JP2005324164A - Method of separating and recovering acid from effluent mixed with multiple acids - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of separating and recovering acid from an effluent mixed with multiple acids capable of reaching a normal state for a short period of time from the starting of operation, keeping the operation state stable, recovering acetic acid at high recovery rate and purity, and having high throughput. <P>SOLUTION: The method of separating and recovering acid has an acetic acid extraction process and an acetic acid exfoliation process. In the acetic acid extraction process, acetic acid is selectively dissolved in an extraction solvent by mixing the effluent containing acetic acid, nitric acid or/and hydrofluoric acid with the extraction solvent containing 8-12C alcohol and acetate of 8-12C alcohol. In the acetic acid exfoliation process, acetic acid is dissolved and moved in exfoliation water to separate and recover acetic acid by making acetic acid containing extraction solvent obtained in the extraction process contact with the exfoliation water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for separating and recovering an acid from a waste liquid in which a plurality of acids discharged from, for example, a semiconductor manufacturing factory or the like are mixed so that the acid can be reused.

  In this specification, in the phrase “acetate ester of an alcohol having 8 to 12 carbon atoms”, “8 to 12 carbon atoms” is a modifier relating to “alcohol”, that is, the alcohol has 8 to 12 carbon atoms. It means that.

  In the semiconductor manufacturing industry, which has grown drastically in recent years, various wastewaters are produced in the manufacturing process, but they are discharged after being subjected to appropriate treatment according to the type and nature of each wastewater. For example, from the chemical etching process of silicon wafers, mixed acid waste liquids containing acetic acid, nitric acid, and hydrofluoric acid (hydrofluoric acid) come out. Each acid is separated and recovered from such mixed acid waste liquids for reuse. It is technically difficult to do this at present, and since this mixed acid waste liquid contains various metals such as Si, Al, and Fe by chemical etching, it cannot be reused as a mixed acid. Generally, the waste liquid is neutralized and drained.

  However, since salt such as acetate and nitrate is generated in the wastewater by the neutralization treatment, it is inevitable that it causes environmental pollution. This neutralization treatment is never a desirable means from the viewpoint of environmental conservation. I can't say that. In recent years, the importance of recycling has been screamed because of the demand for global environmental protection. However, the conventional method of neutralization discharges waste acid without recycling it at all. It was impossible to meet the social demands at all.

Under such circumstances, there has been proposed a method for separating and recovering acetic acid from a mixed acid waste solution in which acetic acid, nitric acid and / or hydrofluoric acid are mixed, using alcohol having 8 to 12 carbon atoms as an extractant (Patent Literature). 1).
JP 2002-126722 A (Claims 1, 2, 4)

  However, in the method for separating and recovering acetic acid described in Patent Document 1, since the acetic acid in the mixed acid waste liquid causes an esterification reaction with the alcohol in the extract liquid, the composition of the extract liquid gradually increases as the extraction operation proceeds. This changes the extraction and dissolution performance of the extractant into acetic acid, nitric acid, and hydrofluoric acid, so that the operation does not reach a steady state over time, and a stable extraction operation is performed. In addition to this, there was a problem that none of acetic acid recovery rate, recovered acetic acid purity and treatment capacity could be improved sufficiently.

  The present invention has been made in view of such a technical background, and reaches a steady state in a short time from the start of operation, stabilizes the operation state, and recovers acetic acid with a high recovery rate and high purity. An object of the present invention is to provide a method for separating and recovering acid from waste liquid in which a plurality of acids are mixed, and which has a high processing capacity.

  In order to achieve the above object, the present invention provides the following means.

  [1] A waste liquid containing acetic acid and nitric acid is mixed with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms. By bringing the acetic acid extraction step of selectively dissolving and extracting the acetic acid into contact with the acetic acid-containing extract obtained in the extraction step and the stripping water, the acetic acid is dissolved and transferred into the stripping water. A method for separating and recovering an acid from a waste liquid in which a plurality of acids are mixed, comprising an acetic acid stripping step for separating and recovering acetic acid.

