Method for fixing carbon dioxide and method for producing carbonate of alkaline earth metal

Abstract

To provide novel technical means capable of fixing CO2 by reacting a silicate mineral containing Mg, Ca, or the like with CO2 for fixing as a carbonate with easy process control and high treatment efficiency.SOLUTION: A method for fixing carbon dioxide includes: an amorphization treatment St1 for amorphizing an alkaline earth metal-containing mineral in an alkaline earth metal by mechanochemical treatment for applying mechanical stress to an alkaline earth metal-containing ore; and a carbon dioxide fixation treatment St2 for fixing the carbon dioxide as a carbonate of an alkaline earth metal by reacting magnesium eluted in a solution by putting the alkaline earth metal-containing ore subjected to the amorphization treatment St1 into the solution with the carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for fixing carbon dioxide and a method for producing alkaline earth metal carbonates such as magnesium carbonate. [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 in minerals, in addition to reducing the amount of carbon dioxide emissions. As a concrete means of realizing carbon capture and utilization (CCSU) technology, various methods of fixing carbon dioxide, such as injecting carbon dioxide deep into seawater or injecting carbon dioxide underground for storage, are being considered. However, all of these methods are uneconomical because of the high cost of carbon dioxide 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), calcium (Ca), etc. with carbon dioxide (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] In carrying out the above-mentioned mineral carbonation technology, it is necessary to sufficiently dissolve magnesium (Mg) and calcium (Ca) into the solution for reacting with CO2. However, in various ores containing Mg and Ca, most of them are silicate compounds with complex crystal structures (e.g., Mg3Si2O5(OH)4, Mg3Si4O 10 (OH)2, CaSiO3, Ca2SiO4, Ca3SiO5, etc.) Therefore, Mg in the solution 2+ Or Ca 2+ Therefore, when implementing the above-mentioned mineral carbonation technology, Mg is not easily dissolved in these ores. 2+ Or Ca 2+ It has been necessary to carry out some kind of pretreatment to promote the dissolution of the compound.

[0005] As a pretreatment required for implementing the mineral carbonation technology, a technique has been proposed in the past in which the ore is heated to promote the dissolution of Mg and Ca contained in the ore into a solution (see Patent Documents 2 and 3). However, in general, most of the ores to be treated are often mined in a high humidity environment and are provided in a state containing an indefinite amount of physically adsorbed moisture, and the reaction caused by the heat treatment to promote the dissolution of Mg and Ca is an endothermic reaction, so that these heat treatments are difficult to control the temperature to allow the reaction to proceed appropriately, and are not methods that can advance pretreatment with high treatment efficiency. In addition, there are concerns about the increase in energy costs required for the heat treatment and the increase in CO2 emissions associated with the heat treatment. [Prior art documents] [Patent documents]

[0006] [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]

[0007] The present invention has been proposed in view of the above-mentioned circumstances, and aims to provide a new technical means for easily managing the process of fixing CO2 by reacting CO2 with silicate minerals containing Mg, Ca, etc. and fixing it as carbonate, with high processing efficiency. [Means for solving the problem]

[0008] The present inventors have found that the above-mentioned problems can be solved by carrying out a unique amorphization treatment in which the crystal structure of the alkaline earth metal-containing mineral (such as alkaline earth metal silicate) in the ore is changed by applying mechanical stress to the alkaline earth metal-containing ore prior to the treatment of dissolving the alkaline earth metal in a solution and reacting it with CO2, and have completed the present invention. The present invention provides the following.

[0009] (1) A method for fixing carbon dioxide, comprising: an amorphization treatment in which an alkaline earth metal-containing ore is subjected to a mechanochemical treatment to apply mechanical stress to the alkaline earth metal-containing ore to make the alkaline earth metal-containing mineral in the alkaline earth metal-containing ore amorphous; and a carbon dioxide fixation treatment in which the alkaline earth metal-containing ore that has been subjected to the amorphization treatment is placed in a solution, and the alkaline earth metal that has been eluted from the alkaline earth metal-containing ore into the solution is reacted with carbon dioxide, thereby fixing the carbon dioxide as a carbonate of the alkaline earth metal.

[0010] According to the carbon dioxide fixation method (1), alkaline earth metals can be sufficiently dissolved from the ore into a solution by applying mechanical stress to the alkaline earth metal-containing ore to make it amorphous. This makes it possible to fix CO2 as alkaline earth metal carbonates with high processing efficiency through a process that is easy to manage.

[0011] (2) The method for fixing carbon dioxide according to (1), wherein the mechanochemical treatment is a treatment carried out by putting the alkaline earth metal-containing ore into a ball mill.

