JP4395924B2 - Fluorine removal method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for removing fluorine from fluorine-containing water.
[0002]
[Prior art]
As a method for removing fluorine from fluorine-containing water, there is a method in which fluorine-containing water is reacted with a calcium compound to produce a calcium fluoride insolubilized product and solid-liquid separation is performed. In this method, a part of sludge separated into solid and liquid is returned and reacted with raw water in contact with the calcium compound to grow calcium fluoride crystals into large particles and facilitate solid-liquid separation. An HDS (High Density Solids) method is known (for example, JP-A-10-479).
[0003]
FIG. 2 is a flowchart of the conventional HDS method. In FIG. 2, 1 is a raw water tank, 2 is a reaction tank, 3 is a coagulation tank, 4 is a solid-liquid separation tank, 5 is a calcium compound tank, 6 is a mixing tank, and 7 is a coagulant tank.
[0004]
In the conventional fluorine removal method, raw water (fluorine-containing water) 11 is introduced and stored in the raw water tank 1 from the raw water channel L1, and sent to the reaction tank 2 from the line L2 by the pump P1 to perform the insolubilization reaction. The reaction liquid 12 is sent from the line L3 to the agglomeration tank 3 for agglutination reaction, and the agglomeration liquid 13 is sent from the line L4 to the solid-liquid separation tank 4 for solid-liquid separation, and the separation liquid 14 is treated from the treatment channel L5. Discharge. A part of the separated sludge 15 is sent as return sludge from the return path L6 to the mixing tank 6 by the pump P2, and the remaining part is discharged as excess sludge from the exhaust mud path L7.
[0005]
A calcium compound 16 such as slaked lime is supplied to the mixing tank 6 from the calcium compound tank 5 through the line L8 by the pump P3, and the returned sludge and the calcium compound are mixed by stirring with the stirrer M1, so that the calcium compound is added to the sludge surface. This forms a sludge mixture 17 to which is attached. This sludge mixture 17 is supplied from the circulation path L9 to the reaction tank 2, and stirred by the stirrer M2 to react fluoride ions and calcium compounds in the raw water to generate calcium fluoride insolubilized material. PH of the reaction vessel 2, more reactive solution 12 to a pH meter to measure, to control the opening of the valve V1 so as to maintain a predetermined pH, controlling the amount of calcium compound supplied to the mixing tank 6. Excess calcium compound circulates from line L10.
[0006]
The reaction liquid 12 containing calcium fluoride generated in the reaction tank 2 is sent to the aggregation tank 3 to perform the aggregation treatment. In the aggregating tank 3, in order to agglomerate the calcium fluoride insolubilized material in the reaction solution, an aggregating agent (for example, a polymer flocculant) 18 is injected from the aggregating agent tank 7 through the line L11 by the pump P4 and stirred by the stirrer M3. A floc is formed by agglomeration reaction. Thereby, the solid-liquid separation property of calcium fluoride is enhanced, and the separation in the solid-liquid separation tank 4 is efficiently performed.
[0007]
In the above treatment method, the sludge of the solid-liquid separation tank 4 mainly containing calcium fluoride crystals precipitated as insolubilized substances in the reaction tank 2 is returned to the mixing tank 6 where it is mixed with the calcium compound to crystallize the calcium compound. Since it adheres to the surface and is sent to the reaction tank 2 and brought into contact with the raw water, the reaction between the fluoride ions and the calcium compound in the raw water occurs on the surface of the crystal, and the crystal grows. For this reason, the solid-liquid separation property of sludge becomes high, and the moisture content of the dewatered cake obtained by mechanically dehydrating the separated sludge in the solid-liquid separation tank 4 is reduced by 30 to 50% by weight as compared with the case where the sludge is not returned. Therefore, when this cake is dried and reused, there is an advantage that the drying cost is lowered.
[0008]
By the way, the precipitation of calcium fluoride in the reaction tank 2 is not only caused by a so-called solid-liquid reaction on the surface of the crystal, but also caused by a liquid-liquid reaction between fluoride ions and calcium ions at a place separated from the crystal. Crystals are formed. The larger the number of returns, the greater the crystal size and the solid-liquid separation properties. However, on the other hand, it is difficult to obtain crystals of uniform size because they are crushed by a pump during return.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to obtain a sludge having excellent dewaterability by returning crystals with a small particle size and using them in the reaction to grow the crystals, and separating and taking out crystals with a large particle size and a uniform particle size. It is to propose a method and apparatus for removing fluorine.
[0010]
[Means for Solving the Problems]
The present invention is the following fluorine removal method and apparatus.
