WO2025075070A1 - Hydrometallurgical method for nickel oxide ore, method for producing nickel-containing sulfide, and method for producing nickel-containing hydroxide - Google Patents

Abstract

The present invention provides a hydrometallurgical method for a nickel oxide ore, with which it is possible to effectively utilize an ore that contains magnesium at a high concentration.　Provided is a hydrometallurgical method for a nickel oxide ore, the hydrometallurgical method including: a first step S1 in which a leaching step S11, a solid-liquid separation step S12, and a neutralization step S13 are performed; and a second step S2 in which a dissolvability improvement treatment step S21, in which the dissolvability of a magnesium-containing ore that has a magnesium concentration exceeding 5 mass% is improved, and a carbonate production step S22, in which the magnesium-containing ore, which has passed through the dissolvability improvement treatment step S21, is put into a solution and magnesium dissolved in the solution is reacted with carbon dioxide so as to produce magnesium carbonate, are performed. The magnesium carbonate produced in the carbonate production step S22 is used as a neutralizing agent in the neutralization step S13.

Description

Hydrometallurgical method for nickel oxide ore, method for producing nickel-containing sulfide, and method for producing nickel-containing hydroxide

The present invention relates to a method for hydrometallurgy of nickel oxide ore, a method for producing nickel-containing sulfides, and a method for producing nickel-containing hydroxides. More specifically, the present invention relates to a method for hydrometallurgy of nickel oxide ore using high pressure acid leaching (hereinafter also referred to as the "HPAL process"), which can effectively utilize ores containing high concentrations of magnesium.

In recent years, the high-temperature pressure acid leaching (HPAL process), a hydrometallurgical method that uses concentrated sulfuric acid under high temperature and pressure to leach metal ions into the liquid phase, has come to be widely used as a hydrometallurgical method for nickel oxide ores, replacing the conventional dry smelting method. This "HPAL process" is a process that is economically superior to the conventional dry smelting method, as it is made up of a consistent wet process.

　Conventionally, so-called laterite ores such as limonite ore and saprolite ore have been widely used as nickel oxide ores used as raw materials in the wet smelting of nickel oxide ores. However, in the above-mentioned wet nickel smelting (nickel smelting by the "HPAL process"), if saprolite ore with a high magnesium concentration (nickel concentration: about 1.8% by mass to about 3.0% by mass, magnesium concentration: 6% by mass or more) is used, Mg is preferentially ionized over valuable metals such as nickel, and the amount of concentrated sulfuric acid required to leach valuable metals increases, reducing the economic advantage of the "HPAL process". Therefore, in wet nickel smelting (nickel smelting by the "HPAL process"), limonite ore with a relatively low magnesium concentration (nickel concentration: about 0.8% by mass to about 1.8% by mass, magnesium concentration: 5% by mass or less) has been mainly used as nickel oxide ore, although it is not necessarily particularly high in nickel concentration.

However, in various fields of metal smelting, technological development is underway to use low-grade ores that have been avoided under conventional technology due to the cost disadvantages, or even waste ores. In line with this trend, in the field of nickel smelting using the "HPAL process," technological development is underway to use raw ores containing high concentrations of Mg, which have not been actively used in the past, without compromising the inherent economic advantages of the "HPAL process."

For example, Patent Document 1 discloses a process in which nickel oxide ore, which is a mixture of ores with various Mg concentrations, is sieved into a fine particle portion with a low magnesium concentration and a coarse particle portion with a high magnesium concentration in the "HPAL process," and the separated and recovered coarse particle portion is further separated by specific gravity, with only the portion with the high specific gravity being charged into the leaching process.

However, the process disclosed in Patent Document 1 is based on the premise that a certain amount of fine grains with low magnesium concentration are present in the raw ore, and the accuracy of separation of Mg from the ore rejected into the coarse grains and recovery of nickel is not necessarily sufficient, leaving room for further improvement. For example, there has been a demand for technical means that can effectively utilize ores that contain high concentrations of magnesium, such as saprolite ore.

JP 2019-65340 A

The present invention has been proposed in light of these circumstances, and aims to provide a method for hydrometallurgy of nickel oxide ore that can effectively utilize ores containing high concentrations of Mg, such as saprolite ore, which have not been actively used in hydrometallurgy nickel smelting such as the "HPAL process."

The present inventors have found that the above-mentioned problems can be solved by forming a nickel oxide ore hydrometallurgical process into a composite process in which a second step of producing _MgCO3 by fixing carbon dioxide ( _CO2 ) to a high-magnesium ore having a magnesium concentration of more than 5 mass% is carried out in parallel, and have completed the present invention. That is, the present invention provides the following.

(1) A method for hydrometallurgical smelting of nickel oxide ore, comprising: a first step of leaching nickel oxide ore with a mineral acid to obtain a leaching slurry; a solid-liquid separation step of separating the leaching slurry into a leaching solution and a leaching residue; and a neutralization step of separating a neutralized precipitate from the leaching solution to obtain a neutralization end solution; a second step of changing the crystal structure of a magnesium-containing ore having a magnesium concentration of more than 5% by mass to improve the leaching of magnesium; and a carbonate generation step of placing the magnesium-containing ore that has been subjected to the leaching improvement treatment step into a solution and reacting the magnesium leached into the solution with carbon dioxide to produce magnesium carbonate, wherein the magnesium carbonate produced in the carbonate generation step of the second step is used as a neutralizing agent in the neutralization step of the first step.

