SG182082A1 - Method for treating fluorine-containing wastewater - Google Patents
Method for treating fluorine-containing wastewater Download PDFInfo
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- SG182082A1 SG182082A1 SG2011091931A SG2011091931A SG182082A1 SG 182082 A1 SG182082 A1 SG 182082A1 SG 2011091931 A SG2011091931 A SG 2011091931A SG 2011091931 A SG2011091931 A SG 2011091931A SG 182082 A1 SG182082 A1 SG 182082A1
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- calcium
- fluorine
- containing wastewater
- ion exchange
- ions
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- 229910052731 fluorine Inorganic materials 0.000 title claims abstract description 79
- 239000011737 fluorine Substances 0.000 title claims abstract description 79
- 238000000034 method Methods 0.000 title claims abstract description 78
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 title claims abstract description 71
- 239000002351 wastewater Substances 0.000 title claims abstract description 56
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 77
- 239000011575 calcium Substances 0.000 claims abstract description 59
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims abstract description 57
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 57
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 claims abstract description 56
- 229910001424 calcium ion Inorganic materials 0.000 claims abstract description 56
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 claims abstract description 50
- 239000001110 calcium chloride Substances 0.000 claims abstract description 50
- 229910001628 calcium chloride Inorganic materials 0.000 claims abstract description 50
- 230000008569 process Effects 0.000 claims abstract description 39
- 229910001634 calcium fluoride Inorganic materials 0.000 claims abstract description 38
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 claims abstract description 37
- 230000008929 regeneration Effects 0.000 claims abstract description 27
- 238000011069 regeneration method Methods 0.000 claims abstract description 27
- 238000004062 sedimentation Methods 0.000 claims abstract description 25
- 238000005342 ion exchange Methods 0.000 claims abstract description 17
- 229910001415 sodium ion Inorganic materials 0.000 claims abstract description 11
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims description 26
- 239000003456 ion exchange resin Substances 0.000 claims description 20
- 229920003303 ion-exchange polymer Polymers 0.000 claims description 20
- 239000007788 liquid Substances 0.000 claims description 18
- 239000002699 waste material Substances 0.000 claims description 13
- 238000005374 membrane filtration Methods 0.000 claims description 5
- 230000003311 flocculating effect Effects 0.000 claims description 2
- 238000011084 recovery Methods 0.000 description 37
- 239000011347 resin Substances 0.000 description 27
- 229920005989 resin Polymers 0.000 description 27
- 238000006243 chemical reaction Methods 0.000 description 24
- 239000012528 membrane Substances 0.000 description 19
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 17
- 239000000920 calcium hydroxide Substances 0.000 description 17
- 235000011116 calcium hydroxide Nutrition 0.000 description 17
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 17
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 16
- 229940003871 calcium ion Drugs 0.000 description 12
- 238000005189 flocculation Methods 0.000 description 12
- 238000000926 separation method Methods 0.000 description 12
- 230000016615 flocculation Effects 0.000 description 10
- 238000001223 reverse osmosis Methods 0.000 description 10
- 239000011780 sodium chloride Substances 0.000 description 10
- 239000000126 substance Substances 0.000 description 9
- -1 fluorine ions Chemical class 0.000 description 8
- 229920000642 polymer Polymers 0.000 description 8
- 239000010802 sludge Substances 0.000 description 8
- 239000003729 cation exchange resin Substances 0.000 description 6
- 238000007796 conventional method Methods 0.000 description 5
- 230000004048 modification Effects 0.000 description 5
- 238000012986 modification Methods 0.000 description 5
- 229920006395 saturated elastomer Polymers 0.000 description 5
- 230000018044 dehydration Effects 0.000 description 3
- 238000006297 dehydration reaction Methods 0.000 description 3
- 125000000524 functional group Chemical group 0.000 description 3
- 239000004065 semiconductor Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000004065 wastewater treatment Methods 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000009833 condensation Methods 0.000 description 2
