WO2005040437A1

WO2005040437A1 - Method of wet treatment of fly ash

Info

Publication number: WO2005040437A1
Application number: PCT/JP2004/016202
Authority: WO
Inventors: Shuji Kuramochi; Taro Aichi; Hiroshi Asada; Hideki Yatsuduka; Kousuke Inoguchi; Tetsuo Dohi
Original assignee: Dowa Mining Co., Ltd.
Priority date: 2003-10-27
Filing date: 2004-10-26
Publication date: 2005-05-06
Also published as: JP2005126798A; JP4431767B2

Abstract

A method of the wet treatment of a fly ash, which comprises a step of subjecting a fly ash obtained from a combustion flue gas generated in the incineration of a municipal refuse or the like to an acid leaching treatment by the use of hydrochloric acid acidic solution having a pH of 3.5 or lower, adding a neutralizing agent to the resultant fluid and neutralizing the fluid so as to have a pH of higher than 3.5 and 5 or lower and subjecting the resultant fluid to a solid-liquid separation to obtain a filtrate (L1) and a gangue based residue (P1); a step of adding a neutralizing agent to the above filtrate (L1) to neutralize the filtrate so as to have a pH of higher than 5 and 9 or lower and subjecting the resultant fluid to a solid-liquid separation to obtain a filtrate (L2) and a zinc-rich residue (P2); and a step of adding sulfuric acid the above filtrate (L2) and subjecting the resultant fluid to a solid-liquid separation to obtain a filtrate (L3) and a gypsum based residue (P3). The above neutralization precipitate residue (P2) is zinc-rich and also is rich in other heavy metals, and contains little amount of Si, Al and the like, and therefore can have a quality sufficient for the supply to a wet zinc refining process as a raw material.

Description

Specification Wet processing method of fly ash

The present invention is a wet treatment for fly ash collected from combustion exhaust gas at the time of incineration of municipal waste etc., or fly ash collected from exhaust gas generated at the time of melting and processing ash and dust at the time of incineration More specifically, the present invention relates to a wet treatment method of separating and recovering heavy metals and gangue components contained in the fly ash in a form that can be effectively used. Prior art

As a method of recovering valuable metals (heavy metals) from the fly ash by the wet method, the heavy metal is leached out with mineral acid and then neutralized to form a neutralized sediment which is enriched with heavy metal, and this sediment is There is a method of separating and using it for non-ferrous kiln processes. In this case, sulfuric acid or hydrochloric acid is generally used as the mineral acid from the viewpoint of processing cost.

Among them, the method using sulfuric acid is cheaper than the method using hydrochloric acid, but 13 and ○ a in the fly ash are not leached, so not only can the 13 The amount of residue will increase significantly. This is particularly problematic in fly ash with high Ca concentration. Although residues containing P b and gypsum can be used in the dry P b making process, there is also a problem that the treatment cost is increased due to the large amount of slag components (gypsum) and C a can not be used effectively. is there.

On the other hand, a method of using hydrochloric acid, the cost rises above method by sulfuric acid, the addition of sulfuric acid to a solution containing a C a C 1 ₂ occurring in fly ash treatment process, achieving generation and hydrochloric acid recovery gypsum Since it can be done, fly ash can be processed inexpensively. As methods using such hydrochloric acid, methods described in, for example, JP-A Nos. 2 00 0 1 0 9 8 8 and 2 9 6 7 3 6 are known. Disclosure of the invention

As valuable metals in fly ash, the existence of Z n, P b, C u, C a, etc. can be seen. This Incorporating and collecting these valuable metals in the operation process of non-ferrous smelting is also advantageous in terms of effective use of resources and non-pollution of fly ash. However, it is not easy to determine what form of valuable metals in fly ash is concentrated or separated and which operation process of non-ferrous kilns is most advantageous.

Among valuable metals in fly ash, for example, focusing on Z n as having economic value, and taking in zinc in fly ash in the process of zinc smelting, the problem of hydrochloric acid as a method of treating fly ash Assuming that the method of acid leaching fly ash with a solution is adopted, for example, in the method of JP-A 2 0 0 0 0 9 8 3, Z n and soluble Si or A 1 are precipitated as the same residue. In order to use this residue as a raw material for wet n n making process,

5 i amount and A 1 amount are large and not necessarily desirable. Similarly, patent 2 9 8

Even in the case of the method of Japanese Patent No. 6736, since Si and A1 leached together with heavy metals are recovered as the same residue, it is not desirable as a raw material to be used in the process of making wet Zn.

