Method for treating tungsten-containing liquid and device for treating tungsten-containing liquid

Abstract

A method for treating a tungsten-containing liquid, said method including a flocculation treatment step for performing a flocculation treatment on a tungsten-containing liquid by using an inorganic flocculant, a solid-liquid separation treatment step for performing a solid-liquid separation treatment on a flocculated sludge obtained in the flocculation treatment step, and a dehydrating treatment step for performing a dehydrating treatment on a separated sludge obtained in the solid-liquid separation treatment step, and said method being characterized by comprising a sludge return step for returning a portion of the separated sludge obtained in the solid-liquid separation treatment step to the flocculation treatment step.

Description

Method for treating tungsten-containing liquid and apparatus for treating tungsten-containing liquid

[0001] The present invention relates to a method for treating a tungsten (W)-containing liquid and a device for treating a tungsten-containing liquid, and more specifically, to a method and apparatus for coagulating a tungsten-containing liquid, separating the resulting coagulated sludge into solid and liquid phases, and dewatering the obtained separated sludge.

[0002] Tungsten, a type of rare metal, is used in a wide range of industrial fields, including semiconductor applications such as sputtering targets, industrial machinery such as automobiles as cutting tools and wear-resistant tools, and chemical industries such as desulfurization and denitrification catalysts. Therefore, tungsten recycling is being considered.

[0003] Patent Document 1 describes a method for recovering tungsten from a tungsten-containing solution, which involves concentrating a rare metal ion-containing solution, such as tungsten, using a membrane, and then extracting the rare metal ions from the concentrated solution with an extractant.

[0004] Patent Document 2 describes a method for obtaining metallic tungsten by hydrogen reduction of tungstate in a tungstate-containing mineral, which is converted to tungsten oxide via alkali tungstate and ammonium tungstate. In this method, an aluminum compound is added to an aqueous solution of alkali tungstate to adsorb impurities in the alkali tungstate onto aluminum hydroxide and precipitate it, thereby purifying the alkali tungstate.

[0005] As a method for recovering tungsten from tungsten-containing materials, the method for recovering tungsten from superalloy scrap described in Non-Patent Document 1 has already been put into practical use.

[0006] Furthermore, Non-Patent Document 2 describes a method for removing tungsten from tungsten-containing liquids, which involves immobilizing the tungsten in tungsten-containing wastewater with an inorganic coagulant, followed by coagulation, sedimentation, and separation for removal. However, Non-Patent Document 2 only describes the removal of tungsten from tungsten-containing wastewater and does not disclose any method for treating the coagulated and settled sludge.

[0007] When treating tungsten-containing wastewater and using the treated water as recovered water, it is necessary to first coagulate the tungsten-containing wastewater, and then perform recovery treatments such as membrane separation and desalination in the treated water recovery process.

[0008] However, in the coagulation treatment of tungsten-containing wastewater, iron-based inorganic coagulants such as ferric polysulfate and ferric chloride are usually used. As a result, iron ions leak into the treated water, placing a heavy load on downstream solid-liquid separation equipment such as turbidity removal membranes and filters, and desalination equipment such as reverse osmosis (RO) membranes. This can cause problems such as blockages, leading to a deterioration in the quality and recovery rate of the recovered water.

[0009] In other words, when tungsten-containing wastewater is treated with an inorganic coagulant, small flocs called pin flocs are generated. These small flocs do not settle in the sedimentation tank and leak to the downstream stage, clogging the ultrafiltration (UF) membranes and filters in the downstream filtration process, causing an increase in differential pressure and an increase in the frequency of membrane cleaning such as backwashing. As a result, this leads to a decrease in treated water volume (a decrease in water recovery rate) and a deterioration in treated water quality.

[0010] Furthermore, under conventional methods, tungsten-containing flocculated and settled sludge generated from the treatment of tungsten-containing wastewater was generally mixed with other sludge, dewatered using a filter press dewatering machine, and then treated as industrial waste. Therefore, conventionally, the optimal dewatering method for recovering flocculated sludge containing only tungsten has not been sufficiently considered.

