JP2021142509A - Cyanide-containing liquid treatment method and cyanide-containing liquid treatment equipment - Google Patents

Abstract

To highly and economically treat cyanide, and stably treat cyanide by accurately controlling an addition amount of a reducing agent, in a treatment of cyanide-containing liquid by a total cyanide method (reduced copper salt method).SOLUTION: There is provided a cyanide-containing liquid treatment method, including: adding a copper compound and a reducing agent to cyanide-containing liquid; and controlling an addition amount of the reducing agent based on a dissolved oxygen concentration of a liquid to be treated to which the reducing agent is added, using a cyanide compound as an insoluble salt. There is also provided cyanide-containing liquid treatment equipment, including: a mixing facility that introduces a cyanide-containing liquid and reacts it with the copper compound; means for adding the reducing agent to the mixing equipment; a dissolved oxygen meter that measures a dissolved oxygen concentration of the liquid in the mixing facility; and control means for controlling the addition amount of the reducing agent based on a measured value of the dissolved oxygen meter.SELECTED DRAWING: Figure 1

Description

The present invention treats a cyanide-containing liquid in which a copper compound is added to a cyanide-containing liquid and reacted in the presence of a reducing agent such as sodium bicarbonate or ferrous sulfate to separate and remove the cyanide as an insoluble salt. It relates to a method and a processing device.
Specifically, a method and a treatment apparatus for a cyanide-containing liquid for efficient and economical treatment by accurately controlling the amount of the reducing agent added to reduce the copper compound in such cyanide wastewater treatment. Regarding.

The morphology of the cyanide in the cyanide-containing wastewater includes free cyanide (CN ⁻ ) and a metal cyano complex (M (CN) _n ^{x −} ). Conventionally, as a method for treating these cyanide compounds, a total cyanide method (reduced copper salt method) is known in which a copper compound is added in the presence of a reducing agent to produce an insoluble salt of cyanide.

For example, in Patent Document 1, a copper compound and a magnesium compound are added and reacted in the presence of a reducing agent such as sodium bisulfite to produce an insoluble salt of cyanide, which is removed. Paragraph 0022 of Patent Document 1 states that the amount of the reducing agent added is an amount required for the reduction of the copper compound and the ferricyan ion.

Conventionally, in such a total cyan method (reduced copper salt method), it is known that the amount of a reducing agent added is determined (controlled) by an oxidation-reduction potential (hereinafter referred to as ORP).
For example, in the examples of Patent Document 2, the reducing agent is added until the ORP reaches 250 mV.
Claim 3 of Patent Document 3 describes that the end point of addition of the sulfite compound as a reducing agent is at least the time when the leap of the redox potential is completed.
Paragraph 0050 of Patent Document 4 describes that the cyanide removal effect is stable and good when the ORP after the addition of the reducing agent is 80 mV or less.

However, according to the studies by the present inventors, it has been found that the amount of the reducing agent added cannot be controlled by the redox potential depending on the wastewater species. Specifically, when the amount of the reducing agent added is on the horizontal axis and the redox potential is on the vertical axis, as described in Patent Document 3, the point where the redox potential changes rapidly is not observed, and reduction is performed. It has been found that the end point of the amount of the agent added may not be controlled by the redox potential.

On the other hand, in Patent Document 5, in the so-called Prussian blue method in which a cyanide is reacted with a ferrous salt to form a water-insoluble salt and the salt is separated and removed, the iron-cyanide complex is targeted by the alkali chlorine method in two steps. A method is disclosed in which the concentration of dissolved oxygen (hereinafter referred to as DO) after decomposition is set to a predetermined value or a point where DO is sharply lowered as the end point of addition of ferrous salt.
In Patent Document 5, the addition of a drug is supervised by DO, but the method of Patent Document 5 is not based on the total cyanide method (reduced copper salt method) performed in the present invention, and conventionally, the total cyanide method (reduced copper salt method) is used. In the law), no proposal has been made to control the drug injection of the reducing agent by DO.

