WO2017149835A1

WO2017149835A1 - Method and apparatus for dissolving and collecting group 5 elements and/or group 6 elements in which water vapor pressure is controlled

Info

Publication number: WO2017149835A1
Application number: PCT/JP2016/081820
Authority: WO
Inventors: 大石　哲雄
Original assignee: 国立研究開発法人産業技術総合研究所
Priority date: 2016-03-03
Filing date: 2016-10-27
Publication date: 2017-09-08
Also published as: JPWO2017149835A1; JP6747641B2

Abstract

Provided are a dissolving method and a collecting method for a group 5 element and/or a group 6 element with which the voltage and power necessary for dissolution can be reduced and the solubility of said element in a molten material can be improved. The methods are characterized in that when electrolyzing a substance comprising a group 5 element and/or a group 6 element in a molten material of an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or a material comprising one of said hydroxides as the main component to dissolve the group 5 element and/or group 6 element in said molten material, the water content of the molten material is 0.2-5 wt%.

Description

Method and apparatus for dissolving and recovering Group 5 element and / or Group 6 element with controlled water vapor partial pressure

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

Conventionally, collection and recycling of various elements have been promoted for the purpose of effective use of resources. For tungsten, molybdenum, niobium, tantalum and other target elements that are in great demand for carbide tools, various metal products, catalysts, etc., there are very high expectations for recovery and recycling due to the uneven distribution and scarcity of their resources. .

As conventional techniques for recovering and recycling tungsten, two methods, a zinc treatment method and an oxidation-wet method, are actually in operation (see Non-Patent Document 1). It has problems such as being unable to be removed, requiring many processes, high energy consumption and high economic cost.

In addition, as a recovery process under study or research, a carbide tool scrap is reacted with molten NaNO ₃ to form Na ₂ WO ₄ , which is dissolved in water to form a Na ₂ WO ₄ solution. , Add soda ash or caustic soda to hot metal at the time of special steel blowing, convert tungsten and molybdenum into water-soluble salt composition, cool and solidify, and simultaneously separate residual metal particles from slag by wet pulverizer, Although what melt | dissolves the tungsten in a slag, molybdenum salt in water is known (refer nonpatent literature 1, patent document 1), each has many problems.

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

JP 50-161500 A JP 2011-32578 A

The technique of anodizing and dissolving the target element in the above-mentioned alkali metal hydroxide or alkaline earth metal hydroxide melt can rapidly dissolve the target element at a relatively low voltage. Although it has excellent features such as less contamination of dissolved impurities and easier control of dissolution compared to other methods, the following problems have been encountered in the course of advancing research. Recognized that it exists.
(1) When the partial pressure of water vapor in the atmosphere containing molten alkali metal hydroxide is low, sodium is generated at the cathode as the counter electrode, which may significantly reduce current efficiency and require extra voltage for electrolysis. As a result, power consumption increases.
(2) When the partial pressure of water vapor in the atmosphere where 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, reaches saturation at an early stage, and further proceeds with electrolysis Requires frequent replacement of the molten alkali metal hydroxide in the electrolytic cell, and enormous amounts of chemicals and energy are required to treat a certain amount of the target element.

The present invention solves the problems recognized in the above-described test and research process, can reduce the voltage and power required for dissolution, and can improve the solubility of the target element in the melt. It is an issue to provide.
Moreover, this invention makes it a subject to provide the collection | recovery method and melt | dissolution and collection | recovery apparatus of the target element using the said dissolution method.

