JP6747641B2 - Method and apparatus for dissolving and recovering group 5 element and/or group 6 element with controlled water vapor partial pressure - Google Patents

Description

The present invention relates to used cemented carbide tools and various metal products containing a Group 5 element and/or a Group 6 element such as tungsten, molybdenum, niobium and tantalum (hereinafter sometimes referred to as “target element”). And the like, the present invention relates to a technique for controlling the partial pressure of water vapor to make the dissolution efficient when the target element is dissolved in a melt of an alkali metal hydroxide or an alkaline earth metal hydroxide by electrolysis.

Conventionally, collection and recycling of various elements have been promoted for the purpose of effective use of resources. Even for target elements such as tungsten, molybdenum, niobium, and tantalum, which are in great demand for cemented carbide tools, various metal products, catalysts, etc., there are great expectations for recovery and recycling due to uneven distribution of resources and scarcity. ..

As a conventional technique for recovering and recycling tungsten, a zinc treatment method and an oxidation-wet method are actually operating (see Non-Patent Document 1). It has problems that it cannot be removed, requires many steps, consumes a lot of energy, and has a high economic cost.

Further, as a recovery process under study or research, a method of reacting cemented carbide tool scrap with molten NaNO ₃ to produce Na ₂ WO ₄ and dissolving it with water to produce a Na ₂ WO ₄ solution, In addition, by adding soda ash or caustic soda to the slag at the time of special steel blowing, converting tungsten and molybdenum to the composition of water-soluble salt and cooling and solidifying, the residual metal particles are separated from the slag by a wet crushing device at the same time, Although it is known that tungsten or molybdenum salt in slag is dissolved in water (see Non-Patent Document 1 and Patent Document 1), each has many problems.

Against the background of such a conventional technique, the present inventor has previously proposed a technique for efficiently dissolving and recovering a target element from a cemented carbide tool or various metal products containing the target element such as tungsten, sodium hydroxide, etc. Has developed a technique for anodizing and dissolving the target element in the melt of the alkali metal hydroxide or alkaline earth hydroxide at 400 to 600°C (see Patent Document 2).

Japanese Patent Laid-Open No. 50-161500 JP, 2011-32578, A

"Metal Resources Report" Vol.38 No.4 Japan Agency for Petroleum, Natural Gas and Metals and Mineral Resources (November 2008) P407-417

The technique of anodizing and dissolving the target element in the melt of the above-mentioned alkali metal hydroxide or alkaline earth metal hydroxide can rapidly dissolve the target element at a relatively low voltage. Although it has advantages such as less contamination of impurities into the melt and easier control of dissolution compared to other methods, the following problems were encountered in the course of the test research. Recognized to exist.
(1) When the partial pressure of water vapor in the atmosphere in which molten alkali metal hydroxide is present is low, sodium may be generated at the cathode that is the counter electrode, and the current efficiency may be significantly reduced, and an extra voltage is required for electrolysis. As a result, power consumption increases.
(2) When the partial pressure of water vapor in the atmosphere in which the molten alkali metal hydroxide is present is low, the solubility of the target element such as tungsten in the molten alkali metal hydroxide is low, and the saturation is reached at an early stage to further promote the electrolysis. It is necessary to frequently replace the molten alkali metal hydroxide in the electrolytic cell, and the amount of chemicals and energy required to treat a certain amount of the target element becomes enormous.

The present invention solves the problems recognized in the above-described test and research process, can reduce the voltage and power required for melting, and can improve the solubility of the target element in the melt The challenge is to provide.
It is another object of the present invention to provide a method of recovering a target element, a dissolution and recovery device, which utilizes the dissolution method.

Under the above-mentioned problems, the present inventor has obtained the following knowledge in the process of proceeding various test studies.
(A) When electrolyzing and dissolving the target element in the melt, if the water content (or steam partial pressure) in the melt is increased, the reaction of the cathode, which is the counter electrode, proceeds more easily than the generation of sodium. Even if the voltage is low, the target element can be dissolved by electrolysis even if the voltage is low, so that the power consumption required for electrolysis can be reduced.
(B) When the water content in the melt is increased, the solubility of the target element in the melt is improved, so that the required amount of melt such as molten alkali metal hydroxide can be reduced, and the subsequent recovery process can be performed. It is also possible to reduce the amount of chemicals required such as neutralization treatment.
(C) After the target element is dissolved in a melt having a high water content, the water content of the melt is lowered or the temperature of the melt is lowered to change the target element to oxo of the target element such as Na ₂ WO ₄ or the like. It can be precipitated and recovered as an acid salt.