Japanese Unexamined Patent Publication No. 2013-226510 Japanese Unexamined Patent Publication No. 58-216778 Japanese Unexamined Patent Publication No. 1-210096 Japanese Unexamined Patent Publication No. 2017-136539 Japanese Unexamined Patent Publication No. 4-83590

According to the present invention, in the treatment of a cyanide-containing liquid by the total cyanid method (reduced copper salt method), the amount of the reducing agent added is accurately controlled to treat the cyanide compound highly, economically and stably. It is an object of the present invention to provide a method and an apparatus for treating a cyanide compound-containing liquid capable of producing a cyanide compound.

As a result of diligent studies to solve the above problems, the present inventors have used dissolved oxygen (DO) as an index when treating a cyanide-containing liquid by the total cyanide method (reduced copper salt method). By performing chemical injection control, it is possible to add reducing agents such as sodium bicarbonate and ferrous sulfate in just proportion, and to treat cyanide highly, economically, and stably. It has been found that the cyanide concentration of the treatment liquid can be sufficiently lowered.

The present invention has been achieved based on such findings, and the gist of the present invention is as follows.

[1] In a method for treating a cyanide-containing liquid in which a copper compound and a reducing agent are added to the cyanide-containing liquid and the cyanide is separated and removed as an insoluble salt, the reducing agent is added to the amount of the reducing agent added. A method for treating a cyanide compound-containing liquid, which is controlled based on the dissolved oxygen concentration of the liquid to be treated.

[2] The method for treating a cyanide compound-containing liquid according to [1], wherein the end point of addition of the reducing agent is when the dissolved oxygen concentration is completely lowered.

[3] In a method in which a copper compound and a reducing agent are added to a reaction vessel in which a cyanide-containing liquid continuously flows, and the cyanide compound is separated and removed as an insoluble salt, the dissolved oxygen concentration in the reaction vessel is measured. A method for treating a cyanide compound-containing liquid, which comprises controlling the amount of the reducing agent added so that the measured value of the dissolved oxygen concentration becomes a predetermined value.

[4] A mixing facility for introducing a cyanide-containing liquid to react with a copper compound, a means for adding a reducing agent to the mixing facility, a dissolved oxygen meter for measuring the dissolved oxygen concentration of the liquid in the mixing facility, and the like. A device for treating a cyanide compound-containing liquid, which comprises a control means for controlling the amount of the reducing agent added based on a measured value of a dissolved oxygen meter.

According to the present invention, in the treatment of a cyanide compound-containing liquid by the total cyanide method (reduced copper salt method), the amount of the reducing agent added is controlled by using the dissolved oxygen (DO) concentration as an index to control sodium barous sulfate or sulfuric acid. By adding a reducing agent such as monoiron in just proportion, it is possible to treat the cyanide compound highly, economically, and stably, and it is possible to obtain a treatment liquid in which the cyanide concentration is sufficiently reduced. ..

It is a system diagram which shows an example of the embodiment of the treatment method and the treatment apparatus of the cyanide compound-containing liquid of this invention.

Embodiments of the present invention will be described in detail below.

The present invention is characterized in that, when treating a cyanide compound-containing liquid by the total cyanide method (reduced copper salt method), the chemical injection control of the reducing agent is performed using the DO concentration as an index instead of the ORP value of the conventional method.

As a result of the present inventors studying wastewater containing cyanide hydrin and wastewater containing complex cyanide such as ferrocyan, which causes variation in treatment by the conventional method based on the ORP value, it is difficult to control chemical injection with such an ORP value. Even if the solution contains a cyanide compound, there is a close relationship between the cyanide concentration and the DO concentration of the treatment solution, and the reducing agent such as sodium bisulfite or ferrous sulfate is used so that the DO concentration becomes a constant level. It was clarified that a treatment solution having a low cyanide concentration can be stably obtained by carrying out injection control.

