JP6930473B2 - Phosphate fertilizer manufacturing method and phosphoric acid fertilizer - Google Patents

Description

The present invention relates to a method for producing a phosphoric acid fertilizer and a phosphoric acid fertilizer using the phosphoric acid fertilizer obtained by this method as a main raw material.

Phosphorus is used in many fields such as agriculture, food, electronic parts, pharmaceuticals, and automobile industry. However, phosphate ore, which is the raw material of phosphorus, depends entirely on imports in Japan.
On the other hand, the grade of phosphate ore is becoming lower in the world, but this is not only the tendency of the ore with high phosphorus content to be depleted, but also Morocco (Non-Patent Document 1), which has the largest economic reserve in the world. There is also a problem that the content of harmful substances such as radioactive substances and cadmium is high in phosphate rock (Non-Patent Document 2). Removal of harmful substances from phosphate rock requires a lot of energy. In other words, while the energy consumption of phosphate rock itself is rising, Japan is consuming more transportation energy and importing the entire amount.

Under these circumstances, phosphoric acid in steelmaking slag is being reviewed as a potential phosphoric acid-containing substance.
It is well known that phosphorus is an important element for plant growth, and the greatest use of phosphate rock is fertilizer. In recent years, attention has been paid to the promotion of growth by fertilizing phosphorus not only for plants that are consumed in a short period of time such as vegetables, but also for plants such as algae in forests and water bodies that have a high sustainable CO2 fixing effect.
That is, effective utilization of phosphoric acid in steelmaking slag, which has not been utilized until now, contributes to the promotion of sustainable CO2 fixation by plants in addition to the reduction of the above-mentioned energy consumption.

Since the hot metal produced in the blast furnace contains about 0.1% by mass of phosphoric acid, among the steelmaking slag generated in the hot metal refining process, the converter slag and the hot metal pretreatment slag contain phosphorus. It contains about 1 to 5% by mass of acid.

However, the phosphoric acid concentration in the hot metal is about 0.1% by mass, and the phosphoric acid concentration of the steelmaking slag is at most about 5% by mass. Since the phosphoric acid concentration is too low, it can be used as a phosphoric acid resource as it is. The reality is that there is almost no such thing. Moreover, since the slag contains Fe ₂ O ₃ and Al ₂ O ₃ that inhibit the solubility of phosphoric acid, phosphoric acid has not been fully utilized as fertilizer.
In view of this situation, various efforts are being made to concentrate phosphoric acid in steelmaking slag in order to expand its applications.

For example, in Patent Document 1, hot metal having a P concentration of 0.15% by mass or less is dephosphorized, and the obtained phosphorus-containing slag is put into a hot metal bath to supply a carbon material and iron oxide and / or oxygen. The first step of reducing and extracting P in the slag into a hot metal bath to produce hot metal with a P concentration of 0.5 to 3% by mass, and the slag produced in the first step are discharged and then treated into hot metal. A second slag is added so that the slag basicity becomes 2 to 8, and then an iron oxide source is added and / or oxygen gas is blown to reduce the carbon concentration contained in the hot metal to 1% or less. A method for obtaining high P slag having a phosphoric acid concentration of 10 to 35% by mass after treatment has been proposed by the step. The slag obtained by this method contains a high concentration of phosphoric acid and can be used directly as fertilizer.

Although the steelmaking slag described in Patent Document 1 can be used as a slag fertilizer containing a high concentration of phosphoric acid, there is no mention of kusoluble phosphoric acid and soluble phosphoric acid, and the obtained slag can be used as a phosphoric acid fertilizer. It is unclear if it retains an effective fertilizer effect. Therefore, even if a large amount of phosphoric acid component is contained in the steelmaking slag, it cannot be said that an effective recycling technique has been established.

Further, in Patent Document 2, phosphorus-containing steelmaking slag is reduced by using a reducing agent such as carbon, silicon, and aluminum, and iron oxide and phosphorus oxide in the steelmaking slag are reduced as phosphorus-containing molten iron. -A technique has been proposed in which the phosphorus-containing molten iron is recovered, the phosphorus-containing molten iron is dephosphorized, and the slag containing a high concentration of phosphoric acid produced by this dephosphorization treatment is recovered as a phosphoric acid resource. Then, the derinsed lag T.I. When the sum of the Fe concentration and the MnO concentration is less than 20% by mass, the phosphoric acid-enriched slag has a high concentration of phosphoric acid, which is said to be superior as a phosphoric acid fertilizer according to a plant growth test.