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

The present invention has been completed based on the above findings, and the present invention provides the following invention.
<1> In a melt containing an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or any of the above hydroxides as a main component, a Group 5 element and / or Or a method for dissolving a Group 5 element and / or a Group 6 element in which a Group 5 element and / or a Group 6 element is dissolved in the melt by electrolyzing a substance containing the Group 6 element, A melting method, wherein the water content of the melt is 0.2 to 5.0 wt%.
<2> 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. The method for dissolving the Group 5 element and / or 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 material according to any one of <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. Method for dissolving Group 5 element and / or Group 6 element.
<5> A melt having an increased concentration of the Group 5 element and / or the Group 6 element obtained by the dissolving method according to any one of <1> to <4> is dissolved in water to A method for dissolving a Group 5 element and / or a Group 6 element in an aqueous solution of a Group element and / or Group 6 element oxoacid salt.
<6> After the Group 5 element and / or Group 6 element is dissolved 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 that precipitates and recovers the compound by reducing the saturation solubility of the compound containing the Group 6 element in the melt.
<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 decreasing the melting temperature. .
<8> An electrolytic cell in which the water content of the melt is 0.2 to 5.0 wt% and a recovery tank in which the water content of the melt is lower than that of the electrolytic cell are provided. The melt with increased concentration of the Group 6 element 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 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 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, 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 of any one of the hydroxides as a main component; and a moisture content adjusting means for adjusting the moisture content of the melt. / Or Group 6 element dissolution or dissolution / recovery device.
<10> a cathode and an anode holding a substance containing a Group 5 element and / or a Group 6 element, an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or An electrolytic cell containing a melt of any 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 any of the above as a main component, a high moisture content adjusting means for maintaining a high moisture content of the melt contained in the electrolytic cell, and a moisture content of the melt contained in the recovery tank. Low moisture content adjusting means that is maintained lower than the electrolytic cell and / or melting temperature adjusting means that maintains the melting temperature of the melt contained in the recovery tank lower than the electrolytic cell, Group 5 element and / or sixth in the electrolytic cell Recovery tank with increased concentration of group elements Group 5 element characterized by comprising melt transfer means for transferring, and return means for returning the melt with reduced concentration of Group 5 element and / or Group 6 element in the recovery tank to the electrolytic cell And / or a Group 6 element dissolution / recovery device.

The present invention can include the following embodiments.
<11> The material according to any one of <1> to <4>, wherein 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. Method for dissolving Group 5 element and / or Group 6 element.
<12> A substance containing a Group 5 element and / or a Group 6 element in advance, either an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the above hydroxide <1> to <4> and <11>, wherein the element of Group 5 and / or Group 6 is contained in the melt. Dissolution method.
<13> The dissolving 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 having an increased concentration of the Group 5 element and / or the Group 6 element obtained by the dissolving method according to any one of the items A method for dissolving a Group 5 element and / or a Group 6 element in an aqueous solution of a Group element and / or Group 6 element oxoacid salt.
<15> After the Group 5 element and / or the Group 6 element are dissolved in the melt 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 that precipitates and recovers the compound by reducing the saturation solubility of the compound containing the Group 6 element in the melt.
<16> The group 5 element and / or the group 6 according to <15>, wherein the saturation solubility in the melt is decreased by decreasing the water content of the melt and / or decreasing the temperature of the melt. Element recovery method.
<17> The water content adjusting means is configured to pass water vapor or a gas containing water vapor into the melt, or supply it into a gas phase of an electrolytic cell containing the melt. An apparatus for dissolving or dissolving / recovering the Group 5 element and / or Group 6 element described.
<18> The apparatus for dissolving or dissolving / recovering a group 5 element and / or a group 6 element according to <17>, wherein the moisture content adjusting means supplies gas passed through a water bath at 20 to 100 ° C. .
<19> The high moisture content adjusting means passes water vapor or a gas containing water vapor into the melt, or supplies it into the gas phase of an electrolytic cell containing the melt. <10> A device for dissolving / recovering a Group 5 element and / or a Group 6 element described in 1.
<20> The apparatus for dissolving / recovering a Group 5 element and / or Group 6 element according to <19>, wherein the high water content adjusting means supplies 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, a voltage necessary for electrolysis can be suppressed.
In addition, according to the present invention, the amount of alkali metal hydroxide or alkaline earth hydroxide such as sodium hydroxide is reduced by appropriately controlling the water content (water vapor partial pressure) in the melt. Therefore, the reagent used for the subsequent neutralization treatment can be reduced in the same manner.
Moreover, if the moisture content (steam partial pressure) in the melt is appropriately controlled, or if 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 is possible to recover an oxo acid compound of a Group 5,6 element such as sodium tungstate without stopping, it is possible to improve the efficiency of the Group 5,6 element recovery process, as well as alkali metal hydroxide and neutralization. The amount of various chemicals used such as processing reagents can be further suppressed.

