JP2022057081A - Method for desalinating chlorine-containing ash and recovering calcium - Google Patents

Abstract

To provide a treatment method enabling chlorine-containing ash to be sufficiently desalinated and calcium included in the ash to be effectively recovered.SOLUTION: A method for desalinating chlorine-containing ash and recovering calcium is provided, including: a hydrochloric acid washing step in which chlorine-containing ash is converted into hydrochloric acid slurry, is subjected to hydrochloric acid washing at a pH of 2.5-6.0, so that calcium and chlorine included in the chlorine-contained ash is eluted; a first solid-liquid separation step in which the slurry after the hydrochloric acid washing is subjected to solid-liquid separation, so that a hydrochloric acid washing filtrate is recovered; an alkali adding step in which the pH of the hydrochloric acid washing filtrate is controlled to be 12.5 or higher by adding alkali to the hydrochloric acid washing filtrate, so that calcium included in the filtrate is converted into calcium hydroxide at a pH of 12.5 or higher and solidified; and a second solid-liquid separation step in which a solid content including the calcium hydroxide is recovered after the alkali adding step.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for effectively recovering calcium by desalting and washing chlorine-containing ash.

Cement raw materials such as incineration ash (main ash, fly ash, cinders, soot and dust) generated by incineration of general waste and industrial waste, incineration ash landfilled at the final disposal site, and cleana dust generated from cement factories. It is being reused as a product. On the other hand, since these incinerator ash and the like contain about 10% of chlorine, the above-mentioned various incinerator ash and cleana dust containing these chlorine (hereinafter referred to as chlorine-containing ash) are recycled. It is necessary to desalt to the extent that it is suitable for the purpose.

In addition, the chlorine-containing ash contains abundant calcium content of about 20% to 50% in terms of oxide, and if this calcium content can be effectively recovered, the recycling of chlorine-containing ash can be expanded. can. For example, if calcium can be recovered from chlorine-containing ash with high purity, it can be reused for various purposes other than cement raw materials. On the other hand, chlorine-containing ash contains silicon, iron, aluminum, titanium, etc. in addition to chlorine and calcium, and if these impurities remain in the recovered calcium content, they can be used for purposes other than cement raw materials. It becomes difficult to do so, and the use for reuse may be limited.

Regarding the desalting of the chlorine-containing ash, most of the chlorine compounds contained in the chlorine-containing ash are water-soluble and can be washed with water to desalt, but some of the chlorine compounds are sparingly soluble in water. It forms 3CaO, Al _{2O 3} , CaCl ₂ , 10H ₂ O), etc., and cannot be sufficiently desalted only by washing with water. On the other hand, a method of desalting by adding an acid to Friedel's salt or the like to lower the pH is known. However, in this method, calcium is eluted together with chlorine as the pH decreases, so that calcium cannot be sufficiently recovered by pickling alone.

Further, a method of adding water containing a carbonate to chlorine-containing ash for cleaning (Japanese Patent Laid-Open No. 2006-326462) or a method of blowing carbonate gas into a water slurry of chlorine-containing ash for cleaning is known (Patent No. 1). 3924822 (Ab.). When washed with carbonate or carbonic acid gas, Friedel's salt is decomposed and desalted, so demineralized washing ash can be obtained, but some of the calcium becomes poorly soluble calcium carbonate in water. This is recovered as solid content together with the washing ash by solid-liquid separation after washing. When this washing ash containing calcium carbonate is used as a raw material for cement, there is a problem that a large amount of CO ₂ is generated in the manufacturing process. Further, since this cleaning ash contains impurities such as silicon (Si), iron (Fe), aluminum (Al), and titanium (Ti), its use is generally limited to cement raw materials.

As described above, in order to expand the use of chlorine-containing ash for reuse, it is required that calcium can be sufficiently demineralized and calcium can be effectively recovered. Further, it is desired that the recovered calcium content is of high purity with sufficient impurities removed. Further, in order to comply with the demand for low carbon dioxide (reduction of CO ₂ emissions) during cement production, it is desired that calcium is in a form other than carbonates (CaCO ₃ , CaMg (CO ₃ ) ₂ , etc.).

