JP4757844B2 - Roasting reduction method of steel by-products - Google Patents

Description

  The present invention relates to a roasting reduction method for recovering valuable metals from steel by-products, and in particular, steel by-products including valuable metals such as iron, nickel, chromium and manganese, steelmaking dust such as pickling sludge and annealing scale. The present invention relates to a roasting reduction method for efficiently reducing living organisms and recovering valuable metals.

  Steel by-products such as steelmaking dust, pickled sludge, and scales during annealing contain valuable metals such as iron, nickel, chromium, and manganese, and many recovery methods have been proposed. It was. Specifically, these by-products are mixed with a carbon source such as coal or coke and molded into a briquette, and as shown in FIG. 1 (a), the briquette 2 is charged into the electric smelting furnace 1, A method has been proposed in which the briquette 2 is heated and melted by an electrode 3 and separated into a slag portion 4 and a reduced metal portion 5 to recover valuable metals (for example, see Patent Documents 1 and 2). However, in the above method, when the briquette 2 is inserted into the electric smelting furnace 1, some briquettes may be collapsed by impact and powder may be generated. When such powder increases, as shown in FIG. 1B, holes 6 are generated in the layer of briquette 2 due to the powder, and shelf suspension 7 is formed. As shown in FIG. 1 (c), when the shelf suspension 7 collapses, a volatile substance such as moisture in the briquette is heated at a stretch, causing an explosion and so-called blowing.

  To solve this problem, the by-product is mixed with a carbon source such as coal or coke, formed into a briquette shape, once baked to remove volatile components such as moisture, and then heated in an arc electric furnace. Thus, a reduction method has been proposed (see, for example, Patent Documents 3 to 6). In these methods, as shown in FIG. 2 (a), the unroasted briquette 11 is charged into the roasting box 12. A burner 13 is provided at the bottom of the roasting box 12. Then, by sucking the exhaust gas in the direction of the arrow 14, an exhaust flow path is formed between the non-roasted briquettes 11 from the bottom to the top of the roasting box 12 as indicated by the arrow 15. In this state, when the unroasted briquette 11 is ignited by the burner 13, the unroasted briquette 11 is roasted into the roasted briquette 16 in the direction indicated by the arrow 15.

  However, as shown in FIG. 3 (a), the strength of the unroasted briquette 21 is not sufficient, and some of the unroasted briquette 21 collapses due to an impact when falling from the forming machine 22 to the belt conveyor 23. And powder will be generated. As shown in FIG. 4 (a), when the belt conveyor 32 is loaded into the briquette transfer box 33, repeated collision occurs due to the concentration of the unburned briquette 31 dropping position, and powder is generated. End up. When a large amount of this powder is deposited on the bottom of the roasting box 12, the deposited powder is abnormally overheated during roasting to form a clinker 17, as shown in FIG. And if the clinker 17 is formed in the bottom part of the roasting box 12, as the arrow 15 shows, the flow path of the exhaust toward the upper part will be blocked, and the progress of roasting will be prevented. Therefore, the unroasted briquette 11 is not roasted in the central portion of the roasting box 12 above the clinker 17, and a raw briquette portion is generated. As a result, the volatile substance in the briquette cannot be removed, and the above-mentioned blowing problem may not be improved.

  Further, in order to effectively recover valuable metals, a method of adding aluminum residual ash in the method of heating and reducing in a submerged arc electric furnace after roasting is proposed (for example, a patent) Reference 7). However, in this method, since the reaction in the electric furnace is too intense, it is difficult to control the furnace, and there are cases where explosions and the like are involved.

Furthermore, steelmaking dust and pickling sludge are used as steel by-products in the prior art. However, since the scale material, which is one of steel by-products, is a raw material containing relatively large particles having a maximum particle diameter of 20 mm, in order to apply this to the conventional technology, for example, a large particle having a particle diameter of 3 mm or more is used. There is a problem that it becomes necessary to sort out and remove the product and to pulverize it, resulting in a very high cost.
JP-A-8-260014 JP 2003-247026 A JP-A 61-15929 JP-A 61-177331 JP 61-177332 A JP-A 61-177337 Japanese Patent Laid-Open No. 10-330822

  Therefore, the present invention actively uses large-scale raw materials as described above to reduce powder generated from briquettes, and while sufficiently removing volatile substances such as moisture, preventing blowing up. An object of the present invention is to provide a method for roasting and reducing steel by-products that can ensure a high recovery rate of valuable metals.

