Fertilizer manufacturing method, fertilizer component recovery method, and solid composition

Abstract

To provide a method of producing a fertilizer capable of obtaining a solid composition at low cost, in which a fertilizer component is recovered from an aqueous solution containing a phosphate ion and an ammonium ion.SOLUTION: A method of producing a fertilizer of this invention includes: adding combusted ash to an ammonium phosphate aqueous solution and agitating / mixing the mix (step 101); and after settling the mix (step 102), obtaining precipitate (solid composition) (step 103). As a result, a fertilizer component can be obtained as a solid material without providing additional energy relating to heating or a reaction except for an agitation operation at a room temperature and under an atmospheric pressure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a fertilizer, in which fertilizer components are recovered from an aqueous solution containing phosphate ions and ammonium ions to obtain a solid composition, a method for recovering fertilizer components from an aqueous solution containing phosphate ions and ammonium ions, and a solid composition obtained by these methods. [Background technology]

[0002] 2. Description of the Related Art In addition to treating wastewater and waste, resources are recovered from the wastewater and waste for reuse. As one such technique, Patent Document 1 discloses a recovery device that recovers resources from livestock wastewater (recovers phosphorus using the MAP reaction). Moreover, Patent Document 2 discloses a technique for recovering phosphorus and ammonia from treated water such as wastewater and using them as fertilizer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-195453 A [Patent Document 2] JP 2004-089931 A Summary of the Invention [Problem to be solved by the invention]

[0004] One example of recycling wastewater and waste is composting livestock manure, but there is a problem of bad odors being generated during the composting process. One of the measures to address this problem is a technology for capturing the bad odor gases generated during the composting process with an acidic solution. As a related technology, paragraph 0047 of Patent Document 2 describes the production of ammonium sulfate, ammonium nitrate, and ammonium phosphate by washing ammonia gas with sulfuric acid, nitric acid, and phosphoric acid. According to the method of recovering ammonia by passing ammonia gas through a phosphoric acid solution, the recovered liquid obtained is an ammonium phosphate solution, which also contains phosphoric acid, and is therefore suitable for use as a fertilizer. However, the recovered material obtained by the above method is a liquid containing a lot of water, and the volume and mass occupied by water is large, and a liquid storage container is required, making it difficult to handle (high cost) in storage, transportation, etc. As a result of these aspects that are not cost-effective, the current situation is that the use of the method of recovering ammonia by contacting ammonia gas generated during the composting process with phosphoric acid and the recovered liquid obtained by this method is not widely used.

[0005] In view of the above, an object of the present invention is to provide a fertilizer production method capable of obtaining, at low cost, a solid composition in which fertilizer components are recovered from an aqueous solution containing phosphate ions and ammonium ions, a method for recovering the fertilizer components, and a solid composition obtained by these methods. [Means for solving the problem]

[0006] (Configuration 1) A method for producing a fertilizer containing a phosphoric acid component, comprising a step of producing a solid composition by mixing an aqueous solution containing phosphate ions and ammonium ions with combustion ash containing at least magnesium.

[0007] (Configuration 2) 2. The method for producing a fertilizer according to claim 1, wherein the combustion ash is biomass combustion ash.

[0008] (Configuration 3) 3. The method for producing a fertilizer according to claim 2, wherein the biomass combustion ash is livestock manure combustion ash.

[0009] (Configuration 4) The method for producing a fertilizer according to claim 3, wherein the livestock manure combustion ash is chicken manure combustion ash.

[0010] (Configuration 5) 3. The method for producing a fertilizer according to claim 2, wherein the biomass combustion ash is wood ash.

[0011] (Configuration 6) A method for producing a fertilizer containing a phosphoric acid component, comprising a step of producing a solid composition by mixing an aqueous solution containing phosphate ions and ammonium ions with a steel slag containing at least magnesium.

[0012] (Configuration 7) 7. The method for producing a fertilizer according to any one of claims 1 to 6, further comprising the step of adding the combustion ash or the steel slag to the aqueous solution and stirring the mixture.

[0013] (Configuration 8) 8. The method for producing a fertilizer according to any one of claims 1 to 7, wherein the combustion ash or the steel slag is added to the aqueous solution in an amount of 5% by mass or more.

[0014] (Configuration 9) 7. The method for producing a fertilizer according to any one of claims 1 to 6, further comprising spraying the aqueous solution onto the combustion ash or the steel slag.