Therefore, while adopting the method of acid leaching fly ash with hydrochloric acid solution, the present invention finds out a method of recovering Zn in fly ash in the most preferable form that can be used for the wet-Zn-making process. Was an issue.

According to the present invention, as a method of treating fly ash to solve the above problems, the fly ash is subjected to acid leaching treatment using a hydrochloric acid solution of pH 3.5 or less, and a neutralizing agent is added to the treatment solution. Neutralization to a range of more than pH 5 to 5 and then solid-liquid separation to collect filtrate L 1 and gangue-based residue P 1; and adding a neutralizing agent to the above-mentioned filtrate L 1 The process of solid-liquid separation after neutralization to a pH exceeding 5 to 9 and collecting the filtrate L 2 and zinc nitrate based residue P 2; solid-liquid separation after adding sulfuric acid to the above-mentioned filtrate L 2 And a step of collecting the filtrate L 3 and the gypsum-based residue P 3. Here, it is preferable that the fly ash to be subjected to the acid leaching treatment is one that has been previously washed with washing water that does not exceed pH 10. Also, the filtrate L 3 is recycled for acid leaching treatment.

When heavy metals are recovered from fly ash as neutralized sediment residue P 2 by the method of the present invention, this is rich in zinc, and other heavy metals are also rich in entrainment, and 31 1 and so on are hardly contained. , It becomes a raw material of quality sufficient to supply to a wet zinc making process. Therefore, it is possible to recover high-quality Z n (electrozinc such as 4 N or more Z n) from Z n in fly ash by supplying this to the wet zinc crucible process. Fly ash Resources can be used advantageously, and no pollution of fly ash can be achieved. Furthermore, the recycling of hydrochloric acid and the by-product of gypsum, which are the advantages of the acid leaching method using a hydrochloric acid solution, can be enjoyed as it is in the method of the present invention, which helps to reduce the cost of recovery of Zn. Brief description of the drawings

FIG. 1 is a view showing an example of the treatment flow of the wet treatment method of fly ash according to the present invention. FIG. 2 is a diagram showing an example flow of the wet processing method of fly ash according to the present invention. Preferred embodiment of the invention

The fly ash to be treated in the present invention is collected from the exhaust gas from a combustion furnace, an incinerator, a melting furnace and the like, and is usually collected by a bag filter or an electric collector installed in the exhaust gas passage. Ru. Most typically, the present invention treats fly ash collected from exhaust gas from general waste incinerators and fly ash collected from exhaust gas when slag (including the above-mentioned fly ash) is slagged in an ash melting furnace. Exhaust gas dusts similar to this can be treated. An example of the fly ash processing flow according to the present invention is shown in FIG. The fly ash as described above is used as a starting material in the present invention, but as shown in FIG. 1, it is preferable to first wash it. It is important to do this flush so that ρ ないよう does not exceed 10. When using alkaline process water generated in various processes as washing water, it is preferable to add hydrochloric acid as necessary so that ρ Η 10 or less. As a result, it is possible to remove the alkali 'salts mixed in the fly ash and to prevent the elution of heavy metals in the wash water. After washing, solid-liquid separation of washing water and fly ash is carried out, and the washed fly ash is recovered. This solid-liquid separation can be performed using a filter press.

The leaching treatment of fly ash with a hydrochloric acid solution is carried out using a hydrochloric acid solution having a ρ 4 or less, preferably ρ 3 未, and more preferably ρ 3 or less. As the hydrochloric acid solution, regenerated aqueous hydrochloric acid obtained in the final step of the present invention can be used. Although some of the heavy metal ions, Ca, etc. may be entrained in the regenerated hydrochloric acid solution, these are also recovered during the treatment process and hydrochloric acid will be recycled. It contributes to the improvement of the collection rate of metals and the cost reduction. This acid leaching process is stirred in the leacher. It is preferable to carry out under stirring. The temperature of the leaching treatment is from room temperature to 80 ° C., and the treatment time is suitably from 30 to 6 Q minutes.