- 230000005494 condensation Effects 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 238000012805 post-processing Methods 0.000 description 2
- 239000013049 sediment Substances 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- SMEGJBVQLJJKKX-HOTMZDKISA-N [(2R,3S,4S,5R,6R)-5-acetyloxy-3,4,6-trihydroxyoxan-2-yl]methyl acetate Chemical compound CC(=O)OC[C@@H]1[C@H]([C@@H]([C@H]([C@@H](O1)O)OC(=O)C)O)O SMEGJBVQLJJKKX-HOTMZDKISA-N 0.000 description 1
- 238000002835 absorbance Methods 0.000 description 1
- 229940081735 acetylcellulose Drugs 0.000 description 1
- 239000003929 acidic solution Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000004760 aramid Substances 0.000 description 1
- 229920003235 aromatic polyamide Polymers 0.000 description 1
- 238000001479 atomic absorption spectroscopy Methods 0.000 description 1
- 238000011001 backwashing Methods 0.000 description 1
- 229920002301 cellulose acetate Polymers 0.000 description 1
- 239000012295 chemical reaction liquid Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 150000002222 fluorine compounds Chemical class 0.000 description 1
- 238000011010 flushing procedure Methods 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000012510 hollow fiber Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000010842 industrial wastewater Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229920002492 poly(sulfone) Polymers 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000000153 supplemental effect Effects 0.000 description 1
- 235000012431 wafers Nutrition 0.000 description 1
- 238000003911 water pollution Methods 0.000 description 1
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- Removal Of Specific Substances (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
- Treatment Of Water By Ion Exchange (AREA)
Abstract
METHOD FOR TREATING FLUORINE-CONTAINING WASTEWATERProvide is a method for treating fluorine-containing wastewater by which high fluorine-containing wastewater can be efficiently treated at a low cost. The method includes generating calcium fluoride by adding first calcium chloride to fluorine-containing wastewater; removing the calcium fluoride by sedimentation to obtain treated water; recovering calcium from the treated water by ion exchange between calcium ions and sodium ions; performing a regeneration process for compensating the ion exchange; and supplying the second calcium chloride to the fluorine-containing wastewater at the generating.FIG. 1
Description
METHOD FOR TREATING FLUORINE-CONTAINING WASTEWATER
1. Field of the Invention
The present invention particularly relates to a method for treating high-concentration fluorine- containing wastewater discharged from semiconductor plants, etc. 2. Description of the Related Art
A fluorine compound is used to clean silicon wafers in plants where electronic components, such as, semiconductors, are manufactured. Consequently, industrial wastewater of such plants contains hydrofluoric acid having a concentration of several hundred mg/L. Therefore, it is necessary to treat the high-concentration fluorine-containing wastewater such that an effluent reference value of the wastewater is less than or equal to 8 (Japan Standard) mg/L according to the environmental quality standard and the effluent standard for water pollution control.
It is known in the art to add calcium hydroxide in raw water to remove fluorine from the fluorine- containing wastewater. FIG. 7 is a drawing explaining a conventional method for treating fluorine-containing wastewater. As shown in FIG. 7, slaked lime (Ca (OH) >) is added to fluorine-containing wastewater, which is raw water, in a reaction tank 1 to generate calcium fluoride (CaF). Thereafter, the generated calcium fluoride is flocculated by adding a polymer (polymer : flocculent) in a flocculation tank 2. The flocculated calcium fluoride is then separated by the way of sedimentation in a sedimentation tank 3 at the next stage. Consequently, a fluorine content in the wastewater is suppressed to less than or equal to 15 mg/L by the reaction of fluorine ions with the slaked lime. To satisfy the effluent standard described above, the fluorine content is brought to less than or equal to 8 mg/L by performing post processing, such as, resin adsorption and aluminum flocculation and sedimentation, and thereafter the wastewater is released into a river, etc.
In a method for treating fluorine-containing water disclosed in Japanese Patent Application Laid-open No.
