Method for smelting nickel-containing oxide ore

Abstract

Provided is a method for smelting a nickel-containing oxide ore with which the amount of CO2 generated is reduced and the nickel recovery rate is high.　The present invention is a method for smelting a nickel-containing oxide ore, the method comprising: a step for using a tubular reaction vessel, introducing a raw material that contains a nickel-containing oxide ore so as to move from above to below within the reaction vessel, and supplying a hydrogen-containing gas as a reducing agent to the raw material from below and from the side to perform a reduction treatment; a step for performing a melting treatment on the reduction product obtained using the reduction treatment; and a step for separating the slag from the melt obtained using the melting treatment and recovering a nickel-containing metal. The gas supplied from below to the raw material is supplied at room temperature. The gas supplied from the side to the raw material is at a temperature of 300°C or higher and is supplied from the side at a position above the position where the raw material for which the reduction treatment has been completed is stored.

Description

Method for smelting nickel-containing oxide ore

[0001] The present invention relates to a method for smelting a nickel-containing oxide ore (nickel-containing oxide ore).

[0002] To address the issue of climate change, the Paris Agreement was adopted at COP21 in 2015, which committed each country to making every effort to keep the global average temperature below 2°C above pre-industrial levels. In 2021, the Sixth Assessment Report of the IPCC (Intergovernmental Panel on Climate Change) stated that "there is no doubt that human influences have warmed the atmosphere, oceans, and land," and subsequently at COP26 it was agreed that "we resolve to pursue efforts to limit the rise in global average temperature to 1.5°C above pre-industrial levels."

[0003] Amid these international trends, the Japanese government set a target in 2016 of "reducing greenhouse gas emissions by 26% by 2030 compared to 1990 levels, and by 80% by 2050," and further set new targets in 2020 of "net-zero emissions by 2050" and by 2021 of "reducing emissions by 46% by 2030 compared to 2013 levels." The movement to reduce greenhouse gas emissions is accelerating in Japan as well.

[0004] The non-ferrous smelting industry is also being called upon to reduce emissions in line with targets and to switch to carbon-neutral processes by 2050, and new processes that use less energy and fossil fuels are being developed.

[0005] For example, the Elkem process is currently mainstream in the ferronickel smelting industry. The Elkem process is a process in which saprolite ore containing nickel oxide is pre-dried in a rotary kiln-type dryer, and then dehydrated to the water of crystallization while gradually increasing the temperature in the rotary kiln, after which the trivalent iron present in the ore is reduced to divalent iron, and then almost all of the nickel and some of the iron are reduced to metal in an electric furnace to obtain an alloy. However, in the Elkem process, fossil fuel burners such as pulverized coal and heavy oil are used in the pre-drying step with the dryer and the reduction step with the rotary kiln, and coal is used as a reducing agent and heat source, which results in the emission of large amounts of CO ２ CO ２ The amount generated is approximately 22.4 tCO ２ / tNi.

[0006] Such CO ２ Reduction with hydrogen is considered as a measure to reduce the amount of nickel generated. It is known that nickel oxide alone can be easily reduced by hydrogen to become metal. However, in the hydrogen reduction of nickel in nickel-containing oxide ores such as saprolite and limonite, the reduction degree is about 10% to 70%, which is significantly lower than the 95% or more achieved by the Elkem process. This is because nickel is in the olivine phase ((Mg,Fe) ２ SiO ４ ) and Magnesiowustite phase ((Mg,Fe)O), and has low activity. Therefore, simply reducing it with hydrogen results in a low nickel recovery rate, making it unfeasible for industrial use.

[0007] The addition of sodium compounds has been proposed as a way to improve the nickel recovery rate during hydrogen reduction, but the amount of compound added is enormous, and the chemical costs are too high to be commercially viable.

[0008] Patent Document 1 discloses a method for producing reduced iron by reducing iron oxide charged into a shaft furnace. Specifically, the method shows a method for reducing iron oxide by blowing a heated mixed gas containing a reducing gas containing 90% by volume or more of hydrogen gas and nitrogen gas into a shaft furnace. However, as mentioned above, in the hydrogen reduction of nickel, the reduction degree is about 10% to 70%, which is significantly lower than the 95% or more achieved by the conventional Elkem process. CO in the smelting of nickel-containing oxide ore ２ The application of hydrogen reduction to reduce the amount of nickel generated is difficult, and there is a need to develop a method that can achieve a high nickel recovery rate even when hydrogen reduction is applied and is cost-effective on an industrial scale.

[0009] International Publication No. 2021 / 230307

[0010] The present invention has been proposed in view of the above circumstances, and ２ The object of the present invention is to provide a method for smelting nickel-containing oxide ore that reduces the amount of nickel generated and has a high nickel recovery rate.

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the reduction rate of nickel can be improved and nickel can be recovered at a high recovery rate by using a tubular reaction vessel, charging raw materials containing nickel-containing oxide ore so that they move from top to bottom, supplying a gas containing hydrogen as a reducing agent to the raw materials from below and from the side at a predetermined gas temperature, and then subjecting the resulting reduced product to a melting treatment, thereby achieving the present invention.