[0012] According to the method for fixation of carbon dioxide of (2), the dissolution of an alkaline earth metal into a solution is promoted more stably in the method for fixation of carbon dioxide as described in (1), and the above-mentioned effects achieved by the method for producing an alkaline earth metal carbonate as described in (1) can be enjoyed more stably.

[0013] (3) The method for fixation of carbon dioxide according to (2), wherein the rotation speed of the ball mill is 10 rpm or more, and the treatment time with the ball mill is 80 minutes or more.

[0014] According to the method for fixing carbon dioxide in (3), the above-mentioned effects achieved by the method for fixing carbon dioxide described in (2) can be enjoyed more stably.

[0015] (4) The method for fixing carbon dioxide according to any one of (1) to (3), wherein the alkaline earth metal is magnesium, the alkaline earth metal-containing mineral is magnesium silicate, and the alkaline earth metal carbonate is magnesium carbonate.

[0016] According to the method for fixing carbon dioxide (4), which is the method for fixing carbon dioxide according to any one of (1) to (3), Mg can be sufficiently dissolved from the ore containing magnesium silicate by the amorphization treatment by applying mechanical stress, thereby promoting the fixation of CO2 to Mg and, at the same time, efficiently producing MgCO3, which is highly useful as a carbon-neutral material.

[0017] (5) The method for fixing carbon dioxide according to (4), wherein the alkaline earth metal-containing ore has a magnesium concentration of 5 mass% or more.

[0018] According to the carbon dioxide fixation method of (5), by using an ore with a high magnesium concentration, the above-mentioned effect of the carbon dioxide fixation method of (4) can be realized in a more favorable manner. On the other hand, as an example, in various metal smelting plants, such as a nickel smelting plant that performs nickel smelting by the "HPAL process", when an ore containing a high concentration of Mg is used for metal smelting, the metal smelting process can be combined with the carbon dioxide fixation method to efficiently produce MgCO3. Furthermore, in this case, by utilizing the CO2 gas discharged in the smelting plant as the CO2 to be reacted with Mg, it is possible to contribute to reducing the CO2 gas emissions from the smelting plant.

[0019] (6) The method for fixing carbon dioxide according to (4), wherein the mass ratio of magnesium to silicon (Mg / Si) in the alkaline earth metal-containing ore is 0.5 or more.

[0020] According to the carbon dioxide fixation method in (6), after the amorphous treatment, Mg is added to the solution. 2+ This makes it possible to more efficiently promote the above-mentioned reaction involved in the fixation of CO2 in the method for fixation of carbon dioxide described in (4).

[0021] (7) The method for fixing carbon dioxide according to any one of (1) to (3), wherein the alkaline earth metal is calcium, the alkaline earth metal-containing mineral is calcium silicate, and the alkaline earth metal carbonate is calcium carbonate.

[0022] According to the method for fixing carbon dioxide in (7), which is the method for fixing carbon dioxide according to any one of (1) to (3), Ca can be sufficiently dissolved from the ore containing calcium silicate by the amorphous treatment caused by applying mechanical stress. This promotes the fixation of CO2 to Ca, and at the same time, makes it possible to efficiently produce CaCO3, which is highly useful as a carbon-neutral material.

[0023] (8) A method for producing an alkaline earth metal carbonate, comprising: an amorphization treatment for applying mechanical stress to an alkaline earth metal-containing ore (mechanochemical treatment) to render the alkaline earth metal-containing mineral in the alkaline earth metal-containing ore amorphous; and a carbon dioxide fixation treatment for placing the alkaline earth metal-containing ore that has been subjected to the amorphization treatment into a solution, reacting the alkaline earth metal eluted from the alkaline earth metal-containing ore into the solution with carbon dioxide to fix carbon dioxide as an alkaline earth metal carbonate, thereby producing the alkaline earth metal carbonate in the solution.

[0024] According to the method for producing alkaline earth metal carbonates in (8), alkaline earth metals such as Mg can be sufficiently dissolved into a solution from alkaline earth metal-containing minerals such as silicate ores by amorphization treatment through application of mechanical stress. This promotes the reaction between the alkaline earth metals and CO2 in the solution, and while reducing CO2 emissions throughout the entire production process, it is possible to produce alkaline earth metal carbonates, which are industrially useful products such as MgCO3 and CaCO3, at a lower cost than conventional methods that rely on heat treatment.

[0025] (9) The method for producing an alkaline earth metal carbonate according to (8), wherein the mechanochemical treatment is carried out by putting the alkaline earth metal-containing ore into a ball mill.

[0026] According to the method for producing an alkaline earth metal carbonate of (9), the dissolution of the alkaline earth metal into the solution is more stably promoted in the method for producing an alkaline earth metal carbonate described in (8), and the above-mentioned effects provided by the method for producing an alkaline earth metal carbonate described in (8) can be more stably enjoyed.

