JP2018158325A - Method for treating liquid to be treated and method for recovering silver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing the treatment cost of the liquid to be treated, and a method for improving the recovery rate of silver .SOLUTION: The present invention provides a method for treating an alkaline liquid to be treated, containing silver, hydrogen peroxide, and a chelating agent which is at least one of EDTA and DTPA, the method comprising: a sulfide adding step of adding a sulfide to the liquid to be treated, a heating step of heating the liquid to be treated to which the sulfide has been added, to remove hydrogen peroxide, a chelating agent adding step of adding a piperazine type chelating agent to the liquid to be treated from which hydrogen peroxide has been removed, a solid-liquid separation step of recovering a silver-containing substance as a solid by subjecting the liquid to be treated to solid-liquid separation after the chelating agent adding step, a neutralizing step of adding an acid to the liquid generated in the solid-liquid separation step to neutralize it, an evaporation concentration step of evaporating and concentrating the neutralized liquid, and a condensed water treatment step of removing formaldehyde contained in the condensed water generated by the evaporation condensation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a treatment method for a liquid to be treated and a silver recovery method.

  When an electronic / electrical circuit board is manufactured, waste liquid containing hydrogen peroxide and various metal elements is generated along with the etching. There is a known problem that hydrogen peroxide bumps when processing such waste liquid. In order to cope with this problem, for example, Patent Document 1 and Patent Document 2 propose a hydrogen peroxide decomposition method using activated carbon or a platinum group element as a catalyst. In addition, Patent Document 3 proposes a method for decomposing hydrogen peroxide by combining pH adjustment and temperature control.

JP 2003-266081 A JP 2012-061455 A JP 2012-55825 A

In the manufacturing process of metal-ceramic bonding substrates used for power modules, etc. among electronic / electrical circuit boards, as a result of using a stripping solution and a cleaning solution, several tens of g / L of hydrogen peroxide, ammonia, and stabilization of the solution For this reason, an alkaline waste liquid containing a metal element such as a chelating agent and copper or silver may be generated.
Regarding the above alkaline waste liquid, hydrogen peroxide is unstable under alkaline conditions and promotes self-decomposition. Therefore, it is possible to remove hydrogen peroxide from the waste liquid by heating the waste liquid and causing the hydrogen peroxide to self-decompose.

As a technique for recovering silver as a valuable resource, for example, a technique of adding hydrochloric acid to the above-mentioned waste liquid and fixing silver in the waste liquid as silver chloride precipitates can be mentioned. As used herein, “immobilization” refers to “precipitation as a silver-containing material”. In addition, when describing a metal element such as “silver”, it includes metal silver and silver ions, but may be referred to as silver ions for the sake of clarity. After fixing the silver, it seems to be sufficient to heat and remove the hydrogen peroxide by self-decomposition.
However, in this method, hydrochloric acid is added to an alkaline waste liquid containing undecomposed hydrogen peroxide, and there is a possibility that severe bumping may occur as the liquid temperature rises due to heat of neutralization and rapid decomposition of hydrogen peroxide. . In addition, when hydrochloric acid is used, a material having corrosion resistance against hydrochloric acid must be used as a material for equipment and facilities related to waste liquid treatment, which increases costs.

  In addition, there is a method of forming an insoluble silver complex with a piperazine chelating agent instead of adding hydrochloric acid to the above waste liquid, but in this case, there is a problem to be improved from the viewpoint of recovery rate of silver from the waste liquid. is there.

  An object of the present invention is to provide a technique for suppressing the processing cost of a liquid to be processed. Another problem is to provide a method for improving the silver recovery rate.

In order to solve the above-mentioned problems, the present inventor has conducted intensive research. Before hydrogen peroxide decomposes and generates heat, first, silver is almost fixed with sulfide to prevent the influence of hydrogen peroxide, and then the waste liquid (liquid to be treated in a broad sense) is heated. As a result, the inventors have come up with a technique of self-decomposing hydrogen peroxide and removing it from the waste liquid.
Furthermore, the piperazine-based chelating agent that did not sufficiently exhibit the effect of silver fixation before the self-decomposition of hydrogen peroxide was used after removing hydrogen peroxide by the above method to recover the remaining silver. I came up with the method.
The aspects of the present invention made based on this finding are as follows.

