MECHANICALLY CARBOXYLATED FLY ASH, METHODS OF ITS PRODUCTION AND USES

Abstract

The present invention relates to mechanically carboxylated fly ash having a BET surface area of ​​less than 50 m² / g and a CO₂ content of more than 1% by weight. The invention further relates to methods of its production and uses thereof, for example, as a filler. The invention also relates to compositions comprising the mechanically carboxylated fly ash and an additional material selected from the group consisting of asphalt, cement, polymer, and combinations thereof, and methods of their production.

Description

MECHANICALLY CARBOXYLATED FLY ASH, METHODS OF ITS PRODUCTION AND USES FIELD OF INVENTION The present invention relates to mechanically carboxylated fly ash. The invention further relates to methods of its production and use, for example, as a filler. The invention also relates to compositions comprising mechanically carboxylated fly ash and an additional material selected from the group consisting of asphalt, cement, polymers, and combinations thereof, and methods of their production. BACKGROUND OF THE INVENTION Concrete is a composite material, comprising an aggregate matrix (typically rock) and a binder (typically Portland cement or asphalt) that holds the matrix together. Concrete is one of the most frequently used construction materials and is said to be the second most widely used material on Earth, after water. To reduce the cost of concrete and the CO2 emissions generated by global cement production, significant research effort has been dedicated to identifying an inexpensive material that can be used as an alternative filler or binder to replace the binding component without adversely affecting the properties of concrete. These secondary cementitious materials are an area of ​​considerable interest within the industry. An example of a widely used cementitious filler is limestone. A comprehensive overview of fillers in cementitious materials can be found in John Vanderley M., et al. “Fillers in cementitious materials — Experience, recent advances and future potential”. Cement and Concrete Research 114 (2018): 65-78. Portland cement production contributes approximately 10% of global carbon dioxide emissions. According to Vanderley et al., traditional mitigation strategies for CO2 emissions in the cement industry are insufficient to ensure the necessary mitigation in a scenario of increasing cement demand. Therefore, the adoption of environmentally risky carbon capture and storage (CCS) has been considered an unavoidable solution by cement industry leaders. Consequently, there remains a need to develop an affordable filler technology that can combine both the CO2 emission reduction achieved by reduced cement production and the CO2 emission reduction achieved by carbon capture technology, and that does not adversely affect the properties of concrete. An objective of the present invention is to provide improved fillers for cement or asphalt binder. A further objective of the present invention is to provide improved fillers for cement or asphalt binder that are inexpensive to produce. An additional objective of the present invention is to provide improved fillers for cement or asphalt binder produced using CO2 storage technology. A further objective of the present invention is to provide improved fillers for the cement or asphalt binder that enhance the properties of the resulting concrete, such as compressive strength. BRIEF DESCRIPTION OF THE INVENTION In a first aspect, the present invention provides mechanochemically carboxylated fly ash having a BET surface area of ​​less than 50 m2 / g and a CO2 content of more than 1% by weight, wherein the CO2 content is determined as the mass loss above 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min and then decreased to ambient temperature at a rate of 15°C / min. As will be shown in the accompanying examples, it was found that when these mechanochemically carboxylated fly ashes are used as a filler in cement, the compressive strength of the resulting concrete increases significantly beyond the values ​​obtained when using pure cement. Furthermore, the time required for strength development decreases. Moreover, a larger quantity of these mechanochemically carboxylated fly ashes can be used as a filler while still achieving acceptable concrete properties. Additionally, the mechanochemical production of fly ash filler relies on a cheap CO2 capture technology platform, so that a filler can be produced in an economically viable way and combines both the CO2 emission reduction achieved by the reduced cement production and the CO2 emission reduction achieved by the