KR20010055477A - A Treatment Method for Surface of Direct Reduced Iron - Google Patents

Abstract

PURPOSE: A method for the surface treatment of direct reduced iron by carrying out surface treatment of direct reduced iron under suitable conditions using naphtenic acid is provided, which improves oxidation resistance and corrosion resistance. CONSTITUTION: The titled surface treatment method of direct reduced iron is characterized in that the direct reduced iron is dipped in a naphtenic acid in the range of temperature of 100 to 130deg.C for 2 min or more and dried under inactive gas atmosphere at 70deg.C or less. This method exhibits excellent oxidation resistance and corrosion resistance to corrosion reaction being in progress by contact of water as well as oxidation reaction being in progress by contact of oxidation in the air.

Description

A treatment method for surface of direct reduced iron

The present invention relates to a method for treating a surface of direct reduced iron, and more particularly, by reducing the surface of the directly reduced iron using a solution of Naphtenic acid (C ₁₀ H ₈ ) to reduce the oxidation and corrosion It relates to a method of improving the matting.

Recently, advanced steel mills are adopting melt-reducing steelmaking methods such as mini-mill and corex as next-generation steelmaking technologies, and are spurring not only the introduction of facilities but also the development of technology, especially the expansion of mini-mill plant for thin slab manufacturing. In line with the trend, supply and demand for iron scrap, which is a raw material, is intensifying. Recently, due to the rising price of iron scrap, the use of direct reduced iron, which can be an alternative source of iron scrap, is increasing. However, such reduced iron is produced only in some countries rich in underground resources such as iron ore and natural gas, and is supplied to various demanded countries.

Direct reduced iron is produced by reducing iron ore pellets at high temperature using coal or natural gas, so that iron oxides, which are the main components of iron ore, release oxygen during the reduction reaction and transfer oxygen to metal iron. It has a very soft tissue that has a very large specific surface area. Direct reduced iron pellets with a large specific surface area are structurally poor in thermal conductivity, but are highly reactive chemically, so they are easily oxidized or corroded by contact with atmospheric oxygen, water, seawater, etc. As the iron oxide or the iron hydroxide transitions, the metallization rate (Metallization, metal Fe / total Fe) gradually decreases over time. In particular, when transporting reduced iron directly by sea due to trade between countries, the corrosion reaction proceeds remarkably by contact with sea water and generates a large amount of hydrogen gas. Therefore, it is a material containing the risk of ignition due to generated hydrogen gas. Therefore, the International Maritime Organization sets and manages appropriate management standards.

The oxidation of direct reduced iron takes place in a dry state, and releases a large amount of heat while forming oxides (magnetite, Fe ₃ O ₄ ) according to the reaction formulas (1) and (2) by reaction with oxygen in the air. Done.

3Fe + 2O ₂ → Fe ₃ O ₄ + heat

2Fe + 3 / 2O ₂ → Fe ₂ O ₃ + heat

When the oxidation reactions such as the two reactions continue, the structure has a very porous structure, so the direct reduced iron itself, which has poor heat transfer characteristics, continuously accumulates heat and eventually reaches the ignition point. Will arrive and ignite.

On the other hand, when the direct reduced iron is present in the presence of moisture and oxygen, as shown in the following equations (3), (4), the corrosion reaction proceeds to form iron hydroxide and simultaneously generate heat. As described above, in the reaction in which oxygen is completely consumed, it proceeds as shown in Equation (5), and in particular, when it is deposited in seawater, it proceeds as in Equation (6) and generates a large amount of hydrogen gas. It is easily ignited by the bay and is very likely to cause a fire.

4Fe + 4H ₂ O + 2O ₂ → 4Fe (OH) ₂ + heat

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

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

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

As described above, since the direct reduced iron is composed of a high content of metal components, not only does the fire and storage risks occur during storage, transportation, and handling due to instability to oxidation and corrosion reactions, Or metallization (Metallization) is reduced by the transition to iron hydroxide, the secondary problem that increases the consumption of the electrode, quicklime, refractory, as well as the primary problem that the metal recovery rate, productivity, cooling capacity, etc. during the operation of steel mills Is holding.

In order to solve the problems caused by the oxidation and corrosion reaction of the direct reduced iron, there are natural maturation method and air contact method to forcibly form the surface portion of the direct reduced iron into a thin oxide film. The hot forming method has been proposed to reduce the chemical reactivity due to the reduction of specific surface area by forming at high pressure above ℃ (direct reduced iron technology and economics of production and use, 1990). Reduction of chemical reactivity against oxidation and corrosion by reducing the specific surface area by coordinating the size of the pores formed by the reduction reaction by adding a reduction reaction. by application of CaO coating -development of a coating process, metalluri gical plant and technology, 1982), and methods for treating the surface of direct reduced iron using wax (US patent 4,692,353).