The present invention has been completed based on the above findings, and in this case, the following inventions are provided.
<1> In a melt of an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or one containing any of the above hydroxides as a main component, a Group 5 element and/or Alternatively, a method for dissolving a Group 5 element and/or a Group 6 element in which a substance containing a Group 6 element is electrolyzed to dissolve the Group 5 element and/or the Group 6 element in the melt, A method for melting, characterized in that the melt has a water content of 0.2 to 5.0 wt %.
<2> To adjust the water content of the melt, steam or a gas containing steam is passed through the melt, or is supplied into the gas phase of an electrolytic cell containing the melt. <5> The method for dissolving a Group 5 element and/or a Group 6 element according to <1>.
<3> The method for dissolving a Group 5 element and/or a Group 6 element according to <1> or <2>, wherein sodium hydroxide is used as the alkali metal hydroxide.
<4> The substance containing a Group 5 element and/or a Group 6 element contains the at least one kind of tungsten, molybdenum, niobium, and tantalum. <1> to <3> A method for dissolving a Group 5 element and/or a Group 6 element.
<5> A melt obtained by the dissolution method according to any one of <1> to <4> in which the concentration of the Group 5 element and/or the Group 6 element is increased is dissolved in water to obtain a fifth group. A method for dissolving a Group 5 element and/or a Group 6 element in an aqueous solution of an oxo acid salt of a Group element and/or a Group 6 element.
<6> After dissolving the Group 5 element and/or the Group 6 element in the melt using the dissolution method according to any one of <1> to <4>, the Group 5 element and/or Alternatively, a method for recovering a Group 5 element and/or a Group 6 element, wherein the saturation solubility of a compound containing a Group 6 element in the melt is lowered to precipitate and recover the compound.
<7> The method for recovering a Group 5 element and/or a Group 6 element according to <6>, wherein the saturation solubility of the melt is decreased by decreasing the water content of the melt and/or the melting temperature. ..
<8> An electrolysis tank having a water content of the melt of 0.2 to 5.0 wt% and a recovery tank having a water content of the melt lower than that of the electrolysis tank are provided, and electrolysis is performed to provide a Group 5 element and/or The melt of which the concentration of the Group 6 element is increased is transferred to the recovery tank to precipitate the Group 5 element and/or the compound containing the Group 6 element, and the Group 5 element and/or the Group 6 element of the recovery tank is precipitated. The method for recovering a Group 5 element and/or a Group 6 element according to <6> or <7>, wherein the melt having a reduced concentration of is returned to the electrolytic cell.
<9> a cathode and an anode holding a substance containing a Group 5 element and/or a Group 6 element, and an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or A Group 5 element comprising: an electrolytic cell containing a melt containing one of the hydroxides as a main component; and a water content adjusting unit for adjusting the water content of the melt, And/or a dissolution or dissolution/recovery device for Group 6 elements.
<10> a cathode and an anode holding a substance containing a Group 5 element and/or a Group 6 element, and an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or An electrolytic cell containing a melt containing one of the hydroxides as a main component, an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the hydroxide. A recovery tank containing a melt of one containing as a main component, a high water content adjusting means for maintaining a high water content of the melt contained in the electrolysis tank, and a water content of the melt contained in the recovery tank. Low water content adjusting means for keeping the temperature lower than that of the electrolytic cell and/or melting temperature adjusting means for keeping the melting temperature of the melt contained in the recovery tank lower than that of the electrolytic cell, and Group 5 element and/or sixth element in the electrolytic cell Melt transfer means for transferring the melt with the increased concentration of the group element to the recovery tank, and return for returning the melt with the decreased concentration of the group 5 element and/or the group 6 element in the recovery tank to the electrolytic cell A dissolution/recovery device for a Group 5 element and/or a Group 6 element, characterized by comprising means.