carbon capture technology. Furthermore, the durability of concrete produced using the mechanochemically treated fly ash filler was found to be significantly increased. Without wishing to be limited by any single theory, the inventors of this concrete believe this is due to improved micro- and submicroscale hydration, reduced chloride permeability, and / or reduced porosity. Finally, the increased oxygen content compared to untreated raw materials may result in better dispersion in polar solvents and improved compatibility with materials containing epoxy and carboxyl functional groups. In one aspect, the invention provides a method for producing mechanochemically carboxylated fly ash, preferably mechanochemically carboxylated fly ash as described herein, comprising the following steps: a) provide a solid raw material comprising or consisting of fly ash, wherein the solid raw material is a particulate material which has a BET surface area of ​​more than 0.01 m2 / g and a D50 within the range of 0.1-5000 pm; b) provide an oxidizing gas comprising CO2; c) introduce the solid raw material and the oxidizing gas into a mechanical stirring unit; and d) subject the solid raw material to a mechanical stirring operation in the presence of the oxidizing gas in a mechanical stirring unit at an oxidizing gas pressure of more than 1 atm (101.325 kPa) to obtain the mechanochemically carboxylated fly ash. In another aspect, the invention provides mechanochemically carboxylated fly ash obtainable by the method for producing mechanochemically carboxylated fly ash described herein. In another aspect, the Invention provides a composition comprising mechanochemically carboxylated fly ash as described herein and an additional material selected from the group consisting of asphalt, cement, polymers and combinations thereof. In another aspect, the invention provides a method for preparing a composition as described herein, the method comprising the following steps: (i) provide mechanochemically carboxylated fly ash as described herein; (i) provide an additional material selected from the group consisting of asphalt, cement, polymers and combinations thereof; and (iii) combine the mechanochemically carboxylated fly ash from step (i) with the material from step (i). In another aspect, the invention provides a method for preparing concrete, the method comprising the following steps: (i) provide a composition as described herein where the additional material is asphalt or concrete; (II) provide a construction aggregate; and (iii) bring into contact, preferably mix, the composition of step (i) with the construction aggregate of step (i). In another aspect, the invention provides concrete obtainable by the method for preparing concrete described herein. In another aspect, the invention provides for the use of mechanochemically carboxylated fly ash as described herein: • as a filler, preferably as a filler of a material selected from the group consisting of asphalt, cement, polymers and combinations thereof; • as a partial replacement for asphalt or cement in concrete; • to increase the compressive strength of concrete; • to improve the durability of concrete; or • to improve the durability of concrete by reducing chloride permeability and / or porosity. DETAILED DESCRIPTION OF THE INVENTION In a first aspect, the invention provides mechanochemically carboxylated fly ash which has a BET surface area of ​​less than 50 m2 / g and a CO2 content of more than 1% by weight, wherein the CO2 content is determined as the mass loss above 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min and then decreased to ambient temperature at a rate of 15°C / min. According to the invention, the BET surface area, the cumulative BJH desorption surface area of ​​the pores, and the average desorption pore width (4V / A per BET) as referred to herein are determined at a temperature of 77 K using a sample mass of 0.5-1 g. A preferred analytical method for determining the BET surface area, the cumulative BJH desorption surface area of ​​the pores, and the average desorption pore width (4V / A per BET) comprises heating samples to 400°C for one desorption cycle prior to surface area analysis. TGA-MS, as used herein, refers to Thermogravimetric Analysis coupled with mass spectrometry, a technique known to the skilled worker in the prior art. A preferred TGA-MS apparatus configuration for determining the CO2 content of raw materials and mechanochemically carboxylated materials in the context of the present invention is a Setaram TAG 16 TGA / DSC dual-chamber balance coupled to an Ametek Dycor Proline MS using a 0.1-2 mg sample. In preferred embodiments, mechanochemically