JP6362000B1 - Complete recycling of diluents in tantalum production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce metal tanta powder by reducing potassium fluorotantalate with metallic sodium. In this reduction reaction, an inorganic salt such as potassium fluoride or potassium chloride is used as a diluent. The present invention relates to a method for recovering these inorganic salts. SOLUTION: After the reduction reaction with metallic sodium is completed in the above reaction, a part of the inorganic salt calculated in advance is introduced into the reactor immediately before entering the cooling to uniformly adjust the composition of the diluent after the reaction. In addition to obtaining a metal tantalum powder of a predetermined quality, an inorganic salt is recovered from the by-produced diluent, purified, and reused. [Selection] Figure 2

Description

Detailed Description of the Invention

  The present invention relates to the recovery and reuse of fluorine compounds and chlorine compounds used as diluents during reactions in the production of high purity tantalum powder used in the electronic component industry. Conventionally, most of these compounds have not been recovered when producing tantalum, but have been landfilled as industrial waste. The present invention provides a method for producing tantalum powder that recovers all of these compounds and does not discharge industrial waste.

  Tantalum (element symbol Ta) existing in nature is usually mined together with niobium (element symbol Nb) in the form of an oxide. Both elements belong to the same genus in the periodic table of elements and have very similar properties. For this reason, in order to obtain each metal industrially, a chemical pretreatment is performed in advance to completely separate the two metals, and then each metal is purified.

The tantalum compound produced by this chemical pretreatment is K ₂ TaF ₇ in the chemical formula and is called potassium fluorotantalate. In order to produce tantalum, a method of reducing this compound with sodium (element symbol Na) is common, and this method is currently used by tantalum manufacturers all over the world. This reaction formula is a weak exothermic reaction and is as follows.
K ₂ TaF ₇ + 5Na = Ta + 2KF + 5NaF
(100) (29) (46) (30) (53)
The numerical value in () is the weight ratio when the main raw material K ₂ TaF ₇ is 100. This reduction reaction is performed in an atmosphere of argon (element symbol Ar) at a high temperature not exceeding the boiling point of sodium (= 892 ° C.) at around 800 ° C., and tantalum powder having a predetermined specific surface area is obtained.

  In the reduction reaction, tantalum powder is directly generated. The main demand for tantalum powder is for tantalum capacitors, but the electronic component industry, which is the manufacturer, demands tantalum powder having various specific surface areas depending on the product grade of each company. In order to adjust this specific surface area, the manufacturer performs a reduction reaction by mixing a diluent such as an inorganic salt with potassium fluorotantalate in the reaction step. A tantalum powder having a larger specific surface area can be obtained by increasing the diluent relative to the main raw material potassium tantalum fluorinate. Typical examples of the diluent are potassium fluoride (hereinafter abbreviated as KF) and potassium chloride (hereinafter abbreviated as KCL), and these inorganic salts are usually used in combination. The reason and combination of these inorganic salts will be explained in the next chapter.

This reduction reaction is performed in a batch mode. After completion of the reaction, the reactor is cooled, the upper lid is opened, and the contents are taken out. At this time, tantalum having a high specific gravity is accumulated at the bottom of the reactor and the diluent having a low specific gravity is clearly separated and accumulated at the top thereof. Therefore, if the reactor is turned over, both can be easily separated and taken out. Details of these reaction processes are published in the following materials.
Patent Document JP-A-2015-078439
The above patent was filed from a manufacturer of tantalum powder. Usually, there are few examples where details of the technical content including such in-house know-how are disclosed as patents, but in line with the recent establishment of TPP (= Pacific Rim Economic Partnership Agreement) It is guessed. This patent has been assessed.

  All inorganic salts in the diluent separated from the reactor are soluble in water. Fluorides in inorganic salts dissolved in water are harmful and have the property of depleting plants in particular and are sent to the wastewater treatment process because they cannot be discarded as they are. Here, the fluorine content is reacted with lime or calcium chloride to fix and recover the soluble fluorine content as calcium fluoride insoluble in water.

  The amount of calcium fluoride recovered varies depending on the quality of tantalum to be obtained, but the water content is several times to sometimes more than 10 times the weight of the product with water, and this processing method is an extremely important task in the production of tantalum. Yes. These calcium fluorides are originally intended to be industrially reused as a raw material for fluorine, but calcium fluoride recovered from the tantalum production process is used in addition to various metal components such as iron, nickel and chromium. Contains a large amount of impurities such as sulfate ions. For this reason, it is difficult to increase its purity, and export to foreign countries such as Southeast Asia is strictly prohibited by the Basel Convention from the viewpoint of environmental protection. As a result, most of the recovered calcium fluoride was landfilled as industrial waste at a domestic management-type treatment plant.

