparation unit, a pH adjustment unit that adds an alkaline additive to the slurry prepared in the slurry preparation unit to adjust the pH of the slurry after gas supply by the gas supply unit to 11 or more, and a solid-liquid separation unit that separates the slurry after gas supply by the gas supply unit and pH adjustment by the pH adjustment unit into solid and liquid.

[0019] In this selenium removal apparatus, a slurry containing a selenium-containing raw material and water is prepared in a slurry preparation unit. A gas supply unit supplies the slurry with a carbon dioxide-containing gas, which allows calcium ions dissolved in the liquid phase to be easily converted into calcium carbonate in a subsequent adjustment process, thereby promoting the dissolution of selenium from the raw material. Furthermore, a pH adjustment unit adds an alkaline additive to the slurry to adjust the pH to 11 or higher, preventing the carbonate ions and calcium ions from reacting to form calcium carbonate and further to form calcium bicarbonate. This further promotes the dissolution of selenium. In a solid-liquid separation unit, after gas supply by the gas supply unit and pH adjustment by the pH adjustment unit, the slurry is subjected to solid-liquid separation, thereby easily obtaining a solid phase (the raw material) from which selenium has been removed.

[0020] [Details of the Mode for Carrying Out the Disclosure] An example of an embodiment of the present disclosure will be described in detail below.

[0021] [Method for removing selenium] The selenium removal method includes the steps of obtaining a slurry containing a selenium-containing raw material and water, supplying a gas containing carbon dioxide to the slurry obtained in the step of obtaining a slurry, adjusting the pH of the slurry obtained in the step of obtaining a slurry by adding an alkaline additive to the slurry so that the pH of the slurry after the supplying step is 11 or higher, and performing solid-liquid separation of the slurry after the supplying step and the adjusting step.

[0022] [Selenium removal device] The selenium removal method may be performed using, for example, a selenium removal apparatus as shown in Fig. 1. The selenium removal apparatus includes a slurry preparation unit 10 that prepares a slurry containing a selenium-containing raw material and water, a gas supply unit 20 that supplies a carbon dioxide-containing gas to the slurry prepared in the slurry preparation unit 10, a pH adjustment unit that adds an alkaline additive to the slurry prepared in the slurry preparation unit 10 to adjust the pH of the slurry after gas supply by the gas supply unit to 11 or higher, and a solid-liquid separation unit 40 that separates the slurry after gas supply by the gas supply unit 30 and pH adjustment by the pH adjustment unit into solid and liquid.

[0023] <Slurry preparation section> The slurry preparation unit 10 is not particularly limited as long as it can store the raw materials and water, and may be, for example, a tank (container), etc. The raw materials and water may be charged into this tank and mixed by stirring, etc., to prepare the slurry.

[0024] The selenium-containing raw material contained in the slurry is not particularly limited and may be, for example, combustion exhaust gas dust, iron ore, coal, rock, soil, etc. Reducing the selenium content of these raw materials can improve resource utilization by recycling them into steelmaking raw materials or coal raw materials, or address environmental issues through soil modification, etc. The raw material may be sinter dust discharged from a sintering plant. The sinter dust can be used as a sintering raw material by removing selenium, thereby reducing industrial waste and reducing the cost of sintering raw materials. Furthermore, adding water to the sinter dust and performing wet treatment can dissolve and remove chlorine compounds, thereby preventing clogging of the exhaust gas discharge line of the sintering plant when used as a sintering raw material. The water contained in the slurry is not particularly limited and may be, for example, distilled water, pure water, ion-exchanged water, etc.

[0025] The particle size of the raw material is not particularly limited, but is preferably small in size from the viewpoint of increasing the contact area with water, i.e., the raw material is preferably in the form of fine particles.

[0026] The upper limit of the content of the raw material in the slurry may be 25 mass%, 15 mass%, 8 mass%, or 7 mass%. The lower limit of the content is not particularly limited and may be 1 mass%, 2 mass%, or 3 mass%. By setting the content within the above range, selenium in the raw material can be efficiently eluted.

[0027] <Gas supply section> The gas supplied by the gas supply unit 20 is not particularly limited as long as it contains carbon dioxide. For example, it may be air (atmospheric air), exhaust gas discharged from facilities such as factories, etc. By fixing the carbon dioxide in the exhaust gas to the calcium as described above, the carbon dioxide emission amount of the facility can be reduced. The gas may be a gas consisting of carbon dioxide. By using a gas consisting of carbon dioxide, the gas supply amount can be reduced. The gas supply unit 20 is not particularly limited, and for example, a known gas injector or the like may be used. The gas may be supplied, for example, into the slurry in the tank.

[0028] <pH adjustment unit> The additive added to the slurry by the pH adjustment unit is not particularly limited as long as it shows alkalinity. For example, an alkaline solution such as a sodium hydroxide solution may be used. Also, a solution using by-product alkali (waste alkali) recovered from other factories, facilities, etc. may be used. When using the alkaline solution, the pH adjustment unit preferably has a solution supply device 30 that supplies the alkaline solution. The addition of the additive is not particularly limited. For example, the solution supply device 30 may drop the additive into the slurry in the tank and stir to adjust the pH to 11 or more.

