Processing method of cold rolling sludge

Abstract

To provide a novel cold rolling sludge processing method capable of removing chlorine and oil components contained in a cold rolling sludge.SOLUTION: A cold rolling sludge is heated and dried to obtain dried sludge. When the temperature during heating and drying of the cold-rolled sludge is less than 600°C and the chlorine concentration of the dried sludge exceeds 0.1 mass%, the dried sludge is crushed to obtain crushed sludge, the crushed sludge is washed with water to obtain a slurry, and the slurry is dewatered to obtain a dewatered cake.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating cold rolling sludge. [Background technology]

[0002] In the blast furnace process, sintered ore and coke are charged into a blast furnace to produce pig iron. The pig iron is then refined in a converter and poured into a mold to produce billets. The billets are then rolled, including hot rolling and cold rolling, to produce various steel products.

[0003] In cold rolling, for example, an acid such as hydrochloric acid is used to remove scale (iron oxide) formed on the surface of the steel material, resulting in the generation of wastewater (hereinafter also referred to as "cold rolling wastewater"). In addition to scale, cold rolling wastewater also contains oils derived from rolling oils, iron powder generated by friction of the steel material, and the like.

[0004] Cold rolling wastewater is usually neutralized at a steel mill wastewater treatment plant, and then subjected to sedimentation, filtration, etc., to separate it into solids and liquids (supernatant) (solid-liquid separation). The supernatant water is generally reused within the steelworks after suspended solids and oil are removed using a flocculant or oil remover. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-199018 [Patent Document 2] Japanese Patent Application Publication No. 2016-141832 Summary of the Invention [Problem to be solved by the invention]

[0006] The solid matter separated from cold rolling wastewater (hereinafter also referred to as "cold rolling sludge") also contains iron, so there is a need to reuse it as a raw material for steelmaking. However, in addition to iron, cold rolling sludge contains chlorine derived from the hydrochloric acid used in removing the scale, and oil derived from rolling oil and the like. Chlorine is avoided because it causes corrosion in blast furnace equipment, and oil is also avoided because it causes smoldering in sintering machines. In other words, cold rolling sludge cannot be reused as it is as a raw material for steelmaking.

[0007] Incidentally, a method for removing chlorine contained in sludge (Patent Document 1) and a method for removing oil contained in sludge (Patent Document 2) have been proposed.

[0008] More specifically, the method described in Patent Document 1 is a method in which an alkaline agent such as sodium hydroxide is added to sludge together with water. However, alkali metals such as sodium are elements that form deposits in the blast furnace and deteriorate the gas permeability, and therefore, like chlorine, are avoided. Therefore, even if chlorine can be removed by this method, the waste cannot be reused as a raw material for iron making unless alkali metals such as sodium are also removed. Furthermore, in this method, some of the oil contained in the sludge is transferred to the alkaline agent, which requires the installation of additional equipment to treat the alkaline agent, which is cumbersome.

[0009] The method described in Patent Document 2 involves adding an auxiliary agent such as converter dust to sludge and then carrying out a heat treatment. However, this method is still complicated because it requires that the sludge and the auxiliary agent be thoroughly mixed before the heat treatment and that the moisture content of the auxiliary agent be reduced as much as possible.

[0010] The present invention has been made in view of the above points, and an object of the present invention is to provide a novel method for treating cold rolling sludge that can remove chlorine and oil contained in cold rolling sludge. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [6]. [1] A method for treating cold-rolled sludge, comprising heating and drying cold-rolled sludge to obtain dried sludge, and, if the temperature during heating and drying of the cold-rolled sludge is less than 600°C and the chlorine concentration of the dried sludge exceeds 0.1% by mass, crushing the dried sludge to obtain crushed sludge, washing the crushed sludge with water to obtain a slurry, and dewatering the slurry to obtain a dehydrated cake. [2] The method for treating cold-rolled sludge according to [1] above, wherein the atmosphere in which the cold-rolled sludge is heated and dried is air or an oxidizing atmosphere, and the temperature in which the cold-rolled sludge is heated and dried is 300°C or higher and 1500°C or lower. [3] The method for treating cold rolling sludge according to [1] or [2] above, wherein the concentration of the slurry is 5% by mass or more and 40% by mass or less. [4] A method for treating cold rolling sludge according to any one of [1] to [3] above, wherein the water used to wash the crushed sludge is a dewatered filtrate of a steelmaking dust slurry or wastewater from a slag yard. [5] The method for treating cold rolling sludge according to any one of [1] to [4] above, wherein the water content of the dehydrated cake is 30% by mass or less. [6] The method for treating cold rolling sludge according to any one of [1] to [5] above, wherein the dewatered cake is charged into a sintering machine, a rotary hearth furnace, or a rotary kiln, thereby reusing the cold rolling sludge as a raw material for ironmaking. [Effects of the Invention]

