Method of recovering molybdenum compound

Abstract

To provide a method of recovering a molybdenum compound, capable of obtaining molybdenum oxide powder of high purity and a high specific surface area, from a solution containing a molybdenum component.SOLUTION: The method of recovering a molybdenum compound, has: a precipitation step of precipitating a molybdate represented by formula (1): AxMoyO3y+z (in the formula (1), A represents an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14. 3y+z represents the number of oxygen atoms included in the molybdate, and z represents 1 / 2 of the number of a valence ×x of A), in a solution containing a molybdenum component; a firing step of generating an oxide represented by formula (2): Aoz, (in the formula (2), A is the same as A in the formula (1), and z represents the number of oxygen atoms connecting with A in the formula (2) to form oxides) and generating vapor comprised of molybdenum trioxide; a cooling step; and a recovery step.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for recovering molybdenum compounds.

Background Art

[0002] Conventionally, molybdenum compounds such as molybdenum trioxide have been suitably used as fluxes when producing inorganic oxides such as alumina, zirconia, titania, and silica using the flux method. Further, molybdenum compounds are also widely used as catalysts. However, molybdenum, which is a raw material for molybdenum compounds, is an expensive element whose price fluctuates easily. For this reason, as a raw material, a method of recycling molybdenum compounds recovered from waste liquid containing molybdenum has been studied.

[0003] As a method for recovering molybdenum from used catalysts containing molybdenum, for example, there is a method described in Patent Document 1. Patent Document 1 describes a method for recovering molybdenum from a treatment solution that is an aqueous solution containing molybdenum. In the molybdenum recovery method described in Patent Document 1, an extraction step of performing solvent extraction with the treatment solution to extract molybdenum, a back-extraction step of back-extracting the extraction solvent obtained in the extraction step, and adding an acid to the back-extraction solution obtained in the back-extraction step to recover molybdenum as a precipitate of molybdate are performed in order.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, among molybdenum compounds, the demand for molybdenum oxide powder with high purity and large specific surface area has been increasing. However, with conventional molybdenum compound recovery methods, it has been difficult to obtain molybdenum oxide powder with high purity and large specific surface area from a molybdenum component-containing solution such as waste liquid containing molybdenum. For this reason, the recovered molybdenum oxide powder had few reusable applications.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for recovering a molybdenum compound capable of obtaining molybdenum oxide powder with high purity and large specific surface area from a molybdenum component-containing solution.

Means for Solving the Problems

[0007] [1] In a molybdenum component-containing solution, A x Mo y O 3y+z (1) (In formula (1), A represents an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14. 3y + z represents the number of oxygen atoms contained in the molybdate, and z represents the number of 1 / 2 of the valence of A × x.) A precipitation step of precipitating a molybdate represented by the formula, By thermally decomposing the molybdate, AO z (2) (In formula (2), A is the same as A in formula (1). z represents the number of oxygen atoms that combine with A in formula (2) to form an oxide.) A firing step of generating an oxide represented by the formula and generating vapor composed of molybdenum trioxide, A cooling step of cooling the vapor composed of molybdenum trioxide to generate powder composed of molybdenum trioxide, A method for recovering a molybdenum compound, comprising a recovery step of recovering powder composed of molybdenum trioxide.

[0008] [2] In the precipitation step, a precipitation accelerator containing a compound containing at least one element selected from the elements of Group 4, Group 8, Group 12, Group 13, and Group 14 is added to the molybdenum component-containing solution and stirred to precipitate the molybdate, the method for recovering a molybdenum compound according to [1]. [3] In the precipitation step, a precipitation accelerator containing an aluminum compound is added to the molybdenum component-containing solution and stirred to precipitate the molybdate, the method for recovering a molybdenum compound according to [1].

[0009] [4] In the precipitation step, a precipitation accelerator containing polyaluminum chloride is added to the molybdenum component-containing solution and stirred to precipitate the molybdate, the method for recovering a molybdenum compound according to [1]. [5] The method for recovering a molybdenum compound according to [4], wherein the pH of the molybdenum component-containing solution to which the precipitation accelerator containing polyaluminum chloride is added is adjusted to be in the range of 8 to 13.

