JP2005288413A - Method for treating flying-ash leachate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating flying-ash leachate which can efficiently reduce Pb components in a liquid after solid-liquid separation. <P>SOLUTION: This method for treating flying-ash leachate includes a process 21 of precipitating Pb components dissolved in the leachate by a coprecipitation effect with heavy metal salts by adding a heavy metal containing solution 17 dissolving heavy metals to the flying-ash leachate 12 dissolving Pb components and a process 22 of solid-liquid separation of coprecipitated precipitates 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a treatment method for separating a Pb component from leachate of fly ash in which the Pb component is dissolved.

  Generally, Pb is dissolved in the leachate of fly ash. As a method for removing the Pb component dissolved in such leachate of fly ash, strong alkaline leachate is neutralized to produce Pb hydroxide, and the solubility of this Pb hydroxide is the lowest. A general method is to adjust the pH to a pH of 9 to 11, and then remove the Pb component from the filtrate by solid-liquid separation by means such as filtration. FIG. 4 shows a processing step showing the above-described method generally known from the prior art.

As a specific embodiment of the above-mentioned method generally known from the prior art, a first pH adjusting agent such as water is added to the incinerated ash to optimize the primary pH of the first obstacle substance in the incinerated ash. Adding a second pH adjusting agent such as CO ₂ gas or acid to the primary slurry after removing the precipitate, removing the first obstacle substance precipitated in the primary slurry, An incineration ash treatment system is disclosed that includes a process for producing a secondary slurry of PH optimum for precipitation of obstacle substances (see, for example, Patent Document 1). In the system disclosed in Patent Document 1, the optimum pH for the precipitation of the obstacle substance is the PH having the minimum solubility of the obstacle substance, and this treatment system can treat the incineration ash very effectively. It can be used effectively as a raw material. In addition, since the water generated during the treatment does not contain heavy metal substances, it can be discarded as it is after adjusting the pH, and no pollution problem occurs.
Japanese Patent No. 3333618 (Claim 1)

  However, in the method generally known from the above and the treatment system shown in Patent Document 1 which is a specific embodiment of the method, the pH range of the filtrate to be treated is strongly alkaline with a pH of 9 to 13. In order to move the pH region to pH 9 to 11, a large amount of acid such as sulfuric acid or hydrochloric acid is required, and this is an economically wasteful system. Moreover, it is difficult to adjust the pH range of the filtrate within the range of pH 9 to 11, and it takes time, and when the pH range of the filtrate becomes pH 9 or less, re-dissolution of Pb starts. In order to adjust the pH to 9 to 11, not only the addition of acid but also the addition of alkali may be necessary.

  Further, even if the above treatment method was applied, sufficient Pb removal could not be performed. Table 1 shows the pH of the filtrate obtained by performing the treatment step shown in FIG. 4 and the Pb dissolution concentration contained in the filtrate.

  As is apparent from Table 1, it can be seen that a large amount of Pb is still dissolved in the filtrate obtained by applying the conventional method.

On the other hand, a chemical such as sodium sulfide or sodium hydrosulfide is added to the filtrate generated by leaching fly ash with water and solid-liquid separation to produce a hardly soluble salt of Pb such as a sulfide salt of Pb, Thereafter, a method of removing Pb by filtration has also been studied.
However, the sulfide salt of Pb has a problem that the filterability is very bad, and in order to remove Pb contained in the filtrate, it is necessary to add a chemical having a Pb equivalent or more contained in the filtrate. There is a problem that the excessively added medicine is wasted. Also, the concentration of Pb contained in the filtrate generated by leaching fly ash with water and performing solid-liquid separation is not constant and varies greatly depending on the type of fly ash, so it is more than the Pb equivalent contained in the filtrate. When the amount of the drug to be added is small, Pb removal from the filtrate becomes insufficient. In order to prevent this, there is a method of adding a large excess of the drug assuming a high Pb concentration in the filtrate, but there is a problem that the excessively added drug is wasted as described above. Also, there is a method of analyzing the Pb concentration in the filtrate each time and determining the amount of drug addition from the result, but it is inefficient and impractical.

