Rare Metal-Containing Cake Drying Method

Abstract

To provide a method of continuously treating metal sludge, capable of very efficiently drying metal sludge of a high water-content to a water content of 5 weight% or less, by carrying out a two-stage continuous treatment using a filter press and a rotary dryer.SOLUTION: The method of continuously treating metal sludge according to the present invention, comprises a step of subjecting metal sludge including rare metal to a filter-press treatment to reduce its water content to 50 weight% or less, and a subsequent step of feeding the rare metal containing cake obtained by the filter-press treatment to a rotary dryer, to apply a heat treatment to the rare metal containing cake in an atmosphere of a temperature in the rotary dryer of from 120 to 200°C for a total heating time from 40 to 70 minutes to reduce its water content to 5 weight% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for drying rare metal-containing cakes, and particularly to a method for drying rare metal-containing cakes using a rotary dryer.

Background Art

[0002] Metal sludge is generally generated in the grinding process. Since it is ground together with pure water at that time, it often contains a large amount of moisture. If such sludge containing a large amount of moisture is directly charged into the blast furnace, a steam explosion will occur in the blast furnace due to the moisture. Therefore, it is necessary to remove the moisture before charging the sludge into the blast furnace.

[0003] In order to efficiently recycle metals from metal sludge, it is desirable to continuously dry it by dry treatment, remove the moisture, and then briquette it for treatment in a blast furnace. At that time, it is possible to efficiently and continuously process stirring and drying simultaneously using a rotary kiln.

[0004] However, when a large amount of metal sludge containing moisture is charged into a rotary kiln, a steam explosion will occur. In particular, in order to dry efficiently, high-temperature treatment is required. However, the higher the temperature, the higher the risk of explosion. In addition, some rare earth magnet alloys contain self-igniting metals, so they are likely to oxidize and burn rapidly in the kiln, causing an explosion. Furthermore, when sludge containing a large amount of water is directly charged into the kiln, there is a problem that the metal sludge adheres to the retort (cylinder) of the kiln like a viscosity.

[0005] Thus, since many difficult technical problems occur when drying metal sludge using a rotary kiln, attempts to heat-treat metal sludge in a rotary kiln have not been made until now.

[0006] Therefore, in order to solve the problems that occur when continuously drying metal sludge using a rotary kiln, the applicant obtained a patent for a continuous treatment method for metal sludge, which involves drying metal sludge containing rare earth magnet alloys to a moisture content of 30% or less, and then charging it into a rotary kiln and heat-treating it at a high temperature until the moisture content reaches 10% or less (see Patent Document 1).

[0007] The object of the patented invention is to provide a method that enables continuous drying treatment using a rotary kiln during the reuse of metal sludge, without causing explosions such as steam explosions or adhesion inside the retort, and is safe and efficient.

[0008] In addition, the inventor of the patented invention found that if the moisture content of the metal sludge is reduced to 30% or less, preferably 20% or less, and more preferably 15% or less by treatment in a drying furnace, no explosion will occur even if the temperature of the rotary kiln is raised to a high temperature of 400°C or more. As a result, by performing a two-stage continuous treatment using a drying furnace and a rotary kiln for drying metal sludge containing a large amount of moisture, it is possible to dry it to a moisture content of 10% or less extremely efficiently.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The patented invention performs a drying process before the heat treatment in a rotary kiln. However, since the drying process mainly assumes a heating furnace (but is not limited to a heating furnace), the optimal conditions for the heat treatment of the rare metal-containing cake in a rotary dryer after the dehydration process by a filter press are not assumed. In particular, the optimal conditions for reducing the water content of the rare metal-containing cake to 5% by weight or less are not assumed. In the filter press process, since the cake-shaped rare metal-containing cake is formed by pressure, in order to reduce the water content to 5% by weight or less, it is effective to perform heat treatment while crushing and pulverizing the rare metal-containing cake by stirring in the rotary dryer. In addition, by reducing the water content to 5% by weight or less, the weight can be significantly reduced, so the transportation cost can be suppressed.

