How to smelt oxide ores

Abstract

To provide a method for smelting an oxide ore which can efficiently recover metal contained in the oxide ore.SOLUTION: A method for smelting an oxide ore includes: a mixing step of obtaining a mixture containing an oxide ore and a carbonaceous reducer; a drying step of drying the mixture by a drying furnace; and a reduction step of subjecting the mixture through the drying step to reduction treatment. The drying step charges the mixture into a treatment space using a drying furnace having a double structure of the treatment space and a gas distribution space positioned outside the treatment space as the drying furnace, distributes high temperature gas into the gas distribution space, and thereby subjects the mixture to drying treatment.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for dry smelting of oxide ores, and more particularly to a method for producing a metal as a reduced product by reducing an oxide ore, such as nickel oxide ore, as a raw material with a carbonaceous reducing agent. [Background technology]

[0002] Known methods for smelting nickel oxide ores called limonite or saprolite, which are a type of oxide ore, include a dry smelting method in which a smelting furnace is used to produce nickel matte, a dry smelting method in which a rotary kiln or a moving hearth furnace is used to produce ferronickel, an alloy of iron and nickel, and a hydrometallurgical method in which an autoclave is used to perform acid leaching at high temperature and pressure to produce a mixed sulfide containing nickel and cobalt (mixed sulfide).

[0003] Among the various methods described above, when nickel oxide ore is reduced and smelted using a pyrometallurgical method, a pretreatment process is carried out in which the raw material nickel oxide ore is crushed into agglomerates of an appropriate size to promote the reaction.

[0004] Specifically, when nickel oxide ore is agglomerated, that is, when powdery or finely granulated ore is agglomerated, the nickel oxide ore is generally mixed with other components, for example, a binder and a reducing agent such as coke, to form a mixture, which is then subjected to moisture adjustment and the like and then charged into an agglomeration machine to form agglomerates (which refer to pellets, briquettes, etc.; hereinafter simply referred to as "pellets") with a side or diameter of, for example, about 10 mm to 30 mm.

[0005] The pellets obtained by agglomeration need to have a certain degree of breathability in order to "evaporate" the moisture contained therein. Furthermore, if the reduction does not proceed uniformly within the pellets in the subsequent reduction treatment, the composition of the resulting reduced product will be non-uniform, resulting in problems such as metal dispersion or uneven distribution. Therefore, it is important to mix the mixture uniformly when producing the pellets, and to maintain as uniform a temperature as possible when reducing the resulting pellets.

[0006] In addition, it is also a very important technology to coarsen the metal (ferronickel) produced by the reduction treatment. If the produced ferronickel is fine, for example, with a size of several tens of μm to several hundreds of μm, it becomes difficult to separate it from the slag produced at the same time, and the recovery rate (yield) of ferronickel drops significantly. Therefore, a process to coarsen the ferronickel after reduction is necessary.

[0007] For example, Patent Document 1 discloses a technology aimed at proposing a technology for further increasing the productivity of granular metal when producing granular metal by heating an agglomerate containing a metal oxide and a carbonaceous reducing agent to reduce and melt the metal oxide contained in the agglomerate.

[0008] Specifically, the method for producing granular metals includes supplying agglomerates containing a metal oxide and a carbonaceous reducing agent onto the hearth of a moving-bed type reduction melting furnace, heating the agglomerates to reduce and melt the metal oxide, and then cooling and discharging the resulting granular metals outside the furnace for recovery. In the heating, the furnace temperature in the front half of the furnace where the iron oxide in the agglomerates is solid-reduced is set to 1300-1450°C, and the furnace temperature in the rear half of the furnace where the reduced iron in the agglomerates is carburized, melted and agglomerated is set to 1400-1550°C. When the relative value of the projected area ratio of the agglomerates spread on the hearth to the maximum projected area ratio of the agglomerates spread on the hearth when the distance between the agglomerates spread on the hearth is set to 0 is set as the spread density, the agglomerates having an average diameter of 19.5 mm to 32 mm are supplied onto the hearth at a spread density of 0.5 to 0.8 during heating.

[0009] Patent Document 1 also shows that the productivity of granular metallic iron can be improved by controlling both the laying density and the average diameter of the agglomerates.

