Powder recovery method and powder recovery equipment

Abstract

To provide a powder recovery method and a powder recovery device capable of reducing oil content removal energy from oil-containing powder and heightening an oil content removal fraction and a solid-liquid separation speed.MEANS FOR SOLVING THE PROBLEM: A method for recovering powder by separating an oil from powder to which oil adheres and contains a magnetic substance to recover the powder comprises: mixing the powder and water such that the viscosity becomes in the range of 0.003 to 2.00 Pa S to form a slurry; first emulsifying for forming a first emulsion by mixing after adding a first volatile hydrophobic aqueous solvent to the slurry; and first electromagnetic separating for separating and recovering a first powder phase by magnetic separation from the first emulsion.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a powder recovery method and a powder recovery system. [Background technology]

[0002] In various manufacturing industries, including the steel industry, large amounts of mixtures containing powders containing hydrophilic particles dispersed in water or aqueous solutions are discharged. The mixtures are often discharged in the form of aqueous slurries. The powders contained in the mixtures are diverse, and in the steel industry, for example, they include scale, grinding dust, etc.

[0003] For example, scale and grinding dust are contaminated with oil and moisture (e.g., rolling oil, lubricating oil, and cooling water used in rolling) that are inevitably generated during industrial production. Scale and grinding dust containing such oil and moisture contain 5 to 50% moisture and a few percent oil. Therefore, for the purpose of recycling or efficient use, it is necessary to remove the oil and moisture from powders such as scale and grinding dust.

[0004] Conventionally, a method for removing oil from powder containing oil (hereinafter also referred to as oil-containing powder) has been known, which involves combustion treatment using a rotary kiln or the like. However, because the oil concentration of oil-containing powder is low, combustion treatment requires a supporting fuel, which poses a problem of requiring a large amount of energy. In particular, when the oil concentration of oil-containing powder is even lower, high-quality (expensive) energy such as COG (coke oven gas) or heavy oil may be used as the supporting fuel, which exacerbates the above problem. Furthermore, combustion treatment also increases CO2 emissions, which goes against the goal of reducing CO2 emissions, which has become a particular challenge in recent years.

[0005] Furthermore, in the case of scale with oil attached (hereinafter also referred to as oil-containing scale), the scale is often used as an iron source in the sintering process after being combusted to remove the oil. However, during the combustion process, the main components of the scale, FeO (wustite) and Fe3O4 (magnetite), are oxidized to Fe2O3 (hematite), which creates the problem of increasing the amount of coke used in the sintering process.

[0006] To address this problem, various methods for separating oil from oil-containing powder without carrying out combustion treatment have been investigated. For example, Patent Document 1 discloses a method in which oil-containing scale is mixed with an organic solvent as an extractant and stirred to extract the oil from the oil-containing scale into the organic solvent, and then centrifugal force is applied by utilizing the difference in specific gravity to separate the scale into a solvent phase, an aqueous phase, and a scale phase. Furthermore, Patent Document 2 discloses a method in which centrifugal force is applied to an emulsion containing scale in a liquid cyclone to separate oil from a mixture containing oil-containing powder, and then the powder is recovered. Furthermore, Patent Document 3 discloses a method of filtering a grinding oil mixture containing sludge generated in a metal strip grinding line to obtain a sludge mixture containing a small amount of grinding oil.

[0007] Furthermore, Patent Document 4 discloses a method in which a coagulant and magnetic particles are added to an oil emulsion obtained by stirring a mixture of oil and water, and the mixture is further stirred to form magnetic flocs, and then the oil and water are separated by magnetic separation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2015-132011 [Patent Document 2] Japanese Patent Application Publication No. 2017-177018 [Patent Document 3] Japanese Patent Application Publication No. 7-116960 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-277771 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the method described in Patent Document 1 has the problem that it requires expensive centrifuges. Furthermore, when a countercurrent continuous process described below is performed to improve the oil removal rate, multiple extractions and phase separations must be connected by pumps and piping, and a control system for controlling them is required, which requires multiple expensive centrifuges and makes the process complicated, which increases the likelihood of operational problems. The method described in Patent Document 2 has a problem in that when the powder has a high content of fine particles, the recovery rate of the particles in the liquid cyclone decreases. Furthermore, when filtering a slurry containing a mixture of water, oil, and powder containing hydrophilic particles using the method described in Patent Document 3, there was a problem that clogging of the filtering surface frequently occurred. Furthermore, because the filtration speed was low, the filtering device became very large, making stable operation difficult. Furthermore, the method described in Patent Document 4 has the problem that the oil content attached to the magnetic particles cannot be separated and reduced to a low oil content. As described above, none of the techniques disclosed in Patent Documents 1 to 4, which involve treatment without combustion treatment, can adequately solve the problem of oil separation from oil-containing powder.

[0010] Given the above background, there is a strong demand for a method for removing oil from oil-containing powder to recover high-purity powder that consumes less energy when removing the oil (oil removal energy) and has a high powder recovery rate.

[0011] The present invention has been made in consideration of the above problems, and the object of the present invention is to provide a powder recovery method and powder recovery equipment which, unlike conventional oil separation by combustion treatment, can reduce the energy required to remove oil from oil-containing powder and increase the oil removal rate and powder recovery rate. [Means for solving the problem]

[0012] The gist of the present invention is as follows.

[0013] [1] A method for recovering powder, which separates oil from powder containing magnetic particles and has oil attached thereto, and recovers the powder, a slurrying step of mixing the powder with water to produce a slurry having a viscosity in the range of 0.003 to 2.00 Pa·S; a first emulsification step of adding a first volatile hydrophobic solvent to the slurry and then mixing to form a first emulsion; a first magnetic separation step of separating and recovering a first powder phase from the first emulsion by magnetic separation; A method for recovering powder, comprising: [2] The method for recovering powder according to [1] above, characterized in that a polymer flocculant is added to the slurry in the slurrying step or the first emulsifying step. [3] The method for recovering powder according to [1] or [2] above, characterized in that the specific gravity of the first volatile hydrophobic solvent is greater than 1.05 and less than 2.0. [4] The method for recovering powder according to any one of the above [1] to [3], wherein the boiling point of the first volatile hydrophobic solvent at normal pressure is lower than 95°C. [5] The method for recovering powder according to any one of the above [1] to [4], characterized in that the washing step consisting of the first emulsification step and the first magnetic separation step is repeated one or more times. [6] a residual solvent volatilization step in which the first powder phase obtained in the first magnetic separation step is put into a hot water bath having a water temperature higher than the boiling point of the first volatile hydrophobic solvent, and the first volatile hydrophobic solvent remaining in the first powder phase is volatilized and removed; The method for recovering powder according to any one of the above [1] to [5], characterized by comprising a dehydration step of dehydrating the slurry containing the first powder phase obtained in the residual solvent evaporation step using a dehydrator. [7] A method for recovering powder according to any one of the above [1] to [5], characterized by comprising a drying step of drying the first powder phase obtained in the first magnetic separation step at a temperature above the boiling point of the first volatile hydrophobic solvent. [8] The method for recovering powder according to any one of the above [1] to [5], characterized in that after the first magnetic separation step, a second emulsification step is carried out in which a second volatile hydrophobic solvent is added to the recovered first powder phase and then mixed to form a second emulsion, and a second magnetic separation step is carried out in which the second powder phase is separated and recovered from the second emulsion by magnetic separation. [9] The method for recovering powder according to [8] above, characterized in that the rinsing step consisting of the second emulsification step and the second magnetic separation step is repeated one or more times.

[10] The powder recovery method according to [9] above, characterized in that the washing step and the rinsing step are performed in a single counterflow tank as a counterflow continuous process.

[11] The method for recovering powder according to any one of the above [8] to

[10] , characterized in that in the second emulsification step, a polymer flocculant is added to the first powder phase.

[12] The method for recovering powder according to any one of the above [8] to

[11] , wherein the specific gravity of the second volatile hydrophobic solvent is greater than 1.05 and less than 2.0.

[13] The method for recovering powder according to any one of the above [8] to

[12] , wherein the boiling point of the second volatile hydrophobic solvent at normal pressure is lower than 95°C.

[14] A method for recovering powder according to any one of the above items [8] to

[13] , characterized by comprising: a residual solvent volatilization step of putting the second powder phase obtained in the second magnetic separation step into a hot water bath having a water temperature higher than the boiling point of the second volatile hydrophobic solvent, and volatilizing and removing the second volatile hydrophobic solvent remaining in the second powder phase; and a dehydration step of dehydrating the slurry containing the second powder phase obtained in the residual solvent volatilization step using a dehydrator.

[15] A method for recovering powder according to any one of the above items [8] to

[13] , characterized by comprising a drying step of drying the second powder phase obtained in the second magnetic separation step at a temperature above the boiling point of the second volatile hydrophobic solvent.

[16] The method for recovering powder according to any one of the above [8] to

[15] , wherein the first volatile hydrophobic solvent and the second volatile solvent are the same solvent.

[17] The method for recovering powder according to any one of the above [1] to

[16] , characterized in that the content of the magnetic substances in the powder is 20 mass % or more.

[18] The method for recovering powder according to any one of the above [1] to

[17] , characterized in that the oily powder is either oily scale or oily grinding dust, or a mixture thereof.

[0014]

[19] A powder recovery system that separates oil from powder containing magnetic particles and recovers the powder, a slurrying device for mixing the powder with water to produce a slurry; a first emulsifying device for adding a first volatile hydrophobic solvent to the slurry and then mixing the mixture to form a first emulsion; a first magnetic separator that separates and recovers a first powder phase from the first emulsion by magnetic force; A powder recovery facility comprising:

[20] The powder recovery equipment according to

[19] above, further comprising: a second emulsification device that adds a second volatile hydrophobic solvent to the recovered first powder phase and then mixes them to form a second emulsion; and a second magnetic separator that separates and recovers the second powder phase from the second emulsion by magnetic force.