The first aspect of the present invention is:
A method for treating an alkaline liquid to be treated containing silver, hydrogen peroxide, and a chelating agent that is at least one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA),
A sulfide addition step of adding sulfide to the liquid to be treated;
A heating step of heating the liquid to which the sulfide is added to remove hydrogen peroxide;
A chelating agent addition step of adding a piperazine chelating agent to the liquid to be treated from which hydrogen peroxide has been removed;
A method for treating a liquid to be treated.

According to a second aspect of the present invention, in the invention according to the first aspect,
After the chelating agent addition step, it further has a solid-liquid separation step of recovering a silver-containing material that is a solid by subjecting the liquid to be treated to solid-liquid separation.

According to a third aspect of the present invention, in the invention according to the second aspect,
It further has a neutralization step of neutralizing the liquid generated in the solid-liquid separation step by adding an acid.

According to a fourth aspect of the present invention, in the invention according to the third aspect,
It further has an evaporation concentration step of evaporating and concentrating the liquid neutralized in the neutralization step.

According to a fifth aspect of the present invention, in the invention described in the fourth aspect,
It further has a condensed water treatment step of removing formaldehyde contained in the condensed water generated by the evaporation concentration in the evaporation concentration step.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects,
Before the heating step, the method further includes a dilution step of diluting the liquid to be processed until the concentration of hydrogen peroxide in the liquid to be processed becomes 20 g / L or less.

According to a seventh aspect of the present invention, in the invention according to the sixth aspect,
A solid-liquid separation step of recovering a silver-containing material that is a solid by solid-liquid separation of the liquid to be treated after the chelating agent addition step;
A part of the liquid generated in the solid-liquid separation process is used as the dilution liquid in the dilution process.

According to an eighth aspect of the present invention, in the invention according to any one of the first to seventh aspects,
The liquid to be treated is a waste liquid in the production of a metal / ceramic bonding substrate.

According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects,
The sulfide is at least one of potassium sulfide, zinc sulfide, and copper sulfide.

The tenth aspect of the present invention provides
A method for recovering silver from an alkaline liquid containing silver, hydrogen peroxide, and a chelating agent that is at least one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA),
A sulfide addition step of adding sulfide to the liquid to be treated;
A heating step of heating the liquid to which the sulfide is added to remove hydrogen peroxide;
A chelating agent addition step of adding a piperazine chelating agent to the liquid to be treated from which hydrogen peroxide has been removed;
After the chelating agent addition step, the solid-liquid separation step of recovering the silver-containing material that is a solid by solid-liquid separation of the liquid to be treated;
A silver recovery process for recovering silver from the silver-containing material;
A method for recovering silver.

  According to the present invention, it is possible to reduce the processing cost of the liquid to be processed. In addition, the silver recovery rate can be improved.

It is a flowchart which shows the processing method of the to-be-processed liquid of this embodiment, and the collection | recovery method of silver. In a present Example, it is a figure which shows the relationship with the silver fixation rate at the time of fixing silver with each conditions and each reagent as a bar graph. In a present Example, it is a figure which shows the relationship between the decomposition time of hydrogen peroxide, and the temperature of B liquid as a bar graph. In a present Example, it is a figure which shows the relationship between a hydrogen peroxide concentration and a temperature change when the liquid temperature setting of an apparatus is 40 degreeC. (1) indicates the concentration of hydrogen peroxide solution (mg / L: right side), and (0) indicates the temperature of the B liquid (° C .: left side). In a present Example, it is a figure which shows the result of having performed the biological treatment (aerobic treatment) by the method described in the present Example with respect to the condensed water.

In the present embodiment, description will be given in the following order, and description will be made with reference to FIG. 1 which is a flowchart.
1. 1. Sulfide addition process 2. Dilution process Warming process 4. 4. Chelating agent addition process Solid-liquid separation process (silver recovery method)
6). Neutralization process 7. Evaporation and concentration step 8. Condensed water treatment process In addition, "-" in this specification points out more than a predetermined numerical value and below a predetermined numerical value.
In addition, as a liquid to be treated used in this embodiment, a waste liquid at the time of producing a metal-ceramic bonding substrate is given as a specific example, and as its composition, silver, hydrogen peroxide, ethylenediaminetetraacetic acid (EDTA) and There is no particular limitation as long as it is an alkaline solution containing a chelating agent that is at least one of diethylenetriaminepentaacetic acid (DTPA), and if it contains these, it does not have to be a waste liquid.