[0012] (1) A first aspect of the present invention is a method for smelting a nickel-containing oxide ore, the method comprising the steps of: using a tubular reaction vessel, charging raw materials containing the nickel-containing oxide ore so that they move from above to below within the reaction vessel, and supplying a gas containing hydrogen as a reducing agent to the raw materials from below and from the side to perform a reduction treatment; melting a reduced product obtained by the reduction treatment; and separating slag from the molten product obtained by the melting treatment to recover a metal containing nickel; the gas supplied from below to the raw materials is supplied at room temperature, and the gas supplied from the side to the raw materials has a temperature of 300°C or higher and is supplied from the side at a position above a position where the raw materials that have been reduced are stored.

[0013] (2) A second aspect of the present invention is the method for smelting a nickel-containing oxide ore according to the first aspect, wherein the nickel-containing oxide ore has an iron content of 5% by mass or more and 30% by mass or less.

[0014] (3) A third aspect of the present invention is the method for smelting a nickel-containing oxide ore according to the first or second aspect, further comprising a step of pelletizing a raw material containing the nickel-containing oxide ore, and subjecting the pelletized raw material to the step of performing the reduction treatment.

[0015] (4) A fourth aspect of the present invention is a method for smelting a nickel-containing oxide ore according to any one of the first to third aspects, further comprising a step of heat-treating a raw material containing the nickel-containing oxide ore at a temperature of 300°C or higher and 1200°C or lower, and subjecting the nickel-containing oxide ore that is a heat-treated product obtained by the heat treatment to the step of performing a reduction treatment.

[0016] (5) The fifth invention of the present invention is any one of the first to fourth inventions, wherein the MgO / SiO in the melt-treated product containing the reduced product in the melt-treatment ２ The method for smelting nickel-containing oxide ore has a mass ratio of 0.5 or more and 0.7 or less.

[0017] (6) A sixth aspect of the present invention is a method for smelting nickel-containing oxide ore, comprising: adding hydrogen as a reducing agent to a raw material containing the nickel-containing oxide ore;２ / (H ２ +H ２ O+CO ２ +O ２ a reduction treatment of the ore by supplying a gas containing nickel and cadmium in a ratio that satisfies the relationship: 0.9; a melting treatment of the reduced product obtained by the reduction treatment; and a recovery of nickel-containing metal by separating slag from the melt obtained by the melting treatment.

[0018] (7) A seventh aspect of the present invention is the method for smelting a nickel-containing oxide ore according to the sixth aspect, wherein the temperature of the gas is 600° C. or higher.

[0019] (8) An eighth aspect of the present invention is a method for smelting a nickel-containing oxide ore according to the seventh aspect, wherein the temperature of the gas is adjusted to 600°C or higher by electrically heating the gas.

[0020] (9) A ninth aspect of the present invention is the method for smelting a nickel-containing oxide ore according to any one of the sixth to eighth aspects, wherein in the reduction treatment, the gas is supplied from below to the raw material containing the nickel-containing oxide ore.

[0021] (10) A tenth aspect of the present invention is the method for smelting a nickel-containing oxide ore according to the ninth aspect, wherein in the reduction treatment, a raw material containing the nickel-containing oxide ore is supplied from above downward.

[0022] (11) A ninth aspect of the present invention is the method for smelting a nickel-containing oxide ore according to any one of the sixth to tenth aspects, wherein the nickel-containing oxide ore has an iron content of 5% by mass or more and 30% by mass or less.

[0023] (12) A ninth aspect of the present invention is the method for smelting a nickel-containing oxide ore according to any one of the sixth to eleventh aspects, further comprising a step of pelletizing the raw material containing the nickel-containing oxide ore, and subjecting the pelletized raw material to the step of performing the reduction treatment.

[0024] (13) A thirteenth aspect of the present invention is a method for smelting a nickel-containing oxide ore according to any one of the sixth to twelfth aspects, further comprising a step of heat-treating a raw material containing the nickel-containing oxide ore at a temperature of 300°C or higher and 1200°C or lower, and subjecting the nickel-containing oxide ore that is a heat-treated product obtained by the heat treatment to the step of performing a reduction treatment.

[0025] (14) The fourteenth aspect of the present invention is any one of the sixth to thirteenth aspects, wherein the MgO / SiO in the melt-treated product containing the reduced product in the melt-treatment is ２ The method for smelting nickel-containing oxide ore has a mass ratio of 0.5 or more and 0.7 or less.

[0026] According to the present invention, CO ２ It is possible to provide a method for smelting nickel-containing oxide ore that reduces the amount of nickel generated and has a high nickel recovery rate.

[0027] FIG. 1 is a process diagram showing an example of the flow of a method for smelting nickel-containing oxide ore. FIG. 2 is a STEM photograph of a cross section of a sample after hydrogen reduction treatment (before melting treatment). FIG. 3 is a schematic diagram of a tubular reduction reaction vessel, and is a diagram for explaining the charging direction of raw materials containing nickel-containing oxide ore and the method of supplying a hydrogen-containing gas. FIG. 4 is a STEM photograph of a cross section of a sample (including a portion where metal particles are not visible) after hydrogen reduction treatment (before melting treatment). FIG. 5 is a schematic diagram of a test apparatus used in the examples. FIG. 6 is a photograph of a sample recovered in the examples.