[0010] [6] In the recovery step, a powder of molybdenum trioxide having a purity of 99% or more and a specific surface area measured by the BET method of 20 m 2 / g or more is recovered, the method for recovering a molybdenum compound according to [1]. [Effect of the Invention]

[0011] According to the method for recovering a molybdenum compound of the present invention, a powder composed of molybdenum trioxide having a high purity and a large specific surface area measured by the BET method can be obtained from a molybdenum component-containing solution. Therefore, the recovered molybdenum trioxide can be preferably used as a flux, for example, when producing inorganic oxides such as alumina, zirconia, titania, and silica using the flux method, and can be reused for various applications. Therefore, the method for recovering a molybdenum compound of the present invention can contribute to the reuse of molybdenum compounds and reduce the environmental load. [Embodiments for Carrying Out the Invention]

[0012] In order to solve the above problems and obtain molybdenum oxide powder with high purity and a large specific surface area from a molybdenum component-containing solution, the inventors focused on the fact that the powder produced by cooling the vapor composed of molybdenum trioxide has high purity and a large specific surface area measured by the BET method, and conducted intensive studies.

[0013] As a result, in the molybdenum component-containing solution, A x Mo y O 3y+z (1) (In formula (1), A represents an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14 elements. 3y + z represents the number of oxygen atoms contained in the molybdate, and z represents the number of 1 / 2 of the valence of A × x.) By precipitating the molybdate represented by this formula and thermally decomposing it, AO z (2) (In formula (2), A is the same as A in formula (1). z represents the number of oxygen atoms that combine with A in formula (2) to form an oxide.) It has been found that an oxide represented by this formula can be generated and at the same time, a vapor composed of molybdenum trioxide can be generated.

[0014] Furthermore, the inventors precipitated the molybdate represented by formula (1) in a molybdenum component-containing solution, thermally decomposed it to generate a vapor composed of molybdenum trioxide, cooled it to generate a powder, and recovered it. As a result, it was confirmed that a powder composed of molybdenum trioxide with high purity and a large specific surface area measured by the BET method could be obtained, and the present invention was conceived.

[0015] Hereinafter, the method for recovering the molybdenum compound of the present invention will be described in detail. The scope of the present invention is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present invention. Also, when a plurality of upper limit values and lower limit values are described for specific parameters, any upper limit value and lower limit value can be combined to form a suitable numerical range.

[0016] The method for recovering the molybdenum compound of the present embodiment includes a precipitation step, a firing step, a cooling step, and a recovery step. The method for recovering the molybdenum compound of the present embodiment may be carried out in a batch manner or a continuous manner.

[0017] In the method for recovering the molybdenum compound of the present embodiment, a powder composed of molybdenum trioxide is recovered from a molybdenum component-containing solution. The molybdenum component-containing solution is one in which a component containing a molybdenum component is dispersed or dissolved in a medium.

[0018] The molybdenum component contained in the molybdenum component-containing solution may be any one that can be dissolved in the molybdenum component-containing solution, and examples thereof include potassium molybdate, sodium molybdate, lithium molybdate, and the like. The medium contained in the molybdenum component-containing solution may be an aqueous medium such as water or brine, an organic medium such as methanol, ethanol, or ethylene glycol, or one containing an aqueous medium and an organic medium. The molybdenum component-containing solution may be a waste liquid containing molybdenum generated by washing a powder containing a molybdenum compound.

[0019] (Precipitation step) In the precipitation step in the method for recovering the molybdenum compound of the present embodiment, A x Mo y O 3y+z (1)(In formula (1), A represents an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14. 3y + z represents the number of oxygen atoms contained in the molybdate, and z represents the number of 1 / 2 of the valence of A × x.) The molybdate represented by the formula (1) is precipitated in the molybdenum component-containing solution. The molybdate represented by the formula (1) precipitated in the molybdenum component-containing solution may be only one kind or two or more kinds.

[0020] In the precipitation step, A in the molybdate represented by formula (1) to be precipitated is an element selected from the elements of Group 4, Group 8, Group 12, Group 13, and Group 14, and is an element that can react with molybdenum oxide and / or molybdic acid to form a molybdenum compound. Examples of the Group 4 element include titanium, zirconium, hafnium, etc. Examples of the Group 8 element include iron, ruthenium, etc. Examples of the Group 12 element include zinc, etc. Examples of the Group 13 element include aluminum, gallium, indium, etc. Examples of the Group 14 element include silicon, germanium, tin, etc.

