JP4543482B2 - Fluorine-containing water treatment method - Google Patents
Fluorine-containing water treatment method Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明はフッ素含有水にカルシウム(Ca)化合物を添加してフッ素をフッ化カルシウム(CaF2)として沈殿分離した後、残留するCa2+イオンをカチオン交換樹脂で除去する方法に係り、特に、この方法において、Ca化合物の必要添加量を適正化して、カチオン交換樹脂の再生頻度を低減するフッ素含有水の処理方法に関する。
【0002】
【従来の技術】
半導体部品製造におけるシリコンウェハ製造工程から排出されるフッ素含有廃水等のフッ素含有水の処理方法としては、フッ素含有水にCa化合物を添加してCaF2を生成させ、これを沈殿分離する方法が、薬剤コストが安価であることから広く普及している。また、特に、半導体製造廃水については、フッ素以外にSO4 2−,NO3 −,NH4 +等の無機塩を含有することから、CaF2を沈殿分離した後、これらSO4 2−,NO3 −,NH4 +等の廃水由来の無機塩と、残留するCa2+とF−を分離して回収水として再利用するために、図1に示す如く、原水槽1、原水にCa化合物を添加する中和槽2、中和処理液を凝集処理する凝集槽3、沈殿を生成させる沈殿槽4及び生成した沈殿を固液分離する濾過器5を経てCaF2の生成、分離を行って得られた処理水(以下、この水を「CaF2処理水」と称す場合がある。)を、更に軟化塔(カチオン交換樹脂塔)6及び逆浸透(RO)膜分離装置7に通水して処理することが行われている。なお、濾過器5の逆洗排水、軟化塔6の再生廃液、RO膜分離装置7の濃縮水は原水槽1に送給され、原水と共に処理される。
【0003】
即ち、半導体製造廃水からCaF2の生成、分離を行って得られたCaF2処理水は、CaF2やCaSO4等の析出塩を生成するスケール原因物質を含有するため、これをそのままRO膜分離装置7に通水して脱塩処理すると、これらのスケール原因物質がRO膜分離装置7内で濃縮されてスケールとして析出し、RO膜を閉塞させ、通水不可能となる。従って、このRO膜の閉塞を防止するために、RO膜分離装置7の前段で、予めこれらのスケール原因物質を十分に除去しておく必要がある。この場合、Ca2+,SO4 2−,F−等のスケール原因物質のすべてを除去する必要はなく、CaF2の生成防止のためにはCa2+とF−のいずれか一方を除去すれば良く、CaSO4の生成防止のためにもCa2+とSO4 2−のいずれか一方を除去すれば良い。このため、図1に示す如く、RO膜分離装置7の前段に軟化塔6を設け、カチオン交換樹脂でCa2+を除去することが一般に行われている。
【0004】
ところで、このような処理プロセスにおいて、回収水が一時的に余剰になる場合には、CaF2処理水、即ち、濾過器5の濾過処理水をそのまま系外へ排出して放流するため、このCaF2処理水のF−濃度については、排水基準である15mg/L以下にまで処理する必要がある。Ca化合物の添加により、原水であるフッ素含有水中のF−をこのように高度に除去するために、一般的には、
Ca2++2F−→CaF2
の反応式に基いて、Ca化合物を原水中のF−に対して当量よりも過剰に添加することが行われており、従って、従来において、Ca化合物の過剰添加でCaF2処理水中に残留するCa2+濃度の指標は100〜300mg/Lとされている。
【0005】
【発明が解決しようとする課題】
しかしながら、100〜300mg/LのCa2+イオンを含むCaF2処理水を軟化塔6に通水してカチオン交換樹脂で処理すると、カルシウム化合物のイオン交換能が早期に飽和に達し、2〜4サイクル/日の頻度でカチオン交換樹脂の再生を行う必要が生じる。
【0006】
このように頻繁に再生を行うことは、装置の保守管理、再生薬剤コスト、再生廃液の処理コスト、軟化塔の稼動効率等の面において、工業的に著しく不利である。一方で、前述の如くCa化合物添加量を減らすことは、CaF2処理水中のF−濃度を高める恐れがあることから、Ca化合物添加量の適正化が求められる。
【0007】
