Method for producing alkali metal salts of tungstic acid and method for producing tungsten

Abstract

A method for producing an alkali metal salt of tungstic acid according to the present invention comprises a process wherein a molten carbonate, which contains metal ions that serve as an oxidant with respect to an alkali metal carbonate and tungsten, and a tungsten-containing material are brought into contact with each other. The metal ions are supplied, for example, from at least one substance that is selected from the group consisting of metal oxides and metal carbonates. The metal ions may include at least one kind of ions that are selected from the group consisting of Cu ions, Fe ions, Ni ions, Sn ions, Mn ions, V ions, Pb ions, Sb ions and Co ions.

Description

Technical Field

[0001] The present invention relates to a method for producing an alkali metal salt of tungstic acid, a method for producing tungsten, and a composition containing an alkali metal salt of tungstic acid.

Background Art

[0002] Tungsten is a metal having characteristics such as high hardness, high heat resistance, high wear resistance, and high melting point, and is used in a wide range of industrial fields. Cemented carbide tools, which account for 80% of the domestic demand for tungsten, are made of a composite material in which 90 wt% of tungsten carbide (WC) particles are bonded with 8 wt% of metallic cobalt as a typical composition. The remaining 2 wt% is an additive such as tantalum. There are two types of scraps of cemented carbide tools: large hard scraps that maintain the shape of the cemented carbide tools and powdery soft scraps.

[0003] As one of the conventional techniques for recycling tungsten carbide, the molten nitrate method is known. In the molten nitrate method, scraps of cemented carbide tools are oxidatively dissolved by the oxidizing power of nitrates to obtain Na2WO4. Na2WO4 is further processed to obtain metallic tungsten (Patent Document 1). According to the molten nitrate method, since the oxide dissolves into the molten salt, the growth of the oxide on the WC surface does not stop, and the treatment can proceed continuously.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] The molten nitrate process has the advantage of being able to process hard scrap because the oxidation and dissolution reaction proceeds rapidly. On the other hand, because it is a highly exothermic reaction with the potential for explosion, it is difficult to process powdered soft scrap with a large surface area using the molten nitrate process. In addition, corrosion of the reaction vessel is severe, so it is necessary to use expensive, corrosion-resistant materials for the reaction vessel. Furthermore, the molten nitrate process produces toxic nitrogen oxides (NOx). x There is also the problem that it is emitted as exhaust gas.

[0007] Therefore, a method using molten carbonate instead of molten nitrate has been proposed (Non-Patent Literature 1). The molten carbonate method can process both hard scrap and soft scrap, NO x This method has advantages such as not generating fumes and having no possibility of explosion. Furthermore, in the dissolution treatment of the product in water, the resulting aqueous solution becomes weakly alkaline, which is advantageous because it allows for good separation of tungsten from other components. On the other hand, the conventional molten carbonate method has the problem of insufficient reaction rate in the oxidative dissolution reaction, resulting in poor efficiency. Possible causes include insufficient oxidizing power of the molten carbonate and low solubility of oxygen ion species (peroxide ions and superoxide ions) in the molten carbonate.

[0008] The objective of this invention is to provide a technology for safely and efficiently recovering tungsten. [Means for solving the problem]

[0009] The present invention This method involves contacting a molten carbonate containing metal ions that act as oxidizing agents for alkali metal carbonates and tungsten with a tungsten-containing material. This invention provides a method for producing alkali metal salts of tungstic acid.

[0010] In another aspect, the present invention is The above invention includes a method for producing alkali metal salts of tungstic acid, This invention provides a method for manufacturing tungsten.

[0011] In yet another aspect, the present invention is The above invention includes a method for producing alkali metal salts of tungstic acid, This invention provides a method for producing ammonium paratungstate.

[0012] In yet another aspect, the present invention is Alkali metal carbonates and Alkali metal salts of tungstic acid, The reduction products of metal ions that act as oxidizing agents for tungsten, The present invention provides a composition containing an alkali metal salt of tungstic acid.

[0013] In yet another aspect, the present invention is Containing tungsten and cobalt, The ratio of cobalt concentration to tungsten concentration is 0.5% or less. We provide alkali metal salts of tungstic acid.

[0014] In yet another aspect, the present invention is Containing tungsten and cobalt, The ratio of cobalt concentration to tungsten concentration is 0.5% or less. Ammonium paratungstate is provided. [Effects of the Invention]

[0015] According to the present invention, tungsten can be recovered safely and efficiently. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a process diagram of a tungsten recovery method according to one embodiment of the present invention. [Figure 2A] Figure 2A is a schematic diagram of the process in step S1 of Figure 1. [Figure 2B] Figure 2B shows the reaction in which oxygen ion species oxidize tungsten. [Figure 2C] Figure 2C shows the reaction in which carbonate ions oxidize tungsten. [Figure 3] Figure 3 is a schematic cross-sectional view of the reaction apparatus used in the example. [Figure 4] Figure 4 is an optical photograph of the carbide tip of Example 1 after the reaction. [Figure 5] Figure 5 shows the XRD pattern of the carbide tip from Example 1 after the reaction. [Figure 6A] Figure 6A is an optical photograph of the carbide tip of Example 3 after the reaction. [Figure 6B] Figure 6B is an optical photograph of the carbide tip of Example 4 after the reaction. [Figure 7A] Figure 7A shows the XRD pattern of the carbide tip from Example 3 after the reaction. [Figure 7B] Figure 7B shows the XRD pattern of the carbide tip from Example 4 after the reaction. [Figure 8] Figure 8 shows optical photographs of the crucibles in Examples 9, 10, 11, and 12 after the reaction. [Modes for carrying out the invention]

[0017] Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

[0018] Figure 1 is a process diagram of a tungsten recovery method according to one embodiment of the present invention. Step S1 is a process of oxidizing and dissolving a tungsten-containing material in molten carbonate. In other words, step S1 is a process of contacting the molten carbonate with the tungsten-containing material. The carbonate is an alkali metal carbonate. Through this process, the tungsten is oxidized to a hexavalent state, and an alkali metal salt of tungstic acid is obtained.

