JP5489766B2 - Method for producing alkali metal silicofluoride and nitric acid from waste liquid - Google Patents
Method for producing alkali metal silicofluoride and nitric acid from waste liquid Download PDFInfo
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Description
本発明は、半導体や太陽電池関係のシリコンを基材とする産業において、シリコン母材の加工やシリコン基盤の洗浄に使用された後のフッ化水素酸と硝酸の混酸の廃液から、有価物である高純度の、ケイフッ化ナトリウムに代表されるアルカリ金属ケイフッ化物と硝酸を製造する方法に関するものである。 In the industry based on silicon for semiconductors and solar cells, the present invention is a valuable material from the waste liquid of hydrofluoric acid and nitric acid mixed acid used after processing of silicon base material and cleaning of silicon substrate. The present invention relates to a method for producing a certain high purity alkali metal silicofluoride represented by sodium silicofluoride and nitric acid.
半導体や太陽電池関係のシリコンを基材とする産業では、基盤洗浄、加工工程において、フッ化水素酸と硝酸の混酸が多量に使用されている。それに伴い、使用後の廃液量も増加しており、環境問題及び資源の有効利用の観点からその適切な処理が望まれている。そして、その処理も産業廃棄物として処理するのではなく、フッ素資源の有効利用のため、その廃液を原料として有価物であるフッ化物を高純度に製造する方法とともに硝酸の回収方法の確立が求められている。 In the industry based on silicon for semiconductors and solar cells, mixed acids of hydrofluoric acid and nitric acid are used in large amounts in the substrate cleaning and processing processes. Along with this, the amount of waste liquid after use has also increased, and appropriate treatment is desired from the viewpoint of environmental problems and effective use of resources. And the treatment is not treated as industrial waste, but for the effective use of fluorine resources, it is required to establish a method for recovering nitric acid as well as a method for producing high-purity fluoride as a raw material from the waste liquid It has been.
半導体、シリコン基板、及び太陽電池の製造工程では、シリコンの加工や洗浄のために、フッ化水素酸と硝酸を適宜な濃度になるよう混合し、混酸として使用している。この使用された後の混酸の廃液は、水酸化カルシウムのようなカルシウム化合物と反応させ、難溶性のフッ化カルシウム等の化合物としてフッ素を固定分離した後、硝酸分を水酸化ナトリウム等で中和してから活性汚泥法で処理されている（例えば、特許文献１参照）。 In the manufacturing process of semiconductors, silicon substrates, and solar cells, hydrofluoric acid and nitric acid are mixed at an appropriate concentration and used as a mixed acid for processing and cleaning silicon. The mixed acid waste liquid after use is reacted with a calcium compound such as calcium hydroxide to fix and separate fluorine as a poorly soluble compound such as calcium fluoride, and then neutralize nitric acid with sodium hydroxide or the like. Then, it is processed by the activated sludge method (see, for example, Patent Document 1).
そして、それぞれの処理で発生した汚泥は、産業廃棄物として埋め立て処理や焼却処理される。これらの処理方法については、いろいろな手法がすでに提案されている（例えば、特許文献２、３参照）が、それらは、廃水処理のためのフッ化水素酸と硝酸を処理する方法で、廃液中のフッ素を原料として、工業用薬品であるケイフッ化ナトリウムで代表されるアルカリ金属ケイフッ化物を製造することと硝酸の回収に関しては、検討されてはいない。 And the sludge which generate | occur | produced in each process is a landfill process or an incineration process as industrial waste. Various methods have already been proposed for these treatment methods (see, for example, Patent Documents 2 and 3), which are methods for treating hydrofluoric acid and nitric acid for wastewater treatment in waste liquid. The production of alkali metal silicofluoride represented by sodium silicofluoride, which is an industrial chemical, and the recovery of nitric acid have not been studied.
本発明は、半導体や太陽電池関係のシリコンを基材とする産業で、シリコン母材の加工やシリコン基盤の洗浄において使用された後のフッ化水素酸と硝酸の混酸の廃液を原料として、有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造する方法を提供することを目的とするものである。 INDUSTRIAL APPLICABILITY In the industry based on silicon related to semiconductors and solar cells, the waste liquid of mixed acid of hydrofluoric acid and nitric acid after being used in processing of silicon base material and cleaning of silicon substrate is used as a raw material. It is an object of the present invention to provide a method for producing high purity alkali metal silicofluoride and nitric acid.
一般に、半導体や太陽電池関係のシリコンを基材とする産業では、シリコン母材の加工やシリコン基盤の洗浄を行うために、濃度５０重量％程度のフッ化水素酸と濃度７０重量％程度の硝酸を混合し適当な濃度に調整された混酸が使用されている。
そして、使用された後のフッ化水素酸と硝酸の混酸の廃液には、その利用度により変化するが、未反応のフッ化水素酸と反応で生成したケイフッ化水素酸、及び硝酸が含まれている。
In general, in semiconductor and solar cell related industries based on silicon, hydrofluoric acid having a concentration of about 50% by weight and nitric acid having a concentration of about 70% by weight are used for processing a silicon base material and cleaning a silicon substrate. A mixed acid adjusted to an appropriate concentration by mixing is used.
The waste liquid of mixed hydrofluoric acid and nitric acid after use contains unreacted hydrofluoric acid and silicohydrofluoric acid and nitric acid, which vary depending on the degree of utilization. ing.
廃液中のフッ化水素酸、ケイフッ化水素酸、及び硝酸のそれぞれを単なる蒸留法で単離することは、水溶液中で共存している場合、それぞれの成分が作用し合った数多くの沸騰状態があるため、非常に困難である。また、水酸化カルシウムのようなカルシウム化合物と反応させてフッ素を分離する場合は、難溶解性のフッ化カルシウムとケイフッ化カルシウムの両方が同時に生成するので、それらの混合物になってしてしまい、得られたものの工業用薬品としての価値は低い。 Isolation of hydrofluoric acid, silicohydrofluoric acid, and nitric acid in waste liquid by simple distillation means that when they coexist in an aqueous solution, there are many boiling states in which the respective components act. Because it is very difficult. In addition, when fluorine is separated by reacting with a calcium compound such as calcium hydroxide, both poorly soluble calcium fluoride and calcium silicofluoride are generated at the same time. The value obtained as an industrial chemical is low.