[0021] Specifically, the molybdate represented by formula (1) is preferably one or more molybdates selected from Ti(MoO4)2 in which A in formula (1) is a Group 4 element, FeMoO4 and Fe2(MoO4)3 in which A in formula (1) is a Group 8 element, ZnMoO4 in which A in formula (1) is a Group 12 element, Al2(MoO4)3 in which A in formula (1) is a Group 13 element, and Si(MoO4)2 in which A in formula (1) is a Group 14 element. These molybdates can be thermally decomposed at a temperature of 1300 °C or lower. Therefore, in the firing step described later, the molybdate represented by formula (1) can be easily thermally decomposed, and vapor composed of molybdenum trioxide can be easily generated.

[0022] In the precipitation step, among the above molybdates, it is preferable to precipitate a compound in which A in the formula (1) is aluminum. In particular, it is preferable to precipitate aluminum molybdate (Al2(MoO4)3). When A in the formula (1) is aluminum, in the firing step described later, the molybdate thermally decomposes to produce aluminum oxide containing alumina (Al2O3) and a molybdenum compound containing molybdenum trioxide (MoO3), and molybdenum trioxide vaporizes. Molybdenum trioxide in the pyrolysis product containing solid aluminum oxide hardly remains in the pyrolysis product and easily becomes vapor and is separated from the pyrolysis product. Therefore, when A in the formula (1) is aluminum, it is possible to recover the powder composed of molybdenum trioxide with a high recovery rate, which is preferable.

[0023] In the molybdate represented by the formula (1), 3y + z represents the number of oxygen atoms contained in the molybdate, and z represents the number of 1 / 2 of the valence of A × x. Therefore, x in the formula (1) is determined according to the type of A in the formula (1).

[0024] The precipitation step is preferably a step of adding a precipitation accelerator to the molybdenum component-containing solution while stirring using a known method, and further stirring to precipitate the molybdate. The precipitation accelerator may be any compound that reacts with the molybdenum component contained in the molybdenum component-containing solution to produce a molybdate, and can be appropriately determined according to the type of the molybdenum component-containing solution and the type of the molybdate to be precipitated in the precipitation step.

[0025] As the precipitation accelerator, in the precipitation step, as the molybdate represented by the formula (1), in order to precipitate a molybdate in which A in the formula (1) is an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14, a precipitation accelerator containing a compound containing an element corresponding to A in the formula (1) is used. Specific examples of the compound containing an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14 elements include TiCl4, TiOSO4, Ti(C3H8)4, Zr(C4H9)4, ZrOCl2, ZrO(CH3COO)2, FeCl2, FeCl3, Zn(CH3COO)2, ZnCl2, AlCl3, Al(NO3)3, Al2(SO4)3, [Al2(OH) n Cl 6-n m , SiCl4, Si(OCH3)4, Si(OC2H5)4, and the like.

[0026] Also, for example, in the precipitation step, when precipitating a molybdate in which A in the formula (1) is aluminum as the molybdate represented by the formula (1), it is preferable to use a precipitation accelerator containing an aluminum compound. Specific examples of the precipitation accelerator containing an aluminum compound include precipitation accelerators containing compounds such as polyaluminum chloride ([Al2(OH) n Cl 6-n m ), aluminum chloride (AlCl3), aluminum nitrate (Al(NO3)3), and aluminum sulfate (Al2(SO4)3). In particular, it is preferable to use a precipitation accelerator containing polyaluminum chloride. The reason is that as the molybdate represented by the formula (1), aluminum molybdate (Al2(MoO4)3) can be efficiently precipitated, and in the firing step described later, the molybdate represented by the formula (1) thermally decomposes to easily generate high-purity vapor composed of molybdenum trioxide. In addition, polyaluminum chloride is an inexpensive one used as a coagulant for water treatment, and is preferable because it has high stability and safety and is easy to handle.