carboxylated fly ash has one, two, or three, preferably three, of the following characteristics: • a SiOa content of less than 50% by weight (in total weight of mechanochemically carboxylated fly ash); • an Al2O3 content of less than 20% (by total weight of mechanically and chemically carboxylated fly ash); • an Fe2U3 content of more than 10% (by total weight of mechanochemically carboxylated fly ash). In preferred embodiments, mechanochemically carboxylated fly ash has one, two, or three, preferably three, of the following characteristics: • a SI₂ content of less than 30% by weight (in total weight of mechanochemically carboxylated fly ash) preferably more than 40% by weight; • an Al2O3 content of 10% or more (by total weight of mechanochemically carboxylated fly ash) preferably more than 15% by weight; • an Fe2U3 content of less than 40% (by total weight of mechanochemically carboxylated fly ash) preferably more than 30% by weight. In highly preferred embodiments, mechanochemically carboxylated fly ash has one, two, or three, preferably three, of the following characteristics: • a SiO2 content within the range of 30-50% by weight (by total weight of mechanochemically carboxylated fly ash); • an Al2O3 content within the range of 10-20% by weight (by total weight of mechanochemically carboxylated fly ash); • an Fe2U3 content within the range of 10-40% by weight (by total weight of mechanochemically carboxylated fly ash). A preferred method for detecting mineral content, such as SiO2, Al2O3, Fe2O3, or CaO, is by X-ray fluorescence spectroscopy, preferably using a Bruker Tracer 5G. As the expert will understand, the SiO2, Al2O3, Fe2O3, and CaO content of both the raw material and the mechanochemically carboxylated fly ash referred to herein is preferably determined using X-ray fluorescence spectroscopy as described herein. In embodiments of the invention, the particle size distribution of the mechanochemically carboxylated fly ash has one, two, three or all, preferably all, of the following characteristics: • a D10 within the range of 0.005-5 pm, preferably 0.01-1 pm, most preferably 0.1-0.5 pm; • a D50 within the range of 0.5-50 pm, preferably 1-25 pm, most preferably 1-10 pm; • a D90 within the range of 5-200 pm, preferably 20-100 pm, most preferably 30-50 pm; • a D(4:3) within the interval of 1 to 100 pm, preferably 10-25 pm. According to the invention, particle size distribution characteristics such as D10, D50, D90, and D(4:3) are determined by measuring with a laser light diffraction particle size analyzer that utilizes Fraunhofer light diffraction theory, such as the Fritsch Analysette 22 Nanotec or another instrument of equal or better sensitivity, and reporting the data using a volume-equivalent sphere model. As is known to the expert, D50 is the mass median diameter, i.e., the diameter at which 50% of the sample mass is comprised of smaller particles. Similarly, D10 and D90 represent the diameter at which 10% or 90% of the sample mass is comprised of smaller particles, respectively. As is known to the expert, D(4:3) is the volume mean diameter. In embodiments of the invention, the mechanochemically carboxylated fly ash has a density of more than 2.5 g / cm3, preferably more than 2.7 g / cm3, more preferably more than 3 g / cm3. In preferred embodiments of the invention, the mechanochemically carboxylated fly ash has a density of more than 2.5 g / cm3, a D10 of less than 1 pm, a D50 of less than 10 pm, and a D90 of less than 50 pm. In one further aspect, the invention provides a method for producing mechanically carboxylated fly ash, preferably mechanically carboxylated fly ash as described herein, comprising the following steps: a) provide a solid raw material comprising or consisting of fly ash, wherein the solid raw material is a particulate material which has a BET surface area of ​​more than 0.01 m2 / g and a D50 within the range of 0.1-5000 pm; b) provide an oxidizing gas comprising CO2; c) introduce the solid raw material and the oxidizing gas into a mechanical stirring unit; and d) subject the solid raw material to a mechanical stirring operation in the presence of the oxidizing gas in a mechanical stirring unit at an oxidizing gas pressure of more than 1 atm (101.325 kPa) to obtain the mechanochemically carboxylated fly ash. It is within the ability of a person skilled in the art, in light of the guidance provided in this description, to adapt the relevant process parameters so as to obtain mechanochemically carboxylated fly ash having the properties listed herein. In preferred embodiments of the invention, the BET surface area of ​​the mechanochemically carboxylated fly ash is at