JP4639398B2 - Method for treating fly ash using sulfur dioxide - Google Patents

Description

  The present invention is a wet ash collected from flue gas collected from combustion exhaust gas at the time of incineration of municipal waste, etc., or fly ash collected from flue gas generated when melting ash and dust at the time of incineration, etc. The present invention relates to a processing method for separating and recovering Ca, Zn, Pb, gangue components, and the like contained in the fly ash in an easy-to-use manner.

Garbage discharged from general business establishments and households (referred to as “urban waste” or “general waste”) is collected and incinerated at municipal waste incineration facilities and industrial waste incineration plants. Incineration ash and fly ash generated from the incinerator at that time are deposited in the final disposal site through intermediate treatments such as chemical treatment, melting treatment, and cement kiln treatment.
However, in intermediate treatment in melting furnaces, cement kilns, etc., heavy metals such as Zn, Pb, and Cd with high vapor pressure volatilize in the furnace and enter the exhaust gas, and then condense again in the exhaust gas treatment equipment. There was a problem that it became fly ash. This second fly ash contains a large amount of heavy metals such as Zn, Pb, Cu and Cd as well as Cl, Na and Ca, and a stable treatment method including recovery of these elements is required. It was.
Various fly ash treatment methods are proposed in the following patent documents.

JP 7-109533 A JP-A-8-117724 JP-A-8-141539 JP 2001-113242 A JP 2001-348627 A JP 2003-164829 A

  The wet processing methods described in the above patent documents are considered to be effective in separating and recovering heavy metals contained in fly ash in a stable form. However, these techniques focus on recovering heavy metals, and further improvements are desired from the viewpoint of effective utilization of Ca and effective utilization of gangue components.

On the other hand, the present applicant adopted a step of leaching fly ash with an aqueous hydrochloric acid solution as a fly ash treatment method intended to recover Zn in the fly ash in the most preferable form that can be used in the wet zinc smelting step. A treatment method was proposed as Japanese Patent Application No. 2003-365706. According to this, it is possible to recover the neutralized residue, which is rich in Zn and accompanied by other heavy metals in a rich manner and hardly contains Si or Al. This residue has a high utility value as a raw material to be supplied to wet zinc smelting.
However, this processing method also has problems. That is, the residue obtained to adhere high liquid of salt concentration is the amount of the residue limited by acceptable chlorine content in smelting process. In order to avoid this limitation, a process for removing the attached liquid is required. Further, the treatment using hydrochloric acid leaching is more expensive than the case of sulfuric acid leaching.

On the other hand, when trying to separate and recover Zn resources that can be supplied to wet zinc smelting using the sulfuric acid leaching process, which is advantageous in terms of cost, a large amount of Ca is present in the fly ash, so there is a by-product obtained in the intermediate process. A large amount of gypsum (CaSO ₄ ) is contained in the gangue residue. Since Pb in fly ash is recovered in this gangue residue, this residue is intended to be used for lead smelting, but since it contains a large amount of gypsum, using it as a raw material for lead smelting is a thermal energy problem. There's a problem. Further, a large amount of Ca in the fly ash used for sulfuric acid leaching is not preferable because it increases the load on the sulfuric acid leaching process.

Therefore, the present applicant has created a technique in which most of Ca is dissolved and removed by washing the fly ash in a liquid having a very low pulp concentration before being subjected to sulfuric acid leaching. Proposed as Japanese Patent Application Nos. 2004-59847 and 2004-59852. In this case, more effective removal of Ca could be achieved by blowing CO ₂ gas at the time of cleaning.
However, this method has a drawback in that a large amount of water is required for cleaning, and it is difficult to implement in a factory with a small facility scale.

  In view of such a current situation, the present invention is a treatment process that can efficiently recover valuable metals such as Ca, Zn, or Pb from fly ash, regardless of the size of the equipment. The aim is to develop and provide a method that can be implemented in many existing wet processing sites.

The inventors conducted extensive research and found that when SO ₂ gas was used to treat the fly ash slurry, Ca and Zn could be recovered in the form of simultaneous dissolution of Pb and the like at that stage. It has been found that residues containing valuable metals can be separated and recovered in a low Ca quality state. Further, when a simple oxidation treatment such as blowing air into the solution in which Ca and Zn are dissolved, or a treatment of adding sulfuric acid, Ca sulfate (gypsum) is insoluble and Zn sulfate is soluble. Thus, it was found that Ca and Zn can be easily separated and recovered. The present invention has been completed based on such findings.

