Method for smelting nickel-containing oxide ore

Abstract

To provide 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.SOLUTION: The present invention provides 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 derived from the reduction treatment; and a step for separating the slag from the melt derived from 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.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] To address the issue of climate change, the Paris Agreement was adopted at COP21 in 2015, under which each country agreed to make 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 influence has caused warming of the atmosphere, oceans and land," and subsequently at COP26 it was agreed that "we resolve to pursue efforts to limit the increase 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 for 2020 of "virtually zero emissions by 2050" and for 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 the mainstream in the ferronickel smelting industry. In the Elkem process, saprolite ore containing nickel oxide is pre-dried in a rotary kiln dryer, and then dehydrated to water of crystallization while gradually increasing the temperature in the rotary kiln, and the trivalent iron 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 process in the dryer and the reduction process in the rotary kiln, and coal is used as a reducing agent and heat source, which results in the generation of a large amount of CO2. The amount of CO2 generated is shown to be approximately 22.4tCO2 / tNi.

[0006] Reduction with hydrogen is being considered as a measure to reduce the amount of CO2 generated. It is known that nickel oxide alone can be easily reduced by hydrogen to 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 value in the Elkem process. This is because nickel is widely dispersed in the olivine phase ((Mg,Fe)2SiO4) and magnesiowustite phase ((Mg,Fe)O) and has low activity. Therefore, simply reducing the nickel with hydrogen has a low nickel recovery rate and is not industrially viable.

[0007] The addition of sodium compounds has been proposed as a method for improving the nickel recovery rate during hydrogen reduction, but the amount of the compounds to be added is enormous, and the cost of the chemicals is too high to be commercially viable.

[0008] Patent Document 1 discloses a method for producing reduced iron by reducing iron oxide charged in 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 described above, in the hydrogen reduction of nickel, the reduction degree is about 10% to 70%, which is significantly lower than the conventional Elkem process, which has a reduction degree of 95% or more. There are difficulties in applying the hydrogen reduction method to reduce the amount of CO2 generated in the smelting of nickel-containing oxide ores, and there is a demand for the development of a method that has a high nickel recovery rate even when the hydrogen reduction method is applied and is industrially cost-effective. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2021 / 230307 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been proposed in view of the above circumstances, and aims to provide a method for smelting nickel-containing oxide ore that reduces the amount of CO2 generated and has a high nickel recovery rate. [Means for solving the problem]

[0011] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they 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 a raw material containing nickel-containing oxide ore so that it moves from above to below, supplying a gas containing hydrogen as a reducing agent from below and from the side to the raw material at a predetermined gas temperature to reduce the raw material, and then performing a melting treatment on the reduced product obtained, thereby completing the present invention.

[0012] (1) A first invention of the present invention is a method for smelting a nickel-containing oxide ore, comprising the steps of: using a tubular reaction vessel, charging a raw material containing the nickel-containing oxide ore into the reaction vessel so that the raw material moves from above to below, and supplying a gas containing hydrogen as a reducing agent to the raw material 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 and recovering a metal containing nickel, wherein the gas supplied from below to the raw material is supplied at room temperature, and the gas supplied from the side to the raw material has a temperature of 300°C or higher and is supplied from the side at a position above a position where the raw material after the reduction treatment is 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 of the present invention, 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 a method for smelting a nickel-containing oxide ore, further comprising the 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 the first aspect of the present invention, 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, which is a heat-treated product obtained by the heat treatment, to the step of performing a reduction treatment.

