Method for purifying an aqueous sodium tungstate solution

Abstract

To provide a purification method that is simple in its treatment process but excellent in the removal of niobium, titanium, and sulfide ions.SOLUTION: A method for purifying aqueous solution of sodium tungstate which is characterized in that a divalent iron compound and a trivalent iron compound are added to a sodium tungstate aqueous solution containing at least one of niobium, titanium, and sulfide ions as impurity ions; the pH of the aqueous solution is adjusted to 9 to 12 to form a precipitate; and the precipitate is filtered to remove the impurity ions. The sodium tungstate aqueous solution containing the impurity ions may be one obtained, for example, by dissolving in water a heated product produced by heating impurity-containing tungsten scrap containing with a sodium salt.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a purification method capable of obtaining an aqueous sodium tungstate solution with few impurities from a tungsten raw material.

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 and 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 a 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 and metallic tungsten, an alkaline agent containing a sodium compound such as sodium hydroxide, sodium sulfate, or sodium nitrate is added to the tungsten scrap and heated to cause a reaction, converting the tungsten in the scrap into sodium tungstate, and dissolving this heat-treated product 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] Tungsten-containing scrap, which is a raw material for sodium tungstate, may contain elements other than tungsten, such as titanium and niobium. In the reaction step of the scrap and the sodium compound, these elements form sodium titanate and sodium niobate in the same way as tungsten, and since they coexist with sodium tungstate, they may be contained as impurities in the aqueous sodium tungstate solution. In particular, niobium has a high solubility and is an element that is particularly likely to be mixed into the aqueous sodium tungstate solution.

[0005] In addition, in the process of manufacturing the above sodium tungstate aqueous solution, sulfide ions and the like may be generated secondarily and may dissolve in the sodium tungstate aqueous solution. Alternatively, when a chemical containing sulfide ions is used as an additive during the above manufacturing process, sulfide ions may dissolve in the sodium tungstate aqueous solution.

[0006] Titanate ions, niobate ions, and sulfide ions contained in the sodium tungstate aqueous solution are difficult to separate and remove by ion exchange methods or solvent extraction methods, and titanium, niobium, and sulfur are likely to be mixed into the final tungsten product as impurities. Alternatively, some of the impurities may undergo air oxidation, hydrolysis, etc. and cause reprecipitation in the solution after a certain period of time. The precipitates generated at such time differences may cause scale formation and equipment blockage troubles, and may seriously hinder the equipment operation. Also, when reprecipitation occurs in the latter stage of the purification process, there is a problem that these impurity-containing precipitates are distributed as solid particles to various tungsten products, deteriorating the product quality.

[0007] Methods for separating tungsten and niobium by a wet process, or methods for purifying a sodium tungstate aqueous solution, are known from Patent Documents 1 to 3 and the like. Patent Document 1 describes a method in which an aqueous sodium hydroxide solution is added to a glass scrap raw material containing tungsten, phosphorus, and niobium, and heat treatment is performed at 50°C or higher to dissolve and remove phosphorus and tungsten in the raw material. However, in this method, in the initial alkali melting treatment, when an aqueous sodium hydroxide solution is added and heat-treated, in addition to tungsten, a part of niobium also dissolves in the solution, resulting in a solution in which tungsten and niobium coexist. In Patent Document 1, the alkali melting slurry is subjected to solid-liquid separation to recover an alkali melting cake containing niobium with high purity, but the method for separating tungsten and niobium in the solid-liquid separated solution is unknown, and it is impossible to recover a sodium tungstate aqueous solution with a low impurity concentration such as niobium.

[0008] In Patent Document 2, regarding an aqueous solution of tungstate (sodium tungstate) contaminated with tantalum, niobium, etc., (first step) carbon dioxide gas is blown in to adjust the pH to 8 to 10 to precipitate a part of the impurities in the solution, followed by solid-liquid separation to partially remove the impurities. (Second step) The solid-liquid separated liquid is ion-exchanged and purified with an anion exchanger (OH-type anion exchange resin) (the solid-liquid separated liquid is passed through a column for adsorption treatment, and further elution treatment with an aqueous sodium hydroxide solution is carried out). After that, (third step) CO 2 and the aqueous NaOH solution are recovered.