  In order to solve the above problems, the inventors have conducted extensive studies on briquette strength and powder generation reduction, and as a result, by mixing a scale material having a relatively large particle size with a steel byproduct at a specific ratio. The relatively large particles effectively act as aggregates, and the strength of the molded briquette can be increased. Further, as shown in FIG. The powder generated when falling on the belt conveyor 23 is reduced by sieving with a sieve 25 installed in the middle, and as shown in FIG. 4B, the briquette is transferred from the belt conveyor 34 to the briquette transfer box 33. When the belt conveyor 34 is loaded, the belt conveyor 34 is loaded while being periodically moved at a constant speed back and forth in the transport direction as indicated by the arrow 35 immediately above the briquette transfer box. Tsu bets can be reduced powder generation transport for the box, and found this by bringing the powder into the roasting box is reduced.

  Therefore, the method of roasting and reducing steel by-product according to the present invention includes a step of charging briquettes from a belt conveyor into a briquette transfer box when transferring to a step of roasting steel by-products in a roasting box. Reduce the powder generated when the briquette of steel by-product produced by the machine falls on the belt conveyor with a sieve having a mesh size of 5 to 30 mm installed in the middle of the belt conveyor, and The briquette is transported at a belt speed of 30 to 60 m / min, and the movable range of the belt conveyor is 300 to 1000 mm in the transport direction at a height of 1000 to 2000 mm directly above the briquette transfer box, and the speed is constant at 1 to 10 m / min. It is characterized by mitigating the generation of powder due to the impact of repeated briquette drops by charging it while moving it back and forth periodically at a speed. .

In addition, the method of roasting and reducing steel by-product according to the present invention comprises steel by-product consisting of steelmaking dust: 10 to 50% by weight, pickling sludge: 5 to 30% by weight, and scale material: 30 to 60% by weight. , A step of mixing oil and fat and carbonaceous material, a step of forming the mixed steel by-product into briquette by a bunker, and sieving the powder with a sieve while transporting the briquette by a belt conveyor Loading the briquette into the briquette transfer box while periodically moving the briquette back and forth in the transport direction at a constant speed with a movable belt conveyor, and charging the briquette from the briquette transfer box into the roasting box step and, slag amount and further mixed with carbonaceous material and limestone and / or quartz sand relative to briquette after the above roasting for basicity adjustment roasting within said roasting box by A step of, with the briquettes, heating was charged a mixture comprising the carbonaceous material and limestone and / or quartz sand to submerged arc type electric furnace, and reducing Fe, Ni, Cr, and valuable metals Mn, The steel by-product has a particle size of 2.8 mm or more and 20 mm or less, and the briquette has a shape of 40 sides on each side. The second feature is that it is ˜60 mm × 40-60 mm × 25-40 mm .

  According to the present invention, by using a scale material having a relatively large particle size, the strength of the briquette to be molded can be sufficiently increased, and not only the strength of the briquette can be improved by blending, but also by a belt conveyor. By reducing the amount of powder generated during transportation of the product and reducing the generation of powder during charging into the briquette transfer box, the removal of volatile substances such as moisture and zinc in the roasting process has been improved. In particular, the phenomenon of blowing up during the reduction process of the electric furnace is reduced, stable operation is realized, and high productivity can be obtained.

  Furthermore, according to the present invention, by mixing steelmaking dust, pickling sludge, and scale material at a specific ratio, the raw material can be controlled to have a chemical composition that provides good slag meltability and fluidity. Since valuable metal recovery rate is obtained and valuable metals such as Fe, Ni, Cr and Mn can be secured stably from steelmaking dust, pickling sludge, scale material, etc., which have been discarded as industrial waste, these raw materials As a result, a part of the cost can be compensated, and the manufacturing cost can be reduced and the global environment can be protected.

  Such an effect is presumed to be due to the following principle. If the slag and metal do not have proper fluidity, the raw material will not pass well when passing through the coke bed, and as a result, the valuable metal recovery rate will decrease. In particular, if the melting point and fluidity of the slag are not within an appropriate range, the falling of the slag will be delayed or too fast. As a result, since the reaction in the furnace cannot be controlled, the valuable metal recovery rate is lowered. In some cases, a blow-up phenomenon is also caused. At the same time, when ZnO in the raw material is higher than 2% by mass, blowing-up occurs remarkably. This is because when ZnO is reduced by C, zinc gas is generated, which raises the atmospheric pressure in the raw material and causes a bumping phenomenon.

