METHOD FOR PRODUCING INORGANIC SUBSTANCE SOLUTION AND DEVICE FOR PRODUCING INORGANIC SUBSTANCE SOLUTION

Abstract

For the purpose of providing a technology that makes it possible to dissolve an inorganic substance typified by lithium ore more easily compared with the conventional technologies disclosed in non-patent document 1 and patent document 1, an inorganic substance solution production method (M10) is provided. The method comprises: a mixing step (S101) for mixing an additive with an inorganic substance that undergoes phase change or is thermally decomposed by heating to produce a first mixture; and a heating step (S102) for heating the first mixture at a heating temperature that is equal to or higher than a predetermined temperature to produce a second mixture comprising the inorganic substance and the additive. In the method, the molar ratio of the amount of the additive to that of the inorganic substance in the mixing step (S101) is 0.5 or more. When (1) the inorganic substance is one which undergoes phase change by heating, the predetermined temperature is a temperature at which the phase change occurs. When (2) the inorganic substance is one which is thermally decomposed by heating, the predetermined temperature is a temperature at which the thermal decomposition occurs.

Description

49 METHOD FOR PRODUCING INORGANIC SUBSTANCE SOLUTION AND DEVICE FOR PRODUCING INORGANIC SUBSTANCE SOLUTION Field of invention

[001] The present invention relates to a method for producing a solution of an inorganic substance and a device for producing a solution of an inorganic substance. Fundamentals of the invention

[002] As lithium ores, spodumene (LiAlSi2O6), lepidolite (K(Al,Li)2(Si,Al)4OI(OH,F)2), petalite (LiAlSiOI), elbaite (Na(Li,Al)3Al6(BO3)3Si6O18(OH)4) and hectorite (NaO3(Mg,Li)3SuO1O(OH)2) are known.

[003] In the case where lithium is recovered from lithium ore, lithium is extracted from the lithium ore by dissolving the lithium ore in a solvent. However, dissolving lithium ore in a solvent is not easy.

[004] Therefore, in Non-Patent Literature 1, a method is used in which lithium ore is calcined at 1000 °C or more and then roasted at 250 °C with concentrated sulfuric acid.

[005] In Non-Patent Literature 1, a method is used in which lithium ore and a residual amount of calcium oxide are mixed and heated to 1000 °C to 1300 °C and then dissolved in an acidic solution at 400 °C under pressure. The amount of calcium oxide mixed with the lithium ore in this technique is 0.08 or more and less than 0.34 in terms of molar ratio relative to the amount of lithium ore. The pressure in the dissolution process is 90 atm or more. List of citations Petition 870250081655, dated 11 / 09 / 2025, p. 55 / 103 / 49

[006] [Patent Literature]

[007] [Patent Literature 1]

[008] U.S. Patent No. 2662809, descriptive report.

[009] [Non-patent literature]

[010] [Non-patent literature 1]

[011] Songyan Jiang et al., Environmental impacts of lithium production, showing the importance of primary upstream process data in life cycle assessment, Journal of Environmental Management, Volume 262, 110253, 2020 Summary of the invention

[012] Technical problem

[013] However, in conventional techniques disclosed in Non-Patent Literature 1 and Patent Literature 1, it is necessary to heat the lithium ore to 250 °C or 400 °C in the dissolution process to dissolve the lithium ore in the acidic solution. In the conventional technique disclosed in Patent Literature 1, in the dissolution process, it is necessary to perform pressurization at a high pressure of not less than 90 atm, in addition to heating.

[014] The invention, according to one aspect of the present invention, is carried out in view of the problems described above, and its objective is to provide a technique that makes it possible to dissolve an inorganic substance, such as lithium ore, more easily than the conventional techniques disclosed in the Non-Patent Literature 1 and in the Patent Literature 1. Solution to the problem

[015] To achieve the objective, a method for producing a solution of an inorganic substance according to an aspect of the present invention includes: a mixing step of an inorganic substance and an additive to obtain a first mixture, the inorganic substance being subjected to a phase change or Petition 870250081655, dated 11 / 09 / 2025, page 56 / 103 / 49 thermal decomposition by heating, and the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; and a heating step to heat the first mixture to a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive.In this production method, a configuration is employed in which the proportion of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio, and the predetermined temperature is (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase must be changed by heating and (2) a temperature at which thermal decomposition occurs in the case where the inorganic substance is an inorganic substance that must be thermally decomposed by heating.

[016] To achieve the objective, a method for producing a solution of an inorganic substance according to an aspect of the present invention includes: a phase change step to change, by heating, a phase of an inorganic substance that is to be altered by heating; a mixing step to mix the inorganic substance that has undergone a phase change and an additive to obtain a first mixture, the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide; and a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive. In this method of producing a solution of an inorganic substance, a configuration is employed in which the ratio of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio.

[017] To achieve the objective, a method for producing a solution of an inorganic substance according to an aspect of the present invention includes: a mixing step of mixing an inorganic substance and an additive to obtain a first mixture, the inorganic substance containing β-spodumene and the additive. Petition 870250081655, dated 11 / 09 / 2025, page 57 / 103 / 49, being at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide; and a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive. In this production method, a configuration is employed in which the proportion of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio.

[018] To achieve the objective, a device for producing a solution of an inorganic substance according to an aspect of the present invention includes: a mixing section for mixing an inorganic substance and an additive to obtain a first mixture, the inorganic substance being subjected to a phase change or thermal decomposition by heating, and the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; and a heating section for heating the first mixture to a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive.In this production device, a configuration is employed in which the proportion of the additive to the inorganic substance in the Mixing Section is 0.5 or more in terms of molar ratio, and the predetermined temperature is (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase must be changed by heating and (2) a temperature at which thermal decomposition occurs in the case where the inorganic substance is an inorganic substance that must be thermally decomposed by heating.

[019] Advantageous effects of the invention

[020] According to one aspect of the present invention, it is possible to provide a technique that makes it possible to dissolve an inorganic substance, such as lithium ore, more easily than the conventional techniques disclosed in Non-Patent Literature 1 and Patent Literature 1. Petition 870250081655, dated 11 / 09 / 2025, p. 58 / 103 / 49 Brief description of the drawings

[021] For a better understanding of the present patent, the following figures are attached:

[022] Figure 1 is a flowchart illustrating a method according to Embodiment 1 of the present invention for producing a solution of an inorganic substance.

[023] Figure 2 is a flowchart illustrating a method according to Embodiment 2 of the present invention for producing a solution of an inorganic substance.

[024] Figure 3 is a flowchart illustrating a method according to Embodiment 3 of the present invention for producing a solution of an inorganic substance.

[025] Figure 4 is a flowchart illustrating a method according to Embodiment 4 of the present invention for producing a solution of an inorganic substance.

[026] Figure 5 is a flowchart illustrating a method according to Embodiment 5 of the present invention for producing a solution of an inorganic substance.

[027] Figure 6 is a view that schematically illustrates a dielectric heating device according to Embodiment 6 of the present invention.

[028] Figure 7 is a perspective view of an insulator included in the dielectric heating device shown in Figure 6.

[029] Figure 8 is a view that schematically illustrates a device for producing an inorganic substance solution included in an inorganic substance solution production system according to embodiment 7 of the present invention.

[030] Figure 9 is a photograph showing a heated mixture obtained in example 1. Petition 870250081655, dated 11 / 09 / 2025, page 59 / 103 / 49

[031] Figure 10 is a graph showing the result of an X-ray diffraction (XRD) test on an inorganic substance contained in the heated mixture obtained in Example 1.

[032] Figure 11 is a graph showing the result of an XRD test on an inorganic substance contained in the solid phase of an inorganic substance solution obtained in Example 1.

[033] Figure 12 is a graph showing the result of an XRD test on an inorganic substance contained in a mixture obtained after heating in Example 2.

[034] Figure 13 is a graph showing the relationship between the elution rate of lithium in an inorganic substance solution obtained in Example 3 and the weight ratio of natural spodumene and calcium carbonate. Description of the achievements

[035] [Implementation 1]

[036] (Method for producing a solution of an inorganic substance)

[037] The following description will discuss an M10 method for producing an inorganic substance solution according to Embodiment 1 of the present invention, with reference to Figure 1. Figure 1 shows a flowchart of the M10 method for producing an inorganic substance solution. Hereinafter, the M10 method for producing an inorganic substance solution may also be referred to simply as the M10 production method. Hereinafter, the inorganic substance solution means a solution in which an inorganic substance that is a starting material is dissolved. Inorganic substance is a generic term for inorganic compounds and metals. Inorganic compound refers to a compound other than an organic substance or an organic compound, i.e., a compound that does not contain carbon. The inorganic compound preferably contains any of the lithium ores (described further below) and metals, such as rare metals and rare earth metals. Metals include noble metals. Petition 870250081655, dated 11 / 09 / 2025, page 60 / 103 / 49 nobles include gold (Au), silver (Ag) and platinum metals (ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt)).

[038] In the present embodiment, lithium ore containing natural spodumene is employed as an inorganic substance used in the M10 production method. Spodumene is an example of naturally occurring lithium ore. Natural spodumene is classified into an α phase and a β phase according to its crystal structure. Hereafter, spodumene in the α phase and spodumene in the β phase are referred to as α-spodumene and β-spodumene, respectively. Natural spodumene obtained from mines is primarily α-spodumene. Furthermore, upon heating to a temperature of 1000 °C or higher, spodumene undergoes a phase change to β-spodumene.