[21] The powder recovery equipment according to

[20] above, characterized in that the first emulsification device, the first magnetic separator, the second emulsification device, and the second magnetic separator are arranged in tandem in a single counterflow tank, and the flow of the first powder phase and the second powder phase is countercurrent to the flow of the aqueous phase and the solvent phase. [Effects of the Invention]

[0015] According to the above aspects of the present invention, it is possible to provide a powder recovery method and powder recovery equipment that can reduce the energy required to remove oil from oil-containing powder and increase the oil removal rate and powder recovery rate. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing the state of oil and water in oil-containing scale. [Figure 2] FIG. 2 is a flowchart illustrating the powder recovery method according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram for explaining an outline of the powder recovery method according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing the powder recovery equipment according to this embodiment and a continuous treatment (continuous process) using the same. [Figure 5] FIG. 5 is a graph showing the relationship between the blending ratio of water to powder (water / powder (g / g)) and the viscosity (Pa·s) of the slurry in Examples 1-8 to 1-12. [Figure 6] FIG. 6 is a graph showing the relationship between the viscosity (Pa·s) of the slurry and the oil removal rate (%) in Examples 1-8 to 1-12. [Figure 7] FIG. 7 is a graph showing the relationship between the blending ratio of cleaning solvent to powder (cleaning solvent / powder (g / g)) and the oil removal rate (%) in Invention Examples 1-10 and 1-17 to 1-19. [Figure 8] FIG. 8 is a graph showing the relationship between the oil concentration in the solvent and the absorbance of the solvent phase in Example 5. [Figure 9] FIG. 9 is a graph showing the relationship between the absorbance of the solvent phase and the oil concentration in the cake in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0017] The powder recovery method and powder recovery equipment according to the present embodiment will be described with reference to the drawings. In this specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, and redundant description will be omitted. A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0018] First, the treatment object, solution, etc. in the powder recovery method will be described together with new findings obtained by the present inventors.

[0019] The powder recovery method of this embodiment is a method of recovering powder from which oil has been removed using magnetic force. Therefore, the object to be treated in the powder recovery method of this embodiment is powder to which oil is attached and which contains magnetically attached matter (oil-containing powder), such as scale and grinding dust generated in the rolling process. The scale referred to here is scale containing oil and moisture, and is sometimes called oil-containing scale or oil-containing sludge.

[0020] The particle size of the oil-containing powder to be treated is not particularly limited, but for example, the oil-containing powder may have an average particle size of 5 μm to 200 μm. The particle size of the powder can be measured by a laser diffraction / scattering method, and the average particle size is based on the volume.

[0021] Next, the state of existence of oil and water in oil-containing scale will be explained using an example in which the oil-containing powder is oil-containing scale. FIG. 1 is a schematic diagram showing the state of oil and moisture in oil-impregnated scale. Note that the shapes and dimensional ratios of the components shown in FIG. 1 are shown to differ from the actual shapes for ease of explanation, but the oil-impregnated powder in this embodiment is not limited to that shown in FIG. 1. As shown in FIG. 1, moisture and oil in oil-impregnated scale exist as oil and moisture in the bulk, oil and moisture in the pores, oil and moisture in the capillaries, and oil and moisture adsorbed to the scale. Oil and moisture refers to a state in which oil and moisture are mixed. Furthermore, the bulk here refers to the outer region of the scale particles that is not in contact with the interface of the scale particles.

[0022] Oil and water in the bulk refers to the water and oil present around scale particles. Oil and water in pores refers to the water and oil surrounded by gaps formed by aggregations of large and small solid particles such as scale. Oil and water in capillaries refers to the water and oil bound together by capillary pressure within the capillaries on the surface of the scale. Oil and water adsorbed to particles such as scale refers to the water and oil chemically adsorbed to the scale.

[0023] The oil and water in the bulk have almost no binding force with particle groups such as scale, and are easily separated by applying external pressure. They can be separated by mechanical force, for example, dehydration and deoiling using a pressurized dehydrator or centrifugal dehydrator, or by natural dehydration and deoiling by leaving them to stand.

[0024] On the other hand, because the oil and water in the gaps are surrounded by solid particles such as scale, it is extremely difficult to separate them by dehydration / deoiling using mechanical force or by leaving them to stand.

[0025] Furthermore, the oil and moisture in the capillaries is water and oil held by capillary force inside the capillaries on the surface of particles such as scale, and like the oil and moisture in the gaps, it is difficult to separate by dehydration / deoiling using mechanical force or by leaving it to stand.

[0026] Furthermore, the oil and moisture adsorbed to particles such as scale is water and oil that is chemically bonded to the surface or interior of the particles, and can only be separated by evaporation due to an increase in temperature or by chemical reaction.In other words, oil and moisture in pores, in capillaries, and oil and moisture adsorbed to particles cannot be easily separated by normal dehydration and deoiling operations (mechanical dehydration and deoiling using a centrifugal dehydrator or filter press, or natural dehydration and deoiling by leaving to stand, etc.).

[0027] To address these issues, the inventors investigated methods of using solvents as a means of separating and removing oil and water, especially oil. Based on the results of their investigation, they concluded that the oil in the bulk, gaps, and capillaries, as well as the oil adhering to the particles, could be adsorbed by a solvent and separated from the powder, and they continued their investigations.

[0028] When an organic solvent is added to oil-containing scale and then stirred to extract the oil from the scale, the oil in the bulk is easily extracted because it comes into contact with the organic solvent. On the other hand, the oil in the gaps and capillaries is surrounded by scale, and water is also present in the gaps and capillaries. Therefore, the oil in the gaps and capillaries and the organic solvent are blocked by the water and scale, and the organic solvent cannot easily come into contact with the oil in the gaps and capillaries. In other words, the oil in the gaps and capillaries is difficult to extract by simply adding an organic solvent and stirring, and the oil content is unlikely to decrease.

[0029] The inventors have discovered that the oil content in oil-containing scale can be reduced by extracting the oil in the gaps and capillaries, which cannot be easily separated by ordinary dehydration and deoiling operations, with an easily volatile hydrophobic organic solvent (hereinafter also referred to as a volatile hydrophobic solvent), and then volatilizing the volatile hydrophobic solvent in the gaps and capillaries.

[0030] Furthermore, when a hydrophobic organic solvent is used as a means of separating oil from oil-containing powder, vigorously stirring a mixture of the organic solvent, oil-containing powder, and water results in an emulsion in which many powder particles are dispersed in the aqueous phase between the solvent droplets, allowing the oil to be extracted by the solvent. However, it has been found that if emulsification is insufficient, oil extraction by the solvent does not proceed sufficiently. In regions where emulsification is insufficient, the powder does not have sufficient fluidity in the slurry consisting of water and oil-containing powder, so the solvent is not mixed uniformly and the probability of contact between the solvent and powder is significantly reduced, which is thought to hinder oil extraction. Therefore, when emulsifying a mixture of a hydrophobic organic solvent and oil-containing powder, it is important to fully understand the emulsification region and then determine the mixing ratio.

[0031] Generally, when a mixture of a hydrophobic organic solvent and water is vigorously stirred and allowed to stand, an emulsion temporarily forms, but the emulsion usually dissolves within a short period of time. However, when a mixture containing a highly hydrophilic (wettable) fine powder, such as the above-mentioned mixture of fine oil-containing powder, organic solvent, and water, is vigorously stirred and allowed to stand, oil extraction can be promoted, but the emulsion may not be easily broken down and may become stable. This is because the solid fine powder functions as an emulsifier, stabilizing the emulsion by being present at the interface between the fine water droplets and the organic solvent phase, or between the fine organic solvent droplets and the aqueous phase. Once the emulsion is stabilized, the hydrophobic organic solvent, water, and fine powder cannot be easily separated, so the emulsion must be broken to recover the powder.

[0032] Therefore, the present inventors investigated a method of applying magnetic force to an emulsion using a magnetic separator capable of magnetic sorting (hereinafter simply referred to as magnetic separation) as a method of breaking down an emulsion and recovering powder containing magnetically attached materials from which oil and water have been removed. As a result, they found that it is possible to break down an emulsion and separate the powder phase using magnetic force, and to recover only the powder phase from which the oil has been removed. In this way, by applying magnetic force to an emulsion, the powder containing magnetically attached materials in the emulsion is moved in the direction of the magnetic force, and the emulsion is dissolved (demulsified), i.e., broken, in a short period of time.

[0033] The present invention was made based on the new findings described above. Next, a powder recovery method and a powder recovery system according to one embodiment of the present invention will be described with reference to the drawings.

[0034] <1. Powder recovery method> Fig. 2 is a flowchart showing the powder recovery method according to this embodiment, and Fig. 3 is a schematic diagram for explaining the outline of the powder recovery method according to this embodiment. As shown in FIG. 2, the powder recovery method according to this embodiment includes a slurrying step S1, a first emulsifying step S2-1, and a first magnetic separation step S2-2. Each step will be described below with reference to Fig. 3. For ease of explanation, Fig. 3 shows a case where a magnetic separator is provided in each step, but the powder recovery method according to this embodiment is not limited by the devices and facilities used.

[0035] (Slurrying step S1) The slurrying step S1 is a step in which oil-containing powder 10 and water 20 are mixed in a container to produce a slurry 30 (FIG. 3(a)). In the slurrying step S1, first, powder 10 and water 20 are put into a container and stirred (mixed) to disperse powder 10 in water 20, thereby generating slurry 30.

