Methods for optimizing the rate of carbon mineralization in alkaline materials at earth surface conditions

Abstract

Methods of capturing carbon dioxide in an alkaline material through a mineralization reaction are provided. Temperature and / or relative moisture can be controlled and / or cycled to maximize a rate of capture of carbon dioxide through the mineralization reaction as the mineralization reaction proceeds through different stages.

Description

METHODS FOR OPTIMIZING THE RATE OF CARBON MINERALIZATION IN ALKALINE MATERIALS AT EARTH SURFACE CONDITIONSCross-Reference to Related Applications

[0001] This application claims priority to, and the benefit of, United States provisional patent application No. 63 / 569923 filed 26 March 2024, the entirety of which is incorporated by reference herein for all purposes.Technical Field

[0002] Some embodiments relate to methods of mineralizing carbon using alkaline materials. Some embodiments relate to methods of mineralizing carbon at atmospheric pressure using alkaline materials.Background

[0003] Historically, work in the field of carbon mineralization has focused on reacting alkaline minerals and / or alkaline waste with carbon dioxide at high temperatures (>150 °C) and pressures (>50 bar pCC>2) in the presence of excess water (i.e. slurries, Gerdemann et al., 2007). While this approach yields high rates of mineralization, the energy and infrastructure requirements of such a process are cumbersome and may explain why such a system has not been successfully implemented at significant scale.

[0004] Several approaches for Earth surface mineralization have been proposed in the prior art. Myers et al. (2019, 2022) performed experiments in which dry alkaline materials are placed into high humidity environments and allowed to react with gas streams with varying CO2 concentrations from atmospheric, 0.04 vol%, to 20 vol%. In this work, the high humidity environment is envisioned as a conventional greenhouse at one end of which are placed large fans to continuously replenish the air. Within the greenhouse, the alkaline minerals are placed on horizontal trays. Myers et al. (2019) and Myers and Nakagaki (2020) conclude that the maximum rate of reaction will occur at 90-100 % relative humidity (RH).Additionally, Myers et al. (2019) argue that, in the context of natural minerals such as olivine and serpentine, amorphization of the mineral structure will decrease the rate of reaction withCO2as compared to intact crystals, although this may not be generally applicable to all minerals such as MgO and Mg(OH)2. Amorphization is hypothesized by these authors to decrease the rate at which metal cations (Mg2+or Ca2+) can diffuse through the carbonate product layer that forms as a result of the mineralization reaction (Myers et al., 2022).

[0005] Another approach to carbon mineralization at Earth surface conditions is presented by McQueen et al. (2020). In this study, the authors propose an ‘oxide looping’ system wherein primary magnesium carbonate (MgCOs) is calcined to form magnesium oxide (MgO) and then exposed to atmospheric CO2and allowed to mineralize for up to one year. Exposure to the atmosphere is performed by layering the MgO up to 0.1 m thick directly on the land surface. Upon completion of mineralization, the secondary MgCOs is calcined, the resulting CO2captured and securely sequestered, and the MgO is ‘looped’ by exposing it once again to atmospheric CO2. Mohammad et al. (2020) and Erans et al. (2020) describe a similar system to that of McQueen et al. (2020), with the exception that CaO is used in lieu of MgO. Patent publication WO 2022 / 187336 A1 builds upon the work of McQueen et al (2020) by teaching that for maximum reaction, alkaline minerals (e.g., MgO, Mg(OH)2, CaO and Ca(OH)2) should 1) be placed on vertically stacked trays open to the surrounding environment and 2) be maintained at a moisture content of between 3-50 wt% H2O. The water content is controlled by spraying water directly onto the alkaline minerals.

[0006] In the examples given above, the relationship between instantaneous rate of mineralization, temperature, relative humidity, water content, salt additives, and non- reactive fillers has not been explored.

[0007] In view of the foregoing, new processes should be developed to allow for economical carbon mineralization at Earth surface conditions.

[0008] The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.Summary

[0009] In one aspect, a method of capturing carbon dioxide in an alkaline material through a mineralization reaction is provided. The alkaline material is exposed to a controlledmoisture level and a temperature of the controlled system is cycled at least once per day between a low temperature value and a high temperature value.

[0010] In one aspect, the alkaline material is placed in a controlled system, and during a first stage of the mineralization reaction the relative humidity of the controlled system is maintained at a moderate level (e.g. between about 35% and about 85% relative humidity) and the temperature of the controlled system (e.g. the air temperature) is cycled between a low temperature value and a high temperature value at least once per day. During a second stage of the mineralization reaction the relative humidity of the controlled system is maintained at a relatively high level (e.g. between about 85% and about 100%), and the temperature of the controlled system (e.g. the air temperature) is cycled between a low temperature value and a high temperature value at least once per day. During a third stage of the mineralization reaction, the temperature of the controlled system (e.g. the air temperature) is cycled between a low temperature value and a high temperature value at least once per day, and while the temperature of the controlled system is increasing, the relative humidity of the controlled system is decreased to a low level (e.g. less than about 30%) and while the temperature of the controlled system is increasing, the relative humidity of the controlled system is increased to a relatively high level (e.g. above about 85%).

[0011] In some aspects, the reaction conditions are moved from the first stage to the second stage upon a determination that the day-over-day average rate of carbon dioxide capture by the alkaline material has been constant for at least one day. In some aspects, the reaction conditions are moved from the second stage to the third stage upon a determination that the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with decreasing temperature. In some aspects, the third stage is considered to be complete when the rate of carbon dioxide capture by the alkaline material is approximately net zero for at least one day. In some aspects, after it has been determined that the alkaline material has reached a desired level of carbon dioxide saturation, the alkaline material is sent for disposal. In some aspects, if it is determined that the alkaline material has not reached a desired level of carbon dioxide saturation, the alkaline material is reground, optionally with a decrease in Pso of at least 10 pm, and the reground alkaline material is returned to the first stage of the mineralization reaction.

[0012] In one aspect, a method of capturing carbon dioxide in an alkaline mineral through a mineralization reaction conducted in a controlled system is provided. Water is added to thealkaline material, optionally in an amount of between about 10% and about 40% by weight, and the temperature (e.g. air temperature) of the controlled system is cycled between a low temperature value and a high temperature value at least once per day. In some aspects, the relative humidity of the controlled system is maintained at a relatively high level (e.g. between about 85% and about 100%) while the temperature is cycled. Once it is determined that there has been no net capture of carbon dioxide for at least one day, the alkaline material can be evaluated to determine if it has been saturated to a desired extent with carbon dioxide. If the alkaline material has been saturated to a desired extent with carbon dioxide, the alkaline material can be sent for disposal. If the alkaline material has not been saturated to a desired extent with carbon dioxide, the alkaline material can be reground and / or additional water can be added to bring the water content of the alkaline material back up into the range of about 10% to about 40% by weight and the steps of maintaining humidity of the controlled system at a relatively high level and cycling the temperature of the controlled system between a low temperature value and a high temperature value at least once per day can be repeated.

[0013] In some aspects, the alkaline material is subjected to controlled reaction conditions as described above for one or more of the first, second and third reaction stages. Once it is determined that the average rate of carbon dioxide capture by the alkaline material has been approximately net zero for at least one day, water is added to the alkaline material, optionally in an amount of between about 10% and about 40% by weight, and the air temperature of the controlled system is cycled between a low temperature value and a high temperature value at least once per day while a relatively high level of relative humidity (e.g. between about 85% and about 100%) is maintained. Cycling can continue until it is determined that there has been no net capture of carbon dioxide for at least one day and the alkaline material can be evaluate for saturation and disposed of (if saturated) or reground or additional water added to bring the water content of the alkaline material back up into the range of between about 10% and about 40% by weight so that temperature cycling under high relative humidity conditions can be repeated.

[0014] In some aspects, inorganic chemical salts and / or non-reactive filler material is added to the alkaline material to help enhance the mineralization of carbon dioxide.

[0015] Further aspects will become clear by reference to the exemplary embodiments described and illustrated herein.Brief Description of the Drawings

[0016] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[0017] FIG. 1A shows an example embodiment of a method for capturing CO2 from air.

[0018] FIG. 1 B shows a second example embodiment of a method for capturing CO2 from air.

[0019] FIG. 1C shows a third example embodiment of a method for capturing CO2 from air.

[0020] FIG. 1 D shows a fourth example embodiment of a method for capturing CO2 from air.

[0021] FIG. 2A shows the rate of capture and cumulative wt% CO2 captured for activated serpentinite samples. FIG. 2B shows the rate of capture and cumulative wt% CO2 captured for fresh, crystalline serpentinite samples.

[0022] FIG. 3A shows the level of mineralized atmospheric carbon in identically activated serpentine at 5, 20 and 40°C after a period of 30 days. FIG. 3B shows the level of mineralized atmospheric carbon in identically activated serpentine at 5 and 10°C after a period of 35 days.

[0023] FIGs. 4A and 4B show a comparison of the rate of carbon dioxide capture into activated serpentine at a constant temperature but varying humidity. FIG. 4A shows the first three hours of CO2 fluxes while FIG. 4B shows CO2 fluxes at 21 to 27 hours.

[0024] FIG. 5A shows data from an experiment in which dry MgO was placed in either 100% or 75% relative humidity conditions and the temperature was cycled (diurnally) between 10-20 °C for fourteen days. FIG. 5B shows data from days 15 to 27 of the 100% relative humidity experiment.