However, in Patent Document 2, while the solubilized phosphoric acid is significantly improved as compared with the conventional dephosphorized slag, the soluble silicic acid is lowered, so that it has a sufficient effect as a phosphoric acid fertilizer in the fertilizer control method. It wasn't there.
Therefore, it is desired to obtain a phosphoric acid fertilizer having a highly soluble silicic acid component while maintaining the content of solubilized phosphoric acid. Silicic acid can also affect the solubility of phosphoric acid.
Like phosphorus, silicon in hot metal is a component that is oxidized by desiliconization and fixed in slag. Silicic acid is effective as a soil conditioner for paddy fields and as a soil conditioner for aging paddy fields. In addition, silicic acid has been attracting attention for its action of strengthening plants and making them less susceptible to pests, and silicic acid is used not only for paddy rice but also for cucumbers and the like.

In addition, efficient input of potassium along with nitrogen and phosphoric acid, which are the three elements necessary for plants, contributes to labor saving in agriculture.
Since the absorption of essential components such as phosphoric acid by plants takes several days to several weeks, some of them are not absorbed during this period and flow away. Fertilizers containing a large amount of soluble components often flow away in this way, and with such fertilizers, it was necessary to apply the fertilizer little by little over and over again. If phosphoric acid and potassium can be added as a slow-release fertilizer at the same time, the effect can be maintained for a long period of time, so that additional fertilizer is not required and labor saving can be achieved.

In this way, the usefulness of fertilizers cannot be evaluated only by the high content of fertilizer-effect components, and the balance between both immediate-acting soluble components and long-lasting k-dissolved components and multiple fertilizer-effect components At the same time, it is important to contain in an appropriate ratio from the viewpoint of labor saving in fertilizer application. The balance between the soluble component and the k-dissolved component can be adjusted by an additive other than the fertilizing component. For example, in a fertilizer produced by a melting method, the addition of silicic acid improves the k-solubility of phosphoric acid.

Here, the cousoluble phosphoric acid is a phosphoric acid in which a substance containing phosphoric acid is soluble in a 2% by mass citric acid solution (pH = 2). Further, the soluble silicic acid refers to a silicic acid that leaches when a substance containing silicic acid is shaken in a 0.5N hydrochloric acid solution at 30 ° C. for 1 hour. The analysis method for soluble silicic acid and kusoluble phosphoric acid is described in the fertilizer analysis method (Ministry of Agriculture, Forestry and Fisheries Agricultural Environmental Technology Research Institute Law).

JP-A-2017-53017 Japanese Patent No. 5935770

U.S. Geological Survey, Mineral Commodity Summaries, Phosphate Rock, January 2017. (p.125) The World Nuclear Association, Naturally-Occurring Radioactive Materials (NORM), 2016.

The present invention has been developed under the above-mentioned background, and provides a phosphoric acid fertilizer using steelmaking slag as a raw material and containing highly soluble phosphoric acid and highly soluble silicic acid component. Make it an issue.

As a result of diligent studies to solve the above problems, the present inventors have produced a phosphorus ore substitute by increasing the phosphoric acid concentration in the steelmaking slag, and silicic acid is contained in the obtained molten slag. It was found that by mixing the sources, a phosphoric acid fertilizer utilizing steelmaking slag with improved solubility of phosphoric acid and solubility of silicic acid can be obtained.
The present invention has been completed based on the above findings.

That is, the gist structure of the present invention is as follows.
1. 1. It is a method of manufacturing phosphoric acid fertilizer.
Phosphorus-containing steelmaking slag generated in the steelmaking refining process is reduced with a reducing agent containing at least one selected from carbon, aluminum and silicon, and the iron oxide in the steelmaking slag is reduced to phosphorus. The first step of recovering as contained molten iron and
The second step of dephosphorizing the phosphorus-containing molten iron obtained in the first step and recovering the obtained high-phosphorus lag, and the second step.
The third step of heating the high rinse lag obtained in the second step to a temperature of 1500 ° C. or higher to separate the two liquid phases and recovering the ultra-high rinse lag in the upper layer.
A method for producing a phosphoric acid fertilizer, which comprises a fourth step of melt-mixing a silicic acid source with the ultra-high phosphorus slag obtained in the third step to obtain a phosphoric acid fertilizer.