[0027] (10) The method for producing an alkaline earth metal carbonate according to (9), wherein the rotation speed of the ball mill is 10 rpm or more, and the treatment time with the ball mill is 80 minutes or more.

[0028] According to the method for producing an alkaline earth metal carbonate of (10), the above-mentioned effects provided by the method for producing an alkaline earth metal carbonate of (9) can be obtained more stably.

[0029] (11) The method for producing an alkaline earth metal carbonate according to any one of (8) to (10), wherein the alkaline earth metal is magnesium, the alkaline earth metal-containing mineral is magnesium silicate, and the alkaline earth metal carbonate is magnesium carbonate.

[0030] According to the method for producing an alkaline earth metal carbonate of (11), which is the method for producing an alkaline earth metal carbonate according to any one of (8) to (10), Mg can be sufficiently dissolved from the silicate ore containing Mg into the solution by the amorphous treatment caused by applying mechanical stress. This promotes the fixation of CO2 to Mg, and MgCO3, which is highly useful as a carbon-neutral material, can be efficiently produced.

[0031] (12) The method for producing an alkaline earth metal carbonate according to (11), wherein the alkaline earth metal-containing ore has a magnesium concentration of 5 mass% or more.

[0032] According to the method for producing alkaline earth metal oxide (magnesium carbonate) of (12), the above-mentioned effect of the method for producing alkaline earth metal carbonate of (11) can be obtained by using ore with a high magnesium concentration. As a result, in various metal smelting plants, such as nickel smelting plants that perform nickel smelting by the "HPAL process", when metal smelting is performed using ore containing a high concentration of Mg, the metal smelting process can be combined with the method for producing alkaline earth metal oxide (magnesium carbonate) to efficiently produce MgCO3. In addition, by utilizing the CO2 gas discharged in the nickel smelting plant as the CO2 to be reacted with Mg, it is possible to contribute to reducing the CO2 gas emissions from the nickel smelting plant.

[0033] (13) The method for producing an alkaline earth metal carbonate according to (11), wherein the mass ratio of magnesium to silicon (Mg / Si) in the alkaline earth metal-containing ore is 0.5 or more.

[0034] According to the method for producing an alkaline earth metal carbonate (a method for producing magnesium carbonate) in (13), after the amorphous treatment, Mg is added to the solution. 2+ This makes it possible to further increase the productivity of MgCO3 production in the method for producing an alkaline earth metal carbonate described in (11).

[0035] (14) The method for producing an alkaline earth metal carbonate according to any one of (8) to (10), wherein the alkaline earth metal is calcium, the alkaline earth metal-containing mineral is calcium silicate, and the alkaline earth metal carbonate is calcium carbonate.

[0036] According to the method for producing an alkaline earth metal carbonate (calcium carbonate) of (14), in the method for producing an alkaline earth metal carbonate according to any one of (8) to (10), Ca can be sufficiently dissolved from a silicate ore containing Ca by amorphization treatment by applying mechanical stress. This promotes fixation of CO2 to Ca, and thus makes it possible to efficiently produce CaCO3, which is highly useful as a carbon-neutral material. Effect of the Invention

[0037] According to the present invention, the fixation of CO2 by reacting CO2 with silicate minerals containing Mg, Ca, etc. and fixing it as carbonate can be easily controlled and performed with high processing efficiency. In addition, by making it possible to replace the heat treatment, which was an essential treatment in the conventional fixation process, with a "mechanochemical treatment", it is possible to produce alkaline earth metal carbonates such as MgCO3 at lower cost while suppressing the emission of new CO2 generated by implementing the CO2 fixation process. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a flow chart showing the flow of a carbon dioxide fixation method of the present invention. [Diagram 2] FIG. 2 is a graph showing that an alkaline earth metal-containing mineral in an alkaline earth metal-containing ore is made amorphous by the amorphization treatment in the carbon dioxide fixation method of the present invention. [Diagram 3] FIG. 2 is a graph showing a change in particle size distribution of an alkaline earth metal-containing ore when an amorphization treatment is carried out in the carbon dioxide fixation method of the present invention. [Figure 4] FIG. 1 is a flow chart of an entire combined process in a combined embodiment in which the carbon dioxide fixation method of the present invention (or the method for producing an alkaline earth metal carbonate) is combined with a nickel oxide ore hydrometallurgical process (HPAL). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] 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.