The present invention can include the following embodiments.
<11> The substance containing a Group 5 element and/or a Group 6 element is a used cemented carbide tool, a catalyst, and/or a weight, according to any one of <1> to <4>. A method for dissolving a Group 5 element and/or a Group 6 element.
<12> A substance containing a Group 5 element and/or a Group 6 element is preliminarily prepared from an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the above hydroxide. Of the Group 5 element and/or the Group 6 element according to any one of <1> to <4> and <11>, which comprises a preliminary dipping step of immersing in a melt containing Dissolution method.
<13> The dissolution method according to <2>, wherein the gas containing water vapor is obtained by passing the gas through a water bath at 20 to 100°C.
<14><11> to <13> The melt obtained by the dissolution method according to any one of the groups 5 and/or 6 in which the concentration of the group 6 element is increased is dissolved in water to obtain a fifth group. A method for dissolving a Group 5 element and/or a Group 6 element in an aqueous solution of an oxo acid salt of a Group element and/or a Group 6 element.
<15> After dissolving the Group 5 element and/or the Group 6 element in the melt by using the dissolution method according to any one of <11> to <13>, the Group 5 element and/or Alternatively, a method for recovering a Group 5 element and/or a Group 6 element, wherein the saturation solubility of a compound containing a Group 6 element in the melt is lowered to precipitate and recover the compound.
<16> The Group 5 element and/or the Group 6 element according to <15>, wherein the saturation solubility in the melt is reduced by reducing the water content of the melt and/or the temperature of the melt. How to recover elements.
<17> The water content adjusting means passes water vapor or a gas containing water vapor through the melt, or supplies the water into the gas phase of an electrolytic cell containing the melt. A device for dissolving or dissolving/recovering the stated Group 5 element and/or Group 6 element.
<18> The apparatus for dissolving or dissolving/recovering a Group 5 element and/or a Group 6 element according to <17>, wherein the water content adjusting means supplies a gas that has passed through a water bath at 20 to 100°C. ..
<19> The high water content adjusting means passes water vapor or a gas containing water vapor through the melt, or supplies the water into the gas phase of an electrolytic cell containing the melt <10>. The dissolution/recovery device for the Group 5 element and/or the Group 6 element described in 1.
<20> The apparatus for dissolving/recovering a Group 5 element and/or a Group 6 element according to <19>, wherein the high water content adjusting means supplies a gas passed through a water bath at 20 to 100°C.

According to the present invention, when a Group 5 element and/or a Group 6 element is dissolved in a melt such as an alkali metal hydroxide by electrolysis, the voltage required for electrolysis can be suppressed.
Further, according to the present invention, by appropriately controlling the water content (steam partial pressure) in the melt, the amount of alkali metal hydroxide such as sodium hydroxide or alkaline earth hydroxide used can be reduced. Therefore, the reagents used for the subsequent neutralization treatment and the like can be similarly reduced.
Further, if the water content (steam partial pressure) in the melt is appropriately controlled or the saturation solubility of the target element in the melt is adjusted by appropriately controlling the temperature of the melt, electrolysis can be performed. Since it becomes possible to recover the oxo acid compound of the Group 5 and 6 elements such as sodium tungstate without stopping, the recovery process of the Group 5 and 6 elements can be made efficient, and the alkali metal hydroxide and neutralization can be performed. It is possible to further suppress the usage amount of various chemicals such as a processing reagent.

Comparison was made between Example 1 and Comparative Example 1 having different water contents (steam partial pressure) in the sodium hydroxide molten bath, and the tungsten alloy carbide tips were electrolyzed and dissolved in the sodium hydroxide molten bath. The figure which showed the time change of an electric current value. The solid line shows Example 1 in which Ar gas was supplied to the reaction vessel (gas phase of the electrolytic cell) in a 90° C. water bath, and the broken line shows Comparative Example 1 in which Ar gas was supplied to the reaction vessel without passing through the water bath. Regarding Comparative Example 2 (solid line) in which WO ₃ in excess of the saturation amount in an Ar atmosphere was added in advance in molten sodium hydroxide and Comparative Example 1 (broken line) in which no addition was made, Ar gas was passed through a reaction vessel (electrolysis tank) without passing through a water bath. FIG. 4 is a diagram showing a time change of a current value when electrolyzing at a constant voltage of 1 V while supplying the same to the gas phase). WO ₃ exceeding the saturation amount in an Ar atmosphere was added in advance to molten sodium hydroxide, and a constant voltage of 0.4 V was applied while supplying Ar gas through a 90°C water bath to the reaction vessel (gas phase of the electrolytic cell). Example 2A (solid line, water content about 2 wt%) electrolyzed in Example 2B (one-dot chain line, water content about 0.2 wt%) electrolyzed at a constant voltage of 1 V while supplying Ar gas to the reaction vessel through a water bath at 23°C. %) and Comparative Example 2 (broken line, water content is less than about 0.2 wt%) in which Ar gas was electrolyzed at a constant voltage of 1 V while supplying Ar gas to the reaction vessel without passing through a water bath. It is a figure.