2. The method for producing a phosphoric acid fertilizer according to 1 above, wherein the steelmaking slag is hot metal dephosphorized slag or decarburized slag.

3. 3. The method for producing a phosphoric acid fertilizer according to 1 or 2 above, wherein the blast furnace slag is used as the silicic acid source in the fourth step.

4. The method for producing a phosphoric acid fertilizer according to 3 above, wherein the mixing ratio of the ultra-high phosphorus slag and the blast furnace slag in the third step is 1: 0.5 to 1.2.

5. The method for producing a phosphoric acid fertilizer according to any one of 1 to 4 above, wherein the potassium source is melt-mixed in addition to the silicic acid source.

6. A phosphoric acid fertilizer comprising the phosphoric acid fertilizer according to any one of 1 to 5 above, or using the phosphoric acid fertilizer as a main raw material.

According to the present invention, phosphorus is recovered from the steelmaking slag by utilizing phosphorus-containing steelmaking slag such as preliminary derinsing slag of hot metal generated in the steelmaking refining process and converter decarburization refining slag, and phosphorus is recovered. By melt-mixing the ultra-high phosphorus slag with a silicic acid source, a steelmaking slag-based phosphoric acid fertilizer having improved solubility of phosphoric acid and solubility of silicic acid can be obtained.
The phosphoric acid fertilizer according to the present invention has excellent fertilizer properties because it is excellent in the solubility and solubility of phosphoric acid and contains an appropriate amount of silicic acid as a fertilizing component.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present invention, as a starting material, phosphorus-containing steelmaking slag such as derinsing slag generated during hot metal preliminary dephosphorization treatment and converter slag generated during decarburization refining in a converter is used.
Then, the iron oxide and the phosphorus oxide in the steelmaking slag are reduced by using at least one selected from carbon, aluminum and silicon in a rotary kiln, and the phosphorus-containing melt having a phosphorus concentration of 0.5% by mass or more is used. Recover iron. Here, as the treatment container used in the reduction treatment step, in addition to the rotary kiln, an arc furnace, a ladle or a topedo car in which the hot metal is held as a heat source and a seed hot water can be used. The amount of the reducing agent to be added is preferably about 30 to 120 kg when carbon is used, 45 to 180 kg when aluminum is used, and about 35 to 145 kg when silicon is used, per ton of molten slag.
When the hot metal is used as a heat source and a seed bath, a part of carbon in the hot metal also acts as a reducing agent, so that the amount is small within the above range, and when the hot metal is not used, the amount is good within the above range. However, excessive addition of the reducing agent not only increases the cost, but also the surplus aluminum and silicon that have not been subjected to the reduction are dissolved in the phosphorus-containing molten iron and Al ₂ O _{3 is contained in the high phosphorus lag described later.} It is not desirable because it invades as _{SiO 2 and reduces the concentration of P 2} O ₅ and inhibits the two-component phase formation.

Then, the obtained phosphorus-containing molten iron is dephosphorized with lime, _{and phosphoric acid is concentrated in the CaO-containing flux so that the P 2} O ₅ concentration is 7% by mass or more to obtain a high phosphorus slag. _{In order to control not only the P 2} O ₅ concentration in the high phosphorus slag but also the SiO ₂ concentration and the manganese oxide concentration, a desiliconization treatment or a demanganese treatment may be performed before the dephosphorization treatment.
Here, the method of supplying the lime source is not particularly limited, and the lime source can be supplied to the hot metal by any method such as injection into the hot metal by a dipping lance or top-loading. Injection into the hot metal by the immersion lance may be performed with a solid oxygen source. Further, in order to increase the dephosphorization efficiency, the lime source can be projected (sprayed) onto the bath surface from above the bath surface of the hot metal using a carrier gas. As the carrier gas, nitrogen, an inert gas or gaseous oxygen can be used.