  The roasting reduction method of the present invention is a method for recovering valuable metals Fe, Ni, Cr and Mn from steel by-products, and mixes water, fats and carbonaceous materials with steel by-products of a specific composition as described later. The briquettes are then made into briquettes by a dumper, the briquettes are roasted in a roasting box, and after further mixing the charcoal material and limestone and / or silica sand, the mixture is submerged arc electric It is a method of charging a furnace and heating, reducing valuable metals and separating them into metal and slag, but in the present invention, as steel by-products, steelmaking dust and pickled sludge are relatively large particles. Scale material with diameter is blended at a specific ratio, this steel by-product is molded into a specific shape briquette to increase briquette strength, and powder generated during transportation on belt conveyor is reduced with sieve And yellowtail It is the greatest feature to alleviate the powder generated due to repeated collisions of instrumentation Nyutoki to Tsu preparative transport boxes. Therefore, the characteristic material composition and process in the present invention will be described below. In other steps, a generally known conventional technique can be used.

  The steel by-product used in the present invention is a mixture of steelmaking dust and pickling sludge with a scale material at a specific ratio, and 3 to 40% by weight of the whole has a particle size of 2.8 mm to 20 mm. is there. In the present invention, such relatively large particles can act as an aggregate, so that the strength of the briquette to be molded can be improved. Specifically, after the briquette molding and before the roasting, The briquette strength can be 20 kgf / piece or more. Thus, by improving the briquette strength before roasting, it is possible to prevent powder generation such as when briquette is inserted into the roasting box, and to solve the problem of raw burning during roasting. . This ratio is preferably 5 to 30% by weight, more preferably 5 to 24% by weight.

  In the present invention, the other 3 to 40% by weight of the steel by-product as a whole has a particle size of 1.2 mm or more and less than 2.8 mm, which is advantageous for enhancing the effect as an aggregate. The ratio is preferably 5 to 30% by weight, more preferably 5 to 24% by weight. In addition, since the scale material has a relatively large particle size, most of the materials having a particle size in the above-mentioned range (particle size of 2.8 mm or more and 20 mm or less and 1.2 mm or more and less than 2.8 mm) are considered to be scale materials. However, other materials may have this particle size.

  On the other hand, steel by-products in the prior art consist of steelmaking dust and pickling sludge, which are mainly in the form of relatively fine powder of about 150 μm or less. However, sufficient briquette strength was not obtained, and the amount of powder generated exceeded 30% by weight.

  In the present invention, since relatively large particles as described above are contained in the steel byproduct, the briquette to be molded must allow this. Therefore, the shape of the briquette was defined as 40-60 mm × 40-60 mm × 25-40 mm on each side. In order for the steel roll to not stop at the large particles, a size of at least 40 x 40 x 25 mm is required. On the other hand, if it is too large, the briquette center will not be easily subjected to pressure during the steel making, and the strength Therefore, the upper limit size was set to 60 × 60 × 40 mm. In addition, for example, a twin roll type machine can be used for briquette production.

  The powder generated when the steel by-product briquette produced by the dumping machine falls onto the belt conveyor is sieved with a sieve installed in the middle of the belt conveyor, so that the powder to the briquette transfer box is removed. Carrying in can be reduced. If the size of the sieve mesh is larger than 30 mm, the briquette will fall together with the powder, so that the productivity is lowered. If the mesh size is less than 5 mm, the powder cannot be reduced to 20% by weight or less. It was specified as 5 to 30 mm. Preferably, it is 10-25 mm.

  When the belt speed of the belt conveyor is less than 30 m / min, the briquette transport efficiency is lowered, and as a result, the productivity is lowered. On the other hand, if it exceeds 60 m / min, the powder cannot be sieved with the above-mentioned sieve, and the briquette transport amount is too large. Since the body was generated and the powder could not be reduced to 20% by weight or less, it was set to 30 to 60 m / min. Preferably, it is 40-50 m / min.

  If the size of the briquette transfer box is longer than 1300 mm × 1300 mm × 900 mm in length × width × height, it becomes difficult to carry by a forklift. Moreover, when length x width x height is less than 1100 mm x 1100 mm x 700 mm, the conveyance efficiency is lowered, and as a result, productivity is lowered. For this reason, the size of the briquette transfer box is defined such that length × width × height is 1100 to 1300 mm × 1100 to 1300 mm × 700 to 900 mm. Preferably, length × width × height is 1150 to 1250 mm × 1150 to 1250 mm × 750 to 850 mm.