That is, the above object is to add SO ₂ to a fly ash slurry in which Ca, Zn, Pb-containing fly ash and an aqueous solvent are mixed, thereby dissolving Ca and Zn in the fly ash in an aqueous solvent , This is achieved by a fly ash treatment method having a step of recovering a Ca, Zn-containing liquid and a Pb-containing residue by liquid separation .

As the above-mentioned fly ash slurry to which SO ₂ is added, it is possible to use a repulped fly ash that has been washed to reduce the contents of Na, K, and Cl.
Here, the “repulped product” means a product obtained by mixing a solid content once separated by solid-liquid separation with a solvent mainly composed of water to make a slurry.

Further, an oxidizing agent (for example, a gas containing oxygen) or sulfuric acid is added to the Ca, Zn-containing liquid separated from the residue by adding SO ₂ as described above, that is, the liquid in which Ca and Zn are dissolved. Provides a method for treating fly ash having a step of selectively precipitating Ca and leaving Zn dissolved in the liquid, and then recovering the Zn-containing liquid and the Ca-containing residue by solid-liquid separation. The
In addition, by blowing an inert gas into the Ca, Zn-containing liquid, Ca and Zn are once precipitated as sulfites using the degassing reaction of SO ₂ , and then Ca is selectively added by adding sulfuric acid. And a method for treating fly ash comprising the steps of precipitating Zn and dissolving Zn in the liquid, followed by solid-liquid separation to recover the Zn-containing liquid and the Ca-containing residue .

Furthermore, Zn is precipitated by adding alkali to the Zn-containing solution separated by selectively precipitating Ca from the Ca- and Zn-containing solution separated from the residue by adding SO ₂ as described above. Then, solid-liquid separation is performed to recover the Zn-containing residue, and after separation of the Zn-containing residue, a fly ash treatment method is provided in which the liquid is reused as water for fly ash treatment.

The present invention has the following merits.
(1) Since it is possible to separate and recover Ca, Zn, or even Pb from fly ash in a form that is industrially easy to use by simply reacting with gas components such as SO ₂ and air, the process is simplified and the purchase of chemicals is reduced. Can reduce the cost.
(2) Since the Pb-containing residue separated and recovered has a low Ca quality, it is easy to use it effectively in Pb smelting.
(3) Ca and Zn can be easily separated by subjecting the Ca and Zn-containing liquid to be separated and recovered to further oxidation treatment.
(4) Since it is not necessary to circulate and use a large amount of water, it is relatively easy to implement even in factories with small facilities.
Therefore, this invention contributes to the spread of the recycling process which collects a valuable metal and a gangue residue from fly ash.

Fly ash treatment method of the present invention is applicable to various fly ash or mixtures fly ash thereof discharged from incinerators and melting furnace waste disposal facilities. Among them, it is particularly effective to apply to fly ash having a relatively high Ca content of, for example, 5 to 30% by mass.
FIG. 1 shows an example of a fly ash treatment flow including the treatment of the present invention. Hereinafter, the present invention will be described along this example.

〔Washing〕
It is desirable that the fly ash is first washed to remove salts, that is, elements such as Na, K, and Cl. Usually, the method of the slurry mixed with water and stirred to dissolve the salts in water is employed. When the fly ash is conditioned, it is desirable to pulverize it beforehand when it is agglomerated into a lump. The thinner the pulp concentration is, the higher the effect of removing salt adhering to the fly ash, but the amount of wastewater treatment increases accordingly, so the conditions that minimize the cost may be adopted according to the actual situation of the equipment . In general, the pulp concentration can be 50 to 500 g / L. When CO ₂ is blown into the slurry at the time of washing, there is an effect of suppressing the elution of heavy metals, and the elution of Ca is promoted, so the load in the subsequent process can be reduced.

The pH varies depending on the type of fly ash, but settles in the range of about 7 to 13. When CO ₂ is added, it is about 5 to 7. You may adjust to arbitrary pH by adding a mineral acid. The washing residence time is effective at about 10 to 120 minutes, but it is generally considered economical to ensure a residence time of about 60 minutes by stirring.