[0028] Specific embodiments of the present invention (hereinafter also referred to as "present embodiments") will be described in detail below. Note that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the present invention.

[0029] The method according to the present embodiment is a smelting method for separating and recovering nickel from an oxide ore containing nickel (nickel-containing oxide ore).

[0030] The nickel-containing oxide ore used as the raw material is not particularly limited, and examples thereof include saprolite ore and limonite ore. Nickel-containing oxide ore is composed of nickel oxide (NiO) and iron oxide (FeO). ２ O ３) and contains.

[0031] Furthermore, the nickel-containing oxide ore preferably has an iron content of 5% by mass or more and 30% by mass or less. If the iron content is less than 5% by mass, the amount of iron reduced in the hydrogen reduction treatment in the reduction step S3 described below will be small, and the amount of iron metal that contributes as a reducing agent in the melting treatment in the melting step S4 will be small, which may result in an inability to improve the nickel reduction rate and a decrease in the nickel recovery rate. If the iron content exceeds 30% by mass, the nickel content of the recovered nickel metal (alloy) may be reduced and the amount of slag may increase.

[0032] 1 is a process diagram showing an example of the flow of a method for smelting a nickel-containing oxide ore (hereinafter simply referred to as the "smelting method") according to this embodiment. This method is characterized by comprising a reduction step S3 in which a raw material containing a nickel-containing oxide ore is reduced while supplying a gas containing hydrogen at a specific ratio as a reducing agent to the raw material, a melting step S4 in which the reduced product obtained by the reduction step is melted, and a recovery step S5 in which slag is separated from the melt obtained by the melting step and a nickel-containing metal is recovered.

[0033] Furthermore, a step of pelletizing the raw material containing nickel-containing oxide ore (pelletizing step S1) may be further provided, and the pelletized raw material may be subjected to a reduction treatment.

[0034] Furthermore, a step (heat treatment step S2) of heat treating the raw material containing nickel-containing oxide ore, or the pelletized raw material in the case where the raw material is pelletized in the pelletizing step S1, at a specific temperature may be further provided, and the nickel-containing oxide ore that is the heat-treated product after the heat treatment may be subjected to a reduction treatment.

[0035] As described above, the smelting method according to the present embodiment involves subjecting a raw material containing nickel-containing oxide ore to a reduction treatment (hydrogen reduction treatment) using a gas containing hydrogen as a reducing agent, and then subjecting the resulting reduced product to a melting treatment. This effectively reduces the nickel contained in the nickel-containing oxide ore, enabling the recovery of nickel-containing metals at a high recovery rate.

[0036] In particular, in the smelting method according to this embodiment, a tubular reaction vessel (reduction reaction vessel) is used in the reduction step S3, and raw materials containing nickel-containing oxide ore are charged so as to move downward within the tubular reaction vessel, and a hydrogen-containing gas is supplied to the raw materials from below and from the side to perform a reduction treatment. The gas supplied to the raw materials from below is supplied at room temperature, and the gas supplied to the raw materials from the side is supplied at a temperature of 300°C or higher from the side at a position above the position where the raw materials that have been reduced are stored.

[0037] By performing the hydrogen reduction treatment in this manner, it is possible to suppress insufficient reduction and prevent oxidation (reoxidation) of the nickel and iron metals produced by reduction, thereby enabling recovery of nickel-containing metals at an even higher recovery rate.

[0038] [Pelletizing Step] Although not an essential aspect, the smelting method according to this embodiment can include a step of pelletizing a raw material containing nickel-containing oxide ore (pelletizing step S1). By pelletizing the raw material containing nickel-containing oxide ore and supplying a hydrogen-containing gas to the pelletized raw material (raw material pellets) to perform a reduction treatment, it is possible to reduce the proportion of carryover from the raw material together with unreacted hydrogen or the exhaust gas containing water vapor after the reaction.

[0039] The method for pelletizing the raw material is not particularly limited. For example, the raw material, nickel-containing oxide ore, is powdered, and the water required for pelletization is added to the ore powder, followed by molding into pellets of a predetermined size and shape using a known pellet manufacturing device such as a tumbling granulator, a compression molding machine, or an extrusion molding machine. Alternatively, the pellets may be formed manually by an operator.

[0040] The shape of the pellets is not particularly limited, but may be, for example, spherical.

[0041] The size of the pellets is not particularly limited. For example, the size of the pellets (diameter in the case of spherical pellets) charged into the reduction reaction vessel in the reduction step S3 is preferably about 5 mm to 50 mm. The pellet size is more preferably 8 mm to 40 mm, and even more preferably 10 mm to 35 mm. If the pellet size is less than 5 mm, the diameter may be too small or small-diameter pellets may break. This may reduce the gaps (gaps) between the pellets when these raw materials are filled into the reduction reaction vessel, impairing the passage of the gas containing hydrogen as a reducing agent. In such cases, if the pressure of the supplied gas exceeds a certain value, the raw materials are pushed up all at once, which may result in most of the gas escaping unreacted. On the other hand, if the pellet size exceeds 50 mm, the contact area between the pellets and the gas is small, which may result in the reduction reaction taking a long time and making the process less efficient.