[0015] (Configuration 10) A method for recovering a fertilizer component from an aqueous solution containing phosphate ions and ammonium ions, the method comprising a step of producing a solid composition containing the fertilizer component by mixing the aqueous solution with combustion ash containing at least magnesium.

[0016] (Configuration 11) A method for recovering fertilizer components from an aqueous solution containing phosphate ions and ammonium ions, the method comprising a step of producing a solid composition containing the fertilizer components by mixing the aqueous solution with iron and steel slag containing at least magnesium.

[0017] (Configuration 12) A solid composition comprising an inorganic substance as a main component, and in which the total of (a) a mixture of a compound of phosphate ions and ammonium ions and a compound of phosphate ions and potassium ions, or a compound of phosphate ions and ammonium ions, (b) a compound of phosphate ions, magnesium ions and ammonium ions, and (c) a compound of phosphate ions and calcium ions is 70 mass% or more. Effect of the Invention

[0018] According to the present invention, a solid composition in which fertilizer components are recovered from an aqueous solution containing phosphate ions and ammonium ions can be obtained at low cost. [Brief description of the drawings]

[0019] [Figure 1] 1 is a flowchart showing an outline of the steps of a method for producing a fertilizer according to an embodiment of the present invention. [Diagram 2] Photographs showing the solid volume ratios obtained in Example 1 and Comparative Example. [Diagram 3] Graph showing the relationship between solid volume ratio and combustion ash addition rate in Example 1 [Figure 4] FIG. 1 shows the analysis results of the reaction product obtained in Example 1. [Diagram 5] Graph showing the solid volume ratio over time in Example 1 [Figure 6] Photographs showing the solid volume ratios obtained in Example 1 and Comparative Example. [Figure 7] Graph showing the relationship between solid volume ratio and combustion ash addition rate in Example 1 [Figure 8] Photograph showing the solid volume ratio obtained in Example 1 [Figure 9] Photograph showing the reaction product obtained in Example 1 [Figure 10] Graph showing the relationship between solid volume ratio and steel slag addition rate in Example 2 [Figure 11] Photograph showing the solid volume ratio obtained in Example 2 [Figure 12] Photograph showing the solid volume ratio obtained in Example 2 [Figure 13] Photograph showing the reaction product obtained in Example 2 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the following embodiment is one form for embodying the present invention, and is not intended to limit the scope of the present invention.

[0021] <Embodiment 1> The method for producing a fertilizer containing a phosphoric acid component according to the first embodiment of the present invention includes a step of producing a solid composition by mixing an aqueous solution containing phosphate ions and ammonium ions with combustion ash containing at least magnesium. As shown in FIG. 1, the method for producing a fertilizer of this embodiment is composed of simple steps of adding combustion ash to an aqueous ammonium phosphate solution (hereinafter referred to as "ammonium phosphate solution") and stirring and mixing the mixture (Step 101), leaving the mixture to stand (Step 102), and obtaining a precipitate (solid composition) (Step 103). This makes it possible to recover fertilizer components as solid materials without inputting additional energy for heating or reactions other than stirring at room temperature and pressure. As shown in the experimental results shown below, the recovered material obtained when combustion ash is added to ammonium phosphate solution has a volume about 2 to 3 times that of when combustion ash is added to water, and contains a large amount of fertilizer components.

[0022] The ammonium phosphate solution may be an aqueous solution containing phosphate ions and ammonium ions. As described above, for example, in livestock facilities, ammonia gas generated during the composting process is contacted with phosphoric acid to recover ammonia, and the recovered solution is obtained. The ammonium phosphate solution may also be generated in other industrial processes. The present invention is a technology that can promote the effective utilization of resources contained in such ammonium phosphate solutions.

[0023] The combustion ash added to the ammonium phosphate solution is "combustion ash containing at least magnesium." The method for producing a fertilizer according to the present embodiment uses the MAP reaction to precipitate fertilizer components from an ammonium phosphate solution, and uses combustion ash to supply magnesium necessary for the MAP reaction and to obtain a pH necessary for the MAP reaction, i.e., uses the magnesium contained in the combustion ash and the alkalinity of the combustion ash. An example of "combustion ash containing at least magnesium" is combustion ash from burning biomass. Specific examples of biomass combustion ash include combustion ash from livestock manure and grass ash. Although "combustion ash containing at least magnesium" is not limited to these, these are preferred because they can be obtained at low cost.