また、塩化ナトリウムのようなアルカリ金属化合物と反応させて、ケイフッ化ナトリウムのようなアルカリ金属ケイフッ化物としてフッ素を分離する場合は、廃液中に存在するフッ化水素酸も反応してアルカリ金属フッ化物であるフッ化ナトリウムやアルカリ金属酸性フッ化物である酸性フッ化ナトリウムが生成して混入し、純度を低下させ、工業用薬品としての価値を低下させる問題がある。 In addition, when fluorine is separated as an alkali metal silicofluoride such as sodium silicofluoride by reacting with an alkali metal compound such as sodium chloride, hydrofluoric acid present in the waste liquid also reacts with the alkali metal fluoride. There is a problem in that sodium fluoride or sodium acid fluoride which is an alkali metal acid fluoride is generated and mixed to lower the purity and the value as an industrial chemical.
本発明者等は、鋭意研究の結果、シリコン母材の加工やシリコン基盤の洗浄において使用された後のフッ化水素酸と硝酸の混酸の廃液を原料として、有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造する方法を見出した。すなわち、工業用薬品として有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造するための、操作の手順、原料化合物の選定、原料化合物の量、原料化合物の投入方法、反応温度、蒸留方法について種々検討し、以下に示すように、工業的に確立する方法を完成するに至った。 As a result of diligent research, the present inventors have used a waste liquid of hydrofluoric acid and nitric acid mixed acid after being used in processing of a silicon base material and cleaning of a silicon substrate as a raw material, and a high-purity alkali metal that is a valuable resource A method for producing silicofluoride and nitric acid was found. That is, to produce high-purity alkali metal silicofluoride and nitric acid that are valuable as industrial chemicals, operating procedures, selection of raw material compounds, amount of raw material compounds, method of charging raw material compounds, reaction temperature, distillation method As a result, various methods have been studied and an industrially established method has been completed as described below.
すなわち、本発明は、廃液からアルカリ金属ケイフッ化物と硝酸を製造する方法に関するものであって、使用後のフッ化水素酸と硝酸の混酸の廃液を原料とし、次の(a)〜(c)の順に処理することによって、有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造することを特徴とするものである。
(a) 廃液に含まれるフッ化水素酸と酸化ケイ素化合物とを、酸化ケイ素化合物のケイ素のモル数がフッ化水素酸のモル数に対して０．１８〜０．３５倍で反応させ、ケイフッ化水素酸に変換する。
(b) (a)でケイフッ化水素酸に変換した後の廃液に、アルカリ金属塩をアルカリ金属塩に含まれるアルカリ金属のモル数がケイフッ化水素酸のモル数に対して２．０４〜３．４０倍で添加し、アルカリ金属ケイフッ化物を製造する。
(c) (b)によりアルカリ金属ケイフッ化物を製造した後、分離した液とアルミニウム化合物、または、ホウ素化合物とを反応させ、液に含まれるケイフッ化水素酸の構成元素であるフッ素を非揮発性のフルオロアルミン酸または高沸点性のホウフッ化水素酸に変換してから、蒸留法によって硝酸を製造する。
That is, the present invention relates to a method for producing alkali metal silicofluoride and nitric acid from waste liquid, using as a raw material a waste liquid of mixed hydrofluoric acid and nitric acid after use, the following (a) ~ (c) By processing in this order, valuable high-purity alkali metal silicofluoride and nitric acid are produced.
(a) The hydrofluoric acid and the silicon oxide compound contained in the waste liquid are reacted with each other so that the number of moles of silicon in the silicon oxide compound is 0.18 to 0.35 times the number of moles of hydrofluoric acid. Convert to hydrofluoric acid.
(b) In the waste liquid after being converted to silicohydrofluoric acid in (a), the number of moles of alkali metal contained in the alkali metal salt is 2.04 to 3 with respect to the number of moles of silicofluoric acid. It was added at .40 times, to produce the alkali metal silicofluoride.
(c) After producing the alkali metal silicofluoride according to (b), react the separated liquid with an aluminum compound or boron compound to make fluorine, which is a constituent element of silicohydrofluoric acid, contained in the liquid non-volatile Then, nitric acid is produced by a distillation method after conversion into fluoroaluminic acid or high-boiling borohydrofluoric acid.
上記の場合において、廃液に含まれるフッ化水素酸と酸化ケイ素化合物とを、酸化ケイ素化合物のケイ素のモル数がフッ化水素酸のモル数に対して０．１８〜０．３５倍で反応させるが、このようにすると、酸化ケイ素化合物とフッ化水素酸の反応において、酸化ケイ素化合物を過剰に添加することで化学平衡をケイフッ水素酸の生成方向へ促進させることができる。 In the above case, hydrofluoric acid and silicon oxide compound contained in the waste liquid are reacted at a silicon oxide compound having a silicon mole number of 0.18 to 0.35 times the mole number of hydrofluoric acid. However, in this case, in the reaction of the silicon oxide compound and hydrofluoric acid, the chemical equilibrium can be promoted in the direction of production of hydrofluoric acid by adding an excessive amount of the silicon oxide compound.
また、アルカリ金属塩に含まれるアルカリ金属のモル数がケイフッ化水素酸のモル数に対して２．０４〜３．４０倍とするが、このようにすると、アルカリ金属塩とケイフッ化水素酸との反応において、アルカリ金属塩を過剰に添加することでアルカリ金属ケイフッ化物が生成される方向へ促進させることができる。 Although the number of moles of the alkali metal contained in the alkali metal salt and from 2.04 to 3.40 times the number of moles of silicon hydrofluoric acid, in this case, the alkali metal salt and silicic hydrofluoric acid In this reaction, the alkali metal salt can be promoted in the direction in which the alkali metal silicofluoride is produced by adding an excessive amount of the alkali metal salt.