[0016] (5) A fifth aspect of the present invention is the method for smelting a nickel-containing oxide ore according to the first aspect of the present invention, wherein a melt treatment product containing the reduced material in the melt treatment has an MgO / SiO2 mass ratio of 0.5 or more and 0.7 or less. Effect of the Invention

[0017] According to the present invention, it is possible to provide a method for smelting nickel-containing oxide ore with reduced CO2 emissions and high nickel recovery rate. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a process diagram showing an example of a flow of a method for smelting nickel-containing oxide ore. [Diagram 2] FIG. 2 is a STEM photograph of a cross section of a sample after hydrogen reduction treatment (before melt treatment). [Diagram 3] FIG. 2 is a schematic diagram of a tubular reduction reaction vessel, illustrating the charging direction of raw materials containing nickel-containing oxide ore and the supply method of gas containing hydrogen. [Figure 4] FIG. 1 is a STEM photograph of a sample cross section (including areas where no metal grains are visible) after hydrogen reduction treatment (before melting treatment). [Diagram 5] FIG. 2 is a schematic diagram of a test device used in the examples. [Figure 6] FIG. 1 is a photograph of a sample collected in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A specific embodiment of the present invention (hereinafter, also referred to as "the present embodiment") will be described in detail below. Note that the present invention is not limited to the following embodiment, and can be implemented with appropriate modifications within the scope of the present invention.

[0020] 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).

[0021] The nickel-containing oxide ore used as the raw material is not particularly limited, and examples thereof include saprolite ore, limonite ore, etc. The nickel-containing oxide ore contains nickel oxide (NiO) and iron oxide (Fe2O3) as constituents.

[0022] In addition, 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 process 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 process in the melting step S4 will be small, which may result in a failure to improve the reduction rate of nickel and a decrease in the nickel recovery rate. If the iron content exceeds 30% by mass, this may result in a decrease in the nickel content of the recovered nickel metal (alloy) and an increase in the amount of slag.

[0023] 1 is a process diagram showing an example of the flow of a method for smelting nickel-containing oxide ore (hereinafter, simply referred to as "smelting method") according to this embodiment. This method is characterized by having a reduction step S3 in which a raw material containing nickel-containing oxide ore is reduced while supplying a gas containing hydrogen at a specific ratio as a reducing agent to the raw material, the reduction 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 to recover a metal containing nickel.

[0024] Also, 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.

[0025] In addition, 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.

[0026] In this way, the smelting method according to the present embodiment performs a reduction process (hydrogen reduction process) on a raw material containing nickel-containing oxide ore using a gas containing hydrogen as a reducing agent, and then performs a melting process on the resulting reduced product. This makes it possible to effectively reduce the nickel contained in the nickel-containing oxide ore, and to recover metals containing nickel with a high recovery rate.

[0027] In particular, in the smelting 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 so as to move from above to below inside the tubular reaction vessel, and a gas containing hydrogen 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 after reduction treatment are stored.

[0028] By performing hydrogen reduction treatment in this manner, it is possible to suppress insufficient reduction and prevent the oxidation (reoxidation) of the nickel and iron metals produced by reduction, thereby enabling the recovery of nickel-containing metals at an even higher recovery rate.

[0029] [Pelletizing process] Although not essential, the smelting method according to the present embodiment may include a step of pelletizing the raw material containing nickel-containing oxide ore (pelletizing step S1). By pelletizing the raw material containing nickel-containing oxide ore and supplying a gas containing hydrogen to the pelletized raw material (raw material pellets) to perform a reduction treatment, it is possible to reduce the proportion of the raw material carried over together with unreacted hydrogen or with the exhaust gas containing water vapor after the reaction.

[0030] The method for pelletizing the raw material is not particularly limited. For example, the raw material, nickel-containing oxide ore, is powdered, and the powdered ore is added with moisture required for pelletization, and the powder is molded 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 molded manually by an operator.

[0031] The shape of the pellets is not particularly limited, but may be, for example, spherical.

[0032] The size of the pellets is not particularly limited, but for example, the size of the pellets (diameter in the case of spherical pellets) to be charged into the reduction reaction vessel or the like in the reduction step S3 is preferably about 5 mm or more and 50 mm or less. The size of the pellets is more preferably 8 mm or more and 40 mm or less, and even more preferably 10 mm or more and 35 mm or less. If the size of the pellets is less than 5 mm, the diameter is too small, or the pellets with a small diameter are broken, and when these raw materials are filled into the reaction vessel of the reduction treatment, the gaps (gaps) between the pellets are small, and the passage of the gas containing hydrogen as the reducing agent may become poor. In such a case, when the pressure of the gas supplied exceeds a certain value, the raw materials are pushed up at once, and the phenomenon that most of the gas escapes without reacting easily occurs. On the other hand, if the size of the pellets exceeds 50 mm, the contact area between the pellets and the gas becomes small, and the reduction reaction takes time, and there is a possibility that the treatment cannot be performed efficiently.

