Method for treating tungsten-containing liquid

Abstract

Provided is a method for treating a tungsten-containing liquid, wherein the tungsten-containing liquid is subjected to flocculation using an inorganic flocculant and then subjected to solid-liquid separation, and the resulting flocculated sludge is subjected to dehydration using a dehydrator and separated into a dehydrated sludge and a dehydrated filtrate. In the method for treating a tungsten-containing liquid, the flocculated sludge is subjected to dehydration such that the concentration of chlorine or sulfur in a dried sludge obtained by drying the dehydrated sludge is a predetermined value or less.

Description

Method for treating tungsten-containing liquid

[0001] The present invention relates to a method for treating a tungsten-containing liquid, and more particularly to a method for coagulating the tungsten-containing liquid and dehydrating the generated coagulated sludge.

[0002] Tungsten, which is a kind of rare metal, is used in a wide range of industrial fields such as the semiconductor field such as sputtering targets, cutting tools, wear-resistant tools in the industrial machinery field such as automobiles, and the chemical industry field such as desulfurization and denitration catalysts. The recycling of tungsten is being studied.

[0003] As a method for recovering tungsten from a tungsten-containing liquid, Patent Document 1 describes a method of concentrating a rare metal ion-containing liquid such as tungsten with a membrane and extracting the rare metal ions in the concentrated liquid with an extractant.

[0004] Patent Document 2 describes a method of obtaining metal tungsten by hydrogen reduction of tungstate in a tungstate-containing mineral through alkali tungstate and ammonium tungstate to form tungsten oxide, and adding an aluminum compound to an aqueous solution of alkali tungstate to adsorb impurities in the alkali tungstate to aluminum hydroxide and precipitate them to purify the alkali tungstate.

[0005] As a method for treating tungsten-containing wastewater, it is conceivable to add an inorganic flocculant to the tungsten-containing wastewater, dehydrate the flocculated sludge, and recover tungsten from the dehydrated sludge.

[0006] As a method for recovering tungsten from tungsten-containing materials, a method for recovering tungsten from superalloy scrap described in Non-Patent Document 1 has already been put into practical use. Also, as a method for removing tungsten from a tungsten-containing liquid, insolubilizing tungsten in tungsten-containing wastewater with an inorganic flocculant and separating it by flocculation and precipitation is described in Non-Patent Document 2. This Non-Patent Document 2 only describes removing tungsten from tungsten-containing wastewater, and does not disclose anything about the treatment method of flocculation and precipitation sludge.

[0007] JP2023-55031A JP2023-107527A

[0008] "Commercialization of Tungsten Recycling from Carbide Alloy Scrap" (July 2016, SEI Technical Review, No. 189, pp. 9-14) "Removal of tungsten oxyanions from industrial wastewater by precipitation, coagulation and flocculation processes" (Journal of Hazardous Materials, Vol. 148, Issue 3, 30 September 2007, Pages 613-615)

[0009] When purifying tungsten-containing sludge to recover and reuse tungsten, it is necessary to reduce the concentration of halogens such as chlorine in the tungsten-containing sludge. In other words, halogens in tungsten-containing liquid sludge can corrode the purification equipment. The permissible concentration of chlorine in tungsten-containing sludge is determined by the recycling destination (end of use), for example, 0.01% by mass (relative to dry) for special steel and 0.05% by mass (relative to dry) for iron refining.

[0010] Furthermore, sulfur is also restricted as an impurity, with permissible concentrations of 0.03% by mass (relative to dry) for special steels and 0.3% by mass (relative to dry) for iron refining. Note that "relative to dry" refers to the concentration in the dry sludge solids.

[0011] The object of this invention is to provide a method for treating a tungsten-containing liquid that can stably reduce the impurity concentration in the dewatered sludge or the dried sludge obtained by coagulating and dewatering the tungsten-containing liquid to a low value.

[0012] The gist of this invention is as follows:

[0013] [1] A method for treating a tungsten-containing liquid, comprising treating the tungsten-containing liquid with an inorganic coagulant, then performing a solid-liquid separation treatment, and separating the resulting coagulated sludge into dewatered sludge and dewatered filtrate by dewatering in a dewatering machine, wherein the coagulated sludge is dewatered so that the concentration of chlorine or sulfur in the dried sludge after drying is below a predetermined value.

[0014] [2] A method for treating the tungsten-containing liquid in [1], which involves measuring the chlorine or sulfur concentration in the dried sludge and controlling the chlorine or sulfur content of the dried sludge.

[0015] [3] A method for treating a tungsten-containing liquid according to [1] or [2], characterized by using an inorganic flocculant whose counterion is a sulfate ion.

