JPS5855083A - Removing method for silicic acid in water - Google Patents

Abstract

PURPOSE:To remove only the silicic acid selectively and effectively at a low cost by adding hydrofluoric acid intermittently to water contg. silicic acid under the conditions where excess hydrofluoric acid exists and passing the water through weakly basic anion exchange resins of OH type. CONSTITUTION:Mineral acid 9 such as hydrochloric acid or sulfuric acid is added to raw water 8 which is subjected to pretreatment such as flocculating and settling to remove the hydrogencarbonate ions as free carbonic acids beforeh and with a decarboxylating device 1. Hydrofluoric acid 10 is added intermittently to the raw water removed of the free carbonic acid, and the raw water is passed through a silicic acid adsorbing tank 2. The water 8' removed of the silicic acid is decreased of the silicic acid in the water 8' considerably in a reverse osmosis membrane device 4, by which the concntrating rate is increased and a large amt. of permeated water 11 is obtained. Thereafter said water 11 is passed to a mixed bed type producing device 5 for pure water, whereby pure water 12 is obtained.

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.

Integrated circuits (Engineering/C) and large-scale integrated circuits (L, S, I
), the amount of cleaning nicroid-like substances and ions in their products is reduced to ppb
It requires so-called ultrapure water that has been reduced to the order of 100 millionths of a liter (per billion). When producing such ultrapure water.

In recent years, reverse osmosis membrane method is often used. In other words, raw water that has been subjected to appropriate pretreatment such as coagulation-sedimentation treatment and activated carbon filtration is treated with a reverse osmosis membrane device to reduce the salt content.9Then, this salt-reduced raw water is sent to a water purification device, a precision filtration device, a polisher, etc. It is common to process 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. Although non-permeable water is discharged, the colloidal substances contained in the raw water can also be blocked by the reverse osmosis membrane during this treatment.
This is convenient 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, but the conventional method for removing silicic acid is None of them are satisfactory and are 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 1, generates a large amount of sludge, and requires secondary treatment. Furthermore, conventional ion exchange methods cannot remove only silicic acid and must also remove other ions. 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, this is a method in which a fluoride such as sodium fluoride or calcium fluoride is added to raw water, and the water is passed through an H-type strongly acidic cation exchange resin and an OH-type weakly basic anion exchange resin. In this way, the silicic acid in the treated water of the strongly acidic cation exchange resin turns into a strong acid called hydrosilicic acid, which 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 of using an ion exchange resin. However, the ion exchange method is basically desalination, and various cations in raw water,
Since other anions are also removed, the processing cost is high.

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 invention provides a method for selectively and effectively removing only silicic acid at a low cost that can be adopted as a pretreatment for reverse osmosis membrane equipment.

Hydrofluoric acid is intermittently added to water containing silicic acid under conditions such that excess hydrofluoric acid coexists, and the water is passed through an OH-type weakly basic anion exchange resin. This invention relates to a method for removing silicic acid from water.

The present invention will be explained in detail below.

When hydrofluoric acid is added to raw water such as industrial water containing silicic acid, the silicic acid and fluorinated/hydrogen acid react as shown in equation (1), producing hydrofluorosilicic acid.

SiQ2+ 6HF-+H281F6 + 2H20
”・・”””・・”・・・・”・(1) This reaction theoretically requires 6 moles of hydrofluoric acid per 1 mole of silicic acid, but the reaction produced by equation (1) As mentioned above, hydrofluoric acid is a strong acid, so for example, if more than the theoretical value of hydrofluoric acid is continuously added to silicic acid in raw water and the water is passed through an OH-type weakly basic anion exchange resin ( 2) The hydrosilicofluoric acid can be removed as shown in the formula.

R=NHOH+H2SiF6→RyoNHH8iF6+H
20・・・・・・・・・(2) However, in raw water such as industrial water, in addition to silicic acid, mineral acid anions such as chloride ions and sulfate ions are also present, so hydrogen fluoride is added to such systems. When an acid is added, hydrosilicic acid, which corresponds to hydrogen ions, and mixed acids such as hydrochloric acid and sulfuric acid are produced. Also, since all of these acids are strong acids, they can be used as OH
When water is passed through a weakly basic anion exchange resin, only hydrofluorosilicic acid cannot be selectively adsorbed, and mineral acid anions are also adsorbed. Therefore, the exchange groups of the anion exchange resin cannot be effectively used only for the removal of silicic acid.

It is not practical because the processing capacity is small.

However, under such conditions where an excess of hydrofluoric acid coexists in the raw water, OH
It has been found that when water is passed through the weakly basic anion exchange resin, the silicic acid removal capacity of the weakly basic anion exchange resin 9 increases dramatically due to the mechanism described below.