[0009] However, the method of Patent Document 2 has many treatment steps, and the treatment time and treatment cost tend to be high. Also, regarding the removal efficiency, only in the first step, the proportion of niobium precipitating in the solution is partial and the removal efficiency is low, and the dissolved niobium tends to migrate to the second step. Furthermore, in the second step, although the purification of the aqueous sodium tungstate solution is carried out by ion exchange treatment, actually niobium forms an oxoanion in the solution similar to tungsten, such as NbO 3 - and is likely to show chemical properties similar to those of the tungsten oxoanion WO 4 2- Therefore, in the ion exchange treatment with an anion exchanger (OH-type anion exchange resin), the selective separation of niobium and tungsten tends to be insufficient. Moreover, the precipitate formed in the first step contains tungsten as well as Al, Ti, Ta, and Nb, and its content is about 15% by weight, resulting in a large loss of tungsten in the first step.

[0010] Patent Document 3 shows a method of adding a divalent iron compound to a sodium tungstate solution containing Cr or V and then adding an acid to adjust the pH of the solution to 8 to 13 to precipitate and remove Cr or V. However, in this method, the separation and removal of impurity elements other than Cr and V contained in the sodium tungstate solution are unclear, and only adding a divalent iron compound and adjusting the pH may result in insufficient separation and removal of elements other than Cr and V in some cases.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0012] The present invention is a method for purifying an aqueous sodium tungstate solution that solves the above problems in the conventional treatment method, and provides a purification method that has a simple treatment process and excellent effects of removing niobium, titanium, and sulfide ions.

Means for Solving the Problems

[0013] (1) A purification method for removing the above impurity ions from an aqueous sodium tungstate solution containing at least any one of niobium, titanium, and sulfide ions as impurity ions, characterized in that a divalent iron compound and a trivalent iron compound are added to the aqueous sodium tungstate solution, the pH of the aqueous solution is adjusted to 9 to 12 to form a precipitate, and the precipitate is filtered off to remove the above impurity ions. A method for purifying an aqueous sodium tungstate solution. (2) The method for purifying an aqueous sodium tungstate solution according to [1] above, wherein the ratio of the addition amounts of the divalent iron compound [Fe(II)] and the trivalent iron compound [Fe(III)] is 10 to 90% by mass of Fe(II) and 10 to 90% by mass of Fe(III) in terms of the mass ratio of the contained iron amount. (3) The method for purifying an aqueous sodium tungstate solution according to [1] or [2] above, wherein the aqueous sodium tungstate solution containing the above impurity ions is an aqueous sodium tungstate solution obtained by dissolving a heat-treated product formed by heating a tungsten-containing scrap together with a sodium compound in water. (4) The method for purifying an aqueous sodium tungstate solution as described in the above [1] or [2], wherein the aqueous sodium tungstate solution containing the impurity ions is an aqueous sodium tungstate solution obtained by dissolving an electrode material scrap containing tungsten or a tungsten concentrate obtained by separating components other than tungsten from an electrode material scrap containing tungsten in an aqueous solution containing a sodium compound.

[0014] 〔Specific Explanation〕 Hereinafter, the purification method of the present invention will be specifically described. Note that % is mass%. The purification method of the present invention is a purification method for removing at least one of niobium, titanium, and sulfide ions as impurity ions from an aqueous sodium tungstate solution. In this method, a divalent iron compound and a trivalent iron compound are added to the aqueous sodium tungstate solution, the pH of the aqueous solution is adjusted to 9 to 12 to form a composite compound precipitate of divalent iron and trivalent iron, and the impurity ions are incorporated into the precipitate. The precipitate is then filtered off to remove the impurity ions. This is a method for purifying an aqueous sodium tungstate solution.

