JP5041744B2 - Continuous drying method of alloy sludge by rotary kiln. - Google Patents

Description

  The present invention relates to a method for continuously drying metal sludge. In particular, the present invention relates to a method for continuously drying sludge containing a rare earth magnet alloy at a high temperature using a rotary kiln.

  Metal sludge is generated as grinding waste containing moisture when grinding an alloy such as a ferrous metal such as bearing steel or carburized steel, or a rare earth magnet based magnet alloy. In particular, rare earth alloys are used in large quantities as permanent magnet alloys and are subjected to machining and grinding in order to be processed into a desired small shape. At that time, sludge such as small pieces of grinding powder is generated. It occurs in large quantities. Therefore, recycling of these sludges is extremely useful.

  In order to efficiently recycle the metal sludge, a regeneration process such as reduction of oxygen content or carbon is required. Conventionally, a wet method has been adopted as such a regeneration process. For example, after scrap containing a rare earth magnet alloy is completely dissolved with a strong acid such as hydrochloric acid, nitric acid, sulfuric acid, etc., the pH is adjusted with an alkali such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. There is a method of precipitation in the form of iron oxide and separation.

However, in the above method, a large amount of acid and alkali are required, and it is difficult to separate a large amount of the produced iron hydroxide, and there are problems such as requiring a lot of manpower.
Therefore, rare earth magnet manufacturers export metal scrap to drums to countries such as China and Southeast Asia and process them locally in order to carry out wet processing with good profitability. Due to changes, things that have been treated as scrap in the past are treated as waste.

  For this reason, establishment of an efficient recycling technique by dry-type metal sludge in Japan is desired.

  As described above, the metal sludge is generally generated by a grinding process, but at this time, it is often ground together with pure water, so that it often contains a large amount of water. When the sludge containing a large amount of moisture is introduced into the blast furnace as it is, a steam explosion occurs in the blast furnace due to the moisture. Therefore, it is necessary to remove moisture before charging the sludge into the blast furnace.

  Sludge can be dried batchwise in a drying furnace, but it is very inefficient and not profitable. For example, Patent Document 1 below discloses that incineration ash is dried to a water content of 10% by mass or less and then charged into a reaction vessel in order to prevent a steam explosion. Is not possible. In addition, since metal sludge such as grinding scraps of rare earth magnets contains a large amount of moisture, in order to reduce the moisture content to 10% by mass or less without causing a steam explosion, it must be dried at a low temperature for a long time. However, the efficiency is still very poor. Furthermore, it takes about one week for cooling after heating, and it is not profitable and is not suitable for commercialization.

  Further, Patent Document 2 below discloses a method of removing moisture and oil by compression-molding a flocculent aggregate containing a grinding fluid and iron-based metal grinding chips. After compression molding, the molded body must be crushed and then briquetted, and the recycling process is not efficient and expensive.

In order to efficiently recycle the metal from the metal sludge, it is desirable to dry continuously by dry processing, remove moisture, and then briquette and process in a blast furnace. At that time, using a rotary kiln, it is possible to efficiently and continuously carry out stirring and drying simultaneously. In particular, since rare earth magnet alloys include self-flammable alloys such as Se and Sm, it is necessary to heat the surface evenly by stirring, and a drying process using a rotary kiln is extremely effective.
JP 2000-326328 A JP 2002-194449 A

  The present invention is intended to solve the problems that occur when metal sludge is continuously dried by a rotary kiln. When a metal sludge containing a large amount of water is charged into the rotary kiln, a steam explosion occurs. In particular, in order to dry efficiently, treatment at a high temperature is necessary, but the higher the temperature, the higher the risk of explosion. In addition, since rare earth magnet alloys also contain self-combustible metals, they tend to oxidize and burn rapidly in the kiln and are prone to explosion. Furthermore, when a sludge containing a large amount of water is put into the kiln as it is, there is a problem that the metal sludge adheres like a viscosity in the retort (cylinder) of the kiln.

  Thus, since many difficult technical problems arise when metal sludge is dried with a rotary kiln, no attempt has been made to heat-treat metal sludge with a rotary kiln.

  Accordingly, the object of the present invention is to enable the drying process by the rotary kiln in the reuse of the metal sludge, so that the drying process can be continuously performed safely and efficiently without causing an explosion such as a steam explosion or the adhesion in the retort. It is to provide a method to perform automatically.

  The method of the present invention reduces the moisture content to 30% or less by drying in a drying furnace before treating the metal sludge with the rotary kiln, and then reduces the moisture content to 10% or less by treating with the rotary kiln. Is. The inventor of the present invention particularly reduces the temperature of the rotary kiln to 400 ° C. or more if the moisture content of the metal sludge is reduced to 30% or less, preferably 20% or less, more preferably 15% or less by treatment with a drying furnace. It was found that no explosion occurred even at a high temperature. Thereby, the drying of the metal sludge containing a large amount of moisture can be dried to a water content of 10% or less very efficiently by performing a two-stage continuous treatment with a drying furnace and a rotary kiln.