  It is extremely unlikely that an industry that discharges a large amount of waste in this way can continue in the future in the country where zero emission is spreading. Furthermore, recently, with the miniaturization of tantalum capacitors in the electronic component industry, the demand for tantalum powder having a large specific surface area tends to increase. In order to produce a tantalum powder having a large specific surface area, it is necessary to use a larger amount of diluent than in the prior art when producing tantalum, and the amount of industrial waste discharged from the tantalum powder manufacturing industry tends to increase in the future. For this reason, countermeasures have been considered as an important issue in the domestic tantalum manufacturing industry. The countermeasures examined are the following three types.

  The first measure is a method that does not increase the diluent used during reduction. As described above, it is necessary to increase the dilution ratio of the diluent with respect to the main raw material in order to increase the specific surface area of the tantalum powder. In the conventional reaction, first, a main raw material and a diluent are charged into a reactor and melted at a high temperature, and then sodium is added in a liquid state continuously or intermittently at a predetermined temperature to complete a reduction reaction. On the other hand, in the new reduction method, first, only the diluent is charged into the reactor, and the main raw material divided into several parts is charged in the melted state and reduced with sodium. This operation is repeated to finally reduce all the predetermined amount of the main raw material. This is because, if this division ratio is increased, the same result as the reaction in which the dilution factor is increased can be obtained.

This improvement method is also described as an example in the patent document described in the text [0005]. However, with this improved method, the amount of diluent used can be reduced, but industrial waste cannot be reduced to zero. For this reason, the next improved measure is a measure to repeatedly use the diluent. The related technology is disclosed as the following patent. Patent Documents 1, 2, and 3 are applications from the same tantalum powder manufacturing company.
JP 2006-002241 A JP 2010-168650 A JP 05-203368 A JP 2000-060862 A

  Patent Documents 1, 2 and 3 do not discard all of the diluent by a single use, but only a part of the diluent is extracted from the reactor in accordance with the calculation formula so as to achieve the target composition, A method for additionally charging a new diluent using a charging machine is disclosed. A similar method has already been practiced in the iron and steel industry blast furnaces for the input of raw iron ore and coke, and for the extraction of generated pig iron and slag. The size of the reactor of tantalum powder is as small as 1/1000 in volume and metallic compared to that of a blast furnace, and the manufacture of related equipment is easy. Furthermore, in recent years, there has been a remarkable progress in automatic weighing scales called load cells, and weighing errors can be measured with an accuracy of 1 / 1,000 or less. When these techniques are combined, there is no technical problem in extracting the diluent and adding it in the molten state. In addition, Patent Documents 1 and 2 have been subsequently rejected because the technology is already known.

  Patent Document 1 describes a method for accurately extracting a reaction product from a lower part of a reactor through a dedicated valve. Patent Document 2 describes a method of extracting using a siphon instead of this valve. Further, Patent Document 3 describes a method of accurately charging a solid material using a load cell into a closed container such as a tantalum reactor. A major advantage of this technology is a significant improvement in tantalum production efficiency. That is, according to the present invention, it is possible to dedicate the reaction while maintaining the reactor at a high temperature, and it is possible to perform several batches, for example, about 10 batches per day using one reactor.

  On the other hand, in conventional batch reactors, it takes a long time, for example, 12 hours or more, to raise and cool the reactor, so that one batch per day is the limit. Disadvantages of Patent Documents 1 and 2 still require treatment of the diluent extracted from the reactor, but this quantity is in combination with the improvement measures described in [0009] compared to the amount of conventional industrial waste generated. Can be greatly reduced, for example, about 1/10 or less.

  Patent Document 4 presents a completely different improvement plan from Patent Documents 1 and 2. In this invention, the entire amount of diluent recovered from the reactor is dissolved in water, and then crystallized using a recrystallization method and dried, and the recovered diluent is used again for the reduction reaction of tantalum powder. . The biggest problem with this proposal is how to recover a mixed salt having a uniform composition from mixed salts having different compositions obtained by the reaction.

To solve this problem, pay attention to the solubility of the three components KF, KCL and NaF in the mixed salt. If the ratio of KF: KCL, which is easy to water, is constant, dissolve the mixed salt . We have found that a mixed salt of KF and KCL having a constant ratio can always be recovered from the aqueous solution, and we have proposed improvement measures using this.