(1) According to the nickel oxide ore hydrometallurgy method, raw ores containing high concentrations of Mg, such as saprolite ore, which have not been actively used in the field of nickel smelting using the "HPAL process", or other low-grade ores or waste ores, which contain trace amounts of nickel but have a high proportion of gangue components and have not been used in the leaching process and have been excluded from the production line of the final product, can be effectively utilized in the neutralization process.

(2) The method for hydrometallurgical smelting of nickel oxide ore described in (1), in which the carbon dioxide gas discharged from the neutralization step of the first step is used as carbon dioxide to react with the magnesium dissolved in the solution in the carbonate production step of the second step.

According to the method for hydrometallurgy of nickel oxide ore in (2), the _CO2 gas discharged in the nickel smelting process, such as the CO2 gas discharged from the neutralization step in the first step, is used as the _CO2 to be reacted with _Mg in the carbonate production step in the second step, thereby contributing to a reduction in the total amount of _CO2 gas emissions from the nickel smelting plant.

(3) A method for producing nickel-containing sulfides, which comprises adding a sulfurizing agent to the neutralization end solution obtained in the neutralization step of the hydrometallurgical method for producing nickel oxide ore described in (1) or (2) to produce nickel-containing sulfides.

The method for producing nickel-containing sulfides (3) provides the above-mentioned effects of the hydrometallurgical method for nickel oxide ore described in (1) or (2), and can improve the productivity of nickel-containing sulfides, which are the target product of nickel smelting using the "HPAL process."

(4) A method for producing nickel-containing hydroxide, which comprises adding a neutralizing agent to the final neutralization solution obtained in the neutralization step of the hydrometallurgical method for producing nickel oxide ore described in (1) or (2) to produce nickel-containing hydroxide.

The method for producing nickel-containing sulfides (4) provides the above-mentioned effects of the hydrometallurgical method for nickel oxide ore described in (1) or (2), and can improve the productivity of nickel-containing hydroxides, which are the target product in nickel smelting by the "HPAL process."

According to the present invention, it is possible to effectively utilize ores containing high concentrations of Mg, such as saprolite ore, which have not been actively used in the past in wet nickel smelting.

FIG. 1 is a flow diagram showing the flow of a hydrometallurgical method for producing nickel oxide ore according to the present invention. FIG. 2 is a graph showing a change in particle size distribution of "high magnesium ore" when "mechanochemical treatment", which is an example of a treatment for improving elution property in the hydrometallurgical method for nickel oxide ore of the present invention, is carried out. FIG. 2 is a graph showing that a "high-magnesium ore" is made amorphous by a "mechanochemical treatment", which is an example of a treatment for improving elution property in the hydrometallurgical method for nickel oxide ore of the present invention.

Below, specific embodiments of the "Method for Hydrometallurgy of Nickel Oxide Ore" of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the present invention.

<Method for hydrometallurgy of nickel oxide ore>
The flow of the entire process of the hydrometallurgy of nickel oxide ore that can be performed by the "hydrometallurgy method for nickel oxide ore" of the present invention (hereinafter also simply referred to as "hydrometallurgy method for nickel oxide ore") is shown in FIG. 1 as an example. The "hydrometallurgy method for nickel oxide ore" is a composite process in which a first step S1 of producing nickel-containing sulfide or nickel-containing hydroxide by hydrometallurgy from nickel oxide ore and a second step S2 of producing MgCO ₃ from Mg contained in magnesium-containing ore (also referred to as "high magnesium ore" in this specification) having a magnesium concentration exceeding 5 mass%, which was difficult to utilize in conventional hydrometallurgy processes, are performed in parallel. In addition, the "hydrometallurgy method for nickel oxide ore" is mainly characterized as an entire process in that MgCO ₃ produced from the "high magnesium ore" in the second step S2 is utilized as a neutralizing agent in the first step S1.

[First step]
The first step S1 is a hydrometallurgical method for nickel oxide ore. As shown in Fig. 1, the first step S1 is a method for hydrometallurgical refining of nickel oxide ore, in which a leaching step S11, a solid-liquid separation step S12, and a neutralization step S13 are sequentially performed, as in the conventional hydrometallurgical refining method (HPAL process). In the first step S1, as the nickel oxide ore used as the raw material ore, limonite ore having a magnesium concentration of 5 mass% or less can be preferably used, as in the conventional method.

In addition, by going through the smelting process consisting of the above three steps (leaching step S11, solid-liquid separation step S12, and neutralization step S13), a sulfurization step S14 in which a sulfurizing agent is added to the neutralization end liquid obtained in the neutralization step S13, or a hydroxide step S15 in which a neutralizing agent is added to the neutralization end liquid, nickel-containing sulfides or nickel-containing hydroxides can be produced by each step.