[0024] Regarding the process of step 101 in FIG. 1, the addition of the combustion ash to the ammonium phosphate solution may be performed by any method that can bring the two into contact. As for the stirring and mixing, any method may be used that can bring the ammonium phosphate solution and the combustion ash into contact with each other completely. Note that stirring and mixing are performed to promote an efficient reaction, but are not necessarily essential. For example, by devising a method for adding the combustion ash to the ammonium phosphate solution (using a method for adding the combustion ash that brings the two into contact efficiently), it may be possible to obtain a sufficient reaction without the need for special stirring. In this embodiment, as a method for bringing the ammonium phosphate solution and the combustion ash into contact with each other, the combustion ash is added to the ammonium phosphate solution and stirred and mixed, but the present invention is not limited to this, and any method capable of bringing the ammonium phosphate solution and the combustion ash into contact with each other may be used. For example, the ammonium phosphate solution may be sprayed onto the combustion ash.

[0025] In the process of step 102 in Fig. 1, the predetermined time of standing after contacting the ammonium phosphate solution with the combustion ash is a time for waiting for the MAP reaction to proceed sufficiently. The "predetermined time" can be appropriately determined by experimentally determining the time required for the necessary reaction to proceed. In some cases, the "predetermined time" may be an extremely short time, so that the standing is not actually performed. Moreover, it is not always necessary to "stand still" the mixture, and for example, it may be possible to continue stirring while waiting for the required reaction time to elapse.

[0026] 1, the solid composition can be collected by any method capable of collecting a solid from a liquid, such as a filtration method. If necessary, the obtained solid composition may be dried.

[0027] Although the reaction principle in the fertilizer manufacturing method of this embodiment is the same as the MAP reaction described in Patent Document 1, etc., the reaction process of this embodiment utilizes magnesium ions contained in the combustion ash and the high pH of the combustion ash itself, and although the obtained material contains MAP that is prone to solidification, it maintains a sandy state like the original combustion ash, making it easy to handle afterwards. By focusing on combustion ash as a material, this method is extremely useful in that it can obtain components solidified into a sandy state by simply adding materials without inputting energy from outside. This makes it possible to produce solid materials containing fertilizer components in high concentrations, and minimizes the impact of material moisture on transportation costs, which has been a constraint on use up to now.

[0028] Example 1 Next, an example of a method for producing fertilizer by adding combustion ash to an ammonium phosphate solution will be described. The ammonium phosphate solution used in Example 1 was modeled after the one obtained as the recovered liquid in the paper entitled “Recovery of ammonia from a closed vertical composting device at a pig farm and use of the recovered liquid” by Yoichiro Kojima, Ryo Nakakubo, Hideki Matsuoka, Takashi Kenjo, Tomotaka Asano and Mika Ishida, Agricultural Facilities, Vol. 50, No. 2 (June 2019). NH4H2PO4 and (NH4)2HPO4 were mixed to obtain the NH4 + and PO4 3- In a molar ratio of NH4 + :PO4 3- = 1.6:1, and a solution prepared to have a nitrogen concentration of 6 mass % and a phosphoric acid concentration of 19 mass % was used. The solution contains 6% by mass of nitrogen, 19% by mass of phosphoric acid, and has a moisture content of about 65% by mass, which meets the standards for ordinary fertilizers and can be used as a raw material for mixed compost compound fertilizers. However, as mentioned above, the recovered liquid is in a liquid state containing more than 60% by mass of moisture, and the costs associated with long-distance transportation, etc., impose restrictions on its use, and it is not currently being fully utilized.

[0029] In Example 1, chicken manure combustion ash and wood ash were used as combustion ash. Although chicken manure combustion ash obtained by burning chicken manure is partially used as a fertilizer ingredient, it is difficult to use on its own and can be obtained cheaply as a low-value, low-utilization material. Wood ash is commonly used as a soil conditioner and fertilizer and is readily and inexpensively available.

[0030] Figure 2 shows the state of chicken manure combustion ash added to the above ammonium phosphate solution at room temperature (mass ratio of solution to combustion ash = 10:1 (addition rate 10%)), shaken and stirred, and then left to stand for about an hour. As comparative examples, chicken manure combustion ash was added to water, and chicken manure combustion ash was added to ammonium sulfate solution. All conditions were the same except for the solution. As can be seen from Figure 2, no change in the volume of the precipitate was observed when chicken manure combustion ash was added to water, but when chicken manure combustion ash was mixed with the ammonium phosphate solution, a precipitate was obtained that was about 2 to 3 times larger than when water and ash were mixed.

