Method for fixing carbon dioxide and method for producing carbonic acid salt of alkaline-earth metal

Abstract

A new technical means is provided by which the fixation of CO2 as a carbonic acid salt through reaction of CO2 with a silicate mineral containing Mg, Ca, etc. can be performed at a high treatment efficiency with easy process management.　This method for fixing carbon dioxide comprises: an amorphization treatment St1 in which mechanical stress is applied to alkaline-earth-metal-containing ore for mechanochemical treatment, and an alkaline-earth-metal-containing mineral contained in an alkaline-earth metal is amorphized; and a carbon dioxide fixation treatment St2 in which magnesium eluted into a solution by putting the alkaline-earth-metal-containing ore that has undergone the amorphization treatment St1 into the solution is reacted with carbon dioxide, thereby fixing the carbon dioxide as a carbonic acid salt of the alkaline-earth metal.

Description

Method for fixing carbon dioxide and method for producing alkaline earth metal carbonates

[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.

[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 involves immobilizing emitted carbon dioxide in minerals and the like, in addition to reducing carbon dioxide emissions. As specific means for realizing carbon capture and utilization (CCSU), various carbon dioxide fixation methods have been considered, such as injecting carbon dioxide deep into seawater or injecting and storing carbon dioxide underground. However, all of these methods are uneconomical due to the high cost required for carbon dioxide treatment, and the subsequent environmental impact is unclear, so there are still many problems to overcome before they can be put into practical use.

[0003] On the other hand, one of the carbon capture and utilization technologies (CCSU) mentioned above is the synthesis of silicate minerals containing magnesium (Mg) and calcium (Ca) with carbon dioxide (CO ２ A technology that reacts magnesium carbonate (MgCO ) with the resulting material 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 ３ These 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] In the implementation of the above-mentioned mineral carbonation technology, magnesium (Mg) and calcium (Ca) are added to CO ２ However, in various ores containing Mg and Ca, most of them are silicate compounds with complex crystal structures (e.g., Mg ３ Si ２ O ５ (OH) ４ , Mg ３ Si ４ O １０ (OH) ２ , CaSiO ３ , Ca ２ SiO ４ , Ca ３ SiO ５ Therefore, Mg is contained in the solution as a compound such as ２＋ and Ca ２＋ Therefore, when carrying out the above-mentioned mineral carbonation technology, Mg is dissolved in these ores. ２＋ and 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 carrying out such mineral carbonation technology, a technique has been proposed in the past in which the ore is heated to promote the elution 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 mined in a high-humidity environment and are often provided in a state containing an inconstant amount of physically adsorbed moisture. In addition, the reaction caused by the heat treatment to promote the elution of Mg and Ca is an endothermic reaction. Therefore, it is very difficult to control the temperature to ensure that the reaction proceeds appropriately, and these heat treatments have not been methods that allow pretreatment to proceed with high treatment efficiency. Furthermore, there are problems such as increased energy costs required for the heat treatment and CO emissions associated with the heat treatment. ２Rising emissions were also a concern.

[0006] JP-A-10-249153 Publication Special Publication No. 2012-500718 Publication Special Publication No. 2013-505124

[0007] The present invention has been proposed in view of the above circumstances, and is a method for producing a silicate mineral containing Mg, Ca, etc., and a CO ２ CO is reacted with the ２ The present invention aims to provide a new technical means for easily controlling the process of immobilizing the above-mentioned compound with high processing efficiency.

[0008] The inventors have discovered that CO ２ The present inventors have found that the above-mentioned problems can be solved by carrying out a unique amorphization treatment in which the crystalline 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 reacting the ore with an alkali metal. This has led to the completion of the present invention.

[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 that applies 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 eluted from the ore into a solution by applying mechanical stress to the alkaline earth metal-containing ore to make it amorphous. This allows CO2 fixation with high processing efficiency through a process that is easy to manage. ２ can be fixed as alkaline earth metal carbonates.