[0036] The oil-containing powder 10 is a powder containing magnetic substances, such as scale and grinding dust. The oil-containing powder 10 may be a mixture of scale and grinding dust. Scale is a magnetic substance, primarily composed of FeO and Fe3O4, but may contain components with low magnetic attraction. When the oil-containing powder 10 is composed of both magnetic and non-magnetic substances, it is preferable to use an oil-containing powder 10 with a high content of magnetic substances in order to improve the efficiency of recovery by magnetic force. Specifically, the content of magnetic substances is preferably 20% by mass or more. Furthermore, when the content of magnetic substances is low, for example, less than 20% by mass, new magnetic substances such as iron powder may be added to the oil-containing powder 10 to increase the total content of magnetic substances in the entire oil-containing powder 10 to 20% by mass or more. This allows both the magnetic substances in the original oil-containing powder and the newly added magnetic substances to be recovered by magnetic force. However, in consideration of the reuse of recovered materials, it is preferable from the viewpoint of energy that the ratio of newly added magnetized materials be smaller than the ratio of magnetized materials originally present in the oil-containing powder.

[0037] Here, scale refers to iron oxide, primarily composed of FeO and Fe3O4, that forms on the surface of a slab during hot rolling. Such scale is finely pulverized during hot rolling and discharged together with the coolant water. That is, a water-containing slurry (water-containing scale) in which fine scale is dispersed in the coolant water is discharged. In such cases, when using this water-containing slurry, the slurrying step S1 may be omitted and the water-containing slurry may be directly used in the first emulsification step described below. Note that the water-containing slurry generated during hot rolling generally contains 3 to 8 mass % of oil (mass % relative to the total mass of the powder).

[0038] The specific gravity of the oil-containing powder 10 used in this embodiment is not particularly limited, but may be greater than 1.05. Furthermore, the oil-containing powder 10 is preferably hydrophilic particles such as scale or grinding dust. Hydrophilic particles are particles that have an affinity for water and have the property of easily mixing with water. It is more preferable that the oil-containing powder 10 is composed only of hydrophilic particles, but it may also contain other types of particles, such as hydrophobic particles, as long as the effects of the present invention are not impaired. Hydrophobic particles are particles that are hydrophobic to water, and examples thereof include coke powder and plastic powder.

[0039] The specific gravity of the oil-containing powder 10 is preferably greater than the specific gravity of the first volatile hydrophobic solvent (hereinafter also referred to as cleaning solvent) 50 used in the subsequent first emulsification step S2-1. This allows the water 20 present between the particles of the oil-containing powder 10 to be replaced with the first volatile hydrophobic solvent 50 when the emulsion is subsequently broken down to effect phase separation, and as a result, the energy required to dry the oil-containing powder 10 can be reduced.

[0040] The particle size of the oil-containing powder 10 is not particularly limited, but the volume-based 50% particle size (d 50 ) is preferably 200 μm or less. In this embodiment, by substituting the water 20 present between the particles of the oil-containing powder 10 with the first volatile hydrophobic solvent 50, the energy required to dry the oil-containing powder 10 is reduced and the powder is efficiently recovered. The first volatile hydrophobic solvent 50 evaporates with less energy than the water 20. Therefore, by substituting the water 20 present between the particles of the oil-containing powder 10 with the first volatile hydrophobic solvent 50, the energy required to dry the oil-containing powder 10 can be reduced. Furthermore, the smaller the particle diameter of the oil-containing powder 10, the larger the gaps present between the particles of the oil-containing powder 10, so that more water 20 can be substituted with the first volatile hydrophobic solvent 50, resulting in an increase in the above-mentioned effect. From this perspective, it is preferable that the particle diameter of the oil-containing powder 10 is small, and the volume-based 50% particle diameter (d 50) is preferably 100 μm or less. More preferably, it is 80 μm or less, and even more preferably, it is 50 μm or less. On the other hand, if the volume-based 50% particle size of the oil-containing powder 10 is less than 1 μm, the amount of capillary water and adsorbed water will be greater than the interstitial water. As a result, the hydrophilicity of the oil-containing powder 10 will be very high, and even if the treatment of this embodiment is performed, it may be difficult to remove the water 20 present between the particles of the oil-containing powder 10. Therefore, the lower limit of the volume-based 50% particle size of the oil-containing powder 10 is preferably 1 μm or more.

[0041] The volumetric 50% particle diameter (d 50 ) can be measured, for example, by the following measurement method using a laser diffraction particle size analyzer. Specifically, first, the sample to be measured is slurried with water, and a small amount of sodium hexametaphosphate solution is added as a dispersant to form a mixed liquid. The mixed liquid is then stirred and irradiated with ultrasonic waves to disperse the sample in the mixed liquid. Next, the mixed liquid is placed in the laser diffraction particle size analyzer, and the particle size distribution is measured.

[0042] The amount of water 20 added in the slurrying step S1 is set to an amount sufficient to turn the powder 10 into a slurry in the water 20. Note that the viscosity of the slurry 30 increases in the subsequent first emulsification step due to the addition of the first volatile hydrophobic solvent 50 to the slurry 30. Therefore, it is preferable to set the viscosity in the slurrying step S1 lower than the target viscosity. Specifically, water 20 is added to the powder 10 so that the viscosity of the slurry in the slurrying step S1 is 2.00 Pa·S or less. The viscosity of the slurry is preferably 0.65 Pa·S or less, more preferably 0.50 Pa·S or less, and even more preferably 0.35 Pa·S or less. On the other hand, if too much water is added in the slurrying step S1, the probability of contact between the oil-containing powder 10 and the first volatile hydrophobic solvent 50 decreases after the first emulsification step. In such a case, it is necessary to extend the oil extraction time from the powder 10 or increase the stirring intensity, which is undesirable from the viewpoint of work efficiency. Therefore, the amount of water 20 added to the oil-containing powder 10 is adjusted so that the viscosity of the slurry becomes 0.003 Pa·S or more, more preferably 0.1 Pa·S or more.

[0043] The viscosity of a slurry can be determined by first measuring the viscous resistance torque using a rotational viscometer and then converting the obtained viscous resistance torque into viscosity. Specifically, 300 ml of the prepared slurry is placed in a tall beaker, and the rotor of the rotational viscometer is immersed in the slurry and rotated to measure the viscous resistance torque of the slurry acting on the rotor. The obtained viscous resistance torque is then converted into viscosity.

[0044] The reason for limiting the viscosity in the slurrying step S1 will now be explained together with the results of the inventor's investigation. The present inventors have investigated the correlation between the degree of emulsification in the first emulsification step S2-1 and the progress of oil extraction, and have found that insufficient emulsification results in insufficient oil extraction by the cleaning solvent. This is thought to be because, when emulsification is insufficient, the oil-containing powder does not have sufficient fluidity in the slurry, and even when the cleaning solvent is added, the solvent is not mixed uniformly, thereby not promoting oil extraction. In other words, to extract oil from the oil-containing powder in the emulsion, each particle of the oil-containing powder must come into contact with a droplet of the cleaning solvent. To achieve this, the oil-containing powder must be able to move freely in the aqueous phase. After investigating an index for evaluating this "ability to move freely in the aqueous phase," the present inventors have found that it can be evaluated using the viscosity of the slurry. As the ratio of oil-containing powder in the slurry increases, the viscosity of the slurry increases rapidly and the fluidity of the slurry decreases significantly, so that even if an emulsification is subsequently performed, the contact between the oil-containing powder and droplets of the cleaning solvent decreases rapidly. For this reason, in this embodiment, as described above, it is important to keep the viscosity of the slurry in the slurry formation step S1 to 2.00 Pa·S or less.

[0045] In addition, in this embodiment, from the viewpoint of stable emulsification, the powder 10 and water 20 are mixed in advance to prepare the slurry 30, and in the next step, the first volatile hydrophobic solvent 50 is added to the slurry 30. When the powder 10, water 20, and first volatile hydrophobic solvent 50 are mixed at the same time, the mixing of the water 20 and the powder 10 may be difficult, making emulsification difficult. In particular, when the water / powder mixing ratio (g / g) is small, emulsification becomes difficult and the oil removal performance decreases. Therefore, in the slurrying step S1, it is preferable to mix the water 20 and the powder 10 in advance, form a slurry, and then add the first volatile hydrophobic solvent 50 to the obtained slurry and mix it to emulsify it.

[0046] The mixing device used in the slurrying step S1 is not particularly limited, but for example, a vessel equipped with stirring blades for stirring the mixture of powder 10 and water 20, a line mixer, or the like can be used.

[0047] (Washing step S2) (First emulsification step S2-1) The first emulsification step S2-1 is a step of adding a first volatile hydrophobic solvent 50 to the slurry 30 produced in the slurrying step S1 and stirring the mixture to form an emulsion 40 (FIG. 3(b)). In the first emulsification step S2-1, first, a first volatile hydrophobic solvent 50 having a specific gravity greater than 1.05 and less than 2.0 is added to a container containing a slurry 30 consisting of powder 10 and water 20, and the mixture is further stirred to form an emulsion 40. Note that in the first emulsification step S2-1, the slurry 30 may be transferred from the container used in the slurrying step S1 to another container to form the emulsion 40.

[0048] Generally, an emulsion is a dispersion solution of two immiscible liquids, one of which is dispersed as fine droplets in the other, and is also called an emulsion. The emulsion 40 according to this embodiment is a dispersion solution in which two liquids (water 20 and a first volatile hydrophobic solvent 50) with different specific gravities and a solid powder 10 are suspended.

[0049] The first volatile hydrophobic solvent 50 is a liquid that is both volatile and hydrophobic, i.e., has a low affinity for water (i.e., is poorly soluble in water or poorly miscible with water). The first volatile hydrophobic solvent 50 is, for example, a liquid whose solubility in water at room temperature (25°C) is 0 g / L or more and 10.0 g / L or less. If the first volatile hydrophobic solvent 50 has a high solubility in water, a large amount of water 20 remains in the first volatile hydrophobic solvent 50 when the water 20 present between particles of the powder 10 is replaced with the first volatile hydrophobic solvent 50. In this case, it may be difficult to sufficiently reduce the energy required to dry the powder 10 after the powder phase recovery step S4. From this perspective, the solubility in water of the first volatile hydrophobic solvent 50 is preferably 10.0 g / L or less, more preferably 5.0 g / L or less, at room temperature. In this case, the amount of water 20 remaining in the first volatile hydrophobic solvent 50 can be further reduced.

