JP7644334B2 - Powder recovery method - Google Patents

Description

The present invention relates to a method for recovering powder.

Manufacturing industries, including the steel industry, discharge large amounts of mixtures in which powders containing hydrophilic particles are dispersed in water or an aqueous solution. The mixtures are often discharged in the form of a water-containing slurry. The powders contained in the mixtures are diverse, and in the steel industry, for example, they include dust, scale, leach residues, fly ash, slag powder, and ore powder. All of these are also hydrophilic particles.

JP 2015-132011 A JP 2017-177018 A JP 2018-176004 A

In some cases, the powder is separated and collected from the mixture for the purpose of recycling the powder or for efficient use. In order to separate the powder from the mixture, it is necessary to remove the moisture from the mixture, i.e., to dry the mixture. Conventional methods for drying the mixture include a method of heating the mixture and a method of drying the mixture in the sun while plowing the mixture in a curing yard (digging up the mixture using a shovel or the like).

However, the method of drying the mixture has a problem that it takes a long time and a large amount of energy to dry the mixture because water has a high boiling point and is difficult to evaporate. In particular, high-grade (expensive) energy such as COG (coke oven gas), LNG (liquefied natural gas), heavy oil, kerosene, etc. may be used to heat the mixture, and in such cases the above problem becomes more serious. In addition, the amount of _CO2 emissions increases, which goes against the _CO2 reduction that has become a particular issue in recent years.

On the other hand, the method of drying the mixture in the sun in a curing yard is used, for example, when the powder generates heat. This is to increase the safety of the powder. For example, converter dust, which is a type of dust, contains a lot of reduced iron and is prone to generating heat. For this reason, mixtures containing converter dust are often dried in the sun in a curing yard. The reduced iron in the converter dust is oxidized to stable iron oxide when dried in the sun. However, this method has the problem that not only does it require a large curing yard, but it also takes a very long time to dry the mixture. Another problem is that it requires large-scale, time-consuming work such as plowing. Furthermore, since reduced iron, a useful iron source, was deliberately oxidized to iron oxide, its usefulness as an iron source was reduced.

In addition, a problem common to both methods is that when the mixture contains an aqueous solution, a large amount of impurities derived from the components of the aqueous solution adhere to the dried powder, reducing the purity of the powder. Although details will be described later, depending on the type of mixture, the liquid that disperses the powder may be an aqueous solution. For example, hot-rolled sheets are pickled in order to remove scale and internal oxide layers from the surface of the hot-rolled sheet after hot rolling. The waste liquid generated by pickling is mainly composed of pickling liquid, but may also contain powder that has been removed from the surface of the steel material by pickling, that is, leaching residue. In addition, the pickling liquid may contain components leached from the steel material or leaching residue (e.g., ions of Fe, Cr, Ni, Zn, etc.). In this case, the mixture is composed of the leaching residue, which is a powder, and the pickling liquid, which is an aqueous solution (containing components leached from the steel material or leaching residue). When the mixture is dried, the components in the pickling liquid (e.g., Cr, Ni, Zn, acid components, etc.) adhere to the remaining residue. Depending on the type of mixture, the mixture may contain oil, in which case the same problem occurs. In other words, oil adheres to the powder after drying, reducing the purity of the powder. Patent documents 1 to 3 disclose techniques for recovering powder from the mixture, but these techniques do not adequately solve the above-mentioned problems.

The present invention has been made in consideration of the above problems, and the object of the present invention is to provide a new and improved method for recovering powder that does not require a curing yard, reduces the energy required to dry the powder, and can reduce impurities in the powder.

In order to solve the above problems, according to one aspect of the present invention, there is provided a powder recovery method comprising a first step of adding a hydrophobic liquid having a specific gravity greater than that of water and less than that of the powder to a first mixture of a powder containing hydrophilic particles and water or an aqueous solution, and stirring a second mixture of the first mixture and the hydrophobic liquid; a second step of applying gravity or centrifugal force by leaving the second mixture to stand to separate the second mixture into a water phase and a hydrophobic liquid phase and transferring the powder to the hydrophobic liquid phase; and a third step of recovering the powder that has been transferred to the hydrophobic liquid phase.

Here, a fourth step may be included in which the powder collected in the third step is dried and the hydrophobic liquid adhering to the powder is removed.

The powder may also have a volume-based 50% particle size of 100 μm or less.

A surfactant may also be added in the first step.

Also, oil may be attached to the surface of the powder.

The boiling point of the hydrophobic liquid may be between 40°C and 95°C at normal pressure, and steps 1 to 3 may be carried out at normal temperature and pressure.

The powder may be one or more selected from the group consisting of dust, scale, leaching residue, fly ash, slag powder, and ore powder.

The above aspects of the present invention make it possible to eliminate the need for a curing yard, reduce the energy required to dry the powder, and reduce impurities in the powder.

FIG. 2 is a schematic diagram for explaining an overview of the powder recovery method according to the present embodiment. FIG. 2 is a schematic diagram for explaining modification of a powder surface by a surfactant.

The preferred embodiment of the present invention will be described in detail below with reference to the attached drawings. In this specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals to avoid repetitive explanation. A numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

<1. Powder recovery method>
First, the powder recovery method according to the present embodiment will be described with reference to Figs. 1 and 2. The powder recovery method according to the present embodiment includes first to third steps. The first step is a step of adding a hydrophobic liquid 50 having a specific gravity greater than that of water and less than that of the powder 10 to a first mixture 30 of a powder 10 containing hydrophilic particles and water or an aqueous solution (hereinafter also simply referred to as "water, etc.") 20, and stirring a second mixture of the first mixture 30 and the hydrophobic liquid 50 (Fig. 1(a)). The second step is a step of separating the second mixture into an aqueous phase 20a and a hydrophobic liquid phase 50a by applying gravity or centrifugal force due to standing to the second mixture, and moving the powder 10 from the aqueous phase 20a to the hydrophobic liquid phase 50a (Fig. 1(b)). The third step is a step of recovering the powder that has moved to the hydrophobic liquid phase 50a (Figs. 1(c) and (d)). Each step will be described in detail below.

(1-1. First step)
In the first step, first, the hydrophobic liquid 50 is added to the first mixture 30. For example, as shown in FIG. 1(a), the first mixture 30 is poured into a container 100, and then the hydrophobic liquid 50 is poured. The order of pouring is not limited to this. Next, the second mixture, which is a mixture of the first mixture 30 and the hydrophobic liquid 50, is stirred. The degree of stirring is not important, but it is preferable to stir until the hydrophobic liquid 50 is substantially uniformly dispersed in the second mixture.

Here, the first mixture 30 contains powder 10 and water, etc. 20. The first mixture 30 often exists as a water-containing slurry. Of course, the first mixture 30 may be a mixture that has a low powder content and is not in the form of a slurry. In other words, the first mixture 30 may be in any form as long as it contains powder 10 and water, etc. 20.

The powder 10 includes hydrophilic particles. Hydrophilic particles are particles that have an affinity for water and have the property of being more easily mixed with water than the hydrophobic liquid 50. The ease of mixing with water can be evaluated, for example, by the following method. That is, a predetermined amount (e.g., 1 g) of the powder 10 to be evaluated is measured and placed in a sealed container together with a predetermined amount (e.g., 100 ml) of water and a predetermined amount (e.g., 100 ml) of hydrophobic liquid. Next, these mixed liquids are thoroughly stirred and allowed to stand. The state of the aqueous phase is observed immediately after the mixed liquid is allowed to stand, and if almost the entire amount of the powder to be evaluated is suspended in the aqueous phase, the powder to be evaluated is evaluated to be a hydrophilic particle.

The powder 10 may be composed of only hydrophilic particles, or may further contain other types of particles, such as hydrophobic particles. Here, the hydrophobic particles are particles that have an affinity for the hydrophobic liquid 50 and have the property of being more easily mixed with the hydrophobic liquid 50 than with water. The ease of mixing with the hydrophobic liquid can be evaluated, for example, by the following method. That is, a predetermined amount (e.g., 1 g) of the powder 10 to be evaluated is measured and placed in a sealed container together with a predetermined amount (e.g., 100 ml) of water and a predetermined amount (e.g., 100 ml) of hydrophobic liquid. Next, the mixture is thoroughly stirred and allowed to stand. Immediately after the mixture is allowed to stand, the state of the water phase and the hydrophobic liquid phase is observed, and if almost the entire amount of the powder to be evaluated is suspended in the hydrophobic liquid phase, the powder to be evaluated is evaluated to be a hydrophobic particle.

In addition, when the powder to be evaluated is suspended in both the aqueous phase and the hydrophobic liquid phase, the powder can be evaluated as a mixture of hydrophilic particles and hydrophobic particles. The hydrophilic particles may exist independently (separately) from other types of particles, or may be combined with other types of particles to form one particle. For example, there are coke powder and fly ash. Fly ash, which will be described later, is an example in which hydrophilic particles (ash made of metal oxides such as Al ₂ O ₃ and SiO ₂ ) and hydrophobic particles (unburned carbon) are combined. Of course, even in fly ash, hydrophilic particles and hydrophobic particles may be separated.

The true specific gravity of the powder 10 is greater than the specific gravity of the hydrophobic liquid 50 (specifically, the hydrophobic liquid 50 used to recover the powder 10). This allows the powder 10 to be moved to the hydrophobic liquid phase 50a in the second step described below. That is, the water, etc. 20 present between the particles of the powder 10 can be replaced with the hydrophobic liquid 50. Note that if the powder 10 is moved to the hydrophobic liquid phase 50a by carrying out the first and second steps described below, it can be determined that the true specific gravity of the powder 10 is greater than the specific gravity of the hydrophobic liquid 50. Furthermore, if hydrophobic particles are contained in the powder 10, the hydrophobic particles move to the hydrophobic liquid phase 50a.