H11-221579, calcium ions are removed from the wastewater containing low-concentration fluorine and calcium by ion exchange in an ion exchange resin column at the previous stage. Thereafter, the fluorine ions are removed with a reverse osmosis membrane (RO membrane) at the next stage. The fluorine is made insoluble by the reaction of a concentrated liquid of the reverse osmosis membrane with calcium chloride that is output as a regenerated waste liquid from the ion exchange resin column. As a result, a water recovery rate can be enhanced as a result of efficiently treating the fluorine-containing water without causing clogging of the reverse osmosis membrane.
However, the following problems arise in the method of treating fluorine-containing wastewater using the slaked lime.
Because the reactivity between the slaked lime and the fluorine is low, it is necessary to add the slaked lime as much as three equivalent (equivalent means the weight of calcium and to the weight of fluorine in the reaction which becomes Ca+2F-CaF2, and "three equivalent" means calcium weight of three 3 times equivalent). Generally, slaked lime is less soluble in water. Therefore, along with sediments of calcium fluoride, unreacted slaked lime is also discharged from the sedimentation tank. As a result, more sludge needs to be treated. The sludge is treated by performing processes such as condensing the sludge, drying by heating, and dehydration; therefore, increased sludge leads to increased energy cost.
Moreover, slaked lime is strongly alkaline; therefore, a chemical whose pH can be adjusted to near neutral is required in the post processing.
Calcium ions are present in a concentration of several hundred mg/L in the treated water that is obtained after removing calcium fluoride by the sedimentation. Therefore, if a reverse osmosis membrane separation process, etc., is performed in in this state, the process cannot be performed due to generation of scales and the generated water cannot be reused.
Moreover, because the slaked lime is used in the form of powder, it easily gets scattered in air, making the working conditions poor.
On the other hand, there is another wastewater treatment method in which calcium fluoride is generated by adding calcium chloride instead of the slaked lime to the fluorine-containing wastewater. However,
calcium chloride is costlier than slaked lime and therefore this method is not practical.
The method disclosed in Japanese Patent
Application Laid-open No. H11-221579 targets at treating fresh water that contains fluorine and that has a low fluorine content of less than or equal to 20 mg/L, and this method is advantageous in being able to treat such low fluorine-containing water. However, in case of high fluorine-containing wastewater that is generally discharged from semiconductor plants, if a large amount of fluorine is to be removed with the reverse osmosis membrane, extra load is put on the processes for applying the pressure for supplying raw water and cleaning the reverse osmosis membrane, leading to poor treatment efficiency. Furthermore, there is a problem that calcium chloride that is present in the regenerated waste liquid alone is not sufficient to react with the fluorine. If the entire regenerated waste liquid is added to the reaction tank, the calcium concentration of the waste liquid will be diluted, resulting in a reduced reaction efficiency with the fluorine.
The present invention is made in view of the above discussion, and it is an object of the present invention to provide a method for treating fluorine- containing wastewater by which high fluorine-containing wastewater can be efficiently treated at a low cost.
A method for treating fluorine-containing wastewater according to an aspect of the present invention includes generating calcium fluoride by adding first calcium chloride to fluorine-containing wastewater; removing the calcium fluoride by sedimentation to obtain treated water; recovering calcium from the treated water by ion exchange between calcium ions and sodium ions; performing a regeneration process for compensating the ion exchange; and supplying second calcium chloride generated at the performing to the fluorine-containing wastewater at the generating.
A method for treating fluorine-containing wastewater according to another aspect of the present invention includes generating calcium fluoride by adding first calcium chloride to fluorine-containing wastewater; flocculating the calcium fluoride by adding a flocculent; removing the calcium fluoride by sedimentation to obtain treated water; causing ion exchange between calcium ions and sodium ions thereby recovering calcium from the treated water; subjecting the treated water to a membrane filtration process after the ion exchange is over in the causing; collecting second calcium chloride from a chemically regenerated waste liquid generated in the ion exchange; and supplying the second calcium chloride to the fluorine-containing wastewater at the generating.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred’ embodiments of the invention, when considered in connection with the accompanying drawings.