[0031] Figure 3 shows the results when chicken manure combustion ash was added to an ammonium phosphate solution and to water, with the addition of chicken manure combustion ash at different rates. These results also confirmed that the volume of the precipitated solids (solid volume ratio) was almost equal to the addition rate in the case of water, whereas the volume ratio in the case of ammonium phosphate solution was two to three times that amount. Regarding pH, in the case of water, even at an addition rate of 0.1%, the pH exceeded 10, but the buffering effect of the ammonium phosphate solution allowed it to maintain the same pH as the original solution even when combustion ash was added (only increasing by about 0.2). As shown in FIG. 3, in order to efficiently obtain a solid composition, it is advisable to add combustion ash to the ammonium phosphate solution in an amount of 5% or more by mass.

[0032] The precipitate (solid composition) obtained by adding chicken manure combustion ash to the above ammonium phosphate solution was filtered and dried at 105° C. for 24 hours to obtain the reaction product. Figure 4 shows the comparison of the concentration (mass%) of the constituent ions for the reaction product obtained and the chicken manure combustion ash used (left) and the chemical formula and semi-quantitative value of the crystal phase (right). The concentration (mass%) of the constituent ions was measured using the infrared combustion method for carbon, the Kjeldahl method for nitrogen, and the X-ray fluorescence method for the others. The reactants had clearly higher phosphorus (P) and nitrogen (N) ion concentrations than the chicken manure combustion ash used, and were mainly composed of crystals containing phosphate ions and ammonium ions. That is, a solid composition is obtained by recovering fertilizer components from the ammonium phosphate solution. As shown in the table on the right side of FIG. 4, the recovered solid composition contains 80% by mass or more (85% by mass) of ammonium dihydrogen phosphate or a mixture of ammonium dihydrogen phosphate and potassium dihydrogen phosphate, magnesium ammonium phosphate (MAP), and calcium phosphate. The total content of (a) a mixture of a compound of phosphate ions and ammonium ions and a compound of phosphate ions and potassium ions, or a compound of phosphate ions and ammonium ions, (b) a compound of phosphate ions, magnesium ions and ammonium ions, and (c) a compound of phosphate ions and calcium ions is preferably 70 mass% or more, and more preferably 80 mass% or more. The solid composition recovered by the above-described method is mainly composed of inorganic matter and basically does not contain organic matter (organic matter is 5 mass % or less).

[0033] 9(a) and 9(b) are photographs showing the reaction products obtained above. As shown in FIG. 9, the reaction product obtained in the example was sand-like and had excellent handleability. MAP (magnesium ammonium phosphate) obtained by the conventional MAP method crystallizes and adheres to the inside of the reaction vessel, making it difficult to recover. https: / / www.naro.affrc.go.jp / project / results / research_digest / digest_technology / digest_animals / 054723.html The above site discloses an apparatus that is equipped with a recovery device such as a wire mesh to which MAP can be attached. This makes it easy to remove the MAP from the reaction vessel, but it requires the work of recovering the MAP that has adhered to the wire mesh. In contrast, in the present embodiment, the components mainly composed of MAP are precipitated from the combustion ash as a nucleus, and a sand-like solid composition is obtained without adhering to each other, which can be easily recovered by filtration or the like, and is therefore very useful. In addition, in the past, bittern (magnesium chloride) was mixed in as a magnesium source for the MAP reaction, and caustic soda (sodium hydroxide) was added to adjust the pH to an alkaline level, and aeration was also required, but in this embodiment, only combustion ash is added, which is easy, inexpensive, and very useful.

[0034] Figure 5 is a graph showing the change in sediment rate (solid volume rate) over time for the above-mentioned ammonium phosphate solution to which chicken manure combustion ash has been added, the solution to which chicken manure combustion ash has been added to water, the solution to which wood ash has been added, and the solution to which wood ash has been added to water. Wood ash is ash obtained by burning grass and wood, and in this study, ash containing 0.4% by mass of nitrogen ions, 11.3% by mass of phosphate ions, 3.8% by mass of magnesium ions, and a pH of 12.2 was used. FIG. 5 is a graph showing the results when the mass of the solution was set to 100 g and ash was added at 10% of the mass of the solution, and FIG. 6 is a photograph of the same results.