[0019] Figure 2A is a schematic diagram of step S1 of Figure 1. In step S1, first, the necessary materials are placed in container 28. The necessary materials are alkali metal carbonate, a metal ion source, and tungsten-containing material 24. After these materials are placed in container 28, the container 28 is heated with heater 18 to produce molten carbonate 22. The molten carbonate 22 contains metal ions derived from the metal ion source and alkali metal carbonate. The tungsten-containing material 24 is placed in container 28 so that it is in contact with the molten carbonate 22. The metal ion source may be added to container 28 after the alkali metal carbonate has been melted. The tungsten-containing material 24 may be added to container 28 after the alkali metal carbonate has been melted.

[0020] According to this embodiment, the oxidizing power derived from the alkali metal carbonate and the oxidizing power derived from the metal ion source act in a superposition manner, so that the tungsten contained in the tungsten-containing material 24 can be efficiently oxidized. The oxidized tungsten dissolves in the molten carbonate 22 in the form of tungstate ions. The oxidation-dissolution reaction proceeds rapidly but is not explosive. Therefore, powdered tungsten-containing materials can also be processed. Since no toxic exhaust gases are produced, the equipment cost is low and there is no pollution of the environment. High corrosion resistance is not required for the container 28, and various materials can be used as the material for the container 28.

[0021] The alkali metal carbonate includes at least one selected from the group consisting of Na2CO3, Li2CO3, and K2CO3. Na2CO3 and K2CO3 are recommended because they are inexpensive. The melting point of Na2CO3 is 851°C. The eutectic point of the Na2CO3-Li2CO3 system is 497°C. The eutectic point of the Na2CO3-K2CO3 system is 702°C. The eutectic point of the K2CO3-Li2CO3 system is 488°C. The eutectic point of the Na2CO3-Li2CO3-K2CO3 system is 390°C. Therefore, using two or three types selected from the group consisting of Na2CO3, Li2CO3, and K2CO3, such as using Li2CO3 and / or K2CO3 in addition to Na2CO3, lowers the melting point of the alkali metal carbonate, enabling tungsten recovery at lower temperatures, which is advantageous in terms of energy consumption. The alkali metal carbonate may be selected depending on the type of metal ion source.

[0022] The metal ion source supplies metal ions that act as an oxidizing agent for tungsten by dissolving in the alkali metal carbonate melt. More specifically, the metal ion source acts as an oxidizing agent for the tungsten component contained in the tungsten-containing material 24. The metal ions derived from the metal ion source include M n+ In addition to metal ions (cations) represented by MO, a b- This also includes metal oxoanions represented by (a, b, and n are positive integers). The metals included in the metal ion source are metals other than alkali metals, alkaline earth metals, lanthanides, and actinides. In this specification, metalloids such as Sb are also included in "metals."

[0023] The metal ion source is NO x The metal compound may be capable of supplying metal ions that act as an oxidizing agent for tungsten without generating any oxidizing agents. Examples of such metal compounds include metal oxides, metal carbonates, and metal sulfates. Preferably, the metal compound comprises at least one selected from the group consisting of metal oxides and metal carbonates.

[0024] For example, the metal oxide dissolves in the melt of the alkali metal carbonate according to the acidic dissolution of the following formula (1a) or the basic dissolution of (1b). The metal ions derived from the metal oxide oxidize the tungsten contained in the tungsten-containing material 24 according to the following formula (2a) or (2b). The metal ions are reduced and changed into a reduction product 26 such as elemental metal. The metal oxide dissolves in the melt of the alkali metal carbonate to generate metal ions and oxide ions. Both the metal ions and the oxide ions act as oxidants, and no unnecessary ions are generated in the molten carbonate. Unnecessary ions may reduce the solubility of the metal salts of oxides and tungstic acid in the molten carbonate 22. Further, the metal oxide may be generated by oxidizing the reduction product 26 (step S8 described later). The obtained metal oxide can be reused as an oxidant. The metal oxide may be a composite oxide. In the following formulas, a, b, p, q, r, and x each represent a positive integer.

[0025] MO x →M n+ +xO 2- ···(1a) MO x +pO 2- →MO a b- ···(1b) W+(6 / n)M n+ +4O 2- →WO4 2- +(6 / n)M ···(2a) qW+rMO a b- →qWO4 2- +rM+(ar-4q)O 2- ···(2b)

[0026] Metal carbonates such as CuCO3 and FeCO3 exist as compounds at normal temperature. However, when dissolved in the melt of the high-temperature alkali metal carbonate, they thermally decompose according to, for example, the following formulas (3a) and (3b). The metal oxide dissolves in the melt of the alkali metal carbonate according to the above formula (1a). CO2 diffuses into the surrounding atmosphere as a gas. That is, when using a metal carbonate, the same result as when using a metal oxide is obtained.

[0027] CuCO3 → CuO + CO2···(3a) FeCO3 → FeO + CO2 ... (3b)

[0028] Metal ions M n+ It is not essential that the metal ion M is completely reduced to a 0 charge. n+ M has a smaller valency. m+ The material may be reduced to (n>m). In this case, the metal ions derived from the metal oxide oxidize the tungsten contained in the tungsten-containing material 24 according to the following formula (2c) or (2d). In the following formula, a, b, c, d, p, q, m, and n each represent a positive integer.

