Method for producing sodium tungstate

Abstract

To provide a production method which can obtain a sodium tungstate aqueous solution having little niobium from a tungsten raw material containing niobium.SOLUTION: A method for producing a sodium tungstate that heats and melts a tungsten raw material together with a sodium salt raw material, and obtains a molten treated product containing a sodium tungstate as a main component, which makes at least one ion raw material of a metallic iron, and an iron sulfate (ferrous sulfate and ferric sulfate) coexist the sodium salt raw material, and thereby immobilizes the niobium of the tungsten raw material as a non-soluble solid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a production method capable of obtaining an aqueous sodium tungstate solution with less niobium from a tungsten raw material containing niobium.

Background Art

[0002] In recent years, tungsten has been used not only as a cemented carbide material for cutting tools, but also as various materials such as electrode materials, wiring materials, and tungsten catalysts, and its demand has been increasing year by year. However, the resources of tungsten raw materials are limited, and in order to ensure its stable supply, it is required to recover tungsten from tungsten scrap and use it effectively.

[0003] As a method for recovering tungsten from tungsten scrap containing tungsten carbide or metallic tungsten, an alkali agent containing sodium such as sodium hydroxide or sodium sulfate is added to the tungsten scrap and heated for reaction to convert the tungsten in the scrap into sodium tungstate, and this melt-treated product is dissolved in water to recover it as an aqueous sodium tungstate solution. The recovered aqueous sodium tungstate solution is purified through various purification steps into ammonium paratungstate, tungsten oxide, metallic tungsten, and tungsten carbide, and then reused.

[0004] Methods such as heating and oxidizing tungsten scrap together with a molten salt containing sodium sulfate to obtain sodium tungstate or an aqueous sodium tungstate solution are known (Patent Documents 1 to 3). For example, Patent Document 1 describes a method for oxidizing tungsten using a molten salt composed of 60 to 90% by weight of NaOH and 10 to 40% by weight of Na 2 SO 4 : 10 to 40% by weight.

[0005] Further, Patent Document 2 discloses that a raw material containing tungsten as a sub-component is composed of 60 to 95% by mass of NaOH and Na 2 SO4 : It is described that a heating reaction is carried out together with a molten salt solution containing 5 to 40% by mass, the produced molten liquid decomposition product is dissolved in water, and an aqueous suspension containing a solution composed of a mixture of a sodium compound and an alkali metalate containing tungsten or the like, a solid metal phase composed of a metal group such as Co, and a solid phase composed of a hydroxide or oxide hydrate such as Al is obtained. It is described that the solution (sodium tungstate aqueous solution) composed of the mixture of the sodium compound and the alkali metalate is separated by filtration.

[0006] Further, Patent Document 3 describes a method of reacting cemented carbide scraps containing tungsten and cobalt with a molten salt added with a metal oxide containing sodium sulfate to obtain sodium tungstate. In this method, an oxide containing iron is used as the metal oxide, and this is added in an amount of 10% by weight or more and less than 30% by weight of the cemented carbide scraps, and sodium sulfate is added in an amount of 70% by weight or more and 100% by weight or less of the cemented carbide scraps.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] The melting treatment methods described in Patent Documents 1 to 3 are highly reactive and efficient as a method that simultaneously causes oxidation of tungsten and conversion to soluble salts. On the other hand, since this method is very highly reactive, trace elements other than tungsten in tungsten scraps and elements in additives also cause secondary reactions, and there is also a problem that the concentration of elements other than tungsten and the impurity concentration in the aqueous sodium tungstate solution, which is the recovered product after melting treatment, are very likely to increase.

[0009] For example, when using a reagent containing sulfur such as sodium sulfate, in a state where oxygen is sufficiently present such as in an air atmosphere, tungsten carbide reacts with sodium sulfate to form sodium tungstate. On the other hand, when the amount of sodium sulfate added is excessive, sodium sulfide (Na 2 S) is generated in large quantities as a secondary product in the melt. When such a melt treatment product containing a large amount of Na 2 S is dissolved in water, it becomes an aqueous sodium tungstate solution in which a large amount of sulfide ions (S 2- ), which are impurities, are dissolved.

