Potassium-containing fertilizer production method

Abstract

To provide a method capable of obtaining a potassium-containing fertilizer which has large concentration of potassium and small concentration of a component adversely affecting a plant and soil, when being used as a fertilizer, from a combustion exhaust gas dust containing potassium.SOLUTION: A potassium-containing fertilizer production method includes: a step of mixing a combustion exhaust gas dust containing potassium and water and obtaining a first slurry; a first solid-liquid separation step of solid-liquid separating the first slurry, and obtaining a first liquid material containing potassium and a first solid content; a first mixing step of mixing one or more kinds selected from the first liquid material, hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide, and obtaining a first mixture; a second mixing step of mixing the first mixture and a water-soluble metal salt and obtaining a second mixture; a third mixing step of mixing the second mixture and a polymer flocculant and obtaining a third mixture; and a second solid-liquid separation step of solid-liquid separating the third mixture, and obtaining a liquid potassium-containing fertilizer and a second solid content.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing potassium-containing fertilizer from potassium-containing flue gas dust, such as dust. [Background technology]

[0002] Conventionally, chlorine, sulfur, alkali, and other substances can cause problems such as clogging of preheaters in cement manufacturing facilities. However, chlorine is particularly problematic. To address this issue, cement manufacturing facilities have adopted a chlorine bypass system in which part of the combustion gas is extracted from the kiln exhaust gas discharge path that runs from the end of the cement kiln to the lowest cyclone to remove chlorine. In the chlorine bypass system, chlorine is concentrated in the fine powder portion of the dust particles generated by cooling the extracted combustion gas. Therefore, a classifier is used to separate the dust into coarse and fine powder, and the coarse powder is returned to the cement kiln system while the fine powder (clinker dust) is recovered. The recovered clinker dust is either (i) added to cement, (ii) washed with water and returned to the cement manufacturing facility as a raw material for cement production, or (iii) discarded.

[0003] Clinker dust contains potassium and chlorine, which are essential nutrients for plants, and depending on the content of these elements, clinker dust can be used as a fertilizer or a raw material for fertilizer. For example, Patent Document 1 describes a dust treatment method including the steps of mixing heavy metal-containing dust with water to prepare a slurry, blowing carbon dioxide gas into the slurry to adjust the pH of the slurry to 10 to 12, adding calcium chloride to the slurry to precipitate the heavy metals in the form of hydroxides or carbonates and removing sulfate ions, allowing the slurry with added calcium chloride to stand to further precipitate the heavy metals dissolved in water and remaining in the slurry through a coprecipitation effect with the carbonates, and performing a solid-liquid separation process to separate the material from the standing step into a filtrate and a residue. The filtrate obtained by this treatment method is primarily composed of potassium and chlorine, and has reduced concentrations of heavy metals and sulfate ions. This method allows for the stable production of potassium fertilizer. Furthermore, Patent Document 2 describes a method for recovering potassium from combustion exhaust gas dust, which comprises the steps of: (a) washing the combustion exhaust gas dust with water; (b) adding a sulfuric acid source to the obtained washing water; and (c) recovering the deposited precipitate by solid-liquid separation. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-269306 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-200842 Summary of the Invention [Problem to be solved by the invention]

[0005] Potassium ore, a natural resource, is used as potassium fertilizer. Since much of the potassium ore is imported, domestic production of potassium fertilizer is desirable from the perspective of food security. Furthermore, due to concerns about the depletion of natural resources, it is preferable to use fertilizer obtained through resource recycling in order to practice sustainable agriculture. Under these circumstances, it is not necessarily desirable to use clinker dust, which can be used as a fertilizer or fertilizer raw material, as a cement raw material. On the other hand, clinker dust can be used as a fertilizer or a fertilizer raw material. However, depending on the conditions under which the clinker dust is generated, it may contain heavy metals such as cadmium. If the clinker dust is used as is, problems such as an increase in the cadmium concentration in plants may occur. An object of the present invention is to provide a method for obtaining a potassium-containing fertilizer having a high potassium concentration and a low concentration of components that have adverse effects on plants and soil when used as a fertilizer, from potassium-containing combustion exhaust gas dust such as clinker dust. [Means for solving the problem]