[0029] W+(6 / (nm))M n+ +4O 2- →WO4 2- +(6 / (nm))M m+ (2c) pW+qMO a b- →pWO4 2- +qMO c d- +(aq-cq-4p)O 2- (2d)

[0030] Figure 2A shows the oxidation and dissolution reaction of tungsten. When tungsten compounds such as tungsten carbide are used, the tungsten is oxidized and dissolved in the molten carbonate 22 by a reaction similar to the above formulas (2a) to (2d).

[0031] The metal ions to be supplied from the metal ion source may include at least one selected from the group consisting of Cu ions, Fe ions, Ni ions, Sn ions, Mn ions, V ions, Pb ions, Sb ions, and Co ions. These metal ions can oxidize tungsten.

[0032] The metal ions to be supplied from the metal ion source may include at least one selected from the group consisting of Cu(+1), Cu(+2), Fe(+2), Fe(+3), Ni(+2), Sn(+2), Sn(+4), Mn(+2), Mn(+4), V(+2), V(+3), V(+4), V(+5), Pb(+2), Pb(+4), Sb(+3), Sb(+4), Sb(+5), Co(+2), and Co(+3). These metal ions can oxidize tungsten. In detail, under the molten carbonate, M n+ / M or M n+ / M m+ If the redox potential of (n>m) is nobler than the elution potential of W, then that metal ion can be used in this embodiment. According to this embodiment, the redox potential of the molten carbonate 22 can be controlled by the type of metal ion, so the processing of powdered tungsten-containing materials having a large surface area is also easy.

[0033] In the conventional molten nitrate method, the redox potential of the molten nitrate is the NO produced in the reaction. x Because it is determined by [the formula], it is virtually impossible to control the redox potential of molten nitrate.

[0034] The metal oxides that can supply the above-mentioned metal ions are CuO, Cu2O, FeO, Fe2O3, NiO, SnO, SnO2, MnO, MnO2, VO, V2O3, VO2, V2O5, PbO, PbO2, Sb2O3, SbO2, Sb2O5, CoO, and Co2O3.

[0035] The metal oxide may contain at least one selected from the group consisting of CuO, Cu2O, VO, V2O3, VO2, and V2O5. Copper oxide has high solubility in molten carbonate 22. Therefore, using copper oxide as the metal oxide ensures the reliable generation of copper ions and oxide ions. Furthermore, if the metal contained in the metal oxide does not form an alloy with the metal contained in the tungsten-containing material 24, the separation of each metal is easy in downstream processes. For example, cemented carbide scrap contains a large amount of Co. Since Cu and Co do not form an alloy, Cu and Co can be separated by known methods such as magnetic separation. Therefore, when processing cemented carbide scrap using the method of this embodiment, it is recommended to use CuO and / or Cu2O as the metal oxide. Vanadium oxide is also recommended because it has a strong ability to oxidize tungsten.

[0036] The amount of alkali metal carbonate used to prepare molten carbonate 22 is, for example, between 0.3 mol and 20 mol per 1 mol of tungsten contained in the tungsten-containing material to be treated. This allows for sufficient oxidation and dissolution of the tungsten. For example, up to 3.3 mol of Na2WO4 dissolves in 1 mol of Na2CO3. From this perspective, the lower limit of the amount of alkali metal carbonate is determined. The upper limit of the amount of alkali metal carbonate is determined from an economic standpoint.

[0037] The amount of metal ion source added to the molten carbonate 22 is not particularly limited. When the amount of alkali metal carbonate used is taken as a baseline (100 mol%), the amount of metal ion source added is, for example, 0.5 mol% to 50 mol%.

[0038] Furthermore, the oxidizing power derived from alkali metal carbonates is due to peroxide ions (O2 2- ), superoxide ions (O2 - ) and carbonate ions (CO3 2- ) is exerted by.

[0039] Figure 2B shows the oxygen ion species (O2 2- ,O2 -This figure shows the reaction in which carbonate ions (CO3) oxidize tungsten. Figure 2C shows the reaction in which carbonate ions (CO3) oxidize tungsten. 2- This figure shows the reaction in which ) oxidizes tungsten. As shown in Figure 2B, in the oxidation reaction by oxygen ion species, O2 in the atmosphere becomes O2 2- Ions or O2 - The ions chemically dissolve in the molten carbonate, diffuse through the molten carbonate, and then oxidize the tungsten. As shown in Figure 2C, in the oxidation reaction by carbonate ions, CO3 present in the molten carbonate... 2- This directly oxidizes tungsten. However, as will become clear from the examples described later, since both the oxidizing power and the solubility of the metal ion source are high, the oxidation-dissolution reaction by the metal ion source proceeds more dominantly than the oxidation-dissolution reaction by these reaction mechanisms.

[0040] The target temperature of the molten carbonate 22 is determined according to the melting point of the alkali metal carbonate. For example, the target temperature of the molten carbonate 22 is between 500°C and 1000°C. The target temperature may also be between 700°C and 950°C. When the target temperature of the molten carbonate 22 is within this range, the oxidation and dissolution reaction of tungsten can proceed sufficiently. Below 1000°C, corrosion of the container 28 is less likely to occur, and the range of materials that can be selected for the container 28 is also broadened. The target temperature of the molten carbonate 22 may also be set considering the solubility of the metal ion source in the molten carbonate 22. This is because if the metal ion source is sufficiently dissolved in the molten carbonate 22, a sufficient supply of metal ions that act as an oxidizing agent is supplied from the metal ion source.