  It has already been described in [0004] of the main text that the ratio of the diluent to the main raw material is changed for each reaction grade. As a result, when the reaction is carried out with a diluent having the same composition for each grade, the ratio of KF: KCL differs from the ratio before the reaction because KF is by-produced during the reaction. For this reason, in Patent Document 4, the composition of the diluent, which is one of the important items of the reducing conditions, that is, the mixing ratio of KF: KCL is calculated based on the calculation formula calculated from the material balance of the diluent after the reaction. Proposals are made for changing grades at each stage.

  The method of recovering the diluent of Patent Document 4 is a very universal operation in chemical factories such as water dissolution, recrystallization, solid-liquid separation, and drying, and the operation temperature is 100 ° C. or lower in all steps, and the operation pressure is safe at around normal pressure. Process. On the other hand, one of the most important reaction conditions is that “diluent composition must be adjusted to each reaction grade and individually adjusted before reaction”. Automatic adjustment of diluent composition is not a technically difficult operation if individual load cells are used for each diluent. However, if this process is actually introduced, this process change is not easy. In particular, this method conversion is very difficult among companies that have acquired “ISO-9000”.

  “ISO-9000” is an international quality control standard set by the International Organization for Standardization, and is related to the quality control system of factories and businesses. It is a system for inspecting quality control and assurance systems. Operators are obliged to receive regular inspections of third parties for such changes. At present, most electronic product manufacturers have already been certified as “ISO-9000”.

  If the tantalum powder manufacturer changes the manufacturing method to `` change the composition ratio of the diluent before the reaction '' like this time, it is considered a major process change and the third organization established the manufacturing method for quality control. And must be inspected for maintenance. The influence also affects downstream electronic component manufacturers and electronic product manufacturers. As long as this result is not so urgent, there will be no incentive for the tantalum powder manufacturer to change the process. In addition, if a proposal is established in-house as in this case, the possibility of a new process change is almost zero. On the other hand, strict regulations on quality assurance are an example of the impediment to changes to environmental conservation.

First, the selection of the diluent used when the main raw material potassium fluorotantalate is reduced with sodium will be described. In this reaction, tantalum is obtained in a powder form at a reaction temperature of about 800 ° C. as shown in the following formula. Diluents have the effect of increasing the specific surface area of the tantalum powder almost proportionally when the ratio to the main raw material is increased, and it is still widely used as a means for adjusting the specific surface area most stably.
The reaction formula is K ₂ TaF ₇ + 5Na = Ta + 2KF + 5NaF, and KF and NaF are by-produced in addition to Ta after the reaction.

  The diluent used in this reaction is a mixed salt of KF and KCL. After the reaction, NaF due to the reaction is added to the diluent, and three kinds of mixed salts are formed. The reason for selecting KF and KCL as diluents is that “the melting point of this mixed salt is low”. When the melting point is high, the energy increases as the temperature rises and the material cost increases as the equipment used increases. In order to avoid this, a combination of mixed salts having a melting point as low as possible is selected.

  The change in melting point when the component ratio of the above three kinds of mixed salts is changed is shown in FIG. Source is Russian literature. In the figure, the vertices of triangles indicate the melting points at which each salt is independent, and the melting point of the mixed salt can be read from the curve in the figure. The component composition of the mixed salt is indicated by the length of a perpendicular drawn from one point in the figure to the base of the triangle. The melting point of the diluent before the reaction is shown on a straight line connecting KF and KCL, but the component composition with the lowest melting point is around KF: KCL = 40: 60, and the temperature is about 610 ° C. The composition ratio of the diluent used in the actual reaction adopts a ratio in the vicinity of this, but in most cases, the composition is 50:50 (= point A in FIG. 1) of the composition that is the simplest and close to the melting point. . This component ratio is also used in the patent documents described in [0005].

  When the reduction reaction is started, the diluent components in the reactor proceed on a straight line from point A to point B in the figure. Point B is the stoichiometric ratio of KF and NaF generated in the previous reduction reaction. The composition ratio of the diluent at the end of the reaction is indicated by point C in the figure. The smaller the dilution ratio for the main raw material, the closer the point C becomes to the B point, and vice versa. What is characteristic here is that when the magnification of the diluent with respect to the main raw material is changed, the point C moves on the straight line and does not stay at the same point. That is, if the dilution factor of the diluent is changed in order to obtain a tantalum powder having a target specific surface area, the component composition of the diluent at the end of the reaction will be different before and after the reaction.