(Leaching process)
The leaching step S11 is a step of performing a leaching treatment in which a mineral acid such as sulfuric acid is added to nickel oxide ore (nickel oxide ore slurry) that has been mixed with water to form a slurry, and the mixture is stirred under pressure under high temperature conditions of about 220° C. to 280° C. to generate a leaching slurry that is composed of a leachate and a leaching residue. Specifically, this leaching treatment can be performed by charging the above-mentioned "nickel oxide ore slurry" into a pressurized leaching reaction vessel such as an autoclave.

In addition, for example, when "nickel oxide ore" having a high magnesium concentration such as "saprolite ore" is used as the "high-magnesium ore" in the second step S2, the slurry which is the residue after _MgCO3 is recovered in the carbonate recovery step S23 of the second step S2 can be charged into the leaching step S11 as "nickel oxide ore slurry" having a reduced Mg concentration.

(Solid-liquid separation process)
The solid-liquid separation step S12 is a step in which the leaching slurry that has been subjected to the leaching step S11 is washed in multiple stages to separate a leaching solution containing nickel (Ni), cobalt (Co) and other impurity elements from a leaching residue. The solid-liquid separation step S12 can be performed, for example, by mixing the leaching slurry with a washing solution and then subjecting the mixture to solid-liquid separation treatment using solid-liquid separation equipment such as a thickener.

(Neutralization process)
The neutralization step S13 is a step of adjusting the pH of the leachate separated in the solid-liquid separation step S12, separating impurity elements as neutralized precipitates, and obtaining a neutralized end solution containing Ni and Co. Specifically, in the neutralization step S13, a neutralizing agent is added to the leachate while suppressing oxidation of the separated leachate so that the pH of the obtained neutralized end solution is 4.0 or less, preferably 3.0 to 3.5, more preferably 3.1 to 3.2, to produce a neutralized end solution and a neutralized precipitate slurry containing trivalent iron (Fe) and aluminum (Al) as impurity elements. In the neutralization step S13, impurities are removed as neutralized precipitates in this way to produce a neutralized end solution that serves as a mother liquor for nickel recovery.

As the neutralizing agent used in the neutralization step of a general nickel oxide ore hydrometallurgy process, various alkaline earth metal carbonates such as calcium carbonate and MgCO ₃ can be preferably used. The above-mentioned various neutralizing agents can also be used in the neutralization step S13 of the first step S1 of the "nickel oxide ore hydrometallurgy process" of the present invention, but in the neutralization step S13, MgCO ₃ generated in the carbonate generation step S22 of the second step S2 is used as at least a part of the neutralizing agent used in this neutralization step S13. In the "nickel oxide ore hydrometallurgy process" of the present invention, it is preferable that 5% or more of the total amount of the neutralizing agent used in this neutralization step S13 is MgCO ₃ generated in the carbonate generation step S22 of the second step S2, and it is most preferable that the total amount of the neutralizing agent used (100%) is MgCO ₃ .

In addition, the neutralization reaction that proceeds when MgCO ₃ is added as a neutralizing agent in the neutralization step S13 as described above is, for example, as shown in the following (formula 1), and iron (Fe) and the like in the solution are removed as a neutralized precipitate slurry.
(Formula 1 _{) Fe2} ( _SO4 ) ₃ +3MgCO3+ _H2O → _3MgSO4 (aq)+2FeOOH↓+ _3CO2 ↑

(Sulfurization process)
As described above, the sulfurization step S14 is a step of adding a sulfurizing agent to the mother liquor for nickel recovery from which Fe and the like have been removed in the neutralization step S13, and further separating the mother liquor into nickel-containing sulfides and poor liquor. In the sulfurization step S14, a sulfurizing agent is blown into the neutralization end liquor, which is the mother liquor for nickel recovery, to cause a sulfurization reaction and generate nickel-containing sulfides and poor liquor. Examples of the sulfurizing agent that can be used in the sulfurization step S14 include hydrogen sulfide, sodium hydrogen sulfide, and sodium sulfide. Among these, hydrogen sulfide is particularly preferably used. In the "wet smelting method for nickel oxide ore" of the present invention, the sulfurization step S14 is further performed to produce nickel-containing sulfides, which are the target product. In other words, the process including the above three steps (leaching step S11, solid-liquid separation step S12, and neutralization step S13) and the sulfurization step S14 is, in other words, the "method for producing nickel-containing sulfides" of the present invention.

The nickel-containing sulfide is generally called MS (Mixed Surfide) and refers to a nickel-cobalt mixed sulfide. Specifically, it contains 50.0 to 60.0 mass% Ni, 0.1 to 26.0 mass% Co, and about 0.1 to 2.0 mass% Fe and other impurities. These nickel-containing sulfides can be electrolytically extracted through chlorine leaching, or nickel sulfate after purification, or nickel powder or nickel briquettes can be obtained by hydrogen reduction through ammonia leaching. The nickel-containing sulfides produced by the "method for producing nickel-containing sulfides" of the present invention can be made into final products such as nickel sulfate, electrolytic nickel, nickel powder, and nickel briquettes by these existing methods.

