Method for treating fluoride-containing water

Abstract

Provided is a method and apparatus for treating fluorine-containing water, which can stably obtain water having a low elemental fluorine concentration from a liquid containing fluoride ions and water. [Solution] A method for treating fluoride-containing water, comprising: adding a coagulant to a dispersion containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water; precipitating the calcium fluoride aggregates in the suspension to separate them into a supernatant liquid 11 and deposits 9, 10; adding a part of the deposits and a calcium ion-containing liquid 4 to a fluoride ion-containing liquid 12 to precipitate calcium fluoride in the presence of sulfate ions to obtain a dispersion containing calcium fluoride and water; and adjusting the amount of sulfate ions present when adding the part of the separated deposits and the calcium ion-containing liquid to a liquid containing fluoride ions and water to 35 mass % or less of the amount of elemental fluorine contained in the liquid containing fluoride ions and water, and adjusting the sulfate ion concentration in the supernatant liquid to 100 mg / L or more.

Description

[Technical field]

[0001] The present invention relates to a method for treating fluorine-containing water, and more particularly to a method for treating fluorine-containing water, which can stably obtain water having a low elemental fluorine concentration from a liquid containing fluoride ions and water. [Background technology]

[0002] The coagulation sedimentation method and HDS method are known as methods for treating fluoride-containing water. - ) and calcium compounds such as calcium hydroxide and calcium carbonate (Ca 2+ The HDS method includes adding a calcium fluoride compound to a fluoride-containing water solution to precipitate calcium fluoride (CaF2), flocculating the precipitated calcium fluoride with a flocculating agent, and separating the calcium fluoride aggregates and water by precipitation. The HDS method includes flocculating the precipitated calcium fluoride with a flocculating agent, separating the calcium fluoride aggregates and water by precipitation, and adding a calcium compound and a part of the calcium fluoride aggregates separated above to fluoride-containing water to precipitate calcium fluoride. The HDS method can make the calcium fluoride aggregates higher density and lower water content than the flocculation precipitation method. Then, hydrofluoric acid can be obtained by reacting the obtained calcium fluoride (CaF2) with an acid such as sulfuric acid.

[0003] In the HDS process, various proposals have been made to further improve the sludge density, reduce the moisture content, and reduce the fluorine concentration of the treated water.

[0004] For example, Patent Document 1 discloses a method for treating wastewater containing fluoride ions, which comprises reacting wastewater containing fluoride ions with a calcium compound in a reaction tank to generate insoluble matter, separating the insoluble matter, and returning the separated insoluble matter to the reaction tank, characterized in that the pH in the reaction tank is adjusted to 9.5 to 11, and the amount of insoluble matter returned to the reaction tank is 20 times or more by weight the amount of insoluble matter generated by the reaction of the calcium compound with the wastewater.

[0005] Patent Document 2 discloses a method for treating fluorine-containing water, which comprises adding a calcium compound to fluorine-containing water to generate calcium fluoride sludge and separating the generated calcium fluoride sludge, in which a part of the generated calcium fluoride sludge is brought into contact with a calcium compound and then added to the fluorine-containing water, and further discloses a method for treating fluorine-containing water, which comprises adding sulfate ions to the fluorine-containing water. Patent Document 2 further discloses that in the method for treating fluorine-containing water, sulfate ions are added in an amount of 0.01 to 0.1 equivalents relative to fluoride ions in the fluorine-containing water.

[0006] Patent Document 3 discloses a fluoride removal device having a reaction tank for reacting fluoride-containing water with a calcium compound, a raw water channel for introducing fluoride-containing water into the reaction tank, a flocculation device for transferring the reaction liquid from the reaction tank and adding a polymer flocculant to perform flocculation, a solid-liquid separation tank for introducing a mixed liquid containing flocs formed in the flocculation device and forming a sludge blanket with upward flowing water to perform solid-liquid separation, and a circulation path for adding a calcium compound to a part of the sludge separated in the solid-liquid separation tank and circulating the sludge to the reaction tank.

[0007] Patent Document 4 discloses a method for treating fluorine-containing wastewater, which is discharged from a semiconductor manufacturing process and contains substantially no sulfate ions, by adding a calcium compound to adjust the pH to 5 to 10, and then separating the resulting insoluble matter by precipitating, characterized in that sulfuric acid and / or a sulfate salt are added to the fluorine-containing wastewater before or during the addition of the calcium compound so that the sulfate ion concentration is 200 to 1000 mg / L.

