Method of producing magnesium carbonate, and method of immobilizing carbon dioxide

Abstract

To prevent the elution of Cr (VI) which is a harmful substance, into a solution in a process of producing MgCO3 from [ore containing Cr and Mg] while sufficiently eluting Mg into the solution by a heat treatment.SOLUTION: The method of producing magnesium carbonate includes a heating treatment St1 of heating ore containing chromium and magnesium, with a magnesium content of 5 mass% or more, and a carbonate generation step St2 of feeding ore subjected to the heating treatment St1 into an aqueous solution to elute magnesium into the solution to react the eluted magnesium with carbon dioxide. The heating treatment St1 is carried out in an inert gas atmosphere or in a reductive atmosphere at a heating temperature of 500°C or more and 800°C or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing magnesium carbonate and a method for fixing carbon dioxide, and more particularly 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. [Background technology]

[0002] With the rapid progress of global warming in recent years, there is a demand for the practical application of carbon capture, storage, and utilization (CCSU) technology, which fixes emitted carbon dioxide (CO2) in minerals, in addition to reducing the amount of carbon dioxide (CO2) emitted. As a concrete means of realizing carbon capture and utilization (CCSU), various methods of fixing CO2 are being considered, such as injecting CO2 deep into seawater or injecting CO2 underground for storage. However, all of these methods are not economical because of the high cost of CO2 processing, and the subsequent impact on the environment is unclear, so there are still many problems to be solved before they can be put into practical use.

[0003] On the other hand, as one of the above-mentioned carbon sequestration and utilization technologies (CCSU), a technology (mineral carbonation technology) that reacts silicate minerals containing magnesium (Mg) and calcium (Ca) with CO2 to immobilize them as carbonates has attracted attention (see Patent Document 1). Carbonates such as magnesium carbonate (MgCO3) and calcium carbonate (CaCO3) are very stable at room temperature and pressure and are not easily affected by environmental changes, so that CO2 can be stably fixed in the minerals for a long period of time. Moreover, MgCO3 and CaCO3 generated by the immobilization of CO2 by the above-mentioned method can be used in a wide range of industrial fields, such as neutralizing agents, rubber and plastic enhancers, pesticides, fertilizers, and feed materials, and are carbon-neutral materials, so that further increase in demand is expected in the future.

[0004] Here, as an example of a manufacturing process that can contribute to fixation of CO2 by using the above-mentioned mineral carbonation technology, there can be mentioned "a manufacturing process of magnesium carbonate (MgCO3) using an ore containing Mg as a silicate mineral." In this manufacturing process, Mg needs to be sufficiently dissolved from the ore into a solution in order to react with CO2. In the ore, Mg is dissolved in a silicate mineral having a complex crystal structure (e.g., Mg3Si2O5(OH)4, Mg3Si4O 10 Since it is contained as a compound such as Mg(OH)2, 2+ Therefore, when carrying out the above manufacturing process, the above-mentioned 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 the mineral carbonation technology, a technology has been proposed in the past in which an ore containing Mg as a silicate mineral is heated to promote the dissolution of Mg contained in the ore into a solution (see Patent Documents 2 and 3).

[0006] Here, in the above-mentioned "manufacturing process of magnesium carbonate (MgCO3) using an ore containing Mg as a silicate mineral", an ore containing Mg as a silicate mineral at a concentration of 5% by mass or more can be preferably used. However, many of these ores often 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. correspond to such ores. Hereinafter, in this specification, ores containing Cr and Mg and having a magnesium concentration of 5% by mass or more, including each of these ores, are referred to as "Cr and Mg-containing ores".

[0007] In the "Magnesium Carbonate (MgCO3) Production and Carbon Dioxide Fixation Process" which is technically closely related to the above-mentioned Mineral Carbonation Technology and is carried out using "Cr- and Mg-containing ores", if the above-mentioned heat treatment is carried out in an oxidizing atmosphere such as air in order to promote the dissolution of Mg contained in the ore as a silicate mineral into the solution, the oxidation of Cr in the ore progresses, and even hexavalent chromium (Cr(VI)), a harmful substance, is dissolved into the solution. This has come to be recognized as a new problem. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-249153 [Patent Document 2] Special Publication No. 2012-500718 [Patent Document 3] Special Publication No. 2013-505124 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been proposed in light of the above-mentioned circumstances, and aims to prevent the harmful substance Cr(VI) from being eluted into solution together with Mg during a heat treatment carried out to increase the elution of Mg from a "Cr- and Mg-containing ore" in a process for producing MgCO3 from carbon dioxide and a "Cr- and Mg-containing ore" that contains chromium and magnesium and has a magnesium concentration of 5 mass% or more. [Means for solving the problem]

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

[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 process for 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.