  What is necessary is just to solid-liquid-separate the slurry after washing | cleaning by a general method. For example, various means such as thickener concentration, filter press, belt type vacuum filter, oliver, screw counter, etc. can be selected. However, if only thickeners are used, the solid-liquid separation property is deteriorated, and a large amount of salts dissolved by washing may be carried over to the solid content side, so care must be taken. Usually, good results are obtained when a filter press is used.

[SO ₂ treatment]
The fly ash (cleaning residue) with the reduced contents of Na, K, and Cl in this way is repulped and used for the “treatment of adding SO ₂ ” (hereinafter referred to as “SO ₂ treatment”) of the present invention. The The simplest method for adding SO ₂ to the fly ash slurry is to blow SO ₂ gas directly into the slurry. Depending on the equipment specifications, it may be easier to put SO ₂ gas in the water and supply the H ₂ SO ₃ liquid equivalent to the slurry. Thus, Ca and Zn in fly ash can be dissolved in the liquid even if SO ₂ is added indirectly.

The reaction in the SO ₂ treatment of the present invention is basically a reaction in which Pb is not eluted but Ca and Zn are eluted, and the reaction mechanism has many unclear parts. It is considered to be a stepwise reaction of “production” + “reaction of sulfite and sulfite”. Ca or Zn sulfites are in the form of CaSO ₃ and ZnSO ₃ , both of which are insoluble in pure water but soluble in an aqueous sulfite solution. That is, Ca (HSO ₃ ) ₂ and Zn (HSO ₃ ) ₂ are soluble and can be recovered in a form separated from the residual components such as Pb and dissolved in the liquid.

When Ca content in the form of fly ash is taken as an example the case of CaO, Scheme in SO ₂ treatment of the present invention are believed to be as follows.
SO ₂ + CaO → CaSO ₃ (neutralization reaction) (1)
SO ₂ + H ₂ O → H ₂ SO ₃ (sulfurous acid production reaction) ...... (2)
CaSO ₃ + H ₂ SO ₃ → Ca (HSO ₃ ) ₂ (3)
According to the experiments by the inventors, elution by SO ₂ is not only in the case where the form of Ca is CaO but also in any of CaSiO ₃ , Ca ₃ (PO ₄ ) ₂ , CaCO ₃ , CaSO ₃ , and CaF _2. It was possible. However, CaSO ₄ (gypsum) was difficult to elute with SO ₂ .

Similarly for Zn, take the case form of Zn component is ZnO as an example, is considered to reaction scheme with SO ₂ treatment is as follows.
SO ₂ + ZnO → ZnSO ₃ (neutralization reaction) ...... (4)
SO ₂ + H ₂ O → H ₂ SO ₃ (sulfurous acid production reaction) ...... (2)
ZnSO ₃ + H ₂ SO ₃ → Zn (HSO ₃ ) ₂ (5)

In the SO ₂ treatment, the fly ash pulp concentration may be about 50 to 500 g / L. Thinning is advantageous in increasing the amount of Ca and Zn elution, but on the other hand, it leads to a decrease in efficiency and an increase in the burden of solid-liquid separation. Generally, it is realistic to set the pulp concentration to about 100 to 200 g / L.
As the SO ₂ gas, one having an SO ₂ concentration of 5 to 100% can be used. For example, SO ₂ gas generated from smelting raw materials can be used. It does not necessarily mean that the reaction does not easily proceed as the SO ₂ concentration decreases.

When the SO ₂ gas is directly blown into the slurry, the G / L ratio (that is, “volume of gas blown during reaction time (L) / volume of slurry (L)”) is desirably 1 or more. As the G / L ratio is increased, the stirring effect by bubbling increases, but the upper limit is limited by the facility capacity. As a practical G / L ratio, about 1 to 100 is appropriate.
During the reaction, it is desirable to perform strong mechanical stirring and bubbling sufficient to sufficiently diffuse SO ₂ into the liquid.