After the acid leaching treatment, the treated solution is subsequently sent to the neutralization tank and subjected to the neutralization 1 treatment. In the neutralization 1 process, a neutralizing agent is added to the acid leached solution, and the pH of the solution is adjusted to the range of 3.5 to 5 to form a neutralized precipitate. The treatment temperature may be from normal temperature to 80 ° C. As a neutralizing agent, use of calcium carbonate aqueous solution is desirable. In the present invention, after the hydrochloric acid leaching treatment, the treated liquid is directly sent to the neutralization step to carry out the treatment of neutralization 1 without taking treatment or operation to separate the leaching residue from the liquid. The neutralized precipitate generated by the treatment is separated simultaneously with the leaching residue from the previous hydrochloric acid leaching treatment and separated simultaneously. It was found that the filterability is greatly improved by the simultaneous solid-liquid separation compared to the case where the acid leaching residue and the neutralized precipitate are separated individually (Comparative Example 1 described later). It is believed that this is because the leaching residue acts as a filter aid. This solid-liquid separation can be performed, for example, using a filter-press, and this solid-liquid separation gives a filtrate L 1 and a residue P 1 (a gangue-based residue).

In neutralization 1, S i, A 1, F e etc. coprecipitate and are separated from Z n, P b, C u etc. in the solution. Therefore, the residue P 1 is enriched in the gangue-side components for zinc preparations such as S i, A 1 and C a in fly ash, but heavy metals such as Z n, P b and C u are the same. There is little to be accompanied, and these heavy metals remain dissolved in the side of the filtrate L1. Although gangue residue P1 does not generally contain harmful substances, it can be disposed of as it is, but it contains many Ca and Si, so it can be used as a flux for dry dredging, and in this case it is valuable. Even if metals are accompanied, they can be recovered in the iron making process. Filtrate L 1 is then subjected to the treatment of neutralization 2 which adds a neutralizing agent to neutralize in the region of pH> 5, preferably to a pH greater than 5 to 9. The treatment temperature may be from normal temperature to 80 ° C. It is preferable to use an aqueous solution of calcium hydroxide as a neutralizing agent. By the treatment of this neutralization 2, heavy metal ions in the solution are precipitated, and Ca ions remain dissolved in the solution as calcium chloride. The slurry obtained after neutralization 2 treatment is subjected to solid-liquid separation to obtain filtrate L 2 and residue P 2. The filtrate L 2 contains a large amount of calcium chloride and metal ions such as Zn, P b and C u. The species contains only traces, and these heavy metals such as Zn, Pb, and Cu shift to residue P2 with high yield. Thus, the residue P 2 contains a high concentration of Z n, It is useful as a raw material or concentrate for zinc wet steelmaking because it is accompanied by P b and C u and contains almost no C a, S i and alkali components. For this reason, residue P 2 can be subjected to zinc kneading as a raw material having economic value, and Z n in fly ash is recovered as high purity Z n, and heavy metals such as P b and C u are also recovered. Collected together.

On the other hand, the filtrate L2 contains a large amount of calcium chloride. Therefore, by adding sulfuric acid to this filtrate L2, gypsum is deposited, and the solution after the deposition of gypsum becomes a hydrochloric acid solution. This gypsum suspension is separated into solid and liquid to obtain filtrate L 3 and 2 hydrogypsum. The filtrate L 3 can be reused in the leaching step as a regenerated hydrochloric acid aqueous solution. On the other hand, solid content can be recovered as high-quality, high-quality dihydrate gypsum. In addition, it is preferable to control the concentration of hydrochloric acid so that the solubility of gypsum decreases as the filtrate L3. For example, by regenerating the hydrochloric acid with a C a concentration of 40 g ZL or more and 1 N hydrochloric acid or less, the solubility of gypsum in the hydrochloric acid regeneration solution can be reduced, and this regenerated hydrochloric acid is repeatedly used in the leaching step. Also, less gypsum is precipitated in the leaching residue, and the amount of residue generation can be reduced. Example

[Example 1]

Fly ash A and B generated from a melting furnace that slags incinerated ash and fly ash, and fly ash derived from a direct melting furnace that enables direct melting and slagging of incinerated ash generated during general waste incineration C And D were mixed equally to make a mixed fly ash. The grade of these fly ash A to E is shown in Table 1.