[0012] According to the manufacturing method of magnesium carbonate in (1), in the process of manufacturing MgCO3 from "Cr- and Mg-containing ore", the heat treatment to increase the elution of Mg from "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 an atmosphere of 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 above-mentioned effect of preventing the dissolution of Cr(VI) into the solution, which is achieved by the method for producing magnesium carbonate described in (1), can be more reliably and with extremely high accuracy.

[0015] (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.

[0016] According to the carbon dioxide fixation method (3), Mg contained in "Cr- and Mg-containing ore" is reacted with CO2 to fix CO2 into MgCO3, i.e., mineral carbonation technology is carried out. In this technology, the heat treatment is carried out to increase the elution of Mg from "Cr- and Mg-containing ore", but 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 an atmosphere of 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 method for fixing carbon dioxide (4), the effect of preventing the dissolution of Cr(VI) into the solution, which is achieved by the method for fixing carbon dioxide described in (3), can be more reliably and with extremely high accuracy. Effect of the Invention

[0019] According to the present invention, in the process of producing MgCO3 from "Cr- and Mg-containing ore", the heat treatment performed to increase 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. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a flow chart showing the flow of a method for producing magnesium carbonate of the present invention. [Diagram 2] FIG. 1 is a flow chart of an entire combined process in a combined embodiment in which the magnesium carbonate production method (or the carbon dioxide fixation method) of the present invention is combined with a nickel oxide ore hydrometallurgy process (HPAL). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of the present invention will be described in detail below. Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the gist of the present invention.

[0022] <Magnesium carbonate manufacturing method> The "method for producing magnesium carbonate" of the present invention is a method for producing MgCO3 from the "Cr- and Mg-containing ore" defined above, i.e., "ore containing Cr and Mg and having a magnesium concentration of 5 mass% or more," and carbon dioxide.

[0023] Fig. 1 is a flow diagram showing the process flow of the "production method of magnesium carbonate" of the present invention. As shown in the figure, the "production method of magnesium carbonate" of the present invention is a process in which a heating process St1 for heating a "Cr- and Mg-containing ore" and a carbonate production process St2 for producing MgCO3 by reacting Mg dissolved in a solution from the "Cr- and Mg-containing ore" with CO2 are sequentially carried out. It is preferable that the produced MgCO3 is further recovered by a carbonate recovery process St3 for recovering MgCO3 from the solution by solid-liquid separation.

[0024] [Cr and Mg-containing ore] The "Cr- and Mg-containing ore" used in the "manufacturing method for magnesium carbonate" of the present invention may be any ore that contains Cr and Mg and satisfies the above-mentioned requirements of having a magnesium concentration of 5% by mass or more, and is not limited to a specific ore. However, it is preferable that the ore contains Mg as magnesium silicate. Examples of the ore include nickel oxide ores such as saprolite ore, limonite ore, as well as lizardite, chrysotile, enstatite, foresterite, talc, magnesite, serpentine, olivine, and smectite, as described above. 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] As described above, most of the Mg in the "Cr- and Mg-containing ore" is contained as silicate minerals (such as magnesium silicate (Mg3Si2O5(OH)4)). Magnesium silicate has a three-dimensional complex crystal structure with Mg at its center, making it difficult for Mg to dissolve from the magnesium silicate into the solution. Therefore, in the carbonate generation process St2 described above, heat treatment of the "Cr- and Mg-containing ore" is effective as a pretreatment to sufficiently promote the dissolution of Mg into the solution.

[0026] Among the above-mentioned "Cr and Mg-containing ores", ores containing Mg as magnesium silicate and having a mass ratio (Mg / Si) of Mg to Si in the ore of 0.5 or more can be particularly preferably used. Ores having the ratio of 1.0 or more can be more preferably used. If the Mg / Si ratio is 0.5 or more, more Mg can be eluted into the aqueous solution after heat treatment. In addition, compounds having a large amount of Si relative to Mg tend to have a complex crystal structure, making it difficult for Mg to be eluted. The content (mass) of Si in the "alkaline earth metal-containing ore" can be specified 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 degrees in an electric furnace and melted, and the sample is leached with hydrochloric acid after cooling and then measured by ICP emission spectrometry. Similarly, the magnesium concentration (mass) in "alkaline earth metal-containing ore" can be determined by leaching 0.5 g of the ore in hydrochloric acid and measuring it using ICP atomic emission spectrometry.

[0027] [Heat treatment] In the "method for producing magnesium carbonate" of the present invention, the heat treatment St1 is a treatment in which the "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 of the heat treatment for the heat treatment St1 is preferably such that the "Cr- and Mg-containing ore" is heated to a temperature of 500°C or more and 800°C or less (furnace atmosphere temperature), more preferably 600°C or more and 750°C or less. The heating time is preferably 2 hours or more, 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 pulverized to a particle size of about 300 μm or less as a pretreatment before being charged into the heat treatment St1, from the viewpoint of ease of handling. The "Cr- and Mg-containing ore" may be pulverized by any common method, and specific examples include pulverization using a rod mill or a ball mill. However, the particle size of the "alkaline earth metal-containing ore" does not have a significant effect on the elution of the alkaline earth metals.

