Method for producing magnesium carbonate, and method for fixing carbon dioxide

Abstract

In a process for producing MgCO3 from a "Cr- and Mg-containing ore", the present invention achieves sufficient elution of Mg into a solution through heat treatment while preventing the elution of toxic Cr(VI) into the solution.　Provided is a method for producing magnesium carbonate comprising a heat treatment St1 in which ore that contains chromium and magnesium and has a magnesium concentration of at least 5 mass% is heated, and a carbonate generation treatment St2 in which carbon dioxide is reacted with magnesium that has eluted into an aqueous solution as a result of introducing the ore that has been subjected to the heat treatment St1 into the solution, wherein the heat treatment St1 is carried out in an inert gas atmosphere or a reducing atmosphere at a heating temperature of 500°C to 800°C.

Description

Method for producing magnesium carbonate and method for fixing carbon dioxide

[0001] The present invention relates to a method for producing magnesium carbonate and a method for fixing carbon dioxide. More specifically, the present invention relates to a method for producing magnesium carbonate from an ore containing magnesium and chromium and carbon dioxide, and a method for fixing carbon dioxide in an ore containing magnesium and chromium.

[0002] With the rapid progress of global warming in recent years, the amount of carbon dioxide (CO ２ ) emissions, along with the reduction of emitted CO ２ There is a demand for the practical application of carbon capture, storage, and utilization (CCSU) technology by fixing carbon dioxide in minerals, etc. A concrete means of realizing carbon capture, storage, and utilization (CCSU) technology is to store CO2 deep in seawater. ２ or CO ２ Various CO ２ However, these methods are not suitable for CO2 fixation. ２ The disposal of this waste requires a lot of money and is not economical, and the subsequent impact on the environment is unclear, so there are still many problems to be solved before it can be put into practical use.

[0003] On the other hand, one of the carbon capture and utilization technologies (CCSU) mentioned above is the use of silicate minerals containing magnesium (Mg) and calcium (Ca) as CO ２ A technology that reacts magnesium carbonate with magnesium carbonate to immobilize it as a carbonate (Mineral Carbonation Technology) has been attracting attention (see Patent Document 1). ３ ) and calcium carbonate (CaCO ３ Carbonates such as ) are very stable at room temperature and pressure and are not easily affected by environmental changes, so they can be used for a long period of time. ２ This is because CO can be stably fixed in the mineral. ２ MgCO produced with the immobilization of ３ and CaCO ３These materials can be used in a wide range of industrial fields, including as neutralizing agents, rubber and plastic enhancers, pesticides, fertilizers, and animal feed ingredients, and because they are carbon-neutral, demand for them is expected to increase further in the future.

[0004] Here, by using the above-mentioned mineral carbonation technology, CO ２ One example of a manufacturing process that can also contribute to the fixation of magnesium carbonate (MgCO ) is the production of magnesium carbonate using ores containing magnesium as silicate minerals. ３ In this manufacturing process, Mg is added to CO ２ In order to react with Mg, it is necessary to sufficiently dissolve Mg from the ore into the solution. In the ore, Mg is dissolved in silicate minerals (e.g., Mg ３ Si ２ O ５ (OH) ４ , Mg ３ Si ４ O １０ (OH) ２ Since it is contained as a compound such as Mg ２＋ Therefore, when carrying out the above manufacturing process, the above ore is dissolved in the solution. ２＋ It has been necessary to carry out some kind of pretreatment to promote the dissolution of the compound.

[0005] As a specific means of pretreatment required when implementing mineral carbonation technology, a technique has been proposed in which ore containing Mg as a silicate mineral is heated to promote the elution of Mg contained in the ore into a solution (see Patent Documents 2 and 3).

[0006] Here, the above-mentioned "magnesium carbonate (MgCO ) produced using ore containing Mg as a silicate mineral" ３In the "manufacturing process for nickel smelting and refining," ores containing Mg as a silicate mineral at a concentration of 5% by mass or more can be preferably used. However, many of these ores also contain chromium (Cr). For example, in addition to limonite ore used as a raw material ore for nickel smelting, oxide ores such as saprolite ore, lizardite, chrysotile, enstatite, foresterite, talc, magnesite, serpentine, olivine, smectite, etc., fall under this category of ores. Hereinafter, in this specification, ores containing Cr and Mg and having a magnesium concentration of 5% by mass or more, including these ores, will be referred to as "Cr- and Mg-containing ores."