When Example 1 and Comparative Example 1 having different water contents (water vapor partial pressure) in the sodium hydroxide molten bath were compared, a tungsten alloy carbide chip was 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 (the gas phase of the electrolytic cell) through a 90 ° C. water bath and the broken line shows Comparative Example 1 in which Ar gas was supplied to the reaction vessel without going through the water bath. In Comparative Example 2 (solid line) in which WO ₃ exceeding the saturation amount in an Ar atmosphere was previously added to molten sodium hydroxide and Comparative Example 1 (dashed line) in which no addition was made, Ar gas was added to the reaction vessel (electrolyzer) without passing through a water bath It is the figure which showed the time change of the electric current value at the time of electrolyzing with a constant voltage of 1V, supplying it to (gas phase). A constant voltage of 0.4 V while adding WO ₃ exceeding the saturation amount in an Ar atmosphere to molten sodium hydroxide in advance and supplying Ar gas through a water bath at 90 ° C. to the reaction vessel (gas phase of the electrolytic cell) Example 2A (solid line, water content of about 2 wt%) electrolyzed in Example 2B (single-dotted line, water content of about 0.2 wt%) while supplying Ar gas to the reaction vessel through a 23 ° C. water bath while supplying a constant voltage of 1 V %) And Comparative Example 2 (dashed line, water content less than about 0.2 wt%) electrolyzed at a constant voltage of 1 V while supplying Ar gas to the reaction vessel without passing through a water bath, the time change of the current value was shown. FIG.

The elements to be dissolved or recovered in the present invention are Group 5 elements and / or Group 6 elements (target elements), and specifically, W, Mo, Cr, V, Nb, and Ta. Of these, W, Ta, and Mo, which have high practical expectations, are desirable.
The substance to be dissolved or recovered containing these elements may be those containing the elements as metals or carbides, used carbide tools, various metal products, catalysts, and Examples include in-process waste generated in these manufacturing processes. However, the present invention is not limited to these, and any substance may be used as long as it is a substance containing at least one of these elements and can apply a voltage as an anode. Good.
Such a substance containing the target element may contain or contain an organic substance such as various plastics as a surface coating material or the like, or 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 subcomponent. 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 chrome nitride.

The alkali metal hydroxide and alkaline earth metal hydroxide used in the dissolution method of the present invention are an electrolyte at the time of anodization and also a solvent 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 the like, and sodium hydroxide is particularly preferably used among them.
These hydroxides may be used alone or as a mixture (mixed hydroxide), and other components and impurities may be mixed or mixed so long as anodization and solubility are not significantly reduced. May be mixed. Examples of 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. The temperature should generally be equal to or higher than the melting point, and the use temperature is determined from the solubility and diffusibility of the target element, the heat resistance of the material used, the economy, the running cost, and the like. The temperature of the melt is advantageous in that the solubility and diffusibility of the target element increase as the temperature increases, but on the other hand, it is disadvantageous in terms of the heat resistance, economics, etc. of the device material. In particular, a temperature of about 200 to 600 ° C. can be preferably 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 moisture content is less than 0.2 wt%, but the moisture content is adjusted to, for example, 1.5 to 2.0 wt% according to the present invention. Thus, electrolysis can be performed even 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 more efficient.
Furthermore, the moisture content dependency and the melting temperature dependency of the saturation solubility of the target element can be used to recover the target element. That is, after dissolving the target element in a state where the moisture content in the molten bath is increased to, for example, 1.5 to 2.0 wt%, the moisture content and / or the melting temperature is made lower than at the time of dissolution to reduce the target element. A compound (an oxoacid salt of a Group 5,6 element such as sodium tungstate) can be precipitated and recovered. At that time, an electrolytic cell with a high water content and melting temperature and a recovery tank with a low water content and melting temperature are provided, and a molten material in which the target element is dissolved by electrolysis in the electrolytic cell and the dissolved concentration of the target element is increased It is possible to recover the target element compound without interrupting the electrolysis by returning the melt of the target element's dissolved concentration to the electrolytic cell. Can be. The water content at the time of recovery or in the recovery tank is preferably 0 wt% or close to it in order to improve the efficiency of precipitation and recovery, but comprehensively determine the time required to sufficiently reduce the water content. Can be determined. A lower melting temperature at the time of recovery or in the recovery tank is desirable for improving the efficiency of precipitation and recovery.However, if the melting temperature is lowered too much, the risk of not being able to maintain the molten state increases and energy consumption increases. It can be determined by comprehensive judgment.

