JPH0143593B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively removing silicic acid from water containing silicic acid by using a weakly basic anion exchange resin under special conditions. The electronics industry, which manufactures integrated circuits (ICs) and large-scale integrated circuits (LSIs), uses ppb (parts per billion) amounts of colloidal substances and ions to clean their products.
It requires so-called ultra-pure water that has been reduced to the order of one-billionth of a billionth of a billionth of a billionth of a billionth of an inch. When producing such ultrapure water, reverse osmosis membrane method is often used in recent years. In other words, raw water that has undergone appropriate pretreatment such as coagulation sedimentation treatment and activated carbon filtration is treated with a reverse osmosis membrane device to reduce salt, and then this salt-reduced raw water is treated with a water purification device, precision filtration device, polisher, etc. It is common to do so. The reverse osmosis membrane device supplies raw water to the reverse osmosis membrane under pressure higher than the osmotic pressure, and the reverse osmosis membrane blocks most of the salts to obtain permeated water with reduced salts as treated water, as well as concentrating the salts. It discharges non-permeable water,
During this treatment, colloidal substances contained in the raw water can also be blocked by the reverse osmosis membrane, which is advantageous for producing the ultrapure water. Since reverse osmosis membrane equipment processes raw water through the operations described above, the higher the concentration ratio of raw water, the more permeated water can be obtained from a fixed supply of raw water, which is advantageous in terms of cost. Become. However, if the concentration ratio is increased too much, silicic acid with relatively low solubility will precipitate in the concentration system, especially near the membrane surface, resulting in contamination of the reverse osmosis membrane and deterioration of its performance. Therefore, if raw water with a high silicic acid content is to be treated with a reverse osmosis membrane device at a high yield, it is necessary to perform some kind of silicic acid removal treatment in the previous stage. None of the methods are satisfactory and difficult to adopt. For example, the conventional coagulation-sedimentation method, in which silicic acid is adsorbed onto flocs such as magnesium hydroxide or aluminum hydroxide and removed by coprecipitation, has a low removal rate of silicic acid, generates a large amount of sludge, and requires secondary treatment. Furthermore, conventional ion exchange methods cannot remove only silicic acid, and other ions must also be removed. For example, the following methods are conventional methods for removing silicic acid by ion exchange, in which silicic acid is removed from water using a weakly basic anion exchange resin with good regeneration efficiency. That is, by adding fluorides such as sodium fluoride and calcium fluoride to raw water,
This method involves passing water through a strongly acidic cation exchange resin in the OH type and a weakly basic anion exchange resin in the OH type. In this way, the silicic acid in the water treated with the strongly acidic cation exchange resin becomes a strong acid called hydrosilicic acid, so that it can be removed even with the weakly basic anion exchange resin. In this conventional ion exchange method, silicic acid, which cannot normally be removed with a weakly basic anion exchange resin, can be removed with a weakly basic anion exchange resin by adding fluoride. The regenerant cost can be reduced compared to the case where resin is used. However, the ion exchange method is basically desalination and also removes various cations and other anions in the raw water.
The processing cost is high, and furthermore, it is not reasonable to install a desalination device using ion exchange, which has a higher processing cost than a reverse osmosis membrane device, upstream of a reverse osmosis membrane device, which is a desalination device. The present inventor has investigated various methods for selectively and effectively removing only silicic acid at a low cost, which can be adopted as a pretreatment for reverse osmosis membrane equipment, and found that a weak It has been found that when water containing silicic acid is passed through the basic anion exchange resin layer, only silicic acid can be selectively and effectively removed. That is, the present invention has been conceived based on the above findings, and is characterized in that it is possible to obtain silicic acid in water by passing water containing silicic acid through a weakly basic anion exchange resin on which hydrofluoric acid has been adsorbed. This relates to a removal method. The present invention will be explained in detail below. When hydrofluoric acid is passed through an OH type weakly basic anion exchange resin, hydrofluoric acid is adsorbed, but when water containing silicic acid is passed through the weakly basic anion exchange resin, silicic acid is absorbed. can be effectively removed. That is, as shown in the example, about 120ppm as
When water containing silicic acid (SiO ₂ ) is treated with the weakly basic anion exchange resin layer, the silicic acid in the treated water is removed.