[0011] (2) The method for fixation of 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 (2), the dissolution of alkaline earth metal into solution can be more stably promoted in the method for fixation of carbon dioxide described in (1), and the above-mentioned effects achieved by the method for producing alkaline earth metal carbonate described in (1) can be more stably enjoyed.

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

[0014] According to the carbon dioxide fixation method of (3), the above-mentioned effects achieved by the carbon dioxide fixation method 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 carbon dioxide fixation method of (4), in the carbon dioxide fixation method according to any one of (1) to (3), Mg can be sufficiently eluted from the ore containing magnesium silicate by the amorphization treatment by applying mechanical stress. ２ MgCO is highly useful as a carbon-neutral material, and at the same time, promotes the fixation of ３ can also be produced efficiently.

[0017] (5) The method for fixation of 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 exhibited in an even better 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 metal smelting is performed using an ore containing a high concentration of Mg, by combining the metal smelting process with the carbon dioxide fixation method, it is possible to achieve a high level of MgCO ３ Furthermore, at this time, CO ２ CO emitted within the smelting plant as ２ By utilizing gas, CO from the smelting plant ２ It can also contribute to reducing gas emissions.

[0019] (6) The method for fixation of 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 (6), after the amorphous treatment, Mg ２＋ This allows for the production of more CO in the carbon dioxide fixation method described in (4). ２ This can further efficiently promote the above-mentioned reaction related to the immobilization of the antibody.

[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 carbon dioxide fixation method of (7), in the carbon dioxide fixation method according to any one of (1) to (3), Ca can be sufficiently eluted from the ore containing calcium silicate by the amorphization treatment by applying mechanical stress. ２ CaCO3 is highly useful as a carbon-neutral material, and at the same time, promotes the fixation of ３can also be produced efficiently.

[0023] (8) A method for producing alkaline earth metal carbonate, comprising: an amorphization treatment in which an alkaline earth metal-containing ore is subjected to a mechanochemical treatment that applies 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 to fix the 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 of (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 using mechanical stress. This allows the alkaline earth metals and CO ２ promotes the reaction with CO throughout the manufacturing process ２ MgCO ３ and CaCO ３ It is possible to produce alkaline earth metal carbonates, which are industrially useful products such as:

[0025] (9) The method for producing 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 of (8), and the above-mentioned effects achieved by the method for producing an alkaline earth metal carbonate of (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 in 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 achieved by the method for producing an alkaline earth metal carbonate of (9) can be more stably enjoyed.

[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 alkaline earth metal carbonate of (11), in the method for producing alkaline earth metal carbonate according to any one of (8) to (10), Mg can be sufficiently eluted from the Mg-containing silicate ore into the solution by the amorphization treatment by applying mechanical stress. ２ This promotes the fixation of MgCO, which is highly useful as a carbon-neutral material. ３ can be efficiently manufactured.

[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), it is possible to enjoy the above-mentioned effects of the method for producing alkaline earth metal carbonate of (11) by using ore with a high magnesium concentration. As a result, as an example, in various metal smelting plants, such as a nickel smelting plant that performs nickel smelting by the "HPAL process", when metal smelting is performed using ore containing a high concentration of Mg, by combining the metal smelting process with this method for producing alkaline earth metal oxide (magnesium carbonate), it is possible to obtain MgCO ３ In addition, the CO reacted with Mg can be efficiently produced. ２ CO emitted in nickel smelting plants as ２ By utilizing gas, CO from nickel smelting plants can be reduced. ２It can also contribute to reducing gas emissions.

[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 (method for producing magnesium carbonate) of (13), after the amorphous treatment, Mg is added to the solution. ２＋ This allows for the production of more MgCO in the method for producing an alkaline earth metal carbonate according to (11). ３ The productivity in the production of the above can be further improved.

