JP2020093229A - Membrane separation method for silica-containing water and membrane separation system for silica-containing water - Google Patents
Membrane separation method for silica-containing water and membrane separation system for silica-containing water Download PDFInfo
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 219
- 239000012528 membrane Substances 0.000 title claims abstract description 181
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 168
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 109
- 238000000926 separation method Methods 0.000 title claims abstract description 34
- 238000001223 reverse osmosis Methods 0.000 claims abstract description 34
- 229910001415 sodium ion Inorganic materials 0.000 claims abstract description 27
- 230000000903 blocking effect Effects 0.000 claims description 46
- 238000000034 method Methods 0.000 claims description 26
- 229920002647 polyamide Polymers 0.000 claims description 15
- 239000004952 Polyamide Substances 0.000 claims description 14
- 230000004907 flux Effects 0.000 claims description 9
- 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 5
- 239000003729 cation exchange resin Substances 0.000 claims description 5
- 238000005341 cation exchange Methods 0.000 claims description 3
- 239000000126 substance Substances 0.000 abstract description 14
- 238000010979 pH adjustment Methods 0.000 abstract description 4
- 238000001556 precipitation Methods 0.000 abstract 1
- 239000003795 chemical substances by application Substances 0.000 description 22
- 239000007788 liquid Substances 0.000 description 11
- 239000012085 test solution Substances 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- FAPWRFPIFSIZLT-UHFFFAOYSA-M sodium chloride Inorganic materials [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 5
- 239000003513 alkali Substances 0.000 description 4
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 239000012466 permeate Substances 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 238000011084 recovery Methods 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- 239000002253 acid Substances 0.000 description 2
- 125000000129 anionic group Chemical group 0.000 description 2
- 125000002091 cationic group Chemical group 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000002270 dispersing agent Substances 0.000 description 2
- 239000008235 industrial water Substances 0.000 description 2
- 238000012806 monitoring device Methods 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 239000008239 natural water Substances 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000002349 well water Substances 0.000 description 2
- 235000020681 well water Nutrition 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 230000003204 osmotic effect Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000008400 supply water Substances 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
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- Treatment Of Water By Ion Exchange (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
Description
本発明は、逆浸透膜を用いたシリカ含有水の膜分離方法、及びその実施に好適な膜分離システムに関する。 The present invention relates to a method for membrane separation of silica-containing water using a reverse osmosis membrane, and a membrane separation system suitable for carrying out the method.
工業用水、井水、市水等を被処理水とし、これらの被処理水から純水を製造するために逆浸透膜（ＲＯ膜）装置が利用されている。ＲＯ膜装置は、ＲＯ膜により塩類等の不純物成分を分離して、被処理水を不純物成分が濃縮された濃縮水と、不純物成分濃度の低い透過水とに分離する。 BACKGROUND ART Industrial water, well water, city water, etc. are treated water, and a reverse osmosis membrane (RO membrane) device is used to produce pure water from these treated water. The RO membrane device separates impurity components such as salts by the RO membrane, and separates the water to be treated into concentrated water in which the impurity components are concentrated and permeate water in which the impurity component concentration is low.
シリカ（ＳｉＯ２）は自然水に含まれる成分であり、被処理水中のシリカはＲＯ膜の濃縮水側表面にシリカスケールとして析出する。このシリカスケールはＲＯ膜を閉塞させ、ＲＯ膜装置の処理効率を低下させてしまう。
ＲＯ膜表面へのシリカスケールの析出を抑制するために、スケール分散剤が汎用されている。また、特許文献１には、シリカを含む被処理水のｐＨを１０．０〜１２．０の範囲に調整し、且つ当該被処理水の水温を２５〜４０℃の範囲に調整した後に、当該被処理水をＲＯ膜装置に供給して、ＲＯ膜装置から排出される濃縮水中のシリカ濃度を５５０ｍｇ／Ｌ以上とすることにより、スケール分散剤や阻止率向上剤などの追加の薬剤を添加せずに、高濃度にシリカを濃縮しながらＲＯ膜の閉塞を抑制できることが記載されている。
Silica (SiO 2 ) is a component contained in natural water, and silica in the water to be treated precipitates as silica scale on the surface of the RO membrane on the concentrated water side. This silica scale blocks the RO membrane and reduces the processing efficiency of the RO membrane device.
Scale dispersants are commonly used to suppress the deposition of silica scale on the surface of the RO film. Further, in
本発明者らが検討を重ねた結果、特許文献１に記載の技術のように被処理水のｐＨを高めてＲＯ膜処理に付した場合には、膜面にシリカスケールが生じにくい一方で、ＲＯ膜の荷電物質の阻止性能が低下し、透過水の純度の向上には制約があることがわかってきた。この問題に対処するには、例えば複数段のＲＯ膜処理とすることが考えられる。しかし、このような対処は設置面積やコストの増大を招く。
そこで本発明は、シリカ含有水（シリカを含有する被処理水）をＲＯ膜により処理する膜分離方法であって、ＲＯ膜表面へのシリカスケールの析出を抑制し、かつシリカ含有水中の荷電物質（塩類等）を高効率に分離・除去することができるシリカ含有水の膜分離方法を提供することを課題とする。また本発明は、上記膜分離方法を実施するのに好適な膜分離システムを提供することを課題とする。
As a result of repeated studies by the present inventors, when the pH of the water to be treated is increased and subjected to the RO membrane treatment as in the technique described in
Therefore, the present invention is a membrane separation method of treating silica-containing water (water to be treated containing silica) with an RO membrane, which suppresses the deposition of silica scale on the surface of the RO membrane, and which is a charged substance in the silica-containing water. An object of the present invention is to provide a method for membrane separation of silica-containing water capable of highly efficiently separating and removing (salts and the like). Another object of the present invention is to provide a membrane separation system suitable for carrying out the above-mentioned membrane separation method.