(1. Sulfide addition process)
In the sulfide addition step, sulfide is added to the waste liquid. By adding sulfide, the silver in the waste liquid is fixed to silver sulfide. In addition, the solubility product of the silver precipitation by sulfide is a hardly soluble precipitate _{(KSP (Ag2S)} = 6.3 × 10 ⁻⁵⁰ ), and re-dissolution hardly occurs even after the heating step described later in the present embodiment. .

Any known sulfide may be used as the sulfide, but it is preferable to use a compound having a solubility product larger than that of silver, and examples thereof include zinc sulfide and copper sulfide. Other examples include potassium sulfide. Specific compound names include metal sulfides such as FeS, Fe ₂ S ₃ , K ₂ S, Na ₂ S, MnS, and PbS and compounds containing them. The amount added is not particularly limited, but is preferably equal to or greater than the amount of silver in the waste liquid.

Of the sulfides, zinc sulfide and copper sulfide are preferable. The reason is as follows.
The waste liquid that is the liquid to be treated according to the present embodiment contains silver, hydrogen peroxide, and at least one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). As mentioned earlier, EDTA and DTPA are contained in the waste solution to stabilize the solution (to coordinate EDTA and DTPA to silver ions so that silver is not highly active). is there. When zinc sulfide or copper sulfide is added to the alkaline waste liquid in this state, zinc sulfide or copper sulfide is ionized into zinc ions, copper ions, or sulfide ions as shown in the following reaction formula.
ZnS → Zn ²⁺ + S ²⁻
CuS → Cu ²⁺ + S ²⁻
The sulfide ions (S ²⁻ ) are combined with silver ions in the waste liquid to produce silver sulfide, thereby fixing silver. On the other hand, zinc ions and copper ions quickly become stable chelate complexes with respect to EDTA and DTPA. For example, the complex formation constant of the complex of EDTA and silver is 7.32 while the complex formation constant of the complex of EDTA and zinc is 16.50, and the complex of EDTA and zinc is more stable ( Source: “Point Analytical Chemistry Exercise”, page 264, Author: Takuji Kawabe et al., Publication: Yodogawa Shoten). DTPA having a carbon skeleton similar to EDTA is also considered to have a complex formation constant comparable to that of zinc, and copper ions can easily form complexes with EDTA and DTPA, and the complexes are stable. .
That is, the zinc ions and copper ions on the right side in the above reaction formula decrease due to complexation with EDTA and DTPA. Then, the reaction in the above reaction formula is further biased to the right side, and zinc sulfide and copper sulfide can be sufficiently ionized. As a result, silver can be sufficiently changed to silver sulfide to sufficiently fix silver. It becomes. Based on this finding, any sulfide other than zinc sulfide or copper sulfide that can quickly form a stable complex with EDTA or DTPA can be used in the sulfide addition process. There is no.

(2. Dilution process)
In the dilution step, the liquid to be treated is diluted with a liquid having a low hydrogen peroxide content. By performing the dilution step, foaming can be reduced when hydrogen peroxide is self-decomposed in the heating step described below.

The dilution step may be performed before the heating step described below, or may be performed before the previous sulfide addition step.
Moreover, it is preferable to dilute until the concentration of hydrogen peroxide is 30 g / L or less, further 20 g / L or less in the dilution step. The dilution liquid used in the dilution step is the following heating step to solid-liquid separation step. It is preferable to use a liquid (for example, a filtrate) after passing through the process because it reduces the amount of waste liquid treated in an industrial process and enables processing at low cost.

(3. Heating process)
In the heating step, the liquid to be treated to which sulfide is added is heated to remove hydrogen peroxide. There are no particular limitations on the specific method and apparatus configuration for heating, but it is desirable to perform heating in the range of 30 to 40 ° C. in consideration of the time required for decomposition and safety.