(Hydroxylation process)
As described above, the hydroxide step S15 is a step of adding a neutralizing agent to the mother liquor for nickel recovery from which Fe and the like have been removed in the neutralization step, and further separating the mother liquor into nickel-containing hydroxide and poor liquor. Examples of neutralizing agents that can be used in the hydroxide step S15 include calcium carbonate, calcium hydroxide, magnesium hydroxide, sodium hydroxide, quicklime, magnesium oxide, and the like. Among these, magnesium hydroxide and magnesium oxide are particularly preferably used. In the hydroxide step S15, a neutralizing agent such as MgO is added to the neutralization end liquor, which is the mother liquor for nickel recovery, and a hydrolysis reaction exemplified by the following formulas (2) and (3) is allowed to proceed, for example, to generate nickel-containing hydroxide and poor liquor. In the "wet smelting method for nickel oxide ore" of the present invention, the hydroxide step S15 is further performed to produce the nickel-containing hydroxide, which is the target product. In other words, the process including the above three steps (the leaching step S11, the solid-liquid separation step S12, and the neutralization step S13) and this hydroxide step S15 is the "method for producing a nickel-containing hydroxide" of the present invention.
(Formula 2) _NiSO4 (aq)+MgO(s)+ _H2O (l)= _MgSO4 (aq)+Ni(OH) ₂ (s)
(Formula 3) _CoSO4 (aq)+MgO(s)+ _H2O (l)= _MgSO4 (aq)+Co(OH) ₂ (s)

The nickel-containing hydroxide is generally called MHP (Mixed Hydroxide Precipitate) and refers to a mixture of nickel hydroxide and cobalt hydroxide. Specifically, it contains 5% to 50% by mass of Ni, 0.05% to 10.0% by mass of CO, and about 0.01% to 10.0% by mass of impurities such as Mg, manganese (Mn), Al, and Fe. These nickel-containing hydroxides can be made into electric nickel by dissolving and purifying the solution, and then electrolytically winning the solution. The nickel-containing hydroxides produced by the present invention can also be made into final products such as electric nickel using these existing methods.

The neutralized end liquid, which is the mother liquor for nickel recovery, is a sulfuric acid solution in which impurities have been reduced by passing the leachate through the neutralization process S13. Note that this mother liquor for nickel recovery may contain several grams per liter of impurities such as Fe, Mg, Mn, etc., but these impurities have low stability as sulfides and will not be contained in the nickel-containing sulfide that is produced.

[Second step]
The second step S2 is a step of producing MgCO ₃ that can be used in the first step S1 from Mg contained in the "high magnesium ore" that was difficult to use in the conventional hydrometallurgical process. As shown in FIG. 1, in the second step S2, the elution improvement treatment step S21 and the carbonate formation step S22 are performed in sequence as essential steps. In addition, the generated carbonate may be recovered by the carbonate recovery step S23, for example. However, the carbonate recovery step S23 is not an essential step in the "hydrometallurgical method for nickel oxide ore" of the present invention. If the magnesium carbonate generated in the carbonate formation step S22 of the second step S2 is used as a neutralizing agent in the neutralization step S13 of the first step S1, it is possible to carry out the present invention regardless of whether or not the carbonate recovery step S23, i.e., the separation and recovery process of the generated carbonate and the solution, which will be described in detail below, is performed, and such an embodiment is naturally within the technical scope of the present invention.

In the "hydrometallurgical method for nickel oxide ore" of the present invention, ore with a magnesium concentration exceeding 5% by mass ("high-magnesium ore") is not charged in the first step S1, but is charged in the second step S2. However, it is not essential that all of the "high-magnesium ore" is charged only in the second step S2, and even if some of the "high-magnesium ore" containing nickel is mixed in with the ore charged in the first step S1, it is within the technical scope of the present invention as long as the "high-magnesium ore" is charged in the second step S2, which is carried out in parallel.

In the "wet smelting method for nickel oxide ore" of the present invention, ores other than "nickel oxide ore" having a magnesium concentration exceeding 5 mass% can also be used as a material ore for generating _MgCO3 in the second step S2. However, the "high-magnesium ore" used in the second step S2 is preferably an ore such as saprolite ore that is normally used as a raw material ore for nickel smelting, and is a "nickel oxide ore" having a high magnesium concentration. By carrying out the present invention in such a manner that "nickel oxide ore" having a high magnesium concentration is used as the "high-magnesium ore" in the second step S2, for example, by carrying out the carbonate recovery step S23, the residue after _MgCO3 is recovered, that is, the "low-magnesium nickel oxide ore slurry" derived from the above-mentioned "high-magnesium nickel oxide ore", can be charged into the leaching step S11 and effectively utilized.

In addition, examples of ores that can be used as "high magnesium ores" in the second step S2 and contain Mg as a silicate mineral include "nickel oxide ores" such as saprolite ore, as well as lizardite, chrysotile, enstatite, foresterite, talc, magnesite, serpentine, olivine, and smectite.

Here, in the "high magnesium ore" that can be used in the second step S2, most of the Mg is contained as silicate minerals (magnesium _silicate ( _Mg3Si2O5 (OH) ₄ ) and _the like). Magnesium silicate has a three-dimensional complex crystal structure, and since Mg is present at the center, it is difficult for Mg to be eluted from the magnesium silicate into the solution. Therefore, in the "method for hydrometallurgy of nickel oxide ore" of the present invention, in the second step S2, first, a leaching improvement treatment step S21, which will be described in detail below, is set as an essential step as a treatment for sufficiently promoting the leaching of the silicate mineral into the solution, and within this step, a leaching improvement treatment for the "high magnesium ore" is performed as will be described in detail below.