[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 a carbonate of an alkaline earth metal (calcium carbonate) of (14), in the method for producing a carbonate of an alkaline earth metal according to any one of (8) to (10), Ca can be sufficiently eluted from a silicate ore containing Ca by amorphization treatment by applying mechanical stress. ２ This promotes the fixation of CaCO3, which is highly useful as a carbon-neutral material. ３ can be efficiently manufactured.

[0037] According to the present invention, a silicate mineral containing Mg, Ca, etc. and CO ２ CO is reacted with the ２ The fixation of CO2 can be easily controlled and can be performed with high processing efficiency. In addition, the heat treatment, which was an essential treatment in the conventional fixation process, can be replaced by the "mechanochemical treatment". ２ The new CO generated during the immobilization process ２ MgCO at lower cost while reducing emissions３ It is possible to produce carbonates of alkaline earth metals such as

[0038] Fig. 1 is a flow chart showing the flow of the carbon dioxide fixation method of the present invention. Fig. 2 is a graph showing that alkaline earth metal-containing minerals in alkaline earth metal-containing ore are made amorphous by the amorphization treatment in the carbon dioxide fixation method of the present invention. Fig. 3 is a graph showing the change in particle size distribution of alkaline earth metal-containing ore when the amorphization treatment in the carbon dioxide fixation method of the present invention is carried out. Fig. 4 is a process diagram of the entire combined process in a combined embodiment in which the carbon dioxide fixation method of the present invention (or a method for producing alkaline earth metal carbonates) is combined with a nickel oxide ore hydrometallurgy process (HPAL).

[0039] 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.

[0040] <Method for Fixing Carbon Dioxide> Fig. 1 is a flow chart 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 (CO ２ ) fixation method for carbon dioxide (CO ２ ) is reacted in solution with an alkaline earth metal-containing mineral to produce magnesium carbonate (MgCO ３ ) and calcium carbonate (CaCO ３ ) or other alkaline earth metal carbonates.

[0041] The "method for fixing carbon dioxide" of the present invention includes amorphization treatment St1, which applies mechanical stress to an ore containing alkaline earth metals such as magnesium (Mg) and calcium (Ca) (referred to as "alkaline earth metal-containing ore" in this specification) to change the crystal structure of the alkaline earth metal-containing mineral (magnesium silicate, calcium silicate, etc.) in the ore; and amorphization treatment St2, which converts the alkaline earth metals eluted from the alkaline earth metal-containing ore into a solution and fixes them to carbon dioxide (CO ２ ) to give CO ２ Alkaline earth metal carbonate (MgCO３ or CaCO ３ This is a process in which carbon dioxide fixation treatment St2 is carried out in which carbon dioxide is fixed in a solution (e.g., a carbonate of an alkaline earth metal) of the present invention. The recovery of the alkaline earth metal carbonate from the solution can be carried out by a carbonate recovery treatment described later. It is preferable to use water as the solution used in carrying out the present invention.

[0042] As described above, alkaline earth metals such as Mg and Ca are contained in alkaline earth metal-containing ores as alkaline earth metal-containing minerals such as magnesium silicate and calcium silicate. Therefore, in the past, heat treatment of alkaline earth metal-containing ores was essential to sufficiently dissolve the alkaline earth metals (Mg, Ca, etc.) into a solution, but the "method for fixation of carbon dioxide" of the present invention is a novel process characterized primarily by a process of amorphizing the alkaline earth metal-containing minerals through a "mechanochemical treatment" that changes the crystalline structure of the minerals 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 crystalline structure of an alkaline earth metal-containing mineral (such as magnesium silicate or calcium silicate) is changed by applying mechanical stress. In this specification, "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, thereby changing the crystalline structure of the alkaline earth metal-containing mineral contained in the treatment target (alkaline earth metal-containing ore) by mechanical energy."

[0044] The above-mentioned "mechanochemical treatment" is not limited to a specific treatment method, and can be carried out using 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. Furthermore, the above-mentioned "mechanochemical treatment" can also be carried out using various other known or unknown stirring or kneading devices that can exert similar effects.

