KR920010529B1 - Mixing method for the pellet of cr ore - Google Patents

Abstract

The batch composition of raw material for preparation of the prereductive chromium ore pellet consists of 75-85 wt.% chromium ore containing 30-40 wt.% T.Cr and 9-26 wt.% T.Fe; 2-5 wt.% bentonite containing 60-70 wt.% silicon oxide (silica) and 10-25 wt.% aluminum oxide (alumina); 10-20 wt.% cokes containing 80-95 fixed carbon; 0.8-6.0 wt.% cement containing 60-70 wt.% calcium oxide, 12-25 wt.% silica, less than 10 wt.% alumina; and 0.5-4.0 wt.% calcium oxide.

Description

Premixed raw materials for manufacturing chrome ore pellets

1 is a graph showing the metallization rate of pre-reduced chromium ore pellets prepared by the present invention method and comparative method.

The present invention relates to a method for producing pre-reduced chrome ore pellets used as a charge during the smelting of Fe-Cr alloy iron, more specifically, for the production of chromium ore pellets used to prepare pre-reduced chrome ore. It relates to a blended raw material.

In general, a method of manufacturing Fe-Cr alloy iron includes a method of charging smelting by charging chrome ore, calcined chrome ore pellets as a chromium source, bulk coke as a reducing agent, limestone, silica and Ni smelting slag as a solvent, and coal ash. There is a method of charging the pre-reduced chromium ore pellets prepared by reducing the mixed chromium ore pellets in a reduction furnace into an electric furnace and smelting by adding the same kind of reducing agent and solvent as the former. The latter method is a recently developed method, which is a method of preliminarily reducing the oxide chromium or chromium ore pellets before charging them into the electric furnace, and injecting the metallized pellets into the electric furnace. It is excellent in operability, such as productivity, and has the merit of drastically reducing the specification unit, such as an electric power source unit.

In order to industrially prepare pre-reduced chrome ore pellets for the smelting of Fe-Cr alloy iron, finely divided chromium ore, coke, 2-5 wt% bentonite (used as a binder) and necessary According to the present invention, carbonaceous mixture chromium ore pellets assembled by mixing water with various solvents (mainly SiO ₂ component-containing materials) are added to a rotary rotary kiln and assembled into pellets by heating them at a high temperature of 1200-1450 ° C. By the reaction in which a metal oxide is converted into a metal carbide by the carbon component in the carbonaceous material, a method for producing pre-reduced chromium ore pellets having a metallization rate of 55% or more is commercially performed. In this kiln operation, the residence time of the pellet in the kiln is about 3-4 hours.

In order to make the pre-reduced chromium ore pellets, chromium ore pellets prepared by mixing and ore and other raw materials (reducing agents, binders, solvents, etc.) must first be prepared, and the chromium ore pellets are mechanically excellent in compressive strength and subsequent reduction. Excellent reducibility is required for rapid reduction in the furnace.

Accordingly, methods for improving the reducibility of carbonaceous mixture chromium ore pellets by adding solvents mainly to pellet blended raw materials are proposed, and representative methods include the addition of SiO ₂ sources and the addition of borate (Japan, iron and steel). 1986, Vol. 72, No. 10, page 33), addition of Fe-Ni smelting slag (Japanese Patent Publication No. 85-53731, method for preparing high-reducing chromium ore pellets) and serpentine rock [蛇 紋 岩, Mg ₃ Si ₂ O ₅ (OH) ₄ ] (Domestic Application No. 88-17833: Method for producing high-reducing chromium ore pellets). However, in the above method, borate and the like are expensive chemicals, and all other additives basically have SiO ₂ as one of the main components, and Fe-Ni smelting slag is generally not easily available. There is a problem.

Accordingly, the present invention is a raw material mixing step, that is, blending in the production of pre-reduced chromium ore pellets divided into raw material mixture-assembly (carbon mixture chrome ore pellets) -reduction (heating furnace) -product (pre-reduction chromium ore pellets) step. By appropriately improving the components and the range of ingredients of raw materials, the strength of the pellets in the granulation and reduction stages is improved and the reaction rate in the reduction stages is promoted to improve the metallization rate of the pre-reduced chrome ore pellets. There is a purpose.