[0010] Also, for example, tungsten scraps may contain titanium (Ti), niobium (Nb), tantalum (Ta), etc. as additives for cutting tools and coating materials in addition to tungsten. These elements easily react with alkalis and, through an oxidation reaction, form soluble sodium titanate (Na 2 Ti 5 O 11 ), sodium niobate (Na 3 NbO 4 ), sodium tantalate (Na 3 TaO 4 ), etc. When a melt treatment product containing these compounds is dissolved in water, titanate ions (HTiO 3 - ), niobate ions (NbO 3 - ), tantalate ions (TaO 3 -) will turn into an aqueous sodium tungstate solution with a large amount of dissolved . In particular, niobium is the most soluble, so there was a problem that it would turn into an aqueous sodium tungstate solution with a lot of impurities.

[0011] The methods of Patent Documents 1 and 2 do not sufficiently address the influence of such sulfide ions. In particular, in the method of Patent Document 1, when using a molten salt with a high sodium sulfate content, the influence of sulfide ions becomes significant. Furthermore, since there is no means for separating impurities such as niobium, it will turn into an aqueous sodium tungstate solution with a high niobium concentration. Also, in the method of Patent Document 2, it is described that a solution composed of a mixture of a sodium compound obtained by dissolving the molten liquid decomposition product in water and an alkali metalate containing tungsten etc., and a solid metal phase etc. are separated by filtration. However, since niobium forms soluble salts and dissolves in the aqueous solution, such a filtration separation method cannot separate and remove the dissolved niobium as an impurity.

[0012] In the method of Patent Document 3, as a countermeasure method for sulfide ions using metal oxides, it is shown that the reaction of sodium sulfide and metal oxides in a molten salt suppresses the generation of sulfide ions. However, in the method of Patent Document 3, a large amount of sodium sulfate of 70% by weight or more is added to the scrap raw material, resulting in an excessive amount of sodium sulfide. To oxidize this excessive sodium sulfide, an even larger amount of metal oxides is added. The treatment load is high, and the removal of niobium is not sufficient.

Means for Solving the Problem

[0013] The present invention has found that when a tungsten raw material containing niobium is subjected to a heat melting treatment together with a sodium salt raw material, by performing the melting treatment together with a specific iron raw material, niobium can be immobilized as an insoluble solid. Based on the above findings, the method of the present invention solves the above conventional problems in the manufacturing method of sodium tungstate. It relates to a manufacturing method that forms a melted product in which niobium is immobilized as an insoluble solid, and can obtain an aqueous sodium tungstate solution with significantly less niobium when the melted product is dissolved in water.

[0014] The manufacturing method of the present invention is a method for manufacturing sodium tungstate having the following configuration. 〔1〕In a method for manufacturing sodium tungstate in which a tungsten raw material is heated and melted together with a sodium salt raw material to obtain a molten product mainly composed of sodium tungstate, for a tungsten raw material containing niobium, at least one of metallic iron or iron sulfate (ferrous sulfate or ferric sulfate) is coexisted with the above sodium salt raw material to immobilize the above niobium as an insoluble solid. A method for manufacturing sodium tungstate, characterized by this. 〔2〕The method for manufacturing sodium tungstate according to the above [1], wherein the addition amount of the above iron raw material is 1.0% by mass or more and less than 10.0% by mass as the iron amount with respect to a tungsten raw material having a niobium content of 0.01% by mass or more to 5.0% by mass. 〔3〕The method for manufacturing sodium tungstate according to the above [1] or the above [2], wherein the heating temperature of the above heat melting is 700 ° C or more and 1000 ° C or less. 〔4〕The method for manufacturing sodium tungstate according to any one of the above [1] to the above [3], wherein the above molten product is dissolved in water to obtain an aqueous sodium tungstate solution.

[0015] 〔Specific Explanation〕 The present invention is a method for manufacturing sodium tungstate in which a tungsten raw material is heated and melted together with a sodium salt raw material to obtain a molten product mainly composed of sodium tungstate. For a tungsten raw material containing niobium, at least one of metallic iron or iron sulfate (ferrous sulfate or ferric sulfate) is coexisted with the above sodium salt raw material to immobilize the above niobium as an insoluble solid. It is a method for manufacturing sodium tungstate, characterized by this.

