JP7229651B2 - Liquid handling method - Google Patents

Description

The present invention relates to a liquid processing method. More particularly, the present invention relates to a method for treating a liquid containing ammonium nitrogen such as ammonium salts generated in non-ferrous metal smelting, plating and the like.

In the process of smelting non-ferrous metals such as copper, nickel, lead, and zinc, various types of waste water are generated during smelting. These wastewaters contain various substances (hereinafter referred to as inclusions) derived from ores used as raw materials or produced during smelting. Such inclusions include, for example, ammonium salts, cadmium ions, lead ions, zinc ions, and organic compounds.

Since wastewater containing these substances cannot be discharged into the sea as it is, it is necessary to separate and remove the substances contained in the wastewater by an appropriate method and reduce the concentration to below a certain standard. .

Here, heavy metals such as lead ions and zinc ions contained in the waste water can be separated by a method such as precipitating by pH adjustment by neutralization.

On the other hand, if the waste water contains ammonium salts, ammonium nitrogen derived from the ammonium salts may be generated. Unlike heavy metals such as lead and zinc, such ammonium nitrogen is difficult to separate by a method such as precipitation by pH adjustment by neutralization.

As a method for effectively removing such ammonium nitrogen from waste water, etc., there is a method using biological treatment. In biological treatment, nitrifying bacteria are mixed with liquids such as wastewater containing ammonia nitrogen, and the nitrifying bacteria oxidize the ammonia nitrogen to nitrite nitrogen, and the nitrite nitrogen produced is oxidized to nitrate nitrogen. do. Then, the nitrate nitrogen is reduced to nitrite nitrogen, and the nitrite nitrogen is further reduced and removed as nitrogen gas from wastewater or the like. That is, in biological treatment, ammonium nitrogen can be removed from waste water or the like as nitrogen gas (see Patent Documents 1 and 2).

JP-A-10-263575 JP 2015-013290 A

However, although biological treatment can be used to remove ammonia nitrogen in wastewater such as sewage, it is difficult to apply it to wastewater generated in the process of smelting non-ferrous metals. Wastewater generated in the smelting of non-ferrous metals usually has a high salt concentration of inorganic salts due to factors such as ores and components added during the smelting process. Moreover, it contains heavy metals as described above. For this reason, it is difficult to adjust waste water to an environment suitable for biological treatment, that is, an environment in which nitrifying bacteria and the like are activated, and it is difficult to perform biological treatment stably and efficiently.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a liquid treatment method capable of stably removing ammonia nitrogen contained in a liquid.

A method for treating a liquid of the first invention is a method for treating a liquid containing ammonia nitrogen and heavy metals, wherein the pH of the liquid to be treated is adjusted to a range of 10 or more and 12 or less, and the sediment containing heavy metals and the treated liquid are treated. are mixed and the ammonia separated from the ammonia nitrogen is dissolved to form a treated slurry, and the soluble and a disk-shaped baffle plate disposed above the stirring blades and having a surface orthogonal to the rotation axis of the stirring blades, as a device for blowing in the gas of and stirring the treated slurry. wherein the baffle plate has a distance from the rotating shaft of the stirring blade to the outer edge of the baffle plate equal to or longer than the length from the rotating shaft of the stirring blade to the tip of the stirring blade It is characterized by using a device formed as follows.
A liquid processing method of a second invention is characterized in that, in the first invention, the soluble gas is one or more of oxygen, air, and carbon dioxide gas.
A third aspect of the present invention is a liquid treatment method according to the first or second aspect, wherein the soluble gas is oxygen or air, and the dissolved oxygen concentration in the treated slurry is maintained at 8 mg/liter or more. Characterized by blowing gas.
The method for treating a liquid according to a fourth invention is characterized in that, in the third invention, the flow rate of oxygen blown into the treated slurry is 0.1 to 6 liters/minute per liter of the treated slurry in terms of air volume. The soluble gas is blown into the treated slurry.
A method for treating a liquid according to a fifth invention is characterized in that , in any one of the first to fourth inventions , the treatment liquid contains at least one of lead and zinc.