Whether or not the reaction by SO ₂ is proceeding sufficiently can be determined by fluctuation of the pH of the solution. It is desirable to continue the reaction until the pH drops below 3.5. It can be seen that a considerable amount of undissolved Ca and Zn still remains at the time when the pH is higher. For example, when pure SO ₂ gas is used, the G / L ratio is 50, and the initial temperature is 30 ° C., the pH drops to about 2 in a reaction time of about 10 minutes, indicating that the dissolution reaction has progressed. In this case, the oxidation-reduction potential (Ag / AgCl electrode reference) is about 100 to 250. The temperature rises to about 40 ° C. after 10 minutes and reaches about 50 ° C. after 30 minutes.

Such changes in pH and redox potential can be used to control the SO ₂ treatment time.
Specifically, after the introduction of SO ₂ gas into the slurry, the reaction may be terminated after the pH becomes 3.5 or less, preferably 2.5 or less.
Alternatively, the reaction may be terminated when the oxidation-reduction potential (Ag / AgCl electrode reference) settles between, for example, 100 to 200 mV after starting the introduction of SO ₂ gas into the slurry. Since the oxidation-reduction potential varies depending on the type of fly ash, the treatment time can be controlled by, for example, determining a potential region at the end of the reaction in advance according to the fly ash to be applied.

The slurry after the SO ₂ treatment is subjected to solid-liquid separation, whereby the liquid and residue in which Ca and Zn are dissolved can be recovered. When Pb is contained in the original fly ash, this residue is recovered as a “Pb-containing residue”. This residue remaining part also Ca, which is intended CaSO ₄ in (gypsum) mainly contained in the fly ash from the beginning. However, compared with the Pb-containing residue separated and recovered by ordinary sulfuric acid leaching, the content of CaSO ₄ is significantly less and can be suitably used as a raw material for Pb smelting.

[Oxidation treatment]
The “Ca, Zn-containing liquid” obtained by removing the residue after the SO ₂ treatment is separated and recovered by, for example, “treatment of adding an oxidizing agent” (hereinafter referred to as “oxidation treatment”). can do. In this Ca, Zn-containing liquid, it is considered that Ca is present in a dissolved form in a sulfurous acid aqueous solution as Ca is Ca (HSO ₃ ) ₂ and Zn is Zn (HSO ₃ ) ₂ as described above. When Ca (HSO ₃ ) ₂ and Zn (HSO ₃ ) ₂ are reacted with an oxidizing agent, both of them easily change to sulfate. At this time, Ca sulfate CaSO ₄ (gypsum) is insoluble, and Zn sulfate ZnSO ₄ is soluble, so that Ca and Zn can be separated into solid and liquid. That is, Ca can be selectively precipitated by adding an oxidizing agent to the Ca, Zn-containing liquid.

This oxidation reaction is considered to be represented by the following reaction formula.
2H ₂ SO ₃ + O ₂ → 2H ₂ SO ₄ (6)
_{Ca (HSO 3) 2 (aq} ) + O 2 + 2H 2 O → CaSO 4 · 2H 2 O (s) + H 2 SO 4 ...... (7)
Ca (HSO ₃ ) ₂ (aq) + 1 / 2O ₂ + H ₂ O → CaSO ₄ .2H ₂ O (s) + SO ₂ (g) (7) '
Zn (HSO ₃ ) ₂ (aq) + O ₂ → ZnSO ₄ (aq) + H ₂ SO ₄ (8)
_{Zn (HSO 3) 2 (aq} ) + 1 / 2O 2 → ZnSO 4 (aq) + SO 2 (g) + H 2 O ...... (8) '
A white precipitate forms up is initially slightly pH of the reaction is believed that occurred both reactions (7) and (7) '. The same applies to (8) and (8) ′.
These reactions can proceed by blowing an oxygen-containing gas such as air into the liquid as an oxidizing agent. As other oxidizing agents, H ₂ O ₂ and O ₃ can also be used. However, when an Mn compound such as KMnO ₄ is used, it is necessary to devise methods for recovering Mn and treating Mn present in the adhering water.
During the reaction, it is desirable to perform strong mechanical stirring and bubbling sufficient to sufficiently diffuse the oxidizing agent into the liquid.