[0007] And, there is a process that is technically closely related to the above-mentioned mineral carbonation technology, and is "magnesium carbonate (MgCO )" that is carried out using "Cr and Mg-containing ore." ３ In the "process for the production of chromium ore and the fixation of carbon dioxide," if the above-mentioned heat treatment is carried out in an oxidizing atmosphere such as the atmosphere in order to promote the elution of Mg contained in the ore as a silicate mineral into the solution, the oxidation of Cr in the ore will progress, and even hexavalent chromium (Cr(VI)), a harmful substance, will be eluted into the solution. This has come to be recognized as a new problem.

[0008] JP-A-10-249153 Publication Special Publication No. 2012-500718 Publication Special Publication No. 2013-505124

[0009] The present invention has been proposed in view of the above circumstances, and relates to a method for producing MgCO from a "Cr- and Mg-containing ore" containing chromium and magnesium and having a magnesium concentration of 5 mass% or more and carbon dioxide. ３ The purpose of this invention is to prevent the harmful substance Cr(VI) from being eluted into the solution together with Mg by the heat treatment carried out to increase the elution of Mg from "Cr- and Mg-containing ore" in the process of manufacturing the above mentioned metals.

[0010] The present inventors have found that the above-mentioned problems can be solved by carrying out a heat treatment in an inert gas atmosphere or a reducing atmosphere to enhance the elution of Mg from a "Cr- and Mg-containing ore," and have thus completed the present invention.

[0011] (1) A method for producing magnesium carbonate, comprising: a heat treatment for heating an ore containing chromium and magnesium and having a magnesium concentration of 5% by mass or more; and a carbonate production treatment for placing the ore that has undergone the heat treatment in an aqueous solution and reacting the magnesium dissolved in the solution with carbon dioxide, wherein the heat treatment is carried out at a heating temperature of 500°C or more and 800°C or less in an inert gas atmosphere or a reducing atmosphere.

[0012] According to the method for producing magnesium carbonate in (1), MgCO is produced from "Cr and Mg-containing ore". ３ In the process of producing Cr(VI), the heat treatment carried out to enhance the elution of Mg from the "Cr- and Mg-containing ore" can prevent the harmful substance Cr(VI) from being eluted into the solution together with Mg.

[0013] (2) The method for producing magnesium carbonate according to (1), wherein the inert gas atmosphere is an argon gas atmosphere, a nitrogen gas atmosphere, or an atmosphere of a mixed gas of argon gas and nitrogen gas, and the reducing atmosphere is a carbon monoxide gas atmosphere, a hydrogen gas atmosphere, a hydrocarbon gas atmosphere, or an atmosphere of a mixed gas of two or more gases selected from carbon monoxide gas, hydrogen gas, and hydrocarbon gas.

[0014] According to the method for producing magnesium carbonate of (2), the effect of preventing Cr(VI) from leaching into the solution, which is achieved by the method for producing magnesium carbonate of (1), can be more reliably and with extremely high accuracy.

[0015] (3) A method for fixating carbon dioxide, comprising: a heat treatment for heating an ore containing chromium and magnesium and having a magnesium concentration of 5% by mass or more; and a carbon dioxide fixation treatment for placing the ore that has been subjected to the heat treatment in an aqueous solution, dissolving magnesium into the solution, and reacting the magnesium with carbon dioxide to fix carbon dioxide as magnesium carbonate, wherein the heat treatment is carried out at a heating temperature of 500°C or more and 800°C or less in an inert gas atmosphere or a reducing atmosphere.

[0016] According to the carbon dioxide fixation method (3), Mg and CO contained in the "Cr and Mg-containing ore" are fixed. ２ and react with CO ２ MgCO ３ When carrying out mineral carbonation technology, which is a technology for fixing Cr (VI) in the ore, the heat treatment is carried out to increase the elution of Mg from the "Cr- and Mg-containing ore." This prevents the harmful substance Cr (VI) from being eluted into the solution together with Mg.