[0027] ​​When using a precipitation accelerator containing polyaluminum chloride as the precipitation accelerator, it is preferable to adjust the pH of the molybdenum component-containing solution added with the precipitation accelerator containing polyaluminum chloride to be in the range of 8 to 13. The reason is that aluminum ions supplied from polyaluminum chloride to the molybdenum component-containing solution are likely to bind to the molybdenum component contained in the molybdenum component-containing solution. As a result, the precipitation of aluminum molybdate, which is a molybdate represented by formula (1), is promoted, and the molybdenum component in the molybdenum component-containing solution can be recovered at a higher recovery rate.

[0028] As a method for adjusting the pH of the molybdenum component-containing solution added with the precipitation accelerator containing polyaluminum chloride to be in the range of 8 to 13, a method of adding a known pH adjuster to the molybdenum component-containing solution and stirring can be used. As the pH adjuster, for example, potassium hydroxide, sodium hydroxide, lithium hydroxide, aqueous ammonia, tetraethylammonium hydroxide, etc. can be used. The type and amount of the pH adjuster can be appropriately determined according to the composition and pH of the molybdenum component-containing solution.

[0029] The molybdate represented by formula (1) precipitated in the molybdenum component-containing solution in the precipitation step is preferably recovered from the molybdenum component-containing solution by a known method. As a method for recovering the molybdate represented by formula (1), for example, a method of filtering the molybdenum component-containing solution to separate it from the medium can be used. The molybdate represented by formula (1) recovered from the molybdenum component-containing solution is preferably dried by a known method to form a powder and then used in the firing step.

[0030] (Firing step) In the firing step of the method for recovering a molybdenum compound according to this embodiment, the molybdate represented by formula (1) precipitated in the precipitation step is thermally decomposed. As a heating method for thermally decomposing the molybdate represented by formula (1), a known method can be used. In this embodiment, a method is used in which the molybdate represented by the formula (1), which is recovered from a molybdenum component-containing solution and made into a powder, is placed in a heat treatment furnace, heated, and thermally decomposed.

[0031] In the firing step, by thermally decomposing the molybdate represented by the formula (1), AO z (2) (In the formula (2), A is the same as A in the formula (1). z represents the number of oxygen atoms that combine with A in the formula (2) to form an oxide.) an oxide represented by is produced, and a vapor composed of molybdenum trioxide is produced. In the oxide represented by the formula (2), z represents the number of oxygen atoms that combine with A in the formula (2) to form an oxide, and is determined according to the type of A in the formula (2) and the like.

[0032] In the firing step, the firing conditions for thermally decomposing the molybdate represented by the formula (1) may be in a temperature range that is equal to or higher than the temperature at which molybdenum trioxide can vaporize and lower than the temperature at which the oxide represented by the formula (2) melts, and can be appropriately determined according to the type (composition) and amount of the molybdate represented by the formula (1). For example, when the molybdate represented by the formula (1) is aluminum molybdate (Al2(MoO4)3), the firing conditions can be 1 hour to 48 hours at a temperature of 900°C to 1300°C under normal pressure in an air atmosphere.

[0033] In the firing step, when thermally decomposing the molybdate represented by the formula (1), it can be carried out according to an arbitrary heating profile, and can be appropriately determined according to the type (composition) and amount of the molybdate represented by the formula (1). That is, when thermally decomposing the molybdate represented by the formula (1), within a predetermined temperature range, the heating temperature can be changed by continuously or stepwise increasing or decreasing the temperature, and it may be maintained at a constant temperature within the predetermined temperature range for a certain period of time. For example, it can be heated from room temperature at a constant heating rate, maintained at a predetermined temperature for a certain period of time, and then cooled to room temperature at a constant cooling rate.

[0034] (Cooling step) The vapor composed of molybdenum trioxide generated in the firing process is cooled using a known method in the cooling process to produce a powder composed of molybdenum trioxide. In this embodiment, in the firing process, it is preferable to discharge the vapor composed of molybdenum trioxide generated in the heat treatment furnace from the heat treatment furnace by a known method, supply it to the cooling pipe, and cool it in the cooling pipe to obtain a powder.

[0035] As a method for cooling the vapor composed of molybdenum trioxide in the cooling pipe, for example, it can be cooled by a known method such as a method of blowing a cooled gas into the cooling pipe or a method of cooling the outside of the cooling pipe with a cooling device.

