JP2021166981A - Method for treating pit wastewater - Google Patents

Abstract

To provide a treatment method which prevents elution of fluorine even when fluorine-containing sediment is mixed with heavy metal segment, and can enhance treatment efficiency by subjecting the sediments to unification treatment.SOLUTION: A method for treating pit wastewater that adds a neutralizer to acidic pit wastewater containing heavy metal and fluorine and converts the heavy metal and the fluorine into sediments and removes the sediments includes: a primary neutralization step of adding a neutralizer containing magnesium oxide to the pit wastewater, and generating heavy metal-containing sediment (primary neutralization sediment); a sediment return step of solid-liquid separating the heavy metal-containing sediment generated in the primary neutralization step, adding the magnesium oxide to the part or the whole of the sediment and converting the sediment to alkali sediment, and using the alkali sediment in a neutralizer in the primary neutralization step; and a secondary neutralization step of adding magnesium oxide and an aluminum source to a liquid content obtained by separating the heavy metal-containing sediment (primary neutralization sediment), and generating fluorine-containing sediment (secondary neutralization sediment).SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for treating wastewater (referred to as mine wastewater) discharged from a closed mine or the like. Specifically, for heavy metals such as manganese and acidic mine wastewater containing fluorine, heavy metals and fluorine are effectively precipitated. Regarding the processing method that can be removed.

Some mine wastewater contains a large amount of heavy metals such as manganese and fluorine. For example, some mine wastewater contains about 5.0 to 10 mg / L of manganese and about 20 to 30 mg / L of fluorine. Conventionally, a treatment method is known in which a neutralizing agent is added to mine wastewater to remove heavy metals and fluorine into starch.

Hydroxides of heavy metals such as manganese precipitate under liquid conditions of pH 10 or higher. On the other hand, as for fluorine, a method is known in which an aluminum source such as aluminum sulfate is used to adsorb and remove fluorine on an aluminum hydroxide precipitate generated near neutrality. As described above, since the pH range for precipitating heavy metals such as manganese (pH 10.0 or higher) and the pH range for causing fluorine-containing precipitation (pH 6.0 to 8.0) are different, manganese and fluorine should be removed at the same time. I can't.

Further, in general, hydroxide precipitation is a bulky precipitation inferior in dehydration property, so that there is a problem that the amount of precipitate increases and the capacity of the disposal site is compressed. Furthermore, the stable pH range of aluminum hydroxide precipitate is limited to near neutral, and when the pH changes from near neutral to the alkaline side or acid side, the precipitate dissolves and fluorine elutes. Therefore, when the precipitate of aluminum hydroxide is formed at pH 10 or higher and mixed with the precipitate of heavy metal hydroxide, there is a problem that fluorine is eluted, and these precipitates cannot be treated in a unified manner.

Further, as a method for removing fluorine, Patent Document 1 states that hydrotalcites and zeolites are added to fluorine-containing wastewater to remove fluorine, and a calcium salt is added to convert fluorine into calcium fluoride for precipitation. The processing method to be performed is described. Further, Patent Document 2 describes a method of forming fluorine-containing sludge and separating and removing it by using slaked lime and an aluminum flocculant.

Japanese Unexamined Patent Publication No. 2007-209886 Japanese Patent No. 4661132

The methods of Patent Documents 1 and 2 relate to the removal of fluorine in wastewater, but mine wastewater often contains heavy metals such as manganese together with fluorine, and the methods of Patent Documents 1 and 2 include heavy metals such as manganese and fluorine. Cannot be removed efficiently. Further, the conventional method for removing fluorine using aluminum sulfate has a problem that the burden of post-treatment is heavy because the aluminum hydroxide starch is bulky.

The present invention solves the above-mentioned conventional problems. By using magnesium oxide as a neutralizing agent, a heavy metal is made into a high-density starch, and even if a fluorine-containing starch is mixed with the heavy metal starch, fluorine is used. Provided is a treatment method capable of improving the treatment efficiency by making it possible to centralize the treatment of these precipitates without elution.