[0010] However, the technology described in Patent Document 1 is only related to the reaction on the outer surface of the agglomerate, and it goes without saying that the most important factor in the reduction reaction is the state inside the agglomerate where the reduction reaction occurs. In other words, it is believed that by controlling the reduction reaction inside the agglomerate, it is possible to realize a more efficient and uniform reduction reaction, which results in the production of high-quality metal.

[0011] Furthermore, if the diameter of the agglomerates is limited to a fixed range as in the technology described in Patent Document 1, a decrease in the yield when manufacturing the agglomerates is unavoidable, which may result in an increase in costs. In addition, if the laying density of the agglomerates is in the range of 0.5 to 0.8, the agglomerates are not densely packed and it is difficult to stack them, resulting in a low-efficiency process.

[0012] As described above, in the production of a metal containing nickel and iron by mixing and reducing nickel oxide ores, although increasing productivity, reducing costs, and improving quality are important factors, there have been many problems. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2011-256414 A Summary of the Invention [Problem to be solved by the invention]

[0014] The present invention has been proposed in view of the above circumstances, and has an object to provide a method for smelting oxide ores that can efficiently produce high-quality metals. [Means for solving the problem]

[0015] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by subjecting a mixture containing an oxide ore and a carbonaceous reducing agent to a drying treatment in a double-walled drying furnace prior to subjecting the mixture to a reduction treatment in the reduction step, and have thus completed the present invention.

[0016] (1) The first aspect of the present invention includes a mixing step for obtaining a mixture containing an oxide ore and a carbonaceous reducing agent; This method for smelting oxide ores includes a drying process in which the mixture is dried using a drying furnace, and a reduction process in which the mixture that has undergone the drying process is reduced. In the drying process, a dual-structure drying furnace having a treatment space and a gas circulation space located outside the treatment space is used as the drying furnace, and the mixture is charged into the treatment space and dried by circulating high-temperature gas through the gas circulation space.

[0017] (2) A second aspect of the present invention is a method for smelting an oxide ore, comprising the steps of: (a) drying the mixture by using a part of the atmospheric gas after the reduction treatment in the reduction step as the high-temperature gas in the drying step in the first aspect of the invention.

[0018] (3) A third aspect of the present invention is a method for smelting oxide ore according to the first or second invention, wherein the drying furnace has a charging port for charging the mixture into the treatment space and a discharge port for discharging the mixture that has been dried in the treatment space, and in the drying step, the high-temperature gas is circulated through the gas circulation space in a countercurrent direction to the flow direction of the mixture moving from the charging port to the discharge port to perform the drying process.

[0019] (4) A fourth aspect of the present invention is a method for smelting an oxide ore according to any one of the first to third aspects of the present invention, wherein in the drying step, a high-temperature gas having a temperature of 300°C or more and 1000°C or less is circulated to dry the mixture.

[0020] (5) A fifth aspect of the present invention is a method for smelting an oxide ore, in which, in the reduction step, a mixture that has been subjected to the drying step is subjected to a reduction treatment to obtain a molten material, in the invention described in any one of the first to fourth aspects.

[0021] (6) A sixth aspect of the present invention is a method for smelting an oxide ore according to any one of the first to fifth aspects of the present invention, wherein the oxide ore is a nickel oxide ore, and in the reduction step, ferronickel is obtained by subjecting the mixture to a reduction treatment. Effect of the Invention

[0022] According to the method for smelting oxide ore of the present invention, high-quality metal can be efficiently produced. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a process diagram showing an example of the flow of a method for smelting nickel oxide ore. [Diagram 2] FIG. 2 is a schematic diagram showing an example of the configuration of a drying furnace, and is a diagram for explaining the state of drying processing in the drying furnace. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will be described in detail below, but the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the present invention. In addition, in this specification, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less."

[0025] 1. Overview of the Invention The present invention relates to a method for smelting an oxide ore, for example, nickel oxide ore, which is a raw material, and which produces a metal as a reduced product by mixing the oxide ore with a carbonaceous reducing agent and reducing the resulting mixture. For example, when nickel oxide ore is used as the raw material ore, ferro-nickel metal, an alloy of iron and nickel, is produced as the reduced product.

