JP7098990B2 - Contaminated water purification method - Google Patents

Description

The present invention relates to a method for purifying contaminated water, specifically, a method for purifying contaminated water contaminated with a cyanide compound.

Cyanides are classified as Class 2 Specified Hazardous Substances under the Soil Countermeasures Pollution Law, and are extremely toxic compounds represented by potassium cyanide (so-called hydrocyanic acid) and the like.

Cyanide compounds generated in factories and the like combine with iron in soil to form cyano complexes. The cyano complex can be insolubilized by forming a salt precipitate if there is a metal salt such as iron ion in the soil. On the other hand, there is also a cyano complex that does not reach a salt precipitate and remains in the soil environment (see Non-Patent Document 1).

Then, the remaining cyano complex seeps out of the soil and contaminates the groundwater, and the contaminated groundwater flows out of the site, resulting in serious environmental pollution.

In order to prevent contamination of groundwater, a method of providing a purification wall mixed with a cyanide compound treatment agent on the downstream side of the groundwater is known.

The mechanism of the method for purifying contaminated water with a cyanide compound treatment agent is to remove the cyano complex from the contaminated water by insolubilizing the cyano complex with iron and then adsorbing the cyan insolubilized with iron with an adsorbent. Can be mentioned.

However, the cyanide compound treatment agent has a problem that its treatment performance deteriorates with time. At that time, it costs a lot of money to reconstruct the purification wall.

Pollution Control Technology and Regulations Editorial Committee, "Fifth Edition Pollution Control Technology and Regulations" Water Quality "", Industrial Environment Management Association, May 1995

In view of these problems, it is an object of the present invention to provide a method for maintaining the treatment performance of the cyanide compound treatment agent for a long period of time without reconstructing the purification wall.

The present inventor has come up with a purification method according to the present invention as a result of diligent studies in order to achieve the above-mentioned object.

That is, the present invention is a method for purifying contaminated water by purifying water contaminated with a cyanide by a purification facility equipped with a cyanide treatment agent, wherein the purification facility is provided on the downstream side where the ground water flows. It is a purification wall mixed with the cyanide treatment agent, and further comprises a step of supplying the purification wall with a reducing agent for recovering the treatment performance of the cyanide treatment agent, which decreases with time. , Contaminated water purification method.

Examples of the step of supplying the reducing agent include a step of providing an injection well underground and injecting the reducing agent into the injection well to supply the reducing agent to the purification wall along the flow of groundwater. ..

Examples of the reducing agent include emulsified vegetable oil.

Further, the cyanide treatment agent preferably contains a sustained release acidic agent.

Further, the cyanide treatment agent preferably contains iron powder.

By using the contaminated water purification method of the present invention, it has become possible to maintain the capacity of the cyanide compound treatment agent for a long period of time without reconstructing the purification wall.

It is a figure which shows one form of the contaminated water purification method. It is a figure which shows one form of the contaminated water purification method. It is the schematic of the structure of an Example. It is the schematic of the structure of an Example. It is a graph which shows the result of an Example.

Hereinafter, one embodiment of the present invention will be described, but the scope of the present invention is not limited to the description including the examples. In the present application, "%" means% by weight unless otherwise specified.

<Cyanide>
The pollutant to be removed in the present invention is a cyanide compound. Examples of the cyanide include organic cyanides such as hydrogen cyanide, potassium cyanide, and sodium cyanide. The "cyanide" as used in the present invention also includes a cyano complex and an inorganic cyanide compound such as a ferricyanide or a ferrocyanide compound formed into a complex compound with a metal atom, which has a risk of generating an organic cyanide by decomposition. It shall be muted.

<Cyanide treatment agent>
The cyanide treatment agent needs to have a function of insolubilizing the cyano complex with iron and then a function of adsorbing cyanide insolubilized with iron with an adsorbent.

Examples of cyanide treatment agents having such a function include those containing sustained release acid agents, adsorbents, and iron. Iron may be contained in either the sustained release acid agent or the adsorbent. Hereinafter, the sustained release acid agent, the adsorbent, and iron will be described.