[0016] [4] A method for treating tungsten-containing liquid according to any one of [1] to [3], wherein a target moisture content is set from at least one of the chlorine concentration, sulfur concentration, and amount of inorganic coagulant added to the water to be treated, and the dewatering machine is controlled to achieve the target moisture content.

[0017] [5] A method for processing a tungsten-containing liquid according to any one of [1] to [4], wherein at least one of the dewatering time and dewatering pressure of the dewatering machine is controlled according to a target moisture content.

[0018] [6] A method for treating tungsten-containing liquids according to any of [1] to [5], wherein the sludge water content calculated by the following formula (1) is less than or equal to a predetermined value in order to reduce the chlorine concentration in the dewatered sludge to a predetermined value or less.

[0019] Sludge moisture content (%) = [Chlorine concentration in dried sludge (%) / (Chlorine concentration in dewatered filtrate (%) + Chlorine concentration in dried sludge (%))] × 100 ... (1)

[0020] [7] A method for treating tungsten-containing liquids according to any of [1] to [5], wherein the sludge is dewatered so that the sludge water content calculated by the following formula (2) is less than or equal to the predetermined water content in order to set the sulfur concentration in the dewatered sludge to a predetermined value.

[0021] Sludge moisture content (%) = [Sulfur concentration in dried sludge (%) / (Sulfur concentration in dewatered filtrate (%) + Sulfur concentration in dried sludge (%))] × 100 ... (2)

[0022] [8] A method for treating the tungsten-containing liquid from [4], wherein the amount of coagulant added is changed according to the target moisture content.

[0023] Lowering the water content of dewatered sludge reduces the amount of liquid (water) in the sludge, thus reducing the amount of chlorine or sulfur in the sludge that originates from the chlorine or sulfur contained in the liquid. Therefore, lowering the water content of dewatered sludge results in a lower concentration of chlorine or sulfur in the sludge.

[0024] According to the present invention's method for treating tungsten-containing liquid, the conditions for dewatering the flocculated sludge are made appropriate, so that the chlorine or sulfur concentration in the dewatered sludge or the dried sludge obtained by flocculating and dewatering the tungsten-containing liquid can be kept at a stable low value.

[0025] A flowchart illustrating one aspect of the present invention.

[0026] The present invention will be described in more detail below.

[0027] A method for treating a tungsten-containing liquid according to one aspect of the present invention is a method for treating a tungsten-containing liquid such as tungsten-containing wastewater, and as shown in Figure 1, comprises a coagulation step of coagulating the tungsten-containing wastewater with a coagulant; a step of settling the coagulated sludge in a sedimentation tank; and a dewatering step of dewatering the settled coagulated sludge.

[0028] [Tungsten-containing liquid] As the tungsten-containing liquid, tungsten-containing wastewater is preferred. Examples of tungsten-containing wastewater include wastewater containing spent tungsten catalysts used in organic synthesis such as heavy oil refining, and NO removal from thermal power plants. Ｘ Examples include, but are not limited to, tungsten-containing wastewater used in the manufacturing process, tungsten-containing liquids produced by alkaline extraction or alkaline dissolution methods in the recycling process of ultrahard alloy scrap, contaminated groundwater and leachate from landfills, and wastewater from electronic component manufacturing processes.

[0029] The tungsten concentration in the tungsten-containing wastewater treated by the present invention is usually 1 to 3,000 mg / L, and particularly preferably 20 to 500 mg / L, but is not limited thereto.

[0030] The tungsten-containing wastewater treated in one aspect of the present invention contains suspended solids (SS). In one aspect of the present invention, more than half of the SS is tungsten.

[0031] In one aspect of the present invention, the tungsten SS concentration in tungsten-containing wastewater is typically 1 to 2000 mg / L, particularly 10 to 300 mg / L, but is not limited thereto.

[0032] In one aspect of the present invention, an inorganic coagulant is added to such tungsten-containing wastewater to perform coagulation treatment, followed by the addition of a polymer coagulant to grow flocs, which are then subjected to sedimentation treatment (solid-liquid separation treatment) in a sedimentation tank, and the settled coagulated sludge is dewatered. A filter may be used instead of a sedimentation tank.

[0033] The supernatant water produced during the sedimentation process is either discharged or recovered as recycled water after undergoing the necessary treatments.

[0034] [Inorganic flocculant] Suitable inorganic flocculants include salts of aluminum, iron, etc., with sulfates or chlorides being particularly preferred. Specifically, aluminum sulfate, iron sulfate, polyferrous sulfate, aluminum chloride, polyaluminum chloride, ferric chloride, etc. are preferred. One aspect of the present invention aims to lower the chloride ion concentration in dewatered sludge, and among the above, sulfates are preferred as the inorganic flocculant.