[0026] Specifically, the method for smelting an oxide ore according to the present invention is characterized in that a mixture containing an oxide ore and a carbonaceous reducing agent is charged into a treatment space of a double-structure drying furnace, and a high-temperature gas is circulated through a gas circulation space located outside the treatment space to dry the mixture.

[0027] According to this method, the generation of dust during the drying process can be suppressed, and high-quality metal can be efficiently produced.

[0028] 2. Nickel oxide ore smelting method Hereinafter, as a specific embodiment of the present invention (hereinafter referred to as "the present embodiment"), a smelting method will be described as an example in which nickel oxide ore is used as a raw ore, nickel (nickel oxide) and iron (iron oxide) contained in the nickel oxide ore are subjected to a reduction treatment to generate a melt of an iron-nickel alloy (ferronickel), and further, metal is separated from the melt to produce ferronickel.

[0029] When a melt is obtained by subjecting a mixture to a reduction treatment, effective reduction can be achieved in a short treatment time, but the mixture is usually dried without being molded into pellets, which makes it relatively easy for dust to be generated during the drying treatment. Although it is not essential to obtain a melt by subjecting the mixture to a reduction treatment in the present invention, by charging the mixture into a double-walled drying furnace and circulating high-temperature gas through a gas circulation space located outside the treatment space, it becomes possible to effectively suppress the generation of dust during the drying treatment, which is likely to be a problem when a melt is obtained by subjecting a mixture to a reduction treatment.

[0030] Fig. 1 is a process diagram showing an example of the flow of a method for smelting nickel oxide ore according to the present embodiment. As shown in Fig. 1, the method for smelting nickel oxide ore includes a mixing step S1 for mixing nickel oxide ore with a carbonaceous reducing agent to obtain a mixture, a drying step S2 for subjecting the mixture to a drying treatment in a drying furnace, a reduction step S3 for subjecting the mixture that has been through the drying step S2 to a reduction treatment, and a recovery step S4 for separating the obtained reduction products, that is, metal and slag, to recover the metal.

[0031] [Mixing process] The mixing step S1 is a step of mixing raw material powders including nickel oxide ore to obtain a mixture. Specifically, in the mixing step S1, the raw material ore, nickel oxide ore, is mixed with a carbonaceous reducing agent, and powders having a particle size of, for example, about 0.1 mm to 0.8 mm, such as iron ore, flux components, and binders, are mixed as optional additives to obtain a mixture.

[0032] The mixing can be performed by adding a predetermined amount of water. By adding water and mixing, the mixability of the raw material powder can be improved. The mixing process can be performed using a known mixer or the like.

[0033] In the mixing step S1, the raw material powders are mixed and may be kneaded to improve mixability. By kneading, a shear force is applied to the mixture obtained by mixing the raw material powders, which can break up the agglomerations of the raw material ores, carbon reducing agent, etc., allowing for more uniform mixing and reducing the gaps between each particle, making it possible to cause a uniform reaction when subjected to reduction treatment. Note that kneading can be performed using a twin-screw kneader or the like.

[0034] Here, the nickel oxide ore as the raw material ore is not particularly limited, but limonite ore, saprolite ore, etc. can be used. Nickel oxide ore is composed of nickel oxide (NiO) and iron oxide (Fe 2 O 3 ) and contains.

[0035] When using nickel oxide ore, it may be classified into a predetermined size, crushed, etc. By performing classification, crushing, etc., it is possible to make the particle size uniform to a certain extent, and by eliminating ore of a large size by crushing, etc., it is possible to improve the mixability with a carbonaceous reducing agent, etc., and to improve the uniformity during the reduction treatment.

[0036] The carbonaceous reducing agent is not particularly limited, but examples thereof include coal powder, coke powder, etc. The carbonaceous reducing agent is preferably one having a particle size equivalent to that of the nickel oxide ore, which is the raw material ore described above. This can increase the mixability with the nickel oxide ore and improve the uniformity during the reduction treatment.