[0029] <Solid-liquid separation unit> The solid-liquid separation unit 40 separates the solid and liquid of the slurry in which selenium has eluted into the liquid phase. The solid phase (the raw material) separated from the slurry can be used as a resource because the selenium has been sufficiently removed. The solid-liquid separation unit 40 is not particularly limited, and for example, a known centrifuge or the like may be used.

[0030] Each step of the selenium removal method will be described below.

[0031] <Step of obtaining a slurry> In the step of obtaining the slurry, the raw materials and the water are introduced to obtain the slurry. Specifically, the raw materials and the water are introduced into the slurry preparation unit 10 and mixed. The raw materials and the water may be stirred.

[0032] <Supply process> In the supplying step, a gas containing carbon dioxide is supplied to the slurry obtained in the slurry obtaining step. By supplying the gas containing carbon dioxide to the slurry, calcium (Ca) eluted from the raw material reacts with carbonate ions dissolved in the slurry in a subsequent adjusting step to become calcium carbonate (CaCO3) and be generated in the liquid phase of the slurry.

[0033] <Adjustment process> In the adjusting step, an alkaline additive is added to the slurry to adjust the pH of the slurry after the supplying step to 11 or higher. Excessive carbonate ions cause acidity (a decrease in pH), which can cause calcium carbonate to become calcium bicarbonate and redissolve in the liquid phase. If calcium bicarbonate redissolves in the liquid phase, calcium selenite (CaSeO4) is formed, which may inhibit the elution of selenium in the raw material into the liquid phase. Since carbonate ions are known to easily become bicarbonate ions when the pH is less than 10, adjusting the pH to 10 or higher, or more reliably 11 or higher, promotes the formation of calcium carbonate, thereby improving the ease and reliability of eluting selenium (SeO3).

[0034] The adjusting step may be performed before the supplying step or during the step of obtaining the slurry (i.e., the step of obtaining the slurry may obtain a slurry containing the raw materials, the water, and the additives), but is preferably performed after the supplying step. By adding the additives after supplying the gas, the pH can be easily adjusted. In addition, excessive use of the additives can be prevented.

[0035] When the adjusting step is performed after the supplying step, it is preferable to adjust the pH of the slurry to less than 7 in the supplying step. That is, it is preferable to supply the gas to the slurry to adjust the pH to less than 7, and then add the additive to the slurry to adjust the pH to 11 or more. Adjusting the pH to less than 7 by supplying the gas promotes the elution of calcium in the raw material and the dissolution of carbonate ions necessary for producing calcium carbonate during the adjustment, and then adding the additive to adjust the pH to 11 or more makes it easier to promote the elution of selenium in the raw material.

[0036] Furthermore, when the adjusting step is performed after the supplying step, the pH of the slurry may be adjusted to 11 or more in the slurry obtaining step. That is, the slurry having a pH of 11 or more may be obtained in the slurry obtaining step, the gas may be supplied to this slurry to adjust the pH to less than 7, and then the additive may be added to the slurry to adjust the pH to 11 or more. This can further promote the elution of selenium in the raw material.

[0037] When the adjusting step is performed before the supplying step, it is preferable to adjust the pH of the slurry to 11 or more in the adjusting step, and then supply the gas in the subsequent supplying step so that the pH does not become less than 11.

[0038] <Solid-liquid separation process> In the solid-liquid separation step, the slurry after the supplying step and the adjusting step is subjected to solid-liquid separation. The separated solid phase has had its selenium reduced by the supplying step and the adjusting step, and can therefore be used as a resource.

[0039] The time interval (elapsed time) from adjusting the pH of the slurry to 11 or higher to performing the solid-liquid separation step may be such that solid-liquid separation is performed immediately after adjusting the pH of the slurry to 11 or higher (i.e., the time interval may be 0 hour), or may be performed after a certain time has elapsed. The lower limit of the time interval may be 0.5 hours, 1.0 hours, 2.0 hours, or 3.0 hours. The upper limit of the time interval is not particularly limited and may be, for example, 24 hours. By setting the time interval within the above range, selenium in the raw material can be sufficiently removed.

[0040] When the solid-liquid separation is carried out a certain time after the pH of the slurry is adjusted to 11 or more, the pH value of the slurry may decrease. The lower limit of the pH value of the slurry in the solid-liquid separation step is preferably 10.5, more preferably 10.7, and even more preferably 10.8. In other words, the pH value of the slurry in the solid-liquid separation step, when rounded to an integer, may be 11 or more.

[0041] [Other embodiments] The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as falling within the scope of the present invention. [Example]

[0042] The present invention will be described in detail below based on examples, but the present invention should not be construed as being limited by the descriptions in these examples.