According to the present invention, since the amount of the reducing agent added is controlled by using the DO concentration as an index, the reducing agent is added in just proportion, and the cyanide compound-containing liquid is treated efficiently, highly and stably. It is possible to obtain a treatment liquid having a low cyanide concentration.

In the treatment of the cyanide-containing liquid according to the present invention, the cyanide-containing liquid is introduced into the reaction vessel, and a reducing agent such as sodium bicarbonate or ferrous sulfate and a copper compound are added thereto, respectively, in the liquid to be treated. It can be carried out by reacting a cyanide compound to produce a water-insoluble salt.
The above reaction may be carried out in a batch type or a continuous type.
When the treatment is performed in a batch system, the DO concentration of the solution in the reaction vessel is measured with a DO meter while adding a reducing agent, or an appropriate amount of copper compound corresponding to the cyan concentration of the raw water is added, and then the DO of the solution in the reaction vessel is added. The operation of measuring the concentration is repeated. Then, when the value of the DO concentration is completely lowered, the end point of the addition of the reducing agent is set.
The time when the value of the DO concentration is completely lowered is, for example, when the decrease in the DO concentration value is 0.002 mg / L or less per 1 mg / L of the addition amount of the reducing agent.

In the case of the continuous formula, the DO concentration is determined by a beaker test or the like so that the DO concentration becomes a predetermined value, that is, the DO concentration when the DO concentration is completely lowered, as in the determination of the end point in batch processing, and is the same as that value. As such, a reducing agent such as sodium sulfite or ferrous sulfate and a copper compound can be added to efficiently produce a water-insoluble salt. Specifically, if the reaction vessel is a completely mixed type, a reducing agent may be added so that the DO concentration value in the reaction vessel becomes a predetermined value, and if the reaction vessel is an extrusion flow type, the flow of the liquid is increased. A plurality of DO meters are installed along the line, and a reducing agent is added so that the DO concentration value of the most downstream DO meter becomes a predetermined value.
In such a method, it is possible to accurately control the injection of the reducing agent, which can surely effectively utilize the added copper compound.

The reaction for producing the insoluble salt can be carried out in a reaction vessel equipped with a stirrer or in a mixing facility such as a line mixer.

When the cyanide-containing solution is treated as described above, the DO concentration of the reaction solution is lowered, so that the copper compound in the water-insoluble salt is sufficiently reduced to monovalent and is combined with cyanide to form raw water. Since it is not affected by ORP or the like, the reducing agent can be operated economically. Therefore, cyan ions do not leak into the treatment liquid, and advanced treatment can be stably performed.

FIG. 1 is a system diagram showing an example of a method for treating a cyanide compound-containing liquid of the present invention and an embodiment of a treatment apparatus according to a continuous method.
The cyanide-containing liquid, which has been subjected to pretreatment such as pH adjustment and aeration treatment as necessary, is introduced into the reaction tank 1, and a reducing agent such as sodium bisulfite or ferrous sulfate and a copper compound are added under stirring. It produces an insoluble salt. The reaction solution containing the insoluble salt is sent to the settling tank 2 for solid-liquid separation, and the separated water is taken out as a treatment solution. The separated sludge extracted from the settling tank 2 is sent to a dehydration facility or the like for treatment.

The reaction tank 1 is provided with a DO total 3 for measuring the DO concentration of the liquid in the tank, and the measured value of the DO concentration is input to the control device 4.

The DO concentration at the time when the DO concentration value has completely dropped is set in advance in the control device 4 by a beaker test or the like, and the chemical injection pump of the reducing agent is set so that the time when the DO concentration reaches the DO concentration is the end point of the addition of the reducing agent. The control signal of P is output.

The appropriate value of the DO concentration varies depending on the substrate in the cyanide compound-containing liquid to be treated (presence or absence of coexistence of cyanhydrin, etc.), but is 1.0 mg / L or less, preferably 0.5 mg / L or less, more preferably. It is also possible to control the end point to be 0.1 mg / L or less.