[0037] The amount of the carbonaceous reducing agent mixed is preferably 80% by mass or less, and more preferably 60% by mass or less, when the amount of the carbonaceous reducing agent required to reduce the nickel oxide and iron oxide constituting the nickel oxide ore without excess or deficiency is taken as 100% by mass. By setting the amount of the carbonaceous reducing agent mixed to 80% by mass or less with respect to the total value of the chemical equivalents of 100% by mass, the reduction reaction can be efficiently promoted. In addition, the lower limit of the amount of the carbonaceous reducing agent mixed is not particularly limited, but is preferably 15% by mass or more, and more preferably 20% by mass or more with respect to the total value of the chemical equivalents of 100% by mass.

[0038] The amount of carbonaceous reducing agent necessary to reduce nickel oxide and iron oxide without excess or deficiency can be rephrased as the total value of the chemical equivalent necessary to reduce all of the nickel oxide to nickel metal and the chemical equivalent necessary to reduce the iron oxide to iron metal (hereinafter also referred to as the "total value of chemical equivalents").

[0039] The iron ore, which is an optional additive, is not particularly limited, but for example, iron ore with an iron content of about 50 mass % or more, hematite obtained by hydrometallurgy of nickel oxide ore, etc. can be used.

[0040] Examples of the binder include bentonite, polysaccharides, resin, water glass, dehydrated cake, etc. Examples of the flux component include calcium oxide, calcium hydroxide, calcium carbonate, silicon dioxide, etc.

[0041] Table 1 below shows an example of the composition (wt %) of some of the raw material powders mixed in the mixing step S1, but the composition of the raw material powders is not limited to this.

[0042] [Table 1]

[0043] [Drying process] The drying step S2 is a step of drying the mixture in a drying oven, which makes it possible to suppress oxidation due to moisture contained in the mixture in the reduction step S3 described below, and to improve the quality of the obtained metal.

[0044] The drying step S2 is characterized in that the mixture M is dried in a double-layered drying furnace 10. An example of a double-layered drying furnace is a cylindrical double-layered drying furnace 10 including a treatment space A having an inlet 11 for charging the mixture M and an outlet 12 for discharging the mixture M, and a gas flow space G located outside the treatment space A, as shown in Fig. 2. Note that the cylindrical double-layered drying furnace 10 shown in Fig. 2 is an example of a double-layered drying furnace, and is not limited to the cylindrical drying furnace 10.

[0045] When the mixture M is dried in this drying furnace 10, first, the mixture M is charged into the treatment space A from the charging port 11. Then, high-temperature gas is circulated through the gas circulation space G located outside the treatment space A, thereby transferring heat to the treatment space A and drying the mixture M in the treatment space A. The mixture M that has been dried is then discharged from the discharge port 12. In this manner, the mixture M is passed through the treatment space A of the cylindrical drying furnace 10, and moved in the direction D1 from the charging port 11 to the discharge port 12.

[0046] For example, when drying is performed using an internally heated drying furnace equipped with a burner inside, such as an internally heated kiln, combustion gas is generated due to the flame of the burner, and nickel oxide ore dust (fine powder) is discharged outside the furnace as exhaust gas together with the combustion gas, resulting in a decrease in metal recovery rate. Furthermore, moisture generated when the fuel is burned may remain in the combustion gas, resulting in insufficient drying of the mixture.

[0047] In addition, when high-temperature gas is circulated within the treatment space of the drying furnace, nickel oxide ore dust (fine powder) is also discharged to the outside of the furnace as exhaust gas.

[0048] Therefore, by using a double-layered drying furnace 10 as the drying furnace and circulating high-temperature gas through the gas circulation space G located outside the treatment space A, it is possible to effectively perform a drying process on the mixture M while effectively preventing nickel oxide ore dust (fine powder) from being discharged outside the furnace.

[0049] Furthermore, since the drying furnace 10 has a double structure, the combustion gas does not circulate inside the treatment space A, so that the drying treatment of the mixture M is not insufficient due to the moisture contained in the combustion gas, and the drying treatment can be performed effectively.

[0050] Specifically, the mixture M can be dried so that the moisture content of the mixture is 10% by mass or less. It is more preferable that the mixture M be dried so that the moisture content of the mixture is 8% by mass or less, and even more preferable that the mixture M be dried so that the moisture content of the mixture is 5% by mass or less.