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

[0030] This "magnesium elution test" was carried out by putting 5 g of the above "Cr- and Mg-containing ore (nickel oxide ore)" with different heating conditions during the heat treatment St1 into 200 mL of solution (pure water at 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% by volume) 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.

[0031] From the test results of this "magnesium elution test", when the heating treatment St1 by firing was not performed, the magnesium elution rate was 1.8%. It was also found that the heating treatment St1 at 600°C, which is a heating temperature of 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.

[0032] [Table 1]

[0033] In the "method for producing magnesium carbonate" of the present invention, the "Cr- and Mg-containing ore" is heated in the heat treatment St1 in a manner of firing in an inert gas atmosphere or a reducing atmosphere. As a result, as will be shown later in the Examples, it is possible to promote the dissolution of Mg contained in the "Cr- and Mg-containing ore" as a magnesium silicate mineral into an aqueous solution, while preventing Cr contained in the "Cr- and Mg-containing ore" from becoming a harmful substance, Cr(VI), and dissolving into an aqueous solution.

[0034] Moreover, 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 when heated in an oxidizing atmosphere such as air, the Cr contained in the ore is oxidized and becomes Cr(VI) and is dissolved into the aqueous solution. 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), and 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] Whether the complex crystal structure of the minerals contained in the "Cr- and Mg-containing ore" has been sufficiently destroyed by heating can be determined by XRD analysis, for example, by checking the peak of the (002) plane of lizardite (Mg3SiO5(OH)4). In addition, peaks of forsterite or talc other than lizardite can also be used. As an apparatus for performing XRD analysis, for example, the X-ray diffractometer "Empyrean (manufactured by Malvern Instruments)" can be suitably used.

[0036] [Carbonate generation treatment] In the "method for producing magnesium carbonate" of the present invention, the carbonate production process St2 carried out following the above-mentioned heat treatment St1 is a process in which Mg is sufficiently dissolved into the solution while preventing the dissolution of Cr from the "Cr- and Mg-containing ore" whose complex crystal structure has been destroyed by the "heat treatment" into the solution, and CO2 gas is blown into the solution to generate MgCO3 by reacting the dissolved Mg with the CO2 blown in as gas within the solution.

[0037] The method of blowing CO2 gas into the solution is not particularly limited, but as an example, it can be performed by blowing CO2 gas using a disk-type diffuser, a cylindrical diffuser, or the like. 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%, MgCO3 can be produced more efficiently.

[0038] The ratio of "Cr- and Mg-containing ore" to the above 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 "Cr- and Mg-containing 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) of alkaline earth metal-containing ore in the solution 30% by mass or less, the viscosity of the solution that becomes a slurry can be appropriately maintained, improving handleability.

[0039] The source of CO used in the carbonate generation process St2 is not particularly limited. As an example, the CO gas emitted in various metal smelting processes, such as the CO gas emitted from the neutralization process carried out in a metal smelting plant using ore containing Mg as an impurity (e.g., nickel smelting using laterite ore), can be utilized to contribute to reducing the total amount of CO gas emissions from these metal smelting processes by carrying out the production method of the present invention in the same plant.

[0040] [Carbonate recovery processing] The carbonate recovery process St3, which is carried out following the carbonate production process St2, is a process for recovering the MgCO3 produced in the carbonate production process St2 from the solution. The specific method for recovering this alkaline earth metal carbonate is not particularly limited, but as an example, it may be 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 of carbon dioxide fixation> The "carbon dioxide fixation method" of the present invention is a method for fixing CO2 in a mineral, in which CO2 is reacted with Mg in a solution to fix it in the mineral as MgCO3. This method is a suitable process for specifically implementing the "Mineral Carbonation Technology", which is one of the "Carbon Sequestration and Utilization Technologies (CCSU)".

[0042] In the "method for fixing carbon dioxide" of the present invention, 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 CO2.

[0043] Moreover, in the "method for fixation of carbon dioxide" of the present invention, the following steps are sequentially carried out: heating treatment St1 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 in a manner similar to that of heating treatment St1 in the "method for production of magnesium carbonate" of the present invention; carbon dioxide fixation treatment in which Mg dissolved into a solution from the "Cr- and Mg-containing ore" is reacted with CO2 to fix CO2 as generated MgCO3; and carbonate recovery treatment St3 in which the MgCO3 with CO2 fixed therein is recovered from the solution by solid-liquid separation treatment in a manner similar to that of carbonate recovery treatment St3 in the "method for production of magnesium carbonate" of the present invention.

