JP7167460B2 - Contaminated water purification method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying contaminated water, and more specifically, to a method for purifying contaminated water contaminated with cyanide compounds.

Cyanide compounds are classified as Class II Specified Hazardous Substances under the Soil Countermeasures and 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 the soil to form cyano complexes. The cyano complex can be insolubilized by forming a salt precipitate if metal salts such as iron ions are present in the soil. On the other hand, there are also cyano complexes that remain in the soil environment without forming salt deposits (see Non-Patent Document 1).

Then, the remaining cyano complex seeps out of the soil to contaminate 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 on the downstream side of the groundwater and a method of trapping cyano complexes by using a chelating agent as a component of the purification wall are known.

However, chelating agents are expensive. In addition, since the cyano complex is consumed or deteriorated by dissolved substances such as iron in groundwater, there is a problem that the ability of the purification wall to remove the cyano complex is lowered. In this case, it is conceivable to construct the purification wall containing the chelating agent again, but there is a problem that this requires a large amount of cost.

Pollution Prevention Technology and Law Editing Committee, ``Fifth Revised Pollution Prevention Technology and Law ``Water Quality Edition'', Japan Environmental Management Association for Industry, May 1995.

In view of such problems, it is an object of the present invention to provide a method for purifying polluted water that does not use an expensive chelating agent and that can maintain the ability to remove cyano complexes for a long period of time.

In order to achieve the above-mentioned object, the present inventor has arrived at the purification method according to the present invention as a result of intensive studies.

That is, the present invention is a contaminated water purification method for purifying water contaminated with cyanide using a purification facility equipped with a cyanide treatment agent, wherein the cyanide treatment agent comprises a sustained-release acidic agent, an adsorbent, and iron.

In the cyanide treatment agent, iron may be contained in either the sustained-release acidic agent or the adsorbent.

The purification equipment is equipment for purifying groundwater contained in soil, and has a purification wall mixed with the cyanide treatment agent provided downstream of the flow of the groundwater, wherein the purification wall is and a method for purifying polluted water, wherein the cyanide compounds in the groundwater permeating through the wall are adsorbed and removed by the cyanide treatment agent.

By using the method for purifying contaminated water of the present invention, the ability to remove cyano complexes can be maintained for a long time without using an expensive chelating agent.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows one form of the cyanogen contaminated water purification method of this invention. 1 is a schematic diagram of the configuration of an embodiment of the present application; FIG. 1 is a graph showing the results of Examples 1 and 2 of the present invention; FIG. 4 is a graph showing the results of Examples 3 and 4 of the present invention; FIG. 4 is a graph showing the results of Comparative Examples 1 and 2 of the present invention;

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

<Cyanide compound>
A contaminant to be removed by the present invention is a cyanide compound. The cyanide includes organic cyanide such as hydrogen cyanide, potassium cyanide and sodium cyanide. In addition, the term "cyanide compound" as used in the present invention includes cyano complexes, and inorganic cyanide compounds such as ferricyanide and ferrocyanide complexes formed with metal atoms, which have the risk of generating organic cyanide compounds by decomposition. shall be taken.

<Cyanide treatment agent>
As a mechanism of the method for purifying contaminated water according to the present invention, first, cyanide is insolubilized by iron compounds such as iron ions and iron salts, and then the cyanide insolubilized by iron is adsorbed by an adsorbent, thereby causing pollution. It removes cyanide from water, and cyanide treatment agents are used for that purpose. The composition of the cyanide treatment contains a slow-release acidic agent, an adsorbent, and iron. Note that iron may be contained in either the sustained-release acidic agent or the adsorbent. The sustained release acidic agent, adsorbent, and iron are described below.

<Slow-release acidic agent>
A sustained-release acidic agent is an agent for maintaining an acidic atmosphere in a purification facility and its surrounding environment when purifying contaminated water. The controlled-release acidic agent is not particularly limited as long as it can maintain an acidic atmosphere for a long period of time. montmorillonite), and iron sulfate-based acid agents (eg, ferrosand). By using a sustained-release acidic agent, an acidic atmosphere can be maintained for a long period of time. As a result, the ability to insolubilize the iron cyanide complex described below can be maintained for a long time.