[0025] FIGs. 6A and 6B show the rate of CO2 capture in a microwave activated serpentinite as a function of time.

[0026] FIG. 7 shows the rate of CO2 capture in a sample that experiences a fixed relative humidity of 100% compared to a sample that experiences a change in humidity from 33% to100%.

[0027] FIG. 8 shows the effect of adding water to a sample experiencing a stagnation in CO2 capture rate.

[0028] FIG. 9 shows the rate of CO2 capture in a sample without additives compared to the same sample with inorganic salt additives (i.e. NaCI and NaHCOa). Relative humidity is increased from 33% to 100% at about 6 days.

[0029] FIG. 10 shows the rate of CO2 capture in a sample without non-reactive filler compared to the same sample with non-reactive filler (i.e. 20% quartz).

[0030] FIG 11 shows the rate of CO2 capture in a sample under a temperature cycling regime as compared to the same sample under a constant temperature regime. Both samples contained 20 wt% water for the duration of the experiment.Description

[0031] Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0032] The inventors have now discovered new relationships between the instantaneous rate of mineralization, temperature, relative humidity, water content and inorganic salt additives when mineralizing carbon at atmospheric conditions. The inventors’ data demonstrate that the instantaneous rate of CO2 capture from air into ‘humid’ alkaline materials (dry material placed into variably humid environments or subjected to controlled addition of water) does not conform to the models proposed in the existing literature, and varies depending on the stage of mineralization. A new method and system that can more effectively mineralize carbon at Earth surface conditions is provided. The method includes subjecting alkaline materials to differing conditions with respect to moisture levels (including relative humidity), temperature and water content as the mineralization reaction proceeds through different stages. Without being bound by theory, the addition of non-reactive fillers such as silica can increase porosity and improve water transport, while the addition ofinorganic salt additives, such as NaCI and NaHCOs, can affect water retention, cation solubility, pH and CO2 transport.

[0033] As used herein, “Earth surface conditions” refers to ambient temperature and atmospheric pressure prevailing at a particular location on Earth. It will be apparent to one skilled in the art that the specific ambient temperature and atmospheric pressure might vary depending on the specific location on Earth and other factors such as the specific season or prevailing weather conditions.

[0034] The inventors have now determined that the mineralization of carbon dioxide in alkaline materials proceeds through potentially three different stages as the mineralization reaction proceeds, and that different conditions of relative humidity, temperature, and water content are desirable at each of these different stages to maximize the rate of mineralization of the carbon dioxide at ambient temperatures and pressures. The inventors have further found that the addition of inorganic salts or non-reactive inorganic material can also influence the mineralization of carbon dioxide in alkaline materials.

[0035] In some embodiments, the system in which the mineralization process occurs can refer to the alkaline materials themselves together with the airspace directly above the alkaline materials, extending from about 1 cm to about 10 m above the alkaline material. In some embodiments, the system in which the mineralization process occurs is a controlled system. In some embodiments, the controlled system is a greenhouse or other structure that allows for better control of the temperature, humidity and water content of the system. As used herein, “greenhouse” encompasses not only traditional greenhouse structures e.g. as used for agriculture or horticulture, but also encompasses any structure that attempts to achieve a similar effect of enabling the admission of light and trapping of heat produced by that light within the structure. In some embodiments, the controlled system is not specifically enclosed, but represents a region of space in which active efforts are taken to control the temperature, humidity and water content of the space, for example by shading or exposure to sunlight, or spraying moisture within the controlled system.

[0036] In some embodiments, when referring to a temperature of the system, what is referred to is the air temperature of the system. It will be appreciated by those skilled in the art that the air temperature will change more rapidly than the bulk temperature of thereaction mixture, so that the temperature of the alkaline material itself may be slightly different than the measured air temperature of the system.

[0037] In some embodiments, the alkaline materials to be used for mineralization can be spread in a thin layer, e.g. about 1 cm deep, or in thicker plots up to about 1 m deep, including any value or subrange therebetween, e.g. about 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80 or 90 cm deep. In some embodiments, the rate of CO2 capture into the alkaline materials is measured. In some embodiments, the temperature (e.g. air temperature) and relative humidity of the system are also monitored using standard measurement techniques, optionally both within the mass of the alkaline material and within the airspace above the alkaline material. In some embodiments, the rate of CO2 capture into the alkaline materials, temperature and relative humidity are measured continuously. In some embodiments, the rate of CO2 capture into the alkaline materials, temperature and / or relative humidity are measured periodically, e.g. occurs at least once every six hours, or optionally more frequently, e.g. at least once every four hours, every three hours, every two hours, every one hour, every half hour, or the like. In some embodiments, temperature, relative humidity and / or water content are adjusted in any appropriate manner based on the measured values for these parameters to maintain or adjust temperature, relative humidity and / or water content as desired at a particular stage of the mineralization reaction, as explained further below.

[0038] In some embodiments, the alkaline material is provided to the controlled system in a dry form. In some embodiments, the alkaline material can be provided in other forms, e.g. deposited as a slurry or the like, and the alkaline material can be permitted to gradually dry over time or be subjected to other processing steps to ensure the alkaline material is in the desired state for the mineralization reaction to occur.

[0039] A first stage of the mineralization process of an alkaline material is characterized by a relatively high rate of CO2 capture that is generally decreasing over time. During the first stage of the carbon mineralization reaction, relative humidity is kept at a moderate level, e.g. between about 35% and about 85%, including between about 50% and about 85% relative humidity, including any value or subrange therebetween, e.g. about 35, 40, 45, 50, 55, 60, 65, 70, 75 or 80% relative humidity. Further, in some embodiments during the first stage of the carbon mineralization reaction, the temperature of the alkaline material is cycled at least once per day (i.e. diurnally). In some embodiments, during the first stage ofthe carbon mineralization reaction the temperature of the alkaline material is cycled by increasing or decreasing the air temperature of the system at a rate of at least about 0.75 °C per hour. After the day-to-day average rate of CO2 capture by the alkaline material has been constant for at least about one day, the alkaline material is considered to have moved to stage 2 of the carbon mineralization reaction.

[0040] A second stage of the mineralization process of an alkaline material is characterized by the rate of CO2 capture increasing with increasing temperature. During the second stage of the carbon mineralization reaction, relative humidity is kept at a high level, e.g. between about 85% and about 100% relative humidity, including any value or subrange therebetween e.g. 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99% relative humidity. Further, during the second stage of the carbon mineralization reaction, the temperature of the alkaline material is cycled at least once per day (e.g. at least diurnally) between a high temperature and a low temperature. In some embodiments, during the second stage of the carbon mineralization reaction the temperature of the alkaline material is cycled by increasing or decreasing the air temperature of the system at a rate of at least about 0.75 °C per hour. In some embodiments, to maximize the rate of CO2 capture during the second stage, the rate of the temperature change is maximized as much as possible. In some embodiments, to maximize the rate of CO2 capture during the second stage, the amplitude of the air temperature change between the high temperature and the low temperature is maximized as much as possible. In some embodiments, the temperature of the alkaline material is cycled three, four, five or more times per day. After the instantaneous rate of CO2 capture by the alkaline material is determined to be increasing with decreasing temperature, the alkaline material is considered to have moved to stage 3 of the carbon mineralization reaction.

[0041] A third stage of the mineralization process of the alkaline material is characterized by the rate of CO2 capture increasing with decreasing temperature. In the third stage, the temperature to which the alkaline material is exposed is minimized to the extent reasonably possible, although the temperature of the alkaline material is maintained above at least 0 °C. Steps that may be taken to minimize the temperature to which the alkaline material is exposed include: shading the alkaline material from sunlight, allowing venting of cool air into an enclosure containing the alkaline material at night time, preventing entry of warm air into the enclosure containing the alkaline material during the day time, and so on. Thetemperature to which the alkaline material is exposed is cycled over a time period at least once per day (e.g. diurnally) between a high temperature value and a low temperature value, and the humidity to which the alkaline material is exposed is also cycled over that time period (e.g. diurnally). The humidity to which the alkaline material is exposed is cycled between a high level of between about 85% to about 100% relative humidity (including any value or subrange therebetween, e.g. about 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99% relative humidity) and a low humidity level of between about 30% to about 50%, including between about 35% to about 50%, relative humidity (including any value or subrange therebetween, e.g. about 31 , 32, 33, 34, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48 or 49% relative humidity). The timing of the cycling of the humidity to which the alkaline material is exposed is selected such that the alkaline material is exposed to the high level of humidity at the same time that the alkaline material is at the low temperature value, and so that the alkaline material is exposed to the low level of humidity at the same time that the alkaline material is at the high temperature value.