The present invention relates to a method for treating mine wastewater, which solves the above problems by the following configuration.
[1] In a treatment method in which a neutralizing agent is added to acidic mineral wastewater containing heavy metal and fluorine to form a starch and remove the heavy metal and fluorine, a neutralizing agent containing magnesium oxide is added to the underground wastewater to remove the heavy metal. A primary neutralization step for producing a contained starch (primary neutralized starch), a heavy metal-containing starch (primary neutralized starch) produced in the primary neutralization step is solid-liquid separated, and a part or all thereof is oxidized. Magnesium oxide is added to an alkaline starch, and this alkaline starch is used as a neutralizing agent in the primary neutralization step. It has a secondary neutralization step of adding an aluminum source and a fluorine-containing starch (secondary neutralized starch) to produce the fluorine-containing starch (secondary neutralized starch), and solid-liquid separation of the fluorine-containing starch (secondary neutralized starch). A method for treating mine wastewater, which is characterized by.
[2] In the primary neutralization step, a neutralizing agent containing magnesium oxide is added to the tunnel wastewater to generate a heavy metal-containing starch (primary neutralized starch) under a liquid state of pH 9.5 or higher, and solidify. The method for treating mineral wastewater according to the above [1], wherein magnesium oxide is added to a part or all of the liquid-separated heavy metal-containing starch (primary neutralized starch) to make an alkaline starch having a pH of 10.5 or higher.
[3] In the secondary neutralization step, magnesium oxide and an aluminum source are added to the liquid content from which the heavy metal-containing starch (primary neutralized starch) has been separated to obtain a liquid property having a pH of 6.0 to 8.0. The method for treating mineral wastewater according to the above [1] or [2], wherein a fluorine-containing starch (secondary neutralized starch) in which fluorine is adsorbed on the aluminum hydroxide precipitate is produced.
[4] The solid-liquid separated fluorine-containing starch (secondary neutralized starch) is sent to the starch return step, and the solid-liquid separated heavy metal-containing starch (primary neutralized starch) is added to the mixed starch. The above-mentioned [1] to [3], wherein magnesium oxide is added to a part or all of the mixed starch to make an alkaline starch, and this is used as a neutralizing agent in the primary neutralization step. How to treat mine wastewater.

[Specific explanation]
Hereinafter, the processing method of the present invention will be specifically described.
The treatment method of the present invention is a treatment method in which a neutralizing agent is added to acidic mineral wastewater containing heavy metal and fluorine to form a starch and remove the heavy metal and fluorine. A primary neutralization step of adding and producing a heavy metal-containing starch (primary neutralized starch), and a solid-liquid separation of the heavy metal-containing starch (primary neutralized starch) produced in the primary neutralization step are performed, and a part thereof is separated. Alternatively, magnesium oxide is added to the whole to make an alkaline starch, and this alkaline starch is used as a neutralizing agent in the primary neutralization step. It has a secondary neutralization step of adding magnesium oxide and an aluminum source to produce a fluorine-containing starch (secondary neutralized starch), and solidifies the fluorine-containing starch (secondary neutralized starch). This is a method for treating mine wastewater, which is characterized by liquid separation.

In the treatment method of the present invention, preferably, the fluorine-containing starch (secondary neutralized starch) separated in the secondary neutralization step is sent to the starch return step, and the heavy metal-containing starch (primary neutralization) separated by solid and liquid is sent. (Stand) is added to make a mixed starch, and magnesium oxide is added to a part or all of the mixed starch to make an alkaline starch, which is used as a neutralizing agent in the primary neutralization step. The outline of this processing method is shown in the process chart of FIG.