[0011] However, solid-liquid separated sludge from tungsten-containing flocculated sludge has small particle sizes, and when attempting to dewater it using a filter press dewatering machine, the sludge particles can clog the filter cloth, resulting in poor dewatering, and in some cases, dewatering becomes impossible due to the blockage of the filter cloth. If the water content of the dewatered sludge is high due to poor dewatering, not only will the refining costs for subsequent W recovery increase, but transportation costs will also increase, significantly diminishing its value as a valuable material.

[0012] JP2023-55031A JP2023-107527A

[0013] "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)

[0014] In view of the above-mentioned conventional situation, the present invention aims to provide a method for treating a tungsten-containing liquid and a treatment apparatus for a tungsten-containing liquid that efficiently recovers tungsten as a valuable material when treating the tungsten-containing liquid and recovering the treated water, while also improving the water quality and recovery rate of the recovered water.

[0015] As a result of repeated studies to solve the above problems, the inventors of the present invention have found that the above problems can be solved by flocculating a tungsten-containing liquid with an inorganic flocculant, then performing solid-liquid separation, and returning a portion of the separated sludge to the flocculation process when dewatering the resulting separated sludge.

[0016] In other words, the gist of this invention is as follows:

[0017] [1] A method for treating a tungsten-containing liquid, comprising a coagulation step of coagulating the tungsten-containing liquid with an inorganic coagulant, a solid-liquid separation step of solid-liquid separation of the coagulated sludge obtained in the coagulation step, and a dewatering step of dewatering the separated sludge obtained in the solid-liquid separation step, wherein the method is characterized by having a sludge return step of returning a portion of the separated sludge obtained in the solid-liquid separation step to the coagulation step.

[0018] [2] The method for treating a tungsten-containing liquid according to [1], characterized in that the sludge return step is a step of returning a portion of the separated sludge to the reaction tank to which the inorganic coagulant in the coagulation treatment step is added.

[0019] [3] The method for treating a tungsten-containing liquid according to [2], characterized in that the pH of the reaction vessel is adjusted to 5.5 or higher.

[0020] [4] A method for treating a tungsten-containing liquid according to any one of [1] to [3], characterized in that the sludge concentration of the separated sludge to be dewatered in the dewatering step is adjusted to 2% or more.

[0021] [5] A method for treating a tungsten-containing liquid according to any one of [2] to [4], characterized in that the concentration of suspended solids in the reaction vessel is adjusted to 1500 mg / L or more.

[0022] [6] A method for treating a tungsten-containing liquid according to any one of [1] to [5], characterized in that the inorganic flocculant is aluminum sulfate, ferrous sulfate, polyferric sulfate, aluminum chloride, polyaluminum chloride, and ferric chloride.

[0023] [7] A method for treating a tungsten-containing liquid according to any one of [1] to [6], characterized in that it includes a pH adjustment step for adjusting the pH of the tungsten-containing liquid prior to the coagulation treatment step.

[0024] [8] A method for treating a tungsten-containing liquid according to any one of [1] to [7], wherein the tungsten concentration of the tungsten-containing liquid is 1 mg-W / L or more.

[0025] [9] A tungsten-containing liquid processing apparatus comprising: a flocculation processing means for flocculating a tungsten-containing liquid with an inorganic flocculant; a solid-liquid separation processing means for solid-liquid separation processing of the flocculated sludge obtained by the flocculation processing means; and a dewatering processing means for dewatering the separated sludge obtained by the solid-liquid separation processing means, wherein the apparatus is characterized by having a sludge return means for returning a portion of the separated sludge obtained by the solid-liquid separation processing means to the flocculation processing means.

[0026] According to the present invention, when a tungsten-containing liquid is subjected to coagulation treatment with an inorganic flocculant, the coagulated sludge is subjected to solid-liquid separation treatment, and the separated sludge is dehydrated to recover tungsten-containing sludge as a valuable W product, and when recovering the treated water, by returning a part of the dehydrated sludge to the coagulation treatment step, tungsten in the tungsten-containing liquid can be efficiently recovered as a valuable W product, and recovered water with good water quality can be obtained at a high recovery rate.

[0027] That is, according to the present invention, the unreacted inorganic flocculant in the coagulation treatment step reacts with the coagulation flocs of the returned sludge containing pin flocs to promote the growth of the flocs, thereby increasing the floc diameter, and improving the water quality and recovery rate of the recovered water, the solid-liquid separation property of the coagulated sludge, and further the dehydration property.