[0006] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that the above-mentioned objects can be achieved by a method for producing a potassium-containing fertilizer, the method including the steps of mixing potassium-containing combustion exhaust gas dust with water to obtain a slurry, performing solid-liquid separation of the slurry to obtain a first liquid matter, mixing the first liquid matter, hydrogen sulfide, one or more selected from the group consisting of a normal salt of a water-soluble metal sulfide and an acid salt of a water-soluble metal sulfide, a water-soluble metal salt, and a polymer flocculant to obtain a mixture, and performing solid-liquid separation of the mixture to obtain a liquid potassium-containing fertilizer and a second solid matter, and have completed the present invention. That is, the present invention provides the following [1] to [4]. [1] A method for producing a potassium-containing fertilizer, comprising: a slurry preparation step of mixing potassium-containing combustion exhaust gas dust with water to obtain a first slurry; a first solid-liquid separation step of subjecting the first slurry to solid-liquid separation to obtain a first liquid material containing potassium and a first solid content; a first mixing step of mixing the first liquid material with one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide to obtain a first mixture; a second mixing step of mixing the first mixture with a water-soluble metal salt to obtain a second mixture; a third mixing step of mixing the second mixture with a polymer flocculant to obtain a third mixture; and a second solid-liquid separation step of subjecting the third mixture to solid-liquid separation to obtain a liquid potassium-containing fertilizer and a second solid content. [2] The method for producing a potassium-containing fertilizer according to claim 1, further comprising a pH adjustment step between the second mixing step and the third mixing step, for adjusting the pH of the second mixture to 6.5 to 9.5. [3] The method for producing a potassium-containing fertilizer according to [1] or [2], further comprising a carbon dioxide gas supplying step, which is provided between the slurry preparation step and the first solid-liquid separation step, of supplying carbon dioxide gas to the first slurry to adjust the pH of the first slurry to 11.0 or less. [4] The method for producing a potassium-containing fertilizer according to any one of [1] to [3] above, further comprising a concentration and drying step of concentrating or drying the liquid potassium-containing fertilizer. [Effects of the Invention]

[0007] According to the method of the present invention, a potassium-containing fertilizer having a high potassium concentration and a low concentration of components that have adverse effects on plants and soil when used as a fertilizer can be obtained from potassium-containing combustion exhaust gas dust such as clinker dust. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing an example of the steps of the method for producing a potassium-containing fertilizer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] The method for producing a potassium-containing fertilizer of the present invention includes a slurry preparation step of mixing potassium-containing combustion exhaust gas dust with water to obtain a first slurry, a first solid-liquid separation step of subjecting the first slurry to solid-liquid separation to obtain a first liquid material and a first solid content containing potassium, a first mixing step of mixing the first liquid material with one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide to obtain a first mixture, a second mixing step of mixing the first mixture with a water-soluble metal salt to obtain a second mixture, a third mixing step of mixing the second mixture with a polymer flocculant to obtain a third mixture, and a second solid-liquid separation step of subjecting the third mixture to solid-liquid separation to obtain a liquid potassium-containing fertilizer and a second solid content. Each step is described in detail below. [Slurry preparation process] This step is a step of mixing potassium-containing combustion exhaust gas dust (hereinafter also simply referred to as "dust") with water to obtain a first slurry. Examples of dust include soot and incineration ash remaining as incineration residue on the bottom of an incinerator, which contains potassium. Examples of dust include dust (molten fly ash) discharged from equipment for melting refuse or incineration ash, dust (incinerator fly ash) discharged from equipment for incinerating refuse or sewage sludge, and clinker dust recovered by a chlorine bypass system that extracts part of the combustion gas from a cement kiln in a cement manufacturing facility. Among these, clinker dust is preferred because it contains a large amount of potassium.