Furthermore, the pH is adjusted by adding an acid such as sulfuric acid or hydrochloric acid to the suspension before leaching the fly ash with water and solid-liquid separation to adjust to the optimum pH range for precipitation of Pb. A method of obtaining a leachate containing no Pb by filtering the leachate is also being studied.
However, this method requires a large amount of drug as in the case of adjusting pH by adding a drug to the leachate of fly ash. Further, since fly ash often contains excess slaked lime and caustic soda, there is a problem that a larger amount of drug is required than when adding a drug assuming only the Pb concentration in the filtrate. In addition, when sulfuric acid is used as a drug, a large amount of gypsum is generated, and there is a problem that the amount of desalted soot is enormous. Furthermore, when hydrochloric acid is used as a drug, the concentration of chlorine in the liquid becomes high, which has a problem that the desalting effect is weakened.

  The objective of this invention is providing the processing method of the fly ash leachate which can reduce efficiently the Pb component in the liquid after carrying out solid-liquid separation.

As shown in FIG. 1, the invention according to claim 1 adds a heavy metal-containing solution 17 in which heavy metals are dissolved to the leachate 12 of fly ash in which the Pb component is dissolved, thereby effecting coprecipitation with heavy metal salts. Is a treatment method for fly ash leachate, which includes a step 21 for precipitating the Pb component dissolved in the leachate and a step 22 for solid-liquid separation of the coprecipitated precipitate 24.
The invention according to claim 2 is the processing method according to claim 1, wherein the Pb concentration in the leachate 12 of fly ash is 0.1 mg / l or more and 10,000 mg / l or less.
The invention according to claim 3 is the invention according to claim 1, wherein the addition ratio of the heavy metal-containing solution 17 added to the fly ash leachate 12 is equal to or more than 1 equivalent of the Pb mole amount contained in the fly ash leach water. It is a certain processing method.
In the invention according to claim 4, as shown in FIG. 2, the Pb component reacts with the leachate 32 of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10000 mg / l or less, and hardly soluble. A heavy metal is dissolved in a step 38 in which a Pb component contained in the leachate is fixed in the form of a hardly soluble salt by adding a fixing agent 37 that generates a salt, and a solution containing a hardly soluble salt in which the Pb component is fixed. The heavy metal-containing solution 39 is added, and the coprecipitation effect with the heavy metal salt precipitates the Pb component dissolved in the liquid without being immobilized in the immobilization step 38 and precipitates the hardly soluble salt in which the Pb component is immobilized. This is a method for treating fly ash leachate, which includes the step 43 of causing the precipitate 47 to separate into solid and liquid.
The invention according to claim 5 is the invention according to claim 4, wherein the addition ratio of the heavy metal-containing solution 39 added to the liquid containing the hardly soluble salt to which the Pb component is immobilized is included in the liquid containing the hardly soluble salt. This is a treatment method that is at least 1 equivalent of the dissolved Pb molar amount.
As shown in FIG. 3, the invention according to claim 6 is hardly soluble by reacting the Pb component with leachate 32 of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10,000 mg / l or less. A step 51 for fixing the Pb component dissolved in the leachate 32 by adding a fixing agent 37 that generates a salt, and a step 52 for solid-liquid separation of the liquid in which the Pb component is fixed. Then, the heavy metal-containing solution 39 in which heavy metals are dissolved is added to the filtrate 53 obtained by solid-liquid separation, and dissolved in the liquid without being immobilized in the immobilization step 51 due to the coprecipitation effect with the heavy metal salt. This is a method for treating fly ash leachate, which includes a step 43 for precipitating the Pb component and a step 44 for solid-liquid separation of the precipitate 47.
The invention according to claim 7 is the treatment method according to claim 6, wherein the addition ratio of the heavy metal-containing solution 39 added to the filtrate 53 is equal to or more than 1 equivalent of the Pb molar amount contained in the filtrate. is there.
The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the heavy metals contained in the heavy metal-containing solutions 17 and 39 are made of Cu, Zn, Cd, Fe, Ni, Mn and Al. It is the processing method which is 1 type, or 2 or more types chosen from the group.
The invention according to claim 9 is the processing method according to claim 4 or 6, wherein the immobilizing agent 37 is CaCO ₃ , Na ₂ CO ₃ , Na ₂ S, NaHS or Na ₂ SO ₄ .