least 110%, preferably at least 120%, more preferably at least 150% by weight of the BET surface area of ​​the solid raw material. Without wishing to be limited by any theory, the inventors of the present invention believe that the observed increase in the surface area of ​​BET with the mechanochemical carboxylation of fly ash according to the present invention can be largely attributed to an increase in the number of pores, observed by a decrease in the average pore width and an increase in the total pore surface area.Accordingly, in embodiments of the invention, the cumulative BJH desorption surface area of ​​the pores of the mechanically carboxylated fly ash is at least 110%, preferably at least 120%, more preferably at least 150%, of the cumulative BJH desorption surface area of ​​the pores of the solid raw material, and the average desorption pore width (4V / A per BET) of the mechanically carboxylated fly ash is not more than 90%, preferably not more than 85%, more preferably not more than 80%, of the average desorption pore width (4V / A per BET) of the solid raw material. In preferred embodiments of the invention, the FesOa content of the mechanochemically carboxylated fly ash is at least 150%, preferably at least 200%, more preferably at least 250% by weight of the Fe2U3 content of the solid raw material. In preferred embodiments of the invention, the CO2 content of the mechanically carboxylated fly ash is greater than 2% by weight (of the total weight of the mechanically carboxylated fly ash), preferably more than 5% by weight, more preferably more than 7% by weight, wherein the CO2 content is determined as the mass loss above 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min and then decreased back to ambient temperature at a rate of 15°C / min. In highly preferred embodiments of the invention, the CO2 content of the solid raw material is less than 0.5% by weight (of the total weight of the solid raw material), preferably less than 0.2% by weight, more preferably less than 0.1% by weight, wherein the CO2 content was determined as the mass loss above 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min and then decreased back to ambient temperature at a rate of 15°C / min. The term “fly ash,” as used herein, refers to any type of fly ash, including coal fly ash and petroleum fly ash. Without wishing to be limited by any theory, the inventors hereof have found that improved performance can be obtained when the solid feedstock is low in carbonaceous fly ash. Carbonaceous fly ash is a particularly characteristic type of fly ash that constitutes a large portion of petroleum fly ash. Accordingly, in preferred embodiments, the fly ash is coal fly ash, such as lignite fly ash, subbituminous coal fly ash, anthracite coal fly ash, bituminous coal fly ash, and combinations thereof. In highly preferred embodiments of the invention, the solid raw material comprises or consists of fly ash that meets the requirements of ASTM C618 (2019), preferably fly ash that meets the requirements of Class C of ASTM C618 (2019). In certain forms, the solid raw material has a combined content of SiO2, Al2O3 and FeOa of more than 60% by weight (in total weight of the solid raw material), preferably greater than 70% by weight, more preferably greater than 75% by weight. Without wishing to be limited by any theory, the inventors of the present invention have found that improved mechanochemical carboxylation results and filler performance are obtained when the raw material comprises at least some CaO. Accordingly, in embodiments of the invention, the solid raw material comprises more than 0.5% by weight (of the total weight of the solid raw material), preferably more than 1% by weight, and more preferably more than 3% by weight CaO. In preferred embodiments of the invention, the solid raw material comprises more than 5% by weight (of the total weight of the solid raw material) or more than 8% by weight CaO. In embodiments of the invention, the particle size distribution of the solid raw material has one, two, three or all, preferably all, of the following characteristics: • a D10 within the range of 0.1-50 pm, preferably 0.5-20 pm, most preferably 1-10 pm; • a D50 within the range of 1-200 pm, preferably 5-100 pm, most preferably 10-50 pm; • a D90 within the range of 50-700 pm, preferably 50-500 pm, more preferably 60-400 pm; • a D(4:3) within the interval of 10-200 pm, preferably 20-130 pm. In embodiments of the invention, the oxidizing gas provided in step (b) comprises more than 80 mol% CO2, preferably more than 95 mol% CO2. In preferred embodiments of the invention, the oxidizing gas provided in step (b) comprises