[0017] (4) The method for fixation of carbon dioxide according to (3), wherein the inert gas atmosphere is an argon gas atmosphere, a nitrogen gas atmosphere, or an atmosphere of a mixed gas of argon gas and nitrogen gas, and the reducing atmosphere is a carbon monoxide gas atmosphere, a hydrogen gas atmosphere, a hydrocarbon gas atmosphere, or an atmosphere of a mixed gas of two or more gases selected from carbon monoxide gas, hydrogen gas, and hydrocarbon gas.

[0018] According to the carbon dioxide fixation method (4), the effect of preventing the dissolution of Cr(VI) into the solution, which is achieved by the carbon dioxide fixation method described in (3), can be more reliably and with extremely high accuracy.

[0019] According to the present invention, MgCO ３ In the process of producing Cr(VI), the heat treatment carried out to enhance the elution of Mg from the "Cr- and Mg-containing ore" can prevent the harmful substance Cr(VI) from being eluted into the solution together with Mg.

[0020] 1 is a flow chart showing the flow of a method for producing magnesium carbonate of the present invention. 2 is a process diagram showing the entire combined process in a combined embodiment in which the method for producing magnesium carbonate (or the method for fixing carbon dioxide) of the present invention is combined with a hydrometallurgical process (HPAL) of nickel oxide ore.

[0021] An embodiment of the present invention will be described in detail below. However, the present invention is not limited to the following embodiment, and various modifications are possible within the scope of the present invention.

[0022] <Method for producing magnesium carbonate> The "method for producing magnesium carbonate" of the present invention is a method for producing magnesium carbonate (MgCO 3 ) from the "Cr- and Mg-containing ore" defined above, i.e., "an ore containing Cr and Mg and having a magnesium concentration of 5 mass % or more," and carbon dioxide. ３ ) is a manufacturing method for producing the same.

[0023] 1 is a flow chart showing the process flow of the "manufacturing method of magnesium carbonate" of the present invention. As shown in the figure, in the "manufacturing method of magnesium carbonate" of the present invention, the "manufacturing method of magnesium carbonate" includes heat treatment St1 in which "Cr- and Mg-containing ore" is heated, and Mg eluted from the "Cr- and Mg-containing ore" into a solution is dissolved in CO ２ By reacting with magnesium carbonate (MgCO ３ This is a process in which carbonate production treatment St2, which produces MgCO ３ Regarding the recovery of magnesium carbonate (MgCO ３ It is preferable that this is carried out by a carbonate recovery treatment St3 in which the carbonate slag is recovered.

[0024] [Cr- and Mg-containing ore] The "Cr- and Mg-containing ore" used in the "method for producing magnesium carbonate" of the present invention is not limited to a specific ore as long as it contains Cr and Mg and satisfies the above-mentioned requirements of having a magnesium concentration of 5 mass% or more. However, an ore containing Mg as magnesium silicate is preferred. Examples of such ores include, as mentioned above, limonite ore, nickel oxide ores such as saprolite ore, lizardite, chrysotile, enstatite, forestellite, talc, magnesite, serpentine, olivine, and smectite. The magnesium concentration (mass) in the "Cr- and Mg-containing ore" can be determined by leaching 0.5 g of the ore in hydrochloric acid and measuring it by ICP atomic emission spectrometry.

[0025] In addition, in the "Cr and Mg-containing ore", as mentioned above, most of the Mg is contained in silicate minerals (magnesium silicate (Mg ３ Si ２ O ５ (OH) ４ ) and the like). Magnesium silicate has a three-dimensional, complex crystal structure, and Mg is present at the center of the structure, so that elution of Mg from the magnesium silicate into the solution is difficult. Therefore, in the carbonate generation treatment St2 described above, heat treatment of the "Cr- and Mg-containing ore" is effective as a pretreatment to sufficiently promote elution of Mg into the solution.