When this oxidation reaction is performed by blowing air, an optimum value can be found in the G / L ratio in the range of usually 1 to 1000. The temperature is preferably about 20 to 50 ° C. Regarding the reaction time, it is preferable to manage the end point of the reaction by the redox potential. In the case of air blowing, the oxidation-reduction potential was initially 100 to 200 mV (Ag / AgCl electrode standard, the same applies hereinafter), but increased to around 350 mV due to consumption of O _{2 in} the initial stage of the reaction, and thereafter It continues to rise gradually and settles at about 400 to 750 mV. If there is almost no potential change, it can be considered that the oxidation reactions of the above formulas (7) and (8) are almost completed.
H ₂ SO ₃ → H ₂ O + SO ₂ (degassing reaction) ...... (9)
The pH temporarily rises about 0.5 to 2.0 from the original pH (for example, around 2) due to the initial SO ₂ degassing, but then settles to a position slightly below the original pH.

[Other Ca / Zn separation methods]
FIG. 1 shows a process of precipitating Ca by oxidation treatment. As another method for separating and recovering Ca and Zn, sulfuric acid is directly added to the Ca and Zn-containing liquid to selectively select Ca. There is a method of precipitation as (sulfuric acid replacement treatment). The reaction formula is considered as follows.
About Ca;
Ca (HSO ₃ ) ₂ (aq) + H ₂ SO ₄ → CaSO ₄ .2H ₂ O (s) + 2SO ₂ (10)
About Zn;
Zn (HSO ₃ ) ₂ (aq) + H ₂ SO ₄ → ZnSO ₄ (aq) + 2H ₂ O + 2SO ₂ (11)

In addition, there is a method in which an inert gas such as N ₂ is blown into the liquid to advance the degassing reaction of SO ₂ and then sulfuric acid is added to selectively precipitate Ca. This reaction formula is considered as follows.
About Ca;
Ca (HSO ₃ ) ₂ (aq) → CaSO ₃ (s) + H ₂ O + SO ₂ (12)
CaSO ₃ (s) + H ₂ SO ₄ + H ₂ O → CaSO ₄ .2H ₂ O (s) + SO ₂ (13)
About Zn;
Zn (HSO ₃ ) ₂ (aq) → ZnSO ₃ (s) + H ₂ O + SO ₂ (14)
ZnSO ₃ (s) + H ₂ SO ₄ → ZnSO ₄ (aq) + H ₂ O + SO ₂ (15)
That is, Ca (HSO ₃ ) ₂ and Zn (HSO ₃ ) ₂ are once precipitated as sulfites by degassing reaction, and when reacted with sulfuric acid, Ca is insoluble sulfate (gypsum) and Zn is soluble sulfuric acid. As a result, it is considered that Ca can be selectively separated as a precipitate.

  After selective precipitation of Ca as described above, the solid-liquid separation, Ca is recovered as gypsum. When this gypsum is commercialized as gypsum that satisfies industrial standards, it is desirable to sufficiently cut off moisture. A filter press or a centrifuge may be used for draining.

[Neutralization]
Zn is dissolved in the form of ZnSO ₄ in the liquid after separating and removing Ca (Zn-containing liquid). This liquid can be directly introduced into the zinc smelting process, but in consideration of handling during transportation and recycling of the liquid, it is necessary to carry out techniques such as neutralization, sulfidation, and solvent extraction to recover Zn as a solid matter. Is desirable.

In the case of neutralization, an alkali such as CaO, Ca (OH) ₂ , or CaCO ₃ may be added to the Zn-containing liquid as a neutralizing agent. Zn precipitates at pH 7-10. If the original solution (Zn-containing liquid) is obtained through the oxidation process, Zn Shingaributsu is intended mainly containing ZnO. Zn can be formed even if NaOH or KOH is used as a neutralizing agent. However, if the solution after neutralization is returned to the previous step and used repeatedly, the sulfates of Na and K are soluble. Therefore, a crystallization process is required.

A Zn-containing residue is recovered by solid-liquid separation of the neutralized slurry. This residue can be used as a raw material for zinc smelting. On the other hand, the post-solution can be reused as water for cleaning or SO ₂ treatment. However, if reuse of the solution is repeated thereafter, NaCl and KCl are concentrated due to the introduction of attached salts. For this reason, it is desirable to bleed off a part of the waste water.

FIG. 2 shows an example of a fly ash treatment flow when the SO ₂ treatment of the present invention is performed without performing the first cleaning. In this case after liquid removal of Zn-containing residues higher salt concentration, it is desirable to wastewater treatment by sending most of after liquid removal Cl process.