  In the previous Patent Document 4, paying attention to the component composition of the diluent after the reaction, if the composition ratio of potassium salt in the diluent, that is, KF: KCL is the same for each reaction batch, recrystallization is performed using water. In this case, it was found that the composition ratios of KF: KCL in the recovered salt obtained were all the same. In order to realize this, it was suggested that the blending ratio of the diluent before the reaction was calculated by a formula obtained from the material balance of the diluent and blended for each batch. However, it has already been described that this patent does not break through the ISO = 9000 barrier and is very unlikely to be practiced at present.

  In order to make use of the findings of the previous paragraph, the KF: KCL ratio for each reaction batch becomes the same at the end of the reaction, not the means of ISO = 9000, that is, the means of “changing important reaction conditions involved in the reaction” Finding the means. This is the first issue.

  The second problem is related to the recovery of the diluent. Although there is no claim in Patent Document 4, in the specification of the patent, “in determining the amount of water in dissolving the diluent, the amount of water that does not significantly exceed the amount of water required for dissolving the target potassium salt” The amount of water is also exemplified in the examples. However, the amount of water shown in the examples is not sufficient to dissolve the total amount of the target potassium salt. If this amount of water is significantly increased, NaF in the solution is dissolved and mixed, causing a decrease in the purity of the diluent. Therefore, this water volume setting is important and must be an accurate recommendation based on academic evidence.

  Further, the patent discloses a recovery of potassium salt from a diluent, but does not describe any residue after recovering the potassium salt. This residue contains a large amount of NaF. If this recovery method is not clarified, it cannot be said that "the complete recycling of the diluent during the production of tantalum". Clearly indicate the dissolution conditions for potassium salts. Specify the method for recovering NaF in the residue. This is the second problem.

  First, means for making the ratio of KF: KCL in the diluent after the reaction the same for all lots will be described. In the method disclosed in Patent Document 4, a method was selected in which the mixing ratio of both was changed according to a predetermined calculation formula for each rod at the stage of adjusting the diluent before the reaction. On the other hand, the method proposed this time is different from the above patent and is a simple and safe measure. Of course, this is a measure that does not correspond to a significant change in the reaction conditions defined in ISO-9000.

  In the reduction reaction of tantalum production, as described above, the main raw material and diluent are charged, the temperature is raised using an electric furnace in an argon atmosphere, the molten state is made uniform at around 800 ° C, and metallic sodium is added continuously or intermittently. The main raw material is reduced. Further, it is kept at a constant temperature for several hours (= usually about 4 hours) and then cooled to open the reactor and take out the contents. That is, the reaction process proceeds in the order of temperature rise, reaction, holding, and cooling.

  During this time, the tantalum particles, in a qualitative expression, become tantalum powder having a target specific surface area through generation, growth and aggregation of tantalum crystal nuclei. The steps for determining the properties of the powder are all completed in this procedure in the post-reaction holding step. The reaction product is a diluent that is a mixed salt of metal tantalum and inorganic salt, but there is a large difference in specific gravity between them, and after cooling, the two layers separate and solidify, so the reactor is opened. Remove both layers and separate.

  In this new recommendation, all of this holding is completed, and KCL, which has been weighed in advance immediately before entering cooling, is charged into the reactor in a powder state via a dedicated charging device. It is extremely important that the time when KCL is added is “executed when all the reactions are completed”. The weight of KCL to be charged is a weight commensurate with KF by-produced by reduction of the main raw material, and the ratio of KF: KCL in the diluent in the reactor after the charging is the KF: KCL ratio of the diluent charged before the reaction. The weight is the same. At this time, the amount of KCL input does not change if the total amount does not change regardless of whether the main raw material input method is batch input or split input.

  The temperature in the reactor is lowered by about several degrees due to the KCL melting heat due to the introduction of KCL, but after a few minutes, it returns to the original cooling line. At this time, the reactor is still in a sufficiently molten state, and the charged KCL is thoroughly mixed with the diluent in the reactor by the stirrer. After this stirring is continued for about 1 hour, the heater is turned off and the stirrer is stopped and mechanically pulled up to the top of the reactor. Thereafter, the cooling of the reactor proceeds gradually. This operation is illustrated in the next example.