[0051] From the viewpoint of preventing moisture from entering the reduction furnace, it is preferable that the moisture content of the mixture is as low as possible. Although the lower limit of the moisture content of the mixture is not particularly limited, for example, if the moisture content of the mixture is 1 mass % or more, nickel oxide ore dust is further prevented from scattering.

[0052] Furthermore, when drying is performed using an externally heated drying oven, heat dissipates to the surrounding areas other than the drying oven, reducing energy efficiency, but by circulating high-temperature gas through the gas circulation space to dry the mixture, it is possible to perform the drying process with high thermal efficiency. Moreover, if a means of circulating high-temperature gas is used, it is possible to suppress uneven distribution of heat inside the drying oven, which is also advantageous in terms of equipment life.

[0053] Furthermore, in the case of a method for drying the mixture by circulating high-temperature gas, it is sufficient to provide a single heat source such as a burner for heating the gas, and therefore the equipment can be simplified compared to an external combustion drying furnace equipped with multiple burners as heating means.

[0054] The flow direction of the high-temperature gas in the gas flow space G is not particularly limited. Among them, it is preferable to dry the mixture M by flowing it in the direction D2 counter to the direction D1 in which the mixture M moves (i.e., the opposite direction to the direction in which the mixture moves). When the high-temperature gas is flowed in the gas flow space G, the inlet 13 of the high-temperature gas becomes hot, and the outlet 14 of the high-temperature gas becomes relatively cold. Therefore, by flowing the high-temperature gas in the direction D2 counter to the direction D1 in which the mixture M moves, the outlet 14 of the high-temperature gas, which becomes the coldest, is located at the inlet 11 of the mixture M. This allows the mixture M to be gradually heated as it moves from the inlet 11 to the outlet 12 in the treatment space A, and the mixture M can be heated slowly, so that the rupture of the mixture M due to the mixture M being suddenly heated can be effectively suppressed.

[0055] For example, combustion gas of a flame ejected from a burner can be used as the high-temperature gas flowing through the gas flow space G. When performing the drying treatment using a burner, the fuel may be a conventionally known fuel such as LPG gas (liquefied petroleum gas), LNG gas (natural gas), heavy oil, coal, coke, or pulverized coal.

[0056] In addition, when drying the mixture M using the drying furnace 10 with a double structure, it is preferable to perform the treatment by applying a negative pressure to the inside of the treatment space A. This makes it possible to more effectively prevent nickel oxide ore dust (fine powder) from being discharged outside the furnace. Specifically, it is preferable to perform the drying treatment by controlling the furnace pressure to be in the range of -3 Pa to -100 Pa, preferably -10 Pa to -70 Pa.

[0057] Also, a part of the atmospheric gas after the reduction treatment in the reduction step S3 described later may be used as high-temperature gas to dry the mixture M. Specifically, a gas circulation space G of a drying furnace in which the drying treatment is performed and a reduction furnace in which the reduction treatment is performed are connected by piping, and the atmospheric gas of the reduction furnace is introduced into the gas circulation space and used as the drying gas in the drying treatment. This allows the atmospheric gas after the reduction treatment to be reused as the drying gas instead of being entirely discharged, thereby making it possible to carry out a smelting operation with even further reduced costs.

[0058] The temperature of the high-temperature gas is not particularly limited, but is preferably, for example, from 300° C. to 1000° C. By passing high-temperature gas at a temperature of from 300° C. to 1000° C. through the mixture to perform a drying treatment, the mixture can be effectively dried.

[0059] The drying temperature (temperature in the processing space of the drying furnace) is not particularly limited, but it is preferable to subject the mixture to a drying process at, for example, 180° C. to 400° C. The drying temperature (temperature in the processing space of the drying furnace) can be controlled by adjusting the temperature of the high-temperature gas or, for example, the size of the gas outlet 14 of the gas flow space G.

[0060] An example of the composition (parts by weight) of the solid content in the mixture after drying is shown in the following Table 2. However, the composition of the mixture is not limited to this. [Table 2]

[0061] <3. Reduction process> The reduction step S3 is a step in which the dried mixture is heated and reduced to obtain a reduced product containing metal and slag. The heating and reduction treatment in the reduction step S3 causes a smelting reaction (reduction reaction) to proceed, and ferronickel metal (hereinafter simply referred to as "metal") and ferronickel slag (hereinafter simply referred to as "slag") are generated separately.