<Modified release acid agent>
The sustained release acid agent is an agent for maintaining the acidic atmosphere of the purification equipment and the environment in the vicinity thereof when purifying contaminated water. Iron can sustain its function of insolubilizing the cyano complex by creating an acidic atmosphere. The sustained-release acidic agent is not particularly limited as long as it can maintain an acidic atmosphere for a long period of time, but is limited to sulfur compounds (for example, sandset which is a sulfur-containing alkaline soil improver) and activated clay (for example, acid-treated soil). Montmorillonite), iron sulfate-based acid agents (for example, ferrosand), and the like. By using the sustained release acid agent, the acidic atmosphere can be maintained for a long period of time.

<Adsorbent>
The adsorbent is an agent for adsorbing a cyano complex insolubilized by iron. By adsorbing the cyano complex insolubilized by iron, environmental pollution due to the outflow of cyanide can be prevented. As the adsorbent, for example, earth-based (clay-based) minerals are preferable in that they have a large effect of extending the functioning life of the adsorbent, but if they have an adsorbing effect on a cyanide compound, they are not limited to these. do not have.

<Iron>
Iron is an agent for insolubilizing a cyano complex.

Iron includes not only simple substances such as iron powder but also iron compounds such as iron sulfate and iron sulfide. When iron powder is used, the iron powder also functions as an adsorbent. Further, when an iron material such as iron sulfate is used, the iron material also functions as a sustained release acid agent.

<Other compositions of cyanide treatment agents>
Further, the cyanide treatment agent of the present invention may contain various agents other than the sustained release acid agent, the adsorbent, and iron as long as the purification performance is not impaired. For example, quartz sand can be used to ensure water permeability. In addition, various solvents, additives, and the like can be used to improve the adsorption efficiency of iron powder and facilitate the separation and recovery of iron powder.

<Reducing agent>
As described above, the treatment performance of the cyanide compound treatment agent may deteriorate over time. As a specific reason, it is conceivable that the contact with oxygen in the groundwater may oxidize iron and make it impossible to supply iron ions. The same can be said when the sustained release acid agent contains iron such as iron sulfate.

Therefore, in the present invention, a reducing agent that restores the treatment performance of the cyanide compound treatment agent is used. By adding a reducing agent, it is possible to create a reducing atmosphere in the environment of the purification wall and its vicinity, and to restore the supply of iron ions.

As the reducing agent, a sustained release organic substance is preferable in order to maintain its effect for a long period of time, and from the viewpoint of safety and prevention of secondary contamination. Examples of sustained release organic substances include emulsified vegetable oils. Among the emulsified vegetable oils, emulsified vegetable oils having high permeability to the ground and fine emulsified particles are preferable.

<Purification equipment>
Purification equipment is equipment that purifies contaminated water contaminated with cyanide compounds. In the present invention, as the purification equipment, a purification wall for preventing contaminated groundwater from flowing out of the site is used.

FIG. 1 shows an example in which a purification wall is used as a purification facility. In the basement of 5 in the factory premises, there is groundwater 1 contaminated with a cyanide compound. The cyanide treatment agent is mixed inside when the purification wall is prepared. The purification wall 2 mixed with the cyanide treatment agent is installed by excavating the ground so that all of the groundwater 1 passes through the purification wall 2, for example, at the boundary between the factory site 5 and the factory site outside 7. To. When the groundwater 1 passes through the purification wall 2, the cyanide in the groundwater 1 is adsorbed by the purification wall 2. As a result, the cyanide compound is removed from the groundwater 1. Therefore, clean groundwater 3 containing no cyanide is discharged to the outside of the factory site 7.

<Supply of reducing agent>
The reducing agent is supplied to the purification equipment by, for example, providing a supply equipment. An example of a supply facility is an injection well installed underground. FIG. 2 is a view of the purification wall 12 and the injection well 13 installed underground as viewed from above. In the example of FIG. 2, a plurality of injection wells 13 are installed on the upstream side of the groundwater flow (arrow 11) with respect to the purification wall 12. The broken line around the well 13 in FIG. 2 shows how the injected reducing agent diffuses.