[0050] In this embodiment, "hydrophobic" may also mean a property including lipophilicity, and the first volatile hydrophobic solvent 50 may be, for example, an organic solvent or various oils having hydrophobic properties.

[0051] The specific gravity of the first volatile hydrophobic solvent 50 is not particularly limited, as it does not significantly affect the magnetic separation that separates oil from the oil-containing powder. Considering the difference in specific gravity of each element after emulsion breaking, the specific gravity of the first volatile hydrophobic solvent 50 is preferably greater than that of water and less than that of the powder 10 to be recovered. Specifically, the specific gravity of the first volatile hydrophobic solvent 50 is preferably greater than 1.05 and less than 2.0. This allows the water generated after emulsion breaking to be separated from the first volatile hydrophobic solvent 50 based on the difference in specific gravity. However, as described above, the specific gravity of the first volatile hydrophobic solvent 50 is not limited to this range and may be 1.05 or less, as long as the water generated after emulsion breaking can be separated from the first volatile hydrophobic solvent 50 based on the difference in specific gravity.

[0052] The boiling point of the first volatile hydrophobic solvent 50 is preferably less than 95°C at normal pressure. If the upper limit of the boiling point is less than 95°C, the first volatile hydrophobic solvent 50 remaining in the powder phase can be easily removed (for example, with steam, which is an inexpensive energy source) after the powder phase is recovered in a subsequent process. There is no particular restriction on the lower limit of the boiling point of the first volatile hydrophobic solvent 50, but it is preferably 50°C or higher because the oil extraction operation can be easily carried out at room temperature.

[0053] Furthermore, the volatilization calorific value of the first volatile hydrophobic solvent 50 is preferably smaller than that of water, which makes it easier to volatilize and remove the first volatile hydrophobic solvent 50, and to separate it from the powder 10.

[0054] Furthermore, it is preferable to select a solvent with a large KB value (kauri-butanol value) as the solvent used as the first volatile hydrophobic solvent 50 in order to remove oil more efficiently from the powder 10. By using a solvent with a large KB value as the first volatile hydrophobic solvent 50, oil can be more easily absorbed. From the viewpoint of the KB value, it is preferable to use, for example, trichloroethylene or 1-bromopropane as the first volatile hydrophobic solvent 50. Furthermore, hydrofluoroether may also be used as the first volatile hydrophobic solvent 50.

[0055] The amount of the first volatile hydrophobic solvent 50 added to the oil-adhered powder 10 (the rate of addition of the cleaning solvent) is not particularly limited, and may be determined appropriately depending on the type of solvent used, the equipment used, etc. From the viewpoint of the rate of removal of oil, a larger amount is preferable.

[0056] In this embodiment, a polymer flocculant may be added to the slurry 30 in addition to the first volatile hydrophobic solvent 50. The powder recovery method of this embodiment recovers the powder using magnetic force. However, if the powder contains a large amount of low-magnetic components or non-magnetic materials, magnetic recovery may be insufficient. Therefore, if the powder contains a large amount of low-magnetic components or non-magnetic materials, it is preferable to add a polymer flocculant together with the first volatile hydrophobic solvent 50. This allows the magnetic and non-magnetic materials to be aggregated, so that non-magnetic materials can also be recovered when recovering the powder using magnetic force. Anionic polymer flocculants are preferably used as the polymer flocculant, such as carboxylic acid-based or sulfonic acid-based polymer flocculants. The timing of adding the polymer flocculant is not limited to the first emulsification step S2-1, but may also be during the slurrying step S1.

[0057] Whether a powder contains a large amount of low-magnetic components or non-magnetic materials can be determined by the proportion of magnetic materials in the powder. For example, if the proportion of magnetic materials is less than 20% by mass, it can be determined that the powder contains a large amount of low-magnetic components or non-magnetic materials. Alternatively, the powder can be actually recovered using magnetic force and the recovery rate can be determined based on the recovery rate. In addition to adding a polymer flocculant, as mentioned above, the recovery rate can also be improved by adding new magnetic materials such as iron powder to increase the proportion of magnetic materials in the powder. The addition of a polymer flocculant and the addition of new magnetic materials can also be used in combination.

[0058] (1st magnetic separation process S2-2) The first magnetic separation step S2-2 is a step of separating and recovering the first powder phase 10a from the first emulsion 40 formed in the first emulsification step S2-2 by magnetic separation (FIG. 3(c)).

[0059] The first magnetic separation step S2-2 is performed using a first magnetic separator 80. From the viewpoint of magnetic separation efficiency, it is preferable to use a drum-type separator as the first magnetic separator 80. Below, a case where a drum-type separator is used as the first magnetic separator 80 will be described.

[0060] First, as shown in Fig. 3(c), the emulsion 40 and the drum 81 of the first magnetic separator 80 are brought into contact with each other, and a magnetic force is applied to the emulsion 40 by a magnet 82 fixed inside the drum 81. When the magnetic force is applied to the emulsion 40, only the powder 10 in the emulsion 40 is magnetically attracted to the surface of the drum 81, and as the drum 81 rotates, the powder phase (first powder phase) 10a is collected.

[0061] When the powder 10 of the emulsion 40 is magnetically attracted to the surface of the drum 81, the solvent droplets in the emulsion coalesce into a solvent phase, resulting in the emulsion 40 being broken down and separated into water 20 and the first volatile hydrophobic solvent 50.

[0062] By the above steps, the powder from which the oil has been removed can be collected. Note that residual water and solvent may be present in the powder phase 10a magnetically attached to the surface of the drum 81. In such cases, it is advisable to apply pressure to the powder phase 10a magnetically attached to the surface of the drum 81 using a squeeze roll 83 as shown in Fig. 3(c) to remove the liquid. The liquid-removing means is not limited to the squeeze roll 83, and a squeeze guide 84 (see Fig. 4) as described later may also be used.

[0063] Furthermore, the washing step S2, which is comprised of the first emulsification step S2-1 and the first magnetic separation step S2-2, may be repeated two or more times, thereby further increasing the oil removal rate.

[0064] Furthermore, in order to further increase the efficiency of removing the residual solvent, the following rinsing step S3 and a residual solvent volatilization step may be further carried out.

[0065] (Rinse step S3) (Second emulsification step S3-1) (Second magnetic separation process S3-2) In this embodiment, a second emulsification step S3-1 (Figure 3(d)) may be carried out in which a second volatile hydrophobic solvent 51 is added to the powder phase 10a obtained in the washing step S2 and then mixed to form a second emulsion 41, and a second magnetic separation step (Figure 3(e)) may be carried out in which the second powder phase 10aa is separated and recovered from the second emulsion by magnetic separation.

[0066] As described above, residual water and solvent may be present in the powder phase 10a magnetically attached to the surface of the drum 81. Therefore, by performing emulsification and magnetic separation again using the powder phase 10a obtained in the washing step S2, it is possible to recover powder (second powder phase 10aa) from which more oil has been removed.

[0067] The specific implementation methods and conditions for the second emulsification step S3-1 and the second magnetic separation step S3-2 may be the same as those for the first emulsification step S2-1 and the first magnetic separation step S2-2, respectively.

[0068] For example, the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 may be the same or different solvents, but from the viewpoint of efficiency in the residual solvent evaporation step and drying step described below, it is preferable that the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 be the same solvent.

[0069] Similarly to the first volatile hydrophobic solvent 50, the specific gravity of the second volatile hydrophobic solvent 51 is not particularly limited because it does not significantly affect the magnetic separation that separates oil from the oil-containing powder. Considering the difference in specific gravity between the elements after the emulsion is broken, the specific gravity of the second volatile hydrophobic solvent 51 is preferably greater than that of water and less than that of the powder 10 to be recovered. Specifically, the specific gravity of the second volatile hydrophobic solvent 51 is preferably greater than 1.05 and less than 2.0. This allows the water generated after the emulsion is broken and the second volatile hydrophobic solvent 51 to be separated based on the difference in specific gravity. However, as described above, the specific gravity of the second volatile hydrophobic solvent 51 is not limited to this range and may be 1.05 or less, as long as the water generated after the emulsion is broken and the first volatile hydrophobic solvent 50 can be separated based on the difference in specific gravity.

[0070] Furthermore, the rinsing step S3, which is composed of the second emulsification step S3-1 and the second magnetic separation step S3-2, may be repeated two or more times, thereby further increasing the oil removal rate.

[0071] In this embodiment, from the viewpoint of improving the efficiency of the recovery operation and the recovery speed, it is preferable to perform the cleaning step S2 and the rinsing step S3 in a counterflow continuous process in one counterflow tank. Details of the recovery equipment employing the counterflow continuous process will be described later.

[0072] The amount of the second volatile hydrophobic solvent 51 to be added is preferably calculated as follows. First, the residual solvent phase removed in the rinsing step S3 is separated by gravity into an aqueous phase containing almost no oil and a solvent phase containing oil, and the absorbance of the solvent phase containing oil is measured. From the absorbance measurement obtained, the amount of oil remaining in the powder phase after the rinsing step S3 is estimated, and the amount of second volatile hydrophobic solvent 51 added is adjusted so that the estimated value of the residual oil amount is equal to or less than a target value.

[0073] That is, if the residual solvent phase removed by the rinsing step S3 contains a large amount of oil (high absorbance), it can be determined that a large amount of oil remains that was not completely removed from the powder phase 10a, and in that case, the amount of the second volatile hydrophobic solvent 51 added should be increased. On the other hand, if the residual solvent phase removed by the rinsing step S3 contains almost no oil (low absorbance), it can be said that the oil has been sufficiently removed from the powder phase 10a, and the amount of the second volatile hydrophobic solvent 51 added should be reduced. This allows the residual solvent phase to be efficiently removed from the powder phase 10a, and also allows the amount of residual oil in the recovered powder phase to be controlled by the absorbance of the residual solvent phase containing the oil removed by the rinsing step S3.