[0045] The "mechanochemical treatment" performed in the present invention differs from general "pulverization treatment" in that it is not a treatment intended to reduce particle size. Even when the "mechanochemical treatment" of the present invention is performed, the particle size of individual particles may be reduced due to the destruction of the ore ore to be treated during the treatment. However, the purpose of the "mechanochemical treatment" of the present invention is to amorphize alkaline earth metal-containing minerals (such as magnesium silicate or calcium silicate) by reducing their crystallinity (changing (destructing) their structure). Therefore, this is a novel treatment method with a different purpose and effect from, for example, the pulverization treatment for particle size adjustment, which is performed to increase the specific surface area of ​​the material to be treated as a pretreatment prior to the conventional amorphization treatment that reduces crystallinity by heat treatment. FIG. 3 shows the change in particle size distribution of alkaline earth metal-containing ore when "mechanochemical treatment" is performed in the "method for fixing carbon dioxide" of the present invention. The particle size distribution shown in the figure shows almost no change, which shows that the "mechanochemical treatment", which is the means for performing the amorphization treatment St1 in the present invention, is a novel treatment method that differs from the general "crushing treatment" that aims to adjust the particle size distribution.

[0046] Furthermore, 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 ball mill rotation speed should be 10 rpm or higher, and the treatment time should be 80 minutes or longer. Furthermore, the rotation speed is preferably 100 rpm or higher, and more preferably 300 rpm or higher. In this case, the treatment time should also be 150 minutes or higher, and more preferably 270 minutes or higher. If the treatment time is further extended while the ball mill rotation speed is set to 300 rpm, the effect of amorphizing the treated material (alkaline earth metal-containing mineral) increases, but even in this case, the rate of increase in the amorphization effect reaches a plateau at a treatment time of about 400 minutes. Therefore, the combination of ball mill rotation speed and treatment time is preferably 300 rpm or higher and a treatment time of 270 minutes or longer. As described below, 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) in the ore of 0.5 or more. However, by setting the treatment conditions in the "mechanochemical treatment" within 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 solution even from alkaline earth metal-containing ores having a low mass ratio (Mg / Si) in the ore. Note that the "mechanochemical treatment" can be carried out in a dry system, but can also be carried out in a wet system, since the amorphized ore is treated in solution in the subsequent carbon dioxide fixation treatment St2.

[0048] In addition, whether or not various alkaline earth minerals contained in alkaline earth metal-containing ores have been sufficiently amorphous can be determined by XRD analysis. ３ Si ２ O ５ (OH) ４ ), forsterite (Mg ２ SiO ４ ), enstatite (MgSiO ３As 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), and this is a finding that was independently discovered by the present inventors. The above-described "amorphization treatment" that constitutes the present invention is a novel technical means for amorphizing minerals that has not been seen before.

[0050] [Carbon dioxide fixation treatment] In the carbon dioxide fixation treatment St2 performed following the amorphization treatment St1, alkaline earth metals are eluted into a solution from the alkaline earth metal-containing mineral that has been amorphized through the amorphization treatment St1, and CO is dissolved in the solution. ２ A gas is blown in, and the eluted alkaline earth metal and the CO blown in as a gas are mixed in the solution. ２ By reacting with CO ２ This is a process in which the metal is fixed as an alkaline earth metal carbonate.

[0051] The ratio of alkaline earth metal-containing ore to the solution for eluting alkaline earth metals 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 alkaline earth metal-containing ore in the solution 2% by mass or more, "alkaline earth metal carbonate (MgCO ３ In addition, 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.

[0052] CO in solution ２ The method of blowing CO is not particularly limited, but an example is to blow CO using a disk-type diffuser or a cylindrical diffuser. ２ This can be done by blowing gas into the solution. ２Gas CO ２ The concentration should be 10% or more. However, if the concentration exceeds 10%, ２ By converting it into a gas, alkaline earth metal carbonate (MgCO ３ etc.) and CO ２ This can promote the immobilization of the protein more efficiently.