[0041] The predetermined time for maintaining the molten carbonate 22 at the target temperature is not particularly limited, and is, for example, 0 hours or more and 50 hours or less, preferably 25 hours or less, more preferably 5 hours or less, and even more preferably 2.5 hours or less. According to this embodiment, the reaction can proceed sufficiently in a short time. "0 hours" means that after the temperature of the molten carbonate 22 is raised at a predetermined rate and the molten carbonate 22 reaches the target temperature, the cooling process begins immediately. As will be clear from the examples described later, the reaction can proceed even in this case. After maintaining the molten carbonate 22 at the target temperature for a predetermined time, the temperature of the molten carbonate 22 may be lowered to room temperature at a predetermined rate.

[0042] As explained earlier, the tungsten-containing material 24 can be scrap of cemented carbide tools containing tungsten carbide as the main component. The scrap of cemented carbide tools may be large hard scrap that retains the shape of the cemented carbide tool, or it may be powdery soft scrap, or it may contain both. According to the method of this embodiment, both hard scrap and soft scrap can be processed safely. "Main component" means the component that is present in the largest amount by mass.

[0043] The material of the container 28 is not particularly limited; for example, it may be a ceramic such as alumina, or a metallic material such as iron or nickel. The molten nitrate method described in Patent Document 1 requires an expensive container with corrosion resistance. However, according to this embodiment, there are no such restrictions, and various materials can be used as the material for the container 28.

[0044] The ambient atmosphere in which the container 28 is placed is not particularly limited. The ambient atmosphere may be an inert atmosphere or an oxidizing atmosphere. An inert atmosphere can be created using an inert gas such as a noble gas or N2 gas. An oxidizing atmosphere may include an atmosphere containing an oxidizing gas such as O2 gas. A mixed gas of an inert gas and an oxidizing gas may be used as the ambient gas. The partial pressure of each component in the mixed gas is appropriately adjusted. The pressure of the ambient atmosphere is not particularly limited and may be approximately equal to atmospheric pressure.

[0045] The atmospheric gas in contact with the molten carbonate 22 may contain CO2 gas. Typically, a mixture of a noble gas and CO2 gas can be used as the atmospheric gas. The partial pressure of each gas is not particularly limited. The partial pressure of CO2 gas is, for example, 1 × 10⁻⁶ -7 The pressure is between atm and 1 atm, preferably 1 × 10⁻⁶. -4 The partial pressure is between 0.8 atm and 0.8 atm. The lower limit of the partial pressure of CO2 gas is determined based on the value expected when the atmosphere is diluted with another gas. The lower limit of the partial pressure of CO2 gas is determined based on the value expected when other gases such as O2 gas are added to pure CO2 gas. By adjusting the partial pressure of CO2 gas, it is possible to control the basicity of the molten carbonate 22. This allows for control of the reaction rate of the oxidation dissolution reaction. By adjusting the partial pressure of CO2 gas, it is also possible to adjust the solubility of the metal ion source in the molten carbonate 22, and the solubility of the alkali metal salt of tungstic acid in the molten carbonate 22. The partial pressure of CO2 gas may be adjusted depending on the type of metal ion.

[0046] In the conventional molten nitrate method, the basicity of the molten nitrate is determined by the NO produced in the reaction. x Because it is defined by [a specific factor], it is virtually impossible to control the basicity of molten nitrate.

[0047] In step S1, the molten carbonate 22 may be stirred. Metal deposits originating from the metal ion source will accumulate on the surface of the carbide tool tip. Stirring can remove the accumulated metal from the tip surface. This allows the oxidative dissolution reaction of tungsten to proceed more smoothly.

[0048] In step S1, O2 gas may be bubbled into the molten carbonate 22. This will introduce oxygen ion species (O2) into the molten carbonate 22. 2- ,O2 -Since it can supply ), the reaction described with reference to Figure 2B can be accelerated. In addition, it may be possible to regenerate metal ions as an oxidizing agent by having the O2 gas re-oxidize the metal after the tungsten has been oxidized.

[0049] When the temperature of the molten carbonate 22 is lowered to room temperature and the contents of the container 28 solidify, a composition containing an alkali metal salt of tungstic acid is obtained. The composition comprises an alkali metal salt of tungstic acid, unreacted alkali metal carbonate, and reduction products 26 of metal ions derived from a metal ion source. The reduction products 26 typically contain elemental metals, may contain salts such as NaVO2, or may contain both. The composition may further contain unreacted tungsten-containing material 24 and by-products. By-products include metal residues, alkali metal oxides, etc. The metal residues include other metals contained in the tungsten-containing material. When the tungsten-containing material 24 is scrap from cemented carbide tools, other metals include Co and Ta.

[0050] Compositions containing alkali metal salts of tungstic acid are, for example, in powder form. Powder X-ray diffraction measurements of the composition can confirm the presence of alkali metal carbonates and alkali metal salts of tungstic acid. Inductively coupled plasma emission spectroscopy can confirm the presence of elemental metals originating from a metal ion source. As described below, an aqueous solution of alkali metal salts of tungstic acid can be easily obtained by simply adding water to the composition containing alkali metal salts of tungstic acid. Furthermore, compositions containing alkali metal salts of tungstic acid have excellent storability and transportability. Therefore, the composition may be transported to another location for downstream processes.

[0051] Next, as shown in step S2 of Figure 1, water is added to container 28 to dissolve the composition containing the alkali metal salt of tungstic acid in the water. This yields an aqueous solution containing the alkali metal salt of tungstic acid. Substances that do not dissolve in water precipitate as solids. The pH of the aqueous solution may also be adjusted as appropriate. The alkali metal salt of tungstic acid is readily soluble in neutral or alkaline water.

[0052] In the conventional molten nitrate method, the aqueous solution containing the alkali metal salt of tungstic acid is weakly acidic. In contrast, the molten carbonate method of this embodiment yields a weakly alkaline aqueous solution. Therefore, the solubility of components other than tungsten is low, and a tungsten aqueous solution with a lower impurity concentration can be obtained.