Hereinafter, each constituent requirement suitable for the treatment of the cyanide compound-containing liquid according to the present invention will be described.

[Cyanide-containing liquid]
The cyanide-containing liquid to be treated in the present invention is water containing a cyanide compound such as free cyanide and complex cyanide. The present invention is suitably applicable when complex cyanide such as free cyanide or ferrocyanide coexists in the cyanide compound-containing liquid. As the complex cyanide, there is a metal complex of cyanide, and an iron cyanide complex such as a ferrocyanine ion or a ferricyanide ion, or another metal complex may be contained.

Examples of such a cyanide-containing liquid include cyanide-containing liquids discharged from metal plating factories, chemical factories, and the like. The cyanide compound-containing liquid may contain a metal such as iron, a chelating agent such as an organic acid, and other impurities. Metals such as iron are generally contained as a cyanide complex. Chelating agents such as organic acids may be included as insolubilizing metals.

The concentration of the cyanide compound in the cyanide compound-containing liquid is not particularly limited, but the total cyanide concentration is usually about 1 to 20 mg / L.

In the case of a cyanide compound-containing liquid in which cyanide is produced by formaldehyde, it is desirable to oxidatively decompose it with an oxidizing agent, aeration, or the like in advance.

[Copper compounds / reducing agents]
In the present invention, a copper compound and a reducing agent are first added to the cyanide compound-containing liquid to produce an insoluble salt.

As the copper compound, divalent copper salts such as water-soluble copper sulfate (II), copper chloride (II), and copper nitrate (II) can be used.

The reducing agent is a reducing agent capable of reducing divalent copper ions to monovalent, and may be, for example, sulfite, sulfite, iron salt (II), hydrazine, etc., but the amount of sludge generated is reduced and availability is easy. From this point of view, sulfites and sulfites are recommended. As these salts, sodium salts such as sodium bisulfite (NaHSO ₃ ) are suitable.

Generally, even if various reducing agents such as sulfite, bicarbonate, iron (II) sulfate, and hydrazine are added to a divalent copper salt such as copper sulfate to adjust the pH to 2-11, apparently monovalent copper ions are not produced. Although not seen, when a divalent copper salt and a reducing agent are added to the cyan compound-containing liquid, the monovalent copper cyan compound becomes an insoluble salt and precipitates.

The above reactions are typified by the three types shown in the formula below.

Cu ⁺ + CN- → CuCN… (1)
4Cu ⁺ + Zn (CN) ₄ ^2- → 4CuCN + Zn ²⁺ … (2)
_{^{Cu + + Ag (CN) 2}} - → CuAg (CN) 2 ... (3)
Of these, Eq. (1) is a reaction of free cyanide, Eq. (2) is a reaction of the easily decomposable cyanide complex salt, and Eq. (3) is a reaction of a persistent cyanide complex salt.

The amount of the divalent copper salt added to the reaction system is preferably equal to or more than the reaction equivalent with the cyanide in the cyanide-containing liquid, and in principle, the reaction equivalent in the above formulas (1) to (3) may be used. However, in order to cope with fluctuations in the cyanide compound concentration in the cyanide compound-containing liquid and to promote the reaction, an amount of 2 to 5 times the cyanide concentration in the cyanide compound-containing liquid is particularly preferable. If the copper compound is already present in the cyanide-containing liquid, the deficiency may be added.

In the present invention, the amount of the reducing agent added is controlled based on the DO value as described above.

The copper compound and the reducing agent are preferably added at the same time, but they may be added separately before and after.

[Reaction conditions]
The pH for adding the copper compound and the reducing agent to the cyan compound-containing liquid to form an insoluble salt (for example, the pH of the reaction vessel to which the copper compound and the reducing agent are added) is preferably 2 to 9.5, particularly preferably. It is 7 to 9.5. Therefore, when the pH of the cyanide compound-containing liquid to be treated is out of this range, it is preferable to adjust the pH by adding an acid or an alkali as necessary.
The reaction temperature (for example, the temperature of the reaction vessel to which the copper compound and the reducing agent are added) is not particularly limited, but is usually 15 to 60 ° C.