The number and depth of the injection wells 13 can be appropriately adjusted depending on the width, distance, and depth of the purification wall 12. By injecting the reducing agent into the injection well 13, the reducing agent diffuses from the injection well 13 and the reducing agent can be supplied to the purification wall 12. The injection well 13 may be provided in a single number or a plurality, but the reducing agent diffused from the injection well 13 covers the entire purification wall 12 as shown in the diffusion range 14 of the reducing agent, for example. Is preferable. As a result, the sustained release acidic agent contained in the cyanide compound treating agent mixed in the purification wall 12 can restore the performance of maintaining the acidic atmosphere.

In addition, instead of providing a well on the upstream side, an injection well may be set up in the purification wall 12. In this case, since the reducing agent can be directly injected into the purification wall 12, the place where the sustained release acidic agent is present can be surely made into a reducing atmosphere.

Next, the present invention will be described with reference to Examples, but the scope of the present invention is not limited to these Examples.

<Outline of test method>
(1) A column filled with a cyanide treatment agent and a column filled with emulsified vegetable oil as a reducing agent were used to imitate the purification wall and the injection well for supplying the reducing agent to the purification wall. A schematic diagram is shown in FIGS. 3A and 3B, and the description will be made based on this.

(2) As a column packed with a cyanide treatment agent, a column 31 having a cyanide treatment agent-filled layer having an inner diameter of 10 cm and a length of 3 cm was used. As a column filled with emulsified vegetable oil, a column 33 having an emulsified vegetable oil-filled layer having an inner diameter of 5 cm and a length of 90 cm was used. The composition of the packed bed of the column 31 and the column 33 is as shown in Table 1.

(3) A ferrocyanic aqueous solution 24 prepared by adding ferrocyanate potassium (trihydrate) to water was used as a material for imitating water contaminated with a cyanide compound. The cyanide concentration of the ferrocyanide aqueous solution 24 (referring to the total cyanide concentration, the same applies hereinafter) is 1 mg / L.

(4) First, as shown in FIG. 3A, the ferrussian aqueous solution 24 is carried to the metering pump 28 through the first pipe line 21, and the column imitating the purification wall from the metering pump 28 through the second pipe line 22. Water is passed through 31. The water flow rate of the ferrussian aqueous solution 24 is controlled by the metering pump 28 at 0.7 to 1.4 L / day.

(5) The ferrussian aqueous solution 24 after passing water through the column 31 is carried to the sampling container 29 through the third pipe line 23.

(6) The water flow rate of the ferrussian aqueous solution 24 carried to the sampling container 29 (hereinafter, simply referred to as “water flow rate”) and the cyan concentration and pH of the water accumulated in the sampling container 29 were appropriately measured. The cyan concentration was measured by the distillation-pyridin acid absorptiometry of JIS K0102 (factory wastewater test method).

(7) The cyan concentration of the ferrussian aqueous solution 24 exceeds the cyan environment standard value of 0.1 mg / L (quantification limit value) specified in "Environmental Standards for Water Pollution of Groundwater (Notice of the Environmental Agency)". At that time, as shown in FIG. 3B, the column 33 was connected to the second pipeline 22 instead of the column 31. The column 31 was connected to the third pipeline 23 in place of the sampling container 29. The sampling container 29 was connected to the column 31 via the fourth conduit.

(8) By passing water through the column 33, the ferrussian aqueous solution 24 is in a reduced state. By passing the reduced ferrussian aqueous solution 24 through the third conduit 23 to the column 31, the iron ion supply capacity of the column 31 is restored, and the cyanide is adsorbed on the column 31.

(9) The ferrussian aqueous solution 24 after passing the column 31 in (8) is carried to the sampling container 29 through the fourth pipe line 25. The water flow rate, concentration, and pH of the ferrussian aqueous solution 24 carried to the sampling container 29 were measured in the same manner as in (6) above.