[039] The inorganic substance used in the M10 production method is not limited to ore containing natural spodumene; it is possible to select the inorganic substance, as appropriate, from inorganic substances whose crystalline structure is altered or thermally decomposed by heating. Examples of an inorganic substance that is thermally decomposed by heating include petalite (LíAISÍ40io).

[040] As shown in figure 1, the production method M10 includes a grinding and mixing step S101, a heating step S102 and a dissolution step S103.

[041] (Grinding and mixing stage)

[042] In the grinding and mixing step S101, which is an example of the mixing step, an inorganic substance is ground to obtain powder of the inorganic substance. By grinding the inorganic substance, it is mechanically broken down to have a smaller particle diameter, thus improving the efficiency of a chemical reaction with hydroxide or oxide. The technique used to grind the inorganic substance is not limited to any one in particular and can be selected from among Petition 870250081655, dated 11 / 09 / 2025, page 61 / 103 / 49 existing techniques, as appropriate. Such a technique may be one that involves the use of a jaw crusher or a ball mill, for example.

[043] In the grinding and mixing step S101, sodium hydroxide (NaOH), which is an example of an additive, is ground to obtain sodium hydroxide powder. Note, however, that if sodium hydroxide powder is purchased and used, the grinding step of sodium hydroxide in the grinding and mixing step S101 can be omitted. If the sodium hydroxide used in the grinding and mixing step S101 is in the form of granules or flakes, it is possible to omit the grinding of sodium hydroxide in the grinding and mixing step S101. The form of the sodium hydroxide used in the grinding and mixing step S101 is not limited. Sodium hydroxide is an example of hydroxides. At least one of the hydroxides and oxides used in the M10 production method is not limited to sodium hydroxide, and may be calcium hydroxide (Ca(OH)2) or calcium oxide (CaO). From sodium hydroxide, calcium hydroxide, and calcium oxide, two or more of these can be selected and combined.

[044] In the grinding and mixing step S101, the ground inorganic substance and the ground additive are mixed to obtain a mixture of the inorganic substance and the additive. The mixture obtained in the grinding and mixing step S101 is an example of the first mixture. In the present embodiment, the mixture is in powder form. Here, the ratio of the additive to the inorganic substance is 0.5 or more in terms of molar ratio. Hereafter, the ratio of the additive to the inorganic substance is expressed using the molar ratio, unless otherwise indicated. As described later, β-spodumene, which is used as the inorganic substance, and sodium hydroxide, which is used as the additive, react in a 1:1 ratio to generate lithium metasilicate (Li2SiO3), which is readily dissolved in acids or water.If the ratio of additive to inorganic substance is excessively greater than 1, the amount of additive (i.e., wasted additive) that is not used in the reaction increases. Petition 870250081655, dated 11 / 09 / 2025, p. 62 / 103 / 49 to convert β-spodumene into lithium metasilicate. Therefore, the ratio is preferably equal to or greater than 0.8 and less than or equal to 4, being more preferably equal to or greater than 1 and less than or equal to 2.

[045] (Warm-up stage)

[046] In the heating step S102, the mixture obtained in the grinding and mixing step S101 is heated to a heating temperature not lower than a predetermined temperature, thus obtaining a mixture of the phase-changed or thermally decomposed inorganic substance and the additive. The predetermined temperature in the heating step S102 is (1) a temperature at which a phase change occurs, in the case where the inorganic substance is an inorganic substance whose phase must be changed by heating, and (2) a temperature at which thermal decomposition occurs, in the case where the inorganic substance is an inorganic substance that must be thermally decomposed by heating.

[047] The mixture obtained in the S102 heating step is an example of the second mixture. In the S102 heating step, the mixture (first mixture) is heated to a temperature at which a phase change or thermal decomposition of the crystalline structure occurs in the inorganic substance. In the present embodiment, dielectric heating is used as the heating method in the S102 heating step, and 700 °C is used as the heating temperature. The heating temperature is a temperature not lower than the temperature (i.e., the predetermined temperature) at which α-spodumene undergoes a phase change. In the present embodiment, a radiation thermometer is used to measure the temperature of the mixture during dielectric heating. The heating temperature here is the temperature at the surface of the mixture measured using the radiation thermometer. Therefore, it is possible that the interior of the mixture during heating reached a temperature higher than 700 °C. Petition 870250081655, dated 11 / 09 / 2025, page 63 / 103 / 49

[048] The heating temperature is not limited to 700 °C and may be defined as appropriate within a temperature range in which phase change or thermal decomposition occurs in the inorganic substance. The heating time may be defined as appropriate within a range in which a reaction described below proceeds sufficiently. It is highly probable that by increasing the heating temperature, the heating time may be reduced.

[049] During the S102 heating step, sodium hydroxide and the inorganic substance convert the energy of the electromagnetic waves (described later) into thermal energy and are heated. Consequently, the natural spodumene (i.e., α-spodumene) contained in the inorganic substance undergoes a phase change to β-spodumene. Furthermore, as indicated below, β-spodumene reacts with sodium hydroxide in a 1:1 ratio to generate nepheline (NaAlSiO4), Li2SiO3, and quartz (SiO2).

[050] 2(e-LiAlSí2O6)+2NaOH^2NaAlSiO4+Li2SiO3+SiO2+H2O

[051] The starting material and sodium hydroxide do not contain moisture. Therefore, even if the temperature of the mixture during heating exceeds 100 °C, it is not necessary to consider the boiling of moisture. Thus, in the heating step S102, it is possible to heat the mixture dielectrically under normal pressure. At least one of the starting materials and the additive may contain moisture. If at least one of the starting materials and the additive contains moisture, drying (evaporation of moisture by boiling) begins when the heating temperature reaches 100 °C, and heating continues after complete removal of moisture. Thus, it is possible to carry out heating under normal pressure, even if moisture is present.

[052] Dielectric heating is a generic term for techniques of applying an electromagnetic wave with a given frequency to a target object in order to heat the target object. According to the waveband Petition 870250081655, dated 11 / 09 / 2025, p. 64 / 103 / 49 electromagnetic heating to be applied, dielectric heating is called radio frequency heating or microwave heating. For example, radio frequency heating applies to the target object an electromagnetic wave (a so-called short wave or ultrashort wave) within a band not lower than 3 MHz and lower than 300 MHz, while microwave heating applies to the target object an electromagnetic wave (a so-called microwave) within a band not lower than 300 MHz and lower than 30 GHz. A microwave oven, widely used in homes as well, is an example of a device that can perform microwave heating.

[053] In the present embodiment, the heating step S102 applies an electromagnetic wave with a frequency of 2.45 GHz to the mixture. The configuration of the device that applies an electromagnetic wave to the mixture in powder form will be described later with reference to Figure 6 or Figure 8.

[054] It appears that by heating the mixture using dielectric heating, it is possible to change the phase of the inorganic substance with greater energy efficiency compared to a case where external heating is used to heat the mixture. As described later, the heated mixture is easily dissolved in an acidic solution (sulfuric acid in the present embodiment). Therefore, it is possible to obtain a sulfuric acid solution in which the inorganic substance is dissolved. Thus, production method M10 can provide a method for producing an inorganic substance solution in which dissolution in the acidic solution can be achieved more easily than conventional production methods. Note, however, that the heating technique used in heating step S102 can be external heating instead of dielectric heating.The concentration of the acidic solution is not particularly limited; it only needs to be at a concentration at which the inorganic substance dissolves.

[055] (Dissolution stage) Petition 870250081655, dated 11 / 09 / 2025, page 65 / 103 / 49

[056] The dissolution step S103 is a step of dissolving the mixture obtained in the heating step S102 in an acidic solution or water to obtain a solution of the inorganic substance contained in the starting material. In the present embodiment, sulfuric acid (H2SO4) is used as the solution, obtaining a sulfuric acid solution of the inorganic substance. In the present embodiment, a sulfuric acid solution is obtained in which Li2SO4, Ab(SO4)3, H2SiO3 and Na2SO4 are dissolved.

[057] The acidic solution used in the dissolution step S103 is not limited to sulfuric acid solution. The acidic solution may be at least one of the following: hydrochloric acid solution, nitric acid solution, hydrofluoric acid solution, hydrobromic acid solution, hydroiodic acid solution. Alternatively, the acidic solution may be a mixed acidic solution obtained by mixing two or more of these acidic solutions. Examples of mixed acidic solutions include a solution of aqua regia, which is obtained by mixing concentrated hydrochloric acid and concentrated nitric acid. In the dissolution step S103, water may be used as the liquid to dissolve the heated mixture obtained in the heating step S102.

[058] The mixture obtained in the heating step S102 is dissolved in the sulfuric acid solution at normal temperature and under normal pressure. The sulfuric acid solution can be heated or pressurized to facilitate the dissolution of the mixture. A suitable way to heat the sulfuric acid solution is a device that applies an electromagnetic wave used in the heating step S102. In the dissolution step S103, it is preferable to set the temperature of the sulfuric acid solution to be below 250 °C (corresponding to the boiling point of concentrated sulfuric acid) in order to inhibit the boiling of the sulfuric acid solution. With this characteristic, pressurization of the sulfuric acid solution is not necessary, and it is possible to carry out the dissolution step S103 under normal pressure.

[059] (Variation 1 of method M10 for producing a solution of an inorganic substance) Petition 870250081655, dated 11 / 09 / 2025, page 66 / 103 / 49

[060] As described above, in the present embodiment, the M10 production method was described using sodium hydroxide as at least one of the hydroxides and oxides. In this variation, the M10 production method will be briefly described for a case where calcium oxide is used instead of sodium hydroxide as an additive.