[0036] The cooling rate for cooling the vapor composed of molybdenum trioxide is preferably in the range of 500 °C / second to 10,000 °C / second, and more preferably in the range of 1,000 °C / second to 10,000 °C / second, in the temperature range from the maximum temperature when decomposing the molybdate represented by formula (1) to 800 °C at which molybdenum trioxide solidifies. When the cooling rate of the vapor composed of molybdenum trioxide in the temperature range from the above maximum temperature to 800 °C is 500 °C / second or more, it is easy to obtain a powder of molybdenum trioxide with a small particle size, and a powder of molybdenum trioxide with a larger specific surface area measured by the BET method can be obtained. Also, when the cooling rate of the vapor composed of molybdenum trioxide in the temperature range from the above maximum temperature to 800 °C is 1,000 °C / second or more, the cooling process can be carried out efficiently, which is more preferable.

[0037] (Recovery process) The powder composed of molybdenum trioxide generated in the cooling process is recovered in the recovery process. As a method for recovering the powder composed of molybdenum trioxide, it can be carried out using known recovery means.

[0038] According to the method for recovering the molybdenum compound of this embodiment, the powder composed of molybdenum trioxide recovered from the molybdenum component-containing solution precipitates a molybdate represented by the formula (1) in the molybdenum component-containing solution (precipitation step), and by thermally decomposing this, an oxide represented by the formula (2) is generated, and at the same time, vapor composed of molybdenum trioxide is generated (firing step), the vapor composed of molybdenum trioxide is cooled to generate a powder (cooling step), and this is recovered (recovery step). For this reason, it is a powder of molybdenum trioxide with high purity and a large specific surface area measured by the BET method.

[0039] Specifically, by using the method for recovering the molybdenum compound of this embodiment, a powder of molybdenum trioxide with a purity of 99% or more and a specific surface area of 20 m2 / g or more measured by the BET method can be recovered. Further, according to the method for recovering the molybdenum compound of this embodiment, a powder of molybdenum trioxide with an average primary particle size of 70 nm or less can be recovered.

[0040] In this specification, the average primary particle size of the powder of molybdenum oxide is a numerical value measured and calculated by the method of <1> or <2> shown below. <1> Using a scanning electron microscope (SEM) and / or a transmission electron microscope (TEM), observe the particles of the molybdenum trioxide powder at a magnification of 100,000 times. Then, for any 50 particles, measure the major axis and the minor axis, calculate the primary particle diameter which is the average value thereof, and calculate the average value thereof.

[0041] <2> Measure the specific surface area of the molybdenum oxide powder with a specific surface area measuring device using a gas adsorption method such as the BET method. Also, measure the density of the molybdenum oxide powder with a true density measuring device using the gas replacement method. Then, use the following (Equation 1) to calculate the primary particle diameter of the molybdenum oxide powder. Specific surface area (m 2 / g) = 6000 / ρd (Equation 1) (In (Equation 1), ρ represents density (g / cm 3 ). d represents the primary particle diameter (nm).)

[0042] The molybdenum trioxide powder obtained by the method for recovering a molybdenum compound according to this embodiment has high purity and a large specific surface area measured by the BET method, so it can be reused for various applications. For example, when producing inorganic oxides such as alumina, zirconia, titania, and silica using the flux method, it can be suitably used as a flux. Further, since the molybdenum trioxide powder has a large specific surface area, it can also be suitably used for applications such as antibacterial agents and antiviral agents. Furthermore, it can also be used as a raw material for a molybdenum compound having high purity and a large specific surface area measured by the BET method. Therefore, the method for recovering a molybdenum compound according to this embodiment can contribute to the reuse of molybdenum compounds and reduce the environmental load.

Examples

[0043] Hereinafter, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to only the following examples.

[0044] [Example 1] As a molybdenum component-containing solution, a waste liquid generated by washing fired alumina with water and containing potassium molybdate used as a flux during the firing of alumina was prepared. Therefore, the molybdenum component-containing solution used in Example 1 is one in which potassium molybdate is dissolved in an aqueous medium containing water.