<Adsorbent>
The adsorbent is an agent for adsorbing the cyano complex insolubilized by iron. By adsorbing the cyano complex insolubilized by iron, it is possible to prevent environmental pollution caused by outflow of cyanide compounds. As the adsorbent, for example, earth-based (clay-based) minerals are preferable because they are highly effective in extending the life of the adsorbent, but are not limited to these as long as they have the effect of adsorbing cyanide compounds. do not have.

<Iron>
Iron is an agent for insolubilizing the cyanide complex.

The scope of iron includes not only simple substances such as iron powder, but also iron compounds such as iron sulfate and iron sulfide. In addition, when iron powder is used, the iron powder also functions as an adsorbent. Moreover, when iron materials such as iron sulfate are used, the iron materials also function as a sustained-release acidic agent.

<Others>
In addition to the sustained-release acidic agent, adsorbent, and iron, the cyanide treatment agent of the present invention may contain various agents as long as the purification performance is not impaired. For example, silica sand can be used to ensure water permeability. Moreover, when iron sulfate is used as the sustained-release acidic agent, the effect of the sustained-release acidic agent may be lost as a result of oxidation of the iron sulfate by groundwater. On the other hand, by adding a sustained-release organic substance to the cyanide compound treatment agent, the effect as a sustained-release acidic agent can be recovered. Slow-release organic substances include, for example, emulsified vegetable oils. In addition, various solvents, additives, and the like can be used for improving adsorption efficiency of iron powder and facilitating separation and recovery of iron powder.

<Purification equipment>
Purification equipment is equipment for purifying contaminated water contaminated with cyanide compounds. In the purification equipment, purification work is performed using the above cyanide treatment agent. An example of a purification facility is a purification wall to prevent contaminated groundwater from flowing off-site.

FIG. 1 shows an example of using a purification wall as the purification equipment. Groundwater 1 polluted with cyanide exists in the basement of factory site 5 . The cyanide treatment agent is mixed inside when the purification wall is produced. The purification wall 2 mixed with a cyanide treatment agent is installed by excavating the ground, for example, at the boundary between the factory premises 5 and outside the factory premises 7 so that all of the groundwater 1 passes through the purification wall 2. be. When the groundwater 1 passes through the purification wall 2 , the cyanide compounds in the groundwater 1 are adsorbed by the purification wall 2 . As a result, cyanide is removed from the groundwater 1 . Therefore, clean groundwater 3 containing no cyanide is discharged outside the factory site 7 .

In addition, when iron sulfate is used as a sustained-release acidic agent, its effectiveness may decrease over time due to the influence of groundwater and the like. To address such problems, it is conceivable to restore the effectiveness of the sustained-release acidic agent by using a sustained-release organic substance to create a reducing atmosphere in the purification facility and its surrounding environment.

The slow-release organics are supplied to the clarification facility, for example, by injection wells. Injection wells can be placed in any number, eg upstream of the groundwater. By injecting the controlled-release organic substance into the injection well, the controlled-release organic substance diffuses downstream along the groundwater flow, and the controlled-release organic substance can be supplied to the purification wall 2 .

It is also possible to form an injection well in advance in the purification wall 2 and inject the sustained-release organic substance directly into the purification wall 2 .

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

<Overview of test method>
(1) A case was assumed in which a purification wall mixed with a cyanide treatment agent was used as the purification equipment. A column filled with a cyanide treatment agent was used as a purifying wall. A schematic diagram is shown in FIG. 2, and the description will be based thereon.

(2) The column is either column 21 having a cyan compound treating agent packed bed 15 with an inner diameter of 10 cm and a length of 3 cm, or column 23 having a cyan compound treating agent packed bed 15 with an inner diameter of 5 cm and a length of 20 cm. . In order to prevent the cyanide treatment agent from flowing out of the packed bed, both ends of the packed bed were sealed with a glass bead layer 16 of about several centimeters and a plug 17 in order from the packed bed. Which column is used will be specified in each example described later.

