WO2005084838A1 - Method for treatment of fly ash - Google Patents

Abstract

A method for a treatment of a fly ash, which comprises [1] a step (washing step) of washing a fly ash in a fluid having a pulp concentration of 5 to 100 g/L, to dissolve out a Ca component in the fly ash into water, and [2] a step of subjecting the slurry formed in the above washing step to a solid-liquid separation, to thereby recover the dissolved Ca component in a solution after washing and also recover a solid component as a washing residue. The blow of a CO2 gas into the above solution after washing forms CaCO3. On the other hand, the above washing residue has a low Ca content, which results in the by-production of a Pb-containing residue having a low content of gypsum through subjecting the washing residue to the leaching with sulfuric acid, and the Pb-containing residue is useful in Pb refining. Further, the solution after the separation of the Pb-containing residue can be used as a raw material for Zn refining.

Description

 Description Fly ash treatment method Technical field

 The present invention is intended for fly ash collected from combustion exhaust gas at the time of incineration of municipal solid waste or the like, or fly ash collected from exhaust gas generated at the time of melting ash or dust during incineration or the like. The present invention relates to a wet treatment method, and particularly to a treatment method for separating and recovering C a, P b, gangue components, Zn content and the like contained in the fly ash in a form that can be effectively used. Conventional technology

 Waste from general establishments and households (referred to as “municipal waste” or “general waste”) is collected at municipal waste incineration facilities, industrial waste incineration plants, etc., and incinerated. I have. At that time, incineration ash and fly ash generated from the incinerator are deposited at the final disposal site through intermediate treatment such as chemical treatment, melting treatment, and cement kiln treatment.

 In the intermediate treatment in a melting furnace or cement kiln, heavy metals such as Zn, Pb, and Cd with high vapor pressure volatilize in the furnace and enter the exhaust gas. In this case, there is a problem that it condenses and becomes fly ash again. This fly ash contains a large amount of heavy metals such as Zn, pb, Cu, and Cd, as well as CI, Na, and Ca. A way was sought. Various fly ash treatment methods are proposed in the following patent documents.

 Patent Document 1 JP-A-7-1095333

 Patent Literature 2 Japanese Patent Application Laid-Open No. Hei 8-1-1 7 7 2 4

 Patent Literature 3 Japanese Patent Application Laid-Open No. H08-14141539 ''

 Patent Document 4 Japanese Patent Application Laid-Open No. 2000-01-1 1 3 2 4 2

 Patent Document 5 Japanese Patent Application Laid-Open No. 2000-01-34 8 6 2 7

 Patent Literature 6 JP 2 Q 03-1 6 4_ 8 229

Patent Document 7 JP-A-8-36555 No. Patent Document 8 JP-A-8-3 2 3 3 2 1

 Patent Document 9 Japanese Patent Application Laid-Open No. 2000-11017

 Patent Document 10 Japanese Patent Application Laid-Open No. 2000-2004

 Patent Literature 1 1 Japanese Patent Application Laid-Open No. 2000-2111

 Patent Document 1 2 Japanese Patent Application Laid-Open No. 2000-200501 Problem to be Solved by the Invention

 It is considered that the wet treatment methods disclosed in the above patent documents are effective in separating and recovering heavy metals contained in fly ash in a stable form. However, these technologies focus on the recovery of heavy metals, and further improvement is desired from the viewpoint of effective use of Ca and effective use of gangue components.

 On the other hand, as a fly ash treatment method intended to recover Zn in fly ash in the most preferable form that can be used in a wet zinc production process, a process of leaching fly ash with an aqueous hydrochloric acid solution is proposed. A processing method that employs the above-mentioned method is proposed as Japanese Patent Application No. 2003-36567706. According to this method, it is possible to collect, as the neutralized sediment residue, those which are enriched with Zn and other heavy metals and hardly contain Si and A 1. This residue is highly useful as a raw material for supplying to the wet zinc production process.

 However, there is a problem with this method. That is, since a liquid with a high salt concentration adheres to the obtained residue, the amount of the residue used is limited by the amount of chlorine that can be accepted in the production process. In order to avoid this limitation, a process for removing the adhering liquid is required. Treatment using hydrochloric acid leaching is more expensive than sulfuric acid leaching.