According to the first invention, by appropriately adjusting the pH of the treatment slurry, it is possible to change the ammonia nitrogen contained in the treatment liquid into the state of ammonia while turning heavy metals in the treatment liquid into precipitates. By blowing a soluble gas into the treatment slurry in which the precipitate in which ammonia is dissolved and the treatment liquid are mixed, the ammonia can be removed as gas from the treatment slurry. Therefore, the treatment liquid containing ammonium nitrogen can be a liquid having a low ammonia nitrogen content, which facilitates the post-treatment of the treatment liquid. In addition, since the contact opportunity between ammonia in the treated slurry and the soluble gas can be increased, the effect of discharging ammonia from the treated slurry can be enhanced. Moreover, since the bubbles not only rise in the treated slurry but also move horizontally along the baffle plate, the residence time of the bubbles in the treated slurry can be increased. As the temperature of the treated slurry rises, the solubility of ammonia in the treated slurry decreases, so that the effect of removing ammonia from the treated slurry can be enhanced.
According to the second aspect of the invention, when the soluble gas dissolves in the treated slurry, the solubility of ammonia decreases, so the effect of removing ammonia from the treated slurry can be enhanced.
According to the third and fourth inventions, when the dissolved oxygen concentration in the treated slurry increases, the solubility of ammonia decreases, so the effect of removing ammonia from the treated slurry can be enhanced.
According to the fifth aspect of the invention , even if the treatment liquid contains lead or zinc and is difficult to be biologically treated, ammonia nitrogen can be removed from the treatment slurry as gaseous ammonia. Therefore, even if the liquid to be treated contains lead, zinc, and ammonia nitrogen, the concentration of lead, zinc, and ammonia nitrogen can be reduced, so that disposal and reuse of the liquid to be treated can be facilitated.

1 is a flowchart of a liquid processing method of the present invention; (A) is a schematic side view of a processing tank 1 equipped with a stirrer 10, and (B) is a view taken along the line BB of (A).

The liquid treatment method of the present invention is a method for removing ammonia nitrogen from a treatment liquid containing ammonia nitrogen such as an ammonium salt, and can remove ammonia nitrogen as gaseous ammonia without biological treatment. It is characterized by the fact that

The liquid containing ammonium nitrogen (treatment liquid) to be treated by the liquid treatment method of the present invention is not particularly limited as long as it is a liquid containing ammonium nitrogen such as an ammonium salt. For example, in addition to ammonium salts generated in nonferrous metal smelting, wastewater containing ammonium salts generated in wastewater containing cadmium ions, lead ions, zinc ions, organic compounds and the like can be mentioned.

In particular, the liquid treatment method of the present invention is suitable for treatment of liquids that contain heavy metals and are difficult to be biologically treated. Specifically, when the liquid to be treated contains at least one of lead and zinc, it is difficult to carry out biological treatment. difficult to remove. However, in the liquid treatment method of the present invention, ammonia nitrogen can be removed as gaseous ammonia from a liquid to be treated that is difficult to be biologically treated. Therefore, even if the liquid to be treated contains lead and zinc in addition to ammonia nitrogen, the concentration of ammonia nitrogen can be reduced together with lead and zinc in the liquid to be treated, so that the liquid to be treated can be discarded or reused. etc. will be easier.

Although the pH of the treatment liquid is not particularly limited, when an alkaline neutralizer is added to the treatment liquid containing lead or zinc to form a precipitate of lead or zinc, the pH of the treatment liquid should be 9 or higher. If it is about 11.5 or less, it can be processed. For example, the wastewater generated in the above-described non-ferrous metal smelting has a pH of about 10 to 11.5, so lead, zinc, etc. can be removed from the treated liquid as precipitates by the liquid treatment method of the present invention. can be done.

In this specification, ammonium nitrogen means an ammonium salt, a decomposition product of organic nitrogen, or the like.

(Processing method of the present invention)
The processing method of the present invention is described below.
The processing method of the present invention comprises the following two steps, as shown in FIG.

First, in the first step, precipitates such as heavy metals are generated in the liquid to be treated to form a treated slurry, and nitrogen is separated from ammonia nitrogen in the treated slurry to form ammonia.
In the second step, the ammonia in the treated slurry formed in the first step is separated (discharged) from the treated slurry as a gas and converted into a post-treatment liquid.