Starting from the mixed fly ash E with a quantity of 3000 Dry-g, the grade of which is shown in Table 2, the process was carried out according to the flow shown in Fig.2. First, the mixed fly ash E was washed with water to obtain the washed fly ash of the grade shown in Table 3. The washing water used for washing was waste water generated from the zinc-making process, and hydrochloric acid was added so that the pH of the treatment solution was 1 Q. The pulp concentration at washing was 300 g / L. As shown in Table 3, the water removal process resulted in a removal rate of 27.2%, a removal rate of Na of 74.1%, and a removal rate of K of 76%, as shown in Table 3. Heavy metals are not eluted.

The obtained washed-off fly ash 22020 Dry- _g was acid leached with a hydrochloric acid solution. used The hydrochloric acid solution was prepared as follows. First, measure 4 g of sodium chloride 41 g and 222 g of calcium chloride to make an 8-litre aqueous solution. To this, add 22 9 mL of 98% concentrated sulfuric acid, mix and stir well, and then solid-liquid separate (filter) the formed white precipitate (gypsum: C a S 0 ₄ · 2 H 20). Obtain 6.5 liters of filtrate. Perform the same operation 3 times to obtain a total filtrate of 19.5 liters. It can be said that this solution contains hydrogen chloride with an acid concentration of 1N (standard: molar ZL). Table 4 shows the grade and volume of the acid leaching simulant used. The acid leaching treatment leached the washed fly ash in a stirred tank using the above-mentioned simulated hydrochloric acid solution in an amount of 6.5 L per 1 kg of dry washed fly ash. At that time, a hydrochloric acid solution was added to maintain the pH of the treatment solution at 2.0. The treated solution after leaching with hydrochloric acid was subsequently subjected to the treatment of neutralization 1. In this treatment of neutralization 1, an aqueous solution of calcium carbonate of 16.7 wt% was added so that the pH of the treatment solution would be 4.0. At this time, an aqueous solution of calcium carbonate was used in an amount of 0.33 75 liters per 1 kg of the washed and washed fly ash. The solution after this neutralization treatment was introduced into a pressure filter, and solid-liquid separation was carried out by this pressure filter into a filtrate L1 and a residue P1 as shown in FIG. The quality and quantity of the filtrate L 1 are shown in Table 5, and the grade and quantity of the residue P 1 (unwashed) are shown in Table 6. As apparent from Table 5 and Table 6, zinc in fly ash remains in the filtrate L 1 side, and copper and lead also remain in the filtrate L 1 side in a large amount, but Si and C a are residues P 1 side Migrate to a lot. That is, the residue P 1 is a gangue-type residue having a high content of Si and Ca. This gangue-based residue can be disposed of for disposal, but it can also be subjected to leaching treatment to further recover Zn, Pb, Cu, etc. coexisting in it.

In the solid-liquid separation carried out after this neutralization 1, the filtration rate under pressure of 0.5 MPa was 15 to 18 L / mVmin, and the water content in the residue was 30 to 40%. The above-mentioned filtrate L 1 was placed in a stirred tank and subjected to neutralization 2 treatment. In this Neutralization 2 treatment, 9. lwt% slaked lime aqueous solution was added while mixing into the stirring tank so that the pH of the treatment liquid was 8.0. In practice, the treatment of neutralization 2 was performed using 74 g of this slaked lime aqueous solution per 1 L of the filtrate. The solution after this neutralization treatment was introduced into a pressure filter and separated into filtrate L2 and residue P2 as shown in FIG. Table 7 shows the grade and quantity of filtrate L2, and Table 8 shows the grade and quantity of residue P2 (after water washing). As apparent from Table 7 and Table 8, zinc shifts to residue P2, and only trace amount remains in filtrate L2. same Similarly, lead and copper shift to residue P2 and hardly remain in filtrate L2. In addition, Si, Na, and K in the residue P 2 are all less than 0.2%, and about 0.3% of Ca. Therefore, the residue P 2 is a zinc-rich residue rich in heavy metals, and is similar to high-grade zinc concentrates with less algal components and gangue components, and is suitable as a raw material for wet production of zinc is there.