On the other hand, if it is attempted to separate and recover Zn resources that can be supplied to wet zinc production using a sulfuric acid leaching process that is advantageous in terms of cost, fly ash contains a large amount of Ca, so it is not possible to obtain in the intermediate process. is the gangue residue byproducts gypsum (C a S 0 ₄₎ many including intends want. Since this residue has a high Pb grade, it is desired to use it effectively for lead production. However, since it has a large gypsum content, its use as a raw material for lead production has a problem in terms of thermal energy.

Accordingly, the present invention relates to a process for recovering heavy metals by treating fly ash, i) Effective use of Ca,

ii) effective use of Pb-containing gangue components,

iii) Lower cost than hydrochloric acid leaching process,

The goal is to achieve these all at once. Means for solving the problem

 Fly ash contains a large amount of Zn and often Pb. In order to use these metals effectively, it is preferable to use Zn for wet zinc herb and Pb for lead with other gangue components. The inventors of the present invention have studied the process of treating fly ash that enables the use of Zn and Pb, and as a result, firstly, in the washing step, as much Ca as possible is dissolved in the liquid "as much as possible" and separated and collected. However, it was found that it would be extremely advantageous to reduce the amount of Ca remaining on the solids side of the washed fly ash as much as possible.

 It was found that washing with very low ash pulp concentration was very effective in dissolving Ca in the solution in the first washing step.

At this time, since the amount of Ca contained in the solid content after washing is reduced, when this is treated by sulfuric acid leaching, the amount of gypsum accompanying the gangue residue can be reduced. The Ca may be separated and recovered as the calcium carbonate (CAC0 ₃₎ and gypsum (CaS 0 _4).

 The present invention has been completed based on these findings.

 That is, according to the present invention, in order to achieve the above object,

 [1] The process of washing the fly ash in a liquid with a pulp concentration of 5 to 100 g / L to elute the Ca in the fly ash into water (washing process)

 [2] a process of collecting the eluted C a in the liquid after washing by solid-liquid separation of the slurry obtained in the washing step, and collecting a solid content as a washing residue; A method is provided.

 It is desirable to perform stirring during washing.

 Further, in order to treat the post-washing solution of the above [2], after the steps of [1] and [2],

[3] Step of depositing by blowing C 0 ₂ gas into the washing after solution of the [2], the Ca component which is dissolved as CAC0 _3, [4] the by solid-liquid separation and the resulting slurries in the process of [3], the step of separating and recovering the CaC 0 ₃ as a solid,

And a method for treating fly ash having the following.

 In this case, the solution after decalcification obtained in the step [4] can be returned to the step [1] and reused as water for washing fly ash.

 On the other hand, in order to treat the washing residue of [2], after the steps of [1] and [2],

 [5] A step of leaching the washing residue of the above [2] with a sulfuric acid-containing aqueous solution having a pH of 1 to 3.5 to transfer Zn to the leaching solution side (sulfuric acid leaching step 1),

 [6] a step of adding alkali to the leached slurry (solid-liquid mixture) of the above [5] to neutralize so that the pH becomes 3-5-5 (neutralization step 1);

 [7] a step of collecting the post-Zn-containing solution and the residue by solid-liquid separation of the neutralized slurry of the above [6],

And a method for treating fly ash having the following.

Further, in order to recover the Zn compound and CaS 0 _4, wherein [1] [2] [5] [6] After about E [7],

[8] A step of forming a Zn compound and CaS 04 by adding CaO or Ca (OH) ₂ to the after-solution containing Zn of the above [7] and neutralizing the solution to a pH of 5 to 9 (medium) Japanese process 2),

[9] the by solid-liquid separation of the slurry after neutralization of [8], recovering the Zn compound and CaS 0 ₄ as solid content,

And a method for treating fly ash having the following.

 In this case, the after-liquid obtained in the step [9] can be reused by returning it to the steps [6] and [8] as [1] or [5] or as lipanolep water.