[0074] The absorbance of the residual solvent phase containing the oil removed in the rinsing step S3 can be measured, for example, by placing the residual solvent phase to be measured in a sealed cell and measuring the absorbance with an absorption spectrometer. Since oil is generally yellowish, an absorption wavelength of around 350 to 500 nm can be used when measuring the absorbance of the residual solvent phase containing oil.

[0075] The oil-containing solvent phase recovered from the waste liquid (washing waste liquid) discharged in the washing step S2 may be distilled and then recycled as an oil-free volatile hydrophobic solvent. This recycled volatile hydrophobic solvent can be used as the first volatile hydrophobic solvent or the second volatile hydrophobic solvent. Furthermore, the solvent phase recovered from the waste liquid (rinse waste liquid) discharged in the rinsing step S3 has a low oil content and can therefore be used as the first volatile hydrophobic solvent (cleaning solvent). From the viewpoint of such reuse, it is preferable to use the same solvent as the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51.

[0076] (Residual solvent evaporation process S4) After the rinsing step S3, a residual solvent evaporation step S4 may be performed to remove the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 remaining in the recovered powder phase 10aa. The recovered powder phase 10aa may contain the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 that have not been completely removed. In such cases, it is preferable to remove these solvents. Specifically, these solvents may be removed by, for example, drying or evaporation.

[0077] When the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 are removed by drying, the drying temperature is preferably set to a temperature higher than the boiling point of the first volatile hydrophobic solvent 50. This allows each solvent to be dried and removed efficiently from the powder phase 10aa. Note that when a hydrophobic solvent different from the first volatile hydrophobic solvent 50 is used as the second volatile hydrophobic solvent 51 in the rinsing step, the solvents may be dried and removed at a temperature higher than the boiling point of the first volatile hydrophobic solvent 50 or the second volatile hydrophobic solvent 51.

[0078] The drying means is not particularly limited, but for example, an indirect heating dryer, a vacuum indirect heating dryer, or the like may be used for drying.

[0079] When removing the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 by volatilization, the powder phase 10aa is first placed in a hot water bath whose temperature is higher than the boiling point of the first volatile hydrophobic solvent 50, where the first volatile hydrophobic solvent 50 is volatilized and removed. The powder phase 10aa placed in the hot water bath is converted into a slurry, and after the solvent is volatilized and removed, the slurry is dehydrated in a dehydrator. This allows the powder 10 from which the solvents have been removed to be recovered. The dehydrator may be a magnetic separator similar to the first magnetic separator 80, or a centrifuge, screw press, or filtration-type dehydrator. Note that when a hydrophobic solvent different from the first volatile hydrophobic solvent 50 is used as the second volatile hydrophobic solvent 51 in the rinsing step S3, the water temperature of the hot water bath may be set to the higher of the boiling points of the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51.

[0080] As described above, a portion of the liquid contained in the powder phase (powder cake) 10aa after the rinsing step S3 is the first volatile hydrophobic solvent 50 or the second volatile hydrophobic solvent 51. Therefore, the powder phase 10aa can be dried with less energy (heat of vaporization). As shown in the examples described later, the energy required to dry the powder phase can be measured by differential scanning calorimetry (DSC), but it can also be measured by other methods, such as the Karl Fischer method.

[0081] The powder recovery method according to this embodiment has been described above, but the temperature and pressure when carrying out each step are not particularly limited, and the steps may be carried out, for example, at room temperature and normal pressure. Furthermore, in the above, the rinsing step S3 is followed by the residual solvent volatilizing step S4, but the rinsing step S3 may be omitted and the residual solvent volatilizing step S4 may be performed after the cleaning step S2.

[0082] In addition, in the powder recovery method according to this embodiment, each of the steps from the slurrying step S1 to the residual solvent evaporation step S4 can be carried out as a batch process. However, from the viewpoints of the solid-liquid separation speed, the powder recovery speed, and productivity, it is preferable to carry out these steps as a continuous process in which they are carried out simultaneously in parallel.

[0083] According to the powder recovery method of this embodiment, a magnetic separator is used to extract and remove oil using a volatile hydrophobic solvent, which significantly reduces the energy required to remove oil from oil-containing powder compared to conventional combustion treatment methods. Furthermore, since the voids in the recovered powder phase contain a large amount of volatile hydrophobic solvent, this can be easily removed, allowing for the efficient recovery of low-moisture, high-purity powder that contains almost no oil. In other words, the powder recovery method of this embodiment provides a new and improved powder recovery method that can increase the oil removal rate and solid-liquid separation speed.

[0084] <2. Powder recovery equipment> Next, an embodiment of a powder recovery facility for carrying out the powder recovery method of the present embodiment will be described.

[0085] The powder recovery equipment according to this embodiment is equipment that separates oil from oil-adhered powder and recovers the powder. Each device in the powder recovery equipment according to this embodiment may be provided as a batch system (see FIG. 3), but from the viewpoint of improving the efficiency of the recovery work and the recovery speed, the equipment may also be provided as a so-called countercurrent continuous process in which the emulsifier and magnetic separator are placed in a single counterflow tank and the respective steps are carried out simultaneously and continuously. In the following description, an example of the recovery equipment of this embodiment will be described, taking as an example a case where the recovery equipment is implemented in a countercurrent continuous process.

[0086] FIG. 4 is a schematic diagram showing a powder recovery facility 1 according to this embodiment and a continuous treatment (continuous process) using the same. The powder recovery equipment 1 of this embodiment includes a slurrying device 60, a first emulsifying device 70, and a first magnetic separator 80 that separates and recovers the first powder phase using magnetic force. The first emulsifying device 70 and the first magnetic separator 80 are arranged in a vertical line from upstream to downstream in a counterflow tank 100 filled with the slurry and each volatile hydrophobic solvent. In this embodiment, "upstream" refers to the first emulsifying device 70 side, and "downstream" refers to the second magnetic separator 90 side. In other words, the flow from upstream to downstream refers to the transport direction of the powder phase. Meanwhile, the flow of the aqueous phase and the solvent phase is from downstream to upstream, countercurrent to the flow of the powder phase.

[0087] The slurrying device 60 is a device that performs the slurrying step S1, and stirs and mixes the oil-containing powder 10 and water 20 to generate the slurry 30. Any known device can be used as the slurrying device 60, and for example, a vessel equipped with a stirring blade and a motor for stirring the mixture of the powder 10 and water 20, a line mixer, or the like can be used.

[0088] The slurrying apparatus 60 can be connected to a downstream first emulsifying apparatus 70, for example, via piping. A pump P is connected to the piping, and the pump P sends the slurry 30 to the emulsifying apparatus 70. Although the slurry 30 is introduced from above the equipment in FIG. 4, it may also be introduced from the side of the equipment.

[0089] The first emulsifier 70 is an apparatus that performs the first emulsification step S2-1, stirring and mixing the slurry 30 and the first volatile hydrophobic solvent 50 to form the emulsion 40. Since this embodiment is a countercurrent type, the solvent phase flows from downstream to upstream. That is, the first volatile hydrophobic solvent 50 used in the first emulsifier 70 flows in from the downstream side, and therefore the introduction position of the first volatile hydrophobic solvent 50 is downstream of the first emulsifier 70. Specifically, the first volatile hydrophobic solvent 50 is preferably introduced from above the second emulsifier 71. However, the introduction position of the first volatile hydrophobic solvent 50 is not limited to one location, and it may be introduced from above the first emulsifier 70. Known devices can be used for the first emulsifier 70, such as a vessel equipped with an agitator blade and a motor for agitating the mixture of the slurry 30 and the first volatile hydrophobic solvent 50, or a line mixer.

[0090] Since the recovery equipment 1 of this embodiment is a countercurrent continuous recovery equipment in which the flow of the powder phase and the flow of the aqueous phase and solvent phase are countercurrent, the second volatile hydrophobic solvent 51 used in the subsequent rinsing step S3 flows into the cleaning step S1. In other words, since the first emulsification device 70 uses two solvents, the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51, it is preferable that the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 are the same type of solvent.

[0091] The first emulsification device 70 stirs and mixes the slurry 30 and the first volatile hydrophobic solvent 50 by rotating the stirring blades with the motor M. As a result, the powder 10, water 20, and first volatile hydrophobic solvent 50 are strongly stirred, thereby producing the emulsion 40 described above. Furthermore, the first volatile hydrophobic solvent 50 acts as an extractant for the oil, extracting the oil from the powder 10.

[0092] The first magnetic separator 80 is a device that performs the first magnetic separation step S2-2, and separates and recovers the first powder phase by magnetic force. The first magnetic separator 80 is disposed downstream of the first emulsifier 70. From the viewpoint of magnetic separation efficiency, it is preferable to use a drum-type separator. Below, a case where a drum-type separator is used as the first magnetic separator 80 will be described.

[0093] The first magnetic separator 80 includes a drum 81, a magnet 82 provided inside the drum 81, and a squeeze guide 84 provided on the upper part of the drum 81. The first magnetic separator 80 is provided so that at least a portion of the drum 81 and the magnet 82 are immersed in the emulsion 40, and a magnetic force is applied to the emulsion 40 by the magnet 82 fixed inside the drum 81. When the magnetic force is applied to the emulsion 40, only the powder 10 in the emulsion 40 is magnetically attracted to the surface of the drum 81, and as the drum 81 rotates, a powder phase (first powder phase) 10a is collected.

[0094] When the powder 10 of the emulsion 40 is magnetically attracted to the surface of the drum 81, the solvent droplets in the emulsion coalesce into a solvent phase, resulting in the emulsion 40 being broken down and separated into water 20 and the first volatile hydrophobic solvent 50.

[0095] The throttle guide 84 is a deliquifying means provided above the drum 81. The throttle guide 84 applies pressure to the residual water and solvent adhering to the recovered powder phase 10a, thereby enabling the first powder phase 10a to be deliquified.

