JP2008261005A - Method for reduction-burning steel dust - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for enhancing a volatilization rate of lead in steel dust without making the burning temperature higher than a normal burning temperature, even if the steel dust is a difficult material to be treated, when reduction-burning the steel dust in a rotary kiln. <P>SOLUTION: In a process of reduction-burning the steel dust of the difficult material to be treated containing zinc and lead, by adding a carbonaceous reducing agent to the steel dust to evaporate and recover zinc and lead, and further recovering iron as the residue, this reduction-burning method includes the steps of: adding iron oxide containing chlorine to the steel dust; mixing them and granulating the mixture to produce a pellet which has a chlorine grade of 3.5 to 4.5 wt.% and the iron grade of 20 to 30 wt.%; adding a carbonaceous reducing agent to the obtained pellet; and reduction-burning them. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention recovers zinc dust and lead by volatilizing and recovering iron and iron by reducing and roasting steel dust generated when steel scrap and the like are processed in a steel making furnace such as an electric furnace, and reducing and roasting iron. The present invention relates to a method for recovering as a residue.

  Steel dust generated from a steelmaking furnace such as an electric furnace contains a large amount of zinc and a small amount of other valuable metals in addition to iron. Therefore, as an object of resource recycling, zinc is mainly recovered from steel dust and iron is recovered as a reduced roasting residue.

  In general, a reduction roasting method using a rotary kiln is adopted as a reduction roasting method of the steel dust. In this reduction roasting method, steel dust is formed into pellets having a size of about 5 to 10 mm in advance as required, and continuously charged in a rotary kiln together with a carbonaceous reducing agent such as coal or coke.

  In the kiln, the maximum temperature is controlled to about 1100 to 1200 ° C. by combustion of heavy oil and combustion of the charged carbonaceous reducing agent. Steel dust is reduced and roasted in the kiln, and the volatilized metallic zinc is re-oxidized in the kiln to become powdered zinc oxide. Similarly, a small amount of lead contained in steel dust is reduced and roasted, and the volatilized metal lead is reoxidized in the kiln to become powdered lead oxide.

  Powdered zinc oxide and lead oxide are introduced into the dust collector together with the exhaust gas from the rotary kiln, captured, and recovered as a product called crude zinc oxide. The recovered crude zinc oxide is sent to a lead / zinc smelter to become zinc bullion and lead bullion. On the other hand, the reduced roasting residue that remains in the kiln without volatilization is recovered from the kiln discharge end as a product called reduced iron pellets because it contains a large amount of reduced iron, and paid to the steel manufacturer as an iron raw material Is done.

  In such a reduction roasting method, the volatilization rates of zinc and lead are 90% or more in a normal actual operation and 80% or more in a laboratory test. However, in the case of steel dust with low volatility of zinc and lead, which is called a difficult-to-process raw material, there are zinc volatility of about 50% and lead volatility of about 40% in actual operation, and the recovery rate of zinc and lead Therefore, the operation efficiency is lowered and zinc and lead as impurities remain in the reduced iron pellet, so that the product quality is deteriorated, which is not preferable for recycling steel dust.

  As a method for improving the volatilization rate of zinc by the reduction roasting method for such difficult-to-process steel dust, there is a method of increasing the reduction roasting temperature to increase the degree of reduction. However, when the reduction roasting temperature is increased to, for example, about 1300 ° C., the reaction product from the reduction roasting is softened and melted and adheres to the inner wall of the rotary kiln, and the deposits grow and increase with the lapse of operation time. Such a raw material becomes an obstacle when moving in the kiln, and there is a drawback that it eventually causes the operation to stop.

  In addition, as a method for improving the volatility of zinc by the reduction roasting method, coke as a reducing agent is mixed and granulated into pellets of steel dust to increase the degree of reduction during operation. . However, the method of incorporating coke as a reducing agent into pellets is effective for improving the volatility of zinc, but has a problem that it is less effective for metallic lead having a lower vapor pressure than metallic zinc.

  Further, as a general method for improving the volatilization rate of lead, there is known a method of volatilizing lead by increasing the vapor pressure by converting lead to chloride, that is, a chlorination refining method. However, the roasting atmosphere in this chloride refining method needs to be an atmosphere in which the reaction of lead chloride proceeds, that is, an oxidizing atmosphere.

  Therefore, in the reducing atmosphere in the operation of the reduction roasting method, lead oxide is reduced to become metallic lead, so that the reaction with chloride is difficult to proceed. Moreover, since metal zinc reacts preferentially with chloride over metal lead, it is necessary to add a large amount of chlorine to convert lead to chloride. Furthermore, when a large amount of chlorine is added, there is a problem that the exhaust gas equipment is corroded by chlorine and a new equipment for removing chlorine is required to remove chlorine.