[0053] In other words, in the alkali metal salt of tungstic acid obtained by the method of this embodiment, the ratio of cobalt concentration M2 (unit: mass ppm) to tungsten concentration M1 (unit: mass ppm) (M2 / M1) is preferably 0.5% or less, and more preferably 0.25% or less, expressed as a percentage. The lower limit of the ratio (M2 / M1) is not particularly limited, and for example, it may be 0.0001%, which may be below the detection limit.

[0054] Next, as shown in step S3 of Figure 1, solid-liquid separation is performed on the aqueous solution containing the alkali metal salt of tungstic acid. This step allows for the separation of water-insoluble precipitates (e.g., Cu, Co, Ta, etc.) from the aqueous solution. The method of solid-liquid separation is not particularly limited, and known methods such as filtration, centrifugation, and precipitation may be employed.

[0055] In step S8, the metal used in step S1 is recovered from the precipitate recovered in step S3. The recovered metal is oxidized to obtain a metal oxide. The obtained metal oxide can be reused in the process of step S1, making it economical.

[0056] Next, as shown in step S4 of Figure 1, the aqueous solution containing the alkali metal salt of tungstic acid is treated by ion exchange using an ion exchange resin. In this step, the alkali metal ions are replaced by ammonium ions, and an aqueous solution of ammonium tungstate ((NH4)2WO4) is obtained.

[0057] Next, as shown in step S5 of Figure 1, the aqueous solution of ammonium tungstate is concentrated to crystallize ammonium paratungstate (APT). In ammonium paratungstate, the ratio of cobalt concentration m2 (unit: mass ppm) to tungsten concentration m1 (unit: mass ppm) (m2 / m1) is preferably 0.5% or less, and more preferably 0.25% or less, expressed as a percentage. The lower limit of the ratio (m2 / m1) is not particularly limited and may be, for example, 0.0001%, which may be below the detection limit.

[0058] Next, as shown in step S6 of Figure 1, the ammonium paratungstate is dried and roasted. This yields tungsten oxide (WO3).

[0059] Finally, as shown in step S7 of Figure 1, the tungsten oxide is reduced. This yields metallic tungsten (W). The reduction of tungsten oxide is carried out by known methods such as hydrogen reduction. [Examples]

[0060] In the process of recovering tungsten from cemented carbide tips as an alkali metal salt of tungstic acid using the molten carbonate method, the following experiment was conducted to determine whether metal oxides function as oxidizing agents.

[0061] (Preliminary experiment) Ar-O2(0.2atm)-CO2(6.0×10 -4 Under an atmosphere of 1 atm, the immersion potential was measured in a molten Na2CO3 bath at 1173K using a W wire, Fe wire, Cu wire, or Co wire as the working electrode and an Au wire as the reference electrode. The total atmospheric pressure was 1 atm. The immersion potential was measured under the gas partial pressure conditions of the atmosphere: O2 / O 2-Calibration was performed using equilibrium potential. The immersion potential is expected to represent the redox potential of the reactions shown in Table 1. The redox potentials of Cu(I) / Cu, Fe(II) / Fe, and Co(II) / Co are nobler than the redox potential of W(VI) / W, which is -0.94V. Therefore, it was expected that adding Cu(I), Fe(II), or Co(II) to molten carbonate would cause the following reaction, allowing for the oxidation and dissolution of tungsten components from tungsten carbide contained in cemented carbide scrap.

[0062] 6Cu(I) + W → W(VI) + 6Cu 3Fe(II) + W → W(VI) + 3Fe 3Co(II) + W → W(VI) + 3Co

[0063] [Table 1]

[0064] (Configuration of the reaction apparatus) Figure 3 is a schematic cross-sectional view of the reaction apparatus used in the embodiment. The reaction apparatus 10 comprises an alumina reaction tube 11, a stainless steel lid 12, and an electric furnace 17. The reaction tube 11 is closed by the stainless steel lid 12. The reaction tube 11 is placed in the electric furnace 17. The stainless steel lid 12 is provided with an inlet port 13 and an outlet port 14. A supply pipe 15 is attached to the inlet port 13. An exhaust pipe 16 is attached to the outlet port 14. The atmosphere inside the reaction tube 11 can be adjusted through the supply pipe 15 and the exhaust pipe 16. A crucible 20 is placed inside the reaction tube 11. Molten carbonate 22 and tungsten-containing material 24 are placed inside the crucible 20. By heating the reaction tube 11, molten carbonate 22 is produced from the raw materials, and the reaction proceeds.

[0065] (Example 1) As raw materials for molten carbonate, Na2CO3 powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), crushed using a mortar and pestle, and a metal oxide to act as an oxidizing agent were packed into an alumina crucible (manufactured by Nikkatoh, SSA-S, outer diameter 37 mm x height 25 mm). The amount of Na2CO3 was 3.1 g, adjusted so that the depth of the molten salt upon dissolution was 6 mm. Cu2O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the metal oxide. The amount of Cu2O added was 6.4 mol%, based on the amount of Na2CO3 used as the standard (100 mol%). The crucible filled with Na2CO3 powder and metal oxide was dried overnight in a vacuum oven at 180°C to remove residual moisture.