[0035] The amount of inorganic coagulant added is preferably about 100 to 4000 mg / L, for example, as polyferrous sulfate (11% total iron), when the tungsten concentration of the tungsten-containing wastewater is about 20 to 500 mg / L.

[0036] It is preferable that tungsten-containing wastewater be treated by adjusting its pH to 5-7 using an acid such as hydrochloric acid or sulfuric acid, or an alkali such as sodium hydroxide, and then coagulating it with an inorganic coagulant.

[0037] [Polymer Flocculant] When using a polymer flocculant in combination, it is preferable to use an acrylamide-based anionic polymer flocculant or a cationic polymer flocculant, etc. The addition amount is preferably 0.1 to 20 mg / L, particularly preferably about 1 to 10 mg / L.

[0038] [Sedimentation Treatment] The flocculation treatment liquid in which flocs have grown by adding a polymer flocculant is subjected to sedimentation treatment in a sedimentation tank, and the sedimented sludge is supplied to a dehydrator.

[0039] Note that a part of the sludge generated by the sedimentation treatment may be returned to the inorganic flocculation treatment step to adjust the concentration of the inorganic flocculant and the impurity concentration.

[0040] [Dehydrator] As a dehydrator for dehydrating the sludge from the sedimentation tank, a filter press dehydrator, a belt press dehydrator, a centrifugal dehydrator, a screw press dehydrator, etc. can be used.

[0041] [Control of Dehydrator] In one aspect of the present invention, in order to make the chlorine concentration and sulfur concentration contained in the dehydrated sludge or the dried sludge obtained by drying this dehydrated sludge below a predetermined value, the dehydrator is operated so that the water content rate of the dehydrated sludge becomes below a predetermined water content rate.

[0042] When the dehydrator is a filter press or a belt press dehydrator, the filtration time or the squeezing pressure is controlled. When the dehydrator is a centrifugal dehydrator, the rotation speed and the treatment time are controlled.

[0043] The above-mentioned predetermined values of the chlorine concentration and sulfur concentration in the dried sludge vary depending on the destination of the recovered tungsten. Generally, the chlorine concentration in the dried sludge is preferably 0.05 mass% or less, more preferably 0.01 mass% or less. The sulfur concentration is preferably 0.3 mass% or less, more preferably 0.03 mass% or less.

[0044] As described above, by treating the dried sludge to produce tungsten oxide and reducing this tungsten oxide with hydrogen, metallic tungsten can be obtained. When using this recovered metallic tungsten for special steel applications, the chlorine concentration in the dried sludge is preferably 0.01 mass% or less, and the sulfur concentration is preferably 0.03 mass% or less.

[0045] When the recovered metallic tungsten is used for iron refining, the chlorine concentration in the dried sludge is preferably 0.05% by mass or less, and the sulfur concentration is preferably 0.3% by mass or less.

[0046] From this, in one aspect of the present invention, by setting the water content rate of the dehydrated sludge obtained by the following formula (1) or (2) according to the chlorine or sulfur concentration in the dehydrated filtrate to be not more than the target water content rate, the chlorine concentration or sulfur concentration in the dried sludge is made not more than a predetermined value.

[0047] <Formula (1): Formula for determining the water content rate for making the chlorine concentration in the dried sludge not more than a predetermined value> Sludge water content rate (%) = [Chlorine concentration in the dried sludge (%) / (Chlorine concentration in the dehydrated filtrate (%) + Chlorine concentration in the dried sludge (%) )] × 100... (1)

[0048] <Formula (2): Formula for determining the water content rate for making the sulfur concentration in the dried sludge a predetermined value> Sludge water content rate (%) = [Sulfur concentration in the dried sludge (%) / (Sulfur concentration in the dehydrated filtrate (%) + Sulfur concentration in the dried sludge (%) )] × 100... (2)

[0049] <Explanation of the formulation of the above formulas (1) and (2)> When the impurity is chlorine, the above formula (1) is formulated based on the mass balance as follows.

[0050] The mass balance formula of chlorine is as follows.

[0051] The amount of chlorine in 100 g of the dehydrated sludge (g) is expressed by the following formulas (a) and (b), respectively.