[061] In the S101 grinding and mixing step, natural spodumene is ground to obtain powder of the inorganic substance. Additionally, by grinding calcium oxide, calcium oxide powder is obtained. In the S101 grinding and mixing step, the ground inorganic substance and the ground additive are mixed to obtain a mixture (first mixture) of the inorganic substance and the additive. Here, the ratio of the additive to the inorganic substance is 0.5 or more in terms of molar ratio. In this variation, the form of the calcium oxide is also not limited to powder.

[062] As described below, β-spodumene, which is used as an inorganic substance, and calcium oxide, which is used as an additive, react in a 1:1 ratio to generate β-eucryptite (LiAlSiO4), which is readily dissolved in acids or water. If the ratio of additive to inorganic substance is excessively greater than 1, the amount of additive (i.e., wasted additive) not used in the reaction to convert β-spodumene to β-eucryptite increases. Therefore, the ratio is preferably equal to or greater than 0.8 and less than or equal to 4, and more preferably equal to or greater than 1 and less than or equal to 2.

[063] e-LiAlSi2O6+CaO^e-LiAlSiO4+CaSiO3

[064] In the S102 heating step, the mixture is heated to a temperature at which a phase change of the crystalline structure occurs in the inorganic substance. In the present embodiment, external heating is used as the heating method in the S102 heating step, and 1050 °C is used as the heating temperature. In the present embodiment, the heating temperature during external heating is measured using a thermometer. Petition 870250081655, dated 11 / 09 / 2025, page 67 / 103 / 49 supplied to an oven used for external heating. Therefore, the temperature of the mixture is considered to be substantially uniform between the surface and the interior of the mixture.

[065] In the S102 heating step, by externally heating the mixture of starting material powder and calcium oxide powder to 1050 °C, natural spodumene (α-spodumene) undergoes a phase change to β-spodumene. In addition, β-eucryptite and CaSiO3 are generated from β-spodumene. In the S102 heating step, dielectric heating can be used instead of external heating.

[066] The dissolution step S103 in this variation is similar to the dissolution step S103 in the case where sodium hydroxide is used as an additive. Therefore, its description is omitted in this variation. In this variation, a sulfuric acid solution is obtained in which Li2SO4, CaSO4, H2SiO3 and Al2(SO4)3 are dissolved.

[067] As described above, in this variation, calcium oxide can be used as an additive to easily produce a solution of inorganic substance.

[068] (Variation 2 of method M10 for producing a solution of an inorganic substance)

[069] As described above, in the present embodiment, natural spodumene (i.e., α-spodumene) is used as the inorganic substance. However, it may be possible that β-spodumene is obtained instead of α-spodumene for some reason. In that case, too, an aspect of the present invention may be suitably utilized.

[070] That is, one aspect of the present invention may include: a mixing step of an inorganic substance containing spodumene β and the aforementioned additive to obtain a mixture (first mixture); and a heating step of the mixture to obtain a mixture (second mixture) of the substance. Petition 870250081655, dated 11 / 09 / 2025, page 68 / 103 / 49 inorganic and additive. In this variation, also, the proportion of the additive in relation to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio.

[071] [Implementation 2]

[072] (M20 method for producing a solution of an inorganic substance)

[073] The following description will discuss an M20 method for producing a solution of an inorganic substance according to Embodiment 2 of the present invention, with reference to Figure 2. Figure 2 shows a flowchart of the M20 method for producing a solution of an inorganic substance. Hereinafter, the M20 method for producing a solution of an inorganic substance may also be referred to simply as the M20 production method.

[074] As shown in figure 2, the production method M20 includes a grinding step S201, a phase change step S202, a mixing step S203, a heating step S204 and a dissolution step S205.

[075] (Grinding stage)

[076] In the S201 grinding step, an inorganic substance is ground to obtain powder of the inorganic substance. In the present embodiment, natural spodumene is used as the inorganic substance used in the M20 production method. In the S201 grinding step, sodium hydroxide (NaOH) is ground to obtain sodium hydroxide powder. The grinding method can be carried out using the method described for the S101 grinding and mixing step of the M10 production method.

[077] (Phase change stage)

[078] In the phase change step S202, the inorganic substance powder obtained in the milling step S201 is subjected to a phase change by heating. In the present embodiment, the natural spodumene (α-spodumene) contained in the inorganic substance is subjected to a phase change to β-spodumene. Petition 870250081655, dated 11 / 09 / 2025, page 69 / 103 / 49 for dielectric heating. The heating method used in the S202 phase change step may be the method described for the S102 heating step of the M10 production method. The heating method used in the S202 phase change step is not limited to dielectric heating and may alternatively be external heating.

[079] (Mixing stage)

[080] The mixing step S203 is a step that must be carried out after the phase change step S202. The β-spodumene obtained in the phase change step S202 and the sodium hydroxide powder obtained in the grinding step S201 are mixed to obtain a mixture of the inorganic substance and the additive. In the mixing step S203, in addition to the ground sodium hydroxide, it is possible to use at least one of the additives described in the grinding and mixing step S101 of the production method M10.

[081] (Warm-up stage)

[082] In the heating stage S204, the mixture obtained in the mixing stage S203 is heated to obtain a mixture of the inorganic substance and the additive. In heating step S204, the mixture is heated to a temperature at which a phase change of the crystalline structure occurs in the inorganic substance. That is, heating step S204 is similar to heating step S102 of production method M10. Therefore, its description is omitted in the present embodiment.

[083] (Dissolution stage)

[084] The dissolution step S205 is a step to be carried out after the heating step S204. The mixture obtained in the heating step S204 is dissolved in an acidic solution or water to obtain a solution of the inorganic substance. The dissolution step S205 is a dissolution step similar to the step of Petition 870250081655, dated 11 / 09 / 2025, page 70 / 103 / 49 dissolution S103 of production method M10. Therefore, its description is omitted in the present embodiment.

[085] By carrying out the present embodiment as described above, the heated inorganic substance and at least one of the hydroxides and oxides can be mixed to easily produce a solution of inorganic substance.

[086] [Implementation 3]

[087] (Method for producing lithium carbonate (U2CO3))

[088] The following description will discuss an M30 method for producing lithium carbonate (Li2CO3) according to Embodiment 3 of the present invention, with reference to Figure 3. Figure 3 shows a flowchart of the M30 production method. Hereinafter, the M30 method for producing lithium carbonate may also be simply referred to as the M30 production method. In the present embodiment, natural spodumene is used as the raw material.

[089] As shown in figure 3, production method M30 includes production method M10 shown in figure 1 (i.e., grinding and mixing step S101, heating step S102 and dissolution step S103), a heating step S301, a first filtration step S302, a first addition step S303, a second filtration step S304, a second addition step S305, a third filtration step S306, an ion exchange step S307, a third addition step S308, a carbon dioxide introduction step S309, a fourth filtration step S310 and a drying step S311.

[090] The grinding and mixing step S101, the heating step S102, and the dissolution step S103 included in production method M30 are similar to the respective steps described in Embodiment 1. Therefore, the descriptions of the heating step S102 and the dissolution step S103 are omitted here. That is, assuming that a solution of inorganic substance has already been obtained, only Petition 870250081655, dated 11 / 09 / 2025, page 71 / 103 / 49 the heating stage S301 and subsequent stages will be described for the production method M30.

[091] The heating step S301 is a step that must be carried out after the dissolution step S103. In the heating step S301, the inorganic substance solution obtained in the dissolution step S103 is heated to 60 °C to leach the inorganic substance.

[092] The first filtration step S302 is a step that must be performed after the heating step S301. The first filtration step S302 is a separation step, using a filter, of the solid and liquid phases contained in the solution. The solid phase contains a Si compound.

[093] The first addition step S303 is a step that must be carried out after the first filtration step S302. In the first addition step S303, sodium hydroxide is added to a liquid phase obtained as a result of the separation in the first filtration step S302 and, thus, the polarity of the liquid phase is adjusted from acidity to basicity.

[094] The second filtration step S304 is a step that must be performed after the first addition step S303. The second filtration step S304 is a separation step, using a filter, of a solid phase and a liquid phase contained in the solution from each other. The solid phase contains an Al compound, a Mg compound, an Fe compound, and an SO4 compound.

[095] The second addition step S305 is a step that must be carried out after the second filtration step S304. In the second addition step S305, sodium carbonate is added to the liquid phase obtained as a result of the separation in the second filtration step S304, thus attenuating the alkalinity of the liquid phase.

[096] The third filtration stage S306 is a stage that must be performed after the second addition stage S305. The third filtration stage S306 is a stage Petition 870250081655, dated 11 / 09 / 2025, page 72 / 103 / 49 of separation, using a filter, of a solid phase and a liquid phase contained in the solution from each other. The solid phase contains CaCO3.

[097] The ion exchange step S307 is a step to be performed after the third filtration step S306. In the ion exchange step S307, the ion exchange of the liquid phase obtained as a result of the separation in the third filtration step S306 is carried out using an ion exchange resin.

[098] The third addition step S308 is a step that must be performed after the ion exchange step S307. In the third addition step S308, at least one of the following compounds: sodium carbonate and sodium hydroxide is added to the liquid phase after the ion exchange.

[099] The carbon dioxide introduction step S309 is a step that must be performed after the third addition step S308. The carbon dioxide introduction step S309 is a step that introduces carbon dioxide into the solution so that lithium carbonate is precipitated in the solution.

[100] The fourth filtration step S310 is a step that must be performed after the carbon dioxide introduction step S309. The fourth filtration step S310 is a step of heating and concentrating the solution and separating the lithium carbonate precipitated in the solution using a filter. The liquid phase contains sodium carbonate (Na2CO3) and sodium sulfate (Na2SO4).