[0042] After pelletizing the raw material containing nickel-containing oxide ore, it is preferable to dry the pellets. When the raw material is pelletized, if moisture necessary for pelletization is added, the pellets become sticky due to the added moisture. Therefore, in order to facilitate subsequent handling, the pellets are subjected to a drying treatment to remove moisture adhering to the pellets. The drying method is not particularly limited, but can be carried out, for example, by blowing hot air at 300°C to 400°C onto the pellets.

[0043] [Heat Treatment Step] Although not an essential aspect, the smelting method according to the present embodiment may include a heat treatment step S2 in which the raw material containing nickel-containing oxide ore, or the pelletized raw material (raw material pellets) in the case where the pelletizing step S1 is included, is heat-treated at a specific temperature.

[0044] Specifically, in the heat treatment step S2, raw material pellets containing nickel-containing oxide ore are heat-treated by increasing the temperature to a temperature of 300° C. or more and 1200° C. or less. The heat treatment is a pretreatment carried out prior to the subsequent hydrogen reduction treatment step (reduction step S3) and the step of melting the reduced product (melting step S4). By subjecting the nickel-containing oxide ore to heat treatment in this manner, water of crystallization contained in the nickel-containing oxide ore can be removed.

[0045] As described above, the heat treatment is performed at a temperature of 300°C or higher and 1200°C or lower. If the heat treatment temperature exceeds 1200°C, there is a possibility that fayalite slag will be formed before the iron metal contained in the nickel-containing oxide ore is formed during the hydrogen reduction treatment in the subsequent reduction step S3. If fayalite slag is formed, the amount of iron metal that contributes as a reducing agent in the melting step S4 will decrease, and the reduction rate of nickel may not be improved. On the other hand, if the heat treatment temperature is lower than 300°C, the reduction reaction in the reduction step S3 or the removal of water of crystallization contained in the nickel-containing oxide ore may be hindered, and the reduction rate of nickel may decrease.

[0046] The temperature of the heat treatment is more preferably in the range of 400° C. to 1000° C. Preferably, by carrying out the heat treatment within such a temperature range, most of the water of crystallization contained in the nickel-containing oxide ore can be effectively removed, and an increase in energy costs can be suppressed.

[0047] [Reduction Step] The smelting method according to this embodiment includes a reduction step S3 in which a raw material containing nickel-containing oxide ore is subjected to a reduction treatment (hydrogen reduction treatment) while supplying a gas containing hydrogen at a specific ratio as a reducing agent.

[0048] In the case where the above-mentioned heat treatment step S2 is provided to heat-treat the raw material nickel-containing oxide ore, the obtained heat-treated product is subjected to a hydrogen reduction treatment. In addition, the "raw material containing nickel-containing oxide ore" means raw material pellets when the pelletizing step S1 is provided.

[0049] In this way, by subjecting a raw material containing a nickel-containing oxide ore to hydrogen reduction treatment, the nickel in the nickel-containing oxide ore is reduced to metal, and most or all of the trivalent iron is reduced to divalent oxide, and further a portion of the iron is reduced to metal.

[0050] The reduction process using a gas containing hydrogen as a reducing agent (hydrogen reduction process) is a carbon-neutral process, and compared to conventional technologies, it produces less CO ２ The amount of carbon dioxide generated can be effectively reduced. The term "carbon-neutral reducing agent" refers to a reducing agent that contains almost no carbon components and contributes to reducing greenhouse gas emissions. ２ / (H ２ +H ２ O+CO ２ +O ２ )<0.9 is a carbon-neutral reducing agent.

[0051] As mentioned above, the hydrogen reduction treatment of nickel-containing oxide ore results in a lower reduction rate to nickel metal than the Elkem process. However, as shown in the STEM photograph of the cross section of the sample after hydrogen reduction treatment (before the melting treatment described below) in Figure 2, the hydrogen reduction treatment can be confirmed to produce metal particles of nickel and iron, although they are fine and not numerous. As will be described in detail later, by melting the reduction product obtained by hydrogen reduction treatment, the produced fine metal particles (metal fine particles) settle and can be collected as agglomerates. In this case, it is desirable to perform the melting treatment in a way that effectively utilizes the nickel and iron metal particles produced by the hydrogen reduction treatment.

[0052] Therefore, in the method according to the present embodiment, a tubular reaction vessel (reduction reaction vessel) is used in the reduction step S3, and raw materials containing nickel-containing oxide ore are charged into the tubular reaction vessel so that they move from top to bottom. A gas containing hydrogen as a reducing agent is supplied to the raw materials from below and from the side to perform the reduction treatment. The gas supplied to the raw materials from below is supplied at room temperature, and the gas supplied to the raw materials from the side is supplied at a gas temperature of 300°C or higher from the side at a position above the position where the raw materials after the reduction treatment are stored.

[0053] FIG. 3 is a schematic diagram of a tubular reduction reaction vessel, illustrating the charging direction of raw materials containing nickel-containing oxide ore and the method of supplying a gas containing hydrogen.