The natural ripening method or air contact method, which causes the thinned oxide layer to be forcibly formed on the surface by naturally leaving the direct reduced iron in air or aging in an oxidizing atmosphere, has some resistance to oxidation reactions that are caused by oxygen in the air. However, since it does not show resistance to corrosion reactions carried out by seawater contact, this technology is applied only to supply to steel mills located in close proximity by land. Hot forming method, which shows the best corrosion resistance against water or seawater, is a method of reducing the internal surface area of direct reduced iron by physical pressurization method. It is a situation that supplies the iron source manufactured by. However, this method also has a problem that it requires a separate additional equipment because it is manufactured by molding the reduced iron directly from high temperature to high pressure, it takes a lot of costs for operating such equipment.

Thus, the present inventors have conducted research and experiments to solve the problems of the prior art, and proposed the present invention based on the results. The present invention provides a surface treatment under a suitable condition using a naphthenic acid solution with a direct reducing iron. By doing so, to provide a method for improving the oxidation resistance and corrosion resistance of direct reduced iron, the purpose is.

In order to achieve the above object, the present invention provides a method for treating a surface of direct reduced iron, wherein the direct reduced iron is deposited on a naphthenic acid solution for 2 minutes or more under a temperature condition in a range of 100 to 130 ° C., and then 70 ° C. It relates to a surface treatment method of a direct reduced iron, characterized by drying in the following inert gas atmosphere.

Hereinafter, the present invention will be described in detail.

In the present invention, it is preferable to control the temperature of the surface treatment by directly depositing reduced iron on the naphthenic acid solution at a temperature in the range of 100 to 130 ° C.

If the temperature deposited in the naphthenic acid solution is less than 100 ° C, not only the naphthenic acid is completely dissolved, but also exhibits a high viscosity even when dissolved, so that it penetrates and diffuses up to numerous pores present in the direct reducing iron. This is because it is impossible to expect a complete surface treatment, and thus cannot achieve excellent oxidation resistance and corrosion resistance. In addition, since the deposition temperature exceeds 130 ° C., the metallization rate is remarkably lowered because it starts to oxidize slowly from the surface of the directly reduced iron.

In the present invention, it is preferable to deposit the reduced iron directly in the naphthenic acid solution and to carry out the surface treatment for 2 minutes or more.

When the deposition time is less than 2 minutes, it is not possible to sufficiently penetrate and diffuse even the numerous pores present in the direct reducing iron to coat the surface thereof, so that it is not expected to improve oxidation resistance and corrosion resistance.

In the present invention, it is preferable to dry in an inert gas atmosphere of 70 ° C. or less in the drying step after the deposition and surface treatment as described above.

Until the drying, it is preferable to maintain in an inert gas atmosphere because it has not yet been completely coated in the direct reduced iron or surface after surface treatment and shows unstable characteristics for oxidation.

The drying temperature is preferably maintained at 70 ° C. or less, because the drying temperature exceeds 70 ° C., since the coating layer coated on the surface or inside of the directly reduced iron is separated and separated from the direct reduced iron by the drying temperature. And improvement of corrosion resistance cannot be expected.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

Invention Examples 1-4

Iron ore pellets were maintained at 950 ° C. for 5 hours in a hydrogen gas atmosphere to prepare direct reduced iron. The metallization rate of the prepared direct reduced iron was 92.3% as calculated by analyzing the T.Fe content and the metal Fe content, respectively, using a component analyzer.

The prepared direct reduced iron was immersed in a naphthenic acid solution heated to 100 ° C. for 2 minutes, 10 minutes, 30 minutes, and 60 minutes, respectively, and then surface-treated, and dried in a drier maintained at 60 ° C. while flowing an inert gas. Directly reduced iron surface-treated with nitric acid was prepared.

The evaluation of the resistance to oxidation and corrosion of surface-treated direct reduced iron was carried out after 10 minutes of immersion in a 3% NaCl aqueous solution similar to seawater after the chemical component heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change of metallization rate, the results are shown in Table 1 below.

(Comparative Examples 1 to 4)

The surface treatment was carried out in the same manner as in the above-described example except that the reduced iron was directly reacted without any surface treatment, and the surface treatment was performed by deposition, surface treatment time of 10 seconds, 30 seconds, and 1 minute. Was carried out to prepare a direct reduced iron surface-treated with naphthenic acid.