[0012] According to the present invention, a novel method for treating cold rolling sludge can be provided, which can remove chlorine and oil contained in cold rolling sludge. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a flowchart showing the flow of a method for treating cold rolling sludge. [Figure 2A] 1 is a graph showing the relationship between heating temperature and oil concentration of dried sludge. [Figure 2B] 1 is a graph showing the relationship between heating temperature and chlorine concentration of dried sludge. [Figure 3] 1 is a graph showing the oil concentration and chlorine concentration before and after heat drying. [Figure 4] 1 is a graph showing the relationship between the concentration of a slurry and the chlorine concentration of a dewatered cake obtained from the slurry. [Figure 5] 1 is a graph showing the relationship between the type of water used for washing and the chlorine concentration and oil concentration of the dehydrated cake. [Figure 6] 1 is a graph showing the relationship between the number of repetitions of water washing and dehydration and the chlorine concentration of the dehydrated cake. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Method for treating cold rolling sludge] The method for treating cold rolling sludge according to this embodiment will be described with reference to FIGS. FIG. 1 is a flowchart showing the flow of a method for treating cold rolling sludge. In summary, first, the cold-rolled sludge is heated and dried to obtain dried sludge. If the temperature during heating and drying of the cold-rolled sludge is less than 600°C and the chlorine concentration of the dried sludge is greater than 0.1% by mass, the dried sludge is crushed to obtain crushed sludge. Next, the crushed sludge is washed with water to obtain a slurry. After that, the slurry is dewatered to obtain a dewatered cake. The method for treating cold rolling sludge will now be described in more detail.

[0015] <Cold rolling sludge> In cold rolling, steel that has been hot-rolled (so-called hot-rolled coil) is rolled thinner at room temperature. During this process, acids such as hydrochloric acid are used to wash off the scale (iron oxide) that formed on the surface of the steel during hot rolling, resulting in the generation of wastewater (cold-rolling wastewater). Cold rolling wastewater contains scale that has peeled off the surface of steel; oils such as rolling oil (lubricant) used in the rolling rolls; and iron powder generated by friction between the rolling rolls and the steel. The cold rolling wastewater may also contain wastewater generated when cooling or cleaning equipment other than the rolling rolls used in cold rolling.

[0016] Cold rolling sludge is obtained from such cold rolling wastewater. The method for obtaining cold rolling sludge from cold rolling wastewater is not particularly limited. For example, cold rolling sludge can be obtained as a solid content by performing solid-liquid separation of the cold rolling wastewater using an appropriate combination of various processes such as coagulation, precipitation, membrane separation, filtration, flotation, and centrifugation. Cold rolling sludge contains iron, as well as chlorine derived from the hydrochloric acid used in removing the scale, and oil derived from rolling oil and the like.

[0017] <Heat drying> First, the cold rolling sludge is heated and dried to remove oil contained therein, thereby obtaining a dried cold rolling sludge (dried sludge).

[0018] For the heating and drying of the cold rolling sludge, general heating equipment such as a rotary kiln, a drying furnace, a batch heating furnace, etc. can be used. From the viewpoint of uniformly heating the entire cold rolling sludge, it is preferable to use a rotary kiln or the like that can heat the object while stirring it.

[0019] As will be described later, cold rolling sludge (dewatered cake) is reused as a raw material for iron making by being charged into a sintering machine, a rotary hearth furnace, or a rotary kiln.

[0020] A sintering machine is a facility that produces sintered ore by burning powdered iron ore together with limestone. A rotary hearth furnace is a type of equipment used to produce reduced iron, and includes a rotating hearth that rotates inside a ring-shaped furnace body. Similar to a rotary hearth furnace, a rotary kiln is also used to produce reduced iron.