上表から明らかのように反応前後の希釈剤中の比率はＫＦ：ＫＣＬ＝１．０：１．０で変化はない。更に追加して投入するＫＣＬ量は主原料の重量が一定なら、どの反応ロットでも常に一定（＝実施例１では３０ｋｇ）である。もし反応前の希釈剤の調節比が上表と異なる場合は追加投入するＫＣＬ量は上表の値にその希釈剤の調整比を乗じた重量とすれば良い。The following reduction reaction (= advanced class with specific surface area) is taken as an example.
Main raw material Potassium fluorotantalate 100kg
Diluent KF 300kg + KCL 300kg
This is charged into a reactor to obtain a uniform molten state, and then reduced with sodium metal. After completion of the reaction, add the pre-calculated KCL to the reactor and mix well.
The weight of the diluent before and after the reaction is as follows. (Unit is kg)

As is clear from the above table, the ratio in the diluent before and after the reaction is KF: KCL = 1.0: 1.0 and there is no change. Further, the amount of KCL added additionally is always constant (= 30 kg in Example 1) as long as the weight of the main raw material is constant. If the adjustment ratio of the diluent before the reaction is different from the above table, the additional amount of KCL to be added may be a weight obtained by multiplying the value in the above table by the adjustment ratio of the diluent.

上表から明らかのようにこの反応でも反応前後の希釈剤中の比率はＫＦ：ＫＣＬ＝１．０：１．０で変化はない。更に追加投入するＫＣＬム量は主原料の重量が一定なら、この反応でも一定量（＝実施例１と同じ３０ｋｇ）である。As an example, the following reduction reaction (= intermediate class with specific surface area) is taken up.
Main raw material Potassium fluorotantalate 100kg
Diluent KF 200kg + KCL 200kg
The weight of the diluent before and after the reaction is as follows. (Unit is kg)

As is clear from the above table, the ratio in the diluent before and after the reaction is KF: KCL = 1.0: 1.0 and there is no change in this reaction. Furthermore, if the weight of the main raw material is constant, the amount of KCL added additionally is also constant in this reaction (= 30 kg as in Example 1).

This fact is very useful when the manufacturer decides on a reaction manual. Usually, when this reaction condition is defined, it proceeds by the following procedure.
(1) Decide the quantity of the main raw material potassium fluorotantalate. ・ Normally, all lots are constant (2) Select the diluent ... Normally, the mixed salt of KF and KCL (3) Determine the mixing ratio of the diluent ... Normally KF: KCL = 50: 50
(4) Determining the dilution factor for the main raw material ... Variable depending on product grade This procedure is the same for most manufacturers. Each manufacturer has its own reaction temperature, main raw material charging method (= batch or split), metallic sodium charging method (= continuous or intermittent), stirring method, and addition of third substances such as nitrogen compounds and sulfur The company has established its own technology as its own know-how by separately determining methods. The embodiment disclosed in the previous [0005] is one example.

According to this procedure, as shown in Examples 1 and 2 above, if the weight of the main raw material is constant, the reaction can be performed for any reaction lot in order to make the composition ratio of the diluent after the reaction constant. It is only necessary to add an additional KCL of the same weight (= 30 kg in the embodiment) when it is completely finished. If this operation is compared with the operation defined in the above Patent Document 4, the difference is clear due to the simplicity of the operation. The above improvement means is defined as claim 1.

  Here, the patentability between the present invention and Patent Document 4 is organized again, and the difference is clarified. Both patents are filed by the same inventor. The principle on which the invention is based is that "when a mixed salt composed of two compounds is dissolved in water and crystals are obtained from the solution using a crystallization operation, the composition ratio of the mixed salt in the solution is constant. It is based on the very universal chemical principle that the composition of the resulting crystals is always constant.

  On the other hand, there is a clear difference in patentability between the two in terms of means for achieving the goal. Patent Document 4 proposes means for changing the composition of the diluent, which is one of the reaction conditions, for each product grade before the reaction in order to achieve this goal. This is clearly a significant change in reaction conditions. In contrast, the present invention adjusts the composition of the diluent by adding a certain amount of inorganic salt specified in the diluent in a process where the reaction is completed and tantalum and diluent are separated into two layers by gravity sedimentation. is there. This operation does not affect the quality of the product tantalum.

  Furthermore, there is a big difference in the difficulty of operation. In the embodiment of the present invention described in [0033], if the method of Patent Document 4 is used in order to make the composition ratio of the potassium salt in the diluent after the reaction constant, the adjustment of the diluent before the reaction is performed for all product grades. The ratio must be calculated separately and accurately weighed into the reactor. If this operation is mistaken, all of the tantalum powder after the reaction becomes a non-conforming product. On the other hand, in the present invention, even if the addition operation of KCL is wrong, the quality of the tantalum powder is not affected at all. Only the composition ratio of the produced diluent changes. The price of tantalum is about 100 times higher than that of the diluent. The difference between the two patents is obvious from the standpoint of preventing "risk of generating non-standard tantalum products".