(1) a reaction step of reacting fluorine-containing water with a calcium compound to precipitate insoluble calcium fluoride;
A solid-liquid separation step for solid-liquid separation of the reaction liquid in the reaction step into treated water and sludge, and a mixing step for mixing a part of the sludge separated in the solid-liquid separation step with a calcium compound and supplying the mixture to the reaction tank,
In the solid-liquid separation process, the sludge is classified into a large particle size sludge and a small particle size sludge according to the particle size and separated into solid and liquid,
The classified large particle size sludge is discharged out of the system without being returned to the mixing process and without being crushed.
A fluorine removing method, wherein the classified sludge having a small particle diameter is returned to the mixing step, mixed with the calcium compound, and the calcium compound is adhered to the surface of the crystal and supplied to the reaction vessel.
(2) In the solid-liquid separation step, the reaction liquid is advanced to a plurality of solid-liquid separation regions that are divided in the liquid traveling direction and have a rectifying plate at the boundary, so that crystals with a large particle size are allowed to settle upstream. The method according to (1), wherein the crystal having a small particle size is allowed to settle on the downstream side, and the sludge having a small particle size separated in the solid-liquid separation region at the tip side in the liquid traveling direction is returned to the mixing device. .
(3) a reaction vessel in which fluorine-containing water is reacted with a calcium compound to precipitate insoluble calcium fluoride;
A solid-liquid separation device that separates the reaction liquid in the reaction tank into treated water and sludge, and classifies the sludge into sludge with a large particle size and sludge with a small particle size according to the particle size. ,
A mixing device for mixing sludge having a small particle size classified by a solid-liquid separator with a calcium compound and supplying the mixture to a reaction tank;
A sludge passage that discharges sludge with a large particle size classified by the solid-liquid separator to the outside of the system without crushing, and a sludge with a small particle size classified by the solid-liquid separator is returned to the mixing device. A fluorine removing apparatus including a return path that does not return sludge having a particle size .
(4) The solid-liquid separation device has a plurality of solid-liquid separation regions that are divided in the liquid traveling direction and have a baffle plate at the boundary, and precipitate large-sized crystals on the upstream side and small on the downstream side. The apparatus according to the above (3), wherein the apparatus is configured to settle crystals having a particle size and return sludge having a relatively small particle size separated in a solid-liquid separation region at a tip side in a liquid traveling direction to a mixing device.
[0011]
The fluorine-containing water to be treated in the present invention is water containing fluorine in the form of fluoride ions. For example, flue gas desulfurization process, aluminum electrolytic scouring process, phosphate fertilizer manufacturing process, and electronic components including semiconductors Examples of the wastewater include a manufacturing process, a uranium smelting process, and a surface treatment cleaning process.
[0012]
As the calcium compound to be reacted with such fluorine-containing water, slaked lime, calcium chloride and the like can be used. The pH range in which these calcium compounds and fluorine compounds react to produce calcium fluoride is pH 5 to 10, preferably pH 6 to 8. For this purpose, an alkali agent can be used if necessary. As the alkali agent, sodium hydroxide, magnesium hydroxide, slaked lime, etc. can be used, but when slaked lime is used, both can be used.
[0013]
In the present invention, the fluorine-containing water and the calcium compound are reacted in the reaction tank as a reaction step. In this case, a part of the sludge separated in the solid-liquid separation step is mixed with the calcium compound in the mixing device, and the calcium is deposited on the crystal surface. The compound is deposited and fed to the reaction vessel. As a result, the calcium compound adhering to the crystal surface reacts with the fluoride to precipitate calcium fluoride on the crystal surface, thereby growing the crystal.
[0014]
The reaction tank is configured to react the fluorine-containing water introduced from the raw water channel with the calcium compound supported on the sludge circulating from the circulation channel. Specifically, a stirrer that rapidly stirs the liquid in the tank and a pH meter that measures the pH of the liquid in the tank are installed, and the amount of alkaline agent injected is adjusted so that the pH is maintained within a certain range. It can comprise so that it may react, stirring. The pH is preferably 6-8. The reaction tank is preferably a continuous type, but may be a batch type, and known ones can be used.
[0015]
The mixing device can be configured to install a stirrer to mix the sludge returned from the solid-liquid separation tank and the calcium compound supplied from the calcium compound tank, and to supply the mixed liquid to the reaction tank. The amount of calcium compound supplied to the mixing device can be controlled by, for example, installing a fluoride ion concentration meter in the raw water tank so as to correspond to the amount of fluoride ion in the raw water, but slaked lime is used as the calcium compound. In this case, it is preferable to control with a pH meter installed in the reaction vessel.
