Dissolution promotor for basic minerals or rocks containing same, and dissolution promotion method

Abstract

[PROBLEM] To provide a dissolution promoter that promotes the dissolution of basic minerals useful for promoting the mineral trapping of CO2. [SOLUTION] A dissolution promoter for basic minerals contains silica sol containing silica particles (a) having an average secondary particle diameter of 5-200 nm according to dynamic light scattering, and an aqueous medium (b); and a dissolution promotion method for rocks in which the dissolution promoter is used.

Description

Dissolution promoter and dissolution promotion method for basic minerals or rocks containing them

[0001] The present invention relates to a dissolution promoter that promotes the dissolution of basic minerals or rocks containing basic minerals.

[0002] CO ２ Carbon dioxide capture and storage (CCS) technology is a technology that captures and stores CO2 emitted from sources such as power plants and steelworks. ２ This technology separates and captures CO and stores it underground or underwater. ２ This prevents CO2 from being released into the atmosphere and is considered an important option for global warming countermeasures. ２ Deep underground aquifers (such as sandstone layers containing many voids) are considered to be promising storage locations for CO, and for example, a geological storage system using deep aquifers has been proposed, as shown in Patent Document 1. Patent Document 2 also proposes the storage of CO in an unstructured reservoir that does not have a sealed structure as an underground storage target layer. ２ CO storage achieved ２ Proposals have been made for underground storage facilities.

[0003] CO injected into a saline aquifer (reservoir) deep underground ２ CO displaces the formation water in the reservoir and spreads, and is trapped in the reservoir by four mechanisms: structural trap, residual gas trap, dissolution trap, and mineral trap. ２ The formation water containing dissolved cations reacts chemically with rock minerals, and the cations (Ca ２＋ , Mg ２＋ etc.) and CO ２ The mineral traps where CO reacts (carbonation) and is fixed underground as secondary minerals such as calcium carbonate and magnesium carbonate are the most stable form of CO. ２ However, as described in Non-Patent Document 1, the injected CO ２However, the drawback is that it is predicted to take 100-1000 years for the rocks to reach mineral traps. Non-Patent Document 2 shows that if the geological layer is rich in rocks containing basic minerals such as basalt, the time required to reach mineral traps can be significantly reduced. On the other hand, Non-Patent Document 3 shows that the supercritical CO ２ It has been shown that the dissolution of basalt is promoted in the presence of ammonium nitrate, but dissolution is not promoted at pH 5-6.

[0004] JP 2008-307483 A JP 2011-147869 A

[0005] Nature Reviews Earth & Environment volume 1 (2020) 90-102Science 352 (6291) 1312-1314Journal of MMIJ 128 (2012) 94-102

[0006] As shown in Non-Patent Document 2, if the rocks containing basic minerals are abundant, CO ２ It is expected that the number of years required to reach mineral trapping due to mineralization of CO2 can be significantly reduced. ２ As mineralization progresses, the cations (metal ions) dissolved in the formation water in the reservoir are consumed, and it is expected that the progress of mineralization will slow down. ２ These ions are supplied by the reaction between the acid produced when it dissolves in the formation water and basic minerals. However, this reaction is slow above the neutral pH range. Therefore, if the reaction proceeds beyond a certain point and the pH in the system rises, the reaction slows down, resulting in a lack of cations (metal ions) and a delay in mineralization.

[0007] In view of the above circumstances, the present inventors have conducted extensive research and found that the dissolution of basic minerals can be promoted by using silica particles having solid acidity as a dissolution promoter.

[0008]

[0006] That is, in a first aspect, the present invention relates to a dissolution promoter for a basic mineral or rock containing the basic mineral, the dissolution promoter comprising a silica sol containing silica particles (a) having an average secondary particle size of 5 to 200 nm as measured by dynamic light scattering and an aqueous medium (b).

[0007] In a second aspect, the present invention relates to the dissolution promoter according to the first aspect, wherein in Dissolution Promotion Evaluation Test 1, in which a mixture of 80 g of an aqueous liquid and 1 g of basalt (a geochemical standard substance) is stored at 60°C for 7 days and the total ion concentration (C) of Ca, Mg, and Fe contained in the supernatant of the mixture is measured, the ratio C1 / C0 of the total ion concentration (C1) when an aqueous liquid having a pH of 3.5 obtained by adding a 0.1 N hydrochloric acid aqueous solution to the dissolution promoter having a silica particle concentration of 1 mass % is used as the aqueous liquid, and the total ion concentration (C0) when an aqueous liquid having a pH of 3.5 obtained by adding a 0.1 N hydrochloric acid aqueous solution to pure water is used as the aqueous liquid, is 2 to 100. As a third aspect, the present invention relates to the dissolution promoter according to the first aspect, wherein 1 g of basalt (geochemical standard material) is added to 80 g of an aqueous liquid having a pH of 3.5, obtained by adding a 0.1 N hydrochloric acid aqueous solution to the dissolution promoter having a silica particle concentration of 1% by mass, and the mixture is stored at 60°C for 7 days, and then the average secondary particle size of the silica particles in the supernatant of the mixture is measured by dynamic light scattering, and in Dispersion Stability Evaluation Test 1 in a Formation Environment, the ratio of the average secondary particle size of the silica particles after the test to the average secondary particle size before the test (average secondary particle size of silica particles after the test / average secondary particle size of silica particles before the test) is 1 to 5. As a fourth aspect, the present invention relates to the dissolution promoter according to the first aspect, wherein at least a portion of the silica particles are coated with a silane compound (c) having a hydrophilic organic group, and the hydrophilic organic group is an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group. As a fifth aspect, the present invention relates to the dissolution promoter according to the first aspect, further comprising an organic acid or a salt thereof. According to a sixth aspect, the present invention relates to the dissolution enhancer according to the fifth aspect, in which the organic acid includes at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid.