When A fly ash shown in Table 1 is used and treated with sulfuric acid leaching and neutralization without using SO ₂ (comparative example) and treated with SO ₂ according to the present invention (invention example) About each liquid after a process, each residue was compared. Moreover, about the invention example, the process of the oxidation process and the process of neutralization were further implemented.

[Comparative example]
1000 g of A fly ash was weighed, and 3 L (liter) of distilled water was added thereto to obtain fly ash mixed water. The fly ash mixed water was stirred for 60 minutes and then separated into solid and liquid with a filter to obtain filtrate a and solid a. The solid a was further washed by adding 0.3 L of distilled water to obtain a filtrate b and a solid (referred to as “washing residue”). About 3 L of a liquid obtained by mixing the filtrate a and the filtrate b (referred to as “liquid after washing”) was obtained.
After the washing residue was sufficiently dried at 105 ° C., composition analysis was performed. The results are shown in Table 2. On the other hand, composition analysis was also performed on the washed solution. The results are shown in Table 3.

Next, after the washing residue was repulped at a pulp concentration of 100 g / L, sulfuric acid was added to adjust pH = 2. This was stirred at 30 ° C. for 60 minutes to carry out sulfuric acid leaching. Next, CaCO ₃ was added to the treatment liquid (slurry after leaching) to adjust to pH = 4, and neutralization was performed by stirring for 60 minutes. The liquid temperature was 30 ° C. Thereafter, solid-liquid separation was performed to obtain a Zn-containing after-solution and a Pb-containing residue. Table 4 shows the analysis results of the Zn-containing post-solution. The Pb-containing residue was sufficiently dried at 105 ° C. and then subjected to composition analysis. The results are shown in Table 5.

[Invention Example]
1000 g of A fly ash was weighed and washed in the same manner as in the comparative example to obtain a washing residue and a washed solution. The washed residue was repulped with a pulp concentration of 100 g / L, it was carried out "SO ₂ process" by blowing pure SO ₂ gas to the slurry 8L. The SO ₂ gas blowing speed was 8 L / min. In this case, the G / L ratio is 60. The liquid temperature was in the range of 15-40 ° C. Mechanical agitation was also performed during gas blowing. During the reaction, the redox potential (Ag / AgCl electrode standard) and pH were monitored. According to this, it was considered that the reaction was almost completed in about 10 to 20 minutes, but after that, gas blowing and mechanical stirring were continued, and the reaction time was finally set to 60 minutes. The final redox potential was 150 mV and the pH was 2.2.

The obtained slurry was subjected to solid-liquid separation with a filter to obtain a SO ₂ -treated solution (Ca, Zn-containing solution) and an SO ₂ treatment residue (Pb-containing residue). Table 6 shows the composition analysis results of the back solution. The residue was thoroughly dried at 105 ° C. and analyzed for composition. The results are shown in Table 7.

Comparing Table 4 (Comparative Example) and Table 6 (Invention Example), it can be seen that the invention example was able to recover Zn and Ca dissolved in the liquid by SO ₂ treatment. Further, when Table 5 (Comparative Example) and Table 7 (Invention Example) are compared, it can be seen that in the Invention Example, the amount of Pb-containing residue is greatly reduced, and the amount and content of Ca in the residue are reduced. . That is, according to the present invention, a Pb-containing residue having a high Pb quality and a low Ca quality is generated directly by SO ₂ treatment, and the amount thereof is also reduced. Can be reduced.

Next, oxidation treatment was performed by blowing air into the solution after SO ₂ treatment (Ca, Zn-containing solution). The air blowing speed was 60 L / min. In this case, the G / L ratio is 600. The temperature was controlled at 45 ° C. Mechanical agitation was also used. During the reaction, the redox potential (Ag / AgCl electrode standard) and pH were monitored. According to this, the oxidation-reduction potential once decreased to 100 mV 10 minutes after the start of the reaction, and the pH also rose above 3.5. Thereafter, the redox potential increased and the pH gradually decreased. After 60 minutes, the oxidation-reduction potential was 400 mV, the pH was 2, and the fluctuation was small. At this point, the reaction was considered to be almost complete, but air blowing and mechanical agitation were continued for 120 minutes to see further. Eventually, the redox potential was 450 mV, and the pH was 2.0. A white precipitate was formed in the liquid, and this was solid-liquid separated with a filter to obtain a cake of a post-oxidation treatment solution (Zn-containing solution) and an oxidation treatment residue (Ca-containing residue). Table 8 shows the analysis results of the rear solution, and Table 9 shows the analysis results of the residue.