[0021] Sintering machines, rotary hearth furnaces, and rotary kilns (hereinafter collectively referred to as "steel manufacturing facilities") each have an upper limit set for the amount of oil in the raw materials charged therein. For this reason, the oil content of cold rolling sludge reused as a steelmaking raw material (if used in combination with other steelmaking raw materials, the total oil content of the other steelmaking raw materials used in combination) must be less than the upper limit of the oil content of the steelmaking equipment to which it is charged. Specifically, the oil concentration of cold rolling sludge depends on the blending ratio (ratio of cold rolling sludge to other steelmaking raw materials), but can be considered to be approximately 0.5 mass % or less as a guideline. The oil concentration is measured using a Soxhlet extractor (the same applies hereinafter).

[0022] If the temperature (heating temperature) when the cold-rolled sludge is heated and dried is too low, the oil content may not be sufficiently removed, and the above-mentioned target may not be achieved. Therefore, the heating temperature is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher. On the other hand, from the viewpoint of avoiding melting of iron (melting point of iron: 1537°C) in the cold rolling sludge, the heating temperature is preferably 1500°C or lower, more preferably 1200°C or lower, and even more preferably 900°C or lower. The heating temperature may be less than 600° C., as will be described later.

[0023] The atmosphere (heating atmosphere) in which the cold rolling sludge is heated and dried is preferably an air atmosphere or an oxidizing atmosphere from the viewpoint of promoting the combustion of carbon contained in the oil.

[0024] The time for heating and drying the cold-rolling sludge (heating time) varies depending on the type of heating equipment used and the amount of cold-rolling sludge to be heated and dried, and is therefore difficult to determine uniquely. For this reason, the heating time is preferably determined experimentally within a range of, for example, 30 minutes to 300 minutes, and may be 60 minutes to 180 minutes.

[0025] Incidentally, when the heating temperature is 600°C or higher, the chlorine in the cold rolling sludge is also removed by evaporation, and the target value (chlorine concentration: 0.1 mass% or less) described below is achieved, so there is no need to carry out the crushing, water washing, and dehydration described below.

[0026] On the other hand, if the heating temperature is less than 600°C, the chlorine may not be sufficiently volatilized and removed, and the target may not be achieved. Therefore, if the heating temperature is less than 600°C, the chlorine concentration of the dried sludge obtained by heating and drying is measured. If the chlorine concentration of the dried sludge exceeds 0.1% by mass, the following crushing, washing with water, and dewatering are carried out. The chlorine concentration is measured using an absorption photometer (the same applies hereinafter).

[0027] <Disintegration> In many cases, dried sludge is formed into large clumps due to aggregation or solidification of particles. If the dried sludge is washed in this state with water, as described below, the water may not penetrate sufficiently deep into the clumps of dried sludge, resulting in insufficient washing. Therefore, before washing the dried sludge with water, the dried sludge is crushed to obtain crushed material (crushed sludge). Crushed sludge has a smaller particle size than dried sludge, so water can easily penetrate deep into the crushed sludge.

[0028] The equipment used for crushing is not particularly limited, and for example, a compression type crusher such as a jaw crusher; an impact type crusher such as an impact crusher; etc. can be used. The particle size of the crushed sludge is preferably 10 mm or less, more preferably 1 mm or less, since if it is too large, the efficiency of washing with water decreases. On the other hand, if the particle size of the crushed sludge is too small, the energy required for crushing increases, resulting in higher costs, so the particle size is preferably 0.01 mm or more, more preferably 0.1 mm or more. The particle size of the crushed sludge is measured using a JIS test sieve or a laser diffraction particle size distribution measuring device.

[0029] <Washing> Next, the disintegrated sludge is washed with water to remove chlorine from the disintegrated sludge. An example of a method for washing with water is a method in which a mixture of water and disintegrated sludge is stirred in a treatment tank using a stirrer, etc. This allows the water and the disintegrated sludge to come into uniform contact with each other, and a slurry in which the disintegrated sludge from which chlorine has been removed is suspended in water is obtained.

