Method for producing granular metal

Abstract

A method for making metal nuggets comprises heating a material containing a metal-oxide-containing substance and a carbonaceous reductant to reduce metal oxide in the material and then further heating the produced metal so as to melt the metal while allowing the metal to separate from a by-product slag component and to form granular iron. A cohesion accelerator for the by-product slag is mixed into the material to produce metal nuggets having a high metal purity, a large diameter, and superior transportation and handling qualities at a high yield and high productivity.

Description

[0001] The present invention relates to methods for manufacturing metal nuggets. In particular, the present invention relates to an improved method for manufacturing high-purity metal nuggets such as iron nuggets that have a large diameter and superior transportation and handling qualities, the method including heating a mixture of a metal-oxide-containing substance and a carbonaceous reductant to reduce the metal oxide, in which an auxiliary material for increasing the fluidity of and promoting the cohesion of molten by-product slag is added to the material. The improved method achieves a high yield and high productivity.[0002] This specification mainly describes a method for manufacturing iron nuggets to which the present invention is most effectively applied. However, the present invention is not limited to the manufacturing of iron nuggets. The present invention can also be effectively applied to the manufacture of ferrochromium or ferronickel by heating and reducing chromium-co...

AI Technical Summary

Benefits of technology

0039] Another effect of using the cohesion accelerator is as follows.

0040] Since the cohesion property of the molten metallic iron is increased as described above, the rate of large metallic iron nuggets in the resulting metallic iron nuggets increases. The generation of micro particles of metallic iron, which are difficult to separate, and the generation of inseparable metallic iron nuggets enclosing slag resulting from cohesion of the molten metallic iron when the molten metallic iron is not adequately separated from the by-product slag, can be prevented as much as is feasibly possible. Accordingly, when the metallic iron nuggets and the by-product slag are discharged from a reduction melting furnace such as a rotary hearth furnace, micro metallic iron particles, slag, and the mixtures of metallic iron nuggets and slag that pass through the clearance of a discharger such as a screw or a scraper and the hearth surface do not return again to the heating zone of the furnace. Moreover, the micro metallic iron particles, slag, and the mixtures of metallic iron nuggets and slag can be prevented from being pressed into a hearth protecting layer, hearth refractories, or a bedding layer on the hearth. These effects prevent damage such as infiltration and erosion of the hearth refractories by the micro metallic iron particles, slag, and the mixtures of the metallic iron particles and the slag, and deterioration and enlargement of the hearth refractories resulting from severe heat cycles. Accordingly, the life of the hearth refractories can be prolonged, a problem of blockage of the product discharge section can be resolved, and long-term continuous operation can be reliably performed.

0041] When the fluidity of the by-product slag is improved by using the cohesion accelerator, the carburization reaction of the metallic iron during the heating and reducing stage is promoted, thereby also accelerating the melting of the by-product slag, and the time taken to reduce and melt the material is shortened. Since the fluidity of the by-product slag is increased, the rate at which the molten metallic iron and molten slag grow into iron nuggets also increases. As a result, the time from the beginning of melting the metallic iron prepared by solid reduction to the completion of the formation of molten metallic iron nuggets can be shortened, in addition to the above-described reduction in the time required for reduction melting. Thus, productivity can be dramatically improved while maintaining a high yield of high-purity, large metallic iron nuggets.

0042] Any type of cohesion accelerator can be suitably used in the present invention as long as the above-described effects and advantages can be achieved. However, a cohesion accelerator that enters the reduced metal and decreases the purity of, for example, reduced iron, should be avoided. A cohesion accelerator which combines with slag components and readily separates from the metallic iron is preferably selected. Preferable examples of the cohesion accelerators include calcium fluoride (CaF.sub.2), boron oxide (B.sub.2O.sub.5), sodium carbonate (Na.sub.2CO.sub.3) and sodium oxide (Na.sub.2O). These components may be used alone or in combination, if necessary. Among these components, CaF.sub.2, and more particularly, fluorite containing CaF.sub.2 as the primary component, is particularly preferable in view of cost and cohesion acceleration effects.

0043] Among these components, sodium carbonate (Na.sub.2CO.sub.3) and sodium oxide (Na.sub.2O) are preferable when coal powder or coke powder is used as the carbonaceous reductant, since sodium carbonate and sodium oxide capture the sulfur component derived from these carbonaceous reductants. As a result, the sulfur content in the resulting metal nuggets can be reduced.

0044] No limit is imposed as to the amount of the cohesion accelerator. The cohesion accelerator does not exhibit sufficient effects when the amount of the cohesion accelerator is insufficient. The effects of promoting cohesion are saturated at an excessive amount of cohesion accelerator. Thus, an excessive amount of the cohesion accelerator is not economical and increases the cost of processing an increased amount of by-product slag. In view of the above, the content of the cohesion accelerator is preferably in the range of 0.2 to 2.5%, and more preferably, 0.4 to 2.0%, of the material. The content of the cohesion accelerator based on the slag component in the material is preferably in the range of 1 to 11%, and more preferably, 3 to 8%.

Problems solved by technology

However, a large degree of limitation is imposed as to the types of the applicable carbonaceous reductant.

In these cases, the amount of by-product slag increases, and the degradation of the cohesion property of the slag is inevitable, which is a problem.

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