[101] The drying step S311 is a step that must be carried out after the fourth filtration step S310. The drying step S311 is a drying step of the lithium carbonate obtained as a result of the separation in the fourth filtration step S310.

[102] By performing the M30 method to produce lithium carbonate, it is possible to obtain lithium carbonate that is a solid.

[103] [Implementations 4 and 5] Petition 870250081655, dated 11 / 09 / 2025, p. 73 / 103 / 49

[104] With reference to Figure 4 and Figure 5, a method M40 for producing lithium carbonate (Li2CO3) according to embodiment 4 of the present invention and a method M50 for producing lithium hydroxide (LiOH) according to embodiment 5 of the present invention will be discussed below. Figure 4 shows a flowchart of the method M40 for producing lithium carbonate and Figure 5 shows a flowchart of the method M50 for producing lithium hydroxide. Hereinafter, the method M40 for producing lithium carbonate and the method M50 for producing lithium hydroxide may also be referred to simply as production method M40 and production method M50, respectively.

[105] (M40 method for producing lithium carbonate)

[106] As shown in figure 4, the production method M40 includes the grinding and mixing step S101, the heating step S102 and the dissolution step S103 included in the production method M10 shown in figure 1, a fourth addition step S401, a fifth filtration step S402, a fifth addition step S403, a sixth filtration step S404, a carbon dioxide introduction step S405, a seventh filtration step S406, an eighth filtration step S407 and a drying step S408.

[107] In the present embodiment, natural spodumene is used as raw material. In addition, calcium oxide is used as at least one of the hydroxides and oxides.

[108] The grinding and mixing step S101, the heating step S102 and the dissolution step S103 included in the production method M40 are similar to the respective steps described in the Embodiment 1 variation. Therefore, the descriptions of the heating step S102 and the dissolution step S103 are omitted here. That is, assuming that a solution of inorganic substance has already been obtained, only the fourth addition step S401 and the subsequent steps are described for the production method M40. Petition 870250081655, dated 11 / 09 / 2025, page 74 / 103 / 49

[109] The fourth addition step S401 is a step that must be carried out after the dissolution step S103. In the fourth addition step S401, calcium hydroxide (Ca(OH)2), calcium carbonate (CaCOa) or sodium hydroxide are added to the inorganic substance solution obtained in the dissolution step S103 and thus the polarity of the solution is adjusted from acidity to basicity.

[110] The fifth filtration step S402 is a step that must be carried out after the fourth addition step S401. The fifth filtration step S402 is a separation step, using a filter, of a solid phase contained in a liquid phase and of the liquid phase from each other. The solid phase contains a Si compound and a reaction residue.

[111] The fifth addition step S403 is a step that must be carried out after the fifth filtration step S402. The fifth addition step S403 is a step of adding, to the liquid phase obtained as a result of the separation in the fifth filtration step, at least one of the following: calcium hydroxide and sodium hydroxide.

[112] The sixth filtration step S404 is a step that must be carried out after the fifth addition step S403. The sixth filtration step S404 is a step to separate, using a filter, a solid phase contained in a liquid phase and the liquid phase from each other. The solid phase contains a Mg compound, an Fe compound and calcium hydroxide.

[113] The carbon dioxide introduction step S405 is identical to the carbon dioxide introduction step S309 included in the lithium carbonate production method M30 shown in Figure 3. Thus, the description of the carbon dioxide introduction step S405 is omitted in the present embodiment. When carrying out the carbon dioxide introduction step S405, calcium carbonate is precipitated in the solution.

[114] The seventh filtration stage S406 is a stage that must be carried out after the carbon dioxide introduction stage S405. The seventh filtration stage S406 Petition 870250081655, dated 11 / 09 / 2025, page 75 / 103 / 49 is a separation step, using a filter, of the calcium carbonate precipitated in the liquid phase of the solution.

[115] The eighth filtration step S407 is a step that must be performed after the seventh filtration step S406. The eighth filtration step S407 is a heating and concentration step of the liquid phase obtained as a result of the separation in the seventh filtration step S406 and separation of the liquid phase from the solid phase in the solution using a filter. The solid phase contains lithium carbonate and the liquid phase contains sodium sulfate and sodium carbonate.

[116] The drying step S408 is identical to the drying step S311 included in the lithium carbonate production method M30 shown in figure 3. In the drying step S408, the lithium carbonate obtained as a result of the separation in the eighth filtration step S407 is dried.

[117] As described above, when performing the M40 method to produce lithium carbonate, it is possible to obtain lithium carbonate that is a solid.

[118] (M50 method for producing lithium hydroxide)

[119] As shown in figure 5, the M50 production method includes a sixth addition step S501, a ninth filtration step S502, a separation step S503 and a drying step S504.

[120] In the present embodiment, lithium carbonate obtained by production method M50 is used.

[121] The sixth addition step S501 is a calcium hydroxide addition step to lithium carbonate obtained in the M50 production method. In the sixth addition step S501, calcium is precipitated by the formation of calcium carbonate (CaCO3), which is carbonate, and lithium is dissolved by ionization with hydroxide ions.

[122] The ninth filtration step S502 is a step that must be performed after the sixth addition step S501. The ninth filtration step S502 is a step of Petition 870250081655, dated 11 / 09 / 2025, page 76 / 103 / 49 separation, using a filter, of the liquid phase and the solid phase in solution from each other. The solid phase contains calcium sulfate. The liquid phase contains lithium that has been ionized along with hydroxide ions.

[123] The separation step S503 is a step that must be carried out after the ninth filtration step S502. The separation step S503 performs the concentration under reduced pressure and centrifugation of the solution containing lithium that has been ionized with hydroxide ions. By performing the separation step S503, a suspension is obtained in which lithium hydroxide is dispersed.

[124] The drying step S504 is an evaporation step of the solution obtained as a result of the separation in the separation step S503 and drying of the deposited lithium hydroxide.

[125] As described above, when performing the M50 method to produce lithium hydroxide, it is possible to obtain lithium hydroxide that is a solid.

[126] [Implementation 6]

[127] The following description will discuss a dielectric heating device D10 according to Embodiment 6 of the present invention, with reference to Figure 6 and Figure 7. The dielectric heating device D10 is an example of the heating section included in the inorganic substance solution production device according to an aspect of the present invention. Figure 6 is a view that schematically illustrates the dielectric heating device D10. The dielectric heating device D10 is a heating device that performs the heating step S102 included in the production method M10 shown in Figure 1. In the case where the sulfuric acid solution is heated in the dissolution step S103 included in the production method M10, it is possible to use the dielectric heating device D10 also for heating.

[128] As described in Implementation 1, dielectric heating is classified into radio frequency heating or micro heating. Petition 870250081655, dated 11 / 09 / 2025, p. 77 / 103 / 49 waves, depending on the band of the electromagnetic wave to be applied. The D10 dielectric heating device is a device that performs, between radio frequency heating and microwave heating, microwave heating in relation to a target object.

[129] <Configuração do dispositivo de aquecimento dielétrico>

[130] As shown in Figure 6, the dielectric heating device D10 includes an electromagnetic wave generator D11, a waveguide D12, an electromagnetic wave application section D13, a container D14, a turntable D15, a stirrer D16, and a thermometer D17. The dielectric heating device D10 also includes an insulator D18, as shown in Figure 7. The dielectric heating device D10 also includes a control section, which is not shown in Figure 6.

[131] (Electromagnetic wave generator)

[132] The electromagnetic wave generator D11 is configured to oscillate an electromagnetic wave with a given frequency. The determined frequency can be selected as appropriate within, for example, the microwave band. In the present embodiment, the determined frequency is 2.45 GHz. The frequency of 2.45 GHz is identical to that of an electromagnetic wave used in microwave ovens for domestic use.

[133] (Waveguide)

[134] The waveguide D12 is a tubular metallic member. The waveguide D12 has a first end connected to the electromagnetic wave generator D11 and a second end connected to the electromagnetic wave application section D13 which accommodates the container D14 described later. That is, the waveguide D12 is provided between the electromagnetic wave generator D11 and the container D14. The waveguide D12 guides, from the first end to the second end, an electromagnetic wave generated by the wave generator. Petition 870250081655, dated 11 / 09 / 2025, page 78 / 103 / 49 electromagnetic waves D11. Next, waveguide D12 discharges the electromagnetic wave from the second end to an internal space of the electromagnetic wave application section D13 that accommodates container D14. That is, waveguide D12 guides, from the electromagnetic wave generator D11 towards container D14, an electromagnetic wave generated by the electromagnetic wave generator D11.

[135] (Insulator)

[136] Figure 7 is a perspective view of the insulator D18 included in the dielectric heating device D10. As shown in Figure 7, the insulator D18 is provided in the middle of the waveguide D12. The insulator D18 includes a circulator D181, a dummy load D182 and a cooling tube D183. The circulator D181 is inserted in the middle of the waveguide D12.

[137] The circulator D181 includes a magnet (for example, made of ferrite) and includes three gates P1 to P3, as shown in figure 7. Gate P1 is connected to the electromagnetic wave generator D11 through a section of the waveguide D12. Gate P2 is connected to the electromagnetic wave application section D13 through the other section of the waveguide D12. Gate P3 is supplied with the dummy load D182.