[0016]
The solid-liquid separation device used in the solid-liquid separation process is configured to classify the sludge dispersed in the reaction liquid according to the particle size, separate it into solid and liquid, and return the sludge having a relatively small particle size to the mixing device. . Such a solid-liquid separation device has a plurality of solid-liquid separation regions divided in the liquid traveling direction, and has a relatively small particle size sludge separated in the solid-liquid separation region on the tip side in the liquid traveling direction. Is preferably sent back to the mixing device. Examples of the solid-liquid separation means include sedimentation separation, filtration separation, and membrane separation. In the case of sedimentation separation, when a plurality of sedimentation separation regions are provided, a rectifying plate such as a perforated plate can be provided at the boundary.
[0017]
It is preferable to perform an aggregating treatment by providing an aggregating device in front of the solid-liquid separator. A floc can be generated by adding a polymer flocculant or other flocculant to the aggregating apparatus and stirring. As the flocculant, polyacrylamide, a polyacrylamide partial hydrolyzate, a copolymer of acrylamide and acrylic acid, and the like can be used.
[0018]
In the fluorine removal method of the present invention, fluorine-containing water is reacted with a calcium compound in the reaction step to precipitate insoluble calcium fluoride, and in the solid-liquid separation step, the reaction solution in the reaction step is solid-liquid separated into treated water and sludge, When a part of the sludge separated in the solid-liquid separation step in the mixing step is mixed with a calcium compound and supplied to the reaction vessel to react, the sludge is sludge having a large particle size according to the particle size in the solid-liquid separation step. Classify sludge of small particle size and separate it into solid and liquid , and discharge the classified large particle size sludge out of the system without returning it to the mixing process and without crushing it. By returning the sludge to the mixing step, mixing it with the calcium compound, adhering the calcium compound to the surface of the crystal and supplying it to the reaction tank, it is possible to grow and take out sludge having a large particle size and a uniform particle size.
[0019]
In this case, when the crystals having a small particle size classified in the solid-liquid separation step are separated and returned to the mixing apparatus, and a calcium compound is attached to the surface of the crystals and supplied to the reaction vessel, calcium fluoride is applied to the crystal surface in the reaction vessel. Therefore, the crystal grows to increase the particle size. Crystals having a large particle size are classified in the solid-liquid separation step and taken out of the system. However, since they have excellent dewaterability, a dehydrated cake having a low water content can be obtained by mechanical dehydration or the like.
[0020]
【The invention's effect】
As described above, according to the fluorine removal method of the present invention, in the solid-liquid separation step, the sludge is classified into a sludge having a large particle size and a sludge having a small particle size according to the particle size, and solid-liquid separation is performed. The sludge with the particle size is discharged out of the system without being returned to the mixing step and without being crushed , and the classified small particle size sludge is returned to the mixing step and mixed with the calcium compound on the surface of the crystal. Since the calcium compound is attached and supplied to the reaction vessel, the crystal is grown by returning the crystal with a small particle size and used for the reaction, and the crystal with a large particle size and a uniform particle size is separated and taken out. Thus, sludge having excellent dewaterability can be obtained.
[0021]
According to the fluorine removing device of the present invention, when the reaction liquid is separated into solid and liquid, the sludge is classified into a large particle size sludge and a small particle size sludge according to the particle size, and solid-liquid separation is performed. A sludge passage that discharges sludge with a large particle size classified by the solid-liquid separator to the outside of the system without crushing, and a sludge with a small particle size classified by the solid-liquid separator is returned to the mixing device. Since a return path that does not return sludge having a particle size is provided, an apparatus suitable for the above-described fluorine removal method can be obtained.
In this case, by providing a plurality of solid-liquid separation regions divided in the liquid traveling direction, classification can be performed efficiently with a simple configuration and operation.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a flowchart showing a fluorine removing method and apparatus according to the present invention, and the same reference numerals as those in FIG. 2 denote the same or corresponding parts.
[0023]
In FIG. 1, the raw water tank 1 communicates with the raw water channel L1, and the line L2 having the pump P1 communicates with the reaction tank 2. The reaction tank 2 has a stirrer M2 and a pH meter pH, and communicates with the coagulation tank 3 by a line L3. The agglomeration tank 3 has a stirrer M3, a line L11 having a pump P4 communicates with the flocculant tank 7, and the line L4 communicates with the solid-liquid separation tank 4. The mixing tank 6 has a stirrer M1, a return path L6 having a pump P2 communicates from the solid-liquid separation tank 4, and a line L8 having a pump P3 and a valve V1 communicates from the calcium compound tank 5, and a circulation path L9 is communicated. The reactor 2 is communicated.