Among the above-mentioned "high magnesium ores", ores containing Mg as magnesium silicate and having a mass ratio of Mg to Si (Mg/Si) of 0.5 or more are particularly preferred. Ores having a ratio of 1.0 or more are more preferred. If the Mg/Si ratio is 0.5 or more, more Mg can be dissolved into the solution after the elution improvement treatment. In addition, compounds containing more Si than Mg tend to have a complex crystal structure, making it difficult for Mg to be dissolved. The Si content (mass) in the "alkaline earth metal-containing ore" can be determined by a method in which 2.5 g each of sodium peroxide and sodium carbonate are mixed with 0.5 g of ore, the mixture is heated to 800°C in an electric furnace and melted, cooled, and then leached with hydrochloric acid, and the sample is measured by ICP atomic emission spectrometry. Similarly, the magnesium concentration (mass) in "alkaline earth metal-containing ore" can be determined by leaching 0.5 g of ore in hydrochloric acid and measuring it with ICP atomic emission spectrometry.

(Elution property improvement treatment process)
As described above, the elution property improvement process S21 is a process for changing the crystal structure of the "high magnesium ore" which has a complex crystal structure and tends to make it difficult for Mg to be eluted, thereby improving the elution property of Mg from the "high magnesium ore" into a solution. The specific process for improving the elution property is not limited to a specific process, and any process method, whether known or not, can be used. As a conventionally known process for improving the elution property, as disclosed in JP-A-10-249153 and JP-T-2012-500718, a process for burning the "high magnesium ore" or a process for crushing the "high magnesium ore" into fine particles and then heating the same can be mentioned. In this way, by changing the crystal structure of the "high magnesium ore" by dehydration or the like, the elution property of Mg from the "high magnesium ore" into a solution can be improved. It is preferable to use water as the above-mentioned solution used when carrying out the present invention.

As an example, if the "elution improvement treatment" is performed by heating the "high magnesium ore" by calcination or the like, the heating temperature for the "elution improvement treatment" is preferably 500°C or more and 800°C or less (furnace atmosphere temperature), and more preferably 600°C or more and 750°C or less, as verified and confirmed in the "Magnesium elution test" below. The heating time is preferably 2 hours or more, and more preferably 4 hours or more.

In addition, in the "hydrometallurgical method for nickel oxide ore" of the present invention, the "high-magnesium ore" may be crushed to a particle size of about 300 μm or less as a pretreatment before being charged into the leaching property improvement treatment step S21, from the viewpoint of ease of handling, to adjust the particle size. The "high-magnesium ore" may be crushed by any common method, and specific examples include crushing with a rod mill or ball mill. However, the particle size of the "alkaline earth metal-containing ore" does not have a significant effect on the leaching property of the alkaline earth metal.

Here, Table 1 below shows the results of a "magnesium leaching test" conducted on nickel oxide ore (saprolite ore: particle size 150 μm to 300 μm) with a magnesium concentration of 6 mass% or more as a specific example of "high magnesium ore" to confirm how the leaching rate of Mg into solution changes depending on the heating temperature when the "leaching improvement treatment" in the leaching improvement treatment step S21 is performed by heating. The heating time (calcination time) in each test example was 4 hours, and the heating temperature was as shown in Table 1.

This "magnesium elution test" was carried out by putting 5 g of the above "high magnesium ore (nickel oxide ore)" which was subjected to different heating conditions during the above "elution improvement treatment" into 200 mL of solution (pure water at a temperature of 60°C) and stirring for 2 hours at a rotation speed of 450 rpm while blowing _CO2 gas (manufactured by Takamatsu Teisan Co., Ltd., concentration 99.995 vol.%) into the solution at a blowing rate of 0.1 L/min. The magnesium elution rate (%) in Table 1 was measured and calculated after the above 2 hours of stirring using the "Method for measuring the amount of eluted magnesium and the method for calculating the elution rate" described below.
(Method of measuring amount of magnesium elution and method of calculating elution rate)
Magnesium elution rate=Magnesium concentration in solution (mg/L)×Amount of eluate (L)/(Magnesium concentration in ore (mass%)÷100×Mass of ore (mg))
The magnesium concentrations were all measured by ICP emission spectrometry.

From the test results of this "magnesium elution test", when "elution improvement treatment" by firing was not performed, the magnesium elution rate was 1.8%. It was also found that the "elution improvement treatment" at a heating temperature of 600°C, which is 500°C or higher, can sufficiently improve the magnesium elution rate to 32.0%. It was also confirmed that the magnesium elution rate decreased to 2.0% at a heating temperature of 900°C, which is higher than 800°C. The reason why the magnesium elution rate decreased by heating at 900° _C is thought to be because magnesium _silicate ( _Mg3Si2O5 (OH) ₄ ), whose complex crystal structure was destroyed by heating, recrystallized in _the form of _Mg2SiO4 .