Next, add in the ratio of 9 2% concentrated sulfuric acid 6 5 2 g to the total amount (approximately 1 3 L) of the filtrate L 2 in the stirring tank, and the Ca in the filtrate L 2 is used as dihydrate gypsum It was precipitated. The resulting suspension was introduced into a pressure filter and separated into filtrate L3 and dihydrate gypsum P3 as shown in FIG. Table 9 shows the grade and quantity of soy sauce L 3 and Table 10 shows the grade and quantity of 2 gypsum D3. Filtrate L3 is a regenerated hydrochloric acid aqueous solution, which can be used as it is for hydrochloric acid leaching. On the other hand, 2 gypsum (P3) does not contain heavy metal components and alkali metals, and can be collected as high-quality gypsum.

Table 11 shows the recovery rates of Z n, P b and C u at each step performed in this example. As can be seen from the results in Table 11, it can be seen that in general, Z n, P b and C u in fly ash are collected with high recovery in residue P2. The second treatment was performed in the same manner as described above except that the filtrate L 3 was used instead of the hydrochloric acid simulation solution used initially, but it was confirmed that the same result as the first was obtained. It was done. The results of recovery of Z n, P b and C u at the second acid leaching and neutralization two steps were similar to those of the first one from the values shown in Table 11 as well. I understand.

Comparative Example 1

After acid leaching treatment, solid-liquid separation (referred to as intermediate solid-liquid separation) with a pressure filter is carried out prior to neutralization 1 treatment, and the filtrate obtained by this intermediate solid-liquid separation is neutralized 1 Example 1 was repeated, except that the process was performed. In this case, the filtration rate under pressure of 0.3 MPa in the intermediate solid-liquid separation is 3 to 10 L / mVmin, the water content in the residue is 30 to 40%, and the solid after the neutralization 1 treatment is In the liquid separation, the filtration rate under a pressure of 0.5 MPa was 1.5 to 5.5 L / m ² / min, and the water content in the residue was 45 to 70%. The filtration rate of the both is very slow as compared with the filtration rate of 15 to 18 L / mV min in solid-liquid separation after the neutralization 1 treatment of Example 1.

That is, rather than performing neutralization after separation of the acid leaching residue as in this example, As shown in Example 1, it can be seen that if the acid leaching residue and the neutralized precipitate are simultaneously separated by solid-liquid separation, the filterability will be better and the operability will be improved.

Table 1 Grades of each fly ash

Grade and quantity of mixed fly ash E

(Washing loss rate Hydrochloric acid simulated solution for acid leaching treatment

Quality and quantity of filtrate L 1

Quality and quantity of residue P 1 (unwashed)

Quality and quantity of filtrate L 2

Table 8 Quality and quantity of residue P 2 (after water washing)

Neutralization 2 ingredients Zn Pb Cu Si C a Na K residue after treatment

P 2 grade% 44.8 10.2 2.5 0.01 0.31 0.02 0.01 volume dry-g total 379 169.8 38.7 9.3 0 1.2 0.1 0 Liquor L 3rd grade and thing:

2 Grade and quantity of water gypsum (after water washing)

Recovery of heavy metals from fly ash (process)

Zn recovery Pb recovery Cu recovery rate% rate% rate water washing process 100.0 100.0 100.0 acid leaching 1 neutralization 1 process 80.5 81.4 80.6 neutralization 2 processes 99.9 99.0 98.0 whole process 80.4 80.6 79.0 second acid leaching 1 neutralization 2 81.0 78.9 90.0

Claims

The scope of the claims

1. Fly ash is acid leached using a hydrochloric acid solution of pH 3.5 or less, and after adding a neutralizer to this treatment solution to neutralize to a range of pH 3.5 to over 5, a solid-liquid separation is performed. Collecting the filtrate L 1 and the gangue-based residue P 1;

A neutralizing agent is added to the above-mentioned filtrate L 1 to neutralize to a range of pH 5 to 9 after solid-liquid separation to obtain a filtrate L 2 and a zinc residue-based residue P 2;

After adding sulfuric acid to the above-mentioned filtrate L 2, solid-liquid separation is carried out to collect filtrate L 3 and gypsum-based residue P 3,

2. The wet ashing method according to claim 1, wherein the fly ash to be subjected to the acid leaching treatment has been pre-washed with washing water having a pH not exceeding 1.0.

3. The wet treatment method of fly ash according to claim 1 or 2, wherein the filtrate L 3 is recycled for acid leaching treatment.