[0008] Patent Document 5 discloses a method for treating fluoride-containing wastewater which comprises adding a calcium salt to the fluoride-containing wastewater and carrying out a coagulation and precipitation treatment, the method comprising: a fluoride ion concentration measuring step of measuring the fluoride ion concentration in the fluoride-containing wastewater by a fluoride ion electrode method; and a calcium concentration calculating step of calculating the calcium concentration of the calcium salt to be added by applying the fluoride ion concentration measured in the fluoride ion concentration measuring step to formula (I). 200≦C 1 -C 2 ×Aw(Ca) / 2Aw(F)≦1500 Formula (I) However, C 1 represents the calcium concentration of the calcium salt [mg / L], and C 2 represents the fluoride ion concentration [mg / L] measured in the fluoride ion concentration measuring step, Aw(Ca) represents the atomic weight of calcium, and Aw(F) represents the atomic weight of fluorine. Furthermore, Patent Document 5 describes that in the above-mentioned method for treating fluoride-containing wastewater, when sulfate ions are present in the fluoride-containing wastewater at a concentration of 1000 mg / L or more, in order to compensate for calcium lost through coagulation and precipitation due to reaction with the sulfate ions, a calcium salt having a calcium concentration calculated by applying formula (II) is further added to the fluoride-containing wastewater. C 3 =(C 4 -1000) × Aw(Ca) / Fw(SO4 2- ) Formula (II) However, C 3 represents the calcium concentration of the supplemented calcium salt, and C 4 represents the concentration of sulfate ions in fluoride-containing wastewater, Aw(Ca) represents the atomic weight of calcium, and Fw(SO4 2- ) represents the formula weight of sulfate ion. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 5-293474 [Patent Document 2] JP 2001-38368 A [Patent Document 3] Japanese Patent Application Publication No. 10-479 [Patent Document 4] JP 2000-334470 A [Patent Document 5] JP 2017-64569 A Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide a method for treating fluorine-containing water and an apparatus for treating fluorine-containing water, which are capable of stably obtaining water having a low elemental fluorine concentration from a liquid containing fluoride ions and water. [Means for solving the problem]

[0011] As a result of investigations conducted in order to achieve the above object, the present invention including the following embodiments has been completed. [1] Adding a flocculant to a dispersion containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water; A method for separating calcium fluoride aggregates from a suspension containing calcium fluoride aggregates and water by precipitating the calcium fluoride aggregates into a supernatant and a sediment; adding a part of the separated deposit and a liquid containing calcium ions to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions to obtain a dispersion containing calcium fluoride and water; and The method includes adding a part of the separated sediment and a liquid containing calcium ions to a liquid containing fluoride ions and water, so that the amount of sulfate ions present is 35 mass% or less relative to the amount of elemental fluorine contained in the liquid containing fluoride ions and water, and the concentration of sulfate ions in the supernatant liquid is 100 mg / L or more. Method for treating fluoride-containing water.

[0012] [2] The method for treating fluoride-containing water according to [1], further comprising passing the supernatant through a membrane filter having a pore size of 0.025 μm to obtain a liquid having a calcium element concentration of 20 mg / L or more.

[0013] [3] The method for treating fluoride-containing water according to [1] or [2], further comprising passing the supernatant through a membrane filter having a pore size of 0.45 μm to reduce the elemental fluorine concentration in the liquid obtained to 15 mg / L or less.

[0014] [4] The method for treating fluoride-containing water according to any one of [1] to [3], wherein the addition of the part of the separated sediments and the liquid containing calcium ions is the addition of a mixed liquid obtained by mixing the part of the separated sediments with the liquid containing calcium ions.

[0015] [5] A method for treating a water purification system comprising: a coagulation tank, a sedimentation tank, a reaction tank, and a control mechanism; The coagulation tank is configured to add a coagulant to a dispersion liquid containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water, the settling tank is configured to be capable of settling the calcium fluoride agglomerates in a suspension containing the calcium fluoride agglomerates and water, and separating the calcium fluoride agglomerates into a supernatant and a sediment, the reaction tank is configured to add a part of the sediment separated in the settling tank and a liquid containing calcium ions to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions, thereby obtaining a dispersion containing calcium fluoride and water; and the adjusting mechanism is configured to adjust the amount of sulfate ions present when adding a portion of the separated sediment and the liquid containing calcium ions to the liquid containing fluoride ions and water to 35 mass % or less relative to the amount of elemental fluorine contained in the liquid containing fluoride ions and water, and to adjust the sulfate ion concentration in the supernatant to 100 mg / L or more. Fluorine-containing water treatment device. Effect of the Invention

