JP4581715B2 - Dust disposal method - Google Patents

Description

The present invention relates to a method for treating kiln dust or the like obtained by bypassing chlorine, alkali or the like from a cement kiln. More specifically, the present invention relates to a dust processing method for recycling valuable metals, dusts containing chlorides, fertilizer raw materials, chemical raw materials, smelting raw materials, cement raw materials, etc. from dust containing heavy metals, chlorine, alkalis and the like. Further, the present invention relates to the production how fertilizer raw or chemical feedstock from dust.

  Conventionally, as a dust treatment method of this type, a sulfiding agent is added to waste water that has been washed with water to precipitate the metal in the liquid, and the liquid component that has been separated into solid and liquid is decalcified to remove the calcium content in the liquid and A wastewater treatment method is disclosed in which sulfate groups are precipitated and the liquid temperature of the solid-liquid separated liquid is adjusted to precipitate and separate chlorides in the liquid (see, for example, Patent Document 1). In this method, the liquid temperature after solid-liquid separation is adjusted to 60 to 80 ° C., the filtrate is concentrated, sodium chloride remaining in the liquid is precipitated, and then the liquid temperature is adjusted to the room temperature range to adjust potassium chloride. It is deposited.

As another dust treatment method, cement kiln exhaust gas dust is washed with water, and the resulting wash water is adjusted to pH 7 to 10, and then a sulfiding agent is added, and the generated precipitate and liquid components are separated into solid and liquid. A method for treating cement kiln exhaust gas dust is disclosed in which the precipitate is recovered, the liquid component is heated and concentrated, and then cooled to precipitate potassium chloride for recovery (see, for example, Patent Document 2).
JP 2002-282867 A (Claims 1 and 4) Japanese Patent No. 3306471 (Claim 1)

However, in the treatment methods shown in Patent Document 1 and Patent Document 2 above, sulfide is added to remove heavy metals, and this sulfide may generate harmful hydrogen sulfide gas. It is extremely difficult to control the amount to be produced, and the sulfide is very fine and has a problem of poor solid-liquid separation performance.
Furthermore, in order to recover potassium chloride, cooling is performed after concentration by heating, but although this method can recover high-grade potassium chloride, it is unavoidable to finally generate waste liquid with concentrated impurities. A treatment process such as waste liquid is required, and the process is complicated.

  Cement dust has a large compositional variation and contains a large amount of various impurities, making it difficult to stably recycle. In particular, when recycling as potassium fertilizer, it is necessary to remove impurities. However, in the methods shown in Patent Document 1 and Patent Document 2, the process is complicated and waste liquid is generated. Is inevitable.

The object of the present invention is to pass through a simple process to efficiently reduce the heavy metal concentration and calcium concentration in the washing filtrate mainly composed of potassium and chlorine after solid-liquid separation during dust treatment. It is to provide a dust treatment method .

In the invention according to claim 1, as shown by the solid line in FIG. 1, the step 12 of preparing the slurry 13 by mixing the dust 10 containing heavy metal and the water 11, and adjusting the pH of the slurry 13 to 10-12. Due to the coprecipitation effect of the step 16, the step 18 of adding potassium carbonate 17 to the slurry 13 to precipitate heavy metals in the form of hydroxide or carbonate, and the slurry to which potassium carbonate has been added A stationary step 19 for further precipitating heavy metals dissolved in water, a solid-liquid separation step 23 for solid-liquid separation of the stationary product in the stationary step into a filtrate 21 and a residue 22, and a solid line in FIG. As shown in FIG . 2, the dust treatment method includes a step 26 of adding hydrochloric acid 24 to the filtrate 21 obtained by solid-liquid separation to decompose unreacted potassium carbonate contained in the filtrate .
The invention according to claim 2 is the invention according to claim 1, wherein a step 27 for evaporating and drying the filtrate 21 obtained by solid-liquid separation and a fertilizer raw material from the solid matter 28 obtained by evaporating to dryness are obtained. Or the process which further includes the process of producing | generating a chemical raw material.
The invention according to claim 3 is the processing method according to claim 1, further comprising a step of generating a smelting raw material or a cement raw material from the residue 22 obtained by solid-liquid separation.