[0015] In the purification method of the present invention, the aqueous sodium tungstate solution containing at least one of niobium, titanium, and sulfide ions as impurity ions is, for example, an aqueous sodium tungstate solution obtained by reacting a tungsten-containing scrap such as a super tool scrap, an alloy scrap, or an electrode material scrap containing tungsten with a sodium compound.

[0016] Specifically, for example, a cemented carbide tool scrap containing 0.6% niobium, 1.0% titanium, and 89% tungsten is used as a tungsten-containing raw material. The raw material is placed in a reaction vessel, and sodium hydroxide and sodium sulfate are added as alkaline agents. After heating at 850 °C for 5 hours and then naturally cooling, the heat-treated product in the reaction vessel is taken out after the temperature drops. 10 times the amount of pure water based on the amount of tungsten in the tungsten raw material is added for water dissolution treatment to form a water dissolution slurry. This water dissolution slurry contains tungstic acid (WO3 ) 90 g / L, sulfide ion (S 2- ) 7250 mg / L, titanium 110 mg / L, niobium 64 mg / L are contained.

[0017] Also, an aqueous sodium tungstate solution obtained from tungsten concentrate derived from electrode material scrap or electrode material scrap can be, for example, an aqueous sodium tungstate solution obtained by dissolving electrode material scrap containing tungsten in an aqueous solution containing a sodium compound, or the above electrode material scrap is acid-leached and filtered, and an aqueous sodium tungstate solution obtained by dissolving this filter residue (tungsten concentrate) in an aqueous sodium-containing solution can be used.

[0018] To the aqueous sodium tungstate solution containing the above impurity ions, a divalent iron compound and a trivalent iron compound are added, the pH of the aqueous solution is adjusted to 9 to 12 to form a composite compound precipitate of divalent iron and trivalent iron, the above impurity ions are incorporated into the precipitate, and the precipitate is filtered off to remove the impurity ions.

[0019] By adding both a divalent iron compound [Fe(II)] and a trivalent iron compound [Fe(III)] to the aqueous sodium tungstate solution, as shown in the following formula (1), a composite compound of divalent iron and trivalent iron represented by magnetite [Fe 3 O 4 (Fe (II) Fe (III) 2 O 4 )] is formed. Magnetite can incorporate dissolved metal ions and the like into its crystal structure during the solid-phase formation process, and can efficiently remove impurities in the liquid. Fe 2+ + 2Fe 3+ + 4H 2 O → Fe 3 O 4 (Fe (II) Fe (III) 2 O 4 ) + 8H + ···(1)

[0020] In addition to tungstic acid in the solution, when anions such as sulfate ions (SO 4 2- ), carbonate ions (CO 3 2- ), and chloride ions (Cl - ) are contained, as shown in the following formulas (2) and (3), layered double hydroxides (such as green rust) of these anion species with divalent iron and trivalent iron are formed.

[0021] 4Fe 2+ +2Fe 3+ +14H 2 O+SO 4 2- → [Fe (II) 4 Fe (III) 2 (OH) 12 [SO 4 ·2H 2 O]+12H + ···(2) 4Fe 2+ +2Fe 3+ +14H 2 O+CO 3 2- → [Fe (II) 4 Fe (III) 2 (OH) 12 [CO 3 ·2H 2 O]+12H + ···(3) 3Fe 2+ +Fe 3+ +8H 2 O Cl - → [Fe (II) 3 Fe (III) (OH) 8 [Cl·2H 2 O]+6H + ···(4)

[0022] These layered double hydroxides can efficiently incorporate dissolved anions in a liquid into the interlayer of their structure through an ion exchange reaction, and as a result, impurities in the liquid can be efficiently removed. For example, niobate ions (NbO 3 - ), titanate ions (HTiO 3 - ), etc. are incorporated into the solid through a partial ion exchange reaction of the layered double hydroxide as shown in the following formulas (5) and (6).