  Powder caused by repeated collisions due to concentration of the briquette drop position by loading the briquette sieved with powder while moving the belt conveyor back and forth periodically at a constant speed in the transport direction directly above the briquette transfer box The generation could be reduced to 20% by weight or less.

  If the installation height of the belt conveyor is less than 1000 mm, there is a risk of contact with the belt conveyor when the briquette transfer box is lifted and transported by a forklift. Since the body could not be reduced, it was defined as 1000 to 2000 mm. Preferably, it is 1200-1800 mm, More preferably, it is 1400-1600 mm.

  If the belt conveyor's movable range is less than 300 mm, the briquette drop position concentrates and powder cannot be reduced to 20% by weight or less, and if it is larger than 1000 mm, the briquette collides with the inner wall of the briquette transfer box. However, since it disintegrates, the powder cannot be reduced to 20% by weight or less. Therefore, the movable range is defined as 300 to 1000 mm. Preferably it is 500-800 mm, More preferably, it is 600-700 mm.

  If the speed of the reciprocating motion of the belt conveyor is less than 1 m / min, the briquette dropping position will be concentrated, so the powder cannot be reduced to 20% by weight or less, and if it exceeds 10 m / min, Since the briquette pops out and collides with the inner wall of the briquette transfer box and collapses, the powder cannot be reduced to 20% by weight or less. Therefore, the speed was defined as 1 to 10 m / min. Preferably, it is 3-7 m / min, more preferably 4-6 m / min.

  In this way, the briquette transfer box loaded with briquettes is transported by a forklift, and the process proceeds to the roasting process described below. As a specific briquette roasting process, the briquette molded as described above is inserted into the roasting box from the briquette transfer box, the upper part of the roasting box is sealed with a duct, and sucked using an exhaust fan. However, the lower part can be ignited with a burner, so-called roasting treatment can be performed, and moisture can be volatilized. As a result, the average moisture content of briquettes in the roasting box can be 6 wt% or less, and preferably the average moisture content of briquettes of 70 wt% or more in the roasting box can be 5 wt% or less. Specifically, the briquette strength after roasting could be 50 kgf / piece or more, and the time required for one electric furnace operation could be shortened within 4.5 hours. Thus, since the briquette after baking suppresses generation | occurrence | production of a powder and the moisture content can also be reduced, even in the reduction | restoration process by a submerged arc electric furnace, it can prevent blowing up favorably.

As a specific valuable metal recovery process, the roasted briquette is charged into a submerged arc electric furnace and heated to separate it into a metal part and a slag part, such as Fe, Ni, Cr, Mn, etc. Collect valuable metals. Moreover, at the time of charging to an electric furnace, limestone and / or quartz sand can be added as appropriate for the purpose of adjusting the amount of slag and basicity (CaO / SiO ₂ ), and depending on the composition of the raw material, carbonaceous materials can be added as appropriate. . In particular, on the slag side, a sufficient amount of slag can be ensured by using the reducing and recycling raw material having the above chemical components, and the meltability and fluidity can be controlled in a preferable region. Although the most desirable slag composition is not particularly limited, it contains CaO, SiO ₂ , Al ₂ O ₃ , MgO at 80% by mass or more, and the ratio of CaO / SiO ₂ is 0.8 to 1.4, preferably 1.0. 1.2, the content of _Al 2 _{O 3} is in the range of 0.6 to 7.0 wt%.

Hereinafter, the material composition suitably used for the roasting reduction method of the present invention will be described.
1. Steelmaking dust Steelmaking dust is generated in the refining process of stainless steel, and in order to secure the content of valuable metals Fe, Ni, Cr and Mn, and also in SiO ₂ , Al ₂ O ₃ and MgO concentrations in steel by-products In order to control the content within a suitable range, the blending ratio was defined as 10 to 50% by weight. Further, since the steelmaking dust contains a large amount of volatile ZnO, it is necessary to limit the mixing ratio of the steelmaking dust to 50% by weight or less in order to suppress the occurrence of blowing up.

2. Pickling sludge Pickling sludge is produced in an annealed pickling line, in order to ensure the content of valuable metals Fe, Ni, Cr and Mn, and also in a suitable range for CaO, F and S concentrations in steel by-products. Therefore, the blending ratio was specified to be 5 to 30% by weight. In addition, since the pickling sludge contains a large amount of S, if the S content is too high, desulfurization becomes difficult, so the mixing ratio of the pickling sludge must be limited to 30% by weight or less.