In the invention according to claim 4 , as shown by the solid line in FIG. 1, the step 12 of preparing the slurry 13 by mixing the dust 10 containing heavy metal and the water 11, and adjusting the pH of the slurry 13 to 10-12. Due to the coprecipitation effect of the step 16, the step 18 of adding potassium carbonate 17 to the slurry 13 to precipitate heavy metals in the form of hydroxide or carbonate, and the slurry to which potassium carbonate has been added A stationary step 19 for further precipitating heavy metals dissolved in water, a solid-liquid separation step 23 for solid-liquid separation of the stationary product in the stationary step into a filtrate 21 and a residue 22, and solid-liquid separation. A step 27 for evaporating and drying the filtrate 21 obtained, a step for producing a fertilizer raw material or a chemical raw material from a solid material 28 obtained by evaporating to dryness , and solid-liquid separation as shown by a solid line in FIG. Add hydrochloric acid 24 to the filtrate 21 obtained Potassium carbonate unreacted contained terrorism liquid is a manufacturing method of the fertilizer raw materials or chemical feedstock comprising the decomposing step 26.

  In the dust treatment method of the present invention, first, dust containing heavy metal and water are mixed and dissolved in a slurry in which halogens such as chlorine and alkali metals are prepared, and the pH of the slurry is adjusted to 10-12. Potassium carbonate is added to the slurry to precipitate heavy metals in the form of hydroxide or carbonate. Addition of potassium carbonate produces carbonates of heavy metal components in the slurry. Moreover, since it reacts with the calcium ion in a slurry and produces | generates a calcium carbonate, the calcium concentration in a liquid can be reduced. Subsequently, the slurry to which this potassium carbonate has been added is allowed to stand to dissolve in water due to the coprecipitation effect with the carbonate to further precipitate the remaining heavy metal. Next, this stationary product is subjected to solid-liquid separation to obtain a filtrate and a residue. The residue is used as a refining raw material or a cement raw material. The filtrate uses a solid material obtained by evaporating and drying the filtrate as a fertilizer raw material or a chemical raw material. Thus, by passing through each said process, the heavy metal density | concentration and calcium density | concentration in the washing | cleaning filtrate which have potassium and chlorine as a main component after solid-liquid separation at the time of a dust process can be reduced efficiently.

A first embodiment of the present invention will be described with reference to FIG. 1 indicated by a solid line.
For example, the dust targeted for the treatment method of the present invention is kiln dust obtained by bypassing chlorine, alkali and the like from a cement kiln. Examples of heavy metals contained in the dust include Cd, Pb, Zn, and Cu.

  First, the slurry 10 is prepared by mixing the dust 10 and the water 11 at a predetermined ratio (step 12). Specifically, the mixing is performed so that the ratio of dust to water is 1: 2 to 1:20, preferably 1: 3 to 1:10. By preparing the slurry 13, halogens such as chlorine and alkali metals such as potassium and sodium contained in the dust are dissolved. In the slurry 13 prepared in this step 12, the solubility of heavy metals contained in dust varies depending on the pH of the slurry, but most of Cu precipitates as hydroxides. Among the heavy metals contained in the dust, for Pb, Zn, and Cd, the pH of the slurry fluctuates from the alkaline region to the acidic region, so the solubility is changed. Except for special cases, Pb, Zn, and Cd 3 The element dissolves in the liquid.

Next, the pH of the slurry 13 is adjusted to a range of 10 to 12, preferably 10 to 11 (step 16). The pH adjusting agent 14 for adjusting the pH of the slurry 13 is preferably HCl as the acid. As the alkali, Ca (OH) ₂ , CaO, CaCO ₃ or the like is preferable because the SO ₄ concentration in the slurry 13 can be reduced. By adjusting the pH of the slurry 13 to a predetermined range, the concentration of dissolved or precipitated Pb, Zn, Cd, etc. changes to the solubility in water at the adjusted pH. When the concentration decreases, part of it becomes a hydroxide. This water-insoluble heavy metal hydroxide precipitates over time.