Means for Solving the Problems

[0011] The continuous processing method of metal sludge of the present invention comprises subjecting metal sludge containing rare metal to filter press treatment to a water content of 50% by weight or less, then charging the rare metal-containing cake generated by the filter press treatment into a rotary dryer, and heating the rare metal-containing cake in an atmosphere where the temperature in the rotary dryer is 120°C to 200°C for a total heating time of 40 minutes to 70 minutes until the water content becomes 5% by weight or less.

Effects of the Invention

[0012] According to the present invention, by subjecting the drying of metal sludge containing a large amount of moisture to a two-stage continuous process using a filter press and a rotary dryer, it is possible to dry the water content to 5% by weight or less extremely efficiently.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] The multi-dryer including the rotary dryer of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of the multi-dryer of the present embodiment.

[0015] As shown in FIG. 1, the multi-dryer 1 includes a rotary dryer 2, an exhaust duct 3, a bag filter 4, a burner 11, and a charging hopper 14. The multi-dryer 1 also includes a rotary valve 5, a chimney 6, a static pressure control unit 7, a pressure measurement unit 8, an exhaust gas temperature measurement unit 9, and an exhaust gas temperature control unit 10.

[0016] The rare metal-containing cake 15 generated by the filter press treatment is conveyed to the charging hopper 14 by the belt conveyor 12. The filter press treatment may be performed by a normal filter press device and is not particularly limited. However, in order to continuously charge the processed material into the rotary dryer, a structure that allows easy removal by a belt conveyor is more preferable. A filter press device having a filtering function, a dehydrating function, and a washing function generates a rare metal-containing cake 15 having a water content of 50% by weight or less from a metal sludge containing a rare metal.

[0017] The rare metal is not particularly limited and can be applied to, for example, rare earth metals such as Co, Li, Ni, Cr, Mo, W, Nd, Sm, and known alloys containing these.

[0018] The rare metal-containing cake 15 conveyed to the charging hopper 14 is charged into the rotary dryer 2. In an atmosphere where the temperature inside the rotary dryer 2 is 120°C to 200°C (under atmospheric pressure or reduced pressure), the rare metal-containing cake 15 is heat-treated for a total heating time of 40 minutes to 70 minutes until the water content becomes 5% by weight or less.

[0019] Preferably, the temperature inside the rotary dryer 2 is 160°C to 190°C, and more preferably, 170°C to 190°C.

[0020] At 120°C or lower, drying is insufficient, and it takes an extremely long time to reduce the water content to 5% by weight or less. Also, at 200°C or higher, the fuel consumption of the burner 11 becomes excessive, and the fuel efficiency becomes low.

[0021] Also, the rare metal-containing cake after heat treatment becomes crushed particles 16, and is accumulated in a lightweight container 18 such as a flexible container bag by the belt conveyor 13. Considering the heat resistance of the lightweight container 18 and the safety of the operation, it is desirable that the accumulated crushed particles 17 be 150°C or lower. In this case, if the heat treatment is performed in an atmosphere where the temperature inside the rotary dryer 2 is 200°C or higher, the accumulated crushed particles 17 will become high temperature, which is not preferable from the viewpoints of the heat resistance of the lightweight container 18 and the safety of the operation.

[0022] The temperature inside the rotary dryer 2 is adjusted by controlling the output of the burner 11 (for example, PID control) by the exhaust gas temperature control unit 10 based on the exhaust gas temperature measured by the exhaust gas temperature measurement unit 9. The pressure inside the rotary dryer 2 is controlled (for example, PID control) by the static pressure control unit 7 based on the pressure measured by the pressure measurement unit 8.

[0023] Also, it is desirable that the rotation speed of the rotary dryer 2 be 8 rpm to 15 rpm, and the rare metal-containing cake 15 is heat-treated while being agitated. Preferably, the rotation speed of the rotary dryer 2 is 9 rpm to 11 rpm.