[0028] In particular, according to one embodiment of the present invention, the floc diameter can be further increased by setting the sludge return location as a reaction tank to which an inorganic flocculant is added.

[0029] Further, according to one embodiment of the present invention, by adjusting the pH of the sludge return location to 5.5 or more, redissolution of the returned sludge can be prevented, and the floc diameter can be further increased.

[0030] Further, according to one embodiment of the present invention, by adjusting the sludge concentration of the returned sludge and the sludge to be subjected to dehydration treatment to 2% or more by sludge return, coarsening of the flocs can be effectively achieved, and the water quality and recovery rate of the recovered water, the solid-liquid separation property of the coagulated sludge, and further the dehydration property can be further improved.

[0031] Further, according to one embodiment of the present invention, by returning sludge to the reaction tank, the turbidity of the treated water can be lowered by setting the concentration of suspended substances in the reaction tank to 1500 mg / L or more.

[0032] From such a situation, according to the present invention, leakage of coagulation flocs containing tungsten into the coagulation-treated water is suppressed, and valuable recovery is promoted by recovering tungsten as an aggregate, and at the same time, leakage of flocs into the coagulation-treated water is suppressed, and improvement of the drained water recovery water quality and improvement of the recovery rate of the recovered water can be promoted.

[0033] According to the present invention, by providing conditions that balance the performance of W valuable material recovery and wastewater recovery treatment, it is possible to achieve stable operation of the entire factory and minimize operating costs such as energy costs.

[0034] FIG. 1 is a flowchart showing an embodiment of a tungsten-containing liquid treatment apparatus of the present invention.

[0035] Hereinafter, embodiments of a tungsten-containing liquid treatment method and a tungsten-containing liquid treatment apparatus of the present invention will be described in detail.

[0036] 〔Tungsten-containing liquid treatment method〕 The tungsten-containing liquid treatment method of the present invention includes a coagulation treatment step of coagulating a tungsten-containing liquid with an inorganic flocculant, a solid-liquid separation treatment step of performing solid-liquid separation on the coagulated sludge obtained in the coagulation treatment step, and a dehydration treatment step of dehydrating the separated sludge obtained in the solid-liquid separation treatment step. In the tungsten-containing liquid treatment method, it is characterized by having a sludge return step of returning a part of the separated sludge obtained in the solid-liquid separation treatment step to the coagulation treatment step.

[0037] [Mechanism] According to the present invention, when a tungsten-containing liquid is coagulated with an inorganic flocculant, the coagulated sludge is subjected to solid-liquid separation, and the separated sludge is dehydrated to recover tungsten-containing sludge as a W valuable material and recover treated water. By returning a part of the dehydrated sludge to the coagulation treatment step, the unreacted inorganic flocculant in the coagulation treatment step reacts with the coagulation flocs of the returned sludge containing pin flocs, promoting the growth of the flocs and increasing the floc diameter. As a result, tungsten in the tungsten-containing liquid can be efficiently recovered as a W valuable material, and recovered water with good water quality can be obtained at a high recovery rate. [[ID=!13]]

[0038] [Tungsten-containing liquid] As the tungsten-containing liquid, tungsten-containing wastewater is preferable. As the tungsten-containing wastewater, used tungsten catalyst-containing wastewater used in organic synthesis such as heavy oil refining, and denitrification in thermal power plants ＸExamples include, but are not limited to, tungsten-containing wastewater used in the manufacturing process, tungsten-containing liquids obtained by alkaline extraction or alkaline dissolution methods in the recycling process of ultrahard alloy scrap, contaminated groundwater and leachate from landfills, and wastewater discharged from electronic component manufacturing processes.

[0039] The tungsten concentration in the tungsten-containing wastewater treated by the present invention is usually 1 mg-W / L or higher, for example, 1 to 3000 mg-W / L, and particularly preferably around 20 to 500 mg-W / L, but is not limited thereto.

[0040] [Agglutination Treatment Process] In the agglutination treatment process, an inorganic flocculant is added to the tungsten-containing liquid described above to perform agglutination treatment. In the agglutination treatment process, a polymer flocculant may also be used to coarseen the flocs.