FIG. 1 is a drawing explaining a method for treating fluorine-containing wastewater according to an embodiment;
FIG. 2 is a drawing explaining a calcium ion recovery process performed in an ion exchange resin column;
FIG. 3 is a drawing explaining resin regeneration performed in the ion exchange resin column;
FIG. 4 is a drawing explaining concentration of effluent calcium ions at the time of the resin regeneration performed in the ion exchange resin column;
FIG. 5 is a drawing explaining an operation pattern followed in the ion exchange resin column;
FIG. 6 is a drawing explaining a modification of the method for treating fluorine-containing wastewater according to the above embodiment; and
FIG. 7 is a drawing explaining a conventional method for treating fluorine-containing wastewater.
Exemplary embodiments of a method for treating fluorine-containing wastewater according to the present invention are explained in detail below with reference to the accompanying drawings. FIG. 1 is a drawing explaining a method for treating fluorine-containing wastewater according to an embodiment of the present invention. The method for treating fluorine-containing wastewater primarily includes a reaction process of . .
calcium fluoride, a flocculation process, a removal process by sedimentation separation, a calcium recovery process, an advanced treatment process, and a collection process.
Calcium fluoride is subjected to the reaction process in a reaction tank 10. Fluorine-containing wastewater 11, which is raw water, is introduced in the reaction tank 10. A first calcium chloride supplying member 12 and a second calcium chloride supplying member 14 communicate with inside of the reaction tank 10. The first calcium chloride supplying member 12 and the second calcium chloride supplying member 14 supply chemicals for generating calcium fluoride by the reaction of calcium ions with fluorine ions in the raw water.
The first calcium chloride supplying member 12 supplies fresh calcium chloride to the reaction tank 10.
In contrast, the second calcium chloride supplying member 14 supplies second calcium chloride that is generated during a regeneration process performed in a calcium recovery column 40 that is described later.
To suppress the concentration of a fluorine obtained after the sedimentation separation of calcium fluoride generated in the reaction tank 10 to less than or equal to 15 mg/L, a calcium content in a reaction liquid needs to be maintained at several hundred mg/L.
To achieve such calcium content, the number of calcium ions needs to be 2.1 to 2.3 equivalent that of the fluorine ions.
In the present embodiment, at an initial stage of an operation, the first calcium chloride supplying member 12 supplies calcium chloride o0f2.1 to 2.3 equivalent so that the calcium ions are of 2.1 to 2.3 equivalent. After the initial stage of the operation, the first calcium chloride supplying member 12 supplies calcium chloride such that the calcium ions that are required are 1.1 to 1.3 equivalent the fluorine ions.
The calcium ions required for generating the calcium fluoride are approximately one equivalent to fluorine; the remaining calcium ions get dissolved in the solution. The present embodiment is configured such that the second calcium chloride supplying member 14 supplies supplemental calcium chloride equivalent to the dissolved calcium ions. Therefore, the second calcium chloride supplying member 14 that supplies high calcium-ion concentration recovered water that is described later to control calcium chloride content such that the calcium ions are approximately more than or equal to one equivalent of fluorine.
The fluorine-containing wastewater is generally an acidic solution (having a pH of 2 to 3). Therefore, slaked lime is added to increase the pH of the fluorine-containing wastewater to 7 to 8 so as to make it neutral.
The flocculation process is performed in a flocculation tank 20. Treated water containing calcium fluoride is introduced in the flocculation tank 20 from the reaction tank 10 and a polymer flocculent supplying member 22 that supplies polymer, such as, a polymer flocculent, is connected to the flocculation tank 20.
The flocculent supplying member 22 supplies the polymer required for flocculation of calcium fluoride to the flocculation tank 20. As a result, calcium fluoride can be flocculated, flocs can be easily sedimented in a sedimentation tank 30 at the next stage, and solid- liquid separation can be easily performed.
The removal process by sedimentation separation is performed in the sedimentation tank 30. Treated water containing calcium fluoride that is flocculated in the flocculation tank 20 is introduced in the sedimentation tank 30. The calcium fluoride, which is sedimented at the bottom of the tank, is subjected to solid-liquid separation and discharged to the outside. Sludge of the discharged calcium fluoride is subjected to a condensation process and thereafter to a dehydration process, and is disposed to the outside. In the process of sedimentation separation, apart from sedimentation, if the solid-liquid separation of the calcium fluoride is enabled, membrane separation, etc., can be used without limiting to the sedimentation.