Furthermore, in order to recover the ZnS 0 ₄ containing liquid that can be used to wet zinc steel kneading, the [1] [2] [5] [6] [7] [8] After the step of [9],

[10] the by leaching with sulfuric acid-containing aqueous solution solids containing Ζηθ and CaS 0 ₄ obtained in step [9], the step of shifting the Zn leachate side (sulfuric leaching step 2),

[11] by slurrying the solid-liquid separation after leaching of the [10], ZnS 0 ₄ containing A perforated after solution, CaS 0 ₄ (gypsum) entities (i.e. CaS 0 ₄ is Included 8 0 wt% or more) recovering solids,

And a method for treating fly ash having the following.

 The method for treating fly ash according to the present invention has the following advantages.

 (1) Most of the Ca contained in the fly ash in large quantities will be dissolved in the liquid in the cleaning process first, so the amount of cleaning residues to be treated can be reduced.

 (2) Since the Ca content of the cleaning residue is reduced, the gypsum content in the Pb-containing gangue residue obtained as a by-product can be reduced when treated by a process using sulfuric acid immersion. For this reason, the Pb-containing residue is obtained in a form that can be easily used for lead production, and recycling can be promoted.

 (3) Zn contained in fly ash can be recovered in a form that can be easily used for wet zinc smelting by a treatment process using sulfuric acid immersion. Therefore, the processing cost can be reduced as compared with the case of hydrochloric acid immersion.

 (4) The Ca in the fly ash is separated and recovered as CaCOa from the solution after washing and as CaS04 from the washing residue side, so it can be effectively used for various purposes.

(5) Since the C0 ₂ gas in the processing steps of cleaning after fluid is fixed as Ca C0 _3, in particular Cu, carbon dioxide emissions of C 0 Using ₂ gas Convenor Bok discharged from manufacturing鍊工field such as Zn It can contribute to the control of the amount. Brief Description of Drawings

 FIG. 1 is a flowchart showing an example of a fly ash treatment process to which the present invention is applied. Preferred embodiments of the invention

 The fly ash treatment method of the present invention can be applied to various fly ash discharged from incinerators and melting furnaces of waste treatment facilities and the like, or mixed fly ash thereof. Above all, it is effective to apply to fly ash having a high Ca content of, for example, 15 to 30% by mass.

FIG. 1 shows an example of the processing flow of the present invention. [1] to [11] in FIG. 1 correspond to the steps [1] to [11] described in the claims. Hereinafter, the steps [1] to [11] will be described in order. <Process [1] (Washing process)> First, make a fly ash mixture with a low pulp concentration. If the fly ash is agglomerated and clumped, such as when the fly ash is conditioned, it is desirable to grind it beforehand. This is because if the fly ash does not become well dispersed in the liquid during washing, the dissolution of Ca will not proceed easily. The liquid for washing may be water, but after the step [4], the liquid can be reused.

 In the present invention, a fly ash mixture having a very low pulp concentration (PD) of 5 to 100 g / L is used for washing. Ability to increase apparent Ca solubility as pulp concentration is higher As a result of various experiments, it has been found that the total amount of Ca dissolved in washing water is more advantageous when the pulp concentration is reduced. Pulp concentration is within the range of 0.01 to 100 g / L. Possible pulp concentration is too low, and the amount of liquid to be treated by solid-liquid separation increases. It is better to do it within the range. Practically, it is preferably from 10 to 100 g / L, and more preferably from 30 to 50 g.ZL.

 When washing, it is desirable to vigorously stir. Specifically, it is preferable that the fly ash be dispersed in the liquid and that the Ca mass in the fly ash be vigorously stirred to a level at which the mass transfer coefficient of the film is negligible to promote the dissolution of Ca.

 The pH during washing does not need to be particularly controlled, but it is possible to increase the amount of dissolved Ca by adding an acid or the like. The pH value varies depending on the composition of the fly ash, but usually falls within the range of 7 to 13.

 The time (residence time) of the cleaning treatment may be generally set to 10 to 150 minutes. The optimal time varies depending on the degree of agglomeration of the agglomerates and the intensity of stirring, but it is desirable to use a sufficiently pulverized fly ash for a processing time of about 10 to 80 minutes.

 Specifically, stirring should be performed at a temperature of 20 to 90 ° C and a processing time of 10 to 150 minutes with a strength that stabilizes the pH 5 to 120 minutes after the start of the processing. Is desirable.