[0054] In the reduction treatment, raw material containing nickel-containing oxide ore (hereinafter also referred to as "raw material M", mainly referring to raw material that has not yet reacted for reduction) is charged into a tubular reduction reaction vessel 1 from the top of the vessel 1 (a position near the position indicated by reference numeral 11 in FIG. 3), and the reduction reaction progresses as raw material M moves successively downward from the top. Then, the raw material that has undergone the reduction treatment (hereinafter also referred to as "raw material M'") is stored at a lower position of the reduction reaction vessel 1 (a position near the position indicated by reference numeral 12 in FIG. 3).

[0055] Meanwhile, within the tubular reduction reaction vessel 1, a hydrogen-containing gas is supplied to the raw material from below (a position near the reference numeral 13 in FIG. 3 ). The hydrogen-containing gas (hereinafter also referred to as "gas D") supplied from below is at room temperature. Therefore, the gas D supplied to the raw material from below is introduced into the reduction reaction vessel 1 from below at room temperature, and then rises while being cooled by contact with the raw material M' (the raw material stored at the reference numeral 12 in FIG. 3 ) that has just undergone reduction treatment. The gas D supplied from below has a temperature of approximately 300°C or higher immediately after passing through the raw material M' that has undergone reduction treatment. As it rises further upward, it reduces the raw material M (a new raw material that has not yet undergone reduction treatment) and is then discharged as exhaust gas from the top of the reduction reaction vessel 1. In this way, by supplying the gas D at room temperature to the raw material from below, the raw material M' that has undergone reduction treatment can be maintained in a reducing atmosphere and cooled, thereby suppressing oxidation (reoxidation) of the raw material M' that has undergone reduction treatment.

[0056] Furthermore, in the tubular reduction reaction vessel 1, a hydrogen-containing gas is also supplied from the side (position 14 in FIG. 3 ) above the position where the reduced raw material M′ is stored (position 12 in FIG. 3 ). The hydrogen-containing gas (hereinafter also referred to as “gas S”) supplied from the side has a gas temperature of 300°C or higher. This gas S is used for the reduction treatment of the unreacted raw material M. Because the reduction reaction using hydrogen is an endothermic reaction, the use of a hydrogen-containing gas (gas S) at a temperature of 300°C or higher can raise the temperature of the raw material M, allowing the reduction reaction to proceed efficiently. Therefore, in order to prevent the generation of insufficiently reduced raw material, it is preferable to introduce the hydrogen-containing gas S at a temperature of 300°C or higher from the side (position 14 in FIG. 3 ) of a position as close as possible above the position where the reduced raw material M′ is stored below the tubular reduction reaction vessel 1 (position 12 in FIG. 3 ). Furthermore, since the gas S is supplied from the side (position 14 in Figure 3) above the position where the raw material M' after reduction treatment is stored, the gas S hardly comes into contact with the raw material M' after reduction treatment, and therefore does not interfere with cooling.

[0057] Regarding the hydrogen content in the gas, H ２ / (H ２ +H ２ O+CO ２ +O ２ ) < 0.9, H ２ O, CO ２ , O ２ These components may act as oxidizing agents, preventing the reduction from proceeding sufficiently, and may also oxidize (reoxidize) the nickel metal particles and iron metal particles produced by hydrogen reduction as described above. For this reason, with regard to gases containing hydrogen as a reducing agent, H ２ / (H ２ +H ２ O+CO ２ +O ２ It is preferable to carry out the hydrogen reduction treatment using a gas containing hydrogen in a ratio that satisfies the relationship: 1.0 wt % or more, 2.0 wt % or less ...

[0058] The temperature of the gas S supplied from the side is preferably a certain temperature or higher. Specifically, the gas temperature is preferably 600° C. or higher, more preferably 700° C. or higher, and even more preferably 800° C. or higher. By supplying the hydrogen-containing gas S at such a gas temperature, the reduction reaction of the raw material can proceed more smoothly.

[0059] An electric heater or the like can be used as a means for heating the gas to be supplied. In this way, by heating the gas electrically, the temperature of the gas can be adjusted to, for example, 300°C or higher. Alternatively, the gas may be heated using a heat exchanger such as a heat exchange heater. When the gas is heated using burner combustion gas as a heat source, the H contained in the combustion gas is ２ O and CO ２ This can act as an oxidizing agent in the furnace, reoxidizing the nickel metal particles and iron metal particles that are produced, which can reduce the nickel recovery rate.

[0060] In this way, by performing a hydrogen reduction treatment by supplying a gas containing hydrogen as a reducing agent to the raw material containing nickel-containing oxide ore from below at room temperature (Gas D) and from the side at a gas temperature of 300°C or higher (Gas S), insufficient reduction can be suppressed and oxidation (reoxidation) of the reduced nickel and iron metals produced by the reduction treatment can be prevented. That is, reoxidation of nickel metal particles and iron metal particles in the reduction product produced by the hydrogen reduction treatment can be prevented. Nickel metal particles serve as nuclei for settling and agglomeration in the subsequent melting treatment. Preventing reoxidation of these nickel metal particles enables the recovery of nickel metal at a high recovery rate through the melting treatment. Furthermore, iron metal particles serve as a reducing agent in the subsequent melting treatment (described in detail below). Preventing reoxidation of these iron metal particles promotes the reduction of nickel during the melting treatment, thereby improving the recovery rate of nickel metal.