[Separation of insoluble salts]
The solid-liquid separation method of the insoluble salt produced by adding a copper compound and a reducing agent to the cyanide compound-containing liquid is not particularly limited, but a method of adding a flocculant to perform coagulation treatment, and then solid-liquid separation after coagulation treatment. Is preferable.

As the flocculant, an inorganic flocculant and an organic polymer flocculant are used. The inorganic flocculant is preferably an iron salt-based flocculant such as iron (III) chloride or iron (III) sulfate, which is suitable for coagulating not only insoluble salts and the like but also residual cyanide complexes, but aluminum such as PAC. A salt-based flocculant or the like can also be used. As described in Patent Document 4, the coagulation treatment efficiency may be higher when the aluminum salt-based coagulant is used than when the iron-based coagulant is used, and the aluminum salt-based coagulant is suitable. In some cases. Examples of the organic polymer flocculant include polyacrylamide, a copolymer of acrylamide and acrylic acid (sodium), and polyacrylamide partial hydrolysis as a flocculant suitable for flocculating and separating agglomerates aggregated by an inorganic flocculant. Anionic polymer flocculants such as decomposition products are preferred.

The amount of the inorganic flocculant added is preferably 20 to 2000 mg / L, particularly preferably about 100 to 500 mg / L. The amount of the organic polymer flocculant added is preferably 0.2 to 10 mg / L, particularly preferably about 0.5 to 2 mg / L.

In addition, in order to remove the excessively added copper compound, a heavy metal collecting agent may be added at the time of the aggregation treatment. Examples of the heavy metal collecting agent include a dithiocarbamic acid-based chelating agent.

Examples of the solid-liquid separation after the agglutination treatment include one or two or more of precipitation separation, levitation separation, and filtration. As the filtration, sand filtration, multi-layer filtration (anthracite / sand two-layer filtration, etc.), membrane filtration and the like can be used.

In FIG. 1, the reaction liquid from the reaction tank 1 is directly separated by the settling tank 2, but an agglutination reaction tank may be provided between the reaction tank 1 and the settling tank 2.
In this case, as the agglutination reaction tank, a rapid stirring tank in which an inorganic flocculant is added and stirred, and a slow stirring tank in which an organic polymer flocculant is added and stirred may be provided. Further, a filter may be further provided after the settling tank 2 to filter the supernatant water from the settling tank 2.

[Example 1]
Hereinafter, the present invention will be described in more detail with reference to experimental examples alternative to the examples.

[Experimental Example I]
An experiment was conducted in which wastewater containing ferrocyanide, cyanhydrin and free cyanide (raw water 1) _{was treated by adding a reducing agent (NaHSO 3} ) and then adding a copper compound (CuSO _4).
Raw water 1 had a total cyanide concentration of 3.4 mg / L, and the measured values of ORP and DO were as shown in Table 1 below.
_{After adding NaHSO 4} as a reducing agent to this raw water 1 in the amount shown in Table 1 below _{, 100 mg / L of CuSO 4} as a copper compound was added and reacted, and the ORP and DO of the reaction solution were measured. It was as shown in. All the reactions were carried out at a water temperature of 50 ° C. and a pH of 8.4.
Anionic polymer flocculants (Kurifarm PA923, Kurita Kogyo Co., Ltd.) were added to each of the obtained reaction solutions, and the mixture was allowed to stand for 30 minutes, and then the total cyanide concentration of the supernatant (treated water) was measured. The results are shown in Table 1.