[0024]
The above configuration is the same as in FIG. 2, but in FIG. 1, the solid-liquid separation tank 4 has a plurality of solid-liquid separation regions 21, 22, and 23 divided in the liquid traveling direction, and the boundary portion is porous. They are partitioned by current plates 24 and 25 made of plates. Lines L11, L12, and L13 are led from the concentration units 26, 27, and 28 formed below the solid-liquid separation regions 21, 22, and 23, and the lines L11 and L12 that are led from the upstream solid-liquid separation region. Are joined to the sludge passage L7, and the line L13 guided from the downstream solid-liquid separation region joins with the line L14 branched from the line L12 and communicates with the return passage L6. Lines L12, L13, and L14 are provided with valves V2, V3, and V4. A treatment water channel L5 communicates with the upper part of the solid-liquid separation region 23 on the downstream side.
[0025]
In the fluorine removal method using the above apparatus, first, raw water (fluorine-containing water) 11 is introduced and stored from the raw water channel L1 into the raw water tank 1, and sent to the reaction tank 2 from the line L2 by the pump P1 to perform the insolubilization reaction. The reaction liquid 12 is sent from the line L3 to the coagulation tank 3 to perform an agglutination reaction, and the coagulation liquid 13 is sent from the line L4 to the solid-liquid separation tank 4 to perform solid-liquid separation. In the solid-liquid separation tank 4, the large-sized crystals settle on the upstream side while the small-sized crystals settle on the downstream side while the reaction liquid proceeds through the solid-liquid separation regions 21, 22, and 23. Is done. The separated separation liquid 14 is discharged from the treatment water channel L5 as treated water, and the separated sludge is extracted from the lines L11, L12, and L13. At this time, the opening degree of the valves V2 and V3 is adjusted, and the sludge having a relatively small particle size separated on the downstream side is sent as return sludge to the mixing tank 6 from the return path L6 by the pump P2, and separated on the upstream side. Sludge having a particle diameter is discharged from the sludge passage L7 as excess sludge. When the sludge having a small particle size is not returned, V2, V3 and V4 are opened and discharged from the mud discharge passage L7.
[0026]
The mixture tank 6 is supplied with slaked lime as a calcium compound 16 such as slaked lime through the line L8 from the calcium compound tank 5 by the pump P3, and stirred by the stirrer M1 to mix the returned sludge and the calcium compound. A sludge mixture 17 having a calcium compound adhered to the surface of the sludge having a particle size is formed. This sludge mixture 17 is supplied from the circulation path L9 to the reaction tank 2, and stirred by the stirrer M2 to react fluoride ions and calcium compounds in the raw water to generate calcium fluoride insolubilized material. In the reaction tank 2, the pH of the reaction solution 12 is measured by a pH meter pH, the opening of the valve V <b> 1 is controlled so as to maintain a predetermined pH, and the amount of calcium compound supplied to the mixing tank 6 is controlled. Excess calcium compound circulates from line L10.
[0027]
The reaction liquid 12 containing calcium fluoride generated in the reaction tank 2 is sent to the aggregation tank 3 to perform the aggregation treatment. In the aggregating tank 3, in order to agglomerate the calcium fluoride insolubilized material in the reaction solution, an aggregating agent (for example, polymer aggregating agent) 18 is injected from the aggregating agent tank 7 through the line L11 by the pump P4 and stirred by the agitator M3. The flocs are formed by agglomeration reaction. Thereby, the solid-liquid separation property of calcium fluoride increases, and the separation in the solid-liquid separation tank 4 is performed efficiently.
[0028]
In the above processing method, sludge containing relatively small calcium fluoride crystals out of the sludge separated in the solid-liquid separation tank 4 is returned to the mixing tank 6, where it is mixed with the calcium compound and the calcium compound is crystallized on the crystal surface. By attaching this to the reaction tank 2 and bringing it into contact with the raw water, the reaction between the fluoride ions and the calcium compound in the raw water occurs on the surface of the crystal, and the crystal grows to increase the particle size. Moreover, since the crystal | crystallization of the large particle size isolate | separated with the solid-liquid separation tank 4 is discharged | emitted from the sludge passage L7, and does not let a pump pass, crushing does not occur.
[0029]
As a result, sludge having a large particle size with good solid-liquid separation property of sludge is taken out from the sludge passage L7, and when the obtained sludge is dehydrated by mechanical dehydration or the like, the dehydration rate is fast and the dehydration has a low water content. A cake is obtained. For this reason, when drying a dehydrated cake, the drying speed is fast and the energy required for drying is small.