[0033] After the raw material containing nickel-containing oxide ore is pelletized, 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 method of drying is not particularly limited, but can be, for example, blowing hot air at 300°C to 400°C onto the pellets.

[0034] [Heat treatment process] In addition, although not essential, the smelting method according to this embodiment can 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 pelletization step S1 is provided, is heat-treated at a specific temperature.

[0035] Specifically, in the heat treatment step S2, the raw material pellets containing the 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, the water of crystallization contained in the nickel-containing oxide ore can be removed.

[0036] 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 generated before the iron metal contained in the nickel-containing oxide ore is generated during the hydrogen reduction treatment in the next reduction step S3. If fayalite slag is generated, 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 the water of crystallization contained in the nickel-containing oxide ore will be hindered, and the reduction rate of nickel may decrease.

[0037] The temperature of the heat treatment is more preferably in the range of 400° C. to 1000° C. By carrying out the heat treatment in 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.

[0038] [Reduction process] The smelting method according to the present 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.

[0039] In addition, when 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.

[0040] In this way, by subjecting raw materials containing 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 some of the iron is further reduced to metal.

[0041] Reduction treatment using a gas containing hydrogen as a reducing agent (hydrogen reduction treatment) is a treatment using a carbon-neutral reducing agent, and can effectively reduce the amount of CO2 generated compared to conventional techniques. Note that a "carbon-neutral reducing agent" means a reducing agent that contains almost no carbon components and contributes to reducing greenhouse gas emissions. Specifically, for example, a gas that contains hydrogen in a ratio represented by the relationship H2 / (H2+H2O+CO2+O2)<0.9 is a carbon-neutral reducing agent.

[0042] As described above, the hydrogen reduction treatment of nickel-containing oxide ore has 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 confirm the generation of nickel and iron metal particles, although they are fine and not many. As described in detail below, by melting the reduction product obtained by the hydrogen reduction treatment, the generated fine metal particles (metal fine particles) settle and can be collected by coagulation. At this time, it is desirable to perform the melting treatment while effectively utilizing the nickel and iron metal particles generated by the hydrogen reduction treatment.

[0043] Therefore, in the method according to the present embodiment, a tubular reaction vessel (reduction reaction vessel) is used in the reduction step S3, raw materials containing nickel-containing oxide ore are charged so as to move from above to below inside the tubular reaction vessel, and 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 that have been reduced are stored.

[0044] 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 supply method of gas containing hydrogen.

[0045] In the reduction process, raw material containing nickel-containing oxide ore (hereinafter also referred to as "raw material M", mainly referring to raw material that has not yet been reduced) is charged into a tubular reduction reaction vessel 1 from the top of the vessel 1 (a position near the reference symbol 11 in FIG. 3), and the reduction reaction proceeds as the raw material M moves successively downward from the top. Then, the raw material after the reduction process (hereinafter also referred to as "raw material M'") is stored at a lower position of the reduction reaction vessel 1 (a position near the reference symbol 12 in FIG. 3).

[0046] Meanwhile, in the tubular reduction reaction vessel 1, a gas containing hydrogen is supplied to the raw material from below (a position near the reference numeral 13 in FIG. 3). The gas containing hydrogen (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 from below the reduction reaction vessel 1 at room temperature, and then comes into contact with the raw material M' (raw material stored at the reference numeral 12 in FIG. 3) immediately after the reduction treatment is completed, and rises while being cooled. Then, the gas D supplied from below has a temperature of about 300°C or higher immediately after passing through the raw material M' after the reduction treatment is completed, and reduces the raw material M (a new raw material that has not yet been reduced) in the process of rising further upward, and is then discharged from the upper part of the reduction reaction vessel 1 as exhaust gas. In this way, by supplying the gas D at room temperature from below to the raw material, the raw material M' after the reduction treatment can be kept in a reducing atmosphere and cooled, and the oxidation (reoxidation) of the raw material M' after the reduction treatment can be suppressed.