(4. Chelating agent addition process)
In the chelating agent addition step, a piperazine-based chelating agent is added to the liquid to be treated from which hydrogen peroxide has been removed. By adding a piperazine chelating agent, it is possible to fix silver (ions) remaining in the waste liquid.
In addition, there is also an effect that the particles of silver fixed in the waste liquid (that is, silver sulfide) are coarsened. If the particles are coarsened, it becomes easier to leave silver sulfide (silver-containing material) on the filter paper as a solid (filtered material) in the subsequent solid-liquid separation (for example, filtration) step, thereby efficiently removing the silver-containing material. It can be recovered, and finally the silver recovery rate can be improved.
As piperazine-based chelating agents, those known (piperazine and derivatives thereof, such as TS-300, TX-30, main component dipotassium = piperazine-1,4bis (carbodithioate) manufactured by Tosoh, etc.), etc. Use it. The amount added is not particularly limited, but is preferably equal to or greater than the amount of silver in the waste liquid.

In this embodiment, a major feature is that a sulfide is added to the waste liquid to fix silver, and furthermore, a piperazine-based chelating agent capable of further fixing silver is added through a heating step. is there.
If the piperazine-based chelating agent is added to the waste liquid instead of sulfide before the heating step, only about 70% of the silver in the waste liquid can be fixed in the items of the examples described later. (Bar graph of i in FIG. 2). This is presumably because the piperazine-based chelating agent has been oxidatively decomposed due to the influence of hydrogen peroxide.
Therefore, the chelating agent addition step is performed after removing hydrogen peroxide from the waste liquid by the heating step. Then, in order to remove hydrogen peroxide safely from the waste liquid and reduce the processing cost, a sulfide that can also immobilize silver is added. In other words, a series of flow of immobilizing most silver by adding sulfide (silver fixing agent) → heating → immobilizing remaining silver by adding piperazine chelating agent (silver fixing agent) It was created because of the knowledge of ensuring the safety, reducing the processing cost of the liquid to be treated, and, in other words, improving the silver recovery rate. Therefore, the treatment method of the liquid to be treated in this embodiment has a great feature in the combination of the sulfide addition step, the heating step, and the chelating agent addition step. On the other hand, the above-described dilution step and the following steps are performed as preferred examples.

(5. Solid-liquid separation step (silver recovery method))
In the solid-liquid separation step, the silver-containing material which is a solid is recovered by solid-liquid separation of the liquid to be treated after the chelating agent addition step. Solid-liquid separation is performed by, for example, filtration. There is no limitation in particular as a specific method and apparatus structure for performing filtration. When carrying out the silver recovery method, metallic silver is further recovered from the recovered silver-containing material (silver sulfide). The specific method may be a known one. This is a silver recovery method (manufacturing method) including the recovery of metal silver, and reflects the technical idea of the present invention described so far.

(6. Neutralization process)
In the neutralization step, an acid is added to neutralize the liquid (eg, filtrate) generated in the solid-liquid separation step (eg, filtration step). The acid added here may be any known acid, for example, sulfuric acid. In addition, the pH at the time of neutralization may be a pH that makes the alkalinity neutral or acidic. For example, the pH is less than 7 (preferably 4.8 or less) as shown in the item of Examples below. In this case, by changing ammonia to ammonium sulfate (ammonium sulfate) (when ammonia is used as an alkali), in the condensed water to be treated in the following condensed water treatment process, ammonia that is a wastewater control substance The content of can be significantly reduced.

(7. Evaporation and concentration step)
In the evaporation concentration step, the neutralized liquid (for example, filtrate) is evaporated and concentrated to remove formaldehyde contained in the condensed water generated by evaporation. By the way, this formaldehyde is presumed to be produced by oxidative decomposition of the side chain of EDTA or DTPA when hydrogen peroxide is autolyzed. Formaldehyde is a wastewater control substance and should be removed before discharge. In recent years, an evaporation concentrator using a heat pump has been developed, and this embodiment can be performed at a relatively low cost.
In addition, what is necessary is just to process the concentrate remaining by evaporation concentration by arbitrary well-known methods, for example, you may process as industrial waste.

(8. Condensate treatment process)
Any known method may be adopted as a method for removing formaldehyde. For example, an aerobic process, an anaerobic process, RO membrane process etc. are mentioned. If it is aerobic treatment, good treated water can be obtained and it is resistant to environmental changes. In addition, anaerobic treatment consumes less power and produces less excess sludge than aerobic treatment.

  Through the above steps, it is possible to reduce the processing cost of the liquid to be processed during the processing of the waste liquid. In addition, the silver recovery rate can be improved.