Whether the complex crystal structures of the minerals contained in the "high magnesium ore" have actually been sufficiently destroyed and made amorphous (i.e., whether elution has been improved) can be determined by confirming the peak of the (002) plane of lizardite (Mg ₃ SiO ₅ (OH) ₄ ) through XRD analysis. As an apparatus for performing XRD analysis, for example, an X-ray diffraction apparatus "Empyrean (manufactured by Malvern Instruments)" can be suitably used.

Another example of a specific method for "elution improvement treatment" is a "mechanochemical treatment" that changes the crystal structure by applying mechanical stress to "high-magnesium ore." "Mechanochemical treatment" is a new ore treatment method independently developed by the inventor of the present application, and refers to "treatment in which mechanical stress is applied to the "high-magnesium ore," which is the treatment target of the "elution improvement treatment," thereby changing the crystal structure of the magnesium-containing mineral contained in the treatment target ("high-magnesium ore") by mechanical energy."

The above-mentioned "mechanochemical treatment" is not limited to a specific treatment method, and can be carried out by various industrial devices capable of applying mechanical stress by stirring or kneading (preferably kneading with a grinding medium (media, etc.)). Specific implementation methods include various stirring and kneading methods using a ball mill or a spiked hammer. In addition, the above-mentioned "mechanochemical treatment" can also be carried out using various other known or unknown stirring or kneading devices that can achieve similar effects.

Mechanochemical processing is not a process aimed at reducing particle size, unlike general "pulverization processing". Even when "mechanochemical processing" is carried out, the particle size of each particle may become smaller due to the destruction of the ore to be processed during the process, but the purpose of "mechanochemical processing" is to make the ore amorphous by reducing the crystallinity (change (destruction) of the structure). Therefore, it is a new processing method with a different purpose and effect from the pulverization processing for particle size adjustment carried out to increase the specific surface area of the object to be processed as a pretreatment preceding the conventional amorphization processing that reduces crystallinity by heat treatment. Figure 2 shows the change in particle size distribution of "high magnesium ore" when "mechanochemical processing" is carried out, but since the particle size distribution shown in the figure has hardly changed, it can be understood that the "mechanochemical processing" that can be a means for carrying out the elution improvement processing step S21 in the present invention is a new processing method different from the general "pulverization processing" aimed at adjusting the particle size distribution.

When "mechanochemical treatment" is performed using a ball mill, the rotation speed of the ball mill should be 10 rpm or more, and the treatment time should be 80 minutes or more. The rotation speed is preferably 100 rpm or more, and more preferably 300 rpm or more, and the treatment time is preferably 150 minutes or more, and more preferably 270 minutes or more. If the treatment time is further extended with the ball mill rotation speed at 300 rpm, the effect of amorphizing the treated object (alkaline earth metal-containing mineral) will increase, but even in this case, the rate of increase in the effect of amorphization will plateau at a treatment time of about 400 minutes. Therefore, the combination of the rotation speed and treatment time of the ball mill is preferably 300 rpm or more, and the treatment time is 270 minutes or more. The "mechanochemical treatment" can be performed either in a dry or wet manner.

Here, Fig. 3 shows the results of an "amorphization treatment test" conducted to verify the effect of amorphization of "high-magnesium ore" when the "elution improvement treatment" in the elution improvement treatment step S21 is performed by the above-mentioned "mechanochemical treatment" for nickel oxide ore (saprolite ore: particle size 150 µm to 300 µm) with a magnesium concentration of 14 mass% or more as a specific example of "high-magnesium ore". The "mechanochemical treatment" was conducted under the following "Test Condition 1", changing the kneading time in the ball mill for each sample, and then each sample was subjected to "crystal structure analysis by X-ray diffraction" to confirm whether amorphization had progressed or not.
(Test condition 1): A planetary ball mill (Star-shaped ball mill Classikline P-5, manufactured by Fritsch) was used as a kneading device for the "mechanochemical treatment" for amorphization, and a sample consisting of 50 g of the above-mentioned "high magnesium ore" and 300 g of zirconia balls (diameter 10 mm) were added as a grinding medium. The table rotation speed of the planetary ball mill was set to 300 rpm, and kneading was performed for a specified time and at a specified table rotation speed, and "mechanochemical treatment" was performed on each sample after the kneading treatment under the above conditions using an X-ray diffraction device Empyrean (manufactured by Malvern Instruments).

From Fig. 3, it was confirmed that the peak of the (002) plane of lizardite (Mg ₃ Si ₂ O ₅ (OH) ₄ ) in each sample (ore) was reduced by the "mechanochemical treatment". This shows that the crystallinity of the ore sample was changed.