[0061] Furthermore, by supplying a hydrogen-containing gas from below and from the side to the raw material containing nickel-containing oxide ore to perform the reduction treatment, the produced exhaust gas can be directed upward. This allows a feed gas with a high hydrogen concentration to be introduced to a region where the nickel oxide concentration is low, and a feed gas with a low hydrogen concentration to be introduced to a region where the nickel oxide concentration is high, thereby allowing the reduction reaction to proceed efficiently.

[0062] Furthermore, by setting the temperature of the gas S supplied from the side to the raw material containing nickel-containing oxide ore to 300° C. or higher, preferably, for example, 600° C. or higher, an upward gas flow is efficiently generated, making it possible to create an even smoother gas flow. As a result, the supply gas or exhaust gas can be efficiently flowed, and the hydrogen reduction reaction can proceed more efficiently.

[0063] Furthermore, as described above, the raw material M containing the nickel-containing oxide ore is charged into the tubular reduction reaction vessel 1 so that it moves from above to below, that is, in the opposite direction to the supply direction of the hydrogen-containing gas, so that it can come into contact with the hydrogen-containing gas in a countercurrent manner, and the reduction reaction proceeds more efficiently. That is, by supplying the hydrogen-containing gas from below to the raw material that is supplied from above downward and guiding the exhaust gas upward, it is possible to introduce a feed gas with a high hydrogen concentration into a region where the nickel oxide concentration is low, and to introduce a feed gas with a low hydrogen concentration into a region where the nickel oxide concentration is high.

[0064] The amount of hydrogen supplied in the hydrogen reduction treatment is preferably 1.2 times or more equivalent to the amount of hydrogen required to reduce the iron and nickel to be reduced in the nickel-containing oxide ore. If the amount of hydrogen supplied is less than 1.2 times the above-mentioned required amount of hydrogen, reduction may be insufficient. There is no particular upper limit to the amount of hydrogen supplied, and it may be set appropriately taking into consideration the cost of supplying hydrogen, the form in which the raw material and hydrogen come into contact in the reduction reaction vessel (i.e., reaction efficiency), etc.

[0065] The reduction reaction vessel used in the hydrogen reduction treatment is not particularly limited as long as it is a tubular vessel, as described above. For example, a vertical shaft furnace or the like can be used.

[0066] As described above, the hydrogen reduction treatment of nickel-containing oxide ore generally results in a lower reduction rate to nickel metal than the conventional Elkem process. In this regard, as will be explained below, in the method according to the present embodiment, after the hydrogen reduction treatment of a raw material containing nickel-containing oxide ore, the resulting reduced product is subjected to a melting treatment (melting step S4). This makes it possible to improve the reduction rate of nickel.

[0067] [Melting Step] In the melting step S4, the reduced product obtained by the hydrogen reduction treatment is charged into, for example, an electric furnace and melted. By melting the reduced product (hydrogen reduction product) thus obtained, the recovery rate of nickel can be improved. Furthermore, the reduction rate of nickel can be improved.

[0068] Nickel is more easily reduced than iron. Therefore, it is presumed that by subjecting the hydrogen reduction product to melting treatment, nickel oxide that remains unreacted even after the hydrogen reduction treatment comes into contact with reduced iron metal and divalent iron oxide, causing an oxygen substitution reaction as shown in the following formulas [1] and [2], and nickel oxide is reduced to nickel metal. In other words, iron metal and divalent iron oxide, which are iron reduction products, can be effectively used as reducing agents to reduce nickel oxide. Fe + NiO → Ni + FeO ... formula [1] 2FeO + NiO → Ni + Fe ２ O ３ ...Formula [2]

[0069] That is, since the sample after hydrogen reduction is in a solid state, the reactions of the above formulas [1] and [2] do not proceed very easily, but melting the hydrogen-reduced product facilitates the movement of the metal in the slag, which is thought to promote the reactions of formulas [1] and [2]. This increases the nickel metallization rate and improves the recovery rate of nickel recovered after treatment in the melting step S4.

[0070] Furthermore, melting the hydrogen reduction product can promote the settling and aggregation of nickel metal particles, which are very fine and therefore difficult to recover by physical separation such as magnetic separation, and this can also improve the recovery rate of nickel.

[0071] Figure 4 is an STEM photograph (along with the results of elemental analysis (EDX analysis)) of the cross section of the sample after hydrogen reduction treatment (before melting treatment), including areas where no metal particles are visible. As shown in Figure 4, even in areas where no metal particles are visible (areas (2) and (3) in the figure), about 1 to 2% of nickel was detected. From these results, it is inferred that a high nickel recovery rate cannot be achieved simply by settling the metal components produced by hydrogen reduction treatment, and that a portion of the nickel in the raw material is reduced from nickel oxide by iron metal or divalent iron oxide based on the reactions of the above formulas [1] and [2].

[0072] The melting treatment temperature is not particularly limited as long as it can melt the hydrogen-reduced product, but a temperature of 1400°C or higher and 1600°C or lower is preferred. A melting temperature of 1400°C or higher can produce slag with good properties, allowing for efficient separation of the slag and metal. Furthermore, a melting temperature of 1600°C or lower can reduce wear on the refractories that make up the melting furnace and energy costs.