[0016] The method for treating fluorine-containing water and the apparatus for treating fluorine-containing water of the present invention can stably obtain water having a low elemental fluorine concentration from a liquid containing fluoride ions and water. [Brief description of the drawings]

[0017] [Figure 1] 1 is a conceptual diagram showing one embodiment of a water treatment device of the present invention. [Diagram 2] FIG. 4 is a conceptual diagram showing another embodiment of a water treatment device of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The method for treating fluoride-containing water of the present invention includes the steps of coagulation, precipitation, reaction and adjustment. The apparatus for treating fluoride-containing water of the present invention includes a coagulation tank 2, a precipitation tank 3, a reaction tank 1 and an adjustment mechanism.

[0019] The agglomeration step involves adding a flocculant to a dispersion comprising calcium fluoride and water to obtain a suspension comprising calcium fluoride agglomerates and water. The coagulation tank 2 is configured to add the coagulant 8 to the dispersion containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water. The dispersion containing calcium fluoride and water can be transferred from the reaction tank 1 or the reaction stage to the coagulation tank 2 or the coagulation stage through a flow path. The coagulant 8 can be transferred from the coagulant preparation tank to the coagulation tank 2 through a flow path. The amount of each transferred can be adjusted using a level meter installed in the reaction tank 1 and / or the coagulation tank 2, and a valve, a flow meter, a pump, etc. installed in each flow path. A means for stirring the added coagulant so that it spreads throughout the coagulation tank can be installed in the coagulation tank. In order to adjust the sulfate ion concentration in the dispersion containing calcium fluoride and water or the supernatant to a desired range, a liquid containing sulfate ions may be added to the dispersion containing calcium fluoride and water as necessary.

[0020] Calcium fluoride (CaF2) is produced by the reaction of fluoride ions with calcium ions. Calcium fluoride is poorly soluble in water, for example, with a solubility of 0.0016 g / 100 ml (20°C), and so precipitates in water. The precipitated calcium fluoride usually contains a large amount of solid suspended particles. In general, the settling speed of solid suspended particles is slow, and the precipitation process takes a long time.

[0021] The flocculant is not particularly limited as long as it promotes the formation of coarse flocs (settling particles) of suspended solid particles. The addition of the flocculant in the flocculation stage or flocculation tank causes calcium fluoride to flocculate into coarse flocs (calcium fluoride aggregates). The formation of calcium fluoride aggregates according to the present invention promotes gravitational settling and centrifugal settling, making it easy to obtain sludge with a low moisture content and water with a low elemental fluorine concentration.

[0022] Examples of the flocculant include polymer flocculants made of anionic polymers, cationic polymers, amphoteric polymers, nonionic polymers, etc. Such polymers preferably have a weight average molecular weight of more than 1 million, more preferably 5 million or more.

[0023] As the polymer flocculant made of a cationic polymer, it is preferable to use a cationic polymer solution or a cationic polymer dispersion (hereinafter, these may be collectively referred to as a "cationic polymer-containing liquid").

[0024] The cationic polymer solution is prepared by dissolving a cationic polymer in water or in a solvent having high affinity with water, and the cationic polymer dispersion is prepared by dispersing a cationic polymer solution in a hydrophobic liquid (W / O type emulsion), etc. The cationic polymer preferably has a weight average molecular weight of more than 1 million, more preferably 5 million or more, and further preferably 6 million to 11 million.

[0025] Examples of the cationic polymer include polymers having cationic structural units derived from quaternary ammonium salts of (meth)acrylic acid esters (e.g., copolymers of acrylamide / [2-(acryloyloxy)ethyl]benzyldimethylammonium chloride / [2-(acryloyloxy)ethyl]trimethylammonium chloride, copolymers of acrylamide / [3-(acryloyloxy)propyl]benzyldimethylammonium chloride / [2-(acryloyloxy)ethyl]trimethylammonium chloride, copolymers of acrylamide / [2-(acryloyloxy)ethyl]benzyldimethylammonium chloride / [3-(acryloyloxy)propyl]trimethylammonium chloride, copolymers of acrylamide / [3-(acryloyloxy)propyl]benzyldimethylammonium chloride / [3-(acryloyloxy)propyl]trimethylammonium chloride, etc.), polyaminoalkyl acrylates, polyaminoalkyl methacrylates, polyethyleneimines, halogenated polydiallyl ammonium, chitosan, urea-formaldehyde resins, etc. These cationic polymers can be used alone or in combination of two or more. The addition of a cationic polymer can prevent redispersion of flocs and can also increase the efficiency of settling, making it easier to obtain sludge with a lower moisture content.

[0026] As the polymer flocculant made of an anionic polymer, it is preferable to use an anionic polymer solution or an anionic polymer dispersion (hereinafter, these may be collectively referred to as "anionic polymer-containing liquid"). The anionic polymer solution is prepared by dissolving an anionic polymer in a solvent having high affinity for water or in water, and the anionic polymer dispersion is prepared by dispersing the solution in a hydrophobic solvent (W / O type emulsion), etc. The weight average molecular weight of the anionic polymer is preferably more than 1 million, more preferably 5 million or more, and further preferably 8 million to 15 million.

[0027] Examples of the anionic polymer include sodium polyacrylate, polyacrylic acid soda amide derivatives, polyacrylamide partial hydrolysates, partially sulfomethylated polyacrylamide, poly(2-acrylamide)-2-methylpropane sulfate, etc. The anionic polymer may be used alone or in combination of two or more. The anionic polymer is preferably one having a degree of anionization of 10 to 30% by mass.

[0028] As the polymer flocculant made of an amphoteric polymer, it is preferable to use an amphoteric polymer solution or an amphoteric polymer dispersion (hereinafter, these may be collectively referred to as "amphoteric polymer-containing liquid"). The amphoteric polymer solution is prepared by dissolving an amphoteric polymer in water or in a solvent having high affinity for water, and the amphoteric polymer dispersion is prepared by dispersing the solution in a hydrophobic solvent (W / O type emulsion), etc. The weight-average molecular weight of the amphoteric polymer is preferably more than 1 million, more preferably 5 million or more, and further preferably 8 million to 10 million.

[0029] Examples of the amphoteric polymer include a copolymer of (meth)acrylamide, a quaternary ammonium alkyl (meth)acrylate, and sodium (meth)acrylate, a copolymer of acrylamide, an aminoalkyl methacrylate, and sodium acrylate, etc. The molar ratio of anion / cation of the amphoteric polymer is preferably 0.2 to 2.0.

[0030] As the polymer flocculant made of a nonionic polymer, it is preferable to use a nonionic polymer solution or a nonionic polymer dispersion (hereinafter, these may be collectively referred to as "nonionic polymer-containing liquid"). The nonionic polymer solution is obtained by dissolving a nonionic polymer in a solvent having high affinity for water or in water, and the nonionic polymer dispersion is, for example, obtained by dispersing the solution in a hydrophobic solvent (W / O type emulsion), etc. An example of the nonionic polymer is polyacrylamide, etc. The weight average molecular weight of the nonionic polymer is preferably more than 1 million, more preferably 5 million or more, and further preferably 8 million to 20 million.

[0031] Of these, the use of a polymer flocculant made of an anionic polymer is preferred in the present invention.

[0032] The dispersion containing calcium fluoride and water immediately before the addition of the flocculant has a temperature of preferably 10 to 70° C., more preferably 10 to 50° C., and a pH of preferably 3 to 10, more preferably 5 to 9. The suspension containing calcium fluoride aggregates and water immediately after the addition of the flocculant has a temperature of preferably 10 to 70° C., more preferably 10 to 50° C., and a pH of preferably 3 to 10, more preferably 5 to 9. The amount of the flocculant (in terms of solid matter) added to the dispersion containing calcium fluoride and water is preferably 0.5 to 20 mg, more preferably 1 to 10 mg, per 1 L of the dispersion containing calcium fluoride and water. The flocculant to be added is preferably in a liquid form such as a solution or dispersion.