[0040] <Method of carbon dioxide fixation> Fig. 1 is a flow diagram showing the process flow of the "method for fixing carbon dioxide" of the present invention. The "method for fixing carbon dioxide" of the present invention is a method for fixing carbon dioxide (CO2) in a mineral, in which carbon dioxide (CO2) is reacted with an alkaline earth metal-containing mineral in a solution to fix it as an alkaline earth metal carbonate such as magnesium carbonate (MgCO3) or calcium carbonate (CaCO3).

[0041] The "carbon dioxide fixation method" of the present invention is a process in which an amorphous treatment St1 is performed to change the crystal structure of an alkaline earth metal-containing mineral (magnesium silicate, calcium silicate, etc.) in an ore containing alkaline earth metals such as magnesium (Mg) and calcium (Ca) (referred to as "alkaline earth metal-containing ore" in this specification) by applying mechanical stress to the ore, and a carbon dioxide fixation treatment St2 is performed to fix CO2 in an alkaline earth metal carbonate (MgCO3, CaCO3, etc.) by reacting the alkaline earth metal eluted from the alkaline earth metal-containing ore into a solution with carbon dioxide (CO2). The alkaline earth metal carbonate can be recovered from the solution by a carbonate recovery treatment described later. It is preferable to use water as the above solution used in carrying out the present invention.

[0042] Here, in the alkaline earth metal-containing ore, alkaline earth metals such as Mg and Ca are contained as alkaline earth metal-containing minerals such as magnesium silicate and calcium silicate, as described above. Therefore, in the past, in order to sufficiently dissolve the alkaline earth metal (Mg, Ca, etc.) into a solution, heat treatment of the alkaline earth metal-containing ore was essential, but the "method for fixing carbon dioxide" of the present invention is a novel process whose main feature is that the mineral is made amorphous by a "mechanochemical treatment" that changes the crystal structure of the alkaline earth metal-containing mineral by applying mechanical stress.

[0043] [Amorphization treatment] The amorphization treatment St1, which is one of the essential steps in the "carbon dioxide fixation method" of the present invention, is carried out by a "mechanochemical treatment" in which the crystal structure of an alkaline earth metal-containing mineral (magnesium silicate, calcium silicate, or the like) is changed by applying mechanical stress. In this specification, the "mechanochemical treatment" refers to a treatment in which mechanical stress is applied to the alkaline earth metal-containing ore, which is the treatment target of the amorphization treatment St1, to change the crystal structure of the alkaline earth metal-containing mineral contained in the treatment target (alkaline earth metal-containing ore) by mechanical energy.

[0044] The embodiment of 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 spikey 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 exert the same action and effect as these.

[0045] The "mechanochemical treatment" performed in the present invention is different from a general "pulverization treatment" in that it is not a treatment aimed at reducing particle size. Even when the "mechanochemical treatment" of the present invention is performed, the particle size of each particle may be reduced by the destruction of the ore to be treated during the treatment, but the purpose of the "mechanochemical treatment" of the present invention is to amorphize the alkaline earth metal-containing mineral (magnesium silicate or calcium silicate, etc.) by reducing the crystallinity (change (destruction) of the structure). Therefore, it is a novel treatment method with a different purpose and effect from the pulverization treatment for particle size adjustment performed to increase the specific surface area of ​​the treatment object as a pretreatment preceding the conventional amorphization treatment that reduces the crystallinity by heat treatment. FIG. 3 shows the change in particle size distribution of alkaline earth metal-containing ore when the "mechanochemical treatment" is carried out in the "method for fixing carbon dioxide" of the present invention. Since the particle size distribution shown in the figure hardly changes, it can be understood that the "mechanochemical treatment", which is the means for carrying out the amorphization treatment St1 in the present invention, is a novel treatment method different from the general "crushing treatment" aimed at adjusting the particle size distribution.

[0046] In addition, when the above-mentioned "mechanochemical treatment" is carried out, a treatment of heating the alkaline earth metal-containing ore to be treated may be carried out as an auxiliary treatment. When such a heat treatment is carried out, it may be carried out in an inert atmosphere or a reducing atmosphere.

[0047] 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, more preferably 300 rpm or more, and the treatment time is preferably 150 minutes or more, 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 treatment object (alkaline earth metal-containing mineral) will increase, but in this case, the rate of increase in the effect of amorphization will reach a plateau when the treatment time is about 400 minutes. Therefore, the combination of the rotation speed of the ball mill and the treatment time is preferably 300 rpm or more and 270 minutes or more. As described later, the alkaline earth metal-containing ore used in the "carbon dioxide fixation method" of the present invention is preferably one having a mass ratio (Mg / Si) of magnesium (Mg) to silicon (Si) of 0.5 or more, but by setting the treatment conditions in the "mechanochemical treatment" to the above range, it is possible to sufficiently promote the elution of Mg and Ca contained as alkaline earth metal-containing minerals (such as alkaline earth metal silicates) into the solution even from alkaline earth metal-containing ores having a small mass ratio (Mg / Si) of Mg to Si in the ore. The "mechanochemical treatment" can be performed in a dry manner, but can also be performed in a wet manner because the amorphized ore is treated in a solution in the subsequent carbon dioxide fixation treatment St2.