[Primary neutralization process]
A neutralizing agent is added to acidic mineral wastewater containing heavy metals and fluorine to make the heavy metals alkaline, and the heavy metals are made into a starch. Normally, the mine wastewater is acidic with a pH of 3.5 to 4.0, and a neutralizing agent is added to this to make it alkaline with a pH of 9.5 or higher, for example, a pH of 9.5 to 10.5, and the mine wastewater is contained in the mine wastewater. Heavy metals are converted into hydroxides to produce heavy metal-containing starches (primary neutralized starches). An alkaline precipitate containing magnesium oxide or magnesium oxide is used as a neutralizing agent.

When the pH of the mine wastewater is raised by the reaction of magnesium oxide added to the mine wastewater and the mine wastewater becomes an alkaline region with a pH of 9.5 to 10.5, heavy metals such as manganese contained in the mine wastewater are manganese hydroxide. It produces hydroxides such as (II) and becomes starch.

[Stand return process]
The heavy metal-containing starch (primary neutralized starch) produced in the primary neutralization step is separated by sedimentation and solid-liquid separation is performed. At this time, if a polymer flocculant is added to form coarse aggregate flocs, the sedimentation rate of the sediment can be increased, so that solid-liquid separation can be performed efficiently. This primary neutralized starch contains heavy metal hydroxides and undissolved magnesium oxide. Magnesium oxide is further added to a part or all of the solid-liquid separated primary neutralized starch to make an alkaline starch having a pH of 10.5 or higher, and the alkaline starch is sent to the primary neutralization step and used as a neutralizing agent. The residual primary neutralized starch is disposed of outside the system.

[Secondary neutralization process]
Magnesium oxide and an aluminum source were added to the liquid content from which the primary neutralized starch was separated to make the liquid property pH 6.0 to 8.0, aluminum hydroxide was precipitated, and fluorine was adsorbed on the aluminum hydroxide. Fluorine-containing starch (secondary neutralized starch) is produced. The liquid content from which the primary neutralized starch is separated is alkaline with a pH of about 9.5 to 10.5, and the pH drops when an aluminum source is added to it, but the pH drop is suppressed by adding magnesium oxide. The pH is controlled to the neutral range of 6.0 to 8.0. As the aluminum source, aluminum sulfate (aluminum sulfate band), polyaluminum chloride (PAC), or the like can be used. In this pH neutral range, aluminum hydroxide precipitates, a fluorine-containing starch on which fluorine is adsorbed is formed, and fluorine is immobilized. This fluorine-containing starch (secondary neutralized starch) is solid-liquid separated.

[Stand mixing process]
In the treatment method of the present invention, preferably, the solid-liquid separated fluorine-containing starch (secondary neutralized starch) is sent to the above-mentioned starch return step, and the mixed starch is added to the solid-liquid separated primary neutralized starch. Then, magnesium oxide is added to a part or all of the mixed starch to make an alkaline starch having a pH of 10.5 or higher, which is used as a neutralizing agent in the primary neutralization step.

The fluorine-containing starch (secondary neutralized starch) is mixed with the primary starch containing magnesium oxide, so that the aluminum component of the secondary neutralized starch reacts with the magnesium oxide of the primary neutralized starch. Form hydrotalcites. These hydrotalcites have the effect of adsorbing and immobilizing anionic components such as fluorine. Since hydrotalcites are chemically stable even when they are alkaline, fluorine does not elute even if magnesium oxide is added to the mixed starch to make an alkaline starch having a pH of 10.5 or higher. Therefore, by mixing the primary neutralized starch with the secondary neutralized starch to obtain a mixed neutralized starch, these neutralized starches can be stably unified.

The treatment method of the present invention can significantly reduce the heavy metal concentration in mineral wastewater by producing and separating heavy metal-containing starch (primary neutralized starch) using a neutralizing agent containing magnesium oxide. .. Further, by separating the fluorine-containing starch (secondary neutralized starch) produced by the secondary neutralization, the fluorine concentration of the tunnel wastewater can be significantly reduced.
Further, in the preferable treatment step of the present invention described in [4] above, a neutralizing agent containing magnesium oxide is used, and the primary neutralizing starch and the secondary neutralizing starch are mixed to form a mixed starch. Since it is possible to form a stable mixed starch in which fluorine does not elute, it becomes possible to unify these starches. By unifying the starch treatment, the burden of the starch treatment generated in the secondary neutralization step can be eliminated.
Furthermore, according to the treatment method of the present invention, a dense starch can be formed. Therefore, the burden on the disposal site can be reduced.