[0033] The precipitation step involves settling the calcium fluoride aggregates in a suspension comprising calcium fluoride aggregates and water to separate the calcium fluoride aggregates into a supernatant and a sediment. The precipitation tank 3 is configured to allow the calcium fluoride aggregates in the suspension containing the calcium fluoride aggregates and water to settle and separate into a supernatant liquid and a sediment. The precipitation of the calcium fluoride aggregates can be performed by a known unit operation utilizing gravity, centrifugal force, or the like. The suspension containing the calcium fluoride aggregates and water can be transferred from the coagulation tank 2 or the coagulation stage to the precipitation tank 3 or the precipitation stage via a flow path. The amount transferred can be adjusted using a level gauge installed in the coagulation tank 2 and / or the precipitation tank 3, and a valve, a flow meter, a pump, or the like installed in the flow path. The suspension containing the calcium fluoride aggregates and water during the precipitation has a temperature of preferably 10 to 70°C, more preferably 10 to 50°C, and a pH of preferably 3 to 10, more preferably 5 to 9.

[0034] The supernatant 11 obtained by the present invention is water having a low concentration of elemental fluorine. In the present invention, the supernatant 11 can be subjected to a neutralization treatment, if necessary.

[0035] The sediment is an aqueous slurry with a high calcium fluoride aggregate concentration. As described later, a part of the sediment obtained in the settling tank 3 or the settling stage (sediment 10) can be used in the reaction stage or the reaction tank 1, and the remaining part (sediment 9) can be used for recovering calcium fluoride. In order to remove water from the sediment 9, it can be subjected to a dehydration treatment such as centrifugal dehydration, filter press dehydration, roll press dehydration, vacuum filter drum dehydration, etc. The sediment 9 obtained by the method and apparatus of the present invention has the property of being easily dehydrated, has a good efficiency in the dehydration treatment, and can be made into a sludge with a low water content.

[0036] The reacting step involves adding the deposit 10 and a liquid containing calcium ions to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions to obtain a dispersion containing calcium fluoride and water. The reaction tank 1 is configured so that the deposit 10 and a liquid containing calcium ions are added to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions, thereby obtaining a dispersion containing calcium fluoride and water.

[0037] The liquid 12 containing fluoride ions and water can be transferred from the source of the liquid to the reaction tank 1 or the reaction stage through a flow path. The liquid 4 containing calcium ions can be transferred from a preparation tank for the liquid to the reaction tank 1 through a flow path. The deposit 10 can be transferred from a precipitation tank 3 or the precipitation stage to the reaction tank 1 or the reaction stage through a flow path. The liquid 5 containing sulfate ions, which is added as needed, can be transferred from a preparation tank for the liquid to the reaction tank 1 through a flow path. The amount of each transferred can be adjusted using a level gauge installed in the reaction tank 1, as well as valves, flow meters, pumps, etc. installed in each flow path. A means for stirring the liquid 4 containing calcium ions, the deposit 10, or the liquid 5 containing sulfate ions, which is added as needed, can be distributed throughout the reaction tank.

[0038] The liquid 12 containing fluoride ions and water may contain fluoride that has not been completely dissolved in water. Examples of fluorides include ammonium fluoride, ammonium hydrogen fluoride, and sodium fluoride. Examples of liquids containing fluoride ions and water include wastewater from factories that manufacture semiconductors, glass processing, and fluororesin, wastewater from mining sites for fluorite, cryolite, and the like, hot springs, mineral springs, river water, and groundwater.

[0039] The liquid 4 containing calcium ions may contain calcium compounds that have not been completely dissolved in water. Examples of the liquid 4 containing calcium ions include aqueous solutions or dispersions of calcium compounds such as calcium carbonate, calcium bicarbonate, calcium chloride, calcium hydroxide, calcium oxide, calcium nitrate, and calcium sulfate. Among these calcium compounds, calcium chloride and calcium hydroxide are preferred, and calcium hydroxide is more preferred.

[0040] The amount of the liquid containing calcium ions added in the reaction stage or in the reaction tank 1 is an amount that makes the calcium element concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm preferably 20 mg / L or more, more preferably 50 mg / L or more. There is no particular upper limit to the amount of the liquid containing calcium ions added in the reaction stage or in the reaction tank 1, but if the amount of the liquid containing calcium ions is increased, sulfate ions tend to react with calcium ions to produce calcium sulfate, thereby reducing the amount of sulfate ions. Therefore, the amount of the liquid containing calcium ions added in the reaction stage or in the reaction tank 1 can be set, for example, to an amount that makes the calcium element concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.45 μm preferably 500 mg / L or less, more preferably 300 mg / L or less, and even more preferably less than 200 mg / L.