3. Scale material The scale material is produced by hot rolling, continuous casting or the like, and is a raw material containing valuable metals Fe, Ni, Cr and Mn. In addition, since the scale material is a raw material containing relatively large particles having a maximum particle diameter of 20 mm, most of the scale materials having a particle size of 2.8 mm or more and 20 mm or less as defined in the present invention are the scale material. The proportion of the particle size contained in the scale material is not limited, but is preferably 10 to 40% by weight. This particle size needs to be blended so as to occupy 3 to 40% by weight of the entire briquette. Therefore, in order to secure the contents of valuable metals Fe, Ni, Cr, and Mn, and to exhibit the effect as an aggregate, the blending ratio of the scale material is specified to be 30% by weight or more. On the other hand, if the blending ratio of the scale material exceeds 60% by weight, the particle size is too coarse to secure the strength. Therefore, the blending ratio of the scale material is set to 30 to 60% by weight.

4). SiC, ferronickel slag, and finish slag In order to control the slag composition in the electric furnace, the steel by-product in the present invention includes at least one of SiC, ferronickel slag, and finish slag in addition to the above material composition. A total of 10% by weight or less may be mixed. Specifically, SiC can be mixed as a SiO ₂ source in slag and as a heat source during combustion. Ferronickel slag is an effective material because it contains Fe, which is a valuable metal, and is mainly composed of MgO and SiO ₂ and can be mixed as a source of MgO or SiO ₂ . In addition, finishing slag is slag generated by refining AOD and VOD of stainless steel and special steel, and is mainly composed of CaO, SiO ₂ , MgO. For adjusting the basicity of slag in electric furnaces It is an effective material.

5. Moisture Moisture is necessary to ensure an initial briquette strength of 20 kgf / piece or more after molding and before roasting. The moisture content was set to 15 to 26% by weight because briquette strength could not be obtained if the moisture content was too low or too high. In addition, this content rate is a ratio with respect to the total weight of said solid raw material. For example, it is 150-260 kg with respect to the raw material 1t.

6). Oils and fats Oils and fats are necessary to secure an initial briquette strength of 20 kgf / piece or more after molding and before baking. Since the briquette strength cannot be obtained if the content of the oil and fat is too low or too high, the content is set to 0.2 to 3% by weight. In addition, this content rate is a ratio with respect to the total weight of said solid raw material. For example, it is 2-30 kg with respect to 1t of raw materials.

7). Charcoal material The carbon material in the present invention may be blended in an amount necessary for the reduction reaction and as a heat source in the roasting step in an amount of 10 to 20% by weight, that is, 100 to 200 kg relative to 1t of the blended raw material. preferable.

8). Chemical component In the present invention, by blending the material composition at the above ratio, the chemical component in the raw material is at least one of FeO, MnO, NiO, Cr ₂ O ₃ : 27% by mass or more in total, al ₂ O _3: 0.3~3.5 wt%, MgO: 2 to 7 wt%, CaO and SiO _2: 35 mass% in total less, F: 1 to 6 wt%, S: 0.1 to 2 Mass%, ZnO: 2 mass% or less can be obtained, whereby the slag obtained in the electric furnace can have characteristics suitable for operation. Below, the reason for limitation of each component is demonstrated.

  In addition, although each said structural component is described as an oxide except S and F, since it is complicated, such as a hydroxide, a fluoride, sulfide, and a sulfate, it is described as an oxide for convenience. . The valuable metals in the present invention are not particularly limited, but include at least iron, nickel, chromium, and manganese.

(1) FeO, MnO, NiO and Cr ₂ O ₃
In the present invention, these are essential components because they are reduced to valuable metals. If the total content of at least one of FeO, MnO, NiO, and Cr ₂ O ₃ is less than 27% by mass, the cost of smelting is not met, so FeO, MnO, NiO, and Cr ₂ O ₃ The content of at least one of them was set to 27% by mass or more. Considering the cost, it is preferably 29% by mass or more.

  Moreover, although an upper limit is not specifically limited, It is desirable to suppress to about 85 mass% or less. The reason is as follows. That is, when it exceeds 85 mass%, the amount of slag will decrease remarkably. If slag is not secured to some extent, temperature control becomes difficult during electric furnace operation, or the desulfurization reaction that occurs between slag and molten steel becomes insufficient, and the S concentration in the molten steel exceeds 0.05% by mass. It is to become. Since the obtained steel ingot is recycled as a raw material in the steelmaking process of stainless steel, if the S concentration is too high, the desulfurization load becomes high, resulting in high costs. For these reasons, it is desirable to keep the upper limit to about 85% by mass or less in order to ensure the amount of slag necessary for the desulfurization reaction in the electric furnace.