The method for treating fly ash leachate of the present invention has the following effects.
(1) By adding a solution such as wastewater containing other heavy metals to the fly ash leachate, the Pb component in the leachate can be removed by coprecipitation with heavy metal salts.
(2) When producing a poorly soluble salt of Pb, it is necessary to add an excess of a fixing agent. However, in the treatment method of the present invention, an excessively added fixing agent is used as a neutralizing agent. Thus, the fixing agent added excessively is not wasted.
(3) Even if the amount of the fixing agent added in the Pb immobilization step is less than the Pb equivalent contained in the fly ash leachate, the Pb component and the heavy metal can be added by adding a solution containing other heavy metals. The Pb component can be removed by coprecipitation with salt. Therefore, even when the amount of the metal salt to be added is smaller than the Pb equivalent contained in the filtrate, an appropriate treatment can be performed.
(4) Excess immobilizing agent is used as a neutralizing agent, and the Pb component that has not become a sparingly soluble salt is removed by coprecipitation. Therefore, the immobilizing agent is strictly adjusted according to the concentration of Pb dissolved in the filtrate. There is no need to determine the amount of addition.
(5) Even if it is Pb sulfide salt with very bad filterability, filterability improves by passing through the process of adding the solution containing another heavy metal.

A first embodiment of the present invention will be described with reference to FIG. 1 indicated by a solid line.
The fly ash leachate 10 to be subjected to the first treatment method of the present invention is obtained by solid-liquid separation of a slurry prepared by mixing fly ash containing at least a Pb component and water at a predetermined ratio. It is a liquid. Examples of the fly ash containing the Pb component include fly ash and molten fly ash obtained from an incinerator, melting furnace, gasification melting furnace, and the like. The Pb concentration in the fly ash leachate 10 is not particularly limited, but is preferably 0.1 mg / l or more and 10,000 mg / l or less, particularly preferably 0.1 to 2000 mg / l, and even more. Preferably it is 0.5-200 mg / l.

  In the first treatment method of the present invention, as shown in FIG. 1, first, a heavy metal-containing solution 11 in which heavy metals are dissolved in a leachate 10 of fly ash in which Pb components are dissolved to add a heavy metal salt and The Pb component dissolved in the filtrate is precipitated by the coprecipitation effect (step 12). The addition ratio of the heavy metal-containing solution 11 added to the leachate 10 is equal to or more than one equivalent of the Pb molar amount contained in the fly ash leachate. If the addition ratio is less than 1 equivalent, sufficient coprecipitation will not be obtained, and the upper limit of the addition ratio is not particularly limited, but it is preferably 1000 equivalents or less. A more preferable addition ratio is 500 times equivalent or less of the Pb molar amount, and an even more preferable addition ratio is 10 to 30 times equivalent.

  The heavy metal contained in the heavy metal-containing solution 11 is one or more selected from the group consisting of Cu, Zn, Cd, Fe, Ni, Mn, and Al. As long as the heavy metal is contained in the heavy metal-containing solution, the heavy metal-containing solution may contain a Pb component. As the heavy metal-containing solution 11, for example, waste water from which waste gas from copper smelting is washed may be used. The pH of the heavy metal-containing solution 11 is preferably 9 or less exhibiting acidity to weak alkalinity. The particularly preferred pH is 4 or less which exhibits strong acidity.

  By adding a heavy metal-containing solution and adjusting the pH to 11.0 to 12.2, the Pb component dissolved in the leachate 10 is precipitated together with the precipitation of the heavy metal salt. Subsequently, the coprecipitated precipitate is subjected to solid-liquid separation by centrifugation, filter press, or the like (step 13). The filtrate 14 and the precipitate 16 are obtained by this solid-liquid separation. Thus, the Pb component can be efficiently removed from the fly ash leachate through the above-described steps.