[0010] The method for mixing the dust and water is not particularly limited as long as the potassium contained in the dust is sufficiently dissolved in the water. For example, the dust and water are placed in a container and then stirred, usually for 15 minutes or more, preferably for 25 to 60 minutes. The mass ratio of the mixed dust to water (dust / water) is preferably 0.05 to 2.0, more preferably 0.1 to 1.0, and particularly preferably 0.15 to 0.5. If the mass ratio is 0.05 or more, a larger amount of potassium can be dissolved in water in a shorter time. If the mass ratio is 2.0 or less, the amount of liquid potassium-containing fertilizer obtained in the second solid-liquid separation step described below will not be excessive, and the amount of potassium in the liquid potassium-containing fertilizer can be increased. The temperature of the water is preferably 15° C. or higher, more preferably 20 to 60° C., and particularly preferably 25 to 55° C. If the temperature is 15° C. or higher, the dissolution of potassium contained in the dust into water can be further promoted.

[0011] [Carbon dioxide gas supply process] This step is an optional step that can be performed between the slurry preparation step and the first solid-liquid separation step, and is a step in which carbon dioxide gas (gaseous carbon dioxide) is supplied to the first slurry to adjust the pH of the first slurry to 11.0 or less. Examples of the carbon dioxide gas supply method include a method in which carbon dioxide gas is blown into the first slurry contained in a container using a carbon dioxide gas supply means (e.g., an exhaust pipe for supplying carbon dioxide gas) installed in the container for containing the first slurry. In addition, from the viewpoint of improving the carbon dioxide gas supply efficiency, carbon dioxide gas may be blown under pressure.

[0012] The carbon dioxide gas supplied may consist solely of carbon dioxide gas, but from the viewpoint of reducing the pH of the first slurry to 11.0 or less in a shorter time, a gas containing carbon dioxide gas at a ratio of preferably 2% by volume or more, more preferably 5% by volume or more, even more preferably 10% by volume or more, even more preferably 15% by volume or more, and particularly preferably 40% by volume or more (carbon dioxide-containing gas) may also be supplied. The pH of the first slurry is preferably 11.0 or less, more preferably 11.0 to 6.0, and particularly preferably 10.5 to 7.0. By adjusting the pH to 11.0 or less by supplying carbon dioxide gas, a larger amount of calcium contained in the first slurry can be precipitated as a solid content, which can be recovered in the first solid-liquid separation step described below.

[0013] [First solid-liquid separation step] This step is a step of performing solid-liquid separation on the first slurry obtained in the first slurry preparation step to obtain a first liquid matter containing potassium and a first solid matter. The solid-liquid separation means is not particularly limited, and examples thereof include a filter press, a centrifuge, and a belt filter. The first solid fraction obtained by solid-liquid separation may be recovered and then charged into the bottom of a cement kiln as a raw material for cement clinker.

[0014] [First mixing process] This step is a step of mixing the first liquid obtained in the first solid-liquid separation step with one or more substances selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide to obtain a first mixture. In this step, by mixing one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide, sulfide ions are supplied to the first liquid material, and components contained in the first liquid material that have an adverse effect on plants and soil can be precipitated. Among these, from the viewpoint of ease of mixing, it is preferable to mix one or more selected from a normal salt of a water-soluble metal sulfide and an acid salt of a water-soluble metal sulfide. The term "water-soluble" refers to the property of dissolving at least 1% by mass in neutral water at room temperature.

[0015] Examples of water-soluble normal salts of metal sulfides include alkali metal sulfides such as sodium sulfide and potassium sulfide, alkaline earth metal sulfides such as calcium sulfide, and aluminum sulfide. Examples of water-soluble acid salts of metal sulfides include alkali metal sulfides such as sodium hydrogen sulfide, etc. These may be used alone or in combination of two or more. Among these, water-soluble normal salts or acid salts of alkali metal sulfides are more preferred from the viewpoint that components that have an adverse effect on plants and soil when a potassium-containing fertilizer is applied to plants can be precipitated in a larger amount in this step and recovered in the second solid-liquid separation step described below; water-soluble normal salts or acid salts of sodium sulfide and water-soluble normal salts or acid salts of potassium sulfide are more preferred from the viewpoint of ease of availability; and sodium hydrogen sulfide is particularly preferred from the viewpoint that a larger amount of sulfide ions can be supplied for the same mass.