[0066] Next, a cemented carbide tip (Daishowa Seiki Co., Ltd., TPG070202FN, 450 mg) was embedded in the Na2CO3 powder in the crucible and left to stand. Then, as explained with reference to Figure 3, the crucible was placed in an airtight container with a reaction tube (outer diameter 80 mm × inner diameter 70 mm × length 500 mm) and a stainless steel lid and left to stand. The supply and exhaust pipes were secured to each port of the stainless steel lid with O-rings. To prevent deterioration of the O-rings, the stainless steel lid was air-cooled with a cooling fan. After inserting the reaction tube into a horizontal electric furnace (Koyo Thermo Systems Co., Ltd., KTF040N1), the temperature was raised from room temperature at 5°C / min, and after reaching 900°C, the temperature was maintained for 25 hours to allow the reaction to proceed. Alumina protective tubes (Nikkatoh Co., Ltd., SSA-S, outer diameter 6.0 mm × inner diameter 4.0 mm) were used as the supply and exhaust pipes. A mixed gas of Ar gas (high-purity argon, >99.998%) and CO2 gas (high-purity carbon dioxide, manufactured by Kyoto Teisan Co., Ltd.), controlled by a mass flow controller (Horiba S-Tech Co., Ltd.), was supplied at a total flow rate of 50 mL / min to maintain an Ar-CO2 atmosphere inside the reaction tube. The partial pressure of CO2 in the Ar-CO2 atmosphere was 0.8 atm. In all of the following examples and comparative examples, the total pressure of the Ar-CO2 atmosphere was 1 atm.

[0067] (analysis) After the reaction was complete, the reaction tube was cooled to room temperature at 5°C / min, and the carbide tips were recovered from the reaction tube. After removing surface deposits, the weight of the carbide tips was measured, and the weight loss rate was calculated. The results are shown in Table 2.

[0068] The obtained salt was dissolved in nitric acid containing tartaric acid, which acts as a chelating agent for tungsten ions, and the tungsten concentration was analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES, AMETEK, SPECTROBLUE). This confirmed that the weight loss rate was due to the oxidation and dissolution of tungsten carbide in the cemented carbide tip. Furthermore, an X-ray diffractometer (XRD, Rigaku Corporation, SmartLab, Cu-Kα rays, 40kV, 30mA) was used to identify the phases of the obtained salt and the remaining cemented carbide tip.

[0069] (Comparative Example 1) Except for the absence of Cu2O, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 1. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 2.

[0070] [Table 2]

[0071] As shown in Table 2, Example 1, in which Cu2O was added, showed a greater weight loss rate than Comparative Example 1. This is because Cu2O acted as an oxidizing agent, and the oxidation and dissolution reaction of tungsten proceeded rapidly.

[0072] If the oxidation elution reaction is represented by the following formula (A1), in other words, assuming that Cu ions are reduced to metallic Cu, then 6.4 mol% Cu2O corresponds to a weight loss of 20.1% of tungsten carbide. The reason why the actual weight loss is greater than 20.1% is that some of the Cu adheres to the surface precipitate and then peels off.

[0073] WC+4Cu2O+2O 2- →WO4 2- +CO22- +8Cu···(A1)

[0074] Figure 4 is an optical photograph of the carbide tip of Example 1 after the reaction. As shown in the left image of Figure 4, an orange-red precipitate had formed on the surface of the carbide tip. As shown in the right image of Figure 4, when the surface precipitate was peeled off, a black, unreacted tip remained inside.

[0075] Figure 5 shows the XRD pattern of the cemented carbide tip from Example 1 after the reaction. Figure 5 also shows the XRD patterns of Cu powder and Co powder. Comparison with the XRD patterns of Cu powder and Co powder confirmed that the precipitate was metallic Cu. The small peak for metallic Co is due to metallic Co adhering to the Cu.

[0076] (Example 2) CO2 partial pressure is 6.0 × 10 -4 Except for changing to ATM, the oxidative dissolution treatment of the cemented carbide tip was performed using the molten carbonate method in the same manner as in Example 1. The weight loss rate was then calculated using the same method as in Example 1. The results are shown in Table 3.

[0077] (Comparative Example 2) Except for the absence of Cu2O, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 2. The weight loss rate was then calculated using the same method as in Example 2. The results are shown in Table 3.

[0078] [Table 3]

[0079] Even with a reduced CO2 partial pressure, Example 2 showed a larger weight loss rate due to the addition of Cu2O. However, Example 1, with a higher CO2 partial pressure, showed a larger weight loss rate than Example 2, which had a lower CO2 partial pressure.

[0080] (Example 3) Except for using 6.4 mol% FeO (manufactured by Fujifilm Wako Pure Chemical Industries) as the metal oxide, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 1. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 4.

[0081] (Example 4) Except for using 2.1 mol% Fe2O3 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the metal oxide, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 1. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 4.

[0082] [Table 4]

[0083] As shown in Table 4, Example 3, in which FeO was added, and Example 4, in which Fe2O3 was added, showed a larger weight loss rate than Comparative Example 1. This is because FeO and Fe2O3 functioned as oxidizing agents, and the oxidation elution reaction proceeded rapidly.

[0084] In Example 3, when the oxidation elution reaction is represented by the following formula (A2), 6.4 mol% of FeO corresponds to a weight loss of 20.1% of tungsten carbide. In Example 4, when the oxidation elution reaction is represented by the following formula (A3), 2.1 mol% of Fe2O3 corresponds to a weight loss of 20.1% of tungsten carbide.

[0085] WC + 4FeO + 2O 2- →WO4 2- +CO2 2- +4Fe···(A2) 3WC + 4Fe2O3 + 6O 2- →3WO4 2- +3CO2 2- +8Fe···(A3)

[0086] Figure 6A is an optical photograph of the carbide tip of Example 3 after the reaction. Figure 6B is an optical photograph of the carbide tip of Example 4 after the reaction. Silvery deposits with a metallic luster were deposited on the surface of the carbide tips of both Example 3 and Example 4.