  A small charging hopper is required to charge a certain amount of KCL into the reactor after completion of the reaction. This charging hopper is attached to the top of the reactor and is connected to the reactor through a rotary valve. KCL, which has been dried in advance using an electric furnace or the like, is placed in this charging hopper and charged into the reactor at a predetermined time. The inside of the charging hopper is kept in an argon atmosphere to prevent moisture and air from entering. Normally, the hopper can be small because it is used only once per batch. However, it is possible to increase the size of the hopper and combine it with a load cell so as to cut out and use each time. The arrangement of the equipment around this reactor is shown in FIG.

  Next, an operation for dissolving the diluent recovered from the reactor in water will be described. In the reduction reaction using metallic sodium, a small amount of sodium is added to the main raw material in order to complete the reaction. As a result, when the diluent after the reaction is dissolved in water, the liquidity becomes alkaline. The reason why the liquid property is kept alkaline is to make impurities Fe, Ni, Cr, etc. in the diluent into a water-insoluble hydroxide salt. A method of selectively dissolving only the potassium salt from the diluent recovered after the reaction under the alkaline solution, that is, three kinds of inorganic salts (= mixed salt of KF, KCL, and NaF) will be described.

  The solubility in the case where these three kinds of inorganic salts are dissolved in water alone is collectively shown in [FIG. 3] (= Source is Chemical Handbook). From this figure, it can be seen that the solubility of NaF is extremely smaller than the solubility of KF and KCL, and only about 5 g is dissolved in 100 g of water at room temperature. If a large amount of water, for example, 20 times or more by weight, is added to the mixed salt of KF and KCL containing NaF, these salts will naturally be dissolved in water.

  When the amount of water is gradually reduced during the dissolution, a part of the mixed salt is not dissolved but remains as a dissolved residue. When the components of the solution and the residue are analyzed using atomic absorption spectroscopy or the like, it can be confirmed that almost all of the potassium salt is present in the solution and NaF is present in the residue. Furthermore, although it is a very small amount, it can also be confirmed that a part of NaF is dissolved in the solution. From this fact, it can be understood that the mixed salt recovered from the reaction process of tantalum production can be dissolved in two groups, that is, a potassium salt group and a sodium salt group, depending on dissolution conditions.

  In general, when two inorganic salts having the same anion soluble in water are dissolved in water, the amount of water required to make a saturated solution of the inorganic salt at the water temperature determined from the solubility of each inorganic salt is obtained. be able to. This amount of water is referred to as the theoretical dissolved water amount in the present invention. At this time, if two kinds of inorganic salts are dissolved in water with an amount of water exceeding the theoretically dissolved amount of the more soluble inorganic salt, the two salts interfere with each other upon dissolution. Of course, the inorganic salt having a high solubility is dissolved first, and then a part of the inorganic salt having a low solubility is dissolved, but the latter has a lower solubility than when it is dissolved alone. This phenomenon is called the law of mass action Law of Mass Action. If this principle is utilized, a high-purity inorganic salt can be recovered from the mixed salt by selecting an appropriate amount of water in the dissolving operation.

  Next, when the mixed salt produced as a by-product in the reaction step is dissolved with water, the most appropriate amount of water for dissolution is examined based on this rule. From here, it was examined on the desk. As a precondition for the study, an allowable target value of NaF mixed in the potassium salt recovered from the diluent after the reaction was determined. There is a description from the example of Patent Document 4 that “the quality of tantalum obtained from the reaction is the same as that of the conventional product if NaF in the recovered diluent is 1% or less”. Based on this description, the allowable limit amount of NaF in the recovered potassium salt was determined to be 1.0% by weight or less.

  In order to achieve this target value, the amount of water required to achieve the target value was calculated in the desktop calculation for the mixed salt of two components of KF and NaF. This calculation was performed according to the following procedure. First, it was assumed that KF dissolved in water was completely ionized, and the KF solubility for each concentration was calculated by changing the dilution factor. Next, the solubility product of NaF alone was calculated from the solubility of NaF, and the solubility of NaF under a solution in which the above KF was already dissolved was determined. The saturated solubilities of KF and NaF used in the calculations are 137 g / 100 g water and 5 g / 100 g water, respectively.

  In an aqueous solution in which KF and NaF coexist, NaF decreases the amount of dissolution as the concentration of KF increases according to the law of mass action. The amount of dissolution is calculated with solutions having various KF concentrations, and if the mixed salt is dissolved in a water amount that is four times or less the theoretical dissolved water amount of KF in the calculation, NaF is dissolved in water alone compared to when it is dissolved alone in water. The result that the solubility was suppressed to 1/5 was obtained. The solubility of NaF finally calculated was 1.190 mol / L alone, and 0.240 mol / L under the above KF solution. The ratio of these two values is 5: 1.