Japanese Unexamined Patent Publication No. 2006-326462 Japanese Patent No. 3294822 Japanese Unexamined Patent Publication No. 2015-218369

The present invention solves the above problems and provides a treatment method capable of sufficiently desalting chlorine-containing ash and effectively recovering calcium contained in ash in the form of calcium hydroxide.

The method of the present invention is a treatment method that solves the above-mentioned problems by the following configuration, and is a method of desalting chlorine-containing ash to efficiently recover calcium.
[1] A chlorine-containing ash is made into a hydrochloric acid slurry and washed with hydrochloric acid at a pH of 2.5 to 6.0 to elute calcium and chlorine contained in the chlorine-containing ash. After the hydrochloric acid washing, the slurry is solidified. The first solid-liquid separation step of liquid separation and recovery of the hydrochloric acid washing filtrate, and the addition of alkali to solidify the calcium contained in the filtrate as calcium hydroxide by adding alkali to the hydrochloric acid washing filtrate to pH 12.5 or higher. A method for desalting chlorine-containing ash and recovering Ca, which comprises a step and a second solid-liquid separation step of recovering the solid content containing calcium hydroxide after the alkali addition step.
[2] In the alkali addition step, the pH is adjusted to 12.5 or higher by adding an alkaline solution, an alkaline powder, or a granular alkali in a closed atmosphere or an inert gas atmosphere, and the liquid temperature is heated to 40 ° C to 80 ° C. 1] The method for desalting chlorine-containing ash and recovering Ca.

[Specific explanation]
The treatment method of the present invention comprises a hydrochloric acid washing step of converting chlorine-containing ash into a hydrochloric acid slurry and washing with hydrochloric acid at pH 2.5 to 6.0 to elute calcium and chlorine contained in the chlorine-containing ash, and after the hydrochloric acid washing. The first solid-liquid separation step of solid-liquid separation of the slurry and recovery of the hydrochloric acid washing filtrate, and the addition of alkali to the hydrochloric acid washing filtrate to make the pH 12.5 or higher and the calcium contained in the filtrate to be calcium hydroxide to solidify. It is a method for desalting chlorine-containing ash and recovering Ca, which comprises a second solid-liquid separation step of recovering the solid content containing calcium hydroxide after the alkali addition step.
The outline of the processing method of the present invention is shown in the process diagram of FIG.

<Hydrochloric acid cleaning process>
The treatment method of the present invention comprises a hydrochloric acid washing step of converting chlorine-containing ash into a hydrochloric acid slurry, washing with hydrochloric acid in a liquid state of pH 2.5 to 6.0, and eluting calcium and chlorine contained in the chlorine-containing ash. Hydrochloric acid may be directly added to the chlorine-containing ash to form a hydrochloric acid slurry, or washing water may be added to the chlorine-containing ash to form a slurry, and then hydrochloric acid may be added to form a hydrochloric acid slurry.

By converting chlorine-containing ash into a hydrochloric acid slurry and stirring with a liquid of pH 2.5 to 6.0 and washing with hydrochloric acid, Ca and Cl are suppressed while suppressing the elution of Si, Fe, Al, and Ti contained in the chlorine-containing ash. Most of it can be eluted from chlorine-containing ash. Under strong acidity of less than pH 2.5, Si, Fe, and Al are likely to elute, and the concentration of Si, Fe, and Al contained in the liquid content is high, which is not preferable. On the other hand, when the pH exceeds 6.0, the amount of Ca eluted decreases, the residual chlorine concentration of the washing ash increases, and the desalting effect decreases.