Next, a second embodiment of the present invention will be described with reference to FIG. 2 indicated by a solid line.
The fly ash leachate 20 that is the target of the second treatment method of the present invention is obtained by solid-liquid separation of a slurry prepared by mixing fly ash containing at least a Pb component and water at a predetermined ratio. It is a liquid. The fly ash containing this Pb component is the same as the target of the first processing method of the present invention. The Pb concentration in the fly ash leachate 20 is not particularly limited, but is preferably 0.1 mg / l or more and 10,000 mg / l or less, particularly preferably 0.1 to 2000 mg / l. Preferably it is 0.5-200 mg / l.

In the second treatment method of the present invention, as shown in FIG. 2, first, the Pb component is reacted with leachate 20 of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10,000 mg / l or less. Then, the immobilizing agent 21 that generates the hardly soluble salt is added to fix the Pb component contained in the leachate 20 in the form of the hardly soluble salt (step 22). The addition amount of the fixing agent 21 is 1 to 500 times the Pb equivalent contained in the leachate of fly ash. If the added amount of the fixing agent 21 is less than 1 equivalent, the Pb component cannot be sufficiently immobilized. A preferable addition amount of the fixing agent 21 is 1 to 50 times equivalent of Pb equivalent contained in the fly ash leachate, and an even more preferable addition amount is 10 to 30 equivalents of Pb equivalent. Examples of the immobilizing agent 21 include CaCO ₃ , Na ₂ CO ₃ , Na ₂ S, NaHS, Na ₂ SO ₄ or a chelating agent.

  Next, a heavy metal-containing solution 23 in which heavy metal is dissolved is added to a liquid containing a hardly soluble salt in which the Pb component is fixed, and the liquid is not fixed in the fixing step 22 due to the coprecipitation effect with the heavy metal salt. The Pb component dissolved in the solution is precipitated and the hardly soluble salt in which the Pb component is immobilized is precipitated (step 24). The addition ratio of the heavy metal-containing solution 23 added to the liquid containing the hardly soluble salt to which the Pb component is immobilized is at least 1 equivalent of the dissolved Pb molar amount contained in the liquid containing the hardly soluble salt. When the addition ratio is less than 1-fold equivalent, sufficient coprecipitation action cannot be obtained. Although there is no restriction | limiting in particular in the upper limit of an addition rate, Preferably it is 1000 times equivalent or less, and a more preferable addition rate is 500 times equivalent or less of Pb molar amount.

  By adding the heavy metal-containing solution, the Pb component dissolved in the liquid containing the hardly soluble salt in which the Pb component is immobilized is precipitated together with the precipitation of the heavy metal salt. Subsequently, the precipitate is subjected to solid-liquid separation by centrifugation, filter press or the like (step 26). The filtrate 27 and the precipitate 28 are obtained by this solid-liquid separation. Thus, the Pb component can be efficiently removed from the fly ash leachate through the above-described steps.

Next, a third embodiment of the present invention will be described with reference to FIG. 3 indicated by a solid line.
The fly ash leachate 20 that is the target of the third treatment method of the present invention is the same as the second treatment method described above. In the third treatment method of the present invention, as shown in FIG. 3, first, the Pb component is reacted with leachate 20 of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10000 mg / l or less. Then, the fixing agent 21 that generates a hardly soluble salt is added to fix the Pb component dissolved in the leachate in the form of the hardly soluble salt (step 31). Next, the liquid in which the Pb component is immobilized is subjected to solid-liquid separation (step 32). By this solid-liquid separation, a filtrate 33 and a desalted salt 34 are obtained. The subsequent process after processing the obtained filtrate 33 is the same process as the process 24 and subsequent steps of the second processing method described above. The Pb component dissolved in the fly ash leachate can also be efficiently removed by this third treatment method.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
Fly ash leachate 10 in which the Pb component was dissolved was prepared. As shown by the broken line in FIG. 1, a part of this fly ash leachate was extracted to obtain leachate. Moreover, as shown with the broken line of FIG. 1, a part of heavy metal containing solution 11 before adding was extracted and the heavy metal containing solution was obtained. Then, after adding the heavy metal containing solution 11 to this fly ash leachate 10 so that it might become 47 times equivalent of the Pb molar amount contained in fly ash leach water, the additive was solid-liquid-separated with the filter press. As shown by the broken line in FIG. 1, a part of the filtrate at this time was extracted and used as a filtrate. The pH of the leachate, heavy metal-containing solution and filtrate obtained in Example 1 were measured, and the chemical analysis was performed on the heavy metal components of each solution. The results are shown in Table 2.