[0096] The powder recovery equipment 1 of this embodiment has been described above, but in order to further increase the efficiency of removing the residual solvent in the powder phase 10a, the equipment may further include the following second emulsifier and second magnetic separator.

[0097] The second emulsification apparatus 71 is an apparatus that carries out the second emulsification step S3-1, in which a second volatile hydrophobic solvent 51 is added to the first powder phase 10a recovered by the first magnetic separator 80, and then the mixture is stirred and mixed to form an emulsion 40. The second volatile hydrophobic solvent 51 used here is the same type of solvent as the first volatile hydrophobic solvent 50. The second emulsification apparatus 71 may be an apparatus having the same configuration as the first emulsification apparatus 70.

[0098] The second magnetic separator 90 is a device that performs the second magnetic separation step S3-2. The first powder phase 10a recovered by the first magnetic separator 80 may contain residual oil-containing solvent or oil on the powder surface. Therefore, by performing magnetic separation again using the second magnetic separator, it is possible to separate and recover powder (second powder phase 10aa) from which more oil has been removed. The second magnetic separator 90 may be a device with the same configuration as the first magnetic separator.

[0099] In addition, the powder recovery equipment 1 of this embodiment may further be provided with a residual solvent removal device 73 and a dehydrator 91 for removing the solvent remaining in the second powder phase 10aa recovered by the second magnetic separator 90 (residual solvent evaporation process S4).

[0100] The residual solvent removal device 73 is a device that removes the first volatile hydrophobic solvent 50 and the second volatile hydrophobic solvent 51 that were not completely removed from the powder phase 10aa by volatilization. While a known configuration can be used, for example, the device may include a hot water tank filled with hot water and a motor M for stirring. The powder phase 10aa is placed in the hot water tank filled with hot water, and the motor M rotates the stirring blades to remove the solvent remaining in the powder phase 10aa. The hot water used for volatilization can be recovered at the most downstream end of the recovery equipment 1 and then re-introduced into the residual solvent removal device 73 for reuse. The solvent removed by volatilization can be recovered in a distillation device (not shown) and rectified to be reused as the first volatile hydrophobic solvent 50 or the second volatile hydrophobic solvent 51.

[0101] Hot water is used in the volatilization removal using the residual solvent removal device 73. Therefore, it is desirable to provide a heat insulating wall W between the second magnetic separator 90 and the residual solvent removal device 73 to prevent thermal energy from being transferred upstream. The heat insulating wall W is desirably provided at a boundary in the cross section (boundary) of the counterflow tank 100 between the second magnetic separator 90 and the residual solvent removal device 73 other than the inlet for transporting and introducing the powder phase 10aa, as long as the height of the heat insulating wall W is at least higher than the water surface of the hot water. It is also desirable to provide a rotary valve or the like with high sealing properties at the inlet for transporting and introducing the powder phase 10aa.

[0102] The dehydrator 91 is a device that dehydrates the slurry from which the solvent has been evaporated in a hot water tank, and recovers the powder 10. The specific configuration of the dehydrator 91 may be the same as that of the first magnetic separator 80 and the second magnetic separator 90. Alternatively, a centrifuge, a screw press, a filter-type dehydrator, or the like may be used.

[0103] The above has described a preferred form of the recovery equipment 1 of this embodiment, but as mentioned above, the recovery equipment 1 can also be applied to a batch type equipment, and in that case the same technical concept as the countercurrent type can be applied.

[0104] Furthermore, the recovery system 1 of this embodiment is a countercurrent continuous recovery system, and the aqueous and solvent phases flow from downstream to upstream. Therefore, to ensure that the volatile hydrophobic solvent introduced from above the second emulsifier contributes sufficiently to emulsification, it is preferable to install an overflow weir between the first magnetic separator and the second emulsifier. This allows the introduced solvent to remain around the second emulsifier, resulting in sufficient emulsification. Furthermore, if the powder 10 can be easily made into a slurry, the powder 10 may be directly charged into the first emulsification device 70 . Furthermore, the rinsing step S3 may be further added and performed multiple times, thereby further increasing the oil removal rate. In addition, a second volatile hydrophobic solvent may be added to the first emulsification step S2-1. [Example]

[0105] Next, examples (experimental examples) of this embodiment will be described. In each example described below, various tests were conducted to confirm the effects of this embodiment. Note that each of the following examples was conducted at room temperature and normal pressure.

[0106] Example 1 Oil-laden powder containing magnetic particles and water were blended and mixed under the conditions shown in Table 1 to create a slurry. A volatile hydrophobic solvent (cleaning solvent) with a specific gravity of 0.65 to 1.46 was then added and mixed. Next, an aqueous solution of a polymer flocculant (anionic polymer flocculant) shown in Table 1 was added and mixed to create an emulsion.

[0107] Next, a neodymium magnet (surface area: 14.5 cm) was placed in the resulting emulsion. 2 After immersing the neodymium magnet in a magnetic flux density of approximately 5,000 gauss at the surface for 5 seconds, the magnet was pulled up and the powder phase (cake before deliquescence) consisting mainly of magnetically attached matter on the magnet surface was collected.

[0108] Next, a rubber plate was pressed against the powder phase magnetically attached to the magnet surface and squeezed to remove the liquid from the magnet surface.

[0109] After dehydration, the powder phase was scraped off the magnet surface, and the heat of vaporization of the powder phase and the oil content in the powder phase were measured to calculate the oil removal rate. The oil removal rate was calculated from the oil content in the powder before and after treatment. Products with an oil removal rate of 20% or more were evaluated as having excellent oil removal rate (passed).

[0110] Furthermore, after removing the powder phase adhering to the magnet surface, the magnet was immersed in the emulsion again to recover the magnetic material remaining in the emulsion. This operation was repeated until the magnetic material was no longer magnetically attached to the magnet surface. After the magnetic material was removed from the emulsion, the emulsion was filtered through filter paper, and the filter paper was dried, after which the increase in weight of the filter paper was measured to determine the amount of solids remaining in the emulsion. The powder recovery rate was calculated from the weight of the powder before treatment and the measured amount of solids remaining in the emulsion. Note that a powder recovery rate of 50% by mass or more was evaluated as having an excellent powder recovery rate (passing).

[0111] Inventive Examples 1-1 to 1-5 and Comparative Example 1-0, the addition rate of polymer flocculant (anionic polymer flocculant) to the powder was 0 to 0.1 (mass%). The scale of the target object contained components with low magnetic attraction, and the magnetic substance content was 58 mass% in all cases. In Example 1-1, where the polymer flocculant was added at 0% by mass, the powder recovery rate was 63% by mass. However, by increasing the polymer flocculant addition rate, the powder recovery rate rose to over 97% by mass, demonstrating that most of the powder could be recovered. Therefore, even if the magnetic content of the powder is low, the addition of a polymer flocculant causes magnetic and non-magnetic particles to aggregate and loosely bond, allowing non-magnetic particles to be magnetically attracted and recovered by a magnet. Furthermore, in both examples, the oil content of the recovered powder phase was confirmed to be reduced. In Comparative Example 1-0, where neither a hydrophobic solvent nor a polymer flocculant was added, the oil removal rate was 0% and the heat of vaporization was 656 J / g-dry. In Example 1-1, where a hydrophobic solvent (1-bromopropane) was added, the oil removal rate was 66% and the heat of vaporization was 335 J / g-dry. Approximately half of the moisture in the pores was replaced, which indicates that the energy required for drying was replaced.

[0112] Next, in Comparative Examples 1-6 to 1-7 and Invention Examples 1-8 to 1-12, the mixing ratio of cleaning solvent to powder (cleaning solvent / powder (g / g)) was kept constant (0.29 (g / g)), and only the mixing ratio of water to powder (water / powder (g / g)) was changed from 0.18 to 1.06 (g / g).

[0113] When the water / powder ratio was 0.33 (g / g) or less (Comparative Examples 1-6 and 1-7), the slurry could not be formed, and when the viscosity of the slurry was measured, it exceeded the measurement range (more than 100 Pa·S), making it impossible to perform the measurement.

[0114] On the other hand, when the water / powder ratio was 0.47 (g / g) or more (Invention Examples 1-8 to 1-12), sufficient slurrying was possible, with all of the viscosity being 2.00 Pa s or less. In addition, the emulsion state was good in all of Invention Examples 1-10 to 1-12, but in Invention Examples 1-8 and 1-9, the slurry viscosity was slightly higher and the emulsion state was slightly inferior to Invention Examples 1-10 to 1-12, but this was not enough to inhibit the effects of the present invention.

[0115] Figures 5 and 6 are graphs showing the relationship between the water and powder blending ratio (water / powder (g / g)) and the slurry viscosity (Pa·s) in Examples 1-8 to 1-12, as well as the relationship between the slurry viscosity (Pa·s) and the oil removal rate (%). As shown in the graphs in Figures 5 and 6, as the water / powder ratio decreases, the viscosity of the slurry increases, which results in insufficient mixing with the cleaning solvent, and as a result, the oil removal rate tends to decrease. For example, when the viscosity of the water slurry was 1.94 Pa·S (Example 1-8), the oil removal rate was 34 mass %, and it was confirmed that oil could be removed.

[0116] On the other hand, when the viscosity exceeded 100 Pa·S (Comparative Examples 1-6 and 1-7), the oil removal rate was 10% or less, indicating that almost no oil was removed. When the slurry viscosity was 0.63 Pa·S (Invention Example 1-9), the oil removal rate increased to 52% by mass. Furthermore, when the slurry viscosity was 0.31 Pa·S or less (Invention Examples 1-10 to 1-12), the oil removal rate significantly increased to 64-70% by mass and remained almost constant. This suggests that by adjusting the slurry viscosity to 0.29 Pa·S, the powder can move freely within the aqueous phase of the emulsion, and contact between the solvent droplets and the powder in the emulsion is not rate-limiting. The heat of vaporization did not vary significantly with the viscosity of the aqueous slurry. For these reasons, the viscosity of the slurry prepared by mixing the powder with water is set to 2.0 Pa·S or less, preferably 0.63 Pa·S or less, and more preferably 0.31 Pa·S or less.