(First step)
Specifically, in the first step, a neutralizing agent is added to the treatment liquid containing ammonium nitrogen such as an ammonium salt. Then, heavy metals such as lead and zinc present in the form of ions in the liquid to be treated react with the neutralizing agent and precipitate as heavy metal salts to form precipitates. As a result, a treated slurry is formed in which the treated liquid contains a sediment as a solid content.

Further, when the treated slurry is formed, ammonia is separated from ammonia nitrogen by the following reaction (reaction formula 1), and the separated ammonia becomes dissolved in the treated slurry.

Reaction formula 1: NH ₄ ⁺ + OH ⁻ ⇒ NH ₃ + H ₂ O

Moreover, the neutralizing agent is added so that the pH of the treated slurry becomes 10 or more and 12 or less. That is, some of the neutralizing agent is consumed in the formation of the precipitate, but the neutralizing agent is added so as to bring the treated slurry to a desired concentration.

Then, at the end of the first step, a treated slurry having a pH of 10 or higher and 12 or lower, in which the precipitate and the treatment liquid are mixed, and in which the ammonia separated from the ammonia nitrogen is dissolved is formed.

(Second step)
In this second step, a soluble gas is supplied to the treated slurry formed in the first step. Specifically, the soluble gas is supplied to the treated slurry by bubbling or the like. Then, as the amount of soluble gas dissolved in the treated slurry increases, the solubility of ammonia decreases, so that ammonia can be discharged from the treated slurry as a gas.

It is desirable to supply the soluble gas to the treatment slurry so that part of it is released from the surface of the treatment slurry as bubbles. Then, the ammonia in the treated slurry can be brought into contact with the gaseous soluble gas, so that the efficiency of discharging the ammonia in the treated slurry as a gas from the treated slurry can be increased.

Moreover, if the treated slurry is stirred by a stirrer (see FIG. 2), the interface between the bubbles of the soluble gas and the treated slurry increases, increasing the chances of contact between the ammonia in the treated slurry and the soluble gas. Then, the efficiency of discharging the ammonia in the treated slurry as gas from the treated slurry can be increased.

(pH of treated slurry)
In the first step, it is desirable to adjust the pH of the treated slurry to 10 or more and 12 or less, preferably 10 to 11.5. If the pH is less than 10, it becomes difficult to transform ammonia nitrogen into an ammonia state, and even if the pH is greater than 12, the effect of transforming ammonia nitrogen into an ammonia state cannot be improved. Moreover, if the pH is higher than 12, the cost of the neutralizing agent increases, and even substances that do not need to be removed from the liquid to be treated (such as magnesium) will form precipitates, increasing the amount of precipitates. I don't like it because Therefore, it is desirable to adjust the pH of the treated slurry to a range of 10 to 12, preferably 10 to 11.5.

(Neutralizer)
The neutralizing agent used in the first step can adjust the pH of the treated slurry to 10 or more and 12 or less, and reacts with heavy metals, metal ions, etc. in the treated slurry to form precipitates. not.

For example, if the liquid to be treated is waste water generated in the smelting of non-ferrous metals, an alkali such as slaked lime or caustic soda can be used as a neutralizing agent. Then, heavy metals and the like contained in the waste water can be removed from the treated liquid as precipitates.

The amount of the neutralizing agent to be supplied to the processing liquid is not particularly limited. The pH of the treated slurry may be appropriately adjusted so as to be 10 or more and 12 or less.

(soluble gas)
As the soluble gas supplied to the treated slurry, it is preferable to use a gas having a practical solubility for removing ammonia contained in the treated slurry. For example, oxygen, air, carbon dioxide gas, ozone gas, etc. can be mentioned as soluble gases used in the liquid treatment method of the present invention. If the amount of such soluble gas dissolved in the treated slurry increases, it becomes difficult for ammonia to maintain its dissolved state, so that it becomes easier to discharge ammonia as gas from the treated slurry. For example, if a soluble gas is supplied to the treated slurry so that the dissolved oxygen concentration in the treated slurry is maintained at 8 mg/liter or more, the ammonia discharge efficiency can be increased.