[0035] As shown in Figure 5, in the "ammonium phosphate solution + 10% chicken manure combustion ash added" condition, the sediment rate increased to about 75% about 24 hours after ash addition and stirring, and then, although there were some fluctuations, it almost stabilized. In the "ammonium phosphate solution + 10% wood ash added" condition, it took 43.2 hours to stabilize, but after stabilization, the same amount of sediment was obtained as in the "ammonium phosphate solution + chicken manure combustion ash" condition. On the other hand, no significant increase in volume was observed in the condition where ash was added to the water. From this, it can be seen that the standing time should be about one day under the condition of "ammonium phosphate solution + 10% chicken manure combustion ash added", and about two days under the condition of "ammonium phosphate solution + 10% wood ash added". It is also possible to leave the solution standing until the reaction reaches a roughly equilibrium state, but this is not intended to limit the present invention. As shown in FIG. 5, the volume of the precipitate is more than doubled immediately after the ash is added to the solution, so it is also possible to collect the precipitate immediately without leaving it standing (the process of step 102 in FIG. 1 is not essential to the present invention).

[0036] Figure 7 is a graph showing the volume fraction of sediment when the mass ratio of ash to solution was 1%, 5%, 10%, 30%, and 50% for each of the following solutions: "ammonium phosphate solution + chicken manure combustion ash added," "water + chicken manure combustion ash added," "ammonium phosphate solution + wood ash added," and "water + wood ash added." Figure 8 is a photograph of the same results. When chicken manure ash or wood ash was added to the ammonium phosphate solution, the volume of the precipitate increased to several times that of the water + ash condition at the same addition rate, depending on the addition rate, and at about 30%, the supernatant was almost invisible. The reason why the precipitate rate was higher in wood ash than in chicken manure combustion ash is because the bulk density of wood ash was smaller and the volume of the additive was larger.

[0037] As described above, according to the above-described fertilizer manufacturing method or fertilizer component recovery method, a solid material containing a large amount of fertilizer components can be obtained from an ammonium phosphate solution by a simple operation of mixing underutilized materials such as an ammonium phosphate solution and chicken manure ash. This makes it possible to effectively utilize underutilized materials that have not been fully utilized in the past from the viewpoint of economy, etc.

[0038] <Embodiment 2> A method for producing a fertilizer containing a phosphoric acid component according to a second embodiment of the present invention includes a step of producing a solid composition by mixing an aqueous solution containing phosphate ions and ammonium ions with a steel slag containing at least magnesium. The method for producing a fertilizer containing a phosphoric acid component (or a method for recovering a fertilizer component) in this embodiment differs from that in the first embodiment in that steel slag is used as an additive material.

[0039] Steel slag is a by-product generated when smelting metals from ores, and is broadly divided into blast furnace slag and converter (steelmaking) slag. Steel slag itself is well known, so a detailed explanation will be omitted here, but blast furnace slag contains the fertilizer components CaO, SiO2, and MgO, while converter (steelmaking) slag also contains FeO, MnO, P2O5, etc., and is therefore used as a fertilizer. Furthermore, steel slag becomes alkaline when it reacts with water due to the lime it contains.

[0040] The fertilizer manufacturing method of this embodiment is conceptually similar to that of embodiment 1, including the reaction principle (the fertilizer components are precipitated from an ammonium phosphate solution by utilizing the MAP reaction, and the magnesium necessary for the MAP reaction and the pH necessary for the MAP reaction are obtained by using the additive material) and the manufacturing process (1. Addition to an ammonium phosphate solution, 2. Stirring and leaving to stand, 3. Recovery), except for the use of steel slag as an additive material. Therefore, a description thereof will be omitted here.

[0041] Example 2 Next, an example of a method for producing a fertilizer by adding steel slag to an ammonium phosphate solution will be described. The ammonium phosphate solution used in Example 2 was prepared by mixing (NH4)2HPO4 and NH4H2PO4 in a molar ratio of 2:1 to give a nitrogen concentration of 6 mass %.

[0042] In Example 2, calcium silicate fertilizer (granulated slag itself is used as fertilizer) was used as blast furnace slag, and converter lime fertilizer (converter slag itself is used as fertilizer) was used as converter (steelmaking) slag.

[0043] Figure 10 is a graph showing the volume fraction of precipitate for each of the cases of "ammonium phosphate solution + blast furnace slag added" and "ammonium phosphate solution + converter slag added" when the mass ratio of slag to solution is 1%, 5%, 10%, 30%, 50%, 70%, and 100%, and Figures 11 and 12 are photographs of the same results. As comparative examples, FIG. 10 shows the volume fraction of precipitates for the cases of "water + blast furnace slag added" and "water + converter slag added" when the mass ratio of slag to solution is 10%, 30%, and 50%. In addition, in the graphs of "ammonium phosphate solution + blast furnace slag added" and "ammonium phosphate solution + converter slag added" in Figure 10, the dotted lines indicate conditions where it was difficult to accurately measure the precipitation rate due to precipitates, etc.