Process [2]>

The slurry after washing is subjected to solid-liquid separation. The Ca dissolved in the washing solution is collected as a solution after washing. On the other hand, the amount of cleaning residue is greatly reduced compared to the original fly ash, and the Ca content is also reduced. In this step, various means can be selected, such as thickening with a thickener, a filter, a press, a belt-type vacuum filter, an Oliver, and a screw counter. However, care should be taken when using thickeners alone, since solid-liquid separation is poor, and a large amount of Ca and salts dissolved by washing may be carried over to the solids side. In general, good results are obtained using a filter press.

Process [3]>

The dissolved Ca is precipitated as Ca CO 3 by blowing CO ₂ gas into the solution after washing. In this case, it is preferable to blow the co ₂ gas so as to have a pH of 8 to 11, preferably 9 to 10. It is desirable to perform stirring. C0 ₂ concentration and the G / L ratio ( "volume of the gas blown per minute (L) / slurries volume (L)") so much regardless CAC0 ₃ gas used is precipitated. However, since the C0 ₂ amount you introduced is excessive CAC0 ₃ will be redissolved, if when high C 0 ₂ concentration of the gas or GZL ratio of blowing high tricky. That is, it is important that Ca C Oa to control the precipitation of CaC 0 ₃ so as not to re-dissolve a Ca (HC0 ₃₎ 2. Considering the easiness of the control, the GL ratio is preferably set to 0.001 to 0.01. The temperature is preferably from 10 to 40 ° C. The processing time is preferably about 5 to 40 minutes, which is the time required for the pH value to fall within the above range.

<Process [4]>

The step [3] obtained CaC 0 ₃ containing slurry to solid-liquid was separated, the separating and recovering CAC0 ₃ as solids. This can be used as a neutralizing agent in the production process. On the other hand, since Ca is removed from the post-solution, it can be returned to step [1] and used for washing water. However, if this solution after Ca removal is repeatedly reused, salts (NaCl and C1) will be concentrated, so it is desirable to perform effluent treatment by partially bleeding off.

Cracking process [5] (Sulfuric acid leaching process 1)>

On the other hand, the washing residue obtained in the step [2] is subjected to a process for recovering a Pb-containing gangue residue that can be used for lead smelting and a Zn-containing liquid that can be used for wet zinc smelting. It is. First, in step [5], repulp and sulfuric acid leaching are performed. The pulp concentration is preferably about 100 to 300 g / L before leaching. By using sulfuric acid, Zn is transferred to the leaching solution side, and Pb and gangue components are retained on the leaching residue side. However, some gangue components also migrate to the leachate side. The pH during leaching is controlled between 1 and 3.5. Increasing the acid concentration so that the pH is less than 1 does not significantly change the leaching rate of Zn. Leaching with a pH of 1.5 to 2.5 is more preferred, including economics. The temperature can be between 20 and 90 ° C and the leaching time can be between 30 and 120 minutes.

Process [6] (Neutralization process 1)>

Neutralization is performed following leaching. This process precipitates gangue components that have been leached once. NaO H and CaO is as a neutralizing _{agent, Ca (OH) 2, CaC} 0 3 power can be used. Here, it is possible to utilize the CaC 0 ₃ obtained in the step [4]. Even if Pb is contained in CaCOs, it is favorable for Pb-bearing gangue residue by neutralization. The pH at the time of neutralization is controlled to 3.5 to 5, preferably 3.5 to 4. Most of the Ca content in fly ash has been removed by the previous washing process, so gypsum will not be produced in large quantities in this neutralization process. The temperature can be 20 to 90 ° C, and the reaction time can be 5 to 120 minutes.

<Process [7]>

Here, the neutralized slurry is subjected to solid-liquid separation, and the post-solution containing Zn and the residue containing Pb are recovered. The post-Zn-containing solution can be used as, for example, a wet zinc raw material by treating in the following step [8]. Pb-containing residue includes Pb component and Si0 ₂ and [alpha] 1 ₂ 0 gangue components such as mainly comprising PBS O. Since this Pb-containing residue has a small amount of accompanying gypsum, it can be suitably used as a raw material for lead production.