[0024] When the rotation speed is 8 rpm or less, the crushing and disintegration of the rare metal-containing cake 15 do not proceed, drying becomes insufficient, and it takes an extremely long time to reduce the water content to 5% by weight or less. Also, when the rotation speed is 15 rpm or more, the crushing and disintegration of the rare metal-containing cake 15 proceed too much, and it becomes powdery and is likely to scatter.

[0025] It is desirable that the rare metal-containing cake 15 is heat-treated by stirring with the rotary dryer 2 until the crushed particles having a particle size of 4.75 mm or more become 25% by weight or less. When the crushed particles having a particle size of 4.75 mm or more become 25% by weight or less, the crushing and disintegration proceed sufficiently and the surface is heated evenly.

[0026] The crushed particles may be briquetted by a briquetting machine. Since the water content is reduced, it can be briquetted extremely easily.

[0027] Hereinafter, the details of the present invention will be described along with specific examples.

[0028] (Example 1) By filter press treatment, a rare metal-containing cake 15 containing nickel, cobalt and 40% to 50% by weight of water was placed on the belt conveyor 12 and inserted into the rotary dryer 2. The rotary dryer 2 was maintained at 120°C to 200°C in an air atmosphere. Although it was treated in the rotary dryer for 40 minutes, it was possible to dry without danger such as explosion. The crushed particles 17 were taken out and the water content was measured by ICP emission spectrometry, and it was 1% to 4% by weight.

[0029] (Example 2) In the heat treatment of the rare metal-containing cake 15 of Example 1, in order to find appropriate heating conditions, experiments were conducted by changing the heating time, heating temperature, heating frequency, and rotation speed of the rotary dryer 2 in the heat treatment.

[0030] Figure 2 shows the results of drying a rare metal-containing cake dehydrated to a moisture content of 45.5 wt% by changing the heating time, heating temperature, number of heating times, and rotation speed in the heat treatment by the rotary dryer 2.

[0031] As can be seen from Figure 2, it can be seen that by heat-treating at a heating temperature of 120.0°C to 189.1°C at each total heating time (i.e., 43 minutes to 65 minutes), the moisture content can be reduced to 5 wt% or less.

[0032] Note that the heating temperature of the first time is measured low due to the heat of vaporization because the rare metal-containing cake 15 loaded into the rotary dryer 2 is not preheated and the moisture content is also high. Therefore, it can be seen that by heat-treating at a heating temperature of 163.2°C to 189.1°C at the heating temperature from the second time on, the moisture content can be efficiently reduced to 5 wt% or less, preferably in the range of 160°C to 190°C, and more preferably in the range of 170°C to 190°C. Here, the actually measured heating temperature is the exhaust gas temperature measured by the exhaust gas temperature measuring unit 9, and the exhaust gas temperature corresponds to the temperature inside the rotary dryer.

[0033] As described above, in order to dry the metal sludge without causing risks such as explosion, the heat treatment of the rare metal-containing cake is preferably carried out in an atmosphere where the temperature inside the rotary dryer is 120°C to 200°C for a total heating time of 40 minutes to 70 minutes. From the viewpoints of the target moisture content, treatment time, etc., it is possible to select appropriate treatment conditions within the above range.

[0034] Also, as can be seen from FIG. 2, the heating time for each cycle is set to 5 to 25 minutes (preferably 7 to 22 minutes, more preferably 7 to 15 minutes), and the above heat treatment is performed multiple times. Then, natural cooling for 5 to 60 minutes is performed between each of the multiple heat treatments. By shortening the heating time for each cycle, a large amount of the rare metal-containing cake 15 can be efficiently heat-treated. That is, rather than heat-treating a large amount of the rare metal-containing cake at once, the supply amount of the rare metal-containing cake 15 supplied to the rotary dryer 2 is limited to 1000 kg / h to 2000 kg / h, and the heat treatment is sequentially performed, discharged sequentially as crushed particles 16, and natural cooling is performed until the next heat treatment. Thus, the amount of the rare metal-containing cake to be heat-treated at once can be limited to a small amount, the stirring efficiency of the rotary dryer 2 is increased, and efficient heat treatment can be performed.