The high-rinse slag obtained as described above is transferred to a slag pan, an electric furnace, etc., and heat is applied from the periphery, upper or lower part of the container, and heated to a temperature at which the slag temperature becomes 1500 ° C. or higher. Separate into phases.
Due to the difference in specific gravity, the obtained two-component phase has P ₂ O ₅ > 25% by mass in _{the upper layer, and the sum of iron oxide (FeO + Fe 2} O ₃ : FeO conversion) and metallic iron (M.Fe: FeO conversion) ≤15. It becomes a high phosphorus phase of mass%. Here, the upper layer of the two-component phase is designated as an ultra-high rinse lag. Table 1 compares the compositions of such ultrahigh phosphate lag and Jordan phosphate rock.
As shown in the table, ultra-high phosphate lag has a phosphate concentration equivalent to that of phosphate rock.

As the above-mentioned method for recovering the ultra-high rinse lag, there is a method of extracting the lower layer of the ultra-high rinse lag from the lower tap in the molten state and recovering the ultra-high rinse lag that remains in the container. Further, after hot water is discharged to the inclined slag field, the boundary between the upper and lower layers may be broken or cut in a solid state to recover the upper layer.
When the melt is withdrawn from the iron port at the bottom in the molten state, the silicic acid source is put into the ultra-high rinse lag remaining in the container, and the mixture is melt-mixed at 1300 ° C. or higher using residual heat. When the boundary between the upper and lower layers is broken or cut and recovered in a solid state, the mixture is reheated at 1300 ° C. or higher, and then a silicic acid source is added to melt and mix the slag.
It is also possible to add a potassium source after adding a silicic acid source. At this time, the potassium source is also heated and melted / decomposed, and fused with the derinsed slag to produce a molten slag having a solubilized potassium compound composition.

As the silicic acid source, at least one of silica sand, blast furnace granulated slag, blast furnace slow cooling slag, and fly ash is used.
Further, as the potassium source, potassium salts such as potassium carbonate, potassium bicarbonate, potassium sulfate and the like, and potassium-containing minerals such as potassium skeletal stone are used.
Here, input of silicate source and potassium source are each molten slag per ton, 100～400Kg of SiO ₂ purity, that the 0~230kg about by K ₂ O purity are preferred.

After melt mixing, the mixed slag is taken out of the container and cooled and solidified. Cooling / solidification may be performed when the slag is taken out from the container, or may be taken out when the mixed slag taken out is taken out from another container containing the mixed slag.

As a method of cooling and solidifying, when cooling the melt or the supercooled liquid, for example, a method of blowing high-pressure air on the generated mixed slag to scatter it, cooling it and granulating it (wind crushing method), or mixing. A method of spraying high-pressure water on the slag to scatter it, cooling it and granulating it (water crushing method), a method of flowing out the mixed slag generated on the thick steel plate, and cooling it by forced cooling by the thick steel plate and heat dissipation to the air. Such methods can be adopted. Further, in the case of slow cooling, a method of receiving the slag in a slag pot and then discharging the slag to a slag treatment plant can be considered.

Through such cooling and solidification, mixed slag, which is a raw material for phosphate fertilizer, is obtained. If the shape after cooling and solidification is lumpy, etc., crush (crush) treatment and / or sizing (grain size adjustment by sieving, etc.) to obtain phosphoric acid fertilizer. Further, depending on the case, other additive components may be blended to prepare a phosphoric acid fertilizer.

The method for crushing (crushing) the raw material for phosphoric acid fertilizer is not particularly limited, and any method may be adopted. For example, the crushing process can be performed using a crusher such as a jaw crusher, a rod mill, a Fred mill, or an impeller breaker. Further, the sizing may be performed using an arbitrary sieving device or the like, and the sizing may be performed after the raw material for phosphoric acid fertilizer is pulverized.

Thus, phosphoric acid (P ₂ O ₅ ) concentration is 14 to 26% by mass, silicic acid (SiO ₂ ) concentration is 9 to 21% by mass, and potassium concentration is 0 to 23% by mass. A highly soluble phosphate fertilizer can be obtained.

Hereinafter, examples of the present invention will be described.
(Example 1)
The blast furnace hot metal ejected from the blast furnace is received by a topeed car, and the blast furnace hot metal housed in the topeed car is subjected to desiliconization treatment and preliminary dephosphorization treatment. The hot metal was desulfurized by a mechanical stirring type desulfurization apparatus, and the blast furnace hot metal after the completion of the desulfurization treatment was charged into a converter and decarburized and refined in the converter. The present invention has been applied in the iron-making-steelmaking process of melting molten steel from such blast furnace hot metal. That is, as a starting material, converter slag produced in the above-mentioned ironmaking-steelmaking process was used.
In advance, the converter slag was magnetically separated by using a magnetic force sorter having a magnetic force of 3000 G and a slag processing capacity of 50 to 150 t / Hr, and metallic iron in the converter slag was separated and removed.