The process drawing which shows an example of the preferable processing process of this invention.

Hereinafter, examples of the present invention will be shown together with comparative examples.
After collecting an anti-waste water sample for water quality analysis including suspension, add 10 wt% of the sample volume to dissolve 35 wt% hydrochloric acid, and chemically quantify using an ICP emission spectroscopic analyzer and an ion chromatograph analyzer. Analysis was carried out. The results are shown in Table 1. Using the mine wastewater (called raw water) shown in Table 1, the test was conducted according to the batch test method described in the "Guidelines for the Repeated Ststillation Neutralization Method" compiled by the Technology Development Department of the Metal Mining Corporation in 1990. Was done.

[Example 1]
Magnesium oxide 0.15 g / L was added to 1 L of raw water in the tank and stirred to adjust the pH to 10 (primary neutralization step). When this pH was not reached, magnesium oxide was added. A polymer flocculant was added thereto, and the mixture was stirred to form aggregate flocs of the starch and allowed to stand, and the primary neutralized starch was precipitated and deposited on the bottom of the tank. After the completion of sedimentation, the height of the starch interface was measured, and the starch concentration was calculated from the amount of starch and the height of the starch interface (volume of starch).
On the other hand, the supernatant of the primary neutralization was collected and quantitatively analyzed by an ICP emission spectroscopic analyzer and an ion chromatograph analyzer to measure the concentrations of residual heavy metal and fluorine contained in the primary neutralized supernatant.
The supernatant and the above-mentioned primary neutralized starch were solid-liquid separated, and magnesium oxide was added to the separated primary neutralized starch to adjust the pH to 11 to obtain an alkaline starch. This alkaline starch was used as a neutralizing agent for the next primary neutralization treatment (starment return step).
_{Next, a predetermined amount of an aluminum sulfate solution (Al 2} O ₃ concentration 8.0 wt%) was added to the separated supernatant, and magnesium oxide, a neutralizing agent, was further added to adjust the pH to 7.0 to prepare a neutralized slurry (). Secondary neutralization step). A polymer flocculant was added to the neutralized slurry and stirred to form aggregated flocs of the starch and allowed to stand, and the secondary neutralized starch was precipitated and deposited on the bottom of the tank. After the completion of sedimentation, the height of the starch interface was measured, and the starch concentration was calculated from the amount of starch and the height of the starch interface (volume of starch).
On the other hand, the supernatant of the secondary neutralization was collected and quantitatively analyzed by an ICP emission spectroscopic analyzer and an ion chromatograph analyzer to measure the concentrations of residual heavy metal and fluorine contained in the secondary neutralized supernatant. .. These results are shown in Table 2.

[Example 2]
In the treatment step of Example 1 above, the secondary neutralized starch produced in the secondary neutralization step was solid-liquid separated and the whole amount was mixed with the primary neutralized starch to prepare a mixed starch. Magnesium oxide was added to this mixed starch to adjust the pH to 11, and the mixture was made into an alkaline starch. This alkaline starch was used as a neutralizing agent in the primary neutralization step. Other than that, the treatment steps from the primary neutralization step to the secondary neutralization step and the starch return step were carried out in the same manner as in Example 1 above. The results are shown in Table 2.

[Comparative Example 1]
Primary neutralization and secondary neutralization were carried out in the same manner as in Example 1 except that slaked lime was used as a neutralizing agent instead of magnesium oxide. The results are shown in Table 2.