[138] A magnetic field formed by the magnet and an electromagnetic wave passing through the circulator D181 interact with each other. Consequently, the electromagnetic wave that entered gate P1 is emitted from gate P2, and the electromagnetic wave that entered gate P2 is emitted from gate P3. With this arrangement, the circulator D181 (i) couples the electromagnetic wave generated by the electromagnetic wave generator D11 to the electromagnetic wave application section D13 and (ii) couples the electromagnetic wave reflected in the internal space of the electromagnetic wave application section D13 to the dummy load D182. Petition 870250081655, dated 11 / 09 / 2025, p. 79 / 103 / 49

[139] The dummy load D182 is made of a material that absorbs an electromagnetic wave with a frequency of 2.45 GHz. Therefore, the dummy load D182 absorbs the electromagnetic wave reflected in the internal space of the electromagnetic wave application section D13 and converts the electromagnetic wave energy into heat.

[140] The dummy load D182 is supplied with the cooling tube D183. The cooling tube D183 has an internal configuration in which a cooled refrigerant (e.g., water or air) is circulated. The cooled refrigerant can remove heat from the dummy load D182. Therefore, it is possible to prevent the temperature of the dummy load D182 from rising excessively.

[141] The circulator D181 configured as described above can (i) couple the electromagnetic wave generated by the electromagnetic wave generator D11 to the electromagnetic wave application section D13 with little loss and (ii) absorb the electromagnetic wave reflected in the internal space of the electromagnetic wave application section D13. That is, the circulator D181 can (i) propagate the electromagnetic wave from the electromagnetic wave generator D11 to the container D14 with little loss and (ii) absorb the electromagnetic wave propagating from the container D14 to the electromagnetic wave generator D11. This makes it possible to reduce the cases in which the electromagnetic wave reflected in the internal space of the electromagnetic wave application section D13 returns to the electromagnetic wave generator D11 and negatively affects the operation of the electromagnetic wave generator D11.

[142] (Section on the application of electromagnetic waves)

[143] The electromagnetic wave application section D13 is a hollow metal box-shaped member with an internal space in which the container D14 can be accommodated. The electromagnetic wave application section D13 applies the wave to the container D14 and to a target object to be heated (i.e., a heating target object) that is accommodated in the container D14. Petition 870250081655, dated 11 / 09 / 2025, page 80 / 103 / 49 electromagnetic wave emitted from the second end of the waveguide D12. The electromagnetic wave application section D13 is configured to confine an electromagnetic wave within the internal space, so that the electromagnetic wave hardly leaks outwards.

[144] (Container)

[145] In the present embodiment, the container D14 is a bowl-shaped container. The shape of the container D14 is not limited, provided that the container D14 can accommodate a mixture of a starting material and sodium hydroxide. However, it is preferable that it be a container with a certain depth and a smaller bottom diameter compared to the diameter of the opening, in order to efficiently apply an electromagnetic wave. If a shallow dish-shaped container is used as container D14, the mixture of the inorganic substance and the additive becomes widely dispersed and therefore may not be heated sufficiently.

[146] To measure the temperature of the inorganic substance or mixture using thermometer D17 (described later), container D14 preferably has an opening with a large diameter. If the dissolution step S103 is carried out while continuously using container D14 after the heating step S102, container D14 preferably has a capacity that can accommodate a certain amount of sulfuric acid solution.

[147] If a pestle is used to mix the raw material powder with sodium hydroxide to obtain a mixture, the pestle acts as the mixing section. If the raw material powder and the sodium hydroxide powder are placed in container D14 and mixed in container D14 to obtain a mixture, container D14 acts as the mixing section.

[148] The D14 container is preferably made of a material with high transmittance for an electromagnetic wave (in the present embodiment, a Petition 870250081655, dated 11 / 09 / 2025, page 81 / 103 / 49 electromagnetic wave of 2.45 GHz) to be oscillated by the electromagnetic wave generator D11. The container D14 is preferably made of a material highly resistant to acids and bases. If the container D14 is made of a material highly resistant to acids and bases, after the heating step S102 is performed, the dissolution step S103 can be performed by pouring a nitric acid solution into the container D14.

[149] In the present embodiment, container D14 is made of a fluorine-based resin, such as polytetrafluoroethylene. The material constituting container D14 is not limited to fluorine-based resin, and may be an aromatic polyether ketone resin, such as polyether ketone, a polyimide resin or an oxide, such as alumina or titanium oxide.

[150] (Turntable table)

[151] The rotary table D15 is a sample table provided in a lower plane of the internal space of the electromagnetic wave application section D13 and has an upper surface on which the container D14 can be placed. The rotary table D15 has a circular shape in a plan view and is configured to rotate, at a certain speed, around a central axis of the circular shape as an axis of rotation. With this configuration, the container D14 placed on the upper surface of the rotary table D15 rotates at a certain speed. This can heat the mixture more uniformly.

[152] (Agitator)

[153] The agitator D16 is a metal blade element supplied to a ceiling plane of the internal space of the electromagnetic wave application section D13. The blade element has a center coupled to a support rod, with which the blade element is rotatably fixed to the ceiling plane. The agitator D16 rotates around the support rod as a rotation axis at a given speed, thus reflecting an electromagnetic wave oscillated by the generator. Petition 870250081655, dated 11 / 09 / 2025, page 82 / 103 / 49 electromagnetic waves D11. Consequently, the electromagnetic wave is spread in the internal space of the electromagnetic wave application section D13. With this configuration, the stirrer D16 spreads the electromagnetic wave. This can heat the mixture more uniformly.

[154] (Thermometer)

[155] Thermometer D17 is a radiation thermometer that detects an infrared ray from the mixture to measure the temperature of container D14. Thermometer D17 is fixed as part of a side wall of the electromagnetic wave application section D13, so that a light-receiving section of thermometer D17 can detect an infrared ray from the powder mixture MP. Thermometer D17 sends a temperature signal to the control section indicating the measured temperature of the mixture.

[156] (Control section)

[157] The control section can control an output of the electromagnetic wave generator D11 so that the output becomes a determined value or so that the temperature indicated by the temperature signal received from thermometer D17 becomes a predetermined temperature. The predetermined temperature can be constant or can be changed over time. In the present embodiment, the control section controls an output of the electromagnetic wave generator D11 so as to change the output value over time. An example of the output control pattern could be a pattern in which an output of 300 W is maintained for 600 seconds and the output is then reduced to 0 W.

[158] The production method M10 is taken as an example. Then, by accommodating the mixture in the internal space of the container D14 of the dielectric heating device D10 configured as above, it is possible to carry out the heating step S102. Furthermore, it is possible to carry out the dissolution step S103 by pouring a sulfuric acid solution into the container D14 after the step of Petition 870250081655, dated 11 / 09 / 2025, page 83 / 103 / 49 heating S102 to be carried out. In the case where the dielectric heating device D10 is used to carry out the dissolution step S103, it is possible to heat the sulfuric acid solution. Therefore, it is possible to promote the dissolution of the heated mixture in the sulfuric acid solution. The sulfuric acid solution of the inorganic substance is an example of a solution of an inorganic substance.

[159] [Implementation 7]

[160] (System for producing a solution of an inorganic substance)

[161] The following description will discuss a device 10 for producing an inorganic substance according to Embodiment 7 of the present invention, with reference to Figure 8. Figure 8 is a view that schematically illustrates a device 10A that produces a solution of an inorganic substance and constitutes a part of the device 10 for producing an inorganic substance. Hereinafter, the device 10 for producing an inorganic substance will also be referred to simply as production device 10, and the device 10A for producing a solution of an inorganic substance will also be referred to simply as production device 10A.

[162] As shown in Figure 8, production device 10 includes production device 10A and performs production method M10 shown in Figure 1. More specifically, production device 10A is a device for performing the steps of production method M10 shown in Figure 1. Note, however, that production device 10 may include a device for isolating an inorganic substance from a solution of inorganic substance obtained by production device 10A. Examples of such a device include a crystallizer for crystallizing an inorganic substance, an anhydrizing device for anhydrizing a solution of inorganic substance, and the like.

[163] In the present embodiment, as in Embodiment 1, an inorganic substance containing natural spodumene is used as raw material. The Petition 870250081655, dated 11 / 09 / 2025, page 84 / 103 / 49 natural spodumene contains α-spodumene which is transformed into β-spodumene by heating. Note, however, that the starting material in production device 10A only needs to be an inorganic substance that undergoes a phase change or thermal decomposition by heating, not being limited to natural spodumene, as exemplified in Embodiment 1. Examples of an inorganic substance that undergoes thermal decomposition by heating include petalite. In the present embodiment, sodium hydroxide is used as the hydroxide, as in Embodiment 1. The additive in production device 10A is not limited to sodium hydroxide, as exemplified in Embodiment 1. The additive only needs to be at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide.Preferred examples of the additive include, in addition to sodium hydroxide, calcium hydroxide and calcium oxide.

[164] (Device 10A for producing a solution of an inorganic substance)

[165] As shown in Figure 8, the production device 10A includes a crusher 11a, a feeder F1a, a crusher 11b, a feeder F1b, valves V1 and V2, a dielectric heating device 12 and a heat exchanger 13. The production device 10A also includes a control section, which is not shown in Figure 8. The control section controls the feeders F1a and F1b, the valves V1 and V2, the dielectric heating device 12 and the heat exchanger 13.

[166] Grinder 11a grinds natural spodumene, which is the starting material loaded into it, into powder. Grinder 11a then supplies the natural spodumene powder to feeder F1a. Grinder 11a can be appropriately selected from existing grinders according to the desired specifications. Thus, a detailed description of grinder 11a is omitted here. When grinding the starting material using grinder 11a, the starting material is broken down. Petition 870250081655, dated 11 / 09 / 2025, page 85 / 103 / 49 mechanically to have a smaller particle diameter and thus the efficiency of a chemical reaction with hydroxide or oxide can be improved.

[167] Feeder F1a, which is controlled by the control section, supplies container 12c of the dielectric heating device 12 (described later) with the initial material supplied by the grinder 11a.