The water content of the molten bath is, for example, a gas supply port and a gas discharge port communicating with the atmosphere, and using an electrolytic cell containing the molten bath, water or a gas containing water vapor is stored in the electrolytic cell. It can adjust by passing in the said melt, or supplying in the gaseous phase of an electrolytic cell. The water content of the molten bath accommodated in the electrolytic bath is made substantially constant by supplying the gas at a constant flow rate per hour to the water bath and then constantly supplying the gas to the gas supply port of the electrolytic bath. can do. For example, the water content in a sodium hydroxide molten bath at 450 ° C. 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.). In the steady state at 90 ° C., it is about 2 wt%. When supplying a gas containing no water without passing through the water bath, the water content of the molten bath is less than 0.2 wt%. In addition, when such a gas is kept in a state where it is not supplied at all, whatever the moisture content before that, in the final steady state, the atmospheric or gas phase water vapor pressure in contact with the molten bath It is thought that the moisture content will correspond to.
Further, the saturated water content of the molten bath can be improved by increasing the pressure of the molten bath atmosphere or the gas phase of the molten bath, so that the control of the pressure further increases the solubility of the target element than under atmospheric pressure. be able to.
The gas is not limited to an inert gas such as Ar or the like, carbon dioxide gas, nitrogen gas, or the like, but can be an inert gas or an oxidizing gas enriched with oxygen in the air. . It is considered that oxygen in the gas contributes to the oxidation and dissolution of a part of the target element and leads to reduction of power consumption.

The apparatus used in the dissolution method of the present invention is not particularly limited, and any apparatus that has been conventionally used for anodization and has heat resistance and alkali resistance can be used as it is, and can be improved in heat resistance. It can also be used by adding. As such an apparatus, not only a batch type but also a continuous type can be used.
In general, if the voltage applied to the cathode during anodization is too high, the current efficiency of the anodization decreases and undesirable side reactions occur, and the energy consumption also increases. On the other hand, if it is too low, a sufficient reaction rate cannot be obtained. In the present invention, the water content in the molten bath is 0.2 to 5.0 wt% (the lower limit is preferably 0.5 wt% or more, more preferably 1.0 wt% or more). Accordingly, undesirable side reactions can be suppressed and current efficiency can be made relatively high.
When the dissolution is performed in a batch manner, the voltage to be applied during the treatment period may be constant. However, in order to shorten the treatment time, the voltage to be applied can be changed within a range where the dissolution treatment can be controlled. The current may be constant, but in this case, it is necessary to check the voltage and adjust the current value, processing time, supply amount of the processing substance, and the like.

In the method of the present invention, target elements such as tungsten, molybdenum, niobium, and tantalum are anodized. When tungsten or molybdenum is taken as an example, an alkali metal hydroxide is used as an ion represented by WO ₄ ²⁻ or MoO ₄ ^2−. , Alkaline earth metal hydroxides, mixed hydroxides thereof, or those containing one 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 dissolved, it is expected to be deposited on the cathode. Can do. Impurities such as Fe and Ni that do not dissolve in the melt remain on the surface of the object to be dissolved, but oxoacid salts of target elements such as Na ₂ WO ₄ and Na ₂ MoO ₄ It is efficiently and controllably dissolved in the melt without much influence. Although the detailed mechanism in that case is not necessarily clear, the oxo acid salt of the target element such as Na ₂ WO ₄ and Na ₂ MoO ₄ has a high solubility in the melt having a high water content and is also high in temperature. The diffusion rate is also high, and it is considered that the dissolution is efficiently and controllable without much influence of residual impurities.
In addition, the melt in which the target elements are dissolved and the concentrations of these elements are increased can be easily dissolved in water, and as a result, an aqueous solution of the target element oxo acid salt can be obtained. When the melt is dissolved in water, from the viewpoint of safety, the temperature should be lowered to a temperature lower than the melting point, desirably less than 100 ° C., more desirably less than 50 ° C. in advance.