[0045] The residue obtained by drying the molybdenum component-containing solution was analyzed using a fluorescent X-ray analysis (XRF) apparatus (trade name; PrimusIV; manufactured by Rigaku Corporation). Using the results, the molybdenum content (in terms of molybdenum trioxide) contained in the molybdenum component-containing solution was calculated. As a result, the molybdenum content (in terms of molybdenum trioxide) in the molybdenum component-containing solution used in Example 1 was 6.85% by mass.

[0046] (Precipitation step) To 5000 g of a solution containing a molybdenum component, 750 g of an aqueous solution of basic polyaluminum chloride (manufactured by Daimyo Chemical Industry Co., Ltd.; Typac) as a precipitation accelerator was added while stirring using a mechanical stirrer, and further stirred. Subsequently, potassium hydroxide as a pH adjuster was added and stirred to adjust the pH of the solution containing the molybdenum component to 9, thereby precipitating a white precipitate.

[0047] Subsequently, the solution containing the molybdenum component with the white precipitate precipitated was subjected to suction filtration while adding ion-exchanged water to wash the white precipitate and separate it from the medium, and then recovered. Thereafter, the recovered white precipitate was dried to obtain a powder.

[0048] The precipitate of Example 1, which was a white precipitate dried to a powder, was identified by the method shown below. First, the precipitate of Example 1 was subjected to elemental analysis using X-ray fluorescence analysis (XRF) (trade name; PrimusIV; manufactured by Rigaku Corporation). Also, the precipitate of Example 1 heat-treated at 600 °C for 1 hour was analyzed using X-ray diffraction analysis (XRD) (trade name; UltimaIV; manufactured by Rigaku Corporation). Then, based on the elemental ratio obtained from the results of elemental analysis by XRF and the spectral intensity obtained from the results of XRD, the components of the precipitate of Example 1 were confirmed. As a result, it was confirmed that the precipitate of Example 1 was a mixture of alumina (Al2O3) and aluminum molybdate (Al2(MoO4)3).

[0049] (Firing step) Next, the white precipitate recovered from the solution containing the molybdenum component and made into a powder was placed in a heat treatment furnace and heated under the firing conditions shown below. That is, in an air atmosphere, the temperature was raised from room temperature to 1100 °C at a heating rate of 5 °C / min, maintained at 1100 °C for 10 hours without controlling the pressure under normal pressure, and then allowed to cool and the temperature was lowered until it reached room temperature. The fired product was recovered from the heat treatment furnace after the firing step and identified by the same method as the precipitate of Example 1. As a result, it was confirmed that the fired product of Example 1 was a mixture of alumina (Al2O3) and molybdenum oxide (MoO3).

[0050] (Cooling process)(Recovery process) On the other hand, in the firing process, the steam generated in the heat treatment furnace is discharged from the heat treatment furnace and supplied to the cooling pipe, and cooled in the cooling pipe to form a powder such that the cooling rate of the steam in the temperature range of 1100°C to 800°C, which is the maximum temperature when pyrolyzing the molybdate of Example 1, is 2000°C / second, and 270 g of the powder was recovered.

[0051] The powder recovered by the recovery method of Example 1 was identified by X-ray diffraction (XRD) measurement and the purity was calculated by X-ray fluorescence analysis (XRF). As a result, it was confirmed that the powder (steam generated in the firing process) recovered by the recovery method of Example 1 was molybdenum trioxide (MoO3) and its purity was 99.7%.

[0052] Also, the recovery rate of the powder recovered by the recovery method of Example 1 was calculated by the following (Equation 2). As a result, the recovery rate was 78.8%. Recovery rate (%) = {(Mo content II / Mo content I) × 100} (Equation 2) (In (Equation 2), Mo content I is the molybdenum content (in terms of molybdenum trioxide) (g) contained in the molybdenum component-containing solution. Mo content II is the molybdenum content (in terms of molybdenum trioxide) (g) in the recovered powder.)

[0053] Also, for the powder recovered by the recovery method of Example 1, the specific surface area measured by the BET method and the average particle size of the primary particles were measured by the methods shown below. As a result, the specific surface area measured by the BET method was 50 m 2 / g, and the average particle size of the primary particles was 30 nm.

[0054] [Method for measuring specific surface area: BET method] Using a specific surface area analyzer (MicrotracBEL, BELSORP-mini), the nitrogen gas adsorption amount of the powder recovered by the recovery method of Example 1 was measured by the BET method. From the results, the surface area per 1 g of the sample was calculated, and the specific surface area (m 2 / g) of the powder recovered by the recovery method of Example 1 was obtained.