Japanese Patent Application Laid-Open No. 2003-342648 describes a method for improving the volatility of zinc by adding iron oxide so as to have a mass ratio of 0.5 or more with respect to zinc in steel dust. However, there is no mention of improving lead volatility.
JP 2003-342648 A

  In the present invention, in view of the above-described conventional circumstances, when reducing and roasting steel dust in a rotary kiln, the volatilization rate of zinc and lead in the steel dust without increasing the roasting temperature to be higher than the normal temperature, In particular, an object is to provide a method capable of improving the volatility of lead.

  In order to achieve the above object, the method of reducing and roasting steel dust provided by the present invention volatilizes zinc and lead by adding a carbonaceous reducing agent to the iron and steel dust containing zinc and lead and then reducing and roasting. In the method of recovering and recovering iron as a residue, iron oxide containing chlorine is added to steel dust and mixed and granulated, and the chlorine quality is 3.5 to 4.5% by weight and the iron quality is 20 to 20%. After forming 30 wt% pellets, a carbonaceous reducing agent is added to the obtained pellets for reduction roasting.

  According to the present invention, in the reduction roasting of steel dust, even if it is a difficult-to-process raw material, the volatility of zinc and lead, particularly the volatility of lead can be improved. Therefore, the recovery efficiency of zinc and lead can be increased, and the zinc and lead remaining in the reduction roasting residue can be reduced to improve the quality of recovered reduced iron pellets.

  In addition, the method for reducing and roasting steel dust according to the present invention does not require the addition of a large amount of chloride, so there is no risk of corrosion of the exhaust gas equipment. Moreover, since it can implement at the roasting temperature in the reduction roasting operation of the steel dust in a normal rotary kiln, it can prevent that a reaction product softens and fuse | melts and adheres to an inner wall of a kiln.

  In the method for reducing and roasting steel dust according to the present invention, first, steel dust added with iron oxide containing chlorine is mixed and granulated into pellets having a size of about 5 to 10 mm. Next, the pellets are used in the same manner as general steel dust used during normal operation, and are continuously charged in a rotary kiln together with a carbonaceous reducing agent such as coke. Reduce roasting at the roasting temperature.

  At that time, the composition of the pellets is set such that the chlorine quality is in the range of 3.5 to 4.5% by weight and the iron quality is in the range of 20 to 30% by weight. By setting it as the pellet composition of this range, even if steel dust is a difficult-to-process raw material, the volatilization rate of lead in actual operation can be improved from the conventional 30 to 40% to about 80 to 90%. The reason why the volatilization rate of lead in the difficult-to-process raw material is improved is that chlorine in the iron oxide promotes volatilization of lead by chlorination. Even if the chlorine quality is increased from 30% by weight, the amount of difficult-to-process raw material is not increased, and only the processing cost of the raw material is increased.

  The steel dust used as a raw material is not particularly limited, and may be steel dust having a low volatility of zinc and lead, which is called a difficult-to-process raw material. The general composition of difficult-to-process raw materials is about 25 to 45% by weight of zinc, 1 to 3% by weight of lead, and about 5 to 15% by weight of iron. Even such difficult-to-process raw materials can be recovered by roasting and reducing zinc and lead at a high volatility as in the case of general steel dust.

  Further, the iron oxide containing chlorine is not particularly limited as long as it can be prepared to the above-described pellet composition according to the composition of steel dust used as a raw material such as a difficult-to-process raw material. In general, in preparing the pellet composition, the iron oxide containing chlorine preferably contains 5 to 10% by weight of chlorine and 45 to 50% by weight of iron. Such iron oxides containing chlorine may be prepared from reagents such as iron oxide and chloride according to the quality of steel dust, but nickel refinement containing about 6% chlorine quality and about 45% iron quality. It is also possible to use iron starch generated in the process.

  A generally used pelletizing apparatus can be used for the mixing granulation operation. For example, using a rotating pan-type pelletizer, continuously supplying steel dust such as difficult-to-process raw materials and iron oxide containing chlorine to a predetermined pellet composition, while adding mist-like moisture Pelletizing. The pellet size is preferably about 5 to 10 mm, and the water content is preferably about 10 to 20% by weight.

  The pellets thus adjusted are charged into the rotary kiln together with the carbonaceous reducing agent, and the operation in the rotary kiln is carried out according to the normal roasting and operating conditions of steel dust. Coal and coke can be used as the carbonaceous reducing agent. The roasting temperature may be the same as that of the prior art, and is specifically controlled so that the maximum temperature is 1100 to 1200 ° C.

  According to the method of the present invention, even if steel dust is a difficult-to-process raw material, the volatility of lead can be improved to 80% or more while maintaining the volatility of zinc at the same level as before. Along with this, the amount of lead remaining in the reduced roasting residue is reduced to about 1/3 to 1/10 of the conventional amount, so it is possible to improve the quality of reduced iron pellets recovered as iron raw materials. It becomes.