[0035] During the natural cooling, the drying of the rare metal-containing cake proceeds due to the residual heat. However, if the cooling is excessive, the temperature of the rare metal-containing cake 15 (hereinafter referred to as "material temperature") in the next heat treatment has to be raised again, resulting in poor heating efficiency. Therefore, the natural cooling time is preferably 5 to 60 minutes.

[0036] Also, as can be seen from FIG. 2, by setting the rotation speed of the rotary dryer 2 to 8.5 rpm to 13.8 rpm, it can be seen that the water content can be reduced to 5% by weight or less. When it is 8 rpm or less, the crushing and disintegration of the rare metal-containing cake 15 do not proceed, the drying is insufficient, and it takes an extremely long time to reduce the water content to 5% by weight or less. Also, when it is 15 rpm or more, the crushing and disintegration of the rare metal-containing cake 15 proceed too much, becoming powdery and easily scattered.

[0037] FIG. 3 is a diagram showing the distribution for each size of the particle size of the crushed particles 16 in the result of performing the heat treatment by changing the rotation speed of the rotary dryer 2. FIG. 4(a) is a diagram showing the crushed particles after the first heat treatment of test number RUN2, and FIG. 4(b) is a diagram showing the crushed particles after the fifth heat treatment of test number RUN2.

[0038] As can be seen from FIG. 3, by rotating and stirring the rotary dryer 2 at a rotational speed of 8.5 rpm to 13.8 rpm, the crushing and disintegration of the rare metal-containing cake 15 proceed (FIG. 4), and it can be seen that the disintegrated particles having a particle size of 4.75 mm or more can be reduced to 25% by weight or less. Also, it can be seen that the disintegrated particles having a particle size of 75 μm or less can be reduced to 5% by weight or less, preventing them from scattering in powder form.

[0039] FIG. 5 is a diagram showing the material temperature in the heat treatment of the rotary dryer 2. As can be seen from FIG. 5, the rare metal-containing cake after the heat treatment has a material temperature (surface temperature) of 50°C to 150°C or less. Thus, heat treatment can be performed in consideration of the heat resistance of the lightweight container 18 and the safety of the operation.

Industrial Applicability

[0040] The present invention is useful as a continuous treatment method for metal sludge that can dry metal sludge containing a large amount of moisture extremely efficiently to a moisture content of 5% by weight or less by performing two-stage continuous treatment using a filter press and a rotary dryer.

Explanation of Reference Numerals

[0041] 1... Multi-dryer 2... Rotary dryer 3... Discharge duct 4... Bag filter 5... Rotary valve 6... Chimney 7... Static pressure control unit 8... Pressure measurement unit 9... Exhaust gas temperature measurement unit 10... Exhaust gas temperature control unit 11... Burner 12, 13 Belt conveyor 14... Feed hopper

Claims

1. After subjecting a metal sludge containing a rare metal to filter press treatment so that the water content is 50% by weight or less, charging the rare metal-containing cake produced by the filter press treatment into a rotary dryer, while stirring the rare metal-containing cake at a rotational speed of 8 rpm to 15 rpm in an atmosphere where the temperature in the rotary dryer is 120°C to 200°C, setting the heating time for one time to 5 minutes to 25 minutes, and performing heat treatment a plurality of times with a total heating time of 40 minutes to 70 minutes, and performing natural cooling for 5 minutes to 60 minutes between each of the plurality of heat treatments, thereby heat-treating the rare metal-containing cake until the water content becomes 5% by weight or less. A continuous treatment method for metal sludge, characterized by this.

2. The continuous treatment method for metal sludge according to Claim 1, characterized in that the rare metal-containing cake after each heat treatment has a surface temperature of 50°C to 150°C or less, and the rare metal-containing cake is heat-treated until it becomes crushed particles with a water content of 5% by weight or less.

3. The continuous treatment method for metal sludge according to Claim 1 or Claim 2, characterized in that the rare metal-containing cake is heat-treated a plurality of times until the crushed particles having a particle size of 4.75 mm or more are 25% by weight or less and the crushed particles having a particle size of 75 μm or less are 5% by weight or less.

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