  The technical scope of the present invention is not limited to the above-described embodiments, and various modifications and improvements may be added within the scope of deriving specific effects obtained by the constituent requirements of the invention and combinations thereof. Including. For example, combinations of the above-described modifications and combinations with the contents exemplified in the above-described embodiments are also within the scope of the technical idea of the present invention.

  Next, an Example is shown and this invention is demonstrated concretely. The present invention is not limited to the following examples.

[Test conditions]
(Waste liquid composition)
In order to reproduce the waste liquid in the production of the metal-ceramic bonding substrate, the simulation liquid was adjusted so as to have the same composition as the stripping liquid after use. Two types of EDTA type and DTPA type were used for the adjusted simulation liquids, respectively. The composition of the simulated liquid is shown in Table 1.

Adjustment of the EDTA-based simulation solution was performed as follows.
Dissolve 0.79 g of silver nitrate (WAKO Junyaku Kogyo), 25.5 g of EDTA · 2Na · 2H ₂ O (DOJINDO), 2.7 g of copper (II) chloride dihydrate (WAKO Junyaku Kogyo) in 500 mL of distilled water. did. Next, 93 mL of 28% ammonia water (WAKO Pure Chemical Industries) and 182 mL of 30% hydrogen peroxide water (WAKO Pure Chemical Industries) were sequentially added, and distilled water was added to quantitate the solution to 1 L.

Adjustment of the DTPA-based simulation solution was performed as follows.
0.11 g of silver nitrate and 20 g of DTPA (Tokyo Kasei) were dissolved in 500 mL of distilled water. Next, after adding 182 ml of 30% hydrogen peroxide solution, distilled water was added and quantified to 1L.

(Analysis equipment)
In this embodiment, the silver fixation rate (%) is calculated as shown in FIG. The silver immobilization ratio was obtained by subtracting from 1 the ratio of the amount of silver (ion) contained in the filtrate produced in the above solid-liquid separation (filtration) step to the amount of silver (ion) contained in the simulated solution. It is a value obtained by multiplying 100 by one.
A HITACHI SII-5100 inductively coupled plasma-atomic emission spectrometer (ICP-AES) was used for analysis of the silver (ion) concentration in the filtrate.
A Kyoritsu Digital Pack test was used for the determination of hydrogen peroxide and formaldehyde. The precise analysis of formaldehyde was performed by acetylacetone absorptiometry after obtaining condensed water by evaporation and concentration.

(Acclimation of microorganisms)
In the removal of formaldehyde contained in the condensed water, the following method was adopted while adopting an aerobic treatment. The pH of the condensed water was adjusted in advance to be in the range of 6-7.
Seed sludge collected from DOWA High-Tech Co., Ltd. was added to a 5 mm square sponge as a biological carrier added to about 20% by volume with respect to water. Furthermore, trace metals, ammonia and ethanol were added and conditioned for about 2 weeks at room temperature.

(Treatment method of liquid to be treated)
2 mL of 200 mg / mL zinc sulfide (WAKO Pure Chemical Industries) slurry was added to 500 mL of the mixture of the two types of EDTA-based and DTPA-based simulated solutions prepared as described above at a volume ratio of 2: 1 (sulfurized). Product addition step). The liquid to which this slurry is added is called A liquid.

  Next, 500 mL of liquid A was collected, and 1 L of water was added to dilute it 3 times. This liquid is called B liquid.

  Thereafter, the solution B was poured into a 5 L beaker and stirred while warming in a hot water bath (heating step). The stirring blade was a two-stage turbine blade and the rotation speed was 200 rpm.

  After confirming that the residual hydrogen peroxide concentration in solution B was 100 mg / L or less, 2 mL / L for solution A (2/3 for solution B obtained by diluting solution A three times) Piperazine chelating agent (Tosoh, TS-300) was added so as to be 0.67 mL / L) (chelating agent addition step).

  Stirring was continued within 15 minutes after the addition of the piperazine chelating agent to form an insoluble complex. Next, 1 mL of 2000 mg / L anionic polymer flocculant was added to form a floc. Thereafter, pressure filtration was performed to separate the liquid phase and the solid phase (filtration step). Specifically, the liquid B was pressurized in the range of 0.2 to 0.35 MPa and filtered with a filter having a pore diameter of 3 μm. 500 mL of the filtrate was subjected to the next neutralization step. The remainder of the filtrate was used as a diluting solution used when diluting solution A in a diluting step in another cycle in various verification tests described later.