The element to be dissolved or recovered in the present invention is a Group 5 element and/or a Group 6 element (target element), and specifically, W, Mo, Cr, V, Nb, and Ta. Of these, W, Ta, and Mo, which are particularly highly expected in practical use, are preferable.
The substance to be dissolved or recovered containing these elements may be one containing the element as a metal, or may be one containing a carbide or the like. Used cemented carbide tools, various metal products, catalysts, and Examples include, but are not limited to, in-process wastes generated in these manufacturing processes, as long as they are substances containing at least one of these elements and capable of applying a voltage as the anode. Good.
The substance containing such a target element may be provided with or contain an organic substance such as various plastics as a surface coating material or the like, and a ceramic composed of an element other than the target element may be used as a surface coating material or a binder. It may be provided or contained as a main component or a sub-component. Examples of ceramics composed of elements other than the target element include titanium nitride, aluminum nitride, alumina, silica, titanium carbide, titanium carbonitride, titanium aluminum nitride, and aluminum chromium nitride.

The alkali metal hydroxide and alkaline earth metal hydroxide used in the dissolution method of the present invention are electrolytes at the time of anodic oxidation, and are also solvents for dissolving the target element. Specific examples thereof include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide and magnesium hydroxide. Practically, alkali metal hydroxides are desirable in terms of reactivity, and among them, sodium hydroxide is particularly preferably used.
These hydroxides may be used alone or as a mixture (mixed hydroxide), and further, other components or impurities may be mixed or mixed within a range that does not significantly reduce anodization or solubility. May be mixed. Other components to be mixed include other hydroxides and electrolytes for adjusting viscosity and conductivity.
In the present invention, an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or one containing any of the hydroxides as a main component is used in a molten state, Generally, the temperature may be equal to or higher than the melting point, and the use temperature is determined by the solubility of the target element, the diffusivity, the heat resistance of the apparatus material used, the economical efficiency, the running cost and the like. The melt temperature is advantageous in that the higher the temperature, the higher the solubility and diffusibility of the target element, but on the other hand, it is disadvantageous in terms of heat resistance of the device material, economical efficiency, etc. Generally, a temperature of about 200 to 600° C. can be suitably used.

According to the present invention, the voltage required for electrolysis of the target element can be reduced by increasing the water content in the molten bath of hydroxides such as alkali metal hydroxides and alkaline earth metal hydroxides. .. For example, the voltage required for electrolysis of the target element is about 1 V when the water content is less than 0.2 wt%, but the water content is adjusted to, for example, 1.5 to 2.0 wt% according to the present invention. This allows electrolysis at about 0.4V.
Further, by increasing the water content in the molten bath, the saturation solubility of the target element in the melt can be improved and the dissolution by electrolysis can be made efficient.
Furthermore, it is also possible to utilize the dependency of the saturated solubility of the target element on the water content and the melting temperature, and to utilize the recovery of the target element. That is, after the target element is dissolved in a state where the water content in the melting bath is increased to, for example, 1.5 to 2.0 wt %, the water content and/or the melting temperature is made lower than that at the time of the dissolution, thereby The compound (oxo acid salt of Group 5 and 6 elements such as sodium tungstate) can be precipitated and recovered. At that time, an electrolytic cell with a high water content and a high melting temperature and a recovery tank with a low water content and a low melting temperature are provided, and the electrolytic solution is used to dissolve the target element by electrolysis and collect the melt with a high dissolved concentration of the target element. It is possible to continuously collect the target element compound without interrupting the electrolysis by returning the melt of the target element with a reduced concentration of the target element to the electrolytic cell. Can be It is desirable that the water content at the time of recovery or in the recovery tank is 0 wt% or close to it in order to facilitate precipitation and recovery, but comprehensively judge the time required to sufficiently reduce the water content. You can decide. A lower melting temperature during collection or in the recovery tank is desirable for efficient precipitation and recovery, but if the melting temperature is too low, the risk of not maintaining the molten state increases and energy consumption also increases. It is possible to make a comprehensive judgment and make a decision.