また、反応温度を３５〜７０℃の間で調整することが望ましい。このようにすると、高純度で大きなアルカリ金属ケイフッ化物の結晶が得られるので、アルカリ金属ケイフッ化物を遠心ろ過機等のろ過機で反応液と分離する作業が円滑になり、工業的製法として有利になる。 Moreover, it is desirable to adjust reaction temperature between 35-70 degreeC. In this way, a high purity and large alkali metal silicofluoride crystal can be obtained, so that the work of separating the alkali metal silicofluoride from the reaction solution with a filter such as a centrifugal filter becomes smooth, which is advantageous as an industrial production method. Become.
さらに、アルカリ金属塩の水溶液を反応温度が３５〜７０℃になるようにあらかじめ加熱して投入することが望ましい。このようにすると、アルカリ金属ケイフッ化物の結晶がより大きく成長し、高純度でより大きなアルカリ金属ケイフッ化物の結晶を得ることができるので、より有利である。 Furthermore, it is desirable to heat and add an aqueous solution of an alkali metal salt in advance so that the reaction temperature is 35 to 70 ° C. This is more advantageous because the alkali metal silicofluoride crystals grow larger and a larger alkali metal silicofluoride crystal can be obtained with high purity.
本発明をさらに詳細に説明する。本発明による廃液からアルカリ金属ケイフッ化物と硝酸を製造する方法は、廃液中の未反応のフッ化水素酸からケイフッ化水素酸を製造する工程(a)と、アルカリ金属ケイフッ化物を製造する工程(b)と、硝酸を製造する工程(c)とからなり、これらを(a)、(b)、(c)の順に処理することにより、本発明の目的とする有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造することができる。 The present invention will be described in further detail. The method for producing alkali metal silicofluoride and nitric acid from the waste liquid according to the present invention includes a step (a) for producing silicohydrofluoric acid from unreacted hydrofluoric acid in the waste liquid, and a step for producing alkali metal silicofluoride ( b) and a step (c) for producing nitric acid, and by treating these in the order (a), (b), (c), a high-purity alkali which is a valuable material targeted by the present invention. Metal silicofluoride and nitric acid can be produced.
以下、工程(a)〜(c)についてさらに詳細に説明する。
（工程(a)：廃液中の未反応のフッ化水素酸からケイフッ化水素酸を製造する）
廃液中の未反応のフッ化水素酸を酸化ケイ素化合物と反応させてケイフッ化水素酸を製造する。
フッ化水素酸が残ると後工程のアルカリ金属ケイフッ化物を製造する過程で、アルカリ金属塩の一部がフッ化水素酸と反応し、アルカリ金属フッ化物やアルカリ金属酸性フッ化物が生成して混入し、アルカリ金属ケイフッ化物の純度が低減するため、フッ化水素酸は完全にケイフッ化水素酸にすることが好ましい。使用し得る酸化ケイ素化合物としては、二酸化ケイ素、一酸化ケイ素、ケイ酸ナトリウム、ケイ酸カリウム等を挙げることができる。
Hereinafter, steps (a) to (c) will be described in more detail.
(Step (a): Silica hydrofluoric acid is produced from unreacted hydrofluoric acid in the waste liquid)
Unreacted hydrofluoric acid in the waste liquid is reacted with a silicon oxide compound to produce silicohydrofluoric acid.
When hydrofluoric acid remains, part of the alkali metal salt reacts with hydrofluoric acid in the process of producing the alkali metal silicofluoride in the subsequent process, and alkali metal fluoride and alkali metal acidic fluoride are generated and mixed In order to reduce the purity of the alkali metal silicofluoride, it is preferable that the hydrofluoric acid be completely silicohydrofluoric acid. Examples of the silicon oxide compound that can be used include silicon dioxide, silicon monoxide, sodium silicate, and potassium silicate.
そして、本発明の目的である高純度のアルカリ金属ケイフッ化物を製造するためには、反応させる酸化ケイ素化合物のケイ素のモル数がフッ化水素酸のモル数に対して０．１８〜０．３５倍とする。
これは、酸化ケイ素化合物として二酸化ケイ素の例を示す式(1)における酸化ケイ素化合物とフッ化水素酸の反応において、酸化ケイ素化合物を過剰にして化学平衡をケイフッ化水素酸が生成される方向へ促進させるためであり、次のアルカリ金属ケイフッ化物を製造する工程(b)において、高純度のアルカリ金属ケイフッ化物を得ることに関しての重要事項であるということができる。
なお、０．１８倍以下であるとフッ化水素酸を完全にケイフッ化水素酸に変換できず、０．３５倍以上の場合は経済的でない。
And in order to manufacture the high purity alkali metal silicofluoride which is the object of the present invention, the number of moles of silicon of the silicon oxide compound to be reacted is 0.18 to 0.35 with respect to the number of moles of hydrofluoric acid. double that.
This is because, in the reaction of the silicon oxide compound and hydrofluoric acid in the formula (1) showing an example of silicon dioxide as the silicon oxide compound, the silicon oxide compound is excessive and the chemical equilibrium is generated in the direction in which silicofluoric acid is generated. This is for the purpose of promoting, and it can be said that this is an important matter for obtaining high-purity alkali metal silicofluoride in the next step (b) of producing the alkali metal silicofluoride.
In addition, when it is 0.18 times or less, hydrofluoric acid cannot be completely converted into silicofluoric acid, and when it is 0.35 times or more, it is not economical.
実際には、反応槽中において廃液を攪拌しながら、酸化ケイ素化合物を添加して行き、フッ化水素酸を酸化ケイ素化合物と反応させてケイフッ化水素酸とし、過剰の酸化ケイ素化合物はろ過して除去する。 In practice, while stirring the waste liquid in the reaction vessel, the silicon oxide compound is added, hydrofluoric acid is reacted with the silicon oxide compound to form silicohydrofluoric acid, and excess silicon oxide compound is filtered. Remove.