  [2] By mixing a waste liquid containing acetic acid and hydrofluoric acid with an extract liquid containing an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms, The acetic acid is dissolved in the stripping water by bringing the acetic acid-extracting step in which the acetic acid is selectively dissolved into the water and the acetic acid-containing extract obtained in the extraction step into contact with the stripping water. And a method of separating and recovering acid from a waste liquid in which a plurality of acids are mixed.

  [3] By mixing a waste liquid containing acetic acid, nitric acid and hydrofluoric acid with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms, the extractant The acetic acid is dissolved in the stripping water by contacting the acetic acid-containing extract obtained in the extraction step with the acetic acid-containing extraction solution obtained by selectively dissolving the acetic acid in the solution and extracting the acetic acid. A method for separating and recovering an acid from a waste liquid in which a plurality of acids are mixed, the method including an acetic acid stripping step of separating and recovering acetic acid by moving it.

  [4] By mixing waste liquid containing acetic acid, nitric acid and hydrofluoric acid with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms, the extractant An acetic acid extraction step in which the acetic acid is selectively dissolved and extracted in the liquid, and an acetic acid-containing extract obtained in the acetic acid extraction step and the stripping water are brought into contact with each other, thereby bringing the acetic acid into the stripping water. The nitric acid is selectively contained in the normal phosphate ester by mixing the acetic acid stripping step of separating and recovering acetic acid by dissolving and transferring, the extraction residual liquid obtained in the acetic acid extraction step, and the normal phosphate ester. The nitric acid extraction step of dissolving and extracting, the nitric acid-containing normal phosphate obtained in the nitric acid extraction step, and the stripping water are brought into contact with each other, so that the nitric acid is dissolved and transferred to the stripping water to separate the nitric acid. Acid process for separating recovered from more acids are mixed waste, characterized in that it comprises a nitrate peeling step of.

  [5] Any one of items 1 to 4 above, wherein a mixing mass ratio in the extractant liquid is alcohol having 8 to 12 carbon atoms / acetic acid ester of alcohol having 8 to 12 carbon atoms = 80/20 to 20/80. A method for separating and recovering acid from a waste liquid in which a plurality of acids are mixed.

  [6] The mixing mass ratio in the extractant is any one of items 1 to 4 above, wherein alcohol having 8 to 12 carbon atoms / acetic acid ester of alcohol having 8 to 12 carbon atoms = 60/40 to 40/60. A method for separating and recovering acid from a waste liquid in which a plurality of acids are mixed.

  [7] The plurality of items 1 to 6, wherein 2-ethylhexanol is used as the alcohol having 8 to 12 carbon atoms, and 2-ethylhexyl acetate is used as an acetate ester of the alcohol having 8 to 12 carbon atoms. A method for separating and recovering acid from waste liquid mixed with acid.

  [8] Between the extraction step and the stripping step, a cleaning step of bringing the extract obtained in the extraction step into contact with a part of the acid aqueous solution separated and recovered in the stripping step is interposed, and the cleaning The plurality of acids according to any one of the preceding items 1 to 7 are mixed while supplying the extraction liquid washed in the step to the next peeling step, and supplying the cleaning residual liquid discharged in the washing step to the extraction step For separating and recovering acid from waste liquid.

  In the invention of [1], since an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms are used as the extractant solution, acetic acid is extracted with high selectivity from a mixed acid waste solution containing acetic acid and nitric acid. This allows the separation and recovery of acetic acid. In addition, since various metals such as Si, Al, and Fe are hardly extracted into the extractant solution, acetic acid with few metal impurities can be separated and recovered. In addition to alcohols having 8 to 12 carbon atoms as the extractant, acetic acid esters of alcohols having 8 to 12 carbon atoms are used in combination, so that a steady state can be reached in a short time from the start of operation and the extraction operation is stable. The acetic acid can be recovered with a high recovery rate and high purity, and the processing capacity can be improved.