[0117] Next, in Examples 1-10 and 1-13 to 1-16, the addition rate of polymer flocculant to the powder was kept constant (0.05 (mass %)), and only the content of magnetized matter in the powder was changed from 14 to 83 (mass %). When the content of magnetic substances in the powder was 14% by mass (Invention Example 1-13), the recovery rate of the powder by magnetic separation was low at 54% by mass, but when the content of magnetic substances in the powder was 23 to 83% by mass (Invention Examples 1-10, 1-14 to 1-16), the recovery rate of the powder by magnetic separation was 78 to 97% by mass or more, and the powder was sufficiently recovered by magnetic separation. From this, it can be said that it is preferable for the content of magnetic substances in the powder to be 20% by mass or more.

[0118] Next, FIG. 7 is a graph showing the relationship between the blending ratio of cleaning solvent to powder (cleaning solvent / powder (g / g)) and the oil removal rate (%) in Invention Examples 1-10 and 1-17 to 1-19. In Example 1-10 and Invention Examples 1-17 to 1-19, the cleaning solvent / powder ratio was changed from 0.21 to 1.23 (g / g). As shown in the graph in FIG. 7, the oil removal rate increased as the cleaning solvent / powder ratio increased, and the oil removal rate reached approximately 65 mass % when the cleaning solvent / powder ratio was 0.3.

[0119] Next, in Example 1-20 of the present invention, polishing dust with oil attached was used as the powder, but in Example 1-21 of the present invention, it was confirmed that the oil could be separated from the polishing dust and that the oil could be removed from the polishing dust.

[0120] Next, in Examples 1-21 to 1-23, trichloroethylene, hydrofluoroether, and n-hexane were used as hydrophobic solvents (cleaning solvents), and it was confirmed that oil could be removed.

[0121] The content of magnetic substances was measured as follows. Approximately 50 g of powder that had been dried for 2 hours at 105°C was placed on a piece of paper to a thickness of approximately 2 mm, and a neodymium magnet (a cylindrical magnet with a magnetic flux density at the surface of approximately 5,000 gauss, a diameter of 21 mm, and a height of 9 mm) was attached to it, causing the magnetic material to be magnetically attached to the surface of the neodymium magnet. After removing the magnetic material from the surface of the neodymium magnet, the neodymium magnet was again attached to the powder remaining on the paper, causing the magnetic material to be magnetically attached to the surface of the neodymium magnet. This magnetic attachment process was repeated until the magnetic material was no longer magnetically attached to the surface of the neodymium magnet. Once it was confirmed that the magnetic material had no longer been magnetically attached, the magnetic material content was calculated from the weight of the powder remaining on the paper and the weight of the powder originally placed on the paper.

[0122] The oil content of the powder before oil removal and the recovered powder phase (cake) was measured as follows. First, the powder before oil removal and the recovered cake were each dried in a dryer at 105°C for 2 hours, and then the oil was extracted with n-hexane using a Soxhlet extractor. Subsequently, the mixture containing the extracted n-hexane and oil was heated to volatilize the n-hexane, and the weight of the residue (oil) was measured, and the oil content in the powder before oil removal and the cake was calculated. The oil removal rate was calculated by subtracting the oil content of the cake (powder phase) after oil removal from the oil content of the powder before oil removal, using the difference in oil content as the numerator and the oil content of the powder before oil removal as the denominator.

[0123] The heat of vaporization of the recovered cake was measured as follows. First, 5–8 mg of sample was collected from the cake deposited at the bottom of the centrifuge vessel. The wet sample was quickly placed in a differential scanning calorimetry (DSC) instrument (DSC8230, Rigaku Corporation). The sample was then heated from room temperature to 80°C, and the heat of vaporization was measured. Because the sample volume was so small, the volatile hydrophobic liquid in the sample evaporated between weighing and the differential scanning calorimetry measurement. Therefore, the measured heat of vaporization is presumably the heat of vaporization due solely to the water content in the sample. In other words, the smaller the heat of vaporization, the less water and other substances carried over into the cake, and the less energy required to dry the collected cake.

[0124] The average particle size of the powder was measured by a laser diffraction / scattering method to determine the average particle size on a volume basis.

[0125] The viscosity of the slurry was determined by first measuring the viscous resistance torque using a rotational viscometer and converting the obtained viscous resistance torque into viscosity. Specifically, 300 ml of the prepared slurry was placed in a tall beaker, and the rotor of the rotational viscometer was immersed in the slurry and rotated to measure the viscous resistance torque of the slurry acting on the rotor. The obtained viscous resistance torque was then converted into viscosity. The rotational viscometer used was a "VISCOMETER DVL-8 model (manufactured by Toki Sangyo)."

[0126] [Table 1A]

[0127] [Table 1B]

[0128] <Example 2> 10 g of the powder phase (oil content: 1.8 mass%) obtained in Example 1-10 after dewatering was mixed with 3.0 g of an oil-free hydrophobic solvent (1-bromopropane) and 7.6 g of water to form a slurry again to prepare an emulsion, which was then subjected to a rinsing step. A neodymium magnet (surface area: 14.5 cm) was then placed in the emulsion. 2 After immersion in the solution, the neodymium magnet was pulled out and the powder phase, mainly consisting of magnetically attached materials on the magnet surface, was collected.

[0129] Next, the powder phase magnetically attached to the magnet surface was dehydrated using two methods. One method involved pressing a rubber plate against the magnet surface and squeezing it to remove the liquid ("squeezing"). The other method involved placing the powder phase in a centrifuge tube and centrifuging it (1,750 G, 10 seconds) to remove the liquid ("centrifugation"). After dehydration, the powder phase was scraped off the magnet surface, or the cake deposited at the bottom of the centrifuge tube was removed, and the heat of vaporization of the cake and the oil content in the powder were measured. The results are shown in Table 2. As shown in Table 2, regardless of the dehydration method, rinsing reduced the oil content to 0.2% (by mass), confirming the oil-reducing effect of the rinsing process.

[0130] [Table 2]

[0131] Example 3 In Example 3, first, water was added to oil-adhered scale (water content 20% by mass, oil content 5% by mass-dry) and then mixed to prepare a slurry (solid content: 50% by mass, viscosity: 0.15 Pa·S) (first slurrying step). Next, the slurry prepared in the first slurrying step was charged into a container at 612 g / min, and a cleaning solvent (1-bromopropane, specific gravity: 1.35, boiling point: 71°C) was further charged at 88 g / min. In addition, an aqueous solution of anionic polymer flocculant was added so that the anionic polymer flocculant was 0.05% by mass relative to the amount of scale, and the mixture was stirred to prepare an emulsion (first emulsification step).

[0132] Next, the emulsion prepared in the first emulsification step was continuously fed at 700 g / min into a first magnetic separator 80 equipped with a drum 81 and a constriction guide 83, as shown in Figure 3(c). The surface of the drum 81 was approximately 9,000 gauss. The charged emulsion was magnetically attached to the surface of the drum 81 and separated into a powder phase, excess water, and washing solvent. The magnetically attached powder phase (cake before deliquifying) was dewatered using a squeeze guide and collected as a powder cake after deliquifying.

[0133] Next, 160 g of an oil-free rinsing solvent (1-bromopropane, specific gravity: 1.35, boiling point: 71°C) and 500 g of water were added to 1,000 g of the recovered, deliquored powder cake, and the mixture was stirred to create an emulsion (second emulsification step, see Figure 3(d)).Then, the mixture was continuously fed at 612 g / min into a second magnetic separator equipped with a drum and a squeeze guide, as shown in Figure 3(e).

[0134] The emulsion was magnetically attached to the surface of the drum, separating it into a powder phase, excess water, and rinsing solvent. The magnetically attached powder phase (pre-deliquoring cake) was dewatered using a squeeze guide and collected as a deliquoring powder cake.

[0135] The oil content and heat of vaporization were measured for the deliquored powder cake after washing and the deliquored powder cake after rinsing, both of which were recovered in Example 3. The results are shown in Table 3. As shown in Table 3, initially, 5% by mass of oil was attached to the scale, but this was reduced to 1.8% by mass (oil removal rate: 64% by mass) in the deliquored cake after the washing step, and to 0.1% by mass (oil removal rate: 98% by mass) in the deliquored cake after the rinsing step, confirming that almost all of the oil could be removed by the rinsing step.

[0136] [Table 3]

[0137] Example 4 1 kg of the powder cake recovered in Example 3 after the rinsing step and subsequent dewatering was added to 2 liters of warm water adjusted to 90°C to form a slurry, which was then stirred for 1 minute to volatilize the hydrophobic solvent remaining in the recovered scale. The slurry was then recovered and subjected to a centrifugal force of 1750 G for 30 seconds in a batch centrifuge to perform solid-liquid separation, yielding a powder cake again. When the residual solvent content in the powder cake after water removal by centrifugation was measured, no residual solvent was detected.

[0138] Next, 1 kg of the powder cake recovered in Example 3 after the rinsing step and subsequent deliquoring was crushed, spread thinly on a drying dish to a thickness of 5 mm or less, and dried for 10 minutes in a drying oven adjusted to 120°C to volatilize the hydrophobic solvent remaining in the scale. After drying, the residual solvent content in the powder cake was measured, and no residual solvent was detected.

[0139] In this example, the residual solvent content in the cake was measured as follows. The cake from which the solvent had been evaporated was mixed with pure water to prepare sample water, which was then placed in a sealed container. The sample was then heated for 10 to 20 minutes at a temperature 30 to 50°C higher than the boiling point of the solvent, causing the solvent components to volatilize from the sample water into the air layer in the sealed container. The gas phase in the sealed container was then sampled with a syringe, and the gas components in the syringe were measured using a gas chromatograph to calculate the residual solvent concentration in the cake.

