JP2013147370A - Method for manufacturing carbonated slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a carbonated slag from a steelmaking slag by a simple, high-productivity and low-cost method.SOLUTION: A steelmaking slag 15 is immersed in water 16 in a reaction tank body 10; a carbon dioxide gas 12 is blown in the water 16 under stirring; and the blowing-in of the gas 12 is finished when pH of the water 16 at this time falls in the range of 11.8 or lower and 8.5 or higher.

Description

  The present invention relates to a method for producing carbonated slag, and more particularly, to a method for producing carbonated slag from slag produced mainly as a by-product in a steelmaking process. More specifically, the present invention relates to the development of technology for promoting effective recycling of slag produced as a by-product in a steelmaking process, and more specifically, efficient carbonation treatment of steelmaking slag, and production of carbonated slag. Regarding the method.

  Steelmaking slag generated in the steelmaking process contains minerals that are effective for the biological environment, such as iron, magnesium, calcium, phosphorus, and silicon. For example, when phosphorus is contained like dephosphorization slag, the utility value as a fertilizer is high.

  However, on the other hand, such slag may cause problems such as generation of alkaline water due to free calcium and white turbidity of seawater upon reuse, and may adversely affect the environment such as living organisms.

Here, free calcium is CaO that does not form a crystal with other oxides (hereinafter also referred to as “f-CaO”).
One effective method for stabilizing free calcium is a carbonation treatment in which f-CaO is CaCO ₃ . Calcium carbonate (CaCO ₃ ) is obtained by carbonation of free calcium, and naturally exists stably as marble, limestone and the like mainly composed of calcium carbonate. For this reason, it can be easily imagined that the influence on the environment is reduced by carbonating free calcium. Thus, the idea of stabilizing free calcium in slag by carbonation is a natural idea in terms of chemical engineering, and many proposals have been made.

Patent Document 1, a steel slag, while applying mechanical stirring in the presence of water, and supplies the CO ₂ containing gas, method of processing steel slag to perform the carbonation reaction are described. Moreover, in order to make the density | concentration of the free CaO in steelmaking slag into 1 mass% or less, the technique which performs the process for about 40 minutes to about 1 hour is disclosed.

Patent Document 2 discloses a method for carbonizing steelmaking slag without installing a large mechanical stirring or pressurizing device by installing ultrasonic application equipment in a water tank.
Patent Document 3 discloses a method for carbonizing steelmaking slag by bringing nanobubble-containing water in which CO ₂ or a CO ₂ -containing gas is dispersed in water in the form of bubbles having a diameter of 1 μm or less into contact with the steelmaking slag. ing.

Patent Document 4 discloses a method for carbonizing steel slag by forming a fluidized bed of steel slag powder with water in which CO ₂ -containing gas is dispersed as microbubbles, as in Patent Document 3. Yes.

  In Patent Document 5, a granular steelmaking slag held in water with a mass ratio of slag to water (slag / water) of 0.6 or less, and water in which carbon dioxide-containing gas was blown and carbonate ions were dissolved, A carbonation treatment method for steelmaking slag is disclosed in which a calcium carbonate layer is formed on the steelmaking slag particle surface layer by maintaining the water temperature at 60 ° C. or lower and making contact for 0.5 hour or more.

Japanese Patent No. 4328215 JP 2009-057257 A JP 2010-120882 A JP 2011-016710 A JP 2011-051831 A

  However, since these conventional technologies are focused on carbonation treatment of slag as smoothly as possible, as a result, expensive equipment investment, complicated treatment conditions and control thereof are necessary. For this reason, further improvement is desired for widespread use on an industrial scale. In addition, among these conventional techniques, there is a carbonation treatment method in which a carbon dioxide-containing gas is blown into a solution of granular slag and water, but the carbonation treatment can be industrially implemented. Is not disclosed at all. This has the problem of incurring a reduction in productivity and a loss cost with respect to the carbonation treatment (production of calcium carbonate) of steelmaking slag.

  The present invention has been made in view of such problems of the prior art, and it is easy to produce carbonated slag by carbonating slag containing free CaO (hereinafter also referred to as steelmaking slag). Therefore, an object of the present invention is to provide a highly practical slag carbonation method that is highly productive and can be reduced in cost.