[0044] <Application of nickel oxide ore to hydrometallurgy> Either of the "method for producing magnesium carbonate" or the "method for fixing carbon dioxide" of the present invention can be implemented as a method for carrying out a pretreatment step (magnesium removal step S1) for 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. Such an embodiment of the production method of the present invention is particularly effective when nickel oxide ore having a magnesium concentration exceeding 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 "method for producing magnesium carbonate" or the "method for fixing carbon dioxide" of the present invention can be used as a partial process to produce a "method for hydrometallurgy of nickel oxide ore", which is a known process as an overall process, and its flow is shown in Fig. 2 as an example. In this overall process, the following steps are sequentially performed: a demagnesium step S1 for the purpose of separating and recovering Mg from nickel oxide ore, a leaching step S2 for adding sulfuric acid to nickel oxide ore with a reduced magnesium concentration and subjecting it to a leaching treatment under high temperature and high pressure to obtain a leaching slurry, a solid-liquid separation step S3 for separating the leaching slurry into a leachate and a leach residue, a neutralization step S4 for adjusting the pH of the leachate to separate a neutralized precipitate containing impurity elements to obtain a neutralization end solution, and a sulfurization step S5 for generating a sulfide containing nickel (Ni) by adding a sulfurizing agent to the neutralization end solution.

[0046] As described above, the "method for producing magnesium carbonate" or the "method for fixing 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 fixing carbon dioxide" of the present invention, the incorporation of Cr(VI) into the aqueous solution discharged from the demagnesium step S1 can be prevented in advance, so that the other steps, the leaching step S2, the solid-liquid separation step S3, the neutralization step S4, and the sulfurization step S5, etc., can be carried out safely in the same manner as in the conventionally known embodiment of the "method for hydrometallurgy of nickel oxide ore".

[0047] [Magnesium removal process] The magnesium removal step S1 is a step in which magnesium is eluted from a "high-Mg nickel oxide ore" such as saprolite ore to produce a "low-Mg nickel oxide ore." In this specification, nickel oxide ore with 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 described above, in "high-Mg nickel oxide ore" such as saprolite ore, Mg is mainly contained as magnesium silicate (Mg3Si2O5(OH)4) having a stable phyllosilicate structure, so that it is not easy to sufficiently dissolve Mg into a solution. However, by carrying out the demagnesium step S1 by the above-mentioned methods of the present invention, it is possible to dissolve Mg from the "high-Mg nickel oxide ore" and to obtain the above-mentioned "low-Mg nickel oxide ore" at low cost, efficiently, and together with a CO2 reduction process. In this embodiment, the source of CO2 to be reacted with the dissolved Mg is not particularly limited, but as an example, by utilizing the CO2 gas discharged in the process, such as the CO2 gas generated from fossil fuels in an autoclave or the like, and the CO2 gas discharged from the neutralization step S4, which is a downstream step, it is possible to contribute to reducing the total amount of CO2 gas emissions from the nickel smelting plant. Furthermore, in the hydrometallurgical refining method for nickel oxide ores, ores containing high concentrations of Mg, such as saprolite ores, which have not been actively used in the past, can now be used as low-Mg nickel oxide ores without reducing the inherent productivity of the "hydrometallurgical refining method (HPAL process)." EXAMPLES

[0049] The effects of the "method for producing magnesium carbonate" of the present invention will be specifically described 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 "magnesium elution test" to investigate how the elution of Mg and Cr(VI) into the solution changes depending on the atmosphere during heating 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 "magnesium elution test" in both Examples and Comparative Examples. The magnesium concentration (mg / L) and chromium concentration (mg / L) in Table 2 below are values ​​measured by ICP emission spectrometry.

[0051] [Table 2]

[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. [Explanation of symbols]

[0053] St1 Heat treatment St2 Carbonate generation treatment St3 Carbonate recovery processing S1 Magnesium removal process S2 leaching process S3 Solid-liquid separation process S4 Neutralization process S5 Sulfurization process

Claims

1. A heat treatment for heating an ore containing chromium and magnesium and having a magnesium concentration of 5 mass% or more; a carbonate production process in which the ore that has been subjected to the heat treatment is put into an aqueous solution, and the magnesium dissolved in the solution is reacted with carbon dioxide; comprising 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. A method for producing magnesium carbonate.

2. 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, 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. The method for producing magnesium carbonate according to claim 1.

3. A heat treatment for heating an ore containing chromium and magnesium, the ore having a magnesium concentration of 5 mass% or more; and a carbon dioxide fixation treatment for fixing carbon dioxide as magnesium carbonate by putting the ore that has been subjected to the heat treatment into an aqueous solution and reacting the magnesium dissolved in the solution with carbon dioxide, 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. Methods for fixing carbon dioxide.

4. 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, 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. The method for fixing carbon dioxide according to claim 3.

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