[0042] In some embodiments, at any stage of the reaction process or from the outset of the reaction, rather than controlling the relative humidity, the alkaline material may be mixed with water to expose the alkaline material to a controlled moisture level, e.g. by addition of between about 10% and about 40% by weight of water relative to the dry weight of the alkaline material, including any value or subrange therebetween, e.g. 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 or 38% by weight of water relative to the dry weight of the alkaline material. It will be apparent to the person skilled in the art that the amount of water added to the alkaline material can be based on the determined moisture content of the alkaline material; e.g. if the alkaline material contains 5% water by weight as provided, then the person skilled in the art would add only 25% water by weight to arrive at a moisture content of 30% water by weight of the alkaline material. In some such embodiments, after the alkaline material has been combined with water, the humidity is maintained at a relatively high level of between about 85% to about 100% relative humidity (including any value or subrange therebetween, e.g. about 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99% relative humidity), and the temperature is cycled. In some embodiments, the rate of air temperature change to which the alkaline material is exposed to change between the low and high temperatures with this controlled exposure to moisture is maintained at or above a change of about 0.75 °C / hour (with temperature increasing during heating and decreasingduring cooling). In various embodiments, the rate of air temperature change to which the alkaline material is exposed may be higher or lower than about 0.75 °C / hour, depending on the rate of temperature change caused by ambient conditions and / or the amount of heating or cooling energy supplied, particularly if temperature is cycled more frequently than diurnally. In some embodiments, temperature is maintained above 0 °C. The range of air temperature through which the alkaline material is cycled may vary depending on the ambient conditions, but in one example embodiment could be between a low TL of between about 5 °C to about 15 °C as a low temperature value (including any temperature or subrange therebetween, e.g. 6, 7, 8, 9, 10, 11 , 12, 13 or 14 °C) and a high TH of between about 25 °C to about 50 °C as a high temperature value (including any subrange or value therebetween, e.g. 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, or 48 °C). In some embodiments, the temperature of the alkaline material is cycled at least once per day (e.g. at least diurnally) between a high temperature and a low temperature. In some embodiments, to maximize the rate of CO2 capture during exposure of the alkaline material to a controlled moisture level, the rate of the temperature change is maximized as much as possible. In some embodiments, to maximize the rate of CO2 capture during the second stage, the amplitude of the air temperature change between the high temperature and the low temperature is maximized as much as possible. In some embodiments, the temperature of the alkaline material is cycled three, four, five or more times per day.

[0043] In some embodiments, the mineralization is carried out using an alkaline material. In some embodiments, the alkaline material is an alkaline mineral such as olivine, peridotite, serpentine, serpentinite, or the like. In some embodiments, the alkaline material is magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, steel slag, precious metal slag, bottom ash, fly ash, red mud, cement kiln dust, cement (including cement waste), concrete (including concrete waste), asbestos (including asbestos waste), or paper mill waste

[0044] With reference to FIG. 1A, an example embodiment of a method 100 for capturing CO2 from air using an alkaline material is illustrated. At 102, the alkaline material is prepared in any suitable manner. For example, where the alkaline material is crystalline olivine or crystalline serpentine, the sample may be prepared by dry grinding until the material has a Pso of less than about 300 pm. Where the alkaline material is MgO, Mg(OH)2, CaO, Ca(OH)2, steel slag, precious metal slag, or the like, at 102 the alkalinematerial may first be dried and then subjected to dry grinding until the material has a Pso of less than about 300 m.

[0045] In some embodiments if appropriate, the alkaline material is subjected to activation at 104. For example, in embodiments in which the alkaline material is olivine or serpentine, the alkaline material may be activated by one or more of thermal, microwave, or mechanical activation at 104.

[0046] In some embodiments, at 103 inorganic salt additives are added. Any suitable combination of cations and anions can be used to provide such inorganic salt additives. For example, suitable cations for inclusion in such salt additives include calcium, magnesium, sodium, potassium, lithium or the like. Suitable anions for inclusion in such inorganic salts include chloride, sulfate, nitrate, hydroxide, bicarbonate, carbonate or the like. Suitable inorganic salt additives include all possible combinations and permutations of calcium, magnesium, sodium, potassium or lithium as the cation with chloride, sulfate, nitrate, hydroxide, bicarbonate or carbonate as the anion. Common examples of such inorganic salts that can be used include without limitation calcium chloride, potassium chloride, sodium hydroxide, sodium chloride, sodium bicarbonate, sodium carbonate, sodium sulfate, magnesium chloride or magnesium sulfate. In some embodiments, the inorganic salt additives are added in an amount of between about 0.1 % to about 10% by weight of the alkaline material on a dry matter basis, including any value or subrange therebetween, e.g. about 0.25, 0.50, 0.75, 1 .0, 1 .5, 2.0, 2.5, 3, 4, 5, 6, 7, 8 or 9% by weight relative to the weight of the alkaline material on a dry matter basis. In some embodiments, no inorganic salt additives are added.

[0047] In some embodiments, at 105 a non-reactive filler material is added to the reaction mixture. In some embodiments, the non-reactive filler material is added in an amount of approximately 20% to about 50% by weight of the alkaline material present on a dry matter basis, including any value or subrange therebetween, e.g. about 25, 30, 35, 40 or 45% by weight relative to the amount of alkaline material present on a dry matter basis. Suitable materials to be added as the non-reactive filler material include all silicate and carbonate minerals, including but not limited to: quartz, anorthite, albite, serpentine (unactivated), olivine, talc, diopside, hydromagnesite, magnesite, calcite, orthoclase, microcline, corundum, rutile, spinel, larnite, and hatrurite, as well as all naturally occurring rocks and industrially produced slags made up of silicate and / or carbonate minerals. Industriallyproduced silica, and particles thereof, are also suitable materials to be used as non-reactive filler. The person skilled in the art will appreciate the combinations of inorganic salts that can be used with certain silicate and carbonate mineral fillers so as to maintain the inert nature of the non-reactive filler material.

[0048] At 106, the prepared alkaline material is exposed to humid air and atmospheric CO2. At 110, the temperature 112, relative humidity 114 and instantaneous rate of CO2 capture 116 are measured.

[0049] At 120, the temperature 122 and relative humidity 124 can be independently controlled based on their measured values and / or the determined state of reaction, as further described herein. At 130, the method can return to measuring step 110, and this process can be repeated as desired. In some embodiments, controlling the temperature at 122 comprises diurnally cycling the temperature of the alkaline material between a low air temperature of about 0 °C and a high air temperature of about 50 °C, including any value or subrange therebetween, e.g. a low air temperature between about 10 °C and about 20 °C and a high air temperature between about 25 °C and about 50 °C or the like. In some embodiments, the high and low air temperatures between which the temperature of the alkaline material is cycled may vary depending on the specific location at which the reaction is being carried out (e.g. at a very warm location on Earth or at a cooler geographic location on Earth). In some embodiments, the high and low air temperatures between which the temperature of the alkaline material is cycled and / or the rate at which the alkaline material is cycled between the high and low air temperatures may vary depending on the stage of the mineralization reaction, as further described below.

[0050] In some embodiments, the cycling of the temperature is caused by fluctuations in the temperature of the alkaline material caused by ambient temperature changes in the external environment, e.g. the diurnal cycles associated with heating during the daytime and cooling at night. In some embodiments, temperature is controlled by allowing or preventing light (e.g. solar energy) from reaching the alkaline material. In some embodiments, a greenhouse or other similar structure may be used to trap heat generated from light in close proximity to the alkaline material. In some embodiments, light is permitted to enter or not enter the greenhouse or the region in which the alkaline material has been deposited (e.g. by deploying appropriate shade mechanisms such as shade cloth or screens) and / or the greenhouse may include ventilation features such as windows, doors, sides that can beraised or lowered or the like, that can be opened if it is desired to allow the alkaline material to cool or closed if it is desired to increase the temperature of the alkaline material.

[0051] In some embodiments, to heat the alkaline material to a higher temperature or to try to maximize the temperature of the alkaline material or maximize the high air temperature reached by the system to maximize the difference between the high and low temperatures during cycling, light can be permitted to enter the greenhouse during daytime hours and ventilation features can be kept closed during daytime hours to maximize heat retention within the system.

[0052] In some embodiments, to cool the alkaline material to a lower temperature or to try to minimize the temperature of the alkaline material or to minimize the low air temperature reached by the system to maximize the difference between the low and high temperatures during cycling, use of shading during daytime hours to minimize heat accumulation, closing ventilation features during daytime hours to minimize influx of warm air into the system if the temperature of the outside environment is warmer than the temperature within the system (or alternatively opening ventilation features during daytime hours to vent warm air if the temperature of the outside environment is cooler than the temperature within the system), opening ventilation features during nighttime hours to maximize influx of cool air into the system, or the like can be used.

[0053] In some embodiments, the alkaline material is actively heated to increase the temperature to the high temperature value and / or actively cooled to decrease the temperature to the low temperature value. For example, in one example embodiment, a heat transfer fluid is passed beneath the system, e.g. beneath the mass of the alkaline material. The heat transfer fluid and the system are separated by a barrier such as a conductive metal plate. To increase the temperature of the system, the heat transfer fluid may be steam, hot water, hot air, hot gases (e.g. exhaust gases), or the like. To decrease the temperature of the system, the heat transfer fluid can be cold water, cold air, or cold gases.