[0041] The calcium fluoride aggregates contained in the deposit 10 added in the reaction stage or reactor 1 act as seed crystals for the precipitation of calcium fluoride. The amount of solid content of the deposit 10 added per hour in the reaction stage or reaction tank 1 is preferably 10 to 90 parts by mass, more preferably 20 to 50 parts by mass, per part by mass of solid content per hour that will be produced from the liquid 12 containing fluoride ions and water in the reaction stage or reaction tank 1.

[0042] The calcium ion-containing liquid 4 and the sediment 10 to be added in the reaction stage or reaction tank 1 can be added in the form of a mixed liquid 14 obtained by mixing them in the reaction stage or reaction tank 1 (see FIG. 2).

[0043] The sulfate ions present when a portion of the separated sediment and the liquid containing calcium ions are added to the liquid containing fluoride ions and water originate from those contained in the liquid containing fluoride ions and water 12, the liquid containing calcium ions 4 or the sediment 10 supplied to the reaction stage or reaction tank, and from those contained in the liquid containing sulfate ions 5 which may be added from outside the system. Examples of the liquid containing sulfate ions include sulfuric acid, a liquid containing ammonium sulfate, a liquid containing calcium sulfate, a liquid containing aluminum sulfate, etc. Of these, sulfuric acid is preferred.

[0044] The dispersion containing calcium fluoride and water obtained in the reaction stage or reaction tank has a pH of preferably 3-10, more preferably 5-9, and further preferably 6-8.

[0045] To adjust the pH of each solution, a basic compound such as sodium hydroxide or sodium carbonate, or an acidic compound such as hydrochloric acid or nitric acid can be used. To adjust the pH, a calcium compound can be used as the basic compound, and sulfuric acid or a sulfate can be used as the acidic compound. However, from the viewpoint of ease of adjusting the pH and controlling the precipitation reaction, it is preferable to use a basic compound other than a calcium compound and an acidic compound other than sulfuric acid or a sulfate.

[0046] In order to promote settling in the precipitation stage or precipitation tank, a coagulation stage or coagulation tank can be provided between the reaction stage or reaction tank and the coagulation stage or coagulation tank. In the coagulation stage or coagulation tank, a coagulant is added to the dispersion containing calcium fluoride and water obtained in the reaction stage or reaction tank to promote coagulation of calcium fluoride. The coagulant is not particularly limited as long as it is a substance that promotes the formation of microflocs, and examples of the coagulant include inorganic coagulants such as aluminum sulfate, PAC, aluminum chloride, polyferric chloride, and organic coagulants such as polyamine and polydadomac. Among these, inorganic coagulants are preferred.

[0047] The adjustment step is to adjust the ratio of the amount of sulfate ions present (SO4 2- / F) to 35 mass % or less, preferably 31 mass % or less, and the sulfate ion concentration in the supernatant is 100 mg / L or more. 2- The lower limit of / F is not particularly limited, but the adjustment step is SO4 2- For example, / F is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. Furthermore, the adjustment step includes adjusting the sulfate ion concentration in the dispersion containing calcium fluoride and water to preferably 100 mg / L or more, adjusting the elemental fluorine concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.45 μm to preferably 15 mg / L or less, more preferably 8.0 mg / L or less, and / or adjusting the elemental calcium concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm to preferably 20 mg / L or more, more preferably 50 mg / L or more. The upper limit of the elemental calcium concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm is not particularly limited, but is preferably 500 mg / L, more preferably 300 mg / L, from the viewpoint of scale generation, etc.

[0048] The adjustment mechanism is to adjust the ratio of sulfate ions (SO4 2- / F) can be 35 mass% or less, and the sulfate ion concentration in the supernatant can be 100 mg / L or more. 2- The lower limit of / F is not particularly limited, but the regulating mechanism is SO4 2- The composition is configured so that / F can be made to be preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. Furthermore, the adjustment mechanism is configured to adjust the sulfate ion concentration in the dispersion containing calcium fluoride and water to preferably 100 mg / L or more, the fluorine element concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.45 μm to preferably 15 mg / L or less, more preferably 8.0 mg / L or less, and / or the calcium element concentration in the liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm to preferably 20 mg / L or more, more preferably 50 mg / L or more.