[0016] The method for mixing the first liquid material with hydrogen sulfide is not particularly limited, but examples include a method in which hydrogen sulfide is blown into the first liquid material contained in a container using a hydrogen sulfide supply means (e.g., an exhaust pipe for supplying hydrogen sulfide) installed in the container for containing the first liquid material. The method for mixing the first liquid material with one or more selected from the group consisting of a normal salt of a water-soluble metal sulfide and an acid salt of a water-soluble metal sulfide is not particularly limited, but examples include a method in which one or more selected from the group consisting of a normal salt of a water-soluble metal sulfide and an acid salt of a water-soluble metal sulfide is added to the first liquid material and stirred for 10 minutes or more, preferably 15 to 60 minutes, and more preferably 20 to 30 minutes.

[0017] The amount of one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide per liter of the first liquid is, in terms of sulfur atoms (as the amount of sulfur atoms contained in one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide), preferably 3 to 1,000 mg, more preferably 5 to 500 mg, even more preferably 8 to 300 mg, and particularly preferably 10 to 100 mg. If the amount is 3 mg or more, when the potassium-containing fertilizer is applied to plants, a larger amount of components that adversely affect plants and soil can be precipitated in this step and recovered in the second solid-liquid separation step described below. If the amount is 1,000 mg or less, material costs can be reduced.

[0018] [Second mixing process] This step is a step of mixing the first mixture obtained in the first mixing step with a water-soluble metal salt to obtain a second mixture. In this step, by mixing a water-soluble metal salt, sulfide ions remaining in the first mixture without reacting in the first mixing step can be precipitated. In particular, it is preferable to use a water-soluble heavy metal salt from the viewpoint of precipitating more sulfide ions. Here, a heavy metal refers to a metal whose simple substance has a specific gravity of 4 or more. The method for mixing the first mixture with the water-soluble metal salt is not particularly limited, but examples include a method in which the water-soluble metal salt is added to the first mixture and stirred for 10 minutes or more, preferably 15 to 60 minutes, and more preferably 20 to 30 minutes.

[0019] Examples of water-soluble metal salts (excluding heavy metal salts) include metal chloride salts such as sodium chloride, potassium chloride, calcium chloride, and aluminum chloride, and metal nitrate salts such as potassium nitrate. Examples of water-soluble heavy metal salts include chloride salts of heavy metals such as ferrous chloride (iron(II) chloride), ferric chloride (iron(III) chloride), cuprous chloride (copper(I) chloride), cupric chloride (copper(II) chloride), zinc chloride, nickel(II) chloride, and manganese(II) chloride; and nitrate salts of heavy metals such as ferrous nitrate (iron(II) nitrate), ferric nitrate (iron(III) nitrate), copper(II) nitrate, zinc nitrate, and nickel(II) nitrate. Among these, heavy metal salts of iron, copper, and zinc (ferrous chloride, ferric chloride, cuprous chloride, cupric chloride, zinc chloride, ferrous nitrate, ferric nitrate, copper(II) nitrate, zinc nitrate, etc.) are preferred from the viewpoint of easy availability and further removing sulfide ions contained in the first liquid material, heavy metal salts of iron are more preferred from the viewpoint of maintaining the quality of the liquid potassium-containing fertilizer, and ferrous chloride and ferric chloride are particularly preferred from the viewpoint of reducing the cost of obtaining materials. The amount of water-soluble metal salt per liter of the first mixture is, in terms of metal (as the amount of metal atoms contained in the water-soluble metal salt), preferably 5 to 2,000 mg, more preferably 10 to 1,000 mg, even more preferably 20 to 500 mg, and particularly preferably 25 to 300 mg. If the amount is 5 mg or more, when the potassium-containing fertilizer is applied to plants, a larger amount of components that have an adverse effect on plants and soil can be precipitated in this step and recovered in the second solid-liquid separation step described below. If the amount is 2,000 mg or less, material costs can be reduced.