[0013] As a seventh aspect, the present invention relates to the dissolution promoter according to the first aspect, wherein the basic mineral or rock containing the basic mineral contains at least one of Ca, Mg, and Fe. As an eighth aspect, the present invention relates to the dissolution promoter according to the seventh aspect, wherein the basic mineral containing at least one of Ca, Mg, and Fe or the rock containing the basic mineral is a rock classified as igneous rock or a group of minerals contained therein. As a ninth aspect, the present invention relates to the dissolution promoter according to the seventh aspect, wherein the basic mineral containing at least one of Ca, Mg, and Fe or the rock containing the basic mineral is a basalt, gabbro, or a group of minerals contained therein, which are classified as mafic rock, or a peridotite, serpentine, komatiite, or a group of minerals contained therein, which are classified as ultramafic rock. According to a tenth aspect, the present invention relates to a method for promoting dissolution of a basic mineral or a rock containing the basic mineral, the method comprising a step of injecting into a subterranean layer the dissolution promoter according to the first aspect or a diluted solution of the dissolution promoter adjusted with an aqueous medium to a silica particle concentration of 0.001 to 30 mass %.

[0009] The dissolution promoter for basic minerals of the present invention can promote the dissolution of basic minerals, and by injecting it into an underground reservoir, it is possible to reduce CO2 in the underground reservoir. ２ Furthermore, the dissolution promoter of the present invention uses silica particles having an average secondary particle size of 5 to 200 nm as measured by dynamic light scattering, i.e., does not contain coarse particles, and therefore can penetrate without blocking pores even when injected into underground bedrock, and is expected to promote the dissolution of basic minerals contained in the rocks that make up the pores, thereby contributing to the mineralization of carbon dioxide.

[0010] The present inventors have addressed the issue of promoting mineral trapping (mineralization) in CCS technology by developing a method for trapping CO ２ We have been studying how to promote the dissolution of rocks and minerals into which the particles are injected. We have focused on the solid acidity of silica particles, and have assumed that this may contribute to promoting the dissolution of rocks and minerals. When silica particles (silica sol) and basic minerals such as basalt are allowed to coexist in a liquid, we have found that the dissolution of the basic minerals is promoted. We have found that promoting the dissolution of basic minerals, and in turn promoting the release of cations from the minerals, increases the CO2 content of the injected CO2. ２The reactivity with CO increases ２ We found that this can be expected to promote mineral trapping.

[0011] Specifically, the present invention relates to a dissolution promoter for a basic mineral, namely, a dissolution promoter containing a silica sol containing (a) silica particles having an average secondary particle diameter of 5 to 200 nm as measured by a dynamic light scattering method and (b) an aqueous medium. At least a portion of the (a) silica particles may be coated with (c) a silane compound having a hydrophilic organic group, which will be described later.

[0012] The basic minerals or rocks containing such minerals targeted by the dissolution promoter of the present invention are, for example, those containing at least one of Ca, Mg, and Fe. Examples of such rocks containing basic minerals include basalt and gabbro, which are classified as mafic rocks, and peridotite, serpentine, and komatiite, which are classified as ultramafic rocks, among rocks classified as igneous rocks. In this specification, basic minerals refer to inorganic substances containing at least one of Ca, Mg, and Fe. Representative examples include silicate minerals such as olivine, pyroxenes (augite, enstatite, etc.), micas (biotite, etc.), amphibole (forsterite amphibole group, etc.), and feldspars (alkali feldspar, plagioclase, etc.). Depending on their composition, olivine can be classified as forsterite (forsterite), fayalite (fayalite), tephroite (manganese olivine, tuffloite), monticellite, serpentine, etc. Olivine is found in mafic rocks such as basalt and gabbro (also known as basic rocks, SiO ２ The content (weight%) is 45-52%, and ultramafic rocks such as peridotite and serpentinite (also known as ultrabasic rocks, SiO ２ The dissolution promoter of the present invention can also function as a dissolution promoter for these mafic rocks (basic rocks) and ultramafic rocks (ultrabasic rocks).

[0013] The dissolution promoter of the present invention has an unprecedented feature in that it promotes the dissolution of the target basic mineral by contacting it with the target mineral. This dissolution promotion ability can be evaluated by the following <Dissolution Promotion Evaluation Test 1>. Furthermore, the stability of the dissolution promoter itself, which is required to exert the dissolution promotion ability, i.e., the dispersion stability of the silica particles that constitute the dissolution promoter, can be evaluated by the <Dispersion Stability Evaluation Test 1 in a Geological Formation Environment>. These evaluation tests are carried out in a CO ２ This simulates the formation water (pH 3 to 4) after dissolution of chlorine.

[0014] Dissolution Promotion Evaluation Test 1: In Dissolution Promotion Evaluation Test 1, a mixture of a target basic mineral and a dissolution promoter is maintained at 60°C for 7 days, and the concentration of cations dissolved therein is evaluated. Specifically, a mixture of 80 g of aqueous liquid and 1 g of basalt (a geochemical reference material) is added, and the mixture is stored at 60°C for 7 days. The total ion concentration (C) of Ca, Mg, and Fe contained in the supernatant of the mixture is measured. The total ion concentration when an aqueous liquid having a pH of 3.5 (aqueous liquid to be evaluated) obtained by adding 0.1 N hydrochloric acid to a dissolution promoter with a silica particle concentration of 1% by mass (aqueous liquid to be evaluated) is defined as C1. The total ion concentration when an aqueous liquid having a pH of 3.5 (aqueous liquid to be evaluated) obtained by adding 0.1 N hydrochloric acid to pure water (aqueous liquid to be controlled) is defined as C0. The dissolution promotion ability of the dissolution promoter is evaluated based on the ratio C1 / C0. In the dissolution promoter of the present invention, C1 / C0 is preferably 2 or greater, and more preferably 2.5 or greater. The upper limit of C1 / C0 is not particularly limited and may vary depending on the composition of the basic mineral. However, by setting the upper limit of C1 / C0 to 100 or less, it is possible to suppress the collapse of the underground reservoir, which is expected to be caused by excessive dissolution of the mineral or rock into which the dissolution promoter is injected. The upper limit of C1 / C0 can be set to a level that does not destroy the underground reservoir, for example, about 100, about 70, about 50, or about 30. The numerical range of C1 / C0 can be 2 to 100, 2 to 70, 2 to 50, 2 to 30, 2.5 to 100, 2.5 to 70, 2.5 to 50, or 2.5 to 30.