[0049] These adjustments include, for example, adjusting the ratio of sulfate ions present to the amount of elemental fluorine in a liquid containing fluoride ions and water (SO4 2- / F), and the sulfate ion concentration in the supernatant, and if necessary, the sulfate ion concentration in a dispersion containing calcium fluoride and water, the fluorine element concentration in a liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm, the fluorine element concentration in a liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.45 μm, the calcium element concentration in a liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.45 μm, and / or the calcium element concentration in a liquid obtained by passing the supernatant through a membrane filter with a pore size of 0.025 μm, and based on the monitoring results, the amount of fluoride ions to be treated (e.g., the flow rate of a liquid containing fluoride ions and water), the amount of calcium fluoride added in a reaction tank or reaction stage, and the like are monitored. The amount of calcium ions (e.g., the flow rate of a liquid containing calcium ions), the amount of sulfate ions added in the reaction tank or reaction stage (e.g., the flow rate of a liquid containing sulfate ions), the amount of sediment 10 added in the reaction tank or reaction stage (the flow rate of sediment 10), the amount of coagulant added in the coagulation tank or coagulation stage (e.g., the flow rate of a liquid containing coagulant), the temperature of each liquid, the pH of each liquid, etc., can be changed, and further, if necessary, the amount of coagulant added in the coagulation tank or coagulation stage (e.g., the flow rate of a liquid containing coagulant), the amount of sulfate ions added to the dispersion containing calcium fluoride and water (e.g., the flow rate of a liquid containing sulfate ions), etc. The flow rate can be changed by manually or automatically changing the opening of a valve. The temperature can be changed by manually or automatically changing the amount of energy supplied to or discharged from the heating means or cooling means. The pH can be changed by manually or automatically changing the opening of a valve in a supply flow path for an acidic compound or a basic compound.

[0050] The present invention will now be described in more detail with reference to examples and comparative examples, although the following examples are not intended to limit the scope of the present invention.

[0051] (experiment) Hydrogen fluoride was dissolved in pure water to prepare water to be treated with a fluorine concentration of 2000 mg / L. The water treatment device shown in Figure 1 was prepared. The water to be treated, the aqueous calcium hydroxide solution 4, the sulfuric acid 5, the deposits 10, and the aqueous sodium hydroxide solution 7 or the hydrochloric acid 6 were continuously supplied to the reaction tank 1. The liquid in the reaction tank 2, which had been withdrawn so as to maintain the liquid in the reaction tank at a predetermined volume, and the polymer flocculant-containing liquid 8 containing an anionic polymer were each continuously supplied to the coagulation tank 2. The liquid withdrawn from the coagulation tank was continuously supplied to settling tank 3 so as to maintain a predetermined amount of liquid therein. To maintain a predetermined amount of liquid in the settling tank, the supernatant liquid 11 and the sediment (slurry) were extracted from the top and bottom of the settling tank, respectively. A part of the extracted sediment (sediment 10) was supplied to the reaction tank 1 as described above. The remaining part of the extracted sediment (sediment 9) was pressed at 0.3 MPa to obtain sludge.

[0052] Calcium ion concentration in the reaction tank, pH of the reaction tank, sulfate ion concentration in the supernatant (supernatant SO4 2- The calcium ion concentration in the liquid in the reaction tank is 200 mg / L, the pH of the liquid in the reaction tank is 7, and the ratio of the amount of sulfate ions in reaction tank 1 to the amount of fluorine in the liquid containing fluoride ions and water (SO4 2- / F) and the sulfate ion concentration in the supernatant (supernatant SO4 2- The amounts of water to be treated 12, calcium hydroxide aqueous solution 4, sulfuric acid 5, deposit 10, and sodium hydroxide aqueous solution 7 or hydrochloric acid 6 supplied were adjusted so that the concentration of the calcium hydroxide aqueous solution (CaOH) was the value shown in Table 1.

[0053] The fluorine concentration in the sludge (sludge F concentration) was measured. The results are shown in Table 1. The amount of solid suspended particles contained in the supernatant 11 was estimated as follows. The supernatant 11 was filtered through a membrane filter with a pore size of 0.45 μm and a membrane filter with a pore size of 0.025 μm. The filtrates obtained through the membrane filter with a pore size of 0.45 μm and the filtrates obtained through the membrane filter with a pore size of 0.025 μm were collected, and the elemental fluorine concentration (supernatant F concentration) and elemental calcium concentration (supernatant Ca concentration) contained in each filtrate were measured. The results are shown in Table 1. The difference between the elemental fluorine concentration in the filtrate obtained from the 0.45 μm pore size membrane filter (0.45 μm filtrate) and the elemental fluorine concentration in the filtrate obtained from the 0.025 μm pore size membrane filter (0.025 μm filtrate) corresponds to the concentration of elemental fluorine derived from solid suspended particles with a particle size of 0.025 μm to 0.45 μm, and the elemental fluorine concentration in the filtrate obtained from the 0.025 μm pore size membrane filter (0.025 μm filtrate) corresponds to the sum of the concentration of elemental fluorine derived from solid suspended particles with a particle size of less than 0.025 μm and the concentration of fluorine ions dissolved in the supernatant.