In the case where the substance containing the target element to be treated of the present invention includes or contains organic substances such as various plastics as a surface coating material, etc., titanium nitride, aluminum nitride, alumina, silica, titanium carbonitride, titanium aluminum When ceramics composed of elements other than the target element, such as nitride and aluminum chrome nitride, are provided or contained as the main component or subcomponent of the surface coating material or binder, the material is previously alkali metal. It can be immersed in a melt containing one of a hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the hydroxide as a main component without energization. By such pretreatment, organic substances such as various plastics exposed on the surface can be decomposed and removed into hydrogen, CO ₂ , low molecular gas, etc., and titanium nitride, aluminum nitride, alumina, exposed on the surface, 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, subsequent anodic oxidation and dissolution of Group 5 and 6 elements is efficient. 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, the impurities derived from the organic matter in the melt obtained by dissolving the Group 5 and 6 elements The amount of impurities 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 the organic substance to be decomposed and the ceramic to be dissolved.
The melting 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 as described above. Adopted to dissolve and remove the ceramics not only as a pretreatment of the dissolution method but also in various treatment methods for recovering the Group 5 and 6 elements from the substances containing the Group 5 and 6 elements. Can do.
In such a pre-immersion process without energization, the target element is hardly dissolved when it is a metal or carbide, and is slightly dissolved when it is a nitride or oxide, but it is anodized by energization. Since the amount of dissolution is smaller than in the case, it is considered that the amount of dissolution in the subsequent anodic oxidation / dissolution process does not have a great influence.

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

(Reference Example 1; Measurement of moisture content in sodium hydroxide molten bath)
A reaction vessel (electrolyzer) having a gas supply port and a discharge port communicating with the atmosphere was prepared, and sodium hydroxide was accommodated and melted at 450 ° C. The water content in the sodium hydroxide molten bath is changed by constantly supplying the reaction vessel from the supply port to the reaction vessel after passing Ar gas having a constant flow rate per unit time at a predetermined temperature, and changing the temperature of the water bath. The rate (or water vapor 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 was considered to be 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 within 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. About 2 wt%. When Ar gas is supplied to the reaction vessel without passing through a water bath, it is clear that the moisture content in the molten sodium hydroxide is difficult to determine, but is less than 0.2 wt%.

(Example 1; Investigation 1 of influence of water content of molten sodium hydroxide on electrolysis)
The same reaction vessel (electrolyzer) and Ar gas supply equipment as used in Reference Example 1 were used, and the water bath temperature was 90 ° C. (water content in the sodium hydroxide molten bath was about 2 wt%). An uncoated tungsten alloy carbide tip (0.6 g, about 90 wt% as tungsten carbide, about 5 wt% cobalt) is placed on a Ni plate as an anode and a nickel plate as a cathode at 450 ° C. In the sodium hydroxide melted in step 1, electrolysis was performed under a constant voltage condition 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 it was a relatively low voltage of 0.4 V, it was completely dissolved in a relatively short time of about 5 hours.

(Comparative Example 1)
Electrolysis was carried out in 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 the water bath (the water content in the sodium hydroxide molten bath was less than 0.2 wt%). Went. The current efficiency was almost 100%. The result is shown by the 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.

(Assessment of the results of Investigation 1 for the effect of water content in the sodium hydroxide molten bath)
From the results of Example 1 and Comparative Example 1, by increasing the water content (water vapor partial pressure) in the sodium hydroxide molten bath, the voltage required for electrolysis can be reduced from 1 V to 0.4 V and dissolved. It was revealed that the time required is about 1/3 and efficient dissolution can be performed.

(Comparative Example 2: Investigation of influence of tungsten concentration in sodium hydroxide molten bath on electrolysis)
Electrolysis was carried out in exactly the same way as in Comparative Example 1, except that WO ₃ (NaOH: WO ₃ = 5: 1) exceeding the saturation amount in the 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 result of Comparative Example 1 is also indicated by a broken line. From this, it can be said that when the concentration of tungsten in the sodium hydroxide molten bath increases, dissolution of tungsten is hindered and electrolysis cannot be performed efficiently. 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%). The tendency that dissolution is inhibited and electrolysis cannot be efficiently performed when the tungsten concentration in the sodium molten bath increases is considered to be the same even when the water content of the sodium hydroxide molten bath is high.

(Example 2, Comparative Example 2; Investigation 2 of influence of water content in sodium hydroxide molten bath on electrolysis)
After adding WO ₃ to the sodium hydroxide molten bath before the start of electrolysis, electrolysis was performed under any of the following conditions (1) to (3).
(1) Example 2A: Water bath temperature 90 ° C. (water content of about 2 wt% in the sodium hydroxide molten bath), voltage 0.4 V, NaOH: WO ₃ = 5: 1 (exceeding saturation in Ar gas atmosphere) Add WO ₃ )
(2) Example 2B: Water bath temperature 23 ° C. (water content of about 0.2 to 0.6 wt% in sodium hydroxide molten bath), voltage 1 V, NaOH: WO ₃ = 4: 1 (saturation amount under these conditions) Add more WO ₃ )
(3) Comparative Example 2: without using a water bath (water content in the sodium hydroxide molten bath is less than 0.2 wt%), voltage 1 V, NaOH: WO ₃ = 5: 1 (exceeding the saturation amount under Ar gas atmosphere) Add WO ₃ )
The results of Examples 2A and 2B and Comparative Example 2 are shown in FIG.