It can be 1 ppm as SiO ₂ or less. Although the mechanism for removing silicic acid is not yet clear,
This is probably due to the following reaction. In other words, it is said that hydrofluoric acid dissociates as shown in equation (1) when it is a dilute solution, and as shown in equation (2) when it is a concentrated solution. When the drug is passed through an anion exchange resin, the ionic form is considered to be F form, HF ₂ form, or a mixture of F form and HF ₂ form, depending on the degree of dissociation. HFH ⁺ +F ^- ...(1) 2HFH ⁺ +HF ^- ₂ ...(2) Such F type or HF ₂ type or F type
It is thought that the weakly basic anion exchange resin in the mixed form of HF ₂ reacts with silicic acid in water as shown in equations (3) and (4). R(≡NHHF) ₆ +SiO ₂ +3H ₂ O→ R≡NHHSiF ₆ +R(≡NHOH) ₅ ……(3) R(≡NHHF ₂ ) ₃ ＋SiO ₂ → R≡NHHSiF ₆ +R(≡NHOH) ₂ ……( 4) Is the silicic acid removal mechanism in the present invention based on formula (3), formula (4), or combination of formula (3) and
Although it is not clear whether formula (4) occurs at the same time, the weakly basic anion exchange resin can reliably remove silicic acid from water. In the present invention, the F type, HF ₂ type, and mixed type F and HF ₂ type weakly basic anion exchange resins are collectively referred to as weakly basic anion exchange resins adsorbed with hydrofluoric acid. . This weakly basic anion exchange resin that has adsorbed hydrofluoric acid hardly reacts with other anions in raw water, such as chlorine ions, sulfate ions, and hydrogen carbonate ions, but selectively reacts with silicic acid in water. Therefore, the adsorbed hydrofluoric acid can be effectively used only for the removal of silicic acid. Note that if the water flow continues, the flow-through point of silicic acid will eventually be reached, but as shown in equation (3) or (4), weakly basic anion exchange resin in the OH form will be produced due to the adsorption of silicic acid. Once the flow-through point has been reached, hydrofluoric acid is passed through the resin layer to form the formula (5) or (6).
As shown in the formula, water flow can be continued again by adsorbing hydrofluoric acid to this OH type weakly basic anion exchange resin. R≡NHOH+HF→R≡NHF+H ₂ O ……(5) R≡NHOH+2HF→R≡NHHF ₂ +H ₂ O
...(6) However, once the flow-through point has been reached, when hydrofluoric acid is passed through the water and the water continues to flow again, the leakage amount of silicic acid in the treated water tends to gradually increase, so it is necessary to pass the water at an appropriate point. The water must be discontinued and recycled as described below. In addition, when the flow-through point of silicic acid is reached as described above, the passage of hydrofluoric acid may be carried out by interrupting water passage as described above and passing hydrofluoric acid through the resin layer, Alternatively, concentrated hydrofluoric acid may be added spot-wise to the raw water without interrupting water flow. Furthermore, when water is passed through a weakly basic anion exchange resin that has adsorbed hydrofluoric acid while adding a small amount of hydrofluoric acid to the raw water from the beginning of the water flow, equation (3) or (4) is obtained.
Since formula (5) or formula (6) can be carried out simultaneously, it is possible to omit the above-mentioned passage of hydrofluoric acid during water passage. However, in this case, if hydrogen carbonate ions exist in the raw water, the added hydrofluoric acid will be neutralized to hydrogen fluoride salt as shown in equation (7), and equations (5) and (6) It is preferable to remove hydrogen carbonate ions from the raw water in advance, since they no longer contribute to the reaction. NaHCO ₃ +HF→NaF+H ₂ CO ₃ ...(7) When the weakly basic anion exchange resin becomes saturated with hydrofluorosilicic acid due to the water flow as explained above, the following regeneration is performed. That is, first, a caustic soda solution is passed through the solution to desorb the hydrosilicofluoric acid, and then a weakly basic anion exchange resin is removed.
