JP7699814B2 - Drying method for cake containing rare metals - Google Patents

Description

The present invention relates to a method for drying a cake containing rare metals, and in particular, to a method for drying a cake containing rare metals using a rotary dryer.

Metal sludge is generally produced during the grinding process, but it often contains a large amount of water because it is ground together with pure water. If sludge containing such a large amount of water is directly charged into a blast furnace, the water will cause a steam explosion in the furnace. Therefore, it is necessary to remove the water from the sludge before charging it into the blast furnace.

To efficiently recycle metals from metal sludge, it is desirable to continuously dry the sludge using a dry process, remove the moisture, briquette it, and process it in a blast furnace. In this case, a rotary kiln can be used to efficiently and continuously mix and dry the sludge at the same time.

However, when metal sludge containing a large amount of water is charged into a rotary kiln, steam explosions can occur. In particular, efficient drying requires high-temperature processing, but the higher the temperature, the greater the risk of explosion. Also, rare earth magnet alloys contain pyrophoric metals, which can rapidly oxidize and burn in the kiln, causing an explosion. Furthermore, if sludge containing a large amount of water is directly charged into the kiln, there is the problem that the metal sludge will adhere to the inside of the kiln retort (cylinder) like clay.

As described above, drying metal sludge in a rotary kiln raises many difficult technical problems, so no attempts have been made to heat-treat metal sludge in a rotary kiln until now.

Therefore, in order to solve the problems that arise when metal sludge is continuously dried in a rotary kiln, the applicant obtained a patent for a method for continuously processing metal sludge, which is characterized by drying metal sludge containing rare earth magnetic alloys to a moisture content of 30% or less, then loading it into a rotary kiln and heating it at high temperatures until the moisture content is 10% or less (see Patent Document 1).

The purpose of this patented invention is to provide a method for safe, efficient and continuous drying without causing explosions such as steam explosions or adhesion to the inside of the retort, enabling drying treatment in a rotary kiln for the reuse of metal sludge.

The inventors of this patent also discovered that if the moisture content of metal sludge is reduced to 30% or less, preferably 20% or less, and more preferably 15% or less by treatment in a drying oven, explosions will not occur even if the temperature of the rotary kiln is set to a high temperature of 400°C or more. As a result, metal sludge containing a large amount of moisture can be dried extremely efficiently to a moisture content of 10% or less by performing two consecutive treatments in a drying oven and a rotary kiln.

Patent No. 6100991

In this patented invention, a drying process is performed before the heating process in a rotary kiln, but since the drying process is mainly (but not limited to) assumed to be performed in a heating furnace, no optimal conditions are assumed for the heating process in a rotary dryer of the rare metal-containing cake that has become cake-like after dehydration process in a filter press. In particular, no optimal conditions are assumed for reducing the moisture content of the rare metal-containing cake to 5% by weight or less. In the filter press process, the rare metal-containing cake becomes cake-like due to pressure, so in order to reduce the moisture content to 5% by weight or less, it is effective to heat-treat the rare metal-containing cake while crushing and disintegrating it by stirring in a rotary dryer. Furthermore, by reducing the moisture content to 5% by weight or less, the weight can be significantly reduced, which can reduce transportation costs.

The continuous metal sludge processing method of the present invention involves filter pressing metal sludge containing rare metals to a moisture content of 50% by weight or less, then loading the rare metal-containing cake produced by the filter press processing into a rotary dryer, and heat-treating the rare metal-containing cake in an atmosphere in which the temperature inside the rotary dryer is 120°C to 200°C for a total heating time of 40 to 70 minutes until the moisture content is 5% by weight or less.

According to the present invention, metal sludge containing a large amount of moisture can be dried extremely efficiently to a moisture content of 5% by weight or less by performing two consecutive steps of processing using a filter press and a rotary dryer.

FIG. 2 is a diagram showing an example of the configuration of a multi-dryer according to the present embodiment. FIG. 2 is a diagram showing the results of drying a rare metal-containing cake in a heat treatment using a rotary dryer according to the present embodiment. FIG. 1 is a diagram showing the distribution of particle sizes of disintegrated particles. FIG. 2 is a diagram showing disintegrated particles after heat treatment. FIG.

The multi-dryer including the rotary dryer of the present invention will be described with reference to the drawings. Figure 1 shows an example of the configuration of the multi-dryer of this embodiment.

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 an input 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.

The rare metal-containing cake 15 produced by the filter press process is transported to the input hopper 14 by the belt conveyor 12. The filter press process may be carried out by a normal filter press device, and is not particularly limited. However, in order to continuously input the processed material into the rotary dryer, it is more preferable that the structure allows easy removal by a belt conveyor. The rare metal-containing cake 15 with a moisture content of 50% by weight or less is produced from metal sludge containing rare metals by the filter press device, which has filtering, dehydrating, and washing functions.