It is not preferable to use nitric acid instead of hydrochloric acid because nitrogen is mixed in the wastewater and a large load is applied to the wastewater treatment. In addition, when sulfuric acid is used instead of hydrochloric acid, sparingly soluble calcium sulfate is produced, so the amount of Ca in the liquid is relatively reduced, and the calcium content in the liquid is reduced to the form of calcium hydroxide by the addition of alkali in the next step. Not suitable for solidification and recovery. Japanese Unexamined Patent Publication No. 2015-218369 (Patent Document 3) discloses a method of recovering gold and silver by leaching dust recovered from exhaust gas of cement manufacturing with sulfuric acid and then leaching with alkali. In this case, calcium sulfate is generated, and separation from impurities such as Si and Fe remaining in the solid content becomes troublesome, and calcium cannot be efficiently recovered. Performing alkali leaching after sulfuric acid leaching is a treatment method completely different from the method of the present invention.

The liquid-solidity ratio of the hydrochloric acid slurry is preferably 2 to 20 (liquid: solid = 2: 1 to 20: 1), more preferably 3 to 10 (liquid: solid = 3: 1 to 10: 1). If the liquid-solidity ratio is smaller than this, the slurry concentration becomes high, and the wear of pipes, pumps, etc. becomes severe. On the other hand, if the liquid-solidification ratio is larger than this, the amount of hydrochloric acid increases, the cost of chemicals increases, and the load of wastewater treatment increases.

Before washing with hydrochloric acid, the chlorine-containing ash can be efficiently desalted and washed by pulverizing the ash. Examples of the crushing device include a vibration mill and a hammer mill. Grinding and washing with hydrochloric acid may be performed at the same time.

<First solid-liquid separation process>
The hydrochloric acid-washed slurry is separated into solid and liquid, and the hydrochloric acid-washed filtrate containing eluted chlorine and calcium is recovered. Most of the impurities Si, Fe, Al, and Ti contained in the raw ash (chlorine-containing ash) remain in the separated solid cleaning ash without elution. can do. The solid dehydrated cake (demineralized and washed ash) can be recovered and used as a raw material for cement.

<Alkali addition process>
The treatment method of the present invention comprises an alkali addition step of adding an alkali to the hydrochloric acid washing filtrate and solidifying the calcium contained in the filtrate into calcium hydroxide in a liquid form having a pH of 12.5 or higher.

The alkali may be a solution or may be powdery or granular. As the type of alkali, a hydroxide of a general alkali metal such as sodium hydroxide and potassium hydroxide can be used.

By adding an alkali to adjust the liquid property to pH 12.5 or higher, calcium in the liquid produces calcium hydroxide and solidifies. When the pH is less than 12.5, most of the calcium in the liquid remains dissolved and hardly forms calcium hydroxide.

In the alkali addition step, in order to prevent the carbonation of calcium due to the mixing of carbon dioxide in the atmosphere, it is preferable to create a closed atmosphere or an atmosphere of an inert gas such as nitrogen gas. Further, the liquid temperature is preferably about 40 to 80 ° C. Since the solubility of calcium hydroxide decreases as the liquid temperature rises, the amount of calcium hydroxide recovered can be increased by heating to the above liquid temperature. Further, since the solubility of CO ₂ gas also decreases as the temperature rises, the carbonation of calcium can be suppressed by setting the liquid temperature. Further, the desalting reaction can be promoted by increasing the liquid temperature. It is not necessary to raise the liquid temperature above 80 ° C.

<Second solid-liquid separation step>
After adding alkali, solid-liquid separation is performed to recover the solid content. This solid content contains the generated calcium hydroxide. Calcium-containing ash (raw ash) is washed with hydrochloric acid to elute calcium, and alkali is added to the hydrochloric acid washing filtrate to convert calcium to calcium hydroxide and immobilized, so that 60% by mass or more of calcium contained in the raw ash is used. Can be recovered as calcium hydroxide. Impurities such as Si, Fe, Al, and Ti contained in the raw ash do not elute in the above-mentioned washing with hydrochloric acid and remain in the washing ash, so that the recovered calcium hydroxide contains almost no of these impurities.

