JPS623204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel manufacturing method for obtaining phosphorus-containing slag suitable for phosphoric acid fertilizer.

In recent years, multi-stage steel manufacturing methods have been attracting attention for the purpose of streamlining steel manufacturing operations. For example, a typical process consists of a desiliconization process, a dephosphorization process, a desulfurization process, and a decarburization process. First, the first step, the desiliconization step, is carried out with priority over this step in order to effectively perform dephosphorization and desulfurization, which will be described later. After the second step of dephosphorization and desulfurization, the third step of decarburization is performed. If this series of steps is carried out, the third
The process allows decarburization with minimal slag, ideally without slag, and is far more advantageous than the current converter process in terms of equipment and operation.

Hot metal usually contains 0.1 to 0.2% phosphorus, which is transferred to the slag produced during refining and removed as phosphate, but in the case of normal converter refining, silicon, A large amount of slag-forming agent is used to simultaneously remove manganese, phosphorus, sulfur, and carbon.
Therefore, the amount of slag produced is 100 to 150 kg per ton of molten steel.
Therefore, the concentration of phosphoric acid contained in it remains at 1 to 3%. The phosphoric acid content in phosphoric acid fertilizers varies depending on the type of fertilizer and purpose of use, but it is effective at 15% when used as a single fertilizer and 5% or more when used in combination with lime or silicate fertilizers. phosphoric acid content is required. Therefore, conventional converter slag has not been used as a phosphate fertilizer. On the other hand, in the case of the multi-stage refining method mentioned above, each step is divided, so the amount of slag produced there is small, and the phosphoric acid concentration in the dephosphorization and desulfurization slag in the second step is 5%. The amount is not less than 20%, and the amount is sufficient to be used as a phosphoric acid fertilizer.

Typically, lime (CaO) is used as the main treatment in the dephosphorization and desulfurization process, and an oxidizing agent such as iron oxide is added to it, and fluorite (CaF) is used as a slag melting point depressant to further accelerate the reaction. ₂ ) is charged and these slag-forming agents and hot metal (hot metal from which silicon has been removed in advance) are mixed and stirred.

However, since fluorite is used in the above treatment, the following difficulties arise. In other words, when fluorite is used, fluorine is incorporated into the crystal structure of calcium phosphate, producing insoluble fluoroapatite, which makes the phosphoric acid in the slag insoluble and does not function as a phosphate fertilizer. be.

Therefore, the present inventors investigated various slag melting point depressants that do not cause phosphoric acid to become insoluble and can replace fluorite, and have confirmed that calcium chloride is a melting point depressant that can replace _CaF2 . In other words, calcium chloride (CaCl ₂ ) itself produces chlorapatite in slag when mixed with it, but this chlorapatite has a much higher phosphoric acid solubility than the fluoroapatite mentioned above, and is used as a phosphate fertilizer for slag. without impairing its use. However, calcium chloride
It is more expensive than CaF ₂ (fluorite) and difficult to obtain.

The present inventors took this situation into consideration and studied ways to reduce the amount of calcium chloride used. the result,
When using calcium chloride, the use of CaF ₂ (fluorspar), which has traditionally been avoided due to the insolubilization effect of phosphoric acid in slag, should not impair its properties as a phosphate fertilizer. I found out.

Figure 1 shows the solubility of P ₂ O ₅ in citric acid and the amount of chlorine in the slag discharged after dephosphorizing and desulfurizing molten iron using a CaO-iron oxide-CaCl ₂ -CaF ₂ based slag forming agent. This shows the relationship with the amount of fluorine. The amount of P ₂ O ₅ in the slag is 8%, and the citric acid solubility rate (%) of P ₂ O ₅ in the slag means the elution of phosphoric acid (P ₂ O ₅ ), in other words, phosphoric acid fertilizer. This is a method to confirm the effectiveness of fertilizers in a short period of time, and is measured using the official method below.

A phosphoric acid (P ₂ O ₅ )-containing substance is immersed in a 2% citric acid solution at 30°C for 1 hour, and the amount of phosphoric acid in the phosphorus-containing substance eluted into the citric acid solution is expressed as a percentage.

Note that the slag in FIG. 1 is one that has been slowly cooled.

As shown in Figure 1, the dephosphorization and desulfurization slag
It was confirmed that if the Cl content is set to 5% or more, the insolubility of phosphoric acid in the slag can be suppressed even if fluorine is present in the slag (that is, the solubility of P ₂ O ₅ in citric acid increases). . However, in this case, if the amount of fluorine in the slag increases too much, it tends to make phosphoric acid insoluble even if the Cl content is 5% or more, so the fluorine content in the slag remains stable at 3% or less as shown in Figure 1. In order to achieve this goal, it is necessary to keep it below 2%. Thus, by using calcium chloride primarily as a melting point depressant for slag in the dephosphorization and desulfurization process, it became possible to use fluorite (CaF ₂ ), which was considered inappropriate for phosphoric acid fertilizers, in combination. This makes it possible to obtain a slag suitable for phosphoric acid fertilizers, as well as an inexpensive and effective slag forming agent. Incidentally, the combined use of calcium chloride and fluorite does not adversely affect dephosphorization and desulfurization. Thus, in the present invention, in the dephosphorization and desulfurization steps, a slag-forming agent in which fluorite is added to a CaO-iron oxide-CaCl ₂ system is used.

However, when slag is refined using the above-mentioned slag-forming agent, the effect of suppressing the insolubility of phosphoric acid can be obtained even if fluorine is mixed in when the Cl content in the slag is 3% or more. If this is done, the effect (solubility of phosphoric acid in citric acid) will vary by up to 30-40%. Generally, when used as a fertilizer, it is required that the fertilizer effect be stable, but if there is a variation of up to 30 to 40% in the elution of phosphoric acid, the commercial value as a phosphate fertilizer is affected. decreases. In the present invention, the dephosphorization and desulfurization slag described above is further treated as follows in order to stabilize the elution of phosphoric acid.

That is, there is rapid cooling, high temperature maintenance, or a combination thereof. First, the quenching is carried out by separating and recovering the molten slag after dephosphorization and desulfurization treatment using the slag forming agent from the hot metal and cooling it with water, for example. This rapid cooling treatment has the effect of making the crystals of the phosphoric acid compound finer, thereby improving and stabilizing the solubility of phosphoric acid in citric acid.

High-temperature holding treatment, such as heat treatment, is carried out after the above-mentioned molten slag is slowly cooled and crushed into appropriate sizes.
It is heated to 800-1100°C and held for about 30-130 minutes. This high temperature holding treatment changes the form of a phosphoric acid compound by holding it at a high temperature, for example by heating, and this treatment has a great effect of improving and stabilizing the solubility of phosphoric acid in citric acid. Therefore, this treatment is suitable when the fluorine content in the slag is large.

As described above, in the present invention, CaO - iron oxide - CaCl ₂ is removed in the dephosphorization and desulfurization process of hot metal from which silicon has been removed in advance.
This method uses a sludge-forming agent as the main ingredient, along with _CaF2 , and processes the resulting slag by quenching it, holding it at a high temperature, or heating it after quenching. It is used to obtain phosphoric acid fertilizer. According to this invention, it is possible to use the slag from the dephosphorization and desulfurization process as a phosphoric acid fertilizer, and it is also possible to use cheap and easily available fluorspar in the dephosphorization and desulfurization process. It also makes it possible to reduce the cost of phosphorus and desulfurization processes.

Next, the present invention will be explained in more detail.

First, in the present invention, prior to the dephosphorization/desulfurization process, hot metal is desiliconized, and this hot metal is produced in a blast furnace. This hot metal component generally contains C: 4.3 to 4.7%,
Si: 0.3~0.8%, Mn: 0.4~0.9%, P: 0.080%~
0.200%, S: 0.015-0.050%. For the desiliconization treatment, commonly known means are employed. However, in this case, it is important to remove the silica without increasing the temperature of the hot metal bath too much. That is, in the final decarburization step, carbon is the only fuel, and it is not preferable to raise the bath temperature too much in this desiliconization step, as this will lead to an unnecessary decrease in the amount of carbon. In this desiliconization process, it is necessary to keep the Si content to 0.20% or less. In other words, when desiliconization is completed beyond this point, a processing agent (CaO) is used to form a processing slag with a basicity (CaO/SiO ₂ ) of 3.5 to 8, which is necessary for smooth dephosphorization and desulfurization treatment in the next step. The amount of input will increase. An increase in the amount of processing agent input in the second step causes an increase in the amount of slag, resulting in a decrease in the concentration of phosphoric acid in the slag, which impedes achievement of the object of the present invention. The lower the silicon content, the more the desired basicity can be ensured even by adding a small amount of processing agent in the second step. However, if you try to reduce the silicon content to less than 0.05%, the decarburization reaction will proceed more than necessary and the oxidation of the hot metal will progress, resulting in an increase in the amount of FeO (MnO) in the slag produced by this desiliconization process. Increase the amount of iron loss. However, in the desiliconization process, Si is 0.20~
Reduce to 0.05%. The slag mainly composed of SiO ₂ produced in this desiliconization process is separated from the hot metal and discharged.

Next, the hot metal whose silicon content has been reduced to 0.20 to 0.05% is subjected to a second treatment of dephosphorization and desulfurization.

The processing agent (slag forming agent) in this second step is CaO
- Iron oxide - Mainly composed of CaCl ₂ and a combination of CaF ₂ is used. It is essential that the proportion of the treatment agent used is 0.2 to 0.5 parts by weight of CaCl ₂ to 1 part by weight of CaO. i.e. 0.2 per part by weight of CaO
Fe ₂ O ₃ , which will be described later, is used in a proportion of more than part by weight.
Even if CaF ₂ is taken into consideration, it is possible to generally ensure a Cl ₂ content of 5% or more in the generated slag (dephosphorization, desulfurization slag). If it exceeds 0.5 parts by weight, the concentration of Cl or Cl ₂ in the exhaust gas during treatment will increase, which is not preferable. Iron oxide is used at a ratio of 1 to 2 parts by weight per 1 part by weight of CaO, and this is consumed as an oxygen source in the dephosphorization reaction. A high dephosphorization rate can be obtained at 1 part by weight or more,
On the other hand, if it exceeds 2 parts by weight, the T.Fe content in the slag becomes too high and the dephosphorization rate decreases. CaF ₂ is the aforementioned CaCl ₂ at a ratio of 0.01 to 0.1 part by weight to 1 part by weight of CaO.
be replaced by Therefore, the proportion of CaCl ₂ and CaF ₂ used is 0.2 to 0.5 parts by weight per 1 part by weight of CaO. _CaF2
As mentioned above, the upper limit of Cl is 0.1 part by weight per part by weight of CaO, and if it exceeds this, the fluorine in the generated slag will be more than 3%, and even if Cl is more than 5%, the elution of phosphoric acid will be suppressed and the intended purpose will not be achieved. . On the other hand, if it is too small, the amount of CaCl ₂ used increases, leading to an increase in cost.

Thus, the above processing agent (slag forming agent) is 12 to 30 kg/
T-pig (1.2 to 3% of the amount of hot metal) is charged. This slag-forming agent is mixed and contacted with hot metal using a known stirring means, and the slag-forming reaction progresses, resulting in basicity (CaO/
A treated slag suitable for dephosphorization and desulfurization with SiO ₂ ) = 3.5 to 8 is produced, P in hot metal: 0.025% or less, S:
Should be 0.020% or less. In this process, Si becomes 0.01% or less and C becomes 3.8% or more.

The composition of the slag obtained as described above is as follows.

_SiO2 : 5-15%, CaO: 40-60%, FeO: 5
~10%, MnO: 1-5%, _P2O5 : 5-10% _,
Cl: 3-10%, F: 0.5-2.0%.

After refining, the above slag is separated from hot metal and subjected to the following heat treatment in order to stabilize the solubility of phosphoric acid in the slag.

(Rapid cooling) The slag at 1250-1350°C separated from the hot metal is brought into contact with water and pulverized. Alternatively, it is dispersed into the atmosphere and becomes fine particles. Or spread it in a thin layer. Such treatment refines the crystals and stabilizes the solubility of phosphoric acid in the slag.

(Holding at high temperature) The slag is once slowly cooled to room temperature, for example, and then heated to 800 to 1100°C and held for about 30 to 120 minutes. This treatment changes the morphology of the slag and stabilizes the solubility of phosphoric acid in the slag.

(Heating after rapid cooling) By combining the above-mentioned rapid cooling and heating and holding at a high temperature, the citric acid solubility of phosphoric acid in the slag is further stabilized.

The hot metal that has been dephosphorized and desulfurized in the above treatment process is sent to the final decarburization process, and if the values of each element are as described above, it will be decarburized oxygen smelting without slag, and the desired carbon value and temperature will be achieved. Do it until you get it.

Next, examples of the present invention will be described.

Example 1 C: 4.5%, Si: 0.53%, P: 0.110%, S:
10 tons of 0.036% hot metal was placed in a ladle equipped with a gas bubbling device. While stirring the hot metal in the ladle with N ₂ gas, 5Nm ³ /t of oxygen gas and 15Kg of iron ore were added.
By supplying t together, Si: reduced to 0.14%, and the bath temperature was 1450.
The desiliconization process was completed at ℃, and approximately 20 kg/t-pig of slag containing SiO ₂ as a main component was discharged. Subsequently, 35 kg/t-pig of treatment agents containing 0.3 parts by weight of CaCl ₂ , 1.5 parts by weight of iron oxide, and 0.06 parts by weight of fluorspar (CaF ₂ ) per 1 part by weight of CaO were supplied into the same ladle, and the hot metal was heated by an impeller. Simultaneous dephosphorization and desulfurization treatment was performed for 10 minutes while stirring. At this time, add 2.2N of oxygen gas from above the bath.
m ³ /t was supplied. The above iron oxide was added in four portions every 2 minutes. At this time, the basicity (CaO/SiO ₂ ) in the slag was 3.9, and T.Fe was maintained at 4%.

By the above treatment, C: 3.86%, Si: trace,
Hot metal containing P: 0.018% and S: 0.017% was obtained. On the other hand, approximately 24 kg/t-pig of slag produced in this treatment was obtained as a raw material for phosphoric acid fertilizer. The composition of this slag is _SiO2 : 12.1%, CaO: 59.0%, FeO:
5.1% _, MnO: 1.3%, _P2O5 : 9.8%, Cl: 10.8
%, F: 1.4%. The 1280°C slag separated from the hot metal was pulverized and rapidly cooled to produce phosphate fertilizer. The particle size of this granulated water was -5 mm, accounting for 73% or more. In order to confirm the effectiveness of this granulated water as a phosphoric acid fertilizer,
When the citric acid solubility (%) of P ₂ O ₅ was measured by sampling 10 test pieces, it was stable at an average of 90%.

Example 2 After 10 tons of hot metal similar to Example 1 was subjected to the same desiliconization treatment and the generated slag was discharged, CaO1 was placed in the same ladle.
A treatment agent of 0.2 parts by weight of CaCl ₂ , 1.5 parts by weight of iron oxide, and 0.1 parts by weight of fluorspar (CaF ₂ ) was added to 38 parts by weight.
Kg/t-pig was supplied and simultaneous dephosphorization and desulfurization treatment was performed for 10 minutes while stirring the hot metal with an impeller.
At this time, 2.2 Nm ³ /t of oxygen gas was supplied from above the bath. The above iron oxide was added in 4 portions every 2 minutes.
At this time, the basicity (CaO/SiO ₂ ) in the slag was 4.3, and T.Fe was maintained at 4%. By the above treatment, C: 3.85%, Si: trace, P: 0.018%,
S:0.019% hot metal was obtained. On the other hand, about 23 kg of slag produced by this treatment was obtained as phosphoric acid fertilizer. In this example, slag at 1250°C is cooled to room temperature, then crushed to -5 mm, and then crushed at 950°C.
It was heated for 30 minutes and then sized to -2 mm. In order to confirm the fertilizing effect of this slag grain, the citric acid solubility rate (%) of P ₂ O ₅ in the slag grain was determined.
When we sampled 10 test pieces and measured them, they were stable at an average of 92%.

Comparative Examples 1 and 2 The dephosphorization and desulfurization slags obtained in Examples 1 and 2 were simply slowly cooled to room temperature and crushed into -5 mm pieces to obtain phosphoric acid fertilizers. In order to confirm the effectiveness of these fertilizers, 10 test pieces were sampled to determine the citric acid solubility (%) of each P ₂ O _5. When measured, the average was 76% in Comparative Example 1, but the difference between the top and bottom was the largest. It was 25% hotter. Comparative Example 2 had an average of 68%, with a maximum difference of 35%.

The sampling results of the citric acid solubility of P ₂ O ₅ in Examples 1 and 2 and Comparative Examples 1 and 2 are summarized in FIG. 2. As is clear from FIG. 2, the citric acid solubility of P ₂ O ₅ in the examples of the present invention is extremely stable and has little variation compared to the comparative examples. This shows that the fertilizer obtained according to the present invention has stable fertilizing effect, and means that it is excellent as a fertilizer.

In addition, Examples 1 and 2 were used for comparison of hot metal treatment efficiency.
10t of desiliconized hot metal is mixed with CaCl ₂ 0.5 to 1 part by weight of CaO.
parts by weight, and 1.5 parts by weight of iron oxide in a CaF ₂ -free slag forming agent for 10 minutes. The treatment agent used was 38 kg/t-pig, and as a result, hot metal having the following composition was obtained.

C Si P S 3.94% Trace 0.016% 0.018% As is clear from the above results, there is almost no difference in hot metal treatment efficiency even when CaF ₂ is used in combination with calcium chloride as a melting point depressant according to the present invention.

As is clear from the above examples, according to the present invention, dephosphorization and desulfurization treatment of hot metal that has been desiliconized in advance is possible.
Since CaCl 2 is mainly used as the melting point depressing agent for the treatment agent mainly composed of CaO-iron oxide, even if a part of CaCl ₂ is replaced with CaF ₂ , there is no problem in using the produced slag as a phosphate fertilizer. Moreover, when the produced slag is used as a phosphoric acid fertilizer, the slag is subjected to treatments such as rapid cooling, slow cooling and then heating, or rapid cooling and then heating, so that a phosphoric acid fertilizer with extremely stable fertilizer effect can be obtained.

In the present invention described above, fluorite (CaF ₂ ) can also be added concentratedly at the final stage of treatment in order to facilitate the recovery of slag. Approx. 1300 for high temperature holding treatment
When cooling the molten slag at 0.degree. C., cooling may be temporarily stopped midway through, and a predetermined temperature (heating equivalent temperature: about 1000.degree. C.) may be maintained for a certain period of time (e.g., heating equivalent time).

In this way, the present invention greatly contributes to the effective use of steelmaking slag.

[Brief explanation of the drawing]

Figure 1 shows the Cl content in dephosphorization and desulfurization slag,
A diagram showing the relationship between the F content and the citric acid solubility of P ₂ O ₅ in the slag. Figure 2 shows a comparison of the citric acid solubility of P ₂ O ₅ in the slag in Examples and Comparative Examples. It is a diagram.

Claims (1)

[Claims] 1. When dephosphorizing and desulfurizing low-Si hot metal with a slag forming agent mainly composed of CaO-iron oxide-CaCl ₂ and also CaF ₂ , the amount of CaCl ₂ is 0.2 to 1 part by weight of CaO.
0.5 parts by weight, 1 to 2 parts by weight of iron oxide, and 1 part by weight of CaO in place of the above CaCl ₂
A slag suitable for phosphoric acid fertilizer is produced by separating and recovering the generated slag using 0.01 to 0.1 parts by weight of CaF ₂ and rapidly cooling or holding the recovered slag, or rapidly cooling and then holding at a high temperature. Steel manufacturing methods that emit emissions.