The evaluation of the resistance to oxidation and corrosion of surface-treated direct reduced iron was carried out after 10 minutes of immersion in a 3% NaCl aqueous solution similar to seawater after the chemical component heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change of metallization rate, the results are shown in Table 1 below.

(Priority Example 1)

Iron ore pellets were maintained at 950 ° C. for 5 hours in a hydrogen gas atmosphere to prepare direct reduced iron. The metallization rate of the prepared direct reduced iron was 92.3% as calculated by analyzing the T.Fe content and the metal Fe content, respectively, using a component analyzer.

The prepared reduced iron was heated to 110 ° C. and deposited on wax melted for 1 minute to carry out surface treatment. Thereafter, the sample was sufficiently dried in a drier under a nitrogen atmosphere maintained at 60 ° C. or lower, and used as a test sample.

The evaluation of the resistance to oxidation and corrosion of surface-treated direct reduced iron was carried out after 10 minutes of immersion in a 3% NaCl aqueous solution similar to seawater after the chemical component heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change of metallization rate, the results are shown in Table 1 below.

Surface treatment condition % Metallization by aging Surface treatment agent Processing time Treatment temperature (℃) 2 days 4 days 10 days Inventive Example One Naphthenic acid 2 minutes 100 92.0 91.9 91.2 2 " 10 minutes " 92.1 92.0 91.6 3 " 30 minutes " 92.1 91.8 91.7 4 " 60 minutes " 92.0 91.9 91.6 Comparative example One - - - 77.2 75.2 70.2 2 " 10 sec " 87.2 86.2 83.2 3 " 30 seconds " 89.3 88.2 86.2 4 " 1 minute " 90.2 89.2 87.3 Conventional example One Wax 1 minute 110 90.2 90.1 88.2

As can be seen in Table 1, in the case of Inventive Examples (1 to 4), the surface treatment time was maintained for 2 minutes or more using the naphthenic acid as the surface treatment agent proposed in the present invention. In comparison with ˜4) and the conventional example (1), it was confirmed that the metallization rate decreased not only in accordance with the aging time but also maintained a high metallization rate of 91% or more after 10 days or more.

On the contrary, in the case of the comparative example manufactured with the surface treatment time of less than 2 minutes, the metallization rate decreases with the aging time. Especially, the reduced metallization rate of the direct reduced iron without any surface treatment is low from the initial aging time. It was found that the metallization rate was remarkably decreased with aging time.

In addition, in the case of the conventional example (1) surface-treated with wax, the metallization rate was 90% or more up to 4 days of initial aging, but the metallization rate gradually decreased as the aging time was longer.

Therefore, it was found from the results of Inventive Examples (1 to 4) that the naphthenic acid solution is suitable as a surface treatment agent for improving the oxidation resistance and corrosion resistance of the direct reduced iron. It was confirmed that it is preferable to keep the treatment time at 2 minutes or more.

Example 2

Invention Examples 5 to 6

Iron ore pellets were maintained at 950 ° C. for 5 hours in a hydrogen gas atmosphere to prepare direct reduced iron. The metallization rate of the prepared reduced iron was 92.3% as calculated by analyzing the T.Fe content and the metal Fe content using a component analyzer.

The prepared direct reduced iron was immersed in a naphthenic acid solution heated at 110 ° C. and 130 ° C. for 2 minutes, and then surface treated, dried in a drier maintained at 60 ° C. while flowing an inert gas, and then surface treated with naphthenic acid. Was prepared.

Evaluation of the resistance characteristics against oxidation and corrosion of surface-treated direct-reduced iron was measured after evaporation of the chemicals heated and maintained at 80 ° C for 10 minutes in 3% NaCl solution similar to seawater, and then left in the air. The metal content according to the analysis, and determined from the change in metallization rate, the results are shown in Table 2 below.

(Comparative Examples 5-6)

A direct reduced iron surface was prepared in the same manner as in the invention, except that the direct reduced iron was surface treated at a temperature of the naphthenic acid solution at 90 ° C. and 140 ° C., respectively.

Evaluation of the resistance to oxidation and corrosion of surface-treated direct-reduced iron was carried out after 10 minutes of immersion in a 3% NaCl solution, similar to seawater, with the chemicals heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change in metallization rate, the results are shown in Table 2 below.