Furthermore, the following Table 2 shows the results of a "dissolution promotion test" conducted on nickel oxide ore (saprolite ore: particle size 150 μm to 300 μm) having a magnesium concentration of 6 mass% or more as a specific example of "high magnesium ore" to confirm how the dissolution rate of Mg into solution changes depending on the treatment time when the "dissolution improvement treatment" in the elution improvement treatment step S21 is performed by the above-mentioned "mechanochemical treatment".
In this test, after the amorphous treatment under the following (Test Condition 2), 5 g of each "ore sample" after the treatment was placed in 200 mL of solution (pure water at 60°C), and while stirring at a rotation speed of 450 rpm, _CO2 gas (manufactured by Takamatsu Teisan Co., Ltd., concentration 99.995% by volume) was blown into the solution at a blowing rate of 0.1 L/min, and the elution rate of Mg or Ca into the solution was measured and calculated by the "Method for measuring the amount of elution of alkaline earth metal (Mg) and the method for calculating the elution rate" described below. The test results are shown in Table 2 below.
(Test condition 2): For each of the "ore samples," 50 g of each "ore sample" and 300 g of zirconia balls (diameter 10 mm) as grinding media were placed in the same planetary ball mill as in the above-mentioned "amorphization treatment test," and mechanochemical amorphization treatment was performed. However, the table rotation speed of the planetary ball mill was 300 rpm, and the treatment time was the treatment time shown in Table 2 below.
(Method for measuring the amount of eluted alkaline earth metal (Mg) and method for calculating the elution rate)
Magnesium elution rate=Magnesium concentration in solution (mg/L)×Amount of eluate (L)/(Magnesium concentration in ore (mass%)÷100×Mass of ore (mg))
The magnesium concentrations were all measured by ICP emission spectrometry.

From the above, it was confirmed that the above-mentioned mechanochemical amorphization treatment improves the elution of Mg from magnesium silicate in the ore. The effect of this mechanochemical amorphization treatment is due to a uniquely discovered new method, but it is believed to be due to the fact that the crystal structure of the alkaline earth metal-containing minerals in the alkaline earth metal-containing ore changes due to externally applied mechanical stress, making it easier for the alkaline earth metal to elute into the solution. Therefore, the effect of the above-mentioned mechanochemical treatment is not limited to stirring and kneading using a ball mill, but is also believed to be an effect that is manifested when similar treatment is performed using various other known or unknown stirring or kneading devices.

The "mechanochemical treatment" described above, i.e., the treatment of amorphizing "high-magnesium ore" by applying mechanical stress, is a novel and unprecedented technical means for amorphizing minerals, based on the unique findings of the inventors.

(Carbonate production process)
The carbonate production process S22 is a process in which Mg is sufficiently dissolved into a solution from the "high-magnesium ore" in which the elution property of Mg into solution has been improved through the elution property improvement treatment process S21, _CO2 gas is blown into the solution, and _MgCO3 is precipitated and produced by reacting the dissolved Mg with the _CO2 blown in as gas in the solution (hereinafter also referred to as a "carbonate production process").

The ratio of "high magnesium ore" to the solution for dissolving Mg is preferably 2% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 20% by mass or less. By making the amount (mass ratio) of "high magnesium ore" in the solution 2% by mass or more, high precipitation efficiency of _MgCO3 can be achieved. In addition, by making the amount (mass ratio) 30% by mass or less, the viscosity of the above-mentioned solution that becomes a slurry can be appropriately maintained, and the handleability of the slurry material is improved.

The method of blowing _CO2 gas into the solution is not particularly limited, but as an example, it can be performed by a method of blowing _CO2 gas using a disk-type diffuser or a cylindrical diffuser. The _CO2 concentration of the _CO2 gas blown into the solution may be 10% or more. However, by using a higher concentration of _CO2 gas exceeding 10%, the production of _MgCO3 can be promoted more efficiently.

The _CO2 supply source and supply method used in the carbonate production step S22 are not particularly limited, but _CO2 gas generated in the neutralization step S13 of the first step S1 using a neutralizing agent derived from fossil fuels or carbonates can be used, which can contribute to reducing the total amount of _CO2 gas emissions from the nickel smelting plant.

(Carbonate recovery process)
The carbonate recovery step S23 is a process for recovering the MgCO ₃ generated in the carbonate generation step S22 from the solution. The specific method for recovering this MgCO ₃ is not particularly limited, but as an example, it may be a method of recovering the MgCO 3 by separating the liquid with a filter such as a filter press, or a method of recovering the MgCO 3 by volatilizing the water in the solution.

[Other steps]
In the "hydrometallurgical method for nickel oxide ore" of the present invention, in addition to the above-mentioned four basic steps in the first step S1 (leaching step S11, solid-liquid separation step S12, neutralization step S13, and sulfurization step S14) and the three basic steps in the second step S2 (elution property improvement treatment step S21, carbonate production step S22, and carbonate recovery step S23), an ore screening step may be performed as an upstream step of the leaching step S11 and the elution property improvement treatment step S21. It is also preferable to further perform a final neutralization step as a downstream step of the sulfurization step S14 in the first step S1. Each of these steps is not necessarily an essential step in the "hydrometallurgical method for nickel oxide ore" of the present invention. Regardless of whether or not each of these steps is performed, or the embodiment of each of these steps, any smelting process that performs the above-mentioned five basic steps in a manner that satisfies the requirements of the present invention falls within the technical scope of the present invention.

(Ore screening process)
When using a raw ore consisting of a mixture of multiple types of nickel oxide ores with different magnesium concentrations, it is preferable to carry out an ore screening process in which the raw ore is screened into coarse ore and fine ore prior to the second process S2. When the ore screening process is carried out, the coarse ore screened into the coarse part is regarded as "high magnesium ore" and charged into the second process S2, and the subsequent processes are carried out. On the other hand, the fine ore screened into the fine part in this ore screening process can be charged into the leaching process S11 without passing through the second process S2.