The water content of the melting bath has, for example, a gas supply port and a gas outlet communicating with the atmosphere, and an electrolytic cell containing the melting bath was used to store water vapor or a gas containing water vapor in the electrolytic cell. It can be adjusted by passing it through the melt or by feeding it into the gas phase of an electrolytic cell. After the temperature of the water bath was kept constant and a constant flow rate of gas per hour was passed through the water bath, the water content of the molten bath contained in the electrolytic cell was made almost constant by constantly supplying it to the gas supply port of the electrolytic cell. can do. For example, the water content in a 450° C. sodium hydroxide molten bath is in the range of 0.2 to 0.6 wt% when the temperature of the water bath is in a steady state at room temperature (around 20° C.), but the temperature of the water bath is It becomes about 2 wt% in the steady state of 90°C. If a gas containing no water is supplied without passing through the water bath, the water content of the molten bath will be less than 0.2 wt %. In addition, when such a gas is kept in a state of not being supplied at all, no matter what the water content before that, in the final steady state, the vapor pressure of the atmosphere or vapor phase in contact with the molten bath It is thought that the water content will correspond to.
Further, since the saturated water content of the molten bath can be improved by increasing the pressure of the atmosphere of the molten bath or the vapor phase of the melting tank, the solubility of the target element is further increased by controlling the pressure as compared with the atmospheric pressure. be able to.
The gas is not limited to a rare gas such as Ar, an inert gas such as a carbon dioxide gas, a nitrogen gas, and the like, and in addition to the air, an inert gas or an oxidizing gas enriched with oxygen in the air can be used. .. It is considered that oxygen in the gas contributes to the oxidation and dissolution of a part of the target element, which leads to a reduction in power consumption.

The apparatus used for the dissolution method of the present invention is not particularly limited, and those conventionally used for anodic oxidation and having heat resistance and alkali resistance can be used as they are, and also improvement of heat resistance, etc. It can also be used by adding. As such a device, not only a batch type but also a continuous type can be used.
When the voltage applied between the cathode and the anode during the anodic oxidation is too high, generally, the current efficiency of the anodic oxidation is lowered, an undesired side reaction occurs, and the energy consumption is increased. On the other hand, if it is too low, a sufficient reaction rate cannot be obtained, and therefore it can be determined by comprehensively considering these. In the present invention, the water content in the molten bath is set to 0.2 to 5.0 wt% (the lower limit is preferably 0.5 wt% or more, more preferably 1.0 wt% or more). It can be reduced, and accordingly, the side effect can be suppressed and the current efficiency can be made relatively high.
When the dissolution is performed in a batch system, the voltage applied during the processing period may be constant, but in order to shorten the processing time, the applied voltage may be changed within the controllable range of the dissolution processing. The current may be constant, but in this case, it is necessary to confirm the voltage and adjust the current value, the processing time, the supply amount of the processing substance, and the like.

In the method of the present invention, the target elements such as tungsten, molybdenum, niobium, and tantalum are anodized, and when tungsten or molybdenum is taken as an example, alkali metal hydroxide is used as ions represented by WO ₄ ²⁻ and MoO ₄ ^2−. , Alkaline earth metal hydroxides, mixed hydroxides thereof, or those containing any of the above hydroxides as a main component are considered to be dissolved in the melt. At that time, even if the object to be dissolved contains impurities, Fe, Ni, etc., which are impurities, are hardly dissolved, or even if they are dissolved, they are expected to be deposited on the cathode. Therefore, the target element should be selectively dissolved. You can Impurities such as Fe and Ni that are not dissolved in the melt remain on the surface of the object to be dissolved, but oxo acid salts of the target element such as Na ₂ WO ₄ and Na ₂ MoO ₄ are included in the residual impurities. It is efficiently and controllably dissolved in the melt without being significantly affected. Although the detailed mechanism at that time is not clear, the oxo acid salt of the target element such as Na ₂ WO ₄ , Na ₂ MoO _4, etc. has a large solubility in the melt having a high water content and, at the same time, is high in temperature. The diffusion rate is also large, and it is considered that the impurities are dissolved efficiently and controllably without being affected by residual impurities.
Moreover, the target element is dissolved, and the melt having the increased concentration of those elements can be easily dissolved in water, and as a result, an aqueous solution of the oxo acid salt of the target element can be obtained. When the melt is dissolved in water, from the viewpoint of safety, it is preferable that the temperature be lowered to a temperature below the melting point, preferably below 100°C, more preferably below 50°C.