[0087] Figure 7A shows the XRD pattern of the carbide tip from Example 3 after the reaction. Figure 7B shows the XRD pattern of the carbide tip from Example 4 after the reaction. Each XRD pattern showed a peak for Fe. From this, it was confirmed that the surface precipitates in Example 3 and Example 4 were metallic Fe.

[0088] (Example 5) CO2 partial pressure is 6.0 × 10 -4 Except for changing to ATM, the oxidative dissolution treatment of the cemented carbide tip was performed using the molten carbonate method in the same manner as in Example 3. The weight loss rate was then calculated using the same method as in Example 3. The results are shown in Table 5.

[0089] (Example 6) CO2 partial pressure is 6.0 × 10 -4 Except for changing to ATM, the oxidative dissolution treatment of the cemented carbide tip was carried out using the molten carbonate method in the same manner as in Example 4. The weight loss rate was then calculated using the same method as in Example 4. The results are shown in Table 5.

[0090] [Table 5]

[0091] Examples 5 and 6 showed a slightly larger weight loss rate than Comparative Example 2. On the other hand, Examples 5 and 6 showed a smaller weight loss rate than Examples 3 and 4. This is because the solubility of FeO and Fe2O3 in carbonates is low at low CO2 partial pressures. Therefore, when using FeO and Fe2O3, controlling the CO2 partial pressure is more important in promoting the oxidative dissolution reaction.

[0092] (Example 7) CO2 partial pressure is 6.0 × 10-4 Except for changing the reaction time to ATM and changing the reaction time to 2.5 hours, the oxidative dissolution treatment of cemented carbide tips by molten carbonate was performed in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 6.

[0093] (Example 8) CO2 partial pressure is 6.0 × 10 -4 Except for changing the reaction temperature to atm, changing the amount of Cu2O added to 12.8 mol%, and changing the reaction time to 0 hours, the oxidative dissolution treatment of cemented carbide tips by molten carbonate was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 6. Note that a reaction time of 0 hours means that the temperature of the molten carbonate was raised to 900°C and then immediately lowered.

[0094] (Example 9) CO2 partial pressure is 6.0 × 10 -4 Except for changing the reaction temperature to atm, changing the amount of Cu2O added to 12.8 mol%, and changing the reaction time to 2.5 hours, the oxidative dissolution treatment of cemented carbide tips by molten carbonate was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 6.

[0095] The measured values ​​obtained by inductively coupled plasma atomic emission spectroscopy of the salt obtained in Example 9 were 40.7 ppm by mass for tungsten and less than 0.01 ppm by mass for cobalt (the detection limit). Therefore, the ratio of cobalt concentration to tungsten concentration in the alkali metal salt was 0.5% or less (0.25% or less). Furthermore, since the tungsten concentration hardly changes during ion exchange, it can be easily inferred that the ratio of cobalt concentration to tungsten concentration in ammonium paratungstate is 0.5% or less (0.25% or less). The cobalt originates from the binder contained in the cemented carbide tip and is an impurity contained in the alkali metal salt of tungstic acid and ammonium paratungstate.

[0096] (Comparative Example 3) CO2 partial pressure is 6.0 × 10 -4 Except for changing the reaction temperature to atm, omitting the addition of Cu2O, and changing the reaction time to 0 hours, the oxidative dissolution treatment of cemented carbide tips by the molten carbonate method was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 6.

[0097] (Comparative Example 4) CO2 partial pressure is 6.0 × 10 -4 Except for changing the reaction temperature to atm, omitting the addition of Cu2O, and changing the reaction time to 2.5 hours, the oxidative dissolution treatment of cemented carbide tips by molten carbonate was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 6.

[0098] [Table 6]

[0099] 6.4 mol% Cu2O and 12.8 mol% Cu2O correspond to a weight loss rate of 20.1% and 40.2% of tungsten carbide, respectively. As can be seen from the results in Examples 7 and 9, the weight loss rate increased with increasing amounts of Cu2O added.

[0100] The weight loss rate in Example 7 was approximately the same as that in Example 2 (Table 3). This indicates that the oxidative dissolution reaction was almost completed in 2.5 hours.

[0101] Example 8, with a reaction time of 0 hours, also showed a weight loss rate of 8.3%. This indicates that the oxidative dissolution reaction proceeded even during the heating and cooling processes.

[0102] (Example 10) CO2 partial pressure is 6.0 × 10 -4Except for changing to atm, using tungsten carbide powder (manufactured by Kojunkagaku Co., Ltd., average particle size 150 μm, 100 mg) instead of cemented carbide tips, changing the amount of Cu2O added to 12.8 mol%, and changing the reaction time to 2.5 hours, the oxidative dissolution treatment of tungsten carbide powder by the molten carbonate method was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 7.

[0103] [Table 7]

[0104] After the reaction, the inside of the reaction tube was visually inspected and it was confirmed that there was no scattering of salt or other debris. This means that even with the powder, no explosion occurred due to a rapid reaction. The weight loss rate in Example 10 was far greater than that in Comparative Example 4 (Table 6), and was also greater than the weight loss rate in Example 9 (Table 6), where all conditions were the same except that the tungsten carbide was in powder form.

[0105] (Example 11) K2CO3 powder was used as the carbonate instead of Na2CO3 powder, and the CO2 partial pressure was set to 6.0 × 10⁻⁶. -4 Except for changing the reaction temperature to atm, changing the amount of Cu2O added to 12.8 mol%, and changing the reaction time to 2.5 hours, the oxidative dissolution treatment of cemented carbide tips by molten carbonate was carried out in the same manner as in Example 1. Subsequently, the weight loss rate was calculated in the same manner as in Example 1. The results are shown in Table 8.