[0023] [Fe (II) 4 Fe (III) 2 (OH) 12 [SO 4 ·2H 2 O + 2NbO 3 - =[Fe (II) 4 Fe (III) 2 (OH) 12 [(NbO 3 ) 2 ·2H 2 O + SO 4 2- ··· (5) [Fe (II) 4 Fe (III) 2 (OH) 12 [SO 4 ·2H 2 O + 2HTiO 3 - =[Fe (II) 4 Fe (III) 2 (OH) 12 [(HTiO 3 ) 2 ·2H 2 O + SO 4 2- ···(6)

[0024] In addition, these layered double hydroxides themselves also change into composite compounds such as magnetite by oxidation in solution. At that time, since impurity ions in the solution are incorporated into the crystal structure, the impurity ions can be removed. Since this composite compound incorporates various anionic species such as niobate ions, titanate ions, sulfide ions, tantalate ions, and molybdate ions in the solution, it also has the effect of removing these impurity ions.

[0025] On the other hand, when a divalent iron compound or a trivalent iron compound is added alone, as shown in the following formulas (7) and (8), iron(II) hydroxide [Fe(OH) 2 or iron(III) hydroxide [Fe(OH) 3 is formed. Although this iron(III) hydroxide [Fe(OH) 3 has a high effect of adsorbing the above-mentioned impurity ions, at the same time, tungstate ions are also very easily adsorbed. Therefore, tungstate ions and the above-mentioned impurity ions cannot be selectively separated. In addition, the amount of the precipitate formed is large, and the volume is likely to be bulky.

[0026] Fe 2+ + 2OH - → Fe(OH) 2 (s) ···(7) Fe 3+ + 3OH - → Fe(OH) 3 (s) ···(8)

[0027] In addition, the generated iron(II) hydroxide [Fe(OH) 2 is gradually oxidized by oxygen in the solution or oxygen supplied from the atmosphere on the solution surface. After a long time, it finally undergoes a solid-phase change to magnetite or green rust. However, since the reaction is very slow, in a general treatment process, for example, in a treatment time of about 1 hour, a sufficient oxidation reaction does not proceed, and the effect of removing impurity ions is lower than that in the case of using a divalent iron compound and a trivalent iron compound in combination. Furthermore, since the reactivity between sulfide ions and divalent iron is low, when sulfide ions are contained in the solution, the effect of removing sulfide ions is often insufficient with only a divalent iron compound.

[0028] As the divalent iron compound and trivalent iron compound to be added to the above-mentioned aqueous sodium tungstate solution, for example, iron(II) sulfate powder, iron(III) sulfate powder, iron(II) chloride powder, iron(III) chloride powder, or a solution in which these compounds are dissolved can be used. Also, as the solution, polyferric sulfate solution, etching solution and its waste liquid, pickling waste liquid of iron-based materials, etc. may be used. The ratio of the divalent iron compound and trivalent iron compound to be added is the mass ratio of the contained iron amount, and the ratio of the divalent iron compound is preferably 10 to 90% by mass, and the trivalent iron compound is preferably 10 to 90% by mass. Within this range, it is desirable to appropriately adjust the above ratio while confirming the tendency of the impurity concentration in the solution. For example, when the ratio of the trivalent iron compound increases, the removal effect of sulfide ions tends to be promoted. On the other hand, when the ratio of the divalent iron compound increases, the amount of precipitate generated decreases, so the load of solid-liquid separation and the treatment cost of the precipitate can be reduced.

[0029] Add a divalent iron compound and a trivalent iron compound, and adjust the pH of the aqueous solution to 9 to 12 to generate a composite compound precipitate of divalent iron and trivalent iron. When the pH exceeds 12, the removal effect of impurities such as niobium tends to decrease. On the other hand, when the pH is less than 9, tungstate ions in the solution also precipitate, resulting in a recovery loss of tungsten. A range of pH 9 or more to 12 or less is preferable. When the pH of the above aqueous solution is outside the above range, an acid or an alkali is added to adjust the pH to the above range, and when the pH of the aqueous solution is within the above range when a divalent iron compound and a trivalent iron compound are added, there is no need to add an acid or an alkali.

