JP6188624B2 - Method for suppressing elution of fluorine and / or hexavalent chromium - Google Patents

Description

  The present invention relates to a method for suppressing elution of fluorine and / or hexavalent chromium.

In recent years, attention has been focused on the use of slag (steel by-product) as civil engineering materials and roadbed materials due to problems such as reduction of waste and depletion of natural resources. It is also recommended to recycle slag from the viewpoint of reducing environmental impact.
In order to use slag as civil engineering materials and roadbed materials, it is necessary to satisfy the soil environmental standards stipulated in Notification No. 46 of the Environment Agency. The amount of elution of fluorine (F) and hexavalent chromium is 0.8 mg / L or less and 0.05 mg / L or less are defined.

As a technique for suppressing the elution amount of fluorine from the recycled slag, the techniques of Patent Documents 1 to 3 are disclosed, and as the technique for suppressing the elution amount of hexavalent chromium, the techniques of Patent Documents 4 to 6 are disclosed. Yes.
In patent document 1, the amount of elution of fluorine is suppressed by mixing the hot metal pretreatment slag containing no fluorine with the base agent in an equal amount (50%) or more. In Patent Document 2, fluorine is inactivated by mixing slag containing a mineral phase containing Ca and P into slag containing fluorine. In Patent Document 3, elution of fluorine is suppressed by mixing a steel mixture containing fluorine with a compound made of water-soluble calcium and / or a calcium mixture containing a compound made of water-soluble calcium.

  In Patent Document 4, a compound containing an alkaline earth metal is mixed, and the elution of sulfur (S) is promoted by increasing the pH of the eluate, thereby promoting the reduction reaction of hexavalent chromium. The amount of elution is suppressed. In patent document 5, after carrying out a reductive reaction to slag from which hexavalent chromium elutes, hexavalent chromium is suppressed by mixing with sulfur-containing slag. In Patent Document 6, hexavalent chromium is suppressed by accelerating the reduction reaction of hexavalent chromium by mixing with a sulfur-containing substance according to the elution amount of hexavalent chromium.

JP 2010-222227 A JP 2009-040650 A JP-A-2005-239509 JP 2005-254082 A JP-A-11-106243 JP 2002-68789 A

  Patent Documents 1 to 3 are techniques for suppressing elution of fluorine from slag, and Patent Documents 4 to 6 are techniques for suppressing elution of hexavalent chromium from slag. Although these technologies can suppress the elution of fluorine or the elution of hexavalent chromium, it is difficult to perform both the suppression of elution of fluorine and the elution of hexavalent chromium (to achieve both). It was. Moreover, even when the elution suppression of fluorine and the elution suppression of hexavalent chromium are performed individually, there is a possibility that they cannot be sufficiently suppressed.

  In view of the above problems, the present invention is capable of sufficiently performing both fluorine elution suppression and hexavalent chromium elution suppression, or fluorine elution suppression and hexavalent chromium elution suppression. An object of the present invention is to provide a method for suppressing elution of valent chromium.

In order to achieve the object, the present invention takes the following technical means.
That is, the technical means of the present invention is to mix the second substance, which is an elution inhibitor, with the first substance whose fluorine elution amount and / or hexavalent chromium elution amount exceeds the environmental standard.
Alternatively, when suppressing elution of hexavalent chromium, the second substance contains Ca and / or S, and the amount of Ca elution and / or S elution of the first substance and from the second substance The mixing amount of the second substance is determined based on the Ca elution amount and / or the S elution amount (other than hexavalent).

Moreover, it is preferable to determine the mixing amount of the second substance so that the Ca elution amount in the mixture of the first substance and the second substance is 300 mg / L or more.
Further, when the elution amount of hexavalent chromium of the first substance is X [mg / L], and the S elution amount of the mixture of the first substance and the second substance is Y [mg / L], It is preferable to determine the mixing amount of the second mixture so as to satisfy the formula (1).

Y ≧ 0.5X (1)
Further, the amount of Ca elution in the mixture of the first substance and the second substance is 300 mg / L or more, and the elution amount of hexavalent chromium of the first substance is X [mg / L]. When the S elution amount of the mixture of the substance and the second substance is Y [mg / L], it is preferable to determine the mixing amount of the second mixture so as to satisfy the formula (1).