The particle size of the powder 10 is not particularly important, but the volume-based 50% particle size (d ₅₀ ) of the powder 10 is preferably 100 μm or less. Although details will be described later, in this embodiment, the water, etc. 20 present between the particles of the powder 10 is replaced with the hydrophobic liquid 50, thereby reducing the energy required to dry the powder 10 and reducing impurities in the powder. The hydrophobic liquid 50 evaporates with lower energy than the water, etc. 20. Therefore, by replacing the water, etc. 20 present between the particles of the powder 10 with the hydrophobic liquid 50, the energy required to dry the powder 10 can be reduced. Furthermore, the impurities in the powder 10 are derived from, for example, components dissolved in the water, etc. 20. Therefore, by replacing the water, etc. 20 present between the particles of the powder 10 with the hydrophobic liquid 50, the components can be removed together with the water, etc. 20. Therefore, the impurities in the powder can be reduced. The smaller the particle diameter of the powder 10, the larger the gaps between the particles of the powder 10, so that more water, etc. 20 can be replaced with the hydrophobic liquid 50. Therefore, the above-mentioned effect of performing the treatment of this embodiment is enhanced. From this viewpoint, it is preferable that the particle diameter of the powder is small, and according to Experimental Example 5 described later, when the volume-based 50% particle diameter (d ₅₀ ) of the powder 10 is 100 μm or less, a particularly large effect is obtained. Therefore, it is preferable that the volume-based 50% particle diameter (d ₅₀ ) of the powder 10 is 100 μm or less. More preferably, it is 25 μm or less, and even more preferably, it is 10 μm or less. On the other hand, the lower limit is preferably 1 μm or more. This is because if the particle diameter is less than 1 μm, the hydrophilicity of the powder 10 becomes very high, and even if the treatment of this embodiment is performed, it may be difficult to remove the water, etc. 20 present between the particles of the powder 10.

The volume-based 50% particle diameter (d ₅₀ ) of the powder 10 can be measured by the following measurement method using, for example, a laser diffraction type particle size distribution measuring device. That is, the sample to be measured is slurried with water, and a small amount of sodium hexametaphosphate solution is added as a dispersant. Next, the sample is dispersed in the mixed liquid by stirring the mixed liquid and irradiating it with ultrasonic waves. Next, this mixed liquid is set in the laser diffraction type particle size distribution measuring device, and the particle size distribution is measured. In the examples described later, the volume-based 50% particle diameter (d ₅₀ ) of the powder 10 is measured by this method.

The powder 10 may be any material having the above-mentioned characteristics, but is preferably one or more selected from the group consisting of dust, scale, leaching residue, fly ash, slag powder, and ore powder. This is because there is a strong demand for recycling or efficient use of these powders. These powders are also hydrophilic particles.

Dust is, for example, secondary ash generated in blast furnaces, converter dust, etc. These dusts are often collected wet, in which case a water-containing slurry is produced. In some cases, the water-containing slurry is treated with a high-concentration treatment liquid (high-concentration acid or alkali aqueous solution) to remove tramp elements (e.g., Zn) from the dust. In this case, the water-containing slurry is composed of powder containing a large amount of iron and the treatment liquid (i.e., the aqueous solution).

Scale is generated, for example, during hot rolling. Specifically, scale forms on the surface of a slab by preheating the slab. Such scale is finely crushed during hot rolling and discharged together with the coolant water. In other words, a hydrous slurry (hydrous scale) in which fine scale is dispersed in the coolant water is discharged. The hydrous slurry generated during hot rolling often contains 3 to 8 mass % oil (mass % relative to the total mass of the powder). The oil adheres, for example, to the surface of the scale. The oil may also be dispersed within the hydrous slurry.

Steel materials are often surface-treated for various reasons. For example, hot-rolled sheets are pickled in order to remove scale and internal oxide layers from the surface of the hot-rolled sheet after hot rolling. Stainless steel is also pickled in order to remove scale and the like from stainless steel. The waste liquid generated by these surface treatments (pickling in the above example) is mainly composed of the surface treatment liquid (pickling liquid in the above example) used in the surface treatment, but may further contain powder that has been desorbed from the surface of the steel material by the surface treatment, i.e., leaching residue. Furthermore, the waste liquid may contain (dissolve) components (e.g., metal ions such as Fe, Cr, Ni, and Zn) that have leached from the steel material or the leaching residue. Furthermore, some kind of treatment may be performed on the waste liquid. For example, if the waste liquid is acidic, a neutralization treatment may be performed. When the waste liquid is neutralized, hydroxides of the components in the waste liquid may precipitate. For example, when the wastewater generated by pickling a hot-rolled sheet is neutralized, a precipitate containing a mixture of hydroxides of Fe, Cr, Ni, and Zn is precipitated, and when the wastewater generated by pickling a stainless steel is neutralized, a precipitate containing a mixture of hydroxides of Fe, Cr, Ni and _CaF2 is precipitated. Since the pH at which these metal components precipitate is different, a precipitate containing a specific metal component can be precipitated by adjusting the pH. Such precipitates are also powders and are a type of leaching residue. Therefore, the surface treatment of the steel material discharges a surface treatment liquid (corresponding to the above-mentioned aqueous solution) and a water-containing slurry containing the leaching residue. Of course, the target of the surface treatment is not limited to the steel material. Therefore, the leaching residue in this embodiment includes powders peeled off from the treated object (steel material in the above example) by the surface treatment, as well as powders (e.g., iron hydroxide, etc.) precipitated in the wastewater by the treatment of the wastewater (neutralization treatment in the above example).

In addition, in recent years, there has been a strong demand for using a large amount of iron scrap from the viewpoint of recycling, _CO2 reduction, etc. Iron scrap often contains tramp elements (e.g., Cu, Zn, Ni, etc.). For this reason, when using iron scrap, the iron scrap is treated in advance with a high-concentration treatment liquid (e.g., high-concentration ammonia water for Cu, Zn, Ni) which is a leaching agent for the tramp elements, so that the tramp elements in the iron scrap are leached as ions (e.g., ammine complex ions, metal ions, etc.) in the high-concentration treatment liquid. This removes the tramp elements from the iron scrap. Therefore, the tramp elements are dissolved in the waste liquid after the treatment. On the other hand, since the waste liquid is a high-concentration treatment liquid, the tramp elements are precipitated, and the tramp element leaching ability of the high-concentration treatment liquid is often regenerated and reused. In this case, _H2S gas is circulated through the waste liquid, which is, for example, high-concentration ammonia water, to precipitate the tramp elements in the waste liquid as sulfides. As a result, a water-containing slurry is produced in which powdery precipitate (which can be interpreted as a type of leaching residue as described above) is dispersed in the waste liquid.

Fly ash is a powder generated during power generation in coal-fired power plants and the like. Fly ash contains unburned carbon, which is a carbon component that remains unburned, in ash made of metal oxides such as Al ₂ O ₃ and SiO _2. Fly ash is an example of hydrophilic particles (ash made of metal oxides such as Al ₂ O ₃ and SiO ₂ ) and hydrophobic particles (unburned carbon) integrated together. Of course, even in fly ash, hydrophilic particles and hydrophobic particles may be separated. Fly ash may be collected after removing hydrophobic particles from the fly ash in a wet process, in which case a water-containing slurry containing the fly ash is discharged. In addition, the water-containing slurry may be acid-treated under heating and pressure in order to remove Al ₂ O ₃ and the like from the fly ash. In this case, the water-containing slurry is composed of fly ash and an aqueous solution of an acid. The aqueous solution of an acid contains components leached from the fly ash, such as Al ions.

Slag powder is generated, for example, in blast furnaces. Specifically, the slag generated in blast furnaces is often wet-ground (so-called water granulation). This water granulation produces a water-containing slurry in which the slag powder is dispersed.

In the steel industry, ore dressing may be carried out to improve the quality of iron ore, the raw material for steel. In general, ore dressing is a process in which iron ore is crushed and then ore powder with a high iron content is separated. Ore dressing may be carried out wet, in which case an aqueous slurry is produced in which the ore powder is dispersed in water. In the non-ferrous industry, raw materials such as copper oxide ore, zinc concentrate, bauxite, and pyrrhotite may be treated with a leaching agent such as acid, alkali, or ammonia to leach and separate the target components or impurities from these raw materials. In this process, an aqueous slurry is produced in which the ore powder is dispersed in an aqueous solution.

The water, etc. 20 is water or an aqueous solution. The composition of the water, etc. 20 varies depending on the mixture. For example, when the powder 10 becomes dust, scale, fly ash, slag powder, or ore powder, the water, etc. 20 is often water. However, when some component (e.g., acid, alkali, or ammonia, etc.) is added to the water, etc. 20, the water, etc. 20 becomes an aqueous solution. The aqueous solution may contain components leached from the powder 10. For example, a water-containing slurry may be acid-treated with hydrochloric acid in order to remove Al ₂ O ₃ , etc. from the fly ash. In this case, the water-containing slurry is composed of fly ash and an aqueous solution of acid. The aqueous solution of acid contains components leached from the fly ash, such as Al ions. On the other hand, when the powder 10 becomes a leaching residue, the water, etc. 20 is almost always an aqueous solution.