In order to maintain the dissolved oxygen concentration in the treated slurry at 8 mg/liter or more, the amount of soluble gas supplied to the treated slurry is not particularly limited. It may be appropriately adjusted according to the substance and amount in the slurry to be treated and the type of soluble gas to be blown. For example, the liquid to be treated is waste water generated in the smelting of non-ferrous metals, and the soluble gas is oxygen or air. In this case, the soluble gas is blown into the treated slurry so that the flow rate of oxygen blown into the treated slurry is 0.1 to 6 liters/minute per liter of treated slurry in terms of the amount of air. Then, the dissolved oxygen concentration in the treated slurry can be maintained at 8 mg/liter or more.

Gases such as nitrogen, argon, helium, and chlorine can also be used in terms of promoting the vaporization of ammonia by increasing the contact opportunities by increasing the area of the gas-liquid interface (the interface between the soluble gas and the slurry to be treated). is. However, nitrogen, argon, and helium have extremely low solubility in the treatment slurry, and chlorine gas, although highly soluble in the treatment slurry, may react with dissolved substances to form chlorides. Therefore, oxygen, air, carbon dioxide gas, ozone gas, and the like are preferable as the soluble gas used in the liquid treatment method of the present invention in order to moderately suppress the generation of precipitates while increasing the efficiency of removing ammonia to some extent.

Also, the soluble gas is desirably supplied to the treated slurry by bubbling. Even if it is not supplied by bubbling, if the concentration of oxygen or carbon dioxide gas dissolved in the treated slurry increases, it becomes difficult for the ammonia in the treated slurry to maintain its dissolved state, making it easier to discharge ammonia from the treated slurry as a gas. . However, if it is supplied by bubbling, it becomes easier to increase the concentration of dissolved oxygen and carbon dioxide gas in the treated slurry, so that it becomes easier to discharge ammonia as a gas from the treated slurry. Moreover, since the interface between the bubbles of the blown soluble gas and the treated slurry increases, the chances of contact between the bubbles and ammonia can be increased. When the bubbles of the blown soluble gas come into contact with the ammonia in the treated slurry, the ammonia tends to become gaseous. Therefore, if the soluble gas is supplied to the treated slurry by bubbling, it becomes easier to discharge the ammonia as a gas from the treated slurry.

In addition, the size of the air bubbles formed when the soluble gas is supplied to the treatment slurry by bubbling is not particularly limited. However, in order to increase the contact interface with the treatment slurry, finer bubbles are desirable. For example, about 100 to 5000 μm is desirable. Further, fine air bubbles (approximately 100 μm or less) such as so-called microbubbles may be used. However, it is desirable that the size of the air bubbles be at least large enough to prevent the air bubbles from being discharged from the liquid surface of the treated slurry due to the fineness of the air bubbles.

Further, in the second step, the pH of the treated slurry may deviate from the above-described range (pH 10 or more and 12 or less) due to carbon dioxide gas or the like while the availability gas is being blown. Therefore, in the second step, the pH of the treated slurry is measured with a pH meter or the like, and a soluble gas is blown in while adding acid or alkali so that the pH of the treated slurry is maintained within the above-described range. is desirable. Substances used for such pH maintenance are also not particularly limited. For example, caustic soda (sodium hydroxide) or slaked lime can be used.

(stirring)
In the second step described above, in order to discharge the ammonia dissolved in the treated slurry as gas, it is desirable to stir the treated slurry when the gas is blown into the treated slurry. By stirring the treated slurry, the air bubbles can be made finer and the time for which the air bubbles stay in the treated slurry can be extended. This facilitates dissolution of the soluble gas into the processing slurry. Moreover, since the contact opportunities between the ammonia dissolved in the treated slurry and the air bubbles can be increased, the efficiency of separating ammonia as a gas from the treated slurry can be enhanced.

The device and method for stirring the treated slurry are not particularly limited, but in order to improve the ammonia discharge efficiency, it is desirable to use a stirrer having the following structure.

(Structure of Stirrer 10)
As shown in FIG. 2, a stirrer 10, a rotating shaft 11, a plurality of stirring blades 12 fixed to the rotating shaft 11, and arranged above the stirring blades 12 (that is, on the liquid surface SF side of the slurry S to be treated). and a baffle plate 13.