[0016] Put the tungsten raw material into a reaction vessel together with the sodium salt raw material and heat it to melt. The sodium salt raw material is either sodium hydroxide or sodium sulfate or both, and sulfuric acid may be added to these sodium salt raw materials. For example, adding sulfuric acid to sodium hydroxide can obtain the same effect as using sodium sulfate.

[0017] The temperature of the above heating and melting is preferably 700 °C or higher and 1000 °C or lower, and more preferably 850 °C or higher and 1000 °C or lower. If it is less than 700 °C, the progress of the reaction is insufficient, and if it exceeds 1000 °C, there is a concern about corrosion and deterioration of equipment and devices due to the high-temperature environment.

[0018] A molten product mainly composed of sodium tungstate is obtained by heating and melting the tungsten raw material and the sodium salt raw material. For example, when tungsten carbide is used as the tungsten raw material and heated and melted together with sodium hydroxide and sodium sulfate as the sodium salt raw materials, as shown in the following formulas [1][2][3], tungsten carbide reacts with sodium hydroxide and sodium sulfate to produce sodium tungstate.

[0019] 2WC(s)+4NaOH(s)+5O 2 → 2Na 2 WO 4 (s)+2H 2 O(g)+2CO 2 (g) ···[1] 2WC(s)+3Na 2 SO 4 (s)+3 / 2O 2 (g) → 2Na 2 WO 4 (s)+Na 2 O(s)+2CO 2 (g)+3SO 2 (g) ·[2] 2WC(s) + 3Na 2 SO 4 (s) → 2Na 2 WO 4 (s) + Na 2 S(s) + 2CO(g) + 2SO(g) ···[3]

[0020] Some tungsten raw materials contain niobium. For example, cemented carbide scrap made of tungsten carbide containing niobium, alloy scrap, etc. can be used as tungsten raw materials. When tungsten scrap containing niobium carbide is heated and melted together with a sodium salt raw material as a tungsten raw material containing niobium, usually, as shown in the following formula [4], the niobium carbide contained in the tungsten raw material forms sodium-soluble salts such as sodium niobate (Na 3 NbO 4 ). When this melted product is dissolved in water and recovered as an aqueous solution of sodium tungstate, as shown in the following formula [5], the niobate ion (NbO 3 - ), which is a soluble salt, dissolves and becomes an impurity in the solution.

[0021] 2NbC(s) + 6NaOH(s) + 15 / 2O 2 → 2Na 3 NbO 4 (s) + 3H 2 O(g) + 2CO 2 (g) ···[4] Na 3 NbO 4 + H 2 O → NbO 3 (aq) + 3Na(aq) + 2OH - (aq) ···[5]

[0022] However, in the above heating and melting, when at least one iron raw material such as metallic iron or iron sulfate (ferrous sulfate or ferric sulfate) coexists, as shown in the following formulas [6][7][8], it has been found that niobium carbide reacts with iron to form iron niobate (FeNbO 3 ) that is insoluble in water. Also, when the coexisting iron raw material undergoes a solid-phase change to iron oxide, it has been found that niobium is incorporated into the crystal structure of the iron oxide and becomes insoluble.

[0023] NbC(s) + Fe(s) + 5 / 2O 2 → FeNbO 3 (s) + CO 2···[6] NbC(s) + FeSO 4 (s) + 2NaOH + 2O 2 → FeNbO 3 (s) + Na 2 SO 4 + H 2 O + CO 2 ··· [7] 2NbC(s) + Fe 2 (SO 4 ) 3 (s) + 6NaOH + 7 / 2O 2 → 2FeNbO 3 (s) + 3Na 2 SO 4 + 3H 2 O + 2CO 2 ··[8]

[0024] Based on the above findings, the manufacturing method of the present invention is a manufacturing method that immobilizes niobium contained in a tungsten raw material as an insoluble solid by coexisting an iron raw material during heat melting. The iron raw material to be used is at least one or more of metallic iron and iron sulfate (ferrous sulfate or ferric sulfate). Iron oxide (Fe 2 O 3 ) is not preferable. Since iron oxide is very stable, the formation of iron niobate (FeNbO 3 ) is insufficient, and hardly any niobium is incorporated into the crystal structure during the solid-phase change of iron oxide, resulting in insufficient immobilization of niobium.