本発明は上記従来の問題点を解決し、フッ素含有水にCa化合物を添加してFをCaF2として沈殿分離した後、残留するCa2+イオンをカチオン交換樹脂で除去するに当たり、Ca化合物の添加量を適正化して、CaF2処理水中のF−濃度を高めることなく、残留Ca2+濃度を低減し、カチオン交換樹脂の再生頻度を低減することができるフッ素含有水の処理方法を提供することを目的とする。
【0008】
【課題を解決するための手段】
本発明のフッ素含有水の処理方法は、難溶性塩生成イオンを含むフッ素含有水にカルシウム化合物を添加して生成したフッ化カルシウムを分離してCaF 2 処理水を得、該CaF 2 処理水中に残留するカルシウムイオンをカチオン交換樹脂で除去する方法において(ただし、フッ素含有水にカルシウム化合物を添加する添加工程と、生成したフッ化カルシウムを分離する分離工程とを複数回繰り返し行う方法を除く)、該フッ素含有水中のカルシウムと難溶性の塩を生成するイオンの量に対して当量となるカルシウム化合物量をAmg(as Ca)/Lとしたとき、該フッ素含有水へのカルシウム化合物の添加量をAmg(as Ca)/L〜(A−200)mg(as Ca)/Lとする方法であって、該カルシウム化合物添加後のフッ素含有水のpHが5〜10であり、前記CaF 2 処理水のF − 濃度が15mg/L以下でCa 2+ 濃度が30mg/L以下であることを特徴とする。
【0009】
前述の如く、従来においては、CaF2処理水中のCa2+濃度は100〜300mg/Lであるが、この濃度が30mg/L或いはそれ以下であれば、カチオン交換樹脂の再生頻度も従来の1/5程度となり、装置の保守管理は軽減され、再生薬剤コスト、再生廃液処理コストの低減、軟化塔の稼動効率の向上が図れる。
【0010】
また、前述の如く、CaF2処理水を放流する場合において、CaF2処理水中のF−濃度は15mg/L以下であることが必要となる。
【0011】
従って、本発明者らは、F−濃度15mg/L以下、Ca2+濃度30mg/L以下のCaF2処理水を確実に得るべく鋭意検討を重ねた結果、原水であるフッ素含有水中に含まれるCa2+と難溶性の塩を生成するイオンの量に対して当量となるCa化合物のCa換算量をAmg/Lとしたとき、Ca化合物添加量をCa換算量でAmg/L〜(A−200)mg/Lの範囲とすれば、上記F−濃度及びCa2+濃度を共に満足し得ることを見出し、本発明を完成させた。(なお、本発明において、原水としてのフッ素含有水とは、Ca化合物が添加される水であって、フッ素含有水以外に、図1に示す如く、後段の処理装置の再生液等が返送される処理プロセスにあっては、中和槽2に流入する水を指す。)。
【0012】
即ち、原水中のF−からCaF2を効果的に生成させてF−を高度に除去するためには、原水中のF−だけでなく、F−以外のCa2+と難溶性塩を生成する共存イオン(以下、このイオンを「難溶性塩生成イオン」と称す。)も考慮する必要があり、Ca化合物は原水中のF−に対してのみならず、原水中のF−以外の難溶性塩生成イオンに対しても必要となる。
【0013】
このF−以外の難溶性塩生成イオンとしては、リン酸イオン(PO4 3−)、硫酸イオン(SO4 2−)、炭酸イオン(CO3 2−)等が挙げられるが、このような難溶性塩生成イオンがCaF2処理水のフッ素濃度に影響を及ぼす機構は次の様に推定される。
【0014】
即ち、例えばSO4 2−の場合、CaSO4の溶解度は2000mg/L,CaF2の溶解度は15mg/Lで、CaF2の溶解度はCaSO4の溶解度に比べて格段に小さいことから、フッ素と当量のCa塩が存在すれば、一般的にはCaF2の生成反応がCaSO4の生成反応に優先して起こるはずである。しかし、実際にはCaF2の沈殿生成と同時に、沈殿を生じないCaSO4(aq.)、いわゆる分子状のCaSO4が生成し、Ca塩がSO4 2−に固定されるため、Ca2++2F−→CaF2の反応が阻害される。従って、このような難溶性塩生成イオンと反応するCa化合物も添加する必要がある。
【0015】