From Tables 8 and 9, it can be seen that Ca was selectively precipitated by the oxidation treatment, and Ca and Zn could be separated and recovered. That is, when SO ₂ treatment and oxidation treatment were combined, Pb, Ca, and Zn could be separated and recovered from the fly ash by a simple operation of blowing gas. As a result of X-ray diffraction, it was confirmed that the Ca-containing residue cake was gypsum.

  Next, the solution after the oxidation treatment (Zn-containing solution) was neutralized by adding NaOH. A solution having an Na concentration of 100 g / L was prepared, and this was added to the solution after the oxidation treatment to neutralize the solution so that the pH became 8. The consumption of NaOH solution was 430 mL. Since white precipitate was formed by neutralization, this was subjected to solid-liquid separation to obtain a post-neutralization solution and a cake of neutralization residue (Zn-containing residue). Table 10 shows the analysis results of the rear solution, and Table 11 shows the analysis results of the residue.

As can be seen from Table 10, the subsequent solution has a low content of Ca, Zn, and Pb, and can be sufficiently reused as water to be supplied to the first cleaning step or the SO ₂ treatment step. As can be seen from Table 11, the cake of neutralization residue has a high Zn content and is preferable as a raw material for zinc smelting.

[Invention Example]
Using fly ash A, cleaning and SO ₂ treatment were performed in the same manner as in the inventive example of Example 1. The obtained SO ₂ after-treatment solution and SO ₂ treatment residue are the same as those shown in Table 6 and Table 7, respectively. Here, selective precipitation of Ca was attempted by a method in which sulfuric acid was added to this SO ₂ -treated solution (Ca, Zn-containing solution).
237 g of sulfuric acid was added to 6.2 L of the SO ₂ -treated solution (Ca, Zn-containing solution) similar to Table 6. The pH was 0.9. Since a white precipitate was formed, the mixture was stirred for 10 minutes and then separated into solid and liquid. Table 12 The results of the analysis of the resulting after liquid (referred to as "sulfate substitution after solution") indicates the residue analysis results of (referred to as "sulfate substituted residue") in Table 13.

From Tables 12 and 13, it can be seen that Ca was selectively precipitated by adding sulfuric acid, and Ca and Zn could be separated and recovered. As a result of X-ray diffraction, it was confirmed that the cake of the sulfuric acid substitution residue (Ca-containing residue) was gypsum.

  Next, the sulfuric acid substitution after solution (Zn-containing solution), and neutralized with a method of adding quicklime CaO here. While performing mechanical stirring, quick lime was gradually poured into the liquid in a powder state, and the pH was adjusted to 8. The total amount of CaO added was 74 g. The reaction time was 60 minutes. The oxidation-reduction potential (Ag / AgCl electrode standard) finally reached 100 mV. Since white precipitate was formed by neutralization, this was subjected to solid-liquid separation to obtain a post-neutralization solution and a cake of neutralization residue (Zn-containing residue). Table 14 shows the analysis results of the rear solution, and Table 15 shows the analysis results of the residue.

As can be seen from Table 14, the subsequent solution has a low content of Ca, Zn, and Pb, and is sufficiently reusable as water to be supplied to the first cleaning step or the SO ₂ treatment step. As can be seen from Table 15, the neutralized residue cake has a high Zn content and is preferable as a raw material for zinc smelting.