[0047] In addition, in the tubular reduction reaction vessel 1, a gas containing hydrogen is also supplied from the side (position 14 in FIG. 3) of a position above the position (position 12 in FIG. 3) where the raw material M' after the reduction treatment is stored. The gas containing hydrogen (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. Since the reduction reaction using hydrogen is an endothermic reaction, the raw material M can be heated by using a gas containing hydrogen (gas S) at a temperature of 300° C. or higher, and the reduction reaction can be efficiently advanced. Therefore, in order to prevent the generation of insufficiently reduced raw material, it is preferable to introduce the gas containing hydrogen S at a temperature of 300° C. or higher from the side (position 14 in FIG. 3) of a position above the position (position 12 in FIG. 3) where the raw material M' after the reduction treatment is stored below the tubular reduction reaction vessel 1 as close as possible. Furthermore, since the gas S is supplied from the side (position 14 in FIG. 3) above the position where the raw material M' after the reduction process is stored, the gas S hardly comes into contact with the raw material M' after the reduction process, and therefore does not interfere with cooling.

[0048] The temperature of the gas S supplied from the side is preferably 600° C. or higher, and more preferably 800° C. or higher. By supplying the gas S containing hydrogen at such a gas temperature, the reduction reaction of the raw material can proceed more smoothly.

[0049] As a means for heating the gas to be supplied, an electric heater or the like can be used. In this way, the temperature of the gas can be adjusted to, for example, 300°C or higher by heating the gas electrically. 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, H2O and CO2 contained in the combustion gas act as oxidizing agents in the furnace and reoxidize the generated nickel metal particles and iron metal particles, which may reduce the nickel recovery rate.

[0050] In this way, by supplying 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) to perform hydrogen reduction treatment, it is possible to suppress insufficient reduction and prevent oxidation (reoxidation) of the reduced nickel and iron metals. In other words, it is possible to prevent reoxidation of nickel metal particles and iron metal particles in the reduction product generated by hydrogen reduction treatment. The nickel metal particles serve as so-called nuclei for settling and agglomerating in the melting treatment in the next step, and by preventing the reoxidation of the nickel metal particles, it is possible to recover nickel metal at a high recovery rate through the melting treatment. In addition, the iron metal particles contribute as a reducing agent in the melting treatment in the next step (described in detail later), and by preventing the reoxidation of the iron metal particles, it is possible to promote the reduction of nickel during the melting treatment, and as a result, to improve the recovery rate of nickel metal.

[0051] In addition, by supplying hydrogen-containing gas from below and from the side to the raw material containing nickel-containing oxide ore to perform the reduction treatment, the generated exhaust gas can be guided upward. This allows a supply gas with a high hydrogen concentration to be introduced into an area where the nickel oxide concentration is low, and a supply gas with a low hydrogen concentration to be introduced into an area where the nickel oxide concentration is high, so that the reduction reaction can be efficiently promoted.

[0052] 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.

[0053] Furthermore, as described above, in the tubular reduction reaction vessel 1, the raw material M containing nickel-containing oxide ore is charged so as to move 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 supplied from above to below and guiding the exhaust gas upward, a supply gas with a high hydrogen concentration can be introduced to a portion where the nickel oxide concentration is low, and a supply gas with a low hydrogen concentration can be introduced to a portion where the nickel oxide concentration is high.

[0054] The amount of hydrogen supplied in the hydrogen reduction treatment is preferably 1.2 times or more the equivalent of 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 necessary amount of hydrogen, the reduction may be insufficient. There is no particular upper limit on the amount of hydrogen supplied, and it may be appropriately set in consideration of the cost of supplying hydrogen, the form in which the raw material and hydrogen come into contact in the reduction reaction vessel (i.e., the reaction efficiency), and the like.

[0055] 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.

[0056] 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 described below, in the method according to the present embodiment, after the hydrogen reduction treatment is performed on the raw material including the 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.