  In the invention of [2], since an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms are used as the extractant solution, acetic acid is extracted with high selectivity from a mixed acid waste solution containing acetic acid and hydrofluoric acid. This makes it possible to separate and recover acetic acid. In addition, since various metals such as Si, Al, and Fe are hardly extracted into the extractant solution, acetic acid with few metal impurities can be separated and recovered. In addition to alcohols having 8 to 12 carbon atoms as the extractant, acetic acid esters of alcohols having 8 to 12 carbon atoms are used in combination, so that a steady state can be reached in a short time from the start of operation and the extraction operation is stable. The acetic acid can be recovered with a high recovery rate and high purity, and the processing capacity can be improved.

  In the invention of [3], an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms are used as the extractant solution, so that acetic acid is selectively selected from a mixed acid waste solution containing acetic acid, nitric acid and hydrofluoric acid. Extraction can be performed well, which enables separation and recovery of acetic acid. In addition, since various metals such as Si, Al, and Fe are hardly extracted into the extractant solution, acetic acid with few metal impurities can be separated and recovered. In addition to alcohols having 8 to 12 carbon atoms as the extractant, acetic acid esters of alcohols having 8 to 12 carbon atoms are used in combination, so that a steady state can be reached in a short time from the start of operation and the extraction operation is stable. The acetic acid can be recovered with a high recovery rate and high purity, and the processing capacity can be improved.

  In the invention of [4], an extract solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms and a normal phosphate ester are separately used as the extractant. Each acid can be separately separated and recovered from a mixed acid waste solution containing acetic acid, nitric acid and hydrofluoric acid. In addition, various metals such as Si, Al, Fe and the like are hardly extracted into an extractant solution and an orthophosphate ester containing the alcohol having 8 to 12 carbon atoms and the acetate ester of the alcohol having 8 to 12 carbon atoms. Therefore, acetic acid and nitric acid with less metal impurities can be separated and recovered. Furthermore, since acetic acid ester of C8-12 alcohol is used in combination with alcohol of C8-12 as the acetic acid extractant solution, it reaches a steady state in a short time from the start of operation, and the extraction operation Can be carried out stably, acetic acid can be recovered with a high recovery rate and high purity, and the processing capacity can be improved.

  In the invention of [5], acetic acid can be recovered with a higher recovery rate and higher purity.

  In the invention of [6], acetic acid can be recovered with a higher recovery rate and with a higher purity.

  In the invention of [7], there is an advantage that the time from the start of operation to the steady state can be further shortened.

  In the invention of [8], since the washing step is provided, the concentration of impurities (metal impurities, acids not extracted in the extraction step) in the extract obtained in the extraction step can be significantly reduced. There are advantages. Furthermore, by providing such a cleaning process, the same level of extraction concentration can be ensured even if the number of steps in each process (extraction process, peeling process) is reduced, so that the equipment space can be reduced and energy saving can be sufficiently achieved. be able to.

  An embodiment of a method for separating and recovering acid from waste liquid in which a plurality of acids are mixed according to the present invention will be described with reference to the flowchart of FIG. In the present embodiment, acetic acid is first separated and recovered from mixed acid wastewater containing acetic acid, nitric acid and hydrofluoric acid, then nitric acid is separated and recovered, and finally hydrofluoric acid is separated and recovered.

  The step of separating and recovering acetic acid includes an acetic acid extraction step, a washing step, and an acetic acid peeling step. First, in the acetic acid extraction step, an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms is supplied into the mixer tank, and acetic acid, nitric acid and hydrofluoric acid are added. The mixed acid wastewater containing is also supplied, stirred and mixed, and then transferred to a settler tank and allowed to stand, whereby two layers of an extraction liquid phase that is an oil phase and an extraction residual liquid phase that is an aqueous phase To separate. At this time, the extract solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms is excellent in extraction selectivity for acetic acid, but hardly extracts nitric acid and hydrofluoric acid. Therefore, acetic acid is selectively dissolved from the mixed acid wastewater into the extractant solution and extracted into the extract liquid phase which is an oil phase.