[0073] As described above, the nickel-containing oxide ore used as the raw material in the method according to the present embodiment preferably has an iron content of 5% by mass or more and 30% by mass or less. If the iron content is less than 5% by mass, the amount of iron reduced during reduction in reduction step S3 will be small, and the amount of iron metal that contributes as a reducing agent during melting in melting step S4 will be small, which may result in a lower nickel recovery rate.

[0074] In addition, during the melting treatment, the MgO / SiO ２ The mass ratio is preferably 0.5 or more and 0.7 or less. ２ If the mass ratio is less than 0.5 or more than 0.7, the melting point of the slag may increase.

[0075] MgO / SiO ２ It is preferable to prepare and adjust the raw materials to be treated so that the mass ratio falls within the above range. ２ In this case, the amount of flux to be added must be considered to determine the ratio of MgO / SiO in the melt-treated material. ２ The mass ratio is set to be within the above-mentioned range. The flux can lower the melting temperature of the slag and promote the sedimentation of the metal (nickel metal) in the slag.

[0076] [Recovery Step] In the recovery step S5, slag is separated from the melt obtained by the melting treatment, and a nickel-containing metal (alloy) is recovered. For example, the melt obtained by melting the reduced material in an electric furnace or the like is separated into an upper layer of slag and a lower layer of metal based on their specific gravities (specific gravity separation). The nickel-containing metal separated from the slag can be efficiently recovered by tapping or other operations through a metal hole provided in the side wall of the furnace.

[0077] All or several of the heat treatment step S2, reduction step S3, melting step S4, and recovery step S5 can be performed in separate areas within a single furnace. Alternatively, they can be performed in a batch system. For example, a shaft furnace or blast furnace can be used, with the heat treatment step S2, reduction step S3, melting step S4, and recovery step S5 being performed in separate areas starting from the top, and the slag and metal can be separated by gravity in the area where the molten metal is stored at the bottom of the furnace.

[0078] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0079] Example 1 Using nickel-containing oxide ore (saprolite ore) having the composition shown in Table 1 below as a raw material, water was added to the raw material powder, and the mixture was molded into spherical pellets having a diameter of 10 mm.

[0080]

[0081] The obtained pellets (raw material pellets) were subjected to hydrogen reduction treatment using a test device shown in the schematic diagram of Figure 5. Specifically, the raw material pellets were placed in a mesh basket, heated to 800°C in nitrogen, and then sintered in a 100% concentration hydrogen gas (H ２ / (H ２ +H ２ O+CO ２ +O ２A reduction treatment (hydrogen reduction treatment) was carried out by flowing a gas (gas temperature: 800°C) satisfying the relationship of ρ = 1.0 from below onto the raw material pellets in the mesh basket while maintaining the condition for 120 minutes. After the hydrogen reduction treatment, the power to the furnace was turned off, and the obtained reduced product sample was cooled to below 300°C while supplying 100% concentration hydrogen (gas temperature: room temperature) to the furnace, and then collected. The amount of hydrogen supplied was in large excess of 10 times or more the amount necessary to reduce the nickel and iron in the nickel-containing oxide ore.

[0082] The collected reduced product sample was mixed with a small amount of flux (SiO ２ The mixture was placed in an alumina crucible together with SiO2, and heated to 1600°C in nitrogen to melt. After holding for 60 minutes to perform the melting treatment, the mixture was cooled and the resulting slag and button-shaped metal were collected. ２ The flux was added to lower the melting temperature of the slag and promote the precipitation of the metal (nickel metal) in the slag. The amount of flux added was determined based on the MgO / SiO ratio in the sample containing the reduced material to be melted. ２ The amounts were adjusted to give a mass ratio of 0.6.

[0083] Figure 6 is a photograph showing the state of the sample recovered after the melting process. As shown in the photograph in Figure 6, the slag was molten, and no metal was visible in the slag. It can be seen that the metal was obtained in the form of button-shaped agglomerates.

[0084] Table 2 below shows the weight of the obtained metal and the metallization rate calculated from chemical analysis by ICP. As shown in Table 2, the metallization rate of the obtained nickel was a high value of 95% or more. The metallization rate is expressed as a percentage of the mass of the recovered nickel metal (or iron metal) relative to the mass of nickel (or iron) contained in the raw material nickel-containing oxide ore.

[0085]

[0086] Table 3 below shows the metallization rates calculated by chemically analyzing the reduction product samples after hydrogen reduction (before melting) using the bromethanol method. As shown in Table 2 above, the nickel metallization rate and iron metallization rate were significantly increased compared to the results shown in Table 3 below.

[0087] The reason why the metallization rate increased despite the absence of a reducing agent during the melting treatment is thought to be that fine nickel and iron metal components were incorporated into the silicate during chemical analysis, and the bromine methanol solution was unable to come into contact with the metals and dissolve them. When the cross section of the sample after hydrogen reduction treatment (before melting treatment) was observed using an STEM, it was confirmed that fine nickel and iron metal particles were incorporated into the silicate, as shown in the photograph in Figure 2. From this, it is thought that by performing melting treatment after hydrogen reduction treatment, the metal particles generated by hydrogen reduction settle and aggregate, making it possible to recover them. The matrix of the sample shown in the photograph in Figure 2 is MgO-SiO ２ -It is thought to be an FeO-based slag.