[0057] [Melting process] 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 reduced product) thus obtained, the recovery rate of nickel can be improved.

[0058] Nickel is easier to reduce than iron. Therefore, it is presumed that by performing melting treatment on the hydrogen reduction product, 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 reduced products of iron, can effectively act as reducing agents to reduce nickel oxide. Fe + NiO → Ni + FeO [1] 2FeO+NiO → Ni+Fe2O3...Formula [2]

[0059] 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 reduction product makes it easier for the metal in the slag to move, 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.

[0060] In addition, 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.

[0061] Figure 4 is a STEM photograph (along with the results of elemental analysis (EDX analysis)) of the cross section of the sample after hydrogen reduction (before melting), including areas where no metal particles were visible. As shown in Figure 4, about 1-2% nickel was detected even in the areas where no metal particles were visible (areas (2) and (3) in the figure). From this result, it is presumed that a high nickel recovery rate cannot be obtained only by settling of the metal components produced by hydrogen reduction, and that some 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].

[0062] In the melting treatment, the temperature conditions are not particularly limited as long as the hydrogen reduction product can be melted, but for example, a temperature of 1400°C to 1600°C is preferable. By setting the melting temperature at 1400°C or higher, slag with good properties can be obtained, and the slag and metal can be separated efficiently. In addition, by setting the melting temperature at 1600°C or lower, wear on the refractories constituting the melting furnace and energy costs can be suppressed.

[0063] 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 the reduction step S3 is small, and the amount of iron metal that serves as a reducing agent during melting in the melting step S4 is small, which may result in a decrease in the nickel recovery rate.

[0064] In addition, during melting, it is preferable that the MgO / SiO2 mass ratio in the melting treatment product containing the reduced material to be melted is 0.5 to 0.7. If the MgO / SiO2 mass ratio is less than 0.5 or more than 0.7, the melting point of the slag may increase.

[0065] It is preferable to prepare and adjust the raw material to be treated so that the MgO / SiO2 mass ratio in the melting treatment falls within the above-mentioned range. In addition, a flux such as SiO2 may be added in the melting treatment, and in that case, the amount of flux added is taken into consideration so that the MgO / SiO2 mass ratio in the melting treatment falls within the above-mentioned range. The flux can lower the melting temperature of the slag and promote the precipitation of the metal (nickel metal) in the slag.

[0066] [Recovery process] In the recovery step S5, the slag is separated from the molten material obtained by the melting process, and the nickel-containing metal (alloy) is recovered. For example, the molten material obtained by melting the reduced material in an electric furnace or the like is separated (gravity separation) into an upper layer of slag and a lower layer of metal, depending on their specific gravities. 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.

[0067] All or a plurality of the above-mentioned heat treatment step S2, reduction step S3, melting step S4, and recovery step S5 can be performed in different areas of one furnace. Alternatively, they may be performed in a batch manner. For example, a shaft furnace or a blast furnace may be used, and the heat treatment step S2, reduction step S3, melting step S4, and recovery step S5 may be performed in that order from the top layer, and finally, slag and metal may be separated by gravity in the area where the molten material is stored at the bottom of the furnace. EXAMPLES

[0068] 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.

[0069] [Example 1] Nickel-containing oxide ore (saprolite ore) having the composition shown in Table 1 below was used as a raw material, and water was added to the raw material powder, which was then molded into spherical pellets having a diameter of 10 mm.

[0070] [Table 1]

[0071] The obtained pellets (raw pellets) were subjected to hydrogen reduction treatment using a test device shown in the schematic diagram of Figure 5. Specifically, the raw pellets were placed in a mesh cage and heated to 800°C in nitrogen, and then 100% hydrogen gas (gas temperature: 800°C) was flowed from below the raw pellets in the mesh cage while holding the pellets for 120 minutes to perform reduction treatment (hydrogen reduction treatment). After the hydrogen reduction treatment, the power to the furnace was turned off, and the obtained reduced product sample was cooled to less than 300°C while supplying 100% hydrogen (gas temperature: room temperature) to the furnace, and then collected. The amount of hydrogen supplied was a large excess of 10 times or more the amount required to reduce nickel and iron in the nickel-containing oxide ore.