[0140] <Example 5> The test was conducted under the same conditions as in Example 3, except that the amount of rinsing solvent added was varied from 0 g to 300 g. The rinse waste liquid and the deliquored powder cake after the rinsing process were collected. The collected rinse waste liquid was allowed to stand and separated into an aqueous phase and a solvent phase by gravity separation. The separated solvent phase was filtered using a JIS P 3801 "Type 5A" filter paper to remove any small amounts of scale, and the filtered solvent was collected.

[0141] When the relationship between the oil concentration in the recovered filtered solvent and the absorbance of the solvent phase at an absorption wavelength of 400 nm was investigated, the relationship shown in Figure 8 was obtained. From this relationship, it was found that in the region of absorbance of 1.5 or less, there is an almost positive correlation between the oil concentration in the solvent and the absorbance of the solvent phase.

[0142] Furthermore, we investigated the relationship between the absorbance of the solvent phase after filtration (absorption wavelength 400 nm) and the oil concentration in the cake, and obtained the relationship shown in Figure 9. From this relationship, it can be concluded that the oil concentration in the cake can be estimated by measuring the absorbance of the solvent phase in the rinse waste. Therefore, if we want to keep the oil concentration in powder, such as scale, below a certain target value, we can estimate the amount of residual oil in the cake from the absorbance of the solvent phase in the rinse waste and adjust the amount of rinsing solvent added so that the estimated value of the residual oil amount is below the target value. This not only allows us to efficiently keep the oil concentration in the powder below the target value, but also allows us to appropriately control the amount of rinsing solvent used, thereby reducing losses due to excessive solvent addition. For example, looking at the relationship in Figure 9, it can be said that in order to reduce the oil concentration in the cake (powder) to 0.2% or less, the absorbance must be 0.5 or less, and the amount of rinsing solvent added is adjusted so that the absorbance falls within this range.

[0143] Furthermore, when the absorbance (absorption wavelength 400 nm) of the solvent phase in the rinse waste liquid was 0.5, the oil concentration in this solvent was as low as 30 mg / ml of solvent, and it was confirmed that it could be used as the first volatile hydrophobic solvent (cleaning solvent).

[0144] Example 6 Using the counterflow continuous recovery equipment shown in Figure 4, oil was extracted from oil-laden scale using the counterflow method.

[0145] Oil-laden scale (oil content: 4.6%, moisture: 20%) was fed into a slurry generator at 3.8 kg / min and mixed with water to produce a slurry with a concentration of 55% by mass. The viscosity of the slurry was 0.2 Pa·S. It was then fed into the first emulsifier and further magnetically separated using the first magnetic separator (washing step). Furthermore, an oil-free volatile hydrophobic solvent (1-bromopropane) was fed into the second emulsifier at 1.9 kg / min, and water was added at 2.2 L / min. The powder cake after magnetic separation using the first magnetic separator was mixed with the water and volatile hydrophobic solvent, emulsified, and further magnetically separated using the second magnetic separator (rinsing step). In this way, the oil adhering to the scale during the washing and rinsing steps was extracted with a volatile hydrophobic solvent, and after deliquification, the powder cake was placed in a residual solvent removal device adjusted to 90°C. The solvent remaining in the powder cake was evaporated and slurried with water. The cake was then dehydrated by magnetic separation in a dehydrator, and the cake was recovered. The water and oil-containing solvent introduced during the washing and rinsing steps moved in the opposite direction to the flow of the scale (toward the left side of the page in Figure 4). The phase separation tank separated the water and oil-containing solvent, and the separated water was reused in the slurrying step or the second emulsification step. The oil-containing solvent was distilled in a distillation device (not shown) to separate the oil and solvent, and the recycled solvent was placed in the second emulsification step. The oil content in the recovered cake was 0.38% by mass, and the oil removal rate was approximately 92%. The moisture content was 28% by mass. [Explanation of symbols]

[0146] 1 Powder recovery equipment 10 Powder (oil-containing powder) 10a 1st powder phase (powder phase) 10aa 2nd powder phase (powder phase) 20 water 30 Slurry 40 Emulsion 50 First volatile hydrophobic solvent (cleaning solvent) 51 Second volatile hydrophobic solvent (rinse solvent) 60 Slurrying equipment 70 First emulsifier 71 Second emulsifier 73 Residual solvent removal device 80 First Magnetic Separator 81 Drums 82 Magnet 90 Second magnetic separator 91 Dehydrator 100 Counterflow tank W Insulated Wall

Claims

1. A powder recovery method for recovering powder by separating oil from powder having oil attached thereto and containing magnetic substances, comprising: a slurrying step of mixing the powder with water to a viscosity in the range of 0.003 to 2.00 Pa·S to produce a slurry; a first emulsification step of adding a first volatile hydrophobic solvent having a specific gravity of more than 1.05 and less than 2.0 to the slurry and then mixing to form a first emulsion; a first magnetic separation step of separating and recovering a first powder phase from the first emulsion by magnetic separation; A method for recovering powder, comprising:

2. 2. The method for recovering powder according to claim 1, wherein a polymer flocculant is added to the slurry in the slurrying step or the first emulsifying step.

3. A method for recovering powder, comprising: separating oil from powder having oil attached thereto and containing magnetic matter; and recovering the powder, a slurrying step of mixing the powder with water to a viscosity in the range of 0.003 to 2.00 Pa·S to produce a slurry; a first emulsification step of adding a first volatile hydrophobic solvent to the slurry and then mixing to form a first emulsion; a first magnetic separation step of separating and recovering a first powder phase from the first emulsion by magnetic separation; and A powder recovery method, characterized in that a polymer flocculant is added to the slurry in the slurrying step or the first emulsifying step.

4. 4. The method for recovering powder according to claim 1, wherein the boiling point of the first volatile hydrophobic solvent at normal pressure is less than 95°C.

5. 5. The method for recovering powder according to claim 1, wherein the washing step consisting of the first emulsification step and the first magnetic separation step is repeated one or more times.

6. a residual solvent volatilization step of introducing the first powder phase obtained in the first magnetic separation step into a hot water bath having a water temperature higher than the boiling point of the first volatile hydrophobic solvent, and volatilizing and removing the first volatile hydrophobic solvent remaining in the first powder phase; The powder recovery method according to any one of claims 1 to 5, further comprising a dehydration step of dehydrating the slurry containing the first powder phase obtained in the residual solvent evaporation step using a dehydrator.

7. The powder recovery method according to any one of claims 1 to 5, further comprising a drying step of drying the first powder phase obtained in the first magnetic separation step at a temperature higher than the boiling point of the first volatile hydrophobic solvent.

8. After the first magnetic separation step, a second emulsification step of adding a second volatile hydrophobic solvent to the recovered first powder phase and then mixing to form a second emulsion; 6. The method for recovering powder according to claim 1, further comprising a second magnetic separation step of separating and recovering a second powder phase from the second emulsion by magnetic separation.

9. 9. The method for recovering powder according to claim 8, wherein the rinsing step consisting of the second emulsification step and the second magnetic separation step is repeated one or more times.

10. A method for recovering powder as described in Claim 9, characterized in that the cleaning step consisting of the first emulsification step and the first magnetic separation step and the rinsing step are carried out in a single counterflow tank in a counterflow continuous process.

11. 11. The powder recovery method according to claim 8, wherein a polymer flocculant is added to the first powder phase in the second emulsification step.

12. The method for recovering powder according to any one of claims 8 to 11, characterized in that the specific gravity of the second volatile hydrophobic solvent is greater than 1.05 and less than 2.

0.

13. The method for recovering powder according to any one of claims 8 to 12, wherein the boiling point of the second volatile hydrophobic solvent at normal pressure is less than 95°C.

14. a residual solvent volatilization step of introducing the second powder phase obtained in the second magnetic separation step into a hot water bath having a water temperature higher than the boiling point of the second volatile hydrophobic solvent, and volatilizing and removing the second volatile hydrophobic solvent remaining in the second powder phase; The powder recovery method according to any one of claims 8 to 13, further comprising a dehydration step of dehydrating the slurry containing the second powder phase obtained in the residual solvent evaporation step using a dehydrator.

15. The powder recovery method according to any one of claims 8 to 13, further comprising a drying step of drying the second powder phase obtained in the second magnetic separation step at a temperature higher than the boiling point of the second volatile hydrophobic solvent.

16. The method for recovering powder according to any one of claims 8 to 15, wherein the first volatile hydrophobic solvent and the second volatile solvent are the same solvent.

17. 17. The method for recovering powder according to claim 1, wherein the content of the magnetic material in the powder is 20% by mass or more.

18. The method for recovering powder according to any one of claims 1 to 17, characterized in that the oily powder is either oily scale or oily grinding dust, or a mixture thereof.

19. A powder recovery system that separates oil from powder having oil attached thereto and containing magnetic substances, and recovers the powder, a slurrying device for mixing the powder with water to produce a slurry; a first emulsifier for adding a first volatile hydrophobic solvent to the slurry and then mixing the mixture to form a first emulsion; a first magnetic separator that separates and recovers a first powder phase from the first emulsion by magnetic force; A powder recovery facility comprising:

20. moreover, a second emulsifier for adding a second volatile hydrophobic solvent to the recovered first powder phase and then mixing them to form a second emulsion; a second magnetic separator that separates and recovers a second powder phase from the second emulsion by magnetic force; The powder recovery equipment according to claim 19, characterized in that it comprises:

21. 21. The powder recovery equipment according to claim 20, wherein the first emulsification device, the first magnetic separator, the second emulsification device, and the second magnetic separator are arranged in tandem in a single counterflow tank, and the flow of the first powder phase and the second powder phase is countercurrent to the flow of the aqueous phase and the solvent phase, forming a countercurrent continuous recovery equipment.

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