From Table 1, it can be seen that when a reducing agent is added so that the DO concentration of the reaction solution is 0.3 mg / L or less, cyanide is not detected in the treated water.
From the result of this Experimental Example I, the cyanide removing effect cannot be obtained even if the reducing agent is added until the ORP becomes 250 mV as in Patent Document 2, and the ORP is 80 mV or less as described in Patent Document 4. However, it can be seen that the cyan removal effect is not sufficient, and the rapid change in ORP as in Patent Document 3 is not observed.

[Experimental Example II]
Factory wastewater (raw water 2) different from the wastewater used in Experimental Example I was treated in the same manner as in Experimental Example I.
The raw water 2 had a total cyanide concentration of 2.8 mg / L, and the measured values of ORP and DO were as shown in Table 2 below, respectively.
_{After adding NaHSO 4} as a reducing agent to this raw water 2 in the amount shown in Table 2 below _{, 100 mg / L of CuSO 4} as a copper compound was added and reacted, and the ORP and DO of the reaction solution were measured. It was as shown in. All the reactions were carried out at a water temperature of 50 ° C. and a pH of 8.4.
Anionic polymer flocculants (Kurifarm PA923, Kurita Kogyo Co., Ltd.) were added to each of the obtained reaction solutions, and the mixture was allowed to stand for 30 minutes, and then the total cyanide concentration of the supernatant (treated water) was measured. The results are shown in Table 2.

From Table 2, the following can be seen.
No. II-1 to No. When the range in which the ORP value suddenly changes from the ORP value of II-3 is used as an index for controlling the addition amount of the reducing agent, for example, the set potential of the ORP is selected in the range of 30 to 50 mV, and the reducing agent is 30 mV. Assuming that the addition is turned off and the addition is turned on at 50 mV, it can be seen that the insolubilization of cyanide is not yet completed by such chemical injection control. Therefore, it is necessary to select an ORP value that allows the addition of a reducing agent. However, when the ORP value is 50 mV or less, the copper compound corresponding to the cyan concentration of the raw water also changes, so that the ORP changes with respect to the amount of the reducing agent added. It is slow and difficult to control. If a low ORP value is set in anticipation of the safety of cyanide treatment, the reducing agent will be over-injected, which is not economical.
On the other hand, when the addition of the reducing agent is controlled based on the DO concentration, the DO concentration value drops sharply after the cyanide complex ion is treated to a low level, for example, the DO concentration becomes 0.3 mg / L or less. It can be seen that if the reducing agent is added until the total cyanide concentration changes, treated water having a total cyanide concentration of 1 mg / L or less can be obtained if the required amount of the copper compound is satisfied even if the cyanide concentration in the raw water changes.

1 Reaction tank 2 Sedimentation tank 3 DO meter 4 Control device

Claims (4)

In the method for treating a cyanide-containing liquid in which a copper compound and a reducing agent are added to the cyanide-containing liquid and the cyanide is separated and removed as an insoluble salt, the amount of the reducing agent added is adjusted to the amount to which the reducing agent is added. A method for treating a cyanide compound-containing liquid, which is controlled based on the dissolved oxygen concentration of the treatment liquid. The method for treating a cyanide compound-containing liquid according to claim 1, wherein the end point of addition of the reducing agent is when the dissolved oxygen concentration is completely lowered. In a method in which a copper compound and a reducing agent are added to a reaction vessel in which a cyanide-containing liquid continuously flows, and the cyanide compound is separated and removed as an insoluble salt, the dissolved oxygen concentration in the reaction vessel is measured and the dissolved oxygen is dissolved. A method for treating a cyanide compound-containing liquid, which comprises controlling the amount of the reducing agent added so that the measured value of the oxygen concentration becomes a predetermined value. A mixing facility for introducing a cyanide-containing liquid to react with a copper compound, a means for adding a reducing agent to the mixing facility, a dissolved oxygen meter for measuring the dissolved oxygen concentration of the liquid in the mixing facility, and the dissolved oxygen meter. A cyanide compound-containing liquid processing apparatus, which comprises a control means for controlling the amount of the reducing agent added based on the measured value of the above.

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