[0015] The basalt (geochemical standard material) used in the <Dissolution Promotion Evaluation Test 1> and the <Dispersion Stability Evaluation Test 1 in a Geological Environment> below was a standard sample of basalt (JB-1b, particle size distribution 4.75-10.8 μm, produced in Sasebo, Nagasaki Prefecture) provided by the National Institute of Advanced Industrial Science and Technology. The Ca, Mg, and Fe contained in the sample were 6.9% by mass, 4.9% by mass, and 6.3% by mass, respectively (CaO, MgO, total Fe). ２ O ３ (calculated from).

[0016] <Dispersion Stability Evaluation Test 1 in a Geological Formation Environment> Similarly to the above <Dissolution Promotion Evaluation Test 1>, the particle size maintenance of the dissolution promoter of the present invention can be evaluated by storing a mixture of the target basic mineral and dissolution promoter at 60°C for 7 days and evaluating the particle size of the dissolution promoter (silica particles) before and after storage. Specifically, 1 g of basalt (geochemical standard material) was added to 80 g of an aqueous liquid (pH 3.5) containing a dissolution promoter with a silica particle concentration of 1% by mass and a 0.1 N hydrochloric acid solution. The mixture was then stored at 60°C for 7 days, and the average secondary particle size of the silica particles in the supernatant of the mixture was measured by dynamic light scattering. The particle size maintenance of the dissolution promoter (dispersion stability in a geological formation environment) was evaluated based on the ratio of the average secondary particle size of the silica particles after the test to the average secondary particle size of the silica particles before the test (average secondary particle size of silica particles after the test / average secondary particle size of silica particles before the test). In the dissolution promoter of the present invention, the ratio of the average secondary particle size of silica particles after the test to the average secondary particle size of silica particles before the test is preferably 1 to 5, and can be 1 to 4, or 1 to 3. A ratio of 1 to 5 means that there is no significant aggregation of silica particles, and in this case, the possibility of causing blockage of gaps in the underground formation or pores in the rock when the dissolution promoter is injected into an underground reservoir can be reduced. By having the ratio be 1 to 5, the dissolution promoter of the present invention can be expected to penetrate without blocking the gaps, even when injected into underground bedrock. Consequently, the dissolution promoter can be expected to exhibit dissolution-promoting properties that promote the dissolution of basic minerals contained in the rock that constitutes the gaps.

[0017] As the silica sol containing the (a) silica particles and the (b) aqueous medium, for example, an aqueous silica sol can be used. The aqueous silica sol is a colloidal dispersion system in which an aqueous solvent (i.e., the (b) aqueous medium) is used as a dispersion medium and colloidal silica particles (i.e., the (a) silica particles) are used as a dispersoid, and can be produced by a known method using water glass (aqueous sodium silicate solution) as a raw material. The (b) aqueous medium in the present invention is usually water, and examples thereof include ordinary industrial water, deionized water, and distilled water.

[0018] In the silica sol containing (a) silica particles and (b) an aqueous medium, which is a dissolution promoter of the present invention, the (a) silica particles have an average secondary particle diameter (DLS average particle diameter: Z-average particle diameter, harmonic mean particle diameter) in the silica sol measured by dynamic light scattering (DLS) in the range of 5 to 200 nm, for example, 5 to 100 nm, 5 to 70 nm, 10 to 70 nm, 5 to 50 nm, 10 to 50 nm, or 10 to 30 nm. The average particle diameter measured by dynamic light scattering (DLS) represents the average value of the secondary particle diameter (dispersed particle diameter), and the larger the DLS average particle diameter, the more the silica particles in the medium are considered to be in an agglomerated state. By using particles with a DLS average particle diameter of more than 5 nm, the particles will not aggregate and will be more stable in the silica sol, while by using particles with an average particle diameter of less than 200 nm, it is expected that they will be able to penetrate into gaps in underground layers and pores in rocks more easily.

[0019] The DLS average particle size value is an (initial) value before the aforementioned Dissolution Promotion Evaluation Test 1 and Dispersion Stability Evaluation Test in a Geological Environment 1 are conducted. However, the silica particles in the dissolution promoter according to the present invention are particles with excellent dispersion stability, and even after the Dispersion Stability Evaluation Test in a Geological Environment 1, the ratio of particle sizes before and after the test can be up to about 5, i.e., the DLS average particle size value can be substantially within the above-mentioned numerical range (range of 5 to 200 nm).

[0020] As mentioned above, particles with a large DLS average particle size are undesirable because they may clog gaps in the underground layer. Therefore, it is preferable to use a silica sol that does not contain coarse particles, for example, a silica sol in which the cumulative particle size distribution D90 of the average particle size (DLS average particle size) measured by dynamic light scattering of silica particles is 5 to 200 nm, 5 to 150 nm, 5 to 100 nm, 5 to 70 nm, 10 to 200 nm, 20 to 200 nm, or 20 to 150 nm. Furthermore, it is preferable that the silica particles contained in the silica sol have salt resistance such that, when they come into contact with saltwater contained in underground layers, the silica particles do not aggregate to an extent that exceeds the DLS average particle size or D90 range. The D90 is the particle size that represents the cumulative 90% from the fine particle side of the cumulative particle size distribution. The cumulative particle size distribution can be obtained, for example, by dynamic light scattering or image analysis. As an example, the cumulative particle size distribution value can be measured using a particle size distribution measurement device using a dynamic light scattering particle size measurement device. There are two methods for analyzing the D value: the number distribution method and the volume distribution method. The number distribution method regards particles as perfect circles with the same area as the particle itself, and measures the percentage of particles with a specific particle diameter. The volume distribution method, on the other hand, assumes that if the particle density is constant, volume and weight are proportional, and measures the mass percentage of particles with a specific particle diameter in a given amount of sample. As an example, it is preferable to determine the D value (D90) using the volume distribution method.