半導体製造廃水等のフッ素含有水にはこれらの難溶性塩生成イオンが含有されている上に、本出願人が先に提案したように、フッ素含有水にCa化合物を添加して処理するに当たり、処理水の水質の向上、CaF2の結晶化促進の目的で、フッ素含有水に硫酸及び/又は硫酸塩を添加する場合もある(特願平11−146822号、特願平11−218990号)。このような場合には、当然、原水中にはF−以外にSO4 2−が存在することとなる。
【0016】
このような難溶性塩生成イオン、例えば、SO4 2−を考慮した場合、原水へのCa化合物の必要添加量は、原水中のF−との反応でCaF2を生成させるために必要なCa化合物量と原水中のSO4 2−との反応でCaSO4を生成させるために必要なCa化合物量との合計量よりもやや少ない程度が、前述のF−:15mg/L以下、Ca2+:30mg/L以下のCaF2処理水を得るための理想的な添加量となる。
【0017】
しかして、前記Amg(as Ca)/L〜(A−200)mg(as Ca)/Lの範囲であれば、この理想的な添加量を実現することができる。
【0018】
【発明の実施の形態】
以下に本発明のフッ素含有水の処理方法の実施の形態を詳細に説明する。
【0019】
本発明においては、図1に示すようなプロセスで半導体製造廃水等のフッ素含有水にCa化合物を添加してCaF2を生成させるに当たり、添加するCa化合物の量を、原水中の難溶性塩生成イオン量に対して当量となるCa化合物のCa換算量Amg/L以下、(A−200)mg/L以上とする。
【0020】
このCa化合物添加量が(A−200)mg(as Ca)/L未満では、Ca化合物が不足して、原水中のF−を高度に除去し得ず、残留F−が増大してF−:15mg/L以下のCaF2処理水を得ることができない。逆に、Ca化合物添加量がAmg(as Ca)/Lを超えると、Ca化合物が過剰となりすぎ、CaF2処理水中のF−濃度は低減するが、Ca2+が大幅に増え、カチオン交換樹脂の再生頻度を高めることとなる。
【0021】
なお、この難溶性塩生成イオンとは、一般的には、Ca2+との反応で、溶解度積に基く溶解量が700mg/L以下であるような難溶性塩を生成するものであり、原水中のF−以外の難溶性塩生成イオンとしては、前述の如く、PO4 3−、SO4 2−、CO3 2−等が挙げられることから、本発明では、原水中のF−濃度、PO4 3−濃度、SO4 2−濃度、CO3 2−濃度に基いて、下記式で算出されるAmg(as Ca)/Lの値に対してCa化合物の添加量はA〜(A−200)mg(as Ca)/Lとなるようにする。
【0022】
A(mg/L)=
(F−濃度×Ca/2F)+(PO4 3−濃度×3Ca/2PO4)
+(SO4 2−濃度×Ca/SO4)+(CO3 2−濃度×Ca/CO3)
=(F−濃度×40/38)+(PO4 3−濃度×120/190)
+(SO4 2−濃度×40/96)+(CO3 2−濃度×40/60)
なお、前述の如く、硫酸及び/又は硫酸塩を添加する場合のように、難溶性塩生成イオンが原水に添加される場合には、原水中の難溶性塩生成イオンとして当然この添加された難溶性塩生成イオンも含まれる。
【0023】
原水中に難溶性塩生成イオンが複数種類ある場合、すべての難溶性塩生成イオン量を測定してCa塩添加量の算出に用いる必要はなく、主要な難溶性塩生成イオン、即ち原水中の濃度が高い、例えば100ppm以上の難溶性塩生成イオンの1種又は2種以上を選択し、この難溶性塩生成イオン量を測定してCa塩添加量を設定しても良い。
【0024】
原水に添加するCa化合物としては、一般に、安価な水酸化カルシウム(消石灰:Ca(OH)2)が用いられているが、これに限らず、生石灰等を用いても良い。また、塩化カルシウムや炭酸カルシウムを水酸化ナトリウムと併用しても良い。
【0025】
このようなCa塩の添加でCaF2が析出するpH条件は、5〜10、好ましくは5.5〜7.5であるため、Ca化合物として特にCa(OH)2を添加した場合、pHが高くなり過ぎ、このようなpH条件に調整することができない場合には、硫酸、塩酸等の酸を添加して適宜pH調整する必要がある。
【0026】
また、前述の如く、処理水の水質の向上、CaF2の結晶化促進の目的で、原水に硫酸及び/又は硫酸塩を添加する場合、添加する硫酸や硫酸塩としては、工業硫酸、硫酸ナトリウム等を用いることができ、また、この硫酸源としてはSO4 2−イオンを含有する他の廃水、例えば、鋼板酸洗廃水、排煙脱硫廃水を用いることもできる。