[0053] In addition, the CO used in the carbon dioxide fixation treatment St2 ２ The supply source and supply method of are not particularly limited. For example, CO generated in 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 (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 present invention in parallel in the same plant, CO from these metal smelting processes can be reduced. ２ This can contribute to reducing the total amount of gas emissions.

[0054] [Carbonate Recovery Treatment] In the "carbon dioxide fixation method" of the present invention, following carbon dioxide fixation treatment St2, ２ Alkaline earth metal carbonate (MgCO ３ If necessary, a carbonate recovery process can be carried out to recover alkaline earth metal carbonates (e.g., carbonates of alkaline earth metals) from the solution. In this carbonate recovery process, the specific method for recovering the alkaline earth metal carbonates is not particularly limited, but examples include a method of recovering the carbonates by separating the liquid using a filter such as a filter press, or a method of recovering the carbonates by volatilizing the water content of the solution.

[0055] [Alkaline earth metal-containing minerals, alkaline earth metals, and carbonates of alkaline earth metals] In the "method for fixing carbon dioxide" of the present invention, ２ The "alkaline earth metals" envisioned as the main raw materials for reacting with the above to form useful "alkaline earth metal carbonates" are primarily Mg or Ca.

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

[0057] Furthermore, as the "alkaline earth metal-containing ore," ores having a mass ratio of Mg to Si (Mg / Si) of 0.5 or more are preferably used. Ores having a ratio of 1.0 or more are more preferably used. When the Mg / Si ratio is 0.5 or more, a larger amount of Mg can be eluted after amorphization treatment. Compounds with a higher Si content relative to Mg have a complex crystal structure, making Mg less likely 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 measuring the resulting sample using ICP atomic emission spectroscopy. Similarly, the magnesium concentration (mass) in "alkaline earth metal-containing ores" can be determined by leaching 0.5 g of ore in hydrochloric acid and measuring the resulting sample using ICP atomic emission spectroscopy.

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

[0059] As mentioned above, the "mechanochemical treatment" used to perform the amorphization treatment St1 in the present invention is a different process from the conventionally known "pulverization treatment" aimed at adjusting the particle size distribution. However, if the above-mentioned general "pulverization treatment" is performed as a preparatory step in the first stage of the present invention as a pretreatment of the ore, it is possible to perform the amorphization treatment St1 by "mechanochemical treatment" simultaneously with such pretreatment. Alternatively, the above-mentioned general "pulverization treatment" and the amorphization treatment St1 by "mechanochemical treatment" can be performed simultaneously in parallel using a large pulverizer (ball mill) or the like. As such, even if other pulverization treatments are performed prior to or in parallel with the "mechanochemical treatment" in the series of carbon dioxide fixation treatments, and regardless of how the particle size distribution of the ore changes as a result, any process in which the "mechanochemical treatment" used to perform the amorphization treatment St1 unique to the present invention is performed is naturally within 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 an alkaline earth metal carbonate by reacting an alkaline earth metal (e.g., Mg or Ca) with carbon dioxide (CO ２ ) to produce magnesium carbonate (MgCO ３ ) and calcium carbonate (CaCO ３ This is a method for producing carbonates of alkaline earth metals such as ammonium hydroxide.

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

[0062] In the same manner as the above-mentioned "method for fixing carbon dioxide," the amorphousization treatment St1 and the carbon dioxide fixation treatment St2 are carried out, whereby alkaline earth metals eluted into a solution from alkaline earth metal-containing ore are fixed in a solution by CO ２ By reacting with CO ２ is fixed in the alkaline earth metal, thereby providing MgCO in solution. ３ or CaCO ３ The carbonate produced in the solution can be recovered by any method, but may be recovered appropriately by the same "carbonate recovery treatment" as in the above-mentioned "method for fixation of carbon dioxide."