Y ≧ 0.5X (1)
The most preferable embodiment of the method for suppressing elution of fluorine and / or hexavalent chromium according to the present invention is to suppress elution with respect to a first substance whose fluorine elution amount and / or hexavalent chromium elution amount exceeds the environmental standard. When the second substance as a material is mixed to suppress elution of fluorine and / or hexavalent chromium, the second substance contains Ca and / or S, and the amount of Ca elution of the first substance and A mixing amount of the second substance is determined based on the elution amount of S and / or the Ca elution amount and / or the S elution amount (other than hexavalent) from the second substance, and the first substance The amount of Ca elution in the mixture of the first substance and the second substance is 300 mg / L or more, and the elution amount of hexavalent chromium of the first substance is X [mg / L]. The amount of elution of S in the mixture containing Y is Y [mg / L] If, to satisfy equation (1), and determines the mixing amount of the second mixture.
Y ≧ 0.5X (1)

  According to the present invention, it is possible to reliably perform both fluorine elution suppression and hexavalent chromium elution suppression, or fluorine elution suppression and hexavalent chromium elution suppression.

It is the figure which showed a mode that a target material was modify | reformed by charging (supplying) the elution suppression material (2nd substance) to a target material (1st substance). It is a related figure of the mixing rate of the elution inhibitor (secondary refining slag B and secondary refining slag C), and F elution amount. It is a related figure of the mixing rate of elution inhibitor (secondary refining slag B and secondary refining slag C), and Ca elution amount. It is a related figure of the mixing rate of the elution inhibitor (secondary refining slag B and secondary refining slag C), and the hexavalent chromium elution amount. It is a related figure of the mixing rate of the elution inhibitor (secondary refining slag B and secondary refining slag C), and the elution amount of S (other than hexavalent).

Hereinafter, an embodiment of a fluorine and / or hexavalent chromium elution suppression method according to the present invention will be described with reference to the drawings.
In steelmaking plants, molten steel having a desired component is manufactured by performing various refining processes such as desiliconization, desulfurization, dephosphorization, and decarburization on hot metal. In such a refining process, steelmaking by-products such as slag are generated along with the refining process. As described above, the slag generated by the refining process is used as a civil engineering material and a roadbed material.

  When this slag is used for civil engineering materials and roadbed materials, the amount of elution of harmful elements such as fluorine and hexavalent chromium needs to satisfy the soil environmental standards stipulated in Notification No. 46 of the Environment Agency. Therefore, in the present invention, the elution amount of fluorine and hexavalent chromium is mixed by mixing the second substance, which is an elution inhibitor, with the first substance in which the elution amount of fluorine and hexavalent chromium exceeds the environmental standard. Meet soil environmental standards.

  As shown in FIG. 1, for example, in an electric furnace 10, main raw materials and auxiliary raw materials such as a cold iron source are put into the container body 11, and the cold iron source and auxiliary raw materials are heated and melted by arc discharge by the electrode 12, Refining treatment is performed by blowing oxygen into the molten metal 13 through the lance 14. Then, in the refining process in the electric furnace 10, the generated slag (first substance Q1) is discharged into the slag pot 1 (a container that receives the slag), and the slag pot 1 is a substance (second substance) that is an elution inhibitor. By supplying the substance Q2), the first substance Q1 is modified to suppress the elution amount of fluorine and the elution amount of hexavalent chromium. That is, by adding the second substance Q2 to the first substance Q1, a mixture Q3 in which the elution amount of fluorine and the elution amount of hexavalent chromium is suppressed is generated, and this mixture Q3 is used for civil engineering materials and roadbed materials. It is correct.

  In FIG. 1, the second substance Q2 is charged after the first substance Q1 is discharged into the slag pot 1, but instead, after the second substance Q2 is charged into the slag pot 1, The first substance Q1 may be charged. Or, it is possible to mix the materials Q1 and Q2 uniformly, such as mixing in a slag yard or in an electric furnace, and does not significantly affect the dissolution behavior of the material Ca and / or sulfur (S). Elution suppression is possible.

Hereinafter, for convenience of explanation, the first substance is referred to as “target material”, and the second substance is referred to as “elution suppression material”.
Next, the mixing of the elution suppressing material Q2 with the target material Q1 will be described in detail.
In the elution of fluorine, it is known that Ca is related, and when the amount of Ca contained in the target material Q1 is small, the amount of elution of fluorine is large, and when the amount of Ca is large, the amount of elution of fluorine tends to be small. . That is, the solubility product [Ca ²⁺ ] [F ⁻ ] ² of CaF ₂ is constant, and when the amount of Ca eluted in the target material Q1 is large, the amount of fluorine eluted is small and the amount of Ca eluted in the target material Q1 is small. And the amount of fluorine elution increases. That is, the elution suppression material Q2 contains Ca that suppresses the elution of fluorine, and the elution suppression material Q2 is added to the target material Q1 to suppress the elution of fluorine. However, since various solubility products of CaF ₂ have been reported and the behavior of various ions in aqueous solution is affected by various coexisting ionic species, Ca elution that can suppress fluorine elution from slag is possible. The amount needs to be determined experimentally.