When the substance containing the target element to be treated in the present invention comprises or contains organic substances such as various plastics as a surface coating material, titanium nitride, aluminum nitride, alumina, silica, titanium carbonitride, titanium aluminum When a ceramic composed of an element other than the target element, such as nitride or aluminum chrome nitride, is provided or contained as a main component or sub-component of the surface coating material or binder, the substance is preliminarily alkali metal. The hydroxide, the alkaline earth metal hydroxide, a mixed hydroxide thereof, or a material containing any of the above hydroxides as a main component can be immersed in a melt without energization. By such a pretreatment, organic substances such as various plastics exposed on the surface can be decomposed and removed into hydrogen, CO ₂ , low-molecular gas, and the like, and titanium nitride, aluminum nitride, alumina, alumina, Since surface coating materials and binders containing ceramics such as silica, titanium carbonitride, titanium aluminum nitride, and aluminum chrome nitride can be dissolved and removed, the subsequent anodic oxidation and dissolution of Group 5 and 6 elements can be efficiently performed. Can be done. Further, by providing the melt used for the pretreatment separately from the melt used for the anodic oxidation and dissolution of the Group 5 and 6 elements, impurities derived from the organic substance in the melt in which the Group 5 and 6 elements are dissolved are provided. The amount and the amount of impurities derived from the ceramics can be reduced. The temperature of the melt used for the pretreatment is appropriately determined according to the type of organic substance that decomposes and ceramics that dissolve.
The dissolution method for dissolving ceramics such as titanium nitride, aluminum nitride, alumina, silica, titanium carbonitride, titanium aluminum nitride, and aluminum chrome nitride exposed on the surface is anodization as described above. Not only as a pretreatment for the melting method, but also for various treatment methods for recovering the Group 5 and 6 elements from the substance containing the Group 5 and 6 elements to be adopted to dissolve and remove the ceramics. You can
In such a pre-immersion treatment without energization, the target element is hardly dissolved in the case of metal or carbide, and is slightly dissolved in the case of nitride or oxide, but is anodized by energization. Since the dissolution amount is smaller than that in the case, it is considered that the dissolution amount in the subsequent anodic oxidation/dissolution process is not significantly affected.

Hereinafter, the present invention will be described more specifically with reference to Examples and the like, but the present invention is not limited to these Examples and the like.

(Reference Example 1: Measurement of water content in sodium hydroxide molten bath)
A reaction vessel (electrolytic cell) having a gas supply port and an exhaust port communicating with the atmosphere was prepared, and sodium hydroxide was contained and melted at 450°C. The water content in the sodium hydroxide molten bath is changed by constantly supplying Ar gas having a constant flow rate per unit time to the reaction vessel through the water bath kept at a predetermined temperature and changing the temperature of the water bath. The rate (or steam partial pressure) was adjusted. The water content in the sodium hydroxide molten bath was determined by titration 24 hours after changing the water temperature, which is considered to have reached a steady state. Specifically, the weight of sodium hydroxide contained in the molten sample was determined by acid-base titration, and the difference from the total weight was evaluated as the water content. As a result, the water content in the sodium hydroxide molten bath is in the range of 0.2 to 0.6 wt% when the temperature of the water bath is room temperature (around 20°C), and when the temperature of the water bath is 90°C. It was about 2 wt %. When Ar gas is supplied to the reaction vessel without passing through the water bath, it is difficult to quantify the water content in the molten sodium hydroxide, but it is clear that it is less than 0.2 wt %.