more than 80 mol% CO2, preferably more than 95 mol% CO2 and less than 1000 ppm (v / v) H2O, preferably less than 100 ppm (v / v) H2O. In embodiments of the invention, step (d) is performed at a pressure of more than 3 atm (303.975 kPa), preferably more than 6 atm (607.95 kPa). In embodiments of the invention, step (d) is performed at a temperature of less than 100°C, preferably less than 60°C, more preferably less than 30°C. In embodiments of the invention, step (d) is performed for at least 1 hour, preferably for at least 4 hours, more preferably for at least 8 hours. In preferred embodiments of the invention, step (d) is carried out at a pressure of more than 3 atm (303.975 kPa), preferably more than 6 atm (607.95 kPa); at a temperature of less than 100°C, preferably less than 60°C, more preferably less than 30°C and for at least 1 hour, preferably for at least 4 hours, more preferably for at least 8 hours. The inventors hereof have further found that the mechanochemical carboxylation methods described herein can be advantageously carried out without employing additional oxidizing agents such as acids. Accordingly, the mechanochemical carboxylation methods described herein are preferably carried out without employing a strong acid, and preferably without employing any additional oxidizing agent other than the oxidizing gas provided in step (b). In preferred embodiments of the invention, the mechanochemical stirring operation of step (d) comprises crushing, grinding, mixing, stirring (low-speed or high-speed stirring), shearing (high-torque shearing), stirring, mixing, a fluidized bed, or ultrasonication, preferably crushing, grinding, mixing, stirring (low-speed or high-speed stirring), shearing (high-torque shearing), and ultrasonication. The inventors hereof have found that the mechanochemical carboxylation process is facilitated if the mechanochemical stirring operation of step (d) is carried out in the presence of inert crushing or grinding media, preferably inert balls or beads. A preferred inert material is stainless steel. In preferred embodiments of the invention, step (d) is carried out in the presence of a catalyst, preferably a transition metal oxide catalyst, more preferably a transition metal dioxide catalyst, more preferably a transition metal dioxide catalyst selected from the group consisting of iron oxides, cobalt oxides, ruthenium oxides, titanium oxides and combinations thereof. Accordingly, as will be understood from the foregoing, in highly preferred embodiments of the invention, step (d) comprises a mechanical stirring operation, preferably crushing, grinding, mixing, stirring (low-speed or high-speed stirring), shearing or cutting (high-torque shearing), stirring, mixing, a fluidized bed, or ultrasonication, in the presence of inert crushing or grinding media and a transition metal oxide catalyst. The inventors hereof have found it advantageous, with a view to the efficiency of the mechanochemical carboxylation (e.g., reaction time, CO2 absorption, and particle size reduction), to employ inert media as described herein before coating with the transition metal oxide catalyst. In another aspect, the invention provides mechanochemically carboxylated fly ash obtainable by the method for producing mechanochemically carboxylated fly ash described herein. As the expert will understand from the present description, the mechanochemically carboxylated fly ash of the present invention constitutes an excellent filler for many applications, combining distinct mechanical properties with an inexpensive CO2 capture technology. Accordingly, in another aspect the invention provides a composition comprising mechanochemically carboxylated fly ash as described herein and an additional material selected from the group consisting of asphalt, cement, polymers and combinations thereof. In certain embodiments, the additional material is a polymer selected from thermoplastic and thermosetting polymers. In preferred embodiments, the additional component is a polymer selected from the group consisting of epoxy resin, phenol-formaldehyde resin, polyethylene terephthalate, aromatic polyamide, polyacrylonitrile, polyimide, aromatic polyester, polyethylene, polypropylene, polyurethane, polyisocyanurate, polyamide, polyether, polyester, polyhydroxyalkanoate, polylactic acid, polyvinylidene fluoride, polyvinyl acetate, polyvinyl chloride, polystyrene, polytetrafluoroethylene, acrylonitrile butadiene styrene, nitrile rubber, styrene butadiene, ethylene vinyl acetate, and combinations thereof. The term “polymer” as used herein includes copolymers, such as block copolymers. In highly preferred modalities, the additional