As shown in FIG. 2, one end of the rotary shaft 11 is connected to a drive source such as a motor.
The other end (lower end in FIG. 2) of the rotating shaft 11 is immersed in the processing slurry S in the processing tank 1, and a plurality of (four in FIG. 2) stirring blades 12 are attached to the other end. is provided. The stirring blades 12 are connected at their base ends to the rotary shaft 11 , and the four stirring blades 12 are provided so as to be rotationally symmetrical about the central axis of the rotary shaft 11 .
A plate-like baffle plate 13 is provided above the plurality of stirring blades 12 . The baffle plate 13 is provided so that the surface on the stirring blade 12 side is perpendicular to the central axis of the rotary shaft 11 . Moreover, the radius of the baffle plate 13, that is, the distance from the central axis of the rotating shaft 11 to the outer edge is set to be equal to or longer than the length from the central axis of the rotating shaft 11 to the tip of the stirring blade 12. there is

With the structure as described above, the processing slurry S can be stirred by the plurality of stirring blades 12 by driving the drive source to rotate the rotary shaft 11 . Then, the mixing of the soluble gas bubbles g supplied to the treatment slurry S and the treatment slurry S can be promoted, and the diameter of the bubbles g can be reduced. Then, the dissolution of the soluble gas into the treated slurry S can be promoted, and the contact interface between the bubbles g and the treated slurry S can be increased.

Moreover, the position in which the stirring blade 12 is provided in the treatment tank 1 is not particularly limited. It is desirable to provide the nozzle above the blowing port for blowing the soluble gas into the treatment slurry S, particularly vertically above the blowing port. By arranging it in such a position, it is possible to effectively bring the bubbles into contact with the stirring blade 12, which makes it easier to reduce the diameter of the bubbles g. Moreover, the air bubbles g rising in the processing slurry S can be brought into contact with the baffle plate 13 . Then, the air bubbles g not only rise in the processing slurry S, but also move horizontally along the baffle plate 13, so that the residence time in the processing slurry S can be increased.

The number of stirring blades 12 is not particularly limited, and may be four or more, or may be three or less. Further, the stirring blade 12 may be arranged so that its surface is parallel to the central axis of the rotating shaft 11, or may be slightly inclined.

The position where the baffle plate 13 is attached is not particularly limited. The distance between the stirring blades 12 and the liquid surface SF of the processing slurry S is not particularly limited as long as it is arranged between the liquid surface SF of the processing slurry S and the plurality of stirring blades 12 . It may be appropriately selected according to the size of the processing tank 1, the components of the processing liquid to be processed, and the type and flow rate of the soluble gas to be supplied.

The fixing method of the baffle plate 13 is also not particularly limited. It suffices if the baffle plate 13 can be held so as not to move relative to the stirring blade 12 .

The shape of the baffle plate 13 is not particularly limited, and may be circular or rectangular. Also, a plurality of through holes may be provided in the baffle plate 13 so as to penetrate the front and back. In this case, if the diameter of the through-hole is made smaller than the diameter of the bubble g that normally exists at the position of the baffle plate 13, the through-hole can be expected to reduce the diameter of the bubble g.

The number of revolutions of the stirring blade 12 is also not particularly limited, and may be appropriately selected according to the size of the processing tank 1, the components of the processing liquid to be processed, and the type and flow rate of the soluble gas to be supplied. However, if the number of revolutions is too low, the dispersion of the bubbles g in the treated slurry S becomes insufficient. Therefore, the rotation speed of the stirring blade 12 is preferably 350 rpm or more, more preferably 400 rpm or more.

It was confirmed that the amount of ammonia nitrogen in a liquid containing heavy metals and ammonia nitrogen can be effectively reduced by adopting the liquid treatment method of the present invention.

In the experiment, slaked lime was added to 1 liter of liquid (original solution) containing 50 mg/liter of ammonium nitrogen, 1.2 mg/liter of lead, and 670 mg/liter of zinc to adjust the pH to 11, and hydroxide ( A treated slurry containing the precipitate) was formed. A gas was supplied to the formed treated slurry by the following method, and the removal efficiency of ammonia nitrogen was confirmed.

(Example 1)
While maintaining the liquid temperature of the treated slurry at 40° C., air was blown in at a rate of 2 liters/minute for 30 minutes.
(Example 2)
The conditions were the same as in Example 1, except that the treated slurry was stirred with a stirrer (see FIG. 2) while blowing air (the stirring blade of the stirrer was rotated at 400 revolutions per minute).
(Example 3)
The conditions were the same as in Example 2, except that the amount of blowing was set at 2 liters/minute and carbon dioxide gas was blown from the cylinder for 25 minutes.
(Example 4)
The conditions were the same as in Example 1 except that the stirring blade was rotated at 350 rpm.