(2) Al ₂ O ₃
Al ₂ O ₃ is an element necessary for controlling the melting point of slag to an appropriate value. When the content of Al ₂ O ₃ is less than 0.3% by mass or more than 3.5% by mass, the melting point becomes high and the fluidity deteriorates, resulting in a decrease in valuable metal recovery rate. Therefore, the content rate of Al ₂ O ₃ is set to 0.3 to 3.5% by mass. Al ₂ O ₃ is a component contained in steelmaking dust, and can be controlled within this range by setting the mixing ratio of steelmaking dust to 10 to 50% by weight.

(3) MgO
MgO is an element necessary for controlling the melting point of slag to an appropriate value. When the content of MgO is less than 2% by mass or more than 7% by mass, the melting point becomes high and the fluidity is deteriorated, resulting in a decrease in valuable metal recovery rate. Therefore, the content of MgO is set to 2 to 7% by mass. MgO is a component contained in the steelmaking dust, and can be controlled within this range by setting the mixing ratio of the steelmaking dust to 10 to 50% by weight. Moreover, you may add with finishing slag and ferronickel slag as needed.

(4) CaO and SiO ₂
CaO and SiO ₂ are main components of slag, and are necessary for adjusting fluidity and melting point. These components can be adjusted with limestone and / or quartz sand before being introduced into the electric furnace. However, if the content of the original raw material is higher than 35% by mass, the amount of slag is increased without adding limestone and / or silica sand, and conversely, the amount of metal is reduced and the cost is increased. . Therefore, the CaO and SiO ₂ content is set to 35% by mass or less. Preferably, the total content of CaO and SiO ₂ is 7.5 to 35% by mass. It is desirable to contain 7.5% by mass in order to reduce the cost of auxiliary materials for limestone and silica sand. More preferably, the CaO content is 3 to 15% by mass, and the SiO ₂ content is 4.5 to 20% by mass. CaO is a component mainly contained in pickling sludge, and the above component range can be obtained when the blending ratio of the pickling sludge is 5 to 30% by weight. SiO ₂ is mainly contained in the steelmaking dust, and can be controlled within this range by setting the mixing ratio of the steelmaking dust to 10 to 50% by weight. Moreover, you may adjust by adding ferronickel slag as needed.

(5) F
F is a component necessary for controlling the fluidity of the slag within an appropriate range. When the F content is less than 1% by mass, the fluidity is poor, and as a result, the valuable metal recovery rate is lowered. On the other hand, if it exceeds 6% by mass, the fluidity is too good, and corrosive gases such as HF and SiF ₄ are generated to corrode and damage the equipment. Therefore, the F content is defined as 1 to 6% by mass. F is a component contained in the pickling sludge. When the mixing ratio of the pickled sludge is 5 to 30% by weight, the above component range can be obtained.

(6) S
S is a component necessary for lowering the surface tension of molten steel and ensuring fluidity in an electric furnace. If the fluidity is not sufficient, the coke bed will not pass well. In the electric furnace, a part of S is desulfurized and distributed in the slag. It is preferable to finally control in the range of 0.01 to 0.05 mass% in molten steel through such a desulfurization reaction. If the S concentration is too high, the desulfurization load becomes high, resulting in high costs. Therefore, in consideration of the desulfurization reaction, in order to ensure this range in the molten steel of the electric furnace, it is necessary to control the S content in the reduced recycled material to 0.1 to 2% by mass. Determined. S is a component contained in the pickling sludge, and when the blending ratio of the pickled sludge is 5 to 30% by weight, the above component range can be obtained.

(7) ZnO
When ZnO is reduced by C, zinc gas is generated, which raises the atmospheric pressure in the raw material and causes a bumping phenomenon, which is a component that must be suppressed. When the ZnO content is higher than 2% by mass, the tendency appears strongly and causes a blowing-up phenomenon in the electric furnace. Therefore, the ZnO content is defined as 2% by mass or less. ZnO is a component contained in steelmaking dust, and can be suppressed to this range by limiting the mixing ratio of steelmaking dust to 50% by weight or less.