【0027】
本発明の方法は、Ca化合物の添加によりCaF2を生成させ、これを分離して得られるCaF2処理水を更にカチオン交換樹脂で処理する方法であれば、どのような処理プロセスにも適用することができる。従って、図1に示す如く、軟化塔6の処理水を更にRO膜分離装置7で処理するものに限らず、軟化塔6から得られる軟化水をそのまま処理水とするものや、この軟化水を更にアニオン交換樹脂に通水して脱塩水を得るもの、或いは、軟化水を電気再生式連続脱塩装置で処理して得た脱塩水を処理水とする処理プロセスであっても良い。
【0028】
【実施例】
以下に実施例及び比較例を挙げて本発明をより具体的に説明する。
【0029】
実施例1〜3、比較例1,2
F−:2500mg/L,SO4 2−:500mg/L(as H2SO4)の人工廃液を原水とし、Ca(OH)2等のCa化合物を表1に示す量添加してpH6.5〜7.0に調整し、30分反応させた後No.5Aの濾紙で濾過して濾過処理水のF−濃度とCa2+濃度を測定し、結果を表1に示した。
【0030】
なお、表1において、当量Aとは、Ca化合物を原水中のF−とSO4 2−との両方の合計に対して当量添加した場合であり、この場合には、Ca化合物としてCa(OH)2のみを添加して、pH6.5〜7.0に調整した。
【0031】
この当量Aに対して、Ca化合物を不足させる場合には、SO4 2−に対応するCa(OH)2が添加されないように、SO4 2−源としてのH2SO4をNa2SO4で置換して添加した。
【0032】
また、当量Aに対して、Ca化合物を過剰とする場合には、SO4 2−源としてH2SO4を使用し、Ca(OH)2の他に更に中性のCaCl2をCa化合物として添加した。
【0033】
【表1】
【0034】
実施例4〜6、比較例3,4
F−:5000mg/L,SO4 2−:1000mg/L(as H2SO4)の人工廃液を原水としたこと以外はそれぞれ実施例1〜3及び比較例1,2と同様に処理を行って、処理水のF−濃度及びCa2+濃度を測定し、結果を表2に示した。
【0035】
【表2】
【0036】
表1,2より、Ca化合物の添加量を当量A〜(A−200)mg(as Ca)/Lとすることにより、F−及びCa2+濃度が共に低い、高水質な処理水を得ることができることがわかる。
【0037】
【発明の効果】
以上詳述した通り、本発明のフッ素含有水の処理方法によれば、フッ素含有水にCa化合物を添加してFをCaF2として沈殿分離し、残留するCa2+イオンをカチオン交換樹脂で除去するに当たり、Ca化合物の添加量を適正化して、CaF2処理水中のF−濃度を高めることなく残留Ca2+濃度を低減することができる。このため、カチオン交換樹脂の再生頻度を低減することができ、装置の保守管理の軽減、再生薬剤コスト、再生廃液の処理コストの低減、軟化塔の稼動効率の向上が図れ、工業的、経済的に極めて有利にフッ素含有水の処理を行うことができる。
【図面の簡単な説明】
【図1】半導体製造廃水の一般的な処理プロセスを示す系統図である。
【符号の説明】
1 原水槽
2 中和槽
3 凝集槽
4 沈殿槽
5 濾過器
6 軟化塔
7 RO膜分離装置[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing residual Ca 2+ ions with a cation exchange resin after adding calcium (Ca) compound to fluorine-containing water and precipitating and separating fluorine as calcium fluoride (CaF 2 ). In the method, the present invention relates to a method for treating fluorine-containing water by optimizing the required addition amount of a Ca compound and reducing the regeneration frequency of the cation exchange resin.