（工程(b)：アルカリ金属ケイフッ化物を製造する）
廃液中の未反応のフッ化水素酸からケイフッ化水素酸を製造する工程(a)でケイフッ化水素酸に変換した後の廃液に、アルカリ金属塩を添加し、アルカリ金属ケイフッ化物を製造する。使用し得るアルカリ金属塩としては、硝酸ナトリウム、水酸化ナトリウム、炭酸ナトリウム、炭酸水素ナトリウム、硝酸カリウム、水酸化カリウム、炭酸カリウム、炭酸水素カリウム等を挙げることができる。
(Step (b): producing alkali metal silicofluoride)
An alkali metal salt is added to the waste liquid that has been converted to silicofluoric acid in the step (a) for producing silicohydrofluoric acid from unreacted hydrofluoric acid in the waste liquid to produce an alkali metal silicofluoride. Examples of alkali metal salts that can be used include sodium nitrate, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium nitrate, potassium hydroxide, potassium carbonate, potassium hydrogen carbonate and the like.
アルカリ金属塩の添加方法は、固体の状態で投入しても良いが、適当な濃度の水溶液にして添加する方が、反応を制御しやすい。また、アルカリ金属塩の投入は、全量を一度に行っても良いが、アルカリ金属ケイフッ化物の析出と分離を何回かに分けながら段階的に行っても良い。 The alkali metal salt may be added in a solid state, but the reaction can be easily controlled by adding an aqueous solution having an appropriate concentration. In addition, the alkali metal salt may be added all at once, or may be performed step by step while separating and separating the alkali metal silicofluoride several times.
アルカリ金属塩の投入量は、アルカリ金属塩に含まれるアルカリ金属のモル数でケイフッ化水素酸のモル数に対し、２．０４〜３．４０倍投入するものとする。
これは、本発明の目的である高純度のアルカリ金属塩を得るためには、アルカリ金属塩とケイフッ化水素酸との反応〔式(2)〕において、アルカリ金属塩を過剰に添加することで化学平衡をアルカリ金属ケイフッ化物が生成される方向へ促進させるためである。
アルカリ金属塩添加量がケイフッ化水素酸のモル数に対して２．０４倍を下回ると、ケイフッ化水素酸をアルカリ金属ケイフッ化物として完全に回収できない。また、３．４０倍を上回ることは、経済的でない。
Input amount of the alkali metal salt to moles of hydrosilicofluoric acid in moles of the alkali metal contained in the alkali metal salt is intended to put 2.04 to 3.40 times.
This is because, in order to obtain a high-purity alkali metal salt that is the object of the present invention, an excess of the alkali metal salt is added in the reaction of the alkali metal salt with silicofluoric acid (formula (2)). This is to promote chemical equilibrium in the direction in which alkali metal silicofluoride is produced.
When the amount of alkali metal salt added is less than 2.04 times the number of moles of silicohydrofluoric acid, the hydrosilicofluoric acid cannot be completely recovered as alkali metal silicofluoride. Moreover, it is not economical to exceed 3.40 times.
アルカリ金属ケイフッ化物を製造する場合において、反応温度を３５〜７０℃の間で調整するのが望ましい。このようにすると、高純度で大きなアルカリ金属ケイフッ化物の結晶が得られるので、アルカリ金属ケイフッ化物を遠心ろ過機等のろ過機で反応液と分離する作業が円滑になり、工業的製法として有利になる。
反応温度が３５℃未満であると、得られるアルカリ金属ケイフッ化物の結晶の粒子が小さくなり、反応液との分離が困難になる。また、反応温度が７０℃以上になると、反応液からケイフッ化水素酸及び硝酸が蒸発すること、さらに、熱エネルギーを過剰に加えることになるので、現実的ではない。
When producing an alkali metal silicofluoride, it is desirable to adjust the reaction temperature between 35-70 ° C. In this way, a high purity and large alkali metal silicofluoride crystal can be obtained, so that the work of separating the alkali metal silicofluoride from the reaction solution with a filter such as a centrifugal filter becomes smooth, which is advantageous as an industrial production method. Become.
When the reaction temperature is less than 35 ° C., the obtained alkali metal silicofluoride crystal particles become small, and separation from the reaction solution becomes difficult. On the other hand, when the reaction temperature is 70 ° C. or higher, the hydrofluoric acid and nitric acid are evaporated from the reaction solution, and furthermore, excessive heat energy is added, which is not realistic.
また、反応温度の調整は、反応装置を加熱して制御しても良いが、アルカリ金属塩の水溶液を反応温度が３５〜７０℃になるようにあらかじめ加熱して投入すると、アルカリ金属ケイフッ化物の結晶がより大きく成長し、高純度でより大きなアルカリ金属ケイフッ化物の結晶を得ることができるので、より有利である。 The reaction temperature may be adjusted by heating the reaction apparatus. However, when an alkali metal salt aqueous solution is heated and introduced in advance so that the reaction temperature is 35 to 70 ° C., the alkali metal silicofluoride This is more advantageous because the crystals grow larger and larger alkali metal silicofluoride crystals can be obtained with high purity.
以上のように製造されたアルカリ金属ケイフッ化物を、遠心分離機等のろ過機で分離した後、乾燥してアルカリ金属ケイフッ化物の粉体を得る。そして、分離された反応液は、次工程(c)の「硝酸を製造する工程」に使用するか、上述のアルカリ金属塩のうちのアルカリ金属水酸化物、アルカリ金属炭酸塩、アルカリ金属炭酸水素塩のいずれかと反応させ、アルカリ金属硝酸塩の水溶液にしてアルカリ金属源として使用することができる。 The alkali metal silicofluoride produced as described above is separated by a filter such as a centrifugal separator and then dried to obtain an alkali metal silicofluoride powder. Then, the separated reaction solution is used in the “step of producing nitric acid” in the next step (c), or alkali metal hydroxide, alkali metal carbonate, alkali metal hydrogencarbonate among the above alkali metal salts. It can be reacted with any of the salts to form an aqueous solution of an alkali metal nitrate and used as the alkali metal source.