50 tons of steelmaking slag containing phosphorus produced in the steelmaking process and 4000 kg of coke (carbon) as a reducing agent are charged into a rotary kiln furnace equipped with a heating burner, and the steelmaking slag and coke are heated to 1000 ° C. or higher by the burner. Was heated to reduce the steelmaking slag. Iron oxide in steelmaking slag was reduced by coke to produce reduced iron. In addition, phosphorus in steelmaking slag is also reduced, and the produced phosphorus reacts with the reduced iron, that is, the produced phosphorus is incorporated into the reduced iron, and the phosphorus-containing reduced iron containing a high concentration of phosphorus (phosphorus-containing molten iron). ) Was generated. In the above reduction treatment, even if silicon or aluminum was used as the reducing agent instead of carbon, iron oxide and phosphorus oxide in the steelmaking slag could be reduced without any problem, but silicon and aluminum were used. In some cases, it is desirable to use it in a much larger amount than the amount required for reduction, because SiO ₂ and Al ₂ O ₃ in the slag will rise in the subsequent dephosphorization treatment and inhibit the formation of two-component phase and silicon-soluble phosphoric acid. No.
The phosphorus-containing reduced iron obtained by the above reduction treatment contained 1.0 to 4.0% by mass of phosphorus. This phosphorus-containing reduced iron was put into a blast furnace hot metal housed in a hot metal holding container to dissolve it, and a phosphorus-containing hot metal having a phosphorus concentration adjusted to 0.5 to 3.0% by mass was melted.

This phosphorus-containing hot metal is charged into an upper-bottom blown converter type reaction vessel, and oxygen gas is blown from the top-blown lance toward the phosphorus-containing hot metal. A dephosphorization treatment was carried out by blowing 25 kg of powdered fresh lime (CaO pure content: about 95% by mass) of 1 mm or less per ton of phosphorus-containing reduced iron. The solvent used is one that does not mix with a fluorine compound such as fluorite.

The high-phosphorus slag obtained by the above dephosphorization treatment is transferred to a slag pan, an electric furnace, etc., heat is applied from around the container, and the slag temperature is reheated to a temperature of 1500 ° C. or higher to separate into two liquid phases. I let you. Due to the difference in specific gravity, the obtained two-component phase has _{a high phosphorus phase with P 2} O ₅ > 25% by mass, the sum of iron oxide and metallic iron (FeO equivalent) ≤15% by mass, and the lower layer with P ₂ O ₅ It became a low phosphorus layer of <25% by mass.

Then, in the molten state, the melt was extracted from the lower tap, and the blast furnace slow-cooled slag was used as a silicic acid source in the ultra-high rinse slag remaining in the pot, and the mass ratio of the ultra-high rinse slag and the blast furnace slow-cooled slag was 1: 0. It was charged so as to be 8, and melt-mixed using residual heat. The slag temperature at the time of charging was 1450 ° C. If the slag temperature 1 hour after charging was less than 1300 ° C., the dissolution was insufficient.
Then, the melt-mixed slag was taken out from the container, cooled by forced cooling with a thick steel plate and radiated to air, and allowed to cool.
The obtained slag was crushed to 1 mm or less, and this was used as a phosphoric acid fertilizer.

Table 2 shows the main components of the obtained phosphoric acid fertilizer. Table 2 shows the slag before mixing the silicic acid source (levels 2 to 4) and the slag composition after mixing the silicic acid source (level 1). Level 1 shows the chemical composition and fertilizer characteristics of slag after mixing with a silicic acid source as Example 1. Levels 2 and 3 show the chemical composition and fertilizer characteristics of high rinse rugs as Comparative Examples 1 and 2, and Level 4 shows the chemical composition and fertilizer characteristics of ultra-high rinse rugs as Comparative Example 3. As fertilizer characteristics, in addition to kusoluble phosphoric acid, soluble phosphoric acid, and soluble silicic acid, phosphoric acid solubilization rate and silicic acid solubility rate are shown. The phosphoric acid solubilization ratio indicates the ratio of solubilizing phosphoric acid to the phosphoric acid concentration in slag, and the silicic acid solubility ratio indicates the value of soluble silicic acid relative to the silicic acid concentration in slag.