  In the next washing step, the extract (containing extracted acetic acid) is supplied into the washing tank, and a part of the acetic acid aqueous solution separated and recovered in the acetic acid peeling step described later is supplied and stirred. These are mixed and then transferred to a settler tank and allowed to stand to separate into two layers of an extraction liquid phase that is an oil phase and an aqueous phase. By performing such a washing operation (scrubbing operation), nitric acid or hydrofluoric acid (that is, an acid not to be extracted in this step) slightly extracted in the extraction liquid phase that is the oil phase is transferred into the aqueous phase. Therefore, the concentration of impurities in the extract (acids that are not extracted in this extraction step) can be significantly reduced. Furthermore, this cleaning operation can also reduce the concentration of metal impurities. In addition, the cleaning residual liquid (aqueous phase) which comes out of this cleaning process is supplied to the said acetic acid extraction process with mixed acid wastewater.

  In the next acetic acid peeling step, the extraction liquid (containing extracted acetic acid) washed in the washing step is supplied into the peeling tank, and also water for peeling is supplied and stirred to mix them. After crushing, move to a settler tank and leave to stand. Since the acetic acid is transferred to the aqueous phase by mixing, it is separated into two layers of an oil phase and an aqueous phase composed of an aqueous acetic acid solution. By collecting this aqueous phase, acetic acid can be separated and recovered. In the present embodiment, as described above, a part of the recovered acetic acid aqueous solution is sent to the washing step, that is, used as the aqueous phase of the washing step. The oil phase remaining in the acetic acid stripping step (extractant liquid containing alcohol having 8 to 12 carbon atoms and acetic acid ester of alcohol having 8 to 12 carbon atoms) is supplied to the acetic acid extracting step and extracted. Reuse as.

  In the acetic acid separation and recovery step, not only alcohol having 8 to 12 carbon atoms but also acetic acid ester of alcohol having 8 to 12 carbon atoms is used as the acetic acid extractant solution. The acetic acid can be recovered with a high recovery rate and high purity.

  Next, the process of separating and recovering nitric acid will be described. This step includes a nitric acid extraction step, a cleaning step, and a nitric acid stripping step. First, in the nitric acid extraction step, the normal phosphate ester as the extractant is supplied into the mixer tank and the extraction residual liquid (water in which nitric acid and hydrofluoric acid are dissolved) is supplied and stirred. After mixing these, they are transferred to a settler tank and allowed to stand to separate into two layers of an extraction liquid phase that is an oil phase and an extraction residual liquid phase that is an aqueous phase. At this time, normal phosphate ester is excellent in extraction selectivity to nitric acid, but hydrofluoric acid is also extracted to some extent. Therefore, normal phosphate ester extract solution in which nitric acid and hydrofluoric acid are dissolved in normal phosphate ester is an oil phase. Extracted into phase.

  In the next washing step, the extract (normal phosphate ester containing extracted nitric acid) is supplied into the washing tank, and a part of the nitric acid aqueous solution separated and recovered in the nitric acid stripping step described below is supplied and stirred. These are mixed together, and then transferred to a settler tank and allowed to stand to separate into two layers of an extraction liquid phase that is an oil phase and an aqueous phase. By performing such a washing operation, hydrofluoric acid that has been extracted in the extraction liquid phase that is the oil phase (that is, acid that is not subject to extraction in this step) can be transferred into the aqueous phase. The concentration of impurities (acids that are not extracted in this extraction step) can be significantly reduced. Furthermore, this cleaning operation can also reduce the concentration of metal impurities. In addition, the cleaning residual liquid (aqueous phase) output from the cleaning process is supplied to the nitric acid extraction process together with the extraction residual liquid (water in which nitric acid and hydrofluoric acid are dissolved) output in the acetic acid extraction process.