（工程(c)：硝酸を製造する）
アルカリ金属ケイフッ化物を製造する工程(b)において、アルカリ金属ケイフッ化物を分離した液中には、揮発成分としては、残留するケイフッ化水素酸と硝酸が存在している。
これらを単なる蒸留法で分離することは、上述したように、それぞれの成分が作用し合った数多くの沸騰状態があるため、非常に困難であるから、式(3)及び式(4)に示すように、ケイフッ化水素酸をアルミニウム化合物またはホウ素化合物と反応させて、その構成元素であるフッ素を非揮発性のフルオロアルミン酸または高沸点性のホウフッ化水素酸に変換してから蒸留することにより、低沸点物である硝酸をケイフッ化水素酸を含有することなく容易に分離できる。
(Process (c): Nitric acid is produced)
In the step (b) for producing the alkali metal silicofluoride, residual hydrosilicofluoric acid and nitric acid are present as volatile components in the liquid from which the alkali metal silicofluoride has been separated.
As described above, it is very difficult to separate them by a simple distillation method because there are many boiling states in which the respective components interact with each other. Therefore, the following equations (3) and (4) are given. Thus, hydrosilicic acid is reacted with an aluminum compound or a boron compound, and fluorine, which is a constituent element thereof, is converted into non-volatile fluoroaluminic acid or high-boiling borohydrofluoric acid and then distilled. Nitric acid, which is a low boiling point substance, can be easily separated without containing hydrofluoric acid.
ここに、使用し得るアルミニウム化合物としては、アルミニウム金属、硝酸アルミニウム、水酸化アルミニウム、硫酸アルミニウム、リン酸アルミニウム、ホウ酸アルミニウム等を挙げることができ、また、使用し得るホウ素化合物としては、ホウ酸、無水ホウ酸、ホウ酸ナトリウム、過ホウ酸ナトリウム等を挙げることができる。
蒸留方法としては、減圧蒸留やその他の蒸留法で行うことができる。また、蒸留装置は、硝酸等の酸性物に耐久性のあるフッ素樹脂等の材質で構成されておれば良い。
Here, examples of the aluminum compound that can be used include aluminum metal, aluminum nitrate, aluminum hydroxide, aluminum sulfate, aluminum phosphate, and aluminum borate, and examples of the boron compound that can be used include boric acid. , Anhydrous boric acid, sodium borate, sodium perborate and the like.
As a distillation method, it can carry out by vacuum distillation or other distillation methods. Moreover, the distillation apparatus should just be comprised with materials, such as a fluororesin durable to acidic substances, such as nitric acid.
請求項１記載の発明によれば、半導体や太陽電池関係のシリコンを基材とする産業において、シリコン母材の加工やシリコン基盤の洗浄に使用された後のフッ化水素酸と硝酸の混酸の廃液を原料として、有価物である高純度のアルカリ金属ケイフッ化物と硝酸を製造することができる。 According to the first aspect of the present invention, in a semiconductor or solar cell related silicon-based industry, a mixed acid of hydrofluoric acid and nitric acid after being used for processing a silicon base material or cleaning a silicon substrate. Using the waste liquid as a raw material, valuable alkali metal silicofluoride and nitric acid can be produced.
特に、フッ化水素酸と酸化ケイ素化合物との反応において、化学平衡をケイフッ化水素酸が生成される方向へ促進させることができるので、高純度のアルカリ金属ケイフッ化物を得るためのケイフッ化水素酸を製造することができる。 In particular , in the reaction between hydrofluoric acid and a silicon oxide compound, the chemical equilibrium can be promoted in the direction in which silicohydrofluoric acid is generated, so that hydrosilicofluoric acid for obtaining high-purity alkali metal silicofluoride is obtained. Can be manufactured.
さらに、アルカリ金属塩とケイフッ化水素酸との反応において、化学平衡をアルカリ金属ケイフッ化物が生成される方向へ促進させることができるので、高純度のアルカリ金属ケイフッ化物を製造することができる。 Furthermore , in the reaction between the alkali metal salt and silicofluoric acid, the chemical equilibrium can be promoted in the direction in which the alkali metal silicofluoride is generated, so that a highly pure alkali metal silicofluoride can be produced.
請求項２記載の発明によれば、高純度で大きなアルカリ金属ケイフッ化物の結晶が得られるので、アルカリ金属ケイフッ化物を遠心ろ過機等のろ過機で反応液と分離する作業が円滑になり、工業的製法として有利になる。 According to the invention described in claim 2 , since a high purity and large alkali metal silicofluoride crystal can be obtained, the work of separating the alkali metal silicofluoride from the reaction solution with a filter such as a centrifugal filter becomes smooth. This is advantageous as a manufacturing method.
請求項３記載の発明によれば、アルカリ金属ケイフッ化物の結晶がより大きく成長し、高純度でより大きなアルカリ金属ケイフッ化物の結晶を得ることができるので、より有利である。 According to the third aspect of the present invention, the alkali metal silicofluoride crystal grows larger, and a larger alkali metal silicofluoride crystal can be obtained with higher purity, which is more advantageous.
以下、本発明を実施例によりさらに詳細に説明するが、本発明はこれらに限定されるものではない。 EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.
（実施例１）
（フッ化水素酸をケイフッ化水素酸にする）
表１に示す組成のシリコン洗浄廃液５００ｋｇを、２ｍ３のポリエチレン製反応器に計り採り、攪拌しながら、フッ化水素酸量のモル数の０．２４倍の二酸化ケイ素粉末２４．１ｋｇを投入し、二酸化ケイ素を溶解させてフッ化水素を完全にケイフッ化水素酸にし、過剰分の二酸化ケイ素をろ過機で分離した。
ろ過液を分析して確認したところ、フッ化水素酸の濃度は０．０１重量％以下で、ケイフッ化水素酸の濃度は、１６．３重量％であった。
Example 1
(Change hydrofluoric acid to silicohydrofluoric acid)
500 kg of silicon cleaning waste liquid having the composition shown in Table 1 was weighed into a 2 m 3 polyethylene reactor, and 24.1 kg of silicon dioxide powder 0.24 times the number of moles of hydrofluoric acid was added while stirring. Then, silicon dioxide was dissolved to completely convert hydrogen fluoride to silicofluoric acid, and excess silicon dioxide was separated by a filter.
When the filtrate was analyzed and confirmed, the concentration of hydrofluoric acid was 0.01% by weight or less, and the concentration of silicohydrofluoric acid was 16.3% by weight.