  Next, 500 mL of the filtrate was neutralized with 98% sulfuric acid so as to have a pH of 4.8 (neutralization step). The amount of sulfuric acid required for neutralization was 10 g.

  Next, the neutralized liquid was set to a reduced pressure condition of 69 ° C. and 210 hPa with an evaporation concentrator (Tokyo Rika Kikai NVC-2000), and separated into a condensate produced by evaporation and a remaining concentrate (evaporation). Concentration step). The concentration rate was set at 10 times while confirming that there was no precipitate. Then, in order to decompose formaldehyde contained in the condensed water, after adding nutrients and phosphoric acid to the condensed water, the pH is adjusted to about 7 with dilute caustic (diluted caustic soda solution), and the biological carrier is 20 volumes of the total liquid volume. %, And the treatment was performed while aeration was performed so that DO (dissolved oxygen amount) was 9 mg / L (condensed water treatment step). The treatment was performed at room temperature and the liquid temperature was 21 ° C.

[Results of this example]
According to this example, there was no bumping or liquid spillage due to hydrogen peroxide without using a substance such as hydrochloric acid that would increase the equipment cost, and safety during work could be ensured. Further, as shown in FIG. 2 described later, silver could be recovered with a high yield of 99% or more.

[Various verification results]
Although the effect of this example was shown, various tests supporting the above effect were also conducted. Hereinafter, various verification results will be described. In the following, items not specifically mentioned are the same as those described in this embodiment.

(Technical significance of the sulfide addition process and chelating agent addition process)
FIG. 2 is a bar graph showing the relationship between the silver immobilization ratio when silver was immobilized with each condition and each reagent with respect to B liquid obtained by diluting A liquid three times. The following conditions and reagents are shown from the left of the bar graph.
i) Add piperazine chelating agent (TS-300) to B solution before heating process
ii) Add zinc sulfide to B liquid before heating process
iii) Heating process performed for ii)
iv) Example above (sulfide addition step → heating step → chelating agent addition step)
As described in the present embodiment, in i), the piperazine-based chelating agent is affected by the oxidative decomposition by hydrogen peroxide before the heating step for removing hydrogen peroxide, and the effect of silver fixation is sufficiently obtained. I don't play.
On the other hand, in ii), in the case of zinc sulfide which is a sulfide, 97% or more of silver was fixed in the B liquid before the heating step.
In iii), 98% or more of silver was recovered without dissolving silver sulfide even after the heating step for removing hydrogen peroxide.
In iv), silver was recovered with a high yield of 99% or more by adding a piperazine chelating agent after the heating step after adding zinc sulfide.
As a result, a series of flows in which most of silver is fixed by adding sulfide (silver fixing agent) → heating → remaining silver is fixed by adding piperazine chelating agent (silver fixing agent). Proved to be significant.

(Technical significance of heating process and dilution process)
FIG. 3 is a bar graph showing the relationship between the hydrogen peroxide decomposition time (that is, the heating time) and the temperature of the B solution in the B solution obtained by diluting the A solution three times. As the temperature of the liquid B was higher, hydrogen peroxide was decomposed in a shorter time. At 20 ° C., it took a whole day and night to decompose. It was 4.5 hours and 2 hours at 30 ° C. and 40 ° C., respectively.
That is, it has been proved that the treatment time can be significantly shortened by performing the heating step.

Furthermore, the relationship between the hydrogen peroxide concentration and the temperature change when the liquid temperature setting of the apparatus is 40 ° C. is shown in FIG. (1) indicates the concentration of hydrogen peroxide solution (mg / L: right side), and (0) indicates the temperature of the B liquid (° C .: left side). At 110 minutes, a sharp decrease in hydrogen peroxide concentration (ie, rapid hydrogen peroxide decomposition) and an increase in liquid temperature were observed. Specifically, the hydrogen peroxide concentration decreased from 13 g / L to less than 100 mg / L. However, the increase in the liquid temperature accompanying the decomposition of hydrogen peroxide was 4 ° C. or lower, and the maximum liquid temperature was suppressed to 45 ° C. or lower. In addition, although visual observation was also conducted to check whether bumping or liquid spillage occurred, the rise in liquid level could be kept to 5% or less of the initial liquid amount.
This good result is due to the preparation of a liquid B which is sufficiently fixed by the sulfide addition step and which is preferably diluted until the concentration of hydrogen peroxide in the liquid to be treated is 20 g / L or less. I think that.