In Comparative Examples 1 to 3 of Levels 2, 3 and 4 shown in Table 2, the P ₂ O ₅ concentration is 15% or more and the iron oxide and metallic iron concentrations are 15 to 25% higher than those of the conventional hot metal pretreatment slag. and slag, P ₂ O ₅ concentration of 30% or more, iron and metallic iron oxide concentrations are produced 10% of ultra-high slag, click-soluble phosphate content with improved phosphate content was improved, soluble silicic acid It was less than 10%. If the amount of soluble silicic acid is less than 10% by mass, the conditions for phosphoric acid fertilizer stipulated in the Fertilizer Control Law are not satisfied, and it cannot be used as a standard product for phosphoric acid fertilizer.
On the other hand, in Example 1 of Level 1, although the solubilized phosphoric acid was slightly lower than that of Comparative Examples 2 and 3, it contained 10% by mass or more of soluble silicic acid, and the solubilities of phosphoric acid and the silicic acid. It can be seen that both the solubility ratios are excellent.

(Example 2)
The high-phosphorus slag after dephosphorization obtained by the above method is transferred to a slag pan, an electric furnace, etc., heat is applied from around the container, and the slag temperature is reheated to a temperature of 1500 ° C. or higher. Separated into phases. In the molten state, the melt is extracted from the lower tap, and the blast furnace slow-cooled slag is used as a silicic acid source for the ultra-high rinse slag remaining in the pot, and the mass ratio of the ultra-high rinse slag and the blast furnace slow-cooled slag is 1: 1.2 (level). 5), 1: 0.5 (level 6) was added, and the mixture was melt-mixed using residual heat.
Table 3 shows the chemical composition and fertilizer characteristics of level 5 and 6 slag. For reference, Table 3 also shows the data of Example 1 of Level 1 in which the mass ratio of the ultra-high rinse slag and the blast furnace slow cooling slag is 1: 0.8.

As shown in Table 3, at level 5 (Example 2) and level 6 (Example 3), similar to Level 1 (Example 1), fertilizers to which kusoluble phosphoric acid and soluble silicic acid were sufficiently satisfied were obtained. ing.
When the same amount of blast furnace granulated slag and fly ash were mixed as the silicic acid source instead of the blast furnace slow cooling slag, the same tendency was obtained.

According to the present invention, _{it is possible to obtain a phosphoric acid fertilizer having a high P 2} O ₅ concentration, a low iron oxide and bare metal concentration, and having a good soluble silicic acid and having a high fertilizer effect.

Claims (5)

It is a method of manufacturing phosphoric acid fertilizer.
Phosphorus-containing steelmaking slag generated in the steelmaking refining process is reduced with a reducing agent containing at least one selected from carbon, aluminum and silicon, and the iron oxide in the steelmaking slag is reduced to phosphorus. The first step of recovering as contained molten iron and
The second step of dephosphorizing the phosphorus-containing molten iron obtained in the first step and recovering the obtained high-phosphorus lag, and the second step.
The third step of heating the high rinse lag obtained in the second step to a temperature of 1500 ° C. or higher to separate the two liquid phases and recovering the ultra-high rinse lag in the upper layer.
_{The concentration of phosphoric acid (P 2} O ₅ ) including the fourth step of melt-mixing the silicic acid source with the ultra-high phosphorus slag obtained in the third step to obtain a phosphoric acid fertilizer was 14 to 26% by mass. A method for producing a phosphoric acid fertilizer containing 10% by mass or more of soluble silicic acid. The method for producing a phosphoric acid fertilizer according to claim 1, wherein the steelmaking slag is hot metal dephosphorized slag or decarburized slag. The method for producing a phosphoric acid fertilizer according to claim 1 or 2, wherein a blast furnace slag is used as the silicic acid source in the fourth step. The method for producing a phosphoric acid fertilizer according to claim 3, wherein the mixing ratio of the ultra-high phosphorus slag and the blast furnace slag in the third step is 1: 0.5 to 1.2. The method for producing a phosphoric acid fertilizer according to any one of claims 1 to 4, wherein the potassium source is melt-mixed in addition to the silicic acid source.