Hereinafter, the present invention will be described in detail.

When smelting Fe-Cr in an electric furnace, the present inventors focus on slag gangue components in the charge by adding silica (SiO ₂ ) and limestone (CaCO ₃ as the main component) in addition to the pre-reduced chrome ore pellets. The present invention was proposed based on the results of adding various materials having CaO components as a raw material for pellets and examining the strength and reducibility of the pellets. The present invention provides a raw material for preparing pre-reduced chrome ore pellets. Chromium ore containing 30-40% by weight of T.Cr and 9-26% by weight of T.Fe: 75-85% by weight; Bentonite containing 60-70 wt% SiO ₂ and 10-25 wt% Al ₂ O ₃ : 2-5 wt%; Coke containing 80-95% by weight of fixed carbon: 10-20% by weight; And cement containing from 60% to 70% by weight of CaO, from 12-25% by weight of SiO ₂ , and up to 10% by weight of Al ₂ O ₃ : 0.8-6.0% by weight; And it relates to a compounding raw material for the production of pre-reduced chromium ore pellets, so that the amount of CaO in the compounding compound is 0.5-4.0% by weight.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The chromium ore is generally produced as a mixed ore in which a compound of FeCr ₂ O ₄ in which chromium (Cr) is mixed with iron (Fe) and gangue components such as MgO, SiO ₂ , and Al ₂ O ₃ are mixed. Ore with less than about 30% by weight of T.Cr (Total Cr) in chromium ore is used as a raw material for refractory, that is, chromite lead, and ore with T.Cr of about 30% by weight or more is used for steel making. .

In addition, iron (Fe) component is essential in chromium ore, and in order to efficiently smelt Fe-Cr alloy iron from chromium ore, it is required that the ratio of chromium content and iron content (Cr / Fe ratio) is 1.5 or more. In the case of high-quality chromium ores, the Cr / Fe ratio is about 3.5. The theoretical maximum content of chromium in chrome ore is 46% by weight, but the maximum content calculated in nature is about 40% by weight.

Thus, a chromium ore suitable for use in steelmaking has a chromium content (T.Cr wt%) of about 30-40 wt% and an iron content (T.Fe wt%) of about 9-26 wt%. Although bentonite is a clay mineral added as a caking agent, the composition of the bentonite is different depending on the region of the bentonite, but typically contains about 60-70 wt% of the SiO ₂ component and about 10-25 wt% of the Al ₂ O ₃ component. .

The coke is added as a reducing agent and usually contains about 80-95% by weight of fixed carbon. In the raw material for preparing pre-reduced chromium ore pellets, the chromium ore is usually 75-85% by weight, bentonite 2-5% by weight and coke 10-20% by weight. The cements in the present invention are conventional cements added as CaO sources, consisting of 60-70% by weight CaO, 15-25% by weight SiO ₂ , 10% by weight or less Al ₂ O ₃ and other impurities.

In the above, the amount of cement added in order to make the amount of CaO in the blended material is 0.5-4.0% by weight is more preferably 0.8-6.0% by weight, which is usually required in the present invention at 0.8% by weight or less. This is because the amount of CaO cannot be secured, and the amount of CaO becomes 4.0% by weight or more in the chemical composition of the pellet at 6.0% by weight or more.

When the amount of CaO is less than 0.5% by weight, there is no effect of adding CaO, and at 4.0% by weight or more, there is almost no effect of increasing the compressive strength and metallization rate. Therefore, considering the economical point, the amount of CaO is the upper limit of 4.0% by weight. It is desirable to maintain.

In the present invention configured as described above, the CaO or cement action to improve the metallization rate of the chromium ore pellets have not yet been identified, but in the case of cement CaO-SiO ₂ -Al ₂ by the moisture added in the raw material assembly step It is also assumed that the O ₃ compound forms a hydrate and the hydrate dehydrates and deforms the crystal lattice at a high temperature, thereby becoming a porous pellet that is relatively easy to reduce the reaction.