[0030] Incidentally, as will be described later, cold rolling sludge (dewatered cake) is reused by being charged into steel making equipment such as a sintering machine as a raw material for steel making. In steelmaking facilities such as sintering machines, an upper limit is set for the amount of chlorine in the raw materials charged, similar to the amount of oil. For this reason, the chlorine content of cold rolling sludge reused as a steelmaking raw material (when used in combination with other steelmaking raw materials, the total chlorine content of the other steelmaking raw materials used in combination) must be less than the upper limit of the chlorine content of the steelmaking equipment to which it is charged. Specifically, the chlorine concentration of cold rolling sludge depends on the blending ratio (ratio of cold rolling sludge to other steelmaking raw materials), but can be considered to be approximately 0.1 mass % or less as a guideline.

[0031] If the concentration of the slurry (the content of disintegrated sludge in the slurry) is too high, the amount of water relative to the disintegrated sludge will be small, and the washing effect when obtaining the slurry may be insufficient. Therefore, the concentration of the slurry is preferably 40% by mass or less, and may be 30% by mass or less, or may be 20% by mass or less. On the other hand, if the slurry concentration is too low, there is too much water relative to the crushed sludge. To obtain such a slurry, a large treatment tank or the like must be used, which can increase equipment costs. For this reason, the slurry concentration is preferably 5% by mass or more, and may be 8% by mass or more, or 10% by mass or more.

[0032] The water washing time (the time for stirring the mixture of water and disintegrated sludge) is preferably determined experimentally within the range of, for example, 30 minutes to 180 minutes, taking into consideration the chlorine concentration of the final dehydrated cake.

[0033] The temperature of the water used for washing may be room temperature, but from the viewpoint of increasing the washing efficiency, it is preferably 50°C or higher.

[0034] Although general industrial water can be used as the water used for washing, it is preferable to use dehydrated filtrate (filtrate obtained by dehydrating sludge, etc.) or wastewater generated within the steelworks from the viewpoint of saving water resources. In particular, alkaline water is useful from the viewpoint of the efficiency of washing away chlorine and oil, and therefore, for example, dewatered filtrate of steelmaking dust slurry or wastewater from a slag yard is preferably used.

[0035] <dehydration> Next, the slurry obtained by washing the crushed sludge with water is dehydrated to obtain a dehydrated cake. More specifically, the water content of the slurry is reduced by mechanically removing the water from the slurry, and a dehydrated cake is obtained as a residue.

[0036] In the slurry, the chlorine removed from the disintegrated sludge is transferred to the water, and by removing this water, the chlorine is also removed from the resulting dehydrated cake.

[0037] The method for dehydrating the slurry is not particularly limited, and for example, a filter press that squeezes out the water in the slurry by compression; a centrifugal dehydrator that dehydrates the slurry by centrifugal force (separates the slurry into solids and water and discharges the water); etc. can be used.

[0038] If the moisture content of the dehydrated cake is too high, it will adhere to the bucket of the vehicle used for transportation, which will likely result in a decrease in yield. On the other hand, if the moisture content of the dehydrated cake is too low, fine powder will likely fly around during transportation by vehicle. Therefore, the moisture content of the dehydrated cake depends on the blending ratio with other ironmaking raw materials, but assuming that it will be transported and used alone as an ironmaking raw material, it is preferably 30 mass% or less, more preferably 28 mass% or less, and even more preferably 25 mass% or less. The moisture content of the dehydrated cake is preferably 10% by mass or more, more preferably 12% by mass or more, and even more preferably 15% by mass or more.

[0039] The chlorine concentration of the obtained dehydrated cake is measured. The chlorine concentration of the dehydrated cake is a value when the dehydrated cake is converted into a dry matter, that is, the chlorine concentration when the moisture content of the dehydrated cake is set to zero (the same applies hereinafter). If the chlorine concentration of the dehydrated cake exceeds 0.1% by mass, for example, the dehydrated cake is washed with water and dehydrated again as shown in FIG. 1 to obtain a dehydrated cake. The dehydrated cake may be crushed before being washed with water. This cycle is repeated once or twice or more times to finally obtain a dehydrated cake having a chlorine concentration of 0.1% by mass or less. The number of repetitions is preferably three or less.