[0021] Commercially available silica sols (aqueous silica sols) can be used. Aqueous silica sols with silica concentrations of 5 to 50% by mass are generally commercially available, which is preferred due to their ease of availability. Aqueous silica sols include alkaline and acidic aqueous silica sols, and both can be used, although acidic aqueous silica sols are preferred. Commercially available acidic aqueous silica sols include Snowtex (trade name) ST-OXS, ST-OS, ST-O, ST-O-40, ST-OL, and ST-OYL manufactured by Nissan Chemical Industries, Ltd.; and Adelite (trade name) AT-series manufactured by ADEKA Corporation. The pH of the dissolution promoter according to the present invention is not particularly limited, but can be set to 0.5 to 6.0, 0.5 to 5.0, 0.5 to 4.0, or 1.0 to 6.0 from the viewpoints of promoting the dissolution of basic minerals and stabilizing the dispersion of silica particles contained in the silica sol. The silica solids concentration of the aqueous silica sol used is preferably 5 to 55% by mass. Here, the silica solid content concentration is a value determined by a calcination method, specifically, the value obtained by dividing the mass of the calcination residue obtained by calcining an aqueous silica sol at 1000°C for 30 minutes or more in the atmosphere by the mass of the aqueous silica sol. The mass of the calcination residue is also referred to as the "silica solid content."

[0022] The concentration of (a) silica particles (silica solids concentration) in the dissolution promoter according to the present invention is not particularly limited, and can be, for example, 0.01% by mass to 50.0% by mass, 0.1% by mass to 50.0% by mass, 1% by mass to 50.0% by mass, 10% by mass to 50.0% by mass, or 10.0% by mass to 25.0% by mass, or for example, 15.0% by mass to 25.0% by mass, based on the total mass of the dissolution promoter.

[0023] In the dissolution promoter of the present invention, the (a) silica particles may be at least partially coated with (c) a silane compound having a hydrophilic organic group.

[0024] In the present invention, "coated with a silane compound" refers to an embodiment in which the surface of a silica particle is coated with a silane compound, and also includes an embodiment in which a silane compound is bonded to the surface of a silica particle. "An embodiment in which a silane compound is coated on the surface of a silica particle" may refer to an embodiment in which a silane compound coats at least a portion of the surface of a silica particle, i.e., an embodiment in which the silane compound covers a portion of the surface of a silica particle, and an embodiment in which the silane compound covers the entire surface of a silica particle. This embodiment does not require bonding between the silane compound and the surface of a silica particle. Furthermore, "an embodiment in which a silane compound is bonded to the surface of a silica particle" may refer to an embodiment in which a silane compound is bonded to at least a portion of the surface of a silica particle, i.e., an embodiment in which the silane compound is bonded to a portion of the surface of a silica particle and covers at least a portion of the surface, and an embodiment in which the silane compound is bonded to the entire surface of a silica particle and covers the entire surface.

[0025] The (c) silane compound may be a silane compound having a hydrophilic organic group such as an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group. In addition to the hydrophilic organic group, the (c) silane compound preferably has a hydrolyzable group such as an alkoxy group, an acyloxy group, or a halogen group.

[0026] Specific examples of these (c) silane compounds include silane coupling agents having an epoxy group-containing organic group or an amino group-containing organic group. Examples of the silane coupling agent having an epoxy group-containing organic group include 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)propyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)propyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2-(3,4-epoxycyclohexyl)methyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)methyltriethoxysilane, 1-(3,4-epoxycyclohexyl)methyltrimethoxysilane, and 1-(3,4-epoxycyclohexyl)methyltriethoxysilane. Examples of silane coupling agents having the amino group-containing organic group include 3-(2-(2-aminoethylamino)ethylamino)propyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrichlorosilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane. Of the above silane compounds, silane compounds having an organic group that exhibits a chelating effect in an aqueous medium can be used. Examples of silane compounds having an organic group that exhibits a chelating effect in an aqueous medium include epoxy-based silane compounds that undergo ring-opening in an aqueous medium to form a diol group, and amino-based silane compounds having a diamine structure.By using a silane compound having an organic group that exhibits a chelating effect in an aqueous medium, the chelating effect of the organic group can promote the desorption of cations (metal ions) from basic minerals or rocks containing them, and the dissolution-promoting effect can be further increased by lowering the concentration of cations (metal ions) in the formation water.

[0027] The silica particles according to the present invention, at least a portion of which is coated with a silane compound having a hydrophilic organic group (also referred to as "silica particles surface-treated with a silane compound"), can be obtained, for example, by adding a silane compound to an aqueous silica sol, followed by heat treatment at 50 to 100°C for about 1 to 20 hours. In this case, the amount of silane compound added relative to the silica particles (silica solid content) in the aqueous silica sol can be, for example, a mass ratio of silane compound / silica particles = 0.1 to 10.0. The amount of surface treatment with the silane compound, i.e., the amount of silane compound bonded to the silica particle surface, is determined based on the amount of silane compound bonded to the silica particle surface within 1 nm of the silica particle surface. ２ It is preferable that the number of particles is, for example, about 0.1 to 12 per particle.

[0028] In addition, when particles coated with the (c) silane compound having a hydrophilic organic group (also referred to as surface-modified silica particles) are used as the (a) silica particles in the dissolution promoter of the present invention, unreacted (c) silane compound may remain in the dissolution promoter, or unmodified silica particles may remain, or a dissolution promoter from which the unreacted (c) silane compound and unmodified silica particles have been removed may also be used.

[0029] The dissolution enhancer according to the present invention may further contain an organic acid or a salt thereof. The addition of an organic acid or a salt thereof is expected to improve dissolution-enhancing ability through a chelating effect. Examples of the organic acid or a salt thereof include acetic acid, lactic acid, malic acid, succinic acid, tartaric acid, butyric acid, oxalic acid, malonic acid, fumaric acid, maleic acid, propionic acid, formic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, thioglycolic acid, ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid sodium salt, L-aspartic acid, L-aspartic acid-diacetic acid tetrasodium salt, and diethylenetriaminepentaacetic acid. Among these, at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid can be used. In addition to the salts listed above, examples of the organic acid salts include alkali metal salts such as sodium salts and potassium salts, ammonium salts, and amine salts. When the organic acid or a salt thereof is contained, the amount thereof, based on the total mass of the dissolution promoter of the present invention, can be, for example, about 0.01% to 20% by mass, about 0.1% to 20% by mass, about 1% to 20% by mass, about 0.01% to 10% by mass, about 0.1% to 10% by mass, or about 0.5% to 5% by mass. The organic acid can be contained in a mass ratio (organic acid / silica particles) relative to the silica particles constituting the dissolution promoter of the present invention of, for example, 0.0001 to 2.