(Technical significance of neutralization process and evaporative concentration process)
Table 2 shows the relationship between the pH of the B solution after the neutralization step and before the evaporation and concentration step, and the quality of the condensed water in the subsequent condensed water treatment step.
As shown in Table 2, when the pH of the B liquid before evaporation and concentration is 7 (that is, when neutralization is not performed to reach less than pH 7), the ammonia is volatilized during the evaporation and concentration, and the condensate side It has moved to.
On the other hand, when evaporating and concentrating the pH 4.8 solution B, which was the result of sufficient neutralization, the ammonia was fixed on the concentrate side, and the concentration of ammonia in the condensed water was less than 2 ppm. . In addition, COD density | concentration in condensed water is 150 ppm, As a result of investigating the component of this COD, it confirmed that it was formaldehyde.
That is, by passing through a neutralization step for sufficiently neutralizing the liquid B from alkaline to neutral to acidic (pH less than 7.0), it is possible to prevent the condensed water from containing ammonia, which is a drainage regulating substance. I was able to.

(Technical significance of condensate treatment process)
FIG. 5 shows the result of biological treatment (aerobic treatment) performed on the condensed water by the method described in this example. As a result of the aerobic treatment, it was confirmed that the concentration of formaldehyde was changed from 30 mg / L to 0 mg / L in 3.5 hours.
That is, it was revealed that formaldehyde contained in the condensed water was successfully removed by the condensed water treatment process.

Claims (10)

A method for treating an alkaline liquid to be treated containing silver, hydrogen peroxide, and a chelating agent that is at least one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA),
A sulfide addition step of adding sulfide to the liquid to be treated;
A heating step of heating the liquid to which the sulfide is added to remove hydrogen peroxide;
A chelating agent addition step of adding a piperazine chelating agent to the liquid to be treated from which hydrogen peroxide has been removed;
A method for treating a liquid to be treated. After the chelating agent addition step, the solid-liquid separation step of recovering the silver-containing material that is a solid by solid-liquid separation of the liquid to be treated;
The processing method of the to-be-processed liquid of Claim 1 which has these. A neutralization step of neutralizing the liquid generated in the solid-liquid separation step by adding an acid;
The processing method of the to-be-processed liquid of Claim 2 which has these. An evaporation concentration step of evaporating and concentrating the liquid neutralized in the neutralization step;
The processing method of the to-be-processed liquid of Claim 3 which has these. A condensed water treatment step for removing formaldehyde contained in the condensed water generated by the evaporation concentration in the evaporation concentration step;
The processing method of the to-be-processed liquid of Claim 4 which has these.   The to-be-processed object in any one of Claims 1-5 which further has a dilution process which dilutes a to-be-processed liquid until the density | concentration of the hydrogen peroxide in a to-be-processed liquid becomes 20 g / L or less before the said heating process. Liquid processing method. A solid-liquid separation step of recovering a silver-containing material that is a solid by solid-liquid separation of the liquid to be treated after the chelating agent addition step;
The processing method of the to-be-processed liquid of Claim 6 using a part of liquid which arose in the said solid-liquid separation process as a dilution liquid in the said dilution process.   The method for processing a liquid to be processed according to claim 1, wherein the liquid to be processed is a waste liquid in manufacturing a metal-ceramic bonding substrate.   The method for treating a liquid to be treated according to claim 1, wherein the sulfide is at least one of potassium sulfide, zinc sulfide, and copper sulfide. A method for recovering silver from an alkaline liquid containing silver, hydrogen peroxide, and a chelating agent that is at least one of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA),
A sulfide addition step of adding sulfide to the liquid to be treated;
A heating step of heating the liquid to which the sulfide is added to remove hydrogen peroxide;
A chelating agent addition step of adding a piperazine chelating agent to the liquid to be treated from which hydrogen peroxide has been removed;
After the chelating agent addition step, the solid-liquid separation step of recovering the silver-containing material that is a solid by solid-liquid separation of the liquid to be treated;
A silver recovery process for recovering silver from the silver-containing material;
A method for recovering silver.