[0063] MgCO produced by the "method for producing alkaline earth metal carbonate" of the present invention ３ can be used as a variety of construction materials, including landfill materials for civil engineering and aggregates for concrete, and also for various industrial purposes, such as a neutralizing agent, a strengthening agent for natural rubber, a gastrointestinal medicine, a fragrance retention agent, and an abrasive.

[0064] <Application to Hydrometallurgy of Nickel Ore> Either the "method for fixation of carbon dioxide" or the "method for producing alkaline earth metal carbonate" 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 the form of silicates from nickel oxide ore during the "hydrometallurgy of nickel oxide ore" shown in Fig. 4. This embodiment of the present invention is particularly effective when 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 during the "hydrometallurgy of nickel oxide ore".

[0065] The "method for smelting nickel oxide ore" that can be carried out using the "method for fixation of carbon dioxide" or the "method for producing alkaline earth metal carbonate" of the present invention as a partial process is a known process as a whole, and an example of the flow of the process is shown in Fig. 4. This whole 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 with a reduced magnesium concentration 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 sulfiding agent is added to the neutralized end solution to produce a nickel-containing sulfide.

[0066] As described above, the "method for fixation of carbon dioxide" or the "method for producing 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 "method for hydrometallurgy of nickel oxide ore." Even when the demagnesium step S1 is carried out by the above-described methods of the present invention, the other steps, such as the leaching step S2, solid-liquid separation step S3, neutralization step S4, and sulfidation step S5, can be carried out in the same manner as in the conventionally known embodiments of the "method for hydrometallurgy of nickel oxide ore."

[0067] [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 5.0% 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 5.0% 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 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 ), it is not easy to dissolve Mg sufficiently into the solution. However, by carrying out the magnesium removal step S1 by the above-mentioned methods of the present invention, the process of dissolving Mg from the "high Mg nickel oxide ore" to produce the above-mentioned "low Mg nickel oxide ore" can be carried out efficiently at low cost and without CO ２ In this embodiment, the CO 2 reacting with the dissolved Mg can be carried out simultaneously. 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 method can also contribute to reducing the total amount of gas emissions. Furthermore, raw material ores containing high concentrations of Mg, such as saprolite ore, 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)."

[0069] The effects of the "method for fixation of carbon dioxide" and the "method for producing 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] <Amorphization Treatment Test> A test was conducted to verify the effect of amorphizing alkaline earth metal-containing minerals using the "method for fixation of carbon dioxide" and "method for producing alkaline earth metal carbonates" 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" of the "method for fixation of carbon dioxide" and "method for producing alkaline earth metal carbonates" of the present invention was performed under "Test Condition 1" below, with the kneading time in a ball mill varied for each sample. Then, each sample was subjected to "crystal structure analysis by X-ray diffraction" to confirm the progress of amorphization. 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 mechanochemical treatment to amorphize the ore. 50 g of alkaline earth metal-containing ore sample and 300 g of zirconia balls (10 mm diameter) were added as grinding media. The table rotation speed of the planetary ball mill was set to 300 rpm, and mechanochemical treatment was performed for a predetermined time and at a predetermined table rotation speed. Then, for each sample after the kneading treatment under the above conditions, "crystal structure analysis by X-ray diffraction" was performed using an X-ray diffractometer, Empyrean (manufactured by Malvern Instruments).

[0071] As can be seen from FIG. 2, the "amorphization treatment" in the "method for producing alkaline earth metal carbonates" of the present invention resulted in the formation of lizardite (Mg ３ Si ２ O ５ (OH) ４ ) was confirmed to decrease in the peak of the (002) plane, which indicates that the crystallinity of the ore sample has changed.