Surface treatment condition % Metallization by aging Surface treatment agent Processing time Treatment temperature (℃) 2 days 4 days 10 days Inventive Example 5 Naphthenic acid 2 minutes 110 92.1 91.9 91.6 6 " " 130 91.9 91.6 91.2 Comparative example 5 " " 90 89.2 88.4 87.2 6 " " 140 84.1 82.2 75.2

As can be seen from Table 2, in the case of Inventive Examples (5 to 6) subjected to deposition and surface treatment using a naphthenic acid, the surface treatment agent proposed in the present invention, under a condition of 100 to 130 ° C, aging. Although the metallization rate is maintained almost constant over time, when the surface treatment temperature is lower than 100 ° C or higher than 140 ° C, the metallization rate decreases rapidly with aging time. As described above, when the temperature is lower than 100 ° C., the high viscosity of naphthenic acid does not sufficiently penetrate and diffuse to the myriad pores existing in the directly reduced iron, so that a perfect surface treatment cannot be expected. It is believed that the metallization rate was lowered from the initial aging time because it slowly oxidized itself from the surface portion of the direct reduced iron when it was above 140 ° C.

Therefore, in the case of the present invention to the surface treatment using naphthenic acid it was confirmed that the surface treatment by adjusting the surface treatment temperature in the range of 100 ~ 130 ℃.

Example 3

(Invention Examples 7-8)

Iron ore pellets were maintained at 950 ° C. for 5 hours in a hydrogen gas atmosphere to prepare direct reduced iron. The metallization rate of the prepared reduced iron was 92.3% as calculated by analyzing the T.Fe content and the metal Fe content, respectively, using a component analyzer.

The prepared direct reduced iron was immersed in a naphthenic acid solution heated to 100 ° C. for 2 minutes, and then surface treated, dried in a drier maintained at 60 ° C. and 65 ° C. while flowing an inert gas, and then directly surface treated with naphthenic acid. Reduced iron was prepared.

The evaluation of the resistance to oxidation and corrosion of surface-treated direct reduced iron was carried out after 10 minutes of immersion in a 3% NaCl aqueous solution similar to seawater after the chemical component heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change of metallization rate, the results are shown in Table 3 below.

(Comparative Examples 7-8)

A surface-treated direct reduced iron was prepared in the same manner as in the invention except that the surface-treated direct reduced iron is dried in a drier maintained at 80 ° C. and dried in a drier maintained at 60 ° C. while flowing oxidizing gas. It was.

The evaluation of the resistance to oxidation and corrosion of surface-treated direct reduced iron was carried out after 10 minutes of immersion in a 3% NaCl aqueous solution similar to seawater after the chemical component heated and maintained at 80 ° C. The metal content according to the analysis, and determined from the change of metallization rate, the results are shown in Table 3 below.

Surface treatment condition Metallization Rate by Aging (%) Dry atmosphere Drying temperature (℃) 2 days 4 days 10 days Inventive Example 7 Inert gas 60 92.0 91.9 91.2 8 " 65 92.1 91.7 91.4 Comparative example 7 " 80 87.2 86.4 85.2 8 Oxidizing gas 60 86.4 84.2 80.2

As can be seen in Table 3, after the surface treatment using the naphthenic acid proposed in the present invention and dried under an inert gas atmosphere of 70 ℃ or less in the case of the invention examples (7 to 8) In contrast to the case of 7 to 8), the metallization rate decreases according to the aging time, and it was confirmed that the metallization rate was higher than 91% even after 10 days.

On the contrary, if the drying conditions during the drying after the surface treatment exceed the oxidizing gas atmosphere or 70 ° C., the oxidation treatment proceeds partially or because the surface treatment layer, which has not yet formed a coating layer, exhibits unstable characteristics for oxidation. Due to the drying temperature condition, the incompletely coated surface treatment layer directly escaped from the reduced iron, which resulted in low metallization rate from the initial aging period, and the decrease in metallization rate also appeared to increase significantly according to the aging time.

Therefore, in the case of the present invention surface-treated using naphthenic acid, it was confirmed that it is preferable to carry out the drying conditions after the surface treatment in an inert gas atmosphere of 70 ° C or less.

The direct reduced iron surface-treated by the method of the present invention as described above has excellent oxidation and corrosion resistance against not only oxidation reactions by contact with oxygen in the atmosphere, but also corrosion reactions by contact with water. It has the effect of showing resistance.

Claims (1)

In the surface treatment method of direct reduced iron, The direct reduced iron is surface-coated by immersing it in a naphthenic acid solution for 2 minutes or more under a temperature condition in the range of 100 to 130 ° C., and then drying it under an inert gas atmosphere of 70 ° C. or less.