[0002]
[Prior art]
As a method for treating fluorine-containing water such as fluorine-containing wastewater discharged from a silicon wafer production process in semiconductor component production, a method of adding Ca compound to fluorine-containing water to produce CaF 2 and precipitating and separating it is as follows. Widespread use due to low drug costs. In particular, semiconductor manufacturing wastewater contains inorganic salts such as SO 4 2− , NO 3 − , NH 4 + in addition to fluorine, so that after precipitation of CaF 2 , these SO 4 2− , NO In order to separate inorganic salts derived from wastewater such as 3 − and NH 4 + and the remaining Ca 2+ and F − and reuse them as recovered water, as shown in FIG. It is obtained by generating and separating CaF 2 through a neutralizing
[0003]
That is, since the CaF 2 treated water obtained by generating and separating CaF 2 from semiconductor manufacturing wastewater contains scale-causing substances that produce precipitated salts such as CaF 2 and CaSO 4 , this is used as it is for RO membrane separation. When the water is passed through the apparatus 7 for desalting, these scale-causing substances are concentrated in the RO membrane separation apparatus 7 and precipitated as scales, blocking the RO membrane and making it impossible to pass water. Therefore, in order to prevent this blockage of the RO membrane, it is necessary to remove these scale-causing substances in advance before the RO membrane separation device 7. In this case, Ca 2+, SO 4 2-, F - there is no need to remove any scale causative agent, such as, for generation preventing CaF 2 is Ca 2+ and F - may be removed either In order to prevent the formation of CaSO 4 , either Ca 2+ or SO 4 2− may be removed. For this reason, as shown in FIG. 1, a softening tower 6 is generally provided at the front stage of the RO membrane separation device 7 to remove Ca 2+ with a cation exchange resin.
[0004]
By the way, in such a treatment process, when the recovered water temporarily becomes surplus, the CaF 2 treated water, that is, the filtered treated water of the filter 5 is discharged out of the system as it is and discharged. 2 Regarding the F − concentration of the treated water, it is necessary to treat it to 15 mg / L or less, which is the drainage standard. In order to highly remove F − in fluorine-containing water, which is raw water, in this manner by adding a Ca compound, generally,
Ca 2+ + 2F − → CaF 2
Based on this reaction formula, the Ca compound is added in excess of an equivalent amount to F − in the raw water. Therefore, conventionally, the Ca compound is excessively added to remain in the CaF 2 treated water. The indicator of Ca 2+ concentration is 100 to 300 mg / L.
[0005]
[Problems to be solved by the invention]
However, when CaF 2 treated water containing 100 to 300 mg / L of Ca 2+ ions is passed through the softening tower 6 and treated with a cation exchange resin, the ion exchange capacity of the calcium compound reaches saturation early, and 2 to 4 cycles. It is necessary to regenerate the cation exchange resin at a frequency of / day.
[0006]
Such frequent regeneration is industrially extremely disadvantageous in terms of maintenance and management of the apparatus, cost of the regenerated chemical, processing cost of the regenerated waste liquid, operation efficiency of the softening tower, and the like. On the other hand, by reducing the Ca compound added amount as described above is, F of CaF 2 treated water - since there is a possibility to increase the concentration, Ca compound addition amount of optimization is required.
[0007]
The present invention solves the above-mentioned conventional problems, and after adding Ca compound to fluorine-containing water and precipitating and separating F as CaF 2 , in removing residual Ca 2+ ions with a cation exchange resin, the addition of Ca compound Providing a method for treating fluorine-containing water that can reduce the residual Ca 2+ concentration and reduce the regeneration frequency of the cation exchange resin without optimizing the amount and increasing the F − concentration in the CaF 2 treated water. Objective.
[0008]
[Means for Solving the Problems]
In the method for treating fluorine-containing water of the present invention, calcium fluoride formed by adding a calcium compound to fluorine-containing water containing hardly soluble salt-forming ions is separated to obtain CaF 2 treated water, and the CaF 2 treated water is In the method of removing residual calcium ions with a cation exchange resin (except the method of repeating the addition step of adding a calcium compound to fluorine-containing water and the separation step of separating the generated calcium fluoride multiple times) When the amount of calcium compound equivalent to the amount of ions forming calcium and sparingly soluble salt in the fluorine-containing water is Amg (as Ca) / L, the amount of calcium compound added to the fluorine-containing water is Amg a (as Ca) / L~ (a -200) mg method of the (as Ca) / L, fluorine after addition the calcium compound PH of Arimizu is 5 to 10, F of the CaF 2 treated water - concentration Ca 2+ concentration below 15 mg / L is equal to or less than 30 mg / L.