On the other hand, elution of hexavalent chromium is known to be related to trivalent chromium in the slag, and when a large amount of trivalent chromium is oxidized, the elution amount of hexavalent chromium increases. Conversely, the elution amount of hexavalent chromium can be suppressed by reducing hexavalent chromium contained in the slag to trivalent chromium.
Therefore, in the present invention, the elution suppression of hexavalent chromium is performed by adding unoxidized sulfur (S) to the target material Q1 containing hexavalent chromium and promoting the reduction reaction of hexavalent chromium. . That is, the elution control material Q2 contains S (other than hexavalent) that suppresses the elution of hexavalent chromium, and the elution suppression material Q2 is added to the target material Q1 to suppress the elution of fluorine. It is said.

In order to suppress the elution of fluorine and hexavalent chromium, first, the elution amount of fluorine and the elution amount of hexavalent chromium in the target material Q1 are predicted. Here, when the elution amount of fluorine satisfies the environmental standard and the elution amount of hexavalent chromium satisfies the environmental standard in the target material Q1, there is no problem even if the target material Q1 is used as a civil engineering material or a roadbed material.
On the other hand, if either the fluorine elution amount or the hexavalent chromium elution amount exceeds the environmental standard in the target material Q1, the Ca elution amount or S elution amount from the target object Q1 and the Ca elution amount from the elution suppression material Q2 Based on the elution amount or the S elution amount, the mixing amount of the elution suppression material Q2 that satisfies the environmental standards is determined, and the determined elution suppression material Q2 and the target material Q1 are mixed to produce a mixture Q3.

Further, when both the elution amount of fluorine and the elution amount of hexavalent chromium in the target material Q1 do not satisfy the environmental standards, the Ca elution amount and S elution amount from the target object Q1 and the Ca elution amount from the elution suppression material Q2 Based on the amount and the S elution amount, the mixing amount of the elution suppression material Q2 that satisfies the environmental standard is determined, and the determined elution suppression material Q2 and the target material Q1 are mixed. In addition, since SO ₄ ²⁻ (hexavalent) does not contribute to the reduction reaction in the S elution amount in the elution control material Q2, the hexavalent elution amount is excluded.

Next, when the elution amount of fluorine of the target material Q1 exceeds the environmental standard and when the elution amount of hexavalent chromium of the target material Q1 exceeds the environmental standard, the elution suppression material Q2 and the target material Q1 The mixing will be specifically described.
First, when the fluorine elution amount of the target material Q1 exceeds the environmental standard, “Ca _A ” that is the Ca elution amount eluted from the target material Q1 is obtained and the Ca elution amount eluted from the elution suppression material Q2 Find “Ca _B ”. Then, the mixing rate Z1 of the elution suppression material Q2 is determined so that the “Ca _average ” which is the Ca elution amount of the mixture Q3 obtained by mixing the target material Q1 and the elution suppression material Q2 is 300 mg / L or more. The elution suppressing material Q2 having the rate Z1 and the target material Q1 are mixed.

Thus, when the Ca elution amount (Ca _average ) after mixing is 300 mg / L, the elution amount of fluorine can be made 0.8 mg / L or less, which is the environmental standard. The relationship between the Ca elution amount (Caaverage) of the mixture Q3, the Ca elution amount (Ca _A ) of the target material Q1, the Ca elution amount (Ca _B ) of the elution suppression material Q2, and the mixing ratio Z1 (%) of the elution suppression material Q2 Is represented by Formula (a).

Ca _average = (Ca _A (100−Z1) + Ca _B × Z1) ÷ 100 (a)
On the other hand, when the elution amount of hexavalent chromium in the target material Q1 exceeds the environmental standard, “S _A = X”, which is the S elution amount eluted from the target material Q1, is obtained and S eluted from the elution suppression material Q2. “S _B ” which is the elution amount is obtained. Then, the mixing rate Z2 of the elution suppression material Q2 is set so that “Y = (S _average )” that is the S elution amount of the mixture Q3 obtained by mixing the target material Q1 and the elution suppression material Q2 satisfies the formula (1). The elution suppression material Q2 and the target material Q1 are mixed so that the mixing ratio Z2 is obtained.