  Next, potassium carbonate 17 is added as a water-soluble carbonate to the slurry 13 (step 18). By adding potassium carbonate 17 to the slurry 13, the dissolved Pb, Zn, Cd and the like generate carbonate. This water-insoluble heavy metal carbonate precipitates over time. Moreover, the potassium carbonate 17 can reduce the calcium concentration in the liquid by reacting with calcium ions in the slurry to produce calcium carbonate. This calcium carbonate also contributes to the coprecipitation effect in the subsequent standing step. Thereby, the potassium content of the potassium chloride fertilizer finally collect | recovered can be improved, and the fertilizer raw material of the stable quality can be obtained.

  Subsequently, the slurry 13 to which potassium carbonate 17 has been added is allowed to stand (step 19). The standing is performed for 30 minutes or more, preferably 1 to 12 hours. Considering the removal efficiency, it is sufficient to stand for 1 hour or more, but the standing time is determined from the above range from the viewpoint of the apparatus and operation. The removal efficiency does not improve so much even if the product is left standing above the upper limit. By this standing, the heavy metal remaining in the water is precipitated together with the precipitation of the calcium salt. This coprecipitation effect further reduces the concentration of heavy metals dissolved in water.

  Subsequently, the stationary product containing the liquid and the precipitate is subjected to solid-liquid separation into the filtrate 21 and the residue 22 by centrifugation, filter press or the like (step 23). Since the obtained filtrate 21 is mainly composed of potassium and chlorine, the filtrate 21 is heated to evaporate and dry the moisture, thereby evaporating all the moisture in the filtrate (step 27). Since the obtained solid 28 contains a large amount of alkali metals such as potassium and sodium and halogens such as chlorine and bromine, fertilizer raw materials and chemical raw materials are produced from the solids. Thus, it is not necessary to carry out a complicated crystallization process, and it is possible to carry out recycling without generating a waste liquid in which salts and impurities are concentrated.

On the other hand, since the residue 22 obtained by solid-liquid separation contains a little heavy metal, most of it is composed of a calcium compound and silica, so that a smelting raw material or a cement raw material is produced from this residue.
In this way, through each step in the treatment method of the present invention, it is possible to recycle regardless of the impurity component of dust and its variation, and reduce the heavy metal concentration and calcium concentration in the filtrate by a simple process. Can be obtained stably. Further, it is possible to effectively use the dust-containing component without generating waste liquid or waste in the treatment process.

A second embodiment of the present invention will be described with reference to FIG. 2 indicated by a solid line.
2, the same reference numerals as those in FIG. 1 denote the same components. This embodiment is different from the above-described embodiment in the following points. That is, a small amount of hydrochloric acid 24 is added to the filtrate 21 obtained by solid-liquid separation to decompose unreacted potassium carbonate contained in the filtrate (step 26). The configuration other than the above is the same as that of the first embodiment. Compared with the first embodiment, in the second embodiment, unreacted potassium carbonate can be decomposed in the filtrate 21 by adding hydrochloric acid 24 to the filtrate 21, and potassium content in the fertilizer can be reduced. The amount can be improved. That is, a fertilizer raw material or a chemical raw material having an improved potassium content can be produced.

Next, a third embodiment of the present invention will be described with reference to FIG. 3 indicated by a solid line.
For example, the dust targeted for the treatment method of the present invention is kiln dust obtained by bypassing chlorine, alkali and the like from a cement kiln. Of this kiln dust, alkaline dust containing a large amount of calcium component and having a slurry having a pH of 12 or more is an object. Examples of heavy metals contained in the dust include Cd, Pb, Zn, and Cu.

  First, the slurry 30 is prepared by mixing the dust 30 and the water 31 at a predetermined ratio (step 32). Specifically, the mixing is performed so that the ratio of dust to water is 1: 2 to 1:20, preferably 1: 3 to 1:10. By preparing the slurry 33, halogens such as chlorine and alkali metals such as potassium and sodium contained in the dust are dissolved. In the slurry 33 prepared in this step 32, most of the heavy metals contained in the dust are hydroxides such as Cd and Cu. This hydroxide precipitates with very low solubility in water. Among heavy metals contained in dust, Pb, Zn, and the like have high solubility in water when the slurry exhibits a pH of 12 or more, and some of them are dissolved in an alkaline aqueous solution.

