JPS6221594B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for detoxifying harmful substances contained in steelmaking dust, and in particular provides a method for detoxifying steelmaking dust that makes it extremely easy to handle and dispose of treated materials, and has significantly improved processing efficiency. It is something to do. Traditionally, steelmaking dust generated from steelmaking furnaces such as arc furnaces has been stored unless the valuable metals contained in the dust are recovered or reused as other raw materials. It may contain hazardous metals, including hexavalent chromium, cadmium, lead, etc., which may be leached out during elution tests stipulated by laws and regulations regarding industrial waste treatment, so they are not regulated as industrial waste. is subject to. In recent years, various methods have been proposed and studied in order to meet the demand for detoxifying steelmaking dust, but all of them have advantages and disadvantages in terms of processing technology, economic efficiency, workability, etc. However, it is still not fully satisfactory in practical terms. Therefore, as a result of various studies in view of the above circumstances, we found that by adding and kneading soluble sulfide, which is alkaline and has a reducing function, to steelmaking dust, the elution of water-soluble harmful substances in the dust can be extremely effectively and easily suppressed. I found out what I can do. The mechanism by which such soluble sulfides detoxify harmful components is expressed by the following formula (CaS ₄ as soluble sulfide).
); CaS ₄ +O ₂ +H ₂ O→CaS ₂ O ₃ +H ₂ S+S The H ₂ S generated as a result of this process causes metals (M; Cd, Pb, Hg, etc.) that may be contained in steelmaking dust to ) ^is stabilized by becoming a metal _sulfide ^as _shown ^{in the} following _{formula ;} O＋4S CrO ₄ ^2- +4CaS ₂ O ₃ →Cr ³⁺ +4CaSO ₄ +4S It is reduced to trivalent chromium according to O＋4S CrO 4 2- +4CaS 2 O 3 , and the generated trivalent chromium is converted to hydroxide depending on the alkalinity of the system. The presence of water (H ₂ O) is essential in the reaction system, as it is thought that this is due to the stabilization caused by the reaction. However, when approximately 30% or more of water is added to steelmaking dust, this mixture generally becomes slurry-like or mud-like, making it difficult to handle and dispose of the reaction product (detoxified material). This will make things extremely difficult. Therefore, an attempt was made to make the steel dust obtained in powder form harmless by adding just enough water to make it easy to handle and not turn it into a muddy form, and to make it harmless according to the reaction described above, but the reaction proceeded slowly. I understood. Moreover, this problem could not be solved quickly even by increasing the amount of soluble sulfide added. Here, as a result of further intensive research in order to solve the above-mentioned problems, the present inventors have discovered an effective method that allows the detoxification reaction to proceed rapidly even when the reaction mixture is in a solid state. This led to the completion of the . That is, the gist of the present invention is to knead powdered steelmaking dust together with soluble sulfide that is alkaline and has a reducing function and add water to an extent that does not become muddy, and to mix the kneaded product as necessary. After forming it into the desired shape, it is heated and cured at a temperature not exceeding 400℃, which allows the reaction between steelmaking dust, soluble sulfide, and water to proceed extremely quickly. Of course, considering the final disposal form of the steelmaking dust, it is possible to form it into a desired shape,
This also led to the advantage that it could be rendered harmless. Furthermore, if the kneaded product obtained according to the present invention is molded into a desired shape such as pellets, briquettes, dumplings, or lumps, such molded products can be formed even if a certain amount of water is added thereto. The shape does not collapse, and therefore water can be added again, and the detoxification reaction can proceed even better, and steam can be used instead of adding water again. A similar effect can be obtained by using the heating curing method. Furthermore, if exhaust gas containing _CO2 , such as combustion exhaust gas discharged from a heating furnace, combustion furnace, etc., exhaust gas discharged from a steelmaking dust collector, etc., is used for heat curing at a predetermined temperature according to the present invention, these exhaust gases can be used. based on CO ₂ as well as effective use of thermal energy.