A filter press, a vacuum belt filter, a centrifugal dehydrator, or the like can be used as the solid-liquid separation device in the first solid-liquid separation step and the second solid-liquid separation step. Easy to use filter press. For example, the dehydrated cake obtained by solid-liquid separation with a filter press (washing ash for the first solid-liquid separation or calcium hydroxide for the second solid-liquid separation) is further washed through with washing water to obtain a desalting effect. It can be further enhanced. Further, the water content of the dehydrated cake obtained by the filter press is as low as about 25 to 40%, and since excess water does not adhere to the dehydrated cake, the weight is reduced and the handleability is improved.

The wastewater generated by the solid-liquid separation is treated as wastewater and discharged, but the wastewater having a low chlorine concentration may be circulated in the hydrochloric acid washing step and used as washing water.

[Processing equipment]
FIG. 2 shows an example of the processing equipment that implements the method of the present invention. In the illustrated processing equipment, a vibration mill 1 for receiving chlorine-containing ash and washing water is provided. Chlorine-containing ash is appropriately pulverized in the vibration mill 1. The chlorine-containing ash slurry discharged from the vibration mill 1 is sent to the stirring and washing tank 2. Hydrochloric acid is supplied to the stirring and washing tank 2, and the pH is adjusted to 2.5 to 6.0 to perform hydrochloric acid washing (hydrochloric acid washing step). The slurry after washing with hydrochloric acid is sent to the filter press 3. Washing water is supplied to the filter press 3 and dehydrated (first solid-liquid separation step). This dehydration cleaning ash is sent out of the system. On the other hand, the recovered dehydrated component (hydrochloric acid washing filtrate) is sent to the reaction tank 4. Further, after the alkali is added to the reaction tank 4, it is sent to the thickener 5 to promote the production of calcium hydroxide (alkali addition step). The supernatant liquid of the thickener 5 is drained, while the slurry extracted from the thickener 5 is sent to the filter press 6. Washing water is supplied to the filter press 6 and dehydrated (second solid-liquid separation step), and the dehydrated cake (calcium hydroxide) is recovered. This dehydrated cake can be reused as a raw material for cement and the like. The wastewater is sent to the wastewater treatment facility 7 for wastewater treatment.

According to the treatment method of the present invention, chlorine-containing ash is removed by washing with hydrochloric acid under a liquid state (pH 2.5 to 6.0) in which impurities Si, Fe, Al, and Ti contained in the ash are difficult to elute. Since it is salted, it is possible to obtain a hydrochloric acid cleaning filtrate with few of these impurities. Add an alkali to this hydrochloric acid cleaning filtrate to adjust the pH to 12.5 or higher, and leave chlorine in the liquid to promote the production of calcium hydroxide. , Calcium can be solidified and easily recovered, and the desalting effect can be enhanced. Furthermore, since calcium is recovered in the form of hydroxide, it emits almost no CO ₂ when used as a raw material for cement, which greatly contributes to low carbonization during cement production. Moreover, since this calcium hydroxide has few impurities, it can be reused for many purposes. Specifically, for example, in addition to cement raw materials, it can be used as a wastewater or exhaust gas treatment agent, fertilizer, or the like.

The process drawing which shows the outline of the processing method of this invention. The schematic diagram of the processing equipment which carries out the processing method of this invention. XRD pattern of the dried cake of the example.

Hereinafter, examples of the present invention will be shown together with comparative examples. The Cl concentration of the recovered washing ash was analyzed by measuring the Cl concentration in the solution after acid-dissolving the washing ash with a coulometric titrator. The Ca concentration, Si concentration, Fe concentration, Al concentration and Ti concentration of the recovered washing ash were measured by fluorescent X-ray analysis (XRF). The results are shown in Table 1. The XRD pattern of the recovered wash ash is shown in FIG.