material is selected from cement, asphalt, or combinations thereof. According to the invention, the cement can be either hydraulic or non-hydraulic cement. In preferred embodiments, the cement is a hydraulic cement, such as Portland cement. In highly preferred embodiments of the invention, the cement is one of the cements defined in EN197-1 (2011), preferably Portland cement as defined in EN197-1 (2011). In embodiments of the invention, the composition comprises more than 0.1% by weight (of the total weight of the composition), preferably more than 1% by weight, more preferably more than 5% by weight of the mechanically and chemically carboxylated fly ash and / or more than 0.1% by weight (of the total weight of the composition), preferably more than 1% by weight, more preferably more than 20% by weight of the additional material. In embodiments of the invention, the composition comprises less than 60% by weight (of the total weight of the composition), preferably less than 50% by weight, more preferably less than 45% by weight of the mechanochemically carboxylated fly ash and / or less than 95% by weight (of the total weight of the composition), preferably less than 90% by weight, more preferably less than 80% by weight of the additional material. In embodiments of the invention, the composition is provided where the weight:weight ratio of the mechanochemically carboxylated fly ash to the additional material is within the range of 1:9 to 2:1, preferably within the range of 1:8 to 1:1, most preferably within the range of 1:6 to 5:6. In embodiments of the invention, the composition comprises 5-70% by weight (of the total weight of the composition), preferably 10-60% by weight, more preferably 20-50% by weight of the mechanically and chemically carboxylated fly ash and 30-95% by weight (of the total weight of the composition), preferably 40-90% by weight, preferably 50-80% by weight of the additional material. In embodiments of the invention, the composition comprises less than 5% by weight (of the total weight of the composition) of water, preferably less than 1% by weight, more preferably less than 0.1% by weight. The amount of water can be suitably determined as the mass loss up to 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min. In embodiments of the invention, the composition consists of the mechanically carboxylated fly ash and the additional material. In another aspect, the invention provides a method for preparing a composition as described herein, the method comprising the following steps: (i) provide mechanochemically carboxylated fly ash as described herein; (i) provide an additional material selected from the group consisting of asphalt, cement, polymers and combinations thereof; (iii) combining the mechanochemically carboxylated fly ash from step (i) with the material from step (i). In another aspect, the invention provides a method for preparing concrete, the method comprising the following steps: (i) provide a composition as described herein where the additional material is asphalt or cement; (ii) provide a construction aggregate; (iii) bring into contact, preferably mix the composition of step (i) with the building aggregate of step (i). In another aspect the invention provides concrete obtainable by the method for preparing concrete described herein. In embodiments of the invention, the construction aggregate is selected from the group consisting of sand, gravel, crushed stone, slag, recycled concrete, clay, pumice, perlite, vermiculite, and combinations thereof. In preferred embodiments, the construction aggregate is one of the aggregates defined in EN 13043 (2002), EN 13383 (2019), EN 12620 (2013), or EN 13242 (2013), preferably the construction aggregate is one of the aggregates defined in EN 12620 (2013). In preferred embodiments of the invention, step (iii) further comprises contacting, preferably mixing, the composition of step (i) with the building aggregate of step (i) and water. According to the invention, the composition of step (i), the building aggregate of step (i), and water can be contacted, preferably mixed substantially, simultaneously or gradually, wherein the composition of step (i) is first contacted, preferably mixed, with water, before being contacted, preferably mixed, with the building aggregate of step (i). In another aspect, the invention provides for the use of mechanochemically carboxylated fly ash as described herein: • as a filler, preferably a filler in a material selected from the group consisting of asphalt, cement, polymers and combinations thereof; • as a partial replacement for asphalt or cement in concrete; • to increase the compressive strength