[0052] Amount of chlorine in 100 g of the dehydrated sludge (g) = 100 (g) × sludge water content rate (%) / 100 × chlorine concentration in the dehydrated filtrate (%) / 100 = sludge water content rate (%) × chlorine concentration in the dehydrated filtrate (%) / 100... (a)

[0053] Amount of chlorine in 100 g of the dehydrated sludge (g) = 100 (g) × dry sludge concentration in the dehydrated sludge (%) / 100 × chlorine concentration in the dry sludge (%) / 100 = 100 (g) × (100 - sludge water content rate (%)) / 100 × chlorine concentration in the dry sludge (%) / 100 = (100 - sludge water content rate (%)) × chlorine concentration in the dry sludge (%) / 100... (b)

[0054] Since the right-hand side of equations (a) and (b) is the same as the amount of chlorine in 100g of dewatered sludge, Sludge moisture content (%) × Chlorine concentration in dewatered filtrate (%) / 100 = (100 - Sludge moisture content (%)) × Chlorine concentration in dried sludge (%) / 100, and rearranging this gives equation (1) above.

[0055] In equation (1), the chlorine concentration in the dewatered filtrate should be a value measured periodically. Since the chlorine concentration in the dewatered filtrate is equal to the chlorine concentration in the water obtained by removing suspended solids from the coagulated water, the chlorine concentration in the dewatered filtrate may also be the measured chlorine concentration of the solid-liquid separated water (sedimented water, filtered water, or turbidity-removed membrane treated water) after the coagulation process.

[0056] By substituting the chlorine concentration with the sulfur concentration, the above equation (2) is obtained.

[0057] Furthermore, since the chlorine and sulfur contained in the dewatered filtrate originate from the treated water and the added inorganic coagulant, if the chlorine and sulfur concentrations in the inorganic coagulant are known, the chlorine and sulfur concentrations in the dewatered filtrate can be calculated using the mass balance from the chlorine and sulfur concentrations in the treated water and the amount of inorganic coagulant added. Based on these calculation results, the target moisture content can be set using equations (1) and (2).

[0058] Furthermore, if there is little fluctuation in wastewater quality, sludge with different moisture content can be collected using a beaker test, and the correlation between the sludge moisture content and the impurity concentration in the dried sludge can be examined. Based on this correlation, the target moisture content can be set. Alternatively, dewatered filtrates with different amounts of inorganic coagulant added can be collected using a beaker test, and the correlation between the amount of inorganic coagulant added and the impurity concentration of chlorine, sulfur, etc. in the dewatered filtrate can be examined. Based on this correlation, the concentration of chlorine, sulfur, etc. in the dewatered filtrate can be estimated from the amount of inorganic coagulant added, and the target moisture content can be set using the above formulas (1) and (2). In any case, the target moisture content may be managed by multiplying it by a safety factor.

[0059] The dewatering machine is operated so that the sludge moisture content is less than or equal to the moisture content calculated using the above formulas (1) and (2). If the dewatering machine is a filter press or belt press dewatering machine, the moisture content of the dewatered sludge is reduced to less than or equal to the above moisture content by controlling at least one of the dewatering time and dewatering pressure.

[0060] It is preferable to periodically measure the chlorine and sulfur concentrations in the dried sludge and manage the chlorine or sulfur concentration in the sludge.

[0061] [Another Embodiment] In the above embodiment, the dewatering machine is controlled to reduce the water content of the dewatered sludge to below the target water content, thereby reducing the chlorine and sulfur concentrations in the dewatered sludge or its dried sludge to below a predetermined value. However, the amount of coagulant added may also be controlled to reduce the chlorine and sulfur concentrations in the dewatered sludge or its dried sludge to below a predetermined value.

[0062] The following describes experimental examples. In the following experimental examples, the following test wastewater was prepared and used as the raw water.

[0063] <Test wastewater> 89.7 g (50 g as W) of reagent-grade tungsten trioxide (WO3) powder (particle size approximately 0.01-0.05 μm) and sodium tungstate (Na ２ WO ４ 63.0 g (50 g as W) of 2H₂O was added to 100 L of pure water and stirred to prepare an aqueous sodium tungstate solution in which tungsten trioxide powder was dispersed, which was used as the test wastewater. Dissolved and undissolved tungsten were present in the wastewater.

[0064] The total concentration of dissolved and undissolved tungsten in the test wastewater is 100 mg / L (W).

[0065] [Experimental Example 1] 50 L of the above test wastewater was placed in a 100 L container, and 750 mg / L of ferric polysulfate (11% total iron) was added as a coagulant (sulfur equivalent concentration 48 mg-S / L). The mixture was rapidly stirred at 120 rpm for 5 min, and then slowly stirred at 40 rpm for 10 min.

[0066] After standing for 10 minutes, the supernatant was removed by decantation to obtain a water-containing sludge (slurry).