[0026] Furthermore, among the above-mentioned "Cr- and Mg-containing 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 with a Mg / Si ratio of 1.0 or more are even more preferred. A Mg / Si ratio of 0.5 or more allows for a greater amount of Mg to be eluted into an aqueous solution after heat treatment. Compounds containing a higher amount of Si relative to Mg tend to have a more complex crystal structure, making it more difficult for Mg to be eluted. The Si content (mass) in "alkaline earth metal-containing ores" can be determined by mixing 2.5 g each of sodium peroxide and sodium carbonate with 0.5 g of ore, heating and melting the mixture in an electric furnace to 800°C, cooling, and then leaching the mixture with hydrochloric acid, followed by ICP atomic emission spectroscopy. Similarly, the magnesium concentration (mass) in the "alkaline earth metal-containing ore" can be determined by leaching 0.5 g of the ore in hydrochloric acid and measuring it by ICP emission spectrometry.

[0027] [Heat Treatment] In the "method for producing magnesium carbonate" of the present invention, heat treatment St1 is a treatment in which "Cr- and Mg-containing ore" such as limonite ore is heated by calcination or the like. As verified and confirmed in the "magnesium elution test" described below, the heating temperature in the heat treatment for heat treatment St1 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. The heating time is preferably 2 hours or more, and more preferably 4 hours or more.

[0028] Furthermore, in the "method for producing magnesium carbonate" of the present invention, the "Cr- and Mg-containing ore" may be crushed to a particle size of about 300 μm or less as a pretreatment before being charged into heat treatment St1, from the viewpoint of ease of handling. The "Cr- and Mg-containing ore" may be crushed by any common method, and specific examples include crushing with a rod mill or a ball mill. However, the particle size of the "alkaline earth metal-containing ore" does not significantly affect the elution of alkaline earth metals.

[0029] Table 1 below shows the results of a "magnesium elution 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 "Cr- and Mg-containing ore" to confirm how the elution rate of Mg into solution changes depending on the heating temperature in heat treatment St1. The heating time (calcination time) in each test example was 4 hours, and the heating temperature was as shown in Table 1.

[0030] In this "magnesium elution test," 5 g of the above-mentioned "Cr and Mg-containing ore (nickel oxide ore)" which were subjected to different heating conditions during the heat treatment St1 were placed in 200 mL of a solution (pure water at a temperature of 60°C), and CO was added to the solution while stirring at a rotation speed of 450 rpm for 2 hours. ２ Gas (manufactured by Takamatsu Teisan Co., Ltd., concentration 99.995% by volume) was blown in at a rate of 0.1 L / min. The magnesium elution rates (%) in Table 1 were measured and calculated after the above-mentioned two hours of stirring had elapsed using the "Method for measuring the amount of eluted magnesium and the method for calculating the elution rate" below. (Method for measuring the amount of eluted magnesium and the method for calculating the elution rate) Magnesium elution rate = magnesium concentration in solution (mg / L) × volume of eluate (L) / (magnesium concentration in ore (mass %) ÷ 100 × mass of ore (mg)) Each of the above magnesium concentrations was measured by ICP atomic emission spectrometry.

[0031] The test results of this "magnesium elution test" showed that the magnesium elution rate was 1.8% when heat treatment St1 by firing was not performed. It was also found that heat treatment St1 at 600°C, which is a heating temperature of 500°C or higher, could 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 when heated to 900°C is that the complex crystalline structure of magnesium silicate (Mg ３ Si ２ O ５ (OH) ４ ) is Mg ２ SiO ４This is thought to be due to the fact that the crystals are re-crystallized in the form of

[0032]

[0033] In the "method for producing magnesium carbonate" of the present invention, the "Cr- and Mg-containing ore" is heated in heat treatment St1 in an inert gas atmosphere or a reducing atmosphere. As will be shown later in the Examples, this promotes the elution of Mg contained in the "Cr- and Mg-containing ore" as a magnesium silicate mineral into the aqueous solution, while preventing Cr contained in the "Cr- and Mg-containing ore" from becoming Cr(VI), a harmful substance, and eluting into the aqueous solution. In this specification, "Cr(VI)" means hexavalent chromium in an ionic state.