Next, the effect of this invention is demonstrated using the Example of this invention.
Steelmaking dust, pickling sludge, scale material, and SiC were blended at the ratio of the material composition shown in Table 1, and carbon materials, moisture, and fats and oils were mixed. A is the most preferred blending pattern, B is less dust and more scale, C is more dust and less sludge. The moisture and oil are externally mixed, and the mixing ratio is based on the weight of the mixed raw material as 100. Subsequently, it was molded into briquettes using a twin roll type machine. In addition, the carbon material was mix | blended with the weight of 100-200 kg with respect to the mix | blended raw material 1t as a part required for a reductive reaction, and a heat source in a roasting process.

  Next, the briquette molded as described above and sieved with powder using a sieve installed in the middle of the belt conveyor is loaded into the briquette transfer box while the belt conveyor is periodically moved back and forth at a constant speed in the transport direction. Then, the roasting box was charged from the briquette transfer box. And the upper part of the roasting box was sealed with a duct, and the lower part was heated with a burner for 20 to 30 minutes while being ignited while being sucked using a wind exhauster, and the roasting process was performed for 120 to 180 minutes. Thereby, while volatilizing a water | moisture content, the raw material particle | grains inside each briquette were sintered. The size of the briquette transfer box was set to 1200 mm × 1200 mm × 800 mm due to restrictions on equipment.

Thereafter, 50 kg of limestone / t raw material and 60 kg of coke as raw material / t raw material t are mixed with the above briquette raw materials to adjust the slag amount and basicity (CaO / SiO ₂ ), and these are installed in a submerged arc electric furnace. I entered. And this was heated and isolate | separated into the reduced metal part and the slag part, and valuable metals, such as Fe, Ni, Cr, and Mn, were collect | recovered. The recovered metal was approximately 5 to 6 t, and the remainder was slag. In addition, the size of the electric furnace was 13 t, and the power consumption was about 1800 kWh / metal t.

  The particle size distribution of the raw material and the strength of the molded briquette when the method of roasting and reducing steel by-products as described above were measured as follows, and the results are shown in Table 2. That is, the particle size distribution of the raw material was measured by weighing about 20 kg of the mixed raw material, sieving with a sieve, and classifying into each particle size. The strength of the molded briquette was measured for crushing strength after curing for 2 days. For the amount of powder in the roasting box, the roasting box was randomly extracted and separated into briquettes and a powder part of 1 mm or less, and the weight of the powder was measured.

  As apparent from Table 2, in the most preferable blending pattern A, since the material composition, briquette shape and steel by-product particle size are all within the blending range of the present invention, the briquette strength is 20 kgf / piece or more. Had strength. On the other hand, B and C were less than 20 kgf / piece.

  The briquettes produced by blending the raw materials of the blending patterns A, B, and C were processed and roasted under various sieve sizes, belt speeds, and bellcon installation conditions. Finally, electric smelting was performed in an electric furnace to obtain metal. The results are shown in Table 3.

  Here, the evaluation of each condition is performed by the amount of powder in the roasting box, the temperature distribution in the roasting box and the moisture content of the roasted briquette, the blowing situation, the productivity, and the overall evaluation is ◎, ○, △, ×. In addition, ◎ and ○ were good operations without problems.

Each item was measured as follows.
(1) Temperature distribution: Measured with a thermocouple at the box upper center position and the lower center position.
(2) Moisture content of the roasted briquette: After the roasting, 10 random briquettes were taken from the box, and each sample was heated at 900 ° C. for 3 hours or more, and the weight became a constant value. After confirmation, it was determined from the weight loss.
(3) Blowing up: ○ indicates that there was no blowing up inside or outside the factory, and Δ indicates that there was blowing up to the extent that no smoke was generated outside the factory.
(4) Productivity: Evaluated based on the time required for electric smelting with an electric furnace. ○ is 4.5 hours / charge or less, Δ is more than 4.5 hours and 5 hours / charge or less, and × is 5 hours / charge or more.
(5) Comprehensive evaluation: Comprehensive evaluation was performed by blowing up and productivity. ◎ is both ◯, ○ is ◯ and △, △ is both △, and x is X on one side.