  As apparent from Table 2, when the amount of fly ash leachate to be treated is small, the Pb component can be efficiently removed from the fly ash leach water by applying the first treatment method of the present invention. It was confirmed.

<Comparative Example 1>
The treatment of fly ash leachate was performed in the same manner as in Example 1 except that the heavy metal-containing solution was added to the leach water so as to be 12 times equivalent to the Pb molar amount contained in the fly ash leach water. The pH of the leachate, heavy metal-containing solution and filtrate obtained in Comparative Example 1 were measured, and chemical analysis was performed on the heavy metal components of each solution. The results are shown in Table 3.

  As is apparent from Table 3, when the amount of fly ash leachate to be treated is large, even if the first treatment method of the present invention is applied, the Pb component cannot be sufficiently removed from the fly ash leach water. I found out.

<Example 2>
A fly ash leachate 10 in which the Pb component was dissolved at a low concentration of 280 mg / l was prepared. As shown by the broken line in FIG. 1, a part of this fly ash leachate was extracted to obtain leachate. Moreover, as shown with the broken line of FIG. 1, a part of heavy metal containing solution 11 before adding was extracted and the heavy metal containing solution was obtained. Then, after adding the heavy metal containing solution 11 to this fly ash leachate 10 so that it might become 21 times equivalent of the Pb molar amount contained in fly ash leach water, the additive was solid-liquid-separated with the filter press. As shown by the broken line in FIG. 1, a part of the filtrate at this time was extracted and used as a filtrate. The pH of the leachate, heavy metal-containing solution and filtrate obtained in Example 1 were measured, and the chemical analysis was performed on the heavy metal components of each solution. The results are shown in Table 4.

  From Table 4, when the dissolution amount of the Pb component contained in the fly ash leachate is low, the Pb component is efficiently removed from the fly ash leachate by applying the first treatment method of the present invention. Confirmed that it can.

<Example 3>
First, fly ash leachate 20 in which the Pb component was dissolved was prepared. As shown by the broken line in FIG. 2, a part of the fly ash leachate 20 was extracted to obtain leachate. Next, NaHS was added as the immobilizing agent 21 so as to be 1 equivalent of Pb equivalent. As shown by the broken line in FIG. 2, a part of the heavy metal-containing solution 23 before being added was extracted to obtain a heavy metal-containing solution. Next, after adding the heavy metal-containing solution 23 to the solution containing the immobilized hardly soluble salt so as to be 12 times equivalent to the Pb molar amount dissolved in the solution containing the hardly soluble salt, the additive is added. Solid-liquid separation was performed with a filter press. As shown by a broken line in FIG. 2, a part of the filtrate 27 at this time was extracted and used as a filtrate. The pH of the leachate, the heavy metal-containing solution and the filtrate obtained in Example 3 were measured, and chemical analysis was performed on the heavy metal components of each solution. The results are shown in Table 5.

  From Table 5, fly ash leachate can be obtained by applying the second treatment method of the present invention even when the dissolved amount of the Pb component contained in the fly ash leachate is high and the treatment amount of the fly ash leachate is large. From this, it was confirmed that the Pb component can be efficiently removed.

<Example 4>
The fly ash leachate was treated in the same manner as in Example 3 except that the amount of NaHS as the immobilizing agent 21 was changed to 3 times the Pb equivalent contained in the fly ash leach water 20. The pH of the leachate, heavy metal-containing solution and filtrate obtained in Example 4 was measured, and chemical analysis was performed on the heavy metal component of each solution. The results are shown in Table 6.

  As apparent from Table 6, the removal efficiency of the Pb component was further improved by making the addition amount of the metal salt more than 1 equivalent of the Pb equivalent contained in the fly ash leachate.