[0034] Furthermore, it is more preferable to heat the "Cr- and Mg-containing ore" in the heat treatment St1 in an inert gas atmosphere such as an argon gas atmosphere or a nitrogen gas atmosphere, or a reducing atmosphere such as a carbon monoxide gas atmosphere, a hydrogen gas atmosphere, or a hydrocarbon gas (methane, propane, butane, etc.) atmosphere. This is because heating in an oxidizing atmosphere such as air oxidizes the Cr contained in the ore and becomes Cr(VI), which dissolves into the aqueous solution. Note that the inert gas atmosphere may be an atmosphere of each of the gases exemplified above, or an atmosphere of a mixed gas of the above gases (argon gas, nitrogen gas). Similarly, the reducing atmosphere may be an atmosphere of a mixed gas of two or more of the above gases (carbon monoxide gas, hydrogen gas, hydrocarbon gas).

[0035] It should be noted that whether the complex crystal structure of the minerals contained in the "Cr- and Mg-containing ore" has actually been sufficiently destroyed by heating can be confirmed by XRD analysis, for example, in the case of lizardite (Mg ３ SiO ５ (OH) ４The presence or absence of lizardite can be determined by checking the peak of the (002) plane of the crystalline silicate. Furthermore, peaks of forsterite or talc, for example, can be used as a substitute for lizardite. An X-ray diffractometer such as "Empyrean (manufactured by Malvern Instruments)" can be suitably used as the XRD analysis device.

[0036] [Carbonate Formation Treatment] In the "manufacturing method for magnesium carbonate" of the present invention, the carbonate formation treatment St2 performed following the heat treatment St1 described above is a treatment for sufficiently dissolving Mg into the solution while preventing Cr from being dissolved into the solution from the "Cr- and Mg-containing ore" whose complex crystal structure has been destroyed through the "heat treatment," and dissolving CO into the solution. ２ Gas is blown in, and the dissolved ionic Mg and the CO blown in as gas are mixed in the solution. ２ by reacting with MgCO ３ This is a process to generate

[0037] CO in solution ２ The method of blowing gas is not particularly limited. For example, CO 2 is blown into the gas using a disk-type diffuser or a cylindrical diffuser. ２ This can be done by blowing gas into the solution. ２ Gas CO ２ The concentration should be 10% or more. However, if the concentration exceeds 10%, ２ By converting it into a gas, MgCO ３ can be generated.

[0038] The ratio of the "Cr- and Mg-containing ore" to the solution is preferably 2% by mass or more and 30% by mass or less, and more preferably 5% by mass or more and 20% by mass or less. By making the amount (mass ratio) of the "Cr- and Mg-containing ore" in the solution 2% by mass or more, MgCO ３ Furthermore, by setting the amount (mass ratio) of alkaline earth metal-containing ore in the solution to 30 mass % or less, the viscosity of the slurry-like solution can be maintained at an appropriate level, improving the ease of handling.

[0039] In addition, the CO used in the carbonate generation process St2 ２The source of CO is not particularly limited, but an example is CO produced from a neutralization process carried out in a plant for metal smelting using ore containing Mg as an impurity (for example, nickel smelting using laterite ore). ２ CO emitted in various metal smelting processes, such as gas ２ By utilizing gas and carrying out the production method of the present invention in parallel in the same plant, CO from these metal smelting processes can be reduced. ２ It can also contribute to reducing the total amount of gas emissions.

[0040] [Carbonate Recovery Treatment] The carbonate recovery treatment St3, which is performed following the carbonate production treatment St2, recovers magnesium carbonate (MgCO ３ The specific method for recovering this alkaline earth metal carbonate is not particularly limited, but examples include a method of recovering the carbonate by separating the liquid using a filter such as a filter press, or a method of recovering the carbonate by volatilizing the water content of an aqueous solution.

[0041] <Method for Fixing Carbon Dioxide> The "method for fixing carbon dioxide" of the present invention is a method for fixing carbon dioxide by fixing carbon dioxide to minerals. ２ The method for immobilizing the compound of claim 1, wherein the compound is a compound of the formula (I) and the compound is a compound of the formula (II). ２ is reacted with Mg to produce magnesium carbonate (MgCO ３ This method is suitable for specifically implementing "Mineral Carbonation Technology," which is one of the "Carbon Sequestration and Utilization Technologies (CCSU)."