[168] Grinder 11b grinds the sodium hydroxide loaded into it into powder. Grinder 11b then supplies the sodium hydroxide powder to feeder F1b. Grinder 11b can be appropriately selected from existing grinders according to the desired specifications. Thus, a detailed description of grinder 11b is omitted here. By grinding sodium hydroxide using grinder 11b, it is possible to reduce the diameter of the sodium hydroxide particles to a desired size. As described above, the form of sodium hydroxide is not limited to powder. Therefore, in production device 10A, grinder 11b can be omitted.

[169] Feeder F1b, which is controlled by the control section, supplies container 12c of the dielectric heating device 12 (described later) with sodium hydroxide powder supplied by grinder 11b. Here, feeder F1a and feeder F1b each supply the inorganic substance and the additive to container 12c, such that the ratio of the additive to the inorganic substance is 0.5 or more.

[170] The dielectric heating device 12 includes an electromagnetic wave generator 12a, a waveguide 12b, the container 12c, a stirring mechanism, and a thermometer. The dielectric heating device 12 is an example of the heating section that heats a mixture of an inorganic substance and an additive to a temperature at which a phase change occurs in the inorganic substance, to obtain a mixture (second mixture) of the inorganic substance and the additive. The dielectric heating device 12 Petition 870250081655, dated 11 / 09 / 2025, page 86 / 103 / 49 performs the heating step S102 and the dissolution step S103 of the production method M10 shown in figure 1.

[171] The electromagnetic wave generator 12a is controlled by the control section and is configured to oscillate an electromagnetic wave with a determined frequency. The determined frequency can be selected as appropriate within, for example, the microwave band. In the present embodiment, the given frequency is 2.45 GHz. The frequency of 2.45 GHz is identical to that of an electromagnetic wave used in microwave ovens for domestic use.

[172] Waveguide 12b is a tubular metallic element with a first end connected to the electromagnetic wave generator 12a and a second end connected to the container 12c. Waveguide 12b guides an electromagnetic wave oscillated by the electromagnetic wave generator 12a from the first end to the second end. Waveguide 12b then discharges the electromagnetic wave into an internal space of the container 12c through the second end. Although not shown in Figure 8, an insulator shown in Figure 7 is provided in the middle of waveguide 12b. In this case, waveguide D12 shown in Figure 7 can be interpreted as waveguide 12b.

[173] In the present embodiment, the dielectric heating device 12 that uses dielectric heating is used as an example of the heating section. However, the heating section could be a furnace, a heater or similar that uses external heating.

[174] Container 12c is a box-shaped member that accommodates, in its internal space, the starting material powder and the sodium hydroxide powder. Similar to container D14 shown in figure 6, container 12c is made of an acid-resistant material. The starting material powder supplied by grinder 11a through feeder F1a and the sodium hydroxide powder are fed to container 12c. Petition 870250081655, dated 11 / 09 / 2025, page 87 / 103 / 49 of sodium supplied by grinder 11b through feeder F1b. Inside vessel 12c, an agitation mechanism is provided (not shown in Figure 8). When the control section causes the agitation mechanism to rotate, the starting material powder and the sodium hydroxide powder supplied to the internal space of vessel 12c are mixed. Thus, vessel 12c is an example of a mixing section that mixes the starting material powder with the sodium hydroxide powder to obtain a mixture (first mixing). Vessel 12c can be a tubular vessel (e.g., a rotary kiln) that can rotate around an axis. By combining a liquid supply section (described later) with the rotary kiln, continuous treatment is possible.

[175] The thermometer (not shown in Figure 8) detects the temperature of a material housed in the internal space of the container 12c and emits a temperature signal indicating the temperature to the control section. The thermometer can be a non-contact type thermometer, such as a radiation thermometer, or a contact type thermometer, such as a thermocouple. In both the case of using a non-contact type thermometer and in the case of using a contact type thermometer, the thermometer is preferably provided in the internal space of the container 12c and is preferably configured to be able to directly detect the temperature of the material housed in the internal space.

[176] The control section can control an output of the electromagnetic wave generator 12a so that the output becomes a determined value or so that the temperature indicated by the temperature signal received from the thermometer becomes a predetermined temperature. The predetermined temperature can be constant or can be changed over time. In the present embodiment, the control section controls an output of the electromagnetic wave generator 12a so as to change the temperature indicated by the temperature signal over time according to a determined profile. An example of the determined temperature profile could be a pattern according to Petition 870250081655, dated 11 / 09 / 2025, page 88 / 103 / 49, in which the temperature is instantly changed to 700 °C and then 700 °C is maintained for 30 minutes.

[177] In a case where the heating step S102 of the production method M10 shown in figure 1 is carried out with the dielectric heating device 12 configured as described above, a mixture (second mixture) is obtained containing the starting material whose phase has been changed and sodium hydroxide.

[178] Next, an H2SO4 solution is supplied through valve V1. By supplying the H2SO4 solution to container 12c through valve V1, the dissolution step S103 is performed. The mechanism that supplies the H2SO4 solution to container 12c through valve V1 functions as the liquid supply section that provides an acidic solution to the heated mixture. In container 12c, the mixture is dissolved in the H2SO4 solution, obtaining an H2SO4 solution containing the inorganic substance. As described above, the liquid for dissolving the mixture containing the starting material and sodium hydroxide is not limited to an acidic solution, such as an H2SO4 solution, but can alternatively be water. If water is used as the liquid, the dissolution step S103 is performed by supplying water to container 12c through valve V1.Thus, container 12c is an example of the dissolution section that dissolves the mixture of the inorganic substance and the additive in an acidic solution or water to obtain a solution of the inorganic substance.

[179] While the dissolution step S103 is being carried out, the control section can control an output of the electromagnetic wave generator 12a so that the output becomes a determined value or so that the temperature indicated by the temperature signal received from the thermometer becomes a predetermined temperature. By performing dielectric heating also during the dissolution step S103, dissolution in the H2SO4 solution is promoted. While the dissolution step S103 is being carried out, the control section can cause the stirring mechanism to continue to operate. Petition 870250081655, dated 11 / 09 / 2025, page 89 / 103 / 49

[180] Valve V2 opens and closes a passage between the internal space of container 12c and a collection line (not shown). The control section closes valve V2 while heating step S102 and dissolution step S103 are being carried out and opens valve V2 after heating step S102 and dissolution step S103 are completed. As a result, the inorganic substance solution containing the inorganic substance obtained in heating step S102 and dissolution step S103 is collected, in the collection line (not shown), from container 12c.

[181] As described above, production device 10A can perform the grinding and mixing step S101, the heating step S102 and the dissolution step S103 of the production method M10 shown in figure 1.

[182] (Variation 1 of device 10 for producing inorganic substance solution)

[183] ​​As described above, in the present embodiment, production device 10 that performs the steps of production method M10 shown in figure 1 has been described. In this variation, production device 10 that performs production method M20 shown in figure 2 will be briefly described. In this variation, production device 10A performs the steps of production method M20 shown in figure 2.

[184] Grinder 11a grinds natural spodumene, which is the starting material loaded into it, into powder (grinding step S201). Grinder 11a then supplies the natural spodumene powder to feeder F1a. Feeder F1a supplies the starting material supplied by grinder 11a to container 12c of the dielectric heating device 12 (described further below).

[185] The dielectric heating device 12 performs the S202 phase change step of the M20 production method shown in figure 2. Petition 870250081655, dated 11 / 09 / 2025, pages 90 / 103 / 49

[186] Grinder 11b grinds the sodium hydroxide that is loaded into it into powder. Grinder 11b then supplies the sodium hydroxide powder to feeder F1b. Feeder F1b supplies the sodium hydroxide powder supplied by grinder 11b to container 12c of the dielectric heating device 12, which performed the phase change step S202.

[187] Inside container 12c, a stirring mechanism is provided (not shown in figure 8). When the control section causes the stirring mechanism to rotate, the heated inorganic substance and the sodium hydroxide powder are mixed in the internal space of container 12c (mixing step S203).

[188] The dielectric heating device 12 performs the heating step S204 of the production method M20 shown in figure 2.

[189] Next, an H2SO4 solution is supplied through valve V1. By supplying the H2SO4 solution to container 12c through valve V1, the dissolution step S205 is carried out. By opening valve V2 after the execution of the dissolution step S205, the inorganic substance solution obtained in the dissolution step S205 is collected, in the collection line (not illustrated), from container 12c.

[190] As described above, in the variation of production device 10, it is possible to perform the grinding step S201, the phase change step S202, the mixing step S203, the heating step S204 and the dissolution step S205 of the production method M20 shown in figure 2.

[191] (Variation 2 of device 10 for producing inorganic substance solution)

[192] As described above, in production device 10, natural spodumene (i.e., α-spodumene) is used as the inorganic substance. However, it may be possible that β-spodumene is obtained instead of α-spodumene for some reason. In that case, too, an aspect of the present invention may be suitably utilized. Petition 870250081655, dated 11 / 09 / 2025, pages 91 / 103 / 49

[193] That is, one aspect of the present invention may include: a mixing section for mixing an inorganic substance containing β-spodumene and the aforementioned additive to obtain a mixture (first mixture); and a heating section for heating the mixture to obtain a mixture (second mixture) of the inorganic substance and the additive. In this variation also, the ratio of the additive to the inorganic substance in the mixing section is 0.5 or more in terms of molar ratio.

[194] [Group of examples]

[195] The following description will discuss a group of examples of the present invention. In the following group of examples, natural spodumene (α-spodumene) was used as raw material.