  In the next nitric acid stripping step, the extraction liquid (normal phosphoric acid ester containing extracted nitric acid) washed in the above-described washing step is supplied into the stripping tank, and stripping water is also supplied and stirred for these. After mixing, move to a settler tank and leave to stand. Since nitric acid is transferred to the aqueous phase by mixing, it is separated into two layers of an aqueous phase consisting of an oil phase and an aqueous nitric acid solution. By collecting this aqueous phase, nitric acid can be separated and recovered. In the present embodiment, as described above, a part of the recovered nitric acid is supplied to the cleaning step. Further, in this embodiment, a small amount of 98% nitric acid is supplied to the cleaning process, but this increases the concentration of nitric acid in the cleaning liquid in the cleaning process, so that the organic phase (oil phase) in the cleaning process has a higher concentration. It is supplied for the purpose of making the acid removal by washing more effective. In addition, the oil phase (normal phosphate ester) remaining in the nitric acid stripping step is supplied to the nitric acid extraction step and reused as an extractant.

  Next, a process for separating and recovering hydrofluoric acid will be described. This step includes a hydrofluoric acid extraction step and a hydrofluoric acid peeling step. First, in the hydrofluoric acid extraction step, the normal phosphate ester as the extractant is supplied into the mixer tank, and the extraction residual liquid (water in which the hydrofluoric acid is dissolved) from the nitric acid extraction step is supplied and stirred. After mixing these, they are transferred to a settler tank and allowed to stand to separate into two layers of an extraction liquid phase that is an oil phase and an extraction residual liquid phase that is an aqueous phase. At this time, hydrofluoric acid is extracted into the orthophosphate extraction liquid phase. The extraction residual liquid (aqueous phase) produced in this hydrofluoric acid extraction step is drained through a neutralization treatment, but since the acid component hardly remains in the extraction residual liquid, the salt component is not contained in the waste water. It hardly occurs, so it can fully meet the social demand for environmental protection.

  In the next hydrofluoric acid stripping step, the extract obtained in the hydrofluoric acid extraction step is supplied into the stripping tank and the water for stripping is also supplied. After stirring and mixing these, the settling tank is filled. Remove and leave. Since the hydrofluoric acid moves to the aqueous phase by mixing, it is separated into two layers of an aqueous phase consisting of an oil phase and an aqueous hydrofluoric acid solution. By collecting this aqueous phase, hydrofluoric acid can be separated and recovered. In addition, the oil phase (normal phosphoric acid ester) remaining in the hydrofluoric acid peeling process is supplied to the hydrofluoric acid extraction process and reused as an extractant.

  In this embodiment, the countercurrent multistage (extraction) method is adopted in any of the acetic acid extraction process, the nitric acid extraction process, the hydrofluoric acid extraction process, each cleaning process, the acetic acid stripping process, the nitric acid stripping process, and the hydrofluoric acid stripping process. Yes. This counter-current multistage (extraction) method will be described by taking an acetic acid extraction step as an example. As shown in FIG. 2, a plurality of extraction tanks (A)... Is a method of performing extraction in each extraction tank while counterflowing an alcohol solution of -12 alcohol and an alcohol ester of C8-12 alcohol), and the same method is adopted in other steps. doing. By adopting such a countercurrent multistage (extraction) method, a recovered acid having a higher extraction concentration and less impurities can be obtained.

  In the above-described embodiment, acetic acid, nitric acid, and hydrofluoric acid are sequentially collected. However, the order of application of the extractant to the mixed acid wastewater is changed (that is, the extraction operation with the normal phosphate ester is performed first), Although it is good also as what collect | recovers in order of nitric acid, an acetic acid, and a hydrofluoric acid, the extraction of acetic acid by the extractant solution containing the C8-12 alcohol and the C8-12 alcohol acetate is another acid. Since it is excellent in separability from (nitric acid and hydrofluoric acid), it is desirable to extract, separate and recover in the order as in this embodiment.

  The extract used in the present invention will be described. As the acetic acid extractant, an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetic acid ester of an alcohol having 8 to 12 carbon atoms is used. The alcohol having 8 to 12 carbon atoms may be, for example, a linear alcohol, a branched alcohol, or a primary alcohol, secondary alcohol, or tertiary alcohol, There is no particular limitation. Examples of acetic acid esters of alcohols having 8 to 12 carbon atoms include 2-ethylhexyl acetate (2-ethylhexanol acetate), decyl acetate (decanol acetate), and the like. Among them, it is preferable to use 2-ethylhexanol as the alcohol having 8 to 12 carbon atoms and 2 ethylhexyl acetate (acetic acid ester of alcohol having 8 carbon atoms) as the acetate ester of the alcohol having 8 to 12 carbon atoms. It should be noted that alcohols having less than 8 carbon atoms are water-soluble and cannot be extracted by two-phase separation of oil phase / water phase, and if the number of carbons exceeds 12, it is difficult to ensure a liquid state at room temperature. Therefore, it is not suitable as an extractant.