<Experimental results>
The experimental results are shown in FIG. In the upper graph, the x-axis is the water flow rate (L) and the y-axis is the cyan concentration (mg / L). In the lower graph, the x-axis is the amount of water flow and the y-axis is pH.

As shown in FIG. 4, the cyanide concentration of the ferrocyanide aqueous solution 24 exceeded the cyanide environmental standard value at the stage when about 40 L of water was passed through the column 31.

At the stage where about 55 L of the ferrussian aqueous solution 24 was passed through the column 31, a column 33 filled with emulsified vegetable oil was installed in place of the column 31 in the same manner as in (7) above. Next, in the same manner as in (8) and (9) above, when the ferrocyanic aqueous solution 24 was passed through the column 33 and then the column 31 was passed through again, the cyan concentration and pH values were found immediately after the column 31 was passed. It dropped significantly.

When the water flow of the column 31 was continued even after the cyan concentration of the ferrussian aqueous solution 24 decreased, the cyan concentration gradually increased and exceeded the cyan environment standard value at a water flow rate of about 60 L. The reason for this may be that the performance of the sustained release acid agent in the column 31 is being restored.

From around 60 L of water flow, the cyan concentration of the ferrussian aqueous solution 24 decreased.
It can be seen that at least up to about 85 L of water flow was below the cyan environmental standard value.

From the above results, by supplying the emulsified vegetable oil to the column 31 and returning the environment of the column 31 to a reducing state, the performance of the sustained-release acidic agent in the column 31 is restored, and as a result, the adsorption of cyanide progresses. It is probable that the cyanide concentration of the ferrocyanide aqueous solution 24 fell below the cyanide environmental standard value again.

1 ... Groundwater contaminated with cyanide 2 ... Purification wall 3 ... Purified clean groundwater 5 ... Inside the factory site 7 ... Outside the factory site 11 ... Groundwater flow 12 ... Purification wall 13 ... Injection well 14 ... Reducing agent diffusion range 21 ... 1st pipeline 22 ... 2nd pipeline 23 ... 3rd pipeline 24 ... Ferrosian aqueous solution 25 ... 4th pipeline 28 ... Metering pump 29 ... Sampling container 31 ... Column 33 with a cyanide treatment agent packing layer having an inner diameter of 10 cm and a length of 3 cm .... Inner diameter 5 cm, length 90 cm. Column with emulsified vegetable oil packed layer

Claims (6)

It is a contaminated water purification method that purifies water contaminated with cyanide by a purification facility equipped with a cyanide treatment agent containing a sustained release acid agent .
The sustained release acid agent contains at least one of a sulfur compound and an iron sulfate-based acid agent.
The purification facility is a purification wall provided on the downstream side where the groundwater flows and mixed with the cyanide compound treating agent.
Further, a method for purifying contaminated water, which comprises a step of supplying the purification wall with a reducing agent for recovering the treatment performance of the cyanide compound treating agent, which decreases with time. The method for purifying contaminated water according to claim 1, wherein the reducing agent is an emulsified vegetable oil. It is a contaminated water purification method that purifies water contaminated with cyanide by a purification facility equipped with a cyanide treatment agent.
The purification facility is a purification wall provided on the downstream side where the groundwater flows and mixed with the cyanide compound treating agent.
Further, the purifying wall is provided with a step of supplying a reducing agent for recovering the treatment performance of the cyanide compound treating agent, which decreases with time.
A method for purifying contaminated water, wherein the reducing agent is an emulsified vegetable oil. The method for purifying contaminated water according to claim 3 , wherein the cyanide treatment agent contains a sustained release acidic agent. The step of supplying the reducing agent is a step of providing an injection well underground and injecting the reducing agent into the injection well to supply the reducing agent to the purification wall along the flow of groundwater. The contaminated water purification method according to any one of claims 1 to 4, which is characterized. The method for purifying contaminated water according to any one of claims 1 to 5, wherein the cyanide compound treating agent contains iron powder.

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