[0054] In some embodiments, relative humidity is increased by spraying a fine mist of water above the alkaline material. In other embodiments, relative humidity can be controlled in other manners, for example allowing fresh outside air having a known relative humidity to mix with air in the system, to either increase or decrease the relative humidity within thesystem. In another example embodiment, controlling relative humidity is achieved by placing a solution of sodium chloride (NaCI) or other salt in contact with air, including by placing a saturated solution of sodium chloride or other salt in contact with air. For example, a saturated solution of sodium chloride (NaCI) in contact with air will maintain a relative humidity of about 75% at temperatures between 0 °C to 60 °C. Changes in temperature may also be used and / or taken into account in adjusting the relative humidity within the system containing the alkaline material. For example, as temperature cools, humidity will increase. Accordingly, as the temperature cools, humidity will increase, and relative humidity can be increased while using solutions of saturated salts to help control the rate of increase of relative humidity, or humidity can be even further increased by spraying a fine mist of water above the alkaline material while the temperature is decreasing. Conversely, as temperature increases, humidity will decrease. Accordingly, as the temperature increases, the system can be exposed to solutions of saturated salts to help further decrease relative humidity, or even if no action is taken to proactively adjust relative humidity, the relative humidity will decrease as the temperature increases. Conversely, if it is desired to increase relative humidity or even to maintain a specific level of relative humidity as the temperature increases, a fine mist of water can be sprayed above the alkaline material while the temperature is increasing. Constant or periodic measurements of relative humidity within the system can be used to provide feedback to control the measures taken to adjust the relative humidity to ensure that the relative humidity is increased, decreased, or remains approximately constant as desired.

[0055] At 140, once a determination is made that the net rate of CO2 capture has been undetectable (e.g. approximately zero) for at least one day, the alkaline material is evaluated to determine if it has been saturated or saturated to a sufficient extent (e.g. to at least 80% of the total mineralization capacity of the alkaline material) with CO2 at 141. A determination that the alkaline material is saturated with CO2 can be made in any suitable manner. For example, in one embodiment, the total mineralization capacity can be calculated using measured oxide composition and well-known equations such as Equation 4 in Bullock et al. (2021). This method is best suited to alkaline hydroxides (e.g., Ca(OH)2 or Mg(OH)2) and alkaline oxides (e.g., CaO or MgO) since the Ca and Mg in these materials reacts readily at ambient conditions and all Ca or Mg can be considered labile. In a second example embodiment, the total mineralization capacity can be determined using either flow-through dissolution or batch dissolution tests as described by Lu (2020) and Lu et al. (2022). Flow-through dissolution and batch dissolution tests are most applicable to silicate minerals, silicate mineral-bearing alkaline materials, and their activated counterparts. In these materials, only a fraction of the total Ca or Mg is labile at ambient conditions. The flow-through dissolution and batch dissolution tests are designed such that only the labile Ca or Mg is measured. For both methods, the total mineralization capacity can be expressed as weight percent CO2, wt% CO2. Here, saturation with respect to CO2 is achieved when, for a given material, 80% or greater of the total carbon mineralization potential has been exceeded. Wt% CO2 can be measured using well established analytical techniques such as, for example, coulometry.

[0056] If the alkaline material has been saturated or saturated to a sufficient extent with CO2, then at 142 the material is sent for disposal. In some embodiments, at 142 the material is sent for secure disposal, e.g. by preventing further interaction with atmospheric air, e.g. by burying the material. If the alkaline material has not been saturated or saturated to a desired extent with CO2, then at 144 the alkaline material can be dried and reground with a decrease in Pso of at least 10 pm, and then the reground alkaline material can again be exposed to humid air and atmospheric CO2 at step 150.

[0057] With reference to FIG. 1 B, a second example embodiment of a method 200 for capturing CO2 from air is illustrated. Method 200 includes steps similar to method 100 for which reference numerals have been incremented by 100 and which are not further described again, including sample preparation step 202 and activation step 204 where appropriate for the alkaline material, as well as step 203 of adding inorganic salt additives and / or step 205 of adding non-reactive material if desired.

[0058] At 260, the alkaline material enters a first stage of the carbon mineralization reaction upon exposure to humid air and atmospheric CO2 at 262. During the first stage 260 of the carbon mineralization reaction, at 264 the relative humidity to which the alkaline material is exposed is maintained at a moderate level between about 35% and about 85%, including between about 50% and about 85%, including any value or subrange therebetween, e.g. 40, 45, 50, 55, 60, 65, 70, 75 or 80%.

[0059] At 266, the temperature to which the alkaline material is exposed is cycled, e.g. at a rate of at least once per day. In some embodiments, the temperature is cycled diurnally at266, although in other embodiments the temperature may be cycled more frequently, e.g. if additional energy was supplied to heat and cool the alkaline material to cycle the temperature more frequently than the diurnal cycle that would be experienced by the alkaline material at ambient conditions due to the cycling of day and night. In some embodiments, the rate of air temperature change to which the alkaline material is exposed at 266 to reach the high or low temperature is maintained at or above a change of about 0.75 °C / hour (with temperature increasing during heating and decreasing during cooling). In various embodiments, the rate of air temperature change to which the alkaline material is exposed at 266 may be higher or lower than about 0.75 °C / hour, depending on the rate of temperature change caused by ambient conditions and / or the amount of heating or cooling energy supplied, particularly if temperature is cycled more frequently than diurnally. In some embodiments, at 266 temperature is maintained above 0 °C. In some embodiments, the range of air temperature through which the alkaline material is cycled may vary depending on the ambient conditions, but in one example embodiment could be between a low TLI of between about 5 °C to about 15 °C as a low temperature value (including any temperature or subrange therebetween, e.g. 6, 7, 8, 9, 10, 11 , 12, 13 or 14 °C) and a high THI of between about 25 °C to about 35 °C as a high temperature value (including any subrange or value therebetween, e.g. 26, 27, 28, 29, 30, 31 , 32, 33, or 34 °C).

[0060] At 268, the instantaneous rate of CO2 capture by the alkaline material is measured. In some embodiments, measurement of the instantaneous rate of CO2 capture occurs at least once every six hours, or optionally more frequently, e.g. at least once every four hours, every three hours, every two hours, every one hour, every half hour, or continuously. If the instantaneous rate of CO2 capture by the alkaline material is still changing, the alkaline material remains in stage 1 at 260 and relative humidity at 264 and temperature parameters at 266 are maintained. After the instantaneous rate of CO2 capture by the alkaline material has been constant for at least one day at 269, the alkaline material is considered to have moved to stage 2 of the carbon mineralization reaction at 270.

[0061] During stage 2 of the reaction at 270, the alkaline material is again exposed to humid air and atmospheric CO2 at 272. At 274, the relative humidity to which the alkaline material is exposed during stage 2 is maintained between about 85% and about 100%, including any value or subrange therebetween, e.g. 87, 90, 92, 94, 96 or 98%. At 276, the temperature to which the alkaline material is exposed is cycled, e.g. at least once per day. In someembodiments, the temperature is cycled diurnally at 276, although in other embodiments the temperature may be cycled more frequently, e.g. if additional energy was supplied to heat and cool the alkaline material to cycle the temperature more frequently than the diurnal cycle that would be experienced by the alkaline material at ambient conditions due to the cycling of day and night. In some embodiments, the rate of air temperature change to which the alkaline material is exposed at 276 to change between the low and high temperatures is maintained at or above a change of about 0.75 °C / hour (with temperature increasing during heating and decreasing during cooling). In various embodiments, the rate of air temperature change to which the alkaline material is exposed at 276 may be higher or lower than about 0.75 °C / hour, depending on the rate of temperature change caused by ambient conditions and / or the amount of heating or cooling energy supplied, particularly if temperature is cycled more frequently than diurnally. In some embodiments, at 276 temperature is maintained above 0 °C. In some embodiments, the range of air temperature through which the alkaline material is cycled may vary depending on the ambient conditions, but in one example embodiment could be between a low TL2 of between about 5 °C to about 15 °C as a low temperature value (including any temperature or subrange therebetween, e.g. 6, 7, 8, 9, 10, 11 , 12, 13 or 14 °C) and a high TH2 of between about 25 °C to about 35 °C as a high temperature value (including any subrange or value therebetween, e.g. 26, 28, 30, 32, or 34 °C).

[0062] At 278, the instantaneous rate of CO2 capture by the alkaline material is measured. In some embodiments, measurement of the instantaneous rate of CO2 capture occurs at least once every six hours, or optionally more frequently, e.g. at least once every four hours, every three hours, every two hours, every one hour, every half hour, or continuously. If the day-over-day average rate of CO2 capture by the alkaline material is constant, the alkaline material remains in stage 2 at 270 and relative humidity at 274 and temperature or other parameters at 276 are maintained. After the instantaneous rate of CO2 capture by the alkaline material is determined to be increasing with decreasing temperature at 279, the alkaline material is considered to have moved to stage 3 of the carbon mineralization reaction at 280.

[0063] During stage 3 of the reaction at 280, the alkaline material is again exposed to humid air and atmospheric CO2 at 282. At 283, the temperature to which the alkaline material is exposed is cycled across a time interval, e.g. at least one per day. In some embodiments,the air temperature to which the alkaline material is exposed is cycled between a low temperature value TLS in the range of about 0 °C to about 10 °C (including any temperature or subrange therebetween, e.g. 1 , 2, 3, 4, 5, 6, 7, 8 or 9 °C) and a high temperature value THS of between about 7 °C to about 25 °C as a high temperature value (including any subrange or value therebetween, e.g. 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23 or 24 °C). In some embodiments, the air temperature is increased as slowly as possible during heating to move from the low temperature value TLS to the high temperature value THS, e.g. less than about 0.25 °C / hour, and is decreased as rapidly as possible during cooling, e.g. at a rate of about 0.75 °C / hour to move from the high temperature value THS to the low temperature value TLS. In such embodiments, the time periods during which the alkaline material is heated and cooled will be different; for example in one non-limiting example if the alkaline material is being heated and cooled with 12-hour heating and cooling cycles, with a 3 °C change in air temperature between the low temperature and the high temperature the alkaline material may be heated for 12 hours at 0.25 °C / hour to increase the temperature of the alkaline material by 3 °C. Then the alkaline material may be cooled for 3 hours at a rate of 0.75 °C / hour to cool the air temperature of the system by 3 °C and return the alkaline material to the low temperature. The alkaline material is then held at the low temperature value for 9 hours, and then heating is again commenced at a rate of 0.25 °C to return the alkaline material to the high air temperature value.