As described above, when the water etc. 20 becomes an aqueous solution, there is a problem that the purity of the powder 10 after drying decreases. For example, the waste liquid generated by pickling of the hot-rolled sheet may contain, in addition to the pickling liquid which is a surface treatment liquid, powder detached from the surface of the hot-rolled sheet by pickling, that is, leaching residue. Furthermore, the waste liquid may contain components leached from the steel material or the leaching residue (e.g., metal ions such as Fe, Cr, Ni, Zn, etc.). In this case, the mixture is composed of the leaching residue which is a powder and the pickling liquid which is an aqueous solution (containing components leached from the steel material or the leaching residue). Then, when the mixture is dried, the components in the pickling liquid (e.g., Cr, Ni, Zn, etc.) adhere to the residual residue. Furthermore, when the waste liquid generated by the pickling of the hot-rolled sheet is neutralized, hydroxides of the metal components in the waste liquid precipitate. Since the pH at which these metal components precipitate is different, it is possible to precipitate a precipitate containing a specific metal component by adjusting the pH. For example, by adjusting the pH of the waste liquid, only the iron hydroxide can be precipitated. However, other metal components (e.g., Cr, Ni, Zn, etc.) remain as ions in the waste liquid. Therefore, when attempting to recover the iron hydroxide powder by drying, the metal components remaining as ions in the waste liquid adhere to the iron hydroxide powder. Depending on the type of mixture, the mixture may contain oil, and in this case, the same problem occurs. In other words, the oil adheres to the powder after drying, and the purity of the powder decreases. In this embodiment, the purity of the powder 10 can be increased by replacing such an aqueous solution with the hydrophobic liquid 50. In particular, when a specific metal component is selectively precipitated, such a specific metal component can be recovered with high purity.

The hydrophobic liquid 50 is a liquid having hydrophobicity, that is, a liquid having a property of having low affinity for water (difficult to dissolve in water or difficult to mix with water). The hydrophobic liquid 50 is, for example, a liquid having a solubility in water at room temperature (25°C) of 0 g/L or more and 10.0 g/L or less. If the solubility of the hydrophobic liquid 50 in water is high, when the water, etc. 20 present between the particles of the powder 10 is replaced with the hydrophobic liquid 50, a large amount of water, etc. 20 remains in the hydrophobic liquid 50. In this case, there is a possibility that the energy required to dry the powder 10 cannot be sufficiently reduced. From this viewpoint, the solubility of the hydrophobic liquid 50 in water at room temperature is preferably 10.0 g/L or less, and more preferably 5.0 g/L or less. In this case, the amount of water, etc. 20 remaining in the hydrophobic liquid 50 can be further reduced.

In this embodiment, hydrophobicity includes lipophilicity. The hydrophobic liquid 50 may be, for example, an organic solvent or various oils having hydrophobic properties.

The solubility of the hydrophobic liquid 50 is often determined from data published by the manufacturer of the hydrophobic liquid, but it can also be measured as follows. For example, 15 ml of water and the hydrophobic liquid are placed in a 50 ml centrifuge tube with a stopper, and shaken at 150 revolutions per minute for 1 hour in a thermostatic bath at 25°C. The mixture is then centrifuged (1,750 G, 5 minutes), and the mixture after centrifugation is allowed to stand in a thermostatic bath at 25°C for about 1 hour. An arbitrary amount of the aqueous phase is then taken, and the amount of solvent in the water is measured by gas chromatography-mass spectrometry (GC/MS). This makes it possible to determine the solubility of the hydrophobic liquid in water. In the following examples, the solubility of the hydrophobic liquid 50 published by the manufacturer of the hydrophobic liquid is used.

The specific gravity of the hydrophobic liquid 50 is greater than that of water and less than that of the powder 10 to be collected. As a result, after the second step described below is performed, the liquid phase in the container 100 becomes the aqueous phase 20a and the hydrophobic liquid phase 50a from the top, and the powder 10 moves into the hydrophobic liquid phase 50a. The specific gravity of the hydrophobic liquid 50 may be, for example, about 1.05 to 1.8. The powder 10 may be porous. Therefore, when selecting the hydrophobic liquid 50, the first and second steps may be actually performed using a candidate hydrophobic liquid 50. Then, as a result of the second step, if the liquid phase in the container 100 becomes the aqueous phase 20a and the hydrophobic liquid phase 50a from the top, and the powder 10 moves into the hydrophobic liquid phase 50a, the hydrophobic liquid 50 may be selected. Only one type of hydrophobic liquid 50 may be used, or multiple types may be mixed and used.

The boiling point of the hydrophobic liquid 50 is preferably higher than the temperature of the first mixture 30 under the same pressure condition. This allows the first to third steps to be performed stably. If the boiling point of the hydrophobic liquid 50 is equal to or lower than the temperature of the first mixture 30 under the same pressure condition, a large amount of the hydrophobic liquid 50 evaporates when the hydrophobic liquid 50 is added to the first mixture 30. In this case, it may be difficult to mix the first mixture 30 and the hydrophobic liquid 50. Furthermore, the first mixture 30 may contain a highly volatile component (e.g., hydrochloric acid, etc.). For example, the above-mentioned pickling may be performed with hydrochloric acid, in which case the first mixture 30 contains highly volatile hydrochloric acid. When the first mixture 30 contains a highly volatile component, it is preferable to perform the process of this embodiment in a sealed working environment from the viewpoint of ensuring the safety of the worker. Therefore, if the boiling point of the hydrophobic liquid 50 is equal to or lower than the temperature of the first mixture 30 under the same pressure condition, a large amount of the hydrophobic liquid 50 evaporates when the hydrophobic liquid 50 is added to the first mixture 30, and the internal pressure of the test environment may increase. Therefore, it is preferable that the boiling point of the hydrophobic liquid 50 is higher than the temperature of the first mixture 30 under the same pressure conditions.

For example, when the temperature of the first mixture 30 is room temperature (25°C), the boiling point of the hydrophobic liquid 50 is preferably 40°C or higher and lower than 200°C under the same pressure conditions. The upper limit of the boiling point is more preferably lower than 100°C, and even more preferably lower than 95°C. When the upper limit of the boiling point is lower than 100°C, the hydrophobic liquid 50 can be easily removed (for example, with water vapor, which is an inexpensive energy source) in the third step described below. In other words, when the first to third steps are performed at room temperature and normal pressure, the boiling point of the hydrophobic liquid 50 is preferably 40°C to 95°C at normal pressure.

In addition, when the temperature of the first mixture 30 is more than 100°C and less than 230°C, it is preferable that the boiling point of the hydrophobic liquid 50 is 30 to 100°C higher than the temperature of the first mixture 30 under the same pressure conditions. Alternatively, the hydrophobic liquid 50 may be added to the first mixture 30 after cooling the first mixture 30, in which case it is preferable that the boiling point of the hydrophobic liquid 50 is 30 to 100°C higher than the temperature of the first mixture 30 after cooling. For example, the acid treatment of fly ash and the acid treatment of ore powder may be performed under heating and pressure, and in these cases, the waste liquid may be heated to more than 100°C and less than 230°C. If the boiling point of the hydrophobic liquid 50 is 30 to 100°C higher than the temperature of the first mixture 30, the first to third steps can be performed stably even in such a working environment (an environment under heating and pressure). The hydrophobic liquid 50 may be added to the first mixture 30 after the temperature of the first mixture 30 is lowered. In this case, as described above, it is preferable that the boiling point of the hydrophobic liquid 50 is 30 to 100°C higher than the temperature of the first mixture 30 after the temperature is lowered. Therefore, even if the first mixture 30 contains a highly volatile component, the first to third steps can be performed without significantly changing the internal pressure of the sealed working environment. This means that the first to third steps can be performed without changing or significantly changing the working environment. Therefore, a series of operations from the operation that produces the first mixture 30 (for example, the acid treatment of fly ash) to the collection of the powder can be performed in the same working environment, which is very efficient. The first mixture 30 may be cooled to room temperature and the first to third steps may be performed at room temperature and pressure, but this is time-consuming and labor-intensive.

Furthermore, it is preferable that the volatile heat value of the hydrophobic liquid 50 is smaller than that of water. In this case, the hydrophobic liquid 50 is easier to volatilize and remove in the third step, and is easier to separate from the powder 10.

In addition, if the powder 10 contains oil, it is preferable that the oil is also separated from the powder 10. In this case, therefore, it is preferable to select a hydrophobic liquid 50 with a KB value (kauri-butanol value) as large as possible. This is because a hydrophobic liquid 50 with a large KB value is more likely to absorb oil. In other words, the oil in the powder 10 is absorbed into the hydrophobic liquid 50 through the first and second steps. Then, through the third step, the hydrophobic liquid 50 is removed together with the oil.

Note that the preferred KB value cannot be specified in general because it varies depending on various factors such as the composition of the oil. Therefore, the hydrophobic liquid 50 with the largest KB value may be selected from among the prepared hydrophobic liquids 50.

The KB value is measured as follows. First, a certain amount of Kauri resin butanol solution is placed in an Erlenmeyer flask and placed on standard type paper. Next, a sample (hydrophobic liquid) is added to the Kauri resin butanol solution in the Erlenmeyer flask, and the number of ml of the sample (hydrophobic liquid) when the solution becomes turbid and the type becomes unreadable is taken as the KB value. The larger the KB value, the stronger the oil and fat dissolving power of the hydrophobic liquid 50. The KB value is considered to be an indicator of the cleaning power of dry cleaning solvents against oily stains. In this embodiment, the KB value is used as an index for selecting the hydrophobic liquid 50. As shown in the examples described later, when the first mixture 30 contains oil, it is preferable to use a hydrophobic liquid 50 with a high KB value, such as trichloroethylene or 1-bromopropane.