Here, the S elution amount of the mixture Q3 (Y = S _average ), the S elution amount of the target material Q1 (S _A ), the S elution amount of the elution suppression material Q2 (S _B ), and the mixing rate of the elution suppression material Q2 (%) ) (Mixing amount of elution inhibitor Q2) Z2 is represented by the formula (b).
Y = S _average ≧ 0.5X (1)
S _average = (S _A × (100−Z2) + S _B × Z2) ÷ 100 (b)
In addition, since the component of S which can be evaluated in the analysis of the eluate is Total.S (total sulfur amount), S ₂ O ₃ ²⁻ , and SO ₄ ²⁻ (ion chromite), the present invention. Then, the amount of S elution (S _A , S _B ) is obtained using the equation (2).

S elution amount (S _A , S _B ) = Total. SS (as S ₂ O ₃ ²⁻ ) −S (as SO ₄ ²⁻ )
... (2)
The elution amount α of S (as S ₂ O ₃ ²⁻ ) can be obtained by the formula (3).
α = α ′ × 2M _S ÷ (2M _S + 3M _O ) (3)
However, alpha 'in the formula _(3), an S ₂ ^{O 3} elution volume of ^2-, _{M S} is the molecular weight of sulfur, _{M O} is the molecular weight of oxygen.

Moreover, the dissolution amount of S (as SO ₄ ^2-) β can be determined by Equation (4).
β = β ′ × M _S ÷ (M _S + 4M _O ) (4)
However, in the beta 'formula _(4), a ^{SO 4} dissolution amount of ^2-, _{M S} is the molecular weight of sulfur, _{M O} is the molecular weight of oxygen.
In addition, in the target material Q1, when both the elution amount of fluorine and the elution amount of hexavalent chromium exceed the environmental standard, as described above, the mixing rate Z1 of the elution suppression material Q2 and the mixing of the elution suppression material Q2 The ratio Z2 is obtained and the one with the larger mixing ratio is adopted.

  In summary, according to the present invention, the elution suppression material (second substance) Q2 is mixed with the target material (first substance) Q1 whose Ca elution amount and / or S elution amount exceeds the environmental standard, and fluorine is mixed. And / or when suppressing the elution of hexavalent chromium, the Ca elution amount and / or S elution amount from the target material Q1, and the Ca elution amount and / or S elution amount from the elution suppression material Q2 (other than hexavalent) Based on the mixing rate (Z1, Z2) of the elution suppression material Q2, in other words, the mixing amount is determined, and the target material Q1 is modified by adding the determined mixing amount of the elution suppression material Q2 to the target material Q1.

  In addition, in the case where fluorine elution suppression is performed, in the mixture Q3 in which the target material Q1 and the elution suppression material Q2 are combined, the mixing rate Z1 is determined so that the Ca elution amount is 300 mg / L or more. When suppressing elution of hexavalent chromium, when the elution amount of hexavalent chromium of the target material Q1 is X [mg / L] and the S elution amount of the mixture Q3 is Y [mg / L], the formula ( A mixing ratio Z2 satisfying 1) is obtained.

  Table 1 summarizes the examples in which the method for suppressing elution of fluorine and / or hexavalent chromium of the present invention and the comparative examples in which methods other than the present invention were performed.

As shown in Table 1, the case where there was an elution suppression effect of fluorine or an elution suppression effect of hexavalent chromium was evaluated as “good”, and it was eluted in both the elution suppression effect of fluorine and the elution suppression effect of hexavalent chromium. The case where there was an inhibitory effect was the best [最 良], and the case where there was no fluorine elution inhibitory effect and hexavalent chromium elution inhibitory effect was judged as poor [×]. Hexavalent chromium was expressed as Cr (VI).
Further, the target material Q1 was A in which oxidized slag (electric furnace oxidized slag) generated during the refining process in the electric furnace was heat-treated at 1600 ° C. for 2 hours to intentionally increase the elution amount of hexavalent chromium. On the other hand, the elution control material Q2 is generated during secondary refining slag B and secondary refining slag C generated during secondary refining, blast furnace slow cooling slag D and blast furnace slow cooling slag E generated in the blast furnace, and decarburization refining of the converter. One of the steelmaking slags made was adopted.

The slag used for the elution control material Q2 contains unoxidized S. Sulfur in the slag used for the elution control material Q2 exists in the form of CaS, MgS, etc. immediately after the generation of the slag. If this slag is exposed to a high temperature, it will be oxidized (CaSO ₄ ), but by mixing with the target material Q1 before being oxidized, the target material Q1 is reduced. For example, in the target material Q1 Since hexavalent chromium changes to trivalent chromium, elution of hexavalent chromium can be suppressed.