（ケイフッ化ナトリウムの製造）
（フッ化水素酸をケイフッ化水素酸にする）で得られたろ過液を攪拌しながら、７０℃に加熱した２０重量％硝酸ナトリウム溶液６００ｋｇ（ケイフッ化水素酸のモル数の２．４４倍）を５０分かけて滴下した。滴下終了後、２時間攪拌した。そのとき、反応熱も発生して、反応温度は４９℃になった。反応液を１日間放冷した。その後、結晶を遠心ろ過機で分離し、乾燥させて、ケイフッ化ナトリウム８３ｋｇを得た。
その分析結果は、純度９９．８重量％、平均粒子径（ｄ５０）が８７μｍであった。
また、ろ過液中の硝酸の濃度は、２０．５重量％で、ケイフッ化水素酸の濃度は１．８重量％であった。
(Manufacture of sodium fluorosilicate)
600 kg of a 20 wt% sodium nitrate solution heated to 70 ° C. while stirring the filtrate obtained from hydrofluoric acid (silicohydrofluoric acid) (2.44 times the number of moles of silicohydrofluoric acid) Was added dropwise over 50 minutes. It stirred for 2 hours after completion | finish of dripping. At that time, reaction heat was also generated and the reaction temperature reached 49 ° C. The reaction was allowed to cool for 1 day. Thereafter, the crystals were separated with a centrifugal filter and dried to obtain 83 kg of sodium silicofluoride.
As a result of the analysis, the purity was 99.8% by weight and the average particle size (d50) was 87 μm.
Further, the concentration of nitric acid in the filtrate was 20.5% by weight, and the concentration of hydrofluoric acid was 1.8% by weight.
（硝酸の製造）
（ケイフッ化ナトリウムの製造）で得られたケイフッ化ナトリウムを分離した後のろ過液を、０．５ｍ３のポリエチレン製反応器に２５０ｋｇ計り採り、水酸化アルミニウム７．３ｋｇを少しずつ投入した後、６時間攪拌した。
その液１００ｋｇをフッ素樹脂製の蒸留装置で蒸留し、５０〜１１０℃の間の留出液６５ｋｇを得た。
その留出液を分析したところ、硝酸濃度は２５．６重量％で、ケイフッ化水素酸の濃度は０．０５重量％以下であった。
(Production of nitric acid)
The filtrate after separating sodium silicofluoride obtained in (Production of sodium silicofluoride) was weighed 250 kg into a 0.5 m 3 polyethylene reactor, and 7.3 kg of aluminum hydroxide was added little by little. Stir for 6 hours.
100 kg of the liquid was distilled with a fluorine resin distillation apparatus to obtain 65 kg of a distillate between 50 and 110 ° C.
When the distillate was analyzed, the nitric acid concentration was 25.6% by weight and the concentration of silicofluoric acid was 0.05% by weight or less.
（実施例２）
（フッ化水素酸をケイフッ化水素酸にする）
表２に示す組成のシリコン洗浄廃液２００ｋｇを、１ｍ３のポリエチレン製反応器に計り採り、攪拌しながら、フッ化水素酸量のモル数の０．２２倍の二酸化ケイ素粉末６．７８ｋｇを投入し、二酸化ケイ素を溶解させてフッ化水素を完全にケイフッ化水素酸にし、過剰分の二酸化ケイ素をろ過機で分離した。
ろ過液を分析して確認したところ、フッ化水素酸の濃度は０．０１重量％以下で、ケイフッ化水素酸の濃度は、１３．４重量％であった。
(Example 2)
(Change hydrofluoric acid to silicohydrofluoric acid)
200 kg of silicon cleaning waste liquid having the composition shown in Table 2 was weighed into a 1 m 3 polyethylene reactor, and while stirring, 6.78 kg of silicon dioxide powder 0.22 times the number of moles of hydrofluoric acid was added. Then, silicon dioxide was dissolved to completely convert hydrogen fluoride to silicofluoric acid, and excess silicon dioxide was separated by a filter.
When the filtrate was analyzed and confirmed, the concentration of hydrofluoric acid was 0.01% by weight or less, and the concentration of silicohydrofluoric acid was 13.4% by weight.
（ケイフッ化カリウムの製造）
（フッ化水素酸をケイフッ化水素酸にする）で得られたろ過液１９０ｋｇを、本体が１ｍ３の鉄製で内面がポリプロピレンライニングされたジャケット付反応器に計り採り、反応器のジャケットに減圧蒸気を流して液温を４０℃に加熱した。次に、液を攪拌しながら、炭酸水素カリウムの粉末３９．４ｋｇ（ケイフッ化水素酸のモル数の２．２５倍）を炭酸ガスの発生を調整しながら、少しずつ添加した。添加終了後、２．５時間攪拌した。そのとき、反応熱も発生して、反応温度は６０℃になった。その後、反応液を１日間放冷した。そして、結晶を遠心ろ過機で分離した後、乾燥させて、ケイフッ化カリウム３５．５ｋｇを得た。
その分析結果は、純度９９．２重量％、平均粒子径（ｄ５０）が８３μｍであった。
また、ろ過液中のケイフッ化水素酸を分析したところ、その濃度は０．８０重量％であった。
(Manufacture of potassium silicofluoride)
The filtrate 190kg obtained in (Kay hydrofluoric acid to the hydrofluoric acid), body picking weighed into a jacketed reactor whose inner surface is a polypropylene lined with iron 1 m 3, reduced pressure steam to the reactor jacket And the liquid temperature was heated to 40 ° C. Next, while stirring the liquid, 39.4 kg of potassium hydrogen carbonate powder (2.25 times the number of moles of silicofluoric acid) was added little by little while adjusting the generation of carbon dioxide gas. After completion of the addition, the mixture was stirred for 2.5 hours. At that time, reaction heat was also generated, and the reaction temperature became 60 ° C. Thereafter, the reaction solution was allowed to cool for 1 day. And after isolate | separating a crystal | crystallization with a centrifugal filter, it was made to dry and the potassium silicofluoride 35.5kg was obtained.
As a result of the analysis, the purity was 99.2% by weight and the average particle size (d50) was 83 μm.
Moreover, when the silicohydrofluoric acid in a filtrate was analyzed, the density | concentration was 0.80 weight%.