Any hydrophobic liquid 50 that satisfies the above conditions can be applied to this embodiment. Examples of hydrophobic liquid 50 include trichloroethylene, 1-bromopropane, tetrachloroethylene, various fluorine-based organic solvents (e.g., 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane, 1,1,1,2,2,3,3,4,4,5,5,6,6,-tridecafluorooctane, hydrofluoroether, etc.).

The effect of this embodiment can be obtained even if the amount of hydrophobic liquid 50 added to the first mixture 30 is small. However, if the amount of hydrophobic liquid 50 added is too small, only a small amount of powder 10 can be moved to the hydrophobic liquid phase 50a in the second step. Therefore, the effect of this embodiment may not be fully achieved. Therefore, it is preferable to set the amount of hydrophobic liquid 50 added so that the entire amount of powder 10 is immersed in the hydrophobic liquid phase 50a after the second step. This makes it possible to obtain the effect of this embodiment more effectively.

In this embodiment, as described below, the powder 10 containing hydrophilic particles is moved to the hydrophobic liquid phase 50a. Therefore, in order to increase the affinity between the powder 10 and the hydrophobic liquid phase 50a, it is preferable to add a surfactant 60 (see FIG. 2) to the first mixture 30 in addition to the hydrophobic liquid 50. For example, the hydrophobic liquid 50 to which the surfactant 60 has been added is added to the first mixture 30. The manner in which the surfactant 60 is added is not particularly limited. For example, the surfactant 60 may be added to the first mixture 30 separately from the hydrophobic liquid 50.

As shown in FIG. 2, the surfactant 60 has a hydrophilic group 61 and a hydrophobic group 62. The hydrophilic group 61 of the surfactant 60 faces the surface side of the powder 10, and the hydrophobic group 62 faces the outside of the powder 10. This allows the surface of the powder 10 to be changed from hydrophilic to hydrophobic, so that when the powder 10 is moved from the aqueous phase 20a to the hydrophobic liquid phase 50a, the amount of water, etc. 20 accompanying the powder 10 can be reduced. That is, more water, etc. 20 can be replaced with the hydrophobic liquid 50. As a result, the energy required to dry the powder 10 can be further reduced. Note that FIG. 2 shows the state in which the surface of the powder 10 is modified by the surfactant 60, and the powder 10 is moved to the hydrophobic liquid phase 50a. It can be seen that the water, etc. 20 is not attached to the part of the surface of the powder 10 to which the surfactant 60 is attached. Therefore, the energy required to dry the powder 10 in the third step can be further reduced. As a result, it is expected that the cost of drying will decrease and the dryness will improve. Furthermore, when the water etc. 20 becomes an aqueous solution, the amount of impurities (each component in the aqueous solution) that migrate to the hydrophobic liquid phase 50a along with the powder 10 will also decrease, and preferably be completely removed.

The surfactant usable in this embodiment is an oil-soluble surfactant, mainly an anionic surfactant, but also a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. More specific examples include sodium sulfonate (also called Na sulfonate), calcium sulfonate (also called Ca sulfonate), magnesium sulfonate (also called Mg sulfonate), etc., which are oil-soluble anionic surfactants. Only one type of surfactant may be used, or multiple types may be mixed and used. It is preferable that the surfactant is stable at the temperature at which the surfactant is used, the functional group portion is ionized at the pH of the first mixture 30, and the surfactant dissolves in the hydrophobic liquid 50 at the temperature at which the surfactant is used at 1 mg/L or more, more preferably 1 g/L or more. When actually selecting a surfactant, the first to third steps are actually performed using a candidate surfactant to be used, and one that requires less energy to dry the powder 10 may be selected. In addition, the amount of surfactant added is not particularly limited. As shown in the examples described later, the more surfactant is added, the more water, etc. 20 can be replaced with the hydrophobic liquid 50. As a result, the energy required to dry the powder 10 can be further reduced. However, as the amount of surfactant added increases, the reduction in the energy required to dry the powder 10 reaches a plateau. The amount of surfactant added at this time becomes the practical upper limit.

(1-2. Second step)
In the second step, as shown in FIG. 1(b), gravity or centrifugal force due to standing is applied to the second mixture, so that the second mixture is separated into an aqueous phase 20a and a hydrophobic liquid phase 50a. Furthermore, the powder 10 is moved from the aqueous phase 20a to the hydrophobic liquid phase 50a. The magnitude and time of the centrifugal force may be adjusted to such an extent that the second mixture exhibits the above-mentioned behavior. When centrifugal force is applied to the second mixture, the second mixture can be separated into an aqueous phase 20a and a hydrophobic liquid phase 50a in a shorter time than gravity. Therefore, it is preferable to apply centrifugal force to the second mixture. Although there is no particular limit to the upper limit of the centrifugal force, since there are almost no centrifugal separators that can be applied when the centrifugal force exceeds 10,000 G, it is preferable that the centrifugal force is 10,000 G or less. In addition, the centrifugal separator to be applied may be a filtration type centrifuge.

In the second step, the powder 10 moves to the hydrophobic liquid phase 50a. At this time, much of the water, etc. 20 around the powder 10, particularly the water, etc. 20 between the particles of the powder 10, is replaced by the hydrophobic liquid 50. By adding a surfactant 60 to the hydrophobic liquid 50, more of the water, etc. 20 can be replaced by the hydrophobic liquid 50. If oil is present between the particles or on the particle surfaces of the powder 10, the oil is absorbed by the hydrophobic liquid.

(1-3. Third step)
In the third step, the powder 10 transferred to the hydrophobic liquid phase 50a is collected. Specifically, as shown in Fig. 1(b) and (c), the part of the hydrophobic liquid phase 50a where the powder 10 is aggregated (this part is often cake-like. Hereinafter, this part is also referred to as "powder cake") is separated and collected from the other parts of the second mixture (the aqueous phase 20a and the part of the hydrophobic liquid phase 50a other than the powder cake). In the example of Fig. 1(c), the collected powder cake is transferred to another container 200.

Next, the powder cake is dried to remove the hydrophobic liquid 50 from the powder cake (fourth step), as shown in FIG. 1(d), and the powder 10 is collected. Here, since most of the liquid contained in the powder cake is the hydrophobic liquid 50, the powder cake can be dried with less energy (heat of vaporization). Therefore, the CO ₂ generated during drying of the powder 10 can be reduced. Even if the water, etc. 20 constituting the first mixture 30 becomes an aqueous solution, the amount of water, etc. 20 carried into the powder cake is reduced. In addition, if the first mixture contains oil, the oil is absorbed into the hydrophobic liquid 50 in the second step, and is removed together with the hydrophobic liquid in the third step. Therefore, impurities (impurities derived from the components of the aqueous solution and oil) remaining in the powder 10 can be reduced. In addition, a curing yard is not required for collecting the powder 10. As shown in the examples described later, the energy required to dry the powder 10 can be measured by differential scanning calorimetry (DSC), but it can also be measured by other methods, such as the Karl Fischer method.

The temperature and pressure when carrying out the first to third steps are not particularly limited, and may be carried out, for example, at room temperature and pressure. However, if the first mixture is produced under heating and pressure, the first to third steps may be carried out in the same environment. In this case, the preferred characteristics of the hydrophobic liquid 50 are as described above.

<1. Experimental Example 1 (Removal of water and the like present between particles)>
Next, examples (experimental examples) of this embodiment will be described. In each of the experimental examples described below, various tests were performed to confirm the effects of this embodiment. Note that each of the experimental examples below was performed under normal temperature and pressure.

In Examples 1-2 to 1-8, first, the fly ash containing 3.5% by mass of unburned carbon relative to the total mass of the fly ash was heated to 600°C under atmospheric conditions to combust the unburned carbon present in the fly ash. The decarbonized fly ash (C-FA-free) obtained in this manner was made into a powder. The C-FA-free is oxide _particles containing 59.5% by mass (mass % relative to the total mass of the C-FA-free), 24.2% by mass of Al ₂ O ₃ , and 6.7% by mass of Fe ₂ O ₃ , and is a powder containing many spherical particles with a volume-based 50% particle diameter of 7 μm. Here, the chemical components of the C-FA-free were measured by the ICP method after dissolving the dried C-FA-free in an acidic aqueous solution. The volume-based 50% particle diameter was measured by the above-mentioned method. The laser diffraction particle size distribution measuring device used was LA-960 (manufactured by Horiba, Ltd.).

Trichloroethylene or 1-bromopropane was used as the hydrophobic liquid. Trichloroethylene has a specific gravity of 1.46, a solubility in water of 1.28 g/L at room temperature, a boiling point at room temperature of 87°C, and a KB value of 130. 1-bromopropane has a specific gravity of 1.35, a solubility in water of 2.5 g/L at room temperature, a boiling point at room temperature of 71°C, and a KB value of 125.

Next, 20 g of dried C-FA-free solution and 150 ml of water were added to a 500 ml container to form a slurry. In other words, a first mixture was prepared. The pH of the first mixture was then measured. Next, 150 ml of a hydrophobic liquid (trichloroethylene or 1-bromopropane) and a surfactant (Na sulfonate solution diluted with trichloroethylene or 1-bromopropane) were added to the first mixture, and the mixture of these, called the second mixture, was stirred for 30 seconds using a high-shear stirring homogenizer.