[0064] In some embodiments, the time interval is a diurnal cycle, i.e. the temperature is cycled to the high temperature value once per day (e.g. during daylight hours when the external environment is warmed by solar radiation) and to the low temperature value once per day (e.g. during nighttime hours when no sun is present). In some embodiments, the temperature is cycled more frequently, e.g. three, four, five times per day or more.

[0065] At 285, the relative humidity to which the alkaline material is exposed is cycled between a high humidity level in the range of about 85 to about 100% relative humidity, including any value or subrange therebetween e.g. about 87, 90, 92, 94, 96 or 98% relative humidity, and a low humidity level in the range of less than about 50% relative humidity, including less than about 30% relative humidity (e.g. including 48%, 46%, 44%, 42%, 40%, 38%, 36%, 35%, 34%, 33%, 32%, 31 % or 30% relative humidity). In some embodiments, the relative humidity to which the alkaline material is exposed is cycled across the same time interval as the temperature at 283. In some embodiments, the relative humidity iscycled so that the alkaline material is exposed to the low humidity level (e.g. <50% RH) at the same time that the alkaline material is exposed to the high temperature value, and so that the alkaline material is exposed to the high humidity level (e.g. 85-100% RH) at the same time that the alkaline material is exposed to the low temperature value. In some embodiments, the low humidity level is as low a level of humidity as can reasonably be achieved given prevailing environmental conditions. In some embodiments, the high humidity level is as high a level of humidity as can reasonably be achieved given prevailing environmental conditions.

[0066] Once it has been determined that the net rate of CO2 capture by the alkaline material has been undetectable (e.g. approximately zero) for at least one day at 289, the alkaline material is evaluated to determine if it has been saturated or saturated to a sufficient extent, (e.g. to at least 80% of the total mineralization capacity of the alkaline material) with CO2 at 290. The determination of the degree of saturation of the alkaline material with CO2 can be made in any suitable manner, for example as described with reference to step 141 above. If it is determined that the alkaline material has been saturated or saturated to a sufficient extent with CO2, then at 292 the material is sent for disposal. If the alkaline material has not been saturated or saturated to a desired extent with CO2, then at 294 the alkaline material can be dried and reground with a decrease in Pso of at least 10 pm, and then the reground alkaline material can again be returned to the first stage of the mineralization reaction at 260.

[0067] In some embodiments, stages 1 and 2 of the mineralization reaction are conducted in a first apparatus, and stage 3 is conducted in a second apparatus that is different from the first apparatus. Using a separate apparatus to conduct stage 3 may facilitate the manipulation of the cycling temperature and relative humidity levels to which the alkaline material is exposed at stage 3, e.g. to maintain the overall temperature at as low a level as possible throughout the cycle.

[0068] If desired, at any stage during the conduct of method 200 the alkaline material can be passed to step 352 of method 300 as described below with reference to step 452A of method 400. In some embodiments, method 200 proceeds to step 452A of method 400 after a determination has been made that the average rate of CO2 capture has been constant for at least one day at step 269. In some embodiments, method 200 proceeds to step 452A of method 400 after a determination has been made that the rate of CO2 captureis increasing with decreasing temperature at step 279. In some embodiments, method 200 proceeds to step 452A of method 400 after a determination has been made that the rate of net CO2 capture has been undetectable (e.g. approximately zero) for at least one day at step 289 and it is determined that the alkaline material has not been saturated to a desired extent at step 290. Without being bound by theory, because control of relative humidity to higher levels in the range of 85% to 100% can require a meaningful input of effort, in one example embodiment it is advantageous to proceed through steps 202 to 269 of method 200 which are conducted at a relatively lower level of humidity, and then after the average rate of capture of CO2 has been determined to be constant for at least one day at step 269, the reaction mixture can be passed to step 352 of method 300 and the remaining steps (i.e. steps 310 and following) can be conducted to complete processing of the alkaline material to the desired level of CO2 saturation.

[0069] In some embodiments, the source of carbon dioxide for the mineralization reactions is atmospheric (i.e. ambient) air.

[0070] With reference to FIG. 1C, a third example embodiment of a method 300 for mineralizing carbon dioxide from air at Earth surface conditions is illustrated. Method 300 is generally similar to method 100 and like features are illustrated with like reference numerals incremented by 200. Method 300 includes the same steps of sample preparation 302, activation 304, addition of inorganic salt additives 303 if desired, and addition of non- reactive material 305 if desired as method 100.

[0071] At step 352, to promote the reaction of carbon dioxide with the alkaline material, water is added. In some embodiments, the water is added in an amount of about 10% to about 40% of the amount of alkaline material present by weight, including any amount or subrange therebetween e.g. 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36 or 38% by weight of the amount of alkaline material present.

[0072] At step 310, the temperature 312, relative humidity 314 and instantaneous rate of CO2 capture 316 are measured.

[0073] At step 320, the temperature 322 and relative humidity 324 can be independently controlled. In some embodiments, at 324 relative humidity is maintained at a relatively high level, e.g. between about 85% and about 100% (including any value or subrange therebetween, e.g. about 86, 87, 88, 89, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99% relativehumidity), to try to minimize drying of the alkaline material. In some embodiments, at 322 the temperature of the alkaline material is cycled diurnally between a low air temperature and a high air temperature. In some embodiments, the rate of air temperature change to which the alkaline material is exposed at 322 to change between the low and high temperatures is maintained at or above a change of about 0.75 °C / hour (with temperature increasing during heating and decreasing during cooling). In various embodiments, the rate of air temperature change to which the alkaline material is exposed at 322 may be higher or lower than about 0.75 °C / hour, depending on the rate of temperature change caused by ambient conditions and / or the amount of heating or cooling energy supplied, particularly if temperature is cycled more frequently than diurnally. In some embodiments, temperature is maintained above 0 °C at 322. The range of air temperature through which the alkaline material is cycled at 322 may vary depending on the ambient conditions, but in one example embodiment could be between a low TL of between about 5 °C to about 15 °C as a low temperature value (including any temperature or subrange therebetween, e.g. 6, 7, 8, 9, 10, 11 , 12, 13 or 14 °C) and a high TH of between about 25 °C to about 50 °C as a high temperature value (including any subrange or value therebetween, e.g. 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46 or 48 °C).

[0074] At step 330, the process can return to step 310 to repeat as desired. At 340, once a determination is made that the net rate of CO2 capture has been approximately zero for at least one day, the alkaline material is evaluated to determine if it has been saturated or saturated to a sufficient extent (e.g. to at least 80% of the total mineralization capacity of the alkaline material) with CO2 at 341. As described for method 100, if the alkaline material has been saturated or saturated to a sufficient extent with CO2, then at 342 the material is sent for disposal. If the alkaline material has not been saturated or saturated to a desired extent with CO2, then at 354 the alkaline material can be reground with a decrease in Pso of at least 10 pm and / or additional water can be added to the alkaline material to bring the moisture content of the material back up into the range of about 10% to about 40% by weight, and at 350 the alkaline material can be returned for further processing by repeating steps 310 and 320.

[0075] With reference to FIG. 1 D, a fourth example embodiment of a method 400 for mineralizing carbon dioxide from air at Earth surface conditions is illustrated. Method 400 is a combination of methods 100 and 300. Steps which correspond to steps of method 100are incremented by 300 and include the same steps of sample preparation 402, activation 404 if desired, addition of inorganic salt additives 403 if desired, addition of non-reactive material 405 if desired, exposure to humid air and atmospheric CO2 406, measurement step 410 including measuring temperature at 412, relative humidity at 414 and instantaneous rate of CO2 capture at 416, adjustment at step 420 of temperature 422 and relative humidity 424, and returning to step 410 at 430 to repeat the process as desired. Method 400 further includes determining at step 440 that there has been no net CO2 capture for at least one day and evaluating whether the alkaline material has been saturated to a desired extent with CO2 at 441. If the material is saturated, at 442 the material can be sent for disposal, or if the material is not saturated to a desired extent with CO2, then the material can be passed to the steps of method 400 that correspond to method 300.

[0076] Steps of method 400 which correspond to steps of method 300 are incremented by 100 and include the letter A after the corresponding reference numeral, including addition of water in an amount of 10 to 40% by weight of the alkaline material at 452A, measurement steps 410A including measurement of temperature 412A, humidity 414A and instantaneous rate of CO2 capture 416A as well as adjustments at step 420A of temperature 422A and relative humidity 424A as described for method 300. At 430A, the process can return to step 410A to repeat as desired. At 440A, once a determination is made that the net rate of CO2 capture has been approximately zero for at least one day, the alkaline material is evaluated to determine if it has been saturated or saturated to a sufficient extent (e.g. to at least 80% of the total mineralization capacity of the alkaline material) with CO2 at 441 A. if the alkaline material has been saturated or saturated to a sufficient extent with CO2, then at 442A the material is sent for disposal. If the alkaline material has not been saturated or saturated to a desired extent with CO2, then at 454A the alkaline material can be reground with a decrease in Pso of at least 10 pm and / or additional water can be added to the alkaline material to bring the moisture content of the material back up into the range of about 10% to about 40% by weight, and at 450A the alkaline material can be returned for further processing by repeating steps 410A and 420A.Examples

[0077] Certain embodiments are further described with reference to the following examples, which are intended to be illustrative and not limiting in nature.Methods:

[0078] Experiments were performed by placing dry samples of either serpentinite or caustic magnesia, MgO, into environments of varying humidity and temperature. Serpentinite samples were either used ‘as-is’ or activated, by either thermal, microwave or mechanical means. Activation refers to disruption of the mineral lattice. Activation can be quantified using common laboratory techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) or x-ray diffraction (XRD). The specific activation parameters used in this work are described below. MgO was purchased from BayMag (Alberta, Canada), a commercial supplier of caustic magnesia, and used directly from the container.