The calcium recovery process is performed in the calcium recovery column 40. Because the treated water obtained after performing solid-liquid separation contains the calcium ions having a dissolved calcium content of several hundred mg/L, the calcium is recovered in the calcium recovery column 40. The calcium recovery column 40 is an Na-type cation exchange resin column, for example. The Na-type cation exchange resin column is filled with an Na-type cation exchange resin.
FIG. 2 is a drawing explaining a calcium ion recovery process performed in the ion exchange resin column. As shown in FIG. 2, when the treated water
(water obtained after flocculation and sedimentation treatment) obtained from the sedimentation tank 30 is introduced in the calcium recovery column 40, sodium ions filled in the resin column are replaced by the calcium ions in the treated water and calcium is captured in a resin functional group. Thus, a treated water (water after calcium treatment) having the fluorine content of 15 mg/L with the calcium ions removed therefrom is discharged from the calcium recovery column 40. In the ion exchange process, if : the ion exchange resin becomes saturated, the calcium ions cannot be captured. Therefore, the ion exchange resin needs to be regenerated before it becomes saturated. A regeneration process described later, and which is indicated by a dotted line, cannot be performed during the calcium ion recovery process.
FIG. 3 is a drawing explaining regeneration of resin performed in the ion exchange resin column. As shown in FIG. 3, the calcium recovery process, which is indicated by a short dashed line, is stopped, and sodium chloride (NaCl) solution having a concentration of a few percent that functions as a resin generation chemical is supplied from a downstream side (the side opposite to the side from where the treated water is introduced) in the calcium recovery column 40. In the resin column, the calcium ions captured in the resin function group are replaced by the sodium ions and regenerated as an Na-type functional group. Thereafter, the calcium ions are discharged as calcium chloride from a regeneration piping 42. A calcium ion monitor 44 is provided on the regeneration piping 42. The calcium ion monitor 44 according to the present embodiment monitors in-line calcium ions by measuring absorbance of light using the technique of atomic absorption spectrometry. Alternatively, an in-line hardness scale can be used. The regeneration piping 42 is bifurcated into a piping 46 for lean regenerated water and a piping 48 for high calcium-ion concentration recovered water. The pipings 46 and 48 are, respectively, provided with a shut-off valve 47 : and a recovery valve 49. The piping 46 for lean regenerated water and the piping 48 for high calcium- ion concentration recovered water can be switched between themselves based on the measurement result of the calcium ion monitor 44. The piping 48 for high calcium-ion concentration recovered water is connected to the reaction tank 10 as the second calcium chloride supplying member 14.
FIG. 4 is a drawing explaining concentration of effluent calcium ions at the time of regeneration of resin performed in the ion exchange resin column. In
FIG. 4, a vertical axis represents the concentration of the effluent calcium ions and a horizontal axis represents a regeneration time. As shown in FIG. 4, the concentration of the effluent calcium ions changes in an upward parabolic shape. If NaCl is injected for regeneration, the concentration increases rapidly in a short time after the startup. This is because the calcium ions and the sodium ions are immediately exchanged and discharged inside a resin tower.
Furthermore, if the flow of the regenerated water is continued for a predetermined time, the concentration of the effluent calcium ion reaches a maximum value, and thereafter, it decreases gradually. In the present embodiment, calcium recovery is started when the calcium concentration in the regenerated water is equal to or above a line (set value) A, and calcium recovery is stopped when the calcium concentration in the regenerated water drops below the set value A. High- concentration calcium can be recovered with this method.
To realize this, the second calcium chloride generated by the regeneration process that is performed above the set value A is collected and added to the reaction tank 10 (collection process). At the point where the concentration of the effluent calcium ions exceeds the set value A, the recovery valve 49 is opened and the shut-off valve 47 is closed. At points where the concentration of the effluent calcium ions is below the set value A, the recovery valve 49 is set in a closed state and the shut-off valve 47 set in an opened state.