Then, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture by the centrifuge for 30 seconds. This caused the second mixture to separate into an aqueous phase and a hydrophobic liquid phase, and the C-FA-depleted mixture moved from the aqueous phase to the hydrophobic liquid phase. The C-FA-depleted mixture settled to the bottom of the centrifuge tube and became cake-like. The centrifuge tube was then tilted to drain the aqueous phase and hydrophobic liquid phase present above the powder cake.

Next, a portion (5-8 mg) of the powder cake deposited at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimetry (DSC) device (DSC8230, manufactured by Rigaku Corporation) while still wet. The sample was then heated from room temperature to 80°C, and the heat of vaporization was measured. Since the amount of sample was very small, the easily volatile hydrophobic liquid in the sample volatilized between the weighing process and the differential scanning calorimetry measurement. For this reason, it is presumed that the measured heat of vaporization is the heat of vaporization due only to the moisture in the sample. In any case, the smaller the heat of vaporization, the less the amount of water, etc. brought into the powder cake, and the less energy is required to dry the powder cake. In Examples 1-2 to 1-8, similar tests were conducted by changing the pH of the first mixture, the type of hydrophobic liquid, the type of surfactant, and the surfactant addition rate (addition rate relative to the powder). The heat of vaporization in all cases was a low value of 400 J/g-dry. The test conditions and heat of vaporization are as shown in Table 1. The test conditions and heat of vaporization for Comparative Example 1-1 and Example 1-9, which will be described below, are also shown in Table 1.

On the other hand, in Comparative Example 1-1, the first mixture used in Example 1-2 (i.e., one to which neither hydrophobic liquid nor surfactant was added) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) for 30 seconds using a centrifuge. This caused the C-FA-free mixture to settle at the bottom of the centrifuge tube. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then recovered. The moisture content of the recovered powder cake was 34% by mass (mass % relative to the total mass of the powder cake). In addition, the heat of vaporization of the powder cake was measured by differential scanning calorimetry in the same manner as in Examples 1-2 to 1-8, and the heat of vaporization was 538 J/g-dry, which was higher than that of Examples 1-2 to 1-8. The moisture content of the powder cake was measured by drying the powder cake in a thermostatic chamber at 105°C, and the reduction in mass before and after drying ((mass before drying - mass after drying) / (mass before drying)) was used as the moisture content.

In Example 1-9, the same experiment as in Example 1-5 was conducted, except that the fly ash (FA) used in Examples 1-2 to 1-8 was powdered without being burned (i.e., without being decarbonated). The heat of vaporization of the powder cake was 80 J/g-dry, which was also lower than that of Comparative Example 1-1.

Comparing Comparative Example 1-1 and Example 1-2, the heat of vaporization in Example 1-2 was smaller than that in Comparative Example 1-1. In Example 1-2, the water, etc. present between the C-FA-free particles was replaced with a hydrophobic liquid. On the other hand, such a treatment was not performed in Comparative Example 1-1. Therefore, in Example 1-2, the amount of water, etc. present between the particles was reduced, and the heat of vaporization was reduced. Furthermore, in Examples 1-3 to 1-8 in which a surfactant was added, the surface of the C-FA-free particles was made hydrophobic by the addition of the surfactant. Therefore, when the water, etc. present between the C-FA-free particles was replaced with a hydrophobic liquid, more water, etc. could be replaced with the hydrophobic liquid. The greater the surfactant addition rate, the smaller the heat of vaporization. Therefore, the greater the surfactant addition rate, the more water, etc. could be replaced with the hydrophobic liquid. In Example 1-6, the heat of vaporization was 0 J/g-dry, so there was substantially no water, etc. present between the C-FA-free particles. Therefore, in Examples 1-6, it is believed that the surfactant made all of the surfaces of the C-FA-free particles hydrophobic, and all of the water between the particles was replaced with a hydrophobic liquid.

In addition, comparing Example 1-6, in which the hydrophobic liquid used was trichloroethylene, with Example 1-8, in which the hydrophobic liquid used was 1-bromopropane, the heat of vaporization was smaller in Example 1-6, even though the surfactant addition rate in Example 1-8 was sufficiently large. This is thought to be because the solubility of trichloroethylene in water is smaller than that of 1-bromopropane in water. That is, in Example 1-6, when the water, etc. present between the C-FA-free particles is replaced with the hydrophobic liquid, the amount of water, etc. taken up by the hydrophobic liquid is less than in Example 1-8. Specifically, in Example 1-6, the heat of vaporization is 0 J/g-dry, so the amount of water, etc. taken up by the hydrophobic liquid is almost zero, whereas in Example 1-8, the heat of vaporization is greater than 0 J/g-dry, so it is thought that a small amount of water is taken up by the hydrophobic liquid.

In addition, in Example 1-9, fly ash (FA) is used as the powder, but as in Examples 1-2 to 1-8, the water, etc. present between the particles of the decarbonated FA is replaced with a hydrophobic liquid. Therefore, in Example 1-9, the amount of water, etc. present between the particles is reduced, and the heat of vaporization is reduced. However, compared to Example 1-5, which is the same condition as Example 1-9 except for the powder, the heat of vaporization in Example 1-9 is greater than that in Example 1-5. Therefore, it is believed that more water, etc. remains between the particles of the fly ash in Example 1-9. Fly ash contains hydrophobic particles (unburned carbon) in addition to hydrophilic particles. Therefore, it is believed that much of the surfactant adhered to the hydrophobic particles and did not adhere sufficiently to the hydrophilic particles. Therefore, it is believed that the surfaces of the hydrophilic particles were not sufficiently hydrophobic, and water, etc. remained between the hydrophilic particles.

Next, about 10 g of each sample was taken from the powder cakes obtained in Comparative Example 1-1, Example 1-4, and Example 1-6, and each sample was placed in a thermostatic dryer and allowed to stand while maintaining the temperature inside the dryer at 105°C. In addition, the mass change of each sample was measured in this state, and the time it took for the mass to become constant was measured. In this test, the mass of each sample was large at 10 g, so that when each sample was placed in the dryer, it contained not only water, etc. (water, etc. remaining after replacement with hydrophobic liquid) but also trichloroethylene, which is a hydrophobic liquid. Therefore, in this test, the time required to remove the water, etc. and hydrophobic liquid contained in each sample was measured. As a result, it was 54 minutes in Comparative Example 1-1, 16 minutes in Example 1-4, and 6 minutes in Example 1-6. Therefore, by replacing the water, etc. present between the particles of the powder with a hydrophobic liquid, the energy required to dry the powder (i.e., the heat of vaporization) was reduced. In other words, it was found that the powder became easier to dry and the drying speed of the powder increased.

<2. Experimental Example 2 (Removal of water and the like present between particles of blast furnace gas ash after removing zinc from blast furnace gas ash with alkali)>
In Examples 2-2 to 2-6, first, blast furnace gas ash containing 39 mass% Fe, 28 mass% C, and 1.3 mass% Zn relative to the total mass of the blast furnace gas ash and having a volume-based 50% particle size of 18 μm was prepared as a powder. Here, the chemical components of the blast furnace gas ash were measured by ICP method after dissolving the dried blast furnace gas ash in an acidic aqueous solution. The volume-based 50% particle size was measured by the above-mentioned method.

Next, Zn, which is a tramp element, was removed from the blast furnace gas ash. Specifically, 20 g of blast furnace gas ash, 200 ml of water, ammonium sulfate containing ammonia ions that convert Zn into an ammine complex, and NaOH were added to a 500 ml container to form a slurry. Next, the NH ₃ concentration of the slurry was adjusted to 30 g/L and the pH to 10.5, and the slurry was stirred with a shaker for 3 hours with the container sealed. This caused Zn to be leached from the blast furnace gas ash into the aqueous solution. That is, a first mixture was prepared.

Next, 200 ml of hydrophobic liquid (1-bromopropane) and surfactant (Ca sulfonate solution diluted with trichloroethylene) were added to the container. Next, the mixture of these, called the second mixture, was stirred for 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture for 30 seconds using a centrifuge. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the blast furnace gas ash moved from the aqueous phase to the hydrophobic liquid phase. The blast furnace gas ash settled at the bottom of the centrifuge tube and became cake-like. Next, the centrifuge tube was tilted to discharge the aqueous phase and hydrophobic liquid phase present on the upper side of the powder cake.

Next, a portion (5-8 mg) of the powder cake that had settled at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured.

The powder cake was then placed in a thermostatic dryer, and the temperature inside the dryer was maintained at 105°C to dry the powder cake. The Zn and S contents (mass % relative to the total mass of the dried powder cake) in the dried powder cake were then measured. The measurements were performed by dissolving the dried powder cake in an acidic aqueous solution and then using an ICP method. Note that Zn and S are components contained in the aqueous solution of the first mixture, and the lower their contents, the fewer the impurities contained in the powder. Zn was leached from the blast furnace gas ash into the aqueous solution of the first mixture, and S originated from the sulfate ions in ammonium sulfate, which is the leaching agent for leaching Zn into the aqueous solution. Table 2 shows the test conditions, heat of vaporization, Zn content, and S content of Examples 2-2 to 2-6.

In Comparative Example 2-1, the first mixture prepared above (i.e., without the addition of hydrophobic liquid or surfactant) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) by a centrifuge for 30 seconds. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then collected. Thereafter, the same treatment as in Examples 2-2 to 2-6 was performed to measure the heat of vaporization, Zn content, and S content. The test conditions, heat of vaporization, Zn content, and S content of Comparative Example 2-1 are shown in Table 2.