[0079] The rate of CO2 capture was measured using either dynamic closed chamber systems or closed system flasks. Both systems are manufactured by LICOR Environmental. Individual measurements lasted between 1-3 minutes and were taken at intervals of 1-4 hours. Positive fluxes indicate capture of CO2 into the alkaline materials, while negative fluxes denote a release of CO2.

[0080] Humidity and temperature were continuously measured using a Vaisala relative humidity (RH) and temperature probe.

[0081] Total inorganic carbon (TIC) was measured by coulometry using a UIC Inc. CM14. Samples were analyzed for TIC before and after exposure to CO2 and the difference in TIC between pre- and post- experiment samples represents the amount of carbon mineralized during an experiment.Experimental Results:

[0082] Example 1 : Comparison of the rate of capture and cumulative wt% CO2 captured between activated serpentinite samples (FIG. 2A) and fresh, crystalline serpentinite (FIG. 2B). Activation was performed by thermally heating the samples at 650°C for 20 minutes. All samples, activated and crystalline, were sieved and the 20-50 pm fraction was used for the experiment. The experiment was run at 5-7 °C and 100% RH. Contrary to the existingliterature, it is clear from the data herein that the activated, or amorphized, samples react more quickly than the un-activated counterparts. Without being bound by theory, it is believed activation of the mineral structure breaks the mineral lattice bonds, thereby allowing the metal cation, Mg2+, to more readily react with CO2. This observation is in contrast to prior art (e.g., Myers et al., 2022) that argue that activation, or amorphization, of a mineral structure will decrease the ability of the metal cation to diffuse through the metal- carbonate that forms on the surface of the primary mineral. The un-activated FGO and CGO samples show either no gain or a loss in wt% CO2 (FIG. 2B). In contrast, all of the activated samples show a cumulative gain in wt% CO2 (FIG. 2A).

[0083] Example 2. Comparison of mineralized atmospheric carbon in splits of identically activated serpentine at various temperatures (5, 10, 20 and 40°C, FIG. 3A and 3B). The temperatures were held constant for the duration of the experiments. The relative humidity was 100% at each temperature and remained constant for the entire experiment.

[0084] This result in which the amount of atmospheric carbon that is mineralized decreases with increasing temperature is surprising given the data in the existing literature. Assima et al. (2014) performed experiments in which alkaline mine tailings were exposed to a series of constant temperatures between 10 and 40 °C and carbon mineralization was measured. In contrast to the present results, these authors showed that higher temperatures lead to high amounts of CO2 mineralization for a set amount of time.

[0085] Additionally, there are well known equations from the chemical engineering literature (e.g., equation 2.10 in (Holmes and Keith, 2012)) that quantify the flux of CO2 from air into alkaline fluids. These equations have the general form:Flux, C02 - [CO2] * KL (1)Where the flux has units of mass per unit area per time, [CO2] is the concentration of CO2 in the gas (e.g., mol / m3) and KL is a mass transfer coefficient, dependent on temperature, among other factors. These equations indicate that the CO2 flux into alkaline fluids will increase with increasing temperature. This is the opposite of the data presented in FIG. 3A and 3B. Without being bound by theory, it is believed that the fluid film produced at the100% RH condition used in the present experiments is relatively thin, so that the CO2 flux ispredominantly impacted by CO2 solubility in water, which increases with decreasing temperature. The KL mass transfer coefficient accounts for CO2 solubility in a thin water film as well as diffusion of CO2 from the thin film to the bulk liquid. Diffusion of CO2 into the bulk liquid increases with increasing temperature and it is this component of KL that dominates the overall flux of CO2.

[0086] Example 3. Comparison of the rate of capture into three splits of identically activated serpentine at constant temperature (21 °C) and varying relative humidity (100%, 75% and 33%, FIGs. 4A and 4B). Relative humidity was maintained constant by using saturated salt solutions (NaCI - 75% RH, MgC - 33% RH) as the source of humidity. Pure water was used for the 100% RH experiment. Contrary to claims made by Myers et al. (2022), the highest rate of capture occurs in the sample with 75% RH, not 100% RH, over the time frame of this experiment.

[0087] FIG. 5A shows data from an experiment in which dry MgO was placed in either 100% or 75% relative humidity (RH) conditions and the temperature was cycled (diurnally) between 10-20 °C. For the first 3.75 days, the MgO in the 75% RH environment shows a higher rate of capture than the 100% RH environment. Beyond 3.75 days, the rates of capture in the two different experiments are indistinguishable. FIG. 5B shows data from days 15 to 27 of the 100% RH experiment. On day 19, the humidity was lowered to 50% RH through introduction of a saturated Mg(NOs)2 solution. There is a clear decrease in the rate of flux as a result of the change in humidity. On day 24, the RH was returned to 100% RH and the flux of CO2 returned to the same rates of capture as before the change in RH.

[0088] Example 4: FIGs. 6A and 6B show the rate of CO2 capture in a microwave activated serpentinite as a function of time. The temperature and humidity were held constant (7 °C and 100% RH) for the first 15 days and then temperature was cycled, between 7-20 °C, starting on day 15. Temperature cycling caused the relative humidity to fluctuate between 90-100%. Between days 17-27 the rate of CO2 capture increases with increasing temperature. Surprisingly, this behavior reverses on day 50 (FIG. 6B); increasing rates of CO2 capture occur with decreasing temperature. During this period there are releases (negative fluxes) of CO2 as the temperature increases.

[0089] Example 5: FIG. 7 shows that the rate of CO2 capture is initially higher for a sample that experiences 100% relative humidity compared to a sample that experiences 33%relative humidity. After six days, the sample with low humidity shows evidence of stagnation in CO2 capture and the relative humidity is subsequently increased to 100%. After approximately 18 days, the net CO2 capture is greater for the sample that underwent this increase in relative humidity. Low relative humidity (33% RH) was maintained using saturated MgCI2 salt solutions, while high relative humidity (100% RH) was achieved using water.

[0090] Example 6: FIG. 8 shows that introducing water to the alkaline material, following stagnation in the CO2 capture curve, enhances the rate of CO2 capture. The rate of CO2 capture exhibits a shallow slope prior to the introduction of 20 wt% water, and becomes steeper following the water addition on or about day 25 of the experiment.

[0091] Example 7: FIGs. 9 and 10 show the effects of additives, such as inorganic salts and non-reactive fillers. FIG. 9 shows that incorporating inorganic salts (specifically NaCI alone or a mixture of NaCI and NaHCOs) enhances the rate of CO2 capture. For the initial period up to six days, the relative humidity is maintained at 33%. After this period, the relative humidity is increased to 100%. The effect of the increase in humidity is stronger for the samples with inorganic salts. FIG. 10 shows that the addition of 20 wt% quartz, a non- reactive filler, to the alkaline material enhances CO2 capture relative to the control sample without quartz. In both experiments, water is periodically added to the alkaline sample to increase CO2 capture rates.Maximizing the rate of CO2 capture at Earth surface conditions

[0092] The experimental data presented herein show that the rate of CO2 capture into alkaline materials is dependent on the temperature, relative humidity, moisture content, and presence of additives. In certain experiments, changing the temperature regime from constant to cycling causes a significant increase in the rate of CO2 capture (FIG. 6A), while in other experiments at constant temperature, the lower temperature sample mineralizes more carbon over the same amount of time as compared to the higher temperature sample, in contrast with the prior art (FIGs. 3A and 3B). The data presented in FIGs. 6A and 6B also demonstrate that the relationship between rate of CO2 capture and temperature changes with continued reaction.

[0093] In general, there are three reaction intervals that can be defined based on the experimental data when temperature and the relative humidity to which the alkaline material is exposed are controlled.

[0094] Interval 1 is the initial stage of reaction characterized by the highest rates of CO2 capture followed by a general decrease in the rate of CO2 capture. For example, in FIG. 5A, interval 1 can be defined as the time period from the start of the experiment to day 7. In FIG. 6A, interval 1 is the time period from the start of the reaction to day 2.

[0095] Interval 2 begins when the average day-over-day rate of CO2 capture remains constant for 24 hours or greater and the rate of CO2 capture increases with increasing temperature. For example, as can be seen from FIG. 6A in which the rate of capture is plotted together with the temperature, during days 17-27, the rate of capture is increasing as the temperature increases.

[0096] Interval 3 begins when the rate of CO2 capture increases with decreasing temperature. For example, as can be seen from FIG. 6B in which the rate of capture is plotted together with the temperature, during days 50-55, the rate of CO2 capture increases as the temperature decreases.