[0030] The reaction temperature is such that the above composite compound precipitate can be sufficiently generated even at room temperature of 25°C. For example, heating to 60°C can promote the formation of the precipitate. When the temperature exceeds 70°C, the temperature burden on the equipment and facilities increases, so the heating temperature is preferably 70°C or less. On the other hand, when the reaction temperature is less than 20°C, the dissolution of the additive and the formation of the precipitate become slow, and the treatment efficiency decreases, so the temperature of the solution is preferably 20°C or more.

[0031] The aqueous sodium tungstate solution to which a divalent iron compound and a trivalent iron compound are added may be in the form of a slurry in which other solid particulate substances are suspended. For example, in the aqueous sodium tungstate solution obtained by reacting scrap raw materials of cemented carbide tools or tungsten alloy products with a sodium compound, niobium, titanium, etc. contained in these raw materials may be dissolved as oxoanions, and in addition, solid particles of metal oxides and hydroxides such as cobalt, nickel, copper, and iron contained in these raw materials may be suspended.

[0032] In addition, for battery materials, electrode materials, or tungsten concentrates such as solid residues and sludges containing tungsten recovered after separating and removing components other than tungsten from these battery materials and electrode materials, which are discharged from the recycling process of battery materials and electrode materials, in the aqueous sodium tungstate solution obtained by reacting a solution containing a sodium compound, solid particles of metal oxides and hydroxides of metal species contained in the electrode material, and solid particles of carbon contained in the electrode material may be suspended. These suspended particles such as metal oxides, metal hydroxides, and carbon do not affect the formation of the above composite compound precipitate or the incorporation of dissolved ions such as niobium, titanium, and sulfide ions into the precipitate. Therefore, the above aqueous solution may be a slurry containing these suspended particles, or an aqueous solution obtained by solid-liquid separation to remove the above suspended particles.

Advantages of the Invention

[0033] The purification method of the present invention makes it difficult to precipitate tungsten in the aqueous sodium tungstate solution containing niobate ions, titanate ions, and sulfide ions. Therefore, it is difficult to cause a recovery loss of tungsten, and the above impurities are selectively incorporated into the composite compound precipitate and solid-liquid separated, so that the above impurities can be effectively removed.

[0034] In addition, the purification method of the present invention can easily separate and remove niobium, titanium, and sulfide ions by generating a composite compound of a divalent iron compound and a trivalent iron compound. For example, in Patent Document 2, the pH is adjusted by blowing carbon dioxide gas, and after solid-liquid separation of the generated precipitate, a sodium tungstate aqueous solution is purified by a multi-step treatment such as an adsorption treatment of impurities with an ion exchange resin and an elution treatment of tungsten from the ion exchange resin. On the other hand, in the purification method of the present invention, since the purification treatment is completed only by adding a divalent iron compound and a trivalent iron compound, adjusting the pH, and solid-liquid separation of the generated precipitate, a sodium tungstate aqueous solution with a significantly low amount of impurities can be obtained quickly and at low cost.

[0035] Since the method of Patent Document 3 uses a divalent iron compound alone, the removal effect of niobate ions, titanate ions, and sulfide ions is low. However, in the purification method of the present invention, since a composite compound of a divalent iron compound and a trivalent iron compound is generated, the removal effect of niobate ions, titanate ions, and sulfide ions contained in the sodium tungstate aqueous solution is high.

[0036] In addition, in the method of using a trivalent iron compound alone, the amount of generated precipitate is large and the volume also increases, so the burden of precipitate treatment is large. In addition, since tungsten is also mixed into the precipitate, a recovery loss of tungsten is likely to occur. On the other hand, in the purification method of the present invention, since a composite compound of a divalent iron compound and a trivalent iron compound is generated, the amount of precipitate is smaller than that when using a trivalent iron compound alone, so the treatment cost can be reduced and the recovery rate of tungsten is also high.