In the method of blowing a carbon dioxide-containing gas into water in which steelmaking slag is immersed, the reaction during the carbonation treatment is as shown in the following formulas (1) and (2).
CaO + H ₂ O Ｃａ Ca (OH) ₂ (1)
Ca (OH) ₂ + CO ₂ Ｃａ CaCO ₃ + H ₂ O (2)
However, if carbon dioxide is supplied excessively, it becomes calcium hydrogen carbonate as shown in the following formula (3), and is almost completely ionized to give a calcium hydrogen carbonate solution.

CaCO ₃ + H ₂ O + CO ₂ Ｃａ Ca (HCO ₃ ) ₂ (3)
Here, if attention is paid to the production of carbonated slag, it is very important to determine whether the carbonation treatment has ended.

When the carbonation reaction is insufficient, unreacted CaO or Ca (OH) ₂ remains, causing an alkaline water problem or consolidation, and the problem to be solved by the present invention cannot be solved.
On the other hand, if carbon dioxide is supplied excessively, the generated calcium carbonate becomes water-soluble calcium hydrogen carbonate, and a new problem arises in the production method of carbonated slag that productivity and yield are reduced, resulting in loss costs. Therefore, a method for solving this problem is also desired.

In order to perform carbonation without excess or deficiency, a sample is taken from the water in which the steelmaking slag being processed is immersed, and the concentrations of Ca ²⁺ , CO ₃ ²⁻ , HCO ₃ ⁻ are analyzed, and the analysis value is obtained. Although it is necessary to confirm the progress of the carbonation treatment, it takes time to find the analysis value and its cost, which is not realistic.

  Therefore, as a result of intensive studies, the present inventors have focused on the pH transition of the immersion water in the method of blowing carbon dioxide-containing gas into the water in which the steelmaking slag particles are immersed, and are simple and high productivity. Furthermore, the inventors have come to the knowledge that a carbonized slag manufacturing method capable of reducing costs can be realized.

  Here, in a broad sense, the present invention blows carbon dioxide-containing gas into water in which steelmaking slag is immersed, and continues to blow this carbon dioxide-containing gas, so that the pH of the water is 11.8 or less, 8.5. The carbonated slag manufacturing method is characterized in that the blowing of the carbon dioxide-containing gas is terminated at the time when the above is reached.

More specifically, the present invention is as follows.
(1) In the reaction tank, blowing the carbon dioxide-containing gas into the water in which the steelmaking slag is immersed. In the reaction tank, while blowing the carbon dioxide-containing gas into the water, the steelmaking slag and While stirring with water, measuring the pH of the water while blowing and stirring the carbon dioxide gas, and the measured value of the pH is in the range of 11.8 or less and 8.5 or more The method for producing carbonated slag from steelmaking slag is characterized in that the blowing of the carbon dioxide-containing gas is terminated.

(2) The method for producing carbonated slag as described in (1) above, wherein the steelmaking slag has a particle size of 40 mm or less.
(3) Carbonation as described in said (1) or (2) characterized by the mass ratio of the said water and the said steelmaking slag being 0.10 or more and 1.0 or less as steelmaking slag / water A method for producing slag.

  (4) The stirring is performed using a stirring blade fixed in the reaction tank or an impeller provided in the water, and the number of revolutions per minute of the reaction tank or the impeller is 10 rpm or more and 50 rpm. The method for producing carbonated slag according to any one of the above (1) to (3), characterized in that:

  ADVANTAGE OF THE INVENTION According to this invention, in manufacturing carbonation slag by carbonizing steelmaking slag, the manufacturing method of carbonation slag which is simple, is highly productive, and can reduce cost can be provided. .

It is a schematic diagram of the reaction tank used for the manufacturing method of carbonation slag from the steelmaking slag concerning this invention.

A mode for carrying out the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view of a reaction tank 1 used for carbonation treatment of a steelmaking slag 15 according to the present invention. The reaction tank 1 includes a reaction tank body 10, a stirring blade 11, a gas blowing pipe 13 for blowing a carbon dioxide-containing gas 12 into the water in the tank, and a pH electrode 14. In the illustrated example, a stirring blade 11 is provided inside the reaction vessel main body 10 so that the reaction vessel rotates.

  The gas blowing pipe 13 blows the carbon dioxide-containing gas 12 into the water 16 introduced into the reaction tank body 10. The pH electrode 14 measures the pH of the water 16 necessary for determining whether the carbonation treatment is complete. In the figure, reference numeral 20 denotes a data processing device.