  Next, carbon dioxide gas 34 is blown into the slurry 33 to adjust the pH of the slurry 33 to a range of 10 to 12, preferably 10 to 11 (step 36). The carbon dioxide gas 34 may be an exhaust gas containing carbon dioxide gas such as a kiln, an incinerator, or a melting furnace. By blowing the carbon dioxide gas 34, heavy metal components in the slurry 33 are precipitated. By adjusting the pH of the slurry 33 to a predetermined range, the dissolved Pb, Zn, and the like generate carbonate. In addition, slightly dissolved Cd and the like also become carbonate. This water-insoluble heavy metal carbonate precipitates over time.

Next, calcium chloride 37 is added to the slurry 33 (step 38). By adding calcium chloride 37 to the slurry 33, SO ₄ ions in the slurry react with calcium to generate CaSO ₄ precipitates, so that the concentration of SO ₄ ions in the liquid can be reduced. Thereby, the potassium content of the potassium chloride fertilizer finally collect | recovered can be improved, and the fertilizer raw material of the stable quality can be obtained. Further, the carbon dioxide gas blown in the above-described step 36 reacts with calcium ions in the liquid to generate calcium carbonate, whereby the calcium concentration in the liquid can be reduced. This calcium carbonate also contributes to the coprecipitation effect in the subsequent standing step.

  Subsequently, the slurry 33 to which calcium chloride 37 has been added is allowed to stand (step 39). The standing is performed for 30 minutes or more, preferably 1 to 12 hours. Considering the removal efficiency, it is sufficient to stand for 1 hour or more, but the standing time is determined from the above range from the viewpoint of the apparatus and operation. The removal efficiency does not improve so much even if the product is left standing above the upper limit. By this standing, the heavy metal remaining in the water is precipitated together with the precipitation of the calcium salt. This coprecipitation effect further reduces the concentration of heavy metals dissolved in water.

  Subsequently, the stationary product containing the liquid and the precipitate is subjected to solid-liquid separation into the filtrate 41 and the residue 42 by centrifugation, filter press or the like (step 43). Since the main component of the obtained filtrate 41 is potassium or chlorine, the filtrate 41 is heated to evaporate and dry the water, thereby evaporating all the water in the filtrate (step 44). Since the obtained solid 46 contains a large amount of alkali metals such as potassium and sodium and halogens such as chlorine and bromine, fertilizer raw materials and chemical raw materials are produced from the solids. It is not necessary to carry out a complicated crystallization process, and it is possible to recycle without generating waste liquid concentrated with salts and impurities.

On the other hand, since the residue 42 obtained by solid-liquid separation contains a little heavy metal, most of it is composed of a calcium compound and silica. Therefore, a smelting raw material or a cement raw material is produced from this residue.
In this way, through each step in the treatment method of the present invention, it is possible to recycle regardless of the impurity component of dust and its variation, and the concentration of heavy metal and SO ₄ ion in the filtrate is reduced by a simple process. And can stably obtain potassium fertilizer. Further, it is possible to effectively use the dust-containing component without generating waste liquid or waste in the treatment process.

A fourth embodiment of the present invention will be described with reference to FIG. 4 indicated by a solid line.
4, the same reference numerals as those in FIG. 3 denote the same components. This embodiment is different from the above-described embodiment in the following points. That is, when the pH of the prepared slurry is less than 10, the slaked lime 47 is added to and mixed with the dust 30 before the slurry preparing step 32 (step 48). The configuration other than the above is the same as that of the third embodiment. Compared to the third embodiment, in the fourth embodiment, for the dust 30 whose pH is less than 10 when the slurry 33 is adjusted by mixing with water 31, the slurry 33 is used. Before preparation, the pH can be adjusted to 10 or more by adding slaked lime 47 to the dust 30.

Next, examples of the present invention will be described in detail together with comparative examples.
<Examples 1 and 2>
First, cement kiln dusts A to C were prepared, and the dust composition was analyzed. Each composition is shown in Table 1, respectively.

Next, dusts A and B were used to mix the dust and water so that the ratio of dust to water was 1: 5 to prepare slurries. The pH of the slurry at this time was measured. Next, the pH of each prepared slurry was adjusted to 10.5 using a pH adjuster shown in Table 2 below. Next, potassium carbonate was added to the slurry. Subsequently, each slurry was allowed to stand for 30 minutes, and then the stationary product was subjected to solid-liquid separation with a filter press to obtain a filtrate and a residue. As shown by the broken line in FIG. 1, a part of these filtrates was extracted to obtain a filtrate 1. The filtrate 1 extracted from the filtrate was subjected to chemical analysis by ICP emission spectroscopy for the heavy metal component of each filtrate. Next, the filtrate was evaporated to dryness to evaporate the entire amount of water to obtain a solid of KCl crystals. Chemical analysis was performed on the calcium component, SO ₄ ion, and potassium component contained in the solid. The results are shown in Table 2 below.