  As is apparent from Table 3, in Invention Examples 1 to 3, in addition to sufficient briquette strength, the sieve size of the sieve installed in the middle of the belt conveyor, the size of the briquette transfer box, and the briquette transfer box Since the installation height, movable range, and speed of the belt conveyor during charging were all within the preferred range, the amount of powder generated was small and uniform roasting was possible. In addition, there was no blowing up due to the operation of the electric furnace, and the operation time was within 4.5 hours, improving productivity. Inventive Example 3 is more powdery than Inventive Examples 1 and 2 because the mesh size and the movable range of the belt conveyor at the time of charging the box for briquette transfer are out of the preferred range of the present invention. Although the amount of body generation was slightly large, it did not lead to blowing up, and the productivity did not change. The reason why the productivity is improved by reducing the amount of powder in addition to the prevention of blowing up is that the ventilation of CO gas between briquettes is improved, and the metal reducibility is improved.

  Inventive Examples 4 to 7 have B and C in Table 1 as the blending patterns of the raw materials, and were not the most preferred blending, so the amount of powder in the roasting box was slightly larger, and the water content after roasting was 6 to 8%. A slightly high value was shown. As a result, a slight blow-up occurred in Invention Example 4, and productivity slightly decreased in 5-7.

  In Comparative Examples 1 to 7, since any one of the blending pattern, sieve size, belt speed, and Belcon condition was deviated, the amount of generated powder was large, and the burning unevenness in the roasting box was also large. As a result, during electric smelting in an electric furnace, blowing-up occurred or productivity was lowered.

  Metals can be efficiently recovered from steel by-products and recycled as high-quality raw materials such as stainless steel and special steel, and the amount of industrial waste can be reduced.

It is the figure which demonstrated blowing up typically. It is the figure which showed the roasting state of the briquette in a roasting box. It is the figure which demonstrated typically from a making machine to the box for briquette transfer. It is the figure which demonstrated typically the insertion to the box for briquette transfer by a belt conveyor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Submerged arc electric furnace, 2 ... Raw material briquette for reduction | restoration recycling, 3 ... Electrode,
4 ... Slag, 5 ... Reduced metal, 6 ... Hole, 7 ... Shelves, 11 ... Unroasted briquette,
12 ... roasting box, 13 ... burner, 14 ... exhaust air, 15 ... ventilation in the box,
16 ... roasting briquette, 17 ... clinker, 21 ... briquette, 22 ... group making machine, 23 ... belt conveyor, 24 ... briquette transfer box, 25 ... sieve, 26 ... movable belt conveyor, 31 ... briquette, 32 ... belt Conveyor, 33 ... Briquette transfer box, 34 ... Movable belt conveyor

Claims (3)

Steelmaking dust: 10 to 50% by weight, pickling sludge: 5 to 30% by weight, scale material: a step of mixing water, oil and fat, and carbon material with steel by-products consisting of 30 to 60% by weight;
A step of bridging the mixed steel by-product into briquettes with a briquetting machine;
When the briquette is transported by a belt conveyor, the powder generated when the briquette is dropped on the belt conveyor is the powder with a sieve having a sieve mesh of 5 to 30 mm installed in the middle of the belt conveyor. Sieving step;
With the movable belt conveyor, the briquette is transported at a belt speed of 30 to 60 m / min, and the movable range of the belt conveyor is 300 to 1000 mm in the transport direction at an installation height of 1000 to 2000 mm directly above the briquette transfer box. The step of charging the briquette into the briquette transfer box while mitigating powder generation due to the impact of repeated dropping of the briquette while periodically moving back and forth at a constant speed of 1 to 10 m / min;
Charging the briquette from the briquette transfer box into a roasting box and roasting in the roasting box;
A step of further mixing carbonaceous material and limestone and / or silica sand to the briquettes after roasting for adjusting the amount of slag and basicity;
A mixture consisting of the briquette, the carbon material and limestone and / or silica sand is charged into a submerged arc electric furnace and heated to reduce valuable metals such as Fe, Ni, Cr, and Mn, and a metal component and slag. And a step of separating in minutes,
The steel by-product has a particle size of 3 to 40% by weight of 2.8 mm to 20 mm, and the briquette has a shape of 40 to 60 mm × 40 to 60 mm × 25 to 40 mm on each side. Roasting reduction method of steel by-product.   2. The method of roasting and reducing steel by-products according to claim 1, wherein the briquette transfer box is made of steel having a length of 1100 to 1300 mm, a width of 1100 to 1300 mm, and a height of 700 to 900 mm. . The formation amount of 1mm or less powder in roasting box is 20 wt% or less, according to claim 1 or 2 the moisture content of the briquette after roasting characterized in that the average 6 wt% or less Roasting reduction method of steel by-products.

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