[0042] In the "carbon dioxide fixation method" of the present invention, CO ２ As in the "method for producing magnesium carbonate" of the present invention described in detail above, a "Cr- and Mg-containing ore", i.e., an ore containing Cr and Mg and having a magnesium concentration of 5 mass% or more, can be used as the ore from which Mg is obtained to react with

[0043] Furthermore, in the "method for fixing carbon dioxide" of the present invention, in the same manner as in the heat treatment St1 in the "method for producing magnesium carbonate" of the present invention, a heat treatment St1 is performed in which the "Cr- and Mg-containing ore" is heated to 500°C or higher and 800°C or lower in an inert gas atmosphere or a reducing atmosphere, and Mg in an ionic state eluted into a solution from the "Cr- and Mg-containing ore" is converted into CO ２ The magnesium carbonate (MgCO ３ ) as CO ２ carbon dioxide fixation treatment to fix CO ２ Magnesium carbonate (MgCO ３ ) is recovered from the solution by solid-liquid separation treatment in the same manner as in the carbonate recovery treatment St3 in the "method for producing magnesium carbonate" of the present invention.

[0044] <Application to Hydrometallurgy of Nickel Oxide Ore> Either the "method for producing magnesium carbonate" or the "method for fixation of carbon dioxide" of the present invention can be implemented as a method for carrying out a pretreatment step (magnesium removal step S1) of removing Mg contained in a raw material ore in the form of silicate as an impurity when carrying out the "method for hydrometallurgy of nickel oxide ore" shown in Fig. 2. This embodiment of the production method of the present invention is particularly effective when a nickel oxide ore having a magnesium concentration of more than 5 mass %, such as "saprolite ore" (hereinafter also referred to as "high-Mg nickel oxide ore" in this specification), is used as the raw material ore when carrying out the "method for hydrometallurgy of nickel oxide ore".

[0045] The "hydrometallurgical method for producing nickel oxide ore" that can be carried out using the "method for producing magnesium carbonate" or the "method for fixation of carbon dioxide" of the present invention as a partial process is a known process as an overall process, and an example of the flow is shown in Figure 2. This overall process sequentially includes a demagnesium step S1 performed to separate and recover Mg from nickel oxide ore, a leaching step S2 in which sulfuric acid is added to nickel oxide ore whose magnesium concentration has been reduced and leaching is performed under high temperature and high pressure to obtain a leached slurry, a solid-liquid separation step S3 in which the leached slurry is separated into a leachate and a leach residue, a neutralization step S4 in which the pH of the leachate is adjusted to separate a neutralized precipitate containing impurity elements to obtain a neutralized end solution, and a sulfurization step S5 in which a sulfurizing agent is added to the neutralized end solution to produce a sulfide containing nickel (Ni).

[0046] As described above, the "method for producing magnesium carbonate" or the "method for fixation of carbon dioxide" of the present invention can be implemented as a suitable technical means for carrying out the demagnesium step S1 among the steps (S1 to S5) of the above-mentioned "method for hydrometallurgy of nickel oxide ore." Even when the demagnesium step S1 is carried out by the "method for producing magnesium carbonate" or the "method for fixation of carbon dioxide" of the present invention, the incorporation of Cr(VI) into the aqueous solution discharged from the demagnesium step S1 can be prevented, and therefore the other steps, such as the leaching step S2, solid-liquid separation step S3, neutralization step S4, and sulfiding step S5, can be carried out safely in the same manner as in the conventionally known embodiments of the "method for hydrometallurgy of nickel oxide ore."

[0047] [Magnesium removal step] The magnesium removal step S1 is a step in which Mg is eluted from a "high-Mg nickel oxide ore" such as saprolite ore to produce a "low-Mg nickel oxide ore." In this specification, a nickel oxide ore having a magnesium concentration of less than 5% by mass is referred to as a "low-Mg nickel oxide ore." However, in the magnesium removal step S1, the magnesium concentration of the "low-Mg nickel oxide ore" obtained by reducing the magnesium concentration of the "high-Mg nickel oxide ore" may be less than 5% by mass, as described above, but is preferably 2.0% by mass or less, and more preferably 0.5% by mass or less.