Reactions such as CaS ₄ +CO ₂ +H ₂ O→CaCO ₃ +H ₂ S+3S offer the advantage of significantly shortening the processing time. The method of the present invention as described above can be applied to all steelmaking dust containing harmful metal components such as chromium (hexavalent), cadmium, and lead, which is normally generated in powder form in steelmaking furnaces such as arc furnaces. For such steelmaking dust, a soluble sulfide that is alkaline and has a reducing function, preferably a soluble polysulfide, such as polysulfide alkali metal salts, polysulfide alkaline earth metal salts, polysulfide ammonium salts, etc. According to the present invention, it is added and kneaded together with a predetermined amount of water. The amount of (water) soluble sulfide blended varies depending on the type and properties of the steelmaking dust, and is determined as appropriate depending on the desired degree of detoxification, but generally it is added to 100 parts by weight of steelmaking dust. On the other hand, sulfide sulfur (S ^2- )
It will be used in a proportion of about 0.01 to 10 parts by weight. In addition, the amount of water added to these steelmaking dust and soluble sulfides should be such that the kneaded material obtained by kneading does not appear muddy, specifically, the amount of water added to the steelmaking dust is generally about 30% or less. The decision will be made as appropriate so that the intended rapid detoxification process can be carried out. In addition, the thus obtained kneaded product of steelmaking dust, soluble sulfide, and water in a predetermined ratio is not slurry-like, so it is extremely easy to handle in subsequent processing, and it can also be used in the desired manner. Since it can be easily formed into shapes, it can be shaped into pellets, briquettes, dumplings (pulverized charcoal),
It is then molded into a block-like molded product as needed. As mentioned above, a certain amount of moisture is added to such a molded product, in other words, an amount of water that does not disintegrate the molded shape, generally about 10% or less of the molded product, is added by means such as spraying. , thereby promoting effective reaction. Further, according to the present invention, the solid kneaded product or the molded product obtained through such a process can be used for 400
By being heat-cured in various ways at temperatures not exceeding ℃, the detoxification reaction can proceed advantageously and quickly even under conditions of insufficient moisture content, and the water-soluble harmful substances caused by soluble sulfides can be effectively and rapidly cured. This maximizes the effect of suppressing the elution of substances. In addition, during this heat curing treatment, it is necessary to ensure that the heating temperature does not exceed 400℃, and if a higher heating temperature is used,
Hazardous metal components that should be suppressed (especially hexavalent chromium)
The amount of elution increases, making it difficult to achieve the original purpose. In addition, heating methods include simple heating using an appropriate furnace, blowing heated air, treatment with superheated steam,
Furthermore, any heating means or methods may be employed, such as a method that uses waste gas containing CO ₂ and aims to utilize waste heat and promote the reaction, which is preferable for the present invention. The steelmaking dust treated product obtained in this way is treated by the effective detoxifying action (reaction) of soluble sulfide which is alkaline and has a reducing function.
While the elution amount of harmful metal components contained in it is effectively suppressed, it is not in a muddy form, so it can be sent to landfill as is, and it is also extremely difficult to transport and handle. It turned out to be an advantage. Examples will be shown below to clarify the present invention more specifically, but it goes without saying that the present invention is not limited in any way by the description of these Examples. Note that all parts and percentages in Examples and Reference Examples are based on weight unless otherwise specified. Reference Example Although the components of steelmaking dust vary greatly depending on the melted raw material and the type of steel, two types of dust A and B having the elution amounts shown in Table 1 were studied here.