< Reference Examples 1 to 4 >
First, slaked lime was added to and mixed with the dust A shown in Table 1 above. Subsequently, using the dust A to which slaked lime was added and the dust B and C shown in Table 1, mixing was performed so that the ratio of the dust and water was 1: 5 to prepare three types of slurries. Moreover, it mixed so that the ratio of the dust A which added and mixed slaked lime and water might be a ratio of 1:10, and prepared the slurry. The pH of the slurry at this time was measured. Next, CO ₂ gas was blown into each prepared slurry to adjust the pH of the slurry to 10 to 11.5. Next, calcium chloride was added to the slurry. Subsequently, each slurry was allowed to stand for 30 minutes, and then the stationary product was subjected to solid-liquid separation with a filter press to obtain a filtrate and a residue. As shown by the broken line in FIG. 3, a part of these filtrates was extracted to obtain a filtrate 1. The filtrate 1 extracted from the filtrate was subjected to chemical analysis by ICP emission spectroscopy for the heavy metal component of each filtrate. Next, the filtrate was evaporated to dryness to evaporate the entire amount of water to obtain a solid of KCl crystals. Chemical analysis was performed on the calcium component, SO ₄ ion, and potassium component contained in the solid. The results are shown in Table 2 below. In addition, the slurry pH in Reference Examples 1 and 4 in Table 2 indicates the slurry pH when the slurry is prepared using the dust A not added and mixed with slaked lime, and the slurry is prepared using the dust A added and mixed with slaked lime. The pH at that time was 12.4.

<Comparative Examples 1-3>
First, dusts A to C shown in Table 1 above were used and mixed so that the ratio of dust to water was 1: 5 to prepare three types of slurries. The pH of the slurry at this time was measured. Next, the pH of each prepared slurry was adjusted to 10.5 using a pH adjuster shown in Table 2 below. This slurry was solid-liquid separated by a filter press to obtain a filtrate and a residue. A part of these filtrates was extracted to obtain filtrate 1. The filtrate 1 extracted from the filtrate was subjected to chemical analysis by ICP emission spectroscopy for the heavy metal component of each filtrate. Next, the filtrate was evaporated to dryness to evaporate the entire amount of water to obtain a solid of KCl crystals. Chemical analysis was performed on the calcium component, SO ₄ ion, and potassium component contained in the solid. The results are shown in Table 2 below.

As is clear from Table 2, in Comparative Examples 1 to 3 in which the slurry was adjusted to pH and then solid-liquid separated without adding any additive, the concentration of calcium contained in the solid material composed of KCl crystals and SO ₄ were reduced. The result was that the ion concentration was high and the potassium content did not meet the fertilizer standard. When the K component of the KCl crystal exceeds 41.5%, the fertilizer standard of 50% or more in terms of K ₂ O is achieved.
On the other hand, in Examples 1 and 2 in which K ₂ CO ₃ was added after adjusting the pH of the slurry, the concentration of calcium contained in the solid material composed of KCl crystals was reduced, and the potassium content satisfied the fertilizer standard. Stable quality fertilizer raw material was obtained. In addition, in Reference Examples 1 to 4 in which CaCl ₂ was added after adjusting the pH of the slurry, the SO ₄ ion concentration contained in the solid material composed of KCl crystals was reduced, and the potassium content rate satisfied the fertilizer standard. Stable quality fertilizer raw material was obtained.