[0054] [Table 1]

[0055] As shown in Table 1, the 0.45 μm filtrate and the 0.025 μm filtrate of the supernatants obtained in Examples 1 and 2 have lower elemental fluorine concentrations than those of the supernatants obtained in Comparative Examples 1 to 4.

[0056] According to the present invention, by making the ratio of the amount of sulfate ions to the amount of elemental fluorine contained in the liquid containing fluoride ions and water 35 mass % or less and making the sulfate ion concentration in the supernatant liquid 100 mg / L or more, water with a low elemental fluorine concentration can be stably obtained from the liquid containing fluoride ions and water. According to the present invention, it is possible to significantly reduce fluorine-containing solid suspended particles small enough to pass through a membrane filter with a pore size of 0.45 μm contained in the treated water, and it is possible to maintain the elemental fluorine concentration, i.e., calcium fluoride concentration, in the sludge at a high level. [Explanation of symbols]

[0057] 1: Reactor 2: Agglomeration tank 3: Sedimentation tank 4: Calcium ion-containing solution 5: Sulfate ion-containing liquid 6: Liquid containing acidic compounds 7: Liquid containing basic compounds 8: Coagulant-containing liquid 9: Sediment (discharge) 10: Sludge (return) 11: Supernatant 12: Fluoride ion-containing liquid 13: Mixing tank 14: Mixed liquid

Claims

1. adding a flocculant to a dispersion containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water; A method for separating calcium fluoride aggregates from a suspension containing calcium fluoride aggregates and water by precipitating the calcium fluoride aggregates into a supernatant and a sediment; adding a part of the separated deposit and a liquid containing calcium ions to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions to obtain a dispersion containing calcium fluoride and water; and The method includes adding a part of the separated sediment and a liquid containing calcium ions to a liquid containing fluoride ions and water, so that the amount of sulfate ions present is 35 mass% or less relative to the amount of elemental fluorine contained in the liquid containing fluoride ions and water, and the concentration of sulfate ions in the supernatant liquid is 100 mg / L or more. Method for treating fluoride-containing water.

2. 2. The method for treating fluoride-containing water according to claim 1, further comprising passing the supernatant through a membrane filter having a pore size of 0.025 μm to obtain a liquid having a calcium element concentration of 20 mg / L or more.

3. 2. The method for treating fluoride-containing water according to claim 1, further comprising passing the supernatant through a membrane filter having a pore size of 0.45 μm to adjust the elemental fluorine concentration in the resulting liquid to 15 mg / L or less.

4. 2. The method for treating fluoride-containing water according to claim 1, wherein the addition of the part of the separated sediments and the liquid containing calcium ions is the addition of a mixed liquid obtained by mixing the part of the separated sediments with the liquid containing calcium ions.

5. The system includes a flocculation tank, a settling tank, a reaction tank, and a regulation mechanism. The coagulation tank is configured to add a coagulant to a dispersion liquid containing calcium fluoride and water to obtain a suspension containing calcium fluoride aggregates and water, the settling tank is configured to be capable of settling the calcium fluoride agglomerates in a suspension containing the calcium fluoride agglomerates and water, and separating the calcium fluoride agglomerates into a supernatant and a sediment, the reaction tank is configured to add a part of the sediment separated in the settling tank and a liquid containing calcium ions to a liquid containing fluoride ions and water to precipitate calcium fluoride in the presence of sulfate ions, thereby obtaining a dispersion containing calcium fluoride and water; the adjusting mechanism is configured to adjust the amount of sulfate ions present when adding a portion of the separated sediment and the liquid containing calcium ions to the liquid containing fluoride ions and water to 35 mass % or less relative to the amount of elemental fluorine contained in the liquid containing fluoride ions and water, and to adjust the sulfate ion concentration in the supernatant to 100 mg / L or more. Fluorine-containing water treatment device.

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