[0020] [pH adjustment process] This step is a step that is optionally provided between the second mixing step and the third mixing step, and is a step for adjusting the pH of the second mixture to 6.5 to 9.5. In this step, by adjusting the pH of the second mixture to 6.5 to 9.5, preferably 7.0 to 9.0, components that have adverse effects on plants and soil when the potassium-containing fertilizer is applied to plants can be precipitated in a larger amount in the third mixing step described below, and can be recovered in the second solid-liquid separation step described below. Examples of a method for adjusting the pH include a method in which an acid such as hydrochloric acid or an alkali such as sodium hydroxide is appropriately added depending on the pH of the second mixture.

[0021] [Third mixing process] This step is a step of mixing the second mixture obtained in the second mixing step or the pH adjusting step with a polymer flocculant to obtain a third mixture. In this step, by mixing a polymer flocculant, it is possible to promote aggregation and precipitation of the metal sulfides contained in the second mixture. The method for mixing the second mixture with the polymer flocculant is not particularly limited, but examples include a method in which the polymer flocculant is added to the second mixture and stirred for 10 minutes or more, preferably 15 to 60 minutes, and more preferably 20 to 30 minutes.

[0022] Examples of polymer flocculants include anionic polymer flocculants, cationic polymer flocculants, nonionic polymer flocculants, and amphoteric polymer flocculants. Among these, anionic polymer flocculants, nonionic polymer flocculants, and amphoteric polymer flocculants are preferred from the viewpoint of being able to neutralize the negative charge caused by the use of water-soluble metal salts, and anionic polymer flocculants are particularly preferred from the viewpoint of further promoting the aggregation and precipitation of metal sulfides contained in the second mixture. Examples of anionic polymer flocculants include reverse-phase emulsion-type anionic polyacrylamide. Examples of cationic polymer flocculants include polyamines, diallyl amines, polyalkylene polyamines, and polyacrylic acid esters. Examples of nonionic polymer flocculants include polyacrylamide-based polymer flocculants.

[0023] The amount of polymer flocculant is preferably 1 to 100 mg, more preferably 2 to 80 mg, even more preferably 4 to 50 mg, and particularly preferably 5 to 20 mg, calculated as solid content per liter of the second mixture. If the amount is 1 mg or more, components that adversely affect plants and soil when the potassium-containing fertilizer is applied to plants can be precipitated in greater amounts in this step and recovered in the second solid-liquid separation step described below. If the amount is 100 mg or less, material costs can be reduced.

[0024] [Second solid-liquid separation step] This step is a step of performing solid-liquid separation on the third mixture obtained in the third mixing step to obtain a liquid potassium-containing fertilizer and a second solid content. As the solid-liquid separation means, the same means as in the first solid-liquid separation step can be used. After being recovered, the second solid content may be charged into the bottom of a cement kiln as a raw material for cement clinker.

[0025] The liquid potassium-containing fertilizer obtained in this step has a high potassium content and a low content of components that have adverse effects on plants and soil when applied to plants as a fertilizer. The potassium content in the liquid potassium-containing fertilizer is, in dry matter terms, preferably 10.0 mass% or more, more preferably 15.0 mass% or more, even more preferably 20.0 mass% or more, and particularly preferably 25.0 mass% or more. If the content is 10.0 mass% or more, it can be more suitably used as a fertilizer. The dry matter equivalent value is the content (mass%) of the component (potassium) in the solid matter (solute) obtained by evaporating and drying the liquid potassium-containing fertilizer.

[0026] Components that can adversely affect plants and soil when potassium-containing fertilizers are applied include heavy metals, thallium and its compounds, nickel and its compounds, titanium and its compounds, ammonium thiocyanate, nitrite, biuret nitrogen, and sulfamic acid. Heavy metals include cadmium and its compounds, hexavalent chromium compounds, cyanide, mercury and its compounds, selenium and its compounds, lead and its compounds, arsenic and its compounds, fluorine and its compounds, and boron and its compounds (listed as Type 2 specified hazardous substances under the Soil Contamination Countermeasures Act (2003)). While fluorine and boron are not heavy metals, they are considered to be heavy metals.