[0048] In addition, whether or not various alkaline earth-containing minerals contained in alkaline earth metal-containing ores have been sufficiently amorphized can be determined by confirming peaks of lizardite (Mg3Si2O5(OH)4), forsterite (Mg2SiO4), enstatite (MgSiO3), etc., by XRD analysis. As an apparatus for performing XRD analysis, for example, an X-ray diffractometer "Empyrean (manufactured by Malvern Instruments)" can be suitably used.

[0049] The above-described "mechanochemical treatment", i.e., the application of mechanical stress, makes it possible to sufficiently amorphize alkaline earth minerals (such as alkaline earth metal silicates) in ores containing alkaline earth metals (such as Mg or Ca), a finding that was independently discovered by the present inventors, and the above-described "amorphization treatment" that constitutes the present invention is a novel technical means for amorphizing minerals that has never been seen before.

[0050] [Carbon dioxide fixation treatment] The carbon dioxide fixation process St2, which is carried out following the amorphization process St1, is a process in which alkaline earth metals are dissolved into a solution from the alkaline earth metal-containing mineral that has been amorphized through the amorphization process St1, CO2 gas is blown into the solution, and the dissolved alkaline earth metals are reacted with the CO2 blown in as a gas in the solution, thereby fixing the CO2 as an alkaline earth metal carbonate.

[0051] The ratio of alkaline earth metal-containing ore to the solution for dissolving the alkaline earth metal 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 alkaline earth metal-containing ore in the solution 2% by mass or more, a high precipitation efficiency of "alkaline earth metal carbonate (MgCO3, etc.)" 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 the handleability.

[0052] The method of blowing CO2 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%, it is possible to more efficiently promote the generation of alkaline earth metal carbonates (MgCO3, etc.) and the fixation of CO2.

[0053] Incidentally, the supply source and supply method of CO2 used in the carbon dioxide fixation treatment St2 are not particularly limited. As an example, by utilizing CO2 gas emitted in various metal smelting processes, such as CO2 gas generated from a neutralization process using a neutralizing agent derived from fossil fuels or carbonates, which is carried out in a metal smelting plant using ore containing Mg as an impurity (e.g., nickel smelting using laterite ore), and carrying out the present invention in the same plant in parallel, it is possible to contribute to reducing the total amount of CO2 gas emissions from these metal smelting processes.

[0054] [Carbonate recovery processing] In the "carbon dioxide fixation method" of the present invention, following the carbon dioxide fixation treatment St2, a carbonate recovery treatment can be carried out as necessary, in which the alkaline earth metal carbonate (MgCO3, etc.) to which CO2 has been fixed in the carbon dioxide fixation treatment St2 is recovered from the solution. In this carbonate recovery treatment, the specific method for recovering the 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 filtering machine such as a filter press, or a method of recovering the carbonate by volatilizing the water content of the solution.

[0055] [Alkaline earth metal-containing minerals, alkaline earth metals, carbonates of alkaline earth metals] In the "method for fixing carbon dioxide" of the present invention, the "alkaline earth metal" assumed as the main raw material for reacting with CO2 to produce a useful "alkaline earth metal carbonate" is mainly Mg or Ca.

[0056] In addition, as the above-mentioned "alkaline earth metal-containing ore", various ores having a Mg or Ca concentration of 5% by mass or more can be preferably used. As an ore having a magnesium concentration of 5% by mass or more, nickel oxide ores such as limonite ore or saprolite ore, lizardite, chrysotile, enstatite, foresterite, talc, magnesite, serpentine, olivine, smectite, etc., and ores obtained by combining and mixing two or more of these ores can be preferably used as "alkaline earth metal-containing ore" in the manufacturing method of the present invention. As an ore having a calcium concentration of 5% by mass or more, ores containing dicalcium silicate, tricalcium silicate, etc., and ores obtained by combining and mixing two or more of these ores can be preferably used as "alkaline earth metal-containing ore" in the manufacturing method of the present invention.