  That is, the solubility of NaF in water is about 5.0% by weight alone at around room temperature, but in a KF solution diluted four times with respect to the theoretical amount of dissolved water, it is 1/5, that is, less than 1.0% by weight. It has been found that it is reduced to 2%. If the dilution rate is lowered, the amount of NaF mixed in is further reduced, so the above magnification (= 4 times) was set as the upper limit of dilution. The above calculation was performed with two components, KF and NaF. However, KCL is added to the diluent after the actual reaction. Therefore, when dissolving the diluent, instead of KF, KF and KCL potassium salts are theoretically dissolved. What is necessary is just to calculate the amount of water and dissolve it with the amount of water of the above dilution ratio.

  In the dissolution operation, the diluent obtained after the reaction is taken out from the reactor as a white or bluish white solid rock mass, and this is made into fine particles using a crusher and dissolved in hot water around 50 ° C. To do. The dissolution time can be shortened by increasing the amount of water in the dissolution operation, but the water must be evaporated in the crystallization operation, so the optimal magnification is selected from the above dilution factor range in consideration of the balance between the two operations. To do. The above dissolution conditions are set as claim 2.

  Next, after the potassium salt was recovered, the recovery of NaF contained in the remaining residue was examined. NaF is sparingly soluble in water and is about 4% at room temperature water, and its value hardly changes even at a high temperature of about 5%. Therefore, the amount of water necessary for dissolving this residue was determined to be equal to or greater than the theoretical amount of dissolved water. As the amount of water increases at the time of dissolution, the energy cost used in the subsequent crystallization process increases. Therefore, in the actual dissolution operation, the amount of water close to the lower limit value is selected within the above specified range. This dissolution condition was added to claim 2.

  The purification method of NaF is a recrystallization method using water as a solvent. NaF obtained by the recrystallization method is dried and can be reused as a raw material for anti-cavities and the like. The last residue of this recrystallization process is a small amount of fine tantalum powder or a heavy metal hydroxide insoluble in water. These are dehydrated and dried, and recycled to a process for producing potassium tantalate fluoride from ores containing tantalum. The residue after recovering tantalum is treated with ore slag. The series of operations described above enables “complete recycling of the diluent in tantalum production”. The outline of the operation procedure from the diluent produced as a by-product in this tantalum reduction reaction to the recovery of various inorganic salts is shown in FIG.

  The potassium salt recovered by the production method proposed in the present invention is a mixed salt of KF and KCL. This mixed salt has a constant composition and high purity, but has no use other than the diluent used in the production of tantalum. That is, the present invention is an invention in a very limited field that improves part of the tantalum production process. Although NaF recovered in the present invention is highly pure, it is an original manufacturing method of recovering from the tantalum manufacturing process, and there is no example in the world that studied the same manufacturing method in the past. Therefore, it is considered that these salt recovery techniques shown in the present invention are sufficiently patentable in their production methods and applications. This application is defined as claim 3.

Effect of the invention

  The mixed salt by-produced in the tantalum reduction process contains three kinds of inorganic salts, KF, KCL, and NaF. If the above solution is utilized, all these inorganic salts are recovered by recrystallization using water, and in the first stage, KF and KCL are recovered as a mixed salt in which the ratio of both is a constant ratio, and the second stage. Thus, it becomes possible to recover NaF as a single salt with high purity.

  The equipment necessary for carrying out the present invention is only a small charging hopper for KCL which is additionally charged into an existing reactor as already described in the present specification [0040]. The remaining problem in carrying out the invention is a series of patents already published by manufacturers of tantalum powders, namely, “improving measures by partial extraction and replenishment of diluent via the reactor” (= (Abbreviated to law).

  The biggest advantage of the alternative method is the overwhelming improvement in production efficiency. Usually, the reduction reaction of tantalum is carried out at a high temperature of about 800 ° C., but it takes a long time to raise and cool the reactor, and at most one batch per day is limited in one reactor. On the other hand, in another method, the reactor is used only for the reaction time (usually about 2 hours), so even if taking out the molten salt and taking the replenishment time into consideration, about 10 batches per day with one reactor. It is fully possible to carry out the reaction. It is also expected that the energy associated with the temperature rise and cooling of the reactor will be greatly reduced. But there is great concern about this alternative.