[0041] <Inorganic Coagulants> As inorganic coagulants used in the coagulation treatment of tungsten-containing liquids, salts of aluminum, iron, etc. are suitable, and sulfates or chlorides are particularly preferred. Specifically, aluminum sulfate, ferrous sulfate, polyferric sulfate, aluminum chloride, polyaluminum chloride, and ferric chloride are preferred. Of these, sulfates are preferred as inorganic coagulants from the viewpoint of impurities that can be tolerated in the recycling process when sludge is used as a resource, and ferrous sulfate and polyferric sulfate are particularly preferred.

[0042] The amount of inorganic flocculant added is appropriately determined depending on the W concentration in the tungsten-containing liquid and the type of inorganic flocculant used. However, when the tungsten concentration in the tungsten-containing liquid is about 20 to 500 mg / L, it is preferable to add about 100 to 4000 mg / L of, for example, ferric polysulfate (11% total iron).

[0043] When treating a tungsten-containing liquid with an inorganic flocculant, particularly an iron-based inorganic flocculant, it is preferable to adjust the pH to 5.5 to 6.4 using a pH adjusting agent (such as hydrochloric acid or sulfuric acid, or an alkali such as sodium hydroxide).

[0044] In other words, if the pH in the coagulation treatment system is less than 5.5, Fe derived from the iron-based inorganic coagulant may leak into the treated water, reducing the coagulation effect and causing tungsten to leak as well. On the other hand, if the pH exceeds 6.4, tungsten will leak into the treated water as the pH increases. This is because if the pH is higher than 6.4, tungsten will be released into the water. ４ ２－ This is because it exists in a form that reduces its reactivity with inorganic flocculants. If the pH is 6.4 or lower, tungsten is W １２ O ４１ １０－ By existing in this form, the co-precipitation reaction with inorganic flocculants is promoted, resulting in an excellent flocculation effect.

[0045] Furthermore, from the viewpoint of reliably obtaining such effects, it is preferable that the returned sludge be added to a reaction tank to which an inorganic coagulant has been added and the pH has been adjusted to 5.5 to 6.4.

[0046] Furthermore, from the standpoint of pH adjustment stability, it is desirable to have a pH adjustment step before the coagulation treatment with an inorganic coagulant if the raw water pH differs from the coagulation pH.

[0047] <Polymer flocculants> After flocculation treatment with inorganic flocculants, further flocculation treatment can be performed by adding polymer flocculants. In this case, it is preferable to use acrylamide-based anionic polymer flocculants or cationic polymer flocculants, and the amount added is preferably 0.1 to 20 mg / L, and particularly preferably about 1 to 10 mg / L.

[0048] [Solid-Liquid Separation Process] In the solid-liquid separation process, the flocculated sludge obtained in the flocculation process is subjected to solid-liquid separation to obtain separated sludge. A portion of the obtained separated sludge is returned to the flocculation process, and the remainder is subjected to dewatering to recover the separated water (flocculated water).

[0049] [Sludge Return Process] The sludge return process is the process of returning a portion of the sludge separated in the solid-liquid separation process to the coagulation process.

[0050] The return point for this separated sludge is preferably a location in the coagulation treatment process where the pH is 5.5 or higher. If the pH at the return point of the separated sludge is less than 5.5, the flocs will be destroyed by the redissolution of the sludge. If the pH at the return point is 5.5 or higher, the redissolution of the returned sludge is prevented, promoting floc growth and increasing the floc diameter.

[0051] Typically, the preferred pH range for the flocculation treatment process using inorganic flocculants is 5.5 to 6.4, as mentioned above. Therefore, a reaction tank treated with inorganic flocculants is preferred as the sludge return point.

[0052] Furthermore, the sludge concentration (SS concentration) of this returned sludge (which is also the sludge used for dewatering) is preferably 2% (by weight) or higher.

[0053] If the concentration of the returned sludge is too low, the effects of the present invention due to sludge return cannot be fully obtained. The concentration of the returned sludge is preferably 2% or more, and more preferably 3% or more. On the other hand, if the sludge concentration is too high, sludge will accumulate and clog the sludge sedimentation tank and sludge transport piping, so it is preferable that the upper limit of the sludge concentration of the returned sludge be 15% or less, and more preferably 10% or less.

[0054] The sludge concentration mentioned above can be controlled by factors such as the amount of sludge returned to the coagulation treatment process from the separated sludge, and the pH conditions at the return location.