(Assessment of results of Moisture Content Impact Survey 2)
The above Example 2A and Comparative Example 2 are the results under the condition that only the moisture content was changed. From these comparisons, the saturation solubility of tungsten was improved by increasing the moisture 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 moisture content was changed in a state where tungsten was saturated. Even in the saturated state of tungsten, the moisture content in the sodium hydroxide molten bath was changed. It was clarified that the current value can be expected to increase somewhat by increasing the value. In addition to Examples 2A and 2B and Comparative Example 2, the results of the same electrolysis experiment when the water bath temperature was 20 ° C. or 50 ° C. showed that the water bath temperature was 20 ° C., 50 ° C., and 90 ° C. The saturation solubility (mass% of pure W) was estimated to be 13 wt%, 26 wt%, and 40 wt% or more, respectively.

The melting / recovering method and the melting / recovering apparatus of the present invention are used for tungsten, molybdenum, niobium, tantalum, etc. from used carbide tools, various metal products, catalysts, and in-process waste produced in these manufacturing processes. These target elements can be efficiently dissolved in a melt such as an alkali metal hydroxide, and thus can be effectively used for recovery and recycling of these target elements.

Claims

In a melt containing an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or any of the above hydroxides as a main component, the Group 5 element and / or the sixth element A method for dissolving a Group 5 element and / or a Group 6 element in which a substance containing a Group element is electrolyzed to dissolve a Group 5 element and / or a Group 6 element in the melt, A dissolution method, wherein the water content is 0.2 to 5 wt%.
The water content of the melt is adjusted by passing water vapor or a gas containing water vapor through the melt or supplying it into the gas phase of an electrolytic cell containing the melt. 2. A 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. / Or a method for dissolving a Group 6 element.
A melt having an increased concentration of the Group 5 element and / or the Group 6 element obtained by the dissolution method according to any one of claims 1 to 4 is dissolved in water to dissolve the 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.
A Group 5 element and / or a Group 6 element after dissolving the Group 5 element and / or the Group 6 element in the melt using the dissolution method according to any one of claims 1 to 4. A method for recovering a Group 5 element and / or a Group 6 element, in which the compound is precipitated and recovered by lowering the saturation solubility of the compound containing the compound 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 decreased by decreasing the moisture content of the melt and / or decreasing the melting temperature.
An electrolytic cell having a melt water content of 0.2 to 5.0 wt% and a recovery tank having a low water content of the melt compared to the electrolytic cell are provided, and Group 5 elements and / or Group 6 are electrolyzed. The molten material having an increased element concentration is transferred to a recovery tank to precipitate a compound containing a Group 5 element and / or a Group 6 element, and the concentration of the Group 5 element and / or 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.
A cathode and an anode holding a substance containing a Group 5 element and / or a Group 6 element; an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the water A Group 5 element and / or a second element comprising an electrolytic cell containing a melt of any of the oxides as a main component and water content adjusting means for adjusting the water content of the melt. Group 6 element dissolution or dissolution / recovery equipment.
A cathode and an anode holding a substance containing a Group 5 element and / or a Group 6 element; an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or the water An electrolytic cell containing any one of oxides as a main component and containing a melt, an alkali metal hydroxide, an alkaline earth metal hydroxide, a mixed hydroxide thereof, or any of the above hydroxides A recovery tank containing a melt of the main component, a high moisture content adjusting means for maintaining a high moisture content of the melt contained in the electrolytic cell, and a moisture content of the melt contained in the recovery tank from the electrolytic cell. Low moisture content adjusting means for keeping low and / or melting temperature adjusting means for keeping the melting temperature of the melt contained in the recovery tank lower than the electrolytic cell, and the group 5 element and / or the group 6 element in the electrolytic cell Transfer melt with increased concentration to recovery tank And a return means for returning the melt in which the concentration of the Group 5 element and / or the Group 6 element in the recovery tank is reduced to the electrolytic cell. / Or Group 6 element dissolution / recovery equipment.