There are no particular limitations on the rare metals, and examples of rare earth metals that can be used include Co, Li, Ni, Cr, Mo, W, Nd, Sm, and other known alloys that contain these metals.

The rare metal-containing cake 15 transported to the input hopper 14 is loaded into the rotary dryer 2. The rare metal-containing cake 15 is heat-treated in an atmosphere (atmospheric pressure or reduced pressure) in which the temperature inside the rotary dryer 2 is 120°C to 200°C, for a total heating time of 40 to 70 minutes, until the moisture content is 5% by weight or less.

The temperature inside the rotary dryer 2 is preferably 160°C to 190°C, and more preferably 170°C to 190°C.

Below 120°C, drying is insufficient and it takes an extremely long time to reduce the moisture content to 5% by weight or less. Also, above 200°C, the burner 11 consumes too much fuel, resulting in low fuel efficiency.

After the heat treatment, the rare metal-containing cake becomes crushed particles 16, which are accumulated in lightweight containers 18 such as flexible container bags on the belt conveyor 13. Considering the heat resistance of the lightweight containers 18 and the safety of the work, it is desirable that the accumulated crushed particles 17 be at 150°C or less. In this case, if the heat treatment is performed in an atmosphere in which the temperature inside the rotary dryer 2 is 200°C or higher, the accumulated crushed particles 17 will become very hot, which is undesirable from the standpoint of the heat resistance of the lightweight containers 18 and the safety of the work.

The temperature inside the rotary dryer 2 is adjusted by controlling (e.g., PID control) the output of the burner 11 with 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 (e.g., PID control) by the static pressure control unit 7 based on the pressure measured by the pressure measurement unit 8.

It is also desirable that the rotation speed of the rotary dryer 2 be 8 rpm to 15 rpm, and that the rare metal-containing cake 15 be heat-treated while stirring. Preferably, the rotation speed of the rotary dryer 2 is 9 rpm to 11 rpm.

At speeds below 8 rpm, the rare metal-containing cake 15 will not be crushed or disintegrated, drying will be insufficient, and it will take an extremely long time to reduce the moisture content to 5% by weight or less. At speeds above 15 rpm, the rare metal-containing cake 15 will be crushed or disintegrated too much, turning into powder and becoming more likely to scatter.

The rare metal-containing cake 15 is desirably heat-treated by stirring in the rotary dryer 2 until the crushed particles having a particle size of 4.75 mm or more are 25% by weight or less. By reducing the crushed particles having a particle size of 4.75 mm or more to 25% by weight or less, the crushing and disintegration is sufficiently advanced and the surface is heated evenly.

The crushed particles may be briquetted using a briquetting machine. Because of the reduced moisture content, they can be briquetted very easily.

The details of the present invention are explained below with reference to specific examples.

Example 1
The rare metal-containing cake 15, which contains rare metals including nickel and cobalt and 40% to 50% by weight of moisture by the filter press process, was placed on a belt conveyor 12 and inserted into a rotary dryer 2. The rotary dryer 2 was kept at 120°C to 200°C in an atmospheric air. The processing was carried out in the rotary dryer for 40 minutes, and drying was possible without causing any risk of explosion or the like. The crushed particles 17 were taken out, and the moisture content was measured by ICP emission spectroscopy, which was found to be 1% to 4% by weight.

Example 2
In order to find suitable heating conditions for the heat treatment of the rare metal-containing cake 15 in Example 1, an experiment was conducted by changing the heating time, heating temperature, number of heating cycles, and rotation speed of the rotary dryer 2 in the heat treatment.

Figure 2 shows the results of drying a rare metal-containing cake that had been dehydrated to a moisture content of 45.5% by weight by changing the heating time, heating temperature, number of heating cycles, and rotation speed during heating treatment using a rotary dryer 2.

As can be seen from Figure 2, the moisture content can be reduced to 5% by weight or less by heat treatment at a heating temperature of 120.0°C to 189.1°C for each total heating time (i.e., 43 minutes to 65 minutes).

The first heating temperature is measured low due to the heat of vaporization because the rare metal-containing cake 15 loaded into the rotary dryer 2 has not been preheated and has a high moisture content. Therefore, in the second and subsequent heating temperatures, the moisture content can be efficiently reduced to 5% by weight or less by heating at a heating temperature of 163.2°C to 189.1°C, preferably 160°C to 190°C, and more preferably 170°C to 190°C. The heating temperature actually measured here 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.