[0072] The collected reduced material sample was placed in an alumina crucible together with a small amount of flux (SiO2) and melted in nitrogen at 1600°C. After holding for 60 minutes for melting treatment, the sample was cooled and the resulting slag and button-shaped metal were collected. The flux SiO2 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 such that the MgO / SiO2 mass ratio in the melting treatment sample containing the reduced material was 0.6.

[0073] 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 melted, and no metal was visible in the slag. It can be seen that the metal was obtained in the form of button-shaped agglomerates.

[0074] Table 2 below shows the weight of the obtained metal and the metallization rate calculated from the chemical analysis by ICP. As shown in Table 2, the metallization rate of the obtained nickel was high, at 95% or more. The metallization rate is shown 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.

[0075] [Table 2]

[0076] Table 3 below shows the metallization rates calculated by chemically analyzing the reduction product samples after hydrogen reduction (before melting) using the bromomethanol 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.

[0077] The reason why the metallization rate increased even though no reducing agent was added during the melting process is that fine nickel and iron metal components were taken up in the silicate during chemical analysis, and the bromomethanol solution was unable to come into contact with the metals and dissolve them. When the cross section of the sample after hydrogen reduction (before melting) was observed by STEM, it was confirmed that fine nickel and iron metal particles were taken up in the silicate, as shown in the photograph in Figure 2. From this, it is believed that by performing melting after hydrogen reduction, 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 believed to be a MgO-SiO2-FeO slag.

[0078] 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 1-2% nickel was detected, as shown in the photograph in Figure 4. For this reason, it is believed that the Ni metallization rate in Table 2 above cannot be obtained by the precipitation of the metal components described above alone. This suggests that some of the nickel has been reduced from nickel oxide to iron metal or divalent iron oxide through the reactions of the above-mentioned formulas [1] and [2], etc.

[0079] [Table 3]

[0080] As can be seen from the results shown in Tables 2 and 3, in the recovery of nickel from nickel-bearing oxide ore, by pelletizing a raw material containing the nickel-bearing oxide ore, subjecting the raw material pellets to a hydrogen reduction treatment and then subjecting them to 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.

[0081] [Comparative Example 1] 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 reduced with hydrogen at a temperature of 800° C. The resulting reduced product sample was then pulverized in a vibration mill, and the metal content was analyzed by the bromomethanol method. That is, in Comparative Example 1, no melting treatment was performed after hydrogen reduction.

[0082] As a result, as shown in Table 3 above, the nickel metallization rate was about 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: a step of using a tubular reaction vessel, charging a raw material containing the nickel-containing oxide ore so that the raw material moves from above to below within the reaction vessel, and supplying a gas containing hydrogen as a reducing agent to the raw material from below and from the side to perform a reduction treatment; A step of melting the reduced product obtained by the reduction treatment; and a step of separating slag from the molten material obtained by the melting process and recovering a metal containing nickel. The gas supplied from below the raw material is supplied at room temperature, the gas supplied from the side to the raw material has a temperature of 300° C. or higher and is supplied from the side at a position above a position where the raw material that has undergone reduction treatment is stored; A method for smelting nickel-bearing oxide ores.

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

3. The method further comprises the step of pelletizing the raw material containing the nickel-containing oxide ore, The pelletized raw material is subjected to the reduction treatment. The method for smelting nickel-containing oxide ore according to claim 1.

4. The method further comprises a step of heat treating the raw material containing the nickel-containing oxide ore at a temperature of 300° C. or more and 1200° C. or less, The heat-treated nickel-containing oxide ore obtained by the heat treatment is subjected to the step of carrying out the reduction treatment. The method for smelting nickel-containing oxide ore according to claim 1.

5. The MgO / SiO in the melt-treated product containing the reduced material in the melt-treatment ２ The mass ratio is 0.5 or more and 0.7 or less. The method for smelting nickel-containing oxide ore according to claim 1.

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