本発明者らは上記課題に鑑み鋭意検討を重ねた結果、ｐＨ５．０〜７．０の範囲におけるナトリウム（Ｎａ）イオンの阻止率の変動幅が一定幅以上である特性のＲＯ膜を用いることにより、シリカ含有水のｐＨを１０．０以上に高めて膜面へのシリカスケールの析出を抑制した状態でＲＯ膜処理を行っても、このＲＯ膜は、シリカ含有水中の荷電物質の阻止能が十分に高い状態を維持できることを見出した。本発明はこの知見に基づきさらに検討を重ねて完成されるに至ったものである。 The inventors of the present invention have made extensive studies in view of the above problems, and as a result, use an RO membrane having a characteristic in which the fluctuation range of the rejection rate of sodium (Na) ions in the range of pH 5.0 to 7.0 is a certain width or more. Thus, even if the RO membrane treatment is performed in a state in which the pH of the silica-containing water is raised to 10.0 or more and the deposition of silica scale on the membrane surface is suppressed, this RO membrane has the ability to block charged substances in the silica-containing water. Has been found to be able to maintain a sufficiently high state. The present invention has been completed through further studies based on this finding.
本発明の上記課題は以下の手段により解決された。
〔１〕
シリカ含有水を逆浸透膜により処理する膜分離方法であって、
前記膜分離方法は、前記シリカ含有水のｐＨを１０．０以上に高めるｐＨ調整工程と、ｐＨを１０．０以上に高めた前記シリカ含有水を逆浸透膜処理に付す膜処理工程とを有し、
前記逆浸透膜が、ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差が１．０％以上である、シリカ含有水の膜分離方法。
〔２〕
前記逆浸透膜が、有効圧力１ＭＰａにおける透過流束が０．６ｍ３／ｍ２／ｄ以上のポリアミド系逆浸透膜である、〔１〕に記載のシリカ含有水の膜分離方法。
〔３〕
前記膜処理工程が単段の逆浸透膜処理である、〔１〕又は〔２〕に記載のシリカ含有水の膜分離方法。
〔４〕
前記膜処理工程の前段において、前記シリカ含有水をＮａ形の陽イオン交換樹脂に通水する、〔１〕〜〔３〕のいずれかに記載のシリカ含有水の膜分離方法。
〔５〕
シリカ含有水を逆浸透膜により処理する膜分離システムであって、
前記膜分離システムは、前記シリカ含有水のｐＨを１０．０以上に高めるｐＨ調整手段と、ｐＨを１０．０以上に高めた前記シリカ含有水を処理する逆浸透膜装置とを有し、
前記逆浸透膜装置が有する逆浸透膜が、ｐＨ５．０〜７．０の範囲におけるナトリウムイオンの最大阻止率と最小阻止率との差が１．０％以上である、シリカ含有水の膜分離システム。
〔６〕
前記逆浸透膜が、有効圧力１ＭＰａにおける透過流束が０．６ｍ３／ｍ２／ｄ以上のポリアミド系逆浸透膜である、〔５〕に記載のシリカ含有水の膜分離システム。
〔７〕
前記逆浸透膜装置が単段である、〔５〕又は〔６〕に記載のシリカ含有水の膜分離システム。
〔８〕
前記逆浸透膜装置の前段において、ｐＨを１０．０以上に高めた前記シリカ含有水を処理するＮａ形の陽イオン交換装置を有する、〔５〕〜〔７〕のいずれかに記載のシリカ含有水の膜分離システム。
The above problems of the present invention have been solved by the following means.
[1]
A membrane separation method for treating water containing silica with a reverse osmosis membrane,
The membrane separation method has a pH adjusting step of increasing the pH of the silica-containing water to 10.0 or more, and a membrane treatment step of subjecting the silica-containing water of which the pH is raised to 10.0 or more to a reverse osmosis membrane treatment. Then
A method for separating silica-containing water, wherein the reverse osmosis membrane has a difference of 1.0% or more between the maximum blocking rate and the minimum blocking rate of Na ions in a pH range of 5.0 to 7.0.
[2]
The method for separating silica-containing water according to [1], wherein the reverse osmosis membrane is a polyamide-based reverse osmosis membrane having a permeation flux of 0.6 m 3 /m 2 /d or more at an effective pressure of 1 MPa.
[3]
The method for separating a silica-containing water membrane according to [1] or [2], wherein the membrane treatment step is a single-stage reverse osmosis membrane treatment.