(3) An aqueous ferrocyanine solution 14 obtained by adding potassium ferrocyanide (trihydrate) to water was used as a solution for removing water contaminated with cyanide. The cyan concentration of the aqueous ferrocyanine solution 14 (referring to the total cyan concentration; the same shall apply hereinafter) is 1 mg/L.

(4) The aqueous ferrocyanine solution 14 is conveyed through the first conduit 11 to the metering pump 18, and from the metering pump 18 through the second conduit 12, the column 21 or 23 simulating a purification wall. . The flow rate of the aqueous ferrocyanine solution 14 is controlled by a metering pump 18 to 0.5 to 2 mL/min.

(5) The aqueous ferrocyanine solution 14 after passing through the column is conveyed to the sampling container 19 through the third pipeline 13 .

(6) The amount of water passing through the aqueous ferrocyanine solution 14 transported to the sampling container 19 (hereinafter simply referred to as “water passing”) and the cyanide concentration and pH of the water accumulated in the sampling container 19 are measured once a week. degree was measured. The concentration of cyanide was measured by the distillation-pyridine acid absorption photometry method of JIS K0102 (test method for industrial wastewater).

(Regarding judgment criteria)
"Environmental Standards for Groundwater Pollution (Environmental Agency Notification)" is the water flow rate that satisfies”. Since the concentration of cyanide in the aqueous ferrocyanine solution immediately after passing through the column is unstable, the judgment of "the amount of water passing that satisfies the cyanide environmental standard value" is based on the amount of water passing through the ferrocyanin aqueous solution of 50 L. shall be done after reaching The reason why the concentration of cyanide in the ferrocyanine aqueous solution is unstable may be that the adsorptive power of the column is not stable.

(Example 1)
A column 21 was packed with a cyanide treatment agent consisting of 100 g of iron powder, 7 g of Sandset (a sulfur-containing pH-lowering material manufactured by Nissan Agri Co., Ltd.) as a sustained-release acidic agent, and 340 g of silica sand. After that, the ferrocyanine aqueous solution was passed through the column 21, and the ferrocyanine aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements. In addition, in Example 1, the iron powder is also used as an adsorbent.

(Example 2)
Column 21 is filled with a cyanide treatment agent consisting of 90 g of iron powder, 18 g of sand set as a sustained-release acidic agent, and 160 g of Akadama soil (granulated product of Kanto loam layer, weakly acidic clay soil) as an adsorbent. did. After that, the ferrocyanine aqueous solution was passed through the column 21, and the ferrocyanine aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements.

(Example 3)
Column 23 was filled with a cyanide treatment agent consisting of 100 g of iron powder, 30 g of montmorillonite (activated clay obtained by heat-treating acid clay) as a sustained-release acidic agent, and 170 g of Akadama clay as an adsorbent. After that, the ferrocyanine aqueous solution was passed through the column 23, and the ferrocyanic aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements.

(Example 4)
A column 23 was filled with a cyanide treatment agent consisting of 80 g of ferrosand (manufactured by Ishihara Techno Co., Ltd., a material containing iron sulfate as a main component) as a sustained release acidic agent and 240 g of Akadama soil as an adsorbent. After that, the ferrocyanine aqueous solution was passed through the column 23, and the ferrocyanic aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements.

(Comparative example 1)
A column 21 was packed with a cyanide treatment agent comprising 100 g of iron powder and 335 g of silica sand. After that, the ferrocyanine aqueous solution was passed through the column 21, and the ferrocyanine aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements.

(Comparative example 2)
A column 23 was packed with a cyanide treatment agent comprising 56 g of iron powder and 560 g of silica sand. After that, the ferrocyanine aqueous solution was passed through the column 23, and the ferrocyanic aqueous solution 14 transported to the sampling container 19 was subjected to the above-described water flow rate, concentration, and pH measurements.

<Experimental results>
The results of the above examples and comparative examples are shown as graphs in FIGS. 3-5. Regarding the upper graph shown in each figure, the x-axis is the water flow rate (L) and the y-axis is the cyan concentration (mg/L). Next, for the lower graph, the x-axis is water flow rate and the y-axis is pH.