[0037] The purified sodium tungstate aqueous solution is further subjected to advanced purification treatments such as ion exchange treatment and solvent extraction treatment. However, if the removal of impurities in the aqueous solution is insufficient at that time, the ion exchange resin, organic solvent, etc. may be contaminated or deteriorated by the above impurities. On the other hand, since the sodium tungstate aqueous solution purified by the method of the present invention has significantly fewer impurities, the risk of such contamination and deterioration can be made very low, and the protection of the purification equipment and the suppression of the running cost can be achieved.

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] Hereinafter, examples of the present invention will be shown. The concentrations of various elements in the solution were measured by ICP-AES. The tungsten residual rate (W residual rate) was shown as an evaluation index for the recovery loss of tungsten. The tungsten residual rate was determined based on the following formula. W residual rate [%] = WO in the recovered solution 3 Concentration [g / L] / WO before treatment 3 Concentration [g / L] × 100

[0039]

Example 1

[0040]

Comparative Example 1

[0041] As shown in Table 1, for Samples A1 and A2 of the present invention, the sulfide ion concentration, titanium concentration, and niobium concentration in the recovered liquid (purified liquid) are all sufficiently reduced. Also, the decrease in the WO 3 concentration in the recovered liquid is small, and the residual rate of tungsten is 96% or more. On the other hand, for Comparative Samples B1 - B8, since only one of ferrous sulfate or ferric sulfate was added, the sulfide ion concentration, titanium concentration, and niobium concentration in the recovered liquid are high, and their removal is insufficient. Also, for Samples B4 and B8 where ferric sulfate was added alone and the addition amount was 4.4 g / L, the tungsten residual rate decreased to 91%, the recovery loss of tungsten was large, and the residue amounts were 34 g / L and 37 g / L, respectively, which is an increase compared to the case where the same amount was added using a combination of Fe(II) and Fe(III). Furthermore, for Comparative Samples B9 and B10 with a liquid pH of 8.0, although the impurities were sufficiently removed, the WO 3 concentration in the recovered liquid decreased significantly, and the recovery loss of tungsten was remarkable. As described above, as shown in Table 1, by using a combination of a ferrous iron compound and a ferric iron compound and forming a composite compound precipitate under a liquid property of pH 9 - 10, it was confirmed that an aqueous sodium tungstate solution with a low impurity concentration can be recovered while suppressing the recovery loss of tungsten.

[0042]

Table 1

[0043] [Example 2] A sodium tungstate aqueous solution (WO 2- : 270 g / L) containing 8690 mg / L of sulfide ion (S 3 ), 160 mg / L of titanium, and 126 mg / L of niobium, and in which 34 g / L of solid particles mainly composed of cobalt hydroxide are suspended, was adjusted so that the [Fe(II) concentration] and [Fe(III) concentration] in the aqueous solution were in the ratios shown in Table 2 by adding iron(II) sulfate powder and iron(III) sulfate powder. Further, the pH of the aqueous solution was adjusted to 12.0 using an aqueous sodium hydroxide solution or sulfuric acid, maintained at room temperature of 25°C, and stirred and mixed for 1 hour. Otherwise, it was treated in the same manner as in Example 1. The results are shown in Table 2. The addition ratios % of Fe(II) and Fe(III) are as follows. Fe(II): 0.44 g / L and Fe(III): 1.76 g / L → Fe(II): 20%, Fe(III): 80% Fe(II): 0.73 g / L and Fe(III): 1.47 g / L → Fe(II): 33%, Fe(III): 67% Fe(II): 1.10 g / L and Fe(III): 1.10 g / L → Fe(II): 50%, Fe(III): 50% Fe(II): 1.47 g / L and Fe(III): 0.73 g / L → Fe(II): 67%, Fe(III): 33% Fe(II): 1.76 g / L and Fe(III): 0.44 g / L → Fe(II): 80%, Fe(III): 20%