<Step [8] (Neutralization step 2)>

After solution excluding the Pb-containing residue is the [7] (Zn-containing after liquid), further pH neutralized with the liquid which had increased to 5-9 and to produce a Zn compound and CaS 0 ₄ such Zetaitashita. If the pH exceeds 9, Zn goes in the direction of redissolution. More preferably, the pH is 7-8. CaO or Ca (OH) ₂ can be used as a neutralizing agent. The temperature can be 20 to 90 ° C, and the reaction time can be 5 to 120 minutes.

<Process [9]> The neutralized slurry is subjected to solid-liquid separation to recover a solid content containing a Zn compound and CaS04. This solid content becomes a raw material made of wet zinc by, for example, treating it in the following step [10]. The after solution can be used as [1] or [5], or returned to the process of [6] or [8] as repulp water.

<Step [10] (Sulfuric acid immersion step 2)>

The solids containing the Zn compound and CaS 0 ₄ obtained in the step [9] repulped and leached with sulfuric acid. Thus shifting to leachate side of Zn in the form of ZnS 0 _4. The pulp concentration is desirably about 100 to 100 g / L before leaching. The pH during leaching should be controlled between 0.1 and 4. The temperature is 20-90. C. The leaching time can be 5 to 120 minutes.

Ku process [11]〉

The slurry after leaching to solid-liquid separation, to recover the solids of ZnS 0 ₄ containing after solution and CaS 0 ₄ (gypsum) main body. The post-solution containing ZnS 04 can be used as an electrolytic solution made of wet zinc. CaS 04 can be used in various industrial fields. Example

 Example 1

Using A fly ash shown in Table 1, which when you washing with blown non conventional methods C0 ₂ gas (Comparative Example), after washing with thin water of fly ash concentration in accordance with the present invention with C0 ₂ gas In the case where Ca was recovered (Invention Example), the solution after washing and the washing residue were respectively treated.

 table 1

(A fly ash)

(Comparative example)

と固形分 （ 「洗浄残渣」 という） を得た。 濾液 a t と濾液 を混合した液 （ 「洗浄后液」 という） が約 3 L得られた。 100 g of fly ash was weighed, and 3 L (liter) of distilled water was added thereto to obtain mixed fly ash water. Thereafter the fly ash mixed water was stirred for 6 0 minutes, solid-liquid separation through a filter to obtain a filtrate a _L and solids a _s. Add further added distilled water 0. 3 L in this solid a _s Wash and filtrate

And a solid content (called "wash residue"). About 3 L of a liquid obtained by mixing the filtrate at and the filtrate (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, a composition analysis was also performed on the solution after washing. The results are shown in Table 3.

Next, the washed residue was repulped at a pulp concentration of 100 g / L, and adjusted to pH = 2 by adding sulfuric acid. This was stirred at 30 ° C. for 60 minutes to perform sulfuric acid leaching (step [5]). Then adjusted to pH = 4 by adding CaC 0 ₃ on the treatment liquid (slurry after leaching), were neutralized by stirring 6 0 minutes (step [6]). The liquid temperature was 30 ° C. Thereafter, solid-liquid separation was performed (step [7]) to obtain a post-solution containing Zn and a residue containing Pb. Table 4 shows the analysis results of the solution containing Zn. After the Pb-containing residue was sufficiently dried at 105 ° C, the composition was analyzed. Table 5 shows the results.

 Table 2

表 3 [Washing residue (Comparative Example)]

Table 3

表 4 [Solution after washing (Comparative Example)]

Table 4

[Zn-containing solution (Comparative Example)]

 Table 5

 [Pb-containing residue (Comparative Example)]

 Total Zn Pb Ca S Na K CI

 Grade (mass%) 0.86 1.61 30.56 8.92 1.09 0.89 0.97

Quantity (g) 576 5 9 176 51 6 5 6 (Invention example)

 100 g of fly ash A was weighed, and 30 L of water to be used repeatedly was added thereto, and 3 L of distilled water was further added to obtain mixed fly ash water. The water to be used repeatedly is defined as [30] after about 30 L of the post-solution obtained in the step [4] of Example 2 is returned as washing water each time, and after the same treatment process has already been repeated for 4 charges, This is the post-liquid obtained in step 4] (However, distilled water is used for the first charge). This fly ash mixed water was stirred at 30 ° C. for 60 minutes. The obtained slurry was subjected to solid-liquid separation with a filter to obtain a liquid after washing and a washing residue. The above is the process [1] and the process [2].