[0043] Example 1 40 g of dried sinter dust (raw material) was mixed with 500 g of distilled water and 300 g of sodium hydroxide solution (1 mol / L) in a tank (beaker) to obtain a first slurry. Carbon dioxide gas was supplied to the first slurry at a flow rate of 0.5 L / min to adjust the pH to 11. The first slurry to which the gas was supplied was vacuum filtered using No. 5A filter paper at 0 hours (Test Example 1), 3 hours (Test Example 2), 6 hours (Test Example 3), and 24 hours (Test Example 4) to separate into a filtrate and a residue. The pH was measured during this solid-liquid separation. The residue was dried under reduced pressure at 10 mmHg and 100°C for 2 hours to remove moisture, and the selenium and calcium concentrations of the filtrate and the residue were measured. As a comparative example, air was supplied to the first slurry, and the selenium and calcium concentrations of the filtrate and the residue were measured 46 days later (Test Example 5). The pH of the first slurry in Test Example 5 was not measured after the air was supplied to the first slurry. The results of Example 1 are shown in Table 1. Note that although the same raw materials were used in Test Examples 1 to 5, the selenium and calcium concentrations before preparation into the first slurry were not consistent among the individual Test Examples. This is thought to be due to the fact that the raw materials were powders, and variations were caused by uneven distribution.

[0044] [Table 1]

[0045] <Example 2> A second slurry (Test Example 6) was prepared by mixing 40 g of dried sinter dust with 740 g of distilled water in a beaker. Carbon dioxide gas was then supplied to the second slurry at a flow rate of 0.5 L / min until the pH reached less than 7. The gas-supplied second slurry was then heated to 70°C in a thermostatic chamber and stirred while adding sodium hydroxide (5 mol / L) dropwise. The addition of sodium hydroxide was stopped when the pH reached 11, and stirring was continued for 180 minutes. The slurry was then filtered under reduced pressure using No. 5A filter paper, resulting in solid-liquid separation into a filtrate and a residue. The residue was then dried under reduced pressure at 10 mmHg and 100°C for 2 hours to remove moisture, and the selenium and calcium concentrations of the filtrate and the residue were measured. The results are shown in Table 2.

[0046] [Table 2]

[0047] Tables 1 and 2 show that calcium was detected in the filtrate, suggesting that calcium in the raw materials was eluted and produced as calcium carbonate. In Example 1, when the elapsed time was 0 hours (Test Example 1), the selenium concentration in the filtrate was low and the selenium concentration in the filter residue was high. However, as the elapsed time increased, the selenium concentration in the filtrate tended to increase and the selenium concentration in the filter residue tended to decrease. Therefore, it is believed that more selenium can be eluted by leaving the slurry for 3 hours or more after increasing the pH of the slurry to 11 or higher.

[0048] In Example 2, the selenium concentration in the sintered dust was also reduced, indicating that the selenium removal effect could be achieved even if the gas was supplied first. Table 3 compares the amount of sodium hydroxide solution used in Example 1 with the amount of sodium hydroxide solution added to the second slurry to which the gas was supplied in Example 2. Table 3 shows that the amount of sodium hydroxide solution added in Example 2 was reduced to approximately 20% of the amount used in Example 1. It can be seen that the amount of alkaline additive added can be reduced by adjusting the pH after the gas supply. This is thought to be because adding the additive first makes it difficult to determine the appropriate amount, resulting in the addition of excess alkali for the carbonate ion neutralization reaction. On the other hand, if the amount added is underestimated, the pH will drop before calcium carbonate is produced relative to the calcium present in the slurry, and the leaching of calcium from the raw materials will not be promoted.

[0049] [Table 3] [Industrial Applicability]

[0050] The selenium removal method can easily remove selenium from raw materials containing selenium, and is therefore particularly suitable for use in sintering plants. [Explanation of symbols]

[0051] 10 Slurry adjustment section 20 Gas supply unit 30 Solution feeder 40 Solid-liquid separation section

Claims

1. obtaining a slurry containing a raw material containing selenium and water; a step of supplying a gas containing carbon dioxide to the slurry obtained in the step of obtaining the slurry; a step of adding an alkaline additive to the slurry obtained in the step of obtaining a slurry, so that the pH of the slurry after the step of supplying is 11 or more; a step of subjecting the slurry after the supplying step and the adjusting step to solid-liquid separation; A selenium removal method comprising:

2. 2. The method for removing selenium according to claim 1, wherein the adjusting step is carried out after the supplying step.

3. 3. The method for removing selenium according to claim 2, wherein the pH of the slurry is adjusted to less than 7 in the supplying step.

4. 4. The method for removing selenium according to claim 2, wherein the pH of the slurry is adjusted to 11 or higher in the step of obtaining the slurry.

5. 5. The method for removing selenium according to claim 1, wherein the raw material is sinter dust discharged from a sintering plant.

6. a slurry preparation unit for obtaining a slurry containing a raw material containing selenium and water; a gas supply unit that supplies a gas containing carbon dioxide to the slurry obtained in the slurry preparation unit; a pH adjusting unit that adjusts the pH of the slurry obtained in the slurry preparation unit to 11 or more after gas is supplied by the gas supply unit by adding an alkaline additive to the slurry; a solid-liquid separation unit that separates the slurry into solid and liquid after the gas supply unit has supplied gas and the pH adjustment unit has adjusted the pH; A selenium removal device comprising:

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