of concrete; • to improve the durability of concrete; or • to improve the durability of concrete by reducing chloride permeability and / or porosity. The expert shall understand that the embodiments of the invention described herein in the context of mechanically carboxylated fly ash or composition, especially with regard to the characteristics of the mechanically carboxylated fly ash or with regard to the characteristics of the additional material, are equally applicable to the method for preparing the composition described herein, the method for preparing concrete described herein, and the uses of mechanically carboxylated fly ash described herein. Examples The BET surface area, the cumulative BJH desorption surface area of ​​the pores, and the average desorption pore width (4V / A per BET) were determined at a temperature of 77 K using a sample mass of 0.5-1 g where the samples were heated to 400°C for one desorption cycle before the surface area analysis. Particle Size Distribution measurements were carried out on a Fritsch Analysette 22 Nanotec using Fraunhofer diffraction theory. The mineral content (S1O2, ALO3, Fe20s and CaO) was determined by X-ray fluorescence spectroscopy using a Bruker Tracer 5G. The CO2 content was determined as the mass loss above 120°C measured by TGAMS using a temperature path, where the temperature was increased from room temperature to 800°C at a rate of 10°C / min and then decreased to room temperature at a rate of 15°C / min using a Setaram TAG 16 TGA / DSC dual chamber balance coupled to an Ametek Dycor Proline MS and a 0.1-2 mg sample. Compressive strength was tested in accordance with ISO 1920:2005, part 4. Example 1 Mechanochemically carboxylated fly ash was produced by inserting a 10 g sample of fly ash into a pressure cell containing 500 g of inert media (stainless steel balls) coated with titanium dioxide. The cell was pressurized to 1 MPa (9.87 atm), placed in a high-energy ball mill, and rotated at 5000 RPM for 48 hours. The reaction was initiated at room temperature, and no heating or cooling was applied. Example 2 Two fly ash samples, A and B, were mechanochemically carboxylated (“treated”) using a process according to Example 1, where the mechanical agitation and CO2 pressure were adjusted to obtain a product with the characteristics shown in the table below. Raw sample A was obtained from the Gennessee Coal Plant, Alberta, Canada, and meets the requirements of ASTM C618 (2019) Class F. Raw sample B was obtained from the Civita Vecchia Coal Plant, Italy. Raw sample C was obtained from the Cordemais Coal Plant, France. The raw fly ash from samples B and C is generally considered lower-grade fly ash, which is suitable for use as a concrete filler at concentrations above 10% by weight. A - raw A - treated B - raw B - treated C - raw C - treated Density (g / cm3) 2.09 3.06 2.36 2.79 2.25 2.33 CO2 (% by weight) <0.1 9 <0.1 6 0.1 4 SiO2 (% by weight) 56.39 39.45 54.71 45.92 53.76 45.95 Al2O3 (% by weight) 23.71 16.31 22.42 18.91 25.23 21.37 Fe2O3 (% by weight) 3.55 24.74 6.59 14.63 5.58 15.08 CaO (% by weight) 9.3 6.4 5.11 4.28 3.58 3.08 D10 (pm) 3.8 0.2 2.6 0.2 6.5 0.1 D50 (pm) 29.6 8.4 14.9 7 39.2 5.5 D90 (pm) 143.3 46.9 68 37.8 358 35.2 D(4;3) (pm) 56.51 20.38 26.87 13.8 114.83 15.11 BET surface area (m2 / g) 16.1858 32.2091 2.95 5.55 5.5 9.8 Average desorption pore width (4V / A per BET) 12.3 8.6 ndndndnd Cumulative BJH desorption surface area of ​​the pores (m2 / g) 24.1221 43.9139 ndndndnd nd = not determined Mechanochemically carboxylated fly ash A and B were used as filler by mixing with Portland cement at a weight:weight ratio of 1:5 (filler:cement). The mixtures obtained from the mechanically carboxylated fly ash and Portland cement were each mixed with fine gravel and water (using identical ratios for each sample) to obtain a concrete slurry. The compressive strength of the resulting concrete was monitored after 2, 7, and 28 days. For comparison, similar concrete slurry was prepared using samples A and B of raw fly ash and pure Portland cement. Compressive strength (MPa) 2 days 7 days 28 days A - Raw 26.6 39.9 53.0 B - Raw 26.3 39.3 54.6 C - Raw 24.9 36.2 49 A - Treated 32.2 42.6 64.1 B - Treated 32.7 42.7 66.2 C - Treated 30.3 45.4 62.8 Portland cement 34.1 48.1 60.9 As can be seen from the compressive strength measurements, the mechanochemically carboxylated mineral fillers of the present invention provide an unexpectedly large increase in performance compared to raw materials (such as fly ash). Furthermore, it was surprisingly found that the mechanochemically carboxylated mineral fillers of the present invention outperform even pure cement mixtures.