[0025] In addition, when using iron sulfate (ferrous sulfate or ferric sulfate) as the iron raw material, since iron sulfate reacts with sodium hydroxide of the sodium salt raw material to generate sodium sulfate, the amount of sodium sulfate used as part of the sodium salt raw material can be reduced. Also, when using metallic iron, it is economical because raw materials containing inexpensive metallic iron such as iron powder and iron scrap can be used.

[0026] The usage amount of the above iron raw material is preferably such that, with respect to the tungsten raw material having a niobium content of 0.01% by mass or more and 5.0% by mass or less, the addition amount of the above iron raw material is 1.0% by mass or more and less than 10.0% by mass in terms of iron content. If the amount of the iron raw material is less than 1.0% by mass, the amount of iron is too small and the immobilization of niobium becomes insufficient. If the amount of the iron raw material is 10.0% by mass or more, a large amount of iron oxide is generated, which inhibits the contact between the sodium salt raw material and the tungsten raw material, and the melting oxidation reaction of tungsten, which is the main reaction, becomes insufficient, so this is not preferable.

[0027] In the above heat melting, the amount ratio of the tungsten raw material and the sodium salt raw material is not limited. When sodium tungstate is generated by the above heat melting, if the generation of secondary sulfides such as sodium sulfide is suppressed, the generation of sulfide ions can be reduced when the melted product is dissolved in water to recover an aqueous sodium tungstate solution. Therefore, by controlling the Na / W molar ratio and the S / W molar ratio for the amount ratio of the above raw materials, sulfide ions can be suppressed.

[0028] For example, if it is controlled within the range of Na / W molar ratio = 3.0 to 5.0 and S / W molar ratio = 0.05 to 0.30, the sulfide ions when the melted product is dissolved in water can be suppressed to 100 ppm or less, and the redox potential of the aqueous solution slurry can be suppressed to -100 mV (vs. Ag / AgCl) or more. Also, if it is controlled at Na / W molar ratio = 6.0 and S / W molar ratio = 0.5, the above sulfide ions can be suppressed to 200 ppm or less, and the above redox potential can be suppressed to -650 mV (vs. Ag / AgCl) or more.

Effects of the Invention

[0029] In the methods of Patent Documents 1 and 2, tungsten raw material and sodium salt raw material are heated and melted without coexisting iron compound. However, in such simple alkali melting, niobium forms a sodium salt soluble in water like tungsten, so niobium and tungsten cannot be selectively separated from the molten product. Further, in the method of Patent Document 3, addition of metal oxide (such as iron oxide) is described, but this is for oxidizing sodium sulfide produced in excess and not for insolubilizing niobium. Since the described additives do not react with each other in the first place, insolubilization of niobium and selective separation of niobium and tungsten cannot be achieved.

[0030] On the other hand, in the production method of the present invention, at the time of melting tungsten raw material and sodium salt raw material, a specific iron raw material is made to coexist to form a stable solid phase of niobium, and dissolution of niobium is suppressed when the melt-treated product is dissolved in water. Therefore, an aqueous sodium tungstate solution with a low impurity concentration containing almost no niobium can be recovered.

[0031] Such an aqueous sodium tungstate solution with a low impurity concentration can recover tungsten chemical species with a low impurity concentration, such as ammonium paratungstate, through a tungsten purification process, and a high-purity tungsten product can be obtained. Further, in the tungsten purification process, for example, ion exchange treatment or solvent extraction treatment is applied. However, if an aqueous sodium tungstate solution with a high impurity concentration is used, there is a risk that ion exchange resins, organic solvents, etc. will be contaminated by impurities and deteriorated. However, such contamination and deterioration can be avoided with sodium tungstate produced by the method of the present invention, and protection of purification equipment and reduction of running costs can be achieved.