[0055] The suspended solid concentration in the reaction tank to which the separated sludge is returned is not particularly limited, but it is preferably 1500 mg / L or more, and more preferably 2500 mg / L or more. This is because when the suspended solid concentration in the reaction tank is 1500 mg / L or more, the suspended solids efficiently collide with each other to coarsen the flocs, resulting in a decrease in the turbidity of the treated water. When the suspended solid concentration is too high, the number of colliding fine particles increases, the flocs do not coarsen, and the turbidity of the treated water increases. Therefore, the suspended solid concentration in the reaction tank is preferably 9000 mg / L or less. The suspended solid concentration in the reaction tank is the sum of the suspended solids (sludge) derived from the returned separated sludge and the suspended solids derived from the tungsten-containing liquid. The suspended solids derived from the tungsten-containing liquid are the sum of the suspended solids originally present in the tungsten-containing liquid and the suspended solids precipitated in the coagulation step.

[0056] [Dewatering treatment step] In the dewatering treatment step, the remaining part of the returned sludge among the separated sludge obtained in the solid-liquid separation treatment step is dewatered. For this dewatering treatment, it is preferable to use a filter press dewatering machine because a low moisture content can be achieved.

[0057] In the present invention, the dewatering of this separated sludge is preferably carried out by squeezing and dewatering using a filter cloth with an air permeability of 40 cm ３ / cm ２ / min or less.

[0058] When the air permeability of the filter cloth used exceeds 40 cm ３ / cm ２ / min, the sludge passes through the filter cloth, resulting in clogging of the filter cloth and poor dewatering. The recovery rate of W valuable substances decreases, and the quality of the dewatering filtrate also deteriorates.

[0059] From the viewpoints of preventing clogging of the filter cloth, improving the recovery rate of W valuable substances, and improving the quality of the dewatering filtrate, the air permeability of the filter cloth used is more preferably 40 cm ３ / cm ２ / min or less, and even more preferably 20 cm ３ / cm ２ / min or less. On the other hand, when the air permeability of the filter cloth is excessively low, the squeezing pressure increases and the dewatering efficiency decreases. Therefore, the air permeability of the filter cloth is 0.01 cm ３ / cm２ / min or more, especially 6cm ３ / cm ２ It is preferable that it be greater than or equal to / min.

[0060] Here, the air permeability of the filter cloth is 1 cm per minute. ２ Volume of air passing through the filter cloth area (cm³) ３ This value represents the degree of air permeability; the higher the degree of air permeability, the coarser the mesh of the filter cloth, and the lower the degree of air permeability, the finer the mesh of the filter cloth.

[0061] There are no particular restrictions on the material, weave, or yarn form of the filter cloth used in the present invention. However, from the viewpoint of sludge release properties and durability, the material of the filter cloth is preferably one of polypropylene, nylon, polyester, Tetron®, Saran®, or Pyrene®, and polypropylene is particularly preferred from the viewpoint of sludge release properties.

[0062] Furthermore, examples of weaving patterns for the filter cloth include plain weave, twill weave, and satin weave, which are preferred from the viewpoint of sludge removal and durability.

[0063] Furthermore, examples of the yarn form used for the filter cloth include spun yarn, multifilament yarn, and monofilament yarn, with multifilament yarn being preferred from the viewpoint of sludge release and durability.

[0064] While there are no particular restrictions on the compression conditions when dewatering separated sludge using such a filter cloth, it is preferable from the viewpoint of dewatering efficiency to set the sludge supply pressure to 0.1 to 0.4 MPa and the compression pressure to 0.4 to 1.0 MPa.

[0065] The dewatered sludge obtained through this dewatering process is typically a highly concentrated sludge with a water content of 70% or less, and contains tungsten from the tungsten-containing liquid with a high recovery rate. Therefore, it can be reused in various fields as a valuable material.

[0066] [Tungsten-containing liquid treatment apparatus] The tungsten-containing liquid treatment apparatus of the present invention includes a flocculation treatment means for flocculating the tungsten-containing liquid with an inorganic flocculant, a solid-liquid separation treatment means for solid-liquid separation treatment of the flocculated sludge obtained by the flocculation treatment means, and a dewatering treatment means for dewatering the separated sludge obtained by the solid-liquid separation treatment means, and is characterized by having a sludge return means for returning a portion of the separated sludge obtained by the solid-liquid separation treatment means to the flocculation treatment means, and is suitably used in carrying out the tungsten-containing liquid treatment method of the present invention described above.