<Examples 3 to 5 >
Using the dust C shown in Table 1 having a high calcium content, three types of slurries were prepared by mixing so that the ratio of dust to water was 1: 5. The pH of the slurry at this time was measured. Next, the pH of each prepared slurry was adjusted to 11 using the pH adjuster shown in the following Table 2. Next, potassium carbonate was added to each slurry while changing the addition amount from 2% to 6%. Specifically, the addition of 2% potassium carbonate against dust 100 weight the slurry of Example 3, the slurry of Example 4 was added 4% potassium carbonate against dust 100 weight Example 5 In this slurry, 6% of potassium carbonate was added with respect to 100 weight of dust. Subsequently, each slurry was allowed to stand for 30 minutes, and then this still product was subjected to solid-liquid separation with a filter press to obtain a filtrate and a residue. As shown by the broken line in FIG. 1, a part of these filtrates was extracted to obtain a filtrate 1. The filtrate 1 extracted from the filtrate was subjected to chemical analysis by ICP emission spectroscopy for the heavy metal component of each filtrate. Next, the filtrate was evaporated to dryness to evaporate the entire amount of water to obtain a solid of KCl crystals. Chemical analysis was performed on the calcium component, SO ₄ ion, and potassium component contained in the solid. The results are shown in Table 3 below.

  As is apparent from Table 3, even when the dust has a high calcium content, it is understood that potassium chloride crystals satisfying the fertilizer standard can be obtained by increasing the amount of potassium carbonate added.

  The present invention can be used for processing kiln dust and the like. Further, fertilizer raw materials, chemical raw materials, smelting raw materials, cement raw materials and the like can be produced from the kiln dust and the like.

The figure which shows the 1st dust treatment process of this invention. The figure which shows the 2nd dust processing process of this invention. The figure which shows the 3rd dust processing process of this invention. The figure which shows the 4th dust processing process of this invention.

10,30 Dust 11,31 Water 12,32 Slurry preparation process 13,33 Slurry 14 pH adjuster 16,36 pH adjustment process 17 Potassium carbonate 18 Heavy metal precipitation process 19,39 Co-precipitation with residual heavy metal salt by standing Step 21, 41 Filtrate 22, 42 Residue 23, 43 Solid-liquid separation step 24 Hydrochloric acid 26 Decomposition step of unreacted potassium carbonate 27, 44 Evaporation to dryness step 28, 46 Solid matter 34 Carbon dioxide gas 37 Calcium chloride 38 Heavy metal precipitation step , Desulfation ion process 47 Slaked lime 48 Mixing process

Claims (4)

A step (12) of preparing a slurry (13) by mixing dust (10) containing heavy metal and water (11);
Adjusting the pH of the slurry (13) to 10-12,
Adding potassium carbonate (17) to the slurry (13) to precipitate the heavy metal in the form of hydroxide or carbonate; and
The standing step (19) of allowing the slurry added with the potassium carbonate to stand still and further precipitating heavy metal remaining dissolved in water by the coprecipitation effect with the carbonate, and
A solid-liquid separation step (23) for solid-liquid separation of the stationary product of the stationary step into a filtrate (21) and a residue (22) ;
A step (26) of adding hydrochloric acid (24) to the filtrate (21) obtained by the solid-liquid separation to decompose unreacted potassium carbonate contained in the filtrate . The method further includes a step (27) of evaporating and drying the filtrate (21) obtained by solid-liquid separation, and a step of producing a fertilizer raw material or a chemical raw material from the solid matter (28) obtained by the evaporation to dryness. processing method according to claim 1 Symbol placement.   The processing method according to claim 1, further comprising a step of producing a smelting raw material or a cement raw material from the residue (22) obtained by solid-liquid separation. A step (12) of preparing a slurry (13) by mixing dust (10) containing heavy metal and water (11);
Adjusting the pH of the slurry (13) to 10-12,
Adding potassium carbonate (17) to the slurry (13) to precipitate the heavy metal in the form of hydroxide or carbonate; and
The standing step (19) of allowing the slurry added with the potassium carbonate to stand still and further precipitating heavy metal remaining dissolved in water by the coprecipitation effect with the carbonate, and
A solid-liquid separation step (23) for solid-liquid separation of the stationary product of the stationary step into a filtrate (21) and a residue (22);
A step (27) of evaporating and drying the filtrate (21) obtained by solid-liquid separation;
Producing a fertilizer raw material or a chemical raw material from the solid (28) obtained by evaporation to dryness ;
Step (26) of adding hydrochloric acid (24) to the filtrate (21) obtained by the solid-liquid separation and decomposing unreacted potassium carbonate contained in the filtrate, thereby producing a fertilizer raw material or a chemical raw material Method.

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