As shown in FIG. 5, Comparative Example 1 exceeded the cyan environmental standard value at the stage of 50 L of water flow. After that, in the stage of about 75 L to about 110 L of water flow, the cyan concentration fell below the cyan environmental standard value, but exceeded the cyan environmental standard value again at about 110 L of water flow.

In Comparative Example 2, although the cyan concentration increased to near the cyan environmental standard value at the stage of the water flow rate of 50 L, the cyan concentration decreased thereafter. However, the concentration of cyanide increased again at a water flow rate of about 80 L, and exceeded the cyanide environmental standard value at a water flow rate of about 105 L.

As shown in FIG. 3, in Example 1, the environmental standard value for cyanide was exceeded at a water flow rate of about 170 L, but the concentration of cyanide decreased again, and the environmental standard value for cyanide was not exceeded until the water flow rate was about 275 L. That is, when compared with Comparative Example 1 in which the column used in Example 1 is similar, the cyanide environmental standard value was exceeded at a water flow rate of about 110 L, even considering that the cyanide concentration once decreased. It can be seen that more water with a lower cyanide concentration can be obtained than in Comparative Example 1. Moreover, since Comparative Example 1 exceeds the cyan environmental standard value at the stage of 50 L of water flow, it is judged that there is a problem in stability.

In Example 2, the cyan environmental standard value was exceeded for the first time at a water flow rate of about 320 L. That is, compared with Example 1, much water with a lower cyanide concentration could be obtained. It is considered that the use of clay-based Akadama soil was preferable to silica sand in terms of adsorption capacity.

Example 3 did not exceed the cyan environmental standard value at least up to about 135 L of water flow. That is, when compared with Comparative Example 2, in which the column used in Example 3 is similar, the cyanide environmental standard value was exceeded at a water flow rate of about 105 L, even considering that the cyanide concentration had once decreased. It can be seen that the amount of water flow is larger than that of Comparative Example 2.

In Example 4, the water flow rate did not exceed the cyan environmental standard value until at least about 250 L, and the water flow rate that satisfied the cyan environmental standard value was significantly increased compared to Comparative Example 2 in which the column used was similar. I was able to In addition, the effect of pH lowering over a long period of time by ferro-sand was remarkably observed.

Reference Signs List 1 Groundwater contaminated with cyanide 2 Purified wall 3 Purified clean groundwater 5 Inside the factory premises 7 Outside the factory premises 11 First pipeline 12 2nd pipeline 13 3rd pipeline 14 Aqueous ferrocyanine solution 15 Cyanide treatment agent filled layer 16 Glass bead layer 17 Stopper 18 Metering pump 19 Sampling container 21 Column having an inner diameter of 10 cm and a cyan compound treating agent packed bed of 3 cm in length 23 : Column having an inner diameter of 5 cm and a cyan compound treating agent packed bed of 20 cm in length

Claims (4)

A polluted water purification method for purifying water contaminated with cyanide using a purification facility equipped with a cyanide treatment agent,
The cyanide treatment agent contains a sustained-release acidic agent, an adsorbent containing Akadama soil, and iron ,
A method for purifying contaminated water , wherein the iron content is 36 to 37 when the total content of the iron and the Akadama soil is 100 . A polluted water purification method for purifying water contaminated with cyanide using a purification facility equipped with a cyanide treatment agent, wherein the cyanide treatment agent is at least one of sulfur trioxide and iron sulfate-based acidic agent. A method for purifying polluted water, characterized by containing a sustained-release acidic agent containing or an adsorbent, and iron. 3. The contaminated water purification method according to claim 1, wherein in said cyanide treatment agent, iron is contained in either said sustained-release acidic agent or said adsorbent. The purification equipment is equipment for purifying groundwater contained in soil, and has a purification wall mixed with the cyanide treatment agent provided downstream of the flow of the groundwater, wherein the purification wall is 4. The polluted water purification method according to claim 1, wherein the cyanide compounds in the groundwater permeating through the wall are adsorbed and removed by the cyanide treatment agent.

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