 After the washing residue was sufficiently dried at 105 ° C., composition analysis was performed. Table 6 shows the results. On the other hand, a composition analysis was also performed on the solution after washing. Table 7 shows the results.

 Comparing Table 2 (Comparative Example) and Table 6 (Inventive Example), it can be seen that the amount of the generated cleaning residue in the inventive example is significantly smaller than that in the comparative example. Also, the C a amount of the cleaning residue is greatly reduced in the case of the invention example.

 Comparing Table 3 (Comparative Example) and Table 7 (Inventive Example), in the inventive example, both the amount of Ca and the Ca concentration in the solution after washing are significantly higher than those in the comparative example. This indicates that a large amount of Ca was dissolved in the wash water by stirring the fly ash mixed water in a diluted state.

Next, as in the comparative example, the washed residue was repulped at a pulp concentration of 100 g ZL, adjusted to pH = 2 by adding sulfuric acid, and stirred at 30 ° C for 60 minutes. Sulfuric acid leaching was carried out (step [5]). Then was adjusted to pH = 4 by addition of Ca C0 ₃ was recovered in step [4] to be described later to the treatment liquid (slurry after leaching), it was neutralized by stirring for 6 0 minutes (step [ 6]). The liquid temperature was 30 ° C. Thereafter, solid-liquid separation was performed (step [7]) to obtain a Zn-containing post-solution and a Pb-containing residue. Table 8 shows the analysis results of the solution containing Zn. After the Pb-containing residue was sufficiently dried at 1 G at 5 ° C, the composition was analyzed. Table 9 shows the results.

 Comparing Table 4 (Comparative Example) and Table 8 (Inventive Example), in the inventive example, the Zn concentration in the liquid after Zn-containing was higher than that in the comparative example, and the C1 concentration was lower. In other words, the Zn-containing post-solution obtained in the invention examples is very advantageous for use as a raw material for wet zinc production.

Comparing Table 5 (Comparative Example) and Table 9 (Invention Example), the invention example shows that Pb grade is higher than comparative example. Also, the amount of Ca was greatly reduced. In other words, the amount of gypsum accompanying the P-containing residue as a by-product is greatly reduced by using the washing residue in which most of the Ca is dissolved and removed on the liquid side in the washing step. This Pb-containing residue can be effectively used for lead production together with gangue components. Example 2

Processing the wash after liquid obtained in the washing step in the above [Inventive Example] An experiment was conducted to collect the CaC 0 _3. That is, pure CO 2 gas was blown into the solution after washing in which Ca was dissolved, with stirring (step [3]). At that time, pure CO ₂ gas was introduced at 33 mL / min. When the pH reached 9.8, gas introduction and stirring were stopped. The temperature was 30 ° C and the reaction time was about 20 minutes. After that, the slurry was separated into solid and liquid.

(Step [4]).

 After the obtained solid was sufficiently dried at 105 ° C., the composition was analyzed. Table 10 shows the results. Composition analysis was also performed on the after solution (after Ca removal). Table 11 shows the results. As described above, the analyzed solution after the removal of Ca was returned to the washing solution, and the bleed-off operation was repeated about 30 L each time. This is the solution obtained by performing the above charging, that is, the solution after the removal of Ca after performing five consecutive chargings. The composition change due to the repetition is almost stable. As can be seen from Tables 10 and 11, from the post-washing solution obtained according to the present invention, for example, CaCOs of a grade usable as an alkali in step [6] was recovered. In addition, the amount of Ca dissolved in the solution after decalcification was smaller than that in the solution after washing, and it was confirmed that the solution could be repeatedly used as washing water.