[4]
The method for membrane separation of silica-containing water according to any one of [1] to [3], wherein the silica-containing water is passed through a Na-type cation exchange resin in the preceding stage of the membrane treatment step.
[5]
A membrane separation system for treating silica-containing water with a reverse osmosis membrane,
The membrane separation system has a pH adjusting means for increasing the pH of the silica-containing water to 10.0 or higher, and a reverse osmosis membrane device for treating the silica-containing water having a pH of 10.0 or higher.
The reverse osmosis membrane included in the reverse osmosis membrane device has a difference between the maximum blocking rate and the minimum blocking rate of sodium ions in the range of pH 5.0 to 7.0 of 1.0% or more. system.
[6]
The silica-containing water membrane separation system according to [5], wherein the reverse osmosis membrane is a polyamide reverse osmosis membrane having a permeation flux of 0.6 m 3 /m 2 /d or more at an effective pressure of 1 MPa.
[7]
The silica-containing water membrane separation system according to [5] or [6], wherein the reverse osmosis membrane device is a single stage.
[8]
The silica-containing one according to any one of [5] to [7], which has a Na-type cation exchange device for treating the silica-containing water whose pH is raised to 10.0 or more in the preceding stage of the reverse osmosis membrane device. Water membrane separation system.
本発明のシリカ含有水の膜分離方法は、シリカ含有水をＲＯ膜処理に付すことを含み、ＲＯ膜表面へのシリカスケールの析出を抑制し、かつシリカ含有水中の荷電物質を高効率に分離・除去することができる。また、本発明のシリカ含有水の膜分離システムは、本発明の上記膜分離方法を実施するのに好適である。 The membrane separation method of the silica-containing water of the present invention comprises subjecting the silica-containing water to an RO membrane treatment, suppressing the deposition of silica scale on the RO membrane surface, and separating the charged substances in the silica-containing water with high efficiency.・Can be removed. The silica-containing water membrane separation system of the present invention is suitable for carrying out the above-mentioned membrane separation method of the present invention.
本発明のシリカ含有水の膜分離方法（以下、単に「本発明の方法」とも称す。）の好ましい実施形態について以下に説明する。 A preferred embodiment of the silica-containing water membrane separation method of the present invention (hereinafter, also simply referred to as “method of the present invention”) will be described below.
本発明の方法では、ＲＯ膜処理に付す被処理水（原水）としてシリカ含有水を用いる。シリカは自然水に含まれる成分であり、工業用水、井水、市水等の一般的に用いられる原水にはシリカが含まれている。したがって、原水は通常、シリカ含有水である。本発明の方法に用いるシリカ含有水中のシリカ濃度に制限はなく、通常は１〜２０００ｍｇ／Ｌであり、１〜５００ｍｇ／Ｌが好ましく、１〜１５０ｍｇ／Ｌがより好ましい。 In the method of the present invention, silica-containing water is used as the water to be treated (raw water) to be subjected to the RO membrane treatment. Silica is a component contained in natural water, and commonly used raw water such as industrial water, well water, and city water contains silica. Therefore, the raw water is usually silica-containing water. There is no limitation on the silica concentration in the silica-containing water used in the method of the present invention, and it is usually 1 to 2000 mg/L, preferably 1 to 500 mg/L, more preferably 1 to 150 mg/L.
本発明の方法は、シリカ含有水のｐＨを１０．０以上に高めるｐＨ調整工程と、ｐＨ調整工程においてｐＨを１０．０以上に高めたシリカ含有水をＲＯ膜処理に付す膜処理工程とを少なくとも有している。 The method of the present invention comprises a pH adjusting step of increasing the pH of silica-containing water to 10.0 or higher, and a membrane treatment step of subjecting the silica-containing water of which pH is raised to 10.0 or higher in the pH adjusting step to RO membrane treatment. Have at least.
＜ｐＨ調整工程＞
ｐＨ調整工程では、被処理水であるシリカ含有水のｐＨを１０．０以上に高める。このｐＨは、ｐＨ調整工程に付されたシリカ含有水の温度におけるｐＨである。
シリカ含有水のｐＨの調整は、水酸化ナトリウム等のアルカリ剤をシリカ含有水に添加することにより行うことができる。アルカリ剤は水溶液の形態であることが好ましい。シリカ含有水へのアルカリ剤の添加は、シリカ含有水のｐＨをモニタリングしながら行うことが好ましい。また、シリカ含有水の性状が安定である場合には、シリカ含有水に一定の添加率でアルカリ剤を連続的に添加しながら、ｐＨを高めたシリカ含有水を続くＲＯ膜処理へと連続的に付すこともできる。
このｐＨ調整工程により、シリカ含有水のｐＨを１０．０〜１２．０とすることが好ましく、ｐＨを１０．５〜１１．５とすることがより好ましい。
シリカ含有水のｐＨが１０．０未満であると、ＲＯ膜表面にシリカが析出しやすく、経時的にＲＯ膜の閉塞が生じて処理効率が低下する。また、シリカ含有水のｐＨを１２．０以下とすることにより、ＲＯ膜の劣化を効果的に抑えることができる。
<pH adjustment process>
In the pH adjusting step, the pH of the silica-containing water that is the water to be treated is increased to 10.0 or higher. This pH is the pH at the temperature of the silica-containing water that has been subjected to the pH adjustment step.
The pH of the silica-containing water can be adjusted by adding an alkaline agent such as sodium hydroxide to the silica-containing water. The alkaline agent is preferably in the form of an aqueous solution. The addition of the alkaline agent to the silica-containing water is preferably performed while monitoring the pH of the silica-containing water. Further, when the property of the silica-containing water is stable, the silica-containing water whose pH is increased is continuously added to the subsequent RO membrane treatment while the alkaline agent is continuously added to the silica-containing water at a constant addition rate. It can also be attached to.
By this pH adjusting step, the pH of the silica-containing water is preferably set to 10.0 to 12.0, and more preferably set to 10.5-11.5.
If the pH of the silica-containing water is less than 10.0, silica is likely to be deposited on the surface of the RO membrane, and the RO membrane is clogged with time to reduce the treatment efficiency. Further, by setting the pH of the silica-containing water to 12.0 or less, deterioration of the RO film can be effectively suppressed.
＜膜処理工程＞
膜処理工程では、ｐＨ調整工程によりｐＨが１０．０以上に高められたシリカ含有水をＲＯ膜処理に付す。ＲＯ膜処理に使用するＲＯ膜は、ｐＨ５．０〜７．０（ｐＨ５．０以上７．０以下）の範囲におけるＮａイオンの最大阻止率と最小阻止率との差が１．０％以上という特性を有する。ここで、ＲＯ膜の特性を決定するためのＮａイオン阻止率は下記式により求める。
−阻止率算出式−
Ｎａイオンの阻止率（％）＝１００−１００×｛［Ａ／(（Ｂ＋Ｃ）／２)］｝
Ａ：透過水中のＮａイオン濃度（ｍｇ／Ｌ）
Ｂ：給水中のＮａイオン濃度（ｍｇ／Ｌ）
Ｃ：濃縮水中のＮａイオン濃度（ｍｇ／Ｌ）
<Membrane treatment process>
In the membrane treatment step, silica-containing water whose pH is raised to 10.0 or higher in the pH adjustment step is subjected to RO membrane treatment. The RO membrane used for the RO membrane treatment has a difference of 1.0% or more between the maximum rejection rate and the minimum rejection rate of Na ions in the range of pH 5.0 to 7.0 (pH 5.0 or more and 7.0 or less). Has characteristics. Here, the Na ion blocking rate for determining the characteristics of the RO film is obtained by the following formula.
-Rejection rate calculation formula-
Na ion blocking rate (%)=100-100×{[A/((B+C)/2)]}
A: Na ion concentration in permeate (mg/L)
B: Na ion concentration in feed water (mg/L)
C: Na ion concentration in concentrated water (mg/L)
上記のＲＯ膜のＮａイオン阻止率を決定するための給水及びＲＯ膜処理条件は下記の通りとする。
−給水−
ＮａＣｌを５０ｍｇ／Ｌの濃度で含有するＮａＣｌ水溶液
−ＲＯ膜処理条件−
水温２５℃、透過流束０．６５ｍ３／ｍ２／ｄ、回収率（注）１５％
（注）：回収率（％）＝１００×［ＲＯ膜処理における透過水の量（ｍ３／ｈ）］／［ＲＯ膜処理に付した給水の量（ｍ３／ｈ）］
Water supply and RO membrane treatment conditions for determining the Na ion blocking rate of the RO membrane are as follows.
-Water supply-
NaCl aqueous solution containing NaCl at a concentration of 50 mg/L-RO membrane treatment conditions-
Water temperature 25°C, permeation flux 0.65 m 3 /m 2 /d, recovery rate (Note) 15%
(Note): Recovery rate (%)=100×[amount of permeated water in RO membrane treatment (m 3 /h)]/[amount of water supplied to RO membrane treatment (m 3 /h)]
ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差（％）は、ｐＨ５．０〜７．０の範囲における阻止率（％）の最大値から、ｐＨ５．０〜７．０の範囲における阻止率（％）の最小値を差し引くことにより決定される。
The difference (%) between the maximum blocking rate and the minimum blocking rate of Na ions in the range of pH 5.0 to 7.0 is from the maximum value of the blocking rate (%) in the range of pH 5.0 to 7.0 to
本発明の方法において、ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差が１．０％以上となる特性のＲＯ膜を用いることにより、シリカスケールの発生を抑えるべくシリカ含有水のｐＨを１０．０以上に高めてＲＯ膜処理を行っても、シリカ含有水中に存在する荷電物質を十分に高い阻止率で除去することができる。この理由は定かではないが、次のように推定される。 In the method of the present invention, by using an RO film having a characteristic that the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5.0 to 7.0 is 1.0% or more, generation of silica scale is caused. Even if the pH of the silica-containing water is increased to 10.0 or more and the RO membrane treatment is performed to suppress the above, the charged substances present in the silica-containing water can be removed with a sufficiently high rejection rate. The reason for this is not clear, but it is estimated as follows.
ＲＯ膜にはポリアミド系とセルロース系の２種類が知られており、いずれもカルボキシ基を有している。このカルボキシ基は、ＣＯＯ−＋Ｈ＋⇔ＣＯＯＨの平衡状態にあり、ｐＨが低いほど平衡は右辺側に移動し（すなわちＣＯＯＨの割合が多くなり）、ｐＨが高いほど平衡は左辺側へと移動する（すなわちＣＯＯ−の割合が多くなる）。ＲＯ膜はこのＣＯＯ-によって、カチオン性、アニオン性荷電物質の引き寄せ、反発をバランスさせ、阻止性能に繋げている。
ｐＨ５．０〜７．０の範囲においてＮａイオンの最大阻止率と最小阻止率との差が１．０％以上であるＲＯ膜は、ｐＨ５．０〜７．０という弱酸の条件において、ＣＯＯ−の割合の変動が大きく、等電点となるｐＨが高いと推定される。
他方、ｐＨ５．０〜７．０の範囲においてＮａイオンの最大阻止率と最小阻止率との差が１％よりも小さいＲＯ膜は、ｐＨ５．０〜７．０という弱酸の条件において、ＣＯＯ−の変動が小さく、等電点となるｐＨが低いと推定される。ｐＨが１０．０以上になると、等電点となるｐＨが低いＲＯ膜のカチオン性、アニオン性荷電物質の引き寄せ、反発のバランスが崩れやすく、阻止性能低下に繋がったと考えられる。
本発明に用いるＲＯ膜は、ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差の上限に特に制限はない。前記の最大阻止率と最小阻止率との差は通常は１０．０％以下であり、５．０％以下であることも好ましい。
Two types of RO membranes are known, a polyamide type and a cellulose type, and both have a carboxy group. This carboxy group is in an equilibrium state of COO − +H + ⇔ COOH, and the equilibrium moves to the right side as the pH becomes lower (that is, the proportion of COOH increases), and the equilibrium moves to the left side as the pH increases. (That is, the ratio of COO − increases). The RO film balances the attraction and repulsion of the cationic and anionic charged substances by this COO − , and leads to the blocking performance.
The RO membrane having a difference between the maximum blocking rate and the minimum blocking rate of Na ions of 1.0% or more in the pH range of 5.0 to 7.0 is COO − under a weak acid condition of pH 5.0 to 7.0. It is presumed that there is a large variation in the ratio and that the pH at the isoelectric point is high.
On the other hand, the RO membrane having a difference between the maximum blocking rate and the minimum blocking rate of Na ions of less than 1% in the pH range of 5.0 to 7.0 is COO − under a weak acid condition of pH 5.0 to 7.0. It is presumed that the pH of the isoelectric point is low. It is considered that when the pH is 10.0 or more, the balance of the cationic and anionic charged substances of the RO film having a low pH, which is the isoelectric point, is easily attracted and the repulsion is lost, leading to a reduction in the blocking performance.
The RO membrane used in the present invention has no particular upper limit on the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5.0 to 7.0. The difference between the maximum blocking rate and the minimum blocking rate is usually 10.0% or less, and preferably 5.0% or less.
ＲＯ膜処理に用いるＲＯ膜は、耐アルカリ性の観点からポリアミド系ＲＯ膜が好ましい。また、透水性の観点から、有効圧力１ＭＰａにおける透過流束が０．６ｍ３／ｍ２／ｄ（ｄａｙ、日）以上のポリアミド系ＲＯ膜が好ましい。有効圧力１ＭＰａにおける透過流束の上限に特に制限はない。例えば、１０．０ｍ３／ｍ２／ｄ以下とするのが実際的であり、５．０ｍ３／ｍ２／ｄ以下のポリアミド系ＲＯ膜を用いることも好ましい。この透過流束は温度２５℃における透過流束である。
「有効圧力」とは、ＪＩＳ Ｋ３８０２：２０１５「膜用語」に記載の、平均操作圧から浸透圧差および二次側圧を差し引いた、膜に働く有効な圧である。なお、平均操作圧は、膜の一次側における膜供給水の圧力（運転圧力）と濃縮水の圧力（濃縮水出口圧力）の平均値で、以下の式により表される。
平均操作圧＝（運転圧力＋濃縮水出口圧力）／２
The RO film used for the RO film treatment is preferably a polyamide RO film from the viewpoint of alkali resistance. From the viewpoint of water permeability, a polyamide RO membrane having a permeation flux at an effective pressure of 1 MPa of 0.6 m 3 /m 2 /d (day, day) or more is preferable. There is no particular upper limit on the permeation flux at an effective pressure of 1 MPa. For example, it is practical to set it to 10.0 m 3 /m 2 /d or less, and it is also preferable to use a polyamide RO membrane of 5.0 m 3 /m 2 /d or less. This permeation flux is a permeation flux at a temperature of 25°C.
The “effective pressure” is the effective pressure acting on the membrane, which is defined in JIS K3802:2015 “Membrane terms”, which is obtained by subtracting the osmotic pressure difference and the secondary side pressure from the average operating pressure. The average operating pressure is an average value of the pressure (operating pressure) of the membrane supply water and the pressure of the concentrated water (the outlet pressure of the concentrated water) on the primary side of the membrane, and is represented by the following formula.
Average operating pressure = (operating pressure + concentrated water outlet pressure)/2
本発明の方法において、ＲＯ膜処理の段数は特に制限されない。本発明の方法は、このＲＯ膜処理を単段としても十分に高い阻止率を実現できる。すなわち、本発明の方法では、シリカ含有水をｐＨ１０．０以上としてもＲＯ膜処理により荷電物質を十分に除去することができるため、ＲＯ膜処理を複数段としなくても、シリカスケールの発生を十分に抑えながら目的の純度の透過水を得ることが可能となる。 In the method of the present invention, the number of stages of RO membrane treatment is not particularly limited. The method of the present invention can realize a sufficiently high rejection rate even if this RO membrane treatment is performed in a single stage. That is, in the method of the present invention, the charged substance can be sufficiently removed by the RO membrane treatment even when the silica-containing water has a pH of 10.0 or more, so that the generation of silica scale can be prevented even if the RO membrane treatment is not performed in multiple stages. It becomes possible to obtain permeated water of the desired purity while sufficiently suppressing it.
本発明の方法は、ＲＯ膜処理の前段において、シリカ含有水をＮａ形の陽イオン交換樹脂に通水する形態とすることも好ましい。Ｎａ形の陽イオン交換樹脂への通水により、シリカ含有水がマグネシウムやカルシウム等の硬度成分を多く含む場合にはこれらを効果的に除去することができ、硬度成分由来のスケールの発生も十分に抑えることができる。このＮａ形の陽イオン交換樹脂への通水は、上記ｐＨ調整工程に付す前のシリカ含有水を通水させる形態としてもよいし、上記ｐＨ調整工程後のシリカ含有水を通水させる形態としてもよい。 In the method of the present invention, it is also preferable that the silica-containing water is passed through the Na-type cation exchange resin before the RO membrane treatment. By passing water through Na-type cation exchange resin, when silica-containing water contains a large amount of hardness components such as magnesium and calcium, these can be effectively removed, and the scale derived from hardness components is sufficiently generated. Can be suppressed to Water passing through the Na-type cation exchange resin may be in the form of passing silica-containing water before being subjected to the pH adjusting step, or may be in the form of passing water containing silica after the pH adjusting step. Good.
本発明の方法において、ＲＯ膜処理における透過水の回収率は５〜２０％とすることが好ましい。また、ＲＯ膜処理に付される、ｐＨが１０．０以上に高められたシリカ含有水の温度は５〜４０℃が好ましく、２５〜３５℃がより好ましい。すなわち、ｐＨが１０．０以上に高められたシリカ含有水は、上記温度条件下でＲＯ膜処理に付されることが好ましい。 In the method of the present invention, the recovery rate of permeated water in the RO membrane treatment is preferably 5 to 20%. Further, the temperature of the silica-containing water that has been subjected to the RO membrane treatment and whose pH has been raised to 10.0 or higher is preferably 5 to 40°C, more preferably 25 to 35°C. That is, the silica-containing water whose pH is raised to 10.0 or higher is preferably subjected to the RO membrane treatment under the above temperature conditions.
本発明の方法の一実施形態について、図面を参照して説明する。図１は、本発明の方法を実施するシステムの一形態を示す系統図である。このシステムは、シリカ含有水（Ｉ）が流通するシリカ含有水流通管（１）と、このシリカ含有水流通管（１）に接続する、アルカリ剤（II）が流通するアルカリ剤流通管（２、ｐＨ調整手段）と、シリカ含有水とアルカリ剤が合流した合流液が流通する合流液流通管（３）と、ＲＯ膜（４）を備えたＲＯ膜装置（７）と、濃縮水（III）が流通する濃縮水流通管（５）と、透過水（IV）が流通する透過水流通管（６）とを有する。図１の形態ではＲＯ膜装置（７）は単段に設けられている。
合流液流通管（３）内を流通する合流液は、アルカリ剤の作用によりｐＨが１０．０以上へと高められている。また、ＲＯ膜装置（７）が有するＲＯ膜は、上述のように、ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差が１．０％以上となる特性を有するものである。上記合流液はＲＯ膜装置（７）によるＲＯ膜処理に付され、合流液中の荷電物質が濃縮された濃縮水（III）と荷電物質が除去された透過水（IV）とに分離される。
An embodiment of the method of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram showing an embodiment of a system for carrying out the method of the present invention. This system comprises a silica-containing water flow pipe (1) through which silica-containing water (I) flows, and an alkali agent flow pipe (2) through which an alkali agent (II) flows, which is connected to the silica-containing water flow pipe (1). , PH adjusting means), a combined liquid flow pipe (3) through which a combined liquid obtained by combining the silica-containing water and the alkali agent, an RO membrane device (7) equipped with an RO membrane (4), and concentrated water (III). 2) has a concentrated water flow pipe (5) and a permeated water (IV) has a permeate flow pipe (6). In the form of FIG. 1, the RO membrane device (7) is provided in a single stage.
The pH of the combined liquid flowing through the combined liquid flow pipe (3) is increased to 10.0 or higher by the action of the alkaline agent. In addition, the RO membrane included in the RO membrane device (7) has a difference between the maximum rejection rate and the minimum rejection rate of Na ions in the range of pH 5.0 to 7.0 of 1.0% or more, as described above. It has characteristics. The combined liquid is subjected to RO membrane treatment by the RO membrane device (7) and separated into concentrated water (III) in which the charged substances in the combined liquid are concentrated and permeated water (IV) in which the charged substances are removed. ..
上記システムは、合流液流通管（３）に合流液のｐＨをモニタリングするｐＨモニタリング装置（図示せず）を備えていることも好ましい。また、アルカリ剤流通管（２）には、アルカリ剤の流通量を調節する調節弁（図示せず）が設置されていることも好ましい。上記のｐＨモニタリング装置からの信号により上記調節弁が自動制御され、合流液を目的のｐＨに自動調整する形態とすることもできる。
上記システムは、ＲＯ膜装置（７）の前段において、上述したＮａ形の陽イオン交換装置（図示せず）を有する形態とすることも好ましい。
It is also preferable that the system is equipped with a pH monitoring device (not shown) for monitoring the pH of the combined liquid in the combined liquid flow pipe (3). It is also preferable that a control valve (not shown) that controls the flow rate of the alkaline agent is installed in the alkaline agent flow pipe (2). The control valve may be automatically controlled by a signal from the pH monitoring device to automatically adjust the combined liquid to a target pH.
It is also preferable that the system has a form having the Na-type cation exchange device (not shown) described above in the preceding stage of the RO membrane device (7).
本発明を実施例に基づきさらに詳細に説明するが、本発明は下記の実施例に限定されるものではない。 The present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.
［調製例] 試験液の調製
純水にシリカと塩化ナトリウムを添加して、導電率が４０００〜４５００μＳ／ｃｍ、シリカ濃度が１００ｍｇ／Ｌであるシリカ含有水（被処理水）を得た。得られたシリカ含有水を、図１からアルカリ剤流通管（２）を除いた構成のシステムを用いて膜分離処理に付した。詳細を以下に示す。
[Preparation Example] Preparation of Test Liquid Silica and sodium chloride were added to pure water to obtain silica-containing water (water to be treated) having a conductivity of 4000 to 4500 μS/cm and a silica concentration of 100 mg/L. The obtained silica-containing water was subjected to membrane separation treatment using a system having a configuration in which the alkaline agent flow pipe (2) was removed from FIG. Details are shown below.
［実施例１］
ＲＯ膜装置のＲＯ膜として、ダウ・ケミカル社製のポリアミド系ＲＯ膜「ＢＷ３０ＨＲ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が２．０％、有効圧力１ＭＰａあたりの透過水量が１．０ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、アルカリ剤（４質量％濃度のＮａＯＨ水溶液）を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Example 1]
As the RO membrane of the RO membrane apparatus, a polyamide RO membrane "BW30HR" manufactured by Dow Chemical Co. was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5 to 7 was 2.0%, and the amount of permeated water per effective pressure of 1 MPa was 1.0 m 3 /m 2 /d.
The test solution prepared above was adjusted to the pH shown in the table below with an alkaline agent (4% by mass concentration of NaOH aqueous solution), and the solution was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m of permeated water. It was separated into 3 /h and concentrated water 4.2 m 3 /h. All the concentrated water was blown.
［実施例２］
ＲＯ膜装置のＲＯ膜として、ダウ・ケミカル社製のポリアミド系ＲＯ膜「ＢＷ３０ＸＦＲ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が１．２％、有効圧力１ＭＰａあたりの透過水量が１．０ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Example 2]
As the RO membrane of the RO membrane apparatus, a polyamide RO membrane “BW30XFR” manufactured by Dow Chemical Co. was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the range of
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
［実施例３］
ＲＯ膜装置のＲＯ膜として、日東電工社製のポリアミド系ＲＯ膜「ＣＰＡ５−ＬＤ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が３．５％、有効圧力１ＭＰａあたりの透過水量が０．８ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Example 3]
As the RO membrane of the RO membrane device, a polyamide RO membrane “CPA5-LD” manufactured by Nitto Denko Corporation was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5 to 7 was 3.5%, and the amount of permeated water per effective pressure of 1 MPa was 0.8 m 3 /m 2 /d.
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
［実施例４］
ＲＯ膜装置のＲＯ膜として、ダウ・ケミカル社製のポリアミド系ＲＯ膜「ＳＥＡＭＡＸＸ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が２．５％、有効圧力１ＭＰａあたりの透過水量が０．６ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Example 4]
As the RO membrane of the RO membrane apparatus, a polyamide RO membrane “SEAMAXX” manufactured by Dow Chemical Co. was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5 to 7 was 2.5%, and the amount of permeated water per 1 MPa of effective pressure was 0.6 m 3 /m 2 /d.
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
［比較例１］
ＲＯ膜装置のＲＯ膜として、日東電工社製のポリアミド系ＲＯ膜「ＬＦＣ３−ＬＤ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が０．１％、有効圧力１ＭＰａあたりの透過水量が１．０ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Comparative Example 1]
As the RO membrane of the RO membrane device, a polyamide RO membrane “LFC3-LD” manufactured by Nitto Denko Corporation was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5 to 7 was 0.1%, and the amount of permeated water per 1 MPa of effective pressure was 1.0 m 3 /m 2 /d.