[0055] [Measurement method of average primary particle size] The powder recovered by the recovery method of Example 1 was photographed with a transmission electron microscope (TEM; manufactured by JEOL Ltd.; JEM1400). For the particles that are the smallest units constituting the aggregates on the obtained two-dimensional image (i.e., primary particles), their major axis (Feret diameter of the longest observed part) and minor axis (short Feret diameter in a direction perpendicular to the Feret diameter of the longest part) were measured, and the average value was taken as the primary particle size. The same operation was performed on 50 randomly selected primary particles, and the average value of the primary particle sizes of the 50 primary particles was calculated, which was taken as the average primary particle size of the powder recovered by the recovery method of Example 1.

[0056] [Example 2] As the molybdenum component-containing solution, a 10 wt% aqueous sodium molybdate solution (molybdenum content (in terms of molybdenum trioxide) is 7 wt%) prepared by adding 4412.5 g of ion-exchanged water to 587.5 g of sodium molybdate dihydrate (reagent manufactured by Kanto Chemical Co., Inc.) was used. The precipitation step, firing step, cooling step, and recovery step were carried out in the same manner as in Example 1. Also, in the same way as in Example 1, the precipitate and the fired product generated in the precipitation step were identified.

[0057] As a result, the precipitate of Example 2 was a mixture of alumina (Al2O3) and aluminum molybdate (Al2(MoO4)3). Also, the fired product obtained in Example 2 was a mixture of alumina (Al2O3) and molybdenum trioxide (MoO3). Also, in Example 2, the mass of MoO3 cooled and recovered in the cooling pipe was 260 g, and the recovery rate was 74.3%.

[0058] [Example 3] A precipitation step, a firing step, a cooling step, and a recovery step were performed in the same manner as in Example 1, except that 940 g of an aqueous aluminum sulfate solution (manufactured by Daimyo Chemical Industry Co., Ltd.) was used instead of the aqueous basic polyaluminum chloride solution as the precipitation accelerator. Also, in the same manner as in Example 1, the precipitate and the fired product produced in the precipitation step were identified.

[0059] As a result, the precipitate produced in the precipitation step of Example 3 was a mixture of alumina (Al2O3) and aluminum molybdate (Al2(MoO4)3). Also, the fired product obtained in Example 3 was a mixture of alumina (Al2O3) and molybdenum oxide (MoO3). Also, in Example 3, the mass of MoO3 cooled and recovered in the cooling pipe was 210 g, and the recovery rate was 61.3%.

[0060] [Comparative Example 1] The same molybdenum component-containing solution as that used in the recovery method of Example 1 was prepared. (Precipitation step) Potassium hydroxide as a pH adjuster was added to 1000 g of the molybdenum component-containing solution and stirred to adjust the pH of the molybdenum component-containing solution to 9. To the molybdenum component-containing solution after adjusting the pH, 300 g of an aqueous solution prepared to 10% by mass with calcium chloride (reagent manufactured by Kanto Chemical Co., Inc.) as a precipitation accelerator was added while stirring using a mechanical stirrer, and further stirred to precipitate a white precipitate.

[0061] Subsequently, the molybdenum component-containing solution in which the white precipitate was precipitated was recovered by suction filtration in the same manner as in the recovery method of Example 1 and dried to obtain a powder. The precipitate of Comparative Example 1, which was a white precipitate dried to a powder, was identified in the same manner as the precipitate of Example 1. As a result, it was confirmed that the precipitate of Comparative Example 1 was a mixture of calcia (CaO) and calcium molybdate (CaMoO4).

[0062] (Firing process) (Cooling process) (Recovery process) Thereafter, except that the white precipitate obtained by drying and pulverizing in the precipitation step of Comparative Example 1 was used instead of the white precipitate obtained by drying and pulverizing in the precipitation step of Example 1, the firing step, the cooling step, and the recovery step were carried out in the same manner as the recovery method of Example 1.