[0030] The dissolution promoter according to the present invention may further contain a chelating agent (sequestering agent). The chelating agent may be any compound other than the compounds listed above as organic acids or salts thereof, as long as it has a chelating effect. For example, phosphate compounds [phosphoric acid, various acidic phosphates, neutral phosphates, basic phosphates], salts of condensed phosphates [salts of polyphosphates such as pyrophosphate, triphosphate, trimetaphosphate, tetrametaphosphate (sodium pyrophosphate, sodium acidic pyrophosphate, sodium tripolyphosphate, sodium tetrapolyphosphate, sodium hexametaphosphate, sodium acidic hexametaphosphate, or potassium salts thereof, etc.)]; nitrilotriacetic acid, hydroxyethylethylenediaminetriacetic acid, propylenediaminetetraacetic acid, bis(2-hydroxyphenylacetic acid)ethylenediamine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, propanediaminetetraacetic acid, glycol ether diaminetetraacetic acid, glutamic acid diacetic acid, ethylenediaminedisuccinic acid, cyclohexadiaminetetraacetic acid, salts thereof, etc., but are not limited to these. When the chelating agent is contained, the blending amount thereof is, for example, about 0.01% by mass to 20% by mass, about 0.1% by mass to 20% by mass, about 1% by mass to 20% by mass, about 0.01% by mass to 10% by mass, about 0.1% by mass to 10% by mass, or about 0.5% by mass to 5% by mass, based on the total mass of the dissolution promoter of the present invention, and the mass ratio of the chelating agent to the silica particles constituting the dissolution promoter of the present invention (organic acid / silica particles) can be, for example, a ratio of 0.0001 to 2.

[0031] <Method for Promoting Dissolution of Rocks, etc.> The present invention also relates to a method for promoting dissolution of rocks, etc. using the dissolution promoter. More specifically, the present invention relates to a method for promoting dissolution, including a step of injecting into a subterranean formation the dissolution promoter, or a diluted solution of the dissolution promoter prepared by adjusting the dissolution promoter in an aqueous medium to a silica particle concentration of 0.001 to 30 mass%, 0.01 to 30 mass%, 0.1 to 30 mass%, 0.001 to 10 mass%, 0.001 to 5 mass%, 0.01 to 10 mass%, 0.1 to 10 mass%, or 0.01 to 5 mass%. By injecting into the subterranean formation the dissolution promoter, or a diluted solution of the dissolution promoter prepared in an aqueous medium to a silica particle concentration of 0.001 mass% or more, the basic minerals present in the subterranean formation are dissolved, promoting the release of cations, and reducing the CO2 to be injected. ２ The reactivity with CO increases ２ By injecting the dissolution promoter or a diluted solution of the dissolution promoter in an aqueous medium so that the silica particle concentration is 30 mass % or less into an underground formation, it is expected that the dissolution promoter will penetrate into the gaps in the underground formation and the pores in the rock without clogging them, and it is therefore expected that the dissolution promoter will exhibit a dissolution-promoting ability that promotes the dissolution of basic minerals contained in the rock that constitutes the gaps.

[0032] As described above, the dissolution promoter according to the present invention can promote the dissolution of basic minerals by the solid acidity of silica particles, and by injecting it into an underground reservoir, it is possible to reduce CO2 in the underground reservoir. ２ Furthermore, the basic mineral dissolution promoter of the present invention is expected to promote mineral trapping by reducing the concentration of minerals such as Ca, Mg, and Fe in the system and disrupting the dissolution equilibrium due to the cation adsorption action of the silanol groups (anionic) on the surface of the silica particles, thereby promoting the dissolution of the basic mineral. ２ This is expected to promote mineral trapping.

[0033] The present invention will be described in further detail below based on synthesis examples, examples, and comparative examples, but it should be understood that the present invention is not limited to these examples in any way.

[0034] (Measuring equipment) DLS average particle size (dynamic light scattering particle size): A dynamic light scattering particle size measuring device, trade name Zetasizer Nano (manufactured by Spectris Corporation, Malvern Division), was used. pH: A pH meter (manufactured by DKK-TOA Corporation, trade name MM43X) was used. Electrical conductivity: An electrical conductivity meter (manufactured by DKK-TOA Corporation, trade name CM-30R) was used. ICP: Trade name Agilent 5110 ICP-OES (manufactured by Agilent Technologies, Inc.)

[0035] [Measurement of silica solid content concentration] The silica sol was placed in a crucible and dried at 150°C, and the resulting gel was calcined at 1000°C for 30 minutes in the atmosphere, and the calcination residue was weighed and calculated. [pH measurement] The pH of the silica sol was measured at 20°C using a pH meter (manufactured by DKK-TOA Corporation, product name: MM-43X). [Electrical conductivity measurement] The electrical conductivity of the silica sol was measured at 20°C using an electrical conductivity meter (manufactured by DKK-TOA Corporation, product name: CM-30R). [Measurement of average primary particle size (particle size by nitrogen adsorption method)] The specific surface area value (S Ｎ２ The specific surface area of ​​the silica sol was measured by removing water-soluble cations in the silica sol with an H-type cation exchange resin (manufactured by The Dow Chemical Company, trade name: Amberlite IR-120B), drying the silica sol at 290°C, and then pulverizing it in a mortar for 10 minutes to prepare a measurement sample. The specific surface area of ​​the silica sol was measured using a nitrogen adsorption method specific surface area measuring device (trade name: Monosorb, manufactured by Quantachrome Instruments Japan, LLC) to measure the specific surface area of ​​the silica sol. ２ The specific surface area was measured by the BET single-point method using a mixture of 30% nitrogen and 70% helium as the carrier gas. Ｎ２ (m ２ / g), the average primary particle size (nm) = 2720 / S Ｎ２ [Measurement of average primary particle size (Sears particle size)] The Sears particle size refers to the average particle size measured based on the method described in the literature as "Rapid method for measuring colloidal silica particle size" by G. W. Sears, Anal. Chem. 28(12), 1981, p. 1956. In detail, 1.5 g of SiO ２The specific surface area of ​​colloidal silica was determined from the amount of 0.1N-NaOH required to titrate colloidal silica equivalent to 100 ppm from pH 4 to pH 9, and the equivalent diameter (specific surface area diameter) was calculated from this. [Measurement of Average Secondary Particle Diameter by Dynamic Light Scattering (DLS)] The average secondary particle diameter by DLS (also referred to as DLS average particle diameter) was measured using a dynamic light scattering particle size analyzer (manufactured by Malvern Panalytical, trade name: Zetasizer Nano). 0.1 g of the target silica sol was dispensed into a glass cell with an optical path length of 10 mm, and a 0.15 mass % NaCl aqueous solution was added to obtain a silica sol with a silica particle concentration adjusted so that the count rate at an attenuator setting of 7 was 200 to 400 kcps. The prepared silica sol was placed in the cell, and the height of the liquid surface from the bottom of the cell was adjusted to about 1 cm, and the DLS average particle size of the silica sol was measured using an attenuator 7. This measuring device can also calculate the number-average particle size and volume-average particle size, but the Z-average particle size was used in this application. [Measurement of cumulative particle size distribution by dynamic light scattering (DLS)] The cumulative particle size distribution by the DLS method (also referred to as D90) was obtained by the same procedure as in [Measurement of average secondary particle size by dynamic light scattering (DLS)], except that the volume-average particle size was calculated using a dynamic light scattering particle size measuring device. The particle size at which the frequency was 90% in the volume distribution of the obtained particles was used.