[196] <Exemplo 1>

[197] In Example 1, in the production method M10 shown in figure 1, the grinding and mixing steps S101 were carried out up to the dissolution step S103. In this example, sodium hydroxide was used as at least one of the hydroxides and oxides to be mixed in the grinding and mixing step S101. In this example, in the dissolution step S103, sulfuric acid was used as the acidic solution.

[198] In this example, in the grinding and mixing step S101, 1 g of natural spodumene was ground to less than 600 μm. In the grinding and mixing step S101, natural spodumene and sodium hydroxide were mixed in a 1:1 molar ratio. In the heating step S102, dielectric heating was performed at 500 °C for 15 to 30 minutes with the dielectric heating device D10 in an air atmosphere under normal pressure. In Test Section 1, a mixture of spodumene and sodium hydroxide was placed on a flat alumina dish and heated dielectrically. In Test Section 2, the mixture was placed on an alumina crucible dish and heated dielectrically. Petition 870250081655, dated 11 / 09 / 2025, page 92 / 103 / 49, performing the heating step S102, the spodumene and sodium hydroxide mixture was solidified according to dielectric heating. In test section 1, the unreacted portion remained as powder. In test section 2, the entire mixture solidified after heating. The mixture after heating is shown in Figure 9.

[199] Next, in the dissolution step S103, the mixture obtained after heating was dissolved in concentrated sulfuric acid at room temperature under normal pressure, thus obtaining a solution of inorganic substance.

[200] An elution rate of Li contained in the inorganic substance solution was calculated. The elution rate was calculated according to formula (1) below, after quantitative measurement using ICP was performed on the inorganic substance solution. The weight percentage of the element Li in the starting material was calculated by quantitative analysis. The results are shown in Table 1.

[201] Elution rate (%) = (Li content in solution) / (Li content in raw material) x 100 (%) ... (1)

[202] [Table 1] Condition Li elution rate Test section 1 64% Test section 2 82%

[203] In test section 1, an X-ray spectroscopy (XRD) test was performed on the solidified portion of the mixture obtained after heating and on the solid phase (residue) in the inorganic substance solution obtained by dissolving the solidified portion. The results are shown in Figure 10 and Figure 11, respectively. Petition 870250081655, dated 11 / 09 / 2025, page 93 / 103 / 49

[204] As shown in Figure 9, the solidified part was larger in test section 2 than in test section 1. As shown in Table 1, the elution rate of Li was higher in test section 2 than in test section 1. Thus, it was indicated that by using the round-bottomed dish instead of the flat dish during dielectric heating, the efficiency of the dielectric heating was increased and the elution rate was raised.

[205] As shown in Figure 10, by heating step S102, it was found that the mixture contained Li2SiO3, nepheline (NaAlSiO4), α-spodumene (LiAlSi2O6), β-spodumene (LiAlSi2O6) and quartz (SO2). As shown in Figure 11, by dissolution step S103, among the compounds shown in Figure 10, compounds other than α-spodumene (LiAlSi2O6) were eluted in the inorganic substance solution. Thus, it has been demonstrated that, according to the method for producing a solution of inorganic substance according to an aspect of the present invention, β-spodumene, Li2SiO3, nepheline and quartz can be generated from natural spodumene (α-spodumene), which is the starting material, by the heating step, and Li can be eluted into the inorganic substance solution.

[206] <Exemplo 2>

[207] In Example 2, in the production method M10 shown in Figure 1, the grinding and mixing steps S101 were carried out up to the dissolution step S103. In this Example, as at least one of the hydroxides and oxides to be mixed in the grinding and mixing step S101, calcium hydroxide was used in test section 3, calcium oxide in test section 4 and calcium carbonate in Reference Example 1. In this Example, in the dissolution step S103, concentrated sulfuric acid was used as the acid solution.

[208] In this example, in the grinding and mixing step S101, 1 g of natural spodumene was ground until it was smaller than 600 μm. In the grinding and mixing step S101, the natural spodumene and at least one of the hydroxides and oxides were Petition 870250081655, dated 11 / 09 / 2025, page 94 / 103 / 49 mixed in a molar ratio of 1:1. In the heating step S102, external heating was carried out at 1050 °C for 30 minutes in an air atmosphere under normal pressure.

[209] Next, in the dissolution step S103, the mixture obtained after heating was dissolved in concentrated sulfuric acid at room temperature under normal pressure, thus obtaining a solution of inorganic substance.

[210] The elution rate of Li contained in the inorganic substance solution was calculated using a method similar to that of Example 1. The results are shown in Table 2.

[211] [Table 2] Condition Li elution rate Test section 3 64% Test section 4 94% Reference example 1 14%

[212] In test section 4, an XRD test was performed on the mixture obtained after heating. The result is shown in figure 12.

[213] As shown in Table 2, in test sections 3 and 4, the elution rate of Li was 50% or more. It was found that by mixing the inorganic substance and at least one of the hydroxides and oxides, Li can be eluted efficiently.

[214] As shown in Figure 12, by heating step S102, it was found that the mixture contained β-eucryptite (LiAlSiO4), CaSiOa and anorthite (CaAl2Si2O8). Thus, it was demonstrated that, according to the method for producing a solution of an inorganic substance according to an aspect of the present Petition 870250081655, dated 11 / 09 / 2025, page 95 / 103 / 49 invention, β-eucryptite, CaSiO3 and anorthite can be generated from natural spodumene (α-spondumene), which is the starting material, by the heating step, and Li can be eluted in the inorganic substance solution.

[215] <Exemplo 3>

[216] In Example 3, in the production method M10 shown in figure 1, the grinding and mixing steps S101 were carried out up to the dissolution step S103. In this Example, calcium oxide was used as at least one of the hydroxides and oxides to be mixed in the grinding and mixing step S101. In this example, concentrated sulfuric acid was used as the acid solution in the dissolution step S103.

[217] In this example, in the grinding and mixing step S101, 1 g of natural spodumene was ground to a size smaller than 600 μm. In the grinding and mixing step S101, the natural spodumene and at least one of the hydroxides and oxides were mixed in molar ratios of 1:1 in test section 5, 1:0.66 in test section 6 and 1:0.33 in Reference Example 2. In the heating step S102, external heating was carried out at 1050 °C for 30 minutes in an air atmosphere under normal pressure.

[218] Next, in the dissolution step S103, the mixture obtained after heating was dissolved in concentrated sulfuric acid at room temperature under normal pressure, thus obtaining a solution of inorganic substance.

[219] The elution rate of Li contained in the inorganic substance solution was calculated using a method similar to that of Example 1. The results are shown in Table 3. Figure 13 shows a relationship between the elution rate of Li and the molar ratio of natural spodumene and calcium carbonate.

[220] [Table 3] Petition 870250081655, dated 11 / 09 / 2025, pages 96 / 103 / 49 Condition Li elution rate Test section 5 89% Test section 6 64% Reference example 2 12%

[221] As shown in Table 3 and Figure 13, in test sections 5 and 6, the elution rate of Li was 50% or more. Therefore, in the case where natural spodumene was used as raw material, it became clear that an inorganic substance solution in which the elution rate of Li was 50% or more could be obtained using calcium carbonate with a weight ratio of 0.2 or more relative to natural spodumene.

[222] [Additional remarks]

[223] The present invention is not limited to the embodiments described, but may be modified by a person skilled in the technical field within the scope of the claims. The present invention also covers, within its technical scope, any embodiment derived from the combination of technical means disclosed in different embodiments.

[224] Aspects of the present invention can also be expressed as follows:

[225] To achieve the objective, a method for producing a solution of an inorganic substance according to aspect 1 of the present invention includes: a mixing step of an inorganic substance and an additive to obtain a first mixture, the inorganic substance being subjected to a phase change or thermally decomposed by heating, and the additive being at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide; and a heating step to heat the first mixture. Petition 870250081655, dated 11 / 09 / 2025, page 97 / 103 / 49 mixing at a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive. In this production method, a configuration is employed in which the proportion of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio, and the predetermined temperature is (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase must be changed by heating and (2) a temperature at which thermal decomposition occurs in the case where the inorganic substance is an inorganic substance that must be thermally decomposed by heating.

[226] The second mixture obtained by this production method can be dissolved in a solvent without high temperature or high temperature and high pressure, unlike the conventional techniques disclosed in Non-Patent Literature 1 and Patent Literature 1. Therefore, according to the above configuration, it is possible to provide a technique that makes it possible to dissolve an inorganic substance, such as lithium ore, more easily than the conventional techniques disclosed in non-patent literature 1 and patent literature 1.

[227] The proportion of the additive to the inorganic substance is then expressed using the molar ratio, unless otherwise indicated.

[228] The method according to aspect 2 of the present invention employs, in addition to the feature of aspect 1 above, a feature in which: the inorganic substance contains α-spodumene which is transformed into β-spodumene by heating.

[229] The inventors of the present invention have discovered that, in the case of using lithium ore as an inorganic substance, it is possible, through the phase change from α-spodumene to β-spodumene, to reduce the amount of additive to be mixed. Petition 870250081655, dated 11 / 09 / 2025, pages 98 / 103 / 49

[230] The method according to aspect 3 of the present invention employs, in addition to the feature of aspect 2 above, a feature in which: the additive is at least one of the following: sodium hydroxide, calcium hydroxide and calcium oxide.

[231] The inventors of the present invention have found that it is preferable to use at least one of the following: sodium hydroxide, calcium hydroxide and calcium oxide as an additive used in this production method.

[232] The method according to aspect 4 of the present invention employs, in addition to the feature of aspect 1 above, a feature in which: the inorganic substance contains petalite which is thermally decomposed by heating.