[0106] [Table 8]

[0107] 12.8 mol% Cu2O corresponds to a weight loss of 40.2% of tungsten carbide. The weight loss in Example 11 was similar to that in Example 9 (Table 6). As can be seen from the results of Example 11, the oxidative dissolution reaction proceeded sufficiently even when K2CO3 was used as the carbonate.

[0108] (Example 12) A mixture of Na2CO3 powder and K2CO3 powder was used as the carbonate, and the CO2 partial pressure was 6.0 × 10⁻⁶. -4 Except for changing the reaction temperature to atm, changing the amount of Cu2O added to 12.8 mol%, changing the reaction time to 2.5 hours, and changing the target temperature of the molten salt to 780°C, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 1. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 9.

[0109] [Table 9]

[0110] 12.8 mol% Cu2O corresponds to a weight loss of 40.2% of tungsten carbide. The weight loss rate in Example 12 was lower than that of Example 9 (Table 6), which used molten Na2CO3 at 900°C, and also lower than that of Example 11 (Table 8), which used molten K2CO3 at 900°C. This is thought to be related to the fact that the eutectic temperature of the Na2O-Cu2O system is 806°C. In other words, although the solubility of Cu2O in the molten salt is high at 900°C, the solubility of Cu2O in the molten salt is low at 780°C, which is why the weight loss rate in Example 12 was low. From these results, it is desirable to set the target temperature of the molten salt in the range of 800°C to 1000°C when using Cu2O or CuO.

[0111] Figure 8 shows optical photographs of the crucibles in Examples 9, 10, 11, and 12 after the reaction. Specifically, Figures 8(a) and 8(b) show the results in Examples 9 and 10, which contained only Na2CO3 as the carbonate, respectively. Figure 8(c) shows the results in Example 11, which contained only K2CO3 as the carbonate. Figure 8(d) shows the results in Example 12, which contained both Na2CO3 and K2CO3 as carbonates.

[0112] As shown in Figures 8(a) and 8(b), in Example 9, where only Na2CO3 was used, metallic Cu (dark colored portion) was concentrated and fixed to the surface of the carbide tip, while in Example 10, metallic Cu (dark colored portion) precipitated at the bottom of the crucible. On the other hand, as shown in Figures 8(c) and 8(d), in Examples 11 and 12, where K2CO3 was used, metallic Cu (dark colored portion) was dispersed throughout the product (mainly alkali metal salt of tungstic acid). This is presumed to be due to differences in the wettability and surface tension of metallic Cu. Cu fixed to the surface of the carbide tip may inhibit ion diffusion and slow down the oxidative dissolution reaction. Using K2CO3 as the carbonate may help avoid such disadvantages.

[0113] (Examples 13 to 16) Except for using 12.8 mol% MnO2, SnO2, Sb2O3, or V2O5 as the metal oxide, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 9. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 10.

[0114] [Table 10]

[0115] 12.8 mol% of MnO2, SnO2, Sb2O3, and V2O5 correspond to 80.4%, 80.4%, 120.6%, and 201% of the weight loss of tungsten carbide, respectively.

[0116] The weight loss rates in Examples 13 to 16 were greater than those in Comparative Example 4 (Table 6), where the experimental conditions were identical except for the absence of metal oxide addition (2.0%). Note that in Example 16, which used V2O5, the carbide tip completely transformed into powder, making weight measurement impossible. In Example 16, when the tungsten concentration in the recovered salt was measured by ICP-AES, it was found that 62.2% of the tungsten in the carbide tip had dissolved. In other words, vanadium oxide exhibited a very high effect.

[0117] (Examples 17 and 18) Except for using Co3O4 or NiO as the metal oxide, the oxidative dissolution treatment of cemented carbide tips was carried out using the molten carbonate method in the same manner as in Example 7. Subsequently, the weight loss rate was calculated using the same method as in Example 1. The results are shown in Table 11.

[0118] [Table 11]

[0119] The weight loss rates of Examples 17 and 18 were greater than those of Comparative Example 4 (Table 6), which had identical experimental conditions except for the absence of metal oxide addition (2.0%). [Industrial applicability]

[0120] This invention is useful for recovering tungsten from tungsten-containing materials.

Claims

1. This method involves contacting a molten carbonate containing metal ions that act as oxidizing agents for alkali metal carbonates and tungsten with a tungsten-containing material. The aforementioned metal ions are supplied from a metal oxide, The metal oxide comprises at least one selected from the group consisting of CuO, Cu₂O, VO, V₂O₃, VO₂, and V₂O₅. A method for producing alkali metal salts of tungstic acid.

2. The alkali metal carbonate is Na 2 CO 3 Li 2 CO 3 and K 2 CO 3 Includes at least one selected from the group consisting of A method for producing an alkali metal salt of tungstic acid according to claim 1.

3. The alkali metal carbonate is Na 2 CO 3 Includes, The oxidation-reduction potential of the metal ions in the melt of the alkali metal carbonate is greater than -0.94 V. The method for producing an alkali metal salt of tungstic acid according to claim 2.

4. The temperature of the molten carbonate is 500°C or higher and 1000°C or lower. A method for producing an alkali metal salt of tungstic acid according to any one of claims 1 to 3.

5. The ambient gas in contact with the molten carbonate contains CO 2 gas, A method for producing an alkali metal salt of tungstic acid according to any one of claims 1 to 4.

6. The tungsten-containing material includes powdered tungsten carbide. A method for producing an alkali metal salt of tungstic acid according to any one of claims 1 to 5.

7. A method for producing an alkali metal salt of tungstic acid according to any one of claims 1 to 6, A method for manufacturing tungsten.

8. A method for producing an alkali metal salt of tungstic acid according to any one of claims 1 to 6, A method for producing ammonium paratungstate.

Images