（硝酸の製造）
（ケイフッ化カリウムの製造）で得られたケイフッ化カリウムを分離した後のろ過液を、０．５ｍ３のポリエチレン製反応器に１００ｋｇ計り採り、ホウ酸６．８ｋｇを少しずつ投入した後、６時間攪拌した。
その液１００ｋｇをフッ素樹脂製の蒸留装置で蒸留し、５０〜９５℃の間の留出液５９ｋｇを得た。
その留出液を分析したところ、硝酸濃度は１９．３重量％で、ケイフッ化水素酸の濃度は０．０５重量％以下であった。
(Production of nitric acid)
100 kg of the filtrate after separating potassium silicofluoride obtained in (Production of potassium silicofluoride) was weighed into a 0.5 m 3 polyethylene reactor, and 6.8 kg of boric acid was added little by little. Stir for hours.
100 kg of the liquid was distilled with a fluorine resin distillation apparatus to obtain 59 kg of a distillate between 50 and 95 ° C.
When the distillate was analyzed, the nitric acid concentration was 19.3% by weight and the concentration of silicofluoric acid was 0.05% by weight or less.
（実施例３）
（フッ化水素酸をケイフッ化水素酸にする）
表３に示す組成のシリコン洗浄廃液５００ｋｇを、２ｍ３のポリエチレン製反応器に計り採り、攪拌しながら、フッ化水素酸量のモル数の０．２７倍の二酸化ケイ素粉末６．０９ｋｇを投入し、二酸化ケイ素を溶解させてフッ化水素を完全にケイフッ化水素酸にした。
その液を分析して確認したところ、フッ化水素酸の濃度は０．０１重量％以下で、ケイフッ化水素酸の濃度は、８．４重量％であった。
(Example 3)
(Change hydrofluoric acid to silicohydrofluoric acid)
500 kg of silicon cleaning waste liquid having the composition shown in Table 3 was weighed into a 2 m 3 polyethylene reactor, and while stirring, 6.09 kg of silicon dioxide powder 0.27 times the number of moles of hydrofluoric acid was added. Then, silicon dioxide was dissolved to completely convert hydrogen fluoride into silicohydrofluoric acid.
When the liquid was analyzed and confirmed, the concentration of hydrofluoric acid was 0.01% by weight or less, and the concentration of silicohydrofluoric acid was 8.4% by weight.
（ケイフッ化ナトリウムの製造）
（フッ化水素酸をケイフッ化水素酸にする）で得られた液を攪拌しながら、実施例１の（ケイフッ化ナトリウムの製造）で得たケイフッ化ナトリウムを分離した液に水酸化ナトリウムを加えて調整した２０重量％硝酸ナトリウム溶液３３４ｋｇ（ケイフッ化水素酸のモル数の２．６５倍）を５０℃に加熱して、１．５時間かけて滴下した。滴下終了後、１．５時間攪拌をした。そのとき、反応熱も発生して、反応温度は６２℃になった。その後、反応液を１日間放冷した。そして、結晶を遠心ろ過機で分離し、乾燥させて、ケイフッ化ナトリウム５０．１ｋｇを得た。
その分析結果は、純度９９．７重量％、平均粒子径（ｄ５０）が１０４μｍであった。
また、ろ過液中の硝酸の濃度は、１８．１重量％で、ケイフッ化水素酸の濃度は０．６０重量％であった。
(Manufacture of sodium fluorosilicate)
While stirring the liquid obtained from (hydrofluoric acid is converted to silicohydrofluoric acid), sodium hydroxide was added to the liquid obtained by separating sodium silicofluoride obtained in Example 1 (production of sodium silicofluoride). 334 kg of a 20% by weight sodium nitrate solution prepared as described above (2.65 times the number of moles of hydrofluoric acid) was heated to 50 ° C. and added dropwise over 1.5 hours. After completion of dropping, the mixture was stirred for 1.5 hours. At that time, reaction heat was also generated, and the reaction temperature reached 62 ° C. Thereafter, the reaction solution was allowed to cool for 1 day. The crystals were separated with a centrifugal filter and dried to obtain 50.1 kg of sodium silicofluoride.
As a result of the analysis, the purity was 99.7% by weight and the average particle size (d50) was 104 μm.
The concentration of nitric acid in the filtrate was 18.1% by weight, and the concentration of silicofluoric acid was 0.60% by weight.
（硝酸の製造）
（ケイフッ化ナトリウムの製造）で得たケイフッ化ナトリウムを分離した後のろ過液を、０．５ｍ３のポリエチレン製反応器に２５０ｋｇ計り採り、硫酸アルミニウム水和物２６ｋｇを少しずつ投入した後、５時間攪拌した。
その液１００ｋｇをフッ素樹脂製の蒸留装置で蒸留し、５０〜８５℃の間の留出液６２ｋｇを得た。
その留出液を分析したところ、硝酸濃度は２４．６重量％で、ケイフッ化水素酸の濃度は０．０５重量％以下であった。
(Production of nitric acid)
The filtrate after separating sodium silicofluoride obtained in (Production of sodium silicofluoride) was weighed 250 kg into a 0.5 m 3 polyethylene reactor, and 26 kg of aluminum sulfate hydrate was added little by little. Stir for hours.
100 kg of the liquid was distilled with a fluorine resin distillation apparatus to obtain 62 kg of a distillate between 50 and 85 ° C.
When the distillate was analyzed, the nitric acid concentration was 24.6% by weight, and the concentration of silicofluoric acid was 0.05% by weight or less.
次に、上記実施例に対する比較例について、詳細に説明する。 Next, a comparative example with respect to the above embodiment will be described in detail.