  The method for producing carbonated slag from the steelmaking slag 15 according to the present invention introduces the steelmaking slag 15 and the water 16 into the reaction tank body 10 and immerses the steelmaking slag 15 in the water 16. The steelmaking slag 15 and the water 16 are stirred while the carbon dioxide-containing gas 12 is blown into the water 16, and the pH of the water 16 being stirred is measured, and the pH is 11.8 or less. And when it becomes in the range of 8.5 or more, the blowing of the carbon dioxide-containing gas 12 is terminated. Details will be described below.

  First, the steelmaking slag 15 and the water 16 are introduced into the reaction tank body 10, and the steelmaking slag 15 as a raw material is immersed in the water 16. The steelmaking slag 15 contains free calcium, and includes hot metal pretreatment slag (desulfurization slag, desiliconization slag, dephosphorization slag), converter slag, electric furnace slag, stainless slag, etc. Slag formed in any smelting vessel that can be used for melting. The particle size of the steelmaking slag 15 is preferably 40 mm or less from the viewpoint of improving reactivity, and more preferably 5 mm or less in consideration of handling at the reuse destination of the carbonated slag.

  Examples of the water 16 include tap water and pure water. The reaction tank body 10 is introduced with such an amount that the immersed steelmaking slag 15 is not visible to the naked eye. The mass ratio of the water 16 introduced into the reaction vessel main body 10 and the steelmaking slag 15 is preferably 0.10 or more and 1.0 or less as steelmaking slag / water. This is because if the mass ratio is smaller than 0.10, the mass of the water 16 increases as compared with the mass of the steelmaking slag 15, so that facilities and power are excessive more than necessary. On the other hand, if the mass ratio exceeds 1.0, the steelmaking slag 15 may not be stably immersed in the water 16 in a stirring operation or the like. More preferably, it is 0.25 to 0.40.

  Next, the steelmaking slag 15 and the water 16 are stirred while the carbon dioxide-containing gas 12 is blown into the water 16 in the reaction vessel body 10. As shown in FIG. 1, the steelmaking slag 15 and the water 16 are stirred by the stirring blade 11 as the reaction vessel body 10 rotates. Stirring may be performed by providing an impeller in the reaction vessel main body 10 instead of the stirring blade 11.

  When stirring is performed using the reaction vessel body 10, the number of rotations per minute of the reaction vessel body 10 is preferably 10 rpm or more and 50 rpm or less. If the rotational speed per minute is less than 10 rpm, the stirring force is not sufficient and the carbonation treatment may not proceed sufficiently. On the other hand, when the rotational speed per minute exceeds 50 rpm, the equipment and power become excessive more than necessary, and the effect is saturated. When stirring is performed using an impeller, although depending on the diameter of the impeller, it is performed at a rotational speed that is approximately the same as the rotational speed of the reaction vessel body 10.

The pH of the water 16 being stirred is measured, and the blowing of the carbon dioxide-containing gas 12 is finished within the range of pH 11.8 or less and 8.5 or more, and the carbonation treatment is finished.
During the stirring, the pH of the water 16 is 11.8 or less, and preferably 8.5 or more.

If the pH is higher than 11.8, unreacted CaO and Ca (OH) ₂ remain, causing an alkaline water problem and caking. On the other hand, if the pH is less than 8.5, the calcium carbonate once produced becomes water-soluble calcium bicarbonate.

  As described above, according to the present invention, the pH of the water 16 is measured during the carbonation treatment of the steelmaking slag 15, and the blowing of the carbon dioxide-containing gas 12 is terminated when entering the predetermined range. The carbonation treatment can be carried out without excess or deficiency. Moreover, in this Embodiment, the pH electrode 14 should just be provided in the conventional stirring apparatus 1, and the carbonation process is complete | finished according to the pH value of the water 16 in the middle of stirring. For this reason, when carbonizing the steelmaking slag 15, it is simple, high productivity, and low cost can be realized.

  In the present invention, the pH range of 8.5 to 11.8 is a region where the reaction transitions from the above formula (2) to (3), and if the gas blowing is stopped within that range, Carbonation treatment can be completed without excess or deficiency, productivity can be increased, and low cost can be realized.

  In this example, the dephosphorization slag having the physical properties shown in the following Table 1 generated in the dephosphorization process was used as the steelmaking slag. 45 kg of this dephosphorization slag and 140 kg of tap water (water 16) are introduced into the reaction tank main body 10 (concrete mixer) shown in FIG. 1, and carbon dioxide gas having a purity of 99.99% is produced while rotating the reaction tank main body 10 at 15 rpm. Carbonation was performed by blowing at 100 Nl / min.