  The method of the present invention is intended for metal sludge generated by grinding or the like. In particular, the demand for rare earth magnet alloys has increased rapidly in recent years, and a large amount of scrap of grinding scrap is generated in the manufacturing process. The rare earth magnet alloy is not particularly limited, and can be applied to known alloys such as cobalt containing a rare earth metal such as Ni, Cr, Mo, W, Nd, and Sm.

  The drying treatment of the present invention is performed by heating at a temperature of 50 to 500 ° C. for 10 minutes to 5 hours at atmospheric pressure or reduced pressure in a drying furnace. Below 50 ° C., drying is insufficient, and it takes a very long time to reduce the water content to 30% or less. Moreover, at 500 degreeC or more, there exists a danger of a steam explosion. The treatment time is preferably 17 to 50 minutes, the treatment temperature is 100 to 350 ° C, more preferably the treatment temperature is 150 to 350 ° C, and still more preferably the treatment temperature is 170 to 300 ° C.

  The drying furnace used in the present invention is not particularly limited as long as it is a normal heating furnace. However, it is more preferable if it has a structure that can be easily taken out by a bell conveyor in order to continuously feed the processed material into the rotary kiln.

  The heat treatment subsequent to the drying treatment of the present invention is performed by directly heating in a rotary kiln at a temperature of 400 to 1,000 ° C. for 10 minutes to 3 hours at atmospheric pressure or reduced pressure. The treatment atmosphere may be air or an inert gas. Below 400 ° C., it takes a long time to make the moisture content 10%, and an efficient treatment cannot be performed. Moreover, at 1,000 degreeC or more, there exists a limit in the heat resistance of a rotary kiln, and danger arises. The treatment time is preferably 8 to 50 minutes, and the heating temperature is 650 to 850 ° C, preferably 700 to 850 ° C, more preferably heating temperature 750 to 850 ° C.

  Since the rotary kiln used in the present invention is processed at a high temperature as described above, the rotary kiln is preferably heat-resistant than a normal kiln. For example, those having a heat-resistant structure such as those whose outer wall is made of heat-resistant stainless steel are preferable.

  In addition, after the high-temperature heat treatment, it is preferable to perform a final drying treatment at a temperature of 100 to 200 ° C. in an atmospheric pressure or reduced pressure state for 10 minutes to 5 hours.

  In general, heat treatment using a heating furnace including a rotary kiln uses a heat source that generates harmful substances such as electric heat, propane gas and other sulfides and phosphorus, and therefore, symmetrical substances may be contaminated by these harmful substances. Therefore, it is preferable that the drying process in the previous step and the heating by the rotary kiln are direct heating. According to direct heating, it is not necessary to use heavy oil, light oil, gasoline, or the like as a heat source, so that the object to be treated can be prevented from being contaminated with harmful substances such as sulfides and phosphorus.

  The scrap having a water content of 10% or less by the method of the present invention is bracketed by a briquette machine in order to be put into the blast furnace. The collected scrap is scattered in powder form and thrown into the blast furnace, and is made into briquettes for easy transportation and the like. For example, in the case of a cobalt-containing rare earth magnet alloy scrap, briquetted metal grinding scraps and pure iron as a base material are added and put into a blast furnace to produce a cobalt-containing shot. Thereby, a shot with a cobalt metal content of 20 to 30% can be obtained. As a blast furnace, an electric furnace is generally used.

  As described above, according to the method of the present invention, metal sludge containing moisture is efficiently subjected to continuous drying treatment, and the obtained metal scrap is briquetted and then melted in a blast furnace and recycled as a shot-like product. The Shot-like products are delivered to a metal processing company and used again as raw materials.

  According to the present invention, the metal sludge containing a large amount of moisture can be dried to a moisture content of 10% or less very efficiently by a two-stage continuous treatment using a drying furnace and a rotary kiln. Further, since heating in the rotary kiln is direct heating without using fuel, there is an advantage that the object to be collected is not contaminated by sulfides or phosphorus.

  Hereinafter, the details of the present invention will be described with reference to specific examples.

  20 ml of a metal sludge containing a rare earth magnet alloy containing cobalt, iron, samarium and neodymium and moisture of 60 to 70% is taken out from a drum can, put into a stainless steel beaker, and heated at a heating rate of 10 ° C./min. After heating to 350 ° C. and holding for 1 hour, taking out and measuring the moisture content by ICP emission spectroscopy, it was 15 to 25%. The obtained scrap was placed on a belt conveyor and inserted into a rotary kiln. The rotary kiln was maintained at 750 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere. Although it was processed in a rotary kiln for 0.5 hours, it could be dried without causing danger such as explosion. The scrap was taken out and the water content was measured by the same method as described above.