  The mixing mass ratio of the acetic acid in the extractant solution is preferably set in the range of alcohol having 8 to 12 carbon atoms / acetic acid ester of alcohol having 8 to 12 carbon atoms = 80/20 to 20/80. If it is set to such a range, acetic acid can be recovered with higher selectivity and higher yield and higher purity. Especially, it is more preferable to set in the range of C8-12 alcohol / acetate ester of C8-12 alcohol = 70 / 30-30 / 70 (mass ratio), and a particularly suitable range is C8. -12 alcohol / acetate ester of alcohol having 8 to 12 carbon atoms = 60/40 to 40/60 (mass ratio).

  In addition, you may add a C1-C40 primary to tertiary amine, a quaternary amine, a trialkyl phosphine oxide, etc. to the said acetic acid extractant liquid.

  The normal phosphate ester is phosphoric acid in which all protons in the chemical structure are lost by the esterification reaction, and is not particularly limited. For example, tri-n-butyl phosphate (TBP), -N-octyl phosphate (TOP) etc. are mentioned. Among these, as the normal phosphate ester, it is preferable to use a normal phosphate ester synthesized from an alcohol having 4 to 8 carbon atoms (esterified with an alcohol having 4 to 8 carbon atoms). The chemical structural formula of tri-n-butyl phosphate is shown below.

  Next, specific examples of the present invention will be described.

<Example 1>
Each acid was separately separated and recovered from the mixed acid waste solution containing acetic acid, nitric acid and hydrofluoric acid according to the separation and recovery method of the embodiment exemplified in the previous section (see FIG. 1). The mixed acid waste liquid used in this example is a mixed acid waste liquid generated in the chemical etching process of the silicon wafer, and is waste water having a composition (acid composition, metal impurity composition) as shown in Table 1. Detailed conditions such as the flow rate at each location, the number of stages in each step, and the phase ratio are shown in FIG. Note that 2-ethylhexanol / 2-ethylhexyl acetate = 43/57 (mass ratio) was used as the acetic acid extractant solution, and tri-n-butyl phosphate (TBP) was used as the normal phosphate ester. The phase ratio is the ratio of the oil phase flow rate to the water phase flow rate (oil phase flow rate / water phase flow rate).

  The results of separation and recovery of each acid are shown in Table 1. As is clear from Table 1, all of acetic acid, nitric acid, and hydrofluoric acid are separated and recovered at a high concentration, and in each of the recovered acids, there are very few metal impurities such as Si, Al, Fe, etc. A level of recovered acid was obtained that could be reused.

<Examples 2 to 10, Comparative Example 1>
Each acid was separately separated and recovered from the mixed acid waste liquid containing acetic acid, nitric acid and hydrofluoric acid in the same manner as in Example 1 except that the acetic acid extractant having the composition ratio shown in Table 2 was used.

<Example 11>
Separately recover each acid from the mixed acid waste solution containing acetic acid, nitric acid and hydrofluoric acid in the same manner as in Example 1 except that decanol / decyl acetate = 50/50 (mass ratio) was used as the acetic acid extractant solution. did.

  As is apparent from Table 2, in Examples 2 to 11, the steady state was reached in a short time from the start of operation, and acetic acid could be recovered with a high recovery rate and high purity.