[0009]
As described above, conventionally, the
[0010]
Further, as described above, when the CaF 2 treated water is discharged, the F − concentration in the CaF 2 treated water needs to be 15 mg / L or less.
[0011]
Therefore, as a result of intensive studies to ensure that CaF 2 treated water having an F − concentration of 15 mg / L or less and a Ca 2+ concentration of 30 mg / L or less has been obtained, the present inventors have found that Ca contained in fluorine-containing water as raw water. 2+ when the Ca equivalent amount of Amg / L of equivalent become Ca compound relative to the amount of ions to produce a sparingly soluble salt, Amg / • L ^ a Ca compound added amount Ca equivalent amount (a-200) It was found that both the F − concentration and the Ca 2+ concentration can be satisfied within the mg / L range, and the present invention has been completed. (In the present invention, fluorine-containing water as raw water is water to which a Ca compound is added, and in addition to fluorine-containing water, as shown in FIG. In this treatment process, it refers to the water flowing into the neutralization tank 2).
[0012]
That is, in order to effectively generate CaF 2 from F − in the raw water and to remove F − to a high degree, not only F − in the raw water but also Ca 2+ other than F − and poorly soluble salts are generated. coexistence ions (. the following, the ion referred to as "sparingly soluble salt-forming ions") also need to be considered, Ca compounds in the raw water F - not only with respect to, the raw water F - other sparingly soluble It is also required for salt-forming ions.
[0013]
Examples of the hardly soluble salt-forming ions other than F − include phosphate ions (PO 4 3− ), sulfate ions (SO 4 2− ), carbonate ions (CO 3 2− ), and the like. The mechanism by which soluble salt-forming ions affect the fluorine concentration of CaF 2 treated water is estimated as follows.
[0014]
That is, for example, in the case of SO 4 2− , the solubility of CaSO 4 is 2000 mg / L, the solubility of CaF 2 is 15 mg / L, and the solubility of CaF 2 is much smaller than the solubility of CaSO 4. In general, the CaF 2 formation reaction should take precedence over the CaSO 4 formation reaction. However, in reality, CaSO 4 (aq.) That does not cause precipitation, that is, so-called molecular CaSO 4 is generated at the same time as the precipitation of CaF 2 , and the Ca salt is fixed to SO 4 2− , so Ca 2+ + 2F - → reaction of CaF 2 is inhibited. Therefore, it is also necessary to add a Ca compound that reacts with such poorly soluble salt-forming ions.
[0015]
Fluorine-containing water such as semiconductor manufacturing wastewater contains these sparingly soluble salt-forming ions, and as previously proposed by the present applicant, in adding Ca compound to fluorine-containing water for treatment, In some cases, sulfuric acid and / or sulfate is added to fluorine-containing water for the purpose of improving the quality of treated water and promoting crystallization of CaF 2 (Japanese Patent Application Nos. 11-146822 and 11-218990). . In such a case, naturally, SO 4 2− exists in addition to F − in the raw water.
[0016]
When such a poorly soluble salt-forming ion, for example, SO 4 2− is taken into consideration, the necessary addition amount of the Ca compound to the raw water is the Ca required to generate CaF 2 by the reaction with F − in the raw water. The above-mentioned F − : 15 mg / L or less, Ca 2+ : slightly less than the total amount of the compound amount and the amount of Ca compound required to produce CaSO 4 by the reaction of SO 4 2− with raw water. It becomes an ideal addition amount for obtaining CaF 2 treated water of 30 mg / L or less.
[0017]
Thus, this ideal addition amount can be realized within the range of Amg (as Ca) / L to (A-200) mg (as Ca) / L.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the method for treating fluorine-containing water of the present invention will be described in detail.
[0019]
In the present invention, when Ca compound is added to fluorine-containing water such as semiconductor manufacturing wastewater by the process as shown in FIG. 1 to produce CaF 2 , the amount of Ca compound to be added is changed to the production of hardly soluble salt in raw water. Ca equivalent amount of Ca compound equivalent to the amount of ions, Amg / L or less, (A-200) mg / L or more.
[0020]
When the amount of Ca compound added is less than (A-200) mg (as Ca) / L, the Ca compound is insufficient and F − in the raw water cannot be removed to a high degree, and the residual F − increases and F − : it is impossible to obtain a 15 mg / L or less of CaF 2 treated water. Conversely, when the Ca compound addition amount exceeds Amg (as Ca) / L, the Ca compound becomes excessive and the F − concentration in the CaF 2 treated water is reduced, but Ca 2+ is greatly increased, and the cation exchange resin The playback frequency will be increased.