(Comparative example 1)
The conditions were the same as in Example 1, except that air was not blown.
(Comparative example 2)
The conditions were the same as in Example 2, except that the liquid temperature of the treated slurry was changed to 20° C. during air blowing.

The removal efficiency of ammonia nitrogen was obtained by the following method.
After gas supply, the treated slurry was subjected to solid-liquid separation using Nutsche and filter paper, and the amount of ammonia nitrogen remaining in the separated liquid (filtrate) was analyzed using a known method (absorption photometry). The removal efficiency ((1−A/B)×100%) was determined from the amount A of the remaining ammonia nitrogen and the amount B of the ammonia nitrogen in the original solution.

The results are shown below.

In Example 1, the amount of residual ammonium nitrogen was 25 mg/liter, and it was confirmed that 50% of the ammonium nitrogen contained in the original solution could be removed.

In Example 2, the amount of residual ammonium nitrogen was 20 mg/liter. It was confirmed that the agitation improves the contact efficiency between air and ammonia nitrogen and improves the removal efficiency of ammonia nitrogen.

In Example 3, the amount of residual ammonium nitrogen was 18 mg/liter. It was confirmed that by blowing carbon dioxide gas, the ammonia nitrogen removal efficiency can be improved up to 60% compared to air.

In Example 4, the amount of residual ammonium nitrogen was 30 mg/liter. It was confirmed that when the rotational speed of the stirring blade is slowed down, the efficiency of contact between air and ammonia nitrogen decreases, and the removal efficiency of ammonia nitrogen decreases.

(Comparative example 1)
In Comparative Example 1, the amount of residual ammonium nitrogen was 37 mg/liter. It was confirmed that when stirring and air blowing were not performed, the ammonia nitrogen was not sufficiently vaporized, and the removal efficiency of the ammonia nitrogen was lowered.
(Comparative example 2)
In Comparative Example 2, the amount of residual ammonium nitrogen was 35 mg/liter. It was confirmed that when the temperature of the treated slurry is low, the ammonia nitrogen is not sufficiently gasified and the removal efficiency of the ammonia nitrogen decreases.

The liquid treatment method of the present invention is suitable as a method for stably removing ammonium nitrogen contained in waste water generated in nonferrous metal smelting, plating, and the like.

REFERENCE SIGNS LIST 1 treatment tank 10 stirrer 11 rotating shaft 12 stirring blade 13 baffle plate S treated slurry SF liquid surface g air bubbles

Claims (5)

A method for treating a liquid containing ammonia nitrogen and heavy metals, comprising:
adjusting the pH of the treatment liquid to a range of 10 or more and 12 or less to form a treatment slurry in which the precipitate containing heavy metals and the treatment liquid are mixed and the ammonia separated from the ammonia nitrogen is dissolved;
blowing the soluble gas into the treated slurry while stirring the treated slurry while maintaining the liquid temperature of the treated slurry at 40° C. or higher ;
As a device for stirring the treated slurry,
a stirring blade;
A disk-shaped baffle plate having a surface perpendicular to the rotation axis of the stirring blade, arranged above the stirring blade,
The baffle plate
Using a device formed so that the distance from the rotating shaft of the stirring blade to the outer edge of the baffle plate is equal to or longer than the length from the rotating shaft of the stirring blade to the tip of the stirring blade A method of treating a liquid characterized by: The soluble gas is
2. The method of treating liquid according to claim 1, wherein at least one of oxygen, air, and carbon dioxide is used. the soluble gas is oxygen or air,
3. The liquid treatment method according to claim 1, wherein said soluble gas is blown in such that the dissolved oxygen concentration in said treated slurry is maintained at 8 mg/liter or more. The soluble gas is blown into the treated slurry such that the flow rate of oxygen blown into the treated slurry is 0.1 to 6 liters/minute per liter of the treated slurry in terms of air volume. Item 4. A method for treating a liquid according to item 3. 5. The liquid processing method according to any one of claims 1 to 4, wherein the processing liquid contains at least one of lead and zinc.

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