That is, when an excess of hydrofluoric acid is added to industrial water containing silicic acid, etc. than the hydrofluoric acid required for the reaction of formula (1), and this water is passed through an OH type weakly basic anion exchange resin, ( 1)
The hydrofluorosilicic acid produced by the formula (2) is adsorbed on the anion exchange resin according to the formula (2), and excess hydrofluoric acid is adsorbed according to the formulas (3) and (4).

R=NHOH+HF→RmiWHIP 10 a, o...
・・・Reason・・・・・・・・・・・・(3) RaNH
OH+ 2HF-+ Ra NHHF2 + H20・
---...Song (4) When hydrofluoric acid is added to raw water, mineral acid anions coexisting in raw water are also adsorbed by the anion exchange resin while the raw water is on the acidic side.

However, when the addition of hydrofluoric acid is interrupted, adsorption stops as the pH of the raw water approaches neutrality.

On the other hand, while the addition of hydrofluoric acid was interrupted, the silicic acid in the raw water was converted to R=NHF, which was generated in equations (3) and (4).
RmiNH)IF2 (hereinafter both are conveniently referred to as hydrofluoric acid form) according to formulas (5) and (6),
Silicic acid is removed.

R(2NHF)6+ 5in2+ 3H20→R-Na
H81F6+R(iii;NHOH)5...
・・・・・・・・・(5) R(miNHHF2)3+SiO
2→RmiNHH8iF, +R(2NHOH)2...
・・・・・・・・・・・・(6) The weakly basic anion exchange resin in the form of hydrofluoric acid hardly reacts with the mineral acid anions in the raw water and selectively reacts with the silicic acid in the water. Because it reacts.

While hydrofluoric acid is not added to the raw water, the exchange groups of the anion exchange resin can be effectively used only for the removal of silicic acid.

When raw water to which no hydrofluoric acid has been added is passed through the anion exchange resin and this process is continued, the anion exchange resin in the hydrogen fluoride form converts into silicic acid through the reactions of equations (5) and (6). However, when hydrofluoric acid is added to the raw water again, the unreacted OH-type weakly basic anion exchange resin and the OH-type weakly basic anion generated by formulas (5) and (6) are removed. Since the exchange resin can be in the hydrofluoric acid form, silicic acid removal can be continued.

The present invention uses the removal mechanism described above.

When hydrofluoric acid is added to silicic acid in raw water (2
), and while the addition of hydrofluoric acid is interrupted, it is removed by the reactions of formulas (5) and (6).

As mentioned above, while adding hydrofluoric acid to raw water, mineral acid anions in the raw water are also removed, so in the present invention, when adding hydrofluoric acid intermittently, relatively high concentration It is preferable to add hydrofluoric acid in a short period of time to prevent the mineral acid from adsorbing onto the resin as much as possible.

In the present invention, the amount of hydrofluoric acid added to the raw water is such that all of the hydrofluoric acid is adsorbed on the OH type weakly basic anion exchange resin, and the total amount of hydrogen fluoride is around 2 eq/ln. It is preferable to add the acid intermittently in at least three times or more.

Note that if hydrogen carbonate ions are present in the raw water, the added hydrofluoric acid will be neutralized to become a hydrogen fluoride salt as shown in equation (7).

Because it no longer contributes to the reaction of equation (3) and equation (4).

When the amount of bicarbonate ions is relatively large, it is preferable to add a mineral acid such as hydrochloric acid to the raw water in advance to convert the bicarbonate ions into free carbonic acid, and then remove the free carbonic acid using a decarboxylation tower or the like.

NaHCO3+I(P→NaF+H2C!03...
・・・・・・・・・・・・・・・・・・・・・(By passing water as explained above, 9 weakly basic anion exchange resin is converted to formulas (2) and (5), ( 6) When saturated with hydrosilicofluoric acid as shown in formula, perform the following regeneration.

That is, the hydrosilicic acid is desorbed by passing an alkaline solution such as sodium chloride into the OH form of the weakly basic anion exchange resin. The reaction at this time follows equations (8) to 01.

R”1NHBiF6 + NaOH−+RmNHOH
+ NaH81F6--- (8) R=NHH81F+
6 + 2NaOH-4R=NHOH+ Na2S 1
P6 + H20・・・・・・・・・・・・(9
)R”1iNHH8iF6+ 8 NaOH-+ Ra
NHOH+f3 NaF'+ Na25in3+ 4H
20・・・・・・・・・・・・0ω Next, after extrusion and washing are carried out in a conventional manner, the above-mentioned water passage is carried out again. Note that if a pure water production device 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.

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/secondary amine, tertiary amine, etc. as the main exchange group, and the base of the resin is a copolymer of styrene and divinylbenzene, acrylic and divinylbenzene. or phenol-based copolymers, such as Amberlite (registered trademark) Engineering RA-93, Engineering RA-94, Engineering RA-68.