[0072] <Alkaline Earth Metal (Mg) Leaching Promotion Test> A test was conducted to verify the effect of promoting the leaching 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, each of the "alkaline earth metal-containing ore samples (ores A to E)" in the examples and comparative examples shown in Table 1 below was 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). CO was added to the solution while stirring at a rotation speed of 450 rpm. ２The gas (manufactured by Takamatsu Teisan Co., Ltd., concentration 99.995% by volume) was blown in at a rate of 0.1 L / min, and the elution rates of Mg or Ca into the solution were measured and calculated using the "Method for Measuring the Amount of Leaching of Alkaline Earth Metal (Mg) and Calculating the Elution Rate" described below. As a reference example, the same test was performed on the same sample (Ore B) that had not been subjected to the "mechanochemical treatment" (amorphization treatment) but had been calcined 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 using the above-mentioned ICP emission spectrometry or other measurement method to confirm the respective mass ratios. The confirmed values ​​of each ratio are also shown in Table 1. The test results obtained under the above conditions were evaluated for elution promotion 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 (10 mm diameter) as grinding media were placed in the same planetary ball mill as in the "amorphization treatment test" above, and an amorphization treatment was performed. The table rotation speed and treatment time of the planetary ball mill were set to the rotation speed and treatment time shown in Table 1 below for each Example and Comparative Example. (Method for measuring the amount of eluted alkaline earth metal (Mg) and calculating the elution rate) Magnesium elution rate = magnesium concentration in solution (mg / L) × eluate volume (L) / (magnesium concentration in ore (mass%) ÷ 100 × ore mass (mg)). Each of the magnesium concentrations was measured by ICP atomic emission spectrometry. (Evaluation criteria for elution 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]

[0074] As mentioned above, Figure 3 is a graph showing the particle size distribution of each nickel oxide ore sample after the "mechanochemical treatment" (mixing treatment using a ball mill). The results shown in Figure 3 show that there was no significant change in the particle size of each ore sample after the "mechanochemical treatment," and that only amorphization progressed without any change in particle size. From this, it can be inferred that the effect of the amorphization treatment of the present invention is not primarily due to physical pulverization for adjusting the particle size of the ore, but is a unique effect achieved by the "mechanochemical treatment."

[0075] From the above, it has been confirmed that the mechanochemical amorphization treatment described above enables sufficient elution of Mg from magnesium silicate in the ore. The effect of this mechanochemical amorphization treatment is the result of a uniquely discovered novel method, but it is believed to be due to the fact that the crystalline structure of the alkaline earth metal-containing mineral in the alkaline earth metal-containing ore is changed by externally applied mechanical stress, making it easier for the alkaline earth metal to be eluted into solution. Therefore, the effect of the mechanochemical treatment described above is not limited to stirring or kneading using a ball mill, and is believed to be an effect that can also be achieved when similar treatments are performed using various other known or unknown stirring or kneading devices.

[0076] St1 Amorphization treatment St2 Carbon dioxide fixation treatment S1 Demagnesium process S2 Leaching process S3 Solid-liquid separation process S4 Neutralization process S5 Sulfurization process

Claims

1. A method for fixing carbon dioxide, comprising the steps of: (amorphization treatment) for applying mechanical stress to alkaline earth metal-containing ore (mechanochemical treatment) to make the alkaline earth metal-containing minerals in the alkaline earth metal-containing ore amorphous; and (b) a carbon dioxide fixation treatment) for placing the alkaline earth metal-containing ore that has been subjected to the amorphization treatment in a solution, and fixing the carbon dioxide as an alkaline earth metal carbonate by reacting the alkaline earth metal eluted from the alkaline earth metal-containing ore into the solution with carbon dioxide.

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

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

4. A method for fixing carbon dioxide according to any one of claims 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.

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

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

7. A method for fixing carbon dioxide according to any one of claims 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.

8. A method for producing alkaline earth metal carbonate, 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, thereby amorphizing the alkaline earth metal-containing mineral in the alkaline earth metal-containing ore; 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 to fix carbon dioxide as an alkaline earth metal carbonate, thereby producing the alkaline earth metal carbonate in the solution.

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

10. The method for producing an alkaline earth metal carbonate according to claim 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.

11. A method for producing an alkaline earth metal carbonate according to any one of claims 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.

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

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

14. A method for producing an alkaline earth metal carbonate according to any one of claims 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.

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