[0062] In the reduction step S3, the reduction reaction of the nickel oxide ore gradually progresses as the mixture containing the nickel oxide ore is heated by a burner in a reduction furnace, and the reduction reaction also occurs in the solid state before the mixture becomes molten. In the burner furnace, as the reduction reaction of the nickel oxide ore progresses, the mixture gradually changes from a solid state to a liquid state, i.e., a molten state, due to the heat from the burner, and finally, molten metal and slag are obtained as a result of the heating and reduction treatment by the burner.

[0063] The metal and slag obtained by melt reduction are separated due to the difference in specific gravity. Specifically, the metal with a higher specific gravity is separated so as to be formed in a lower layer than the slag. When the molten metal is piled up below the slag in this way, even if the partial pressure of oxygen or the partial pressure of CO in the furnace atmosphere fluctuates, the effect on the composition of the metal accumulated at the bottom of the furnace below the slag can be suppressed, and the oxidation of the metal can be effectively suppressed.

[0064] The heat source of the reducing furnace is not particularly limited, and may be an electric heater or a burner. Among these, the reducing furnace is preferably a burner furnace equipped with a burner. Treatment can be performed at a significantly lower cost than heating using electricity or the like, and economic efficiency can also be improved. Furthermore, in a burner furnace, maintenance is very easy, continuous operation can be effectively performed, and operation efficiency can be improved.

[0065] [Recovery process] The recovery step S4 is a step of separating the metal and slag obtained by reduction and recovering the metal. As described above, in the reduction process in the reduction step S3, the mixture is reduced in a molten state, so that molten metal and molten slag are generated. Since the metal has a larger specific gravity than the slag and is heavier, they naturally separate due to the difference in specific gravity, and the metal accumulates at the bottom of the reduction furnace. Therefore, by removing and recovering the metal from near the bottom of the reduction furnace, it is possible to selectively recover only the metal. On the other hand, since the slag floats on top of the metal, it can be removed from, for example, the furnace wall and recovered. In this way, since the obtained metal and slag are in a molten state, they can be easily separated and recovered due to the difference in specific gravity.

[0066] Alternatively, the metal and slag may be collected in a mixed state from one hole in the reduction furnace. In this way, the structure of the reduction furnace can be simplified and the workability can be improved. When the metal and slag are extracted in a mixed state from one hole, the collected metal and slag are cooled and solidified, and then separated by magnetic separation or the like, so that the metal can be collected. Note that since the metal and slag are already separated when they are in a molten state, the metal and slag basically remain separated even in the solid state, and the metal can be easily collected by a method such as magnetic separation.

[0067] Since the metal and slag are already separated when in a molten state, they basically remain separated even in a solid state, and the metal can be easily recovered by methods such as magnetic separation.

[0068] By easily separating the metal and slag in this way, the metal can be recovered at a high rate. EXAMPLES

[0069] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0070] Examples and Comparative Examples (Mixing process) The raw material ore, nickel oxide ore, iron ore, flux components, silica sand and limestone, binder, and carbonaceous reductant (coal powder, carbon content: 80 mass%, average particle size: about 75 μm) were mixed in a mixer while adding an appropriate amount of water to obtain a mixture. The carbonaceous reductant was made of nickel oxide (NiO) and iron oxide (Fe 2 O 3 ) was contained in an amount of 32% by mass, assuming that the amount necessary for reducing them exactly is 100% by mass.

[0071] (drying process) The mixtures of Examples 1 to 9 were dried in a double-structure drying furnace as shown in FIG. 2. Specifically, the mixtures of Examples 1 to 9 were charged into the treatment space from the charging port without being molded, and were dried for 1 hour. The mixtures were then discharged from the discharge port. At this time, the combustion gas of a flame ejected from a burner using the fuels shown in the table below was used as the high-temperature gas, and the high-temperature gas was circulated in the gas circulation space in a direction countercurrent to the direction in which the mixture moved. The temperature of the high-temperature gas at this time is shown in Table 3.