[Table] * The elution amount of each metal component was determined by an elution test in accordance with Environment Agency Notification No. 13 (Final revised Environment Agency Notification No. 4).
100 parts of each of these two types of dust,
A 27.5% calcium polysulfide aqueous solution and water were added and mixed in the proportions shown in Table 2, and after being left at room temperature for a day and night, each elution test was conducted, and the results are shown in Table 2.

【table】

[Table] As is clear from the results in Table 2, it is difficult to completely render hexavalent chromium, one of the harmful metal components, harmless by leaving it for a day and night unless a large amount of water (approximately 30%) is present in the reaction system. This problem is difficult to solve even if the amount of calcium polysulfide added is increased. It is recognized that by adding calcium polysulfide, which is an alkaline soluble sulfide, the PH of the resulting mixture becomes more alkaline. Example 1 To 100 parts of steelmaking dust (B) shown in the reference example, 27.5
% concentration calcium polysulfide aqueous solution 3.6 parts and water 15
After thoroughly kneading the mixture, it was formed into a charcoal shape, which was then placed in a Matsufuru furnace and heat-cured for various times under various temperature conditions as shown in Table 3. The elution amount (mg/) of Cr ⁶⁺ was determined for each sample obtained, and the results are shown in Table 3. As is clear from Table 3, when the heating temperature becomes significantly higher, the amount of Cr ⁶⁺ eluted increases, and therefore it is desirable to avoid temperatures exceeding 400°C. Further, it is understood that the desirable temperature range is about 100 to 300°C, particularly about 150 to 250°C.

[Table] Example 2 To 100 parts of the steelmaking dust shown in Example 1, 3.6 parts of a 27.5% calcium polysulfide aqueous solution and 15 parts of water were added, kneaded, and then formed into a briquette. Furthermore, approximately 5% moisture of the molded article was added by water sprinkling. The molded products that were sprinkled with water and the molded products that were not sprinkled with water were subjected to heat curing treatment at a temperature of 200° C. with various treatment times, and the amount of Cr ⁶⁺ eluted from the resulting treated products was determined. The results are shown in Table 4.

[Table] As is clear from Table 4, it is understood that the detoxification of Cr ⁶⁺ by calcium polysulfide is significantly promoted by water sprinkling. Example 3 The briquettes of the kneaded product obtained in Example 2 were subjected to heat curing treatment as shown in Table 5. From the results shown in Table 5, it is understood that the detoxification reaction is also promoted by the curing treatment by steam heating.

[Table] Example 4 The kneaded product (not shaped) obtained in Example 2 was subjected to simple heating at 200°C or exhaust gas heating for various treatment times, and the Cr The amount of ⁶⁺ elution was determined. The exhaust gas used was boiler exhaust gas containing about 10% (by volume) of _CO2 . The results are shown in Table 6. As is clear from Table 6, by employing exhaust gas heating, Cr ⁶⁺ in steelmaking dust can be rendered harmless in an extremely short period of time.

[Table] Example 5 To 100 parts of the dust shown in Example 1, 1 part of sodium polysulfide dissolved in 20 parts of water was added and kneaded, and then formed into a briquette. Heat curing treatment was performed under these conditions, and the amount of Cr ⁶⁺ eluted from the resulting treated product was determined. The results are shown in Table 7.

【table】

Claims (1)

[Scope of Claims] 1. Powdered steelmaking dust is kneaded together with soluble sulfide that is alkaline and has a reducing function, and water is added to an extent that it does not become muddy, and if necessary, after molding into a desired shape, A method for detoxifying steelmaking dust, comprising heating and curing it at a temperature not exceeding 400°C to promote a reaction between the steelmaking dust, soluble sulfide, and water. 2. After the kneaded product of the steelmaking dust, soluble sulfide, and moisture is formed into a desired shape, the formed product is further added with moisture to an extent that does not collapse the shape, and then heated and cured. The treatment method described in Section 1. 3. The treatment method according to claim 1, wherein the kneaded product of the steelmaking dust, soluble sulfide, and water is formed into a desired shape and then cured by steam heating. 4 After forming the kneaded product of the steelmaking dust, soluble sulfide, and water into a desired shape as necessary,
The treatment method according to claim 1, wherein the treatment method is heated and cured in exhaust gas containing CO ₂ .