[233] In the case where petalite is used as an inorganic substance, it is possible, through the thermal decomposition of petalite, to reduce the amount of additive to be mixed.

[234] The method according to aspect 5 of the present invention employs, in addition to the feature of any of aspects 1 to 4 above, a feature in which: in the heating step, the first mixture is heated using dielectric heating.

[235] According to the configuration above, it is possible to heat the first mixture efficiently. Therefore, it is possible to reduce the production cost of the inorganic substance solution. In addition, it is possible to contribute to the SDGs.

[236] The method according to aspect 6 of the present invention employs, in addition to the feature of any of aspects 1 to 5 above, a feature that also includes: a dissolution step of the second mixture, which was obtained in the heating step, in an acidic solution or water to obtain a solution of the inorganic substance.

[237] The second mixture obtained by this production method allows the inorganic substance to be dissolved in a solvent without high temperature or high Petition 870250081655, dated 11 / 09 / 2025, p. 99 / 103 / 49 temperature and high pressure, unlike conventional techniques disclosed in non-patent literature 1 and patent literature 1. Therefore, according to the configuration above, it is possible to obtain a solution of an inorganic substance, such as lithium ore, more easily than conventional techniques disclosed in non-patent literature 1 and patent literature 1.

[238] To achieve the objective, a method for producing a solution of an inorganic substance according to aspect 7 of the present invention includes: a phase change step to alter, by heating, the phase of an inorganic substance that is to be altered by heating; a mixing step to mix the inorganic substance that has undergone a phase change and an additive to obtain a first mixture, the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide; and a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive. In this method of producing a solution of an inorganic substance, a configuration is employed in which the proportion of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio.

[239] In the method for producing a solution of an inorganic substance according to aspect 7 of the present invention, the thermal energy for the phase change of the inorganic substance and the thermal energy for causing the inorganic substance after the phase change to react with a compound that readily dissolves the inorganic substance are applied to the inorganic substance using the same step (heating step). Note, however, that in a method for producing a solution of an inorganic substance according to an aspect of the present invention, it is possible to apply the two thermal energies described above to the inorganic substance using separate steps (phase change step and heating step), as in this production method. Petition 870250081655, dated 11 / 09 / 2025, pages 100 / 103 / 49

[240] To achieve the objective, a method for producing a solution of an inorganic substance according to aspect 8 of the present invention includes: a mixing step of an inorganic substance and an additive to obtain a first mixture, the inorganic substance containing β-spodumene and the additive being at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; and a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive. In this production method, a configuration is employed in which the ratio of the additive to the inorganic substance in the mixing step is 0.5 or more in terms of molar ratio.

[241] One aspect of the present invention can also be suitably used in a case where a starting material containing β-spodumene is used as an inorganic substance.

[242] To achieve the objective, a device for producing a solution of an inorganic substance according to aspect 9 of the present invention includes: a mixing section for mixing an inorganic substance and an additive to obtain a first mixture, the inorganic substance being subjected to a phase change or thermal decomposition by heating, and the additive being at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; and a heating section for heating the first mixture to a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive.In this production device, a configuration is employed in which the proportion of the additive to the inorganic substance in the mixing section is 0.5 or more in terms of molar ratio, and the predetermined temperature is (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase must be changed by heating and (2) a temperature at which decomposition occurs. Petition 870250081655, dated 11 / 09 / 2025, page 101 / 103 / 49 thermal in the case where the inorganic substance is an inorganic substance that must be thermally decomposed by heating.

[243] The device according to aspect 10 of the present invention employs, in addition to the feature of aspect 9 above, a feature in which: the inorganic substance contains α-spodumene which is transformed into β-spodumene by heating.

[244] The device according to aspect 11 of the present invention employs, in addition to the feature of aspect 10 above, a feature in which: the additive is at least one of the following: sodium hydroxide, calcium hydroxide and calcium oxide.

[245] The device according to aspect 12 of the present invention employs, in addition to the feature of aspect 9 above, a feature in which: the inorganic substance contains petalite which is thermally decomposed by heating.

[246] The device according to aspect 13 of the present invention employs, in addition to the feature of any of aspects 9 to 12 above, a feature in which: the heating section heats the first mixture using dielectric heating.

[247] The device according to aspect 14 of the present invention employs, in addition to the feature of any of aspects 9 to 12 above, a feature that also includes: a dissolution section for dissolving the second mixture, which was obtained by the heating section, in an acidic solution or water to obtain a solution of the inorganic substance.

[248] The devices for producing a solution of an inorganic substance according to aspects 9 to 14 of the present invention correspond to the methods for producing a solution of an inorganic substance according to aspects 1 to 6 of the present invention, respectively. Therefore, devices for Petition 870250081655, dated 11 / 09 / 2025, p. 102 / 103 / 49 producing a solution of an inorganic substance according to aspects 9 to 14 of the present invention produce the same effects as the respective methods for producing a solution of an inorganic substance according to aspects 1 to 6 of the present invention.

[249] List of reference signs

[250] M10: Production method (method for producing a solution of an inorganic substance)

[251] S102: Heating stage

[252] S103: Dissolution stage

[253] D10, 22: Dielectric heating device (device for producing a solution of an inorganic substance)

[254] D11, 12a: Electromagnetic wave generator

[255] D12, 12b: Waveguide

[256] D14, 12c: Container

[257] D18: Insulator Petition 870250081655, dated 11 / 09 / 2025, page 103 / 103

Claims

1 / 4 CLAIMS 1. METHOD FOR PRODUCING A SOLUTION OF AN INORGANIC SUBSTANCE, characterized by comprising: a mixing step of an inorganic substance and an additive to obtain a first mixture, the inorganic substance being altered in phase or thermally decomposed by heating, and the additive being at least one of an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide;and a heating step of the first mixture to a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive, the proportion of the additive to the inorganic substance in the mixing step being 0.5 or more in terms of molar ratio, and the predetermined temperature being (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase is to be changed by heating and (2) a temperature at which thermal decomposition occurs in the case where the inorganic substance is an inorganic substance that is to be thermally decomposed by heating.

2. METHOD, according to claim 1, characterized in that the inorganic substance contains α-spodumene which is transformed into β-spodumene by heating.

3. METHOD, according to claim 2, characterized in that the additive is at least one of the following: sodium hydroxide, calcium hydroxide, and calcium oxide.

4. METHOD, according to claim 1, characterized by the inorganic substance containing petalite which is thermally decomposed by heating. Petition 870250081114, dated 10 / 09 / 2025, page 67 / 132 2 / 4 5. METHOD, according to any one of claims 1 to 4, characterized in that, in the heating step, the first mixture is heated using dielectric heating.

6. METHOD, according to any one of claims 1 to 4, characterized by further comprising a step of dissolving the second mixture, which was obtained in the heating step, in an acidic solution or water to obtain a solution of the inorganic substance.

7. METHOD FOR PRODUCING A SOLUTION OF AN INORGANIC SUBSTANCE, characterized by comprising: a phase change step to change, by heating, a phase of an inorganic substance that is to be altered by heating; a mixing step to mix the inorganic substance that has been altered by heating and an additive to obtain a first mixture, the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide; and a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive, the proportion of the additive to the inorganic substance in the mixing step being equal to or greater than 0.5 in terms of molar ratio.

8. METHOD FOR PRODUCING A SOLUTION OF AN INORGANIC SUBSTANCE, characterized by comprising: a mixing step of mixing an inorganic substance and an additive to obtain a first mixture, the inorganic substance containing β-spodumene and the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide and an alkaline earth metal oxide; and Petition 870250081114, dated 10 / 09 / 2025, page 68 / 132 3 / 4 a heating step to heat the first mixture to obtain a second mixture of the inorganic substance and the additive, the proportion of the additive to the inorganic substance in the mixing step being 0.5 or more in terms of molar ratio.

9. DEVICE FOR PRODUCING A SOLUTION OF AN INORGANIC SUBSTANCE, characterized by comprising: a mixing section for mixing an inorganic substance and an additive to obtain a first mixture, the inorganic substance being either phase-changed or thermally decomposed by heating, and the additive being at least one of the following: an alkali metal hydroxide, an alkaline earth metal hydroxide, and an alkaline earth metal oxide;and a heating section for heating the first mixture to a heating temperature not lower than a predetermined temperature to obtain a second mixture of the inorganic substance and the additive, the proportion of the additive to the inorganic substance in the mixing section being 0.5 or more in terms of molar ratio, and the predetermined temperature being (1) a temperature at which a phase change occurs in the case where the inorganic substance is an inorganic substance whose phase is to be changed by heating and (2) a temperature at which thermal decomposition occurs in the case where the inorganic substance is an inorganic substance that is to be thermally decomposed by heating.

10. DEVICE, according to claim 9, characterized in that the inorganic substance contains α-spodumene which is phase-changed to β-spodumene upon heating.

11. DEVICE, according to claim 10, characterized in that the additive is at least one of the following: sodium hydroxide, calcium hydroxide, and calcium oxide. Petition 870250081114, dated 10 / 09 / 2025, page 69 / 132 4 / 4 12. DEVICE, according to claim 9, characterized in that the inorganic substance contains petalite which is thermally decomposed by heating.

13. DEVICE, according to any one of claims 9 to 12, characterized by the heating section heating the first mixture using dielectric heating.

14. DEVICE, according to any one of claims 9 to 12, characterized by further comprising a dissolution section for dissolving the second mixture, which was obtained by the heating section, in an acidic solution or water to obtain a solution of the inorganic substance. Petition 870250081114, dated 10 / 09 / 2025, pp. 70 / 132

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