[0027] Among these, cadmium and its compounds, hexavalent chromium compounds, mercury and its compounds, lead and its compounds, arsenic and its compounds, boron and its compounds, thallium and its compounds, nickel and its compounds, and titanium and its compounds may be contained in combustion exhaust gas dust (particularly clinker dust). According to the method for producing a potassium-containing fertilizer of the present invention, even if the combustion exhaust gas dust contains the above components, the content of the above components in the obtained liquid potassium-containing fertilizer can be reduced to a level that does not adversely affect plants or soil. In particular, cadmium, lead, and thallium are components that are likely to be contained in large amounts in clinker dust. However, according to the method for producing a potassium-containing fertilizer of the present invention, even when clinker dust is used as the combustion exhaust gas dust, the amounts (mg) of cadmium, lead, and thallium contained in one liter of liquid potassium-containing fertilizer can each be preferably less than 1 mg.

[0028] The liquid potassium-containing fertilizer may be used as a liquid fertilizer as it is, but taking into consideration the potassium concentration in the potassium-containing fertilizer and the form of use, a concentration and drying step of concentrating or drying the liquid potassium-containing fertilizer may be carried out after the second solid-liquid separation step. Examples of the concentration method include a method in which a liquid potassium-containing fertilizer is heated to evaporate a part of the water contained in the liquid potassium-containing fertilizer. In addition, examples of the drying method include a method of spraying the liquid potassium-containing fertilizer using a nozzle or the like and drying the liquid potassium-containing fertilizer using a hot air introducing device or the like, and a method of heating the liquid potassium-containing fertilizer to evaporate the water contained in the liquid potassium-containing fertilizer and obtain a solid content. [Example]

[0029] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Combustion exhaust gas dust A to D (shown as "Dust A to D" in Table 1): Clinker dust obtained from different cement manufacturing plants, with the chemical composition shown in Table 1. (2) Water-soluble acid salt of metal sulfide; sodium hydrogen sulfide aqueous solution (sodium hydrogen sulfide content: 25% by mass) (3) Water-soluble metal salt: ferric chloride aqueous solution (ferric chloride content: 38% by mass) (4) Dilute hydrochloric acid: concentrated hydrochloric acid diluted 100 times with water (hydrochloric acid content: 1% by volume) (5) Polymer flocculant: anionic polymer flocculant, manufactured by Taiheiyo Cement Corporation, trade name "KOTO FLOCK A-122", solid content: 0.1% by mass

[0030] [Table 1]

[0031] [Example 1] A slurry was obtained by mixing the combustion exhaust gas dust A and tap water at 45°C in amounts such that the mass ratio of the combustion exhaust gas dust to the water was 1:4. While stirring the slurry, industrial carbon dioxide gas (carbon dioxide purity: 99.5% by volume or more) was supplied until the pH of the slurry reached 10.5, and then the slurry was subjected to suction filtration to separate into a first liquid matter and a first solid matter. An aqueous solution of sodium hydrogen sulfide was added to the first liquid in an amount of 165 mg (24 mg in terms of sulfur atom) per liter of the first liquid, and the mixture was gently stirred for 20 minutes to obtain a first mixture. An aqueous solution of ferric chloride was added to the first mixture in an amount of 315 mg (42 mg in terms of metal atoms) per liter of the first mixture, and mixed to obtain a second mixture. Dilute hydrochloric acid was added to the second mixture to adjust the pH of the second mixture to about 8.0, and then the mixture was gently stirred for 20 minutes. An aqueous solution of an anionic polymer flocculant was added to the second mixture in an amount of 6000 mg per liter of the second mixture, and the mixture was gently stirred for 20 minutes to obtain a third mixture. The third mixture was suction filtered to obtain a liquid (liquid potassium-containing fertilizer) and a second solid fraction.