As shown in Table 2, the concentration of the primary neutralized precipitate was 180 g / L in Examples 1 and 2, but the ratio (100 g / L in Comparative Example 1 was lower than that in Examples 1 and 2). It can be seen that the concentration of the precipitate is higher in Examples 1 and 2. The volume of the secondary neutralized precipitate is 4.0 ml in Examples 1 and 2, which is very small, but in Comparative Example 1. The volume is 60 ml, which is a bulky precipitate. This is because MgO used as a neutralizing agent in Examples 1 and 2 has a slower dissolution rate in water than that of slaked lime in Comparative Example 1. This is because the new precipitates are likely to precipitate in the vicinity of the particles at a high density, which contributes to the concentration and volume reduction of the precipitates.

Further, when the fluorine concentration of the supernatant after the primary neutralization is compared, it is almost the same concentration as the raw water in Example 1 and Comparative Example 1, but it is 12 mg / L in Example 2, and even in the primary neutralization, it is one of fluorine. The part has been removed. This is because the secondary neutralized starch was mixed with the primary neutralized starch to make an alkaline starch in Example 2, so that MgO in the starch reacts with the aluminum component in the secondary neutralized starch. It is considered that this is because hydrotalcites are formed and fluorine is taken in and removed from the hydrotalcites. Comparing the amount of the secondary neutralized aluminum sulfate added and the fluorine concentration of the secondary neutralized supernatant, in Example 1 and Comparative Example 1, 0.80 g / L of aluminum sulfate was added to the supernatant. While the fluorine concentration was 6.7 mg / L and 6.9 mg / L, respectively, in Example 2, even if only 0.60 g / L was added, the fluorine concentration of the supernatant was 3.8 mg / L. It has dropped dramatically. This is because the fluorine concentration of the supernatant of the primary neutralization is as low as 12 mg / L in Example 2, so that the load of the secondary neutralization is reduced, and even if the amount of aluminum sulfate added is small, the fluorine concentration can be increased. It is considered that this is because it can be sufficiently reduced.

Claims (4)

In a treatment method in which a neutralizing agent is added to acidic mineral wastewater containing heavy metal and fluorine to form a starch and remove the heavy metal and fluorine, a neutralizing agent containing magnesium oxide is added to the underground wastewater to form a heavy metal-containing starch. A primary neutralization step for producing (primary neutralized starch), a heavy metal-containing starch (primary neutralized starch) produced in the primary neutralization step is solid-liquid separated, and magnesium oxide is added to a part or all of the solid-liquid separation. Alkaline starch is used as a neutralizing agent in the primary neutralization step. It has a secondary neutralization step of adding fluorine-containing starch (secondary neutralized starch) to produce the fluorine-containing starch (secondary neutralized starch), and is characterized by solid-liquid separation of the fluorine-containing starch (secondary neutralized starch). How to treat mine wastewater. In the primary neutralization step, a neutralizing agent containing magnesium oxide was added to the tunnel wastewater to generate a heavy metal-containing starch (primary neutralizing starch) under a liquid property of pH 9.5 or higher, and solid-liquid separation was performed. The method for treating mineral wastewater according to claim 1, wherein magnesium oxide is added to a part or all of the heavy metal-containing starch (primary neutralized starch) to make an alkaline starch having a pH of 10.5 or higher. In the secondary neutralization step, magnesium oxide and an aluminum source are added to the liquid in which the heavy metal-containing starch (primary neutralized starch) is separated to make the liquid having a pH of 6.0 to 8.0, and water is used. The method for treating mineral wastewater according to claim 1 or 2, wherein a fluorine-containing starch (secondary neutralized starch) in which fluorine is adsorbed on aluminum oxide precipitate is produced. The solid-liquid separated fluorine-containing starch (secondary neutralized starch) is sent to the starch return step, and is added to the solid-liquid separated heavy metal-containing starch (primary neutralized starch) to form a mixed starch. The method for treating mineral wastewater according to any one of claims 1 to 3, wherein magnesium oxide is added to a part or all of the mixed starch to form an alkaline starch, which is used as a neutralizing agent in the primary neutralization step. ..

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