  The difficult-to-process raw material was subjected to a laboratory roasting reduction roasting test under the following conditions. A horizontal rotary roasting furnace shown in FIG. 1 was used as an apparatus capable of reproducing roasting in a rotary kiln. In this horizontal rotary roasting furnace, a furnace core tube 3 (length: 200 mm × diameter: 125 mm) made of SUS310S is installed in a furnace body 1 having a heating element 2 so as to be rotatable by a rotary shaft 4. Note that the temperature of the core tube 3 is controlled by a thermocouple 5.

The composition of the difficult-to-process raw material used for the test was: Zn: 42.18% by weight, Pb: 2.60% by weight, Fe: 7.26% by weight, Cd: 0.14% by weight, Cr: 1.27% by weight It is. In addition, an iron oxide containing chlorine (additive 1) has a composition of Zn: 0.51% by weight, Pb: 0.05% by weight, Fe: 46.2% by weight, C: 0.13% by weight, Cl : 6.9% by weight was prepared using the reagent ZnO, PbO, Fe ₂ O ₃ , CaCl ₂ and a coke lump having a particle size of 1.0 to 2.0 mm. For comparison, CaCl ₂ was used as additive 2.

The additive 1 or additive 2 was added to the difficult-to-process raw material and mixed and granulated to produce pellets having a particle size of 5.4 to 9.6 mm. For each of the produced pellets of Samples 1 to 6, the parts by weight of additive 1 (iron oxide containing chlorine) or additive 2 (CaCl ₂ ) added to 100 parts by weight of the difficult-to-process raw material are as follows. Table 1 shows. In addition, the sample 1 of a comparative example is a pellet which consists only of the said difficult-to-process raw material without an additive.

The obtained pellets of samples 1 to 6 are charged together with the carbonaceous reducing agent into the core tube 1 of the horizontal rotary roasting furnace shown in FIG. did. As the carbonaceous reducing agent, a coke lump having a particle size of 1.0 to 2.0 mm was used, and the charging amount was 60 g with respect to 300 g of pellets of each sample. The conditions for reduction roasting are estimated from the operating temperature distribution and residence time of the actual machine to be the same as the normal operating conditions, and the temperature is raised from room temperature to 1050 ° C. over 1 hour and held at 1050 ° C. for 1 hour. The temperature condition was selected. In addition, the atmosphere gas was set to CO ₂ : N ₂ = 1: 5 assuming an actual heavy oil combustion atmosphere, and the air flow rate was set to 2 liters / minute.

  After completion of the reduction roasting test, the residue remaining in the core tube 1 is taken out and analyzed, and compared with the sample before the reduction roasting test, the volatilization rates of zinc and lead are obtained, and in the reduction roasting residue Sought lead grade. These results are shown in Table 2 below together with the chlorine quality and iron quality before the reduction roasting test. The analysis of iron, zinc, lead content and chlorine was carried out by ICP method (manufacturer name: Seiko Instruments, apparatus name: SPS3000). Moreover, the chlorine quality and iron quality of the pellet were determined by analyzing the composition of the pellet after mixed granulation.

As can be seen from the above results, the lead volatilization rate is only 33% in the reduction roasting test of Sample 1 consisting only of difficult-to-process raw materials as a comparative example. Further, in Comparative Samples 2 to 3 in which chloride (CaCl ₂ ) is mixed and granulated as a difficult-to-process raw material, the lead volatilization rate is 36 to 38%, which is almost the same as that of Sample 1 above. It was.

  On the other hand, when samples 5 to 6 of the present invention, that is, iron oxide containing chlorine is mixed and granulated to a difficult-to-process raw material to prepare a chlorine quality of 3.5 to 4.5% by weight, A lead volatility of 80% or more, similar to steel dust, was obtained. However, in Sample 4, the iron oxide containing chlorine was mixed and granulated in the difficult-to-process raw material, but the chlorine quality was too low at 2.4% by weight, so that a sufficient lead volatilization rate was not obtained.

1 is a schematic cross-sectional view showing a horizontal rotary roasting furnace used in a laboratory-level roasting test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace 2 Heating body 3 Core tube 4 Rotating shaft 5 Thermocouple

Claims (3)

  In a method in which zinc and lead are volatilized and recovered by adding a carbonaceous reducing agent to steel dust containing zinc and lead and then reduced and roasted, and iron is contained in the steel dust as a residue. After adding oxide and mixing and granulating, pellets with a chlorine grade of 3.5 to 4.5% by weight and an iron grade of 20 to 30% by weight are added, and then a carbonaceous reducing agent is added to the obtained pellets. A method for reducing and roasting steel dust, characterized by subjecting to reduction roasting.   The method for reducing and roasting steel dust according to claim 1, wherein the iron oxide containing chlorine contains 5 to 10% by weight of chlorine and 45 to 50% by weight of iron.   The steel dust according to claim 1 or 2, wherein the steel dust has an iron grade of 5 to 15 wt%, a zinc grade of 25 to 45 wt%, and a lead grade of 1 to 3 wt%. Reduction roasting method.

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