(Example 1; Investigation 1 of influence of water content of molten sodium hydroxide on electrolysis)
Using the same reaction vessel (electrolysis cell) and Ar gas supply equipment as used in Reference Example 1, the water bath temperature was set to 90° C. (water content in the sodium hydroxide molten bath of about 2 wt %). One uncoated tungsten alloy carbide tip (0.6 g, about 90 wt% tungsten carbide, about 5 wt% cobalt) was placed on a Ni plate as an anode, and a nickel plate as a cathode at 450°C. Electrolysis was carried out in the sodium hydroxide melted in step 1 under constant voltage conditions of 0.4 V. The electrolysis was terminated when the current value became almost zero (the chip was completely dissolved). The current efficiency was almost 100%. The result is shown by the solid line in FIG. Although the voltage was relatively low at 0.4 V, total dissolution was achieved in a relatively short time of about 5 hours.

(Comparative Example 1)
Electrolysis was carried out in exactly the same manner as in Example 1 except that the constant voltage was 1 V and that Ar gas was supplied to the reaction vessel without passing through a water bath (water content in the sodium hydroxide molten bath was less than 0.2 wt%). I went. The current efficiency was almost 100%. The result is shown by a broken line in FIG. When the water content in the sodium hydroxide molten bath was as low as less than about 0.2 wt %, the total dissolution required a voltage of 1 V and about 14 hours.

(Evaluation of the results of Investigation 1 on the effect of water content in the sodium hydroxide molten bath)
From the results of Example 1 and Comparative Example 1 described above, by increasing the water content (steam partial pressure) in the sodium hydroxide molten bath, the voltage required for electrolysis can be reduced from 1V to 0.4V, and at the same time dissolution It became clear that the time required was about 1/3 and efficient dissolution could be performed.

(Comparative Example 2: Investigation of effect of tungsten concentration in sodium hydroxide molten bath on electrolysis)
Electrolysis was performed in exactly the same manner as in Comparative Example 1 except that WO ₃ (NaOH:WO ₃ =5:1) exceeding the saturation amount in an Ar gas atmosphere was added to the sodium hydroxide molten bath before the start of electrolysis. It was The result is shown by the solid line in FIG. For comparison, the results of Comparative Example 1 are also shown by a broken line. From this, it can be said that when the concentration of tungsten in the sodium hydroxide molten bath is increased, the dissolution of tungsten is hindered and the electrolysis cannot be efficiently performed. Comparative Example 2 is the result under the condition of no water vapor (Ar gas was supplied to the reaction vessel without passing through a water bath and the water content of molten sodium hydroxide was less than 0.2 wt%). It is considered that the tendency that when the concentration of tungsten in the sodium molten bath increases, the dissolution is hindered and the electrolysis cannot be performed efficiently even if the sodium hydroxide molten bath has a high water content.

(Example 2, Comparative Example 2; Investigation 2 of influence of water content in sodium hydroxide molten bath on electrolysis)
After addition of WO ₃ in sodium hydroxide molten bath prior to initiation of the electrolysis was subjected to electrolytic in one of the following conditions (1) to (3).
(1) Example 2A: Water bath temperature 90° C. (water content in molten sodium hydroxide about 2 wt %), voltage 0.4 V, NaOH:WO ₃ =5:1 (saturated amount in Ar gas atmosphere exceeded. WO ₃ added)
(2) Example 2B: Water bath temperature 23° C. (water content in sodium hydroxide molten bath of about 0.2 to 0.6 wt %), voltage 1 V, NaOH:WO ₃ =4:1 (saturation amount under these conditions More than WO ₃ added)
(3) Comparative Example 2: Without passing through a water bath (water content in a sodium hydroxide molten bath of less than 0.2 wt%), voltage of 1 V, NaOH:WO ₃ =5:1 (exceeds saturation amount in Ar gas atmosphere) WO ₃ added)
The results of Examples 2A and 2B and Comparative Example 2 are shown in FIG.

(Evaluation of the results of the water content impact survey 2)
The above-mentioned Example 2A and Comparative Example 2 are the results under the condition that only the water content is changed. From these comparisons, it is possible to improve the saturated solubility of tungsten by increasing the water content in the sodium hydroxide molten bath. It has been clarified that the factors that inhibit electrolysis can be reduced, and as a result, efficient electrolysis can be performed. Further, both Example 2B and Comparative Example 2 are the results under the condition that only the water content is changed in the state where tungsten is saturated, and even in the state where tungsten is saturated, the water content in the sodium hydroxide molten bath is It became clear that the increase in the current value can be expected by increasing the value. In addition to the above Examples 2A and 2B and Comparative Example 2, the results of the same electrolysis experiments were conducted at water bath temperatures of 20°C and 50°C. The results show that the water bath temperature was 20°C, 50°C and 90°C in a sodium hydroxide water bath. The saturated solubilities (mass% of pure W) of tungsten were estimated to be 13 wt%, 26 wt% and 40 wt% or more, respectively.