  It is a concern that “the concentration of impurities in the diluent does not increase with the reaction”. It is well known that high-purity pig iron is produced in the iron and steel industry blast furnaces as a result of most of the impurities in the iron ore and auxiliary materials being transferred into the slag. If a similar phenomenon occurs in the tantalum reactor, impurities contained in the main raw material, auxiliary raw material, and equipment used, for example, part of heavy metals such as Fe, Ni, Cr, etc. migrate into the diluent, and in turn pull tantalum. Move in equilibrium.

  These impurities greatly deteriorate the electrical characteristics of the tantalum capacitor. The previous alternative does not disclose any description of protective measures against this contamination. In another method, the criterion for determining the extraction amount and replenishment amount of the diluent is the constituent ratio of the inorganic salt in the diluent. The degree of accumulation of the above impurities varies greatly depending on the purity of the main raw material and auxiliary raw material used in the reaction and the material of the equipment. If high-grade materials such as high-purity raw materials or Inconel are used, the accumulation of impurities is naturally suppressed. Therefore, in the case of adopting another method, it is indispensable to make a prior examination in accordance with the conditions on the user side for this impurity contamination.

  Furthermore, in another method, a part of the extracted diluent must be treated as industrial waste, which is insufficient for the goal of “complete recycling of the diluent accompanying tantalum production”. In contrast, the present invention proposes a means for generating no industrial waste in addition to the advantage of recovering the diluent with high purity. The present invention makes use of these advantages and contributes to the reduction of industrial waste associated with tantalum production. This is the best mode for carrying out the invention.

  Regarding the reduction of industrial waste associated with tantalum production, measures have already been demonstrated by specialized manufacturers in Japan, and have been established as measures to improve the same target. On the other hand, looking at the current situation on a global scale, diluents still by-produced in China and Southeast Asian countries, which are major manufacturers of tantalum powder, are disposed of as industrial waste. If this industrial waste comes into contact with highly acidic waste, hydrofluoric acid is generated from calcium fluoride in the industrial waste, and there is a danger of causing serious pollution that depletes plants. The production of tantalum powder will continue in the global region. Response across borders is required.

  The present invention provides an extremely simple production method of “all the diluent produced as a by-product in the reaction is recovered with high purity by adding a part of the diluent in the reaction step of tantalum production”. . By introducing this production method, the amount of industrial waste generated in the production of tantalum powder is reduced, and it is highly possible to contribute to the conservation of the global environment.

  It is a phase diagram which shows melting | fusing point of the mixed salt of KF, KCL, and NaF.   It is the schematic which shows the structure of the apparatus of this invention.   It is a figure which shows the solubility to water of KF, KCL, and NaF alone.   It is the schematic which shows the operation procedure of this invention.

DESCRIPTION OF SYMBOLS 1 Reactor 2 Reactor 3 Heater 4 Sodium introduction valve 5 Argon filling valve 6 Sodium condenser 7 Stirrer 8 Potassium chloride introduction hopper 9 Potassium chloride introduction valve 10 Pressure regulator

Claims (3)

In the reduction reaction in which potassium fluorinated tantalate is reduced with sodium to obtain tantalum in powder form, a mixed salt of potassium fluoride and potassium chloride in a predetermined mixing ratio as a reaction diluent to adjust the specific surface area of tantalum powder In the production method used in the above, the amount of potassium chloride corresponding to the amount of potassium fluoride produced as a by-product in the reduction reaction is added to the reactor immediately before the reduction reaction with sodium is completed and the cooling step is started, thereby A method for producing tantalum powder, characterized in that the mixing ratio of potassium and potassium chloride is the same as that previously determined before the reaction. After separation of the diluent removed from the cooled reactor tantalum diluent obtained by the reduction reaction according to claim 1 of tantalum, a two-stage dissolution step in the dissolution step of dissolving in water, the first In one stage, the solution is kept alkaline, and the amount of water required for dissolution calculated from the saturated solubility of potassium fluoride and potassium chloride contained in the diluent after reaction is in the range of 1 to 4 times the amount of water required for dissolution. In the second stage, the entire amount from the dissolution residue in the first stage is regarded as sodium fluoride, and the amount of water required for dissolution calculated from the saturation solubility of the amount of sodium fluoride is the same A method for producing tantalum powder, characterized by dissolving in the above amount of water. As a diluent in a reduction reaction in which potassium fluoride tantalate is reduced with sodium fluoride, and the mixed salt of potassium fluoride and potassium chloride obtained by recovering from the first stage of the dissolution process according to claim 2 is obtained. A method for producing tantalum powder, characterized in that sodium fluoride obtained by reuse and recovery from the second stage is reused as a product.

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