[0044] As shown in FIG. 10, when blast furnace slag or converter slag was added to the ammonium phosphate solution, the volume of precipitate increased to several times that of the water + blast furnace slag or converter slag condition with the same addition rate. In both cases of adding blast furnace slag and converter slag, the amount of precipitate clearly increased when 5% or more of the ammonium phosphate solution was added compared to when it was added to water. Therefore, in order to efficiently obtain a solid composition, it is recommended to add 5% or more of steel slag by mass to the ammonium phosphate solution.

[0045] FIG. 13 is a photograph showing the dried reaction products obtained in Example 2 (for "ammonium phosphate solution + blast furnace slag added" and "ammonium phosphate solution + converter slag added," the mass ratio of slag to solution was 50%). As shown in Fig. 13, the reaction product obtained in Example 2 is also sand-like and easy to handle. The dried product of "ammonium phosphate solution + blast furnace slag added" is a slightly hard solid, but it is hard enough to be crushed by hand and becomes sand-like when crushed.

[0046] As described above, according to the above-described fertilizer production method or fertilizer component recovery method, a solid material containing a large amount of fertilizer components can be obtained from the ammonium phosphate solution by a simple operation of mixing the ammonium phosphate solution with steel slag. This makes it possible to effectively utilize underutilized materials that have not been fully utilized in the past from the viewpoint of economy, etc.

Claims

1. A method for producing a fertilizer containing a phosphoric acid component, comprising the steps of: an aqueous solution containing phosphate ions and ammonium ions, which is obtained as a recovered liquid by contacting ammonia gas generated during the composting process of livestock manure with phosphoric acid to recover ammonia; Alkaline combustion ash containing at least magnesium; and mixing the above-mentioned combustion ash to produce a solid composition, and using the above-mentioned combustion ash to supply magnesium and adjust pH, which are necessary for precipitating fertilizer components from the aqueous solution by utilizing a MAP reaction.

2. The method for producing a fertilizer according to claim 1, wherein the combustion ash is biomass combustion ash.

3. The method for producing a fertilizer according to claim 2, wherein the biomass combustion ash is livestock manure combustion ash.

4. The method for producing a fertilizer according to claim 3, wherein the livestock manure combustion ash is chicken manure combustion ash.

5. The method for producing a fertilizer according to claim 2, wherein the biomass combustion ash is wood ash.

6. A method for producing a fertilizer containing a phosphoric acid component, comprising the steps of: an aqueous solution containing phosphate ions and ammonium ions, which is obtained as a recovered liquid by contacting ammonia gas generated during the composting process of livestock manure with phosphoric acid to recover ammonia; an alkaline steel slag containing at least magnesium; and mixing the iron and steel slag to produce a solid composition, and the iron and steel slag is used to supply magnesium and adjust pH, which are necessary for precipitating fertilizer components from the aqueous solution using a MAP reaction.

7. 7. The method for producing a fertilizer according to claim 1, further comprising the step of adding the combustion ash or the steel slag to the aqueous solution and stirring the mixture.

8. The method for producing a fertilizer according to any one of claims 1 to 7, wherein the combustion ash or the steel slag is added to the aqueous solution in an amount of 5% by mass or more.

9. 7. The method for producing a fertilizer according to claim 1, further comprising the step of spraying the aqueous solution onto the combustion ash or the steel slag.

10. A method for recovering fertilizer components from an aqueous solution containing phosphate ions and ammonium ions, which is obtained by contacting ammonia gas generated during the composting process of livestock manure with phosphoric acid to recover ammonia, comprising the steps of: The method for recovering a fertilizer component includes a step of producing a solid composition containing a fertilizer component by mixing the aqueous solution with alkaline combustion ash containing at least magnesium, and the supply of magnesium and pH adjustment required for precipitating the fertilizer component from the aqueous solution utilizing the MAP reaction are performed by using the combustion ash.

11. A method for recovering fertilizer components from an aqueous solution containing phosphate ions and ammonium ions, which is obtained by contacting ammonia gas generated during the composting process of livestock manure with phosphoric acid to recover ammonia, comprising the steps of: The method for recovering a fertilizer component includes a step of producing a solid composition containing a fertilizer component by mixing the aqueous solution with alkaline iron and steel slag containing at least magnesium, and the supply of magnesium and pH adjustment required for precipitating the fertilizer component from the aqueous solution utilizing the MAP reaction are performed by the iron and steel slag.

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