[0067] This water-containing sludge was dewatered using a small filter press dewatering machine. The sludge delivery pressure during dewatering was 0.4 MPa, the compression pressure was 0.2 MPa, the sludge delivery time was 10 min, and the compression time was 20 min.

[0068] The water content of the sludge after dewatering was measured. Furthermore, the sulfur content (sulfur concentration) of the dried sludge, obtained by drying the dewatered sludge at 105°C for approximately 12 hours, was measured. The results are shown in Table 1.

[0069] [Experimental Examples 2-4] The same tests as in Experimental Example 1 were conducted, except that the pressure and time during sludge compression were as shown in Table 1.

[0070] Table 1 shows the measurement results for the water content of the dewatered sludge and the sulfur content in the dried sludge.

[0071]

[0072] [Experimental Examples 5-8] The tests were conducted in the same manner as in Experimental Examples 1-4, except that 750 mg / L of ferric chloride was added as a flocculant (chlorine equivalent concentration of 187 mg-Cl / L), and the pressing time and pressing pressure were as shown in Table 2. The concentration of ferric chloride added was set to be equivalent to that of ferric polysulfate in terms of flocculation effect.

[0073] Table 2 shows the measurement results of the water content of the sludge after dehydration and the Cl content (Cl concentration) in the dried sludge.

[0074]

[0075] [Discussion] As shown in Tables 1 and 2, the lower the water content of the dewatered sludge, the lower the S and Cl concentrations in the dry sludge.

[0076] Experimental examples 1 to 4 showed that using ferric polysulfate as a flocculant could reduce the Cl content in the dried sludge to 0.01 wt% or less. By reducing the moisture content to approximately 83.9 wt% or less, it was found that the S content in the dried sludge could be reduced to 0.03 wt% or less, indicating that it can be applied to special steel applications.

[0077] Furthermore, experimental examples 5 to 8 showed that using ferric chloride as a flocculant could reduce the sulfur content in the dry sludge to 0.01 wt% or less. By reducing the moisture content to approximately 65.9 wt% or less, the chlorine content in the dry sludge could be reduced to 0.05 wt% or less, suitable for iron refining applications. However, even with a moisture content of 56.7 wt%, the chlorine content of 0.01 wt% or less, suitable for special steel applications, could not be achieved.

[0078] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications are possible within the scope of achieving the effects of the invention. This application is based on Japanese Patent Application No. 2025-026939, filed on 21 February 2025, which is incorporated herein by reference in its entirety.

Claims

1. A method for treating a tungsten-containing liquid, comprising treating the tungsten-containing liquid with an inorganic coagulant, then performing solid-liquid separation, and separating the resulting coagulated sludge into dewatered sludge and dewatered filtrate by dewatering in a dewatering machine, wherein the coagulated sludge is dewatered so that the concentration of chlorine or sulfur in the dried sludge after drying is below a predetermined value.

2. A method for treating a tungsten-containing liquid according to claim 1, wherein the chlorine or sulfur concentration in the dried sludge is measured and the chlorine or sulfur content of the dried sludge is controlled.

3. A method for treating a tungsten-containing liquid according to claim 1, characterized in that an inorganic flocculant whose counterion is a sulfate ion is used as the inorganic flocculant.

4. A method for treating a tungsten-containing liquid according to claim 1, wherein a target moisture content is set from at least one of the chlorine concentration, sulfur concentration, and amount of inorganic coagulant added to the water to be treated, and the dewatering machine is controlled to achieve the target moisture content.

5. A method for processing a tungsten-containing liquid according to claim 1, wherein at least one of the dewatering time and dewatering pressure of a dewatering machine is controlled according to a target value of moisture content.

6. A method for treating a tungsten-containing liquid according to claim 1, wherein the sludge is dewatered so that the sludge moisture content calculated by the following formula (1) is less than or equal to a predetermined moisture content, in order to reduce the chlorine concentration in the dewatered sludge to a predetermined value or less. Sludge moisture content (%) = [Chlorine concentration in dry sludge (%) / (Chlorine concentration in dewatered filtrate (%) + Chlorine concentration in dry sludge (%))] × 100 … (1) 7. A method for treating a tungsten-containing liquid according to claim 1, wherein the coagulated sludge is dewatered so that the sludge moisture content calculated by the following formula (2) is less than or equal to the predetermined moisture content, in order to set the sulfur concentration in the dewatered sludge to a predetermined value. Sludge moisture content (%) = [Sulfur concentration in dry sludge (%) / (Sulfur concentration in dewatered filtrate (%) + Sulfur concentration in dry sludge (%))] × 100 … (2) 8. The method for treating a tungsten-containing liquid according to claim 4, wherein the amount of coagulant added is changed according to the target value of the target water content.

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