[0036] Example 1 A 2000 ml glass recovery flask was charged with 1000 g of aqueous silica sol (Snowtex (trade name) ST-O, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5 mass%, average primary particle size measured by BET method: 11.0 nm, average secondary particle size measured by DLS method: 19.0 nm) and a magnetic stirrer. Then, while stirring with the magnetic stirrer, 149.7 g of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KBM-403) was added. The recovery flask was then placed in an oil bath preheated to 60°C, and a cooling tube through which tap water was flowing was attached to the top of the recovery flask. The mixture was refluxed and maintained at 60°C for 3 hours, after which it was cooled. After cooling to room temperature, the aqueous sol was removed and filtered using a 460 mesh filter, yielding 1145 g of aqueous silica sol of Example 1 that had been surface-treated with a silane compound. The aqueous silica sol of Example 1 was evaluated for pH, electrical conductivity, solid content, DLS average particle size, and D90. The results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 1 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test in Geological Formation Environment 1], and [Solid Acidity Evaluation Test 1].

[0037] Example 2 228.2 g of lactic acid (manufactured by Kanto Chemical Co., Ltd., concentration 89% by mass) was further added to 1000 g of aqueous silica sol (Snowtex (trade name) ST-O, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5 mass%, average primary particle size measured by BET method 11.0 nm, average secondary particle size measured by DLS method 19.0 nm), and the mixture was stirred with a magnetic stirrer. The same procedure as in Example 1 was repeated, except that 130.7 g of aminoethylaminopropylmethyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-602) was added instead of 3-glycidoxypropyltrimethoxysilane, to obtain 1352 g of aqueous silica sol of Example 2 that had been surface-treated with a silane compound. The pH, electrical conductivity, solids content, DLS average particle size, and D90 of the aqueous silica sol of Example 2 were evaluated. The results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 2 was evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0038] Example 3 The same procedure as in Example 1 was repeated, except that a solution prepared by previously mixing 114.1 g of lactic acid and 140.2 g of aminopropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name KBE-903) and stirring for 30 minutes was added to 1000 g of aqueous silica sol (Snowtex (trade name) ST-O, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5 mass%, average primary particle size by BET method 11.0 nm, average secondary particle size by DLS method 19.0 nm) and stirring was performed without adding 3-glycidoxypropyltrimethoxysilane. The pH, electrical conductivity, solids content, DLS average particle size, and D90 of Example 3 were evaluated. The results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 3 was evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0039] Example 4 An aqueous silica sol (Snowtex (trade name) ST-O manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5 mass%, average primary particle size measured by the BET method of 11.0 nm, average secondary particle size measured by the DLS method of 19.0 nm) was used as the aqueous silica sol of Example 4, and its pH, electrical conductivity, solid content, DLS average particle size, and D90 were evaluated. The results obtained are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 4 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0040] Example 5 2 g of the aqueous silica sol prepared in Example 1 was placed in a centrifugal cell with a filter (Merck, trade name: Amicon Ultra-15, molecular weight cutoff: 100,000, centrifugal ultrafiltration filter unit), followed by the addition of 4 g of pure water. The centrifugal cell was installed in a centrifuge (Tomy Seiko Co., Ltd., trade name: Supreme 21), and centrifuged at 3,000 rpm for 20 minutes. After recovering and quantifying the filtrate, pure water in an amount corresponding to the mass of the filtrate was added to the centrifugal cell, and the cell was centrifuged again at 3,000 rpm for 20 minutes. This process was repeated five times, and then pure water was added to the silica sol remaining in the filter portion so that the mass was 2 g, thereby obtaining 2 g of aqueous silica sol of Example 5 from which the excess silane compound had been removed. The pH, electrical conductivity, solids content, DLS average particle size, and D90 of the aqueous silica sol of Example 5 were evaluated. The results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 5 was evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0041] Example 6 Except for using 2 g of the aqueous silica sol prepared in Example 3 instead of the aqueous silica sol prepared in Example 1, the same procedure as in Example 5 was repeated to remove the excess silane compound, thereby obtaining 2 g of aqueous silica sol of Example 6. The pH, electrical conductivity, solid content, DLS average particle size, and D90 of the aqueous silica sol of Example 6 were evaluated. The results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 6 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0042] Example 7 An aqueous silica sol (Snowtex (trade name) ST-OXS manufactured by Nissan Chemical Industries, Ltd., silica concentration = 10.4 mass%, average primary particle size measured by the Sears method: 5.3 nm, average secondary particle size measured by the DLS method: 15.7 nm) was used as the aqueous silica sol of Example 7, and its pH, electrical conductivity, solid content, DLS average particle size, and D90 were evaluated. The results obtained are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 7 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0043] Example 8 An aqueous silica sol (Snowtex (trade name) ST-O-40, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 40.5 mass%, average primary particle size measured by the BET method: 23.0 nm, average secondary particle size measured by the DLS method: 37.0 nm) was used as the aqueous silica sol of Example 8, and its pH, electrical conductivity, solid content, DLS average particle size, and D90 were evaluated. The results obtained are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 8 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0044] Example 9 20.5 g of malonic acid (manufactured by Junsei Chemical Co., Ltd., concentration of 99% by mass or more) was added to 1,000 g of aqueous silica sol (Snowtex (trade name) ST-O, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5% by mass, average primary particle size measured by BET method of 11.0 nm, average secondary particle size measured by DLS method of 19.0 nm), and the mixture was stirred with a magnetic stirrer for 1 hour to obtain an aqueous silica sol of Example 9. The pH, electrical conductivity, solid content, DLS average particle size, and D90 of the aqueous silica sol of Example 9 were evaluated. The obtained results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 9 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0045] Example 10 26.4 g of DL-malic acid (manufactured by Kanto Chemical Co., Inc., concentration of 99% by mass or more) was added to 1,000 g of aqueous silica sol (Snowtex (trade name) ST-O, manufactured by Nissan Chemical Industries, Ltd., silica concentration = 20.5% by mass, average primary particle size measured by BET method of 11.0 nm, average secondary particle size measured by DLS method of 19.0 nm), and the mixture was stirred with a magnetic stirrer for 1 hour to obtain an aqueous silica sol of Example 10. The pH, electrical conductivity, solid content, DLS average particle size, and D90 of the aqueous silica sol of Example 10 were evaluated. The obtained results are shown in Table 1. The dissolution promotion performance of the aqueous silica sol of Example 10 was also evaluated according to [Dissolution Promotion Evaluation Test 1], [Dispersion Stability Evaluation Test 1 in a Geological Formation Environment], and [Solid Acidity Evaluation Test 1].