[0063] The fired product was recovered from the heat treatment furnace after the firing step and identified in the same manner as the precipitate of Example 1. As a result, it was confirmed that the fired product of Comparative Example 1 was a mixture of calcia (CaO) and calcium molybdate (CaMoO4). In addition, in Comparative Example 1, no steam was generated in the heat treatment furnace during the firing step, and the formation of powder in the cooling pipe could not be confirmed during the cooling step.

[0064] For the precipitate in the precipitation step of the recovery methods of Examples 1 to 3 and Comparative Example 1 and the fired product recovered from the heat treatment furnace after the firing step, the molybdenum content (in terms of molybdenum trioxide) was measured based on the elemental analysis results by fluorescence X-ray analysis (XRF). The results are shown in Tables 1 and 2.

[0065] In addition, Table 1 shows the "precipitation accelerator", "pH of the molybdenum component-containing solution", "A in the molybdate represented by formula (1)", "components of the precipitate precipitated in the precipitation step", and "molybdenum content (in terms of MoO3) in the precipitate" used in the recovery methods of Examples 1 to 3 and Comparative Example 1 described above.

[0066] [Table 1]

[0067] Table 2 shows the "components of the fired product", "molybdenum content (in terms of MoO3) in the fired product", "purity", "specific surface area", "average particle size of primary particles", and "recovery rate" of MoO3 recovered by cooling in the cooling pipe in the firing step of the recovery method of Example 1.

[0068]

Table 2

[0069] As shown in Table 2, in the recovery methods of Examples 1 to 3, molybdenum oxide powder with high purity, large specific surface area, and small average particle size of primary particles could be recovered from the molybdenum component-containing solution. Also, the recovery rates in the recovery methods of Examples 1 to 3 were 60% or more, and it was confirmed that molybdenum trioxide could be recovered from the molybdenum component-containing solution at a high recovery rate. This is because in Examples 1 to 3, Al2(MoO4)3 precipitated in the precipitation step was thermally decomposed in the firing step, generating vapor composed of molybdenum trioxide.

[0070] On the other hand, in the recovery method of Comparative Example 1, since CaMoO4 precipitated in the precipitation step was not thermally decomposed in the firing step, vapor composed of molybdenum trioxide was not generated, and molybdenum trioxide could not be recovered.

Claims

1. In a solution containing a molybdenum component, A ｘ Mo ｙ O ３ｙ＋ｚ (1) (In formula (1), A represents an element selected from Group 4, Group 8, Group 12, Group 13, and Group 14. 3y + z represents the number of oxygen atoms contained in the molybdate, and z represents the number of 1 / 2 of the valence of A × x.) A precipitation step of precipitating a molybdate represented by the formula is carried out, By thermally decomposing the molybdate, AO ｚ (2) (In formula (2), A is the same as A in formula (1). z represents the number of oxygen atoms that combine with A in formula (2) to form an oxide.) A firing step of generating an oxide represented by the formula and generating a vapor composed of molybdenum trioxide, A cooling step of cooling vapor composed of molybdenum trioxide to produce powder composed of molybdenum trioxide, and A recovery step of recovering the powder composed of molybdenum trioxide, a method for recovering a molybdenum compound.

2. In the precipitation step, by adding a precipitation accelerator containing a compound containing one or more elements selected from elements of Group 4, Group 8, Group 12, Group 13, and Group 14 to the molybdenum component-containing solution and stirring, the molybdate is precipitated. The method for recovering a molybdenum compound according to Claim 1.

3. In the precipitation step, by adding a precipitation accelerator containing an aluminum compound to the molybdenum component-containing solution and stirring, the molybdate is precipitated. The method for recovering a molybdenum compound according to Claim 1.

4. In the precipitation step, by adding a precipitation accelerator containing polyaluminum chloride to the molybdenum component-containing solution and stirring, the molybdate is precipitated. The method for recovering a molybdenum compound according to Claim 1.

5. The method for recovering a molybdenum compound according to Claim 4, wherein the pH of the molybdenum component-containing solution to which the precipitation accelerator containing polyaluminum chloride is added is adjusted to be in the range of 8 to 13.

6. In the recovery process, a powder of molybdenum trioxide having a purity of 99% or more and a specific surface area measured by the BET method of 20 m ２ / g or more is recovered, and the method for recovering a molybdenum compound according to claim 1.

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