In both Comparative Example 2-1 and Examples 2-2 to 2-6, the Zn content was reduced from the initial Zn content (1.3 mass%) contained in the blast furnace gas ash. Therefore, in all examples, at least Zn was removed. However, when comparing Comparative Example 2-1 with Examples 2-2 to 2-6, the heat of vaporization in Comparative Example 2-1 was higher than in Examples 2-2 to 2-6, and both the Zn content and S content in Comparative Example 2-1 were higher than in Examples 2-2 to 2-6.

First, comparing Comparative Example 2-1 and Example 2-2, in Example 2-2, water, etc. present between the particles of blast furnace gas ash is replaced with a hydrophobic liquid. On the other hand, such a treatment is not performed in Comparative Example 2-1. Therefore, in Example 2-2, the amount of water, etc. (here, aqueous solution) present between the particles is reduced, and the heat of vaporization is reduced. Furthermore, since Zn and S dissolved in water, etc. are also replaced by the hydrophobic liquid together with the water, etc., the Zn content and S content are also reduced. Furthermore, in Examples 2-3 to 2-6 in which a surfactant is added, the surface of the particles of blast furnace gas ash is made hydrophobic by the addition of the surfactant. Therefore, when the water, etc. present between the particles of blast furnace gas ash is replaced with the hydrophobic liquid, more water, etc. can be replaced with the hydrophobic liquid. Therefore, the heat of vaporization, Zn content, and S content are further reduced. Furthermore, the greater the surfactant addition rate, the lower the heat of vaporization, Zn content, and S content. In Example 2-6, the heat of vaporization was 10 J/g-dry, which means that there was a small amount of water between the blast furnace gas ash particles. In Example 2-6, it is believed that the surfactant made all of the surfaces of the blast furnace gas ash particles hydrophobic, and all of the water between the particles was replaced with hydrophobic liquid, but it is believed that this result was obtained because a small amount of water was dissolved in the hydrophobic liquid.

<3. Experimental Example 3 (Removal of water and the like present between particles of blast furnace gas ash after removing zinc from blast furnace gas ash with acid)>
In Examples 3-2 to 3-6, first, Zn, which is a tramp element, was removed from the blast furnace gas ash used in Experimental Example 2. Specifically, 20 g of blast furnace gas ash and 200 ml of water were added to a 500 ml container to form a slurry. Next, a hydrochloric acid solution with a concentration of 36 mass% was added to the slurry to adjust the pH of the slurry to 1. Next, the slurry was stirred with a shaker for 1 hour with the container sealed. This caused Zn to be leached from the blast furnace gas ash into the aqueous solution. That is, a first mixture was prepared.

Next, 200 ml of a hydrophobic liquid (1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane, a fluorine-based organic solvent) and a surfactant (Mg sulfonate solution diluted with the fluorine-based organic solvent) were added to the container. Here, the specific gravity of 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane is 1.43, its solubility in water is 20 mg/L at room temperature, its boiling point at room temperature is 76°C, and its KB value is 10. Next, the second mixture, which is a mixture of these, was stirred for 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the blast furnace gas ash moved from the aqueous phase to the hydrophobic liquid phase. The blast furnace gas ash settled to the bottom of the centrifuge tube and formed a cake. The centrifuge tube was then tilted to drain the aqueous phase and hydrophobic liquid phase that were present on the top of the powder cake.

Next, a portion (5-8 mg) of the powder cake that had settled at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured.

The powder cake was then placed in a thermostatic dryer, and the temperature inside the dryer was maintained at 105°C to dry the powder cake. The Zn and Cl contents (mass % relative to the total mass of the dried powder cake) in the dried powder cake were then measured. The Zn content was measured by dissolving the dried powder cake in an acidic aqueous solution, and then using an ICP method. The Cl content was measured by extracting the Cl component by subjecting the dried powder cake to a hot water extraction process, and then using an ion chromatography method. Note that Zn and Cl are components contained in the aqueous solution of the first mixture, and the lower their contents, the fewer the impurities contained in the powder. Zn was leached from the blast furnace gas ash into the aqueous solution of the first mixture, and Cl was derived from hydrochloric acid, which is a leaching agent for leaching Zn into the aqueous solution. Table 3 shows the test conditions, heat of vaporization, Zn content, and Cl content of Examples 3-2 to 3-6.

In Comparative Example 3-1, the first mixture prepared above (i.e., without the addition of hydrophobic liquid or surfactant) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) by a centrifuge for 30 seconds. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then collected. Thereafter, the same treatment as in Examples 3-2 to 3-6 was performed to measure the heat of vaporization, Zn content, and Cl content. The test conditions, heat of vaporization, Zn content, and Cl content of Comparative Example 3-1 are shown in Table 3.

In both Comparative Example 3-1 and Examples 3-2 to 3-6, the Zn content was reduced from the initial Zn content (1.3 mass%) contained in the blast furnace gas ash. Therefore, in all examples, at least Zn was removed. However, when comparing Comparative Example 3-1 with Examples 3-2 to 3-6, the heat of vaporization in Comparative Example 3-1 was higher than in Examples 3-2 to 3-6, and both the Zn content and S content in Comparative Example 3-1 were higher than in Examples 3-2 to 3-6.

First, comparing Comparative Example 3-1 and Example 3-2, in Example 3-2, water, etc. present between the particles of blast furnace gas ash is replaced with a hydrophobic liquid. On the other hand, such a treatment is not performed in Comparative Example 3-1. Therefore, in Example 3-2, the amount of water, etc. (here, aqueous solution) present between the particles is reduced, and the heat of vaporization is reduced. Furthermore, since Zn and Cl dissolved in water, etc. are also replaced by the hydrophobic liquid together with water, etc., the Zn content and Cl content are also reduced. Furthermore, in Examples 3-3 to 3-6 in which a surfactant is added, the surface of the particles of blast furnace gas ash is made hydrophobic by the addition of the surfactant. Therefore, when the water, etc. present between the particles of blast furnace gas ash is replaced with the hydrophobic liquid, more water, etc. can be replaced with the hydrophobic liquid. Therefore, the heat of vaporization, Zn content, and Cl content are further reduced. Furthermore, the greater the surfactant addition rate, the lower the heat of vaporization, Zn content, and Cl content. In Example 3-6, the heat of vaporization was 0 J/g-dry, meaning that there was essentially no water or other substances between the blast furnace gas ash particles. Therefore, in Example 3-6, it is believed that the surfactant made all of the surfaces of the blast furnace gas ash particles hydrophobic, and all of the water or other substances between the particles was replaced with a hydrophobic liquid.

<4. Experimental Example 4 (Removal of water and oil between particles)>
In Examples 4-2 to 4-5, first, a water-containing slurry (oil-containing slurry) containing oil was prepared as the first mixture. Here, the scale in the water-containing slurry contains 63 mass% Fe and 3.1 mass% oil with respect to the total mass of the scale, and the particle size at 50% by volume is 48 μm. Here, the chemical components of the scale were measured by ICP method after dissolving the dried scale in an acidic aqueous solution. The oil content of the scale was measured by the following method. That is, the dried scale was immersed in normal hexane to extract the oil from the scale. Then, the extraction liquid was heated to 100 ° C. to volatilize the normal hexane, and the oil content was calculated from the amount of residue. The particle size at 50% by volume was measured by the above-mentioned method.

Next, 150 ml of the first mixture (52 g solids) and 200 ml of hydrophobic liquid (1-bromopropane) were placed in a 500 ml container, and the mixture, called the second mixture, was stirred for 30 seconds using a high-shear stirring homogenizer. Next, a surfactant (Na sulfonate solution diluted with 1-bromopropane) was added to the second mixture, and the second mixture was stirred for another 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the scale moved from the aqueous phase to the hydrophobic liquid phase. The scale settled at the bottom of the centrifuge tube and became cake-like. Next, the centrifuge tube was tilted to drain the aqueous phase and hydrophobic liquid phase present on the upper side of the powder cake.

Next, a portion (5-8 mg) of the powder cake that had settled at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured.

The powder cake was then placed in a thermostatic dryer, and the temperature inside the dryer was maintained at 105°C to dry the powder cake. The oil content in the dried powder cake (mass % relative to the total mass of the dried powder cake (excluding oil)) was then measured. The oil content was measured using the method described above. The test conditions, heat of vaporization, and oil content for Examples 4-2 to 4-5 are shown in Table 4.

In Comparative Example 4-1, 150 ml (52 g solids) of the first mixture (i.e., an aqueous slurry to which no hydrophobic liquid or surfactant was added) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) for 30 seconds using a centrifuge. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then collected. The same treatment as in Examples 4-2 to 4-5 was then performed to measure the heat of vaporization and the oil content. The test conditions, heat of vaporization, and oil content of Comparative Example 4-1 are shown in Table 4.

Comparing Comparative Example 4-1 with Examples 4-2 to 4-5, the oil content in Comparative Example 4-1 did not change from the oil content of the original scale, and the oil was not removed. Furthermore, the heat of vaporization in Comparative Example 4-1 was higher than in Examples 4-2 to 4-5. On the other hand, the oil content was greatly reduced in all of Examples 4-2 to 4-5, indicating that the oil had been removed. The heat of vaporization also greatly decreased.

First, comparing Comparative Example 4-1 and Example 4-2, in Example 4-2, the water and other substances present between the scale particles are replaced with a hydrophobic liquid. On the other hand, such a treatment is not performed in Comparative Example 4-1. As a result, in Example 4-2, there is less water and other substances present between the particles, and the heat of vaporization is smaller. In addition, the oil present between the particles is absorbed by the hydrophobic liquid and is removed together with the hydrophobic liquid. As a result, the oil content is also reduced. However, when the hydrophobic liquid is removed, some of the oil dissolved in the hydrophobic liquid may remain. As a result, a small amount of oil remained in Example 4-2.