It will be OH type. The reaction at this time is thought to follow formula (8), formula (9), or formula (10). R≡NHHSiF ₆ +NaOH→ R≡NHOH+NaHSiF ₆ …(8) R≡NHHSiF ₆ +2NaOH→ R≡NHOH+Na ₂ SiF ₆ +H ₂ O …(9) R≡NHHSiF ₆ +8NaOH→ R≡NHOH+6NaF+Na ₂ SiO ₃ +4H ₂ O ...(10) Then, after extrusion and washing in a conventional manner,
Hydrofluoric acid is passed through it, and the hydrofluoric acid is adsorbed onto the weakly basic anion exchange resin as shown in formula (5) or (6), and then extruded and washed using a conventional method to complete the regeneration. do. In addition, if a pure water production apparatus using a strong basic anion exchange resin is also installed, the recycled waste liquid of the strong basic anion exchange resin can be used for desorption of the hydrosilicofluoric acid. As explained above, silicic acid can be selectively and effectively removed by passing water containing silicic acid through a weakly basic anion exchange resin that has adsorbed hydrofluoric acid, but silicic acid can be removed selectively and effectively. However, fluoride and silicic acid leak. However, if this treated water is passed through a weakly basic anion exchange resin layer in the OH form, fluoride and silicic acid can be further removed. It is recommended to install an OH type weakly basic anion exchange resin layer after the ion exchange resin. In this way, raw water was passed in series through the weakly basic anion exchange resin layer (first column) on which hydrofluoric acid was adsorbed and the OH type weakly basic anion exchange resin (second column). Regarding the desorption of hydrosilicofluoric acid in the first column during treatment, it is preferable to pass the caustic soda solution from the second column to the first column in series. Next, the weakly basic anion exchange resin used in the present invention will be explained. The weakly basic anion exchange resin used in the present invention has polyamine, primary and secondary amines, tertiary amines, etc. as main exchange groups, and the resin matrix is a copolymer of styrene and divinylbenzene, a copolymer of acrylic and divinylbenzene, etc. Amberlite (registered trademark) IRA- is a polymer or phenol-based material.
93, IRA-94, IRA-68, IRA-47, IR-45,
Diamondion (registered trademark) WA10, WA20,
WA30, Revachit (registered trademark) WP62, MP64
or equivalents can be used. There are various types of weakly basic anion exchange resins, ranging from those with strong basicity to those with weak basicity.In some cases, weakly basic anion exchange resins with relatively strong basicity are Although sometimes referred to as an anion exchange resin, the weakly basic anion exchange resin as used in the present invention also includes such medium basic anion exchange resins. Next, embodiments of the present invention will be described. FIG. 1 is an explanatory diagram of the flow when the present invention is implemented as a pretreatment for a desalination device consisting of a reverse osmosis membrane device and a mixed-bed pure water production device, which is an ultrapure water production process in the electronics industry. , 1 is a decarboxylation device, 2 is a silicic acid adsorption tower filled with a weakly basic anion exchange resin 3 adsorbing hydrofluoric acid, and 4 is a W- filled with an OH type weakly basic anion exchange resin 3'. The OH tower, 5 is a reverse osmosis membrane device, and 6 is a mixed bed pure water production device filled with a strong basic anion exchange resin 7 and a strong acid cation exchange resin 8. First, to explain water passage, a mineral acid 10 such as hydrochloric acid or sulfuric acid is added to raw water 9 that has been pretreated by coagulation-sedimentation, filtration, or activated carbon filtration, and the bicarbonate ions contained in the raw water 9 are converted into free carbonate. The carbon dioxide is removed in advance by the decarboxylation device 1. The reason why bicarbonate ions in the raw water are removed in advance is that it is difficult to remove bicarbonate ions with the reverse osmosis membrane device 5, and in the desiliconization method of the present invention, the lower the amount of bicarbonate ions in the raw water, the better the This is because the hydrolysis rate of the weakly basic anion exchange resin to which hydrohydric acid has been adsorbed is small, so it is somewhat advantageous in terms of throughflow capacity. However, in the present invention, it is not always necessary to remove hydrogen carbonate ions in raw water, and this step may be omitted depending on the situation. Next, the raw water from which free carbonate has been removed is passed through the silicic acid adsorption tower 2. Due to the water flow, the above-mentioned formula (3) or (4)
Silicic acid in raw water can be removed by formula or formulas (3) and (4). The treated water in the silicic acid adsorption tower 2 contains on average 2 ppm as SiO ₂ silicic acid and 1 ppm as
Fluorine before and after F leaks, but by passing the treated water through the W-OH tower 4 as shown in the figure,
Furthermore, the amounts of silicic acid and fluorine can be reduced. It should be noted that most of the silicic acid in the raw water can be removed by just treating it in the silicic acid adsorption tower 2, and the amount of fluorine leaked is small, so the treated water in the silicic acid adsorption tower 2 must be treated with an OH-type weakly basic anion exchange resin. 3'
There is no need to pass water through the W-OH tower filled with W-OH, and depending on the situation, the installation of the W-OH tower can be omitted. The raw water 9' from which silicic acid has been removed in this manner is treated by a reverse osmosis membrane device 5. In the reverse osmosis membrane device 5, since the amount of silicic acid in the raw water 9' is greatly reduced, the concentration can be increased and a large amount of permeated water 11 can be obtained. Next, the permeated water is passed through the mixed bed pure water production equipment 6.