[0021]
In addition, this poorly soluble salt-forming ion generally generates a poorly soluble salt having a solubility based on a solubility product of 700 mg / L or less by reaction with Ca 2+ , Examples of the hardly soluble salt-forming ions other than F − include PO 4 3− , SO 4 2− , CO 3 2− , and the like as described above. Therefore, in the present invention, F − concentration in raw water, PO The addition amount of the Ca compound is A to (A-200) with respect to the value of Amg (as Ca) / L calculated by the following formula based on 4 3 -concentration, SO 4 2 -concentration, and CO 3 2 -concentration. ) Mg (as Ca) / L.
[0022]
A (mg / L) =
(F − concentration × Ca / 2F) + (PO 4 3− concentration × 3Ca / 2PO 4 )
+ (SO 4 2− concentration × Ca / SO 4 ) + (CO 3 2− concentration × Ca / CO 3 )
= (F - concentration × 40/38) + (PO 4 3− concentration × 120/190)
+ (SO 4 2− concentration × 40/96) + (CO 3 2− concentration × 40/60)
As described above, when a hardly soluble salt-forming ion is added to the raw water as in the case of adding sulfuric acid and / or sulfate, it is naturally difficult to add this as a hardly soluble salt-forming ion in the raw water. Soluble salt-forming ions are also included.
[0023]
When there are multiple types of poorly soluble salt-forming ions in the raw water, it is not necessary to measure the amount of all the poorly soluble salt-forming ions and use it to calculate the Ca salt addition amount. The Ca salt addition amount may be set by selecting one or more of the poorly soluble salt-forming ions having a high concentration, for example, 100 ppm or more, and measuring the amount of the hardly soluble salt-forming ions.
[0024]
In general, inexpensive calcium hydroxide (slaked lime: Ca (OH) 2 ) is used as the Ca compound added to the raw water, but not limited to this, quick lime or the like may be used. Further, calcium chloride or calcium carbonate may be used in combination with sodium hydroxide.
[0025]
The pH for CaF 2 precipitation with the addition of such a Ca salt is 5 to 10, preferably because it is 5.5-7.5, especially when adding Ca (OH) 2 as a Ca compound, pH is If the pH is too high to be adjusted to such pH conditions, it is necessary to adjust the pH appropriately by adding an acid such as sulfuric acid or hydrochloric acid.
[0026]
Further, as described above, when sulfuric acid and / or sulfate is added to raw water for the purpose of improving the quality of treated water and promoting crystallization of CaF 2 , the sulfuric acid and sulfate to be added include industrial sulfuric acid and sodium sulfate. Further, as this sulfuric acid source, other waste water containing SO 4 2- ion, for example, steel plate pickling waste water and flue gas desulfurization waste water can also be used.
[0027]
The method of the present invention is applicable to any treatment process as long as CaF 2 treated water obtained by producing CaF 2 by adding a Ca compound and separating it is further treated with a cation exchange resin. be able to. Therefore, as shown in FIG. 1, not only the treated water of the softening tower 6 is further treated by the RO membrane separation device 7, but the softened water obtained from the softening tower 6 is used as the treated water as it is, Furthermore, it may be a treatment process in which water is passed through an anion exchange resin to obtain demineralized water, or a demineralized water obtained by treating softened water with an electric regeneration type continuous demineralizer is treated water.
[0028]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
[0029]
Examples 1 to 3, Comparative Examples 1 and 2
An artificial waste liquid of F − : 2500 mg / L, SO 4 2− : 500 mg / L (as H 2 SO 4 ) is used as raw water, and a Ca compound such as Ca (OH) 2 is added in an amount shown in Table 1 to pH 6.5. To 7.0, and after reacting for 30 minutes, No. The F - concentration and Ca 2+ concentration of the filtered water were measured by filtering with 5A filter paper, and the results are shown in Table 1.
[0030]
In Table 1, the equivalent A is a case where the Ca compound is added in an equivalent amount to the total of both F − and SO 4 2− in the raw water. In this case, Ca (OH) is used as the Ca compound. ) Only 2 was added to adjust the pH to 6.5-7.0.