[0057] In addition, as the above-mentioned "alkaline earth metal-containing ore", one having a mass ratio (Mg / Si) of Mg to Si in the ore of 0.5 or more can be preferably used. In addition, one having the same 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 after the amorphization treatment. In addition, a compound having a large amount of Si relative to Mg has a complex crystal structure, and Mg tends to be difficult to elute. In addition, the content (mass) of Si 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 temperature is raised to 800°C in an electric furnace, the mixture is melted, and the sample is cooled and leached with hydrochloric acid, and the resultant is measured by ICP emission spectrometry. In addition, the magnesium concentration (mass) in the "alkaline earth metal-containing ore" can be determined by a method in which 0.5 g of ore is leached with hydrochloric acid, and the resultant is measured by ICP emission spectrometry.

[0058] Furthermore, although not particularly limited, the "alkaline earth metal-containing ore" may be pulverized to a particle size of about 300 μm or less as a pretreatment before being charged into the amorphization treatment St1 in order to adjust the particle size from the viewpoint of ease of handling. The ores 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 amorphization of the alkaline earth metal-containing mineral or the elution of the alkaline earth metal.

[0059] As described above, the "mechanochemical treatment" which is the means for implementing the amorphization treatment St1 in the present invention is a treatment different from the conventionally known general "pulverization treatment" aimed at adjusting the particle size distribution. However, when the above-mentioned general "pulverization treatment" is performed as a preparatory step in the first stage of the present invention as a pretreatment for the ore, it is possible to perform the amorphization treatment St1 by the "mechanochemical treatment" at the same time as such pretreatment. Alternatively, the above-mentioned general "pulverization treatment" and the amorphization treatment St1 by the "mechanochemical treatment" can be performed simultaneously in parallel using a large-sized pulverizing device (ball mill) or the like. In this way, even if other pulverization treatments are performed prior to or in parallel with the "mechanochemical treatment" in the series of treatments for fixing carbon dioxide, and even if the particle size distribution of the ore changes as a result, as long as the process in which the "mechanochemical treatment" which is the means for implementing the amorphization treatment St1 unique to the present invention is performed is a process that naturally belongs to the technical scope of the "carbon dioxide fixation method" of the present invention.

[0060] <Method for producing alkaline earth metal carbonate> The "method for producing alkaline earth metal carbonate" of the present invention is a method for producing alkaline earth metal carbonate such as magnesium carbonate (MgCO3) or calcium carbonate (CaCO3) by reacting an alkaline earth metal (Mg, Ca, etc.) with carbon dioxide (CO2).

[0061] In the "method for producing alkaline earth metal carbonate" of the present invention, the amorphization of an alkaline earth metal-containing mineral by the amorphization treatment St1 and the production of carbonate by the carbon dioxide fixation treatment St2 are carried out in a manner similar to the "method for fixing carbon dioxide" of the present invention described in detail above.

[0062] By carrying out the amorphization process St1 and the carbon dioxide fixation process St2 in the same manner as in the above-mentioned "method for fixing carbon dioxide", the alkaline earth metal eluted from the alkaline earth metal-containing ore into the solution is reacted with CO2 to fix CO2 in the alkaline earth metal, thereby producing carbonates such as MgCO3 or CaCO3 in the solution, and these carbonates can be produced efficiently. The method for recovering the carbonates produced in the solution is not particularly limited, and may be appropriately carried out by the same "carbonate recovery process" as in the above-mentioned "method for fixing carbon dioxide".

[0063] The MgCO3 produced by the "method for producing alkaline earth metal carbonates" of the present invention can be used as a variety of construction materials, including as a landfill material for civil engineering and as an aggregate for concrete, and can also be used for various industrial purposes, such as a neutralizing agent, a strengthening agent for natural rubber, a gastrointestinal medicine, a fragrance retaining agent, and an abrasive.

[0064] <Application of nickel oxide ore to hydrometallurgy> Either of the "method for fixing carbon dioxide" or the "method for producing an alkaline earth metal carbonate" of the present invention can be implemented as a method for performing a pretreatment step (magnesium removal step S1) of removing Mg contained in the form of silicate in nickel oxide ore when carrying out the "method for hydrometallurgy of nickel oxide ore" shown in Fig. 4. Such an embodiment 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".

[0065] The "method for smelting nickel oxide ore" which can be carried out by using the "method for fixing carbon dioxide" or the "method for producing an alkaline earth metal carbonate" of the present invention as a partial process is a known process as an overall process, and its flow is as shown in Fig. 4 as an example. In this overall process, the following steps are sequentially carried out: 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 carrying out 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 nickel-containing sulfide by adding a sulfurizing agent to the neutralization end solution.

[0066] As described above, the "method for fixing carbon dioxide" or the "method for producing an alkaline earth metal carbonate" 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 above-mentioned methods of the present invention, 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 in the same manner as in the embodiment of the conventionally known "method for hydrometallurgy of nickel oxide ore".

[0067] [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.