The regenerated water that contains a low concentration of the calcium ions has a reduced efficiency with the fluorine, and therefore, the recycled water cannot be used as a chemical additive.
FIG. 5 is a drawing explaining an operation pattern followed in the ion exchange resin column. If a standard calcium recovery process is performed, the ion exchange resin becomes saturated. Because the calcium ions leak from the saturated resin column, it is necessary to perform the regeneration process. In the regeneration process, first, water is removed up to a resin surface of the resin column and the treated water inside the tower is discharged. Thereafter, the resin layer is separated, and backwashed with the upward flowing water by flushing intermingled impurities. After allowing the resin to settle down for a predetermined period, water is filled in the resin column. Thereafter, saline water, having a concentration of a few percent, that functions as the regenerated water is injected for a predetermined period or a predetermined amount of the saline water is added into the resin column. The recovered calcium chloride is mixed with the regenerated waste liquid by an influent process of the saline water. Thereafter, : regenerated water remaining in the resin column is discharged by slowly pushing it out by the water in a downward flow. By letting pure water flow at the same speed as when the calcium is recovered in the downward flow, a small amount of regenerated water that is remaining in the resin column is sufficiently flushed out (water washing). This regeneration process can be performed within a shorter time than the calcium recovery process. Therefore, when a plurality of calcium recovery columns is to be alternately operated, a standby time needs to be secured after end of the regeneration process till beginning of the next calcium recovery process. The present embodiment explains a method in which the regenerated chemical is made to flow upward; however, the regenerated chemical can be injected in a downward flow or in an upward and downward flow.
The advanced treatment process is a process in which the treated water having the fluorine content of 15 mg/L that is treated by an ion exchange resin process performed by an advanced treatment unit 50 is treated such that the fluorine content is suppressed to less than or equal to 8 mg/L that is the effluent standard. In the present embodiment, as an example of the advanced treatment unit 50, the reverse osmosis membrane is used to perform a membrane treatment, which is explained below. In the reverse osmosis membrane, to remove the fluorine in the treated water, acetylcellulose, aromatic polyamide, polyvinyl alcohol, polysulfone, etc., can be used as a material of the membrane. Furthermore, the membrane can be a hollow fiber membrane, a spiral membrane, a tubular membrane, etc.
The method for treating fluorine-containing wastewater according to the present embodiment performed using the processes described above is explained below.
When the fluorine-containing wastewater is introduced in the reaction tank 10, the first calcium chloride supplying member 12 supplies the first calcium chloride of 1.1 to 1.3 equivalent. The second calcium chloride supplying member 14 supplies the second calcium chloride generated by the regeneration process performed in the calcium recovery column 40 at the next stage.
The calcium fluoride generated in the reaction tank 10 is introduced in the flocculation tank 20, and flocculated by supplying the polymer, such as, the polymer flocculent, by the flocculent supplying member 22.
The calcium fluoride that is introduced in the sedimentation tank 30 is removed by sedimentation separation, and disposed to the outside after performing condensation and dehydration processes. The treated water containing the calcium ions is introduced in the calcium recovery column 40.
In the calcium recovery column 40, the sodium ions filled in the resin column are replaced by the calcium ions in the treated water and the calcium is captured in the resin functional group. From the treated water having a fluorine concentration of 15 mg/L that has passed through the calcium recovery column 40, fluorine ions are recovered with the reverse osmosis membrane that is the advanced treatment unit 50. The fluorine concentration in the treated water that is treated by a membrane separation process performed using the reverse osmosis membrane is brought to less than or equal to 8 mg/L, and as a result, the treated water is reused.