[0040] As described above, according to this embodiment, cold rolling sludge (dehydrated cake) from which chlorine and oil have been removed can be easily obtained. The obtained cold rolling sludge (dewatered cake) is reused as a raw material for iron making by being charged into, for example, a sintering machine, a rotary hearth furnace, or a rotary kiln. [Example]

[0041] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0042] Example 1 Cold rolling sludge separated from wastewater (cold rolling wastewater) generated in a cold rolling line was heated and dried in an air atmosphere for 60 minutes using a batch heating furnace to obtain dried sludge. The heating temperature was varied between 200 and 1000°C, and a portion of the resulting dried sludge was sampled to measure the oil concentration (unit: mass%) and chlorine concentration (unit: mass%). The results are shown in the graphs in Figures 2A and 2B.

[0043] FIG. 2A is a graph showing the relationship between heating temperature and oil concentration of dried sludge. FIG. 2B is a graph showing the relationship between heating temperature and chlorine concentration of dried sludge. In each graph, the oil concentration and chlorine concentration of the cold rolling sludge before heating and drying are shown by dotted lines. As shown in FIGS. 2A and 2B, when the heating temperature was 600° C. or higher, the oil concentration and the chlorine concentration were both reduced to approximately 0.1 mass % or less. Therefore, if there is heating equipment capable of heating and drying at 600°C or higher, the process can be completed by heating and drying alone.

[0044] Example 2 Cold rolling sludge separated from cold rolling wastewater generated in a cold rolling line different from that in Example 1 was heated and dried at 400°C to obtain dried sludge (other conditions were the same as in Example 1). A portion of the obtained dried sludge was sampled, and the oil concentration (unit: mass%) and chlorine concentration (unit: mass%) were measured. The results are shown in the graph in Figure 3. FIG. 3 is a graph showing the oil concentration and chlorine concentration before and after heat drying. 3, the chlorine concentration before heating and drying (cold-rolled sludge) was lower than that in Example 1, and therefore the chlorine concentration after heating (dried sludge) was 0.1 mass% or less. Therefore, although the heating temperature was less than 600°C, the treatment was terminated.

[0045] Example 3 The cold-rolled sludge was dried in an air atmosphere at 400°C for 60 minutes using a batch-type heating furnace to obtain dried sludge. A portion of the obtained dried sludge was sampled and the chlorine concentration was measured, which was found to be more than 0.1% by mass. Therefore, the dried sludge was crushed using a crusher to obtain crushed sludge with a particle size of 1 mm or less. The crushed sludge was then washed with industrial water at 50°C (washing time: 60 minutes) to obtain a slurry. Slurries with concentrations of 3 to 50 mass% were prepared. The prepared slurry was dehydrated, and the chlorine concentration of the obtained dehydrated cake (value when the dehydrated cake was converted into a dry matter) was determined. The results are shown in the graph in Figure 4. Figure 4 is a graph showing the relationship between the concentration of a slurry and the chlorine concentration of a dewatered cake obtained from the slurry. In Figure 4, the chlorine concentration before washing (i.e., the dried sludge) is shown by a dotted line. As shown in FIG. 4, regardless of the concentration of the slurry, the chlorine concentration was reduced compared to before washing (dried sludge). It was found that when the slurry concentration is 5% by mass or less, the chlorine concentration remains almost unchanged even if the slurry concentration is further reduced. As mentioned above, when obtaining a slurry with a low concentration, the amount of water used increases, the treatment tank becomes larger, and costs may increase. For this reason, a slurry concentration of 5% by mass or more is preferable. On the other hand, when the slurry concentration exceeds 40% by mass, the efficiency of water washing decreases, and when the slurry concentration is 50% by mass, the chlorine concentration decreases by only about 0.04% by mass compared to the sludge before water washing (dried sludge). This is thought to be because the increased slurry concentration increases the viscosity of the slurry, preventing sufficient contact between the water and the solids (crushed sludge). For this reason, a slurry concentration of 40% by mass or less is preferable.