[0031]
When the Ca compound is deficient with respect to this equivalent A, H 2 SO 4 as the SO 4 2− source is changed to Na 2 SO 4 so that Ca (OH) 2 corresponding to SO 4 2− is not added. And added.
[0032]
Also, per equivalent A, when the excess of Ca compound, using H 2 SO 4 as SO 4 2-sources, the Ca (OH) in addition to further CaCl 2 neutral 2 as Ca compound Added.
[0033]
[Table 1]
[0034]
Examples 4 to 6, Comparative Examples 3 and 4
F -: 5000mg / L, SO 4 2-: performing the same procedure as 1000mg / L (as H 2 SO 4) respectively, in Examples 1-3 and Comparative Examples 1 and 2 except that was used as a raw artificial waste The F − concentration and Ca 2+ concentration of the treated water were measured, and the results are shown in Table 2.
[0035]
[Table 2]
[0036]
From Tables 1 and 2, by setting the amount of Ca compound to be equivalent to A to (A-200) mg (as Ca) / L, high-quality treated water having low F − and Ca 2+ concentrations can be obtained. You can see that
[0037]
【The invention's effect】
As described above in detail, according to the method for treating fluorine-containing water of the present invention, a Ca compound is added to fluorine-containing water, F is precipitated as CaF 2 and the remaining Ca 2+ ions are removed with a cation exchange resin. In this case, the residual Ca 2+ concentration can be reduced without increasing the F − concentration in the CaF 2 treated water by optimizing the amount of Ca compound added. As a result, the frequency of regeneration of the cation exchange resin can be reduced, the maintenance and management of the apparatus can be reduced, the cost of the regenerated chemicals, the processing cost of the regenerated waste liquid can be reduced, and the operation efficiency of the softening tower can be improved. The treatment of fluorine-containing water can be carried out very advantageously.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a general treatment process of semiconductor manufacturing wastewater.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1
Claims (5)
該フッ素含有水中の、カルシウムと難溶性の塩を生成するイオンの量に対して当量となるカルシウム化合物量をAmg(as Ca)/Lとしたとき、該フッ素含有水へのカルシウム化合物の添加量をAmg(as Ca)/L〜(A−200)mg(as Ca)/Lとする方法であって、
該カルシウム化合物添加後のフッ素含有水のpHが5〜10であり、
前記CaF 2 処理水のF − 濃度が15mg/L以下でCa 2+ 濃度が30mg/L以下であることを特徴とするフッ素含有水の処理方法。Calcium fluoride is generated by adding a calcium compound to fluorine-containing water containing hardly soluble salt-forming ions to obtain CaF 2 treated water, and calcium ions remaining in the CaF 2 treated water are removed with a cation exchange resin. In the method (except the method of repeating the addition step of adding the calcium compound to the fluorine-containing water and the separation step of separating the generated calcium fluoride multiple times) ,
The amount of calcium compound added to the fluorine-containing water when the amount of calcium compound that is equivalent to the amount of ions that form a sparingly soluble salt with calcium in the fluorine-containing water is Amg (as Ca) / L Amg (as Ca) / L to (A-200) mg (as Ca) / L ,
The pH of the fluorine-containing water after addition of the calcium compound is 5 to 10,
A method for treating fluorine-containing water, wherein the F − concentration of the CaF 2 treated water is 15 mg / L or less and the Ca 2+ concentration is 30 mg / L or less .
A(mg/L)=A (mg / L) =
(F−濃度×Ca/2F)+(PO(F−concentration × Ca / 2F) + (PO 44 3−3- 濃度×3Ca/2POConcentration x 3Ca / 2PO 44 ))
+(SO+ (SO 44 2−2- 濃度×Ca/SOConcentration x Ca / SO 44 )+(CO) + (CO 33 2−2- 濃度×Ca/COConcentration x Ca / CO 33 ))
=(F= (F −− 濃度×40/38)+(POConcentration x 40/38) + (PO 44 3−3- 濃度×120/190)(Density x 120/190)
+(SO+ (SO 44 2−2- 濃度×40/96)+(COConcentration x 40/96) + (CO 33 2−2- 濃度×40/60)(Density x 40/60)
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JP5665002B2 (en) * | 2010-12-20 | 2015-02-04 | 株式会社日立製作所 | Treatment method for fluorine-containing wastewater |
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