On the other hand, in the calcium recovery column 40, the calcium ions cannot be captured if the ion exchange resin is saturated in a standard calcium recovery process. Therefore, the process is switched to the regeneration process before the calcium ions leak. In the regeneration process, the saline water (NaCl solution), having a concentration of a few percent, that functions as a resin generation chemical is supplied from the downstream side (the side opposite to the side from where the treated water is introduced) in the calcium recovery column 40. At this time, the concentration of the calcium ions in the chemically regenerated waste liquid that is discharged from the regeneration piping 42 is measured with the calcium ion monitor 44. In the present embodiment, with reference to the concentration curve of the concentration of the effluent calcium ions shown in FIG. 4, calcium recovery is started when the calcium concentration in the regenerated water is equal to or above the set value A, and calcium recovery is stopped when the calcium concentration in the regenerated water drops below the set value A. High-concentration calcium can be recovered with this method. The high-concentration recovered water containing the second calcium chloride, which is generated by the regeneration process performed in a region above the set value A, is supplied to the reaction tank 10.
According the method for treating fluorine- containing wastewater, an amount of the sludge to be treated is significantly reduced as compared to when the calcium ions are added when the slaked lime is used in the conventional method and the cost required for the wastewater treatment can be reduced. By adding the second calcium chloride, which is contained in the regenerated water generated in the ion exchange resin : column, to the reaction tank, the amount of the first calcium chloride that needs to be added can be significantly reduced.
FIG. 6 is a drawing explaining a modification of the method for treating fluorine-containing wastewater according to the present invention.
In the modification of the method for treating fluorine-containing wastewater, calcium recovery columns 40a and 40b are arranged in parallel between the sedimentation tank 30 and the advanced treatment unit 50. Specifically, in the treatment method explained in FIG. 6, two cation exchange resin columns are arranged in parallel. Rest of the structure is similar to that of the treatment method explained in
FIG. 1. The same constituents are assigned the same symbols, and a detailed explanation thereof is omitted.
With this structure, in one cation exchange resin column, a standard process of replacing the sodium ions by the calcium ions is performed and the calcium ions in the treated water are recovered. In the other 10% exchange resin column, a recovery operation of the calcium ions is stopped and the cation exchange resin column remains in a standby state or performs a regeneration process. Specifically, preparations for regeneration, such as, water removal, back washing, settling, and water filling are performed. The aqueous solution of sodium chloride that functions as the chemical is injected from the downstream side of the resin column. By injecting the chemical of a predetermined amount for a predetermined time, the calcium ions captured in the resin column are replaced by the sodium ions. Thereafter, a water washing process is performed and the sodium chloride inside the resin column is discharged to the outside.
In the method for treating fluorine-containing wastewater according to the modification, in the ion exchange resin columns arranged in parallel, an ion exchange process is alternately switched between these columns. Therefore, it is not necessary to stop the calcium recovery process to perform the regeneration : process in the calcium recovery column 40, and the calcium recovery process can be continuously performed.
Furthermore, similar to the method for treating fluorine-containing wastewater explained in FIG. 1, the amount of the sludge to be treated is significantly reduced as compared to when the calcium ions are added when the slaked lime is used in the conventional method, and the cost of the wastewater treatment can also be reduced. By adding the second calcium chloride that is the regenerated water generated in the ion exchange resin column to the reaction tank 10, the amount of the first calcium chloride that needs to be added can be significantly reduced.
According to the method for treating fluorine- containing wastewater described above, a sediment is composed almost entirely of calcium fluoride and includes no unreacted slaked lime as in the conventional method in which slaked lime is added.
Therefore, an amount of sludge to be treated is significantly reduced and a cost for treating the wastewater is reduced.
Second calcium chloride more than or equal to an : amount required for generating the calcium fluoride is collected and added to the reaction tank. Therefore, an amount of first calcium chloride that needs to be added is significantly reduced.
Calcium chloride in regenerated waste liquid can be efficiently recovered. Therefore, as an incidental advantage, scaling relating to membrane filtration at the next stage can be prevented from occurring.
Fluorine ions in the fluorine-containing wastewater are removed in a sedimentation tank and in a second stage of an advanced treatment. Therefore, a burden on a membrane filtration process that is the advanced treatment at the next stage is reduced and treated water that fulfills a reference value of effluent standard is obtained.