As described above, in order to dry metal sludge without risking explosion, the rare metal-containing cake should be heated for a total heating time of 40 to 70 minutes in an atmosphere where the temperature inside the rotary dryer is 120°C to 200°C. Appropriate processing conditions can be selected within the above range from the viewpoint of the target moisture content, processing time, etc.

As can be seen from FIG. 2, the heating time for each heating is 5 to 25 minutes (preferably 7 to 22 minutes, more preferably 7 to 15 minutes), and the heating is performed multiple times. Then, natural cooling is performed for 5 to 60 minutes between each of the multiple heating treatments. By shortening the heating time for each heating, a large amount of rare metal-containing cake 15 can be efficiently heat-treated. In other words, rather than heat-treating a large amount of rare metal-containing cake at once, the supply amount of rare metal-containing cake 15 to the rotary dryer 2 is limited to 1000 kg/h to 2000 kg/h, and the cake is successively heat-treated, discharged as crushed particles 16 in succession, and naturally cooled until the next heat treatment is performed. This limits the amount of rare metal-containing cake to be heat-treated at one time to a small amount, increases the mixing efficiency of the rotary dryer 2, and allows for efficient heat treatment.

While the rare metal-containing cake is being naturally cooled, residual heat continues to dry it. However, if it is cooled too much, the temperature of the rare metal-containing cake 15 (hereinafter referred to as the "material temperature") must be raised again in the next heating process, resulting in poor heating efficiency. Therefore, it is preferable that the natural cooling time be 5 to 60 minutes.

As can be seen from FIG. 2, the moisture content can be reduced to 5% by weight or less by setting the rotation speed of the rotary dryer 2 to 8.5 rpm to 13.8 rpm. At 8 rpm or less, the rare metal-containing cake 15 is not crushed or disintegrated, drying is insufficient, and it takes an extremely long time to reduce the moisture content to 5% by weight or less. At 15 rpm or more, the rare metal-containing cake 15 is crushed or disintegrated too much, turning into powder and becoming easily scattered.

Figure 3 shows the distribution of particle size of the crushed particles 16 as a result of heat treatment performed by changing the rotation speed of the rotary dryer 2. Figure 4(a) shows the crushed particles after the first heat treatment of test number RUN2, and Figure 4(b) shows the crushed particles after the fifth heat treatment of test number RUN2.

As can be seen from Figure 3, by stirring the rotary dryer 2 at a rotation speed of 8.5 rpm to 13.8 rpm, the rare metal-containing cake 15 is crushed and disintegrated (Figure 4), and the amount of crushed particles with a particle size of 4.75 mm or more can be reduced to 25% by weight or less. It can also be seen that the amount of crushed particles with a particle size of 75 μm or less can be reduced to 5% by weight or less, preventing them from scattering in powder form.

Figure 5 shows the material temperature during the heat treatment in the rotary dryer 2. As can be seen from Figure 5, the material temperature (surface temperature) of the rare metal-containing cake after heat treatment is 50°C to 150°C or less. This allows the heat treatment to be performed while taking into consideration the heat resistance of the lightweight container 18 and the safety of the work.

The present invention is useful as a method for continuously processing metal sludge, which contains a large amount of moisture, by performing two consecutive processes using a filter press and a rotary dryer, and can extremely efficiently dry the sludge to a moisture content of 5% by weight or less.

Reference Signs List 1... Multi-dryer 2... Rotary dryer 3... Exhaust 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... Input hopper

Claims (3)

The rare metal-containing metal sludge is subjected to a filter press treatment to reduce the moisture content to 50% by weight or less, and then the rare metal-containing cake produced by the filter press treatment is charged into a rotary dryer,
A method for continuously treating metal sludge, characterized in that the rare metal-containing cake is heat-treated multiple times for a total heating time of 40 to 70 minutes, with each heating time being 5 to 25 minutes, while stirring the rare metal-containing cake at a rotation speed of 8 to 15 rpm in an atmosphere where the temperature inside the rotary dryer is 120°C to 200°C, and natural cooling is performed for 5 to 60 minutes between each of the multiple heating treatments, thereby heat -treating the rare metal-containing cake until its moisture content becomes 5% by weight or less. A method for continuous treatment of metal sludge as described in claim 1, characterized in that the rare metal-containing cake after each heating treatment has a surface temperature of 50°C to 150 °C or less, and is heated until the moisture content of the rare metal-containing cake becomes 5% by weight or less. A method for continuous treatment of metal sludge as described in claim 1 or claim 2, characterized in that the rare metal-containing cake is heat-treated multiple times until the amount of crushed particles with a particle size of 4.75 mm or more is 25% by weight or less and the amount of crushed particles with a particle size of 75 μm or less is 5% by weight or less.