[0048] As mentioned above, in "high Mg nickel oxide ores" such as saprolite ores, Mg is mainly present in magnesium silicates (Mg ３ Si ２ O ５ (OH) ４ However, by carrying out the magnesium removal step S1 by the above-described methods of the present invention, Mg can be eluted from the "high Mg nickel oxide ore" to produce the above-described "low Mg nickel oxide ore" efficiently at low cost and without CO ２ In this embodiment, the CO ions reacting with the dissolved ionic Mg can be used together with the reduction treatment. ２ The source of CO is not particularly limited, but an example is CO generated from fossil fuels in an autoclave or the like. ２ Gas, CO emitted from the downstream neutralization step S4 ２ CO emitted in the process, such as gas ２ By utilizing gas, CO from nickel smelting plants can be reduced. ２ This can also contribute to a reduction in the total amount of gas emissions. Furthermore, ores containing high concentrations of Mg, such as saprolite ores, which have not been actively used in the hydrometallurgical refining of nickel oxide ores, can now be used as low-Mg nickel oxide ores without reducing the productivity of the "hydrometallurgical refining method (HPAL process)."

[0049] The effects of the "method for producing magnesium carbonate" of the present invention will be specifically explained below using examples, but the present invention is not limited to the following examples.

[0050] Table 2 below shows the results of a "magnesium and hexavalent chromium elution test" conducted on the nickel oxide ore used in the above-mentioned "magnesium elution test" to investigate how the elution of Mg and Cr(VI) into solution changes depending on the heating atmosphere in heat treatment St1. The heating atmosphere was changed to an inert gas atmosphere in Example 1 and a reducing atmosphere in Example 2, but the tests were conducted under the same conditions as the above-mentioned "magnesium elution test" for both the examples and comparative examples. The magnesium concentrations (mg / L) and chromium concentrations (mg / L) in Table 2 below are values ​​measured by ICP optical emission spectrometry.

[0051]

[0052] From the test results of the "Magnesium and hexavalent chromium elution test" shown in Table 2, it was found that by performing the heating in the heat treatment St1 in a manner of firing in an inert gas atmosphere or a reducing atmosphere, the elution of Mg contained in the "Cr- and Mg-containing ore" can be sufficiently promoted while the elution of Cr(VI) into the aqueous solution can be sufficiently prevented.

[0053] St1 Heat treatment St2 Carbonate production treatment St3 Carbonate recovery treatment S1 Demagnesium removal step S2 Leaching step S3 Solid-liquid separation step S4 Neutralization step S5 Sulfurization step

Claims

1. A method for producing magnesium carbonate, comprising: a heat treatment for heating an ore containing chromium and magnesium and having a magnesium concentration of 5% by mass or more; and a carbonate production process for placing the ore that has undergone the heat treatment in an aqueous solution and reacting the magnesium dissolved in the solution with carbon dioxide, wherein the heat treatment is carried out at a heating temperature of 500°C or more and 800°C or less in an inert gas atmosphere or a reducing atmosphere.

2. A method for producing magnesium carbonate according to claim 1, wherein the inert gas atmosphere is an argon gas atmosphere, a nitrogen gas atmosphere, or an atmosphere of a mixed gas of argon gas and nitrogen gas, and the reducing atmosphere is a carbon monoxide gas atmosphere, a hydrogen gas atmosphere, a hydrocarbon gas atmosphere, or an atmosphere of a mixed gas of two or more gases selected from carbon monoxide gas, hydrogen gas, and hydrocarbon gas.

3. A method for fixing carbon dioxide, comprising: a heat treatment for heating an ore containing chromium and magnesium and having a magnesium concentration of 5% by mass or more; and a carbon dioxide fixation treatment for fixing carbon dioxide as magnesium carbonate by placing the ore that has been subjected to the heat treatment in an aqueous solution and reacting the magnesium dissolved in the solution with carbon dioxide, wherein the heat treatment is carried out at a heating temperature of 500°C or more and 800°C or less in an inert gas atmosphere or a reducing atmosphere.

4. The method for fixing carbon dioxide according to claim 3, wherein the inert gas atmosphere is an argon gas atmosphere, a nitrogen gas atmosphere, or an atmosphere of a mixed gas of argon gas and nitrogen gas, and the reducing atmosphere is a carbon monoxide gas atmosphere, a hydrogen gas atmosphere, a hydrocarbon gas atmosphere, or an atmosphere of a mixed gas of two or more gases selected from carbon monoxide gas, hydrogen gas, and hydrocarbon gas.

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