[0068] As described above, in "high-Mg nickel oxide ore" such as saprolite ore, Mg is mainly contained as magnesium silicate (Mg3SiO5(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, Mg is dissolved from the "high-Mg nickel oxide ore" to obtain the above-mentioned "low-Mg nickel oxide ore", and the process can be carried out efficiently at low cost and together with the 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 ore, raw material ores containing high concentrations of Mg, such as saprolite ore, 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

[0069] The effects of the "method for fixation of carbon dioxide" and the "method for producing an alkaline earth metal carbonate" of the present invention will be specifically described below using examples, but the present invention is not limited to the following examples.

[0070] <Amorphous Treatment Test> A test was conducted to verify the effect of amorphization of alkaline earth metal-containing minerals by the "method for fixation of carbon dioxide" and the "method for producing carbonates of alkaline earth metals" of the present invention. In this test, an ore (saprolite ore: particle size 150 μm to 300 μm) with a magnesium concentration of 14 mass% was used as the "alkaline earth metal-containing ore sample". The "amorphization treatment" in the "method for fixation of carbon dioxide" and the "method for producing carbonates of alkaline earth metals" of the present invention was carried out under the following "Test Condition 1" by varying the kneading time in a 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. Figure 2 is a graph showing the results. (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" to amorphize the samples, and 50 g of the "alkaline earth metal-containing ore sample" and 300 g of zirconia balls (diameter 10 mm) were added as grinding media. The table rotation speed of the planetary ball mill was set to 300 rpm, and the "mechanochemical treatment" was carried out for a specified time and at a specified table rotation speed. Then, for each sample after the kneading treatment under the above conditions, "crystal structure analysis by X-ray diffraction" was carried out using an X-ray diffractometer Empyrean (manufactured by Malvern Instruments).

[0071] From FIG. 2, it can be confirmed that the peak of the (002) plane of lizardite (Mg3Si2O5(OH)4) in each sample (ore) is reduced by the "amorphization treatment" in the "production method of alkaline earth metal carbonates" of the present invention, and this shows that the crystallinity of the ore samples is changed.

[0072] <Alkaline earth metal (Mg) elution acceleration test> A test was conducted to verify the effect of promoting the dissolution of alkaline earth metals (Mg) from alkaline earth metal-containing ores into a solution by the "method for producing alkaline earth metal carbonates" of the present invention. In this test, the "alkaline earth metal-containing ore samples (ores A to E)" of the examples and comparative examples shown in Table 1 below were subjected to an amorphization treatment under the following (test condition 2), and 5 g of each of the "alkaline earth metal-containing ore samples" after the treatment was placed in 200 mL of a solution (pure water at a temperature of 60°C), and while stirring at a rotation speed of 450 rpm, CO2 gas (manufactured by Takamatsu Teiso Co., Ltd., concentration 99.995% by volume) was blown into the solution at a blowing rate of 0.1 L / min, and the dissolution rate of Mg or Ca into the solution was measured and calculated by the "method for measuring the amount of dissolution of alkaline earth metals (Mg) and the method for calculating the dissolution rate" described below. As a reference example, the same test was also carried out on the same sample (ore B) that had not been subjected to the "mechanochemical treatment" (amorphization treatment) but had been subjected to a firing treatment at 600°C for 4 hours, and the results were compared. The test results are shown in Table 1 below. For each of the "alkaline earth metal-containing ore samples" in the Examples and Comparative Examples, the mass ratio of Mg to Si (Mg / Si) in each sample was previously measured by the above-mentioned measurement method using ICP emission spectrometry or the like to confirm each mass ratio. The confirmed values ​​of each ratio are also shown in Table 1. The results of the test carried out under the above conditions were evaluated for the dissolution promoting effect based on the following evaluation criteria. (Test condition 2): For the various "alkaline earth metal-containing ore samples" of the Examples and Comparative Examples, 50 g of each "alkaline earth metal-containing ore sample" of the Examples and Comparative Examples and 300 g of zirconia balls (diameter 10 mm) as grinding media were put into the same planetary ball mill as in the above "amorphization treatment test" to carry out the amorphization treatment. However, the table rotation speed and treatment time of the planetary ball mill were the rotation speed and treatment time shown in Table 1 below for each Example and Comparative Example. (Method for measuring the amount of alkaline earth metal (Mg) elution 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. (Evaluation criteria for dissolution promotion effect) A: Magnesium elution rate is 40% or more B: Magnesium elution rate is 20% or more C: Magnesium elution rate is less than 20%

[0073] [Table 1]

[0074] As mentioned above, Fig. 3 is a graph showing the particle size distribution of each nickel oxide ore sample after the above-mentioned "mechanochemical treatment" (mixing treatment by ball mill). From the results shown in Fig. 3, it can be seen that there was no significant change in the particle size of each ore sample even after the above-mentioned "mechanochemical treatment", and only amorphization proceeded without changing the particle size. From this, it can be inferred that the action and effect of the amorphization treatment of the present invention is not primarily due to physical crushing for adjusting the particle size of the ore, but is a unique action and effect expressed by the "mechanochemical treatment".