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
［比較例２］
ＲＯ膜装置のＲＯ膜として、東レ社製のポリアミド系ＲＯ膜「ＴＭＬ−Ｄ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が０．１％、有効圧力１ＭＰａあたりの透過水量が０．８ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Comparative example 2]
As the RO membrane of the RO membrane device, a polyamide RO membrane “TML-D” manufactured by Toray Industries, Inc. was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the range of
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
［比較例３］
ＲＯ膜装置のＲＯ膜として、日東電工社製のポリアミド系ＲＯ膜「ＥＳＰＡ２−ＬＤ」を用いた。このＲＯ膜は、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が０．５％、有効圧力１ＭＰａあたりの透過水量が１．６ｍ３／ｍ２／ｄであった。
上記で調製した試験液を、実施例１と同じアルカリ剤を用いて下表に示すｐＨに調整し、これを５ｍ３／ｈでＲＯ膜装置に供給し、透過水０．８ｍ３／ｈと濃縮水４．２ｍ３／ｈに分離した。濃縮水は全量ブローした。
[Comparative Example 3]
As the RO membrane of the RO membrane apparatus, a polyamide RO membrane “ESPA2-LD” manufactured by Nitto Denko Corporation was used. In this RO membrane, the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the pH range of 5 to 7 was 0.5%, and the amount of permeated water per 1 MPa of effective pressure was 1.6 m 3 /m 2 /d.
The test solution prepared above was adjusted to the pH shown in the table below using the same alkaline agent as in Example 1, and this was supplied to the RO membrane device at 5 m 3 /h to obtain 0.8 m 3 /h of permeated water. The concentrated water was separated into 4.2 m 3 /h. All the concentrated water was blown.
上記各実施例及び比較例の結果を下表に示す。 The results of the above Examples and Comparative Examples are shown in the table below.
上記表に示されるように、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が１．０％よりも小さなＲＯ膜を用いてシリカ含有水を膜分離処理した場合、シリカ含有水が中性であれば荷電物質を十分に阻止できる。しかし、シリカ含有水のｐＨが上昇するにつれて荷電物質の阻止率が低下しやすいことがわかる（比較例１〜３）。
これに対し、ｐＨ５〜７の範囲におけるＮａイオンの最大阻止率と最小阻止率の差が１．０％以上のＲＯ膜を用いてシリカ含有水を膜分離処理した場合には、シリカ含有水のｐＨを上昇させても荷電物質の阻止率が十分に高い状態を保てることがわかった（実施例１〜４）。
As shown in the above table, when the silica-containing water is subjected to a membrane separation treatment using an RO membrane in which the difference between the maximum blocking rate and the minimum blocking rate of Na ions in the range of
On the other hand, when the silica-containing water is subjected to a membrane separation treatment using an RO membrane having a difference between the maximum blocking rate and the minimum blocking rate of Na ions in the range of
Ｉ シリカ含有水（被処理水）
II アルカリ剤
III 濃縮水
IV 透過水
１ シリカ含有水（被処理水）流通管
２ アルカリ剤流通管
３ 合流液流通管
４ 逆浸透膜
５ 濃縮水流通管
６ 透過水流通管
７ ＲＯ膜装置
I Silica-containing water (water to be treated)
II Alkaline agent
III Concentrated water
IV Permeated
7 RO membrane device
Claims (8)
前記膜分離方法は、前記シリカ含有水のｐＨを１０．０以上に高めるｐＨ調整工程と、ｐＨを１０．０以上に高めた前記シリカ含有水を逆浸透膜処理に付す膜処理工程とを有し、
前記逆浸透膜が、ｐＨ５．０〜７．０の範囲におけるＮａイオンの最大阻止率と最小阻止率との差が１．０％以上である、シリカ含有水の膜分離方法。 A membrane separation method for treating silica-containing water with a reverse osmosis membrane,
The membrane separation method has a pH adjusting step of increasing the pH of the silica-containing water to 10.0 or more, and a membrane treatment step of subjecting the silica-containing water of which the pH is raised to 10.0 or more to a reverse osmosis membrane treatment. Then
A method for separating silica-containing water, wherein the reverse osmosis membrane has a difference of 1.0% or more between the maximum blocking rate and the minimum blocking rate of Na ions in a pH range of 5.0 to 7.0.
前記膜分離システムは、前記シリカ含有水のｐＨを１０．０以上に高めるｐＨ調整手段と、ｐＨを１０．０以上に高めた前記シリカ含有水を処理する逆浸透膜装置とを有し、
前記逆浸透膜装置が有する逆浸透膜が、ｐＨ５．０〜７．０の範囲におけるナトリウムイオンの最大阻止率と最小阻止率との差が１．０％以上である、シリカ含有水の膜分離システム。 A membrane separation system for treating silica-containing water with a reverse osmosis membrane,
The membrane separation system has a pH adjusting means for increasing the pH of the silica-containing water to 10.0 or higher, and a reverse osmosis membrane device for treating the silica-containing water having a pH of 10.0 or higher.
The reverse osmosis membrane included in the reverse osmosis membrane device has a difference between the maximum blocking rate and the minimum blocking rate of sodium ions in the range of pH 5.0 to 7.0 of 1.0% or more. system.
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