[0046] Example 4 The cold-rolled sludge was dried in an air atmosphere at 400°C for 60 minutes using a batch-type heating furnace to obtain dried sludge. A portion of the obtained dried sludge was sampled and the chlorine concentration was measured, which was found to be more than 0.1% by mass. Therefore, the dried sludge was crushed using a crusher to obtain crushed sludge with a particle size of 1 mm or less. The crushed sludge was then washed with industrial water at 50°C or a dehydrated filtrate of a steelmaking dust slurry (hereinafter simply referred to as "dehydrated filtrate") (washing time: 60 minutes) to prepare a slurry with a concentration of 10% by mass. The prepared slurry was dehydrated, and the chlorine concentration and oil concentration of the obtained dehydrated cake (both values ​​were calculated by converting the dehydrated cake into a dry matter) were determined. The results are shown in the graph in Figure 5. Fig. 5 is a graph showing the relationship between the type of water used for washing and the chlorine concentration and oil concentration of the dehydrated cake. In Fig. 5, the chlorine concentration and oil concentration before washing (i.e., the dried sludge) are shown by dotted lines. As shown in Figure 5, when the dehydration filtrate was used, both the chlorine concentration and the oil concentration were reduced more than when industrial water was used. In particular, the oil concentration was reduced by about 40% by mass when the dehydration filtrate was used compared to when industrial water was used.

[0047] Example 5 The cold-rolled sludge was dried in an air atmosphere at 400°C for 60 minutes using a batch-type heating furnace to obtain dried sludge. A portion of the obtained dried sludge was sampled and the chlorine concentration was measured, which was found to be more than 0.1% by mass. Therefore, the dried sludge was crushed using a crusher to obtain crushed sludge with a particle size of 1 mm or less. The crushed sludge was then washed with industrial water at 50°C (washing time: 60 minutes) to prepare Slurry 1 with a concentration of 10 mass%. The prepared Slurry 1 was dehydrated to obtain Dehydrated Cake 1 (first run). Dehydrated cake 1 was washed with water in the same manner as in the first run to prepare a slurry 2 with a concentration of 10 mass %. The prepared slurry 2 was dehydrated to obtain a dehydrated cake 2 (second run). Dehydrated cake 2 was washed with water in the same manner as in the first and second times to prepare a slurry 3 with a concentration of 10 mass %. The prepared slurry 3 was dehydrated to obtain a dehydrated cake 3 (third time). Dehydrated cake 3 was washed with water in the same manner as in the first to third times to prepare slurry 4 with a concentration of 10 mass %. The prepared slurry 4 was dehydrated to obtain dehydrated cake 4 (fourth time). The chlorine concentration (value when the dehydrated cake was converted into a dry matter) was determined for each of the dehydrated cakes 1 to 4. The results are shown in the graph of FIG. FIG. 6 is a graph showing the relationship between the number of repetitions of water washing and dehydration and the chlorine concentration of the dehydrated cake. As shown in FIG. 6, it can be seen that the chlorine concentration decreased as the number of repetitions increased. After three repetitions, the chlorine concentration decreased to 0.008% by mass. However, after four repetitions, the chlorine concentration remained almost the same as after three repetitions. Therefore, the preferred number of repetitions is between one and three.

Claims

1. The cold rolling sludge is heated and dried to obtain dried sludge; When the temperature when heating and drying the cold-rolled sludge is less than 600 ° C. and the chlorine concentration of the dried sludge is more than 0.1 mass%, the dried sludge is crushed to obtain crushed sludge, The disintegrated sludge is washed with water to obtain a slurry, The method for treating cold rolling sludge comprises dewatering the slurry to obtain a dewatered cake.

2. The atmosphere when heating and drying the cold rolling sludge is air or an oxidizing atmosphere, 2. The method for treating cold rolling sludge according to claim 1, wherein the temperature when heating and drying the cold rolling sludge is 300°C or higher and 1500°C or lower.

3. 3. The method for treating cold rolling sludge according to claim 1, wherein the concentration of the slurry is 5% by mass or more and 40% by mass or less.

4. 3. The method for treating cold rolling sludge according to claim 1, wherein the water used for washing the crushed sludge is a dewatered filtrate of a steelmaking dust slurry or wastewater from a slag yard.

5. 3. The method for treating cold rolling sludge according to claim 1, wherein the moisture content of the dehydrated cake is 30% by mass or less.

6. 3. The method for treating cold rolling sludge according to claim 1, wherein the dewatered cake is charged into a sintering machine, a rotary hearth furnace, or a rotary kiln, thereby reusing the cold rolling sludge as a raw material for iron making.

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