[0075] From the above, it was confirmed that the mechanochemical amorphization treatment described above enables sufficient elution of Mg from magnesium silicate in the ore. The effect of the 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 mineral in the alkaline earth metal-containing ore is changed by the mechanical stress applied from the outside, making it easier for the alkaline earth metal to be eluted into the solution. Therefore, the effect of the mechanochemical treatment described above is not limited to stirring or kneading by a ball mill, but is also considered to be an effect that is expressed when similar treatment is performed using various other known or unknown stirring or kneading devices. [Explanation of symbols]

[0076] St1 Amorphization treatment St2 Carbon dioxide fixation treatment S1 Demask removal project S2 Leaching Process S3 Solid-Liquid Separation Engineering S4 Neutralization Engineering S5 Vulcanization Engineering

Claims

1. an amorphization treatment for subjecting the alkaline earth metal-containing ore to a mechanochemical treatment of applying mechanical stress to the alkaline earth metal-containing ore to amorphize the alkaline earth metal-containing minerals in the alkaline earth metal-containing ore; a carbon dioxide fixation treatment in which the alkaline earth metal-containing ore that has been subjected to the amorphization treatment is placed in a solution, and the alkaline earth metal that has been eluted from the alkaline earth metal-containing ore into the solution is reacted with carbon dioxide, thereby fixing the carbon dioxide as a carbonate of the alkaline earth metal; Methods for fixing carbon dioxide.

2. The mechanochemical treatment is a treatment performed by putting the alkaline earth metal-containing ore into a ball mill. The method for fixing carbon dioxide according to claim 1.

3. The rotation speed of the ball mill is set to 10 rpm or more, and the treatment time by the ball mill is set to 80 minutes or more. The method for fixing carbon dioxide according to claim 2.

4. The alkaline earth metal is magnesium, The alkaline earth metal-containing mineral is a magnesium silicate, The alkaline earth metal carbonate is magnesium carbonate. The method for fixing carbon dioxide according to any one of claims 1 to 3.

5. The magnesium concentration of the alkaline earth metal-containing ore is 5% by mass or more. The method for fixing carbon dioxide according to claim 4.

6. The mass ratio of magnesium to silicon (Mg / Si) in the alkaline earth metal-containing ore is 0.5 or more. The method for fixing carbon dioxide according to claim 4.

7. The alkaline earth metal is calcium, The alkaline earth metal-containing mineral is calcium silicate, The alkaline earth metal carbonate is calcium carbonate. The method for fixing carbon dioxide according to any one of claims 1 to 3.

8. a mechanochemical treatment for applying mechanical stress to the alkaline earth metal-containing ore to amorphousize the alkaline earth metal-containing mineral in the alkaline earth metal-containing ore; a carbon dioxide fixation process in which the alkaline earth metal-containing ore that has been subjected to the amorphization process is placed in a solution, and the alkaline earth metal that has been dissolved from the alkaline earth metal-containing ore into the solution is reacted with carbon dioxide to fix carbon dioxide as an alkaline earth metal carbonate, thereby producing an alkaline earth metal carbonate in the solution; To carry out A method for producing alkaline earth metal carbonates.

9. The mechanochemical treatment is carried out by putting the alkaline earth metal-containing ore into a ball mill. The method for producing an alkaline earth metal carbonate according to claim 8.

10. The rotation speed of the ball mill is set to 10 rpm or more, and the treatment time by the ball mill is set to 80 minutes or more. The method for producing an alkaline earth metal carbonate according to claim 9.

11. The alkaline earth metal is magnesium, The alkaline earth metal-containing mineral is magnesium silicate, The alkaline earth metal carbonate is magnesium carbonate. A method for producing an alkaline earth metal carbonate according to any one of claims 8 to 10.

12. The magnesium concentration of the alkaline earth metal-containing ore is 5% by mass or more. The method for producing an alkaline earth metal carbonate according to claim 11.

13. The mass ratio of magnesium to silicon (Mg / Si) in the alkaline earth metal-containing ore is 0.5 or more. The method for producing an alkaline earth metal carbonate according to claim 11.

14. The alkaline earth metal is calcium, The alkaline earth metal-containing mineral is calcium silicate, The alkaline earth metal carbonate is calcium carbonate. A method for producing an alkaline earth metal carbonate according to any one of claims 8 to 10.

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