[0088] Furthermore, when the sample after hydrogen reduction treatment (before melting treatment) was analyzed at locations where no metal particles were found (locations (2) and (3) in Figure 4), approximately 1 to 2% nickel was detected, as shown in the photograph in Figure 4. For this reason, it is thought that the Ni metallization rate shown in Table 2 above cannot be obtained simply by the sedimentation of the metal components described above. This suggests that some of the nickel is reduced from nickel oxide by iron metal or divalent iron oxide through the reactions of the above-mentioned formulas [1] and [2], etc.

[0089]

[0090] As can be seen from the results shown in Tables 2 and 3, in the recovery of nickel from nickel-containing oxide ore, by pelletizing a raw material containing the nickel-containing oxide ore, and subjecting the raw material pellets to a hydrogen reduction treatment and then a melting treatment, it was confirmed that a high nickel recovery rate of, for example, 95% or more can be achieved by the hydrogen reduction treatment, i.e., reduction with a carbon-neutral reducing agent.

[0091] In Comparative Example 1, a raw material containing nickel-containing oxide ore was pelletized in the same manner as in Example 1, and the raw material pellets were subjected to hydrogen reduction at a temperature of 800°C. The resulting reduced product sample was then pulverized in a vibration mill and analyzed for metal content by the bromethanol method. That is, in Comparative Example 1, no melting treatment was performed after hydrogen reduction.

[0092] As a result, the nickel metallization rate was about 3%, as shown in Table 3. Even if all of these metals were recovered, it would not be industrially viable.

Claims

1. A method for smelting nickel-containing oxide ore, comprising the steps of: using a tubular reaction vessel, charging raw materials containing the nickel-containing oxide ore into the reaction vessel so that the raw materials move from top to bottom within the vessel, and supplying a gas containing hydrogen as a reducing agent to the raw materials from below and from the side to perform a reduction treatment; melting the reduced product obtained by the reduction treatment; and separating slag from the molten product obtained by the melting treatment and recovering metal containing nickel, wherein the gas supplied to the raw materials from below is supplied at room temperature, and the gas supplied to the raw materials from the side has a temperature of 300°C or higher and is supplied from the side at a position above a position where the raw materials that have completed the reduction treatment are stored.

2. The method for smelting nickel-containing oxide ore according to claim 1, wherein the nickel-containing oxide ore has an iron content of 5 mass% or more and 30 mass% or less.

3. The method for smelting a nickel-containing oxide ore according to claim 1 or 2, further comprising a step of pelletizing the raw material containing the nickel-containing oxide ore, and subjecting the pelletized raw material to the step of performing the reduction treatment.

4. The method for smelting a nickel-containing oxide ore according to any one of claims 1 to 3, further comprising a step of heat-treating a raw material containing the nickel-containing oxide ore at a temperature of 300°C or more and 1200°C or less, and subjecting the nickel-containing oxide ore obtained by the heat treatment, which is the heat-treated product, to the step of carrying out the reduction treatment.

5. MgO / SiO in the melt-treated product containing the reduced material in the melt-treatment ２ The method for smelting a nickel-containing oxide ore according to any one of claims 1 to 4, wherein the mass ratio is 0.5 or more and 0.7 or less.

6. A method for smelting nickel-containing oxide ore, comprising: adding hydrogen as a reducing agent to a raw material containing the nickel-containing oxide ore; ２ / (H ２ +H ２ O+CO ２ +O ２ )≧0.9, carrying out a reduction treatment, melting a reduced product obtained by the reduction treatment, and separating slag from the molten product obtained by the melting treatment to recover a nickel-containing metal.

7. The method for smelting nickel-containing oxide ore according to claim 6, wherein the temperature of the gas is 600°C or higher.

8. The method for smelting nickel-containing ore according to claim 7, wherein the temperature of the gas is adjusted to 600°C or higher by electrically heating the gas.

9. The method for smelting a nickel-containing oxide ore according to any one of claims 6 to 8, wherein in the reduction treatment, the gas is supplied from below to the raw material containing the nickel-containing oxide ore.

10. The method for smelting nickel-containing oxide ore according to claim 9, wherein in the reduction treatment, the raw material containing the nickel-containing oxide ore is supplied from above downward.

11. The method for smelting a nickel-containing oxide ore according to any one of claims 6 to 10, wherein the nickel-containing oxide ore has an iron content of 5 mass% or more and 30 mass% or less.

12. The method for smelting a nickel-containing oxide ore according to any one of claims 6 to 11, further comprising a step of pelletizing the raw material containing the nickel-containing oxide ore, and subjecting the pelletized raw material to the step of performing the reduction treatment.

13. The method for smelting a nickel-containing oxide ore according to any one of claims 6 to 12, further comprising a step of heat-treating a raw material containing the nickel-containing oxide ore at a temperature of 300°C or higher and 1200°C or lower, and subjecting the nickel-containing oxide ore obtained by the heat treatment, which is the heat-treated product, to the step of carrying out the reduction treatment.

14. MgO / SiO in the melt-treated product containing the reduced material in the melt-treatment ２ The method for smelting a nickel-containing oxide ore according to any one of claims 6 to 13, wherein the mass ratio is 0.5 or more and 0.7 or less.

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