Engineering RA-47, Engineering R-45, Diaion (registered trademark)
WAIO, WA20, WA30, Revachit (registered trademark) MP62, MP64, etc., or equivalents thereof can be used. There are various types of weakly basic anion exchange resins ranging from those with strong basicity to those with weak basicity, and weakly basic anion exchange resins have relatively strong basicity.

In some cases, it may be called a medium basic anion exchange resin, but 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. ,l
is a decarboxylation device, 2 is an OH type weakly basic anion exchange resin 3
4 is a reverse osmosis membrane device.

Reference numeral 5 denotes a mixed bed pure water production apparatus filled with a strongly basic anion exchange resin 6 and a strongly acidic cation exchange resin 7.

First, to explain water flow, it is coagulation and precipitation.

A mineral acid 9 such as hydrochloric acid or sulfuric acid is added to raw water 8 that has been pretreated by filtration or activated carbon filtration, and hydrogen carbonate ions contained in the raw water are removed in advance as free carbonic acid in a decarboxylation device 1.

Next, hydrofluoric acid 1O is intermittently added to the raw water from which free carbonic acid has been removed, and this water is passed through the silicic acid adsorption tower 2.

Silicic acid in the polyhydric water can be removed by the water passage according to formulas (2) and (3), formulas (4) and (5), and formulas (6). The raw water 8' from which silicic acid has been removed in this way is treated with a reverse osmosis membrane device. In the reverse osmosis membrane device number, since the silicic acid in the raw water 8' is greatly reduced, the concentration can be increased and a large amount of permeated water 11 can be obtained. Next, the permeated water 11 is transferred to the mixed bed pure water production device 5.
to obtain pure water 12.

Although not shown, the pure water 12 is subjected to a precision filtration device, sterilization treatment, and further treated with a polisher to produce ultrapure water. When the silicic acid adsorption tower 2 reaches saturated adsorption with hydrosilicic acid due to such water flow, the following regeneration is performed.

That is, the mixed bed pure water production apparatus 5 is backwashed and separated using a conventional method, and a strong soda solution 13 of about 5% by weight is passed through the strong basic anion exchange resin 6 to regenerate the anion exchange resin. The regenerated waste liquid 14 is backwashed and settled by a conventional method and then passed through the silicic acid adsorption tower 2. Thereafter, extrusion cleaning is performed using a conventional method.

The strongly acidic cation exchange resin in the mixed bed pure water production apparatus 5 is regenerated with hydrochloric acid 15 in a conventional manner.

As shown in the figure, when a hot bed type water purification device 5 is installed, the recycled waste liquid 14 can be used to regenerate the silicic acid adsorption tower 2 in this way. If there is no waste liquid, the silicic acid adsorption tower 2 may be regenerated using a 2 to 5% by weight seeder solution.

For refilling the nose or regenerating waste liquid 14 (8
Hydrosilicofluoric acid is desorbed according to the ) formula to the QCj formula, and as a treatment for the desorption liquid, it is preferable to add lime or the like to precipitate and remove the fluorine component in the desorption liquid as calcium fluoride.

In addition, in the electronics industry that manufactures integrated circuits and large-scale integrated circuits, hydrofluoric acid is used to clean the products.
Washing acid waste containing hydrofluoric acid is discharged. Therefore, when the purity of the hydrofluoric acid in the cleaning sour-smelling liquid is relatively high, the cleaning sour-smelling liquid can be used as hydrogen fluoride that is intermittently added to raw water.

Furthermore, hydrofluoric acid can also be obtained by treating a sodium fluoride solution with an H-type strongly acidic cation exchange resin, so in some cases, it is okay to use hydrofluoric acid obtained by this method. do not have.

As explained above, the present invention selectively removes silicic acid from water by intermittently adding hydrofluoric acid to water containing silicic acid and passing the water through an OH type weakly basic anion exchange resin. It can be removed effectively, and weakly basic anion exchange resins have good regeneration efficiency, so only a small amount of regenerant is needed.

Furthermore, when the present invention is applied to the manufacturing process of ultrapure water in the electronics industry, cleaning acid waste liquid containing hydrofluoric acid or recycled waste liquid from mixed bed pure water production equipment can be used as a regenerating agent. The cost can be further reduced, and the overall ultrapure water production cost can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a flow of an example of an embodiment of the present invention. 1... Decarboxylation device 2... Silicic acid adsorption tower 3...
・OH type weakly basic anion exchange resin 4... Reverse osmosis membrane device 5... Mixed bed pure water production device 6... Strongly basic anion exchange resin 7... Strongly acidic cation exchange resin

Claims (1)

[Claims] Hydrofluoric acid is intermittently added to water containing silicic acid under conditions such that excess hydrofluoric acid coexists, and the water is passed through an OH-type weakly basic anion exchange resin. How to remove silicic acid from water.