[0044] [Comparative Example 2] It was treated in the same manner as in Example 2 except that the pH of the above aqueous solution was set to 13.0. The results are shown in Table 2. As shown in Table 2, for Samples A10 - A14 of the present invention, the sulfide ion concentration in the recovered liquid is reduced to 1 mg / L or less, the titanium concentration is reduced to 8 mg / L or less, and the niobium concentration is reduced to 29 mg / L or less, indicating that impurities have been sufficiently removed. Also, the WO 3 concentration in the recovered liquid is 266 g / L or more, and almost no tungsten recovery loss occurs. On the other hand, for Comparative Samples B10 - B14, the WO 3 concentration in the recovered liquid is 267 g / L or more, and almost no tungsten recovery loss occurs. However, sulfide ions, titanium, and niobium also remain in the recovered liquid in large amounts, indicating insufficient impurity removal. Thus, from the results in Table 2, when adding both divalent iron compounds and trivalent iron compounds, it is preferable to adjust the pH to 12.0 or less.

[0045]

Table 2

[0046] 〔Example 3〕 Under the treatment conditions of Example 2, the treatment was carried out in the same manner as in Example 2 except that the reaction temperature was heated to 60°C. The results are shown in Table 3. As shown in Table 3, for Samples A20 - A24 of the present invention, the sulfide ion concentration in the recovered liquid is reduced to 15 mg / L or less, the titanium concentration is reduced to 6 mg / L or less, and the niobium concentration is reduced to 25 mg / L or less. The titanium concentration and niobium concentration are less than those in Example 2. Also, the WO 3 concentration in the recovered liquid is 266 g / L or more, and almost no tungsten recovery loss occurs. It can be confirmed that the removal effect of titanium and niobium is higher at a treatment temperature of 60°C.

[0047]

Table 3

[0048] 〔Example 4〕 Under the treatment conditions of Example 2, the treatment was carried out in the same manner as in Example 2 except that the reaction temperature was heated to 60°C and the pH was adjusted to 9.0, 10.0, and 11.0. The results are shown in Table 4. As shown in Table 4, for Samples A30 to A35 of the present invention, the sulfide ion concentration in the recovered solution is reduced to 9 mg / L or less, the titanium concentration is reduced to 6 mg / L or less, and the niobium concentration is reduced to 24 mg / L or less. Also, the WO 3 concentration in the recovered solution is 265 g / L or more, and almost no tungsten recovery loss occurs. From the results of Table 3 and Table 4, it was confirmed that an aqueous sodium tungstate solution with a significantly low impurity concentration can be recovered by adding both a divalent iron compound and a trivalent iron compound, adjusting the pH to 9.0 to 12.0, and reacting under heating.

[0049]

Table 4

Claims

1. A purification method for removing impurity ions from an aqueous sodium tungstate solution containing at least one of niobium, titanium, and sulfide ions as impurity ions, comprising adding a divalent iron compound and a trivalent iron compound to the aqueous sodium tungstate solution, adjusting the pH of the aqueous solution to 9 to 12 to form a precipitate, and filtering off the precipitate to remove the impurity ions. A method for purifying an aqueous sodium tungstate solution, characterized in that.

2. The purification method of the aqueous sodium tungstate solution according to Claim 1, wherein the ratio of the addition amounts of the divalent iron compound [Fe(II)] and the trivalent iron compound [Fe(III)] is 10 to 90% by mass of Fe(II) and 10 to 90% by mass of Fe(III) in terms of the mass ratio of the contained iron amount.

3. The purification method of the aqueous sodium tungstate solution according to Claim 1 or Claim 2, wherein the aqueous sodium tungstate solution containing the impurity ions is an aqueous sodium tungstate solution obtained by dissolving a heat-treated product formed by heating tungsten-containing scrap together with a sodium salt in water.

4. The purification method of the aqueous sodium tungstate solution according to Claim 1 or Claim 2, wherein the aqueous sodium tungstate solution containing the impurity ions is an aqueous sodium tungstate solution obtained by dissolving an electrode material scrap containing tungsten or a tungsten concentrate obtained by separating components other than tungsten from an electrode material scrap containing tungsten in an aqueous solution containing a sodium compound.

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