When performing the ore sieving step, it is preferable to sieve the portion in which the proportion of particles with a particle size of less than 45 μm is 40 mass% or less of the solid content to the coarse particle side, and the remaining portion to the fine particle side. By treating the portion sieved to the coarse particle side in this way as coarse ore and "high magnesium ore", the portion containing a relatively high concentration of Mg can be separated from the raw ore, which is a mixture of multiple types of nickel oxide ores with different magnesium concentrations, and charged into the second step S2, thereby enjoying the effects of the "wet smelting method for nickel oxide ore" of the present invention.

(Final neutralization step)
The final neutralization step is a step of performing a neutralization process (detoxification process) on the poor liquid containing impurity elements such as Fe, Mg, and Mn discharged in the sulfurization step S14 to adjust the pH to a predetermined range that meets the discharge standard. The method of detoxification process in the final neutralization step, that is, the method of adjusting the pH, is not particularly limited, but for example, a calcium carbonate (limestone) slurry, a calcium hydroxide (slaked lime) slurry, or, as described above, MgCO ₃ separated and recovered in the second step S2 can be added as a neutralizing agent to adjust the pH to a predetermined range. In addition, although not shown, this final neutralization step can also be performed using MgCO ₃ as a neutralizing agent, similar to the neutralization step S13 in the present invention. This process is also one of the neutralization steps in that it is a process of separating neutralized precipitate to obtain a neutralized final liquid. Therefore, an embodiment in which MgCO ₃ generated in the carbonate generation step S22 is used as the neutralizing agent used in this final neutralization step is naturally within the technical scope of the present invention.

[Characteristics of the overall process]
The overall process of the "hydrometallurgical method for nickel oxide ore" consisting of the above steps is characterized in that, first, MgCO ₃ generated in the carbonate generation step S22 of the second step S2 is utilized as a neutralizing agent used in the neutralization step S13 of the first step S1. As a second characteristic, in the "hydrometallurgical method for nickel oxide ore", CO ₂ gas generated in the smelting plant can be utilized as CO ₂ used to generate MgCO ₃ in the carbonate generation step S22 of the second step S2. Furthermore, as a third characteristic, in the "hydrometallurgical method for nickel oxide ore", nickel oxide ore slurry, which is the residue (of "high magnesium ore") after MgCO ₃ is recovered in the carbonate recovery step S23 of the second step S2, can be charged as a raw material that has been subjected to a treatment to reduce the magnesium concentration in the leaching step S11 of the first step S1. The "nickel oxide ore hydrometallurgy method" is a composite process in which the first step S1 and the second step S2 are performed in parallel, and thus it is possible to effectively utilize "high magnesium ore" that was difficult to utilize in the conventional hydrometallurgy process. In addition to being able to effectively utilize ore that was previously unused, it is also possible to enjoy the additional effects of reducing the amount of neutralizing agent used and reducing _CO2 emissions in the entire process. Furthermore, the magnesium carbonate production process performed in the "nickel oxide ore hydrometallurgy method" of the present invention is also an excellent technology as a method for fixing _CO2 in minerals. In other words, the "nickel oxide ore hydrometallurgy method" of the present invention is also a suitable process for specifically implementing "Mineral Carbonation Technology", which is one of the "Carbon Sequestration and Utilization Technologies (CCSU)".

S1 First step S11 Leaching step S12 Solid-liquid separation step S13 Neutralization step S14 Sulfurization step S15 Hydroxylation step S2 Second step S21 Elution improvement treatment step S22 Carbonate generation step S23 Carbonate recovery step

Claims (4)

a leaching step of leaching the nickel oxide ore with a mineral acid to obtain a leach slurry;
a solid-liquid separation step of separating the leaching slurry into a leachate and a leach residue;
a neutralization step of separating a neutralized precipitate from the leaching solution to obtain a neutralization end solution;
A first step in which
a leaching improvement treatment step for improving the leaching of magnesium by changing the crystal structure of a magnesium-containing ore having a magnesium concentration of more than 5% by mass;
a carbonate production step in which the magnesium-containing ore that has been subjected to the elution improvement treatment step is put into a solution, and the magnesium eluted into the solution is reacted with carbon dioxide to produce magnesium carbonate;
A second step in which
having
The magnesium carbonate produced in the carbonate production step of the second step is used as a neutralizing agent in the neutralization step of the first step.
A hydrometallurgical process for nickel oxide ores. The carbon dioxide gas discharged from the neutralization step of the first step is used as carbon dioxide to react with the magnesium dissolved in the solution in the carbonate production step of the second step.
2. The method for hydrometallurgy of nickel oxide ore according to claim 1. A sulfurizing agent is added to the neutralization end solution obtained in the neutralization step of the hydrometallurgical method for producing nickel oxide ore according to claim 1 or 2 to generate nickel-containing sulfide.
A method for producing nickel-containing sulfides. A neutralizing agent is added to the neutralization end solution obtained in the neutralization step of the hydrometallurgical method for producing nickel oxide ore according to claim 1 or 2 to generate a nickel-containing hydroxide.
A method for producing nickel-containing hydroxide.

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