Furthermore, in Examples 4-3 to 4-5 in which a surfactant was added, the surface of the scale particles became hydrophobic due to the addition of the surfactant. Therefore, when the water, etc. present between the scale particles was replaced with the hydrophobic liquid, more water, etc. could be replaced with the hydrophobic liquid. This further reduced the heat of vaporization. Furthermore, the greater the surfactant addition rate, the lower the heat of vaporization. Therefore, the greater the surfactant addition rate, the more water, etc. could be replaced with the hydrophobic liquid. In Example 4-5, the heat of vaporization was 13 J/g-dry, which means that there was a small amount of water, etc. between the scale particles. In Example 4-5, it is thought that the surfactant made all the surfaces of the scale particles hydrophobic, and all the water, etc. between the particles was replaced with the hydrophobic liquid, but it is thought that such a result was obtained because a small amount of water, etc. was dissolved in the hydrophobic liquid.

On the other hand, the oil content increased slightly as the surfactant addition rate increased. The greater the surfactant addition rate, the more hydrophobic liquid containing oil was present between the particles. Therefore, the greater the surfactant addition rate, the more oil remained when the hydrophobic liquid was removed. Of course, the mass % of oil in each of Examples 4-2 to 4-5 was significantly reduced compared to Comparative Example 4-1, and the effect of this embodiment was fully obtained.

<5. Experimental Example 5 (Consideration of the effect of _d50 )>
In Examples 5-2, 5-4, and 5-6, fine sand with different volume-based 50% particle diameters (d ₅₀ ) was used as the powder. The volume-based 50% particle diameters (d ₅₀ ) of the fine sand used in each Example are shown in Table 5. The fine sand is an oxide particle mainly composed of SiO ₂ and Al ₂ O _3. In Examples 5-8 and 5-10, several types of fly ash with different chemical compositions and volume-based 50% particle diameters were heated to 600°C under atmospheric conditions to combust the unburned carbon present in each fly ash. The several types of de-C-FA thus obtained were made into powder. These de-C-FA are oxide particles containing 52 to 64 mass% SiO ₂ (mass % relative to the total mass of the de-C-FA), 19 to 28 mass% Al ₂ O ₃ , and 3 to 8 mass% Fe ₂ O ₃ , and contain many spherical particles. Furthermore, the volume-based 50% particle diameters of these C-FA-free materials are different from one another. The volume-based 50% particle diameters (d ₅₀ ) of the C-FA-free materials used in each Example are shown in Table 5. Here, the chemical components of the fine sand and the C-FA-free materials were measured by ICP method after dissolving the dried fine sand and the C-FA-free materials in an acidic aqueous solution. The volume-based 50% particle diameters (d ₅₀ ) were measured by the method described above.

Next, in Examples 5-2, 5-4, 5-6, 5-8, and 5-10, 20 g of dried powder and 150 ml of water were added to a 500 ml container to form a slurry. That is, a first mixture was prepared. Next, the pH of the first mixture was measured. The pH was 7.1 to 8.9. Next, 150 ml of hydrophobic liquid (trichloroethylene) was added to the first mixture, and the mixture, that is, the second mixture, was stirred for 30 seconds using a high-shear stirring homogenizer. Thereafter, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the powder (fine sand or de-C-FA) moved from the aqueous phase to the hydrophobic liquid phase. The powder settled to the bottom of the centrifuge tube and became cake-like. The centrifuge tube was then tilted to drain the aqueous phase and hydrophobic liquid phase present on the top of the powder cake.

A portion (5-8 mg) of the powder cake deposited at the bottom of the centrifuge tube was then taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured. The test conditions and heat of vaporization for Examples 5-2, 5-4, 5-6, 5-8, and 5-10 are shown in Table 5.

In Example 5-11, the second mixture prepared in Example 5-2 was left to stand for 2 minutes instead of being centrifuged. In other words, in Example 5-11, gravity was applied to the second mixture by leaving it to stand. In Example 5-11, the second mixture in the container also separated into an aqueous phase and a hydrophobic liquid phase, and the powder (fine sand) moved from the aqueous phase to the hydrophobic liquid phase. The powder settled to the bottom of the centrifuge tube and became cake-like. Thereafter, the heat of vaporization of the powder cake was measured by differential scanning calorimetry in the same manner as in Example 5-2. The test conditions and heat of vaporization of Example 5-11 are shown in Table 5.

In Comparative Examples 5-1, 5-3, and 5-5, the first mixture (i.e., without the addition of hydrophobic liquid) prepared in Examples 5-2, 5-4, and 5-6 was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) for 30 seconds using a centrifuge. This caused the powder to settle at the bottom of the centrifuge tube. The centrifuge tube was then tilted to drain the aqueous phase. The powder cake that had settled at the bottom was then collected. The heat of vaporization of the powder cake was then measured by differential scanning calorimetry in the same manner as in Examples 5-2, 5-4, and 5-6. The test conditions and heat of vaporization for Comparative Examples 5-1, 5-3, and 5-5 are shown in Table 5.

In Comparative Examples 5-7 and 5-9, the first mixture prepared in Examples 5-8 and 5-10 (i.e., without the addition of hydrophobic liquid) was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the first mixture by a centrifuge for 30 seconds. This caused the powder to settle at the bottom of the centrifuge tube. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then collected. The heat of vaporization of the powder cake was then measured by differential scanning calorimetry in the same manner as in Examples 5-8 and 5-10. The test conditions and heat of vaporization for Comparative Examples 5-7 and 5-9 are shown in Table 5.

When comparing each example with a comparative example using the same powder as in these examples (for example, comparing Example 5-2 with Comparative Example 5-1), the heat of vaporization in each example was lower than that of the corresponding comparative example. In each example, water, etc. present between the particles of the powder was replaced with a hydrophobic liquid. On the other hand, such treatment was not performed in each comparative example. Therefore, in each example, the amount of water, etc. present between the particles was reduced, and the heat of vaporization was reduced. Furthermore, the smaller the volume-based 50% particle size of the powder, the greater the reduction in the heat of vaporization, and the reduction was particularly significant when the volume-based 50% particle size was 100 μm or less, 25 μm or less, or 10 μm or less. Therefore, it was found that the volume-based 50% particle size (d ₅₀ ) of the powder is preferably 100 μm or less, more preferably 25 μm or less, and more preferably 10 μm or less.

Furthermore, when comparing Comparative Example 5-1, Example 5-2, and Example 5-11, it was confirmed that the heat of vaporization also decreased in Example 5-11, in which the fine sand was allowed to settle by standing still. However, the heat of vaporization did not decrease as much as in Example 5-2, in which centrifugal force was applied.

6. Example 6 (Removal of water and the like present between particles of slag powder or iron ore powder)
In Examples 6-2 and 6-4, slag powder or ore powder was prepared as the powder. Here, the slag powder was obtained by wet grinding slag generated from a blast furnace. The slag powder is an oxide particle containing 41.7 mass% CaO (mass% relative to the total mass of the slag powder), 33.8 mass% SiO ₂ , and 13.4 mass% Al ₂ O ₃ , and the volume-based 50% particle diameter is 67 μm. Here, the chemical components of the slag powder were measured by an X-ray fluorescence analyzer (XRF) (ZSX Primus II, manufactured by Rigaku Corporation) using the glass bead method. The volume-based 50% particle diameter was measured by the above-mentioned method. On the other hand, the ore powder is iron ore powder. The iron ore powder is an oxide particle containing 89.4 mass% Fe ₂ O ₃ (mass% relative to the total mass of the iron ore powder), and the volume-based 50% particle diameter is 110 μm. Here, the chemical components of the iron ore powder were measured by ICP method after dissolving the dried iron ore powder in an acidic aqueous solution. The volume-based 50% particle size was measured by the above-mentioned method.

Next, 20 g of dried powder and 150 ml of water were added to a 500 ml container to form a slurry. In other words, a first mixture was prepared. Next, the pH of the first mixture was measured. Next, 150 ml of a hydrophobic liquid (trichloroethylene) and a surfactant (Na sulfonate solution diluted with trichloroethylene) were added to the first mixture, and the mixture, which was a second mixture, was stirred for 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and a centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the powder moved from the aqueous phase to the hydrophobic liquid phase. The powder settled at the bottom of the centrifuge tube and became a cake. Next, the centrifuge tube was tilted to discharge the aqueous phase and the hydrophobic liquid phase present on the upper side of the powder cake.

Next, a portion (5-8 mg) of the powder cake deposited at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured. The test conditions and heat of vaporization for Examples 6-2 and 6-4 are shown in Table 6.

In Comparative Examples 6-1 and 6-3, the first mixture (i.e., without the addition of hydrophobic liquid and surfactant) prepared in Examples 6-2 and 6-4 was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the first mixture by a centrifuge for 30 seconds. This caused the powder to settle at the bottom of the centrifuge tube. The centrifuge tube was then tilted to drain the aqueous phase. The powder cake that had settled at the bottom was then collected. The moisture content of the collected powder cake was then measured in the same manner as in Experimental Example 1, and the moisture content was found to be 34% by mass (mass % relative to the total mass of the powder cake). Furthermore, the heat of vaporization of the powder cake was measured by differential scanning calorimetry in the same manner as in Examples 6-2 and 6-4. The test conditions and heat of vaporization of Comparative Examples 6-1 and 6-3 are shown in Table 6.