Embodiments for Carrying Out the Invention

[0032] Hereinafter, examples of the present invention are shown together with comparative examples. 〔Example 1〕 As the tungsten raw material containing niobium, cemented carbide scrap containing 0.6 mass% of niobium and 89 mass% of tungsten was used. Approximately 50 g of this tungsten raw material was placed in a reaction vessel, and an iron raw material powder (metallic iron powder, ferrous sulfate powder, or ferric sulfate powder) was added to achieve an iron content of 2.0 mass% based on the weight of the tungsten raw material. Further, a sodium salt raw material (sodium hydroxide and sodium sulfate) was added in an amount such that the Na / W molar ratio was 3.5 and the S / W molar ratio was 0.1 based on the amount of tungsten in the tungsten raw material. The reaction vessel containing the tungsten raw material, sodium salt raw material, and iron raw material powder was heated to 850 °C, held for 5 hours, and then naturally cooled. After the temperature dropped, the molten product in the reaction vessel was taken out and suspended (primary water dissolution) using four times the amount of pure water based on the amount of tungsten in the tungsten raw material to obtain a primary water dissolution slurry. This primary water dissolution slurry was mixed and stirred for 1 hour, the oxidation-reduction potential (ORP: mV vs. Ag / AgCl) was measured, and then filtered using a 1.0 μm membrane filter to obtain a primary recovered liquid and a primary dehydrated residue. Furthermore, the primary dehydrated residue was suspended again using the same amount of pure water as the amount of water used for the primary water dissolution to obtain a secondary water dissolution slurry. After this secondary water dissolution slurry was mixed and stirred for 1 hour, it was filtered through a 1.0 μm membrane filter to obtain a secondary recovered liquid and a secondary dehydrated residue. The secondary dehydrated residue was further dried at 105 °C for 24 hours to obtain a dried residue. When the dried residue contained unreacted tungsten raw material from the non-molten reaction, it was sorted by sieving and recovered as a solid residue. The dried residue after recovering the solid residue was recovered as a powder residue. The dissolved element concentrations of the primary recovered liquid and secondary recovered liquid were measured by ICP-AES. The contained element concentrations of the solid residue and powder residue were measured by chemical analysis treatment (ICP-AES after complete alkali dissolution with nitrate). The results are shown in Table 1 (Samples A1 - A3). The W recovery rate and Nb fixation rate were calculated as percentages using the following formulas. W recovery rate = (amount of W in the primary recovered liquid and secondary recovered liquid) / (total amount of W in the primary recovered liquid, secondary recovered liquid, solid residue, and powder residue) Nb fixation rate = (amount of Nb in the solid residue and powder residue) / (total amount of Nb in the primary recovered liquid, secondary recovered liquid, solid residue, and powder residue)

[0033] [Comparative Example 1] The treatment was carried out in the same manner as in Example 1 except that no iron raw material was used or ferric oxide was used. The results are shown in Table 1 (Samples B1, B2).

[0034] As shown in Table 1, for Samples A1, A2, and A3 using metallic iron powder, ferrous sulfate powder, and ferric sulfate powder as the iron raw material, the W recovery rate was 92% or more, and the Nb immobilization rate was 93% or more, achieving selective W recovery and compatible good Nb immobilization and W recovery. On the other hand, in Sample B1 of Comparative Example 1, although the W recovery rate was as high as 93%, since no iron raw material was added, the Nb immobilization rate was as low as 49%, resulting in the recovery of an aqueous sodium tungstate solution with a large amount of dissolved Nb. In addition, in Sample B2 of Comparative Example 1, the W recovery rate was 89% and the Nb immobilization rate was 79%, both of which were low, indicating that ferric oxide powder had insufficient Nb immobilization ability and that the melting oxidation of W was inhibited. Also, the oxidation-reduction potential (ORP) of the primary water-soluble slurry was higher than -100 mV (vs. Ag / AgCl), and no dissolved sulfide ions (S 2- ) were observed in the primary recovery solution.