An amount of first and second calcium chloride to be added can be made 2.1 to 2.3 equivalent fluorine ions. Accordingly, a concentration of dissolved calcium required for keeping a fluorine concentration at less than or equal to 15 mg/L after reaction is maintained at several hundred mg/L.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be : thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Claims (7)
1. A method for treating fluorine-containing wastewater comprising: generating calcium fluoride by adding first calcium chloride to fluorine-containing wastewater; removing the calcium fluoride by sedimentation to obtain treated water; recovering calcium from the treated water by ion exchange between calcium ions and sodium ions; performing a regeneration process for compensating the ion exchange; and supplying second calcium chloride generated at the performing to the fluorine-containing wastewater at the generating.
2. The method for treating fluorine-containing wastewater according to Claim 1, wherein the recovering includes detecting a calcium concentration of a chemically regenerated waste liquid generated as a result of the ion exchange; and recovering calcium more than or equal to one equivalent required for generating the calcium fluoride from the chemically regenerated waste liquid.
3. The method for treating fluorine-containing wastewater according to Claim 1 or 2, further comprising subjecting the treated water to a membrane filtration process after the ion exchange is over in the recovering.
4. A method for treating fluorine-containing wastewater comprising: generating calcium fluoride by adding first
. calcium chloride to fluorine-containing wastewater; flocculating the calcium fluoride by adding a flocculent; removing the calcium fluoride by sedimentation to obtain treated water; causing ion exchange between calcium ions and sodium ions thereby recovering calcium from the treated water; subjecting the treated water to a membrane filtration process after the ion exchange is over in the causing; collecting second calcium chloride from a chemically regenerated waste liquid generated in the ion exchange; and supplying the second calcium chloride to the fluorine-containing wastewater at the generating.
5. The method for treating fluorine-containing wastewater according to Claim 4, wherein the collecting includes detecting a calcium concentration of the chemically regenerated waste liquid generated as a result of the ion exchange resin with a calcium ion monitor; and recovering calcium more than or equal to at least one equivalent required for generating the calcium fluoride from the chemically regenerated waste liquid.
6. The method for treating fluorine-containing wastewater according to any one of Claims 1 to 5, wherein the generating includes adding the first calcium chloride of 1.1 to 1.3 equivalent.
7. The method for treating fluorine-containing wastewater according to any one of Claims 1 to 6, wherein the recovering and the performing are alternately executed in a plurality of ion exchange resin columns arranged in parallel.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2010282977A JP5665002B2 (en) | 2010-12-20 | 2010-12-20 | Treatment method for fluorine-containing wastewater |
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| SG182082A1 true SG182082A1 (en) | 2012-07-30 |
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| SG2011091931A SG182082A1 (en) | 2010-12-20 | 2011-12-13 | Method for treating fluorine-containing wastewater |
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| JP (1) | JP5665002B2 (en) |
| SG (1) | SG182082A1 (en) |
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| JP5692278B2 (en) * | 2013-04-25 | 2015-04-01 | 栗田工業株式会社 | Method and apparatus for treating fluoride-containing water |
| CN105668863A (en) * | 2016-04-15 | 2016-06-15 | 林淑录 | Method for treating fluoride containing waste water in silicon wafer production process |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JPH0753276B2 (en) * | 1989-10-03 | 1995-06-07 | 栗田工業株式会社 | Fluoride-containing water treatment method |
| JPH0615265A (en) * | 1992-07-03 | 1994-01-25 | Miura Co Ltd | Operation control method of water softening devices connected in parallel |
| JP4543482B2 (en) * | 2000-03-06 | 2010-09-15 | 栗田工業株式会社 | Fluorine-containing water treatment method |
| JP2001276851A (en) * | 2000-03-29 | 2001-10-09 | Japan Organo Co Ltd | Drain treatment equipment |
| JP4669625B2 (en) * | 2001-03-30 | 2011-04-13 | オルガノ株式会社 | Crystallization reactor equipped with crystallization reaction component recovery means |
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2010
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| JP2012130833A (en) | 2012-07-12 |
| JP5665002B2 (en) | 2015-02-04 |
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