When comparing each example with a comparative example that uses the same powder as the example (for example, comparing Example 6-2 with Comparative Example 6-1), the heat of vaporization in each example was lower than that of the corresponding comparative example. In each example, the water and other substances present between the powder particles were replaced with a hydrophobic liquid. On the other hand, no such treatment was performed in each comparative example. As a result, there was less water and other substances present between the particles in each example, and the heat of vaporization was smaller.

<7. Experimental Example 7 (Example in which powder becomes leaching residue)>
First, an ammonium sulfate solution (20 g-NH ₃ /L) (ammonia equivalent concentration) as a leaching solution (leaching agent) was placed in a leaching vessel, and its pH was adjusted to pH 9.8 to 10.2 with a 20 mass% NaOH aqueous solution. Furthermore, a surface-treated steel plate plated with Zn and Ni (surface area 0.08 m ² ) was placed in the leaching vessel, and the mixture was stirred for 3 hours with a stirring pump. Thereafter, the stirring pump was stopped, and the leaching vessel was allowed to stand. Next, the leaching solution in the leaching vessel was discharged from the leaching vessel and filtered to obtain a leaching waste liquid. The composition of the leaching waste liquid is shown in Table 7. As shown in Table 7, the leaching waste liquid contains Zn ions and Ni ions (which exist as ammine complex ions) leached from the surface-treated steel plate in addition to NH ₃ , which is a leaching solution component. The Zn and Ni concentrations in the leachate were measured by ICP method, the _NH3 concentration in the leachate was measured by spectrophotometry after distillation, and the ^S2- concentration in the leachate was measured by iodometric titration after distillation.

Next, the leaching waste liquid was placed in a regeneration vessel, and while stirring with a stirring pump, hydrogen sulfide gas was added to the leaching waste liquid until the redox potential reached -200 mV. This caused the Zn ions and Ni ions forming the ammine complex ions to precipitate as sulfides (Zn sulfide and Ni sulfide). During this process, the pH of the leaching waste liquid was measured with a pH meter, and the pH of the leaching waste liquid was maintained at 9.8 to 10.2. The hydrogen sulfide concentration in the gas phase in the regeneration vessel was 0.1 ppm or less. Through the above steps, a first mixture was produced. Here, the powder is the leaching residue, i.e., Zn sulfide and Ni sulfide (sulfide particles), and the water, etc. is the leaching waste liquid.

Next, 200 ml of the first mixture was placed in a 500 ml container, and 200 ml of hydrophobic liquid (trichloroethylene) and 0.6 mass% Na sulfonate liquid relative to the amount of precipitated sulfide were added to the container. Next, the second mixture, which is a mixture of these, was stirred for 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the leaching residue moved from the aqueous phase to the hydrophobic liquid phase. The leaching residue settled at the bottom of the centrifuge tube and became cake-like. Next, the centrifuge tube was tilted to discharge the aqueous phase and hydrophobic liquid phase present on the upper side of the powder cake.

Next, the discharged aqueous phase and hydrophobic liquid phase were transferred to another container, and separated into two phases by gravity separation by standing. Next, the aqueous phase (i.e., the leaching waste liquid excluding the leaching residue) was collected. The composition of the leaching waste liquid excluding the leaching residue is shown in Table 7. The measurement method was the same as above. As shown in Table 7, the NH ₃ concentration of the leaching waste liquid excluding the leaching residue was approximately the same as the NH ₃ concentration of the original leaching waste liquid, and no sulfide ions derived from hydrogen sulfide gas were detected. On the other hand, the Zn ion and Ni ion concentrations of the leaching waste liquid excluding the leaching residue were significantly reduced to values that could be reused as a leachate. Therefore, it was confirmed that the leachate used in Experimental Example 7 has the function of leaching Zn and Ni, and that the leachate waste liquid can be regenerated into a leachate by the treatment of this Experimental Example 7 (the treatment of this embodiment).

Next, a portion (5 mg) of the powder cake deposited at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured. As a result, the heat of vaporization was 125 J/g-dry.

Meanwhile, the first mixture (i.e., leaching waste liquid containing leaching residue and to which no hydrophobic liquid or surfactant has been added) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) for 30 seconds using a centrifuge. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then collected. The same process as above was then carried out, and the heat of vaporization was measured. As a result, the heat of vaporization was 735 J/g-dry. Therefore, it was confirmed that even when the powder becomes a sulfide-based leaching residue, the heat of vaporization can be significantly reduced by replacing the water, etc. present between the powder particles with a hydrophobic liquid.

<8. Example 8 (Recovery of _CaF2 from leaching wastewater after stainless steel treatment)>
A fluoride ion-containing waste liquid was prepared by pickling a Cr-Ni stainless steel as the stainless steel. The composition of the fluoride ion-containing waste liquid is shown in Table 8. The Fe, Cr, and Ni concentrations in the fluoride ion-containing waste liquid were measured by ICP method, and the F concentration in the fluoride ion-containing waste liquid was measured by ion chromatography.

Next, 10 L of the fluoride ion-containing waste liquid was placed in a container, and quicklime (CaO) was added while stirring the fluoride ion-containing waste liquid, adjusting the pH of the fluoride ion-containing waste liquid to 3. This caused the fluoride ions in the fluoride ion-containing waste liquid to precipitate as _CaF2 . The fluoride ion-containing waste liquid was then left to stand, causing a precipitate containing _CaF2 as the main component to precipitate. The supernatant was then discarded to prepare a water-containing slurry, which is the first mixture. The powder here is the precipitate (main component is _CaF2 ), which is the leaching residue, and the water, etc. is the fluoride ion-containing waste liquid.

Next, 200 ml of the first mixture was placed in a 500 ml container, and 200 ml of hydrophobic liquid (trichloroethylene) and 1.0 mass% Na sulfonate liquid relative to the amount of precipitated solids were added to the container. Next, the second mixture, which was a mixture of these, was stirred for 30 seconds using a high-shear stirring homogenizer. After that, the second mixture was placed in a centrifuge tube, and centrifugal force (1,750 G) was applied to the second mixture using a centrifuge for 30 seconds. As a result, the second mixture was separated into an aqueous phase and a hydrophobic liquid phase, and the leaching residue moved from the aqueous phase to the hydrophobic liquid phase. The leaching residue settled at the bottom of the centrifuge tube and became cake-like. Next, the centrifuge tube was tilted to discharge the aqueous phase and hydrophobic liquid phase present on the upper side of the powder cake.

Next, a portion (5 mg) of the powder cake deposited at the bottom of the centrifuge tube was taken as a sample, and the sample was immediately placed in a differential scanning calorimeter while still wet. The differential scanning calorimeter used was the same as that used in Experimental Example 1. The sample was then heated from room temperature to 80°C, and the heat of vaporization at this time was measured. As a result, the heat of vaporization was 39 J/g-dry.

On the other hand, the first mixture (i.e., the leaching waste liquid containing the leaching residue and to which no hydrophobic liquid or surfactant was added) was placed in a centrifuge tube, and the first mixture was subjected to centrifugal force (1,750 G) by a centrifuge for 30 seconds. The centrifuge tube was then tilted to discharge the aqueous phase. The powder cake that had settled at the bottom was then recovered. The same process as above was then performed to measure the heat of vaporization. As a result, the heat of vaporization was 693 J/g-dry. Therefore, it was confirmed that even when the powder becomes a leaching residue mainly composed of _CaF2 , the heat of vaporization can be significantly reduced by replacing the water, etc. present between the powder particles with a hydrophobic liquid.

10 Powder 20 Water, etc. 20a Aqueous phase 30 First mixture 50 Hydrophobic liquid 50a Hydrophobic liquid phase 100, 200 Container

Claims (6)

a first step of adding a hydrophobic liquid having a specific gravity greater than that of water and less than that of the powder to a first mixture of a powder containing hydrophilic particles and water or an aqueous solution, and stirring a second mixture of the first mixture and the hydrophobic liquid;
a second step of applying gravity or centrifugal force to the second mixture by standing to separate the second mixture into an aqueous phase and a hydrophobic liquid phase and transferring the powder to the hydrophobic liquid phase;
and a third step of recovering the powder that has transferred to the hydrophobic liquid phase ;
the powder containing hydrophilic particles is any one or more selected from the group consisting of dust, scale, leach residue, fly ash, slag powder, and ore powder, or when 1 g of the powder is put into a sealed container together with 100 ml of water and 100 ml of the hydrophobic liquid, the mixture is stirred and allowed to stand, and the state of the aqueous phase is observed, the powder at least floats in the aqueous phase,
the hydrophobic liquid is trichloroethylene, 1-bromopropane, tetrachloroethylene, a fluorine-based organic solvent, or a liquid whose solubility in water at room temperature (25° C.) is 0 g/L or more and 10.0 g/L or less,
In the first step, a surfactant is added,
After the second step, the entire amount of the powder is immersed in the hydrophobic liquid phase.
A method for recovering powder comprising the steps of: The powder recovery method according to claim 1, further comprising a fourth step of drying the powder recovered in the third step to remove the hydrophobic liquid adhering to the powder. The powder recovery method according to claim 1 or 2, characterized in that the powder has a volume-based 50% particle size of 100 μm or less. The method for recovering powder according to any one of claims 1 to 3, wherein the surfactant is an oil-soluble anionic surfactant. The method for recovering powder according to any one of claims 1 to 4, characterized in that oil is attached to the surface of the powder. The boiling point of the hydrophobic liquid is 40° C. to 95° C. at normal pressure;
The powder recovery method according to any one of claims 1 to 5, wherein the first step to the third step are carried out at room temperature and normal pressure.

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