[0072] On the other hand, the mixtures of Comparative Examples 1 to 3 were subjected to a drying treatment in an internal combustion drying furnace (internal heat kiln) equipped with an internal burner.

[0073] (Dust generation rate and moisture rate) The dust that flowed out of the drying oven together with the exhaust gas during drying for each sample was collected by a dust collector, and the dust generation rate was calculated from the amount of mixture charged. In addition, the moisture content of the mixture after drying was measured.

[0074] [Table 3]

[0075] As shown in the results of Table 3, in Examples 1 to 9 in which the reduction treatment was performed using a double-structure drying furnace, the dust generation rate was low at 3.0% or less, and good results were obtained. For example, when the temperature inside the drying furnace was set to 300°C, in Examples 2, 5, and 8 in which the reduction treatment was performed using a double-structure drying furnace, the dust generation rate was 2.1% on average, whereas in Comparative Examples 1 to 3 in which the drying treatment was performed using an internal combustion drying furnace (internal heat kiln), the dust generation rate was 21.7% on average, showing a significant difference even when the temperature inside the drying furnace was the same. From these results, it is inferred that the method for smelting oxide ores of the present invention in which the mixture is dried using a double-structure drying furnace can improve the metal recovery rate.

[0076] In addition, in Examples 1 to 9 in which the reduction treatment was performed using a double-structure drying furnace, the moisture content of the mixture was 9.6% or less. For example, when the temperature inside the drying furnace was set to 300°C, the moisture content of the mixture was 5.6% on average in Examples 2, 5, and 8 in which the reduction treatment was performed using a double-structure drying furnace, whereas the moisture content of the mixture was 11.0% on average in Comparative Examples 1 to 3 in which the drying treatment was performed using an internal combustion drying furnace (internal heat kiln), and a significant difference was observed even when the temperature inside the drying furnace was the same. From this result, the moisture content of the mixture after drying was sufficiently low and good results were obtained in the smelting method of oxide ore of the present invention in which the mixture is dried in a double-structure drying furnace and reduced, and it is therefore presumed that the smelting method of oxide ore of the present invention in which the mixture is dried in a double-structure drying furnace and reduced can suppress oxidation due to the moisture contained in the mixture in the reduction step, improve the grade of the obtained metal, and produce a higher quality metal. [Explanation of symbols]

[0077] 10. Double-layered drying oven 11 Charging port 12 Outlet 13 Gas inlet 14 Gas outlet A Processing Space G Gas distribution space D1 Mixture movement direction D2 Flow direction of hot gas

Claims

1. A method for producing a nickel oxide ore, comprising the steps of: obtaining a mixture comprising a nickel oxide ore and a carbonaceous reductant; a drying step of subjecting the mixture to a drying treatment in a drying oven; A reduction step of obtaining ferronickel metal by subjecting the mixture that has been subjected to the drying step to a reduction treatment, In the drying step, As the drying furnace, a drying furnace having a double structure including a treatment space and a gas circulation space located outside the treatment space is used, The mixture is charged into the treatment space, and a high-temperature gas is circulated through the gas circulation space to perform a drying treatment on the mixture; The drying furnace has an inlet through which the mixture is charged into the treatment space, and an outlet through which the mixture that has been dried in the treatment space is discharged, In the drying step, the high-temperature gas is circulated through the gas circulation space in a countercurrent direction to the flow direction of the mixture moving from the inlet to the outlet, thereby obtaining a mixture having a moisture content of 10% by mass or less. A method for smelting nickel oxide ores.

2. A part of the atmospheric gas after the reduction treatment in the reduction step is used as the high-temperature gas in the drying step to perform a drying treatment on the mixture.

2. The method for smelting nickel oxide ore according to claim 1.

3. In the drying step, a high-temperature gas having a temperature of 300° C. or more and 1000° C. or less is circulated to dry the mixture.

3. A method for smelting nickel oxide ore according to claim 1 or 2.

4. In the reduction step, a molten material is obtained by subjecting the mixture that has been subjected to the drying step to a reduction treatment. A method for smelting nickel oxide ore according to any one of claims 1 to 3.

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