<Example 5>
Fly ash leachate in the same manner as in Example 3 except that CaCO ₃ was used as the immobilizing agent 21 instead of NaHS, and the amount of CaCO ₃ added was changed to 10 times the Pb equivalent contained in the fly ash leach water 20. Was processed. The pH of the leachate, heavy metal-containing solution and filtrate obtained in Example 5 were measured, and chemical analysis was performed on the heavy metal components of each solution. The results are shown in Table 7.

As is clear from Table 7, it was confirmed that the Pb component can be efficiently removed from the fly ash leachate even when CaCO ₃ is used as the immobilizing agent.

  INDUSTRIAL APPLICABILITY The present invention can be used for treating kiln dust, fly ash obtained from an incinerator, melting furnace, gasification melting furnace or the like, molten fly ash, dust and the like. The treated product can be used as a fertilizer raw material, a chemical raw material, a smelting raw material, a cement raw material and the like.

The figure which shows the process process in the 1st Embodiment of this invention. The figure which shows the process process in the 2nd Embodiment of this invention. The figure which shows the process process in the 3rd Embodiment of this invention. The figure which shows the conventional process process.

Explanation of symbols

10 leachate of fly ash 11 heavy metal containing solution 12 coprecipitation Pb component precipitation process 13 solid-liquid separation process

Claims (9)

Pb component dissolved in the leachate by adding a heavy metal-containing solution (11) in which heavy metal is dissolved to the leachate (10) in which fly metal is dissolved in Pb component and coprecipitation with heavy metal salt Precipitating (12),
And a step (13) of solid-liquid separation of the co-precipitated precipitate.   The treatment method according to claim 1, wherein the Pb concentration in the leachate (10) of fly ash is 0.1 mg / l or more and 10,000 mg / l or less.   The treatment method according to claim 1, wherein the addition ratio of the heavy metal-containing solution (11) to be added to the fly ash leachate is not less than 1 equivalent of the Pb molar amount contained in the fly ash leach water. Addition of a fixing agent (21) that reacts with the Pb component to leachate (20) of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10,000 mg / l or less to produce a hardly soluble salt. And fixing the Pb component contained in the leachate in the form of a hardly soluble salt (22),
The heavy metal-containing solution (23) in which heavy metal is dissolved is added to the liquid containing the hardly soluble salt in which the Pb component is immobilized, and the immobilization step with the heavy metal salt does not fix in the immobilization step (22). Precipitating the Pb component dissolved in the solution and precipitating a hardly soluble salt having the Pb component immobilized thereon (24);
A process (26) for solid-liquid separation of the precipitate (28);   The addition ratio of the heavy metal-containing solution (23) added to the liquid containing the hardly soluble salt to which the Pb component is immobilized is at least one equivalent of the dissolved Pb molar amount contained in the liquid containing the hardly soluble salt. 4. The processing method according to 4. Addition of a fixing agent (21) that reacts with the Pb component to leachate (20) of fly ash in which the Pb component is dissolved at a concentration of 0.1 mg / l or more and 10,000 mg / l or less to produce a hardly soluble salt. And fixing the Pb component dissolved in the leachate (20) in the form of a hardly soluble salt (31),
Solid-liquid separation of the liquid having the Pb component immobilized thereon (32);
A heavy metal-containing solution (23) in which heavy metals are dissolved is added to the filtrate (33) obtained by the solid-liquid separation, and is immobilized in the immobilization step (31) by the coprecipitation effect with heavy metal salts. (24) the step of precipitating the Pb component dissolved in the liquid without
A process (26) for solid-liquid separation of the precipitate (28);   The processing method according to claim 6, wherein the addition ratio of the heavy metal-containing solution (23) to be added to the filtrate (33) is at least one equivalent of the Pb molar amount contained in the filtrate.   The heavy metal contained in the heavy metal-containing solution (11, 23) is one or more selected from the group consisting of Cu, Zn, Cd, Fe, Ni, Mn, and Al. The processing method as described in. The processing method according to claim 4 or 6, wherein the immobilizing agent (21) is CaCO ₃ , Na ₂ CO ₃ , Na ₂ S, NaHS or Na ₂ SO ₄ .

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