 Table 6

 [Washing residue (Invention example)]

 Total Zn Pb Ca S Na CI

 Grade (% by mass) 7.88 0.01 21.10 6.80 3.19 2.37 4.78

Quantity 583 46 0.1 123 39 19 14 28 Table 7

表 8 [Liquid after washing (Invention example)]

Table 8

表 9 [Zn-containing post-solution (Invention example)]

Table 9

 [: Pb-containing residue (Invention example)]

表 1 1 Ca后液 （発明例） 〕

Table 11 1 Ca after solution (Invention example)]

Example 3

In the [Inventive Example] of Example 1, the Zn-containing post-liquid (Table 8) obtained in Step [7] was subjected to the treatment of Step [8] and subsequent steps. That is, slurried lime Ca was added to the solution after the Zn content while stirring to neutralize (step [8]). At that time, pH The pH was monitored so that it was 9. The temperature was 30 ° C and the reaction time was 60 minutes. The slurry was solid-liquid separation (step [9]), was recovered Zn compound and CaS 0 ₄ of ZnO mainly as solids. In addition, the post-solution was recovered. The liquid after this could be reused as water, for example, returned to step [1] or step [5].

And repulping the residue containing Zn compound and CaS 0 ₄ recovered as solids and pulp concentration 3 0 0 GZL, this was adjusted to p H = 2 by addition of sulfuric acid, which in 6 0 ° C Sulfuric acid leaching was carried out by stirring for 20 minutes (step [10]). Then subjected to solid-liquid separation (step [11]), ZnSO * to recover solids containing after solution and CaS 0 ₄ (gypsum) mainly. ZnS 0 ₄ containing after liquid was shall be used as a raw material quality to wet zinc steel鍊. On the other hand, the gypsum obtained had relatively few impurities and could be used in various fields.

Claims

The scope of the claims  1. [1] A process in which fly ash is washed in a pulp concentration of 5 to 100 g / L to elute the Ca in fly ash into water (washing process)  [2] a fly ash treatment method comprising: a step of solid-liquid separation of the slurry obtained in the above-mentioned washing step to collect the eluted Ca in the solution after washing, and to collect solids as washing residues. . 2. [1] The step of dissolving the fly ash in water by stirring and washing the fly ash in a liquid with a pulp concentration of 5 to 100 gZL (washing step)  [2] a process of collecting the eluted C a in the liquid after washing by solid-liquid separation of the slurry obtained in the washing step, and collecting a solid content as a washing residue; Method. 3. [3] Step of depositing by blowing C0 ₂ gas in the cleaning after solution of the [2], the Ca component which is dissolved as Ca COa, [4] the by solid-liquid separation of the resulting slurry in the step of [3], the step of separating and recovering the CaC 0 ₃ as a solid,  The method for treating fly ash according to claim 1, comprising: 4. The fly ash according to claim 3, wherein the after-solution (after Ca removal) obtained in the step [4] is returned to the step [1] and reused as a solution for washing fly ash. Processing method. 5. [5] The washing residue of the above [2] is leached with a sulfuric acid-containing aqueous solution having a pH of 1 to 3.5 to transfer Zn to the leaching solution side (sulfuric acid leaching step 1).  [6] a step (neutralization step 1) of adding an alkali to the leached slurry (solid-liquid mixture) of the above [5] to neutralize the slurry to a pH of 3.5 to 5;  [7] a step of collecting the post-Zn-containing solution and the residue by solid-liquid separation of the slurry after the neutralization of the above [6], The method for treating fly ash according to claim 1, comprising: 6. [8] A Zn compound, Ca S 04, is generated by adding Ca 0 or Ca (OH) 2 to the Zn-containing post solution of the above [7] and neutralizing the solution so that the pH becomes 5 to 9. Process (neutralization process 2),  [9] a step of recovering the Zn compound and Ca S 04 as a solid by solid-liquid separation of the slurry after the neutralization of the above [8],  6. The method for treating fly ash according to claim 5, comprising: 7. The method for treating fly ash according to claim 6, wherein the after-liquid obtained in the step [9] is returned to the step [1] or [5] for reuse. 8. [10] the [9] of the Zn compound and solid content containing CaS 0 ₄ obtained by leaching with sulfuric acid-containing aqueous solution to a step, the step of Ru transitions the Zn leachate side (sulfuric leaching step 2), [11] by slurrying the solid-liquid separation after leaching of the [10], recovering the solid of ZnS0 ₄ containing chromatic after solution and CaS OA (gypsum) mainly  7. The method for treating fly ash according to claim 6, comprising: