KR20020016242A - The Method For Treatment of Metal Pellet - Google Patents

Abstract

PURPOSE: Provided is a method for treating a surface of a metallic pellet by dipping metallic pellet in a maleimide solution for a given time, followed by drying, whereby the pellet will have improved oxidation resistance and corrosion resistance. CONSTITUTION: The method is performed by dipping metallic iron pellets in a maleimide solution at a temperature in a range of 100 to 130 deg.C. The dipping is performed for a period of 5 minutes or more. After the surface treatment at a temperature of 100 to 130 deg.C for 5 minutes, the pellets may still have defects on the surface or the inside. Therefore, the pellets are sufficiently dried at a temperature of 60 deg.C or less for solid hardening of the treated surface. During performing this method, the defined temperature or the reaction time should be abided. When a temperature or a reaction time out of the defined range, the oxidation resistance and corrosion resistance of the final pellets can be deteriorated.

Description

The Method For Treatment of Metal Pellet

The present invention provides a method for surface treatment of metal pellets, and more specifically, metal pellets are coated with a maleimide (Maleimide: C₄H₃NO ₂ ) solution, coated under appropriate conditions, surface treated, and cured to improve oxidation and corrosion resistance of the metal pellets. The present invention relates to a method for surface treatment of metal pellets.

In general, advanced steel mills have recently adopted melt-reducing steel production methods such as mini mills and Korex as the next-generation steelmaking technologies, which not only promote the introduction of facilities, but also accelerate the development of technologies. As a result, supply and demand shortages have been intensified due to the shortage of iron scrap as a raw material. Accordingly, the amount of metal iron pellets that can be used as an alternative resource due to the rising price of iron scrap is increasing.

Since metal iron pellets are manufactured by chemically reducing iron ore pellets, they have a porous structure in which numerous pores remain in water and oxygen molecules separated by the reaction with gas, and thus have a very large specific surface area per unit weight. It is very dangerous because it is highly chemically reactive and highly oxidized or corroded by weather and environment during transport or storage by sea and on land.

Reoxidation of the metal iron pellets occurs in a dry state, and reacts with oxygen in the air to form an oxide in a form as shown in Schemes 1 and 2 to release a large amount of heat.

[Scheme 1]

3Fe + 20 ₂ → Fe ₃ O₄ + heat

[Scheme 2]

2Fe + 3/20 ₂ → Fe ₂ 0 ₃ + heat

If the reaction continues, the pellet itself contains heat and eventually ignites due to the structural properties of the metal iron pellets, which have poor heat transfer properties.

On the other hand, when the metal iron pellets are in the condition of the presence of moisture and oxygen, as shown in the following reaction equations 3 and 4, when the corrosion reaction proceeds to form hydrates and generate heat at the same time, as shown in the above equation, oxygen In the case of completely consumed reactions, hydrogen gas is generated in the same reaction as in Scheme 5, and thus it is very likely to be ignited by contact with air.

Scheme 3

4Fe + 4H ₂ 0 → 4Fe (OH) ₂ + heat

[Scheme 4]

4Fe (OH) ₂ + 2H ₂ 0 + 0 ₂ → 4Fe (OH) ₃ + heat

[Scheme 5]

3Fe (OH) ₂ + heat → Fe ₃ 0 ₄ + 2H ₂ 0 + H ₂ ↑

Scheme 6

3Fe + 4H ₂ 0 + heat → Fe ₃ 0 ₄ + 4H ₂ ↑

As described above, there is a risk of fire during storage, transportation and handling due to instability of the oxidation and corrosion reactions of the metal iron pellets, as well as the metallization rate is reduced, the recovery rate, productivity and cooling of the metal during the operation of the steel mill. The problem is that the performance is lowered, and at the same time, the electrode, quicklime, and refractory consumption increase.

Conventional methods that have been carried out or proposed to solve the problems caused by oxidation and corrosion of the metal iron pellets include a natural aging method and an air contact method for forming an oxide layer on the surface of the metal iron pellets by an appropriate method. Hot forming is applied to reduce the specific surface area by applying a pressure above 650 ° C (direct reduced iron technology and economics of production and use, 1980).

In addition, a method of reducing the chemical reactivity against oxidation and corrosion by reducing the specific surface area by coarsening pores by adding Ca0 when preparing metal iron pellets has been proposed (improvement of the reoxidation and corrosion behavior) Direct reduced iron by application of Ca0 coating-development of a coating process, metallurgical plant and technology, 1982), and a method of treating the surface of metal iron pellets using waxes have also been proposed (US patent 4,692,353).

The natural aging method and air contact method, which form a thin oxide layer (magnetite layer: Fe ₃ 0 ₄ ) on the surface of the metal iron pellets, have a poor corrosion resistance to water or seawater, and thus are mainly used when sold only to nearby steel mills. to be.

The hot forming method, which shows the best corrosion resistance to water and seawater, is a method of reducing the internal surface area of metal iron pellets. The water content is very low, about 4%.

However, this method has a problem in that the metal iron pellets are molded and manufactured at a high temperature and a high pressure, so that additional equipment and a large cost are required.

The present invention was devised in view of the above problems of the conventional method for treating metal iron pellets, and its purpose is to deposit metal iron pellets in a maleimide solution for a predetermined time, and then surface-treat the metal iron pellets through a process of drying. It is to provide a method for surface treatment of metal pellets that can impart oxidation and corrosion resistance.

In order to achieve the above object, the present invention provides a method for surface treatment of metal iron pellets, in which the metal iron pellets are immersed in a maleimide solution at a temperature ranging from 100 to 130 ° C. for at least 5 minutes, and then the metal iron pellets which have been treated are deposited. It is characterized in that it is sufficiently dried to a temperature of less than ℃ to cure the surface treatment layer to improve oxidation and corrosion resistance.

Hereinafter, the surface treatment method of the metal pellet of this invention is demonstrated in detail.

In the present invention, the temperature for depositing the iron pellets in the maleimide solution is preferably carried out in the range of 100 ~ 130 ℃.

When the surface treatment temperature is less than 100 ° C, not only does the maleimide not completely transition to the liquid phase, but also has low fluidity and high viscosity, and thus does not diffuse into the inside of the metal iron pellet having many pores. Improvement in resistance to oxidation and corrosion cannot be expected.

When the surface treatment temperature is 130 ° C. or more, the metal iron pellets start to burn slowly, resulting in deterioration of oxidation resistance and corrosion resistance.

In the present invention, it is preferable to deposit the metal iron pellets in the maleimide solution for 5 minutes or more to perform the surface treatment.

In this case, if the time for deposition and surface treatment is less than 5 minutes, it is difficult to fully penetrate and diffuse into the numerous pores remaining in the metal iron pellets, and thus, the complete surface treatment cannot be performed.

In addition, in the present invention, since the inside or the surface of the surface-treated metal iron pellet is still incompletely bonded after the deposition and surface treatment as described above, it is preferable to dry it sufficiently at a temperature of less than 60 ° C. for solid curing of the surface treatment layer. desirable.

If the drying temperature is more than 60 ℃, since the coating layer formed on the inside or surface of the metal iron pellets begins to separate from the metal iron pellets, it is not expected to improve the oxidation resistance and corrosion resistance.

Hereinafter, the surface treatment method of the metal pellet of the present invention will be described in more detail with reference to Examples.

Example 1:

Inventive Examples 1 to 5

Iron ore pellets were heat-treated at about 950 ° C. for 5 hours under a hydrogen gas atmosphere to reduce metal iron pellets. At this time, the metallization rate of the prepared metal iron pellet was 94.2%.

The metal iron pellets were immersed in a maleimide solution heated to 100 ° C. for 6 minutes, 8 minutes, 10 minutes, 30 minutes, and 60 minutes, and then taken out and placed in a mesh container smaller than the average diameter of the pellets. After removal of the absorbed or coated solution, the solution was placed in a dryer maintained at about 50 ° C. and dried for 24 hours to prepare a surface-treated metal iron pellet.

The evaluation of the resistance to oxidation and corrosion resistance of surface-treated metal iron pellets was carried out by immersion for 10 minutes at 80 ° C. in a 3% NaCI aqueous solution similar to the chemical composition of seawater, followed by natural leaving in the air. Judgment was made by measuring the change over time, and the results are shown in Table 1 below.

Comparative Examples 1 to 4

The same method as in the present invention was carried out in the maleimide solution, except that the metal iron pellets were not deposited and surface treated, and the surface treatment was performed for 1 minute, 3 minutes, and 5 minutes, respectively. The results are shown in Table 1 below.

Conventional Example 1

The wax was heated to 110 ° C. to melt, and then the metal iron pellet was deposited and maintained for 1 minute and then taken out to remove excess solution from a mesh container smaller than the average diameter of the pellet.

Thereafter, after sufficiently drying at a temperature of 50 ℃ or less to prepare a surface-treated metal iron pellets. The evaluation of the resistance to oxidation and corrosion of surface-treated iron pellets was made by immersing at 80 ° C for 10 minutes in a 3% NaCI aqueous solution similar to seawater, and then changing the metallization rate with elapsed time as it was left in the air. Judging from the measurement, the results are shown in Table 1 below.

Surface treatment condition Change of Metallization Over Time (metalFe / T.Fe%) Surface treatment agent Surface treatment time (minutes) Surface treatment temperature (℃) 2 days 4 days 10 days Inventive Example One Maleimide 6 100 93.4 93.0 92.4 2 〃 8 93.6 93.0 92.1 3 〃 10 93.5 93.1 92.5 4 〃 30 93.3 93.2 92.4 5 〃 60 97.3 93.5 92.8 Comparative example One 〃 - 79.2 76.3 72.1 2 〃 One 82.3 81.4 80.0 3 〃 3 86.4 85.3 85.0 4 〃 5 89.2 88.4 87.2 Conventionally One Wax One 110 90.9 88.2 88.0

Therefore, as can be seen in Table 1, the inventive examples 1 to 5 prepared by maintaining the surface treatment time for 6 minutes or more using the maleimide solution which is the surface treating agent of the present invention are comparative examples 1 to 4 and conventionally. Compared with Example 1, it was confirmed that the change in the metallization rate was not only small but also maintained a high metallization rate of 90% or more after 10 days or more.

Therefore, it can be seen that the maleimide solution acts as a coating layer that significantly improves the resistance to oxidation and corrosion of the metal iron pellets. When it is used as a surface treatment agent, the surface treatment time is maintained at 5 minutes or more. It can be confirmed that it is desirable to.

Example 2:

Inventive Examples 6-8

Iron ore pellets were heat-treated and reduced at 950 ° C. for 5 hours under a hydrogen gas atmosphere to prepare metal iron pellets. At this time, the metallization rate of the prepared metal iron pellet was 94.2%.

Metal iron pellets were immersed in a maleimide solution heated to 110 ° C., 120 ° C. and 130 ° C. for about 10 minutes, and then taken out to remove the solution absorbed or coated excessively in a container of mesh smaller than the average diameter of the pellets. Into a dryer maintained at ℃ ℃ dried for 24 hours to prepare a surface-treated metal iron pellets.

The evaluation of the resistance to oxidation and corrosion resistance of surface-treated metal iron pellets was carried out by immersion for 10 minutes at 80 ° C in a 3% NaCl aqueous solution similar to the chemical composition of seawater, followed by natural leaving in the air. Judgment was made by measuring the change over time, and the results are shown in Table 2 below.

Comparative Examples 5-7

The maleimide was heated to 85 ° C., 95 ° C., 140 ° C. and 150 ° C., respectively, and was then subjected to the same method as the invention example except that the metal iron pellets were deposited and surface treated, and the results are shown in Table 2 below. It was.

Surface treatment condition Change of Metallization Over Time (metal Fe / T.Fe) Surface treatment agent Surface treatment time (minutes) Surface treatment temperature (℃) 2 days 4 days 10 days Inventive Example 6 Maleimide 10 110 93.1 92.8 92.2 7 〃 120 93.4 93.0 92.4 8 〃 130 92.9 92.6 92.0 Comparative example 5 〃 85 89.2 85.2 81.2 6 〃 95 89.7 86.3 84.4 7 〃 140 83.8 81.2 76.3 8 〃 150 82.0 79.4 75.9

As can be seen in Table 2, when the temperature of deposition and surface treatment is less than 100 ° C or exceeds 130 ° C, it can be confirmed that the change in metallization rate rapidly progresses and the metallization rate is significantly lowered. .

When the temperature of deposition and surface treatment is less than 100 ° C, the low fluidity due to the high viscosity of the maleimide solution makes it difficult to diffuse and penetrate into the metal iron pellets containing numerous pores. Since the coating treatment by sufficient diffusion and penetration did not proceed to the pores, the change in the metallization with time seems to be large.

On the other hand, if the deposition and surface treatment temperatures exceed 130 ℃, the viscosity of the maleimide solution decreases and the diffusion rate increases due to the increase of fluidity, but the metallization rate is low since the self oxidation reaction proceeds gradually from the surface of the metal iron pellets. Is considered to be.

Therefore, in the present invention in which deposition and surface treatment using maleimide, the deposition and surface treatment temperature within the range of 100 ~ 130 ℃ suitable conditions that can improve the resistance to oxidation and corrosion of metal iron pellets You can see that.

Example 3:

Inventive Example 9

Iron ore pellets were heat-treated and reduced for 5 hours at 950 ° C. under hydrogen gas atmosphere to prepare metal iron pellets. At this time, the metallization rate of the prepared iron pellets was 94.2%.

The metal iron pellets were immersed in a maleimide solution heated to 100 ° C. for 10 minutes, and then taken out, placed in a container of a mesh smaller than the average of pellets, to remove the excess absorbed or coated solution, and then to a dryer maintained at 40 ° C. Put to dry for 24 hours to prepare a surface-treated metal iron pellets.

The evaluation of the resistance to oxidation and corrosion resistance of surface-treated metal iron pellets was carried out by immersion for 10 minutes at 80 ° C. in a 3% NaCl aqueous solution similar to the chemical composition of seawater, followed by natural leaving in the air. Judgment was made by measuring the change over time, and the results are shown in Table 3 below.

Comparative Examples 9-11

Exposed and surface-treated metal iron pellets were carried out in the same manner as in the present invention except for drying for 24 hours in a dryer holding 60 ℃, 70 ℃, 80 ℃, respectively, the results are shown in Table 3 below Indicated.

Surface treatment condition Change of metallization rate over time (metal Fe / T.Fe%) Surface treatment time (minutes) Surface treatment temperature (℃) Drying temperature (℃) 2 days 4 days 10 days Inventive Example 9 10 10 40 93.2 92.8 92.3 Comparative example 9 〃 〃 60 91.4 87.9 87.2 10 〃 〃 70 89.2 86.7 85.3 11 〃 〃 80 87.2 85.3 82.4

As can be seen in Table 3, in the case of Inventive Example 9 which is dried by setting the drying temperature to less than 60 ℃ after deposition and surface treatment using the maleimide solution of the present invention in the case of Comparative Examples 9-11 In contrast, the change in metallization rate is very small and it can be seen that the metallization rate is maintained at 92% or higher even after 10 days left in the atmosphere.

However, if the drying temperature during drying after deposition and surface treatment is higher than 50 ℃, the surface treatment layer unstable by high drying temperature starts to separate and separate from the metal iron pellets. It is confirmed that the oxidation and corrosion reaction proceeded remarkably from the early stage of air leaving due to the disappearance of the coating layer which suppresses the progress of not only the low metallization rate, but also the large change of the metallization rule over time depending on the elapsed time.

Accordingly, it is understood that in the case of the present invention in which deposition and surface treatment using maleimide, it is preferable to set the drying temperature conditions for drying the surface treatment layer after deposition and surface treatment to be less than 60 ° C. Can be.

Such a method for treating the surface of the metal pellets of the present invention proceeds by contact with water as well as oxidation reaction by contact with oxygen in the atmosphere by depositing and surface treating the metal iron pellets in maleimide by a simple process. There is an effect of showing a very excellent resistance to corrosion reactions, etc., there is also an advantage that can suppress the change over time of the metallization rate.

Claims (1)

A method for surface treatment of metal pellets, wherein the metal iron pellets are immersed in a maleimide solution at a temperature in the range of 100 to 130 ° C. for at least 5 minutes, and then surface-treated by sufficiently drying them to a temperature condition of less than 60 ° C.