Claims

1. Mechanochemically carboxylated fly ash which has a BET surface area of ​​less than 50m2 / g and a CO2 content of more than 1% by weight, characterized in that the CO2 content is determined as the mass loss above 120°C measured by TGA-MS using a temperature path where the temperature was increased from ambient temperature to 800°C at a rate of 10°C / min and then decreased to ambient temperature at a rate of 15°C / min.

2. Mechanochemically carboxylated fly ash according to claim 1, further characterized in that it has one, two or three, preferably three, of the following characteristics: • a SiO2 content within the range of 30-50% by weight (in the total weight of the mechanochemically carboxylated fly ash); • an Al2O3 content within the range of 10-20% by weight (in the total weight of the mechanochemically carboxylated fly ash); • a Fe2Os content within the range of 10-40% by weight (in the total weight of the mechanochemically carboxylated fly ash).

3. The mechanically carboxylated fly ash according to claim 1 or 2 is further characterized in that it has one, two, three or all, preferably all, of the following features: • a D10 within the range of 0.005-5 pm, preferably 0.01-1 pm, more preferably 0.1-0.5 pm; • a D50 within the range of 0.5-50 pm, preferably 1-25 pm, more preferably 1-10 pm; • a D90 within the range of 5-200 pm, preferably 20-100 pm, more preferably 30-50 pm; • a D(4:3) within the range of 1-100 pm, preferably 10-25 pm.

4. A method for producing mechanochemically carboxylated fly ash as claimed in any of claims 1 to 3, characterized in that it comprises the following steps: a) providing a solid raw material comprising or consisting of fly ash, wherein the solid raw material is a particulate material having a BET surface area of ​​more than 0.01 m2 / g and a D50 within the range of 0.1-5000 pm; b) providing an oxidizing gas comprising CO2; c) introducing the solid raw material and the oxidizing gas into a mechanical stirring unit; and d) subjecting the solid raw material to a mechanical stirring operation in the presence of the oxidizing gas in the mechanical stirring unit at an oxidizing gas pressure of more than 1 atm (101.325 kPa) to obtain the mechanochemically carboxylated fly ash.

5. The method according to claim 4, further characterized in that the solid raw material has a combination of SiO2, Al2O3 and Fe2U3 content of more than 60% by weight (in total weight of the solid raw material), preferably more than 70% by weight, more preferably more than 75% by weight.

6. The method according to claim 4 or 5, further characterized in that the solid raw material comprises or consists of fly ash which meets the requirements of ASTM C618, more preferably fly ash which meets the requirements of class F of ASTM C618.

7. The method according to any of claims 4 to 6, further characterized in that the oxidizing gas provided in step (b) comprises more than 90 mol% CO2, preferably more than 95 mol% CO2.

8. The method according to any of claims 4 to 7, further characterized in that step (d) is carried out • at a pressure of more than 3 atm (303.975 kPa), preferably more than 6 atm (kPa); • at a temperature of less than 100°C, preferably less than 60°C, more preferably less than 30°C; and / or • for at least 1 hour, preferably for at least 4 hours, more preferably at least 8 hours.

9. The method according to any of claims 4 to 8, further characterized in that the mechanochemical stirring operation of step (d) comprises mixing, stirring (low-speed stirring or high-speed stirring), shearing or cutting (high-torque shearing), stirring, mixing, a fluidized bed or ultrasonication, preferably mixing, stirring (low-speed stirring or high-speed stirring), shearing or cutting (high-torque shearing) or ultrasonication.

10. The method according to any of claims 4 to 9, further characterized in that step (d) is carried out in the presence of a catalyst, preferably a transition metal oxide catalyst, more preferably a transition metal dioxide catalyst, more preferably a transition metal dioxide catalyst selected from the group consisting of iron oxides, cobalt oxides, ruthenium oxides, titanium oxides and combinations thereof.

11. The mechanochemically carboxylated fly ash obtainable by the method in accordance with any of claims 4 to 10.

12. A composition characterized in that it comprises mechanically and chemically carboxylated fly ash according to any of claims 1 to 3 or 11 and an additional material selected from the group consisting of asphalt, cement, polymers and combinations thereof, preferably cement, more preferably Portland cement.

13. The composition according to claim 12, further characterized in that the weight:weight ratio of the mechanically carboxylated fly ash to the additional material is within the range of 1:9 to 2:1, preferably within the range of 1:8 to 1:1, more preferably within the range of 1:6 to 5:

6.

14. A concrete obtainable by a method for preparing concrete comprising said method characterized in that it comprises the following steps: (i) providing a composition according to claim 12 or 13, wherein the additional material is asphalt or concrete; (ii) providing a construction aggregate; (iii) contacting, preferably mixing, the composition of step (i) with the construction aggregate of step (ii).

15. Use of mechanochemically carboxylated fly ash according to any of claims 1 to 3 or 11: • as a filler, preferably as a filler in a material selected from the group consisting of asphalt, cement, polymers and combinations thereof; • as a partial replacement of asphalt or cement in concrete; • to increase the compressive strength of concrete; • to improve the durability of concrete; or • to improve the durability of concrete by reducing chloride permeability and / or porosity.