The melting and collecting method and the melting and collecting apparatus of the present invention are used for tungsten, molybdenum, niobium, tantalum, etc. from used cemented carbide tools, various metal products, catalysts, and in-process wastes produced in the manufacturing process thereof. Since the target element of (1) can be efficiently dissolved in a melt such as an alkali metal hydroxide, it can be effectively used for recovery and recycling of the target element.

Claims (10)

In a melt of an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or one containing any of the above-mentioned hydroxides as a main component, a Group 5 element and/or a Group 6 element A method for dissolving a Group 5 element and/or a Group 6 element, comprising electrolyzing a substance containing a Group element to dissolve the Group 5 element and/or the Group 6 element in the melt, comprising: A dissolution method characterized in that the water content is 0.2 to 5 wt %. In order to adjust the water content of the melt, water vapor or a gas containing water vapor is passed through the melt, or is supplied into the gas phase of an electrolytic cell containing the melt. 1. The method for dissolving a Group 5 element and/or a Group 6 element according to 1. The method for dissolving a Group 5 element and/or a Group 6 element according to claim 1 or 2, wherein sodium hydroxide is used as the alkali metal hydroxide. The Group 5 element according to any one of claims 1 to 3, wherein the substance containing a Group 5 element and/or a Group 6 element contains at least one of tungsten, molybdenum, niobium, and tantalum. And/or a method for dissolving a Group 6 element. A molten material having an increased concentration of a Group 5 element and/or a Group 6 element obtained by the dissolution method according to any one of claims 1 to 4 is dissolved in water to obtain a Group 5 element and/or A method for dissolving a Group 5 element and/or a Group 6 element in an aqueous solution of a Group 6 element oxoacid salt. After dissolving the Group 5 element and/or the Group 6 element in the melt using the melting method according to any one of claims 1 to 4, the Group 5 element and/or the Group 6 element A method for recovering a Group 5 element and/or a Group 6 element, which comprises precipitating and recovering a compound containing, by reducing the saturated solubility thereof in the melt. The method for recovering a Group 5 element and/or a Group 6 element according to claim 6, wherein the saturation solubility of the melt is lowered by lowering the water content of the melt and/or lowering the melting temperature. An electrolysis tank having a water content of the melt of 0.2 to 5.0 wt% and a recovery tank having a water content of the melt of which is lower than that of the electrolysis tank are provided, and electrolysis is performed to provide a group 5 element and/or a group 6 The melt having the increased element concentration is transferred to the recovery tank to precipitate the compound containing the Group 5 element and/or the Group 6 element, and the concentration of the Group 5 element and/or the Group 6 element in the recovery tank is increased. The method for recovering a Group 5 element and/or a Group 6 element according to claim 6 or 7, wherein the lowered melt is returned to the electrolytic cell. An alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the above water, which is provided with a cathode and an anode holding a substance containing a Group 5 element and/or a Group 6 element A Group 5 element and/or a Group 5 element characterized by comprising an electrolytic cell containing a melt containing one of the oxides as a main component and a water content adjusting means for adjusting the water content of the melt. Dissolution or dissolution/recovery device for Group 6 elements. An alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the above water, which is provided with a cathode and an anode holding a substance containing a Group 5 element and/or a Group 6 element An electrolytic cell containing a melt containing one of the oxides as a main component, an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or one of the hydroxides. The recovery tank containing the melt of the one containing as a main component, a high water content adjusting means for maintaining a high water content of the melt contained in the electrolysis tank, the water content of the melt contained in the recovery tank from the electrolytic tank A low water content adjusting means for maintaining a low temperature and/or a melting temperature adjusting means for maintaining a melting temperature of the melt contained in the recovery tank lower than that in the electrolytic cell; and a group 5 element and/or a group 6 element in the electrolytic cell. A melt transfer means for transferring the melt with an increased concentration to the recovery tank, and a return means for returning the melt with a decreased concentration of the Group 5 element and/or the Group 6 element in the recovery tank to the electrolytic cell A dissolution/recovery device for a Group 5 element and/or a Group 6 element, characterized in that

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