（比較例１）
（フッ化水素酸をケイフッ化水素酸にする）
表４に示す組成のシリコン洗浄廃液５００ｋｇを、２ｍ３のポリエチレン製反応器に計り採り、攪拌しながら、フッ化水素酸量のモル数の０．１７倍の二酸化ケイ素粉末１４．６ｋｇを投入し、二酸化ケイ素を溶解させてフッ化水素をケイフッ化水素酸にした。
分析して確認したところ、フッ化水素酸の濃度は１．１重量％で、ケイフッ化水素酸の濃度は、１４．７重量％であった。
(Comparative Example 1)
(Change hydrofluoric acid to silicohydrofluoric acid)
500 kg of silicon cleaning waste liquid having the composition shown in Table 4 was weighed into a 2 m 3 polyethylene reactor, and 14.6 kg of silicon dioxide powder 0.17 times the number of moles of hydrofluoric acid was added while stirring. Then, silicon dioxide was dissolved to convert hydrogen fluoride into silicohydrofluoric acid.
As a result of analysis, the concentration of hydrofluoric acid was 1.1% by weight, and the concentration of silicohydrofluoric acid was 14.7% by weight.
（ケイフッ化ナトリウムの製造）
前記液を攪拌しながら、室温で２０重量％硝酸ナトリウム溶液６００ｋｇ（ケイフッ化水素酸のモル数の２．０倍）を５０分かけて滴下し、滴下終了後、２時間攪拌をした。そのとき、反応熱も発生したが、反応温度は３２℃にとどまった。その後、反応液を１日間放冷した。そして、実施例１のときの３倍の時間をかけて結晶を遠心ろ過機で分離し、乾燥させて、ケイフッ化ナトリウム６５ｋｇを得た。
その分析結果は、純度８４．４重量％、平均粒子径（ｄ５０）が１５μｍであった。
また、Ｘ線回折分析で調査したところ、ケイフッ化ナトリウムの他に、フッ化ナトリウム、酸性フッ化ナトリウムが含まれており、工業用薬品として要求される品位を大きく下回ることが判明した。
また、ろ過液中の硝酸の濃度は、１８．７重量％で、ケイフッ化水素酸の濃度は２．７重量％であった。
(Manufacture of sodium fluorosilicate)
While stirring the solution, 600 kg of a 20 wt% sodium nitrate solution (2.0 times the number of moles of silicofluoric acid) was added dropwise at room temperature over 50 minutes, and the mixture was stirred for 2 hours after completion of the addition. At that time, heat of reaction was also generated, but the reaction temperature remained at 32 ° C. Thereafter, the reaction solution was allowed to cool for 1 day. And the crystal | crystallization was isolate | separated with the centrifugal filter over 3 times the time in Example 1, and it was made to dry, and 65 kg of sodium silicofluoride was obtained.
As a result of the analysis, the purity was 84.4% by weight, and the average particle size (d50) was 15 μm.
Further, as a result of investigation by X-ray diffraction analysis, it has been found that sodium fluoride and sodium acid fluoride are contained in addition to sodium silicofluoride, which is far below the quality required for industrial chemicals.
Further, the concentration of nitric acid in the filtrate was 18.7% by weight and the concentration of silicofluoric acid was 2.7% by weight.
（硝酸の製造）
（ケイフッ化ナトリウムの製造）で得られたケイフッ化ナトリウムを分離した後のろ過液１００ｋｇを、フッ素樹脂製の蒸留装置で蒸留し、５０〜１１０℃の間の留出液７５ｋｇを得た。
その留出液を分析したところ、硝酸濃度は２１．６重量％で、ケイフッ化水素酸の濃度は３．５２重量％であった。また、フッ化水素が０．４重量％含まれていた。したがって、得られたものは工業薬品としては、低価値であることが判明した。
(Production of nitric acid)
100 kg of the filtrate after separating the sodium silicofluoride obtained in (Production of sodium silicofluoride) was distilled with a distillation apparatus made of a fluororesin to obtain 75 kg of a distillate between 50 and 110 ° C.
When the distillate was analyzed, the nitric acid concentration was 21.6% by weight and the concentration of silicofluoric acid was 3.52% by weight. Further, 0.4% by weight of hydrogen fluoride was contained. Therefore, it was found that the obtained product was low value as an industrial chemical.
Claims (3)
(a) 廃液に含まれるフッ化水素酸と酸化ケイ素化合物とを、酸化ケイ素化合物のケイ素のモル数がフッ化水素酸のモル数に対して０．１８〜０．３５倍で反応させ、ケイフッ化水素酸に変換する。
(b) (a)でケイフッ化水素酸に変換した後の廃液に、アルカリ金属塩をアルカリ金属塩に含まれるアルカリ金属のモル数がケイフッ化水素酸のモル数に対して２．０４〜３．４０倍で添加し、アルカリ金属ケイフッ化物を製造する。
(c) (b)によりアルカリ金属ケイフッ化物を製造した後、分離した液とアルミニウム化合物、または、ホウ素化合物とを反応させ、液に含まれるケイフッ化水素酸の構成元素であるフッ素を非揮発性のフルオロアルミン酸または高沸点性のホウフッ化水素酸に変換してから、蒸留法によって硝酸を製造する。 Producing high-purity alkali metal silicofluoride and nitric acid, which are valuable materials, by using the waste liquid of mixed acid of hydrofluoric acid and nitric acid after use as a raw material and processing in the order of the following (a) to (c) A method for producing alkali metal silicofluoride and nitric acid from waste liquid.
(a) The hydrofluoric acid and the silicon oxide compound contained in the waste liquid are reacted with each other so that the number of moles of silicon in the silicon oxide compound is 0.18 to 0.35 times the number of moles of hydrofluoric acid. Convert to hydrofluoric acid.
(b) In the waste liquid after being converted to silicohydrofluoric acid in (a), the number of moles of alkali metal contained in the alkali metal salt is 2.04 to 3 with respect to the number of moles of silicofluoric acid. It was added at .40 times, to produce the alkali metal silicofluoride.
(c) After producing the alkali metal silicofluoride according to (b), react the separated liquid with an aluminum compound or boron compound to make fluorine, which is a constituent element of silicohydrofluoric acid, contained in the liquid non-volatile Then, nitric acid is produced by a distillation method after conversion into fluoroaluminic acid or high-boiling borohydrofluoric acid.
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| CN105174269B (en) * | 2015-09-14 | 2017-07-28 | 福建省漳平市九鼎氟化工有限公司 | A kind of technique that potassium fluosilicate is reclaimed in potassium fluotitanate production process |
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