  On the other hand, in Comparative Example 1 in which an alcohol having 8 to 12 carbon atoms was used alone as an acetic acid extractant, not only did it reach a steady state no matter how many hours passed from the start of operation, and the purity of recovered acetic acid was also low. . That is, in Comparative Example 1, since the amount of hydrofluoric acid dissolved in the extractant is large, the hydrofluoric acid leaks to the acetic acid peeling step without being completely washed in the washing step, thereby returning the washing back. Since the hydrofluoric acid concentration in the aqueous phase gradually increases and the hydrofluoric acid returns to the acetic acid extraction step, the hydrofluoric acid concentration in the acetic acid extraction step and the washing step gradually increases with time. For this reason, normal steady operation could not be performed in about 12 hours from the start of operation (the system was not stable at all).

It is a flowchart which shows the separation-and-recovery process of the acid from mixed acid wastewater. It is explanatory drawing of a countercurrent multistage (extraction) method.

Explanation of symbols

  A ... Extraction tank

Claims (8)

By mixing a waste liquid containing acetic acid and nitric acid with an extract liquid containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms, the acetic acid is mixed into the extract liquid. An acetic acid extraction step of selectively dissolving and extracting;
An acetic acid stripping step of separating and recovering acetic acid by dissolving and transferring the acetic acid in the stripping water by bringing the acetic acid-containing extract solution obtained in the extraction step into contact with the stripping water. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed. By mixing a waste liquid containing acetic acid and hydrofluoric acid with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms, the acetic acid is mixed into the extractant liquid. Acetic acid extraction step of selectively dissolving and extracting
An acetic acid stripping step of separating and recovering acetic acid by dissolving and transferring the acetic acid in the stripping water by bringing the acetic acid-containing extract solution obtained in the extraction step into contact with the stripping water. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed. A waste liquid containing acetic acid, nitric acid and hydrofluoric acid is mixed with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms. Acetic acid extraction step of selectively dissolving and extracting the acetic acid;
An acetic acid stripping step of separating and recovering acetic acid by dissolving and transferring the acetic acid in the stripping water by bringing the acetic acid-containing extract solution obtained in the extraction step into contact with the stripping water. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed. A waste liquid containing acetic acid, nitric acid and hydrofluoric acid is mixed with an extractant solution containing an alcohol having 8 to 12 carbon atoms and an acetate ester of an alcohol having 8 to 12 carbon atoms. Acetic acid extraction step of selectively dissolving and extracting the acetic acid;
An acetic acid peeling step of separating and recovering acetic acid by dissolving and moving the acetic acid in the peeling water by bringing the acetic acid-containing extractant obtained in the acetic acid extraction step into contact with the peeling water;
A nitric acid extraction step of selectively extracting and dissolving the nitric acid in the normal phosphate ester by mixing the extraction residue obtained in the acetic acid extraction step and the normal phosphate ester;
A nitric acid stripping step of separating and recovering nitric acid by bringing the nitric acid-containing orthophosphate obtained in the nitric acid extraction step into contact with stripping water to dissolve and move the nitric acid into the stripping water. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed.   5. The mixing mass ratio in the extractant liquid is alcohol having 8 to 12 carbon atoms / acetic acid ester of alcohol having 8 to 12 carbon atoms = 80/20 to 20/80. 5. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed.   5. The mixing mass ratio in the extractant liquid is alcohol having 8 to 12 carbon atoms / acetic acid ester of alcohol having 8 to 12 carbon atoms = 60/40 to 40/60. 5. A method for separating and recovering acid from waste liquid in which a plurality of acids are mixed.   The plurality of acids according to any one of claims 1 to 6, wherein 2-ethylhexanol is used as the alcohol having 8 to 12 carbon atoms, and 2-ethylhexyl acetate is used as an acetate ester of the alcohol having 8 to 12 carbon atoms. Method for separating and recovering acid from mixed waste liquid.   Between the extraction step and the peeling step, there is interposed a washing step for bringing the extract obtained in the extraction step into contact with a part of the acid aqueous solution separated and recovered in the peeling step, and washing in the washing step. A plurality of acids according to any one of claims 1 to 7, wherein the extracted extract is supplied to the next stripping process, and the cleaning residual liquid discharged in the cleaning process is supplied to the extraction process. A method for separating and recovering acid from waste liquid.

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