Pure water 12 is obtained by passing water through the water. Although not shown, the pure water 12 is subjected to precision overtreatment, sterilization treatment, and further treatment with a polisher to produce ultrapure water. Due to the water flow, silicic acid temporarily leaks in the silicic acid adsorption tower 2 as described above, but in this case, the water flow is interrupted and approximately 5% by weight of hydrofluoric acid 13 is removed.
is passed through the silicic acid adsorption tower 2, and as shown in equation (5) or (6), hydrofluoric acid is adsorbed on the weakly basic anion exchange resin in the OH form produced by water passing, and the water is passed again. continue. Note that when the silicic acid removal ability is not recovered significantly even after such hydrofluoric acid treatment during water passage, the following regeneration is performed. That is, the mixed bed type pure water production equipment 6 is backwashed and separated by a conventional method, and 5% by weight is
The caustic soda solutions 14 before and after are passed through the strong basic anion exchange resin 7 to regenerate the anion exchange resin, and the regenerated waste liquid 15 is passed in series to the W-OH tower 4 and the silicic acid adsorption tower 2. do. After that, extrusion cleaning is performed by a conventional method, and about 5% by weight is added to the silicic acid adsorption tower 2.
Hydrofluoric acid 13 is passed through the resin, and the hydrofluoric acid is adsorbed onto the weakly basic anion exchange resin 3 again. Note that the strongly acidic cation exchange resin 8 of the mixed bed pure water production apparatus 6 is regenerated with hydrochloric acid 16 in a conventional manner, and both ion exchange resins are mixed. As shown in the figure, if a mixed bed type pure water production device 6 is installed, the recycled waste liquid 15 is used as described above.
can be used to regenerate the W-OH tower 4 and the silicic acid adsorption tower 2. However, if there is no such regenerated waste liquid containing caustic soda, a 2-5% by weight caustic soda solution can be used to regenerate the W-OH tower 4 and the silicic acid adsorption tower 2. The tower and the silicic acid adsorption tower 2 may be regenerated. By passing caustic soda or recycled waste liquid 15 through it, hydrosilicofluoric acid is desorbed according to equations (8) to (10), but the desorption liquid can be treated by adding lime or the like to the desorption liquid. It is preferable to precipitate and remove the fluorine component therein as calcium fluoride. Furthermore, in the electronics industry that manufactures integrated circuits and large-scale integrated circuits, hydrofluoric acid is used to clean the products, so cleaning acid waste liquid containing hydrofluoric acid is discharged. Therefore, when the purity of the hydrofluoric acid in the cleaning acid waste liquid is relatively high, the cleaning acid waste liquid can be used for adsorbing hydrogen fluoride onto a weakly basic anion exchange resin. Furthermore, hydrofluoric acid can also be obtained by treating a sodium fluoride solution with an H-type strongly acidic cation exchange resin. It's okay to use it. As explained above, the present invention can selectively and effectively remove silicic acid from water using a weakly basic anion exchange resin adsorbed with hydrofluoric acid, and furthermore, the weakly basic anion exchange resin can be regenerated. Due to its high efficiency, only a small amount of regenerating agent is required, and when the present invention is applied to ultrapure water production processes in the electronics industry, it can be used to produce cleaning acid waste liquid containing hydrofluoric acid and mixed bed pure water production. Since recycled waste liquid from the apparatus can also be used, the cost of regenerating agent can be further reduced, and the overall cost of producing ultrapure water can be significantly reduced. Examples of the present invention will be described below, but the gist of the present invention is as explained above, and the present invention is not limited to the following examples. Example Weakly basic anion exchange resin Amberlite IRA