[0097] Without being bound by theory, the duration of the three intervals may depend strongly on the alkaline material. For example, more reactive material such as CaO or MgO may have a longer interval 1 and 2 than activated serpentinite. Moreover, CaO or MgO may never enter reaction interval 3 if the material is sufficiently reactive that it is completely reacted before interval 3 is reached. However, it is the change in the physical properties of the system (i.e. the environmental conditions associated with the highest rate of CO2 uptake by the alkaline material), that can be used to confirm the transition of the material between the three different stages of the reaction.

[0098] Additional enhancements can be applied to increase CO2 capture efficiency. For example, introducing water to the alkaline material when the CO2 capture rates plateau and full saturation is not yet achieved can lead to an increase in CO2 capture (FIG. 8). Furthermore, the addition of additives such as inorganic salts or non-reactive fillers is demonstrated to significantly elevate CO2 capture rates. The integration of inorganic salts, including NaCI or a mixture of NaCI and NaHCOs, notably enhances the rate of CO2 capture, especially when this addition is coupled with an increase in relative humidity fromlow to high after a period of lower capture rates (FIG. 9). Similarly, incorporating a non- reactive filler, such as quartz sand, has been shown to improve CO2 capture rates compared to controls without quartz sand (FIG. 10). The strategic combination of these additives can be tailored based on the specific needs of the capture process and the properties of the alkaline material utilized.

[0099] Example 8: Fig 11 shows the effect of temperature cycling on the rate of CO2 capture into two identical samples of activated serpentinite that had been combined with water in an amount of 20% by weight. For one sample, the temperature was cycled diurnally between 8-18 °C for the duration of the experiment. For the other case, the temperature was not controlled and remained at 19.5 ± 2 °C. Humidity in both cases was maintained between 95-100% for the duration of the experiment. The results demonstrate the role of temperature cycling in increasing the rate of CO2 capture for otherwise identical samples.

[0100] While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are consistent with the broadest interpretation of the specification as a whole.References

[0101] The following references are of interest with respect to the subject matter described herein. Each of the following references is hereby incorporated by reference in its entirety herein.Assima G. P., Larachi F., Molson J. and Beaudoin G. (2014) Impact of temperature and oxygen availability on the dynamics of ambient CO2 mineral sequestration by nickel mining residues. Chemical Engineering Journal 240, 394-403.Bullock L. A., James R. H., Matter J., Renforth P. and Teagle D. A. H. (2021) Global Carbon Dioxide Removal Potential of Waste Materials From Metal and Diamond Mining. Frontiers in Climate 3.Erans M., Nabavi S. A. and Manovic V. (2020) Carbonation of lime-based materials under ambient conditions for direct air capture. Journal of Cleaner Production 242, 118330.Gerdemann S. J., O’Connor W. K., Dahlin D. C., Penner L. R. and Rush H. (2007) Ex Situ Aqueous Mineral Carbonation. Environ. Sci. Technol. 41 , 2587-2593.Holmes G. and Keith D. W. (2012) An air-liquid contactor for large-scale capture of CO2 from air. Philos Trans A Math Phys Eng Sci 370, 4380-4403.Lu X. (2020) Characterization of ultramafic mine tailings reactivity for carbon capture and storage. University of British Columbia.Lu X., Carroll K., Turvey C. C. and Dippie G. M. (2022) Rate and capacity of cation release from ultramafic mine tailings for carbon capture and storage. Applied Geochemistry, 105285.McQueen N., Kelemen P., Dippie G., Renforth P. and Wilcox J. (2020) Ambient weathering of magnesium oxide for CO2 removal from air. Nat Commun 11 , 3299.Mohammad S., Firas R., Vasilije M., Macchi A., Anthony E. J. (2020) Direct capture of carbon dioxide from air via lime-based sorbents. Mitigation and Adaptation Strategies for Global Change; Dordrecht 25, 25-41 .Myers C. A., Nakagaki T. and Akutsu K. (2019) Quantification of the CO2 mineralization potential of ironmaking and steelmaking slags under direct gas-solid reactions in flue gas. International Journal of Greenhouse Gas Control 87, 100-111 .Myers C. and Nakagaki T. (2020) Direct mineralization of atmospheric CO2 using natural rocks in Japan. Environ. Res. Lett. 15, 124018.Myers C., Nakagaki T., Akutsu H. and Yamashita T. (2022) Acceleration of Gas-Solid CO2 Mineralization with Low Energy Consumption. Proceedings of the 16th Greenhouse Gas Control Technologies Conference, SSRN Journal.

Claims

CLAIMS:1 . A method of capturing carbon dioxide in an alkaline material through a mineralization reaction in a controlled system, the method comprising: exposing the alkaline material to a controlled moisture level; and cycling a temperature of the controlled system between a low temperature value TL and a high temperature value TH at least once per day.

2. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, including a method as defined in claim 1 , the method comprising:(i) placing the alkaline material in a controlled system;(ii) during a first stage of the mineralization reaction: maintaining a relative humidity of the controlled system at a value of between about 35% and about 85%; and cycling an air temperature of the controlled system between a low temperature value TLI and a high temperature value THI at least once per day;(iii) during a second stage of the mineralization reaction: maintaining a relative humidity of the controlled system at a value of between about 85% and about 100%; cycling the air temperature of the controlled system between a low temperature value TL2 and a high temperature value TH2 at least once per day; and(iv) during a third stage of the mineralization reaction: cycling the air temperature of the controlled system between a low temperature value TLS and a high temperature value THS at least once per day; while the temperature of the controlled system is increasing, decreasing the relative humidity of the controlled system to less than 30%; and while the temperature of the controlled system is decreasing, increasing the relative humidity of the controlled system to above 85%.

3. The method as defined in any one of claims 1 to 2, wherein placing the alkaline material in the controlled system comprises placing dry alkaline material in the controlled system.

4. The method as defined any one of claims 1 to 3, comprising monitoring a rate of carbon dioxide capture by the alkaline material and, after a day-over-day average rate of carbon dioxide capture by the alkaline material remains constant for at least one day, advancing from the first stage to the second stage of the mineralization reaction.

5. The method as defined in claim 4, comprising, after it has been determined that the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with decreasing temperature, advancing from the second stage to the third stage of the mineralization reaction.

6. The method as defined in any one of claims 2 to 5, wherein during the first stage: the cycling of the air temperature of the controlled system is carried out at a rate of at least 0.75 °C / hour; the low temperature TLI is between about 5 °C and about 15 °C; the high temperature THI is between about 25 °C and about 35 °C; a difference between TLI and THI is maximized in the controlled system; and / or the controlled system is cycled between TLI and THI two, three, four or five times per day.

7. The method as defined in any one of claims 2 to 6, wherein during the second stage: the cycling of the air temperature of the controlled system is carried out at a rate of at least 0.75 °C / hour; the low temperature TL2 is between about 5 °C and about 15 °C; the high temperature TH2 is between about 25 °C and about 35 °C; a difference between TL2 and TH2 is maximized in the controlled system; and / or the controlled system is cycled between TL2 and TH2 two, three, four or five times per day.

8. The method as defined in any one of claims 2 to 7, wherein during the third stage:the cycling of the air temperature of the controlled system is carried out at a rate of not more than 0.25 °C / hour while the temperature is increasing; the cycling of the air temperature of the controlled system is carried out at a rate of at least 0.75 hour while the temperature is decreasing; the relative humidity is maintained between about 33% and about 50% the low temperature TLS is between about 0 °C and about 10 °C; the high temperature THS is between about 7 °C and about 25 °C; the low temperature TLS is less than TLI and less than TL2; the high temperature THS is less than THI and less than TH2; the low temperature TLS and the high temperature THS are minimized in the controlled system; and / or the controlled system is cycled between TLS and THS two, three, four or five times per day.

9. The method as defined in any one of claims 1 to 8, further comprising, after determining that an average rate of carbon dioxide capture by the alkaline material is approximately zero for at least one day, disposing of the alkaline material, optionally wherein said determining is conducted after the third stage of the mineralization reaction.

10. The method as defined in any one of claims 2 to 9, further comprising, after the third stage of the mineralization reaction has been completed and it has been determined that an average rate of carbon dioxide capture by the alkaline material is approximately zero for at least one day, evaluating if the alkaline material has reached a desired level of carbon dioxide saturation, wherein the desired level of carbon dioxide saturation is optionally at least 80%, and if it is determined that the alkaline material has not yet reached the desired level of carbon dioxide saturation, regrinding the alkaline material, optionally with a decrease in Pso of at least 10 pm, and returning the reground alkaline material to the first stage of the mineralization reaction.1 1 . The method as defined in claim 10 wherein, if it is determined that the desired level of carbon dioxide saturation has been reached, disposing of the alkaline material.

12. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction conducted in a controlled system, including a method as defined in claim 1 , the method comprising: adding water to the alkaline material, optionally in an amount of between about 10% and about 40% by weight; and cycling the air temperature of the controlled system between a low temperature value TL and a high temperature value TH at least once per day.

13. The method as defined in claim 12, further comprising maintaining a relative humidity of the controlled system at a value of between about 85% and about 100%.

14. The method as defined in either one of claims 12 or 13, wherein TL is in the range of about 5 °C and about 15 °C and TH is in the range of about 25 °C and about 50 °C.

15. The method as defined in any one of claims 12 to 14, wherein the air temperature is cycled two, three, four or five times per day.