[0046] <Evaluation Tests> [Dissolution Promotion Evaluation Test 1] The aqueous silica sols (dissolution promoters) of Examples 1 to 10 were diluted with pure water to a silica concentration of 1.0% by mass, and then 0.1 N hydrochloric acid (manufactured by Kanto Chemical Co., Inc.) was used to adjust the pH to 3.5 to prepare aqueous liquids (aqueous liquids to be evaluated). 80 g of this aqueous liquid was placed in a sealed container (Duran bottle, manufactured by DWK Life Science, product name: Round Screw-Cap Bottle (Duran)), and 1 g of basalt (geochemical standard material, igneous rock from Nagasaki Prefecture, product name JB-1b) was added to form a mixture, and the container was sealed. The sealed container was stored in an oven at 60°C for 7 days. Thereafter, the supernatant of the mixture was separated so as not to be contaminated with basalt, and this was filtered using a 0.1 μm filter (manufactured by Pall Corporation, trade name: Acrodisc 25 mm w / 0.1 μm Supor STRL 50 / pk). The total dissolved amount of calcium, magnesium, and iron (total amount of ion concentration: total ion concentration: C1) in the filtered supernatant was measured using an ICP (trade name: Agilent 5110 ICP-OES (Agilent Technologies, Inc.)). The ion concentration (ppm) was calculated on a volume basis (mg / L). The total dissolved amounts of calcium, magnesium, and iron were also measured in the same manner for the mixture before storage at 60°C for 7 days. The results are shown in Table 1.

[0047] Additionally, as a sample (Control Example 1) without the use of a dissolution promoter, an aqueous liquid (control aqueous liquid) was prepared by adding 0.1 N hydrochloric acid (Kanto Chemical Co., Inc.) to pure water to adjust the pH to 3.5. The same procedure was followed, except that the control aqueous liquid was used instead of the aqueous liquid to be evaluated. After storing the mixture in an oven at 60°C for 7 days, the total dissolved amounts of calcium, magnesium, and iron (total amount of ion concentration: total ion concentration: C0) were measured. The total dissolved amounts of calcium, magnesium, and iron were also measured for the mixture before storing it at 60°C for 7 days. The results are shown in Table 1.

[0048] The dissolution-promoting ability of the dissolution promoters of Examples 1 to 10 was evaluated according to the following formula. The results are shown in Table 1. If the value of this dissolution-promoting ability is 2 or more, the dissolution-promoting ability can be evaluated as good.

[0049] [Test 1 for evaluating dispersion stability in a geological environment] As in Test 1 for evaluating dissolution promotion, the aqueous silica sols (dissolution promoters) of Examples 1 to 10 were diluted with pure water to a silica concentration of 1.0% by mass, and then 0.1 N hydrochloric acid (Kanto Chemical Co., Inc.) was used to adjust the pH to 3.5 to prepare aqueous liquids (aqueous liquids to be evaluated). 80 g of this aqueous liquid was placed in a sealed container (Duran bottle, manufactured by DWK Life Science, trade name: Round Screw-Cap Bottle (Duran)), and 1 g of basalt (geochemical standard material, igneous rock from Nagasaki Prefecture, trade name JB-1b) was added to form a mixture. The container was then sealed and stored in an oven at 60°C for 7 days. The supernatant of the mixture was then separated so as not to be contaminated with basalt, and filtered using a 0.1 μm filter (manufactured by Pall Corporation, trade name: Acrodisc 25 mm w / 0.1 μm Supor STRL 50 / pk). The average secondary particle size (after the test) of the filtered supernatant was measured by dynamic light scattering (DLS), and the pH (after the test) was also measured. In addition, for each mixture before storage at 60° C. for 7 days (before the test), the average secondary particle size (before the test) of the silica particles was measured by dynamic light scattering (DLS) and the pH (before the test) were measured in the same manner.

[0050] The ratio of the average secondary particle size (DLS average particle size) of the silica particles after the test to the average secondary particle size (DLS average particle size) before the test was calculated as <average secondary particle size of silica particles after the test (DLS average particle size after the test) / average secondary particle size of silica particles before the test (DLS average particle size before the test)>. The results are shown in Table 1. If this average secondary particle size ratio is 1 to 5, it can be evaluated that the dispersion stability in a geological formation environment is good.