[0067] The tungsten-containing liquid processing apparatus of the present invention will be described more specifically below with reference to Figure 1, which shows one embodiment of the present invention. However, the tungsten-containing liquid processing apparatus of the present invention is not limited to the one shown in Figure 1.

[0068] In the tungsten-containing liquid treatment apparatus shown in Figure 1, the tungsten-containing liquid is supplied to the neutralization tank 2 via the raw water tank 1, where its pH is adjusted to a predetermined pH using a pH adjusting agent, and then supplied to the reaction tank 3, where an inorganic coagulant is added for coagulation treatment. In the reaction tank 3, a further pH adjusting agent is added as needed to adjust the pH to a pH suitable for coagulation treatment. The treated liquid from the reaction tank 3 is further treated in the coagulation tank 4 with the addition of a polymer coagulant, and the coagulated sludge, with its flocs becoming coarser, is separated into solid and liquid in the sedimentation tank 5.

[0069] The separated water (sedimented water) from the sedimentation tank 5 is sent to the wastewater recovery facility 7 via the sedimentation treatment tank 6. The wastewater recovery facility 7 is equipment for reusing the sedimentation treatment water for various uses within the facility, and includes filtration devices such as ultrafiltration (UF) membranes and microfiltration (MF) membranes for removing suspended solids, and reverse osmosis (RO) membrane devices for desalination. The sedimentation treatment water may be discharged as is if it meets the discharge standards.

[0070] Meanwhile, a portion of the separated sludge from the sedimentation tank 5 is returned to the reaction tank 3, and the remainder is sent to the sludge dewatering machine 9 via the sludge storage tank 8 for dewatering treatment.

[0071] The sludge dewatering machine 9 is preferably a filter press dewatering machine equipped with a filter cloth having the aforementioned degree of permeability, and efficiently dewaters the separated sludge.

[0072] The dewatered sludge obtained from the sludge dewatering machine 9 is sent to the W valuable material recovery equipment 11 via the dewatered sludge storage tank 10, where it is further subjected to processes such as alkaline fusion and extraction and reused as W resource.

[0073] Meanwhile, the dewatered filtrate obtained from the sludge dewatering machine 9 is sent to the wastewater treatment facility 13 via the dewatered filtrate storage tank 12. In this invention, since the dewatered filtrate obtained from the sludge dewatering machine 9 is of good water quality with a low SS concentration, the wastewater treatment facility 13 performs discharge or advanced treatment depending on the dissolved components.

[0074] The present invention will be explained more specifically below with reference to experimental examples that can be used in place of the embodiments.

[0075] [Test wastewater] The following preparations were used as the test wastewater.

[0076] Reagent-grade tungsten trioxide (WO ３ ) Powder (particle size approximately 0.01-0.05 μm) 89.7 g (50 g as W) and sodium tungstate (Na ２ WO ４ ・2H ２ O) 63.0 g (50 g as W) was added to 100 L of pure water and stirred to prepare an aqueous sodium tungstate solution in which tungsten trioxide powder was dispersed, and this was used as the test wastewater. Dissolved and undissolved tungsten coexisted in the wastewater.

[0077] The total concentration of dissolved and undissolved tungsten in this test wastewater is 100 mg / L (W).

[0078] [Experimental Example 1] 50 L of the above test wastewater was placed in a 100 L container, and a pH adjuster was added to adjust the pH to 5.9. Then, 750 mg / L of ferric polysulfate (11% total iron) was added as a coagulant, and the mixture was rapidly stirred at 120 rpm for 5 min, followed by slow stirring at 40 rpm for 10 min. After standing for 10 min, the supernatant was removed by decantation to obtain a water-containing sludge (slurry). Note that a pH adjuster was added after the addition of ferric polysulfate to maintain the pH at 5.9.

[0079] The turbidity of the removed supernatant was measured using an NTU turbidimeter, and the state of suspended flocs was visually observed and evaluated according to the following criteria. The results are shown in Table 1. The measurement of turbidity of the supernatant and the observation of the state of suspended flocs were performed in the same manner in the following experimental examples.