16. The method as defined in any one of claims 12 to 15, further comprising, after it has been determined that an average rate of carbon dioxide capture by the alkaline material is approximately zero for at least one day, evaluating if the alkaline material has reached a desired level of carbon dioxide saturation, wherein the desired level of carbon dioxide saturation is optionally at least 80%, and if it is determined that the alkaline material has not yet reached the desired level of carbon dioxide saturation, adding water to the alkaline material, optionally to bring the water content of the alkaline material back to the range of about 10% to about 40% by weight, and continuing to cycle the temperature of the controlled system between a low temperature value TL and a high temperature value TH at least once per day.

17. The method as defined in claim 16 wherein, if it is determined that the desired level of carbon dioxide saturation has been reached, disposing of the alkaline material.

18. A method comprising conducting all or part of the method as defined in any one of claims 1 to 11 before conducting the method as defined in any one of claims 12 to 17.

19. A method as defined in claim 18 comprising conducting steps (i) and (ii) as defined in claim 2, and then conducting the method as defined in any one of claims 12 to 17.

20. The method as defined in any one of claims 1 to 19, wherein inorganic chemical salts are added to the alkaline material in an amount between about 0.1 to about 10 % by weight of the alkaline material on a dry matter basis.21 . The method as defined in claim 20, wherein the inorganic chemical salts include as a cation one or more of calcium, magnesium, sodium, potassium, or lithium, and wherein the inorganic chemical salts include as an anion chloride, sulfate, nitrate, hydroxide, bicarbonate, or carbonate.

22. The method as defined in any one of claims 1 to 21 , wherein the alkaline material is mixed with a non-reactive filler material comprising 20-50 % by weight of the mixture23. The method as defined in claim 22, wherein the non-reactive filler material comprises a silicate mineral or a carbonate mineral, a naturally occurring rock or an industrially produced slag made up of silicate and / or carbonate minerals, or industrially produced silica or particles thereof.

24. The method as defined in claim 23, wherein the silicate mineral or the carbonate material comprises quartz, anorthite, albite, unactivated serpentine, olivine, talc, diopside, hydromagnesite, magnesite, calcite, orthoclase, microcline, corundum, rutile, spinel, larnite, or hatrurite.

25. The method as defined in any one of claims 1 to 24, wherein the alkaline material is magnesium oxide, magnesium hydroxide, calcium oxide, calcium hydroxide, olivine, peridotite, serpentine, serpentinite, activated serpentine, activated serpentinite, steel slag, precious metal slag, bottom ash, fly ash, red mud, cement kiln dust, cement, concrete, asbestos, or paper mill waste.

26. The method as defined in any one of claims 1 to 25, wherein the source of the carbon dioxide is atmospheric air.

27. The method as defined in any one of claims 1 to 26, wherein the step of cycling the air temperature of the controlled system, including the step of cycling the airtemperature of the controlled system at any one or more of the first, second and third stages of the mineralization reaction, comprises alternately heating the controlled system to move a temperature of the controlled system towards the respective high temperature value TH, THI, TH2 or THS and cooling the controlled system to move the temperature of the controlled system towards the respective low temperature value TH, THI , TH2 or THS-28. The method as defined in claim 27, wherein the step of heating the controlled system comprises one or more of: enclosing the controlled system within a greenhouse; allowing ambient sunlight to enter the greenhouse; allowing the temperature of the controlled system to increase as the ambient temperature increases during daytime hours; or actively heating the controlled system, optionally by passing a warming heat transfer fluid beneath the controlled system, wherein the warming heat transfer fluid is optionally steam, hot water, hot air, or hot gases.

29. The method as defined in any one of claims 27 or 28, wherein the step of cooling the controlled system comprises one or more of: opening vents on the greenhouse in which the controlled system is enclosed; shading the greenhouse to limit or block entry of ambient sunlight into the greenhouse; allowing the temperature of the controlled system to decrease as the ambient temperature decreases during nighttime hours; or actively cooling the controlled system, optionally by passing a cooling heat transfer fluid beneath the controlled system, wherein the cooling heat transfer fluid is optionally cold water, cold air or cold gases.

30. The method as defined in any one of claims 6 or 7, wherein the step of maximizing the difference between TLI and THI or the step of maximizing the difference between TL2 and TH2 comprises one or more of: permitting light to enter the greenhouse during daytime hours; closing ventilation features of the greenhouse during daytime hours;actively heating the controlled system, optionally by passing a warming heat transfer fluid beneath the controlled system, wherein the warming heat transfer fluid is optionally steam, hot water, hot air, or hot gases; opening ventilation features of the greenhouse during nighttime hours; actively cooling the controlled system during nighttime hours, optionally by passing a cooling heat transfer fluid beneath the controlled system, wherein the cooling heat transfer fluid is optionally cold water, cold air or cold gases.31 . The method as defined in claim 8, wherein the step of minimizing the low temperature TLS and the high temperature THS in the controlled system comprises one or more of: shading the alkaline material from light during daytime hours; if a temperature of the outside environment is warmer than a temperature within the greenhouse, closing ventilation on the greenhouse during daytime hours; if a temperature of the outside environment is cooler than a temperature within the greenhouse, opening ventilation on the greenhouse; opening ventilation on the greenhouse during night time hours; or actively cooling the controlled system, optionally by passing a cooling heat transfer fluid beneath the controlled system, wherein the cooling heat transfer fluid is optionally cold water, cold air or cold gases.

32. The method as defined in any one of claims 2 to 11 or 18 to 31 , wherein relative humidity of the controlled system is adjusted or maintained by: spraying a fine mist of water above the alkaline material; allowing external air having a known relative humidity to enter the controlled system; or placing a saturated salt solution in contact with air within the controlled system.

33. The method as defined in claim 32, wherein relative humidity of the controlled system is adjusted by increasing the relative humidity of the controlled system, or the method as defined in any one of claims 2 to 11 or 18 to 31 wherein said increasing the relative humidity of the controlled system comprises: spraying a fine mist of water above the alkaline material; or allowing external air having a known relative humidity to enter the controlled system.

34. The method as defined in claim 32 or 33, wherein the relative humidity of the controlled system is adjusted by decreasing the relative humidity of the controlled system, or the method as defined in any one of claims 2 to 11 or 18 to 31 wherein said decreasing the relative humidity of the controlled system comprises: allowing external air having a known relative humidity to enter the controlled system; or placing a saturated salt solution in contact with air within the controlled system.

35. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, the method comprising: placing the alkaline material in a controlled system; during a first stage of the mineralization reaction: maintaining a relative humidity of the controlled system at a value of between about 50% and about 80%; and cycling an air temperature of the controlled system between a low temperature value TLI and a high temperature value THI at least once per day, wherein TLI and THI optionally have values corresponding to TLI and THI as defined in claim 6.

36. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, the method comprising: placing the alkaline material in a controlled system; determining if both conditions (i) a day-over-day average rate of carbon dioxide capture by the alkaline material remains constant for at least one day, and (ii) the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with increasing temperature, are met; if it is determined that both conditions (i) and (ii) are met: maintaining a relative humidity of the controlled system at a value of between about 85% and about 100%; and cycling the air temperature of the controlled system between a low temperature value TL2 and a high temperature value TH2 at least once per day, wherein TL2 and TH2 optionally have values corresponding to TL2 and TH2 as defined in claim 7.

37. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, the method comprising: placing the alkaline material in a controlled system; determining if both conditions (i) a day-over-day average rate of carbon dioxide capture by the alkaline material remains constant for at least one day, and (ii) the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with increasing temperature, are met; if it is determined that both conditions (i) and (ii) are met: adding water to the alkaline material in an amount of between about 10% and about 40% by weight; maintaining a relative humidity of the controlled system at a value of between about 85% and about 100%; and cycling the air temperature of the controlled system between a low temperature value TL and a high temperature value TH at least once per day, wherein TL and TH optionally have values corresponding to TL and TH as defined in claim 14.

38. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, the method comprising: placing the alkaline material in a controlled system; determining if the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with decreasing temperature; if it is determined that the instantaneous rate of carbon dioxide capture by the alkaline material is increasing with decreasing temperature: cycling an air temperature of the controlled system between a low temperature value TLS and a high temperature value THS at least once per day, wherein TLS and THS optionally have values corresponding to TLS and THS as defined in claim 8; while the temperature of the controlled system is increasing, decreasing the relative humidity of the controlled system to less than 50%; and while the temperature of the controlled system is decreasing, increasing the relative humidity of the controlled system to above 85%.

39. A method of capturing carbon dioxide in an alkaline material through a mineralization reaction, the method comprising: placing the alkaline material in a controlled system; during a first stage of the mineralization reaction: maintaining a relative humidity of the controlled system at a value of between about 50% and about 80%; and cycling an air temperature of the controlled system between a low temperature value TLI and a high temperature value THI at least once per day, wherein TLI and THI optionally have values corresponding to TLI and THI as defined in claim 6; after it has been determined that a day-over-day average rate of carbon dioxide capture by the alkaline material has remained constant for at least one day: adding water to the alkaline material, optionally in an amount of between about 10% and about 40% by weight; and cycling the air temperature of the controlled system between a low temperature value TL and a high temperature value TH at least once per day, wherein TL and TH optionally have values corresponding to TL and TH as defined in claim 14.

40. The method as defined in any one of claims 35 to 38 comprising carrying out some or all of the steps of any one of claims 1 to 34 or 39.

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