[0051] [Solid Acidity Evaluation Test 1] 20 g of the aqueous silica sol (dissolution promoter) of Examples 1 to 10 was placed in a Petri dish, and the water contained in the aqueous silica sol was evaporated to a solid on a hot plate heated to 100°C to obtain a solid acidity measurement sample. 0.20 g of the solid acidity measurement sample was placed in a 20 mL vial, and 5 mL of a methyl red solution previously diluted with 100 mL of toluene per 0.05 g of methyl red was added to obtain a solid acidity measurement solution. In the control example, the measurement solution was obtained using the same process except that no solid acidity measurement sample was added. While stirring the solid acidity measurement solution with a magnetic stirrer, 20 μL of 1-aminodecane (Tokyo Chemical Industry Co., Ltd., purity 98% by mass) was added as a base. Methyl red is red at pH 4.4 or below and yellow at pH 6.2 or above. Even if the supernatant color of the solid acidity measurement solution is yellow, if the solid acidity measurement sample precipitated in the solution is red, it can be determined that the solid acidity measurement solution contains solid acid. To the solution containing 1-aminodecane, 5 ml of methanol and 5 ml of pure water were added, stirred, and allowed to stand for 5 minutes. The color of the sample (precipitate) and the pH of the solution were then measured. If the sample (precipitate) was red or the pH of the solution was 9.2 or less, it was determined to contain a solid acid.

[0052] As shown in Table 1, the aqueous silica sols (dissolution promoters) of Examples 1 to 10 all had a total ion concentration ratio (C1 / C0) of 2 or more relative to Control Example 1, which did not contain a dissolution promoter, confirming their excellent dissolution-promoting ability. In particular, Examples 2 and 3 containing lactic acid, Example 9 containing malonic acid, and Example 10 containing DL-malic acid had a total ion concentration ratio of 10 or more, confirming their excellent dissolution-promoting ability. Furthermore, the aqueous silica sols (dissolution promoters) of Examples 1 to 5, 9, and 10 had DLS average particle size ratios in the range of 1 to 5 before and after storage at 60°C for 7 days. This result confirmed that there was almost no aggregation of the silica particles themselves, and that the aqueous silica sols (dissolution promoters) could penetrate without blocking pores even when injected into underground bedrock. Furthermore, the aqueous silica sols (dissolution promoters) of Examples 1 to 10 all had a solution pH of 9.2 or less after Solid Acidity Evaluation Test 1, and the color of the solid acidity measurement sample (precipitate) was red. This result confirmed that the aqueous silica sol (dissolution promoter) had solid acidity. In particular, Examples 2, 3, 9, and 10, in which the solution pH after Solid Acidity Evaluation Test 1 was 8.0 or less, were confirmed to have strong solid acidity.

Claims

1. A dissolution promoter for basic minerals or rocks containing such minerals, comprising a silica sol containing silica particles (a) having an average secondary particle diameter of 5 to 200 nm as measured by dynamic light scattering and an aqueous medium (b).

2. The dissolution enhancer according to claim 1, wherein a mixture of 80 g of aqueous liquid and 1 g of basalt (geochemical standard substance) is stored at 60°C for 7 days, and the total ion concentration (C) of Ca, Mg, and Fe contained in the supernatant of the mixture is measured, wherein the ratio C1 / C0 of the total ion concentration (C1) when an aqueous liquid of pH 3.5 obtained by adding 0.1 N hydrochloric acid aqueous solution to the dissolution enhancer having a silica particle concentration of 1 mass% is used as the aqueous liquid, to the total ion concentration (C0) when an aqueous liquid of pH 3.5 obtained by adding 0.1 N hydrochloric acid aqueous solution to pure water is used as the aqueous liquid, is 2 to 100.

3. The dissolution enhancer according to claim 1, wherein 1 g of basalt (geochemical standard substance) is added to 80 g of an aqueous liquid of pH 3.5 obtained by adding 0.1 N hydrochloric acid aqueous solution to the dissolution enhancer having a silica particle concentration of 1% by mass, and the mixture is stored at 60°C for 7 days, and then the average secondary particle size of the silica particles in the supernatant of the mixture is measured by dynamic light scattering, and in Dispersion Stability Evaluation Test 1 in a geological formation environment, the ratio of the average secondary particle size of the silica particles after the test to the average secondary particle size before the test (average secondary particle size of silica particles after the test / average secondary particle size of silica particles before the test) is 1 to 5.

4. The dissolution promoter according to claim 1, wherein the silica particles are at least partially coated with a silane compound (c) having a hydrophilic organic group, and the hydrophilic organic group is an epoxy group-containing organic group, an amino group-containing organic group, a hydroxy group-containing organic group, or a carboxy group-containing organic group.

5. The dissolution enhancer according to claim 1, further comprising an organic acid or a salt thereof.

6. The dissolution enhancer of claim 5, wherein the organic acid comprises at least one selected from the group consisting of formic acid, acetic acid, propionic acid, sulfonic acid, sulfinic acid, thiocarboxylic acid, malic acid, tartaric acid, butyric acid, fumaric acid, maleic acid, thioglycolic acid, oxalic acid, malonic acid, succinic acid, and lactic acid.

7. The dissolution promoter according to claim 1, wherein the basic mineral or rock containing the basic mineral contains at least one of Ca, Mg, and Fe.

8. The dissolution promoter according to claim 7, wherein the basic mineral containing at least one of Ca, Mg, and Fe or the rock containing the basic mineral is a rock classified as igneous rock or a group of minerals contained therein.

9. The dissolution promoter according to claim 7, wherein the basic mineral containing at least one of Ca, Mg, and Fe or the rock containing the basic mineral is basalt, gabbro, or a group of minerals contained therein, which are classified as mafic rock, or peridotite, serpentine, komatiite, or a group of minerals contained therein, which are classified as ultramafic rock.

10. A method for promoting the dissolution of basic minerals or rocks containing basic minerals, comprising the step of injecting into an underground layer the dissolution promoter according to claim 1 or a diluted solution of the dissolution promoter in an aqueous medium adjusted to a silica particle concentration of 0.001 to 30 mass %.