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

EXAMPLE

Various raw materials having the chemical composition shown in Table 1 were mixed at the ratio of Table 2 below to adjust the CaO analytical value in the pellet to 0-4.6% by weight while spraying 6-10% by weight of water in a disk granulator. The pellets were assembled into pellets of about 12 mm. Here, the mixing ratio of bentonite and coke was set at the level of normal operation (about 2-5 wt% of bentonite and about 10-20 wt% of coke), and the mixing ratio of CaO-containing material was 0-6.9 wt% of cement. It was. The mixing ratio at the time of using quicklime performed in Comparative Example F of Table 2 was 3.4% by weight, which was CaO content (3.4% by weight) in pellets at the same level as the invention example D, in which the amount of cement added was 5.1% by weight. In addition, the mixing ratio of the coke used in the manufacturing operation of the pre-reduced chrome ore pellets is usually in the range of 10-20% by weight. The mixing ratio of the coke added in the present embodiment is different from the metal oxides in the blending raw material, that is, iron oxide and chromium oxide components. It was set as 13.9-15 weight% which is 80 weight% of the stoichiometric amount of carbon used for complete reduction. The compressive strength (kg / pellet) of the carbonaceous mixture chromium ore pellets prepared from the blended raw materials as described above was measured by the method specified by Japanese Industrial Standard (JIS) M-8718, and the measurement results are shown in Table 3 below. .

TABLE 1

TABLE 2

TABLE 3

As shown in Table 3, Inventive Example BD with cement added in accordance with the present invention and Comparative Example E added in an amount greater than the range of the present invention, Comparative Example A without the addition of cement and Ca It can be seen that it has strength properties superior to Comparative Example F to be added.

In addition, the carbonaceous mixture chromium ore pellets prepared as described above were isothermally reduced in a horizontal tubular furnace of a nitrogen atmosphere containing SiC as a heating element, and the reducing conditions at this time were maintained at a predetermined temperature such as 1200, 1300, and 1400 ° C. while maintaining the nitrogen atmosphere. The pellets were charged in a preheated tubular furnace and allowed to react while maintaining the same temperature for 60 minutes, followed by chemical analysis of the pre-reduced pellets cooled in a nitrogen atmosphere to investigate the metallization rate, and the results are shown in FIG. . As shown in FIG. 1, in the case of Inventive Example BD and Comparative Examples E and F to which CaO-containing material was added, the metallization rate was remarkably improved compared to Comparative Example A without CaO-containing material. It can be seen that in the case of Inventive Example BD using a metallization rate higher than that of Comparative Example F using quicklime.

On the other hand, Comparative Example E having a cement addition amount of 6.9 wt% showed little increase in metallization rate compared to Inventive Example D having an cement addition amount of 5.1 wt%. Therefore, it can be seen that the upper limit of the amount of cement added to significantly improve the metallization rate is about 6.0 wt%, which corresponds to about 4.0 wt% of CaO in the chemical composition of the pellets. This effect shows almost the same effect in the case of ordinary ordinary cements-portland cement-and cement clinker.

In Table 3 and FIG. 1 of the above embodiment, when 1.7-5.1 wt% of the cement is added to the chromium ore pellet and the CaO composition is 1.2-3.4 wt% of the pellet, the cement is not added or the quicklime is added. In comparison, the compressive strength was greatly improved from 5.1-6.2kg / pellet to 6.4-38.1kg / pellet, and the metallization rate, which is the most important property of the pellet, was reduced from 15-34.5% to 60-69.2% when the reduction temperature was 1200 ℃. It can be seen that the metallization rate is significantly improved over the entire temperature range from 7 to 70.7% to 77.5-95% at 1300 ° C and from 84.4 to 96.7% at 1400 ° C.

Claims (1)

In the blended raw material for producing the pre-reduced chrome ore pellets, chromium ore containing 30-40 wt% T.Cr and 9-26 wt% T.Fe: 75-85 wt%; Bentonite containing 60-70 wt% SiO ₂ and 10-25 wt% Al ₂ O ₃ : 2-5 wt%; Coke containing 80-95% by weight of fixed carbon: 10-20% by weight; And cement containing from 60% to 70% by weight of CaO, from 12-25% by weight of SiO ₂ , and up to 10% by weight of Al ₂ O ₃ : 0.8-6.0% by weight; And a compound material for preparing pre-reduced chromium ore pellets, characterized in that the amount of CaO in the compounding material is 0.5-4.0% by weight.