[0080] <Condition of floating flocs> ○: No floating flocs present △: Small amount of floating flocs present ×: Many floating flocs present

[0081] [Experimental Example 2] 50 L of the above test wastewater was placed in a 100 L container, and a pH adjuster was added to adjust the pH to 5.9. Then, to simulate sludge return, 7.5 L of pre-prepared water-containing sludge was added to this container so that the sludge concentration of the water-containing sludge to be dewatered would be as shown in Table 1. At the same time, 750 mg / L of ferric polysulfate (11% total iron) was added as a coagulant, and the mixture was rapidly stirred at 120 rpm for 5 min, followed by slow stirring at 40 rpm for 10 min. After standing for 10 min, the supernatant was removed by decantation to obtain water-containing sludge (slurry). Note that a pH adjuster was added to maintain the pH at 5.9 even after the addition of ferric polysulfate. Here, the turbidity and suspended floc state of the removed supernatant are shown in Table 1.

[0082] The water-containing sludge obtained above was dewatered using a small filter press dewatering machine with the following filter cloth. The sludge supply pressure during dewatering was 0.4 MPa, the compression pressure was 0.7 MPa, the sludge supply time was 120 min, and the compression time was 20 min.

[0083] Filter cloth: Made of polypropylene multifilament yarn, thickness: 0.99 mm, breathability: 20 cm ３ / cm ２ / min twill weave filter cloth

[0084] The moisture content of the dewatered sludge obtained from this dewatering process was measured using an infrared moisture meter.

[0085] Furthermore, as an indicator of sludge leakage, the SS concentration of the dewatered filtrate was obtained by measuring the weight before and after filtering through filter paper with a pore size of 1 μm.

[0086] Furthermore, the dewatering properties of the filter cloth were examined using a small filter press dewatering machine, and its suitability (good / bad) was confirmed.

[0087] These results are shown in Table 1.

[0088] [Experimental Example 3] 50 L of the above test wastewater was placed in a 100 L container, and a pH adjuster was added to adjust the pH to 4.1. Then, to simulate sludge return, 7.5 L of pre-prepared water-containing sludge was added to this container so that the sludge concentration of the water-containing sludge to be dewatered would be as shown in Table 1. Next, the pH was adjusted to 5.9, and then 750 mg / L of ferric polysulfate (11% total iron) was added as a coagulant. The mixture was rapidly stirred at 120 rpm for 5 min, and then slowly stirred at 40 rpm for 10 min. After standing for 10 min, the supernatant was removed by decantation to obtain water-containing sludge (slurry). Note that a pH adjuster was added after the addition of ferric polysulfate to maintain a pH of 5.9. Here, the turbidity of the removed supernatant and the state of suspended flocs are shown in Table 1.

[0089] The water-containing sludge obtained above was dewatered using a small filter press dewatering machine, as in Experimental Example 2, and measured and evaluated in the same manner as in Experimental Example 2. The results are shown in Table 1.

[0090] [Experimental Example 4] The coagulation treatment was carried out in the same manner as in Experimental Example 2, except that 7.5 L of pre-prepared water-containing sludge was added so that the sludge concentration of the water-containing sludge subjected to dewatering was as shown in Table 1.

[0091] In this experimental example, the turbidity of the removed supernatant was 0.9, but a small amount of suspended flocs was present. The results of the measurement and evaluation of the supernatant are shown in Table 1.

[0092] [Experimental Example 5] The experiment was conducted in the same manner as in Experimental Example 2, except that 7.5 L of pre-prepared water-containing sludge was added so that the sludge concentration of the water-containing sludge subjected to dewatering reached the sludge concentration shown in Table 1. The results are shown in Table 1.

[0093] [Experimental Example 6] The flocculation treatment was carried out in the same manner as in Experimental Example 3, except that the pH was set to 4.1 when ferric polysulfate was added.

[0094] In this experimental example 6, the pH was 4.1 both when adding the water-containing sludge and when adding the coagulant ferric polysulfate. Therefore, even when the same amount of water-containing sludge at the same concentration as in experimental example 3 was added, the sludge concentration did not increase, the turbidity of the removed supernatant was high, and a large number of suspended flocs were present.