[0035] [Table 1]

[0036] [Example 2] Using approximately 50 g of the same tungsten raw material as in Example 1, the treatment was carried out in the same manner as in Example 1 except that a sodium salt raw material (sodium hydroxide and sodium sulfate) in an amount such that the Na / W molar ratio was 6.0 and the S / W molar ratio was 0.5 with respect to the amount of tungsten in the tungsten raw material was added. The results are shown in Table 2 (Samples A4 - A6).

[0037] [Comparative Example 2] The treatment was carried out in the same manner as in Example 2 except that no iron raw material was used or ferric oxide was used. The results are shown in Table 2 (Samples B3, B4).

[0038] As shown in Table 2, in Samples A4, A5, and A6 using metallic iron powder, ferrous sulfate powder, and ferric sulfate powder as iron raw materials, the W recovery rate was 98% or higher and the Nb immobilization rate was 91% or higher, achieving selective W recovery and achieving both good Nb immobilization and W recovery. On the other hand, in Sample B3 of Comparative Example 2, the W recovery rate was as high as 99%, but since no iron raw material was added, the Nb immobilization rate was as low as 33%, resulting in the recovery of an aqueous sodium tungstate solution in which Nb was dissolved. Also, in Sample B4 of Comparative Example 2, the W recovery rate was 95%, but the Nb immobilization rate was 68%, indicating insufficient Nb immobilization ability. In addition, for Samples A4, A5, and A6, the oxidation-reduction potential (ORP) of the primary water-dissolved slurry was higher than -560 mV (vs. Ag / AgCl), and the sulfide ion (S 2- ) in the primary recovered liquid was 101 ppm or less, which was lower than that of Comparative Example Samples B3 and B4.

[0039]

Table 2

[0040] 〔Example 3〕 Using metallic iron powder as the iron raw material, the metallic iron powder was added so that the amount of iron relative to the weight of the tungsten raw material was 0%, 1.0%, 4.0%, 6.0%, 7.0%, 9.0%, and 11.0%. Also, except that the molar ratio of the sodium salt raw material to the tungsten raw material was controlled so that the Na / W molar ratio was 3.5 or 4.0 and the S / W molar ratio was 0.05 or 0.1, the treatment was the same as in Example 1. The results are shown in Table 3.

[0041] As shown in Table 3, the sample without addition of iron raw material (No. 1) had a high W recovery rate but a low Nb fixation rate. Also, the sample with an iron raw material addition amount of 11.0 mass% (No. 7) had a decreased W recovery rate among the groups with the same Na / W molar ratio and S / W molar ratio with the addition of the iron raw material. This is presumably because when the addition amount of the iron raw material is 11.0 mass%, a large amount of iron oxide is generated during the reaction, inhibiting the contact between the sodium salt raw material and the tungsten raw material and making the melting oxidation reaction of tungsten insufficient. On the other hand, for the samples (No. 2 to 6) to which 1.0 mass% to 9.0 mass% of iron raw material was added, the W recovery rate was 90% or more and the Nb fixation rate was 80% or more. From this result, the addition amount of the iron raw material is preferably 1.0 mass% to 10.0 mass% as the iron amount with respect to the tungsten raw material.

[0042]

Table 3

Claims

1. In a method for producing sodium tungstate, wherein a tungsten raw material is heated and melted together with a sodium salt raw material to obtain a molten product mainly composed of sodium tungstate, for a tungsten raw material containing niobium, at least one iron raw material selected from metallic iron or iron sulfate (ferrous sulfate or ferric sulfate) is coexisted with the sodium salt raw material to immobilize the niobium as an insoluble solid. A method for producing sodium tungstate, characterized by this.

2. The method for producing sodium tungstate according to Claim 1, wherein, with respect to a tungsten raw material having a niobium content of 0.01% by mass or more and 5.0% by mass or less, the addition amount of the iron raw material is 1.0% by mass or more and less than 10.0% by mass in terms of iron amount.

3. The method for producing sodium tungstate according to Claim 1 or Claim 2, wherein the heating temperature of the heating and melting is 700°C or more and 1000°C or less.

4. The method for producing sodium tungstate according to any one of Claims 1 to 3, wherein the molten product is dissolved in water to obtain an aqueous sodium tungstate solution.

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