[0032] The resulting liquid was analyzed by ICP-OES to measure the amount (mg) of each component contained in 1 liter of the liquid. The results are shown in Table 2. The resulting liquid was evaporated to dryness to obtain a solid. The resulting solid was subjected to XRF analysis. The results are shown in Table 3. The contents of mercury (Hg), arsenic (As), cadmium (Cd), nickel (Ni), chromium (Cr), lead (Pb), titanium (Ti), sulfamic acid (amidosulfuric acid), ammonium thiocyanate (sulfocyanate), nitrous acid (HNO2), and biuret nitrogen in the obtained solids were measured according to the method shown in Table 4 of the "Testing Methods for Fertilizers, etc. (2023)." The results are shown in Table 4. The measurements were performed three times, and all the results were the same (below the lower limit of quantification).

[0033] [Example 2] A liquid material (liquid potassium-containing fertilizer) and a second solid content were obtained in the same manner as in Example 1, except that combustion exhaust gas dust B was used instead of combustion exhaust gas dust A. The obtained liquid material was evaporated to dryness, and the obtained solid content was subjected to XRF analysis and the like in the same manner as in Example 1. The results are shown in Tables 3 and 4.

[0034] [Comparative Example 1] The combustion exhaust gas dust A and tap water at 45°C were mixed in amounts such that the mass ratio of the combustion exhaust gas dust to the water was 1:4, and the mixture was stirred for 30 minutes to obtain a slurry. The slurry was subjected to suction filtration to separate into a first liquid matter and a first solid matter. The resulting liquid was analyzed by ICP-OES to measure the amount (mg) of each component contained in 1 liter of the liquid. The results are shown in Table 2.

[0035] [Table 2]

[0036] [Table 3]

[0037] [Table 4]

[0038] From Table 2, it can be seen that the contents of Pb and Tl in the liquid potassium-containing material of Example 1 were undetectable, whereas the contents of Pb and Tl in the liquid material of Comparative Example 1, which was subjected to only water washing treatment, were 4 mg / L and 165 mg / L, respectively, indicating that Pb and Tl remained. Tables 2 to 5 show that in Examples 1 and 2, no content of components that have adverse effects on plants or soil was detected.

[0039] Comparative Example 2 A first liquid material was obtained in the same manner as in Comparative Example 1, except that combustion exhaust gas dust C was used instead of combustion exhaust gas dust A. ICP-OES analysis was performed using the obtained first liquid material. The results are shown in Table 5. Comparative Example 3 A first liquid material was obtained in the same manner as in Comparative Example 1, except that combustion exhaust gas dust D was used instead of combustion exhaust gas dust C. ICP-OES analysis was performed using the obtained first liquid material. The results are shown in Table 5.

[0040] [Table 5]

[0041] Table 5 shows that when clinker dust is only washed with water, Pb remains in the liquid.

Claims

1. a slurry preparation step of mixing the potassium-containing combustion exhaust gas dust with water to obtain a first slurry; a first solid-liquid separation step of subjecting the first slurry to solid-liquid separation to obtain a first liquid material containing potassium and a first solid content; a first mixing step of mixing the first liquid material with one or more selected from hydrogen sulfide, a normal salt of a water-soluble metal sulfide, and an acid salt of a water-soluble metal sulfide to obtain a first mixture; a second mixing step of mixing the first mixture with a water-soluble metal salt to obtain a second mixture; a third mixing step of mixing the second mixture with a polymer flocculant to obtain a third mixture; a second solid-liquid separation step of subjecting the third mixture to solid-liquid separation to obtain a liquid potassium-containing fertilizer and a second solid content; A method for producing a potassium-containing fertilizer, comprising:

2. A process provided between the second mixing process and the third mixing process, 2. The method for producing a potassium-containing fertilizer according to claim 1, further comprising a pH adjustment step of adjusting the pH of the second mixture to 6.5 to 9.

5.

3. 3. The method for producing a potassium-containing fertilizer according to claim 1, further comprising a carbon dioxide gas supplying step, which is provided between the slurry preparation step and the first solid-liquid separation step, of supplying carbon dioxide gas to the first slurry to adjust the pH of the first slurry to 11.0 or less.

4. 3. The method for producing a potassium-containing fertilizer according to claim 1, further comprising a concentrating and drying step of concentrating or drying the liquid potassium-containing fertilizer.

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