[0095]

[0096] From the results above, we can conclude the following:

[0097] Experimental examples 1 and 2 show that by adding water-containing sludge that mimics sludge return, the turbidity of the coagulated water can be reduced to 0.83 NTU, no suspended flocs like pin flocs are observed, and recovered water of good quality can be obtained.

[0098] In contrast, as in Experimental Example 1, when no water-containing sludge is added (sludge is not returned) and the concentration of suspended solids during the coagulation process is low, it can be seen that there are many suspended flocs in the coagulated treated water, and the water quality of the treated water deteriorates.

[0099] Experimental examples 2, 4, and 5 show that the higher the sludge concentration of the separated sludge and the concentration of suspended solids in the coagulation process, i.e., the reaction tank, by adding water-containing sludge that simulates sludge return, the lower the turbidity of the coagulated treated water and the better the water quality tends to be.

[0100] Experimental Example 3 shows that when the pH is 4.1 when water-containing sludge is added, the turbidity of the treated water is high at 1.3 NTU, and the SS concentration of the dewatered filtrate is also high. From this, it is thought that when the pH at the sludge return point is low at 4.1, the turbidity of the treated water worsens and the SS concentration of the dewatered filtrate also increases.

[0101] Experimental Example 6 shows that when both the pH at the sludge return point (when water-containing sludge is added) and the pH when the inorganic coagulant is added are 4.1, the turbidity of the coagulated water becomes 1.3 NTU or higher, which is the highest.

[0102] 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, and Japanese Patent Application No. 2025-135890, filed on 18 August 2025, which are incorporated herein by reference in their entirety.

[0103] 1. Raw water tank 2. Neutralization tank 3. Reaction tank 4. Coagulation tank 5. Sedimentation tank 6. Sedimentation treatment tank 7. Wastewater recovery equipment 8. Sludge storage tank 9. Sludge dewatering machine 10. Dewatered sludge storage tank 11. W valuable material recovery equipment 12. Dewatered filtrate storage tank 13. Wastewater treatment equipment

Claims

A method for treating a tungsten-containing liquid, comprising a coagulation step of coagulating the tungsten-containing liquid with an inorganic coagulant, a solid-liquid separation step of performing solid-liquid separation on the coagulated sludge obtained in the coagulation step, and a dewatering step of performing dewatering on the separated sludge obtained in the solid-liquid separation step, A method for treating a tungsten-containing liquid, characterized by having a sludge return step in which a portion of the separated sludge obtained in the solid-liquid separation step is returned to the coagulation step. 　 The method for treating a tungsten-containing liquid according to claim 1, characterized in that the sludge return step is a step of returning a portion of the separated sludge to the reaction tank to which the inorganic coagulant is added in the coagulation treatment step. 　 The method for treating a tungsten-containing liquid according to claim 2, characterized in that the pH of the reaction vessel is adjusted to 5.0 or higher. 　 The method for treating a tungsten-containing liquid according to claim 1, characterized in that the sludge concentration of the separated sludge to be dewatered in the dewatering step is adjusted to 2% or more. 　 The method for treating a tungsten-containing liquid according to claim 2, characterized in that the concentration of suspended solids in the reaction vessel is adjusted to 1500 mg / L or more. 　 The method for treating a tungsten-containing liquid according to claim 1, characterized in that the inorganic flocculant is one of aluminum sulfate, iron sulfate, polyferrous sulfate, aluminum chloride, polyaluminum chloride, and ferric chloride. 　 The method for treating a tungsten-containing liquid according to claim 1, characterized in that it includes a pH adjustment step for adjusting the pH of the tungsten-containing liquid prior to the coagulation treatment step. 　 A method for treating a tungsten-containing liquid according to any one of claims 1 to 7, wherein the tungsten concentration of the tungsten-containing liquid is 1 mg-W / L or more. 　 A tungsten-containing liquid processing apparatus comprising: a flocculation processing means for flocculating a tungsten-containing liquid with an inorganic flocculant; a solid-liquid separation processing means for solid-liquid separation processing of the flocculated sludge obtained by the flocculation processing means; and a dewatering processing means for dewatering the separated sludge obtained by the solid-liquid separation processing means, A tungsten-containing liquid treatment apparatus, characterized by having a sludge return means for returning a portion of the separated sludge obtained by the solid-liquid separation treatment means to the coagulation treatment means.

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