[0030]
【Example】
Examples of the present invention and comparative examples will be described below.
[0031]
Comparative Example 1
Waste water containing pH 1.7, F 1.750 mg / l, Cl 4200 mg / l, and SO ₄ 1500 mg / l was reacted with slaked lime as a calcium compound by the apparatus shown in FIG. 2 and adjusted to pH 6.5. Sludge was returned to 10 liter / hr for 100 liter / hr of raw water. The sedimentation tank is circular and has a diameter of 80 cm and a height of 100 cm. As a result of measuring the particle size distribution of the CaF ₂ sludge obtained at this time, the average diameter was 24 μm.
[0032]
Example 1
The same raw water as in Comparative Example 1 was treated with the apparatus shown in FIG. The solid-liquid separation tank 4 has a rectangular parallelepiped shape with a depth of 80 cm, a width of 35 cm, and a length of 150 cm, and the solid-liquid separation regions 21, 22, and 23 are 20 cm, 40 cm, and 90 cm long in the traveling direction with the rectifying plates 24 and 25, respectively. There is a partition. The rectifying plates 24 and 25 are formed in a zigzag shape with holes having a diameter of 3 cm, and the reaction solution proceeds to the right in FIG. Other conditions are the same as in Comparative Example 1.
[0033]
As a result of the above treatment, the particle size of the crystals recovered from the solid-liquid separation region 21 was 60 to 80 μm, 10 to 30 μm from the solid-liquid separation region 22, and 10 μm or less from the solid-liquid separation region 23. From this result, the crystals obtained from the solid-liquid separation region 21 can be recovered as they are, and the crystals obtained from the solid-liquid separation region 23 are preferably returned, and the crystals obtained from the solid-liquid separation region 22 are recovered or returned as necessary. It turns out that you can choose whether to do.
[Brief description of the drawings]
FIG. 1 is a flowchart of a fluorine removal method and apparatus according to an embodiment.
FIG. 2 is a flow diagram of a conventional fluorine removal method and apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Reaction tank 3 Coagulation tank 4 Solid-liquid separation tank 5 Calcium compound tank 6 Mixing tank 7 Coagulant tank 21, 22, 23 Solid-liquid separation area

Claims (4)

A reaction step of reacting fluorine-containing water with a calcium compound to precipitate insoluble calcium fluoride;
A solid-liquid separation step for solid-liquid separation of the reaction liquid in the reaction step into treated water and sludge, and a mixing step for mixing a part of the sludge separated in the solid-liquid separation step with a calcium compound and supplying the mixture to the reaction tank,
In the solid-liquid separation process, the sludge is classified into a large particle size sludge and a small particle size sludge according to the particle size and separated into solid and liquid,
The classified large particle size sludge is discharged out of the system without being returned to the mixing process and without being crushed.
A fluorine removing method, wherein the classified sludge having a small particle diameter is returned to the mixing step, mixed with the calcium compound, and the calcium compound is adhered to the surface of the crystal and supplied to the reaction vessel.   In the solid-liquid separation step, the reaction liquid is advanced to a plurality of solid-liquid separation regions that are divided in the liquid traveling direction and have a rectifying plate at the boundary, and large-sized crystals are precipitated on the upstream side. The method according to claim 1, wherein the sludge having a small particle size separated from the solid-liquid separation region at the front end side in the traveling direction of the liquid is returned to the mixing device. A reaction vessel in which fluorine-containing water is reacted with a calcium compound to precipitate insoluble calcium fluoride;
A solid-liquid separation device that separates the reaction liquid in the reaction tank into treated water and sludge, and classifies the sludge into sludge with a large particle size and sludge with a small particle size according to the particle size. ,
A mixing device for mixing sludge having a small particle size classified by a solid-liquid separator with a calcium compound and supplying the mixture to a reaction tank;
A sludge passage that discharges sludge with a large particle size classified by the solid-liquid separator to the outside of the system without crushing, and a sludge with a small particle size classified by the solid-liquid separator is returned to the mixing device. A fluorine removing apparatus including a return path that does not return sludge having a particle size .   The solid-liquid separation device has a plurality of solid-liquid separation regions that are divided in the liquid traveling direction and have a rectifying plate at the boundary, and precipitate large-sized crystals on the upstream side and small-sized particles on the downstream side. The apparatus according to claim 3, wherein the apparatus is configured to settle the crystals and return the sludge having a relatively small particle size separated in the solid-liquid separation region at the front end side in the liquid traveling direction to the mixing apparatus.

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