  Table 2 shows pH transition and component transition during carbonation treatment of dephosphorized slag.

When the treatment time was 45 minutes or less, the pH was almost constant at 12.4 to 12.5, and Ca ²⁺ = 702 to 749 mg / L and CO ₃ ²⁻ = 3.3 to 7.2 mg / L. Further, HCO ₃ ⁻ <0.1 mg / L was hardly present. In this region, as shown in the above formula (1) (2), CO 2 blown with Ca _{(OH) 2} generated in the slag and tap water are reacted, since the CaCO ₃ to produce, ^{Ca 2+} and CO ₃ ²⁻ is present but HCO ₃ ⁻ is hardly present.

At the start of treatment from 45 minutes to 75 minutes or less, the pH decreases from 12.4 to 8.5, Ca ²⁺ decreases from 702 to 20.2 mg / L, and CO ₃ ²⁻ decreases from 3.3 to 0.5 mg / L. Decreased to L. HCO ₃ ⁻ increased from less than 0.1 to 34.1 mg / L. In this region, the supply of Ca (OH) ₂ from the slag stagnates, and the reaction changes from the above formula (2) to (3), so Ca ²⁺ , CO ₃ ²⁻ and HCO ₃ ⁻ exist, The concentration was minimized.

From 75 minutes to 180 minutes treatment time, the pH decreased from 8.5 to 6.8, Ca ²⁺ increased from 20.2 to 48.9 mg / L, and HCO ₃ ²⁻ increased from 34.1 to 541 mg / L. Increased to L. In addition, CO ₃ ²⁻ was low and constant at 0.2 to 0.5 mg / L. In the reaction in this region, the above-described formula (3) is dominant, and the blown CO ₂ reacts with the produced CaCO ₃ to produce Ca (HCO ₃ ) _2, and the produced Ca (HCO ₃ ) ₂ is dissociated. As a result, Ca ²⁺ and HCO ₃ ⁻ increase.

From the above, it was confirmed that it is most efficient to end the treatment at 8.5 ≦ pH ≦ 11.8.
Subsequently, the carbonated slag after the above-mentioned carbonation treatment was collected, pure water was passed through 10 g of the carbonated slag, and the pH of the solution after passing through was measured. For comparison, the same pH measurement was also performed on dephosphorized slag that was not carbonized. The pH was measured using a commercially available measuring instrument (D-54S manufactured by Horiba, Ltd.).

  Table 3 shows the physical properties of the carbonated slag after the carbonation treatment. Table 4 shows the slag water passing test results after the carbonation treatment. Table 5 shows the results of the water removal test of the dephosphorized slag not subjected to the carbonation treatment. In Tables 4 and 5, the liquid-solid ratio is the ratio (pure water / slag) between the mass of slag and the mass of pure water that has passed through the slag.

  From Table 4, the carbonated slag generally showed pH <10 from the beginning of water flow. Further, from Table 5, the dephosphorization slag not subjected to the carbonation treatment showed a high transition of pH> 11 from the initial stage of water flow. Thus, in carbonated slag, even if it increased water flow volume, the increase in pH was not recognized and it was confirmed that long-term alkali elution can also be reduced.

DESCRIPTION OF SYMBOLS 1 Reaction tank 10 Reaction tank main body 11 Stirring blade 12 Carbon dioxide containing gas 13 Carbon dioxide containing gas blowing pipe 14 pH electrode 15 Steelmaking slag 16 Water

Claims (4)

In the reaction tank, carbon dioxide-containing gas is blown into the water in which the steelmaking slag is immersed. In the reaction tank, while blowing the carbon dioxide-containing gas into the water, the steelmaking slag and water While stirring, blowing the carbon dioxide gas and stirring, the pH of the water was measured, and the measured pH value was within the range of 11.8 or less and 8.5 or more. Sometimes, the carbon dioxide-containing gas blowing is terminated, and a method for producing carbonated slag from steelmaking slag. The carbonized slag manufacturing method according to claim 1, wherein the steelmaking slag has a particle size of 40 mm or less. The mass ratio of the said water and the said steelmaking slag is 0.10 or more and 1.0 or less as steelmaking slag / water, The manufacturing method of the carbonated slag of Claim 1 or 2 characterized by the above-mentioned. The stirring is performed using a stirring blade fixed in the reaction tank or an impeller provided in the water, and the number of rotations per minute of the reaction tank or the impeller is 10 rpm or more and 50 rpm or less. The method for producing carbonated slag according to any one of claims 1 to 3.

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