[Example 1]
Incinerated fly ash (Cl concentration, Ca concentration, etc. are shown in Table 1) is dried at 105 ° C., sieved, and 6.0 mol / L hydrochloric acid and water (100 mL in total) are added to 10 g of ash of 1 mm or less to form a slurry. The pH was adjusted to the pH shown in Table 1, shaken, and washed with hydrochloric acid. After this hydrochloric acid washing, the slurry is filtered to recover the hydrochloric acid washing filtrate, and the solid content (hydrogenic washing ash) is washed with 200 mL of pure water to recover the washing ash, which is dried at 105 ° C. to obtain dry washing ash. Obtained. By measuring the Ca concentration of the dry wash ash and the like, the transfer rate of each component to the dry wash ash and the hydrochloric acid wash filtrate was calculated. The results are shown in Table 2.

As shown in Table 2, the samples Nos. 3 to 6 having a pH of 2.6 to 5.1 during washing with hydrochloric acid have a large amount of Ca elution and a small amount of residual Ca in the washing ash. In addition, the amount of chlorine eluted is large, the residual chlorine in the washing ash is small, and the desalination effect is high. On the other hand, the samples No. 1 and 2 having pH 8.2 and pH 6.5 at the time of washing with hydrochloric acid have a large amount of residual Ca in the washing ash because the amount of Ca eluted is small. Furthermore, there is a large amount of residual chlorine in the washing ash, and the desalination effect is low. In the sample No. 7 having a pH of 2.2 during washing with hydrochloric acid, the amount of Ca and chlorine eluted is large, but Si, Fe, and Al are also eluted in a small amount, and the separation from these impurities becomes insufficient in the subsequent step.

[Example 2]
To 100 mL of the hydrochloric acid washing filtrate recovered in Sample No. 4 of Example 1, a 1.0 mol / L sodium hydroxide solution was added to adjust the pH to the pH shown in Table 3, and the liquid temperature was 25 ° C to 60 ° C for 1 hour. The mixture was stirred to solidify Ca in the liquid. The slurry was filtered to recover the desalted cake. 100 mL of pure water was added to this desalted cake for washing, dehydration was performed, and the washed cake was recovered. This washed cake was vacuum dried to obtain a dried cake. The chlorine concentration and Ca concentration of this dried cake were measured. The results are shown in Table 3. The XRD pattern of the recovered dried cake is shown in FIG.

As shown in Table 3, the samples No. 20 to No. 23 having a pH of 12.6 to 13.5 in the alkali addition step have a high Ca concentration in the dried cake and a Ca recovery rate of 60% or more. On the other hand, in the samples Nos. 24 and 25 having pH 12.2 and pH 11.5 in the alkali addition step, the Ca concentration of the dried cake was very low, and the Ca recovery rate was 1%. Further, as shown in FIG. 3, most of the recovered dried cakes of Samples No. 20 to No. 23 are calcium hydroxide.

Claims (2)

The chlorine-containing ash is made into a hydrochloric acid slurry and washed with hydrochloric acid at pH 2.5 to 6.0 to elute the calcium and chlorine contained in the chlorine-containing ash. After the hydrochloric acid washing, the slurry is solid-liquid separated. A first solid-liquid separation step of recovering the hydrochloric acid washing filtrate, and an alkali addition step of adding an alkali to the hydrochloric acid washing filtrate to make the pH 12.5 or higher and converting the calcium contained in the filtrate into calcium hydroxide to solidify. A method for desalting chlorine-containing ash and recovering Ca, which comprises a second solid-liquid separation step of recovering the solid content containing calcium hydroxide after the alkali addition step. The first aspect of claim 1 is that in the alkali addition step, an alkaline solution, an alkaline powder, or a granular alkali is added to bring the pH to 12.5 or higher and heat the liquid to a liquid temperature of 40 ° C to 80 ° C in a closed atmosphere or an inert gas atmosphere. Desalting of chlorine-containing ash and Ca recovery method.

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