  The scrap was briquetted with a briquette machine. Briquetting could be done very easily due to the low water content. The obtained briquette was poured into an electric furnace together with pure iron and melted to produce a cobalt-containing shot. The resulting shot had a cobalt content of 25%.

  In the drying / heating treatment of the rare earth alloy sludge of Example 1, experiments were conducted by changing the drying temperature and drying time in the drying treatment and the heating temperature and drying time in the heating treatment in order to find appropriate drying / heating conditions.

  FIG. 2 shows the relationship between the treatment temperature and the moisture content when the drying time in the initial drying treatment is 1000 seconds (17 minutes), 2000 seconds (33 minutes), and 3000 seconds (50 minutes), respectively.

  As can be seen from FIG. 2, it can be seen that the water content can be reduced to 20% or less by heat treatment at a treatment temperature of 100 to 350 ° C. in each treatment time (ie, 17 to 50 minutes). Further, by heat treatment at a processing temperature of 150 to 350 ° C., it can be efficiently reduced to a moisture content of 15% or less, and more preferably from the viewpoint of efficiently reducing the moisture content while avoiding high temperatures. It turns out that it is good to carry out in the range of 170-300 degreeC.

  FIG. 3 shows the relationship between the treatment temperature and the water content when the drying time in the stirring heat treatment is 500 seconds (8 minutes), 1000 seconds (17 minutes), 2000 seconds (33 minutes), and 3000 seconds (50 minutes), respectively. Indicates.

  As can be seen from FIG. 3, it can be seen that the moisture content can be reduced to 5% or less by heating to 650 to 850 ° C. in any treatment time (that is, 8 to 50 minutes). Moreover, in order to make a moisture content 3% or less, it is necessary to heat at 700-850 degreeC, and in order to make it 2% or less especially, select an appropriate heating temperature and heating time in 750-850 degreeC. I know you need to do that.

  As described above, in order to dry the rare earth alloy sludge without causing danger such as explosion, the drying treatment is performed at a treatment temperature of 100 to 350 ° C. for 17 to 50 minutes, and the high temperature heat treatment is heated for 8 to 50 minutes. The temperature is preferably in the range of 650 to 850 ° C. From the viewpoint of the target moisture content, treatment time, etc., it is possible to select an appropriate treatment condition in the above range.

  Steel grinding scraps containing 0.3% carbon and 20 ml of sludge containing 70 to 80% moisture were placed in a stainless beaker and held for 1 hour, then taken out and the moisture content measured to be 15 to 25%. The obtained scrap was placed on a belt conveyor and inserted into a rotary kiln. The rotary kiln was held at 700 to 800 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere. Although it processed for 0.5 to 1 hour in the rotary kiln, it was able to dry without danger, such as an explosion. The scrap was taken out and the water content was measured and found to be 1 to 5%.

The outline of the continuous processing process of this invention is shown. The relationship between processing temperature and moisture content is shown for each drying time in an initial drying process. The relationship between processing temperature and moisture content is shown about each drying time in stirring heat processing (high temperature processing).

Claims (8)

A metal sludge containing a rare earth magnet-based alloy is dried to a moisture content of 30% or less, and then charged in a rotary kiln and heat-treated at a high temperature until the moisture content becomes 10% or less. . The continuous treatment method according to claim 1, wherein the moisture content after the drying treatment is 20% or less, and the moisture content after the high-temperature heat treatment is 5% or less. The continuous treatment method according to claim 1 or 2, wherein a final drying treatment is further performed at a temperature of 100 to 200 ° C for 10 minutes to 5 hours after the high temperature treatment. The continuous treatment method according to any one of claims 1 to 3, wherein the drying treatment is performed by heating in a drying furnace at a temperature of 50 to 500 ° C at atmospheric pressure or reduced pressure for 10 minutes to 5 hours. The continuous heat treatment according to any one of claims 1 to 4, wherein the heat treatment is performed by direct heating in a rotary kiln at a temperature of 400 to 1,000 ° C at atmospheric pressure or reduced pressure for 10 minutes to 3 hours. Processing method. The continuous processing method according to claim 4, wherein the drying process is performed by heating in a drying furnace at a temperature of 100 to 350 ° C. in an atmospheric pressure or reduced pressure state for 17 to 50 minutes. The continuous processing method according to claim 6, wherein the heat treatment is performed by directly heating in a rotary kiln at a temperature of 650 to 850 ° C. in an atmospheric pressure or reduced pressure state for 8 to 50 minutes. The continuous processing method according to claim 1, wherein the rotary kiln has a heat resistant structure using heat resistant stainless steel as an outer wall.

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