[Invention Example]
Using fly ash A, cleaning and SO ₂ treatment were performed in the same manner as in the inventive example of Example 1. The obtained SO ₂ after-treatment solution and SO ₂ treatment residue are the same as those shown in Table 6 and Table 7, respectively. Here, the selection of Ca is carried out by a method in which a degassing reaction of SO ₂ proceeds by blowing an inert gas (N ₂ gas) into this SO ₂ -treated solution (Ca, Zn-containing solution) and then sulfuric acid is added. Attempts were made to precipitate.
Table 6 similar SO ₂ treatment after solution (Ca, Zn-containing solution) to 6.2 L, was blown for 120 minutes N ₂ gas at a flow rate of 60L / min. During the N ₂ gas blowing, SO ₂ gas was generated and released from the liquid. The pH was 3.9 and a white precipitate was formed. The oxidation-reduction potential (Ag / AgCl electrode reference) was 230 mV. Subsequently, 356 g of sulfuric acid was added to 6.2 L of a liquid (slurry) from which SO ₂ was degassed. The pH was 1.9 and the redox potential was 300 mV. The white precipitate was apparently intact. Then, after stirring for 60 minutes, the slurry was subjected to solid-liquid separation.
The analysis results of the resulting back solution (referred to as “N ₂ + sulfuric acid replacement post-solution”) are shown in Table 16, and the residue (referred to as “N ₂ + sulfuric acid replacement residue”) is sufficiently dried at 105 ° C. Is shown in Table 17.

Table 16, Table 17, selectively precipitate Ca by inert gas blowing + the addition of sulfuric acid, it is understood that could be separated recover Ca and Zn. As a result of X-ray diffraction, it was confirmed that the cake of N ₂ + sulfuric acid substitution residue (Ca-containing residue) was gypsum.

Next, neutralization was performed by adding quick lime CaO to the N ₂ + sulfuric acid-substituted solution (Zn-containing solution). While performing mechanical stirring, quick lime was gradually poured into the liquid in a powder state, and the pH was adjusted to 8. The total amount of CaO added was 89 g. The reaction time was 60 minutes. The oxidation-reduction potential (Ag / AgCl electrode standard) was 300 mV. Since resulting white precipitate by neutralization, which was solid-liquid separation to obtain a cake of neutralized after solution neutralization residue (Zn-containing residue). Table 18 shows the analysis results of the rear solution, and Table 19 shows the analysis results of the residue.

As can be seen from Table 18, the subsequent solution has a low content of Ca, Zn, and Pb, and is sufficiently reusable as water to be supplied to the first cleaning step or the SO ₂ treatment step. As can be seen from Table 19, the neutralized residue cake has a high Zn content and is preferable as a raw material for zinc smelting.

The flowchart of the fly ash processing process including the process of this invention. The flowchart of the fly ash processing process including the process of this invention.

Claims (7)

By adding SO ₂ to the fly ash slurry in which the fly ash containing Ca, Zn, and Pb and the aqueous solvent are mixed , Ca and Zn in the fly ash are dissolved in the aqueous solvent . A method for treating fly ash comprising a step of recovering a Zn-containing liquid and a Pb-containing residue . 2. The fly ash treatment method according to claim 1, wherein the fly ash slurry is obtained by repulping fly ash that has been washed to reduce the content of Na, K, and Cl. 3. Claim 1 or 2 Ca which is more recovered processing method according to, by adding an oxidizing agent to the Zn-containing solution, leaving in a state of being dissolved Zn in the solution with to selectively precipitate Ca, then The processing method of fly ash which has the process of collect | recovering Zn containing liquid and Ca containing residue by solid-liquid separation . The fly ash treatment method according to claim 3 , wherein the oxidizing agent is a gas containing oxygen. Claim 1 or Ca that is more recovered processing method according to 2, by adding sulfuric acid to Zn-containing solution, leaving in a state of being dissolved Zn in the solution with to selectively precipitate Ca, then, A fly ash treatment method comprising a step of solid-liquid separation to recover a Zn-containing liquid and a Ca-containing residue . Claim 1 or 2 Ca which is more recovered processing method according to, by blowing an inert gas into the Zn-containing solution, allowed to proceed for degassing reaction SO _2, followed by the addition of sulfuric acid, choose the Ca manner with precipitating dissolved Zn in the liquid, then the processing method of fly ash comprising the step of by solid-liquid separation and recovery of Zn-containing solution and Ca-containing residue. 7. Zn is precipitated by adding an alkali to the Zn-containing liquid separated and recovered by the treatment method according to any one of claims 3 to 6 to neutralize it , followed by solid-liquid separation to separate Zn. A method for treating fly ash, in which the residue is collected and the separated liquid is reused as water for fly ash treatment.

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