-Resin layer height 600mm filled with 0.5 each of 94
Two test columns were prepared, a 5% by weight caustic soda solution was passed through them, and the weakly basic anion exchange resins were completely converted into OH form by extrusion and washing in a conventional manner. Next, 1 eq/resin of about 5% by weight of hydrofluoric acid was passed through only one column using SV8, and extrusion cleaning was performed in a conventional manner to adsorb hydrofluoric acid onto the weakly basic anion exchange resin. Next, one column packed with a weakly basic anion exchange resin adsorbed with hydrofluoric acid was used as the front column.
The other column packed with the weakly basic anion exchange resin in the OH form was used as the latter column, and the raw water shown in Table 1 was passed through the series at a flow rate of LV20 m/H.
Furthermore, water flow was interrupted at the point where silicic acid leaked into the treated water in the front column, and 0.5 eq/-resin of about 5% by weight hydrofluoric acid was passed through the front column, and water was flowed again.
The same operation of adding hydrofluoric acid during water passage was performed twice. The above water flow results are shown in Figure 2. In Figure 2, the solid line A indicates the silicic acid concentration of the treated water in the previous column (column packed with a weakly basic anion exchange resin adsorbing hydrofluoric acid);
A' indicates the silicic acid concentration of the treated water in the latter column (a column packed with an OH type weakly basic anion exchange resin), dotted line B indicates the fluorine concentration of the treated water in the preceding column, and dotted line B' indicates the fluorine concentration of the treated water in the latter column. As shown in Figure 2, it exists in raw water.
Silicic acid of 120ppm as SiO ₂ is averaged by a weakly basic anion exchange resin adsorbed with hydrofluoric acid in the first stage.
It was possible to remove up to around 2ppm as SiO ₂ , and further remove down to 0.5ppm as SiO ₂ using the OH type weakly basic anion exchange resin installed in the latter stage. In addition, by passing hydrofluoric acid through the front column during water flow, the silicic acid removal ability of the front column was restored. 【table】

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a flow showing an example of an embodiment of the present invention, and FIG. 2 is a graph showing leakage curves of silicic acid and fluorine in an example of the present invention. The horizontal axis shows the processing amount, and the solid lines A and A' in the figure show the silicic acid concentration, and the dotted lines B and B' show the fluorine concentration. 1... Decarboxylation device, 2... Silicic acid adsorption tower, 3... Weakly basic anion exchange resin, 4... W-OH tower, 5... Reverse osmosis membrane device, 6... Mixed bed pure water production device, 7... Strong base 8... Strongly acidic cation exchange resin, 9... Raw water, 10... Mineral acid, 11... Permeated water, 12
...Pure water, 13.. Hydrofluoric acid, 14.. Caustic soda solution, 15.. Recycled waste liquid, 16.. Hydrochloric acid.

Claims (1)

[Scope of Claims] 1. A method for removing silicic acid in water, which comprises passing water containing silicic acid through a weakly basic anion exchange resin on which hydrofluoric acid has been adsorbed. 2. The method for removing silicic acid in water according to claim 1, wherein water is passed through the water containing silicic acid while adding hydrofluoric acid. 3. The method for removing silicic acid in water according to claim 1, wherein hydrofluoric acid is passed through a weakly basic anion exchange resin during water passage. 4 Add water treated with weakly basic anion exchange resin to
A method for removing silicic acid in water according to claim 1, 2, or 3, wherein water is passed through an OH-type weakly basic anion exchange resin.