  Here, in order to maximize the elution suppression effect of hexavalent chromium (elution suppression by adding a small amount), the slag used for the elution suppression material Q2 can be rapidly cooled (not to be vitrified), or in a non-oxidizing atmosphere. It is effective to perform cooling in a state where the specific surface area is small. As a matter of course, depending on the S concentration in the slag, it is inappropriate to add sulfur S separately to increase the S concentration because it causes an increase in cost.

  [A] to [E] shown in the name column of Table 2 indicate the type of slag, and the slag used in the symbol column of Table 1 is described. In addition, the elution amount of each slag is as shown in Table 2.

  As shown in Table 1, in Experiments 1 to 3, the Ca elution amount of the elution suppression material Q2 is larger than that of the target material A, and the elution suppression effect of fluorine is recognized rather than diluted, but the Ca elution amount in the mixture Q3 is Since it was less than 300 mg / L (Ca column), environmental standards for fluorine (0.8 mg / L or less) could not be satisfied. In Experiment 3, the hexavalent chromium elution suppression effect was observed.

In Experiments 4 to 6, since the Ca elution amount in the secondary smelting slag B used as the elution suppression material Q is larger than that of the target material A and the Ca elution amount is 300 mg / L or more, the fluorine elution suppression effect is recognized. It was. In Experiments 4 to 6, an effect of suppressing elution of hexavalent chromium was also observed.
In Experiments 7 to 11, since the amount of Ca elution in the secondary refining slag C used as the elution suppressing material is the same as that of the target material A, even if the secondary refining slag C is added, only the fluorine is diluted. In some cases, environmental standards (0.8 mg / L or less) could not be satisfied. In Experiments 10 and 11, the environmental standard for fluorine (0.8 mg / L or less) was satisfied at the stage of the target material A (before mixing the elution inhibitor).

  In Experiments 12 to 20, all the environmental standards for hexavalent chromium (0.05 mg / L or less) could be satisfied. On the other hand, in Experiments 12 to 20, environmental standards for fluorine (0.8 mg / L or less) may not be satisfied. In Experiments 14 and 17 to 20, the environmental standard for fluorine (0.8 mg / L or less) was satisfied at the stage of the target material A. Further, in Experiment 18 and Experiment 20, the environmental standard for hexavalent chromium (0.05 mg / L or less) was satisfied at the stage of the target material A (before mixing the elution inhibitor).

In addition, the present inventors have conducted various experiments before conceiving the knowledge of the present invention. The results of such experiments are shown in FIGS. That is, the elution amount of fluorine (F elution amount), Ca elution amount, hexavalent chromium elution amount, and S (other than hexavalent) elution amount with respect to the mixing ratio of the secondary refining slag B and the secondary refining slag C are shown in FIG. The results shown in FIG.
As mentioned above, according to this invention, elution suppression based on Ca elution amount and / or S elution amount from the target material Q1, and Ca elution amount and / or S elution amount (other than hexavalent) from the elution suppression material Q2. By determining the mixing amount of the material Q2 and supplying the elution suppressing material Q2 of the determined mixing amount to the target material Q1, both elution suppression of fluorine and elution suppression of hexavalent chromium, suppression of elution of fluorine and hexavalent It is possible to sufficiently suppress the elution of chromium.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Slag pot 10 Electric furnace 11 Container main body 12 Electrode 13 Molten metal 14 Lance Q1 Target material (1st substance)
Q2 Elution inhibitor (second substance)
Q3 Mixture (modifier)

Claims (1)

When the second substance, which is an elution inhibitor, is mixed with the first substance whose fluorine elution amount and / or hexavalent chromium elution amount exceeds the environmental standard, elution suppression of fluorine and / or hexavalent chromium is performed. ,
The second substance contains Ca and / or S, the Ca elution amount and / or S elution amount of the first substance, the Ca elution amount and / or S elution amount from the second substance (six based on the non-valence) been made to determine the mixing amount of the second material,
The amount of Ca elution in the mixture of the first substance and the second substance is 300 mg / L or more, and the elution amount of hexavalent chromium of the first substance is X [mg / L]. the S elution of the mixture obtained by mixing a second substance in the case of the Y [mg / L], to satisfy equation (1), you and determining a mixing amount of the second mixture off Method for suppressing elution of nitrogen and / or hexavalent chromium.
Y ≧ 0.5X (1)